This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2017 New J. Chem. Cite this: DOI: 10.1039/c7nj00495h A quaternary TiO 2 /ZnO/RGO/Ag nanocomposite with enhanced visible light photocatalytic performance† Divya K. S., a Marilyn Mary Xavier, b Vandana P. V., a Reethu V. N. a and Suresh Mathew * ab ‘‘Together we can make the difference’’. A quaternary TiO 2 /ZnO/RGO/Ag nanocomposite exhibits enhanced photoactivity compared to TiO 2 /ZnO/RGO and TiO 2 /ZnO for the degradation of rhodamine B under visible light. The quaternary composite was synthesized via facile microwave irradiation of dispersed TiO 2 /ZnO and RGO/Ag nanocomposites. X-ray diffraction analysis and high-resolution transmission electron microscopy revealed the presence of TiO 2 , ZnO, RGO and Ag in the composite. Photoelectrochemical measurements and time correlated single photon counting (TCSPC) analysis confirmed that the presence of RGO sheets and Ag enhanced the photocatalytic properties of the nanocomposite. The enhanced charge separation and the low recombination rate of photogenerated charge carriers in the composite with the assistance of excellent co-catalysts, RGO and Ag, have also been investigated. Introduction Photocatalysis, a ‘‘green’’ technique, is of significant practical interest for a variety of applications, especially for the degrada- tion of pollutants by utilizing an abundant and clean energy source. Heterogeneous photocatalysis assisted by various semi- conductor metal oxides has attracted immense attention in recent years due to the creation of electrons and holes upon irradiation, which can then be transferred to other molecules at the photocatalyst surface. 1–3 Among various metal oxide semi- conductors, TiO 2 4 and ZnO 5–13 have been the most extensively studied due to their unique photocatalytic efficiency, low cost, nontoxicity, and high stability. However, the fast electron–hole pair recombination of TiO 2 and ZnO significantly limits the photocatalytic efficiency. 14 Coupled ZnO/TiO 2 nanocomposites display a largely improved photocatalytic activity compared to the single elements ZnO and TiO 2 , for the degradation of organic pollutants such as phenol, chlorophenol, 2-chlorophenol etc. 15–19 This enhanced photocata- lytic behaviour is attributed to the effective separation of photo- generated charge carriers. Wang et al. studied the photocatalytic performance of TiO 2 /ZnO nanohybrid structures by site-specific deposition of TiO 2 on ZnO nanorods. One of the primary draw- backs of these systems is the poor quantum efficiency under visible light. The photocatalytic efficiency found for these photo- catalytic systems is due to the fast charge recombination of the photogenerated electron–hole pairs. 20–22 The conduction of photogenerated electrons in the semiconductor materials is mainly due to the diffusion among the nanoparticles. The efficiency of electron diffusion decreases in semiconductors due to some surface defects, which results in an increased recombination of photogenerated electrons and holes, thereby decreasing the photocatalytic efficiency. 23 The improved photocatalytic efficiency of a semiconductor hybridized with carbonaceous materials has been a centre of attraction in photocatalytic research and has been recently attracting the scientific community with regard to the bene- ficial role of carbonaceous materials hybridized with semi- conductors to improve their photocatalytic efficiency. 5,24–26 Among various carbonaceous materials, graphene (GR) is an exotic material due to its unique two-dimensional p conjugated structure, high electron conductivity and mobility, high specific surface area and high Young’s modulus. 27–31 Graphene-based semiconductor nanocomposites have been extensively applied to various applications such as degradation of organic pollutants, photocatalytic hydrogen generation, solar cells and selective organic transformations. 32–36 The photocatalytic performance of RGO/TiO 2 /ZnO nanocomposites fabricated via hydrothermal reaction revealed that the best photocatalytic performance was shown by the composite with the higher amount of RGO. 37 a School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, Kerala, India. E-mail: sureshmathewmgu@gmail.com b Advanced Molecular Materials Research Centre, Mahatma Gandhi University, Kottayam 686 560, Kerala, India † Electronic supplementary information (ESI) available. See DOI: 10.1039/c7nj00495h Received 11th February 2017, Accepted 4th June 2017 DOI: 10.1039/c7nj00495h rsc.li/njc NJC PAPER Published on 08 June 2017. Downloaded by Mahatma Gandhi University on 17/06/2017 06:12:02. View Article Online View Journal