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Arsenic Adsorption and As (III) Oxidation on TiO2 Nanoparticles: Macroscopic and Spectroscopic Investigations
Citation:
JEGADEESAN, G., S. R. AL-ABED, H. Choi, AND K. G. SCHECKEL. Arsenic Adsorption and As (III) Oxidation on TiO2 Nanoparticles: Macroscopic and Spectroscopic Investigations. Presented at 2008 International Environmental Nanotechnology Conference: Applications and Implications, Chicago, IL, October 07 - 09, 2008.
Impact/Purpose:
To evaluate (1) the sorption of As (III) and As (V) on amorphous TiO2 particles; (2) arsenic sorption behavior and the effect of crystalline composition by comparing the sorption capacities of different crystalline TiO2 and amorphous TiO2 particles; and (3) the structure of the two arsenic species on both TiO2 surfaces using x-ray absorption spectroscopy techniques.
Description:
Engineered nanoparticles (NPs) (particle sizes ranging from 1-100 nm) have unique physical and chemical properties that differ fundamentally from their macro-sized counterparts. In addition to their smaller particle size, nanoparticles possess unique characteristics such as large surface to volume ratio and higher chemical reactivity, which are conducive for their application in environmental remediation, especially adsorption of target contaminants. In this study, we examined the sorption of arsenite (As (III)) and arsenate (As (V)) on amorphous and crystalline TiO2 nanoparticles. Macroscopic investigations on arsenic sorption indicated that maximum As (V) coverage on both crystalline and amorphous TiO2 occurred in the pH range of 3.8-6.5. The effect of pH on As (III) sorption onto amorphous TiO2 was less pronounced, in comparison to crystalline TiO2. XAS analysis provided evidence of partial As (III) oxidation on amorphous TiO2 and not on the crystalline TiO2, likely due to the surface chemistry of the particles and the presence/absence of surface hydroxyl groups. Electrophoretic mobility measurements and XAS analysis indicated that As (III) and As (V) form binuclear bidentate inner-sphere complexes with amorphous TiO2. As (III) and As (V) sorption isotherms indicated that sorption capacities of the different TiO2 polymorphs were dependent on the sorption site density, surface area (particle size) and crystalline structure. When surface coverages were normalized to specific surface areas, crystalline TiO2 appeared to exhibit higher capacities. However, a reverse trend was observed when arsenic sorption was expressed on a per unit mass basis.