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Controlled Synthsis CdTe Nanocrystals By Thio-functionalized Ionic Liquid

Posted on:2014-09-06Degree:MasterType:Thesis
Country:ChinaCandidate:K L DuFull Text:PDF
GTID:2251330401467459Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Ionic liquids (ILs) as a new type of environmentally friendly solvent have shown to be the goodalternatives of the conventional organic solvents, and found wide applications in chemical synthesis,catalysis, separation, and material preparation, owing to their low melting point and vapor pressure, andhigh thermal stability. Currently, many functionalized ILs have been developed widely to meet the specialrequirements in the application fields. In the present work, thio-functionalized ionic liquid was prepared,and used as the surface stabilizer in the synthesis of CdTe nanocrystals. The main contents are as follows:1. CdTe nanocrystals were prepared by the hydrothermal synthesis. Compared with the reflux method,this work showed hydrothermal method can achieve a higher temperature, accelerate the growth rate ofnanocrystals, shorten the reaction time, and reduce the impact of CdTe nanocrystals by the Oswald ripeningprocess.2. The synthesis of CdTe nanocrystals was studied in both H2O-ethylenediamine-IL andH2O-diethylenetetramine-IL systems. According to the experimental results, it is shown that both systemsrequired the same ratio of HTe-/Cd2+=0.2. For the preparation of CdTe nanocrystals, however, the optimalconditions in H2O-ethylenediamine-IL system are react time for6h at160℃and the ethylenediamineconcentration with0.01mol/L; and in H2O-diethylenetetramine-IL system are react time for2h at180℃and the diethylenetetramine concentration with0.0075mol/L.3. The size of CdTe nanocrystals can be controlled by changing the concentration of the ILs in thereaction system. The fluorescence emission wavelength can be regulated from530nm to650nm, cover thecolor range from green to red. The experimental results show that the more the concentration of ILs, thesmaller the radius of nanocrystals. This results from the Cd-S-C10min stable layers on the surface ofnanocrystals, which get thicker with the increase of the concentration of ILs, and limit the ion movementson nanocrystals and hence the growth of nanocrystals.4. Combining the several experimental results from the measurements of XRD, TEM, UV-vis, and PL,it is suggested that the growth mechanism of CdTe nanocrystals possibly is: Cd2+can form a complexeswith the organic amines; the strong basicity in these solutions promotes the mercapto of ILs to substitute the organic amines and produce the complex of Cd-S-C10min. With injection of NaHTe solution, the OH-ofthe solution reacts with the HTe2-to release Te2-, and the Te2-combines with the complex of Cd-S-C10minto form CdTe precursors. After heat treatment, the surfaces of CdTe precursors crystallize and rearrange,CdTe nanocrystals grown in these solutions.
Keywords/Search Tags:Mercapto, Functionalized ionic liquid, CdTe, Nanocrystal, Aqueous synthesis
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