An Isopolymolybdate-Incorporated Metal–Organic Framework with Sulfite Oxidase-Mimicking Activity for Photocatalytic Oxidation of Sulfides Utilizing In Situ-Generated Singlet Oxygen

Developing new photocatalysts for sulfide oxidation utilizing in situ-generated ¹O₂ is very significant. Inspired by natural enzymatic processes, we synthesized a mimic sulfite oxidase (SO), {[Co(Mo₄O₁₃)(TPT)₂]} (CoMo-TPT), by incorporating an isopolymolybdate anion [Mo₄O₁₃]^2- into a 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT)-based metal-organic framework under mild hydrothermal conditions. In this structure, {Mo₄O₁₃} units with intrinsic SO-like catalytic sites are beneficial for the selective oxidation of sulfite and thioether. The ultraviolet-visible spectra of CoMo-TPT exhibited strong absorption from 250 to 650 nm and potential application in the utilization of solar energy. Mott-Schottky measurements indicated that CoMo-TPT is an n-type semiconductor with a LUMO value of -0.70 V (vs NHE) and a HOMO value of 1.39 V. The transient photocurrent responses with strong current density cycles with visible light indicated CoMo-TPT has a high photochemical activity. The lower resistance indicated that CoMo-TPT has a higher efficiency of photoinduced electron and hole separation. CoMo-TPT displayed a high efficiency of 99% and a selectivity of 97.3% in photocatalytic oxidation of sulfides by utilizing in situ-generated ¹O₂ through a tandem process of formation of H₂O₂ from O₂ followed by catalyzed disproportionation of H₂O₂.