Preparation And Performance Enhancement Of CO₂ Separation Membranes Based On Layered Double Hydroxides

Nowadays,energy-efficient CO2 separation technologies are imperative.Membrane-based gas separation has unique advantages such as environmentally benign and low energy consumption,holding great promise in carbon capture.Aiming at obtaining high separation performance of membranes,a series of facilitated transport mixed matrix membranes(MMMs)has been designed with PEO-based polymer as the membrane matrix and functionalized layered double hydroxide(LDH)as the filler.By optimizing the physical and chemical microenvironment in the membranes,the integration of the solution-diffusion-reaction multi-selection mechanism is achieved,and finally the CO2 separation performance of membranes is significantly improved.Preparation of Pebax/AA-LDH membranes and synergistic enhancement of diffusion-reaction mechanism: Based on the exchangeability of anions in the LDH interlayer gallery,amino acids were introduced into LDH to obtain AA-LDH and Pebax was utlized as the membrane matrix to prepare MMMs.The diffusion mechanism is enhanced by the expanded interlayer channel of AA-LDH.Acid-base pairs in amino acids provide carriers for CO2 transport thus strengthening the reaction mechanism of membranes.Compared with pristine Pebax,the CO2 permeability and CO2/CH4 selectivity of Pebax/Glu-LDH(5)increase by 64.6% and 83.9% respectively.Preparation of Pebax/NH2-LDH membranes and synergistic enhancement of solution-reaction mechanism: Based on the modifiability of laminated LDH sheets,amino groups were introduced into the surface of LDH to obtain NH2-LDH and Pebax was utlized as the membrane matrix to prepare MMMs.Amino groups on the surface of NH2-LDH afford affinity toward CO2 enhancing the solution mechanism.Multiple CO2 carriers in intra-and inter-laminate of NH2-LDH provide double facilitated transport channels to enhance the reaction mechanism of membranes.Compared with pristine Pebax,the CO2 permeability and CO2/CH4 selectivity of Pebax/AMPTSLDH(10)increase by 65.0% and 86.3% respectively.Preparation of Pebax/ZIF-8@LDH membranes and synergistic enhancement of solution-diffusion-reaction mechanism: Based on the composibility of LDH with porous MOF materials,the heterostructured filler(ZIF-8@LDH)was synthesized by in-situ growth of ZIF-8 on the surface of LDH,which was then incorporated into Pebax matrix to fabricate MMMs.ZIF-8 affords favorable affinity toward CO2,enhancing the the solution mechanism of membranes.Oriented distribution of ZIF-8 elevates the diffusion rate of CO2 and the efficiency of CO2 facilitated transport,enhancing the diffusion mechanism and the reaction mechanism collaboratively.Specifically,Pebax/ZIF-8@LDH(2)exhibits a CO2 permeability of 1307 Barrer and a CO2/CH4 selectivity of 31.6 which increase by 161% and 51% respectively compared with pristine Pebax.