Department of Geosciences and Center for Environmental Molecular Science, Stony Brook University , Stony Brook, New York 11794-2100, United States.
Environ Sci Technol. 2011 Nov 15;45(22):9687-92. doi: 10.1021/es200750b. Epub 2011 Oct 24.
Structural information is important for understanding surface adsorption mechanisms of contaminants on metal (hydr)oxides. In this work, a novel technique was employed to study the interfacial structure of arsenate oxyanions adsorbed on γ-alumina nanoparticles, namely, differential pair distribution function (d-PDF) analysis of synchrotron X-ray total scattering. The d-PDF is the difference of properly normalized PDFs obtained for samples with and without arsenate adsorbed, otherwise identically prepared. The real space pattern contains information on atomic pair correlations between adsorbed arsenate and the atoms on γ-alumina surface (Al, O, etc.). PDF results on the arsenate adsorption sample on γ-alumina prepared at 1 mM As concentration and pH 5 revealed two peaks at 1.66 Å and 3.09 Å, corresponding to As-O and As-Al atomic pair correlations. This observation is consistent with those measured by extended X-ray absorption fine structure (EXAFS) spectroscopy, which suggests a first shell of As-O at 1.69 ± 0.01 Å with a coordination number of ~4 and a second shell of As-Al at ~3.13 ± 0.04 Å with a coordination number of ~2. These results are in agreement with a bidentate binuclear coordination environment to the octahedral Al of γ-alumina as predicted by density functional theory (DFT) calculation.
结构信息对于理解污染物在金属（氢）氧化物表面的吸附机制非常重要。在这项工作中，采用了一种新的技术来研究砷酸盐氧阴离子在γ-氧化铝纳米颗粒上吸附的界面结构，即同步加速器 X 射线全散射的差分配分函数（d-PDF）分析。d-PDF 是在吸附和未吸附砷酸盐的样品之间获得的适当归一化 PDF 的差异，否则制备方法完全相同。实空间图案包含了关于吸附砷酸盐和γ-氧化铝表面上的原子（Al、O 等）之间原子对相关的信息。在 1 mM As 浓度和 pH 5 下制备的γ-氧化铝上吸附砷酸盐的样品的 PDF 结果显示在 1.66 Å 和 3.09 Å 处有两个峰，分别对应于 As-O 和 As-Al 原子对相关。这一观察结果与扩展 X 射线吸收精细结构（EXAFS）光谱测量结果一致，表明第一壳层的 As-O 在 1.69 ± 0.01 Å 处，配位数约为 4，第二壳层的 As-Al 在约 3.13 ± 0.04 Å 处，配位数约为 2。这些结果与密度泛函理论（DFT）计算预测的八面体γ-氧化铝的双齿双核配位环境一致。
