Photochemical valorization of hydrogen sulfide: a study of UV-induced decomposition pathways

Hydrogen sulfide (H₂S) is a toxic and environmentally hazardous gas, yet it also represents a potential source of valuable hydrogen. This study investigates the direct gas-phase decomposition of H₂S into hydrogen (H₂) and elemental sulfur (S_x) using UV-C light sources through both photolytic and photocatalytic pathways. Experiments were conducted using a 220 nm UV laser and a 254 nm mercury (Hg) lamp in distinct reactor configurations. Photolysis of 5% H₂S/N₂ achieved conversion efficiencies of up to 44% and 52% within 60 minutes using the laser and Hg lamp, respectively. In flow experiments (space velocity ∼15 h⁻¹), conversion decreased to 13-16%. In both static and flow modes, sulfur deposition on optical surfaces hindered UV transmission, thereby reducing overall efficiency. Incorporating a CuS photocatalyst significantly enhanced H₂S decomposition, reaching 66% conversion under UV-C illumination. X-ray photoelectron spectroscopy (XPS) confirmed the presence of mixed Cu⁺/Cu^1+δ valence states in CuS, enabling localized surface plasmon resonance (LSPR) that promotes charge separation and catalytic activity. These findings underscore the promise of UV-C-driven H₂S splitting as a sustainable approach for hydrogen and sulfur co-production, offering a cleaner alternative to conventional treatment methods.