Silver-doped TiO2 catalysts for efficient methylene blue removal

Ag-doped TiO2 nanoparticles were synthesized via a facile sol–gel method to investigate the synergistic effects of silver doping and pH on the photocatalytic degradation of methylene blue (MB). The catalysts, characterized comprehensively by XRD, SEM–EDS, FTIR, and UV–Vis DRS, revealed that Ag doping (1–2 mol%) successfully enhanced visible-light absorption and modified surface properties. However, characterization confirmed significant spatial heterogeneity in Ag distribution, which resulted in localized charge-separation "hot spots". Consequently, the TiO2-Ag 1% catalyst exhibited optimal performance, achieving superior degradation kinetics (kₐₚₚ = 82.8 × 10⁻3 min⁻1) specifically at pH 9. This enhanced activity is attributed to its balanced Ag dispersion, which, when combined with alkaline conditions, promoted enhanced •OH generation from surface-bound water and improved MB adsorption. Thus, this study demonstrates that photocatalytic efficiency depends critically not only on successful doping but also on the interplay between optimal Ag distribution (1% > 2%) and pH-dependent surface charge, offering key insights for designing TiO2 catalysts for organic pollutant remediation.