Abstract
In a natural environment, Fe(ii) adsorbed onto the surfaces of natural particles to form various surface complex species can influence the transformation of contaminants. The reductive reactivity of the [[triple bond, length as m-dash]Fe(iii)]/[[triple bond, length as m-dash]Fe(ii)] couples are close correlated with the surrounding conditions. In this study, we investigated the effects of Si(iv) on the reductive reactivity of [[triple bond, length as m-dash]Fe(iii)]/[[triple bond, length as m-dash]Fe(ii)] couples adsorbed onto γ-Al(2)O(3). Experiments were conducted under different conditions to investigate the effects of Si(iv) on the reactivity of [[triple bond, length as m-dash]Fe(iii)]/[[triple bond, length as m-dash]Fe(ii)] couples for 2-nitrophenol (2-NP, selected as the model pollutant) reduction in γ-Al(2)O(3) suspensions. Kinetics results revealed that chemical adsorption is the rate limiting step in Fe(ii) and Si(iv) adsorption processes and the reduction of 2-NP is an endothermic reaction. The linear correlations between the reduced peak oxidation potential (E (p)) (versus SCE) and 2-NP reduction rate (ln k), and between the adsorbed Fe(ii) density (ρ (Fe(II))) and ln k, illustrated that E (p) and ρ (Fe(II)) are two key factors in the inhibiting effects of Si(iv) on the reductive reactivity of Fe(iii)/Fe(ii) couples on γ-Al(2)O(3). The results of Fe K-edge X-ray absorption spectroscopy revealed that the increase of Si(iv) concentration resulted in the gradual change in the composition of the adsorbed Fe species from pure [triple bond, length as m-dash]AlOFe(+) (γ-Al(2)O(3) surface-bound Fe(ii) species with higher reductive reactivity) to a mixture of [triple bond, length as m-dash]AlOFe(+) and [triple bond, length as m-dash]SiOFe(+) (SiO(2) surface-bound Fe(ii) species with lower reductive reactivity), leading to the decrease in ρ (Fe(II)), the positive shift in E (p), the increase in activation energy (E (a)), and consequently the decrease in the reduction rate (ln k) of 2-NP.