Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan.
J Colloid Interface Sci. 2012 Oct 15;384(1):99-104. doi: 10.1016/j.jcis.2012.06.072. Epub 2012 Jul 6.
Complexation reactions of environmentally important inorganic anions such as nitrate, chloride, sulfate, arsenate, and phosphate on the surface of hydrotalcite-like compounds (HT) were investigated to understand the role of HT in the immobilization of hazardous anions in an alkaline environment. The effects of surface complexation reactions on the solid state properties of HT were also evaluated to understand their stability. Synthetic HT was used for the adsorption and post-adsorption experiments. The obtained adsorption isotherms showed that the order of selectivity of HT for anions was NO(3)<Cl<SO(4)<<AsO(4)<PO(4). To distinguish the adsorption mechanisms (inner-sphere complexes or outer-sphere complexes) of these anions, zeta potential measurements and infrared absorption spectroscopic analysis were performed. The results indicated that NO(3) and Cl were adsorbed as diffuse ions on the outer surfaces of the HT, while SO(4) formed outer-sphere complexes with a strong electrostatic interaction. Moreover, AsO(4) and PO(4) formed inner-sphere complexes via a ligand substitution reaction on the HT surfaces. And it was suggested that oxyanions with low ionic potential, such as AsO(4) and PO(4), had a tendency to form inner-sphere complexes with the HT surfaces. The formation of inner-sphere complexes shifted the isoelectric point and the surface charge of the HT. Furthermore, the solubility of the HT was reduced by the inner-sphere complexes with PO(4) and AsO(4). It was revealed that the formation of inner-sphere complexes on the HT surfaces contributed to the stabilization of the HT, as well as a decrease in the mobility of these anions.
研究了环境中重要的无机阴离子（如硝酸盐、氯化物、硫酸盐、砷酸盐和磷酸盐）与类水滑石化合物（HT）表面的络合反应，以了解 HT 在碱性环境中固定有害阴离子的作用。还评估了表面络合反应对 HT 固体状态特性的影响，以了解其稳定性。合成 HT 用于吸附和后吸附实验。获得的吸附等温线表明，HT 对阴离子的选择性顺序为 NO(3)<Cl<SO(4)<<AsO(4)<PO(4)。为了区分这些阴离子的吸附机制（内球络合物或外球络合物），进行了动电电位测量和红外吸收光谱分析。结果表明，NO(3)和 Cl 作为扩散离子被吸附在 HT 的外表面上，而 SO(4)则通过强静电相互作用形成外球络合物。此外，AsO(4)和 PO(4)通过 HT 表面的配体取代反应形成内球络合物。并且表明，具有低离子势能的含氧阴离子，如 AsO(4)和 PO(4)，有与 HT 表面形成内球络合物的趋势。内球络合物的形成改变了 HT 的等电点和表面电荷。此外，PO(4)和 AsO(4)与 HT 形成的内球络合物降低了 HT 的溶解度。结果表明，HT 表面形成内球络合物有助于 HT 的稳定以及这些阴离子的迁移率降低。
