Synthesis And Hydrogen-production Performance Of Amorphous Molybdenum Sulfides-based Photocatalytic Materials

Exploiting novel and high-performance electron-cocatalysts without noble metallic element is of great significance for photocatalytic H2-evolution reaction.Molybdenum sulfide is one of the most promising candidates of such electron-cocatalysts.However,its present performance is still very limited due to its poor electrical conductivity and the scarce active sites of unsaturated S atoms.Therefore,to further improve its electron-cocatalyst performance,this study mainly focuses on the synthesis,microstructure characterization,photocatalytic hydrogen-production and mechanism of the molybdenum sulfide-based photocatalytic materials,namely,?1?constructing amorphous molybdenum sulfide cocatalyst with rich unsaturated S-atom active sites for enhanced photocatalytic H₂-evolution performance,?2?establishing homogeneous molybdenum-based bimetallic sulfid cocatalyst to tune the microstructure and photocatalytic H₂-evolution activity of the host material.The main results could be summarized and shown as follows:First,tuning the microstructure of molybdenum sulfide with more unsaturated S atoms is one of the most effective methods to improve its cocatalytic performance.In this study,the amorphous MoS_x nanoparticles,as a new and highly efficient electron cocatalyst,have been successfully loaded on the g-C₃N₄ surface via an adsorption-in situ transformation method.It was found that the photocatalytic activity of g-C3N4photocatalyst could be obviously improved by loading amorphous MoS_x nanoparticle cocatalyst,which is obviously higher than the that of well-known crystalline MoS₂-modified g-C₃N₄ by a factor of 5.42 times.More importantly,in addition to the g-C₃N₄,the amorphous MoS_x nanoparticles could also work as the efficient electron cocatalyst to greatly enhance the photocatalytic performance of conventional H2-evolution materials such as TiO2 and CdS.Based on the above experimental results,a possible electron-cocatalyst mechanism of amorphous MoS_x was proposed to account for the improved photocatalytic H₂-evolution activity of various photocatalytic materials.Namely,compared with the crystalline molybdenum sulfide,the amorphous MoS_x can provide more unsaturated active S atoms as the efficient active sites to rapidly capture protons from solution,and then promote the direct reduction of H⁺to H₂ by photogenerated electrons.Second,constructing homogeneous molybdenum-based bimetallic sulfid is one of the most significant and effective methods to optimize its electronic and surface structures for enhanced photocatalytic H₂-evolution performance.In this study,the a-CoMoS_x/CdS photocatalyst with obviously improved photocatalytic performance was synthesized by a facile photo-deposition method.The result showed that the a-CoMoS_x/CdS?Co:Mo=1:2?photocatalyst exhibited the highest photocatalytic H₂-evolution activity,which is significantly higher than that of pure CdS,a-MoS_x/CdS,Co?II?/CdS and Pt/CdS by a factor of 26.18,3.08,7.51 and 5.45 times,respectively.More importantly,in addition to the CdS,the a-CoMoS_x nanoparticles could also work as the efficient electron cocatalyst to greatly enhance the photocatalytic performance of TiO₂ and g-C₃N₄ materials.In addition,the other Mo-based bimetallic sulfides?a-MMoS_x,M=Zn,Ni and Ag?have also been loaded on the CdS surface and the resultant a-MMoS_x/CdS showed an obviously enhanced photocatalytic H₂-evolution performance.Based on the photo-electrochemical?PEC?characteristic results,it can be found that a-MMoS_x not only can rapidly transfer photogenerated electrons,but also can provide more active sites,to obviously improve the photocatalytic H₂-evolution performance.