Enhanced photocatalytic efficacy of organic dyes using β-tin tungstate–reduced graphene oxide nanocomposites

doi:10.1016/j.matchemphys.2014.01.046

Materials Chemistry and Physics

Volume 145, Issues 1–2, 15 May 2014, Pages 108-115

https://doi.org/10.1016/j.matchemphys.2014.01.046 Get rights and content

Highlights

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Photocatalytic behavior of Leaf-like β-SnWO₄–rGO nanocomposites.
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Surfactant free microwave technique for β-SnWO₄ preparation.
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Nanocomposite was characterized by XRD, AFM, SEM, HR-TEM, UV, TGA and Raman.
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Excellent Photocatalytic activity was found in β-SnWO₄–rGO nanocomposite.
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β-SnWO₄–rGO nanocomposite is suitable for environmental eco-friendly applications.

Abstract

In this study, we report first time about the synthesis and photocatalytic behavior of β-Tin Tungstate–reduced Graphene Oxide (β-SnWO₄–rGO) nanocomposites. The β-SnWO₄–rGO was prepared by surfactant free microwave method followed by graphene oxide (GO) reduction process. The dye degradation was observed by decrease in absorption spectrum and decolorization in the presence of visible light. The degradation efficiency was found to be dependent on the amount of catalyst added in dye solution because rGO reduces the recombination of the charge carriers resulting in high mobility. The degradation efficiency of 55% and 60% were achieved by β-SnWO₄ alone, whereas in the presence of rGO, the photocatalytic degradation efficiency was found to be increased up to 90% and 91% in methylene orange (MO) and rhodamine B (RB) respectively. It reveals the excellent photocatalytic activity of the catalyst (composite) in short time. The crystalline phase of nanocomposite was studied by using X-ray diffraction technique. Further the surface morphology was analyzed by using SEM and HR-TEM. Presence of rGO was confirmed by using Raman spectroscopy. Our results show the potential future in development of futuristic rGO based nanocomposites for photocatalytic applications.

Introduction

The role of industrial waste water treatment in environmental pollution has been an important issue for the past few years [1]. Industrial waste water mostly contains organic-synthetic dyes like MO, RB etc, which are used in textile industries [2]. These organic dyes have to be removed in order to reuse the water as these are very hazardous for environment. Photocatalysis process has been used for water purification for the past few decades, since it is an eco-friendly and low expenditure process [3], [4]. Nanoparticles are being employed for photocatalysis process as they have high aspect ratio and abridged recombination of charge carriers [5].

Plenty of metal oxide semiconductor nanoparticles have been used for photocatalysis process, such as TiO₂, ZnO, CeO₂ [6], [7] etc. This is attributed to the fact that these semiconductors have narrow band gap which is equal to ultra violet or visible light. TiO₂ is a well known UV photocatalyst having a band gap of 3.2 eV [8]. Since solar light having more part of visible light, so visible light catalysis is important, the visible light catalyst was achieved by converting UV catalyst in unusual ways, for instance by doping of different ions into the semiconductors [9] and making a composite with other semiconductors or metals [10]. Tin tungstate is one of the multi metal oxide semiconductor which exists in two phases, specifically in low temperature, α-SnWO₄ and in the high temperature, β-SnWO₄ exists [11]. Both α-SnWO₄ and β-SnWO₄ has photocatalytic property in visible light due to the interfacial area between solid catalysis and liquid water dye [12]. Metal nanocomposites and ion doped metal nanoparticles have been synthesized for photocatalytic applications like Cu doped ZnO, Zn²⁺ ion doped SnWO₄ nanoparticles [13].

Graphene is a two dimensional nanomaterial, that has been synthesized from graphite by various methods [14], [15]. Among these methods, chemical synthesis is the potential method for making nanocomposites. Even after reduction of GO, a few of the functional groups are still present between the planes. These functional groups attach themselves with metal and metal oxide nanoparticles. The rGO possesses the ability to accept the electrons and to prevent recombination. Also electron transfer occurs in rGO [16]. Most of the rGO atoms attached with aromatic functional groups, which form conjugates with the dye. Reduced graphene oxide owns pristine mechanical performance to stabilize the catalysis and offers the two-dimensional plane to deposit catalyst [17], [18] resulting rGO be a good supporting site for photocatalysis process.

The rGO based nanocomposites have gained much attention due to their wide range of applications. Some rGO and GO based nanocomposites have been reported to have high photocatalytic activity compared with pure metal oxide such as TiO₂–GO, graphene–ZnS, CdS–TiO₂–graphene, CdS–graphene, graphene–ZnO and WO₃–rGO [19], [20], [21], [22], [23], [24], [25], [26]. The rGO–TiO₂ composite has very sensitive UV light photocatalytic activity and this is attributed to rGO which plays a major role. When compared to UV photocatalyst (TiO₂), visible photocatalyst (β-SnWO₄) has small band gap, hence the photogenerated electron hole recombination process is very fast and thus it results in drawback of visible light photocatalysis. We believe rGO act as back up material and the electron can move easily through the rGO sheet as well as has large surface area which addresses the above drawback. Unfortunately the visible light photocatalysis based rGO composites are of very few attentions; particularly no work has been reported so far on β-SnWO₄–rGO nanocomposite. We refined our work to synthesis and photocatalytic behavioral studies of nano-sized β-SnWO₄–rGO nanocomposite against two different organic dyes and also discussed about the role of rGO.

Section snippets

Materials and methods

Expandable graphite powder of size lesser than 25 μm, Tin chloride, Sodium tungstate, MO and RB dye were procured from Rankem chemicals (India). All reactions were carried out by using double distilled deionized (DD) water. Structural characterization of the prepared photocatalyst was performed with powder X-ray Diffractometer system (X-6000 Shimadzu). The sample morphology was studied using Scanning Electron Microscope (JEOL JSE-6390). The UV–Vis spectroscopy measurements were done using

Physical characterizations of β-SnWO₄–rGO nanocomposites

Fig. 1 illustrates the XRD pattern of graphite, GO and β-SnWO₄–rGO nanocomposite respectively. This was prepared by surfactant-free microwave reduction approach. Fig. 1(a) ensembles the GO which is having lattice constant of 7.3 Å calculated from XRD pattern [28]. Furthermore, GO shows the most prominent peak at 2θ = 10.54° along the (002) reflection, which is much higher than that of the lattice constant of graphite, its XRD pattern shows in bottom of Fig. 1(a). Fig. 1(a) shows the XRD pattern

Conclusion

In conclusion, a simple surfactant-free synthesis procedure was developed and the photocatalytic property of β-SnWO₄–rGO nanocomposite was studied. β-SnWO₄–GO nanocomposite was further reduced by using microwave irradiation method. The HR-TEM image confirmed that the β-SnWO₄ nanoparticles were grown on single layer rGO sheets. Based on the optical studies, it was found that the band gap of β-SnWO₄–rGO is 2.3 eV. The photocatalytic studies were done through the degradation of MO and RB dye under

Acknowledgments

The author (T.S.) is so thankful to the management of Karunya University (KU) for providing Silver Jubilee Fellowship (SJF) scholarship to carry out the research work. Also, all the authors extend their sincere thanks to Mr. A. Raja and Mr. M.B.S. Pravin at Center for Research in Nanotechnology (CRN) at Karunya University for the timely help in doing sample characterization. This research was also supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)

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Enhanced photocatalytic efficacy of organic dyes using β-tin tungstate–reduced graphene oxide nanocomposites

Highlights

Abstract

Introduction

Section snippets

Materials and methods

Physical characterizations of β-SnWO4–rGO nanocomposites

Conclusion

Acknowledgments

Powder Technol.

Sol. Energy

Mater. Chem. Phys.

Electrochem. Commun.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Mater. Chem. Phys.

Solid State Commun.

J. Catal.

J. Colloid Interface Sci.

J. Sol. Energy

Mater. Chem. Phys.

Chem. Rev.

Sci. Adv. Mater.

Appl. Phys. Lett.

Sci. Adv. Mater.

Adv. Funct. Mater.

J. Phys. Chem. C.

Physical characterizations of β-SnWO₄–rGO nanocomposites