Abstract

Subsurface silver-modified Bi<inf>3</inf>NbO<inf>7</inf> photocatalysts were synthesized via a hydrothermal method to investigate the role of metal spatial distribution in photocatalytic pathways. Integrated structural, physicochemical, spectroscopic and theoretical analyses confirm that Ag is in the subsurface region rather than forming surface nanoparticles or substituting into the Bi<inf>3</inf>NbO<inf>7</inf> lattice, inducing localized distortions without altering the bulk crystal structure or the electronic band structure. Despite these minimal thermodynamic changes, the photocatalytic activities for Rhodamine B degradation and hydrogen evolution vary significantly across samples. Photoelectrochemical and transient absorption spectroscopic studies reveal that the catalytic activities and selectivity are primarily driven by charge carrier kinetics. Specifically, subsurface Ag dispersion modulates the competition between oxidation, governed by hole availability, and reduction, which is sensitive to electron-hole separation efficiency. This study presents a ‘subsurface-mediated kinetic control’ strategy, offering tuneable reaction selectivity through engineering the spatial location of metallic species.