Synthesis and characterization of ZnO decorated reduced graphene oxide (ZnO-rGO) and evaluation of its photocatalytic activity toward photodegradation of methylene blue.

Photocatalytic treatment is one of the techniques used for the treatment of dyes-contaminated wastewater. It is important to develop an effective visible-light-driven catalyst for the treatment of dyes-contaminated wastewater. This study reports the synthesis of ZnO-reduced graphene oxide catalyst for the degradation of methylene blue. Graphene oxide was prepared by Hammer and Offeman process, while ZnO-rGO (1:1) was prepared by the chemical reduction method. The prepared ZnO-rGO composite was characterized by XRD, TEM, SEM, UV-Vis, DRS, N2 adsorption-desorption, FTIR, and XPS analyses. The photocatalytic activity was evaluated by photodegradation of methylene blue solution under irradiation. It was found that ZnO-rGO is capable of removing the dye from water and achieved the highest dye degradation efficiency of ~99% within 60 min. Furthermore, the ZnO-rGO was recycled in degradation experiments without any loss in its catalytic performance. The reaction kinetics was described in terms of the Langmuir-Hinshelwood mechanism, one of the kinetics mechanisms of surface catalyzed reaction. 36.2 and 13.1 kJ/mol were calculated as the apparent and true activation energy for photodegradation of methylene blue respectively.