Preparation Of Graphene/MoS₂/Sulfide Photocatalysts And Their Applications In Hydrogen Evolution

The issues of energy crisis and environmental pollution caused by thecombusting of foil fuels has draw much attention, and a new type of energy sources iscalled for replacing the blank. Among all new technologies, semiconductorphotocatalysis provides a new solution for converting the solar energy to chemicalenergy.Metal sulfides, a kind of semiconductor always with high photocatalyticefficiency, were widely studied due to their excellent physical and chemicalproperties. Among them, ZnS and CdS have been intensively investgitated. Withsuitable bandgap and excellent reduction potential, these two semiconductors owngreat advantages in photocatalytic hydrogen evolution. Graphene is a kind of carbonmaterials with a lamellar structure and an excellent electronic conductivity, resultedfrom the conjugated monolayer containing the sp2hybridization of carton atoms. Itendows Graphene play obvious action in the enhancement of the charge-carriersseparation. MoS2, a lamellar material, has demonstrated that its edges own greatreducing capacity of proton, and more MoS2edges would obtained by exfoliation.In this dissertation, the composite materials GO/MoS2/ZnS, GO/MoS2/CdS andGO/MoS2/Cd0.2Zn0.8S were successfully prepared under hydrothermal conditions,where GO nanosheets were used as the crystallized platform for the nanoparticles ofsulfides and the deposited platform for MoS2nanosheets. The as-prepared compositeswere well characterized by the means of XRD, TEM, SEM, UV-vis DRS, XPS andother technologies, and their photocatalytic activity in the hydrogen evolution fromwater were evaluated.TEM and SEM showed that the nanoparticles of composite materials grow onthe surface of graphene uniform, whereas the MoS2nanosheets disperse betweenthem. Such structure led to the formation of the homogeneous heterojuctionphotocatalysts, in which the metal sulfide as the active component and the GO andMoS2nanosheets as the cocatalysts. Such heterojuctions provide several solutions forthe transportation of electrons, resulting in the enhancement of photocatalytic activity in the hydrogen evolution. The results of UV-vis DRS demonstrated that both of thegraphene and MoS2nanosheets broaden the absorption range of the compositematerials by red-shifting their absorption edges, and improve the absorptionintensities of the composites. XPS revealed that the efficient heterojuction has formedbetween the components in the composites, which is benefit for the separation of thecharge carriers. The transient photocurrent responses and the hydrogen productionevaluation demonstrated that the addition of graphene and MoS2improve the transferrates of charge carriers. The synergistic effect among graphene, MoS2nanosheets andmetal sulfides will further inhibit the charge recombination, leading to higherhydrogen-production rates in the reaction of the hydrogen evolution from water.Among all the as-synthsized materials, the hydrogen production of GO/MoS2/ZnScontaining0.25wt%GO and2atom%MoS2is2258mol·h-1·g-1under theirradiation of xeon lamp，GO/MoS2/CdS with0.1wt%GO and1atom%MoS2showsat511.6mol·h-1·g-1under the excitation of visible light, and GO/MoS2/Cd0.2Zn0.8Swith0.5wt%GO and1atom%MoS2shows at4556mol·h-1·g-1under the irradiationof xeon lamp. This study shows that the graphene and MoS2served as cocatalyst willsuppress the photocorrosion of metal sulfide which result in the composites anefficient photocatalysts with excellent stability and repeatability.