Site-selective Pt localisation controls interfacial charge transfer in g-C₃N₄/TiO₂ heterojunctions

Abstract

Understanding how cocatalyst localisation influences interfacial electron-transfer processes in carbon nitride-based heterojunctions remains a major challenge for the rational design of visible-light photocatalysts. Here, we systematically investigate how the preferential localisation of Pt nanoparticles within g-C₃N₄/TiO₂ heterostructures regulates interfacial electronic coupling and visible-light photocatalytic performance. Four synthetic pathways were deliberately designed to direct Pt deposition selectively onto g-C₃N₄, TiO₂, both components simultaneously, or the pre-formed heterojunction interface, thereby decoupling cocatalyst-location effects from compositional and surface-area contributions. Combined XRD, XPS, TEM-EELS, EPR, FTIR, and DRIFTS analyses reveal that Pt positioning strongly modulates crystallinity, surface chemistry, oxygen-defect formation, and Pt–support electronic interactions. In particular, pyridine-, CO₂-, and CO-DRIFTS provide molecular-level insight into how Pt localisation alters the distribution of acid-base sites and the electronic state of Pt species. Visible-light photocatalytic degradation of bisphenol A demonstrates a pronounced dependence on Pt spatial placement, with Pt deposited at the pre-formed g-C₃N₄/TiO₂ interface exhibiting the most efficient interfacial charge separation and photocatalytic activity. In contrast, Pt predominantly localised on g-C₃N₄ promotes nanoparticle agglomeration and less effective charge-transfer pathways. The results demonstrate that Pt does not significantly modify the experimentally determined optical band gaps of g-C₃N₄ or TiO₂ but instead governs interfacial electron-transfer pathways through the formation of metal-semiconductor Schottky junctions and efficient interfacial electron extraction. Consequently, the photocatalytic performance is governed by the efficiency of interfacial charge separation rather than changes in the intrinsic electronic structure of the semiconductor components. These findings establish cocatalyst spatial organisation as a decisive design parameter governing interfacial electron-transfer processes in hybrid photocatalysts and provide mechanistic design principles for engineering multi-component semiconductor architectures beyond empirical catalyst optimisation.