Structure Design,Control Synthesis And Application Of Copper-based Chalcogenide Nanocrystals

Semiconductor nanomaterials have been widely researched due to their special physic and chemistry properties coming from quantum effect.In the past decades,the fabrication and application of semiconductor materials have been rapidly developed.However,the typical semiconductor materials is often difficult to achieve low cost,easy synthesis and nontoxic,which have limited the industrial application.Copper based multinary chalcogenide nanocrystals is a novel semiconductor which can be synthesized in simple methods,consist of abundance elements,exhibit excellent light-harvesting properties,and possess band gap energies that are well-suited for solar photon absorption.The special element composition and crystal structure of copper based multinary chalcogenide nanocrystals lead to the novel physic and chemistry properties.Design rational methods to synthesis of copper based multinary chalcogenide nanocrystals with special structure,composition and morphology is still a challenge.This dissertation will focus on the structure design,control synthesis and application of copper based multinary chalcogenide nanocrystals.We have attained a series of polytypic nanocrystals constructed by zinc belende and wurtzite structure through colloidal method,and studied the effect of polytypic interface in the photoelectrochemical application.On this bases,we have successfully synthesis of copper based quaternary sulfide nanobelts through the synergistic effect of surfactant and precursor,and large-scale synthesis of copper based multinary chalcogenide nanocrystals.The main results can be summarized as follows:1.A colloidal method have been developed to synthesis copper based ternary alloy polytypic nanocrystal.Copper based ternary ?-?-?2 polytypic nanocrystals with different ratio of S/Se have been synthesized through colloidal approach by using diphenyl disenenide as selenium source and sulfur powder as sulfur source.Each obtained polytypic nanocrystal is constructed with a wurtzite hexagonal column and a zinc blende/chalcopyrite cusp,regardless of the S/Se ratio.The growth mechanisms of polytypic CuInS₂ and CuInSe₂ nanocrystals have been studied by time-dependent experiments.The polytypic nanocrystals are solution-deposited on indium-tin oxide glass substrate and used as a photoelectrode,thus showing stable photoelectrochemical activity in aqueous solution.Density functional theory calculation was used to study the electronic structure and the bandgap alignment.2.A common approach have been designed and developed to synthesis of copper based quaternary chalcogenide polytypic nanoctystals.A facile,solution-based approach have been used to the synthesis of polytypic Cu₂CdSn(S_1-xSe_x)₄?CCTSSe?nanocrystals with zinc-belende selectively engineered on?000±2?wz facets of wurtzite cores by using diphenyl disenenide as selenium source and 1-dodecanethiol?DDT?as sulfur source and ligands.Accordingly,two typical morphologies,i.e.,bullet-like nanocrystals with a WZ-derivative core and one ZB-derivative end,and rugby-like nanocrystals with a WZ-derivative core and two ZB-derivative ends,can be selectively prepared.The ratio of rugby-like and bullet-like polytypic CCTSSe nanocrystals can be tuned through changing the amount of Cd precursor to adjust the reactivity difference between?0002?wz and?000-2?wz facets.Cu₂MSnS₄?M=Zn,Cd,Co,Mn,Fe?polytypic nanocrystals have been synthesized by using DDT as sulfur source and ligands.The effect of the amount and kind of mercaptan,solvent,the amount of zinc precursor and temperature for polytypic nanocrytal synthesis have been studied.Compared with wurztite and zinc-blende Cu₂ZnSnS₄,the polytypic nanocrystals have more excellent photocatalytic property and the rugby Cu₂ZnSnS₄ polytypic nanocrystals is the best.It indicates that polytypic interface is beneficial for separation of photoinduced electrons and holes,the separation efficiency increases with the polytypic interfaces,and then the photocatalytic properties can be enhanced.3.A colloidal method is developed to synthesis two dimensional copper based quaternary sulfide nanobelts.Wurtzite Cu-Zn-M-S?M=In,Ga?single-crystalline nanobelts with ca.10 nm thickness and micro length have been synthesize though the synergistic effect of oleylamine and 1-dodecanethiol.Based on the strong absorption in visible light region,the obtained nanobelts was used to photocatalytic water splitting for hydrogen production.When the ratio of ZnS/CuInS₂ is 4,the photocatalytic property of Cu-Zn-In-S nanobelts is the best and revises to 67?mol h-1?30mg?.The hydrogen evolution rate of Cu-Zn-Ga-S nanobelts is 80?mol h-1?30mg?with the same Zn content.4.A colloidal approach have been designed and developed to large-scale synthesis of copper based chalcogenide nanocrystals.Copper based chalcogenide nanocrystals is a kind of important material for energy conversion,so the large-scale synthesis is the bases for industrial application.A series of Cu₂Sn(S_xSe_1-x)₃ alloy nanocrystals have been scale-up synthesized through a hot-injection method by using SeO₂ and S as anion precursors.And then,we have studied the influence of sulfur isovalent substitution of Se for thermoelectric performance of Cu₂SnSe₃ nanocrystals.It indicates that the ZT value is the highest?ZT=0.42 at 380??when the content of S is equal to Se in the products.Monodisperse wurzite Cu₂ZnSnSe₄ and Cu₂CdSnSe₄ nanocrystals have been successfully scale-up synthesized by a hot-injection method by using diphenyl disenenide as selenium source and 1-dodecanethiol as ligands.