Preparation Of Hydrophilized And Functionalized Polyacrylonitrile Membrane-immobilized NZVI For Metronidazole Removal

Metronidazole(MNZ),one of the nitroimidazole antibiotics,is employed to cure bacterial and protozoal diseases.The features of low biodegradability and high solubility for MNZ make it continuously accumulated in the aquatic environment,resulting in high risks to aquatic organisms.The technology based on nano zero-valent iron(NZVI)provides a new way for aqueous MNZ removal.NZVI has been used in pollution abatement in recent years for removal of toxic contaminants due to its high surface reactivity and environmental benignity.But the iron nanoparticles are easy to aggregate and passivate due to its smaller size and magnetism,hence decreasing its reactivity.In this study,hydrophilized and functionalized polyacrylonitrile(PAN)membrane was synthesized and used for immobilization of NZVI.The reactivity of prepared PAA/PAN-NZVI composites(abbreviated as PPN)for removal of MNZ was evaluated.The procedures for preparation of PPN composites includes:Firstly,hydrophilized PAN membrane was fabricated with addition of polyvinyl alcohol(PVA).Then,the prepared membrane was functionalized via in situ polymerization of acrylic acid(AA),and the composites based on NZVI were further prepared by KBH4 reduction of Fe2+.And the advantage of synthetic method lied in:(1)the remarkably increased loading and decreased agglomeration of NZVI;(2)the potential risk of released iron ions being not a concern due to strong chelation of grafted carboxyl groups;(3)the entire process for materials synthesis conducting under aerobic condition,avoiding the complicated operation under inert atmosphere.Analyses of morphological characteristics(FE-SEM),chemical structure(FTIR),element valence and groups(XPS),and water contact angles of samples confirmed the favorable hydrophilicity of membrane and the successful graft of massive carboxylic acid groups onto membrane.Moreover,iron nanoparticles were uniformly distributed onto PAA/PAN membrane with no obvious agglomeration and these nanoparticles were clearly spherical in shape with relatively uniform size of 20-30 nm.The results suggest significant reactive sites of immobilized NZVI.The reactivity of PPN composites for removal of MNZ was investigated.The results show that the composites possessed superior reactivity for MNZ with removal efficiency 2.03 and reaction rate 4.77 times higher than that by bare NZVI.Meanwhile,the enhanced stability and recyclability of PPN composites were maintained over repeated cycles.The co-solutes except humic acid had a negligible effect on MNZ removal.The removal of MNZ by composites/air process was lower than that by composites/N2 process within 90 min.The neutral and weak acidic conditions were beneficial for removing MNZ.And reasonable decrease of MNZ concentration,increases of temperature and loading capacity of NZVI were advisable for the removal of MNZ.Kinetic study indicated that removal of MNZ by the composites was well-described by a modified pseudo-first-order decay model.The rapid adsorption and subsequent reduction are the main removal mechanism of MNZ by composites.The findings suggest that the novel composites possess huge potential for MNZ wastewater treatment.