Solar-Driven Photocatalytic C─S Coupling for Organosulfur Synthesis Via Upcycling SO₂ and Plastic Waste

Hydroxymethylsulfonate (HMS) is an important cleaning agent in the electronics industry and serves as a crucial intermediate in the synthesis of surfactants and pharmaceuticals. Conventional industrial production of HMS relies on toxic and volatile formaldehyde, presenting considerable safety and environmental risks. Herein, we report a solar-driven photocatalytic route for the synthesis of HMS from waste SO₂ and polyethylene terephthalate (PET)-derived ethylene glycol (EG) under ambient conditions, using a Cu single-atom-decorated TiO₂ catalyst (Cu₁/TiO₂). The optimized Cu₁/TiO₂ catalyst achieves an HMS yield rate of ∼ 2.31 mmol g_cat ^-1 h^-1 with a 77.5% carbon selectivity, along with a H₂ evolution rate of ∼ 4.36 mmol g_cat ^-1 h^-1. Mechanistic studies reveal that the atomically dispersed Cu sites act as electron sinks, which enhance charge separation and induce electronic modulation of TiO₂. This modulation facilitates the adsorption and activation of reactants while lowering the energy barrier for the formation of a key *CHOH─CH₂OH intermediate via EG dehydrogenation. This resulting intermediate then undergoes nucleophilic attack by hole-generated •SO₃ ^-, triggering C─C cleavage to form HMS. This work establishes a sustainable and waste-valorizing route for organosulfur synthesis.