title: Differential pair distribution function study of the structure of arsenate adsorbed on nanocrystalline γ-alumina.
abstract: 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.
authors: Department of Geosciences and Center for Environmental Molecular Science, Stony Brook University , Stony Brook, New York 11794-2100, United States. weili@udel.edu
authors: Wei
authors: W
authors: Li
authors: Richard
authors: R
authors: Harrington
authors: Yuanzhi
authors: Y
authors: Tang
authors: James D
authors: JD
authors: Kubicki
authors: Masoud
authors: M
authors: Aryanpour
authors: Richard J
authors: RJ
authors: Reeder
authors: John B
authors: JB
authors: Parise
authors: Brian L
authors: BL
authors: Phillips
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry*; D001149:Arsenates / Q000737:chemistry*; D008958:Models, Molecular; D053758:Nanoparticles / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D001149:Arsenates; D000537:Aluminum Oxide; C025657:arsenic acid