Construction And Performance Of Metal Chalcogenide Cluster-based Photocatalysts

With the rapid growth of global population and the development of world economy,issues such as energy shortage and environmental pollution have been becoming more and more prominent.It is urgent to change the existing energy structure and develop clean,pollution-free,and renewable energy.Hydrogen energy,as a kind of efficient,clean,and pollution-free secondary energy,has been widely concerned.Solar water splitting is one of the most important ways to produce hydrogen energy.While,the key is to develop excellent semiconductor photocatalysts.An excellent semiconductor photocatalyst usually includes the following characteristics:wide light absorption range,suitable position of valence and conduction band,fast photo-induced carrier separation,and rapid surface reaction.Among them,photogenerated carrier separation plays a decisive role in improving the photocatalytic performance.At present,common methods to accelerate carrier separation include:heter-elements doping,heterjunction photocatalysts,co-catalysts engineering.The heter-elements doping can form specific dopants or defects in the photocatalysts to capture photogenerated electrons or holes to accelerate the carrier separation to improve the photocatalytic performance.The heterjunction photocatalysts is to use the different functions between semiconductors to achieve the separation of photogenerated electron-hole pairs for better photocatalytic performance.Last,co-catalysts engineering can reduce the catalytic overpotential to improve the utilization of photogenerate carrier by speeding up the surface reaction,then achieve high-efficiency photocatalytic performance.Metal chalcogenide clusters,as an important branch of metal sulfide,not only inherit the excellent light absorption and semiconductor properties,but also exhibit unique characteristics in terms of structural accuracy,uniform size and tunability,component diversity,and so on.At present,most researches on metal chalcogenide clusters in the field of photocatalysis focus on optimizing the photocatalytic activity by regulating the internal components,while had insufficient attention on developing excellent strategies for better carrier separation efficiency.Herein,we selected metal chalcogenide clusters as the main research subject,and made full use of the characteristics of precise cluster structure,multi-component coexistence,and surface charge-richness to make metal chalcogenide clusters into a series of excellent photocatalysts through post-treatment or other methods,and also progressed to explore the specific photocatalytic mechanism.The research contents are as follow:(1)Taking advantage of precise structure and the coexistence of multiple components inside metal chalcogenide clusters,interstitial oxygen-doped CdxZn1-xS solid solution with rich S vacancies was fabricated by pyrolyzing the mixture of oxygen-containing chalcogenide microcrystals(ZSP)and CdCl2 salt.By reasonably controlling the pyrolysis temperature,the oxygen components inside ZSP clusters were successfully converted into interstitial oxygen dopants in CdxZn1-xS photocatalysts.The as-prepared CdxZn1-xS photocatalyst contains both interstitial oxygen and accompanied sulfur vacancies.Further research showed that these two kinds of defects formed new intermediate energy levels near the valence band of the solid solution and between the conduction band and the Fermi level,respectively,which can effectively trap holes and electrons to accelerate the photogenerated carrier separation in the photocatalytic process,and improved photocatalytic hydrogen evolution performance.(2)Taking advantage of the surface charge-richness characteristics of metal chalcogenide clusters,a nano-heterojunction photocatalyst(ZIS-MSB)with unique external electric field(EEF)was successfully fabricated by chemically loading positively-charged clusters([Mo3S7]4+)on the S-Zn side of asymmetric ZnIn2S4(ZIS)monolayers.The EEF allowed the control of charge separation,transportation and transfer at the atomic level.The photogenerated electrons from the ZIS were first driven to the S-Zn side by positively-charged[Mo3S7]4+ and further transferred to[Mo3S7]4+for reduction reaction via the Mo-S bonds between ZIS and[Mo3S7]4+.Meanwhile,the holes were transported to the S-In side to oxidize TEOA scavenger.The optimized ZISMSB nano-heterojunction exhibited a PHE rate(6.44 mmol g-1 h-1)that was four times higher than pristine ZIS(1.6 mmol g-1 h-1).(3)Taking advantage of the precise clusters structure,the Pt1 single atoms are anchored by the determined positions,which was used as a cocatalyst to improve the photocatalytic performance of ZnIn2S4.Firstly,the negatively charged T2 cluster(Ge4S104-)was anchored on the sulfur vacancy(Vs)of ZnIn2S4 by electrostatic selfassembly method to form[1Vs-1T2]2-(Vs-T2)photocatalyst.Subsequently,Pt1 single atom was stabilized on the surface of T2 cluster by photodeposition to form Vs-T2-Pt1 photocatalyst.This photocatalyst showed excellent PHE performance.On the one hand,Pt1 single atom as a cocatalyst accelerated the surface reaction and reduced the photocarrier recombination during photocatalytic process.On the other hand,the interaction between T2 and monatomic Pt1(Ge-S-Pt bonds)may change the electronic structure of Pt1,which greatly improves the photocatalytic activity of Pt1 and reduces the reaction barrier.This paper not only expands the application of metal chalcogenide clusters in the field of photocatalysis,but also provides a new way to develop the relationship between the physicochemical properties and photocatalytic performance of metal chalcogenide clusters.