Fall 2021 PhD Seminar One

Mixed matrix materials (MMMs) containing porous fillers merge the excellent processability of polymers with the well-controlled pores of the fillers. Gas permeability of MMMs is often described using the Maxwell model, and high loadings are often required to maximize the benefits of the porous fillers. Herein, we demonstrate that MMMs comprising low loading of metal-organic polyhedra (MOP) and cross-linked polyethers exhibit unexpectedly high gas permeability compared with the Maxwell model. MOPs are discrete nanocages with high porosity and excellent compatibility with polymers. Similar behavior was observed for several MOPs (Cu-MOP, Fe-MOP, and Zr-MOP) in different polyethers. For instance, as the Cu-MOP content increases from 0 to 3 wt.%, CO₂ permeability increases from 510 to 1000 Barrer while retaining the high CO₂/N₂ selectivity at 35 °C; a further increase of loading to 5 wt.% decreases CO₂ permeability to 730 Barrer without influencing CO₂/N₂ selectivity. By contrast, at the Cu-MOP loading of 10 wt.% or above, the gas permeability can be satisfactorily described by the Maxwell model. These MMMs were thoroughly characterized using FTIR, DSC, SEM, PALS, WAXD, and SAXS, and a perloration model is proposed to explain such a peculiar result. The MMMs with low loadings and much-improved permeability (superior to state-of-the-art membrane materials) can also be integrated into current processes of manufacturing industrial thin film composite membranes.

BIO

Talieh is a 4^th year PhD student under the advisement of Dr. Haiqing Lin, and her research focuses on the development of sorption-enhanced mixed-matrix membranes for post-combustion carbon capture. Talieh has first-authored two research articles and is preparing a few more. She has won the Elias Klein Founders’ Travel award from the North American Membrane Society and the Students’ Choice Award of the CBE Graduate Research Symposium.

• Time: 11.30 AM
• Location: 206 Furnas Hall
• Seminar Flyer

Hydrogen (H₂) has great potential as an emission-free energy carrier to replace fossil fuels. Its usage, however, is limited by its lower explosion limit (4%) and high permeability through many materials that make storage and handling of H₂ a challenging task. Hence, the development of low-cost, fast, and sensitive H₂ detection technologies is of paramount importance to any future hydrogen-based energy economy. The United States Department of Energy (US-DOE) has set a target for the cost of H₂ sensors to be used for fuel-cell-powered vehicles at <$15 including the cost of electronics. Paper is a flexible, porous, adaptable, environment-friendly, and degradable material that has huge potential for use in sustainable electronics. We report ultra-low-cost paper-based sensors for room-temperature detection of hydrogen (H₂) using palladium nanowires (PdNWs) and prepared by a simple drop-casting method. PdNWs of three different morphologies and crystallinity were synthesized by a combination of solution phase methods. Surfactants used in the synthesis of nanowires occupy active sites on PdNWs, adversely affecting sensor response and producing non-monotonic sensor response (“reverse sensing” at low concentration). We found that UV-ozone treatment of the Pd NW-on-paper sensors degrades the ligand and improves contact between Pd NWs, which eliminates the reverse sensing phenomenon. A UV-O-treated sensor using straight, penta-twinned PdNWs gave a response (fractional change in resistance) of 7% to 1% H₂ in air, with response and recovery times of 13 s and 11s and could easily detect as little as 100 ppm H₂ in air. Upon coating the Pd NWs with a small amount of Pt (<10% by weight), the response time improved dramatically to 5 s for 1% H₂. We similarly found that response time could be improved using ultrathin PdNWs and compared the performance of polycrystalline and single-crystalline ultrathin PdNWs. The polycrystalline PdNWs showed a response of 4.3% to 1% H₂ with response and recovery times of 4.9 s and 10.6 s, respectively. The single-crystalline PdNWs showed an 8% response to 1% H₂ with slightly slower response and recovery times of 9.3 s and 13.0 s, respectively. The polycrystalline PdNWs provided a limit of detection of 10 ppm of H₂ in air. We attribute the fast response and recovery times to synergistic effects of their ultrathin (< 5 nm) diameter, strain-coupled grain boundaries, and the porous paper substrate that facilitates rapid transport to exposed PdNWs. Our paper-based sensors, using only ~100 μg Pd per device on a substrate of negligible cost are among the fastest chemiresistive H₂ sensors and could be orders of magnitude less expensive than current state-of-the-art H₂ sensing solutions.

BIO

Abhishek Kumar obtained his B.Tech degree from Sardar Vallabhbhai National Institute of Technology, India. He is currently a final-semester doctoral candidate in Prof. Mark T. Swihart’s group in the Chemical and Biological Engineering department of the University at Buffalo (SUNY). His research focus is on palladium-based nanowire synthesis for gas sensing and separation applications. To date, he has co-authored nine published refereed journal manuscripts, with several more in preparation or in review. After graduation, he will continue his research career as a post-doctoral fellow at EPFL in Lausanne, Switzerland.