Mechanochemical engineering of platinum‑titanium dioxide interfaces directs localized oxidation pathways in visible-light photocatalysis

Visible-light photocatalysis over metal-modified TiO₂ is commonly interpreted in terms of enhanced reactive oxygen species (ROS) generation; however, the relationship between ROS production and effective pollutant mineralization remains poorly understood. Here, TiO₂ photocatalysts modified with various noble and transition metals were prepared via ball milling (BM) and incipient wetness impregnation (IWI) to investigate how metal-support interactions influence charge-transfer pathways. Among all investigated systems, Pt/TiO₂ prepared by ball milling (Pt/TiO₂-BM) exhibited markedly enhanced photocatalytic mineralization of bisphenol A (BPA), despite generating only negligible coumarin-detectable ^•OH radicals in the bulk solution. In contrast, Au- and Ag-containing catalysts produced substantially higher ROS signals yet showed inferior mineralization efficiency. These findings reveal a pronounced disconnect between bulk ROS generation and photocatalytic mineralization efficiency. Combined spectroscopic and photocatalytic analyses provided evidence for a strongly coupled, oxygen-deficient Pt-TiO₂ interface formed through ball milling, associated with Ti³⁺ centers, oxygen-vacancy-related states and intense visible photoluminescence centered at approximately 600 nm, consistent with the formation of Pt-induced interfacial electronic states. The emergence of these states was associated with photocatalytic behaviour consistent with localized, surface-confined oxidation pathways and highly efficient BPA mineralization despite low bulk ROS generation. Conversely, catalysts prepared by incipient wetness impregnation showed behaviour consistent with a greater contribution from non-selective bulk ROS pathways, resulting in lower mineralization efficiency despite stronger radical generation in solution. The results indicate that photocatalytic efficiency under visible light depends strongly on the nature and localization of interfacial charge-transfer pathways rather than simply on the total ROS concentration generated in the bulk phase. Overall, this work highlights mechanochemical control of metal-TiO₂ interfaces as a promising strategy for directing photocatalytic oxidation pathways and improving visible-light photocatalytic efficiency.