Carbonic Anhydrase-Embedded ZIF-8 Electrospun PVA Fibers as an Excellent Biocatalyst Candidate.

There is a growing concern that the increasing concentration of CO2 in the atmosphere contributes to a potential negative impact on global climate change. To deal with this problem, developing a set of innovative, practical technologies is essential. In the present study, maximizing the CO2 utilization and precipitation as CaCO3 was evaluated. In this manner, bovine carbonic anhydrase (BCA) was embedded into the microporous zeolite imidazolate framework, ZIF-8, via physical absorption and encapsulation. Running as crystal seeds, these nanocomposites (enzyme-embedded MOFs) were in situ grown on the cross-linked electrospun polyvinyl alcohol (CPVA). The prepared composites displayed much higher stability against denaturants, high temperatures, and acidic media than free BCA, and BCA immobilized into or on ZIF-8. During 37 days of storage period study, BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA maintained more than 99 and 75% of their initial activity, respectively. The composition of BCA@ZIF-8 and BCA/ZIF-8 with CPVA improved stability for consecutive usage in recovery reactions, recycling easiness, and greater control over the catalytic process. The amounts of calcium carbonate obtained by one mg each of fresh BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA were 55.45 and 49.15 mg, respectively. The precipitated calcium carbonate by BCA@ZIF-8/CPVA reached 64.8% of the initial run, while this amount was 43.6% for BCA/ZIF-8/CPVA after eight cycles. These results indicated that the BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA fibers could be efficiently applied to CO2 sequestration.

Preparation and characterization of nanofibrous metal-organic frameworks as efficient catalysts for the synthesis of cyclic carbonates in solvent-free conditions.

Environmental concerns, particularly global warming, represent serious threats to public health globally. Metal-organic frameworks (MOFs) are innovative materials with prominent features such as ultrahigh surface area, high porosity and tunable cavities, which make them unique materials both in adsorption of carbon dioxide and catalysis. The design of new nanocomposites by using metal-organic frameworks as building materials has received broad attention recently. Here, nanocrystals of two unique MOF structures (UiO-66 and ZIF-67) were incorporated into electrospun polyvinyl alcohol (PVA) and polystyrene (PS) fibers (noted as MOFibers) by an ex situ method, to transform non-toxic, abundant, economical and renewable CO2 gas to cyclic carbonates in a solvent-free medium. In order to improve the composites' performance, different electrospinning parameters, including applied voltage, flow rate, collection distance, PVA and PS weight fraction in solution, and MOF weight fraction relative to the polymer, were intensively investigated. The synthesized samples were characterized by multiple techniques, such as FTIR, XRD, SEM, UV-vis and TGA, as well as N2 and CO2 adsorption measurement. It was found that all of the composites show properties combining the advantages of MOFs and polymers, such as thermal, chemical, and mechanical stability, structural flexibility, lightweight, adsorption performance and catalytic properties. Additionally, all systems were environment-friendly and the PVA/MOF fibers were easily separated and recycled for consecutive cycles.