Species-Specific Uptake of Arsenic on Confined Metastable 2-Line Ferrihydrite: A Combined Raman-X-Ray Photoelectron Spectroscopy Investigation of the Adsorption Mechanism

The present study is targeted toward understanding the interaction between important and technologically relevant poly morphs of iron oxides/oxyhydroxides with arsenic species at neutral pH. The existence of various arsenic (As) species in solution was verified by Raman measurements. Their species-dependent adsorption on the affordable arsenic removal media, confined metastable 2-line ferrihydrite (CM2LF) was investigated. The results were compared with common adsorption media, hematite (alpha-Fe2O3) and magnetite (Fe3O4). X-ray photoelectron spectroscopy was used to investigate the changes in the core levels of Fe 2p and As 3d resulting from the uptake of arsenic species. Binding of various As species with CM2LF was confirmed by FTIR studies. Raman adsorption data were found to fit a pseudo-second-order model. Results of this study show the synthesized nanocomposite of CM2LF to be very effective for the removal of As(III) and As(V) species in comparison to various materials at neutral pH. A model for the adsorption of As(III) and As(V) species in water on a ferrihydrite particle was developed. This accounted for the large uptake capacity.