Browsing by Author "Alazmi, Abdullah"

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    Enabling Solution Processable COFs through Suppression of Precipitation during Solvothermal Synthesis
    (American Chemical Society, 2022) Khalil, Safiya; Meyer, Matthew D.; Alazmi, Abdullah; Samani, Mohammad H. K.; Huang, Po-Chun; Barnes, Morgan; Marciel, Amanda B.; Verduzco, Rafael; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    Covalent organic frameworks (COFs) are crystalline, nanoporous materials of interest for various applications, but current COF synthetic routes lead to insoluble aggregates which precludes processing for practical implementation. Here, we report a COF synthesis method that produces a stable, homogeneous suspension of crystalline COF nanoparticles that enables the preparation of COF monoliths, membranes, and films using conventional solution-processing techniques. Our approach involves the use of a polar solvent, diacid catalyst, and slow reagent mixing procedure at elevated temperatures which altogether enable access to crystalline COF nanoparticle suspension that does not aggregate or precipitate when kept at elevated temperatures. On cooling, the suspension undergoes a thermoreversible gelation transition to produce crystalline and highly porous COF materials. We further show that the modified synthesis approach is compatible with various COF chemistries, including both large- and small-pore imine COFs, hydrazone-linked COFs, and COFs with rhombic and hexagonal topologies, and in each case, we demonstrate that the final product has excellent crystallinity and porosity. The final materials contain both micro- and macropores, and the total porosity can be tuned through variation of sample annealing. Dynamic light scattering measurements reveal the presence of COF nanoparticles that grow with time at room temperature, transitioning from a homogeneous suspension to a gel. Finally, we prepare imine COF membranes and measure their rejection of polyethylene glycol (PEG) polymers and oligomers, and these measurements exhibit size-dependent rejection and adsorption of PEG solutes. This work demonstrates a versatile processing strategy to create crystalline and porous COF materials using solution-processing techniques and will greatly advance the development of COFs for various applications.
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    Sulfonated polymer coating enhances selective removal of calcium in membrane capacitive deionization
    (Elsevier, 2022) Nnorom, Njideka C.; Rogers, Tanya; Jain, Amit; Alazmi, Abdullah; Elias, Welman Curi; DuChanois, Ryan M.; Flores, Kenneth R.; Gardea-Torresdey, Jorge L.; Cokar, Marya; Elimelech, Menachem; Wong, Michael S.; Verduzco, Rafael; NSF Nanosystems Engineering Research Center, Nanotechnology-Enabled Water Treatment
    There is a need for membranes and processes that can selectively separate target ions from other similar ionic species. Recent studies have shown that electrified processes for ion removal such as membrane capacitive deionization (MCDI) and electrodialysis (ED) are selective towards specific ionic species, but selectivities are generally limited. Here, we demonstrate that an ion-selective polymer coating can significantly enhance ion selectivities for MCDI processes. We focused on the preferential removal of Ca2+ over Na+ and used the conductive and sulfonated polymer poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a model selective ion-exchange coating. We first measured the permeability of Ca2+ and Na+ in freestanding PEDOT:PSS membranes of varying crosslink density and found that the permeability of Ca2+ was six times greater than that for Na+ in optimized membranes. Next, we used PEDOT:PSS in an MCDI process by depositing thin PEDOT:PSS coatings on top of composite electrodes. We found that the PEDOT:PSS coatings significantly enhanced the preferential permeability of Ca2+ over Na + relative to unmodified electrodes and produced a preferential removal as high as 8:1 on a molar basis. This work demonstrates a new approach to enhance selective ion removal in MCDI and other electro-driven ion separation processes.
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    Surface Modified Silica Nanoparticles as Solid Electrolytes for CO2 Electrolyzers
    (2022-08-12) Alazmi, Abdullah; Verduzco, Rafael
    The CO2 reduction reaction (CO2RR) enables the capture of CO2 and conversion into chemical species that can be utilized as chemical feedstocks in other industrial processes. The CO2RR is a challenging electrolytic reaction due to the thermodynamic and kinetic stability of the CO2 molecule. Driving this process requires an efficient CO2 electrolyzer with nanostructured catalysts to improve product selectivity. Although the decreasing cost of renewable energy has significantly improved the competitiveness of chemical feedstocks produced through such an electrolytic process, the liquid fuels and chemicals produced through CO2RR electrolysis are of low purity. In this regard, continuous optimization of both CO2 electrolyzer assembly parts are essential to enhance the catalytic performance of these devices. Achieving a CO2RR electrolyzer device that is highly efficient requires not only the selective and stable catalysts for CO2RR on the cathode and oxygen evolution reaction (OER) on the anode but also electrolyzer devices with sufficient mass transport and low Ohmic resistance. In this work, we present a new class of solid particle electrolytes for use in CO2 electrolyzers. This approach enables water to flow through the solid electrolyte layer while also transporting ions, mediated by the particle surface functionality. Using this approach, we are able to produce sulfonated silica nanoparticles with an ionic conductivity of 5.31 x 10-2 S cm-1, better than commercial particulate electrolytes. Our work details the synthesis and characterization of the particles, their use with a polymeric binding to improve stability, and their performance in a CO2 electrolyzer. This general approach provides a porous solid electrolyte layer capable of producing pure liquid products more efficiently than competing materials.