Preparation And Photocatalytic Hydrogen Production Of MoS₂,CdS And Their Composite

Photocatalytic hydrogen production from water splitting has potential application in solving the problems of energy crisis and environmental pollution.While up to now,development of efficient,stable and low-cost photocatalysts is still a key challenge impeding its practical application.Among various semiconductor materials,molybdenum disulfide?MoS₂?with two-dimensional layered structure is considered as one of the most promising photocatalysts for hydrogen evolution reaction?HER?originating from its low cost,non-toxic natures.Simultaneously,in view of the unique band structure?band gap is 2.4 e V?and good visible-light response,cadmium sulfide?CdS?is also an excellent semiconductor photocatalytic material with great attention.However,both of these two catalysts have some shortcomings,such as poor conductivity and fast recombination of electrons and holes.It leads to low photocatalytic performances and can't meet the needs of practical application.Then in this article,on one hand,activated carbon?C?with good conductivity was in-situ introduced into MoS₂.On the other hand,based on the successful synthesis of cubic CdS by precipitation method,a three-component composite was obtained by combing the in-situ formed CdS with MoS₂/C,so as to obtain excellent photocatalytic materials.The specific contents are as follows:?1?Through in-situ introduction of activated carbon?C?during the liquid-phase synthesis process of MoS₂,a MoS₂/C composite was prepared.The morphology and structure of the composite were characterized by XRD,TEM,XPS,etc.Under LED light irradiation,the hydrogen evolution performance was determined by using erythrosin B sodium salt?EB?as photosensitizer and triethanolamine?TEOA?as sacrificial agent,respectively.The results showed that the photocatalytic hydrogen production performance of the MoS₂/C sample is much higher than that of pure MoS₂.The highest H₂ evolution rate of MoS₂/10%C was up to 872.3?mol/h,approximately 1.8 times that of pure MoS₂.At the same time,the stability of composite catalyst was determined.The reasons for the enhanced photocatalytic performance of MoS₂/C and the hydrogen evolution mechanism of the system were preliminarily studied.?2?Cubic CdS was obtained by a simple liquid-phase precipitation method and the effects of ratio of Cd to S in the starting materials and the sedimentation time on the photocatalytic performances of CdS were investigated.In addition,XRD,SEM,TEM and XPS technologies were used to characterize the crystalline phases and microstructures of the samples obtained under different conditions.The results showed that when the ratio of Cd to S is 5:8 and sedimentation time is 6 h,the obtained CdS exhibits the best hydrogen evolution activity of 37.6?mol/h.?3?By using MoS₂/10%C?denote as MC?as a co-catalyst,a ternary composite CdS-MC was obtained by in-situ liquid phase precipitation method and characterized by XRD,SEM,TEM,etc.Irradiated by LED light and using lactic acid as sacrificial agent,its photocatalytic hydrogen evolution performance and stability were studied in detail.The results indicated that MC loading can significantly improve the photocatalytic hydrogen evolution performance of CdS.When the loading content of MC was 10 wt%,the photocatalytic H₂ evolution rate was up to 879.6?mol/h,which was 23.3 times that of pure CdS.Cyclic hydrogen evolution test showed that the catalyst has poor stability,and the stability can be improved with the modification of4-mercaptobenzoic acid?4-MBA?,although the photocatalytic performance decreased.In addition,a composite catalyst of hexagon CdS?named CdS-MC-h?obtained by calcining under nitrogen atmosphere had good stability,but its performance was very low.The maximum hydrogen evolution rate was only 265.6?mol/h.