Ag₂O/TiO₂ nanostructures for the photocatalytic mineralization of the highly recalcitrant pollutant iopromide in pure and tap water

TiO₂ was modified by the deposition of Ag₂O nanoparticles to increase the photocatalytic degradation of iopromide in water under UV–C (λ = 254 nm) and UV–A/visible light irradiation (380–800 nm) using pure and tap water. Several loadings of Ag₂O were deposited on TiO₂, namely 0.03, 0.15, 0.25, 0.65, 1.0, 1.15, 1.35 and 1.8 wt. %. XRD, TEM, BET, ICP-OES, XPS, DRS and cathodoluminescence spectroscopy were carried out to characterize the materials, while semiconducting properties of the composite were elucidated through electrochemical and photoelectrochemical characterization. Under UV–C light irradiation, the Ag₂O/TiO₂ heterostructures showed higher mineralization of iopromide (up to 86%, using the 1.15 wt. % Ag₂O/TiO₂ material) than unmodified materials (37% for TiO₂ and 14% for Ag₂O), indicating a synergistic effect by the combination of both compounds in the composite. Under UV–A/visible light irradiation, mineralization achieved with the 1.15 wt. % Ag₂O/TiO₂ material decreased up to 65%, which was again higher than that obtained for its single components. Stability of the photocatalyst was observed through three consecutive reaction cycles under UV–A/visible light irradiation. In tap water, environmentally relevant concentrations of iopromide were tested (Co = 50 μg L⁻¹), resulting in a high degradation rate, while mineralization dramatically decreased because of the matrix effect. Some by-products were identified by mass spectroscopy and a possible degradation path was proposed. The outstanding photocatalytic activity of the Ag₂O/TiO₂ materials was explained by the electron trap effect exerted by Ag₂O, along with the appearance of different silver species (Ag₂O, Ag₂O₂ and Ag°) throughout the photocatalytic reaction, enhancing the mobility of the charge carriers and thus the generation of reactive species on the photocatalyst surface.