Highly active ZnS-UV was obtained in situ from ZnS(en)(0.5) hybrid during the hydrogen formation using a methanol-water solution under UV irradiation. X-ray diffraction patterns and UV spectroscopy for both ZnS-UV and ZnS-400 obtained from the calcination of the ZnS(en)(0.5) hybrid showed similar structural and photophysical properties; however, the efficiency of the ZnS-UV semiconductor was 7 times higher (4825 mu mol h(-1) g(-1)) compared to the ZnS-400. The highest H-2 production was obtained using a UV lamp of very low intensity (2.2 mW cm(-1)) and it is attributed to a quantum size effect caused by the slow elimination of ethylenediamine (en) in the structural ZnS layer during the UV irradiation. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.