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Gas-liquid membrane contactor (GLMC) has been regarded as a promising alternative to conventional contacting processes for CO 2 absorption. In this work, a composite hollow fiber (HF) membrane with an aminosilane-modified zeolitic imidazolate framework-8 (mZIF-8) based dense skin layer was designed and synthesized for high-efficiency biogas upgrading in the GLMC process, by dispersing mZIF-8 nanocrystals into poly(dimethylsiloxane) matrix and then depositing on a porous polyvinylidene fluoride (PVDF) substrate. (3-aminopropyl)triethoxysilane was introduced to modify the ZIF-8 nanocrystals, thereby enabling the chemical bonding with PDMS chains for avoiding interfacial voids and further enhancing hydrophobicity. Compared with the control membrane, the newly developed mZIF-8 based composite membrane with a dense skin exhibited competitive hydrophobicity with a contact angle of 130°, ensuring its anti-wetting ability. It exhibited an enhanced biogas upgrading performance with the absorption fluxes of 2.3 and 3.8 × 10−3 mol m−2·s−1 using water and 1 M monoethanolamine (MEA) as absorbents, respectively (liquid velocity = 0.25 m s−1). In particular, a comparable selectivity of CO 2 /CH 4 with the value of ∼20 was achieved by using MEA as absorbent in the GLMC process. A robust long-term stability of the mZIF-8 based composite HF membrane was also achieved in a 15-day operation. This work offers a new perspective for promoting CO 2 mass transfer with mZIF-8 based composite HF membranes, thereby improving the biogas upgrading performance in GLMC applications. • A composite hollow fiber membrane with a ZIF-8 based dense skin layer was designed and synthesized. • The ZIF-8 nanocrystals were modified to cross-link with PDMS chains for further hydrophobicity enhancement. • The newly developed membrane exhibited competitive hydrophobicity, ensuring its anti-wetting ability. • An enhanced biogas upgrading performance was achieved in gas-liquid membrane contact applications. [ABSTRACT FROM AUTHOR]

Abstract A highly efficient biocatalytic carbonic anhydrase (CA)-polydopamine (PDA)/polyethylenimine (PEI)-polyvinylidene fluoride (PVDF) (referred to as CA-m-PVDF) composite membrane was fabricated for CO 2 conversion and capture in the gas-liquid membrane contactor (GLMC) process. The co-deposition of PDA/PEI with amino functional groups was employed to amine-functionalize a PVDF substrate as support for subsequent in-situ CA immobilization by cross-linking with glutaraldehyde. This enhances the enzyme stability and prolongs its lifespan, thus facilitates CO 2 hydration efficiency in the GLMC process. In this work, different immobilization CA protocols were compared based on the CA activity and activity recovery. For biocatalytic CA-m-PVDF membranes, the best activity of 498 U m−2 (membrane) and a corresponding activity recovery of 31.5% were achieved (m(5 h)-PVDF as support, 0.67 (v/v)% GLU as cross-linking agent, 600 μg mL−1 CA solution, pH 8.0, temperature at 25 °C, and 24 h reaction time). By using water as absorbent with a liquid velocity of 0.25 m s−1 in a bench-scale GLMC setup, a high-efficiency CO 2 absorption flux of 2.5 × 10−3 mol m−2 s−1 was obtained, which was ~165% higher than that of the non-biocatalytic m-PVDF membrane. The long-term stability test showed a good enzyme activity for CO 2 hydration capacity for the CA-m-PVDF membranes during 40 days of test duration. Overall, the results achieved in this work may provide promising insights into enzyme immobilization on polymeric supports for the development of high-efficiency biocatalytic membranes for CO 2 capture in GLMC applications. Highlights • A highly efficient biocatalytic composite membrane was fabricated for CO 2 conversion and capture. • PDA/PEI with amino functional groups was co-deposited to amine-functionalize a PVDF substrate. • Subsequent in-situ carbonic anhydrase (CA) immobilization was conducted by cross-linking. • The resultant membrane shows a high CO 2 absorption flux of 2.5 × 10-3 mol m-2 s-1 in the gas-liquid membrane contactor. [ABSTRACT FROM AUTHOR]