纳米钛酸钙粉体的制备及其对水中铅和镉的吸附行为

采用柠檬酸络合溶胶-凝胶法制备了纳米钛酸钙粉体. 以X射线衍射(XRD)、透射电子显微镜(TEM)和傅立叶变换红外光谱(FTIR)对其进行了表征. 考察了该纳米粉体对水中重金属铅和镉的吸附性能, 并以镉离子为例, 系统地研究了吸附热力学和动力学. 结果表明, 该法合成的钛酸钙为钙钛矿结构的纳米粉体, 粒径大小受灼烧温度的影响, 灼烧温度越高, 粉体平均粒径越大, 600 ℃灼烧2 h条件下, 粉体的平均粒径最小, 约为20 nm. 当介质的pH值为4～8时, 钛酸钙对水中的铅和镉具有很强的吸附能力. 其对镉离子的吸附行为符合Langmuir 吸附等温模型和HO准二级动力学方程式, 吸附过程焓变(ΔH)为39.312 kJ•mol－1, 各温度下的自由能变(ΔG)均小于零, 熵变(ΔS)均为正值, 吸附过程的活化能(Ea)为20.359 kJ•mol－1. 该吸附过程是自发的吸热物理过程. 被吸附的铅和镉均可用1 mol•L－1的硝酸完全洗脱回收. 对铅和镉的富集因子均超过200. 将其应用于水中痕量铅和镉的吸附富集和测定, 回收率分别为96.3%～107.2%和93.5%～104.0%, 与石墨炉原子吸收光谱法测定结果一致.

Preparation of Nano-calcium Titanate Powder and Its Adsorption Behavior for Lead Ion and Cadmium Ion in Water

Nano-calcium titanate powder was successfully prepared by a citric acid complex sol-gel method, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectrophotometry (FTIR). Its adsorption capabilities for lead ion and cadmium ion were investigated. Taking the cadmium ion as an example, the thermodynamics and kinetics of the adsorption were completely studied. The results showed that the calcium titanate was perovskite nanometer powder. The particle diameter relied on the burning temperature, which became larger at the higher burning temperature. When the temperature was at 600 ℃ for 2 h, the average particle diameter was the smallest, about 20 nm. This adsorbent had strong adsorption capacity for the lead ion and cadmium ion in water at pH 4～8. The adsorption behavior followed a Langmuir adsorption isotherm and a pseudo-second-order kinetic model. The enthalpy change (ΔH) of the adsorption process was 39.312 kJ•mol－1. At various temperatures, Gibbs free energy changes (ΔG) were negative, and entropy changes (ΔS) were positive. The activation energy (Ea) was 20.359 kJ•mol－1 for the adsorption. These showed that the adsorption of cadmium ion by the nano-calcium titanate powder was an endothermic and spontaneous physical process. The adsorbed lead ion and cadmium ion could be completely eluated using 1 mol•L－1 HNO3. The pre-concentration factors for lead ion and cadmium ion were all more than 200. The method has been applied to the preconcentration and flame atomic absorption spectrometry (FAAS) determination of trace lead ion and cadmium ion in water samples. The recoveries were 96.3%～107.2% and 93.5%～104.0% respectively, and the results were found to be in agreement with those by graphite furnace atomic absorption spectrometry.