Harnessing Z-scheme heterojunction synergy in B₄C decorated with nano TiO₂ for solar-driven degradation of biocidal pollutants

Conventional type-II heterojunctions broaden visible-light absorption and enhance charge separation but weaken redox potentials via charge migration, reducing thermodynamic driving force for surface catalysis. A novel direct Z-scheme heterojunction photocatalyst was constructed by decorating B₄C with TiO₂ nanoparticles for efficient solar-driven degradation of 1,2-benzisothiazolin-3-one and other biocidal pollutants. The optimized TiO₂/B₄C photocatalyst achieved 98% BIT degradation within 4 h under simulated solar irradiation, with an apparent rate constant of 1.00 h⁻¹, approximately 38 and 6.2 times higher than those of pristine B₄C and TiO₂, respectively. The incorporation of B₄C broadened visible-light absorption and promoted interfacial charge separation, while the formation of an internal electric field enabled a direct Z-scheme charge-transfer pathway that preserved strong redox potentials. As a result, photogenerated electrons accumulated on B₄C and generated O₂^•− radicals, whereas holes retained on TiO₂ produced ^•OH radicals, jointly driving the oxidative degradation of pollutants. Electron Spin Resonance and radical scavenger analyses confirmed O₂^•− and ^•OH as the key reactive species. Density functional theory (DFT) calculations further elucidated the interfacial charge-transfer mechanism and the degradation pathway of BIT. This work demonstrates that the TiO₂/B₄C Z-scheme heterojunction provides an efficient strategy for solar-driven photocatalytic removal of biocidal pollutants, providing insights into rational design of high-performance photocatalysts for environmental remediation.