Photocatalytic H2 production from H2S with new MoS2/ZnS photocatalysts
Résumé
Photocatalytic process is a way to convert H2S into H2 and polysulfide ions. Under irradiation, semiconductors could produce photogenerated excitons. Consequently, the overall reaction consists in the reduction of protons into H2 with photogenerated electrons and the oxidation of sulfide ions with photogenerated holes. The key point is to use photocatalysts that will not be poisoned by reactants and products. To identify the most active photocatalyst for this reaction, various materials have been tested in the photocatalytic H2 production from H2S. The tests have been performed in aqueous solution using Na2S as model reactant for dissolved H2S. TiO2, Pt/TiO2, Ru/TiO2, ZnS, Ru/ZnS, Ru/ZnO, MoS2, and new fullerene-like ZnS/MoS2 have been compared. The preparation of ZnS/MoS2 fullerene-like particles is based on the use of ZnS spherical seeds on which deposition of amorphous molybdenum sulfide occurs through a control of the MoSx nucleatio n. As it could be expected, the presence of HER sites seems necessary to produce H2. TiO2, MoO3 and MoS2 exhibit no activity. The addition of Pt or Ru particles onto TiO2 or ZnS leads to a large enhancement of the photocatalytic activity of the samples. However, deactivation of the catalyst is observed with irradiation time likely due to the poisoning of the co-catalyst (Pt or Ru) (Figure 1). Only ZnS/MoS2 catalyst shows a good activity with no or a slight deactivation without the use of noble metal. This could be related to a synergetic effect between the photocatalytic properties of ZnS and the ability of MoS2 to release polysulfide.