RESEARCH PAPER One-step solvothermal synthesis of TiO 2 -reduced graphene oxide nanocomposites with enhanced visible light photoreduction of Cr(VI) Aasiya Shaikh & Shailendra Prasad Mishra & Priyabrata Mohapatra & Smrutiranjan Parida Received: 5 December 2016 /Accepted: 16 May 2017 # Springer Science+Business Media Dordrecht 2017 Abstract Hexavalent chromium, Cr(VI), is a mutagenic and carcinogenic heavy metal environmental pollutant. Photoreduction is one of the remediation methods of the hexavalent chromium Cr(VI), which necessitates design of an efficient catalyst for visible light performance. Here, we report a one-step solvothermal synthesis of TiO 2 - reduced graphene oxide (TiO 2 -xRGO) composite cata- lysts using a mild reducing agent, dimethylformamide (DMF). Nanoscale TiO 2 particles in the size range of 4– 9 nm were formed on the reduced graphene sheets. The formation of the composite catalysts was accompanied by the appearance of a large fluorescence quenching, which indicates an efficient separation of photogenerated elec- trons and holes. The composites displayed excellent pho- toreduction of Cr(VI) in the visible light, which was found to be a function of the weight percentage of RGO in the composite. At the optimum composition of TiO 2 - xRGO, a maximum removal rate of 96% was recorded, which was higher than that of the pristine TiO 2 , which showed no appreciable catalytic activity under the same condition. The performance degraded with increasing RGO content in the composite, which can be attributed to the higher electron-hole recombination on the RGO surface. The Cr(VI) photoreduction also exhibited a pH dependence. The highest removal rate was observed in the acidic medium. Keywords TiO 2 -RGO composites . RGO . TiO 2 nanoparticle . Hexavalent chromium . Solvothermal method . Environmental remediation Introduction The hexavalent chromium Cr(VI) can easily contaminate different sources of water because it is highly soluble and adsorbs easily on various surfaces. Because of its carci- nogenic and mutagenic properties (Wang et al. 2015a), Cr(VI) poses serious health issues (Wang et al. 2015b). On the other hand, trivalent chromium Cr(III) is a non- toxic oxidation state of the heavy metal, which is less mobile and can be easily separated by precipitation (Rauf et al. 2015). Therefore, one of the methods of remediation of Cr(VI) is to reduce Cr(VI) to Cr(III). The natural process of reduction of Cr(VI) is extremely slow, which requires special environmental conditions not easily real- ized under the ambient condition (Sadik et al. 2014). The other method of remediation is the chemical reduction of Cr(VI). However, chemicals used in the chemical reduc- tion process are harsh and cause secondary pollution (Khalil et al. 1998). Therefore, efficient remediation methods for Cr(VI) need to be explored. There has been significant research on the remedia- tion of Cr(VI) by photoreduction process. Various tran- sition metal oxide semiconductor photocatalysts such as J Nanopart Res (2017) 19:206 DOI 10.1007/s11051-017-3894-7 A. Shaikh : S. Parida (*) Department of Metallurgical Engineering and Materials Science, I.I.T. Bombay, Mumbai 400076, India e-mail: paridasm@iitb.ac.in S. P. Mishra : P. Mohapatra (*) Department of Chemistry, C.V. Raman College of Engineering, Bhubaneswar 752054, India e-mail: priyabratm@gmail.com