Effects of Preparation Conditions on the Efficiency of Visible-Light-Driven Hydrogen Generation Based on Ni(II)-Modified Cd0.25Zn0.75S Photocatalysts

Noble metal-free bimetallic phosphide-decorated Zn0.5Cd0.5S with efficient photocatalytic H2 evolution

The rapid recombination of charge carriers in semiconductor-based photocatalysts results in a low photocatalytic activity. Co-catalysis is considered a promising strategy to improve the photocatalytic performance of semiconductors. In this study, a bimetallic phosphide was grown by a facile in situ growth method. Loading the cocatalyst (7 wt% NiCoP) leads to activity enhancement by a factor of approximately 27 times in the visible-light-driven hydrogen evolution relative to the pristine Zn0.5Cd0.5S. The photocatalysis shows a high hydrogen evolution rate of 19.5 mmol g-1 h-1, which is much higher than that of the single metal phosphide (Ni2P: 7.0 mmol g-1 h-1; CoxP: 8.1 mmol g-1 h-1) and 7 wt% Pt modified Zn0.5Cd0.5S (0.3 mmol g-1 h-1). Its apparent quantum efficiency reaches 41.6% at 420 nm. Moreover, the photocatalyst exhibits a remarkable photostability for five consecutive cycles of photocatalytic activity measurements with a total reaction time of 15 hours. The excellent photocatalytic activity of the photocatalyst was attributed to the in situ-formed NiCoP cocatalyst, which not only acts as a reactive site but also accelerates the separation of charge carriers.

Photocatalytic H2 Production by Visible Light on Cd0.5Zn0.5S 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 H₂S or its alkaline solution. The most common catalysts used for H₂ production from Na₂S solution are the CdS-ZnS type catalysts, whose efficiency can be further enhanced by Ni-modification. In this work, the surface of Cd_0.5Zn_0.5S composite was modified with Ni(II) compound for photocatalytic H₂ 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 Na₂S-Na₂SO₃ sacrificial solution. This corresponded to an outstanding rate of 170 mmol H₂/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.

Fabrication of WS2/WSe2 Z-Scheme Nano-Heterostructure for Efficient Photocatalytic Hydrogen Production and Removal of Congo Red under Visible Light

In this study, a novel tungsten disulfide/tungsten diselenide (WS2/WSe2) heterojunction photocatalyst by a facile hydrothermal process with great capable photocatalytic efficiency for hydrogen evolution from water and organic compound removal was discussed. The WS2/WSe2 heterojunction photocatalyst to form heterojunctions to inhibit the quick recombination rate of photo-response holes and electrons is reflected to be a useful method to enhance the capability of photocatalysis hydrogen production. The hydrogen production rate of the WS2/WSe2 photocatalyst approach is 3856.7 μmol/g/h, which is 12 and 11 folds the efficiency of bare WS2 and WSe2, respectively. Moreover, the excellent photocatalytic performance for Congo Red (CR) removal (92.4%) was 2.4 and 2.1 times higher than those of bare WS2 and WSe2, respectively. The great photocatalytic efficiency was owing to the capable electrons and holes separation of WS2/WSe2 and the construction of Z-scheme heterostructure, which possessed vigorous photocatalytic oxidation and reduction potentials. The novel one-dimensional structure of WS2/WSe2 heterojunction shortens the transport pathway of photo-induced electrons and holes. This work provided an insight to the pathway of interfacial separation and transferring for induced charge carriers, which can refer to the interfacial engineering of developed nanocomposite photocatalysts. It possessed great capable photocatalytic efficiency of hydrogen production and organic dye removal. This study offers an insight to the route of interfacial migration and separation for induced charge carriers to generating clean hydrogen energy and solve environmental pollution issue.