Catalytic activity of HO by goethite and lepidocrocite: Insight from 5-bromosalicylic acid removal mechanism and density functional theory calculation (ID:CHEM114760).

We have compared the elimination of 5-bromosalicylic acid (BSA) in the systems of goethite (α-FeOOH)/HO and lepidocrocite (γ-FeOOH)/HO. The results demonstrated that BSA (10 mg L) could be successfully adsorbed on α- and γ-FeOOH (0.5 g L) and then effectively degraded after the addition of HO (14.7 mM). BSA adsorption on both α- and γ-FeOOH followed pseudo-second order adsorption kinetic models, with γ-FeOOH having greater adsorption ability than α-FeOOH. In the α-FeOOH/HO system, BSA degradation was well fitted with the pseudo-second order kinetics, whereas the oxidation in γ-FeOOH/HO system had a two-stage pseudo-first order kinetics. Electron paramagnetic resonance (EPR) results for these two systems revealed the presence of •OH and •OOH, and further tests with radical captures demonstrated their dominance in degrading BSA. Based on the electronic structure analysis, electrons were more easily transferred from the HO molecule to the Fe atoms of α-FeOOH, explaining the density functional theory (DFT) calculation results, which showed that α-FeOOH performed better in catalyzing the decomposition of HO. However, the free radicals are more likely to desorb from γ-FeOOH, which made the γ-FeOOH/HO system more efficient in degrading BSA.