Synthesis of ε-MnO2@MIL-100(Fe) composite for p-arsanilic acid removal

p-Arsanilic acid (p-ASA), a feed additive in poultry and swine production, tends to be converted into more toxic inorganic arsenic in the environment, thus posing hazards to the environment and humans. In this work, novel ε-MnO2@MIL-100(Fe) nanocomposites were successfully synthesized by a wet impregnation method to remove p-ASA by simultaneously oxidation and adsorption. Batch experiments demonstrated that the ε-MnO2@MIL-100(Fe) had an outstanding adsorption capacity toward p-ASA and the oxidized products (486.99 μmol g-1), and the adsorption fitted well with pseudo-second-order kinetic model and Freundlich isotherm model, while intra-particle diffusion was a rate-limiting step. In the composites, manganese oxide was responsible for the oxidation of p-ASA and MIL-100(Fe) played a dominant role in the in-situ adsorption through a joined force from coordination, hydrogen bonding, and π-π stacking. Thus the combination of adsorption and oxidation resulted in excellent removal performances. Additionally, ε-MnO2@MIL-100(Fe) achieved good removal efficiency for p-ASA in a wide pH range (5−11) and was robust to some co-existing substances, which enables its good removal performance towards p-ASA in natural water bodies. The fixed-bed column experiments further confirmed the continuous removal of p-ASA from the water flow by ε-MnO2@MIL-100(Fe).