Green deep eutectic solvent synthesis of ultrasmall BiOCl with Bi-S interfacial coordination bonds for visible-light-driven organic pollutant degradation and CO2 photoreduction.

Developing efficient visible-light photocatalysts remains challenging for solar fuels and pollution remediation. Here, a thiourea-choline chloride deep eutectic solvent was adopted to synthesize a series of BiOCl-XTU photocatalysts with Bi-S interfacial coordination bonds through coprecipitation. Surface-anchored thiourea creates steric hindrance to miniaturize BiOCl nanoparticles and boost surface area. Its polar resonance forms Bi-S bonds, substituting oxygen vacancies, narrowing the 2.15 eV band gap, extending visible absorption, and introducing defects to suppress charge recombination. Benefiting from effective spatial separation of charge carriers enabled by Bi-S interfacial states, BiOCl-3TU delivers superior photocatalytic activity: RhB is almost completely degraded within 20 min, its degradation efficiencies for tetracycline (30 min) and methylene blue (2 h) are 3 and 4 times those of the original BiOCl, and the CO yield of CO2 photoreduction rises to 4.6 times that of pristine BiOCl. Mechanism analyses reveal that photogenerated holes and superoxide radicals dominate the catalytic reaction, and Bi-S interfacial states act as electron transfer bridges to hinder carrier recombination. DFT calculations confirm Bi-S electronic modulation: S doping induces defect states near Fermi level and charge redistribution, while Bi-S bonds synergize with oxygen vacancies to promote light absorption and charge separation, consistent with experiments. This work guides broad-spectrum photocatalyst design.