Efficient degradation of bisphenol A over facilely optimized ternary Ag/ZnO/ZnAl‒LDH composite with enhanced photocatalytic performance under visible light irradiation

For the advanced treatment of micropollutants from wastewater, this study synthesized a ternary Ag/ZnO/ZnAl‒LDH composite photocatalyst with performance optimization based on the Taguchi approach. The optimal synthesis parameters were statistically determined as the Ag doping amount of 5 wt%, Zn2+ and Al3+ with a molar ratio of 3:1, Ag/ZnO and ZnAl‒LDH with composite ratio of 3:2, and PEG-200 dosage of 25 mL. The optimally synthesized Ag/ZnO/ZnAl‒LDH achieved the efficient degradation of bisphenol A (BPA) under visible light irradiation, and the reaction rate constant was about 4.8-, 2.2- and 12.0-fold higher than that of ZnO, Ag/ZnO and ZnAl‒LDH, respectively. As proved by various characterizations, the enhanced photocatalytic performance of Ag/ZnO/ZnAl‒LDH can be attributed to the improvements of optoelectronic properties, such as the widened visible light responsivity and facilitated charge transfer, thus resulting in a significant increase of hydroxyl radicals (·OH) formation. Fluorescence measurements and radical quenching experiments indicated that ·OH mainly contribute to the degradation of BPA, and the oxidation of H2O by holes was the dominant formation pathway. According to the above results, this study summarized and proposed the enhanced photocatalytic mechanism of Ag/ZnO/ZnAl‒LDH for ·OH production and BPA removal.