255982 Membrane – Iron Oxide Nanoparticle System for Pollutant Degradation
The removal of chlorinated organic contaminants from the Superfund sites has always been a critical issue due to the toxicological and recalcitrant properties of those compounds. Some emerging ways employing the functionalized membranes and nanotechnology have attracted more and more attentions in the water remediation of hazardous waste sites. Here we developed the reactive membrane system with Fe/Pd and iron oxide nanoparticles (NPs) immobilized in polyacrylic acid (PAA) functionalized polyvinylidene fluoride (PVDF) microfiltration membranes for the degradation of chloro-organics such as polychlorinated biphenyls (PCBs) at the neutral pH.
PAA matrix inside the PVDF membranes is obtained by in-situ polymerization of acrylic acid (AA). The ion exchange capacity of the functionalized membranes allows the in-situ synthesis of iron/iron oxide core-shell and iron oxide NPs inside the pores. 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 can’t be disposed to environment. On the other hand, toxic intermediates like chloroacetic acids can be generated during the direct PCB oxidation. By the development of controlled nanostructured membranes, we first dechlorinate 2,2’-dichlorobiphenyl (PCB4) to biphenyl. 2-chlorobiphenyl (PCB1) was detected as the intermediates. Depending on the Fe/Pd NP loading and composition, the complete dechlorination of PCB4 can be achieved. The further oxidative degradation of biphenyl by the heterogeneous Fenton reaction will lead to significant reduction in toxicity by forming aromatic ring breakdown products with no chlorine. The catalysis of iron oxide NPs (obtained by controlled air or H2O2 oxidation of iron NPs) can promote the decomposition of hydrogen peroxide (H2O2), generating the highly oxidative hydroxyl radicals (OH•) for the destruction of toxic organic compounds.
Convective flow experiments with membranes have also been conducted to study the intrinsic kinetics of PCB degradation, reducing the diffusion resistance of reactants through the membranes. The biphenyl obtained from the Fe/Pd loaded membranes was destructed in the iron oxide immobilized membranes by the addition of H2O2. Hydroxybiphenyl (dihydroxy-, trihydroxy-) and benzoic acid (hydroxy-, dihydroxy-) were detected by GC-MS and LC-MS/MS as the main intermediates during the biphenyl oxidation.
This research is supported by NIEHS-SRP grant and by the DOE-KRCEE programs.