Optimization, Kinetics, and Thermodynamics Study on the Degradation of RhB by ZnO Modified with Nitrogen and Sulfur Co-Doped Carbon Quantum Dots

Carbon quantum dots (CQDs) have been increasingly applied in the field of photocatalysis due to their unique optical and electrochemical properties, which can significantly enhance the catalytic property of photocatalyst. In this paper, thermodynamic and kinetic analysis of the experimental process were carried out to investigate the mechanism of CQDs enhancing the photocatalytic performance of ZnO based on the adsorption and degradation test data. Firstly, the nitrogen and sulfur co-doped carbon quantum dots (NSCQDs) were synthesized using a one-step hydrothermal method, while zinc oxide (ZnO) nanocrystals were prepared via the direct precipitation method. The composite material of NSCQDs/ZnO was synthesized through a room temperature impregnation method. The next, the catalysts were characterized by a series of scientific methods. Besides, it creatively used the relevant knowledge of thermodynamics and kinetics in this paper to study the adsorption and photocatalytic processes of ZnO and NSCQDs/ZnO. The photocatalytic results showed that the degradation rate of RhB by NSCQDs/ZnO was up to 91.5% under optimal catalyst conditions at room temperature, which was higher than that of ZnO (49%), and the degradation curves were accorded with the pseudo-first-order kinetic model, and the kinetic constant of NSCQDs/ZnO(0.02666 min-1) is 3.45 times that of ZnO (0.00772 min-1). What is more, the result of the free radical quenching experiment proved center dot O2- and OH center dot were the main active substances. Finally, the aim of this study was to synthesize an efficient and environmentally friendly catalyst and to investigate its mechanism.