The influence of Si( iv ) on the reactivity of [Fe( iii )]/[Fe( ii )] couples for 2-nitrophenol reduction in γ-Al 2 O 3 suspensions

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 [Fe( iii )]/[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 [Fe( iii )]/[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 [Fe( iii )]/[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 AlOFe + (γ-Al 2 O 3 surface-bound Fe( ii ) species with higher reductive reactivity) to a mixture of AlOFe + and 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.