Photocatalytic mechanism and degradation pathway of acid red 1 by TiO2@Ag core-shell nanocomposites using UV-irradiation

The photocatalytic degradation mechanism and pathway of the azo dye Acid Red 1 (AR1) were investigated using titanium dioxide nanoparticles (TiO 2 NPs) under long-wavelength UV irradiation. The photocatalytic efficiency of TiO 2 NPs was significantly enhanced by coating with a silver shell, forming titanium dioxide–silver core–shell nanocomposites (TiO 2 @Ag NCs). Structural and physicochemical characterization of TiO 2 NPs and TiO 2 @Ag NCs was performed using FTIR, XRD, SEM–EDX, HRTEM, and UV–Vis spectroscopy. XRD confirmed the retention of the anatase phase of TiO 2 , while SEM images showed spherical morphologies, with TiO 2 @Ag NCs exhibiting slightly larger diameters due to silver encapsulation. EDX revealed the presence of Ag with an atomic ratio of ∼12 %. The optical bandgap decreased from 3.18 eV (TiO 2 ) to 2.91 eV (TiO 2 @Ag), while electrical conductivity increased from 2.5 μS cm −1 to 7.5 μS cm −1 . At a dye concentration of 15 mg L −1 , TiO 2 @Ag NCs (500 mg L −1 ) achieved 81 % degradation within 50 min of UV irradiation, compared to 67 % degradation by TiO 2 NPs in 120 min. Kinetic analysis revealed that TiO 2 NPs followed single first-order kinetics (k 1 = 0.0085 min −1 , T 1 / 2 = 87 min), whereas TiO 2 @Ag NCs exhibited biphasic first-order kinetics: rapid initial degradation (0–7 min, k 1 = 0.0899 min −1 , T 1 / 2 = 8 min) followed by slower oxidation of intermediates (7–50 min, k 2 = 0.0138 min −1 , T 1 / 2 = 50 min). The degradation pathway of AR1 was elucidated using LC–MS, confirming cleavage of the azo bond and subsequent oxidative transformations. These results demonstrate that Ag-shell modification substantially improves TiO 2 photocatalytic performance under UV irradiation by enhancing charge separation and facilitating rapid pollutant mineralization.