Hindawi Publishing Corporation Journal of Nanomaterials Volume 2015, Article ID 257547, 20 pages http://dx.doi.org/10.1155/2015/257547
Review Article Nanotechnological Advances in Catalytic Thin Films for Green Large-Area Surfaces Suzan Biran Ay1 and Nihan Kosku Perkgoz2 1
Department of Chemical Engineering, Faculty of Engineering, Anadolu University, 26555 Eskisehir, Turkey Department of Electrical and Electronics Engineering, Faculty of Engineering, Anadolu University, 26555 Eskisehir, Turkey
2
Correspondence should be addressed to Nihan Kosku Perkgoz;
[email protected] Received 23 April 2015; Revised 21 August 2015; Accepted 23 August 2015 Academic Editor: Stefano Bellucci Copyright © 2015 S. Biran Ay and N. Kosku Perkgoz. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Large-area catalytic thin films offer great potential for green technology applications in order to save energy, combat pollution, and reduce global warming. These films, either embedded with nanoparticles, shaped with nanostructuring techniques, hybridized with other systems, or functionalized with bionanotechnological methods, can include many different surface properties including photocatalytic, antifouling, abrasion resistant and mechanically resistive, self-cleaning, antibacterial, hydrophobic, and oleophobic features. Thus, surface functionalization with such advanced structuring methods is of significance to increase the performance and wide usage of large-area thin film coatings specifically for environmental remediation. In this review, we focus on methods to increase the efficiency of catalytic reactions in thin film and hence improve the performance in relevant applications while eliminating high cost with the purpose of widespread usage. However, we also include the most recent hybrid architectures, which have potential to make a transformational change in surface applications as soon as high quality and large area production techniques are available. Hence, we present and discuss research studies regarding both organic and inorganic methods that are used to structure thin films that have potential for large-area and eco-friendly coatings.
1. Introduction Structuring thin films at nanometer scale enables distinctive mechanical, chemical, and physical surface functionalities including higher surface area, self-cleaning, photocatalytic, antibacterial, nontoxic, antifouling, hydrophobic, and oleophobic properties [1–6]. In addition to these, abrasion resistant and mechanically resistive features are important for durable and functional applications to save energy and provide clean air and water [7, 8]. Thus, green approaches are essential considering the population increase and growth in industry and their inevitable impact on the world’s natural resources. Such smart and functional coatings can be utilized in different fields including construction industry to enhance material properties and provide energy conservation [9], flexible surfaces with high hydrophobicity [10] and high conductivity [11], large-area solar modules [12, 13], structures with high mechanical strength [14], bioremediation [15], textiles [16], biomedical applications [17], antifouling [18],
and photocatalytic applications [19, 20]. Hence, with their superior surface properties, the nanostructured coating applications can be extended from self-cleaning processes [21–23] to the protection of cultural heritage assets [24] and food packaging [25]. In this review, we specifically focus on catalytic nanostructured large-area thin films that have potential to provide solutions for environmental pollution problems either at present time or in the future after some further advancement. These will include photocatalytic coatings since large-area photocatalytic applications offer potential solutions such as self-cleaning and receive industrial attention also regarding their additional properties (e.g., antibacterial, hydrophobic, and oleophobic properties). However, to examine organic and inorganic methods at once, catalytic enzymatic methods of implementing potentially green and low-cost coatings have been reported considering recent advances in genetic engineering and reduced cost of enzymes [26–29]. With the advances in the last years, incorporating biocatalysts in thin
2 films and coatings has been receiving considerable attention by different research groups due to superior biodegradability, selectivity, and less by-product formation compared to inorganic catalysts [30–32]. To remain in the scope of the topic, only the nanoscale and eco-friendly catalytic process research studies are included. This review excludes prior thin film nanoelectronics research work that cannot be associated with eco-friendly applications and focuses on novel methods to improve solid film catalytic efficiencies preferably at low cost for wide spread usage.
2. Increasing the Performance of Catalytic Thin Films 2.1. Methods for Enhanced Photocatalytic Efficiency. For about 40 years, photocatalysis in the presence of metal oxides [19, 33–37] and for the last decade enhancement of photocatalytic reactions in the presence of nanostructured particles have been investigated [38–43]. Different photocatalytic metal oxide semiconductors have been studied for numerous applications, some of which are water splitting [44, 45], oxidation of organic and inorganic pollutants [46–48], photocatalytic destruction of gaseous organic pollutants [49, 50], and photo disinfection [51]. Additionally, such photocatalytic materials have been used for different applications such as solar cells [52], chemical sensors [53], photoelectrochemical cells [54], and other novel devices [55]. Such a wide range of applications is viable for metal oxides because of their variety of electronic and structural possibilities allowing possible compounds with magnetic, conducting, insulating, or semiconducting behavior [56]. Among the metal oxides, in consequence of its specific properties such as high photocatalytic activity, stability and inertness together with its low cost, and nontoxicity, TiO2 has been exploited most thoroughly by a vast number of researchers and associated fundamental studies have been already discussed by several review articles [19, 20, 57–59]. There are numerous publications and considerable review reports for metal oxide photocatalysis in aqueous environment [48, 60, 61], which clearly shows that using metal oxide photocatalysis is a viable option for decomposing many inorganic contaminants including heavy metals as well as for destroying the microorganisms such as bacteria and viruses [62–65]. In these studies, although complete mineralization in remediation processes can be achieved, the processes are long, expensive, and not practical and lack flexibility to manufacture devices. Thus, photocatalytic reaction in solid form is an important requirement [66]. By this way, utilization of the metal oxides for large-area applications will be enabled. Apparently when photocatalytic particles are immobilized in thin films instead of being used in water environment, the activation environment is to be regulated cautiously due to the inherent reduction of photocatalytic area [67] and the emerging recombination problem [68, 69]. Photo-induced carriers are transmitted at the boundary of the photocatalyst and the adsorbed material and reaction efficiency is reduced for solid films because of reduced effective catalyst surface [57, 70]. Photocatalytic activity is found to improve with
Journal of Nanomaterials increasing TiO2 surface area and understandably higher UV light intensity is observed to have a positive effect on photocatalytic reactions [62]. Another important factor is the rather large energy bandgap of the common metal oxides for efficient optical absorption of solar spectrum. The most commonly used metal oxide, TiO2 , can absorb less than 5% of the solar energy irradiation if no modification is carried out [71]. Although photocatalyst with large bandgaps can still be applied effectively, obviously improving the light response range will make an important impact on such coatings to become economically viable for large areas. Hence, up to date, different techniques for better light absorption are implemented to overcome the issues related with wide application of such photocatalytic coatings [72]. Figure 1 shows the schematic diagram of methods, mechanisms, and challenges for higher efficiency of photocatalytic reactions in thin films. For photocatalytic functionality to become available for green applications with self-cleaning or antibacterial properties, it is essential to obtain high photocatalytic efficiency at large areas for the visible spectral range. Therefore, first of all, one must choose the photocatalytic material since its structural characteristics such as its crystallinity, geometric, and electronic properties are crucial to determine the overall performance [41, 73]. As it will be reviewed in more detail, size effect, in other words using nanoparticles, is of great importance for increased efficiency in solid films [74]. Another essential criterion for better performance is related to surface properties and, among the techniques to modify the surface features, nanostructuring techniques are promising [75]. Again, as it will be examined with a closer look, synergistic effect with a cocatalyst can improve the activation of redox radicals, decrease recombination of the generated electron-hole pairs, enhance carrier diffusion in bulk, and increase carrier transfer to surface. In general, the utilized techniques can enable changes on the surface or the bulk of the photocatalytic material or they can transform the material’s electronic structure. Thus, there are numerous production, doping, and hybridization techniques to enhance the photocatalytic activity and add other functionalities. Using such techniques, the active spectral range of photocatalytic materials can be controlled and electron-hole generation, recombination, and diffusion reactions can be regulated [76]. In this respect, nanotechnology can potentially present solutions to the current problems related to reaction efficiency and recombination rate in photocatalytic processes such as bandgap engineering, building heterostructured junctions and integration with cocatalysts. Additionally, to utilize the visible light from the sun, and hence improve the photocatalytic performance under solar light, nanostructure design is of great importance [77]. 2.1.1. Nanosize Effect. In the case of working with photocatalytic activation in aqueous environment, typically, photocatalytic particles are added into water and are later recovered from the environment after the photocatalytic process is completed, which increases both operation duration and expenses. For the processes to be less-priced and to take less time, these particles are immobilized in thin films, which also leads to new functionalities for coatings with innovative properties, which is not otherwise possible in aqueous
Journal of Nanomaterials
3
Growth and thin film formation techniques (i) Solvo-hydrothermal method, sol-gel, spray pyrolysis deposition, plasma, electrochemical and chemical vapor deposition, physical vapor deposition, magnetron sputtering, and so forth Choosing the photocatalyts: (i) Material properties (crystallinity,
Effective photocatalysis mechanisms
geometric, electronic properties, etc.) (ii) Surface properties
(i) Activation of redox radicals
(iii) Size effect
(ii) Carrier diffusion in bulk (iii) Carrier transfer to surface
(iv) Synergistic effect with a cocatalyst
Enhancement with: (i) Nanosize effect (ii) Bandgap engineering (iii) Heterojunctions (iv) Hybridizing with 1D and 2D materials (v) Doping (vi) Surface modification techniques (vii) Plasmonics
Challenges: (i) Large bandgap (absorption spectra) (ii) Recombination of photogenerated carriers (iii) Bulk and surface charge separation (iv) Control of redox potentials (v) Large-area applications
Figure 1: Schematic diagram of methods, mechanisms, and challenges for higher efficiency of photocatalytic reactions in thin films.
environment. On the other hand, because photo-induced carrier transfer happens at the boundary of the photocatalyst material and the adsorbed material [70], immobilization is expected to lower the catalyst surface and degrade the photocatalytic effectiveness [68, 78]. For example, when photocatalytic efficiency is compared in different forms of titanium dioxide between the forms of inorganic fiber, sputtering, slurry, and sol-gel, the slurry structure showed the highest performance [68]. The reason suggested for the lower efficiency in solid form is the higher recombination rate because of ionic specimen, relatively smaller active surface, and less chance of ion exchange [79]. Hence, the main problem in immobilization of metal oxides is the relatively low photocatalytic efficiency [80] for large-area photocatalytic applications to be widely used and provide solutions to pollution and environmental remediation. In this respect, one of the first approaches that aim to increase the photocatalytic efficiency of photocatalytic solids has been via employing nanostructured semiconductors, increasing charge carrier transfer on the reaction surface, or decreasing the recombination rate of electron-hole pairs [81, 82]. Thus, using nanoscale photocatalytic particles is beneficial to overcome the efficiency reduction because of their high surface-to-volume ratio [71, 83] when photocatalytic materials are immobilized in thin films and when it is expected for the photocatalytic activity to take place on the surface of a solid structure [84]. Specifically, the photochemistry of nanocrystalline metal oxides has taken great interest where the photophysical properties have been investigated thoroughly [74, 85, 86]. Transition between molecular and
bulk phases occurs when the diameter range is 1–10 nm and consequently different properties are obtained thanks to quantum effects [87]. For the case of bulk materials, the kinetic energies of photoexcited electrons can take various values as the density of states in the conduction band is rather high [85]. However, when the size of the particles gets as small as the size of the first excited state (or smaller), the generated electronhole pairs are enforced to move to an upper kinetic energy state [88]. Therefore, reduction of particle sizes to smaller than a threshold brings confined carriers in a potential well, similar to “particle in a box” case, which includes quantum mechanically interacting nanoparticles [89]. Hence, particle size directly affects the redox potential of holes in the valence band and that of electron in the conduction band [90] where holes and electrons are present on the nanoparticle surface together enabling simultaneous oxidative and reductive reactions [91]. Up to date, nanoparticles with various geometries and structures have been demonstrated: for example, 3D-ordered films of titania hollow spheres with adjusted sphere diameters have provided higher absorbance of visible light resulting in photocatalytic enhancement [92]. An ideal photocatalytic thin film should be stable, be of low cost, and allow for safe processes with high photocatalytic efficiency. Semiconductor metal oxides that are used as catalysts utilize the energy of incident light that exceeds the bandgap of the metal oxide material and produces electron-hole pairs. Upon the optical excitation of the material system by a photon with energy equal to or higher than bandgap energy of the photocatalytic
4
Journal of Nanomaterials COOH OH OH
AgCl RGO
h
Ag e
−
−−
−
−
H2
−
−
−
−
C −
h
MoS2
+
COOH
−
OH −
VB +
CO2 + H2 O
H+ H2
CB
UV light +
+
OH OH
−
H2 O
++
MoS2
COOH
OH OH COOH
+
TiO2
H2 O H 2
COOH
RhB (a)
(b)
Figure 2: Schematic drawings of photocatalytic activity of 2D material hybridized photocatalysts: (a) Ag@AgCl/RGO hybrids, “reprinted with permission from [103] Copyright 2011 American Chemical Society.” (b) TiO2 /MoS2 /graphene “reprinted with permission from [106] Copyright 2012 American Chemical Society.”
system, electron makes transition from the valence band to the conduction band and leaves a hole in the valence band. This photo-generated electron-hole pair then diffuses to the surface and initiates a chain of reactions. As a result, these excited states supply H+ , OH− , H2 O2 , and O2 − species, which degrade the existing pollutants. In fact, most common metal oxides have large bandgaps, which decrease the efficient utilization of solar light. This is due to the small portion of the UV light in natural sunlight (5%–8% of the solar spectrum at sea level) [93] reducing the fraction of the generated electronhole pairs, which limits the degradation of the organic materials. Another problem is related to losing electron-hole pairs in a very short time as recombination can be critically high when the conditions such as pH of the environment, size of the photocatalytic material, and adsorption are not appropriate [94]. Therefore, nanotechnological methods to improve the catalytic efficiency is appealing as surface area for catalytic reactions can be increased; the bandgap of the catalyst can be modified or recombination rate can be lowered. 2.1.2. Hybridizing with Other Systems. There are various surface structuring techniques including porous nanosphere, nanotube, nanorod, and nanowire formation to achieve surface functionality [71, 95]. Also, hybrid nanostructures, which include photocatalysts grown on graphene flakes [96– 98], microspheres coated with photocatalysts [99], polymer coated photocatalysts [100], hollow spherical hybrid photocatalysts [101], and other composites [102], have appealed considerable attention. Among these, as future prospects, 2D material hybridized photocatalysts are promising from perspectives of large-area applications and high efficiency. Figure 2 shows different hybrid models for increasing the photocatalytic efficiency. It is possible to use the interaction of plasmonic photocatalyst with a graphene sheet, facilitating enhanced absorbance in the visible region as a result of surface plasmon resonance absorption of Ag nanocrystal [103]. Figure 2(a) shows Ag@AgCl/RGO hybrids with rather low
charge recombination and enhanced photocatalytic activity [103]. Higher photocatalytic activity is explained by the effective charge transfer from plasmon-excited Ag nanocrystal to reduced graphene oxide [104] and the reduced charge recombination during photocatalytic process. Similar to graphene hybridization effect, BN-Ag3 PO4 composites showed higher photocatalytic activity than the pure Ag3 PO4 due to suppression of the electron-hole pair recombination [105]. ZnO/graphene composites have also been used to increase photocatalytic efficiency [107] where the coverage of graphene on the surface of ZnO nanoparticles has been found to be crucial for higher photocatalytic activity since the enhancement of photocatalytic activity of the hybrid structure is explained by the higher separation efficiency of electron-hole pairs. Similarly, TiO2 (P25)-graphene nanocomposite photocatalyst is shown to exhibit improved charge separation and enhanced light absorption [108]. In general, graphene in the composites is reported to act as an electron acceptor and transporter [109]. Figure 2(b) describes layered MoS2 /graphene hybrid as a high-performance photocatalyst for H2 evolution [106]. Although this study focuses on solar H2 generation system, the research work can be adopted to coatings technology as long as progress on largearea growth of 2D thin films continues [104, 110]. The enhanced photocatalytic activity in the case of MoS2 /graphene hybrid is attributed to the synergetic effect between the MoS2 and graphene components acting as an electron collector and a source of active adsorption sites, respectively. 2.1.3. Techniques for Surface Modification. The methods related to surface modification include a wide range of techniques which involve surface modification of metal oxide particles before embedding them in thin films and/or alteration of metal oxide-hybridized thin film surface [72, 111–113]. We will briefly examine the advancements of such surface techniques enhancing the photocatalytic activity. The extent of electron-hole pair diffusion into interfacial charge-transfer
Journal of Nanomaterials reactions determines photocatalytic efficiency directly [114]. Such charge-transfer reactions can be increased by different surface methods such as surface derivatization [115], chemical solution deposition with metal oxides such as Fe2 O3 and Al2 O3 [113], complexation-chelation [116], platinization [117], grafting polymer [118], using polymeric g-C3 N4 photocatalysts loaded with Ag nanoparticles [119], and depositing metals [120]. Adsorption of complexants is suggested to enhance the electron transfer from the conduction band to the acceptors [121]. Complexation of titanium surface ions is found to shift the redox level of Ti(IV)/Ti(III) electronic state to the conduction band avoiding electron trapping. Chelation relies on metal ions that react with organic molecules. Film derivation by using the suspension of nanoparticles takes interest due to low-temperature process enabling economic and largearea deposition. However nonuniform film surface is formed because of agglomerations [122]. Surface coverage by dyes is found to enhance optical absorption in the visible range [123]. Surface platinization of TiO2 has been investigated in the literature [124] as the platinized TiO2 shows high photocatalytic activity due to lower recombination rate under the presence of Pt deposits on TiO2 . It has been demonstrated that Pt provides electron trapping and enables interfacial electron transfer to acceptors [125]. Therefore, noble metals including Rh, Ni, Pt, and Pd can increase the electron transfer to O2 and hence the quantum yield [126, 127]. Electron-hole pair separation and reduction rates are improved by depositing these catalytic metals on semiconductor catalysts [111, 120]. 2.1.4. Combination of Photocatalysts. When cocatalysts are used to enhance each other’s catalytic activity, this leads to important benefits including higher photocatalytic efficiency and higher absorption of solar irradiation especially in the visible range. In the case of using composites, electron and hole transfer from one side to the other can decrease electronhole pair recombination rate. For the TiO2 -ZnO composite example, the hole transfer occurs from the valance band of ZnO to the valance band of TiO2 and the electron transfer occurs from the conduction band of TiO2 to the conduction band of ZnO [128]. In this process, the narrower indirect bandgap of TiO2 provides charge transfer to ZnO, whose conduction band is energetically equal to that of TiO2 [42]. There are other reports showing photocatalytic synergy effect and enhanced photocatalytic activity due to charge transfer [43, 129]. Also, such higher photocatalytic activity of composites is explained by the increased electron-hole transfer between the conduction and valence bands due to the high binding energy of ZnO together with the high reactivity of TiO2 [130]. The mechanisms of combined semiconductor systems and the obtained benefits such as higher electron-hole pair separation and holding reduction and oxidation reactions at two different reaction sites are demonstrated; when two different metal oxides establish a heterojunction, their work functions cause negatively charged carriers to transfer from the semiconductor with lower work function to the other semiconductor up to the state of thermal equilibrium [76, 131]. As an example for composite photocatalysts, g-C3 N4 / BiOBr material system is shown in Figure 3, indicating that
5 the obtained bandgap is lower than that for the pure BiOBr and an enhanced photocatalytic activity is obtained [132]. The most extensively considered photocatalyst, TiO2 , is in the form of either anatase, rutile, or brookite where these might also be mixed [133]. In the case of using mixed forms of TiO2 , electron transfer from the conduction band of anatase to that of rutile provides higher photodegradation. The cocatalysts stimulate operational transfer of photo-induced carriers by acting as an antenna to collect the carriers and contribute to increasing the efficiency of the charge-transfer process [134]. Bandgap engineering is another important approach for improving photocatalytic activity where conduction and valance bands are modified using the elements of the composite photocatalysts [135]. Regarding this method, it particularly focuses on water splitting processes [136] but considering its potential for large-area surfaces, recent advancements are included to this review. In this respect, Cu(II) modified Cd𝑥 Zn1−𝑥 O materials system is shown to have an extended absorption edge into the visible region and high mobility of holes in the valence band upon visible-light illumination [137]. 2.1.5. Doping Effect. To change the properties of photocatalytic materials, doping is commonly used and doping of various elements including transition metals and nonmetals together with their effect on the photocatalytic activity has been studied [76, 138–140]. Doping is found to be useful to enhance absorption properties of the large bandgap photocatalyst materials. Among the studied transition metal ion dopants, Fe3+ was shown to contribute to reduction in recombination of carriers [141, 142]. In fact, there are controversial results in literature because the way that the dopant is added to the system is crucial for the operation. For example, Cr3+ both can have a positive effect [143] and a negative effect [144] on photocatalytic performance. Mesoporous Au/TiO2 nanocomposites have also been found to show enhanced light absorption and relatively higher quantum efficiency resulting in superior photocatalytic efficiency [145]. Introduction of Zn and S has provided red shift of absorption edge for TiO2 based nanomaterials [146]. In addition to metals, nonmetals are also used for the modification of the electronic structure and hence photocatalytic efficiency and absorption regime. One of the possible elements is nitrogen [147, 148], which shows effect of bandgap narrowing down behavior. Another effective material can be boron, enhancing visible-light absorption and improving photocatalytic activity [149]. Using combination of boron and nitrogen as dopants [134] also exhibits higher visiblelight reactions whereas nitrogen might reduce surface charge transfer [41]. For the case of both carbon and sulphur doping, again improved photocatalytic activity under indoor daylight is observed [150, 151]. Liu et al. suggest that dopant locations and their chemical states allow for the intended surface conditions for efficient photocatalysis [76]. Figure 4 shows the possible mechanisms of nonmetal doping in TiO2 , which is found to be more beneficial than metal doping causing deterioration of surface structure due to the clusters.
6
Journal of Nanomaterials O2
O2 − Visible light
Visible light
CB − − −
CB − − −
−1.12 eV
0.29 eV 2.69 eV
2.77 eV
1.57 eV + + + VB
3.06 eV + + + VB
g-C3 N4
BiOBr
Organics
Products
Figure 3: Schematic of the separation and transfer of photogenerated charges in the g-C3 N4 /BiOBr composite, reproduced from [132] with permission from The Royal Society of Chemistry.
Conduction band −
−
− +
− 2E
F−
+
+
Higher melamine condensation products as sensitizers
+
Valence band (a)
F+
(b)
(c)
(d)
(e)
Figure 4: Suggested schemes for visible-light absorption in doped anatase TiO2 by nonmetal doping: (a) narrowing of bandgap; (b) introduction of localized states above valence band; (c) introduction of localized states below conduction band; (d) formation of color centres in the bandgap; and (e) sensitization by compounds containing nitrogen species, reproduced from [76] with permission from The Royal Society of Chemistry.
Although Figures 4(a)–4(e) show the possible reasons of visible-light absorption, the doping influence determining the electronic network is not totally clear. 2.1.6. Effect of Plasmonics. Plasmonic photocatalysis has been another alternative for increasing photocatalytic efficiency under visible-light irradiation [152–155]. This enhancement is explained by the excitation of localized plasmon polaritons on the surface of silver nanoparticles that provides a significant increase in the near-field intensities in the near UV supporting the photocatalytic behavior of TiO2 [152]. The schematics in Figure 5 show that the Au nanoparticle can absorb visible light and can excite more holes and electrons when compared to TiO2 itself [154]. The first intention of using plasmonic effect arises from the fact that the effective thickness of a TiO2 photocatalytic layer is limited due to its opaqueness. The structures consisting of noble metal nanoparticles distributed on semiconductor photocatalysts can also behave like a Schottky junction in addition to localized surface plasmonic resonance [154, 156]. Such Schottky diode structures are found to be useful because of their contribution to charge separation and transfer performance where localized surface plasmonic resonance is important for absorption of visible light.
2.2. Methods for Enhanced Biocatalytic Efficiency. In the recent years, an increasing interest has developed towards environment-friendly paints and coatings. In this respect, enzyme-added films receive a considerable attention [31, 157]. Biocatalysts are favored in green process applications [32] due to their low chemical consumption requirements and absence of toxic byproducts. In addition, they are safe, easy to use, effective in low doses, applicable for a specific- or wide-range use, environmentally benign, and cost-effective [23]. These biocatalytic coatings are used for bioremediation applications, such as easy-cleaning [22], detoxifying, and self-decontaminating surfaces [22, 158, 159], demonstrating strong antiviral, bactericidal, and sporicidal effects [23, 160, 161]. In this review, we discuss the methods used for incorporation of enzymes into and onto surface coatings specifically for large-area applications, namely, enzyme entrapment and using nanostructures for enzyme immobilization such as nanoparticles [160], single-walled [162], and multiwalled nanotubes [163]. Figure 6 shows different methods, challenges, and effective parameters to be considered for generation of high-performance biocatalytic thin films. Incorporation of enzymes into or onto solid materials is mostly achieved by either physical adsorption, covalent attachment, or matrix entrapment [164]. However,
Journal of Nanomaterials
7 Visible light
UV light
Acceptor
−
−
−
− − − Reduction product
−
−
−
+
+
+
− −
− (B)
+
E
+ + − + + − (A) + (C)
−
Adsorbed acceptor
+
−
−
+
Donor
Adsorbed donor
+
+ Oxidation product Au particle
Space charge region
TiO2 particle
Figure 5: Mechanism in plasmonic photocatalysis, reproduced from [154] with permission from IOP publishing.
Principle objective High biocatalytic efficiency for Large-area applications Challenges Incorporation methods of biocatalysts into Large-area coatings
(i) Improving catalytic efficiency (ii) Preventing enzyme leakage from the coating (iii) Obtaining uniformly dispersed
(i) Physical adsorption (ii) Covalent binding (iii) Entrapment (iv) Using nanocompositeenzyme conjugates
biocatalytic film (iv) Optimum enzyme loading high biocatalytic stability (long-term use)
Parameters to be considered (i) Selection of polymer/ paint matrix (ii) Understanding enzymematrix interactions (iii) Controlling leaching by bonding (iv) Enhancement in surface to volume ratio (v) Selection of coating method
Support material (i) Morphology (nanoparticles, single walledor multiwalled nanotubes; nanofibers) (ii) Surface functionality (iii) Porosity (iv) Composition
Figure 6: Schematic diagram of methods, challenges, and effective parameters for higher performance of biocatalytic thin films.
the relatively fragile nature of enzymes requires additional stabilization protocols before incorporation of the biocatalysts into the thin film coatings. Noncompatibility of the enzymes with hydrophobic polymers is another challenging aspect of incorporation of biocatalysts into plastic materials [157]. In this respect, nanostructured materials have been recognized as highly effective immobilization supports providing promising stabilization and performance solutions [32, 164, 165] to overcome the major catalytic, stability, leaching, and dispersibility problems in functional large-area coatings. Although the techniques for enzyme immobilization have already been exploited commonly [166], there are still critical drawbacks for practical applications including stability and catalytic functionality issues. In general, although storage stability is significantly enhanced [160, 167], the activity of
biocatalyst is substantially reduced upon immobilization [161, 168]. The major challenges related to enzyme immobilization are identifying new matrix materials with suitable structural characteristics such as morphology and surface functionality and compositions as well as understanding the interactions between enzymes and the matrix to enhance the biocatalytic efficiency. Another point of consideration is the dispersibility of the enzymes in the bioreactive coatings. In other words, it is required to construct a film with uniform activity per unit area throughout the polymeric and paint composites [163, 169]. 2.2.1. Polymer-Enzyme Coatings. Implementing enzymes into biocatalytic coatings requires finding a suitable matrix for immobilization, which will not compromise their activity
8 and stability. Physical entrapment within and covalent attachment to polymer matrixes are the two strategies used for immobilization. Covalent attachment usually requires multistep protocol involving chemical modification of the enzyme. This type of immobilization may result in loading of solid matrixes with enzymes possessing unfavorable conformational changes which leads to lower activity and weaker substrate binding [168]. Physical entrapment on the other hand provides means to incorporate enzymes in polymer matrixes by retaining their native conformation [170]. Physical retention of enzymes into porous solid matrixes or films of polymers is defined as entrapment. Entrapment is considered as the easiest immobilization technique that generally results in no significant conformational alterations of the enzyme. However, this method is characterized by low enzyme loading and noticeable mass transfer limitations. Enzymes can be incorporated into functional films by mixing the biocatalysts with polymer precursors and through emulsion-polymerization procedure coating metal plates by a draw-down method [22, 171], by standard solution coating technique [31], or using a paint spreader [169, 172]. Another entrapment method is generation of sol-gel coatings. A sol is a suspension of dispersed colloids with diameters of around 1–100 nm. A rigid porous gel is generated as the sol is interconnected by cross-linking and the solution viscosity is increased by evaporation of water or alcohol in the suspension [173]. The main advantage of generating biocatalytic coatings via sol-gel entrapment is that the coatings retain a significant amount of water [170], which is crucial for enzyme structural, operational, and storage stability. In addition, sol-gel processes involve low-temperature hydrolysis of monomeric precursors and are thus highly suitable for the microencapsulation of fragile biomolecules [167]. The main problem reported for physically entrapped enzymes within a coating matrix is the decrease in biocatalytic efficiency of the film and loss of biocatalyst due to leaching upon use [174–176]. To reduce the rate and extent of leaching, one strategy is to further treat the polymer film composites with a cross-linking agent, such as glutaraldehyde, to bound the protein to the polymer network [31] or covalently immobilize the enzymes to the two-component system prior to polymerization [169]. The latter method also results in uniform distribution of enzymes within the polymer coating [169]. Another method is to produce the polymer film and then surface-attach the enzymes to the solid support via various strategies such as physical adsorption [177], covalent binding, and intermolecular cross-linking. Kim et al. (2001) investigated the effect of incorporation of proteolytic enzymes (𝛼-chymotrypsin and pronase) into films for applications as fouling-resistant coatings [167]. They compared the effectiveness of sol-gel entrapment technique, covalent attachment of enzymes to the polydimethylsiloxane (PDMS) matrix, and direct surface attachment of the enzymes to the film. Stability-wise, the enzymatic films and paints showed higher thermal stability compared to the enzymes that are free in solution and the ones that are surfaceattached to the PDMS support. However, while the covalently attached films exhibited no apparent enzyme leakage from
Journal of Nanomaterials the films, they observed that some sol-gel particles were released into solution [167, 170] during application studies. 2.2.2. Enzyme-Nanostructure Conjugate Containing Coatings. In particular, oil- and water-based paints represent cheap and readily available materials that can easily be applied to various surfaces. Incorporation of enzyme-nanostructural conjugates into these paints can create the biocatalytic surfaces with desired functional properties [167, 174]. However, the paint should not contain volatile organic solvents that could inactivate the enzyme [159, 172]. The use of nanostructural materials such as nanoparticles, nanotubes, and nanofibers, offers high surface-to-volume ratio, resulting in higher enzyme loadings and improved thermal, operational, and storage stability [21]. Moreover, addition of enzyme-nanostructural conjugates within paint matrix produces more porous composites that are not diffusionally limited, compared to polymer coatings, even at high thicknesses of 400 nm [163]. Nevertheless, the immobilization efficiency, including optimal protein loading, favorable conformation, and high activity of the enzymes, is greatly affected by the properties of a nanomaterial such as its surface chemistry, morphology, and size [168]. Table 1 summarizes different immobilization techniques applied in the generation of biocatalytic thin film coatings and points out observations regarding their performances. Covalent attachment of listeria bacteriophage endolysin Ply500 onto functionalized silica nanoparticles and incorporation of the conjugates into a thin poly-hydroxymethyl methacrylate (pHEMA) films resulted in highly stable (95% killing efficiency after 40-day storage) and effective biocatalytic films capable of completely killing present L. innocua cells and preventing further growth at 4∘ C [160]. Upon continuous washing of the films, no leaching of the enzyme conjugates was observed. The study illustrates that the SNPPly500-containing pHEMA films are promising candidates for applications as antilisteria coatings of cold storage rooms or food processing equipment [160]. Single-walled carbon nanotubes (SWNTs) are fine structures having diameter of 1.3–2.0 nm and length of tenths of microns, hence having a very high surface area to volume ratios [162]. Incorporation of these nanostructures into the polymeric matrix offers a high surface for interaction with biocatalysts or polymer chains that comprise the film. This enhanced interaction results in profound retention of the enzymes in the biocatalytic coatings and films [162]. In addition, owing to their surface curvature, SWNTs and nanoparticles provide means for enzyme attachment by ensuring their structural and functional stability keeping them in more native-like conformation than when attached to flatter surfaces [174, 175, 179]. Enzymes bound to SWNTs or silica nanoparticles retained higher catalytic activity compared to MWNTs at similar loading [175]. Biocatalytic surfaces for large-area applications are also generated by immobilization of enzymes onto multiwalled carbon nanotubes (MWNTs) and subsequently mixing the resulting conjugates with eco-friendly paints [23, 161, 163, 176]. MWNTs are preferred support materials for enzyme immobilization due to their ease of surface functionalization,
Covalent attachment
Covalent attachment
MWNTs with dPEG12 spacer PEG-functionalized MWNT Functionalized pHEMA films
Microbicidal and sporicidal decontamination
Staphylococcal disinfection
Oxidation of phenolic compounds
Antifouling surface
Elimination of surface biofouling
Antifouling coating
Organophosphorus decontamination
Perhydrolase (AcT)
Lysostaphin
Laccase
Subtilisin Carlsberg
Subtilisin, dextranase, peroxidase
𝛼-chymotrypsin
Di-isopropyl europhosphatase
Water-borne polyurethane
Covalent attachment
Entrapment within polymer (pMMA)
Polymer-SWNT composites
39%
—
—
46%
Physical absorption; GA cross-linking Adsorption
71%
33%
28%
30%
11.5%
Adsorption
SWNT
Polystyrene thin film
PEG functionalized, Covalent attachment acid oxidized MWNT
Paraoxon decontamination
Organophosphorus hydrolase (OPH)
Encapsulation within titania matrix
—
Defluorination of toxic compounds
DFPase
—
Sol-gel entrapment in ceramic coating
—
Laccase: 10%; CPO: 25%
52%
Covalent attachment
Covalent attachment
Antifouling surface
Oxidized MWNT
Oxidized SWNTs
—
Savinase
Laccase and chloroperoxidase (CPO)
Sporicidal decontamination Self-decontamination against spores and bacteria
—
Entrapment in solvent-borne polyurethane
Easy-cleaning surface
𝛼-amylase, lipase and thermoase
Perhydrolase (AcT)
33%
Covalent attachment
Functionalized silica nanoparticles (SNP)
Pathogen decontamination (L. innocua)
Listeria bacteriophage endolysin
—
Covalent attachment
Self-decontamination MWNTs with against spores and viruses dPEG12 spacer
% Activity∗
Perhydrolase
Immobilization method
Application
Enzyme
Support material
Biocatalytic film stability
Notes on film performance
300 mg/g paint
>99.99% influenza virus 50% after 90 days at killed within 10 min, ∘ minimum 6-log reduction 4C in spore levels Complete killing of Listeria 95% killing activity 0.14 mg/mg SNP cells on contact and prevent after 40 days at 4∘ C growth at 4∘ C 100% after 90 days Rinsing time accelerated by at room a factor of 105 compared to 0.05–0.22 mg/cm2 temperature (RT) regular coatings 150 mg/g SWNT; 40 mg/g >99% killing of B. cereus — paint spores in 1 h >99.99% >99% bactericidal activity Laccase: 230 mg/g; bactericidal activity within 30 min; >98% CPO: 290 mg/g MWNT after 6 days at RT sporicidal activity Reduced bacterial 78% after 25 months attachment by 2 orders of 16 500 mg/g coating of dry storage magnitude Specific and nonspecific — 73.2% after 24 h decontamination 90% under dry and >95% decontamination 60% under wet within 30 min; No leaching 70 mg/g MWNT conditions after 15 of bioconjugates for 15 days days Paint: >50% after 6-day incubation >99% killing of B. cereus 60 mg/g MWNT and 5 reaction spores within 20 min cycles >99% storage and >99% killing of 50% operational 2000 mg/g paint methicillin-resistant S. stability after 30 aureus (MRSA) in 2 h days at RT 81% p-chlorophenol 74% after 28 days at removal; 54% activity 2 0.139 mg/cm retention after 6 re-use 4∘ C cycles Improved thermal stability 85% after reused 5 and good hydrolyzing 0.013 mg/cm2 cycles activity in aqueous and solid-state >90% after 30 days 85% reduction in protein — adsorption at RT and 70∘ C 158% (comparing 1 mg/g pMMA activity after 48 to — 1 h) 60% after 100 days 3.6 mg/g coating — at RT
Protein loading
Table 1: Summary of applications of enzymes incorporated into thin film/coatings with various immobilization methods.
[169]
[162]
[174]
[157]
[177]
[176]
[163]
[159]
[15]
[170]
[161]
[175]
[22]
[160]
[23]
Ref.
Journal of Nanomaterials 9
Fouling-resistant coating
𝛼-chymotrypsin and pronase
% Residual activity with respect to free enzyme.
Antifouling surface
𝛼-chymotrypsin and trypsin
∗
Application
Enzyme
Sol-gel entrapment; polydimethylsiloxane covalent (PDMS) immobilization (ci)
—
Support material
—
—
% Activity∗
Table 1: Continued. Immobilization method Entrapment in pST, pMMA, and pVAc
70% after 30 days 92% after 8 days at RT
56 mg enz/g support (sol-gel); 42 mg/g support (ci); 13 g enz/g paint
Biocatalytic film stability
50 mg/g polymer
Protein loading
>60% reduction in the protein adsorption to the film
100 times reuse with modest activity loss
Notes on film performance
[167]
[31]
Ref.
10 Journal of Nanomaterials
Journal of Nanomaterials very high surface-area-to-volume ratios that afford high enzyme loading without diffusional limitations [176]. Moreover, their light weight and high mechanical strength make them excellent filling materials to reinforce polymers and ensure entrapment of the biocatalyst and thus retain the enzyme within the composite (with no enzyme leaching) [163]. However, pristine carbon nanotubes tend to aggregate in both aqueous and organic solutions due to surfacesurface van der Waals interactions. This, however, reduces the available area for protein attachment as well as the nanotube dispersion within polymer matrix or paint [163]. Similar studies with carbon nanoparticles showed that aggregation of nanoparticles created agglomerates ranging from several hundred nm to several 𝜇m [168]. This agglomeration influenced enzyme loading and activity by reducing the available adsorption surface. To improve dispersibility, it has been shown that functionalization of nanotubes with flexible poly ethylene glycol (PEG) spacer arms increases nanotube dispersion in solution and prevents clumping of the nanostructures by blocking hydrophobic side walls of the carbon nanotubes [159]. Moreover, it is crucial to optimize spacer lengths, since long ones (>2000) might potentially create porous composites with altered mechanical properties [163]. In addition, oxidizing MWNT generates highly hydrophilic structures (carboxyl acid “handles” on the surface) that enables them to become water soluble/dispersible [161, 175]. 2.2.3. Enzyme Loading. Enzyme-carrier materials with reduced size can generally improve the efficiency of enzyme immobilization by providing larger surface area for attachment, leading to higher protein loading per unit mass of particles [164]. The amount of enzyme molecules immobilized per unit area (i.e., protein loading) may increase or decrease the performance of biocatalytic film. For some enzymes, too much loading on the surface may restrict the spatial orientation of the protein chain, limit the accessibility of the enzyme’s active site, or denature the enzymes, thereby, reducing their activity [180]. Rather than the enzyme loading, it is critical to obtain optimum surface accessibility and functional stability for the biocatalyst, so that the reactions take place. However, it has been shown that, upon active site titration of enzyme-containing polymeric films, the observed high activity is mainly due to enzymes embedded within the polymeric coating rather than on the surface only [31].
3. Growth Techniques towards Large-Area Catalytic Coatings Growth techniques are critical in determining size, orientation, and shape of catalytic material systems in addition to the characteristics of thin film that these particles or enzymes are embedded. Naturally crystallinity and surface features significantly affect catalytic reactions in thin films. Hence, various process methods have been used to form the thin film and the photocatalytic metal oxides and determine the crystal, surface, and electronic structure of materials, which affects bulk diffusion, surface transfer, and redox
11 potentials [76]. Liquid based processes can be advantageous because they start forming the structures in aqueous solution and they allow for forming homogeneous films and enabling control of growth parameters and hence film properties [57]. However, for wide utilization of photocatalytic effect and to get rid of recycling problems, thin film forming needs to be performed while the photocatalytic activity is still kept at high levels. Up to now, there have been significant efforts to obtain high photocatalytic efficiency on large areas. We will present the major film formation methods in this section. Using hydrothermal and solvo methods photocatalytic particles are crystallized at high temperature and high vapor pressure conditions, utilizing organic solvents including methanol [181] and toluene [182]. With the ability to tune synthesis conditions, grain size, morphology, and crystalline phase can be controlled. TiO2𝑛 H2 O gels are treated with hydrothermal methods in mineralizing additives including fluorides, hydroxides, and chloride and also in pure water [57, 183]. TiSO4 , powder of Ti, TiCl4 , H2 , and TiO(C2 O4 ) can be used to obtain TiO2 [184] where inorganic materials are realized at low temperatures [185]. Also different from coprecipitation, this method does not need extra thermal processing. Chemical solution decomposition [186], two-step wet chemical method [187], and chemical vapor decomposition [188] techniques have also been used to obtain photocatalytic particles. In the case of sol-gel technique, there are important advantages such as the ability to control the structure of a nanosized material starting from the first steps of the process and also homogenous coatings that can be formed at rather low temperatures [189]. These show its potential for coating large and complex areas at a relatively low cost [190] with multifunctionality [191]. The films commonly show mesoporous structures by ionic and neutral surfactants [192]. Hydrolysis and polycondensation occur during the formation of solid thin film where either alkoxide or nonalkoxide techniques can be used depending on the intended physical and chemical properties of the end products. In the case of commonly used alkoxide route, metal alkoxides are the raw materials [193] and for the nonalkoxide technique, inorganic salts are needed to be used [194]. The sol-gel method exhibits another advantage where different metals such as Ca2+ [195], Pb2+ [196], Ag+ [197], Fe3+ [198], V5+ [199], Co2+ [200], Au3+ [201], and La3+ [202] can be added to films to increase photocatalytic effect. In many cases, chemical vapor deposition (CVD) is beneficial because of its versatility and fast processing abilities [203], which enables large-area processing. According to the activation method, pressure, and precursors, compounds are formed either by a chemical reaction or from decomposition of gas phase precursors [204]. Physical vapor deposition (PVD) deposits compounds physically from gas phase to coat substrate instead of chemical reactions. As thermal evaporation is the most commonly used technique in PVD systems, to realize sufficiently conductive TiO2 , it is required to heat up to 900∘ C in hydrogen atmosphere ambient [205]. Spray pyrolysis uses aerosol precursor solution and directs this aerosol to the target, contrary to chemical vapour
12
Journal of Nanomaterials Photoactive layer 10–20 nm TiO2 / n = 1.8 Antireflective layer 180–50 nm Me-SiO2 n = 1.24
Substrate SiO2 glass n = 1.49
Figure 7: Scheme of a hybrid system showing photocatalyst and antireflective properties at the same time, adapted with permission from [178] Copyright 2010 American Chemical Society.
deposition, which needs diffusion [206, 207]. This method is also beneficial with its low cost, high reproducibility, and speed to coat large areas with moderately good structural properties whereas uniformity is still a problem. There are some other techniques for growing metal oxide particles; although they may not be proved to be used for large-area surfaces at low cost, they are still worth being mentioned. Despite the fact that microemulsions were observed to be encouraging in early experimental works, the synthesis of controlled titania with microemulsions has not been straightforward up to date [208]. Advanced film properties of structures such as nanoporosity, epitaxial layers, superlattice, and quantum dot structures can be controlled by using electrochemical synthesis. The desired properties are obtained by altering the parameters including temperature, potential value, pH, and current density where acidic and oxygen-free environment is required for electrolysis to be successful [209]. It has been reported that overcoming this problem is possible by using nonaqueous solutions [210]. In addition to these techniques, magnetron sputtering [211] and atomic layer deposition [212] are of significance considering their potential to realize large-area films which can be structured with the desired properties. Undoubtedly, the science, technology, and industry of large-area catalytic coatings will continue to gain importance for green applications that will find their place in different fields including architecture and automotive and environmental remediation. There is already an important progress in the last few decades and is already providing answers with growing expectations for the future.
4. Large-Area Applications of Multifunctional Catalytic Films Future Prospects Up to present, catalytic thin films have been studied from different aspects by numerous researchers as they can be employed on surfaces with a wide range of purposes including optical, optoelectronic, magnetic, electrical, thermal, photoelectrochemical, photovoltaic, mechanical, biomedical, and catalytic applications [178, 213–217]. Figure 7 shows an integrated sol-gel produced material system exhibiting antireflectivity, water repellence, antifogging, and
photocatalytic activity where the coating is proposed to be used for photovoltaic applications [178]. Obviously, high potential of catalytic coatings to combat environmental problems with widespread exploitation is of great significance. Greenhouse gasses are being released constantly and increasingly on global scale [218–220]. Hence, using smart and functional coatings provides an important alternative to this serious green gas emission problem and will make contribution to the solution of environmental pollution [221–224]. Nanotechnology obviously enhances the performance of the coatings considering the final objective of decreasing greenhouse gases by massive environmental remediation. However, it is still not straightforward to commercialize such products because of the industrial difficulties including the levels of catalytic efficiencies in the visible spectral range and economical manufacturing methods for ecological and sustainable coatings with the intended functionalities. On the other hand, as reviewed in this paper, there are numerous possible organic and/or inorganic solutions, which enhance the performance parameters to realize functional and innovative structures [225].
5. Conclusions Considering the incrementally increasing environmental pollution and its impacts on global scale, there is substantial need for development and application of advanced, lowcost, large-scale, green solutions capable of reducing and even eliminating the pollution. In this respect, large-area catalytic thin films are highly promising for green technology applications to save energy and combat pollution and global warming. To date, organic and inorganic catalytic materials have been investigated comprehensively, considering their geometrical and electronic structures, surface reactions, synergistic behavior with other material systems, and stability issues. In general, catalysts lose their effectiveness when they are immobilized in thin films compared to the case when they operate in aqueous environment. However, there is a wide range of methods that have been reported to enhance the efficiency of these catalysts when embedded in coatings. This review paper covers the developments of photoand biocatalytic thin films and coatings formed using nanotechnology. Therefore, it is a subset of “catalytics and nano” focusing on formation of thin films containing catalytic
Journal of Nanomaterials nanostructures for large-area applications. The reviewed research work not only includes large-area applications that offer solutions for environmental pollution but also covers the reports that potentially can make a contribution to the low catalytic efficiency and solar spectrum absorption problem. Among these methods, hybridizing catalytic particles with other structures are attention-grabbing considering also enhancement in surface functionalities. Therefore, we gave special attention to the research studies implementing hybrid systems and, specifically, two-dimensional materials are found to be promising because of their superior properties and 2D geometries allowing for mass production capabilities. To make use of highly appealing functionalities of these immobilized catalytic material systems, it is needed to increase the catalytic efficiency and improve the yield and feasibility. In this review, recent advancements specifically focusing on the catalytic efficiency enhancement and solar spectrum absorption are discussed. Different research reports show that the potential of nanostructuring or hybridizing methods for catalytic thin films is enthusing for the future, also providing novel applications due to enhanced functionalities. As a result, catalytic thin films will provide promising solutions to decontamination as they are embedded into systems to obtain mineralization of a variety of environmental contaminants. However, two critical challenges still remain. To begin with, significant effort continues for understanding the generic mechanisms within the matrix and interactions between the nanocatalysts and the embedded thin film system. For instance, the relationships between the biocatalystnanostructured carriers and the polymer matrix are to be yet investigated systematically. Such fundamental information is significantly important in the development of hybrid structures or multifunctional coatings. These fascinating challenges require interdisciplinary collaborations of material scientists, chemists, and engineers. Another impediment is the commercialization. Reducing the cost of production and demonstrating the feasibility and effectiveness of these functional coatings by long-term operation studies are the major hurdle for universalization of large-scale applications.
Conflict of Interests The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgment Nihan Kosku Perkgoz acknowledges the support from Anadolu University (BAP-1404F214 and 1407F335) for this project.
References [1] I. P. Parkin and R. G. Palgrave, “Self-cleaning coatings,” Journal of Materials Chemistry, vol. 15, no. 17, pp. 1689–1695, 2005. [2] L. Zhao, H. Wang, K. Huo et al., “Antibacterial nano-structured titania coating incorporated with silver nanoparticles,” Biomaterials, vol. 32, no. 24, pp. 5706–5716, 2011.
13 [3] P. Roach, N. J. Shirtcliffe, and M. I. Newton, “Progess in superhydrophobic surface development,” Soft Matter, vol. 4, no. 2, pp. 224–240, 2008. [4] C.-H. Xue, S.-T. Jia, J. Zhang et al., “Large-area fabrication of superhydrophobic surfaces for practical applications: an overview,” Science and Technology of Advanced Materials, vol. 11, no. 3, Article ID 033002, 2010. [5] M. Gorjanc, J. Vasiljevi´c, A. Vesel, M. Mozetic, and B. Simonˇciˇc, “Plasma and sol-gel technology for creating nanostructured surfaces of fibrous polymers,” Proceedings of the International Conference. Nanomaterials: Applications and Properties, vol. 1, no. 4, 4 pages, 2012. [6] H. Ishiguro, R. Nakano, Y. Yao et al., “Photocatalytic inactivation of bacteriophages by TiO2 -coated glass plates under lowintensity, long-wavelength UV irradiation,” Photochemical and Photobiological Sciences, vol. 10, no. 11, pp. 1825–1829, 2011. [7] Y. Wang, S. Jiang, M. Wang, S. Wang, T. D. Xiao, and P. R. Strutt, “Abrasive wear characteristics of plasma sprayed nanostructured alumina/titania coatings,” Wear, vol. 237, no. 2, pp. 176–185, 2000. [8] A. Leyland and A. Matthews, “Design criteria for wear-resistant nanostructured and glassy-metal coatings,” Surface and Coatings Technology, vol. 177-178, pp. 317–324, 2004. [9] J. Lee, S. Mahendra, and P. J. J. Alvarez, “Nanomaterials in the construction industry: a review of their applications and environmental health and safety considerations,” ACS Nano, vol. 4, no. 7, pp. 3580–3590, 2010. [10] A. Steele, I. Bayer, and E. Loth, “Inherently superoleophobic nanocomposite coatings by Spray Atomization,” Nano Letters, vol. 9, no. 1, pp. 501–505, 2009. [11] C. Luo, X. Zuo, L. Wang et al., “Flexible carbon nanotubepolymer composite films with high conductivity and superhydrophobicity made by solution process,” Nano Letters, vol. 8, no. 12, pp. 4454–4458, 2008. [12] F. C. Krebs, H. Spanggard, T. Kjær, M. Biancardo, and J. Alstrup, “Large area plastic solar cell modules,” Materials Science and Engineering B, vol. 138, no. 2, pp. 106–111, 2007. [13] M. George, “Large area optical and opto-electronic solar thin film applications,” in Optics for Solar Energy, Optical Society of America, 2010. [14] B. S. Shim, J. Zhu, E. Jan et al., “Multiparameter structural optimization of single-walled carbon nanotube composites: toward record strength, stiffness, and toughness,” ACS Nano, vol. 3, no. 7, pp. 1711–1722, 2009. [15] S. Filocamo, R. Stote, D. Ziegler, and H. Gibson, “Entrapment of DFPase in titania coatings from a biomimetically derived method,” Journal of Materials Research, vol. 26, no. 8, pp. 1042– 1051, 2011. [16] R. Dastjerdi and M. Montazer, “A review on the application of inorganic nano-structured materials in the modification of textiles: focus on anti-microbial properties,” Colloids and Surfaces B: Biointerfaces, vol. 79, no. 1, pp. 5–18, 2010. [17] K. M. L. Taylor-Pashow, J. Della Rocca, R. C. Huxford, and W. Lin, “Hybrid nanomaterials for biomedical applications,” Chemical Communications, vol. 46, no. 32, pp. 5832–5849, 2010. [18] P. Gunawan, C. Guan, X. Song et al., “Hollow fiber membrane decorated with Ag/MWNTs: toward effective water disinfection and biofouling control,” ACS Nano, vol. 5, no. 12, pp. 10033– 10040, 2011. [19] U. Diebold, “The surface science of titanium dioxide,” Surface Science Reports, vol. 48, no. 5–8, pp. 53–229, 2003.
14 [20] A. Fujishima and X. T. Zhang, “Titanium dioxide photocatalysis: present situation and future approaches,” Comptes Rendus Chimie, vol. 9, no. 5-6, pp. 750–760, 2006. [21] N. Grover, C. Z. Dinu, R. S. Kane, and J. S. Dordick, “Enzymebased formulations for decontamination: current state and perspectives,” Applied Microbiology and Biotechnology, vol. 97, no. 8, pp. 3293–3300, 2013. [22] S. Wu, A. Buthe, H. Jia, M. Zhang, M. Ishii, and P. Wang, “Enzyme-enabled responsive surfaces for anti-contamination materials,” Biotechnology and Bioengineering, vol. 110, no. 6, pp. 1805–1810, 2013. [23] N. Grover, M. P. Douaisi, I. V. Borkar et al., “Perhydrolasenanotube paint composites with sporicidal and antiviral activity,” Applied Microbiology and Biotechnology, vol. 97, no. 19, pp. 8813–8821, 2013. [24] P. N. Manoudis, I. Karapanagiotis, A. Tsakalof, I. Zuburtikudis, B. Kolinkeov´a, and C. Panayiotou, “Superhydrophobic films for the protection of outdoor cultural heritage assets,” Applied Physics A, vol. 97, no. 2, pp. 351–360, 2009. [25] A. Arora and G. W. Padua, “Review: nanocomposites in food packaging,” Journal of Food Science, vol. 75, no. 1, pp. R43–R49, 2010. [26] H. N. Cheng, A. G. Richard, and B. S. Patrick, Eds., Green Polymer Chemistry: Biocatalysis and Materials II, ACS Symposium Series 1144, American Chemical Society, 2013. [27] M. Misson, H. Zhang, and B. Jin, “Nanobiocatalyst advancements and bioprocessing applications,” Journal of the Royal Society Interface, vol. 12, no. 102, 2015. [28] K. W. Guo, “Green nanotechnology of trends in future energy: a review,” International Journal of Energy Research, vol. 36, no. 1, pp. 1–17, 2012. [29] P. Tufvesson, J. Lima-Ramos, M. Nordblad, and J. M. Woodley, “Guidelines and cost analysis for catalyst production in biocatalytic processes,” Organic Process Research and Development, vol. 15, no. 1, pp. 266–274, 2011. [30] “Combating climate change,” Nature Nanotechnology, vol. 2, no. 6, article 325, 2007. [31] S. J. Novick and J. S. Dordick, “Protein-containing hydrophobic coatings and films,” Biomaterials, vol. 23, no. 2, pp. 441–448, 2002. [32] M. Misson, H. Zhang, and B. Jin, “Nanobiocatalyst advancements and bioprocessing applications,” Journal of the Royal Society Interface, vol. 12, no. 102, Article ID 20140891, 2015. [33] A. Heller, “Conversion of sunlight into electrical power and photoassisted electrolysis of water in photoelectrochemical cells,” Accounts of Chemical Research, vol. 14, no. 5, pp. 154–162, 1981. [34] A. Fujishima, T. N. Rao, and D. A. Tryk, “Titanium dioxide photocatalysis,” Journal of Photochemistry and Photobiology C: Photochemistry Reviews, vol. 1, no. 1, pp. 1–21, 2000. [35] M. Anpo, H. Nakaya, S. Kodama, Y. Kubokawa, K. Domen, and T. Onishi, “Photocatalysis over binary metal oxides. Enhancement of the photocatalytic activity of TiO2 in titanium-silicon oxides,” Journal of Physical Chemistry, vol. 90, no. 8, pp. 1633– 1636, 1986. [36] M. Anpo and Y. Kubokawa, “Photoinduced and photocatalytic reactions on supported metal oxide catalysts. Excited states of oxides and reaction intermediates,” Reviews of Chemical Intermediates, vol. 8, no. 1, pp. 105–124, 1987. [37] K. Hashimoto, H. Irie, and A. Fujishima, “TiO2 photocatalysis: a historical overview and future prospects,” Japanese Journal of Applied Physics R, vol. 44, no. 12, pp. 8269–8285, 2005.
Journal of Nanomaterials [38] P. V. Kamat, “Photophysical, photochemical and photocatalytic aspects of metal nanoparticles,” The Journal of Physical Chemistry B, vol. 106, no. 32, pp. 7729–7744, 2002. [39] F. Gao, X. Chen, K. Yin et al., “Visible-light photocatalytic properties of weak magnetic BiFeO3 nanoparticles,” Advanced Materials, vol. 19, no. 19, pp. 2889–2892, 2007. [40] X. Hong, Z. Wang, W. Cai et al., “Visible-light-activated nanoparticle photocatalyst of iodine-doped titanium dioxide,” Chemistry of Materials, vol. 17, no. 6, pp. 1548–1552, 2005. [41] E. Mart´ınez-Ferrero, Y. Sakatani, C. Boissi`ere et al., “Nanostructured titanium oxynitride porous thin films as efficient visibleactive photocatalysts,” Advanced Functional Materials, vol. 17, no. 16, pp. 3348–3354, 2007. [42] N. K. Perkgoz, R. S. Toru, E. Unal et al., “Photocatalytic hybrid nanocomposites of metal oxide nanoparticles enhanced towards the visible spectral range,” Applied Catalysis B: Environmental, vol. 105, no. 1-2, pp. 77–85, 2011. [43] H. Y. Yang, S. F. Yu, S. P. Lau, X. Zhang, D. D. Sun, and G. Jun, “Direct growth of ZnO nanocrystals onto the surface of porous TiO2 nanotube arrays for highly efficient and recyclable photocatalysts,” Small, vol. 5, no. 20, pp. 2260–2264, 2009. [44] A. Kudo, “Photocatalyst materials for water splitting,” Catalysis Surveys from Asia, vol. 7, no. 1, pp. 31–38, 2003. [45] A. Kudo and Y. Miseki, “Heterogeneous photocatalyst materials for water splitting,” Chemical Society Reviews, vol. 38, no. 1, pp. 253–278, 2009. [46] G. Jiang, Z. Lin, C. Chen et al., “TiO2 nanoparticles assembled on graphene oxide nanosheets with high photocatalytic activity for removal of pollutants,” Carbon, vol. 49, no. 8, pp. 2693–2701, 2011. [47] K. Woan, G. Pyrgiotakis, and W. Sigmund, “Photocatalytic carbon-nanotube-TiO2 composites,” Advanced Materials, vol. 21, no. 21, pp. 2233–2239, 2009. [48] M. R. Hoffmann, S. T. Martin, W. Choi, and D. W. Bahnemann, “Environmental applications of semiconductor photocatalysis,” Chemical Reviews, vol. 95, no. 1, pp. 69–96, 1995. [49] U. I. Gaya and A. H. Abdullah, “Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: a review of fundamentals, progress and problems,” Journal of Photochemistry and Photobiology C: Photochemistry Reviews, vol. 9, no. 1, pp. 1–12, 2008. [50] R. Cai, K. Hashimoto, K. Itoh, Y. Kubota, and A. Fujishima, “Photokilling of malignant cells with ultrafine TiO2 powder,” Bulletin of the Chemical Society of Japan, vol. 64, no. 4, pp. 1268– 1273, 1991. [51] T. Matsunaga, R. Tomoda, T. Nakajima, and H. Wake, “Photoelectrochemical sterilization of microbial cells by semiconductor powders,” FEMS Microbiology Letters, vol. 29, no. 1-2, pp. 211– 214, 1985. [52] N.-G. Park, J. Van de Lagemaat, and A. J. Frank, “Comparison of dye-sensitized rutile- and anatase-based TiO2 solar cells,” The Journal of Physical Chemistry B, vol. 104, no. 38, pp. 8989–8994, 2000. [53] Y.-C. Kim, S. Sasaki, K. Yano, K. Ikebukuro, K. Hashimoto, and I. Karube, “Photocatalytic sensor for the determination of chemical oxygen demand using flow injection analysis,” Analytica Chimica Acta, vol. 432, no. 1, pp. 59–66, 2001. [54] M. Gr¨atzel, “Photoelectrochemical cells,” Nature, vol. 414, no. 6861, pp. 338–344, 2001.
Journal of Nanomaterials [55] G. Palmisano, M. C. Guti´errez, M. L. Ferrer et al., “TiO2 /ORMOSIL thin films doped with phthalocyanine dyes: new photocatalytic devices activated by solar light,” Journal of Physical Chemistry C, vol. 112, no. 7, pp. 2667–2670, 2008. [56] L. Vayssieres, “Advanced semiconductor nanostructures,” Comptes Rendus Chimie, vol. 9, no. 5-6, pp. 691–701, 2006. [57] O. Carp, C. L. Huisman, and A. Reller, “Photoinduced reactivity of titanium dioxide,” Progress in Solid State Chemistry, vol. 32, no. 1-2, pp. 33–177, 2004. [58] S. Sarkar, R. Das, H. Choi, and C. Bhattacharjee, “Involvement of process parameters and various modes of application of TiO2 nanoparticles in heterogeneous photocatalysis of pharmaceutical wastes—a short review,” RSC Advances, vol. 4, no. 100, pp. 57250–57266, 2014. [59] Z. Tong, Y. Jiang, D. Yang et al., “Biomimetic and bioinspired synthesis of titania and titania-based materials,” RSC Advances, vol. 4, no. 24, pp. 12388–12403, 2014. [60] D. F. Ollis, “Photocatalytic purification and remediation of contaminated air and water,” Comptes Rendus de l’Acad´emie des Sciences Series IIC: Chemistry, vol. 3, no. 6, pp. 405–411, 2000. [61] S. Ahmed, M. G. Rasul, W. N. Martens, R. Brown, and M. A. Hashib, “Advances in heterogeneous photocatalytic degradation of phenols and dyes in wastewater: a review,” Water, Air, & Soil Pollution, vol. 215, no. 1–4, pp. 3–29, 2011. [62] J. C. Sjogren and R. A. Sierka, “Inactivation of phage MS2 by iron-aided titanium dioxide photocatalysis,” Applied and Environmental Microbiology, vol. 60, no. 1, pp. 344–347, 1994. [63] S. Banerjee, J. Gopal, P. Muraleedharan, A. K. Tyagi, and B. Raj, “Physics and chemistry of photocatalytic titanium dioxide: visualization of bactericidal activity using atomic force microscopy,” Current Science, vol. 90, no. 10, pp. 1378–1383, 2006. [64] K. Kabra, R. Chaudhary, and R. L. Sawhney, “Treatment of hazardous organic and inorganic compounds through aqueousphase photocatalysis: a review,” Industrial & Engineering Chemistry Research, vol. 43, no. 24, pp. 7683–7696, 2004. [65] F. A. Harraz, O. E. Abdel-Salam, A. A. Mostafa, R. M. Mohamed, and M. Hanafy, “Rapid synthesis of titania-silica nanoparticles photocatalyst by a modified sol-gel method for cyanide degradation and heavy metals removal,” Journal of Alloys and Compounds, vol. 551, 7 pages, 2013. [66] L. Obalov´a, M. Reli, J. Lang et al., “Photocatalytic decomposition of nitrous oxide using TiO2 and Ag-TiO2 nanocomposite thin films,” Catalysis Today, vol. 209, pp. 170–175, 2013. [67] T. Kimura, N. Yoshikawa, N. Matsumura, and Y. Kawase, “Photocatalytic degradation of nonionic surfactants with immobilized TiO2 in an airlift reactor,” Journal of Environmental Science and Health A-Toxic/Hazardous Substances and Environmental Engineering, vol. 39, no. 11-12, pp. 2867–2881, 2004. [68] A. Rachel, M. Subrahmanyam, and P. Boule, “Comparison of photocatalytic efficiencies of TiO2 in suspended and immobilised form for the photocatalytic degradation of nitrobenzenesulfonic acids,” Applied Catalysis B: Environmental, vol. 37, no. 4, pp. 301–308, 2002. [69] B. Ohtani, “Titania photocatalysis beyond recombination: a critical review,” Catalysts, vol. 3, no. 4, pp. 942–953, 2013. [70] H. D. Jang, S.-K. Kim, and S.-J. Kim, “Effect of particle size and phase composition of titanium dioxide nanoparticles on the photocatalytic properties,” Journal of Nanoparticle Research, vol. 3, no. 2-3, pp. 141–147, 2001. [71] H. Zhou, Y. Qu, T. Zeid, and X. Duan, “Towards highly efficient photocatalysts using semiconductor nanoarchitectures,” Energy & Environmental Science, vol. 5, no. 5, pp. 6732–6743, 2012.
15 [72] S. G. Kumar and L. G. Devi, “Review on modified TiO2 photocatalysis under UV/visible light: Selected results and related mechanisms on interfacial charge carrier transfer dynamics,” Journal of Physical Chemistry A, vol. 115, no. 46, pp. 13211–13241, 2011. [73] N. Wu, J. Wang, D. N. Tafen et al., “Shape-enhanced photocatalytic activity of single-crystalline anatase TiO2 (101) nanobelts,” Journal of the American Chemical Society, vol. 132, no. 19, pp. 6679–6685, 2010. [74] D. Beydoun, R. Amal, G. Low, and S. McEvoy, “Role of nanoparticles in photocatalysis,” Journal of Nanoparticle Research, vol. 1, no. 4, pp. 439–458, 1999. [75] L. Zhang, H. Yang, J. Yu et al., “Controlled synthesis and photocatalytic activity of ZnSe nanostructured assemblies with different morphologies and crystalline phases,” The Journal of Physical Chemistry C, vol. 113, no. 14, pp. 5434–5443, 2009. [76] G. Liu, L. Wang, H. G. Yang, H.-M. Cheng, and G. Q. Lu, “Titania-based photocatalysts-crystal growth, doping and heterostructuring,” Journal of Materials Chemistry, vol. 20, no. 5, pp. 831–843, 2010. [77] L. Guo, D. Jing, M. Liu et al., “Functionalized nanostructures for enhanced photocatalytic performance under solar light,” Beilstein Journal of Nanotechnology, vol. 5, no. 1, pp. 994–1004, 2014. [78] I. M. Arabatzis, S. Antonaraki, T. Stergiopoulos et al., “Preparation, characterization and photocatalytic activity of nanocrystalline thin film TiO2 catalysts towards 3,5-dichlorophenol degradation,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 149, no. 1–3, pp. 237–245, 2002. [79] A. Fern´andez, G. Lassaletta, V. M. Jim´enez et al., “Preparation and characterization of TiO2 photocatalysts supported on various rigid supports (glass, quartz and stainless steel). Comparative studies of photocatalytic activity in water purification,” Applied Catalysis B, Environmental, vol. 7, no. 1-2, pp. 49–63, 1995. [80] R. L. Pozzo, M. A. Baltan´as, and A. E. Cassano, “Towards a precise assessment of the performance of supported photocatalysts for water detoxification processes,” Catalysis Today, vol. 54, no. 1, pp. 143–157, 1999. [81] H. Tong, S. Ouyang, Y. Bi, N. Umezawa, M. Oshikiri, and J. Ye, “Nano-photocatalytic materials: possibilities and challenges,” Advanced Materials, vol. 24, no. 2, pp. 229–251, 2012. [82] R. Comparelli, P. D. Cozzoli, M. L. Curri, A. Agostiano, G. Mascolo, and G. Lovecchio, “Photocatalytic degradation of methyl-red by immobilised nanoparticles of TiO2 and ZnO,” Water Science and Technology, vol. 49, no. 4, pp. 183–188, 2004. [83] A. Henglein, “Nanoclusters of semiconductors and metals: colloidal nano-particles of semiconductors and metals: electronic structure and processes,” Berichte der Bunsengesellschaft f¨ur physikalische Chemie, vol. 101, no. 11, pp. 1562–1572, 1997. [84] V. Subramanian, E. Wolf, and P. V. Kamat, “Semiconductormetal composite nanostructures. To what extent do metal nanoparticles improve the photocatalytic activity of TiO2 films?” Journal of Physical Chemistry B, vol. 105, no. 46, pp. 11439–11446, 2001. [85] A. Henglein, “Mechanism of reactions on colloidal microelectrodes and size quantization effects,” in Electrochemistry II, vol. 143 of Topics in Current Chemistry, pp. 113–180, Springer, Berlin, Germany, 1988. [86] A. Henglein, “Small-particle research: physicochemical properties of extremely small colloidal metal and semiconductor particles,” Chemical Reviews, vol. 89, no. 8, pp. 1861–1873, 1989.
16 [87] D. W. Bahnemann, “Ultrasmall metal oxide particles: preparation, photophysical characterization, and photocatalytic properties,” Israel Journal of Chemistry, vol. 33, no. 1, pp. 115–136, 1993. [88] H. Weller and A. Eychm¨uller, “Photochemistry and photoelectrochemistry of quantized matter: properties of semiconductor nanoparticles in solution and thin-film electrodes,” in Advances in Photochemistry, vol. 20, chapter 4, pp. 165–216, John Wiley & Sons, 2007. [89] A. Hagfeld and M. Gr¨atzel, “Light-induced redox reactions in nanocrystalline systems,” Chemical Reviews, vol. 95, no. 1, pp. 49–68, 1995. [90] A. J. Hoffman, G. Mills, H. Yee, and M. R. Hoffmann, “Q-sized cadmium sulfide: synthesis, characterization, and efficiency of photoinitiation of polymerization of several vinylic monomers,” The Journal of Physical Chemistry, vol. 96, no. 13, pp. 5546–5552, 1992. [91] P. V. Kamat, “Tailoring nanostructured thin-films,” Chemtech, vol. 25, no. 6, pp. 22–28, 1995. [92] Y. Li, T. Kunitake, and S. Fujikawa, “Efficient fabrication and enhanced photocatalytic activities of 3D-ordered films of titania hollow spheres,” The Journal of Physical Chemistry B, vol. 110, no. 26, pp. 13000–13004, 2006. [93] A. O. Ibhadon and P. Fitzpatrick, “Heterogeneous photocatalysis: recent advances and applications,” Catalysts, vol. 3, no. 1, pp. 189–218, 2013. [94] G. Rothenberger, J. Moser, M. Gr¨atzel, N. Serpone, and D. K. Sharma, “Charge carrier trapping and recombination dynamics in small semiconductor particles,” Journal of the American Chemical Society, vol. 107, no. 26, pp. 8054–8059, 1985. [95] S. Deng, S. W. Verbruggen, Z. He et al., “Atomic layer deposition-based synthesis of photoactive TiO2 nanoparticle chains by using carbon nanotubes as sacrificial templates,” RSC Advances, vol. 4, no. 23, pp. 11648–11653, 2014. [96] Y. Liang, H. S. Wang, H. S. Casalongue, Z. Chen, and H. Dai, “TiO2 nanocrystals grown on graphene as advanced photocatalytic hybrid materials,” Nano Research, vol. 3, no. 10, pp. 701–705, 2010. [97] Z. Wang, J. Sha, E. Liu et al., “A large ultrathin anatase TiO2 nanosheet/reduced graphene oxide composite with enhanced lithium storage capability,” Journal of Materials Chemistry A, vol. 2, no. 23, pp. 8893–8901, 2014. [98] Q. Li, B. Guo, J. Yu et al., “Highly efficient visible-light-driven photocatalytic hydrogen production of CdS-cluster-decorated graphene nanosheets,” Journal of the American Chemical Society, vol. 133, no. 28, pp. 10878–10884, 2011. [99] X. Song and L. Gao, “Fabrication of hollow hybrid microspheres coated with silica/titania via sol-gel process and enhanced photocatalytic activities,” The Journal of Physical Chemistry C, vol. 111, no. 23, pp. 8180–8187, 2007. [100] X. Shen, L. Zhu, J. Li, and H. Tang, “Synthesis of molecular imprinted polymer coated photocatalysts with high selectivity,” Chemical Communications, no. 11, pp. 1163–1165, 2007. [101] S. Xuan, W. Jiang, X. Gong, Y. Hu, and Z. Chen, “Magnetically separable Fe3 O4 /TiO2 hollow spheres: fabrication and photocatalytic activity,” The Journal of Physical Chemistry C, vol. 113, no. 2, pp. 553–558, 2009. [102] M. Dahl, Y. Liu, and Y. Yin, “Composite titanium dioxide nanomaterials,” Chemical Reviews, vol. 114, no. 19, pp. 9853– 9889, 2014.
Journal of Nanomaterials [103] H. Zhang, X. Fan, X. Quan, S. Chen, and H. Yu, “Graphene sheets grafted Ag@AgCl hybrid with enhanced plasmonic photocatalytic activity under visible light,” Environmental Science & Technology, vol. 45, no. 13, pp. 5731–5736, 2011. [104] X. Li, W. Cai, J. An et al., “Large-area synthesis of high-quality and uniform graphene films on copper foils,” Science, vol. 324, no. 5932, pp. 1312–1314, 2009. [105] Y. Song, H. Xu, C. Wang et al., “Graphene-analogue boron nitride/Ag3 PO4 composite for efficient visible-light-driven photocatalysis,” RSC Advances, vol. 4, no. 100, pp. 56853–56862, 2014. [106] Q. Xiang, J. Yu, and M. Jaroniec, “Synergetic effect of MoS2 and graphene as cocatalysts for enhanced photocatalytic H2 production activity of TiO2 nanoparticles,” Journal of the American Chemical Society, vol. 134, no. 15, pp. 6575–6578, 2012. [107] T. Xu, L. Zhang, H. Cheng, and Y. Zhu, “Significantly enhanced photocatalytic performance of ZnO via graphene hybridization and the mechanism study,” Applied Catalysis B: Environmental, vol. 101, no. 3-4, pp. 382–387, 2011. [108] H. Zhang, X. Lv, Y. Li, Y. Wang, and J. Li, “P25-graphene composite as a high performance photocatalyst,” ACS Nano, vol. 4, no. 1, pp. 380–386, 2010. [109] Q. Liu, Z. Liu, X. Zhang et al., “Polymer photovoltaic cells based on solution-processable graphene and P3HT,” Advanced Functional Materials, vol. 19, no. 6, pp. 894–904, 2009. [110] K.-K. Liu, W. Zhang, Y.-H. Lee et al., “Growth of large-area and highly crystalline MoS2 thin layers on insulating substrates,” Nano Letters, vol. 12, no. 3, pp. 1538–1544, 2012. [111] A. L. Linsebigler, G. Lu, and J. T. Yates Jr., “Photocatalysis on TiO2 surfaces: principles, mechanisms, and selected results,” Chemical Reviews, vol. 95, no. 3, pp. 735–758, 1995. [112] C. Minero, “Surface-modified photocatalysts,” 2013. [113] T. K. Kim, M. N. Lee, S. H. Lee, Y. C. Park, C. K. Jung, and J.H. Boo, “Development of surface coating technology of TiO2 powder and improvement of photocatalytic activity by surface modification,” Thin Solid Films, vol. 475, no. 1-2, pp. 171–177, 2005. [114] W. Y. Choi, A. Termin, and M. R. Hoffmann, “The role of metal ion dopants in quantum-sized TiO2 : correlation between photoreactivity and charge carrier recombination dynamics,” Journal of Physical Chemistry, vol. 98, no. 51, pp. 13669–13679, 1994. [115] A. P. Hong, D. W. Bahnemann, and M. R. Hoffmann, “Cobalt(II) tetrasulfophthalocyanine on titanium dioxide: a new efficient electron relay for the photocatalytic formation and depletion of hydrogen peroxide in aqueous suspensions,” The Journal of Physical Chemistry, vol. 91, no. 8, pp. 2109–2117, 1987. [116] J. Moser, S. Punchihewa, P. P. Infelta, and M. Graetzel, “Surface complexation of colloidal semiconductors strongly enhances interfacial electron-transfer rates,” Langmuir, vol. 7, no. 12, pp. 3012–3018, 1991. [117] D. W. Bahnemann, J. Moenig, and R. Chapman, “Efficient photocatalysis of the irreversible one-electron and two-electron reduction of halothane on platinized colloidal titanium dioxide in aqueous suspension,” The Journal of Physical Chemistry, vol. 91, no. 14, pp. 3782–3788, 1987. [118] R. Y. Hong, J. H. Li, L. L. Chen et al., “Synthesis, surface modification and photocatalytic property of ZnO nanoparticles,” Powder Technology, vol. 189, no. 3, pp. 426–432, 2009. [119] L. Ge, C. Han, J. Liu, and Y. Li, “Enhanced visible light photocatalytic activity of novel polymeric g-C3 N4 loaded with
Journal of Nanomaterials
[120]
[121]
[122]
[123]
[124]
[125]
[126]
[127]
[128]
[129]
[130]
[131]
[132]
[133]
[134]
Ag nanoparticles,” Applied Catalysis A: General, vol. 409-410, pp. 215–222, 2011. A. Sclafani and J.-M. Herrmann, “Influence of metallic silver and of platinum-silver bimetallic deposits on the photocatalytic activity of titania (anatase and rutile) in organic and aqueous media,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 113, no. 2, pp. 181–188, 1998. H. Frei, D. J. Fitzmaurice, and M. Graetzel, “Surface chelation of semiconductors and interfacial electron transfer,” Langmuir, vol. 6, no. 1, pp. 198–206, 1990. S. Y. Chae, M. K. Park, S. K. Lee, T. Y. Kim, S. K. Kim, and W. I. Lee, “Preparation of size-controlled TiO2 nanoparticles and derivation of optically transparent photocatalytic films,” Chemistry of Materials, vol. 15, no. 17, pp. 3326–3331, 2003. J. Hodak, C. Quinteros, M. I. Litter et al., “Sensitization of TiO2 with phthalocyanines. 1. Photo-oxidations using hydroxoaluminium tricarboxymonoamidephthalocyanine adsorbed on TiO2 ,” Journal of the Chemical Society-Faraday Transactions, vol. 92, no. 24, pp. 5081–5088, 1996. J. S. Lee and W. Y. Choi, “Photocatalytic reactivity of surface platinized TiO2 : substrate specificity and the effect of Pt oxidation state,” Journal of Physical Chemistry B, vol. 109, no. 15, pp. 7399– 7406, 2005. U. Siemon, D. Bahnemann, J. J. Testa, D. Rodr´ıguez, M. I. Litter, and N. Bruno, “Heterogeneous photocatalytic reactions comparing TiO2 and Pt/TiO2 ,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 148, no. 1–3, pp. 247–255, 2002. S. Sakthivel, M. V. Shankar, M. Palanichamy, B. Arabindoo, D. W. Bahnemann, and V. Murugesan, “Enhancement of photocatalytic activity by metal deposition: characterisation and photonic efficiency of Pt, Au and Pd deposited on TiO2 catalyst,” Water Research, vol. 38, no. 13, pp. 3001–3008, 2004. J. Papp, H.-S. Shen, R. Kershaw, K. Dwight, and A. Wold, “Titanium(IV) oxide photocatalysts with palladium,” Chemistry of Materials, vol. 5, no. 3, pp. 284–288, 1993. G. Marc`ı, V. Augugliaro, M. J. L´opez-Mu˜noz et al., “Preparation characterization and photocatalytic activity of polycrystalline ZnO/TiO2 systems. 2. Surface, bulk characterization, and 4nitrophenol photodegradation in liquid-solid regime,” The Journal of Physical Chemistry B, vol. 105, no. 5, pp. 1033–1040, 2001. S. Janitabar-Darzi and A. R. Mahjoub, “Investigation of phase transformations and photocatalytic properties of sol-gel prepared nanostructured ZnO/TiO2 composites,” Journal of Alloys and Compounds, vol. 486, no. 1-2, pp. 805–808, 2009. M. Pelaez, N. T. Nolan, S. C. Pillai et al., “A review on the visible light active titanium dioxide photocatalysts for environmental applications,” Applied Catalysis B: Environmental, vol. 125, pp. 331–349, 2012. V. Etacheri, G. Michlits, M. K. Seery et al., “A highly efficient TiO2−𝑥 C𝑥 nano-heterojunction photocatalyst for visible light induced antibacterial applications,” ACS Applied Materials & Interfaces, vol. 5, no. 5, pp. 1663–1672, 2013. J. Di, J. Xia, S. Yin et al., “A g-C3 N4 /BiOBr visible-light-driven composite: synthesis via a reactable ionic liquid and improved photocatalytic activity,” RSC Advances, vol. 3, no. 42, pp. 19624– 19631, 2013. T. Kawahara, Y. Konishi, H. Tada, N. Tohge, J. Nishii, and S. Ito, “A patterned TiO2 (anatase)/TiO2 (rutile) bilayer-type photocatalyst: effect of the anatase/rutile junction on the photocatalytic activity,” Angewandte Chemie, vol. 41, no. 15, pp. 2811–2813, 2002. G. Liu, Y. Zhao, C. Sun, F. Li, G. Q. Lu, and H.-M. Cheng, “Synergistic effects of B/N doping on the visible-light photocatalytic
17
[135]
[136]
[137]
[138]
[139]
[140]
[141]
[142]
[143]
[144]
[145]
[146]
[147]
[148]
[149]
activity of mesoporous TiO2 ,” Angewandte Chemie International Edition, vol. 47, no. 24, pp. 4516–4520, 2008. W. Y. Teoh, J. A. Scott, and R. Amal, “Progress in heterogeneous photocatalysis: from classical radical chemistry to engineering nanomaterials and solar reactors,” The Journal of Physical Chemistry Letters, vol. 3, no. 5, pp. 629–639, 2012. K. Maeda and K. Domen, “Photocatalytic water splitting: recent progress and future challenges,” The Journal of Physical Chemistry Letters, vol. 1, no. 18, pp. 2655–2661, 2010. S. Anandan, N. Ohashi, and M. Miyauchi, “ZnO-based visiblelight photocatalyst: band-gap engineering and multi-electron reduction by co-catalyst,” Applied Catalysis B: Environmental, vol. 100, no. 3-4, pp. 502–509, 2010. J. A. Navio, F. J. Marchena, M. Roncel et al., “A laser flashphotolysis study of the reduction of methyl viologen by conduction-band electrons of TiO2 and Fe-Ti oxide photocatalysts,” Journal of Photochemistry and Photobiology A— Chemistry, vol. 55, no. 3, pp. 319–322, 1991. D. Dvoranov´a, V. Brezov´a, M. Maz´ur, and M. A. Malati, “Investigations of metal-doped titanium dioxide photocatalysts,” Applied Catalysis B: Environmental, vol. 37, no. 2, pp. 91– 105, 2002. A.-W. Xu, Y. Gao, and H.-Q. Liu, “The preparation, characterization, and their photocatalytic activities of rare-earth-doped TiO2 nanoparticles,” Journal of Catalysis, vol. 207, no. 2, pp. 151– 157, 2002. P. Yang, C. Lu, N. Hua, and Y. Du, “Titanium dioxide nanoparticles co-doped with Fe3+ and Eu3+ ions for photocatalysis,” Materials Letters, vol. 57, no. 4, pp. 794–801, 2002. C.-Y. Wang, C. B¨ottcher, D. W. Bahnemann, and J. K. Dohrmann, “A comparative study of nanometer sized Fe(III)doped TiO2 photocatalysts: synthesis, characterization and activity,” Journal of Materials Chemistry, vol. 13, no. 9, pp. 2322– 2329, 2003. K. Palmisano, V. Augugliaro, A. Sclafani, and M. Schiavello, “Activity of chromium-ion-doped titania for the dinitrogen photoreduction to ammonia and for the phenol photodegradation,” Journal of physical chemistry, vol. 92, no. 23, pp. 6710–6713, 1988. W. Mu, J.-M. Herrmann, and P. Pichat, “Room temperature photocatalytic oxidation of liquid cyclohexane into cyclohexanone over neat and modified TiO2 ,” Catalysis Letters, vol. 3, no. 1, pp. 73–84, 1989. H. Li, Z. Bian, J. Zhu, Y. Huo, H. Li, and Y. Lu, “Mesoporous Au/TiO2 nanocomposites with enhanced photocatalytic activity,” Journal of the American Chemical Society, vol. 129, no. 15, pp. 4538–4539, 2007. Q. Xu, X. Wang, X. Dong, C. Ma, X. Zhang, and H. Ma, “Improved visible light photocatalytic activity for TiO2 nanomaterials by codoping with zinc and sulfur,” Journal of Nanomaterials, vol. 2015, Article ID 157383, 8 pages, 2015. R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, and Y. Taga, “Visible-light photocatalysis in nitrogen-doped titanium oxides,” Science, vol. 293, no. 5528, pp. 269–271, 2001. X. Zhang, J. Zhou, Y. Gu et al., “Visible-light photocatalytic activity of N-doped TiO2 nanotube arrays on acephate degradation,” Journal of Nanomaterials, vol. 2015, Article ID 527070, 6 pages, 2015. S. In, A. Orlov, R. Berg et al., “Effective visible light-activated B-doped and B,N-codoped TiO2 photocatalysts,” Journal of the American Chemical Society, vol. 129, no. 45, pp. 13790–13791, 2007.
18 [150] S. Sakthivel and H. Kisch, “Daylight photocatalysis by carbonmodified titanium dioxide,” Angewandte Chemie—International Edition, vol. 42, no. 40, pp. 4908–4911, 2003. [151] W. K. Ho, J. C. Yu, and S. C. Lee, “Low-temperature hydrothermal synthesis of S-doped TiO2 with visible light photocatalytic activity,” Journal of Solid State Chemistry, vol. 179, no. 4, pp. 1171– 1176, 2006. [152] K. Awazu, M. Fujimaki, C. Rockstuhl et al., “A plasmonic photocatalyst consisting of silver nanoparticles embedded in titanium dioxide,” Journal of the American Chemical Society, vol. 130, no. 5, pp. 1676–1680, 2008. [153] P. Wang, B. Huang, X. Zhang et al., “Highly efficient visible-light plasmonic photocatalyst Ag@AgBr,” Chemistry, vol. 15, no. 8, pp. 1821–1824, 2009. [154] X. Zhang, Y. L. Chen, R.-S. Liu, and D. P. Tsai, “Plasmonic photocatalysis,” Reports on Progress in Physics, vol. 76, no. 4, Article ID 046401, 2013. [155] J. Jiang, H. Li, and L. Zhang, “New insight into daylight photocatalysis of AgBr@Ag: synergistic effect between semiconductor photocatalysis and plasmonic photocatalysis,” Chemistry—A European Journal, vol. 18, no. 20, pp. 6360–6369, 2012. [156] F. Pincella, K. Isozaki, and K. Miki, “A visible light-driven plasmonic photocatalyst,” Light: Science & Applications, vol. 3, no. 1, article e133, 2014. [157] X. D. Tong, A. Trivedi, H. F. Jia, M. Zhang, and P. Wang, “Enzymic thin film coatings for bioactive materials,” Biotechnology Progress, vol. 24, no. 3, pp. 714–719, 2008. [158] D. Han, S. Filocamo, R. Kirby, and A. J. Steckl, “Deactivating chemical agents using enzyme-coated nanofibers formed by electrospinning,” ACS Applied Materials & Interfaces, vol. 3, no. 12, pp. 4633–4639, 2011. [159] I. V. Borkar, C. Z. Dinu, G. Y. Zhu, R. S. Kane, and J. S. Dordick, “Bionanoconjugate-based composites for decontamination of nerve agents,” Biotechnology Progress, vol. 26, no. 6, pp. 1622– 1628, 2010. [160] K. Solanki, N. Grover, P. Downs et al., “Enzyme-based listericidal nanocomposites,” Scientific Reports, vol. 3, article 1584, 2013. [161] N. Grover, I. V. Borkar, C. Z. Dinu, R. S. Kane, and J. S. Dordick, “Laccase- and chloroperoxidase-nanotube paint composites with bactericidal and sporicidal activity,” Enzyme and Microbial Technology, vol. 50, no. 6-7, pp. 271–279, 2012. [162] K. Rege, N. R. Raravikar, D.-Y. Kim, L. S. Schadler, P. M. Ajayan, and J. S. Dordick, “Enzyme-polymer-single walled carbon nanotube composites as biocatalytic films,” Nano Letters, vol. 3, no. 6, pp. 829–832, 2003. [163] C. Z. Dinu, G. Zhu, S. S. Bale et al., “Enzyme-based nanoscale composites for use as active decontamination surfaces,” Advanced Functional Materials, vol. 20, no. 3, pp. 392– 398, 2010. [164] J. Kim, J. W. Grate, and P. Wang, “Nanostructures for enzyme stabilization,” Chemical Engineering Science, vol. 61, no. 3, pp. 1017–1026, 2006. [165] J. Ge, D. N. Lu, Z. X. Liu, and Z. Liu, “Recent advances in nanostructured biocatalysts,” Biochemical Engineering Journal, vol. 44, no. 1, pp. 53–59, 2009. [166] C. Mateo, J. M. Palomo, G. Fernandez-Lorente, J. M. Guisan, and R. Fernandez-Lafuente, “Improvement of enzyme activity, stability and selectivity via immobilization techniques,” Enzyme and Microbial Technology, vol. 40, no. 6, pp. 1451–1463, 2007. [167] Y. D. Kim, J. S. Dordick, and D. S. Clark, “Siloxane-based biocatalytic films and paints for use as reactive coatings,”
Journal of Nanomaterials
[168]
[169]
[170]
[171]
[172]
[173]
[174]
[175]
[176]
[177]
[178]
[179]
[180] [181]
[182]
[183]
Biotechnology and Bioengineering, vol. 72, no. 4, pp. 475–482, 2001. R. Pang, M. Z. Li, and C. D. Zhang, “Degradation of phenolic compounds by laccase immobilized on carbon nanomaterials: diffusional limitation investigation,” Talanta, vol. 131, pp. 38–45, 2015. G. F. Drevon, K. Danielmeier, W. Federspiel et al., “High-activity enzyme-polyurethane coatings,” Biotechnology and Bioengineering, vol. 79, no. 7, pp. 785–794, 2002. V. R. Regina, H. Søhoel, A. R. Lokanathan et al., “Entrapment of subtilisin in ceramic sol-gel coating for antifouling applications,” ACS Applied Materials & Interfaces, vol. 4, no. 11, pp. 5915–5921, 2012. U. Kharchenko and I. Beleneva, “Evaluation of coatings corrosion resistance with biocomponents as antifouling additives,” Corrosion Science, vol. 72, pp. 47–53, 2013. C. S. McDaniel, J. McDaniel, M. E. Wales, and J. R. Wild, “Enzyme-based additives for paints and coatings,” Progress in Organic Coatings, vol. 55, no. 2, pp. 182–188, 2006. J. E. Gittens, T. J. Smith, R. Suleiman, and R. Akid, “Current and emerging environmentally-friendly systems for fouling control in the marine environment,” Biotechnology Advances, vol. 31, no. 8, pp. 1738–1753, 2013. P. Asuri, S. S. Karajanagi, R. S. Kane, and J. S. Dordick, “Polymer-nanotube-enzyme composites as active antifouling films,” Small, vol. 3, no. 1, pp. 50–53, 2007. C. Z. Dinu, I. V. Borkar, S. S. Bale, A. S. Campbell, R. S. Kane, and J. S. Dordick, “Perhydrolase-nanotube-paint sporicidal composites stabilized by intramolecular crosslinking,” Journal of Molecular Catalysis B: Enzymatic, vol. 75, pp. 20–26, 2012. R. C. Pangule, S. J. Brooks, C. Z. Dinu et al., “Antistaphylococcal nanocomposite films based on enzyme-nanotube conjugates,” ACS Nano, vol. 4, no. 7, pp. 3993–4000, 2010. G. Bayramoˇglu and M. Y. Arica, “Immobilization of laccase onto poly(glycidylmethacrylate) brush grafted poly(hydroxyethylmethacrylate) films: enzymatic oxidation of phenolic compounds,” Materials Science and Engineering C, vol. 29, no. 6, pp. 1990–1997, 2009. M. Faustini, L. Nicole, C. Boissi`ere, P. Innocenzi, C. Sanchez, and D. Grosso, “Hydrophobic, antireflective, self-cleaning, and antifogging sol-gel coatings: an example of multifunctional nanostructured materials for photovoltaic cells,” Chemistry of Materials, vol. 22, no. 15, pp. 4406–4413, 2010. P. Asuri, S. S. Karajanagi, H. C. Yang, T.-J. Yim, R. S. Kane, and J. S. Dordick, “Increasing protein stability through control of the nanoscale environment,” Langmuir, vol. 22, no. 13, pp. 5833– 5836, 2006. J. N. Talbert and J. M. Goddard, “Enzymes on material surfaces,” Colloids and Surfaces B: Biointerfaces, vol. 93, pp. 8–19, 2012. S. Yin, Y. Fujishiro, J. Wu, M. Aki, and T. Sato, “Synthesis and photocatalytic properties of fibrous titania by solvothermal reactions,” Journal of Materials Processing Technology, vol. 137, no. 1–3, pp. 45–48, 2003. C.-S. Kim, B. K. Moon, J.-H. Park, B.-C. Choi, and H.-J. Seo, “Solvothermal synthesis of nanocrystalline TiO2 in toluene with surfactant,” Journal of Crystal Growth, vol. 257, no. 3-4, pp. 309– 315, 2003. S. T. Aruna, S. Tirosh, and A. Zaban, “Nanosize rutile titania particle synthesis via a hydrothermal method without mineralizers,” Journal of Materials Chemistry, vol. 10, no. 10, pp. 2388– 2391, 2000.
Journal of Nanomaterials [184] Y. V. Kolen’ko, V. D. Maximov, A. V. Garshev, P. E. Meskin, N. N. Oleynikov, and B. R. Churagulov, “Hydrothermal synthesis of nanocrystalline and mesoporous titania from aqueous complex titanyl oxalate acid solutions,” Chemical Physics Letters, vol. 388, no. 4–6, pp. 411–415, 2004. [185] Y. Mao, T.-J. Park, F. Zhang, H. Zhou, and S. S. Wong, “Environmentally friendly methodologies of nanostructure synthesis,” Small, vol. 3, no. 7, pp. 1122–1139, 2007. [186] T. K. Ghorai, D. Dhak, S. K. Biswas, S. Dalai, and P. Pramanik, “Photocatalytic oxidation of organic dyes by nano-sized metal molybdate incorporated titanium dioxide (M𝑥 Mo𝑥 Ti1−𝑥 O6 ) (M=Ni, Cu, Zn) photocatalysts,” Journal of Molecular Catalysis A: Chemical, vol. 273, no. 1-2, pp. 224–229, 2007. [187] D.-E. Gu, B.-C. Yang, and Y.-D. Hu, “V and N co-doped nanocrystal anatase TiO2 photocatalysts with enhanced photocatalytic activity under visible light irradiation,” Catalysis Communications, vol. 9, no. 6, pp. 1472–1476, 2008. [188] B.-H. Kim, J.-Y. Lee, Y.-H. Choa, M. Higuchi, and N. Mizutani, “Preparation of TiO2 thin film by liquid sprayed mist CVD method,” Materials Science and Engineering B: Solid-State Materials for Advanced Technology, vol. 107, no. 3, pp. 289–294, 2004. [189] L. L. Hench and J. K. West, “The sol-gel process,” Chemical Reviews, vol. 90, no. 1, pp. 33–72, 1990. [190] J. Yu, X. Zhao, and Q. Zhao, “Effect of surface structure on photocatalytic activity of TiO2 thin films prepared by sol-gel method,” Thin Solid Films, vol. 379, no. 1-2, pp. 7–14, 2000. [191] N. P. Mellott, C. Durucan, C. G. Pantano, and M. Guglielmi, “Commercial and laboratory prepared titanium dioxide thin films for self-cleaning glasses: Photocatalytic performance and chemical durability,” Thin Solid Films, vol. 502, no. 1-2, pp. 112– 120, 2006. [192] R. L. Putnam, N. Nakagawa, K. M. McGrath et al., “Titanium dioxide—surfactant mesophases and Ti-TMS1,” Chemistry of Materials, vol. 9, no. 12, pp. 2690–2693, 1997. [193] Y. Haga, H. An, and R. Yosomiya, “Photoconductive properties of TiO2 films prepared by the sol-gel method and its application,” Journal of Materials Science, vol. 32, no. 12, pp. 3183–3188, 1997. [194] U. Bach, D. Lupo, P. Comte et al., “Solid-state dye-sensitized mesoporous TiO2 solar cells with high photon-to-electron conversion efficiencies,” Nature, vol. 395, no. 6702, pp. 583–585, 1998. [195] N. I. Al-Salim, S. A. Bagshaw, A. Bittar et al., “Characterisation and activity of sol-gel-prepared TiO2 photocatalysts modified with Ca, Sr or Ba ion additives,” Journal of Materials Chemistry, vol. 10, no. 10, pp. 2358–2363, 2000. [196] J. Yu, J. C. Yu, B. Cheng, and X. Zhao, “Photocatalytic activity and characterization of the sol-gel derived Pb-doped TiO2 thin films,” Journal of Sol-Gel Science and Technology, vol. 24, no. 1, pp. 39–48, 2002. [197] H. E. Chao, Y. U. Yun, H. U. Xingfang, and A. Larbot, “Effect of silver doping on the phase transformation and grain growth of sol-gel titania powder,” Journal of the European Ceramic Society, vol. 23, no. 9, pp. 1457–1464, 2003. [198] A. R. Phani and S. Santucci, “Structural characterization of iron titanium oxide synthesized by sol-gel spin-coating technique,” Materials Letters, vol. 50, no. 4, pp. 240–245, 2001. [199] J. Wang, S. Uma, and K. J. Klabunde, “Visible light photocatalysis in transition metal incorporated titania-silica aerogels,” Applied Catalysis B: Environmental, vol. 48, no. 2, pp. 151–154, 2004.
19 [200] A. Di Paola, G. Marc`ı, L. Palmisano et al., “Preparation of polycrystalline TiO2 photocatalysts impregnated with various transition metal ions: characterization and photocatalytic activity for the degradation of 4-nitrophenol,” The Journal of Physical Chemistry B, vol. 106, no. 3, pp. 637–645, 2002. [201] F. B. Li and X. Z. Li, “Photocatalytic properties of gold/gold ionmodified titanium dioxide for wastewater treatment,” Applied Catalysis A: General, vol. 228, no. 1-2, pp. 15–27, 2002. [202] F. B. Li, X. Z. Li, and M. F. Hou, “Photocatalytic degradation of 2-mercaptobenzothiazole in aqueous La3+ -TiO2 suspension for odor control,” Applied Catalysis B: Environmental, vol. 48, no. 3, pp. 185–194, 2004. [203] D. Byun, Y. Jin, B. Kim, J. Kee Lee, and D. Park, “Photocatalytic TiO2 deposition by chemical vapor deposition,” Journal of Hazardous Materials, vol. 73, no. 2, pp. 199–206, 2000. [204] K. L. Choy, “Chemical vapour deposition of coatings,” Progress in Materials Science, vol. 48, no. 2, pp. 57–170, 2003. [205] R. van de Krol, A. Goossens, and J. Schoonman, “Mott-schottky analysis of nanometer-scale thin-film anatase TiO2 ,” Journal of the Electrochemical Society, vol. 144, no. 5, pp. 1723–1727, 1997. [206] A. Smith and R. Rodriguez-Clemente, “Morphological differences in ZnO films deposited by the pyrosol technique: effect of HCl,” Thin Solid Films, vol. 345, no. 2, pp. 192–196, 1999. [207] D. F. Paraguay, L. W. Estrada, N. D. R. Acosta, E. Andrade, and M. Miki-Yoshida, “Growth, structure and optical characterization of high quality ZnO thin films obtained by spray pyrolysis,” Thin Solid Films, vol. 350, no. 1-2, pp. 192–202, 1999. [208] R. Zhang and L. Gao, “Preparation of nanosized titania by hydrolysis of alkoxide titanium in micelles,” Materials Research Bulletin, vol. 37, no. 9, pp. 1659–1666, 2002. [209] I. Zhitomirsky, “Cathodic electrosynthesis of titanium and ruthenium oxides,” Materials Letters, vol. 33, no. 5-6, pp. 305– 310, 1998. [210] K. Kamada, M. Mukai, and Y. Matsumoto, “Electrodeposition of titanium(IV) oxide film from sacrificial titanium anode in I2-added acetone bath,” Electrochimica Acta, vol. 47, no. 20, pp. 3309–3313, 2002. [211] S. Takeda, S. Suzuki, H. Odaka, and H. Hosono, “Photocatalytic TiO2 thin film deposited onto glass by DC magnetron sputtering,” Thin Solid Films, vol. 392, no. 2, pp. 338–344, 2001. [212] V. Pore, A. Rahtu, M. Leskel¨a, M. Ritala, T. Sajavaara, and J. Keinonen, “Atomic layer deposition of photocatalytic TiO2 thin films from titanium tetramethoxide and water,” Chemical Vapor Deposition, vol. 10, no. 3, pp. 143–148, 2004. [213] J. Boucl´e, P. Ravirajan, and J. Nelson, “Hybrid polymer-metal oxide thin films for photovoltaic applications,” Journal of Materials Chemistry, vol. 17, no. 30, pp. 3141–3153, 2007. [214] M. Miyauchi, A. Nakajima, T. Watanabe, and K. Hashimoto, “Photocatalysis and photoinduced hydrophilicity of various metal oxide thin films,” Chemistry of Materials, vol. 14, no. 6, pp. 2812–2816, 2002. [215] Y. Gushikem and S. S. Rosatto, “Metal oxide thin films grafted on silica gel surfaces: recent advances on the analytical application of these materials,” Journal of the Brazilian Chemical Society, vol. 12, no. 6, pp. 695–705, 2001. [216] D. Gong, C. A. Grimes, O. K. Varghese et al., “Titanium oxide nanotube arrays prepared by anodic oxidation,” Journal of Materials Research, vol. 16, no. 12, pp. 3331–3334, 2001. [217] S. G. Kandalkar, J. L. Gunjakar, and C. D. Lokhande, “Preparation of cobalt oxide thin films and its use in supercapacitor application,” Applied Surface Science, vol. 254, no. 17, pp. 5540– 5544, 2008.
20 [218] J. H. Seinfeld and S. N. Pandis, Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley & Sons, 2012. [219] M. Azhar Khan, M. Zahir Khan, K. Zaman, and L. Naz, “Global estimates of energy consumption and greenhouse gas emissions,” Renewable and Sustainable Energy Reviews, vol. 29, pp. 336–344, 2014. [220] D. Buchan, “Energy and climate change: Europe at the crossroads,” Journal of Contemporary European Research, vol. 6, no. 3, p. 419, 2010. [221] M. F. Montemor, “Functional and smart coatings for corrosion protection: a review of recent advances,” Surface and Coatings Technology, vol. 258, pp. 17–37, 2014. [222] D. G. Rickerby and M. Morrison, “Nanotechnology and the environment: a European perspective,” Science and Technology of Advanced Materials, vol. 8, no. 1-2, pp. 19–24, 2007. [223] J. M. Gadekar and K. D. Kadam, “Nanotechnology: green innovation,” International Journal of Science and Research, vol. 3, no. 1, 2014. [224] R. A. McIntyre, “Common nano-materials and their use in real world applications,” Science Progress, vol. 95, no. 1, pp. 1–22, 2012. [225] T. P. Chou, C. Chandrasekaran, S. J. Limmer et al., “Organic– inorganic hybrid coatings for corrosion protection,” Journal of Non-Crystalline Solids, vol. 290, no. 2-3, pp. 153–162, 2001.
Journal of Nanomaterials
Journal of
Nanotechnology Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
International Journal of
International Journal of
Corrosion Hindawi Publishing Corporation http://www.hindawi.com
Polymer Science Volume 2014
Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Smart Materials Research Hindawi Publishing Corporation http://www.hindawi.com
Journal of
Composites Volume 2014
Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Journal of
Metallurgy
BioMed Research International Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Nanomaterials
Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Submit your manuscripts at http://www.hindawi.com Journal of
Materials Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Journal of
Nanoparticles Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Nanomaterials Journal of
Advances in
Materials Science and Engineering Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Journal of
Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Journal of
Nanoscience Hindawi Publishing Corporation http://www.hindawi.com
Scientifica
Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Journal of
Coatings Volume 2014
Hindawi Publishing Corporation http://www.hindawi.com
Crystallography Volume 2014
Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
The Scientific World Journal Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
Journal of
Journal of
Textiles
Ceramics Hindawi Publishing Corporation http://www.hindawi.com
International Journal of
Biomaterials
Volume 2014
Hindawi Publishing Corporation http://www.hindawi.com
Volume 2014
