Fabrication of a CO2-selective membrane by stepwise liquid-phase deposition of an alkylether functionalized pillared-layered metal-organic framework [Cu2L2P]n on a macroporous support

Metal-organic framework (MOF) membranes were prepared by stepwise deposition of reactants. Two pillared layered MOFs with the general formula [Cu2L2P]n (L = dicarboxylate linker, P = pillaring ligand) were selected. Within this family, fine tuning of adsorption affinity and pore size is possible by variation or functionalization of the L and P linkers. Compound 1 was chosen to be non-polar (L = 1,4-naphtalenedicarboxylate = ndc, P = 1,4-diazabicyclo(2.2.2)octane = dabco); in contrast, compound 2 included a polar linker L with two conformationally flexible ether side chains (L = 2,5-bis(2-methoxyethoxy)-1,4-benzene-dicarboxylate = BME-bdc, P = dabco). The polar functionalization is expected to increase the framework affinity for CO2 compared to CH4. The step-by-step, liquid phase deposition of 1 and 2 resulted in pore-plugging of macroporous ceramic supports. The performances of the two MOF membranes were evaluated in gas separation experiments of equimolar CO2/CH4 mixtures using a modified Wicke–Kallenbach technique. Anti-Knudsen CO2/CH4 separation factors in the range of ∼4–4.5 were obtained for the membrane consisting of the polar 2, whereas the separation of the membrane formed from the non-polar 1 was found to be Knudsen-like.

Graphical abstractUsing a stepwise liquid-phase deposition method, membranes featuring a polar functionalized [Cu2L2P]n-type MOF as active layer were prepared and their CO2/CH4 separation performance were compared with the performance of MOF membranes fabricated with a non-functionalized [Cu2L2P]n-type MOF.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A [Cu2L2P]n type MOF membrane was prepared by stepwise liquid phase deposition. ► By functionalizing the linker L by two ether groups, CO2 selectivity could be tuned. ► Separation factor of CO2/CH4 equimolar mixtures was 4–4.5 in favor of CO2. ► An isoreticular, non-functionalized MOF membrane showed only Knudsen-like separation in favor of CH4.