A mechanistic study of the photocatalytic activity of AgI–WO3 in an experimentally designed approach toward methylene blue photodegradation

Abstract

The visible light–active AgI/WO₃ binary photocatalyst has been characterized using XRD, FTIR spectroscopy, SEM-EDX, cyclic voltammetry (CV), photoluminescence (PL), and UV–vis DRS techniques. An average crystallite size of 37.7 nm was obtained for AgI/WO₃, including the hexagonal wurtzite β-AgI and monoclinic WO₃ crystallites. Band gap energies of 2.27, 2.87, and 2.52 eV were obtained for AgI, WO₃, and AgI/WO₃ samples, and the potential positions of the valence and conduction bands were also estimated. The superior photodegradation activity of AgI/WO₃ concerning the individual system was confirmed, with a methylene blue (MB) degradation efficiency of 95% in a 5 ppm MB solution. The optimal RSM run with the best response occurred with pH 6.63, catalyst dosage of 1.12 g L⁻¹, irradiation time of 47 min, and C_MB of 3.26 ppm. Further, the RSM central point run conditions were pH 6.1, catalyst dosage of 1.05 g L⁻¹, irradiation time of 35 min, and C_MB of 5.5 ppm. Radical trapping experiments using scavenging agents revealed that hydroxyl radicals (˙OH) and holes (h⁺) were the predominant reactive species during MB photodegradation using the AgI/WO₃ system. The direct Z-scheme mechanism was the best photocatalytic system to describe MB photodegradation based on the results and potential positions of the VB and CB of the semiconductors.