Optimization of the dosage of ZnO photocatalyst for the degradation of sunlight driven multi dose organic dye brilliant green

Abstract

In this study, we prepared ZnO nanocrystals using a chemical precipitation approach with different precursor concentrations for optimization. The structural, optical, and morphological properties of the synthesized nanocrystals were analyzed. Sunlight-driven photocatalysis was investigated for its ability to degrade a low concentration (70 ppm) of brilliant green (BG) dye using the optimized ZnO at different dosages (0.05, 0.1, and 0.15 g). Among the different dosages of ZnO, it was noted that at a low catalyst concentration of 0.05 g, the degradation efficiency was only 58.47 % even after 120 min of light exposure. When the concentration increased to 0.1 g, the rate of degradation reached 95.33 % within 90 min. At a higher dosage of 0.15 g, only 86.26 % degradation was recorded within 90 min, indicating that the optimal catalyst dosage was 0.1 g. To investigate how the dye dosage affected the degradation efficiency of the catalyst, experiments were performed using higher dye concentrations of 100 and 120 ppm with 0.1 g of catalyst. As the dye concentration was increased, the degradation rate decreased. Tests were conducted using different scavengers, including EDTA (a hole scavenger), benzoquinone (a superoxide radical scavenger), and isopropyl alcohol (a hydroxyl radical scavenger), to determine which free radical was mainly breaking down BG. In the presence of EDTA, the degradation ability of the catalyst decreased to 35 %. When the superoxide radical scavenger benzoquinone was used, the degradation efficiency decreased to approximately 22 %. On the other hand, the hydroxyl radical scavenger IPA reduced the degradation efficiency to 13 %. Based on the above discussion, the synergistic effect of holes and superoxide radicals is mainly responsible for the degradation of brilliant green. To test the practical use of the ZnO catalyst, we conducted an experiment to assess its reusability. Even after the third cycle, the ZnO exhibits 94 % degradation, confirming its reusability.