University of Iowa College of Engineering

The improvement of ion and gas transport in fuel cells, flow battery, electrodialysis, and gas purification technologies can help provide for future demands in the transportation and water sectors. One cheap class of materials that is suitable for these applications is ionomers. Specifically, ionomers have exhibited their potential by excelling in key properties such as gas permeability and selectivity, mech. robustness, ionic conductivity, and thermal transitions. The industry standard for many electrochem. based processes is Nafion by Dupont. However, the bicontinous morphol. of Nafion has led to selectivity issues. To overcome this issue while retaining functionality thin film ionomers like homogeneously sulfonated Diels-Alder poly(phenylene) (DAPP) have been created. The homogeneous sulfonation is limited in DAPP as the mech. stability has been shown to be compromised at an ionic exchange capacity greater than 2.2 As an alternative direct post sulfonation completed by a heterogeneous solid-state reaction initially showed promising thermal, mech. and gas transport properties. The aim of the present study is to optimize the processing of post sulfonated DAPP complexed with a monovalent metal counter-ion. Previous TGA data confirmed the existence of a copolymer system, however further processing attempts revealed sulfonic acid groups had crosslinked via ether linkages. Addnl. studies were performed to find optimal solid-state reaction windows. Due to a restriction of chain rearrangement in the solid-state reaction, polymer morphol. and FFV was tuned via thermal and solvent vapor annealing. Morphol. and chem. composition is planned using TEM and FTIR-ATR. Mech. and gas permeability studies were performed. Future studies will explore further forms of metal counter-ion complexation and their effects on transport properties.

Industrial and com. use of chlorinated ethenes (CEs) such as cis-1,2-dichlrorethene (cis-DCE) and trichloroethene (TCE) for cleaning purposes has led to groundwater contamination causing harm to human and environmental health. Iron(II) minerals within the surrounding soil have been shown to degrade these contaminants abiotically into nonharmful carbon gases (ethane, ethene, and acetylene). However, the minerals and conditions in the subsurface that lead to degradation of CEs are often poorly understood, or have only been observed in the laboratory under extreme conditions of pH and iron(II) or mineral concentrations To determine iron(II)-minerals ability to reduce CEs, we conducted experiments with ferrous sulfide (FeS), iron(II) hydroxide (Fe(OH)₂), and chukanovite (ferrous hydroxy-carbonate) over a range of pHs and iron(II) concentrations We measured cis-DCE and TCE loss and carbon gas production using gas chromatog. The rate of CE degradation varies for each of the different pHs and iron(II) concentrations, but is slow with 55.9% carbon products (12% ethane, 41% ethene, 0% acetylene) observed for Fe(OH)₂ at pH of 8.3 over three months and 31.4% carbon products (7% ethane, 18% ethene, 2% acetylene) for FeS at pH 10.3 with 2 mM excess iron(II) over three months. So far, we have observed most rapid production of products with Fe(OH)₂ and FeS, however in comparison, little reduction of CEs has been observed at with chukanovite over time. Our work suggests that conditions favoring the precipitation of Fe(OH)₂ is most likely to result in significant CE reduction

Pesticide contamination of surface waters is a critical concern for potential impacts on the ecosystem and drinking water supplies. Current passive sampling techniques, like POCIS, often need deployment times around 4-6 wk, and may not be well-suited for anal. of small, polar organic contaminants and charged species. Here, we fabricated electrospun polymer nanofiber mats, or ENMs, with embedded carbon nanotubes for use as fast-equilibrating passive sampling materials. Using polyacrylonitrile (PAN) with embedded carboxylated carbon nanotubes, we show that these composite ENMs can quickly achieve equilibrium with a range of organic chems., including common pesticides. Moreover, through rapid, reversible uptake, ENMs are responsive to temporal changes in dissolved pollutant concentrations that occur over short timescales compared to more traditional passive samplers. The extent of pollutant uptake can also be tuned through integration of addnl. species into the ENMs including surface-segregating surfactants and the use of porogens to increase pore volume and sp. surface area. Ongoing work includes field performance validation, where ENMs are being deployed in an agriculturally impacted creek over short timescales (1-2 h) to study temporal trends in the concentration of atrazine and other widely used pesticides. Results from ENMs are being compared to corresponding grab samples collected across the deployment period. Ultimately, these materials represent a promising passive sampling technol. that complements existing approaches for its ability to capture shorter temporal trends and tighter spatial resolution