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摘要
Water-dispersible ZnS:Mn nanocrystals were synthesized by capping the surface with cysteamine (Cyst) molecules at three different pH conditions (pH 6, 9, and 12). The selected pH conditions were closely related to the isoelectric point (pKa(1) = 8.21, and pKa(2) = 10.26 for the cysteamine in water) of the capping ligand. The obtained ZnS: Mn-Cyst nanocrystals were physically and optically characterized by spectroscopic methods. The UV-Visible absorption spectra and room temperature photoluminescence (PL) emission spectra showed broad peaks at 325 and 580 nm respectively. The calculated relative quantum efficiencies compared to a commercial organic dye standard were in the range 2.1 to 3.1%. The average particle sizes measured from the HR-TEM images were 3.50 nm, which were also supported by the Debye-Scherrer calculations using the XRD data. Moreover, the surface charges of the corresponding ZnS: Mn-Cyst nanocrystals were determined by the electrophoretic method, indicating different surface charge values accordingly the preparation conditions of the nanocrystals: (+) 12.32 mV (pH 6), (+) 0.22 mV (pH 9), and (+) 6.39 mV (pH 12). The degrees of aggregation of the nanocrystals in aqueous solutions were determined by the hydrodynamic light scattering method. As a result, the formation of agglomerates in water with various sizes from 40 to 7500 nm for the ZnS: Mn-Cyst nanocrystals were observed at room temperature. Finally, the relative photocatalytic efficiencies of the ZnS: Mn-Cyst nanocrystals were evaluated by measuring the degradation rate of an organic dye (methylene blue, MB) molecule under the UV-visible (white) light irradiation. As a result, the ZnS: Mn-Cyst nanocrystal prepared at the pH 6 showed the best photodegradation efficiency of the MB molecule with a pseudo first-order reaction constant (k(obs)) of 2.2x10(-3) min(-1).
- 出版日期2016-10
