Calcination of reduced graphene oxide decorated TiO2 composites for recovery and reuse in photocatalytic applications

Reduced graphene oxide (RGO)-TiO2 composites were synthesized hydrothermally. Then the samples were calcined at 450 °C for 30 min under air atmosphere to recovery and improve their photocatalytic efficiency. Those composites were characterized by XRD, TEM, SEM, TGA, BET, XPS, Raman, FTIR and DRS. Photocatalytic activities of RGO-TiO2 composites and calcinated samples were measured by decomposition of methyl orange (MO) under UV, visible and solar light irradiation. Results showed that some RGO was burn out, and others turned into GO after calcination. Both RGO-TiO2 composites and calcined samples exhibited red shift of the absorption edge. TiO2 particles were well dispersed on the surface of GO sheets, and calcinated samples with smaller TiO2 particles were observed. Graphene amount showed an apparent influence on photocatalytic activities of both RGO-TiO2 composites and calcined samples. At 5 wt% graphene concentration, both samples exhibited the best photocatalytic activities under UV light irradiation, while the concentration was 10 wt% under visible light irradiation. Moreover, calcined samples showed better photocatalytic activities than that of RGO-TiO2 composites. The enhanced photocatalytic activities were because of the oxidation of residual organics in the RGO-TiO2 composites, and better crystalized TiO2 particles with smaller diameter after calcination. Calcination is a valid method to recover the photocatalytic activities of RGO-TiO2 composites.