Nanoscale AgI-WO3 binary photocatalyst: Synthesis, brief characterization, and investigation of its photocatalytic activity

Abstract

A novel AgI/WO3 binary system with good visible-light photocatalytic performance was fabricated and characterized by XRD, FTIR, SEM-EDX, X-ray map, photoluminescence (PL), and UV–Vis DRS techniques. A hexagonal wurtzite type β-AgI and monoclinic WO3 crystallites were detected. The average crystallite size of about 37.7 nm (by Scherrer formula) and 34.7 nm (by Williamson-Hall formula) was obtained for the binary catalyst. W–O–W and O–W-O vibrational modes showed intense absorption bands at 591, 761, and 828 cm−1 (or at 816 cm−1), and Ag-I around 595 and 640 cm−1 (that were broadened due to ionic future of AgI) in FTIR spectra. Absorption edge wavelengths of 506, 464, and 465 nm correspond to Eg-values of 2.45, 2.67, and 2.66 eV were estimated for AgI, WO3, and AgI/WO3 samples, respectively. PL spectra showed the most negligible intensity for the binary catalyst regarding the individual AgI and WO3 systems. PL intensity as a function of AgI: WO3 mole ratio of binary catalyst in two acetone and ethanol solvents was followed and good illustrated. The system with a mole ratio of 1:2 showed the lowest PL intensity and the highest photocatalytic activity. The peak intensity in ethanol as a higher polar solvent than acetone was increased. Synergistic photocatalytic activity of the proposed binary catalyst was observed toward methylene blue (MB) that depended on the AgI: WO3 mole ratio. The kinetics of the process obeyed the pseudo-first-order Hinshelwood model with k-values of 0.0123, 0.0216, and 0.0395 min−1 for WO3, AgI, and AgI/WO3 catalysts, respectively. The rate constant for the binary catalyst is 1.83 and 3.21 times greater than the values obtained for WO3 and AgI NPs, respectively. The Hinshelwood plot constructed based on COD data for the binary catalyst showed a rate constant of 0.0365 min−1, comparable with that obtained based on the photodegradation data.