Enhanced removal of Cr(Ⅵ) from wastewater by dielectric barrier discharge plasma coupled with TiO2/rGO nanocomposites: Catalytic performance and reduction mechanism

Abstract

Dielectric barrier discharge (DBD) plasma system coupled with titanium dioxide/reduced graphene oxide (TiO2/rGO) nanocomposites for enhanced hexavalent chromium (Cr(Ⅵ)) reduction has explored. TiO2/rGO nanocomposites were prepared by a modified hydrothermal method. The characterization of morphology, structure and optical properties showed that the TiO2/rGO nanocomposites could be successfully synthesized with large specific surface area and high charge carrier separation rate. The effects of the discharge voltage, initial concentration and solution pH on the reduction of Cr(Ⅵ) in the alone DBD system were experimentally analyzed. The results exhibited that the reduction efficiency of 100 mg/L Cr(Ⅵ) was 100% after 55 min discharge treatment at the discharge voltage 22 kV and at pH = 2. Moreover, the results of the DBD-TiO2/rGO system showed that the Cr(Ⅵ) reduction efficiency was greatly improved from 72% to 100% after 40 min discharge treatment with adding 0.3 g/L TiO2/rGO-5 nanocomposite, indicating the TiO2/rGO nanocomposites exhibited greatly synergistic effect with DBD plasma. To illustrate the mechanism of Cr(Ⅵ) reduction in DBD combined with TiO2/rGO nanocomposites, quenching tests were performed by adding active species scavengers and the concentrations of H2O2 and O3 were also detected. Photogenerated electrons, •O2– and photo-generated H2O2 were found to play a vital role in accelerating the reduction of Cr(Ⅵ) to Cr(III).