Preparation of graphene–carbon nanotube–TiO2 composites with enhanced photocatalytic activity for the removal of dye and Cr (VI)

Abstract

Graphene–carbon nanotubes (CNTs)–TiO2 composites were successfully synthesized by a one-pot solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and diffuse reflectance UV–vis spectra. The photocatalytic activity of as-prepared composite photocatalysts was tested by degradation of dye methylene blue (MB) and photoreduction of Cr(VI) in aqueous solution under UV light irradiation. The experiment results showed that the composites exhibited enhanced photocatalytic performance compared to binary one (i.e. graphene–TiO2) and pristine TiO2. The effect of CNTs content on the photocatalytic activity was also studied. It showed that the photocatalytic performance of the graphene–CNTs–TiO2 hybrids was dependent on the proportion of CNTs in the composite. The mass ratio of CNTs:TiO2=5% was proved to be the optimal ratio. The apparent rate constants k for MB degradation and Cr(VI) reduction were 2.2 and 1.9 times as graphene–TiO2 composite, respectively. The enhanced activity can be ascribed to the addition of CNTs, which can be severed as charge transmitting paths thus decrease the recombination rate of photoinduced electron–hole pairs. This mechanism for the enhanced photoactivity was further confirmed by measuring the hydroxyl radical and transient photocurrent.