Ternary heterojunction stabilized photocatalyst of Co-TiO2/g-C3N4 in boosting sulfite oxidation during wet desulfurization

Highlights: • The photocatalyzed oxidation rate of MgSO₃ was increased by 11.1-folder higher than the uncatalyzed benchmark. • SO₅⁻ was the major active species in the MgSO₃ oxidation. • O₂⁻, ·OH and h⁺ promote the production of ·SO₅⁻ free radicals. • The production of more oxidizing species under light conditions promotes the oxidation of MgSO₃. Visible light can promote a catalyst to generate a large number of oxidative free radicals. The photocatalysis of sulfite oxidation is an efficient and economical approach for reclaiming wet desulfurization byproducts. In the present study, a cost-effective photocatalyst with a low metal concentration, namely Co-TiO₂/g-C₃N₄ (CTO/CN), was synthesized using a simplified one-pot hydrothermal procedure. The structure and characteristics of this photocatalyst were assessed using various characterization methods_. The as-prepared CTO/CN exhibited enhanced photocatalytic activities for the oxidation of MgSO3, which was 11-fold higher than that of the uncatalyzed benchmark. Under irradiation, ternary heterojunction photocatalyst accelerated the charge transfer, reduced the band gap and enhanced the production of strong oxidizing species (·O₂⁻, ·OH and h⁺), which promote the formation of the ·SO₅⁻ radical, the active species in the MgSO₃ oxidation. The as-prepared CTO/CN increased the critical mass concentration of magnesium sulfate from 10% to 19.9%, which reduced the recovery cost of magnesium sulfate. This paper proposes an environmentally friendly strategy for improving the overall performance of wet desulfurization with low cobalt doping levels for photocatalytic oxidation reactions under visible light.