Platinum Is Not a Universal Electron Sink: Support-Dependent Charge Transfer and Reactive Oxygen Species Pathways in Photocatalysis

The performance of noble-metal photocatalysts is commonly attributed to the intrinsic properties of the deposited metal, while the role of the semiconductor support is often considered secondary. In this work, we show that platinum (Pt) functionality is electronically programmed by the support, resulting in fundamentally different charge-transfer pathways, reactive oxygen species (ROS) generation, and environmental catalytic performance. To isolate support-dependent effects, TiO₂ nanorods and graphitic carbon nitride (g-C₃N₄) materials with comparable surface areas were modified with identical Pt loading (1 wt%) using the same impregnation–reduction protocol. Structural characterisation confirmed similar Pt contents and homogeneous nanoparticle dispersion, enabling direct comparison of metal–support interactions. The resulting photocatalysts were evaluated in visible-light-driven bisphenol A (BPA) degradation and H₂-assisted NO₂ reduction, while interfacial charge-transfer properties were investigated using XPS, electrochemical impedance spectroscopy, time-correlated single-photon counting, and ROS probing experiments. The results revealed pronounced support-controlled electronic behaviour. Pt/TiO₂ formed highly metallic Pt nanoparticles and a low Schottky barrier, promoting rapid electron extraction, efficient charge separation, and enhanced hydroxyl radical generation. Consequently, Pt/TiO₂ exhibited the highest BPA degradation rates and the lowest activation temperatures for NO₂ reduction. In contrast, Pt/g-C₃N₄ generated stronger interfacial band bending and mixed Pt⁰/Pt²⁺ surface states, suppressing hydroxyl radical formation while favouring selective one-electron oxidation pathways. These differences produced distinct ROS landscapes and catalytic responses despite identical Pt loading. Furthermore, improved textural properties of high-surface-area g-C₃N₄ enhanced interfacial charge transfer and catalytic performance, highlighting the importance of coupling structural optimisation with electronic engineering. Overall, this study shows that platinum cannot be regarded as a universal electron sink. Instead, its catalytic behaviour is defined by support-dependent electronic interactions that determine charge-transfer kinetics, ROS selectivity, and photocatalytic performance. These findings provide important design principles for the development of next-generation photocatalytic and photothermal systems for sustainable environmental remediation.