Wet-Chemistry Preparation And Photoelectric Properties Of Sb₂E₃ （E=S,Se） Nanorods

Group V-VI compounds（V=Sb,Bi;VI=S,Se,Te）are a class of narrow band gap semiconductor materials（E_g=0.1–1.89 e V）,which has abundant earth reserves,low toxicity,long carrier lifetime,high light absorption coefficient(>10⁵ cm^-1),combined with high carrier mobility,excellent photoconductivity and chemical stability.It can generate photoelectric response in the wide spectrum from visible light to near-infrared,and has broad application prospects in photodetection,solar cells and ion batteries,photocatalysis,thermoelectric cooling devices,thin film transistors,phase change memory applications,optical devices and other fields.Especially in its orthorhombic crystal structure,this type of compound presents a one-dimensional chain structure along the[001]crystallographic direction,so that crystal growth often forms highly anisotropic one-dimensional nanowires or nanorods.Based on the background of the above topic selection,this thesis takes antimony-based sulfur/selenium compounds as the research object,mainly exploring new methods of synthesis of Sb₂Se₃,Sb-Se-S and Sb₂S₃ nanowires/rods,studying the growth mechanism,characterizing the optical band gap of the product and photoelectric response performance in the visible-near infrared region.Based on the cation exchange reaction,this paper also conducted a preliminary chemical conversion study of Sb₂Se₃ nanorods to Cu_2-xSe nanorods.The results confirmed the possibility of rod-rod conversion and proved a feasible path for precise preparation of nanorods/wires.1.Using potassium selenocyanate（KSe CN）as a novel molecular selenium source,uniform Sb₂Se₃ nanorods were synthesized by the reflux method,and the phase structure,chemical purity and element chemical state,optical absorption and photoelectric properties of the substance were characterized in detail,which indicate that the product has good optical conductivity and broad spectrum absorption（E_g=1.35e V）.At the same time,the molecular reaction mechanism of the new selenium source is proposed,which involves the thermal decomposition and rupture of the Se-CN bond,releasing elemental Se（0）,and then thermally reducing by oleylamine to generate Se^2-anions,and the formation of metal selenide precipitates will accelerate the reaction process.In addition,the SEM and TEM morphology analysis of the products with different reaction time showed that the product was completely transformed from the coexistence state of nanorods and nanotubes to the growth process of nanorods.The photoelectric test evaluated the photoelectric performance of the material and showed good photocurrent enhancement and light stability.2.Selenium disulfide（Se S₂）was used as the single selenium/sulfur source to prepare ternary Sb-Se-S nanorods.In the study,the molar ratio of Se S₂/Sb Cl₃precursor（0.5:1,1:1 and 1.5:1）was adjusted,and Sb-Se-S alloy nanorods with uniform morphology and size and different Se/S content were prepared by the reflux method.As the molar ratio of the precursor increases,the length×diameter of the resulting nanorods and the corresponding lattice parameters increase,while the band gap（E_g）decreases.The EDS micro-element analysis results based on a single nanorod showed that when the molar ratio of the precursors is higher（1:1 and 1.5:1）,the inhomogeneous distribution of Se and S elements appears which is specifically reflected that S is concentrated in the center of the nanorods,and the content gradually decreases from the center to the edge,but Se mainly occupies both ends of nanorods.Based on the growth kinetics of nanorods,the paper further explained the reasons for the inhomogeneous distribution of Se and S elements,including the order and rate of generation of H₂S(S^2-)and H₂Se(Se^2-),the volatility of H₂S and H₂Se,and the difference in K_sp between binary Sb₂S₃ as well as Sb₂Se₃ and the difference in the growth rate of nanorods driven by the anisotropy of the crystal structure in their axial and radial directions.Photoelectric tests showed that Sb-Se-S nanorods exhibit good photoelectric response performance and photochemical stability in the visible spectrum.3.In the liquid phase reaction system of oleylamine-dodecanethiol,the Sb₂Se₃nanorods synthesized in the first part and Cu⁺are used for cation exchange reaction(Sb³⁺→Cu⁺),which are converted into cubic phase Cu_2-xSe nanorods.Combined with EDS-mapping analysis,it was proved that the cation exchange reaction preferentially proceeds at both ends of the Sb₂Se₃ nanorods grown in the[001]crystal orientation,and then produces axial Sb₂Se₃-Cu_2-xSe,Cu_2-xSe-Sb₂Se₃-Cu_2-xSe mesophase of heterostructure,in which Cu_2-xSe is concentrated at one or both ends of the Sb₂Se₃nanorods,and it proves the high reactivity and intermediate transition morphology at both ends of the nanorods.Based on the different coordination and chelation capabilities of the amine-thiol system for Sb³⁺and Cu⁺ions,the thermodynamic and kinetic reasons for the Sb³⁺→Cu⁺cation exchange reaction were preliminarily discussed,in order to extend it to other cation exchange reaction processes and realize the chemical transformation of more nano-material systems.In addition,the optical absorption and photoelectric properties of Cu_2-xSe nanorods were also evaluated.