Reactive Functionalized Membranes for Pollutants Degradation

Membranes are widely used in water remediation (e.g. desalination and heavy metal removal) because of the ability to control membrane pore size. The incorporation of nanomaterials into the membranes provides added benefits through increased reactivity with different functionality. In this study, we developed a reactive membrane system with iron-related nanoparticles (i.e. Fe, Fe/Pd and Fe_xO_y) immobilized in polyacrylic acid (PAA) functionalized polyvinylidene fluoride (PVDF) microfiltration membranes for degradation of polychlorinated biphenyls (PCBs) and removal of Selenium (Se) from the power plant scrubber water.

The functionalized membranes are obtained by in-situ polymerization of acrylic acid (AA) inside the PVDF pores. The ion exchange capacity of functional groups in polymer domain (carboxyl groups) allows the synthesis of metal NPs. PCBs can be dechlorinated to biphenyls by using Pd doped zero-valent iron NPs made by borohydride reduction. However, biphenyl is still mildly toxic and requires a further treatment. On the other hand, chlorinated dechlorination byproducts can be generated during the direct oxidation of PCBs. By the development of nanostructured membranes, 2-chlorobiphenyl was successfully converted into biphenyl. The convective mode experiment shows that the mass transfer resistance was effectively eliminated since the rate constant of Fe/Pd NPs inside the membrane pores was 1.3 times higher than that in the batch study. The oxidation of biphenyl by OH• from iron catalyzed H₂O₂ decomposition was accomplished with the same membrane platform. Mono-, di- and trihydroxybiphenyls and benzoic acid were detected as the main products. Thus the oxidation of biphenyl started with the hydroxylation of aromatic ring followed by the ring cleavage. The dissolved Fe²⁺ and iron oxide (magnetite) on the Fe surface both enhanced the oxidative dechlorination. This combined pathway (reductive/oxidative) could reduce the toxicity of PCBs effectively while eliminating the formation of chlorinated degradation byproducts.

To demonstrate the feasibility of our functionalized membranes in continuous manufacturing, full-scale PAA/PVDF flat sheets and modules (40 inches wide and 300 feet long) were made at Sepro Membranes Inc. in Oceanside, CA. Our recent studies proved the possibility of using this reactive system for the practical water remediation.

This research is supported by NIEHS-SRP and DOE-KRCEE grants.