เอกสารประชุมวิชาการระดับขาติมหาวิทยาลัยทักษิณ ครั้งที่ 28 2561

925 งานวิจัยและนวัตกรรมเพื่อสังคมที่มั่นคง มั่งคั่ง และยั่งยืน (Research and Innovation for Social Stability, Prosperity and Sustainability) Synthesis of thiol-capped CdTe QDs Thiol-caped CdTe QDs were synthesized following the protocol of a previous work [6]. Briefly, 0.0457 g of CdCl 2 ·H 2 O and 29.6 μ L of TGA were dissolved in 100 mL of deionized water. The mixture solution was adjusted to pH 11.5 with 1.0 mol L -1 NaOH solution. The solution was purged with nitrogen for 20 min, placed in a three-necked flask and refluxed until the temperature was 90°C. Then, 0.50 mL NaHTe in aqueous solution, prepared by mixing 0.0508 g Te powder and 0.0454 g of NaBH 4 in deionized water, was injected into the mixture solution. The resulting solution was refluxed for 10 min. The thiol-capped CdTe QDs were precipitated with ethanol and the excess chemical reagents were eliminated by centrifugation at 5000 rpm for 10 min. Finally, the powder of thiol-capped CdTe QDs was stored in a desiccator until used. Procedure Thiol-capped CdTe QDs were dispersed in 150 µL of 0.2 M phosphate buffer solution (pH 9.0) and mixed with 50 µL of various concentrations of Pb 2+ standard solution or sample solution. After incubation for 1 min, the fluorescence intensity of the mixture solution was measured at room temperature (25ºC). An excitation wavelength was set at 400 nm with the emission range of 480-700 nm. Results & Discussion Characterization of thiol- capped CdTe QDs Synthesized thiol-capped CdTe QDs were optically characterized by UV-vis and fluorescence spectroscopy. The TGA-capped CdTe QDs showed a narrow and symmetrical fluorescence emission spectrum Figure 1A), which indicates that the CdTe QDs were monodisperse and homogeneous. The fluorescence emission peak at 567 nm indicates that the CdTe QDs had good fluorescence properties. The UV-vis absorption spectrum of CdTe QDs shows the absorption maximum at 493 nm. The particle sizes of the CdTe QDs were calculated from the absorption maximum of the UV-vis spectrum according to the following equation: D = (9.8127 × 10 -7 )  3  (1.7147 × 10 -3 )  2  (1.0094)   194.84 (1) where D is the size of the CdTe QDs, and  is the wavelength of the first excitonic absorption peak. The concentrations of the CdTe QDs were calculated using Lambert-Beer’s law; A =  CL, where A is the absorbance of the first excitonic absorption peak, C is the concentration (mol L -1 ) of the CdTe QDs, L is the path length (cm) of the radiation beam used for recording the absorption spectrum, and  is the extinction coefficient per mole of CdTe QDs obtained from the formula  = 10043 (D) 2.12 [8]. The average size of CdTe QDs was estimated to be about 2.14 nm.