Three dimensional graphene based materials

Advances in Colloid and Interface Science 221 (2015) 41–59

Contents lists available at ScienceDirect

Advances in Colloid and Interface Science journal homepage: www.elsevier.com/locate/cis

Historical perspective

Three dimensional graphene based materials: Synthesis and applications from energy storage and conversion to electrochemical sensor and environmental remediation Hou Wang a,b, Xingzhong Yuan a,b,⁎, Guangming Zeng a,b, Yan Wu c, Yang Liu a,b, Qian Jiang a,b, Shansi Gu a,b a b c

College of Environmental Science and Engineering, Hunan University, Changsha 410082, P.R. China Key Laboratory of Environment Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, P.R. China College of Environment and Energy, South China University of Technology, Guangzhou 510006, P.R. China

a r t i c l e

i n f o

Available online 3 May 2015 Keywords: Graphene Hydrogels Aerogels Energy storage and conversion Hydrogen production Environmental remediation

a b s t r a c t With superior electrical/thermal conductivities and mechanical properties, two dimensional (2D) graphene has become one of the most intensively explored carbon allotropes in materials science. To exploit the inherent properties fully, 2D graphene sheets are often fabricated or assembled into functional architectures (e.g. hydrogels, aerogels) with desired three dimensional (3D) interconnected porous microstructures. The 3D graphene based materials show many excellent characteristics including increased active material per projected area, accessible mass transport or storage, electro/thermo conductivity, chemical/electrochemical stability and flexibility. It has paved the way for practical requirements in electronics, adsorption as well as catalysis related system. This review shows an extensive overview of the main principles and the recent synthetic technologies about fabricating various innovative 3D graphene based materials. Subsequently, recent progresses in electrochemical energy devices (lithium/lithium ion batteries, supercapacitors, fuel cells and solar cells) and hydrogen energy generation/ storage are explicitly discussed. The up to date advances for pollutants detection and environmental remediation are also reviewed. Finally, challenges and outlooks in materials development for energy and environment are suggested. © 2015 Elsevier B.V. All rights reserved.

Contents 1. 2.

3.

4.

Introduction . . . . . . . . . . . . . . . . . . . . . . . Synthesis of 3D graphene-based materials . . . . . . . . . . 2.1. Hydrogels . . . . . . . . . . . . . . . . . . . . . 2.2. Aerogels . . . . . . . . . . . . . . . . . . . . . . 2.2.1. Graphene-surface modified aerogels . . . . . 3D graphene-based materials for energy applications . . . . . 3.1. Electrochemical energy devices . . . . . . . . . . . 3.1.1. Lithium-ion batteries . . . . . . . . . . . . 3.1.2. Lithium–sulphur (oxygen) batteries . . . . . 3.1.3. Supercapacitors . . . . . . . . . . . . . . 3.1.4. Fuel cells . . . . . . . . . . . . . . . . . 3.1.5. Dye-sensitized solar cells . . . . . . . . . . 3.2. Hydrogen energy production and storage . . . . . . . 3.2.1. Hydrogen production . . . . . . . . . . . . 3.2.2. Hydrogen storage . . . . . . . . . . . . . 3D graphene-based materials for environmental application . . 4.1. Pollutants detection . . . . . . . . . . . . . . . . . 4.2. Application of 3D graphene-based materials in adsorption 4.2.1. Inorganic pollutants in water . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

⁎ Corresponding author at: College of Environmental Science and Engineering, Hunan University, Changsha 410082, P.R. China. Fax: +86 731 88823701. E-mail address: [email protected] (X. Yuan).

http://dx.doi.org/10.1016/j.cis.2015.04.005 0001-8686/© 2015 Elsevier B.V. All rights reserved.

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

42 42 43 44 45 46 46 46 47 48 49 51 51 51 52 52 52 53 53

42

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

4.2.2. Organic pollutants in water . . . . . . 4.2.3. Gas adsorption . . . . . . . . . . . . 4.3. Photocatalytic decomposition of organic pollutants 5. Conclusions and outlook . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

1. Introduction Energy shortage, fossil fuels usage and environmental pollution have become important and urgent global problems due to urbanization, industrialization and the changing lifestyles of people [1,2]. Given the recognized threats, critical challenges and driving global research have attracted extensive attention by scientific community [3]. Accompanied with the more stringent rules and regulations concerning energy usage and environmental protection, various technologies are urgently needed to satisfy the increasing demand in energy and environment field. In parallel, enhancing nanotechnology and nano-materials hold out great promise for the immense improvements [4]. In recent years, emerging as a new class of carbon nano-materials, graphene has attracted tremendous attention and becomes a rapidly developing area. It displays versatile properties including thermal conductivity, mobility of charge carriers, electrical and mechanical properties, magnetism and so on [5]. These features as well as large surface area play a crucial role in electronics, optoelectronics, and electrochemical and biomedical applications [6]. Most importantly, the recent focus on graphene as a general platform for various composites has inspired many possibilities in energy and environmental aspect [4]. However, two dimensional graphene sheets are limited for many specific fields due to that (i) the weak absorption for light and the low capacitance of graphene; (ii) the easy stack and agglomeration in solvent; (iii) the zero-gap semi-metal nature of graphene [4,6,7]. Realizing these shortages, a growing exploration to modify graphene surface and construct dimension-tailored functional graphene structures, including graphene quantum dots (0D), graphene fibers (1D), graphene sheets/films (2D) and graphene gel (3D), has been exerted to expand the scope of application in quantum computing, catalysis, sensors and even more [8]. Among them, graphene-based macroscopic materials with threedimensional (3D) porous network have received increasing attention for energy and environmental field. Compared with carbon nanotubebased 3D architectures, graphene-based 3D materials offer more advantages, including easy preparation, high efficiency and economical devices [9]. The integration of individual chemically modified 2D graphene sheets into monoliths with 3D macroporous structures through various gelation technologies could be referred as 3D graphene-based materials (3D GBMs), which can be further classified into hydrogels and aerogels (sponges or foams) throughout this review. The gels could achieve long range order and conductivity between the individual graphene sheets, and have more “space” towards the transportation or storage for the electron/ion, gas and liquid [10]. This will be important for maintaining graphene’s properties in bulk and to enhance graphene utilization for practical applications. Moreover, the resulting gels present strong mechanical strengths/flexibility, surface hydrophobicity, good electrical conductivity and electrochemical performance, fast mass and electron transport kinetics, and self-healing performance [11]. Such bulk materials with desired structures and properties hold the key to the realization of their extensive potential applications for energy storage and conversion, and environmental remediation [12–17]. As shown in Fig. 1, the number of publications (according to ISI Web of KnowledgeSM) on 3D GBMs over the past five years increases dramatically after 2011. In particular, the impact in energy and environmental applications has been realized well. Although the existence of several reviews highlights the applications of 3D GBMs [7–10,18–22], a review from materials synthesis to both

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

53 54 55 56 57 57

energy and environmental-related applications is still missing. This review article has presented the recent progresses related to the synthesis of innovative 3D graphene based materials, followed by placing the emphases on recent advancements about the applications in the fields of energy storage devices (supercapacitors, lithium batteries, fuel cells, solar cell, etc.), hydrogen energy production and environment protection (pollutants detection and environmental remediation). Challenges and outlook are offered to inspire more exciting developments in future.

2. Synthesis of 3D graphene-based materials The morphology and structure of 3D graphene-based architecture not only makes up the shortages of individual graphene sheets during assembling process but also provides sufficient adsorption space and contact area between electrolyte and electrode [10]. Chemically modified 2D graphene sheets can be intergrated into 3D macroporous structures via various gelation technologies to form graphene-based gels, which could be referred as hydrogels and aerogels (sponges or foams). The 3D networks of graphene-based gels have strong mechanical strengths, high electrical conductivities and superior thermal, chemical or electrochemical stability, which are attractive for energy storage and conversion devices, sensor and catalytic system. Moreover, several inherent merits including large specific surface areas, stimuli responsive property, ample oxygen-containing functional groups and conjugated domains make them become suitable candidates for removing pollutants from the contaminated water [20]. Various approaches, adopted for the preparations of 3D graphene-based architectures, can be divided into four categories: self-assembly of chemically modified graphene and their derivatives in solution and/or at interfaces, template-guided approaches, solvothermal/organic sol–gel reaction and lightscribe patterning technology [7,8]. The driving force behind formation of the 3D structures is supramolecular interactions such as van der Waals forces, hydrogen bonding, dipole interactions, electrostatic interactions and π-π stacking [23]. In this section, we will summarize some typical examples including hydrogels and aerogels (foams or sponges) to outline the synthetic methods and characteristic of 3D GBMs. For more comprehensive information, the readers may consult previous reviews and references [7–9,20]. In addition, the synthesis and preparation of 2D GBM

Fig. 1. Number of publications on 3D GBMs over the past five years.

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

materials will not be introduced since they have been stated comprehensively in our previous reviews and others [4,24,25]. 2.1. Hydrogels A gel is usually defined as a non-fluid colloidal or polymer network expanded throughout its whole volume by a fluid. A hydrogel can be formed if the swelling agent is water and the network component is a hydrophilic polymer [20]. Chemically modified graphene (e.g. graphene oxide) is a kind of 2D amphiphilic material with unique edge-to-center arrangement of hydrophilic and hydrophobic segments. Based on the molecular structure and morphology, modified graphene sheets can be served as polymer gelators since 2D laminated structure with many conjugated domains facilitates contact with each other to form the network junction points. Graphene hydrogels (GH) are formed by self-assembling modified graphene sheets into 3D network structure with relatively lower critical gelation concentration through hydrogen bonding, electrostatic interaction or π-π interactions. Xu et al. fabricated GH using a modified hydrothermal reducing method by mixing the graphene oxide (GO) and ascorbic acid [26]. The extended π-conjugation in graphene sheets is advantageous to the extended π-stacking interactions between graphene sheets to form strong bindings, leading to highly robust cross-links in the graphene hydrogels. Moreover, the partial overlapping of graphene sheets via hydrophobic and π-π interactions in 3D space also benefits to the formation of graphene hydrogels. Chen et al. first reported a convenient hydrothermal process for synthesis of nitrogen-doped graphene hydrogel (NGH) using organic amine and GO as precursors at mild temperature [27]. The organic amine is not only as an important structural modifier to adjust the microscopic structure of 3D graphene structures, but also as nitrogen sources to prepare the nitrogen-doped graphene. Therefore, it should be note that in the procedures of GH preparation, dispersive GO solution is usually mixed with another solution contained the gelator molecules. Gelator molecules, as physical or chemical cross-linkers, are responsible for the preservation of 3D structure and, eventually, may provide functionality of resulting materials. The cross-linkers are generally involving in amides, peptides, ureas, saccharides, nucleobases, molecules with long alkyl chains and steroid derivatives [28]. Sahu et al. formed a self-assembled GO hydrogel by physically crosslinking GO nanosheets in Pluronic solution [29]. Acting as a physical cross-linker among GO sheets, pluronic chains were adsorbed onto GO sheet via hydrophobic association and interact with nearby GO sheets via H-bonding. The gels showed good elastic moduli, denser network structure, pH-responsive behaviour, near-IR light absorption properties and biocompatibility. Homologous way was used to synthesized reduced graphene oxide hydrogel (rGH) through chemical crosslinking reaction between GO and ethylene diamine (EDA) [23].

43

According to this route, numerous graphene-based organic or inorganic composites hydrogels have been synthesized. Using organic monomers as gelator molecules, graphene-based polymer composite hydrogels can be fabricated via in situ polymerization of monomer in graphene or GO dispersion. During the polymerization, GO/graphene sheets act as 2D template [30–33]. The main crosslinked mechanisms may involve in π–π interaction, electrostatic interaction and hydrogen bonding [34]. For example, Zhou et al. employed 3,4-ethylene dioxythiophene as reducing agent and monomer simultaneously to react with GO [30]. Polymerization was carried out without agitation at 80 °C for achievement of graphene and poly(3,4-ethylenedioxythiophene) (PEDOT) hydrogel. Aqueous dispersion of GO containing N-acryloyl-6-aminocaproic acid monomer in presence of Ca(NO3)2 had been used for the preparation of GO/ poly(acryloyl-6-aminocaproic acid) (PAACA) composite hydrogel [35]. The dual-network GO/PAACA was cross-linked via hydrogen bonding due to the polar groups of the PAACA side chains interacting both with other PAACA side chains and with oxygen-containing groups of GO nanosheets. Calcium ions functioned with both the polar groups of the PAACA side chains and oxygen-containing groups of GO nanosheets via coordination interactions. Das et al. synthesized graphene/polyacrylamide (PAM) hydrogels via in situ polymerization of acrylamide monomer in PAM-stabilized graphene dispersion and the preparation protocol was shown in Fig. 2 [36]. In this process, graphene nanosheets not only acted as an effective physical cross-link junction but also aided in the process of energy dissipation and prevent crack-tip propagation. The PAM chains entangled with the PAM-stabilized graphene sheets through physisorption and noncovalent absorption leaded the formation of the network. Natural polymers (cellulose [37] and chitosan [38]) and biomacromolecules (DNA [39] and proteins [40,41]) are capable of interacting with GO sheets to form multifunctional graphene composite hydrogels. For instance, Wang and coworkers designed a light-controlled graphene elastin composite hydrogels by three-step strategy [41]. A hybrid was primarily created by funcinalizing rGO nanosheets with a rationally designed elastin-like polypeptides (ELPs). The composite was then cross-linked into ELP-based network using water vapor diffusion method to create an anisotropic microstructure. In this process, water absorption induced an inverse temperature transition-induced phase separation, resulting in localized porous structure at exposed surface. The entire gel curled in response to heating and cooling. Lastly, the hydrogel was irradiated with near-infrared light to locally shrink the ELP network and induce bending motions. Xu et al. reported a 3D self-assembly method to prepare GO/DNA hydrogels [39]. During the heating process (the temperature was increased from 40 °C to 90 °C), double-stranded DNA (dsDNA) was unwound to single-stranded DNA (ssDNA). In situ formed ssDNA chains bridged adjacent GO via strong noncovalent interactions, resulting in

Fig. 2. Schematic of preparation protocol of compressible graphene-PAM hydrogels; Reproduced with permission from Ref. [36]. Copyright 2013 American Chemical Society.

44

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

2.2. Aerogels

mesopores within the hydrogel precursors were fused together to form macropores impelled by gradual growth of ice crystals. In addition to GO as a precursor, carbon nanotube (CNT) sponge was able to be directly converted into graphene nanoribbon (GNR) aerogel via in-situ unzipping method [61]. As shown in Fig. 3, an oxidative chemical solution was infiltrated into CNT porous sponge to induce intercalation of the nanotube walls from the defects, and then open the walls by introducing KMnO4, therefore realizing the in-situ unzipping process. After that, supercritical drying was performed to obtain GNR aerogels in which a large portion of multi-walled nanotubes had been converted into multilayered GNRs. However, a litter part of unzipped CNT sponges still existed in those aerogels, which needed to optimize the reactive condition. The aerogel inherits three-dimensional network and porosity from the original CNT sponges. Graphene hydrogels may lose mechanical strength and even collapsed if it is dried directly by freezed method. In order to obtain compressive GA, different reinforcers such as metal salts [45], polymer [51], ammonia [57], tri-isocyanate, [58] and others [54,59], have been employed to strengthen the aerogels structure. Han and coworker fabricated a strengthened GA with macro-porous structure by soaking GH in ammonia solution before freeze drying [57]. After that, the 3D structure of strengthened GA was maintained and the compressive strength was enhanced to 152 kPa at a static load. Possible mechanisms may be that ammonia solution not only lessen the structure damage during freeze drying but also form covalent bonds between graphene sheets. More exciting, a general but creative approach was presented to make GO aerogel by assembling 2D GO sheets edge-to-edge into 3D hydrogel networks with subsequent supercritical fluid drying [53]. From Fig. 4, GO hydrogels could be obtained using La3+ or polyethylenimine (PEI) to crosslink the GO sheets in the presence of glucone-δ-lactone (GDL) as the gel promoter. After that, the aerogels were aquired by supercritical drying. In these systems, the pH value of the mixtures controlled by GDL can affect the release of La3+ from La(OH)3 or protonate the amino groups attached to PEI to crosslink the GO sheets, to form uniform and reinforced hydrogel networks, leading to the enhancement of mechanics of GO aerogels to some extent. The randomly distributed macropores in GO aerogels turned out to be smaller and denser, and some of the macropores disappeared after compression. Thus, GO aerogels owned outstanding mechanical performance (up to 20 MPa Young’s modulus, 1 MPa yield strength) with superb adsorption capacity in mechanical energy (up to 45 J g−1 specific energy adsorption). Carbon nanotubes (CNTs) can also be incorporated into graphene aerogels to improve their compressibility, strength, conductivity and porosity [62–66]. In aerogels, CNTs act as a scaffold to resist compressive stress and prevent structure collapse. For example, Sun et al. fabricated carbon aerogels by freeze-drying aqueous solutions of CNTs and giant GO sheets, followed by chemical reduction of GO into graphene with

Graphene-based aerogels (GBAs), a kind of emerging monolithic carbon-based materials with 3D micro- and nano-architectures, generally result from their hydrogel precursors by drying to replace liquid entrapped in the networks with air. Different physico-chemical properties such as low density, large open pores, large specific surface area, tunable porosity, superior electrical and mechanical properties have been exhibited [52,53]. Therefore, two-stage synthetic route has been used to prepare GBA: (i) the fabrication of GBH by self-assembly technology and cross-linking process; (ii) the obtain of GBA via freeze drying and supercritical fluid/CO2 drying process [7,9,54–60]. Zhang et al. devoloped a graphene aerogel (GA) from aqueous graphene hydrogel via supercritical CO2 drying or freeze-dried drying [55]. The cross-linked hydrogel was formed through the reduction of GO by L-ascorbic acid and the formation of physical cross-links between graphene sheets via strong π-π interaction. Both drying methods produced different pore characteristics: macropores and mesopores. Comparing to freeze-dried method, the supercritical CO2 drying presented much more mesopores with ample volume of 2.48 cm3 g−1. During freeze drying process, many

Fig. 3. The transformational process of CNT sponge to GNR aeroge. Reproduced with permission from Ref. [61]. Copyright 2014 John Wiley & Sons.

the formation of a stable GO/DNA hydrogel. Similarly, an eco-friendly GO/ chitosan (GO/CS) hydrogel was prepared via self-assembly of GO sheets and CS chains [38]. The formation mechanism of the hydrogel may be ascribed to that (i) positively charged polysaccharide (e.g. amino groups) can strongly attract negatively charged GO sheets; (ii) multiple hydrogen bonds are formed between GO sheets and CS chains, increasing the bonding force among GO sheets. Apart from the above mention, various inorganic nanoparticles including metal (Au [42], Pd and Cu [43]) and metal oxides/hydroxides (Co3O4 [44], Fe3O4 [45], TiO2 [46,47], Mn3O4 [48], Ni(OH)2 [49]), can be decorated/anchored onto graphene sheets or hydrogels to form graphene inorganic composite hydrogels. A gel-based nanohybrid system was made by a simple one-step hydrothermal method, in which bimetallic PdCu nanoparticles (NPs) were decorated GH [43]. The PdCu/ GH exhibited an interconnected microporous framework with PdCu NPs dispersed and encapsulated within the graphene layers, resulting in improved electrocatalytic activities and stability. Yuan et al. fabricated Co3O4/GH composite with free-standing 3D structure [44]. Typically, 5 mg mL−1 GO suspension and glycol was mixed with Co(CH3COO)2 solution, then transferred into a Teflon-lined stainless steel autoclave and heated at 180 °C for 24 h. In this process, spherical Co3O4 particles were in situ grown on the rGO sheets uniformly and the self-assembly of graphene sheets simultaneously occurred under hydrothermal conditions, resulting in the formation of GBHs. Act as a mechanical buffer, the GH played a great important role in avoiding excessive volume expansion of Co3O4 particles. Similarly, Gao et al. developed a nanocomposite GH based on green chemistry and used as a robust host for stabling TiO2 semiconductor [47]. Vitamin C was the green reducing agent to attain GH. Very recently, multicomponent composites hydrogels such as GO/ sodium alginate/polyacrylamide hydrogels and poly(vinyl alcohol)/ poly(acrylic acid)/TiO2/GO nanocomposite hydrogels have also been reported [50,51]. During the synthetic processes, radical polymerization, condensation reaction and cross-linked function may be involoved. For instance, Fan et al. fabricated GO/sodium alginate/polyacrylamide ternary nanocomposite hydrogel through free radical polymerization of acrylamide and sodium alginate in the presence of GO in aqueous system [50]. Subsequently, the hydrogel was formed in the presence of Ca2+ because of ionic cross-linking via calcium bridges between the sodium alginate and polyacrylamide adjacent chains. Meanwhile, GO nanosheets are acted as fresh chemical crosslinking points in hydrogel formation. The synergistic effect of multicomponent graphene-based hydrogels lead to more superior performance than that of raw materials or single component, which could meet various requirements in practical applications.

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

45

Fig. 4. Schematic synthesis of both La3+ and PEI-crosslinked GO aerogels. Reproduced with permission from Ref. [53]. Copyright 2013 John Wiley & Sons.

hydrazine vapor [62]. The aerogel with an average pore size of ~123 nm offered an integrated properties including recyclable compressibility, good electical conductivity and thermal stability, which were ascribed to the ideal combination of the giant size of constituent graphene sheets and the cooperative effect between graphene and CNTs. Chen et al. used graphene/CNTs as the scaffold to be backfilled with poly(dimethylsiloxane) by vacuum assisted suction method to obtain highly conductive and stretchable polymer composite [66]. The composite with only 1.3 wt% GCNA loading remains constant after 100 times repeated stretching by 20% and 5000 times bending. Because the randomly oriented nanotubes or graphene sheets are forced to align along the stretching direction by stress, and the “binder” is not strong enough to fasten junction points to resist mechanical deformation. Further, super-strong and super-stiff polymer composite materials could be obained by CNTs and grephene reinforcement. For example, the inherent properties of poly(lactide) including glass transition temperature, crystallization kinetic, dynamic mechanical properties, strength, and elongation at break were concurrently improved via the incorporation of a small amount of surface functionalized carbon nanotubes [67]. The concurrent improvement in poly(lactide) properties was ascribed to the strong interfacial interaction between the nanotubes’ outer surface and the poly(lactide) chains. Dervishi et al. also found that incorporating the CNTs/graphene mixture into polymers could improve the modulus of elasticity, thermal attributes and maximum stress [68]. Because the high surface area allowed for graphitic sheets or nanotubes to better intercalate within the polymer chains, generating better mechanical behavior. 2.2.1. Graphene-surface modified aerogels 3D graphene-based bulk materials, analogous with aerogels in terms of sturcture and morphology, are often refered as foams or sponges, which have been prepared by directed chemical vapor deposition [69–74], freeze-drying technique [75–77], centrifugal vacuum evaporation method [78,79], and other tailor-made approaches [80–82]. Among them, using chemical vapor deposition (CVD) with nickel foam as the template is one of the most widely applied approaches to fabricate graphene foam (GF) [70,83]. Compared to 2D pristine graphene, foamlike graphene is a promising architecture because of its ease usage and macroscopic/microscopic structure. For example, Singh et al. prepared an integrated graphene foam-like network with well-controlled microscale porosity and roughness via template-directed CVD [74]. Briefly, 3D nickel scaffold was used as a template for the growth of graphene films by decomposing CH4 at ∼ 1000 °C under peripheral pressure. Then, a continuous 3D network of graphene with thin interconnected sheets of graphene was obtained after etching of the nickel scaffold. CH4

concentration made a significant contribution to control the structure of GF, average number of graphene layers, specific surface area and density. Freeze-drying technique is also of importance and convenience in making graphene-based foams. Different freezing methods including unidirectional freezing drying, non-directional freezing drying, and air freezing drying play important roles in the pore sizes and volumes. The size and shape of the 3D foams are also influenced by the mold utilized for freezing. For example, a unidirectional ice-template freezing method was reported by Kuang et al. for fabricating hierarchically porous structure GO foam [84]. The channel size was ranged from 30 μm to 75 μm by varying the cooling media. Channel-walls were composed of highly stacked GO platelets of several tens of nanometers thick. The high ratio of channel width to wall thickness, approximately 103 produced macroporous and light weight structures with a density ranging from 6 mg cm−3 to 12 mg cm−3. The channel dimensions are mainly determined by the ice rod templates. A larger degree of supercooling and a higher freezing rate produce a smaller average channel size with more homogeneous channel microstructures. Further, a comparison of three freezing drying methods for preparing rGO foams had been made by He et al [85]. Among the three kinds of foams, the rGO foams made by unidirectional freezing drying (UDF) had the largest and most ordered pores (~ 50 μm). GO concentration did not change the pore diameters. Whereas, with the GO concentration decreasing from 2.0% to 0.8%, the pore sizes in the foams prepared by non-directional freezing drying (air freezing drying) increased from about 5–20 μm (about 5–25 μm). Other tailor-made approaches involving centrifugal vacuum evaporation method, leavening strategy, nucleate boiling method and in-situ unzipping method have been also applied to synthesize rGO foams [61,78–81,86]. GO sheets suspension can be assembled to generate

Fig. 5. Synthetic scheme of 3D GO sponge; Reproduced with permission from Ref. [78]. Copyright 2012 American Chemical Society.

46

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

network-linked GO sponges by the combined effect of the vacuum evaporation, temperature of a vacuum chamber and centrifugal force. For example, GO sponges were produced at 40 °C using a speed vacuum concentrator and without the need for substrates, electrodes or further drying steps [78,79]. At low temperature, GO sheets formed spongeslike morphology with 3D network structure via van der Waals force during water evaporation due to the outward centrifugal force that was more dominant than the upward evaporation force, as indicated in Fig. 5. But the evaportion rate was accelerated at higher temperture and GO sheets tend to assemble with each other at the liquid/vacuum interface rapidly to form the GO film layer. Interestingly, incorporating gaseous species (e.g. H2O, CO2, hydrazine vapor) released during chemical reduction of GO into compact GO layered films, porous rGO foams just like “leavened bread” could be formed, as shown in Fig. 6 [80]. Graphene oxide films were firstly obtained from vacuum filtration using anodized aluminum oxide membrane. The films were then peeled off and reduced by hydrazine monohydrate (98%) at 90 °C in a stainless steel autoclave to synthesize rGO foams. The as-obtained graphene foam showed an open porous network with pore sizes in the range of sub-micrometer to several micrometers. The success of leavening GO layered films to rGO foams is ascribed to that: i) compact layered GO structures as “dough” and ii) the rapid evolution of gaseous species (hydrazine vapor) to reduce GO to rGO. These pioneering examples and methods pave a way to prepare graphene-based composites foam/sponge. In a series of follow-up studies, they have been successfully extended to polymers (polymethylmethacrylate [87], polystyrene [88], polypyrrole [89,90], polycarbonate [91]), inorganic nanoparticles (Pt-Ru alloy nanoparticles [92], ZnO [93,94], MnO2 [95,96], Mn3O4 [97], Fe3O4 [98,99], Co3O4 [100]), carbon nanotubes [101,102] and graphene/CNT/metal nanoparticle composites [103–112]. For example, Tour et al. reported that graphene could be grown directly on porous nickel films, followed by the growth of controlled lengths of vertical CNT forests that seamlessly emanate from the graphene surface [105]. This structure exhibited many advantages such as adequate CNT-metal-electrode contact, high surface-area- utilization efficacy of bulk metals, and post-transfer facility. Dervishi et al. synthersized CNTs on few-layer graphene sheets decorated with ~ 5 nm iron oxide nanoparticles under argon/hydrogen environment at temperatures as low as 150 °C (± 5 °C) [104]. It was

claimed that the low-temperature, facile technique opened the door to a wide range of applications for metal nanoparticle/graphene/CNT systems in areas varying from photovoltaic devices to sensing. 3. 3D graphene-based materials for energy applications Nowadays, the ever-reducing dependence on fossil fuels has sparked the great interest in the development of exploiting clean and recyclable energy. Apparently, the achievements of material science are critical for development of energy conversion and storage techniques. With exceptional porous structure, larger surface area, excellent electronic conductivity and mechanical strength, 3D graphene-based materials have been intensively explored for applications in energy storage and conversion system [113]. In this section, only a limited number of works involving in lithium-ion/lithium batteries, supercapacitors, fuel cells, solar cells and hydrogen energy are covered to keep a balanced view of these fields due to the fast progress and large numbers of publications. 3.1. Electrochemical energy devices 3.1.1. Lithium-ion batteries Rechargeable lithium-ion batteries (LIBs) have been widely employed as one of the main power sources in modern society, such as portable electronics, electric/hybrid electric vehicles, and renewable energy systems [114]. To acquire remarkable performance LIBs with remarkable capacity, superior charging efficiency and long cycling life, the design and synthesis of novel electrode materials play a paramount role in lithium storage behavior [115,116]. So far, various carbon materials such as carbon nanofibers, carbon nanotubes, mesoporous carbons and 2D GBMs have been developed for this purpose [6,117]. Recent years, 3D GBMs as a kind of newly-emerged materials attract enormous concerns for lithium-ion batteries. When used as electrodes for LIBs, 3D graphene-based architecture offers multidimensional electron transport pathways and minimizes transport distances between electrode and electrolyte, thus resulting in enhancing rate performance and cycling stability [118]. Further, in order to improve the performance of LIBs, carbonaceous materials, metal/metal oxide, metal sulfide and metal-free elements can be integrated into 3D graphene network to form composites for LIBs cathode [119]. What’s more, they are also

Fig. 6. Schematic drawings illustrating the leavening process to prepare rGO foams. Reproduced with permission from Ref. [80]. Copyright 2012 John Wiley & Sons.

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

favorable electrode candidates for lithium-sulfur batteries and Li-O2 batteries. For instance, composites incorporated silicon and metallic element (e.g. Sn [120–124], Ge [114], Ag [125], Cu [126]) with 3D graphene architecture show great potential for LIBs electrodes. Silicon (Si) has a theoretical capacity of 4200 mA h g− 1 and low discharge potential [115]. But extremely poor cycling stability is the key issue to limit Si anode application due to severe volume change (~ 300%) during the lithiation and delithiation processes. It seems that Si anode aided with 3D graphene will exhibit markedly improved anodic performance in terms of specific capacity, cycling stability, and rate capability [127–130]. Wang et al. synthesized Si/graphene material via microwave plasma-enhanced chemical vapor deposition method, by which Si thin films were scattered on graphene scaffold [129]. The as-obtained anode showed a capacity of 1560 mA h g− 1 at a current density of 797 mA g−1. At the current density of 2390 mA g−1, the specific capacities still remained as high as 1083 mA h g− 1 even after 1200 cycles. Graphene scaffold provides a fast way between Si and current collector for electrons and at the same time it effectively reduces the stress generated during the charge–discharge processes inside Si anode. Compared to Si, metallic element may exhibit a higher diffusivity of Li+ (room-temperature), higher electrical conductivity and more moderate operating voltage. However, dramatic volume change commonly occurs in metallic element (metal nanoparticles) during lithium ion insertion/ extraction, which causes rapid capacity decay and poor cyclability. In order to solve this problem, Qin et al. fabricated 3D graphene networks anchored with Sn nanoparticles encapsulated with graphene shells by in situ CVD and self-assembly method [124]. The flexible graphene shells suppressed the aggregation of Sn nanoparticles and accommodated the volume expansion, and alleviated the side reactions at the interface between Sn and electrolyte (directly contacting between Sn cores and electrolyte was prevented). So this 3D hybrid anode exhibited good rate performance (the average reversible capacities are 1022, 865, 780, 652, 459, and 270 mAh/g for 0.2, 0.5, 1, 2, 5, and 10 A/g, respectively) and long cycling stability at high rates (a capacity of 682 mAh/g was achieved at 2 A/g and was maintained approximately 96.3% after 1000 cycles). The good reversible capacity and rate are due to that (i) the graphene networks with superior electrical conductivity, 3D porous nature, and large surface area promote the diffusion and transport of electrons and ions; (ii) small Sn nanoparticles offer a lot of active sites for lithium ion storage and a short pathway for lithium ion transport. What’s more, the robust and elastic graphene networks as a buffer reinforce the structural integrity of the electrode via tightly pinning the Sn@ graphene core-shell nanostructures, thereby leading to fine cycling stability. 3D graphene/metal oxides composites are another route to improve the capacity of lithium batteries. The metal oxides are usually including Fe3O4 [99,131–134], Fe2O3 [135,136], CuO [137,138], MnO2 [139], SnO2 [140], Co3O4 [141,142], TiO2 [143] and WO3 [144]. Li et al. synthesized 3D hierarchical Fe3O4/graphene composites and the prepared anode showed a stable capacity of ∼ 605 mA h g−1 with no noticeable fading for up to 50 cycles in the voltage range of 0.001–3.0 V, significantly outperforming bare Fe3O4 electrode [132]. Chang et al. designed 3D nitrogen-doped graphene/Fe3O4 (30 wt% Fe3O4) and the anode showed a reversible charge capacity of 1130 mA h g−1 after 200 cycles [134]. According to these good performances, it is worth to summarize that such a unique 3D network can not only act as buffer matrix provides double protection against the aggregation and volume changes of Fe3O4 active materials during charge/discharge cycling but also ensure favorable transport kinetics for both electrons and lithium ions. Besides, Fe3O4 has some advantages over other oxides in terms of low cost, ecofriendliness, and natural abundance. Liang et al. reported that SnO2/ graphene aerogel (SGA) with interconnected macroporous networks could obtain a discharge capacity of 602 mA h g−1 after 60 cycles [145]. With a continuous porosity and large surface area, the SGA produces a larger contact area between active material and electrolyte. More

47

importantly, graphene sheets in the aerogel can promote electron transfer, and provide fast and versatile transport pathways for the electrolyte ions. Other materials such as SnS2 [118], MoS2 [146], LiFePO4 [147–149], and carbon nanospheres [150] are also alternative candidates to form 3D graphene composites anode materials to meet the ever-growing performance demands. For instance, special layered structure of metal sulfide (e.g. SnS2, MoS2) with swelling tolerant hosting spaces can facilitate the moving of Li+ ions and electrons through the active materials and compensate the alloying/dealloying volume change to some degree, thus making the improved capacity and cycling stability possible. Jiang et al. demonstrated that SnS2/graphene aerogels could achieve a reversible capacity of 656 mA h g− 1 with a coulombic efficiency of over 95% after 30 cycles and rate capability (240 mA h g−1 at the rate of 1000 mA g−1) [118]. Chang et al. reported that MoS2/graphene (the molar ratio of MoS2 to graphene is 1:2) exhibited a specific capacity of ∼1100 mAh g−1 at a current density of 100 mA g−1 and no capacity fading after 100 cycles. The synergistic effects between the layered metal sulfide and the 3D network structure of graphene aerogels leads to the fine electrochemical properties. LiFePO4 is a cathode material for LIB because of its low cost, good cycling stability and striking theoretical specific capacity (1700 mA h g−1). With the aid of graphene 3D network, the electrical conductivity and efficient use of the LiFePO4 cathodes are both enhanced [148]. This cathode had a reversible capacity of 146 mA h g− 1 at 17 mA g− 1 up to100 cycles, which was more than 1.4 times higher than that of pure LiFePO4. 3.1.2. Lithium–sulphur (oxygen) batteries Apart from the application in LIBs, 3D porous graphene hybrids exhibit significantly improved reversible capacity, rate capability, and desirable cycling performance as electrodes for both Li-S batteries and LiO2 batteries. Sulphur can react with metallic lithium to form Li2S with a large negative free energy change, which can be harnessed in a battery. It is an attractive cathode material in rechargeable Li batteries because of its lightweight and capability of multi-electron reaction. A 3D hierarchical sandwich-type architecture consisting of CNTs/sulfur composite and graphene sheets was prepared and exhibited a capacity of 1396 mA h g−1 at a current density of ~335 mA g−1 [151]. The superior performance mainly results from the synergistic function of graphene and carbon nanotube. The as-obtained 3D conductive network structure can not only supply many routes and channels for electron transfer and ion diffusion but also provide strong confinement of soluble polysulfides and effective buffer for volume expansion of the S cathode during discharge. Very recently, Zhang et al. synthesized binder free 3D sulphur/few-layer graphene foam cathode [152]. The cathode showed good electrochemical stability and high rate discharge capacity retention for up to 400 discharge/charge cycles at a current density of 3200 mA g−1 with an average columbic efficiency of 96.2%. The network provides a direct conductive pathway for the rapid ion-electron exchange and external electron transport. Thus, the graphene foam loaded with sulphur cathode can be a current collector for Li–S batteries. More interestingly, the weight of the cathode was reduced by typically 20–30 wt% since the system did not require any additional binding agents, conductive additives or separate metallic current collector. Rechargeable lithium-oxygen (Li-O2) batteries can theoretically store 5–10 times more energy than current lithium-ion batteries [153]. But insoluble lithium peroxide (Li2O2) or lithium oxide (Li2O) will be produced at the cathode upon discharge, which limits the rate capability, capacity, and cyclic life of Li-O2 batteries. Thus, designing a highly effective carbon cathode is important for high performance Li-O2 batteries. Bind-free graphene foams were also used as O2 electrodes for Li-O2 batteries [82]. Side products (e.g. CH3CO2Li, HCO2Li) would be formed faster in graphene foams with the structural defects after 20 charge-discharge cycles. However, after being annealed in Ar at 800 °C, the round-trip

48

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

efficiency of this graphene foams could reach up to 80% and with a stable discharge voltage at ~2.8 V and a stable charge voltage below 3.8 V for 20 cycles. The superior properties are attributed to: (i) effective interaction between the O2 and Li+ during cycling results from the well prepared 3D graphene structure with large surface areas; (ii) lower amount of defects improve the charge transfer kinetics, which is beneficial to the efficient oxygen reduction/generation reactions. Wang et al. used porous carbon derived from GO gel in nickel foam as an O2 cathode without any additional treatment [153]. The maximum specific capacity was as high as 11060 mA h g−1 and, most importantly, a high capacity of 2020 mA h g−1 could be obtained even the current density increased by a factor of ten times up to 2 mA cm−2 (2.8 A g−1). This excellent performance results from the synergistic effect of the loose packing of the carbon, the hierarchical porous structure, and the high electronic conductivity of the Ni foam. Almost all of the surface area of active carbon participates in the cell reaction and the loose packing of carbon affords more abundant O-2 and electrolyte-transportation paths in the electrode. Ni particles can adjust the porous structure of the carbon sheets and increasing the conductivity. 3.1.3. Supercapacitors Supercapacitors can be divided into two types according on energy storage mechanism: the electrical double layer capacitors (EDLCs) and the pseudo-capacitors [19]. Both of them are surface phenomena during the charge–discharge processes so that the performance of supercapacitors greatly depends on the surface area of materials. Graphene with large surface area (~2630 m2 g−1) and high conductivity (~2000 S cm−1) becomes an ideal medium for increasing the capacitance of both EDLCs and pseudo-capacitors [154,155]. Recently, 3D graphene materials with various morphologies, such as hydrogels and aerogels

(foams or sponges) show great potentiality in supercapacitors because of the maximization exposure of the surfaces to electrolyte. What’s more, the architecture incorporated energy electrode materials, such as transition metal oxides [156], carbonaceous materials [157] and conductive polymers [158], will remarkably enhance the energy density of supercapacitors without the sacrifice of power density. Table 1 lists a part of recent reports about the performance of graphene-based 3D nanocomposites for EDLCs and pseudo-capacitors. As a first example, 3D macrostructures graphene hydrogel (GH), produced by the self-assembly of 2D graphene sheets via hydrothermal method, was used for the electrodes of supercapacitors [184]. The GH contained numerous pores with size from submicrometer to several micrometers, and also possessed an electrical conductivity of 5 × 10−3 S cm−1. The supercapacitor delivered a specific capacitance of 175 F g−1 at 10 mV s−1. Subsequently, a flexible solid-state supercapacitor based on GH films using H2SO4-polyvinyl alcohol (PVA) gel as the electrolyte acquired a specific capacitance of 186 F g−1, unprecedented areal specific capacitance of 372 mF cm−2, low leakage current (10.6 μA) and cycling stability (only 8.4% capacitance decay over 10000 cycles) [26]. Yoon et al. reported a bi-continuous 3D graphene nano-network with a conductivity of 52 S cm− 1 and a large surface area of 1025 m2 g− 1 [185]. The EDLC had a specific capacitance of 245 F g−1 at 5 mV s− 1 in H2SO4 solution (1 M) and 96.5% retention after 6,000 cycles. The 3D GH macrostructure not only provides a conductive network for electrical transport but also offers an open network for efficient electrolyte diffusion to make full use of the large EDLC of graphene hydrogel. Moreover, the pores with controlled sizes of ~10 nm in diameter can be effectively used for electrochemical reaction sites. Although more effective surface area of graphene can be obtained by constructing graphene 3D structures, the specific capacitances are

Table 1 Performance of EDLCs and pseudo-capacitors based on 3D graphene-based materials. Materials

Capacitance (F g−1)

Rate Capability

Energy density (Wh/kg)

Cycle life

Ref

GA GH N-doped G G/Ag G/CeO2 G/Co3O4 G/CoMoO4 G/MnO2 rGO/MnO2 G/MnCO3 G/Ni G/NiO G/Ni(OH)2 rGO/β-Ni(OH)2 G/SiO2 G/TiO2 G/ZnO G/carbon black rGO/carbon sphere G/CNTs G/CS G/β-cyclodextrin rGO/cellulose G/glucose G/PANI GO/polymer G/polypyrrole G/Co(OH)2/Ni G/CNT/Pd rGO/CNT/α-Ni(OH)2 G/CNT/PANI G/MnO2/Ni G/Ni/NiO G/Ni/MnO2 rGO/Ni − Al/CNT G/Ni3S2/Ni(OH)2 GO/PANI/CNT

153 186 205 147.1 208 1100 2741 380 450 645.5 366 778.7 1247 1551.8 226 206.7 400 175 180 286 89.3 130.1 71.2 161.6 463 231 350 693.8 597 1320 271 266.8 783 305 1869 1277 589

2A/g (71%) 0.2 V/s (73%) 1 V/s (70.6%) 30A/g (42%) 400A/g (96.36%) 5 mA/cm2 (65%) 0.1 V/s (50%) 10A/g (50%) 20A/g (49%) 1.5A/g (44%) 0.04 V/s (63%) 36.67A/g (69%) 10A/g (52%) 0.5 V/s (67%) 0.1 V/s (58%) 0.1 V/s (80%) 6A/g (65.3%) 6A/g (70.1%) 6A/g (64.4%) 0.1 V/s (44%) 32A/g (73%) 0.1 V/s (58%) 15A/g (76%) 2A/g (60%) 1A/g (62%) 100 mA/cm2 (38%) 0.02 V/s (56%) 5A/g (70%)

21.4 0.61 3.65 20.4 42.19 8.34 43 39.72 98 26.5 188 23.2 70.6 -

10000 (91.6%) 3000 (92.6%) 1000 (82.8%) 1000 (93%) 10000 (87.42%) 3000 (95%) 10000 (90%) 500 (85.3%) 2000 (60%) 2000 (95%) 2000 (102%) 5000 (100%) 150 (96.4%) 1000 (100%) 6000 (90.9%) 10000 (93%) 85000 (99.34%) 100 (90%) 500 (90.6%) 5000 (99%) 1000 (99%) 3000 (91.9%) 1000 (100%) 1000 (92.2%) 1000 (82%) 5000 (83.4%) 1000 (84%) 1000 (80%) 1000 (96.5%) 2000 (99.1%) 1000 (81%)

[56] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [49] [170] [171] [46] [93] [157] [172] [102] [173] [173] [37] [173] [158] [15] [89] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183]

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

still far from the theoretical capacitance of graphene, e.g. 550 F g−1 calculated based on the intrinsic capacitance and theoretical specific surface area of graphene. The capacitive behavior of graphene sheets can be further improved by chemical doping or etching, both the presence of electro-active species and surface area of the pores can contribute to the total specific capacitance. For example, N-doped graphene hydrogels (NGHs) prepared by a solvothermal method displayed a specific capacitance of 205 F g−1 at scan rate of 1.0 mV s−1 [160]. After 3000 cycle tests at a scan rate of 80 mV s−1, about 92.6% of the capacitance was preserved. Furthermore, an energy density of 3.65 Wh kg−1 was exhibited when a power density of 20.5 kW kg−1 was achieved at discharging current density of 100 A g−1. Using hydrothermal process, Chen et al. synthesized a NGH using organic amine and GO as precursor and the prepared hydrogels were immersed in KOH aqueous before the electrochemical measurement [27]. The supercapacitors exhibited a power density of 205.0 kW kg−1 at a charge/discharge rate of 185.0 A g−1 and a specific capacitance of 113.8 F g− 1 with good cycling stability (95.2% of capacitance was retained after 4000 cycles). There are two reasons for these remarkable performances: (i) a larger binding energy of the basal-plane pyridinic N and pyrrolic N results in a larger number of ions to be accommodated on the electrode surface; (ii) big porous network and flat graphene structure contribute to fast adsorption and diffusion of potassium ion on electrode surface, leading to a fast charge/discharge rate and a very high power density. Incorporating “stabilizer” or “spacer” into 3D graphene architectures is one of the most promising ways to improve supercapacitors performance, especial in using pseudo-active materials, such as metal [161, 186], metal oxides [46,49,93,96,156,162–167,169–171,174,178–180, 187–194], conductive polymers [15,30,37,89,173,158,195–201] and carbon nanotubes [103]. For example, 3D graphene/Ni(OH)2 composite hydrogels prepared by Xu and coworkers exhibited a specific capacitance of ~ 1212 F g− 1 at a discharge rate of 2 A g− 1, while only ~ 309 F g− 1 for the physical mixture of these two components was obtained [49]. After the cycling test at 16 A g−1 for 2000 charge and discharge cycles, only a slight decrease in capacitance (~5%) was exhibited. Similarly, using 3D hierarchical β-Ni(OH)2 hollow microspheres wrapped in rGO, Wang et al. [170] obtained a specific capacitance of 1551.8 F g−1 at a current density of 2.67 A g−1 and a capacity retention of 102% after 2000 cycles. The good performance of these composites mainly results in the synergetic effect of graphene and the other components. First, the pseudo-capacitive materials contribute pseudocapacitance to the whole composite electrode. Second, graphene sheets can effectively prevent the aggregation of nanoparticles and make full use of the electrochemically active material. Third, the interconnected porous 3D structure facilitates electrolyte diffusion as well as electron transport through electrically conductive channel. Tour et al. fabricated a supercapacitor based on seamless three-dimensional carbon nanotube and graphene hybrid material [103]. The devices worked properly up to 4 V and the energy density reached a value 460 Wh kg−1, which was due to the high surface area and the covalent bonding between the graphene substrate and the CNT roots. The covalently bonded graphene and CNT carpets were synthesized using a sandwich structure with the catalyst layer between the graphene substrate and top buffer alumina layer. The growth metal substrates are directly used as the current collector for the supercapacitor. Towards the development of lightweight, flexible, and wearableelectronic devices, graphene foam-like structures with high porosity, flexibility, and robustness have the potential as highly compression-tolerant electrode materials for fabrication of compressible supercapacitors. Zhao et al. developed a unique method for in situ formation of poly(pyrrole)graphene (PPy-G) foam with a specific surface area of 463 m2 g−1, showing a specific capacitance of 350 F g−1 at the current of 1.5 A g−1 [89]. Remarkably, the specific capacitances of the supercapacitor with or without compressive strain of 50% did not change significantly even up to 1000 cycles. PPy is an important active material for supercapacitors

49

because of its stability and the high redox pseudocapacitive charge storage. The presence of conjugated polymer of PPy can not only enhance the capacitance performance of Ppy/G foam, but also increase the strength of 3D structure by strong π–π interaction to bear a certain extra force. Li et al. fabricated three dimensional polyaniline (PANI) array/graphenefilm alternatively formed 3D network structure through multistep nanowire growth and graphene deposition, displaying a power-density of 7622 W kg−1 and an energy density of 126 Wh kg−1 [200]. The highest specific capacitance obtained was 561 F g−1, and the electrochemical properties could retain 78% after 1000 cycles. Although binary materials exhibit good electrochemical performance as electrode for supercapacitors, each type of them has its pros and cons. So a great deal of attention has been focused on designing and synthesizing ternary 3D graphene-based composite electrode materials to fully overcome their disadvantages [105,175–177,181–183]. Yang et al. developed a Ni − Al layered double hydroxide (LDH), CNT and rGO ternary nanocomposite electrode material, and acquired a specific capacitance of 1562 F g−1 at 5 mA cm−2, the residual capacitance of 713.4 F g−1 at the current density of 100 mA cm−2, and a 96.5% capacitance retention after 1000 cycles [181]. The improvement of the electrochemical performances is mainly due to the synergic effect of three components. Firstly, low internal electrical resistance for efficient charge transport in the hybrid electrode is obtained since graphene sheets are used as conductive substrate and CNTs are the electron transmission channels; Secondly, a great deal of mesopores in the interconnected Ni − Al LDH platelets benefit electrolyte transport and ions diffusion; Thirdly, the individual components utilization efficiency is improved since the agglomeration phenomenon is hindered by the porous open nanostructure of LDH/CNTs/graphene composite with large surface area. Tour et al. fabricated field-emitter devices and doublelayer capacitors using the porous nickel/graphene/CNT structure [105]. An almost constant specific capacitance as the scan rate increased from 0.2 A/g to 1.00 A/g was obtained, indicating the high diffusion conductivity of the active material and the electrolyte. The excellent performance is due to the fact that the 3D nanostructured hybrid materials have good interfacial contacts and volume utilization. 3.1.4. Fuel cells Fuel cell is an important device for energy conversion and storage, which generates electricity by oxidizing fuel at anode and reducing oxygen from air at cathode [24]. Considerable efforts have been dedicated to the design of fuel cells with outstanding energy density, suitable operating temperatures and low impact for environment. Electrocatalyst is the key to improve the oxygen reduction reaction and fuel oxidation reaction in fuel cell. Up to date, graphene-based catalysts attest fastidious concerns due to fantastic conductivity, optical transparency, and thermal, optical and electrochemical stability [6,202]. Especially, with rich porosity and multidimensional electron transport path, 3D graphene structure is highly desirable for catalyst loading to facilitate the mass transfer and maximize the accessibility to the catalyst surfaces [203–208]. Catalysts for the oxygen reduction reaction (ORR) are critical components of fuel cells. Wu et al. developed a CNTs-supported graphenerich non-precious metal (Fe) oxygen reduction catalyst [209]. No performance loss for 500 hours in a hydrogen/air fuel cell was exhibited in the catalyst, resulting from the unique composite structure comprised of carbon nanotubes and graphene. The improved catalyst stability in acid media benefited the oxygen mass transfer, water removal from catalyst surfaces, corrosion resistance, and electronic conductivity. Sattayasamitsathit et al. [210] demonstrated that Pt nanoparticles on 3D graphene catalysts exhibited a more excellent electrocatalytic activity for ORR than that of Pt nanoparticles on a 3D carbon substrate and on a glassy carbon electrode, bare 3D graphene and Pt black. Such metal nanoparticle decorated multi-layer 3D graphene allowed for high mass transport access and catalytic activity. However, the high cost and low durability of Pt-based catalysts remain major obstacles for

50

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

further development of this technology. Doped graphene-based 3D materials have become a kind of hopeful metal-free or non-precious metal catalysts for ORR due to the superior catalytic activity, long-term tolerance and stability, and environmental friendliness [204,205,211,212]. Lin and coworkers observed that the linear-sweep voltammetric (LSV) measurements of 3D nitrogen-doped graphene exhibited a one-step four-electron pathway for ORR with a mean transferred electron number of 3.7 in an alkaline electrolyte, and much higher diffusion current density than that of Pt/C electrode, undoped graphene and glassy carbon electrode [211]. Wu et al. made a comparison between 3D Ndoped graphene aerogel-supported Fe3O4 nanoparticles (Fe3O4/NGAs), Fe3O4 nanoparticles supported on N-doped carbon black (Fe3O4/ N-CB) and N-doped graphene sheets (Fe3O4/N-GSs) for ORR performance in acidic media [204]. Fe3O4/N-GAs exhibited a more positive onset potential, higher cathodic density, lower H2O2 yield, and predominant electron transfer number. The enhanced ORR activity is beneficial to (i) the presence of two forms of nitrogen, namely, pyrrolic N and pyridinic N serves as catalytically active sites for oxygen reduction; (ii) the macropores structure of 3D graphene materials makes for the diffusion rate of the electrolyte and the full exposure of active sites; (iii) the large surface area and porosity enhance interfacial contact. Very recently, Chen et al. found that sulfur doped graphene foam had well-defined characteristic ORR peak, centered at about 0.45 V, while the current was apparently low and the oxygen reaction peak was also weak for S-doped graphene sheet and GO [212]. After being cycled 1000 times in an alkaline electrolyte, no significant decrease in the peak current density for the oxygen reduction reaction could be detected. The stable and good electrochemical catalytic activity can be ascribed to the cooperative catalytic effect of the doped sulfur and the 3D structure of the graphene foam. Another vital requirement for improving fuel cell performances is developing highly active catalysts for oxidation of fuel molecules, such as methanol, ethanol, glucose, sucrose, or lactose [206,208,213–216]. For example, Qiu et al. investigated the electrocatalytic activity of 3D graphene-supported Pt (Pt/3D graphene) for methanol oxidation [213]. As shown in Fig. 7a, in the cyclic voltammetry curves, the specific current density at ∼ 0.7 V on Pt/3D graphene was higher than that on Pt/rGO sheets and over twice as high compared to that of Pt/carbon black. According to the ratio of two anodic current densities, the oxidation of methanol on the Pt/3D graphene was more efficient than that of commercial Pt/carbon black and Pt/rGO sheets. The electrochemically active surface area of the Pt/3D graphene retained ∼ 65% after 2000 cycles. The improved catalytic activity and stability benefit from the 3D structures with large void volume, good electrical conductivity and large surface area. It should be noted that (i) the interconnected network offers continuous and multiplexing routes for electron transfer; (ii) the porous

structure is conducive to fluid flow and mass transfer process within catalyst layer, leading to further improvement for Pt usage; (iii) high corrosion resistance of graphene material can significantly reduce the support corrosion problem, thus acquiring fine stability. In an effort to substitute precious metal, Chen et al. developed a unique fuel cell based on Co3O4/3D graphene to efficiently harvest electricity from various sweet fuels (glucose, sucrose, or lactose) [217]. The glucose-powered fuel cell with good long-term stability (only ~ 27% run-down after 30 days) offered an open circuit voltage of ~1.1 V and a power density output of 2.38 ± 0.17 mW cm−2. Such performance is due to the synergistic effect between the exceptional dual catalytic abilities of Co3O4 and the extraordinary properties of 3D graphene network. As shown in Fig. 7b, at the anode, the Co(III) sites of Co3O4 nanostructures efficiently catalyze glucose oxidation via conversion of the Co(III) to Co(II). Then the produced electrons are rapidly transferred to the cathode through the multiplexed conductive highways of the graphene foam. At the cathode, O2 molecules will be reduced by the Co(II) sites via its conversion to higher valence states (Co(III) or Co(IV)). After receiving electrons from the anode, Co(III) or Co(IV) soon return to the divalent state. The current in the solution is produced by the proton flux from the anode to the cathode. In this process, graphene foam provides a 3D scaffold to support the abundant Co3O4 catalysts as well as a highly-conductive 3D network and macroporous structure for rapid charge transport and the diffusion of ions and substances. Very recently, the same author demonstrated a novel enzymatic biofuel cells equipped with enzyme-functionalized 3D graphene/ CNTs hybrid electrodes using glucose as the fuel and oxygen as the oxidizer [218]. Such biofuel cells can almost attain the theoretical limit of open circuit voltage (~ 1.2 V) and a power density of 2.27 ± 0.11 mW cm−2. Microbial fuel cells (MFCs), another kind of green and renewable energy source, can convert chemical energy in organic materials into electricity via a bio-oxidation process. However, the low anode loading of bacteria and the sluggish electron transfer between bacteria and electrodes lead to a low power density, which limits its practical applications. 3D GBMs seem to be the favorable competitor for microbial fuel cells. For instance, Yong et al. reported a macroporous and monolithic MFC anode based on polyaniline hybridized 3D graphene (3D G/PANI) [207]. The maximum power density of 3D G/PANI MFC was ∼ 768 mW m− 2, higher than that from the carbon cloth MFC (∼158 mW m−2) and carbon fiber brush anode (~332 mW m−2). The output power density depends on the bacterial loading and extracellular electron transfer efficiency. The macroporous structure of this 3D electrode facilitates sufficient substrate exchange to support bacteria (S. oneidensis MR-1) colonization. The foam can harvest electrons via direct electron transfer from OmcA cytochrome proteins on S. oneidensis

Fig. 7. (a) CVs of Pt/3D graphene, Pt/rGO, and Pt/C electrodes in 0.5 M H2SO4 + 1.0 M methanol solution. Reproduced with permissio from Ref. [213]. Copyright 2013 American Chemical Society. (b) Illustration of glucose-powered FC based on a 3D graphene/Co3O4 anode and cathode. Reproduced with permission from Ref. [217]. Copyright 2013 Royal Society of Chemistry.

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

MR-1, and then promote direct electron transfer between bacteria and electrode by the synergistic integration between 3D graphene and PANI. What’s more, the multiplexing and highly conductive pathways of graphene network are also advantageous to the improved electric performance. However, the role of 3D GBM in MFCs inspires more exciting developments in this still young yet very promising field in the future. 3.1.5. Dye-sensitized solar cells Solar cell is able to convert solar energy into electrical power, and thus has been considered as one of the state-of-the-art solutions to satisfy the global energy requirements. Dye-sensitized solar cells (DSSCs) have been proved to be one of the cost-effective potential options due to their decent photon-to-electric efficiency, low fabrication costs and convenient manufacturing process [219]. Recently, it has been demonstrated that 3D GBMs can replace Pt-based counter electrodes, improve TiO2 photoanode and enhance the stability of electrolyte solvent [220–227]. Counter electrode, an indispensable component in DSSCs, aims to inject charge into the electrolyte and catalyzes the reduction of tri-iodide. Xue and coworkers found that N-doped graphene foams (N-GF) can be used as a metal-free counter electrode for DSSC [228]. The resultant DSSC showed a power conversion efficiency up to 7.07%, which was comparable to the efficiency of 7.44% achieved with a platinum counter electrode and surpassed that of undoped rGO sponge (4.84%) or a spin coated nitrogen doped rGO film (4.2%). Ahn et al. reported that CVDgrown P-doped 3D graphene nanonetworks (3D GNs) as the counter electrode material exhibited a maximum photoconversion efficiency of 8.46%, which was 6.01% greater than that of Pt [227]. It is believed that an optimized 3D graphene-based DSSC can be used as massproducible and cost-efficient replacement for platinum in DSSCs. This excellent performance results from the heteroatom doping-induced high electrical conductivity and good electrocatalytic activity, coupled with the 3D foam structure with large surface area, good surface hydrophilicity, and well-defined porosity for enhanced electrolyte–electrode interaction and electrolyte/reactant diffusion. The TiO2 layer is the pivotal component as a “bridge” between photoelectrons generated from dye molecules and anode in DSSC. Incorporating a conductive network into TiO2 is an effective way to promote charge transfer and reduce backward recombination. For instance, Tang et al. added 3D graphene networks (3D GN) into the photoanode to boost the photovoltaic performance of DSSC. The cell with 3D GN (1 wt%)/P25 gave a short circuit current density (Jsc) of 15.9 mA cm−2, an open-circuit voltage (Voc) of 677 mV, a fill factor (FF) of 63.9%, and a power conversion efficiency of 6.87% [222]. The outstanding electrical property is attributed to the rapid electron transport at the interface, the depressed recombination of electro-holes pairs, large surface area, increased dye adsorption and low defect density, which benefit from the 3D GN. Analogously, Yen et al. incorporated 3D graphene/CNTs hybrid material within TiO2 matrix and used it as a photoanode [226]. The DSSCs demonstrated a conversion efficiency of 6.11%, which was 31% higher than that of conventional TiO2-based devices. Organic solvents such as acetonitrile with low viscosity and fantastic dielectric constant are usually used as the electrolyte for DSSC. The leakage problem and the poor stability over time that resulted from the volatile of organic solvents are the important obstructions for the commercialization of DSSCs. Gel electrolyte as quasi-solid state electrolyte shows great potential in DSSC due to its good stability and photovoltaic efficiency. Neo et al. reported the formation of organogels of 3methoxypropionitrile (MPN) using graphene oxide as the gelator and used the gels as the quasi-solid state electrolyte in DSSC [221]. This DSSC with a GO/MPN gel electrolyte showed a photovoltaic efficiency of 6.70%, which was quite close to that (7.18%) of the control liquid DSSC. The improved efficiency of DSSC can be explained that small GO sheets caused by ultrasonication can promote the ion transport in gels. Moreover, GO/MPN gel electrolyte of DSSC dropped by only 11% after

51

31 days, which was better stability than the liquid electrolyte (dropped by 19%) due to the less volatile. 3.2. Hydrogen energy production and storage With the ever-aggravating environmental impacts caused by consumption of fossil fuels, the sustainable and renewable energy are acquiring more and more attention [115]. Hydrogen is regarded as a desirable candidate for the alternate fuel source due to its nonpolluting abundance, clean combustion and fantastic energy density [229–231]. Nevertheless, the production and storage of hydrogen become the restrictive factors for practical applications [230]. Recently, it has been demonstrated that 3D GBMs may be a kind of promising materials due to tunable 3D hierarchical interconnected network, macroscopic monolithic and porous structure and large surface area, electrical conductivity, and chemical stability [13,47,232]. 3.2.1. Hydrogen production Photocatalytic water splitting is considered as a hopeful strategy for clean, low-cost, and environmental friendly production of H2 by utilizing solar energy [233]. Although many materials are capable of photocatalytically producing hydrogen, the energy conversion efficiency is still low and far from practical application. Because the three crucial steps for the water splitting reaction: solar light harvesting, charge separation and transportation, and the catalytic reduction and oxidation reactions, are not efficient enough or simultaneously [234]. It seems that 3D graphene-based photocatalysts can solve these limitations. For instance, Gao et al. designed a system of nanocomposite graphene hydrogel (NGH) consisting of a photostable TiO2 and Au nanostructure for photocatalytic H2 production under xenon arc lamp

Fig. 8. (a) Photocatalytic H2 production studies of the various samples. (b) The photocatalytic mechanism of the NGH/Au/TiO2 under ultraviolet and visible light irradiation. Reproduced with permission from Ref. [47]. Copyright 2013 Royal Society of Chemistry.

52

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

[47]. In Fig. 8a, a thoughtful comparison was carried out about the photocatalytic activities among pure TiO2 nanorods, 2D rGO/TiO2 and NGH with different Au loading under different light wavelength irradiations. The photocatalytic activity of NGH increased to 167–242 μmol h−1 g−1, which outperformed TiO2 nanorods (~156 μmol h−1 g−1) and 2D rGO/ TiO2 (51 μmol h−1 g−1). As illustrated in Fig. 8b, the incident photons are absorbed by Au nanoparticles via the localized surface plasmon resonance excitation under visible light irradiation. The generated electrons from the Au nanoparticles are injected into the TiO2 conduction band leading to the generation of holes in the Au nanoparticles. The holes are quenched by sacrificial electron donors. Upon UV-vis irradiation, TiO2 absorbs photons of energy greater than the band gap which generates electron–hole pairs. All the excited electrons are in turn transferred from the TiO2 conduction band to the graphene active sites to produce protons in the solution to form H2. The outstanding performance is due to that (i) NGH 3D framework with large surface area have desirable pores that facilitate liquid access and diffusion and open structure for the integration of functional nano-materials (e.g. TiO2, Au); (ii) the rapid recombination of photogenerated electrons and holes are prevented via interconnected highly conductive electrical pathways. Electrocatalytic water splitting is the other central to the area of hydrogen energy. The electrochemical hydrogen evolution reaction (HER, i.e., 2H+ + 2e− → H2) from water splitting also needs advanced catalysts with a high current density at a low overpotential. Liao et al. developed a highly active and stable electrocatalyst via an in situ formation of MoS2 nanocomposite on 3D architectural graphene foam (MGF) with a nanometer scale pore size [235]. The MoS2/MGF nanocomposites exhibited reformative HER activity with low overpotential and large apparent cathodic currents. Such enhanced catalytic activity stems from the abundance of catalytic sulfur edge sites, the increase of electrochemically accessible surface area and the unique synergic effects between the MGF support and active catalyst. The hydrogen evolution at MoS2 catalytic edge sites is prominent by Volmer-Heyrovsky (rate determining step) mechanism. In detail, the overall HER reaction occurs via a rapid discharge step (Volmer-reaction, Eq. (1)) followed by an ion and atom reaction (Heyrovsky reaction, Eq. (2)) in acidic media; Discharge reaction

kV

H3 Oþ þ M þ e− ⇄ H2 O þ M‐H

Ion and atom reaction

kV−

ð1Þ

kH

M‐H þ H3 Oþ þ e− ⇄ H2 þ M þ H2 O ð2Þ kH−

nature of MGFs might be specially suited to H2 uptake. Using a 3D platform consisting of GO layers and 1D CNTs, Aboutalebi et al. obtained a hydrogen capacity of up to 2.6 wt% at room temperature, which outperformed pure GO, MWCNTs, and rGO/MWCNTs [240]. Utilising the intercalation of MWCNTs as 1D spacers was the key factor to induce reformative hydrogen storage capacity while the presence of reducing graphene oxide resulted in inadequate interspacing between layers. Well-defined layered GO structure with less structural defects and suitable interlayer spacing results in much higher. Further, Wu et al. investigated the adsorption of molecular hydrogen on 3D pillared graphene under various environments [231]. A low temperature, a high pressure, and a large gap between graphene sheets could maximize the hydrogen adsorption capacity while only slightly improvement was acquired by increasing the CNT diameter. An unstable adsorption stage would result from the instantly repulsive interaction between C and H2 because of an overlap. Moreover, the H2 molecules adsorbed on graphene were easily desorbed at high temperature due to a weaker C-H2 binding energy. Storage of atomic hydrogen based on hydrogen spillover is the other approaches for hydrogen storage. Hydrogen spillover is the dissociative chemisorption of hydrogen on metal nanoparticles, and followed by transporting hydrogen or H atom produced from activator to receptor via surface diffusion. 3D graphene doped with nickel (0.83 wt%) and boron (1.09 wt%) revealed a hydrogen storage capacity of 4.4 wt% at 77 K and 106 kPa, which was higher than that of pristine graphene and all carbon-based materials [229]. The presence of Ni–B alloys in 3D graphene was the main reason for the dissociative chemisorption of hydrogen molecules by spillover, and therefore, causing a high hydrogen storage capacity. In details, the hydrogen molecules attached to the Ni–B nanoalloys were dissociated to hydrogen atoms and then diffused to the sites of the graphene to form C–H bond. This study opens a new approach to explore the mechanisms of hydrogen storage based on hydrogen spillover in 3D graphene-based materials. 4. 3D graphene-based materials for environmental application 3D graphene-based monolith can be used as a general platform for sensing pollutants in water or air, and also as a platform for removing hazardous species by the means of adsorption or catalytic degradation. Compared with functionalized graphene sheets featured with 2D layer structure, large surface area, conjugated domains and oxygenated groups, 3D GBMs with a high porosity have more advantages, including the improved adsorption and catalytic capability, and the ease of separation from solution without needing auxiliary magnetic or centrifugation techniques [20].

Where M denotes an active edge site of the catalyst and M-H denotes a hydrogen atom adsorbed at that edge site.

4.1. Pollutants detection

3.2.2. Hydrogen storage The design of hydrogen storage materials with high gravimetric and volumetric density need urgently to be developed. Porous carbons materials for hydrogen storage have received significant attention due to their large surface area, large pore volume, good chemical stability and ease tailored porosity [236]. Among them, GBMs with 3D network nanostructure have been confirmed to possess outstanding hydrogen storage capacity based on theoretical predictions and experimental results [230,231,237–240]. Hydrogen is a non-polar molecule and its interactions with graphenebased systems are based on instantaneous dipole–dipole induced forces. A hierarchical micro- and mesoporous metallomacrocycle-graphene framework (MGFs) was constructed using two distinct building blocks, GO and metallomacrocycle [13]. This hybrid exhibited H2 adsorption capacity of 1.54 wt% at 77 K and 1 bar with a large hysteresis. The H2 storage capacity of MGFs was enhanced via three factors: (i) more sp2 C species that served as the H2 uptake site were exposed since the GO layers were significantly reduced; (ii) high valent Ni(III) opened metal centers as strong Lewis acidic sites appeared to the pores; (iii) the microporous

Electrochemical method for detecting pollutants in water or air shows properties of high sensitivity, fast response, low cost and which is suitable for constructing portable devices. In order to sensitively and electrochemically detect explosives, the electrode of electrochemical sensor should have good adsorptive characteristics, fast charge transfer capability, and low background current [241]. 3D graphene porous material with large surface area owns highly conductive performance, chemical stability and low electrical noise, and thereby, making it an ideal candidate for chemical sensors [242]. For example, Guo et al. reported that ionic liquid (IL)/3D graphene composites with mesoporosity and large specific surface area (487 m2 g−1) could be used for detecting trace trinitrotoluene [243]. The hybrids showed low background current, a sensitivity of 1.65 μA cm−2 per ppb and low detection limit of 0.5 ppb, which were much superior to that of IL/CNT (0.99 μA cm−2 per ppb) and IL/graphite (0.36 μA cm−2 per ppb) composites. Over 200 measurements, about 92% of the original response was retained, demonstrating that the electrodes had good stability. The improved sensitivity is believed that 3D graphene material can significantly increase the reaction surface area of electrodes and enhance

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

the current of the charge transfer reaction between the electrode and solution species for lower electrode polarization. Utilizing 3D graphene micropillar/enzyme (Tyrosinase) biosensor, Liu et al. obtained a determined detection sensitivity of 3.9 nA μM− 1 cm− 1 and a detection limit of 50 nM for phenol [244]. 3D graphene micropillar structure with large surface area enhances the enzyme biosensing capability by increasing the amount of the immobilized enzymes as well as the superlative graphene conductivity property. The measurement of harmful gases (e.g. NO, NO2, NH3) is desirable in environmental monitoring, chemical process controlling and personal safety. Yavari et al. demonstrated a parts-per-million level detection of NO2 and NH3 in air at room temperature using macroscopic and continuous graphene foam-like (GF) 3D networks device [14]. NH3 is a reducing agent with a lone electron pair that can be donated to the ptype GF thereby reducing the conductance, while NO2 acts as a p-type dopant for the GF resulting in a decrease in the resistance. Ng et al. applied a 3D graphene/ionic liquid nanocomposite as electrodes to detect NO gas [245]. The sensor showed a fast response of less than 4 seconds, an sensitivity of 11.2 μA cm−2 (μmol L−1)−1 and a low detection limit of 16 nM, which was more superior than that of other NO sensing devices based on gold nanoparticles and CNTs. Reformative sensitivity and stable operation of the device are due to that (i) graphene with large electrochemically active surface area makes charge carrier transport through the foam highly sensitive to the adsorption/desorption of gas species; (ii) the large porosity makes it possible for gas molecules to infiltrate uniformly into the entire structure. Interestingly, Yang et al. produced a highly sensitive 3D graphene foam-based NO2 sensor on a flexible paper substrate without photolithographic and electron-beam evaporation processes [242]. Under either compressive or tensile strain conditions, the sensor on a paper substrate owned sensitivity up to 13.5–16.7% (200 ppm) and 22.6–23.4% (800 ppm), respectively. The performance of flexible chemical sensors is mainly due to that the electrical conductance of GF shows less dependence on the strain when compared with that of 2D graphene layers. It should be believe that the paper and 3D graphene foam with light-weight and pliable character are suitable for advanced flexible electronic devices. 4.2. Application of 3D graphene-based materials in adsorption Adsorption is a surface phenomenon in which the adsorbates are attracted to the surface of solid adsorbent and form attachments via physical or chemical bond [2]. A large number of adsorbents including zeolites [2], silica gel [246], activated carbon [247], clay [248], plastic resin pellets [249], carbon nanotube, etc. have been widely used for purifying polluted water. In recent years, it has been demonstrated that 3D graphene-based monoliths can be used as effective sorbents for inorganic and organic contaminants removal because of large surface area, highly porous structures, strong mechanical strengths, interconnected channels, flexibility and stability [7,9,46,250–255]. Table 2 lists the recent reports on the adsorption of organic and inorganic pollutants by 3D graphene-based materials. 4.2.1. Inorganic pollutants in water The adsorption of inorganic pollutants (e.g. heavy metal, ClO-4, fluoride) on graphene-based 3D monoliths is very complicated and appears attributable to ligand exchange, static electrical attraction, precipitation and surface complexation [258,265,266]. For example, 3D graphene macroscopic objects (3D GMOs) were synthesized by CVD process and used for the removal of Cd2 +, Pb2 +, Ni2+ and Cu2+ ions [259]. From Fig. 9a, platinum (Pt) foils and free-standing 3D-GMOs were served as the anodes and the cathodes, repectively. Aqueous solutions containing single heavy metal ions (e.g. Cd2 +, Pb2 +, Cu2 +, Ni2 +) were used as electrolytes. As shown in Fig. 9b, after 20 min deposition, an electrical adsorption capacity of 434, 882, 1683 and 3820 mg g−1 corresponded to Cd2 +, Pb2 +, Ni2 + and Cu2 + were obtained, respectively. Such

53

Table 2 Previous researches in the utilization of 3D graphene-based materials as adsorbents for the removal of pollutants in water. Materials

Adsorbate

Adsorption capacity (mg/g)

Ref.

GO/CS GO/CS GO/CMC

Cu(II), Pb(II) Cu2+ Cu2+, Pb2+, Ni2+ Co2+, Cd2+ Pb(II), Cd(II) Cr(VI), Pb(II) Cd2+, Pb2+ Ni2+, Cu2+ Malachite green

70, 90 25.4 82.93, 76.7, 72.04, 59.99, 41.13 336.32, 145.48 139.2, 373.8 434, 882 1683, 3820 186, 242 960 397, 467 800 390, 326 184, 72.5, 11.5 160 (g g−1) 87.63, 120 207.06, 260.38 1100 1350

[38] [256] [257]

G/PDA G/α-FeOOH Graphene foam GO/agarose rGO/agarose GO/DNA GO sponge GO/PEI GO/CS Graphene sponge

rGO/polyurethane G/P25 G/TiO2 G/PDA GO/biopolymer

Safranine O Methylene blue, Methyl violet Amaranth Methylene blue, Eosin Y Methylene blue, Rhodamine B, Methyl orange Chloroform Methylene blue Rhodamine B, p-nitrophenol Methylene blue, Methyl violet

[258] [45] [259] [260] [261] [78] [262] [38] [263]

[113] [264] [258] [265]

outstanding adsorption capacity has been attributed to (i) large area templates (560 m2 g−1) for the deposited products of metal ions offer the electrolytic deposition continuously; (ii) the remarkable conductivity (12 S cm−1) ensures the good electrolytic deposition rate; (iii) the density (100 mg cm−3) and cross-linked structure sustain the stability of 3D GMOs during the deposition process. Functional molecules, including CS, DNA, polydopamine (PDA), carboxymethyl cellulose (CMC), α-FeOOH, iron oxides etc, can be anchored onto 3D graphene platform to improve the adsorption capacity and stability, and thus satisfying practical requirements [38,45,256–258, 265–269]. Vadahanambi et al. synthesized 3D graphene-carbon nanotube-iron oxide nanostructures for arsenic removal (Fig. 10a) [267]. As illustrated in Fig. 12a, carbon nanotubes vertically were standing on graphene sheets and iron oxide nanoparticles were attached on both graphene surfaces and carbon nanotubes. From Fig. 10b, the 3D nanostructures showed almost double adsorption capacity in comparison with 2D iron-decorated graphene hybrids. This remarkable performance originates directly from following reasons: (i) 3D nanostructure with mesoporosity and open pore network facilitates fast molecular diffusion as well as promotes the accessibility of iron oxides; (ii) the concentrated, uniformly dispersed, and spatially separated iron oxide nanoparticles provide enough active sites for arsenic capture; (iii) arsenic is bound as a surface complex layer on the Fe2O3 and FeOOH particles. Zhang et al. used 3D graphene-polypyrrole (Ppy) film as an electrically switched ion exchanger for perchlorate removal from wastewater [270]. The green process of electrically switched anion exchange almost finished within 20 s. The film exhibited a significantly improved uptake capacity for ClO-4 in comparison with Ppy film alone. The better uptake is possibly attributed to the 3D porous nanostructure (with pore diameters ranging from 200 to 800 nm) that facilitates ClO-4 to easily diffuse into or out of the film. 4.2.2. Organic pollutants in water Graphene-based 3D materials have been applied in removing various organic contaminants from wastewater, such as dyes [78,252,255, 258,260,261,264,265,271–273], aromatic compounds [258], chloroform [113,263,271], toluene [271], and oil [58,85,90,101,102,253,255,263, 274–277]. With regards to the interactions between the organic

54

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

Fig. 9. Removing heavy metal ions by electrolytic deposition on 3D GMOs. Reproduced with permission from Ref. [259]. Copyright 2013 Nature Publishing Group.

pollutants and the adsorbents, many mechanisms may have simultaneous interactions, including van der Waals type interactions, π–π bonds (cation–π bond), electrostatic interactions, hydrogen bonds and anion–cation interaction, hydrophobic interactions [45,57,78,91,156, 258,259,263,268,272–274]. But the predominant adsorption mechanism is not the same for different organic pollutants. For instance, 3D rGO-based hydrogels with large surface area (298.2 m2 g−1) and mesoporous structure showed effective removal capabilities for methylene blue (MB) (~ 100%) and Rhodamine B (RhB) (~ 97%) because of strong π–π stacking and anion–cation interactions [272]. Sui et al. reported that 3D GO/PEI porous composite can be served as a suitable adsorbent for acidic dyes (amaranth) with an adsorption capacity of 800 mg g−1 [262]. Several factors result in the reformative adsorption capacity: (i) pore diameter (~11.1 nm) is large enough to facilitate the diffusion of dye; (ii) the driving force between protonated amine groups and sulfonated groups of dye is beneficial for acidic dye adsorption; (iii) large specific surface area and abundant conjugated domains of GO can greatly increase the contact opportunity of dye molecules on GO sheets. Graphene foams or sponges with high surface area, uniform structure, chemical stability in organic solvents, ability to withstand high temperatures, highly hydrophobic and oleophillic surfaces and flexibility have been proved to be feasible for the removal of oil and other organic solvents. For instance, graphene/CNT hybrid foam showed good removal capacity for oils and organic solvents owing to its superhydrophobic and superoleophilic property (the water contact angle was 152.31°) [101]. The adsorption capacity of this foam ranged from 80 to 130 times of its own weight, relying on the density, viscosity

and surface tension. Li et al. exploited 3D graphene/polypyrrole foam with wide range of macropores as an absorber [90]. The adsorption process completed within 5 min and the sorption capacity was more than 100 g g−1 for oil. Oil sorption mainly occurred in large pores and the disordered mesoporous structure. The σ electron in the absorbed molecules can couple with the π electron on the graphene/polypyrrole composite. Recycling tests demonstrated that more than 95% sorption capacity of this foam for diesel oil could be preserved after 10 cycles. Besides, other hybridized materials, including rGO/polyurethane sponge [113], Ni-doped graphene/carbon cryogels [278], and graphene/ polydopamine [279], have also been used for oil-water separation. After adsorption process, absorbed liquids can be readily released by mechanical extrusion or heating or completely burned off in air without destroying the original structures over many cycles, resulting in superior regenerated and reused performance. Fig. 11 shows the whole process of oil–water separation, oil recycling and treatment, and materials regeneration, which has been outlined in our previous report [17]. According to these excellent characteristics, graphene-based foam or sponge can be considered as new generation materials for oil spill cleanup. 4.2.3. Gas adsorption Gaseous pollutants into atmosphere, specifically governed by the precipitation of rain water, volatilization (diffuse-source inputs) or accidental spillage, constitute an accumulative, persistent and detrimental terrorist towards the survival of aquatic compartments, flora, fauna and environmental matrix (water and soil) [280]. With tunable pore widths, volumes, binding sites and large surface area, 3D GBMs as

Fig. 10. (a) Schematic diagram of 3D G/CNT/Fe nanostructures. (b) Adsorption isotherms of 3D G/CNT/Fe nanostructures and 2D iron-decorated graphene for arsenic removal. Reprinted with permission from Ref. [267]. Copyright 2013 American Chemical Society.

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

candidates of adsorbers are used for removing various gaseous pollutants (e.g. sulfur dioxide (SOx), nitrogen oxides (NOx) and acetone gas and purifying natural gas, such as methane, N2, H2, H2O, CO2 etc [75, 262,281–284]. The sorption of gas-phase molecules may strongly depends on the static electrical interaction, van der Waals interaction or chemical interaction between gas molecules and functional groups of materials. He et al. endeavored to advocate an initial study examining the adsorption behavior of acetone gas onto GO foams (Fig. 12a) with different GO concentrations (0.2–0.8 wt%), complying saturation adsorption efficiency (ade) of over 100%, which outperformed rGO foam, CNT powder, bamboo carbon (BC) and active carbon (AC) (Fig. 12b) [77]. The good performance is due to that acetone is a polar molecule, and the polarity of GO is the closest to that of acetone compared to rGO, AC, CNT, and BC. Sudeep et al. obtained an ordered, stacked macroscopic 3D GO network solid (poly-GO) with highly porous interconnected structures [284]. The poly-GO sample had a CO2 uptake capacities of 2.7 mmol g− 1 at a pressure of 20 atm, which was better than that of many other carbon-based materials. The facts are benefited from the following four reasons: (i) the micro- and mesopores presented in 3D network act efficiently as active sites for CO2 adsorption; (ii) the van der Waals weak interaction and chemical interaction between polyGO network and gas molecules contributes to the CO2 uptake; (iii) the cross-linked 3D network of poly-GO is propitious to maximize the interaction potential between CO2 molecules and GO surface. Polyethylenimine (PEI) has high amine density and accessible primary amine sites on chain ends. Utilizing 3D GO/polyethylenimine with uniform porous network and high amine density, Sui et al. exhibited an adsorption capacity of 11.2 wt % at 1.0 bar and 273 K for carbon dioxide, which was larger than hydrothermal reduced graphene (HTG) and GO samples and comparable to the carbon material reported previously at the same condition [262]. The uptake capacity of CO2 is related to the basic sites, the large specific surface area and the interaction between amino groups of PEI and CO2 molecular. 4.3. Photocatalytic decomposition of organic pollutants Organic species have been one of most serious pollutants of the environment. The photodegradation of organic pollutants has been

55

considered as an energy-effective pathway for environmental remediation. 3D graphene architectures have been incorporated with functional nanoparticles to form composite catalysts, which exhibit significantly enhanced activities in the photodegradation of organic pollutants. Moreover, the photocatalysts also show surpassing mechanical strength, stability and durability [9,202,264]. 3D graphene-based composites consisting of graphene and metal oxides (TiO2 [46,264], CuO2 [285] and Fe2O3 [286]) or metal nanoparticles (Au [42], Ag [287], Cu [274] or Ni [288]) or others [252,289–291], have been constructed for photocatalytic degradation of organic pollutants. Hou et al. studied the photocatalytic activity of graphene/P25 hydrogels for the degradation of MB under visible irradiation [264]. This hydrogels showed better photocatalytic efficiency compared with the bare P25 and P25-MWCNTs-graphene hydrogels, as indicated in Fig. 13a. Similar report had been shown by Zhang et al. and in the presence of TiO2/graphene hydrogels, the degradation of MB can be completed within 30 min [46]. In contrast, nearly 33% of the initial dye still remains in solution after the same time period for neat TiO2 nanoparticles. After five cycles of photocatalytic reaction, 53% of photocatalytic activity of TGH still remained. According to Fig. 13b, the improved performance can be explained by (i) graphene act as an acceptor of the photogenerated electrons by TiO2 and suppress charge recombination; (ii) electrons transfer stereoscopically in TiO2/graphene hydrogels through the 3D graphene networks whereas they would be restricted to a plane in 2D TiO2/graphene sheets; (iii) 3D porous stereostructure benefits to the adsorptivity of hydrogel for pollutants. Zeng et al. prepared 3D CNTs/rGO implanted Cu2O composite spheres for degrading methyl orange (MO) under visible illumination in the presence of H2O2 [285]. About 99.8%, 77.6%, 72.3% and 67.9% of MO was degraded on CNTs/rGO/Cu2O, rGO/Cu2O, CNTs/Cu2O and pure Cu2O spheres, respectively, which may attribute to the synergistic effect between CNTs/rGO and Cu2O. Cu2O matrix with sphere morphology can provides enough active substance for catalytic action. Under visible illumination, electrons are excited from the valence band (VB) to the conduction band (CB). The photogenerated electrons in CB of Cu2O tend to transfer to the 3D embedded structure of the CNTs/rGO. CNTs/rGO can function as an electron collector and transporter to lengthen the lifetime of the charge carriers, leading to the hole-electron separation. Meanwhile,

Fig. 11. The schematic diagram of oil–water separation, oil recycling and treatment, and materials regeneration process. Reprinted with permission from Ref. [17]. Copyright 2014 Springer.

56

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

Fig. 12. (a) SEM image of GO foam. (b) Ade of different carbon materials for acetone. Reprinted with permission from Ref. [77]. Copyright 2013 Elsevier Ltd.

•OH radicals generated from the reduction of H2O2 by the photogenerated electrons directly decompose the dye. Zhang et al. pillared chemically exfoliated graphene oxide with carbon nanotubes using acetonitrile as the carbon source and nickel nanoparticles as the catalyst [288]. The Ni metal particle presented at the end of CNTs was a good electron mediator, surface-adsorbed O2 could easily trap the electrons from the Ni particles to form various reactive oxygen species, leading to an efficient pollutants degradation.

5. Conclusions and outlook 3D GBMs with macro-, micro- and nano-structures have been applied to construct various attractive electrochemistry energy devices, sorbents and catalysts. A variety of methods including hydrothermal/ solvothermal reaction, self-assembly, organic sol–gel reaction and template guided growth have been developed for preparing 3D graphenebased materials. The 3D architectures do not only assemble graphene nanosheets into macroscopic materials for practical applications but also provide fundamental frameworks with more “space” for loading inorganic nanoparticles, organic or biological molecules. Although extensive efforts have been devoted, studies about materials fabrication and their applications in energy and environmental-related field are still in primary stages. At least, the following challenges still remain. A green and facile method is highly required to synthesize 3D graphene architectures with designed compositions, shapes, pore sizes and porosity. For instance, large pores with size up to a few hundred nanometers in 3D graphene framework are not good for electrolyte filtration in supercapacitors, resulting in low electric double layer

capacitance. Moreover, the exact relationship between structure and properties for forming 3D GBMs has not been clearly understood. It is essential to develop novel and efficient materials for energy storage and produce. To enhance the capacitance (or energy density) of pure 3D graphene, pseudo-capacitive materials are usually suitable. How to combine 3D graphene with these functional materials including metal oxides, conductive polymers and metal organic framework to utilize their synergistic effect? Among the numerous potential dopants, what are the most suitable and efficient dopants and methods for the improved capacitive behavior of 3D graphene materials? So there is tremendous room available in the design and synthesis of novel 3D graphene-based materials for energy-related applications. Although some literatures indicated that 3D graphene-based products have prominent ability in the field of pollutants detection and environmental remediation. There are a lot of pollutants and microorganism that exist in circumstance, and only a small part of them have been explored. Thus, the mechanisms of pollutants detection and removal based on multifunctional 3D GBMs need to be further developed. Porous graphene-based 3D architectures with the porosity and flow characteristics can be applied for flow-through reactors in separation and catalytic processes. The safe operation and “green chemistry” in environmental protection should also be considered for practical applications. With tunable pore widths, volumes, binding sites and large surface area, 3D graphene materials exhibit interesting properties for gaseous pollutants capture. But the researches are still at their initial stage. Whether composites based on 3D graphene architectures are promising strategies for carbon capture, gaseous pollutants removal and even dust capture in atmosphere or indoor environment?

Fig. 13. (a) The concentration changes of MB during photodegradation; (b) The charge behavior at interfaces in 2D P25/graphene sheets and 3D P25/graphene networks; Reprinted with permission from Ref. [264]. Copyright 2012 Elsevier Ltd.

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

Last but not least, graphene-like 2D materials (e.g. boron nitride, transition metal dichalcogenides, metal halides) have been found to own great potential for energy and environmental-related application [292]. However, research about the transition from 2D systems to 3D systems for energy and environmental applications is almost blank and may be an interesting and promising field. These issues present the research communities with challenges and opportunities to exploit the potential of 3D graphene-based materials. It is deeply believed that the ever-increasing efforts to search new 3D graphene-related functional materials will bring more exciting results in various fields. Acknowledgements The authors gratefully acknowledge the financial support provided by the National Water Pollution Control and Management Technology Major Project of China (No. 2009ZX07212-001-02), the National Natural Science Foundation of China (No. 21276069, 71221061), and the Hunan Province Innovation Foundation for Postgraduate (No. CX2014B142). References [1] Li SL, Xu Q. Energy Environ Sci 2013;6:1656. [2] Khin MM, Nair AS, Babu VJ, Murugan R, Ramakrishna S. Energy Environ Sci 2012;5: 8075. [3] Thavasi V, Singh G, Ramakrishna S. Energy Environ Sci 2008;1:205. [4] Wang H, Yuan X, Wu Y, Huang H, Peng X, Zeng G, et al. Adv Colloid Interface Sci 2013;195–196:19. [5] Geim KA, Novoselov SK. Nat Mater 2007;6:183. [6] Chang H, Wu H. Energy Environ Sci 2013;6:3483. [7] Li C, Shi G. Nanoscale 2012;4:5549. [8] Zhang J, Zhao F, Zhang Z, Chen N, Qu L. Nanoscale 2013;5:3112. [9] Nardecchia S, Carriazo D, Ferrer ML, Gutierrez MC, Monte FD. Chem Soc Rev 2013; 42:794. [10] Jiang L, Fan Z. Nanoscale 2014;6:1922. [11] Lim HN, Huang NM, Lim SS, Harrison I, Chia CH. Int J Nanomedicine 2011;6:1817. [12] Chen S, Qiao S. ACS Nano 2013;7:10190. [13] Kim TK, Cheon JY, Yoo K, Kim JW, Hyun SM, Shin HS, et al. J Mater Chem A 2013;1: 8432. [14] Yavari F, Chen Z, Thomas AV, Ren W, Cheng HM, Koratkar N. Sci Rep 2011;1:166. [15] Zhang L, Zhang F, Yang X, Long G, Wu Y, Zhang T, et al. Sci Rep 2013;3:1408. [16] Zhang DW, Li XD, Li HB, Chen S, Sun Z, Yin XJ, et al. Carbon 2011;49:5382. [17] Wang H, Yuan X. Environ Sci Pollut Res 2014;21:1248. [18] Biener J, Stadermann M, Suss M, Worsley MA, Biener MM, Rose KA, et al. Energy Environ Sci 2011;4:656. [19] Jiang H, Lee PS, Li C. Energy Environ Sci 2013;6:41. [20] Li C, Shi G. Adv Mater 2014;26:3992. [21] Chabot V, Higgins DC, Yu A, Xiao X, Chen Z, Zhang J. Energy Environ Sci 2014;7: 1564. [22] Cao XH, Yin ZY, Zhang H. Energy Environ Sci 2014;7:1850. [23] Luan VH, Tien HN, Hoa LT, Hien NTM, Oh ES, Chung J, et al. J Mater Chem A 2013;1: 208. [24] Guo S, Dong S. Chem Soc Rev 2011;40:2644. [25] Huang X, Qi X, Boey F, Zhang H. Chem Soc Rev 2012;41:666. [26] Xu YX, Lin ZY, Huang XQ, Liu Y, Huang Y, Duan X. ACS Nano 2013;7:4042. [27] Chen P, Yang JJ, Li SS, Wang Z, Xiao TY, Qian YH, et al. Nano Energy 2013;2:249. [28] Adhikari B, Biswas A, Banerjee A. Langmuir 2012;28:1460. [29] Sahu A, Choi WI, Tae G. Chem Commun 2012;48:5820. [30] Zhou H, Yao W, Li G, Wang J, Lu Y. Carbon 2013;59:495. [31] Zhang L, Wang T, Wang H, Meng Y, Yu W, Chai L. Chem Commun 2013;49:9974. [32] Huang P, Chen W, Yan L. Nanoscale 2013;5:6034. [33] Li W, Wang J, Ren J, Qu X. Adv Mater 2013;25:6737. [34] Bai H, Sheng K, Zhang P, Li C, Shi G. J Mater Chem 2011;21:18653. [35] Cong HP, Wang P, Yu SH. Chem Mater 2013;25:3357. [36] Das S, Irin F, Ma L, Bhattacharia SK, Hedden RC, Green MJ. ACS Appl Mater Interfaces 2013;5:8633. [37] Ouyang W, Sun J, Memon J, Wang C, Geng J, Huang Y. Carbon 2013;62:501. [38] Chen Y, Chen L, Bai H, Li L. Mater J Chem A 2013;1:1992. [39] Xu YX, Wu Q, Sun YQ, Bai H, Shi G. ACS Nano 2010;4:7358. [40] Huang C, Bai H, Li C, Shi G. Chem Commun 2011;47:4962. [41] Wang E, Desai MS, Lee SW. Nano Lett 2013;13:2826. [42] Li J, Liu CY, Liu Y. Mater J Chem 2012;22:8426. [43] Yua M, Liu A, Zhao M, Dong W, Zhao T, Wang J, et al. Sens Actuator B Chem 2014; 190:707. [44] Yuan J, Zhu J, Bi H, Meng X, Liang S, Zhang L, et al. Phys Chem Chem Phys 2013;15: 12940. [45] Cong HP, Ren XC, Wang P, Yu SH. ACS Nano 2012;6:2693. [46] Zhang Z, Xiao F, Guo Y, Wang S, Liu Y. ACS Appl Mater Interfaces 2013;5:2227.

[47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120]

57

Gao M, Peh CKN, Ong WL, Ho GW. RSC Adv 2013;3:13169. Li L, Hu ZA, Yang YY, Liang PJ, Lu AL, Xu H, et al. Chin J Chem 2013;31:1290. Xu Y, Huang X, Lin Z, Zhong X, Huang Y, Duan X. Nano Res 2012;6:65. Fan J, Shi Z, Lian M, Li H, Yin J. Mater J Chem A 2013;1:7433. Moon YE, Jung G, Yun J, Kim HI. Mater Sci Eng B 2013;178:1097. Ye S, Feng J, Wu P. J Mater Chem A 2013;1:3495. Huang H, Chen P, Zhang X, Lu Y, Zhan W. Small 2013;9:1397. Worsley MA, Pauzauskie PJ, Olson TY, Biener J, Satcher JJH, Baumann TF. J Am Chem Soc 2010;132:14067. Zhang X, Sui Z, Xu B, Yue S, Luo Y, Zhan W, et al. J Mater Chem 2011;21:6494. Wu X, Zhou J, Xing W, Wang G, Cui H, Zhuo S, et al. J Mater Chem 2012;22:23186. Han Z, Tang Z, Li P, Yang G, Zheng Q, Yang J. Nanoscale 2013;5:5462. Li J, Wang F, Liu CY. J Colloid Interface Sci 2012;382:13. Hu H, Zhao Z, Wan W, Gogotsi Y, Qiu J. Adv Mater 2013;25:2219. Xu Z, Zhang Y, Li PG, Gao C. ACS Nano 2012;6:7103. Peng Q, Li Y, He X, Gui X, Shang Y, Wang C, et al. Adv Mater 2014;26:3241. Sun H, Xu Z, Gao C. Adv Mater 2013;25:2554. Kim KH, Oh Y, Islam MF. Nat Nanotechnol 2012;7:562. Zhang F, Tang J, Wang Z, Qin LC. Chem Phys Lett 2013;590:121. Zhang M, Gao B, Cao X, Yang L. RSC Adv 2013;3:21099. Chen M, Tao T, Zhang L, Gao W, Li C. Chem Commun 2013;49:1612. Ramontja J, Ray SS, Pillai SK, Luyt AS. Macromol Mater Eng 2009;294:839. Dervishi E, Hategekimana F, Boyer L, Watanabe F, Mustafa T, Biswas A, et al. Chem Phys Lett 2013;590:126. Dong X, Wang X, Wang L, Song H, Zhang H, Huang W, et al. ACS Appl Mater Interfaces 2012;4:3129. Brownson DAC, Figueiredo-Filho LCS, Ji X, Gomez-Mingot M, Iniesta J, FatibelloFilho O, et al. J Mater Chem A 2013;1:5962. Ahn HS, Kim JM, Park C, Jang JW, Lee JS, Kim H, et al. Sci Rep 2013;3:1960. Li N, Zhang Q, Gao S, Song Q, Huang R, Wang L, et al. Sci Rep 2013;3:1604. Zhang X, Yeung KK, Gao Z, Li J, Sun H, Xu H, et al. Carbon 2014;66:201. Singh E, Chen Z, Houshmand F, Ren W, Peles Y, Cheng HM, et al. Small 2013;9:75. Lu X, Wei A, Fan Q, Wang L, Chen P, Dong X, et al. Mater Res Bull 2012;47:4335. Ming R, Zhang P, He X, Feng J, Ding Y, Chang F, et al. Microsc Nano Lett 2013;8:66. He Y, Zhang N, Wu F, Xu F, Liu Y, Gao J. Mater Res Bull 2013;48:3553. Liu F, Chung S, Oh G, Seo TS. ACS Appl Mater Interfaces 2012;4:922. Liu F, Seo TS. Adv Funct Mater 2010;20:1930. Niu Z, Chen J, Hng HH, Ma J, Chen X. Adv Mater 2012;24:4144. Ahn HS, Kim H, Kim JM, Park SC, Kim JM, Kim J, et al. Carbon 2013;64:27. Zhang W, Zhu J, Ang H, Zeng Y, Xiao N, Gao Y, et al. Nanoscale 2013;5:9651. Chen Z, Ren W, Gao L, Liu B, Pei S, Cheng HM. Nat Mater 2011;10:424. Kuang J, Liu L, Gao Y, Zhou D, Chen Z, Han B, et al. Nanoscale 2013;5:12171. He Y, Liu Y, Wu T, Ma J, Wang X, Gong Q, et al. J Hazard Mater 2013;260:796. Ahn HS, Jang JW, Seol M, Kim JM, Yun DJ, Park C, et al. Sci Rep 2013;3:1396. Zhang HB, Yan Q, Zheng WG, He Z, Yu ZZ. ACS Appl Mater Interfaces 2011;3:918. Li C, Yang G, Deng H, Wang K, Zhang Q, Chen F, et al. Polym Int 2013;62:1077. Zhao Y, Liu J, Hu Y, Cheng H, Hu C, Jiang C, et al. Adv Mater 2013;25:591. Li H, Liu L, Yang F. J Mater Chem A 2013;1:3446. Gedler G, Antunes M, Realinho V, Velasco JI. Polym Degrad Stabil 2012;97:1297. Kung CC, Lin PY, Buse FJ, Xue Y, Yu X, Dai L, et al. J Biosens Bioelectron 2014;52:1. Dong X, Cao Y, Wang J, Chan-Park MB, Wang L, Huang W, et al. RSC Adv 2012;2: 4364. Yue HY, Huang S, Chang J, Heo C, Yao F, Adhikari S, et al. ACS Nano 2014;8:1639. Zhao YQ, Zhao DD, Tang PY, Wang YM, Xu CL, Li HL. Mater Lett 2012;76:127. Dong X, Wang X, Wang J, Song H, Li X, Wang L, et al. Carbon 2012;50:4865. Si P, Dong XC, Chen P, Kim DH. J Mater Chem B 2013;1:110. Luo J, Liu J, Zeng Z, Ng CF, Ma L, Zhang H, et al. Nano Lett 2013;13:6136. Wei W, Yang S, Zhou H, Lieberwirth I, Feng X, Mullen K. Adv Mater 2013;25:2909. Dong XC, Xu H, Wang XW, Huang YX, Park MB, Zhang HL, et al. ACS Nano 2012;6: 3206. Dong X, Chen J, Ma Y, Wang J, Chan-Park MB, Liu X, et al. Chem Commun 2012;48: 10660. Wang W, Guo S, Penchev M, Ruiz I, Bozhilov KN, Yan D, et al. Nano Energy 2013;2: 294. Zhu Y, Li L, Zhang C, Casillas G, Sun Z, Yan Z, et al. Nat Commun 2012;3:1225. Dervishi E, Biris AR, Driver JA, Watanabe F, Bourdo S, Biris AS. J Catal 2013;299:307. Yan Z, Ma L, Zhu Y, Lahiri I, Hahm MG, Liu Z, et al. ACS Nano 2013;7:58. Dervishi E, Bourdo S, Driver JA, Watanabe F, Biris AR, Ghosh A, et al. ACS Nano 2012;6:501. Pint CL, Alvarez NT, Hauge RH. Nano Res 2009;2:526. Lee DH, Lee JA, Lee WJ, Choi DS, Lee WJ, Kim SO. J Phys Chem C 2010;114:21184. Lin Y, Baggett DW, Kim J, Siochi EJ, Connell JW. ACS Appl Mater Interfaces 2011;3: 1652. Kaniyoor A, Jafri RI, Arockiadoss T, Ramaprabhu S. Nanoscale 2009;1:382. Machado BF, Marchionni A, Bacsa RR, Bellini M, Beausoleil J, Oberhauser W, et al. J Nat Gas Chem 2013;22:296. Lu J, Liu S, Ge S, Yan M, Yu J, Hu X. Biosens Bioelectron 2012;33:29. Liu Y, Ma J, Wu T, Wang X, Huang G, Liu Y, et al. ACS Appl Mater Interfaces 2013;5: 10018. Zhong C, Wang JZ, Gao XW, Wexler D, Liu HK. J Mater Chem A 2013;1:10798. Xu C, Xu B, Gu Y, Xiong Z, Sun J, Zhao XS. Energy Environ Sci 2013;6:1388. Chen S, Wang Y, Ahn H, Wang G. J Power Sour 2012;216:22. Sun Y, Wu Q, Shi G. Energy Environ Sci 2011;4:1113. Jiang X, Yang X, Zhu Y, Shen J, Fan K, Li C. J Power Sour 2013;237:178. Zhou G, Li F, Cheng HM. Energy Environ Sci 2014;7:1307. Wang G, Wang B, Wang X, Park J, Dou S, Ahn H, et al. J Mater Chem 2009;19:8378.

58

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59

[121] Ji L, Tan Z, Kuykendall T, An EJ, Fu Y, Battaglia V, et al. Energy Environ Sci 2011;4: 3611. [122] Wang C, Li Y, Chui YS, Wu QH, Chen X, Zhang W. Nanoscale 2013;5:10599. [123] Jian Q, He CN, Zhao NQ, Wang ZY, Shi CS, Liu EZ, et al. ACS Nano 2014;8:1728. [124] Hsieh CT, Lin CY, Chen YF, Lin JS, Teng H. Carbon 2013;62:109. [125] Hu C, Zhai X, Liu L, Zhao Y, Jiang L, Qu L. Sci Rep 2013;3:2065. [126] Xin X, Zhou X, Wang F, Yao X, Xu X, Zhu Y, et al. J Mater Chem 2012;22:7724. [127] Chen S, Bao P, Huang X, Sun B, Wang G. Nano Res 2014;7:85. [128] Wang C, Chui YS, Ma R, Wong T, Ren JG, Wu QH, et al. J Mater Chem A 2013;1: 10092. [129] Wu P, Wang H, Tang Y, Zhou Y, Lu T. ACS Appl Mater Interfaces 2014;6:3546. [130] Wang JZ, Zhong C, Wexler D, Idris NH, Wang ZX, Chen LQ, et al. Chem Eur J 2011; 17:661. [131] Li X, Huang X, Liu D, Wang X, Song S, Zhou L, et al. J Phys Chem 2011;115:21567. [132] Wang R, Xu C, Sun J, Gao L, Lin C. J Mater Chem A 2013;1:1794. [133] Chang Li J, Wang B, Luo H, He H, Song Q, Zhi L. J Mater Chem A 2013;1:14658. [134] Chen D, Wei W, Wang R, Zhu J, Guo L. New J Chem 2012;36:1589. [135] Zhou GW, Wang J, Gao P, Yang X, He YS, Liao XZ, et al. Ind Eng Chem Res 2013;52: 1197. [136] Wang B, Wu XL, Shu CY, Guo YG, Wang CR. J Mater Chem 2010;20:10661. [137] Lu LQ, Wang Y. Electrochem Commun 2012;14:82. [138] Zhang Y, Liu H, Zhu Z, Wong KW, Mi R, Mei J, et al. Electrochim Acta 2013;108:465. [139] Liang J, Liu Y, Guo L, Li L. RSC Adv 2013;3:11489. [140] Choi BG, Chang SJ, Lee YB, Bae JS, Kim HJ, Huh YS. Nanoscale 2012;4:5924. [141] Sun F, Huang K, Qi X, Gao T, Liu Y, Zou X, et al. J Ceram Int 2013;40:2523. [142] Shen L, Zhang X, Li H, Yuan C, Cao G. J Phys Chem Lett 2011;2:3096. [143] Yu M, Sun H, Sun X, Lu F, Hu T, Wang G, et al. Mater Lett 2013;108:29. [144] Liang J, Liu Y, Guo L, Li L. RSC Adv 2013;3:11489. [145] Chang K, Chen W. ACS Nano 2011;5:4720. [146] Zhou X, Wang F, Zhu Y, Liu Z. J Mater Chem 2011;21:3353. [147] Yang J, Wang J, Wang D, Li X, Geng D, Liang G, et al. J Power Sour 2012;208:340. [148] Ding YH, Ren HM, Huang YY, Chang FH, Zhang P. Mater Res Bull 2013;48:3713. [149] Yang Y, Pang R, Zhou X, Zhang Y, Wu H, Guo S. J Mater Chem 2012;22:23194. [150] Chen R, Zhao T, Lu J, Wu F, Li L, Chen J, et al. Nano Lett 2013;13:4642. [151] Xi K, Kidambi PR, Chen R, Gao C, Peng X, Ducati C, et al. Nanoscale 2014;6:5746. [152] Wang Z, Xu D, Xu J, Zhang L, Zhang X. Adv Funct Mater 2012;22:3699. [153] Fang Y, Luo B, Jia Y, Li X, Wang B, Song Q, et al. Adv Mater 2012;24:6348. [154] Zhai YP, Dou YQ, Zhao DY, Fulvio PF, Mayes RT, Dai S. Adv Mater 2011;23:4828. [155] Bello A, Fashedemi OO, Lekitima JN, Fabiane M, Dodoo-Arhin D, Ozoemena KI, et al. AIP Adv 2013;3:082118. [156] Yan J, Wei T, Shao B, Ma F, Fan Z, Zhang M, et al. Carbon 2010;48:1731. [157] Liu H, Wang Y, Gou X, Qi T, Yang J, Ding Y. Mater Sci Eng B 2013;178:293. [158] Xu Y, Lin Z, Huang X, Liu Y, Huang Y, Duan X. ACS Nano 2013;7:4042. [159] Chang Y, Han G, Yuan J, Fu D, Liu F, Li S. J Power Sour 2013;238:492. [160] Quan H, Shao Y, Hou C, Zhang Q, Wang H, Li Y. Mater Sci Eng B 2013;178:769. [161] Wang Y, Guo CX, Liu J, Chen T, Yang H, Li CM. Dalton Trans 2011;40:6388. [162] Dong XC, Xu H, Wang XW, Huang YX, Chan-Park MB, Zhang H, et al. ACS Nano 2012;6:3206. [163] Yu X, Lu B, Xu Z. Adv Mater 2014;26:1044. [164] Yu G, Hu L, Liu N, Wang H, Vosgueritchian M, Yang Y, et al. Nano Lett 2011;11: 4438. [165] Ge J, Yao HB, Hu W, Yu XF, Yan YX, Mao LB, et al. Nano Energy 2013;2:505. [166] Yuan J, Zhu J, Bi H, Zhang Z, Chen S, Liang S, et al. RSC Adv 2013;3:4400. [167] Ye S, Feng J, Wu P. ACS Appl Mater Interfaces 2013;5:7122. [168] Ge C, Hou Z, He B, Zeng F, Cao J, Liu Y, et al. J Sol-Gel Sci Technol 2012;63:146. [169] Wang Y, Gai S, Niu N, He F, Yang P. J Mater Chem A 2013;1:9083. [170] Wu ZS, Sun Y, Tan YZ, Yang S, Feng X, Mullen K. J Am Chem Soc 2012;134:19532. [171] Wang W, Guo S, Penchev M, Ruiz I, Bozhilov KN, Yan D, et al. Nanoscale 2013;5: 6291. [172] Ji CC, Xu MW, Bao SJ, Cai CJ, Lu ZJ, Chai H, et al. Colloid Interface Sci 2013;407:416. [173] Zhao C, Wang X, Wang S, Wang Y, Zhao Y, Zheng W. Int J Hydrogen Energy 2012; 37:11846. [174] Sridhar V, Kim HJ, Jung JH, Lee C, Park S, Oh IK. ACS Nano 2012;6:10562. [175] Chen XA, Chen X, Zhang F, Yang Z, Huang S. J Power Sour 2013;243:555. [176] Cheng Q, Tang J, Shinya N, Qin LC. J Power Sour 2013;241:423. [177] Gao H, Xiao F, Ching CB, Duan H. ACS Appl Mater Interfaces 2012;4:2801. [178] Bello A, Makgopa K, Fabiane M, Dodoo-Ahrin D, Ozoemena KI, Manyala N. J Mater Sci 2013;48:6707. [179] Bello A, Fashedemi OO, Fabiane M, Lekitima JN, Ozoemena KI, Manyala N. Electrochim Acta 2013;114:48. [180] Yang W, Gao Z, Wang J, Ma J, Zhang M, Liu L. ACS Appl Mater Interfaces 2013;5: 5443. [181] Zhou W, Cao X, Zeng Z, Shi W, Zhu Y, Yan Q, et al. Energy Environ Sci 2013;6:2216. [182] Ning G, Li T, Yan J, Xu C, Wei T, Fan Z. Carbon 2013;54:241. [183] Xu Y, Sheng K, Li C, Shi G. ACS Nano 2010;4:4324. [184] Yoon JC, Lee JS, Kim SI, Kim KH, Jang HJ. Sci Rep 2013;3:1788. [185] Chen J, Sheng K, Luo P, Li C, Shi G. Adv Mater 2012;24:4569. [186] Li Z, Wang J, Liu S, Liu X, Yang S. J Power Sour 2011;196:8160. [187] Yu G, Hu L, Vosgueritchian M, Wang H, Xie X, McDonough JR, et al. Nano Lett 2011; 11:2905. [188] Zhu Y, Murali S, Stoller MD, Ganesh KJ, Cai W, Ferreira PJ, et al. Science 2011;332: 1537. [189] Li Z, Wang J, Wang Z, Ran H, Li Y, Han X, et al. New J Chem 2012;36:1490. [190] Wang L, Wang D, Zhu J, Liang X. Ionics 2012;19:215. [191] Huang HF, Xu LQ, Tang YM, Tang SL, Du YW. Nanoscale 2014;6:2426. [192] He YM, Chen WJ, Li XD, Zhang ZX, Fu JC, Zhao CH, et al. ACS Nano 2013;7:174.

[193] Zhai T, Wang F, Yu M, Xie S, Liang C, Li C, et al. Nanoscale 2013;5:6790. [194] Lee YJ, Park HW, Kim GP, Yi J, Song IK. Curr Appl Phys 2013;13:945. [195] Dong X, Wang J, Wang J, Chan-Park MB, Li X, Wang L, et al. Mater Chem Phys 2012; 134:576. [196] Tai Z, Yan X, Xue Q. J Electrochem Soc 2012;159:A1702. [197] Gao K, Shao Z, Li J, Wang X, Peng X, Wang W, et al. J Mater Chem A 2013;1:63. [198] Han Y, Shen M, Wu Y, Zhu J, Ding B, Tong H, et al. Synth Met 2013;172:21. [199] Li L, Qiu J, Wang S. Electrochim Acta 2013;99:278. [200] Kim TY, Jung G, Yoo S, Suh KS, Ruoff RS. ACS Nano 2013;7:6899. [201] Huang C, Li C, Shi G. Energy Environ Sci 2012;5:8848. [202] Ren L, Hui KS, Hui KN. J Mater Chem A 2013;1:5689. [203] Wu ZS, Yang S, Sun Y, Parvez K, Feng X, Mullen K. J Am Chem Soc 2012;134:9082. [204] Ma Y, Sun L, Huang W, Zhang L, Zhao J, Fan Q, et al. J Phys Chem C 2011;115:24592. [205] Maiyalagan T, Dong X, Chen P, Wang X. J Mater Chem 2012;22:5286. [206] Yong Y, Dong X, Chan-Park MB, Song H, Chen P. ACS Nano 2012;6:2394. [207] Hu C, Cheng H, Zhao Y, Hu Y, Liu Y, Dai L, et al. Adv Mater 2012;24:5493. [208] Wu G, More KL, Xu P, Wang H, Ferrandon M, Kropf AJ, et al. Chem Commun 2013; 49:3291. [209] Sattayasamitsathit S, Gu Y, Kaufmann K, Jia W, Xiao X, Rodriguez M, et al. J Mater Chem A 2013;1:1639. [210] Lin Z, Waller GH, Liu Y, Liu M, Wong CP. Nano Energy 2013;2:241. [211] Chen L, Cui X, Wang Y, Wang M, Qiu R, Shu Z, et al. Dalton Trans 2014;43:3420. [212] Qiu H, Dong X, Sana B, Peng T, Paramelle D, Chen P, et al. ACS Appl Mater Interfaces 2013;5:782. [213] Jhan JY, Huang YW, Hsu CH, Teng H, Kuo D, Kuo PL. Energy 2013;53:282. [214] Wang Y, Liu H, Wang L, Wang H, Du X, Wang F, et al. J Mater Chem A 2013;1:6839. [215] Hu C, Zhai X, Zhao Y, Bian K, Zhang J, Qu L, et al. Nanoscale 2014;6:2768. [216] Chen Y, Prasad KP, Wang X, Pang H, Yan R, Than A, et al. Phys Chem Chem Phys 2013;15:9170. [217] Prasad KP, Chen Y, Chen P. ACS Appl Mater Interfaces 2014;6:3387. [218] Graetzel M. Acc Chem Res 2009;42:1788. [219] Wang H, Sun K, Tao F, Stacchiola DJ, Hu YH. Angew Chem Int Ed 2013;52:9210. [220] Neo CY, Ouyang J. Carbon 2013;54:48. [221] Tang B, Hu G, Gao H, Shi Z. J Power Sour 2013;234:60. [222] Xue Y, Liu J, Chen H, Wang R, Li D, Qu J, et al. Angew Chem Int Ed 2012;51:12124. [223] Lee JS, Ahn HJ, Yoon JC, Jang JH. Phys Chem Chem Phys 2012;14:7938. [224] Kim HN, Yoo H, Moon JH. Nanoscale 2013;5:4200. [225] Yen MY, Hsiao MC, Liao SH, Liu P, Tsai HM, Ma CM, et al. Carbon 2011;49:597. [226] Ahn HJ, Kim IH, Yoon JC, Kim SI, Jang JH. Chem Commun 2014;50:2412. [227] Xue Y, Liu J, Chen H, Wang R, Li D, Qu J, et al. Angew Chem Int Ed 2012;51:12124. [228] Wang Y, Guo CX, Wang X, Guan C, Yang H, Wang K, et al. Energy Environ Sci 2011; 4:195. [229] Wang Y, Wang K, Guan C, He Z, Lu Z, Chen T, et al. Int J Hydrogen Energy 2011;36: 13663. [230] Wu CD, Fang TH, Lo JY. Int J Hydrogen Energy 2012;37:14211. [231] Hou J, Yang C, Cheng H, Wang Z, Jiao S, Zhu H. Phys Chem Chem Phys 2013;15: 15660. [232] Ran J, Zhang J, Yu J, Jaroniec M, Qiao SZ. Chem Soc Rev 2014;43:7787. [233] Yang J, Wang D, Han H, Li C. Acc Chem Res 2013;46:1900. [234] Liao L, Zhu J, Bian X, Zhu L, Scanlon MD, Girault HH, et al. Adv Funct Mater 2013;23: 5326. [235] Sevilla M, Mokaya R. Energy Environ Sci 2014;7:1250. [236] Burress JW, Gadipelli S, Ford J, Simmons JM, Zhou W, Yildirim T. Angew Chem Int Ed 2010;49:8902. [237] Paul RK, Ghazinejad M, Penchev M, Lin J, Ozkan M, Ozkan CS. Small 2010;6:2309. [238] Kim G, Jhi SH. J Phys Chem C 2009;113:20499. [239] Aboutalebi SH, Aminorroaya-Yamini S, Nevirkovets I, Konstantinov K, Liu HK. Adv Energy Mater 2012;2:1439. [240] Alizadeh T, Zare M, Ganjali MR, Norouzi P, Tavana B. Biosens Bioelectron 2010;25: 1166. [241] Yang G, Lee C, Kim J. J Electrochem Soc 2013;160:B160–. [242] Guo CX, Lu ZS, Lei Y, Li CM. Electrochem Commun 2010;12:1237. [243] Liu F, Piao Y, Choi JS, Seo TS. Biosens Bioelectron 2013;50:387. [244] Ng SR, Guo CX, Li CM. Electroanalysis 2011;23:442. [245] Gupta VK, Suhas. J Environ Manag 2009;90:2313. [246] Mohan D, Singh KP. Water Res 2002;36:2304. [247] Qurie M, Khamis M, Manassra A, Ayyad I, Nir S, Scrano L, et al. Sci World J 2013; 2013:942703. [248] Holmes LA, Turner A, Thompson RC. Environ Pollut 2012;160:42. [249] Kemp KC, Seema H, Saleh M, Le NH, Mahesh K, Chandra V, et al. Nanoscale 2013;5: 3149. [250] Fan Z, Tng DZY, Nguyen ST, Feng J, Lin C, Xiao P, et al. Chem Phys Lett 2013; 561–562:92. [251] Nguyen-Phan TD, Shin EW, Pham VH, Kweon H, Kim S, Kim EJ, et al. J Mater Chem 2012;22:20504. [252] Cong HP, Ren XC, Wang P, Yu SH. ACS Nano 2012;6:2683. [253] Xiao X, Beechem TE, Brumbach MT, Lambert TN, Davis DJ, Michael JR, et al. ACS Nano 2012;6:3573. [254] Yin S, Niu Z, Chen X. Small 2012;8:2458. [255] Yu B, Xu J, Liu JH, Yang ST, Luo J, Zhou Q, et al. J Environ Chem Eng 2013;1:1044. [256] Zhang Y, Liu Y, Wang X, Sun Z, Ma J, Wu T, et al. Carbohydr Polym 2014;101:392. [257] Gao H, Sun Y, Zhou J, Xu R, Duan H. ACS Appl Mater Interfaces 2013;5:425. [258] Li W, Gao S, Wu L, Qiu S, Guo Y, Geng X, et al. Sci Rep 2013;3:2125. [259] Wang Y, Zhang P, Liu CF, Huang CZ. RSC Adv 2013;3:9240. [260] Xu Y, Wu Q, Sun Y, Bai H, Shi G. ACS Nano 2010;4:7358. [261] Sui ZY, Cui Y, Zhu JH, Han BH. ACS Appl Mater Interfaces 2013;5:9172.

H. Wang et al. / Advances in Colloid and Interface Science 221 (2015) 41–59 [262] [263] [264] [265] [266] [267] [268] [269] [270] [271] [272] [273] [274] [275] [276] [277] [278]

Zhao J, Ren W, Cheng HM. J Mater Chem 2012;22:20197. Hou C, Zhang Q, Li Y, Wang H. J Hazard Mater 2012;205–206:229. Cheng CS, Deng J, Lei B, He A, Zhang X, Ma L, et al. J Hazard Mater 2013;263:467. Chen Y, Zhang Q, Chen L, Bai H, Li L. J Mater Chem A 2013;1:13101. Vadahanambi S, Lee SH, Kim WJ, Oh IK. Energy Environ Sci 2013;47:10510. Cong HP, Ren XC, Wang P, Yu SH. ACS Nano 2012;6:2693. Li L, Zhou G, Weng Z, Shan XY, Li F, Cheng HM. Carbon 2014;67:500. Zhang S, Shao Y, Liu J, Aksay IA, Lin Y. ACS Appl Mater Interfaces 2011;3:3633. Bi H, Xie X, Yin K, Zhou Y, Wan S, He L, et al. Adv Funct Mater 2012;22:4421. Tiwari JN, Mahesh K, Le NH, Kemp KC, Timilsina R, Tiwari RN, et al. Carbon 2013; 56:173. Cheng JS, Du J, Zhu W. Carbohydr Polym 2012;88:61. Wu T, Chen M, Zhang L, Xu X, Liu Y, Yan J, et al. J Mater Chem A 2013;1:7612. Wang J, Shi Z, Fan J, Ge Y, Yin J, Hu G. J Mater Chem 2012;22:22459. Wu C, Huang X, Wu X, Qian R, Jiang P. Adv Mater 2013;25:5658. Wang H, Yuan X. Environ Sci Pollut Res 2014;21:1248. Wei G, Miao YE, Zhang C, Yang Z, Liu Z, Tjiu WW, et al. ACS Appl Mater Interfaces 2013;5:7584. Cheng C, Li S, Zhao J, Li X, Liu Z, Ma L, et al. Chem Eng J 2013;228:468.

[279] [280] [281] [282] [283] [284] [285] [286] [287] [288] [289] [290] [291]

59

Foo KY, Hameed BH. Adv Colloid Interface Sci 2011;162:22. Long Y, Zhang C, Wang X, Gao J, Wang W, Liu Y. J Mater Chem 2011;21:13934. Wang Y, Guan C, Wang K, Guo CX, Li CM. J Chem Eng Data 2011;56:642. Burress JW, Gadipelli S, Ford J, Simmons JM, Zhou W, Yildirim T. Angew Chem Int Ed 2010;49:8902. Sudeep PM, Narayanan TN, Ganesan A, Shaijumon MM, Yang H, Ozden S, et al. ACS Nano 2013;7:7034. Zeng B, Chen X, Ning X, Chen C, Deng W, Huang Q, et al. Appl Surf Sci 2013;276: 482. Cao X, Zheng B, Rui X, Shi W, Yan Q, Zhang H. Angew Chem Int Ed 2014;53:1404. He Y, Zhang N, Gong Q, Li Z, Gao J, Qiu H. Mater Chem Phys 2012;134:585. Zhang LL, Xiong Z, Zhao XS. ACS Nano 2010;4:7030. Li K, Chen T, Yan L, Dai Y, Huang Z, Guo H, et al. Catal Commun 2012;28:196. Zhang L, Xiong Z, Zhao X. ACS Nano 2010;4:7030. Yuan X, Wang H, Wu Y, Chen X, Zeng G, Leng L, Zhang C. Catal Commun 2015;61: 62. Varoon K, Zhang X, Elyassi B, Brewer DD, Gettel M, Kumar S, et al. Science 2011; 334:72.