Solar photocatalytic disinfection of water using titanium dioxide graphene composites

Interest has grown in the modification of titanium dioxide with graphene to improve the photocatalyticbehaviour. In this work, titanium dioxide–reduced graphene oxide (TiO2–RGO) composites were synthesisedby the photocatalytic reduction of exfoliated graphene oxide (GO) by TiO2 (Evonik P25) under UVirradiation in the presence of methanol as a hole acceptor. The composite materials were characterisedusing high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy(XPS) and Raman spectroscopy. Raman and XPS analysis provided evidence that GO was converted toRGO by photocatalytic reduction. The TiO2–RGO composites were compared to TiO2 in suspension reactorsfor the disinfection of water contaminated with Escherichia coli and Fusarium solani spores under realsunlight. Very rapid water disinfection was observed with both E. coli and F. solani spores. An enhancementin the rate of inactivation of E. coli was observed with the TiO2–RGO composite compared to P25alone. The rate of inactivation of F. solani spores was similar for both the TiO2–RGO and P25. When themajor part of the solar UVA was cut-off (k > 380 nm) using a methacrylate screen, there was a markedincrease in the time required for inactivation of E. coli with P25 but no change in the inactivation ratefor the TiO2–RGO. There is evidence of singlet oxygen production with visible light excitation of theTiO2–RGO composites which would lead to E. coli inactivation.