Study On The Synthesis And Performance Of Mn_0.5Cd_0.5S Solid Solution-based Composite Materials

The continuous consumption of fossil fuels promotes the rapid development of society and economy,but leads to the depletion of fossil energy and the aggravation of environmental pollution simultaneously.To solve these problems,scientists have been actively committed to the exploration and development of new energy sources,with a view to replacing traditional fossil energy with high-efficiency,clean and pollution-free new energy Photocatalytic hydrogen production from water splitting is a technology that can produce clean hydrogen energy under the solar irradiation of semiconductors.Photocatalytic hydrogen production technology can effectively convert low-density solar energy into high-density hydrogen energy,and is considered to be an effective strategy to solve the current increasing energy crisis and environmental pollution.As well known,the performance of semiconductor plays the most important role in photocatalytic hydrogen production.Given the large-scale industrial production,preparation of high-activity and high-stability photocatalysts has always been the focus of photocatalytic materials research.In this paper,many strategies including cocatalyst loading,construction of Z-system and p-n heterostructures,etc.,have been adopted to modify Mn_0.5Cd_0.5S solid solution,and the inherent relationship between the microstructure structure and the photocatalytic hydrogen production activity has been clarified based on XRD,XPS,SEM,UV-vis characterizations.The main research contents are as follows:（1）The ternary Mn_0.5Cd_0.5S/CB/CuS composite photocatalyst has been fabricated via ultrasonic method using the as-prepared Mn_0.5Cd_0.5S nanoparticles CuS nanotubes and cheap carbon black（CB）as raw materials.When loading0.5%CB,the as-formed Mn_0.5Cd_0.5S/0.5CB composite exhibit the highest hydrogen production rate of 393.83μmol/h,which is 2.3 times higher relative topure Mn_0.5Cd_0.5S.When further loading2%CuS,the hydrogen production rate of as-formed Mn_0.5Cd_0.5S/0.5CB/2CuS composite reaches 819.94μmol/h,more4.75 times higher than that of pure Mn_0.5Cd_0.5S.The characterization results suggest that the enhanced photocatalytic hydrogen production activity can be attributed to the positive synergistic effect between CB and CuS dual cocatalystswhich can effectively reduce the recombination rate photoinduced electrons and holes and simultaneously promote the H₂-evolution kinetics thereby leading to the enhanced photocatalytic H₂-production performance over Mn_0.5Cd_0.5S.（2）A ternary Mn_0.5Cd_0.5S/CdWO₄/CoS_x composite has been prepared by hydrothermal method using the as-prepared Mn_0.5Cd_0.5S nanoparticles,CdWO₄ nanorods,and CoS_x hollow polyhedrons as raw materials.When loading 30%of CdWO₄,the hydrogen production rate of the as-formed Mn_0.5Cd_0.5S/30CdWO₄ composite reaches the maximum（409.72μmol/h）,which is 2.4 times higher relative to pure Mn_0.5Cd_0.5S.When further loading 3%of CoS_x,the as-prepared Mn_0.5Cd_0.5S/30CdWO₄/3CoSx composite exhibit the optimum H₂-production rate（760.75μmol/h）,more 4.4 times higher than that of pure Mn_0.5Cd_0.5S.The results indicate that the improved photocatalytic activity of ternary Mn_0.5Cd_0.5S/CdWO₄/CoS_x composite is mainly attributed to the Z-system heterojunction formed by Mn_0.5Cd_0.5S and CdWO₄,which can effectively promote the transfer and separation of photogenerated electron-hole pairs.On the other hand,the introduction of hollow polyhedral CoS_x cocatalyst with a larger specific surface are can provide more active sites for the photocatalytic reaction,and further improve the charge separation efficiency as well as H₂-evolution reaction kinetics,thereby significantly boosting the photocatalytic hydrogen production performance.（3）Binary Mn_0.5Cd_0.5S/Cu₃P photocatalytic material has been constructed by ultrasonic method using Mn_0.5Cd_0.5S nanoparticles prepared by hydrothermal method and Cu₃P nanoparticles prepared by high temperature calcination method as raw materials.The study finds that Cu₃P mainly acts as a cocatalyst to improve the photocatalytic hydrogen production reaction when its loading content is2%.At this time,the hydrogen production rate of the obtained Mn_0.5Cd_0.5S/₂Cu₃P composite material reaches 700.38μmol/h,which is 4.0 times higher than that of pure Mn_0.5Cd_0.5S.When the loading content of Cu₃P is 9%,Cu₃P mainly acts as a p-type semiconductor to construct p-n heterostructure with Mn_0.5Cd_0.5S.And hydrogen production rate over the as-formed Mn_0.5Cd_0.5S/9Cu₃P p-n heterostructured photocatalyst reaches 798.01μmol/hμmol/h,more 4.67-folds enhancement than pure Mn_0.5Cd_0.5S.The photoelectric characterization results indicate that Cu₃P acts as a dual role as a co-catalyst and p-type semiconductor during the photocatalytic hydrogen production process.When acting as a co-catalyst,the introduction of Cu₃P is beneficial to capture photogenerated electrons and provide reactive sites for hydrogen evolution reaction,thus leading to the improved photocatalytic hydrogen production performance.When acting as a p-type semiconductor,Cu₃P can couple with Mn_0.5Cd_0.5S to construct p-n heterojunction structure,which can promote the rapid charge transfer and reduce the recombination rate of photoinduced electrons and holes,thereby improve the efficiency of photocatalytic hydrogen production.