Enhancement of visible and UV light photocatalytic activity of rGO-TiO2 nanocomposites: The effect of TiO2/Graphene oxide weight ratio

In this study, rGO - TiO2 nanocomposites were prepared by means of a simple hydrothermal approach using TiO2 powder and GO nanosheets as starting materials. The TiO2/GO weight ratio varied from 0.25 to 2 wt%. The prepared samples were characterized using AFM, SEM and TEM microscopy as well as XRD, EDX, Raman, FTIR and UV-Vis spectroscopies. BET and BJH measurements were also performed to obtain the specific surface area and pore diameter size of the synthesized samples. It was found that the samples with TiO2/GO weight ratio below one have high effective surface area about 124 g/m(2) and pore size of 6 nm. Photocatalyst evaluation revealed that only 0.06 mg/ml of prepared composite degraded 90% of 20 ppm Methylene blue (MB) in 15 min under 50 mW/cm(2) UV light intensity. The linear kinetic rate constant (k) of the samples promoted from 22 x 10(-3) min(-1) for TiO2 under UV exposure up to 153 x 10(-3) min(-1) and 65 x 10(-3) min(-1) for composites under UV and visible irradiation, respectively. More detailed analyses showed that the photocatalytic activity of samples obtained figure of merit below unity. To the best of our knowledge this seems to be an impressive result. Impedance spectroscopy analysis revealed that the enhancement of charge transfer in composites as well as high effective surface area and their mesoporous structure are mainly responsible for the significant enhancement of MB photodegradation. The reactive species trapping experiments were performed by a series of radical scavengers. On the basis of the experimental results, the electrons and superoxide ions species play the main role in degradation of MB.