Enhanced photocatalytic degradation of bisphenol A with Ag-decorated S-doped g-C3N4 under solar irradiation: Performance and mechanistic studies

Ag-decorated S-doped g-C3N4 composites with different % w/w Ag were synthesized via chemical reduction method. The Ag/S-doped g-C3N4 composites were used as photocatalysts for aqueous bisphenol A (BPA) degradation under solar irradiation. Investigation of the photocatalysts using various characterization methods including X-ray diffractometry, scanning electron microscopy and transmission electron microscopy indicated that the Ag nanoparticles (average size= 10-20 nm) were well-crystalline and uniformly distributed on the S-doped g-C3N4 (SCN) surface. The photocatalytic performance of SCN was similar to 3 times more efficient than that of the g-C3N4, while the Ag/SCN with 12% w/w Ag (Ag-SCN-12) exhibited the highest photocatalytic activity for BPA degradation followed by 8% w/w Ag/SCN, 4% w/w Ag/SCN, SCN, and Ag. The effects of pH and Ag-SCN-12 loading on photocatalytic BPA degradation were also investigated. The results showed that the Ag-SCN-12 was highly stable (<40 mu g L-1 Ag leaching) and could be reused for at least 4 cycles without significant deterioration to its catalytic activity. The incorporation of Ag into the SCN enhanced the photocatalytic activity of SCN due to the improved electron-hole pair separation and decreased electron-hole pair recombination rate as evidenced by the photoluminescence emission study. The predominant reactive oxygen species (ROS) generated by the Ag-SCN-12 photocatalytic system was O-2(center dot-) which formed secondary ROS ((OH)-O-center dot, and O-1(2)) for BPA degradation. The mechanism of ROS generation during the photocatalytic process is also proposed. Based on the BPA degradation intermediates identified using the LC/MS/MS, the BPA degradation pathways in the photocatalytic system are elucidated.