Photocatalytic hydrogen generation with simultaneous organic degradation by a visible light-driven CdS/ZnS film catalyst

A layered CdS/ZnS catalyst film was synthesized on glass using the stepped chemical bath deposition method. The film catalyst was shown as visible light-driven photocatalyst capable of producing H2 under visible light. The ZnS outer layer helped suppress the recombination of photo-generated electron–hole pairs on the CdS base layer, leading to faster H2 generation. The use of the ZnS layer also greatly improved the stability of the catalyst film and prevented the leaching of Cd2+ from the CdS layer. Deposition of Ru on the catalyst film further increased its photoreactivity for H2 production. The photocatalyst was effective in H2 production together with the degradation of model organic substances, such as formic acid, methanol, and ethanol. The greatest H2 production rates were achieved using the CdS/ZnS/Ru film in the formic acid solution at 123 μmol/m2-h under visible light and 135 mmol/m2-h under the simulated solar light. The corresponding theoretical reduction rates of chemical oxygen demand (COD) were 1.9 and 2.1 g/m2-h, respectively. As the multilayer CdS/ZnS/Ru film catalyst can be easily separated from water, it has a great potential for simultaneous photocatalytic hydrogen generation and organic wastewater treatment using solar energy.