Coupling plasmonic and electron-mediated effects in Ag_<i>x</i>@r–TiO₂/g-C₃N₄ heterostructures for enhanced catalytic hydrogen generation

This study presents a sustainable strategy for sunlight-driven hydrogen production <i>via</i> seawater splitting. We designed Z-scheme heterostructures using silver-decorated r-TiO₂ and g-C₃N₄. These materials were synthesized <i>via</i> chemical reduction, hydrothermal treatment, and controlled calcination. The synthesized materials were characterized using advanced techniques, <i>i.e.</i> XRD and Raman analysis, which confirmed the successful integration of r-TiO₂, metallic Ag, and g-C₃N₄, showing strong crystallinity and interfacial coupling. UV-vis DRS analysis depicted enhanced visible-light absorption in silver-decorated r-TiO₂/g-C₃N₄ composites due to the combined effects of Ti³⁺ defects, plasmonic Ag nanoparticles, and the interfacial charge transfer between their components. Mott-Schottky analysis confirmed their n-type behaviour with optimal band alignment (-0.45 <i>vs.</i> NHE for r-TiO₂; -1.35 <i>vs.</i> NHE for g-C₃N₄), promoting charge separation. SEM revealed lump-like morphology with dispersed particles, while AFM indicated distinct surface roughness. Particle size distribution ranged from 20.3 to 243.1 μm (diameter) and 30.6 to 235.6 μm (length), reflecting structural heterogeneity. Moreover, the mesoporous nature of the ternary composite was confirmed using BET. The photoreaction was conducted in a glass reactor, and the hydrogen evolution rates were monitored using GC-TCD (Shimadzu, Japan). Under optimized conditions, the recorded maximum hydrogen evolution rate was 11.76 mmol g^-1 h^-1 in seawater and 6.63 mmol g^-1 h^-1 in deionized water with 4 mg of Ag _<i>x</i> @r-TiO₂/g-C₃N₄ (2 w% Ag). The amount of hydrogen evolved over Ag_2.0@r-TiO₂/g-C₃N₄ was ∼9.56- and 6.21-fold higher than that over pristine g-C₃N₄ and r-TiO₂ in seawater and ∼37.94- and 14.16-fold higher in deionized water under optimized conditions, respectively. Moreover, five-run durability tests confirmed the sustainability of the catalyst. These results suggest that Ag _<i>x</i> @r-TiO₂/g-C₃N₄ is a reliable material for advancing efficient energy conversion and fuel generation.