Coal-based graphene as a promoter of TiO2 catalytic activity for the photocatalytic degradation of organic dyes

Abstract

Graphene oxide (GO) obtained from coal-based graphite by the Hummers method was hydrothermally treated to obtain reduced GO (rGO). TiO2 was mixed with aqueous suspensions of GO and rGO and dried at 70 °C to obtain GO-TiO2 and rGO-TiO2 with 95 wt% TiO2. TiO2 was also combined with a GO suspension by hydrothermal treatment to obtain rGO-hTiO2 with 95 wt% TiO2. The three hybrids were used as catalysts for the photocatalytic degradation of rhodamine B (Rh B) and methyl orange (MO). Of the three materials, rGO-hTiO2 had the highest catalytic activity for the degradation of Rh B and MO under visible light irradiation. The reasons for having the best catalytic activity are that the incorporation of rGO into TiO2 helps increase its adsorption capacities for Rh B and MO as evidenced by adsorption in dark, and a narrowing of the TiO2 band gap as revealed by diffuse UV reflectance spectroscopy. This reduces the rate of recombination of electron-hole pairs by there being intimate contact between the TiO2 particles and rGO, forming Ti-O-C bonds as confirmed by XPS, with the TiO2 particles being uniformly decorated on the rGO sheets.