Preparation And Photocatalytic Hydrogen Production Of MoS₂/CN And Composite With CdS

Hydrogen production form water splitting driven by solar energy is considered to be one of the effective ways to solve the problems of energy shortage and environmental pollution.For many years,people have been committed to the development of cheap,stable and efficient photocatalytic materials.Among various semiconductor photocatalytic materials,graphite carbon nitride(CN)and cadmium sulfide(CdS)are favored by researchers due to their low cost,suitable band structure and good visible light absorption.Molybdenum disulfide(MoS2)is a promising photocatalytic material owing to its excellent performance for hydrogen evolution and good photostability.Up to now,many investigations on the photocatalytic hydrogen production of MoS2/CN and MoS2/CdS composites have been reported.However,most of the MoS2/CN composites were prepared by two-step methods and the activity is still not too high.For the photocatalytic hydrogen evolution of MoS2/CdS materials,most of the studies focused on the more stable hexagonal CdS and research on the easily prepared cubic CdS is still rare.In addition,researches on improving the photostability of cubic CdS-based catalysts are also needed.Based on the above aspects,in this paper,composite of MoS2 and CN was prepared by a simple one-step reaction and the obtained MoS2/CN has an excellent photocatalytic hydrogen production performance.Then by an in-situ precipitation at room temperature,cubic CdS was combined with the MoS2/CN and the ternary composite catalyst MoS2/CN/CdS with excellent performance and good stability was successfully prepared.The specific research contents are as follows:(1)Binary composite MoS2/CN was obtained by one-pot calcination of melamine and molybdenum trisulfide(MoS3)under N2 atmosphere and characterized by XRD,SEM,TEM,XPS to get its particle size,crystal phase and microstructure.The photocatalytic hydrogen production performance was studied by using LED lamp as light source,erythrosin B sodium salt(EB)as photosensitizer and triethanolamine(TEOA)as sacrificial agent.The results showed that the hydrogen evolution activity of CN is significantly improved by the introduction of MoS2 and the optimum loading amount of MoS2 was 43 wt%.The average hydrogen production rate of 43%MoS2/CN is 1091.2 μmol·h-1,about 330 times that of pure CN.In addition,the activity of MoS2/CN obtained by this one-pot method is significantly higher than that of MoS2/CN obtained by other three conventional methods.Based on the results of fluorescence quenching experiments and photoelectrochemical tests,the hydrogen production mechanism of MoS2/CN sensitized by EB was proposed.The high performance of MoS2/CN is attributed to the intimate interface between MoS2 and CN and the thin layered structure of MoS2,which not only lead to the separation of photogenerated carriers and effectively inhibit the recombination,but also provide sufficient active sites for catalytic reaction.(2)Ternary composite material MoS2/CN/CdS was obtained through in-situ precipitation of cubic phase CdS on the 43%MoS2/CN at room temperature and characterized by XRD,TEM,UV-Vis DRS,etc.By using lactic acid as sacrificial agent,its photocatalytic hydrogen production performance was measured.The results indicated that the hydrogen production activity is the highest when the loading content of MoS2/CN is 10%.The average hydrogen production rate reaches 1253.2 μmol·h-1,about 110 times that of pure CdS.Cyclic hydrogen evolution experiments showed that although the photocorrosion of CdS makes a decrease in the hydrogen production activity of the second cycle,the introduction of CN can effectively inhibit the recombination of photogenerated electrons and holes and then the hydrogen production performances of the last three cycles are remained.Besides,the hydrogen production mechanism of MoS2/CN/CdS was preliminarily speculated.