Iron nanoparticle functionalized membrane for PCB degradation from water

The development of functionalized membranes with catalytic metal nanoparticles provides an effective method of environmental remediation and wastewater treatment. Polyvinylidene fluoride (PVDF) is an excellent polymer for both chemical and mechanic resistance as well as thermal stability. By immobilizing zero-valent iron (ZVI) or bimetallic nanoparticles (NPs), functionalized PVDF membranes can be used in chlorinated organic treatment. Polyacrylic acid (PAA) was polymerized inside PVDF membrane pores to maximize iron adsorption. Adsorbed iron was reduced to form NPs in-situ in order to prevent metal ion loss, NPs aggregation and iron precipitation. Furthermore, tunable membrane pore size could be achieved by changing the environmental pH because of ionization of PAA. This study includes three major aspects: 1. Reactivity toward model toxic chlorinated organic compounds-polychlorinated biphenyl (PCBs) in both batch and convective flow study; 2. NPs characterization of its average sizes, composition, extent of oxidation and distribution inside membrane pores; 3. Simulating pH responsive behavior and PCB reaction within the membrane. PCBs are not biodegradable and tend to cycle between air, water and soil, which might accumulation in living organisms. PCBs dechlorination can be achieved by Fe/Pd reductive pathway. The hydrogen, generated from reaction between ZVI and water, gets activated by Pd for hydrodechlorination. In batch study, 95% of PCB 126 ([Co]=15 μM) was consumed and 67% was converted to biphenyl in 5 hours. In convective flow study, 96% of PCB 126 was consumed at 26s residence time. However, the final product biphenyl still showed toxicity. In order to degrade biphenyl, the further oxidative pathway was combined to break down the aromatic ring and eventually form organic acid. Both iron oxide with H₂O₂ method (Fenton Reaction) and persulfate method significantly reduced toxicity of the products of PCB degradation. Fe/Pd NPs size distribution was analyzed by SEM and TEM (TEM samples were prepared by Focus Ion Beam) and the average size of NPs was 19.4±3.2nm. Iron core and discontinuous palladium shell was tested by STEM-EELS line scan and elemental mapping and extent of oxidation was studied by XRD. Furthermore, membrane permeability change from 32.2LMH/bar to 1.1LMH/bar when environmental pH change from 2 to 6.5. The pH-responsive behavior was simulated and fitted with experimental data, which is a part of PCBs reactivity model.