Support-dependent charge transfer and ROS pathways in Pt/g-C3N4 and Pt/TiO2 photocatalysts

Understanding how platinum cocatalysts interact with semiconductor supports remains a central challenge in photocatalysis. Although Pt nanoparticles are often assumed to act as a universal electron sink, this study demonstrates that their catalytic behaviour is governed by the electronic structure, defect chemistry, and interfacial energetics of the support. To isolate support-induced effects, TiO 2 nanorods (S BET = 93.3 m 2 g −1 ) and two texturally distinct forms of g-C 3 N 4 (a low-surface-area CN-L (20 m 2 g −1 ) and a high-surface-area CN-H (85.0 m 2 g −1 )) deliberately matched to TiO 2 were modified with identical 1 wt% Pt nanoparticles using the same impregnation-reduction protocol. Despite comparable surface areas for TiO 2 and CN-H, Pt-modified catalysts exhibit fundamentally different interfacial energetics and charge-transfer behaviour. TiO 2 stabilizes highly metallic Pt nanoparticles (~1.0 nm) and forms a very low Schottky barrier (0.16 eV), enabling rapid electron extraction and pronounced Pt-mediated visible-light ROS generation. In contrast, g-C 3 N 4 induces strong band bending and stabilizes mixed Pt 0 /Pt 2+ states, resulting in higher interfacial barriers (0.26–1.19 eV), suppressed hydroxyl radical formation, and enhanced selective one-electron oxidation, more than doubling ABTS generation compared to pristine CN-L. These electronic effects translate directly into photocatalytic performance. TiO 2 @Pt exhibits efficient visible-light BPA degradation and the lowest NO 2 reduction onset temperature, while CN-H@Pt outperforms CN-L@Pt due to improved charge separation and approximately 40% lower charge-transfer resistance. The persistence of these contrasts between TiO 2 @Pt and CN-H@Pt confirms that Pt nanoparticles functionality is electronically programmed by the support rather than dictated by surface accessibility. This insight provides a rational framework for engineering noble-metal photocatalysts through deliberate control of semiconductor electronic structure and interfacial chemistry. • Platinum reactivity is determined by the electronic structure of the support. • Comparable surface areas isolate support-controlled charge-transfer behaviour. • g-C 3 N 4 induces band bending and directs Pt towards selective one-electron oxidation. • TiO 2 stabilizes metallic Pt and enables Pt-driven visible-light ROS generation. • Support-dependent Pt chemistry governs both photocatalytic and thermocatalytic reactivity.