Preparation and photochemical properties of cadmium sulphide-zinc sulphide incorporated into the interlayer of hydrotalcite

Semiconductor particles composed of mixed CdS and CdS-ZnS were incorporated into an interlayer of hydrotalcite by chemical reaction between Cd(edta)²⁻ and S²⁻ in the interlayer. The incorporated particles seemed to be very small, less than 0.4 nm thick. The band gap energies of CdS and sequentially precipitated CdS followed by ZnS in the interlayer were slightly larger than that of normal-crystalline CdS. On the other hand, the band gap energy of CdS-ZnS mixture coprecipitated in the interlayer was almost equal to the average value of those of normal-crystalline CdS and ZnS. The CdS and CdS-ZnS mixture incorporated into hydrotalcite were capable of efficient hydrogen evolution following irradiation with visible light in the presence of Na₂S and/or Na₂SO₃ as a sacrificial donor. The hydrogen production activities of the catalyst incorporated in hydrotalcite were in the order of sequentially precipitated CdS followed by ZnS > simultaneously precipitated CdS-ZnS mixture ⪢ CdS. The difficulty of mass transfer of the hydrogen evolved in response to visible light through the interlayer restricted the efficiency of the semiconductor incorporated into hydrotalcite. Almost equal amounts of S₂O₆²⁻ and SO₄²⁻ were formed by the photochemical oxidation of SO₃²⁻ in aqueous solution catalysed by unsupported CdS/ZnS, but the amount of S₂O₆²⁻ produced in the same reaction with CdS/ZnS incorporated into hydrotalcite was significantly less.