Coupling Molecular-Scale Spectroscopy with Stable Isotope Analyses to Investigate the Effect of Si on the Mechanisms of Zn-Al LDH Formation on Al Oxide
Coupling Molecular-Scale Spectroscopy with Stable Isotope Analyses to Investigate the Effect of Si on the Mechanisms of Zn-Al LDH Formation on Al Oxide
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DOI：
10.1021/acs.est.2c05140
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发表时间：
2022-09-22
影响因子：
11.4
通讯作者：
Sparks, Donald L.
中科院分区：
文献类型：
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作者：
Gou, Wenxian;Li, Wei;Sparks, Donald L.
虽然硅酸盐影响金属在矿物表面的吸附已为人所知，但其机制仍然知之甚少。采用X射线吸收精细结构(XAFS)、锌稳定同位素分析和扫描电子显微镜(STEM)相结合的方法，研究了硅酸盐对Al_2O_3在pH 7.5条件下吸附锌的影响，并阐明了吸附机理。XAFS分析表明，在无硅酸盐或低硅浓度(0.64 mm)条件下，由于表面诱导硅齐聚，生成了锌铝层状双氢氧化物(LDH)析出物。在硅酸盐浓度为0.64 mm时，测得显著的锌同位素分馏(Delta 66ZN吸附-水溶液=0.63+/-0.03%O)，大于Al_2O_3吸附锌引起的分馏(0.47+/-0.03%O)，但更接近锌与硅氧化物表面键合引起的分馏(0.60~0.94%O)，表明存在锌-硅键环境。STEM结果表明，吸附后的硅酸盐与γ-Al_2O_3具有紧密的空间偶联关系，表明>；Si-Zn内球络合物(“>；”表示表面)可能与γ-Al_2O_3表面键合形成>；Al-Si-Zn三元内球络合物。这项研究不仅证明了自然环境中的溶解硅酸盐对锌的去向和生物有效性具有重要作用，而且突出了光谱和同位素联用方法在探索复杂环境过程中的潜力。
While silicate has been known to affect metal sorption on mineral surfaces, the mechanisms remain poorly understood. We investigated the effects of silicate on Zn sorption onto Al oxide at pH 7.5 and elucidated the mechanisms using a combination of X-ray absorption fine structure (XAFS) spectroscopy, Zn stable isotope analysis, and scanning transmission electron microscopy (STEM). XAFS analysis revealed that Zn-Al layered double hydroxide (LDH) precipitates were formed in the absence of silicate or at low Si concentrations (0.64 mM) due to surface-induced Si oligomerization. Significant Zn isotope fractionation (Delta 66Znsorbed-aqueous = 0.63 +/- 0.03%o) was determined at silicate concentrations >0.64 mM, larger than that induced by sorption of Zn on Al oxide (0.47 +/- 0.03%o) but closer to that caused by Zn bonding to the surface of Si oxides (0.60-0.94%o), suggesting a presence of Zn-Si bonding environment. STEM showed that the sorbed silicates had a close spatial coupling with gamma-Al2O3, indicating that >Si-Zn inner-sphere complexes (">" denotes surface) likely bond to the gamma-Al2O3 surface to form >Al-Si-Zn ternary inner-sphere complexes. This study not only demonstrates that dissolved silicate in the natural environment plays an important role in the fate and bioavailability of Zn but also highlights the potential of coupled spectroscopic and isotopic methods in probing complex environmental processes.