In situ interface oxidation-adsorption by ferrate (VI)/PMS self-excitation: Unique dual-reaction platform for phenylarsonic acid degradation and immobilization

In this study, we dexterously constructed a unique in situ interface oxidation–adsorption dual-reaction platform through the self-excitation of ferrate (Fe(VI))/peroxymonosulfate (PMS) for phenylarsonic acid (PAA) and inorganic As(V) removal. When the molar ratio of Fe(VI)/PMS was 1:2, 80% degradation of PAA could be achieved within 180 min and the apparent constant value of the reaction rate (kobs) would reach up to 0.185 min−1. 1O2 and Fe(IV) were the main active species for degradation of PAA in Fe(VI)/PMS reaction system. In addition, we explored the possible degradation intermediates and pathway of PAA. In situ Fe(III) oxides generated from Fe(VI) decomposition could adsorb arsenic pollutants through ligand exchange with inorganic As(V) through surface hydroxyl groups to form Fe-O-As bonds. The effect of coexisting anions on the removal performance of the system was investigated, and the results showed that the presence of PO43− and CO32− promoted the oxidative degradation of PAA owing to the activation of PMS by PO43− and CO32−, but Cl− can inhibit the PAA degradation through a free radical scavenging mechanism. PO43− and SiO32− affected the adsorption and removal of the released inorganic As(V) due to their competitive adsorption of in situ Fe(III) oxides. Density functional theory (DFT) calculations indicated an obvious electron transfer (1.83 e) between the in situ Fe(III) oxides and inorganic As(V) with a high adsorption energy of −10.30 eV. These results indicate that the combination of Fe(VI) and PMS can effectively control the total arsenic (total-As) in water bodies.