Photocatalytic H2 production from H2S with new MoS2/ZnS photocatalysts; comparison with TiO2.
Résumé
Photocatalytic process is a way to convert H2S into H2 and polysulphide ions. Under right irradiation, semiconductors could produce photogenerated electrons and holes. Consequently, the overall reaction consists in the reduction of protons into H2 with photogenerated electrons and the oxidation of sulphide ions with photogenerated holes. The key point is to use photocatalysts that will not be poisoning by by-products. It is also known that photocatalytic H2 production is a bifunctionnal mechanism needing the presence of a cocatalyst as reduction sites to recombine H atoms into H2. However, even if platinium particles are largely use as cocatalyst, they could not be use in presence of sulphide. In order to identify the most active photocatalyst for this reaction, several ones 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 ZnS/MoS2 have been compared. As it could be expected, the presence of reduction sites is necessary to produce H2. TiO2, MoO3 and MoS2 exhibit no activity. The addition of Pt or Ru particles onto TiO2 or ZnS leads to the enhancement of the photocatalytic activity of the samples. However a desactivation of the catalyst is observed with irradiation time probably due to the poisoning of the cocatalyst. Only Ru/ZnO and MoS2/ZnS show a good activity and no or a slight deactivation. In the case of MoS2/ZnS, this could be related to a synergetic affect between the photocatalytic properties of ZnS and the ability of MoS2 to evacute polysulphide by-product.