Cheng Wei-qing, Liu Di, Yan Zheng-yu
Department of Analytical Chemistry, China Pharmaceutical University, Nanjing 210009, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2008 Jun;28(6):1348-52.
CdS nanoparticles capped by mercaptoacetic acid have been successfully synthesized by microwave method employing thioacetamide as sulfur source, which was proved to be a simple, rapid and specific mothod compared with traditional synthetical methods, such as precipitation, sol-gel, solvo-thermal method and so on. The concrete procedure synthesizing CdS nanoparticles was as follows: Cd(NO3)2 (40 mL, 5 mmol c L(-1)) was titrated with mercaptoacetic acid to pH 2.0, resulting in a turbid blue solution. NaOH (0.1 mol x L(-1)) was then added dropwise until the pH was 7 and the solution was again colorless. While quickly stirring the solution, 40 mL of 5 mmol x L(-1) CH3CSNH2 was added. Subsequently, the solution was adjusted to pH 9.0 and placed in a microwave oven for 25 min with power 30% (it means that if microwave works in a 30 s regime, it works 6 s, and does not work 24 s. This is some kind of pulse regime, but the totalpower is still 100%). This kind of nanoparticles were water-soluble and symmetrical. The diameter of CdS nanoparticles which have a spherical morphology was determined to be 12 nm by transmission electron microscopy(TEM), which posess perfect uniforminty. According to literatures report, there are two kinds of emission peak: one is edge-emission peak, and the other is surface blemish emission. In contrast to edge-emission peak, the surface blemish emission shows red shift on fluorescence spectra. In the present paper, the prominent peak of CdS QDs fluorescence spectrum was located at 490 nm, the humpbacked peak caused by surface blemish of CdS nanoparticles was located at 565 nm. However, the surface blemish emission was unconspicuous, thus we can conclude that the synthetical CdS QDs possesses excellent luminescence capability and favorable structure. The size and absorption and fluorescence spectra of CdS nanoparticles at different microwave power, pH value, reaction time and different sulfur source were investigated. The result showed that the better nanoparticles could be obtained in the condition of 30% microwave power, pH 9.0 at the beginning of reaction, and the time of microwave reaction of 25 min. The synthesized nanoparticles were compared with the nanoparticles with CH3 CSNH2, NH2CSNH2 and Na2S as sulfur source. The experiment indicated that CdS nanoparticles applying CH3CSNH2 as sulfur source showed strong edge-emission, and blemish emission was weak, so the fluorescence quality is excellent; but CdS nanoparticles applying NH2CSNH2 as sulfur source showed weak edge-emission; and CdS nanoparticles applying Na2S as sulfur source showed mainly fluorescence blemish emission. At the same time, the mercaptoacetic acid capped CdS nanoparticles were employed to study the quantitative analysis of Cu2+. According to the results of experiment, in a certain range of concentration(6.4-512 microg x L(-1)), Cu2+ quenched the fluorescence intensity of mercaptoacetic acid capped CdS nanoparticles with good linearity, which can be used in the determination of trace Cu2+ in samples. In conclusion, this kind of method supplied a new way to study synthesizing the CdS nanoparticles.
以硫代乙酰胺为硫源，采用微波法成功合成了巯基乙酸包覆的硫化镉纳米粒子。与传统合成方法（如沉淀法、溶胶 - 凝胶法、溶剂热法等）相比，该方法简单、快速且具有特异性。合成硫化镉纳米粒子的具体步骤如下：用巯基乙酸滴定硝酸镉（40 mL，5 mmol·L⁻¹）至pH 2.0，得到浑浊的蓝色溶液。然后逐滴加入氢氧化钠（0.1 mol·L⁻¹）直至pH为7，溶液再次变为无色。在快速搅拌溶液的同时，加入40 mL 5 mmol·L⁻¹的硫代乙酰胺。随后，将溶液调至pH 9.0，并置于微波炉中以30%的功率加热25分钟（这意味着如果微波炉以30秒为一个周期工作，它工作6秒，不工作24秒。这是一种脉冲模式，但总功率仍为100%）。这种纳米粒子是水溶性且对称的。通过透射电子显微镜（TEM）测定，具有球形形态的硫化镉纳米粒子直径为12 nm，具有完美的均匀性。根据文献报道，有两种发射峰：一种是边缘发射峰，另一种是表面缺陷发射峰。与边缘发射峰相比，表面缺陷发射峰在荧光光谱上表现为红移。在本文中，硫化镉量子点荧光光谱的主峰位于490 nm，由硫化镉纳米粒子表面缺陷引起的驼峰状峰位于565 nm。然而，表面缺陷发射不明显，因此可以得出结论，合成的硫化镉量子点具有优异的发光能力和良好的结构。研究了不同微波功率、pH值、反应时间以及不同硫源下硫化镉纳米粒子的尺寸、吸收光谱和荧光光谱。结果表明，在微波功率30%、反应开始时pH 9.0以及微波反应时间2�分钟的条件下可以获得较好的纳米粒子。将合成的纳米粒子与以硫代乙酰胺、氨基硫脲和硫化钠为硫源的纳米粒子进行了比较。实验表明，以硫代乙酰胺为硫源的硫化镉纳米粒子边缘发射强，缺陷发射弱，荧光质量优异；而以氨基硫脲为硫源的硫化镉纳米粒子边缘发射弱；以硫化钠为硫源的硫化镉纳米粒子主要表现为荧光缺陷发射。同时，采用巯基乙酸包覆的硫化镉纳米粒子研究了铜离子的定量分析。根据实验结果，在一定浓度范围（6.4 - 512 μg·L⁻¹）内，铜离子能很好地线性猝灭巯基乙酸包覆的硫化镉纳米粒子的荧光强度，可用于样品中痕量铜离子的测定。总之，这种方法为研究硫化镉纳米粒子的合成提供了一种新途径。
