Stephen Michael Martin

The fields of contaminant destruction and polymer nanocomposites are converging to immobilize photocatalysts for the degradation of conventional and emerging contaminants. Novel work exploits the design freedom of high-surface-area structures enabled by Additive Manufacturing to produce customizable, high-surface-area infilled structures containing photocatalysts. While investigations of nanoparticle dispersion in polymers for mechanical performance are available, there remains a specific need for environmental application-focused research to understand how processing impacts nanocomposite structure-property relationships for 3D printing in water treatment applications. This study investigated twin screw extrusion process parameters (temperature, screw speed, and number of extrusions) on the dispersion of photocatalytic TiO₂ particles in a 3D printable polylactic acid (PLA) composite, the resulting effects on thermal processing properties, and ultimately whether there were benefits to photocatalytic performance. A Design of Experiments evaluated the aforementioned compounding parameters on the number, size, and location of TiO₂ agglomerates in PLA (≈20% w/w TiO₂). Significant correlations between different TiO₂ dispersion states and thermal processing parameters were revealed. Higher TiO₂ loadings (≈30 w/w) resulted in higher viscosity and modulus and a smaller processing window for reliable 3D printing. However, all printed structures tested demonstrated similar photocatalytic rates (≈0.32 to 0.37 ± 0.02 h^-1). This is attributable to the observation of better dispersed TiO₂ at the surfaces of printer extrudates and the actual printed structures, despite the differences in the initial agglomerate state related to larger agglomerates within the interior of the filament. These results suggest that TiO₂ dispersion and distribution by twin screw extrusion are sufficient to achieve environmentally effective degradation rates if agglomerates are less than approximately 20 μm (an image analysis cutoff) and if these smaller agglomerates remain near the surface of printed structures. When such dispersion states are achieved, additional efforts to break up agglomerates appear nonessential for acceptable photocatalytic performance.

Engineers and scientists have a key role to play in the creation and implementation of government policy. Policymakers need access to the technical expertise that is critical to our national progress and security; however, this need is often overlooked by engineering students, faculty, and professionals. Even though a substantial fraction of scientists and engineers end up pursuing jobs in government, engineering curricula do not usually provide any background in policy and for many, the policy-making process remains a black box. The good news is that there are some simple ways to make it more accessible and to encourage increased involvement. In this paper, we provide a brief overview of the federal policy-making process and present a collection of classroom learning activities that link policy-making and implementation to science and engineering. These can easily be added to existing courses without wholesale curricular changes. We also suggest professional development activities for engineers at all stages of their careers and discuss ways for engineers to become involved in the policy process. Introducing learning and career development activities focused on science and engineering policy will better prepare engineers to provide needed technical expertise to policymakers. It may also encourage engineers to consider careers in local, state, and federal government.

Nanorods of PCN-222, a large-pore, zirconium-based porphyrinic metal-organic framework (MOF), have been prepared through coordination modulation – controlled crystal growth through competing monodentate ligands known as modulators – for incorporation into reverse osmosis thin film nanocomposite (TFN) membranes. Post-synthetic modification of the MOF node through binding of myristic acid (MA) altered channel dimensions and pore size distribution. The extent of MOF modification was characterized through Brunauer-Emmett-Teller (BET) gas sorption, as well as 1H NMR following digestion of the particles. TFN membranes containing PCN-222 nanoparticles modified with varying levels of myristic acid (MA) were fabricated via dispersion in the aqueous phase during interfacial polymerization, and the resulting flux and rejection performance of each membrane was evaluated. Increased water flux was observed with increasing MA content in the PCN-222 nanorods. Up to a 95% increase in water flux was observed for a TFN containing a 0.01 wt% loading of PCN-222 nanorods with a 10:1 MA to linker ratio, while maintaining high salt rejection. The flux change was attributed to tunable water transport through the nanorod pore structure and also through rapid water transport pathways at the nanorod-polymer interface.

Stable, cross-linked, liquid crystalline polymer (LCP) films for membrane separation applications have been fabricated from the mesogenic monomer 11-(4-cyanobiphenyl-4′-yloxy) undecyl methacrylate (CNBPh), non-mesogenic monomer 2-ethylhexyl acrylate (2-EHA), and cross-linker ethylene glycol dimethacrylate (EGDMA) using an in-situ free radical polymerization technique with UV initiation. The phase behavior of the LCP membranes was characterized using differential scanning calorimetry (DSC) and X-ray scattering, and indicated the formation of a nematic liquid crystalline (LC) phase above the glass transition temperature. The single gas transport behavior of CO₂, CH₄, propane, and propylene in the cross-linked LCP membranes was investigated for a range of temperatures in the LC mesophase and the isotropic phase. Solubility of the gases was dependent not only on the condensability in the LC mesophase, but also on favorable molecular interactions of penetrant gas molecules exhibiting a charge separation, such as CO₂ and propylene, with the ordered polar mesogenic side chains of the LCP. Selectivities for various gas pairs generally decreased with increasing temperature and were discontinuous across the nematic–sotropic transition. Sorption behavior of CO₂ and propylene exhibited a significant change due to a decrease in favorable intermolecular interactions in the disordered isotropic phase. Higher cross-link densities in the membrane generally led to decreased selectivity at low temperatures when the main chain motion was limited by the lack of mesogen mobility in the ordered nematic phase. However, at higher temperatures, increasing the cross-link density increased selectivity as the cross-links acted to limit chain mobility. Mixed gas permeation measurements for propylene and propane showed close agreement with the results of the single gas permeation experiments.

The separation of greenhouse gases from industrial processes is an ongoing focus for research aimed at mitigating environmental impacts. As a result, it is important to develop experimental techniques for the characterization of the transport of gases through porous crystalline materials with potential applications in gas separations. We report on the fabrication and characterization of gas transport in supported Zn(II)-based MOF membranes. The MOF membranes were used to develop an approach to study membrane quality and determine the transport mechanism through the pores of the crystalline membrane. Membranes were synthesized via a solvothermal method with structural defects sealed by a low-permeability polymer coating, allowing for the measurement of permeation in materials that do not form uniform, defect-free films. Membrane permeation was proportional to the inverse square root of the molecular weight of the permeant gases, indicating that diffusion occurs via Knudsen diffusion. Membrane quality was studied via selectivity measurements as a function of temperature. A study of the gas permeation through a polymer coated sparse MOF membrane, was used to confirm that gas transport occurs through the pores of the MOF, rather than through pinholes or defects in the structure.