Hierarchical CuS Nanoflowers via Atmosphere-Controlled Sulfurization: Enhanced Visible-Light Photocatalysis

Hierarchical flower-like copper sulfide (CuS) nanocrystals with exceptional visible-light photocatalytic activity were synthesized via atmosphere-controlled sulfurization of electrodeposited metallic precursor films. Through systematic comparison of three sulfurization protocols—tubular furnace, sealed ampoule, and pre-oxidation approaches—we demonstrate that sulfur-saturated conditions (≥ 7 mg S) are critical for producing covellite CuS with distinctive hierarchical nanoflower morphologies (200–500 nm diameter, 89–96 m²/g surface area) on substrate-adhered films, while insufficient sulfur yields mixed oxide-sulfide phases. The optimized CuS nanoflowers exhibited superior photocatalytic performance: 94.3% Rhodamine B degradation in 120 min under visible light with rate constant 43.8 × 10⁻³ min⁻¹ (10.4-fold enhancement over P25 TiO₂), primarily through superoxide radical-mediated oxidation. The narrow bandgap (1.45 eV), high surface area, and phase purity synergistically enabled efficient visible-light harvesting and charge separation. Thermodynamic calculations rationalized the formation mechanism via preferential SO₂/SO₃ formation that prevents oxidation and maintains reducing conditions throughout the sulfurization process. Excellent reusability (90.2% activity retention after 6 cycles) demonstrates practical applicability. This atmosphere-controlled synthesis strategy provides rational design principles for scalable production of high-performance nanostructured photocatalysts, with broad implications for chalcogenide materials synthesis.