bstract

A simple and feasible hydrothermal process was designed to synthesize MoS2/CdS composite catalyst. The surface morphology and crystal morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The surface chemical state, the chemical structure and the ultraviolet–visible light response were investigated by using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). The results revealed that MoS2 was uniformly loaded on the surface of CdS, and the XPS measurement discovered strong interactions between CdS and MoS2. The intimate contact is beneficial for the enhancement of the photocatalytic activity. By loading 2.0 wt% MoS2 on CdS, the hydrogen production rate of CdS was enhanced by 17 times. The maximal hydrogen production rate of the composite catalyst reached 4.06 mmol g^-1 h^-1 under visible light irradiation.

Materials and methods

Photocatalytic reaction Photocatalytic hydrogen production reaction was carried out in an online photocatalytic hydrogen production system (CEL-SPH2 N, AuLight, Beijing). 0.1 g MoS2/CdS composite catalyst was suspended in a 100 mL of aqueous solution containing 10 mL lactic acid as sacrificial agent. The solution was then degassed and irradiated by a 300 W Xenon lamp (CEL-HXF300, AuLight, Beijing) with an optical filter (k > 400 nm) to cut off the light in the ultraviolet region. The hydrogen evolution rate was determined using an online gas chromatograph (SP7800, TCD, nitrogen as a carrier gas and 5A molecular sieve column, Beijing Jingkeruida Limited). As a reference, the photocatalytic activity of prepared CdS, pure MoS2 and MoS2 + CdS were also evaluated under identical conditions.

XRD diffraction patterns of hydrothermal synthesized CdS, MoS2 (prepared under the same condition with MoS2/CdS composite catalyst) and MoS2/CdS composite catalysts with different loading amount (0.2 wt%, 0.5 wt%, 1.0 wt%, 2.0 wt%, 5.0 wt%) of MoS2 in the 2h range of 10–80°.

(a) XPS spectra of Mo 3d of MoS2 prepared under the same condition with MoS2/CdS composite catalyst, MoS2/CdS-2.0 catalyst (synthesized by loading 2.0 wt% MoS2 on CdS) and CdS/Na2MoO4 sample (prepared by impregnating Na2MoO4 on CdS with the same amount of the precursors of MoS2/CdS-2.0 catalyst); (b) XPS spectra of Cd 3d of hydrothermal synthesized CdS, MoS2/CdS-2.0 and CdS/Na2MoO4.

Conclusion

 MoS2/CdS composite catalyst has been prepared by a hydrothermal process in this work. The rate of H2 evolution from CdS was significantly enhanced by loading MoS2 as a co-catalyst on it, which was increased by 17 times when CdS was loaded with 2.0 wt% MoS2. The maximal H2 evolution rate was 4.06 mmol g^-1 - h^-1. The heterojunction between CdS and MoS2 were discovered through the various analytical instrument measurements. With the heterojunction, photo-induced electrons from CdS could be transferred to MoS2 effectively and reduce protons to H2. Besides, the cycling experiment showed that the MoS2/CdS composite was a stable catalyst. In conclusion, MoS2/CdS photocatalyst can be successfully prepared with hydrothermal process and the interaction between CdS and MoS2 plays an important role in improving the photocatalytic H2 production activity of MoS2/CdS composite catalyst.