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Precise Synthesisand Properties Research Of Ⅱ-Ⅵ Core-shell And Doped Semiconductor Nanocrystals: New Applications Of Cation Exchange Reaction

Posted on:2016-08-09Degree:MasterType:Thesis
Country:ChinaCandidate:J GuiFull Text:PDF
GTID:2298330452965264Subject:Materials Science and Engineering
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In this paper, the semiconductor nanocrystals(NCs) and hybrid noblemetal@semiconductor core-shellNCs were studied. Au@CdX(X means chalcogen)core-shell nanocrystals and heterovalent doped CdS nanocrystals were synthesized by themethods of non-epitaxial growth as well as different phosphines initialized cation exchange.Moreover, research on efficient photocatalytic hydrogen evolution and doped luminescencehad been done.Here, we reported a controllable water-phase synthesis of high crystallineAu@CdScore/shell colloidal NCswith tunable shell thickness, clear interface andsingle-crystalline shell on metal Au core withhigh curvedthree-dimensional surface vianon-epitaxial growth. Underincident lightirridation, localized surface plasmon resonance(LSPR) of Au core can enhancethe charge separation and the injection of electronsto CdSshell. The H2evolution in aqueous solution was measured by exploring the Au@CdS NCswith different shell thickness as photocatalysts. Comparing to the same weight of5nmsized CdS NCsphotocatalysts, as-preparedAu@CdS NCs with35nm sizedAu core and5nm thickness shell have enhancedH2evolution activity (24mmol.h-1.g-1) that manifested adramatic enhancement of~1000times. In addition, with the increasing ofshell thickness,the LSPR of Au@CdSNCs become weakgradually. Based onfinite difference time domain(FDTD) simulation calculation and experimental confirmations,wefound that high efficientphotocatalytic hydrogen evolution was dueto the dominant role of plasmon enhancement.The thermodynamicsand kinetics of cation exchangereaction were tailored moreflexiblyby taking advantage of different kinds of phosphine initialization.Due to theirdifferent σ-donating capabilities to transitional metal ions and the steric effect derived fromcarbonyl ligands, traditional cation exchange reaction could be particularly used tosynthesize semiconductor nanostructures with more flexible degree control ofcrystallization, composition, morphology and related optical properties,especiallynew-emerging metal/semiconductor core/shell nanocrystals and dopednanocrystals. In contrast of widely used tributylphosphine (TBP), triphenylphosphine (PPh3)was found as a green and air-stable alternative to initiate cation exchangereaction tosynthesize Au@CdS, Pt@CdS core/shell NCswith bettercrystallization.Futhermore, PPh3could also make more complex hetero-NCssuch as Au@CdS1-xSexwith precisecompositional tailoring. Especially, it is provided that doped semiconductor NCs withprecise control of heterovalent doping and dopant related fluorescencewere realized by different phosphine initialized cation exchange reaction.
Keywords/Search Tags:Core-shell nanocrystals(NCs), Localized surface plasmon resonance (LSPR), Photocatalytic hydrogen evolution, Cation exchange, Phosphines, Doped nanocrystals, Doped luminescence
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