Enhancing the solar photocatalytic hydrogen generation of ZnS films by UV radiation treatment


E. Puentes-Prado , C.R. Garcia b, J. Oliva , R. Galindo ,
J.J. Bernal-Alvarado , L.A. Diaz- Torres , C. Gomez-Solis

This work reports the synthesis of transparent ZnS films for the hydrogen production using
a low-cost chemical bath deposition method (CBD). Some ZnS films were subjected to UV
treatment and became darker. According to the X-ray diffraction patterns, both, the
transparent and dark films presented the same crystalline wurtzite phase. However, the
morphological analysis by scanning electron microscopy (SEM) revealed that the dark ZnS
films were formed by smaller ZnS grains (10e46 nm) in comparison with the transparent
films (17e70 nm). The dark coloration of the films was caused by the presence of Zn vacancies,
S vacancies and sulfate groups as confirmed by the XPS spectra and absorbance
measurements. In fact, the presence of these defects and sulfates enhanced the absorbance
and photocurrent in the dark ZnS films with respect to the transparent ZnS films.
Consequently, the maximum hydrogen generation rate was 250% higher in the dark ZnS
films (655 mmol∙h1 g1) in comparison to the transparent ZnS films (187 mmol∙h1 g1). In
presence of a sacrificial agent (Na2SO3), the hydrogen generation rates increased up to 2903.6 and 5202.4 mmol∙h1 g1 for the transparent ZnS and dark ZnS films, respectively.
The ZnS films studied here represent advance with respect to the previous powder-type
binary/ternary photocatalyst nanocomposites, since they can be easily removed from
water after the photocatalytic reaction (an advantage over the powders), they do not
contain expensive/rare metals and their synthesis procedure is not as complex as these
reported for binary/ternary nanocomposites.
Artículo-CEGR 7 2020