Unveiling the role of bisulfide in the photocatalytic splitting of H₂S in aqueous solutions

Anaerobic photocatalytic conversion of aqueous H₂S to H₂ was tested on Pt-decorated N-doped TiO₂ grown on graphene. The hydrogen production increased linearly (rate: 32.3 μmol/h/g, quantum yield: 1.4 × 10^–4) with HS⁻ concentration, until the critical value of 0.029 mol/dm³, after which it declined to negligible values. The latter was attributed to photon-blockage caused by sulfur-containing species formed on catalyst surface, which could be removed by simple washing of the catalyst leading to its regeneration, as highlighted by the characterization of fresh and used catalyst. Similar tests performed at constant HS⁻ concentration and variable pH did not yield a correlation, thus suggesting HS⁻ as the major source of H₂, and not H⁺. A new kinetic model assessing the competitive adsorption mechanism reiterated the important role of sulfide ionic species in hydrogen production. A strong correlation between the latter and HS⁻ concentration was established based on the reactivity results and proposed mechanism.