Design of a highly efficient ternary AgI/rGO/BiVO4 nanocomposite and its direct solar light induced photocatalytic activity

A solar light responsive Z-scheme AgI/rGO/BiVO4 ternary nanocomposite was designed by ultrasonic assisted hydrothermal and wet impregnation methods. XPS spectra showed a gradual positive peak shift in the binding energy of Bi, after rGO and AgI incorporation, indicating chemical bonding and electrons migration pathway from BiVO4 to AgI through the rGO layer. Furthermore, Raman analysis revealed a red shift in the characteristic Raman band of BiVO4, suggesting local structural changes upon rGO and AgI loading. In addition, the band gap of the nanocomposite for bare BiVO4 was found to be shifted to 2.24 eV from 2.36 eV, therefore, increasing the overall visible light absorption. Photocurrent measurements indicated the presence of significantly high surface charge trap states in bare BiVO4. However, the detrapping process was not observed suggesting fast recombination of trapped charges on the surface of bare BiVO4. After AgI and rGO loading, the surface charge trap states of BiVO4 disappeared, which reveals the quick shuttling of charge carriers via close interface bonding in the nanocomposites. The photocatalytic performance of the nanocomposites was tested with Tetracycline (TC), a common antibiotic and RhB dye, as model pollutants. The AgI/rGO/BiVO4 nanocomposite displayed nearly 84% and 99% photocatalytic degradation for TC and RhB, respectively under direct solar light irradiation in 25 min. The Total Organic Carbon (TOC) analysis revealed more than 35% and 25% mineralization efficiency for both TC and RhB under 2 h of reaction. The AgI/rGO/BiVO4 nanocomposite exhibited not only enhanced photocatalytic activity but also high stability because of the strong chemical bonding among AgI, BiVO4, and rGO, which largely circumvented the electron-hole recombination. Based on XPS, Mott-Schottky, and reactive radical trapping experiments, a Z-scheme charge carrier separation and migration pathway in the nanocomposite is proposed.