Facile synthesis of graphene quantum dots/ZSM-5 type metalosilicate composites and evaluating their performance in photocatalytic degradation of methylene blue and electrochemical water splitting

Abstract

Graphene quantum dots (GQDs)/ZSM-5 type cobaltosilicate and GQDs/ZSM-5 type chromosilicate composites were prepared by two methods; direct and solid state dispersion (SSD) method. The composites were characterized using XRD, FT-IR, UV–vis absorption, and SEM techniques. The photocatalytic activities of composites were evaluated by degradation of methylene blue (MB) under both UV and vis light irradiation. The composites prepared by direct method showed better photocatalytic activity and the GQDs/chromosilicate composite had a superior performance. This composite could remove about 96 % and 87 % of MB at first 30 min under UV and vis light, respectively. The results of photocatalytic degradation kinetic studies revealed that the composites follow the pseudo-second-order kinetic model (R2 = 0.99) with rate constants ranging from 0.295 to 0.581 g mg−1 min−1 for different composites prepared by direct method. The GQDs/metalosilicate composites were also examined for the electrochemical water splitting. The GQDs/cobaltosilicate composites required lower overpotentials for HER and OER in comparison to the pure GDQs and cobaltosilicate. Moreover, the charge transfer resistance and Warburg impedance was lower than the corresponding values obtained for the pure cobaltosilicate and GQDs. These new GQDs-based composites are expected to open new windows in materials science and electrocatalytic-related processes.