Controllable Synthesis And Optoelectronic Properties And Applications Research Of Metal/Semiconductor Hetero-Nanocrystals Via Ions Exchange Reaction Method

Ions Exchange Reaction?IER?is one of traditional molecular reaction among molecular in inorganic synthetic chemistry and coordination chemistry.As the“old conception and new applications”,it became a flexible and controllable strategy for synthesizing semiconductor-based nanocrystals in recent years.In this dissertation,thermodynamics and kinetics of IER was taken into account to prepare metal/semiconductor hetero-nanostructure.Based on the exploration of the effect of ligands,high pressure and temperature,several novel semiconductor hetero-nanocrystals were synthesized via IER.The mechanism and versatility of IER in preparing of new semiconductor hetero-nanostructures were discovered and their optoelectronic properties was investigated.The main results were as following:1.High-pressure induced solid phase transition of Au@CdS core/shell nanocrystals prepared via IERAu@CdS core/shell nanocrystals were treated under high pressure and its CdS shell transited from wurtzite phase into rocksalt phase graually.By employing ADXRD,it was found that the phase transition pressure?5.5-9.4 GPa?was higher than pure CdS.During the phase transition,Au@CdS core/shell nanocrystals still remained its structure and mono-crystalline shell.Raman scatting characterization reveled some fine structure of CdS structure might change before the phase transition.2.Morphology and composition tailoring as well as photothermal application in NIR range of Au@Cu_2-x S core/shell nanocrystals prepared via CERBy using CER,in-situ reaction was carried out employing Au@CdS nanocrystals and Cu⁺to form Au@Cu_2-x S core/shell nanocrystals with monocrystalline shell.Characterized by HRTEM and Scanning transition electron microscopy?STEM?,mono-crystalline shell and tight connecting of Au and core were proved.The optical properties of Au@Cu_2-x S core/shell nanocrystals could be tuned by precisely controlling its shape and their resonance absorption of Au and Cu_2-x S in near infrared range?800–1200 nm?was enhanced.Both experiment data and theory simulation proved that two kind of surface plasma resonance affection reacted each other.Hence,affective photothermal transition was obtained in Window I?750–900 nm?and Window II?1000–1400 nm?in NIR range and their efficiency reac hed up to 59.01%and 43.25%under irradiation of 808 nm laser?1 W/cm²?and 1064 nm laser?0.7 W/cm²?respectively.It was found that it can be applied on photothermal therapy and killing HaLe cells affectivly.3.Preparation of Au/CdS heterodimer via thermodynamic and kinetic controlling of CERIn this study,kinds of phosphine ligands containing lone-pair electron were employed for CER:Ag₂S+Cd²⁺?CdS+Ag⁺.Followed by their thermodynamics,kinetics and reaction process were studied during the prepar ation of semiconductor nanocrystals.The results showed that the formation of?bonding and?backbonding as well as stereo-hindrance effects played key roles in activities for driving CERs.By comparing ³¹P NMR spectrum of various coordination complexes produced in the formation of nanocrystals,the difference of coordination between cations and phosphine ligands were obtained and it showed new principle of phosphine driving CERs to prepare semiconductor nanostructures.Taking advantage of the temperature effects on kinetics of CERs,amorphous or crystalline Ag2S media were controlled and combining with CERs and utilizing the strain difference on the interface,the in-situ morphologyevolution of Au/CdS hetero-nanocrystals was tailored from centric core/shell nanostructure to heterodimer.The changes of structure lead to different Plasmon/exciton coupling affection.Applied on photocatalysis of water splitting and hydrogen evolution,the hydrogen evolution rate of Au/CdS heterodimer was up to 7.3 mmol·g^-1·h^-1 and 700 times as that of core/shell nanostructure.Namely,the different nanostructure resulted in the different electron-transition director and affection on the metal/semiconductor interface.4.Preparation of hollow and Yolk-shell nanostructure by using CER method and its universalityCER was extended to oxides semiconductor nanostructure,then hollow and Yolk-shell nanocrystals was prepared by utilizing IER between Cu₂O nanocrystals and S^2-ions and CER with Cd²⁺.And kinds of nanostructures were synthesized:semiconductor hollow nanostructure?Cu₂ShollownanocrystalsandCdShollownanocrystals?,semiconductor/semiconductoryolk-shellnanostructure?Cu₂O@Cu₂Syolk-shell nanocrystals and Cu₂O@CdS yolk-shell nanocrystals?,metal/semiconductor yolk-shell nanocrystal?Au@Cu₂S Yolk-shell nanocrystals,Au@CdS Yolk-shell nanocrystals?.5.Preparation of 2D single-crystalline nanosheets by aqueous ions-oxidation corrosionCER between soft acid-soft base was extend to that between hard-acid and hard-base in aqueous solution and 50 nm of Bi₂Te₃ single crystalline nanoplate was exfoliated layers by layers into 1.2 nm ultrathin Bi₂Te₃ single crystalline nanosheet by using ions-oxidation corrosion.Combining with the characterization HRTEM,atom force microscopy?AFM?,X-ray powder diffraction?XRD?and Raman scattering,the process of exfoliation layers by layers and the relationship of mechanism and Bi₂ Te₃ nanostructure were discovered.By employing various of oxidized reagents for controlling morphology of Bi₂ Te₃ nanopalte,the same results were obtained and that showed universality of morphology controlling of Bi₂Te₃ nanoplate via ions corrosion.