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Materials Express 2158-5849/2015/5/309/010

Copyright © 2015 by American Scientific Publishers All rights reserved. Printed in the United States of America

doi:10.1166/mex.2015.1242

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A simple large-scale method for preparation of g-C3 N4/SnO2 nanocomposite as visible-light-driven photocatalyst for degradation of an organic pollutant Anise Akhundi and Aziz Habibi-Yangjeh∗ Department of Chemistry, Faculty of Sciences, University of Mohaghegh Ardabili, P. O. Box 179, Ardabil, Iran

In this work, we report a simple large-scale method for preparation of g-C3 N4 /SnO2 nanocomposite as visiblelight-driven photocatalyst. The nanocomposite was prepared by a facile refluxing method at 96 C for one hour using g-C3 N4 , SnCl4 , and NaOH as the starting materials. The prepared samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive analysis of X-rays, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, Fourier transform-infrared spectroscopy, and photoluminescence (PL) techniques. Photocatalytic activity of the samples was investigated by degradation of rhodamine B (RhB) under visible-light irradiation. The degradation rate constant of RhB on g-C3 N4 (90%)/SnO2 nanocomposite is about 2.1 and 9.3-fold higher than those of g-C3 N4 and SnO2 , respectively. Increase of the photocatalytic activity was related to the separation of electron–hole pairs, confirmed by PL technique. Moreover, the degradation rate constant was initially increased with refluxing time up to one hour and then decreased. It was found that superoxide ions and holes are the main reactive species in the degradation reaction. This work can be applied for preparation of other visible-light-driven photocatalysts based on g-C3 N4 . Keywords: g-C3 N4 /SnO2 , Nanocomposite, Photocatalyst, Visible-Light-Driven, Photodegradation.

1. INTRODUCTION In recent years, heterogeneous photocatalysis using semiconductors, as a green technology, has gained a lot of attention owing to its potential applications in many fields such as hydrogen production by splitting of water, degradation of different organic pollutants, and reduction of carbon dioxide to value added chemicals to address the increasing global energy and environmental crises.1–4 Among various semiconductors, TiO2 and ZnO have been the most widely used catalysts in photocatalytic processes.5 6 However, these photocatalysts can be excited by ultraviolet or near-ultraviolet irradiation, which ∗

Author to whom correspondence should be addressed. Email: [email protected]

strictly limits their practical applications in large scale; because the sunlight consist of about 5% UV, 43% visible and 52% infrared.7 Visible-light-driven photocatalysts can provide an appropriate way to make full using of the solar radiation in photocatalytic processes. For this reason, in recent years many attempts have been paid to prepare novel visible-light-driven photocatalysts with high efficiency.8–12 Graphitic carbon nitride (g-C3 N4 is the most stable allotrope of carbon nitrides under ambient conditions.13 This polymeric n-type “metal free” semiconductor is potentially promising candidate for different applications.14–18 Environment-friendly, its “earth abundant” elements, high chemical stability, reasonable photochemical and thermal stability, 2D layered structure,

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ABSTRACT

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A simple large-scale method for preparation of g-C3 N4 /SnO2 nanocomposite Akhundi and Habibi-Yangjeh

and low band gap of about 2.7 eV are the main reasons for the widespread acceptability of g-C3 N4 as visiblelight-driven photocatalyst for hydrogen energy production, reducing carbon dioxide to fuel molecules, and removal of environmental pollutants.19–22 However, a major hindrance for efficient photocatalytic activity of pristine g-C3 N4 is fast recombination of the photogenerated electron–hole pairs.23 To address this limitation, one effective strategy is combining g-C3 N4 with other semiconductors with proper energy levels (such as TiO2 , ZnO, CdS, BiVO4 , polyaniline, BiOBr, Co3 O4 , (BiO)2 CO3 , and Ag3 PO4 .24–32 Valence band (VB) and conduction band (CB) energy levels of SnO2 are lower than those of g-C3 N4 .33–35 Hence, by combining g-C3 N4 with SnO2 , photogenerated electrons on CB of g-C3 N4 can easily transfer to CB of SnO2 , leading to separation of electron–hole pairs in g-C3 N4 . Recently, Zang et al. prepared g-C3 N4 /SnO2 composites by calcinations g-C3 N4 and SnO2 at 400 C and their photocatalytic activities were investigated by degradation of methyl orange under visible-light irradiation.33 Moreover, ultrasonic assisting deposition method has been applied for preparation of the nanocomposite using g-C3 N4 and SnO2 as the starting materials.34 Very recently, Chen et al. have reported preparation of the nanocomposite by heating a mixture of SnO2 nanoparticles and melamine in a furnace.35 It is evident that these preparation methods are not simple and they use SnO2 as starting material. Moreover, they require high calcination temperature or long preparation time. Hence, preparation of the nanocomposites with simple method at low temperature will be highly valuable. Herein, we report a simple method for preparation of g-C3 N4 /SnO2 nanocomposite in water by refluxing a mixture of g-C3 N4 , SnCl4 and NaOH as the starting materials at 96 C for one hour. Photocatalytic activity of the samples was evaluated by degradation of rhodamine B (RhB) under visible-light irradiation. Meanwhile, the effects of refluxing time, calcination temperature, and scavengers of the reactive species on the degradation reaction were studied and the results were discussed.

2. EXPERIMENTAL DETAILS 2.1. Materials and Methods Melamine (C3 H6 N6 , tin (IV) chloride (SnCl4 , sodium hydroxide, RhB, 2-propanol, potassium iodide, benzoquinone, and ethanol with high quality were

SnCl4

employed without further purification. Double distilled water was used for the experiments. The g-C3 N4 powder was prepared by heating melamine powder up to 520 C according to the literature method.13 For preparation of g-C3 N4 (90%)/SnO2 nanocomposite, 0.63 g of g-C3 N4 powder was dispersed into 100 mL of distilled water using an ultrasonic bath for 30 min. After that, 54 L of SnCl4 and 0.1114 g NaOH were added to the above solution and the suspension was vigorously stirred magnetically for 30 min at room temperature. Then, the mixture was refluxed at 96 C for 60 min. The schematic diagram for preparation of the nanocomposites can be illustrated in Figure 1. Photocatalysis experiments were performed in a cylindrical Pyrex reactor with about 400 mL capacity. Temperature of the reactor was maintained at 25 C using a water circulation arrangement. The solution was magnetically stirred and continuously aerated by a pump to provide oxygen and complete mixing of the reaction solution. A tungsten lamp with 500 W was used as visible-light source. The emission spectrum of this commercial source has high intensity in visible range and its intensity rapidly decreases in wavelengths near to UV range. The lamp was fitted on the top of the reactor. Prior to illumination, a suspension containing 0.1 g of the photocatalyst and 250 mL of RhB (25 × 10−5 M) was continuously stirred in the dark for 60 minutes, to attain adsorption equilibrium. Samples were taken from the reactor at regular intervals and centrifuged to remove the photocatalyst before analysis by spectrophotometer at 553 nm corresponding to maximum absorption wavelength of RhB. 2.2. Characterizations The X-ray diffraction (XRD) patterns were recorded on a Philips Xpert X-ray diffractometer with Cu K radiation ( = 015406 nm). Diffuse reflectance spectra (DRS) were recorded by a Scinco 4100 apparatus. Surface morphology and distribution of particles were studied by LEO 1430VP scanning electron microscopy (SEM), using an accelerating voltage of 15 kV. The purity and elemental analysis of the products were obtained by energy dispersive analysis of X-rays (EDX) on the same SEM instrument. For SEM and EDX, samples mounted on an aluminum support using a double adhesive tape coated with a thin layer of gold. Also, the X-ray photoelectron spectroscopy (XPS) of the nanocomposite was recorded on a X-ray 8025 BestTec spectrometer and all binding energies were corrected by

NaOH refluxing

g-C3N4 (in water)

ultrasonic Suspension I

Suspension II

g-C3N4 + Sn(OH)4

g-C3N4/SnO2 nanocomposite

Fig. 1. Schematic diagram for preparation of g-C3 N4 /SnO2 nanocomposites.

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using the peak for contaminant carbon (C 1s = 2846 eV) as an internal standard. Fourier transform-infrared (FT-IR) spectra were obtained using Perkin Elmer Spectrum RX I apparatus. Photoluminescence (PL) of the samples was studied using a Perkin Elmer (LS 55) fluorescence spectrophotometer with an excitation wavelength of 300 nm. The conditions were fixed in order to compare the PL intensity. The pH of solutions was measured by Metrohm digital pH meter of model 691.

3. RESULTS AND DISCUSSION Figure 2 shows the XRD patterns for SnO2 , g-C3 N4 , and g-C3 N4 /SnO2 nanocomposites. In the case of SnO2 , the diffraction peaks correspond to (110), (101), (211) and (112) planes of the tetragonal rutile SnO2 (JCPDS card No. 41-1445).36 The average particle size calculated by Scherrer’s equation is about 3 nm. For g-C3 N4 , there are two distinct well-defined diffraction peaks at 13.63 and 27.67, (a) 150

which could be ascribed to (100) and (002) diffraction planes (JCPDS 87-1526).13 In the case of the nanocomposites, when the amount of SnO2 nanoparticles is lower than 15 wt%, the characteristic peaks of SnO2 cannot be seen and the XRD patterns nearly are the same as for the pure g-C3 N4 , due to low content of SnO2 in the nanocomposite, low diffraction intensity of SnO2 nanoparticles and well dispersion of that on the surface of g-C3 N4 . However, for g-C3 N4 (85%)/SnO2 nanocomposite, the XRD pattern exhibits characteristic peaks for both g-C3 N4 and SnO2 counterparts. Purity of the as-prepared samples and presence of SnO2 nanoparticles on g-C3 N4 sheets were confirmed by EDX technique and the corresponding results for g-C3 N4 and g-C3 N4 (90%)/SnO2 are shown in Figure 3. For g-C3 N4 , the peaks are clearly related to C and N elements. In the case of g-C3 N4 (90%)/SnO2 nanocomposite, the peaks correspond to C, N, Sn, and O elements. Hence, it can be concluded that SnO2 nanoparticles have been successfully deposited on the g-C3 N4 sheets. Other peaks in the figure are related to the elements applied for sputter coating of the samples on the EDX stage.

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Fig. 3. The EDX spectra for: (a) g-C3 N4 , and (b) g-C3 N4 (90%)/SnO2 nanocomposite.

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A simple large-scale method for preparation of g-C3 N4 /SnO2 nanocomposite

Surface components, chemical states, and structural environment of g-C3 N4 (90%)/SnO2 nanocomposite was examined by XPS technique and the results are shown in Figure 4. The survey scan spectrum of the nanocomposite

Akhundi and Habibi-Yangjeh

displays only C, N, O, and Sn elements, confirming purity of g-C3 N4 (90%)/SnO2 nanocomposite (Fig. 4(a)). The high-resolution C 1s spectrum in Figure 4(b) displays four deconvoluted peaks at 284.1, 285.48, 287.32, (b)

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Fig. 4. XPS spectra for g-C3 N4 (90%)/SnO2 nanocomposite. (a) survey scan, and high-resolution spectra for: (b) C 1s, (c) N 1s, (d) Sn 3d, and (e) O 1s.

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Optical properties of the samples were investigated by DRS technique and the results are shown in Figure 6(a). The SnO2 nanoparticles have an absorption edge at 360 nm. Hence, these nanoparticles cannot (a)

1.4 g-C3N4 g-C3N4(95%)/SnO2 g-C3N4(90%)/SnO2 g-C3N4(85%)/SnO2 SnO2

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and 287.69 eV. The peaks at 284.1 and 285.48 eV are related to the graphitic carbon and C–N groups, respectively. Moreover, the signal at 287.32 eV is characteristic of C N groups, while the peak for N–C N groups is appeared at 287.69 eV.33 The high-resolution N 1s spectrum in Figure 4(c) displays four deconvoluted peaks at 397.99, 398.11, 400.09, and 404.34 eV. The peaks at 397.99 and 398.11 eV come from sp2 -hybridized aromatic N and ternary N bonded to C atom, respectively.33 The peak at 400.09 is related to the N–H groups, while the peak at 404.34 eV is ascribed to excitation. Figure 4(d) shows the high-resolution XPS spectrum for Sn 3d3/2 and Sn 3d5/2 at 486.0 and 495.6 eV, respectively, indicating the presence of Sn4+ .33 For the oxygen element, the peak at about 532.5 eV is assigned to the lattice oxygen of SnO2 (Fig. 4(e)). Morphology of the samples was investigated by TEM and the images are shown in Figure 5. In the case of gC3 N4 , it can be seen that the nanosheets are very thin and transparent to the electron beam. For g-C3 N4 (90%)/SnO2 nanocomposite, very small SnO2 nanoparticles with size of about 3 nm are clearly seen on the g-C3 N4 sheets.

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Fig. 6. (a) UV-vis DRS for SnO2 nanoparticles, g-C3 N4 , and gC3 N4 /SnO2 nanocomposites with different contents of SnO2 . (b) Plot of h 2 versus hv for SnO2 nanoparticles, (c) Plots of h 1/2 versus hv for g-C3 N4 and g-C3 N4 (90%)/SnO2 nanocomposite.

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(a) SnO2 (b) g-C3N4 (c) g-C3N2(90%)/SnO2

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absorb the visible-light irradiation. This absorption spectrum is comparable with the reported spectra for SnO2 nanomaterials.36 For pure g-C3 N4 , similar to the literature, there is an absorption edge at 470 nm.13 The absorption spectra of the nanocomposites, similar to the pure g-C3 N4 , have strong absorption in visible-light region. Similar results have been reported for g-C3 N4 /ZnO, g-C3 N4 /TiO2 , and g-C3 N4 /ZnS nanocomposites.24 25 37 Band gap Eg of the samples were calculated using equation h = Bhv − Eg )n/2 where , and B are absorption coefficient, the light frequency, and proportionality constant, respectively.38 In this equation, n depends on the characteristics of the transition in the semiconductor (the value of n for SnO2 and g-C3 N4 are 1 and 4, respectively). The Eg values were estimated by extrapolation

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Fig. 7. FT-IR spectra for: (a) SnO2 nanoparticles, (b) g-C3 N4 , and (c) g-C3 N4 (90%)/SnO2 nanocomposite.

of the linear part of the curves obtained by plotting (h 1/2 or (h 2 versus hv. For SnO2 , g-C3 N4 , and gC3 N4 (90%)/SnO2 nanocomposite, the Eg values were 3.60, 2.62, and 2.68 eV, respectively (Figs. 6(b) and (c)). In the case of g-C3 N4 (90%)/SnO2 nanocomposite, there is an increase in its band gap, due to formation of a heterojunction between g-C3 N4 with narrow band gap and SnO2 with wide band gap. The FT-IR spectra for SnO2 , g-C3 N4 and gC3 N4 (90%)/SnO2 nanocomposite are shown in Figure 7. For all of the samples, the absorption bands centered at about 3150 cm−1 are assigned to the O–H stretching vibration of adsorbed water molecules on the samples. For SnO2 , the Sn–O characteristic peaks are clearly seen at 550 and 640 cm−1 .33 In the case of pure g-C3 N4 , the strong bands in the range of 1200–1650 cm−1 are found, corresponding to the typical stretching vibration modes of C–N and C N in heterocycles. Moreover, the typical band at

SnO2

g-C3N4

g-C3N4(90%)/SnO2

Type of photocatalyst Fig. 9. (a) Photodegradation of RhB on SnO2 , g-C3 N4 , and gC3 N4 (90%)/SnO2 nanocomposite along with photolysis experiment. (b) The degradation rate constant for RhB on different samples.


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pairs.5 6 In Figure 10, PL spectra of g-C3 N4 and gC3 N4 (90%)/SnO2 nanocomposite are shown. Although the both samples have similar spectrum, the emission intensity of the nanocomposite is much lower than that of g-C3 N4 . Decrease of the emission intensity in PL spectrum is generally attributed to increase of electron–hole separation. In the nanocomposite, g-C3 N4 is excited under visible-light irradiation and produces holes and electrons in its VB and CB, respectively. The energy level for the CB of g-C3 N4 is higher than that of SnO2 nanoparticles.33–35 Hence, the photogenerated electrons are injected from the CB of gC3 N4 to that of SnO2 , thus preventing the electrons from recombination with the holes. Therefore, it can be concluded that the charge carriers in the nanocomposite can be efficiently separated and migrated to surface of that to participate in the degradation reactions. Preparation time can affect crystallinity, size and morphology of nanomaterials.41 Hence, the preparation time could change activity of photocatalysts. To investigate the (a)

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806 cm−1 is related to the breathing mode of the heptazine arrangement.33 Photocatalytic activities of the prepared samples were evaluated by degradation of RhB under visible-light irradiation. In Figure 8, the plots of absorbance versus wavelength for degradation of RhB on g-C3 N4 (90%)/SnO2 nanocomposite ([RhB] = 250 × 10−5 M, composite weight = 01 g) at various irradiation time have been shown. As can be seen, under the light irradiation, intensity of the absorption peaks in UV and visible ranges gradually decreases without any changes in position of them. Hence, it can be concluded that the degradation reaction takes place by aromatic ring opening mechanism without formation of stable de-ethylated intermediates.38 39 In Figure 9(a), absorbances for RhB at 554 nm have been plotted versus the irradiation time. It is evident that in presence of the irradiation and without using the photocatalyst, only about 11% of RhB molecules were degraded after irradiation for 420 min. In presence of SnO2 nanoparticles, about 25% of RhB molecules have been degraded at this time. Due to the wide band gap of SnO2 nanoparticles, they cannot produce electron–hole pairs under the visiblelight irradiation. Hence, degradation of RhB on SnO2 nanoparticles takes place by dye-sensitized mechanism.40 In presence of g-C3 N4 and g-C3 N4 (90%)/SnO2 nanocomposite, nearly 66 and 90% of the molecules were degraded, respectively. The observed first-order rate constant of the degradation reaction (kobs was calculated10 and the results are shown in Figure 9(b). The degradation rate constant on SnO2 , g-C3 N4 , and g-C3 N4 (90%)/SnO2 nanocomposite are 544 ×10−4, 238 ×10−4, and 506 ×10−4 min−1 , respectively. Hence, the photocatalytic activity of the nanocomposite is about 2.1 and 9.3-fold higher than those of g-C3 N4 and SnO2 , respectively. It is well known that photocatalytic activity closely related to separation of photogenerated electron–hole

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Fig. 11. The degradation rate constant of RhB on g-C3 N4 (90%)/SnO2 nanocomposite: (a) prepared at different refluxing times, (b) calcined at different temperatures.

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influence of refluxing time applied for preparation of gC3 N4 (90%)/SnO2 nanocomposite, four comparative samples were prepared by refluxing for 0.5, 1, 2, and 4 h and the results are shown in Figure 11(a). It is evident that the degradation rate constant initially increases up to 1 h and then decreases. Increase of the degradation rate constant with increasing refluxing time may be related to increasing crystallinity of the photocatalyst.41 However, further increase of refluxing time can increase size and aggregation of the photocatalyst. As a result, the degradation rate constant decreases at higher refluxing time. In order to confirm aggregation of the SnO2 particles on the g-C3 N4 sheets to produce greater sizes, SEM images of

(a)

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g-C3 N4 (90%)/SnO2 nanocomposite prepared by refluxing for 1 and 4 h are shown in Figures 12(a) and (b). It is clearly evident that size of the SnO2 nanoparticles on the g-C3 N4 sheets increases by increasing the preparation time. Hence, the photogenerated electrons are not efficiently migrate from g-C3 N4 to SnO2 particles. As a result, more recombination of the charge carriers takes place, leading to decrease of the photocatalytic activity. To study the effect of calcination temperature on the photocatalytic activity, g-C3 N4 (90%)/SnO2 nanocomposite was calcined at 200, 300, 400, and 500 C for 2 h and the results are shown in Figure 11(b). It is clearly evident that the degradation rate constant decreases with increasing the calcination temperature and the degradation reaction on the nanocomposite without any thermal treatment is faster than those of the calcined photocatalysts. Generally, size of nanomaterials increases with increasing the calcination temperature.42 Decrease of the degradation rate constant can be related to aggregation and crystalline growth at higher temperatures.41 Increase of average sizes for the SnO2 nanoparticles on the g-C3 N4 is clearly shown in SEM image of the nanocomposite calcined at 500 C (Fig. 12(c)). Photocatalytic reactions proceed by reactive species, produced during illumination of photocatalysts.2 5 6 The role of the reactive species was investigated by measuring the effects of various scavengers on the degradation rate constant and the results are shown in Figure 13. As can be seen, decrease of the degradation rate constant in presence of benzoquinone (1 mmol/L) and KI (0.1 mmol/L) is greater than that of 2-PrOH (1 mmol/L). Benzoquinone, + KI and 2-PrOH are scavengers for • O− and • OH 2, h 43 44 • − species. Hence, it can be concluded that O2 and h+ have vital role in degradation of RhB on the nanocomposite under visible-light irradiation.

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4. CONCLUSION In summary, we report a simple method for preparation of g-C3 N4 /SnO2 nanocomposite by refluxing the mixture of reactants at 96 C for one hour. Photocatalytic activities of the samples were evaluated by degradation of RhB under visible-light irradiation. The degradation reaction proceeds by decrease of absorbance in UV and visible ranges without any changes in position of the peaks. As a result, it was concluded that the degradation reaction takes place by aromatic ring opening mechanism. The photocatalytic activity of the nanocomposite is about 2.1 and 9.3-fold higher than those of pure g-C3 N4 and SnO2 , respectively. Based on PL spectra, it was revealed that increase of the photocatalytic activity of the nanocomposite is related to separation of electron–hole pairs. Meanwhile, the effects of refluxing time, calcination temperature, and different scavengers of reactive species on the degradation reaction were studied. Based on the effects + of scavengers, it was concluded that • O− 2 and h have vital role in degradation of RhB on the nanocomposite under the visible-light irradiation.

References and Notes


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28.

29.

Nb2 O5 /ZnO nanorod composites and the mechanism study; Appl. Catal. A: General 471, 126 (2014). S. C. Yan, Z. S. Li, and Z. G. Zou; Photodegradation performance of g-C3 N4 fabricated by directly heating melamine; Langmuir 25, 10397 (2009). Y. Li, Y. Gong, X. Xu, P. Zhang, H. Li, and Y. Wang; A practical and benign synthesis of amines through Pd@mpg-C3 N4 catalyzed reduction of nitriles; Catal. Commun. 28, 9 (2012). L. Ge, C. Han, X. Xiao, L. Guo, and Y. Li; Enhanced visible light photocatalytic hydrogen evolution of sulfur-doped polymeric g-C3 N4 photocatalysts; Mater. Res. Bull. 48, 3919 (2013). L. Xu, J. Xia, H. Xu, S. Yin, K. Wang, L. Huang, L. Wang, and H. Li; Reactable ionic liquid assisted solvothermal synthesis of graphite-like C3 N4 hybridized -Fe2 O3 hollow microspheres with enhanced supercapacitive performance; J. Power Sources 245, 866 (2014). T. Lin, L. Zhong, J. Wang, L. Guo, H. Wu, Q. Guo, F. Fu, and G. Chen; Graphite-like carbon nitrides as peroxidase mimetics and their applications to glucose detection; Biosens. Bioelectron. 59, 89 (2014). F. He, G. Chen, Y. Yu, S. Hao, Y. Zhou, and Y. Zheng; Facile approach to synthesize g-PAN/g-C3 N4 composites with enhanced photocatalytic H2 evolution activity; ACS Appl. Mater. Interfaces 6, 7171 (2014). Z. Jin, N. Murakami, T. Tsubota, and T. Ohno; Complete oxidation of acetaldehyde over a composite photocatalyst of graphitic carbon nitride and tungsten(VI) oxide under visible-light irradiation; Appl. Catal. B: Environ. 150–151, 479 (2014). S.-W. Cao, X.-F. Liu, Y.-P. Yuan, Z.-Y. Zhang, Y.-S. Liao, J. Fang, S. C. Joachim Loo, T. C. Sum, and C. Xue; Solar-to-fuels conversion over In2 O3 /g-C3 N4 hybrid photocatalysts; Appl. Catal. B: Environ. 147, 940 (2014). S. Shi, M. A. Gondal, A. A. Al-Saadi, R. Fajgar, J. Kupcik, X. Chang, K. Shen, Q. Xu, and Z. S. Seddigi; Facile preparation of g-C3 N4 modified BiOCl hybrid photocatalyst and vital role of frontier orbital energy levels of model compounds in photoactivity enhancement; J. Colloid Interf. Sci. 416, 212 (2014). L. Ge, C. Han, X. Xiao, and L. Guo; Synthesis and characterization of composite visible light active photocatalysts MoS2 -g-C3 N4 with enhanced hydrogen evolution activity; Int. J. Hydrogen Energy 38, 6960 (2013). X. C. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K. Domen, and M. Antonietti; A metal-free polymeric photocatalyst for hydrogen production from water under visible light; Nat. Mater. 8, 76 (2009). W. Liu, M. Wang, C. Xu, and S. Chen; Facile synthesis of g-C3 N4 /ZnO composite with enhanced visible light photooxidation and photoreduction properties; Chem. Eng. J. 209, 386 (2012). L. Gu, J. Wang, Z. Zou, and X. Han; Graphitic-C3 N4 -hybridized TiO2 nanosheets with reactive {001} facets to enhance the UVand visible-light photocatalytic activity; J. Hazard. Mater. 268, 216 (2014). F. Jiang, T. Yan, H. Chen, A. Sun, C. Xu, and X. Wang; A g-C3 N4 – CdS composite catalyst with high visible-light-driven catalytic activity and photostability for methylene blue degradation; Appl. Surf. Sci. 295, 164 (2014). Y. Ji, J. Cao, L. Jiang, Y. Zhang, and Z. Yi; g-C3 N4 /BiVO4 composites with enhanced and stable visible light photocatalytic activity; J. Alloys Compd. 590, 9 (2014). Y. Sun, W. Zhang, T. Xiong, Z. Zhao, F. Dong, R. Wang, and W.-K. Ho; Growth of BiOBr nanosheets on g-C3 N4 nanosheets to construct two-dimensional nanojunctions with enhanced photoreactivity for NO removal; J. Colloid Interf. Sci. 418, 317 (2014). D. Jiang, J. Zhu, M. Chen, and J. Xie; Highly efficient heterojunction photocatalyst based on nanoporous g-C3 N4 sheets modified by Ag3 PO4 nanoparticles: Synthesis and enhanced photocatalytic activity; J. Colloid Interf. Sci. 417, 115 (2014).

317

Article

1. A. Kudo and Y. Miseki; Heterogeneous photocatalyst materials for water splitting; Chem. Soc. Rev. 28, 253 (2009). 2. B. Ohtani; Photocatalysis A to Z-What we know and what we do not know in a scientific sense; J. Photochem. Photobiol. C: Photochem. Rev. 11, 157 (2010). 3. Y. Lan, Y. Lu, and Z. Ren; Mini review on photocaatlysis of titanium dioxide nanoparticles and their solar applications; Nano Energy 2, 1031 (2013). 4. K. Li, X. An, K. H. Park, M. Khraisheh, and J. Tang; A critical review of CO2 photoconversion: Catalysts and reactors; Catal. Today 224, 3 (2014). 5. L. Gomathi Devi and R. Kavitha; A review on non metal ion doped titania for the photocatalytic degradation of organic pollutants under UV/solar light: Role of photogenerated charge carrier dynamics in enhancing the activity; Appl. Catal. B: Environ. 140–141, 559 (2013). 6. S.-M. Lam, J.-C. Sin, A.Z. Abdullah, and A. R. Mohamed; Degradation of wastewaters containing organic dyes photocatalysed by zinc oxide: A review; Desalin. Water Treatment 41, 131 (2012). 7. W. B. Hou, and S. B. Cronin; A review of surface plasmon resonance-enhanced photocatalysis; Adv. Funct. Mater. 23, 1612 (2013). 8. Y. Wang, Q. Wang, X. Zhan, F. Wang, M. Safdar, and J. He; Visiblelight-driven type II heterostructures and their enhanced photocatalysis properties: A review; Nanoscale 5, 8326 (2013). 9. T. Li, Y. He, H. Lin, J. Cai, L. Dong, X. Wang, M. Luo, L. Zhao, X. Yi, and W. Weng; Synthesis, characterization and photocatalytic activity of visible-light plasmonic photocatalyst AgBr– SmVO4 ; Appl. Catal. B: Environ. 138–139, 95 (2013). 10. M. Pirhashemi and A. Habibi-Yangjeh; Simple and large scale onepot method for preparation of AgBr–ZnO nanocomposites as highly efficient visible light photocatalyst; Appl. Surf. Sci. 283, 1080 (2013). 11. F.-J. Zhang, F.-Z. Xie, J. Liu, W. Zhao, and K. Zhang; Rapid sonochemical synthesis of irregular nanolaminar-like Bi2 WO6 as efficient visible-light-active photocatalysts; Ultrason. Sonochem. 20, 209 (2013). 12. S.-M. Lam, J.-C. Sin, I. Satoshi, A. Z. Abdullaha, and A. R. Mohamed; Enhanced sunlight photocatalytic performance over

13.

Materials Express

Materials Express


Article

30. L. Ge, C. Han, and J. Liu; In situ synthesis and enhanced visible light photocatalytic activities of novel PANI-g-C3 N4 composite photocatalysts; J. Mater. Chem. 22, 11843 (2012). 31. C. Han, L. Ge, C. Chen, Y. Li, X. Xiao, Y. Zhang, and L. Guo; Novel visible light induced Co3 O4 -g-C3 N4 heterojunction photocatalysts for efficient degradation of methyl orange; Appl. Catal. B: Environ. 147, 546 (2014). 32. W. Zhang, Y. Sun, F. Dong, W. Zhang, S. Duan, and Q. Zhang; Facile synthesis of organic–inorganic layered nanojunctions of gC3 N4 /(BiO)2 CO3 as efficient visible light photocatalyst; Dalton Trans. 43, 12026 (2014). 33. Y. Zang, L. Li, X. Li, R. Lin, and G. Li; Synergistic collaboration of g-C3 N4 /SnO2 composites for enhanced visible-light photocatalytic activity; Chem. Eng. J. 246, 277 (2014). 34. R. Yin, Q. Luo, D. Wang, H. Sun, Y. Li, X. Li, and J. An; SnO2 /gC3 N4 photocatalyst with enhanced visible-light photocatalytic activity; J. Mater. Sci. 49, 6067 (2014). 35. L.-Y. Chen and W.-D. Zhang; A simple strategy for the preparation of g-C3 N4 /SnO2 nanocomposite photocatalysts; Sci. Adv. Mater. 6, 1091 (2014). 36. V. Taghvaei, A. Habibi-Yangjeh, and M. Behboudnia; Preparation and characterization of SnO2 nanoparticles in aqueous solution of [EMIM][EtSO4 ] as a low cost ionic liquid using ultrasonic irradiation; Powder Technol. 195, 63 (2009). 37. Y. Shi, S. Jiang, K. Zhou, B. Wang, B. Wang, Z. Gui, Y. Hu, and R. K. K. Yuen; Facile preparation of ZnS/g-C3 N4 nanohybrids for enhanced optical properties; RSC Adv. 4, 2609 (2014).

38. X. Li and J. Ye; Photocatalytic degradation of rhodamine B over Pb3 Nb4 O3 /fumed SiO2 composite under visible light irradiation; J. Phys. Chem. C, 111, 13109 (2007). 39. A. Martinez-dela Cruz and U. M. Garcia Perez; Photocatalytic properties of BiVO4 prepared by the co-precipitation method: Degradation of rhodamine B and possible reaction mechanisms under visible irradiation; Mater. Res. Bull. 45, 135 (2010). 40. M. Zhou, X. Gao, Y. Hu, J. Chen, and X. Hu; Uniform hamburgerlike mesoporous carbon-incorporated ZnO nanoarchitectures: Onepot solvothermal synthesis, high adsorption and visible-light photocatalytic decolorization of dyes; Appl. Catal. B: Environ. 138–139, 1 (2013). 41. M. Pirhashemi and A. Habibi-Yangjeh; Preparation of AgCl–ZnO nanocomposites as highly efficient visible-light photocatalysts in water by one-pot refluxing method; J. Alloys Compd. 601, 1 (2014). 42. S. Y. Kim, T. H. Lim, T. S. Chang, and C. H. Shin; Photocatalysis of methylene blue on titanium dioxide nanoparticles synthesized by modified sol-hydrothermal process of TiCl4 ; Catal. Lett. 117, 112 (2007). 43. L. S. Zhang, K. H. Wong, H. Y. Yip, C. Hu, J. C. Yu, C. Y. Chan, and P. K. Wong; Effective photocatalytic disinfection of E. coli K-12 using AgBr–Ag–Bi2 WO6 nanojunction system irradiated by visible light: the role of diffusing hydroxyl radicals; Environ. Sci. Technol. 44, 1392 (2010). 44. G. T. Li, K. H. Wong, X. W. Zhang, C. Hu, J. C. Yu, R. C. Y. Chan, and P. K. Wong; Degradation of acid orange 7 using magnetic AgBr under visible light: the roles of oxidizing species; Chemosphere 76, 1185 (2009).

Received: 5 November 2014. Revised/Accepted: 17 March 2015.

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