Study On CdS Semiconductor Quantum Dots Synthesized In Aqueous And Performance

In recent years, semiconductor quantum dots have received much attention dueto their excellent optical properties and catalytic activity based on their quantumeffect. Although the preparation technology has gained great improvements during thepast years, but the surface of quantum dots prepared in the aqueous have many defects.These defects lead to broad half-peak width and low fluorescence quantum yield.To obtain a high fluorescence quantum yield, water-soluble CdS quantum dots（QDs） were prepared, characterized and explored in their fluorescence performanceand catalytic activity. Firstly, the CdS QDs with high dispersion, water solubility andexcellent fluorescence performance, were prepared in the aqueous phase. Cadmiumchloride and thiosemicarbazide were used as cadmium source and sulfur sourcerespectively. The CdS QDs were characterized by X-ray diffraction （XRD） andtransmission electron microscopy （TEM）. Based on the fluorescence spectrumanalysis, the optimum preparation conditions were determined as follows: the ratio ofCd²⁺and S^2-is1:1, the amount of thioglycollic acid （TGA） is20μl, pH11.0, thereaction temperature is80℃and the reaction time is1h. Secondly, In order to studymodification of QDs with polymers, the fluorescence change were studied inpolyvinylpyrrolidone （PVP） media. The fluorescence intensity of CdS QDs increaseto as high as20%in PVP media, compared with that of QDs in aqueous media. Theoptimum preparation conditions were determined as follows:the concentration of CdSis3.0g·L^－1, the concentration of PVP is1.0g·L^－1, the wavelength excitation light is330nm. PVP modified the CdS QDs has reduced surface defects.Finally, the CdS nanoparticles were prepared by precipitation method inaqueous condition, and characterized by X-ray diffraction （XRD）, X-rayphotoelectron spectroscopy （XPS）, scanning electron microscope （SEM）, andtransmission electron microscope （TEM）. The photocatalytic degradation ofrhodamine B （RhB） and methylene blue（MB） was used as probe reactions toevaluate the photocatalytic activities of the catalysts under visible light by tracing theUV-Vis spectrum. The results indicated that the CdS nanoparticles responde well tovisible light nce and photocatalytic activity. The UV-Vis absorption spectra weremeasured under different irradiation time during the photocatalytic process. Theexperimental result indicated that photodegradation mechanism of the RhB mainlyinvolved the break down of benzene ring in RhB together with de-ethylation process,and the degradation of MB involved the process of oxygenolysis.