Roberts Darryl R, Ford Robert G, Sparks Donald L
Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19717, USA.
J Colloid Interface Sci. 2003 Jul 15;263(2):364-76. doi: 10.1016/s0021-9797(03)00281-9.
Zn(II) sorption onto Al and Si oxides was studied as a function of pH (5.1-7.52), sorption density, and ionic strength. This study was carried out to determine the role of the various reaction conditions and sorbent phases in Zn complexation at oxide surfaces. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to probe the Zn atomic environment at the metal oxide/aqueous interface. For both amorphous silica and high-surface-area gibbsite, Zn sorption kinetics were rapid and reached completion within 24 h. In contrast, Zn sorption on low-surface-area-gibbsite was much slower, taking nearly 800 h for a sorption plateau to be reached. In the case of silica, EXAFS revealed that Zn was in octahedral coordination with first-shell oxygen atoms up to a surface loading of approximately 1 micro molm(-2), changing to tetrahedral coordination as surface loading and pH increased. For the high-surface-area gibbsite system, the Znz.sbnd;O first-shell distance was intermediate between values for tetrahedral and octahedral coordination over all loading levels. Zn formed inner-sphere adsorption complexes on both silica and high-surface-area gibbsite over all reaction conditions. For Zn sorption on low-surface-area gibbsite, formation of Znz.sbnd;Al layered double hydroxide (LDH) occurred and was the cause for the observed slow Zn sorption kinetics. The highest pH sample (7.51) in the Zn-amorphous silica system resulted in the formation of an amorphous Zn(OH)(2) precipitate with tetrahedral coordination between Zn and O. Aging the reaction samples did not alter the Zn complex in any of the systems. The results of this study indicate the variability of Zn complexation at surfaces prevalent in soil and aquatic systems and the importance of combining macroscopic observations with methods capable of determining metal complex formation mechanisms.
研究了锌（II）在铝和硅氧化物上的吸附情况，该吸附是pH值（5.1 - 7.52）、吸附密度和离子强度的函数。进行这项研究是为了确定各种反应条件和吸附剂相在锌在氧化物表面络合过程中的作用。扩展X射线吸收精细结构（EXAFS）光谱用于探测金属氧化物/水界面处锌的原子环境。对于无定形二氧化硅和高比表面积水铝石，锌的吸附动力学很快，在24小时内达到吸附平衡。相比之下，锌在低比表面积水铝石上的吸附要慢得多，达到吸附平台需要近800小时。在二氧化硅的情况下，EXAFS显示，在表面负载量达到约1微摩尔每平方米之前，锌与第一壳层氧原子呈八面体配位，随着表面负载量和pH值的增加，转变为四面体配位。对于高比表面积水铝石体系，在所有负载水平下，锌 - 氧第一壳层距离介于四面体和八面体配位的值之间。在所有反应条件下，锌在二氧化硅和高比表面积水铝石上都形成了内球吸附络合物。对于锌在低比表面积水铝石上的吸附，形成了锌 - 铝层状双氢氧化物（LDH），这是观察到的锌吸附动力学缓慢的原因。锌 - 无定形二氧化硅体系中pH值最高的样品（7.51）导致形成了无定形氢氧化锌沉淀，锌与氧之间呈四面体配位。对反应样品进行老化处理并没有改变任何体系中的锌络合物。这项研究的结果表明，在土壤和水生系统中普遍存在的表面上锌络合的变异性，以及将宏观观察与能够确定金属络合物形成机制的方法相结合的重要性。
