Key Laboratory of Novel Thin Film Solar Cells, Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei, 230031, PR China.
Dalton Trans. 2012 Sep 21;41(35):10803-10. doi: 10.1039/c2dt31057k. Epub 2012 Aug 2.
The influence of humic acid (HA) on Ni(II) sorption to Ca-montmorillonite was examined by using a combination of batch sorption experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy technique. The sorption of Ni(II) on HA-montmorillonite hybrids is strongly dependent on pH and temperature. At low pH, the sorption of Ni(II) is mainly dominated by Ni-HA-montmorillonite and outer-sphere surface complexation. The EXAFS results indicate that the first coordination shell of Ni(II) consists of ∼6 O atoms at the interatomic distances of ∼2.04 Å in an octahedral structure. At high pH, binary Ni-montmorillonite surface complexation is the dominant sorption mechanism. EXAFS analysis indicates the formation of mononuclear complexes located at the edges of Ca-montmorillonite platelets at pH 7.5, while a Ni-Al layered double hydroxide (LDH) phase at the Ca-montmorillonite surface formed with pH 8.5. At pH 10.0, the dissolved HA-Ni(II) complexation inhibits the precipitation of Ni hydroxide, and Ni-Al LDH phase forms. The rise of temperature increases the sorption capacity of Ni(II), and promotes Ni-Al LDH phase formation and the growth of crystallites. The results are important to evaluate the physicochemical behavior of Ni(II) in the natural environment.
采用批量吸附实验和扩展 X 射线吸收精细结构（EXAFS）光谱技术研究了腐殖酸（HA）对 Ca-蒙脱石中 Ni(II)吸附的影响。Ni(II)在 HA-蒙脱石杂化体上的吸附强烈依赖于 pH 值和温度。在低 pH 值下，Ni(II)的吸附主要由 Ni-HA-蒙脱石和外球表面络合作用控制。EXAFS 结果表明，Ni(II)的第一配体壳层由约 6 个 O 原子组成，在八面体结构中原子间距离约为 2.04 Å。在高 pH 值下，二元 Ni-蒙脱石表面络合是主要的吸附机制。EXAFS 分析表明，在 pH 7.5 时，单核配合物位于 Ca-蒙脱石片的边缘形成，而在 pH 8.5 时，在 Ca-蒙脱石表面形成 Ni-Al 层状双氢氧化物（LDH）相。在 pH 10.0 时，溶解的 HA-Ni(II)络合抑制了 Ni 氢氧化物的沉淀，形成了 Ni-Al LDH 相。温度的升高增加了 Ni(II)的吸附容量，促进了 Ni-Al LDH 相的形成和晶粒的生长。这些结果对于评估 Ni(II)在自然环境中的物理化学行为非常重要。
