Photocatalytic H 2 Production by Visible Light on Cd 0.5 Zn 0.5 S Photocatalysts Modified with Ni(OH) 2 by Impregnation Method.

Nowadays, the study of environmentally friendly ways of producing hydrogen as a green energy source is an increasingly important challenge. One of these potential processes is the heterogeneous photocatalytic splitting of water or other hydrogen sources such as H 2 S or its alkaline solution. The most common catalysts used for H 2 production from Na 2 S solution are the CdS-ZnS type catalysts, whose efficiency can be further enhanced by Ni-modification. In this work, the surface of Cd 0.5 Zn 0.5 S composite was modified with Ni(II) compound for photocatalytic H 2 generation. Besides two conventional methods, impregnation was also applied, which is a simple but unconventional modification technique for the CdS-type catalysts. Among the catalysts modified with 1% Ni(II), the impregnation method resulted in the highest activity, for which a quantum efficiency of 15.8% was achieved by using a 415 nm LED and Na 2 S-Na 2 SO 3 sacrificial solution. This corresponded to an outstanding rate of 170 mmol H 2 /h/g under the given experimental conditions. The catalysts were characterized by DRS, XRD, TEM, STEM-EDS, and XPS analyses, which confirmed that Ni(II) is mainly present as Ni(OH) 2 on the surface of the CdS-ZnS composite. The observations from the illumination experiments indicated that Ni(OH) 2 was oxidized during the reaction, and that it therefore played a hole-trapping role.