In Situ Fabrication of Metal–Organic Framework Thin Films with Enhanced Pervaporation Performance

Abstract

The intrinsic porosity in the periodic structures of metal-organic frameworks (MOFs) endows them with a great potential for membrane separation. However, facile fabrication of crystalline MOF membranes has been challenging and limited to few materials for economic and environmental considerations. Herein, a continuous Zr-MOF thin film with a thickness of ≈180 nm has been fabricated via in situ recrystallization of MOF nanoparticles on the porous support under formic acid vapor. Owing to the inherent microporosity and the well-established hydrophilicity during membrane fabrication, the MOF thin films exhibit excellent pervaporation performance with separation factors of 2630, 501 and fluxes of 1.45, 1.41 kg m −2 h −1 ) for n-butanol dehydration and methanol/methyl tert-butyl ether (MeOH/MTBE) separation, respectively. The structural stability of the film has been further confirmed by its steady performance in the 10-day pervaporation test. This in situ recrystallization method induced by a trace amount of acid vapor with no extra ingredients opens a new avenue for the facile membrane fabrication of various MOF materials to feasibly realize their versatile potential as membrane materials.

Polycrystalline Metal–Organic Framework Membranes for Pervaporation

“…To achieve these goals, the prepared membrane should be continuous and defect-free with a small thickness. The relevant preparation methods that have been reported can be referenced, including electrochemical deposition, vapor-phase deposition, gel-vapor deposition, confined counter-diffusion-assisted epitaxial growth, vapor-phase recrystallization, and top-down exfoliation. , …”

“…An innovative method of vapor recrystallization was used to synthesize NU-906 membranes . Zr 6 -based NU-906 was first dissolved in DMF and then coated onto a porous substrate surface.…”

“…PV performance of polycrystalline MOF membranes: (a) dehydration of ethanol, (b) dehydration of organics (excluding ethanol), (c) recovery of organics from water, (d) organic/organic separation with the same carbon number, (e) organic/organic separation with different carbon numbers, and (f) water desalination. The figures were created on the basis of the data listed in Table S4. ,− ,− ,,,,− ,− …”

“…Other membranes, including ZIF-67, UiO-66, , UiO-66-NH 2 , , and M-Zn/Co-ZIF membranes, were also used to separate methanol and MTBE, but the separation performance or/and stability of these membranes were not that outstanding. On the basis of the ultrathin thickness (∼180 nm) of the NU-906 membrane, its high hydrophilicity, and its suitable pore size (∼1.0 nm), it has a high separation factor (501) and a high flux (1.41 kg m –2 h –1 ) in methanol/MTBE separation . On the basis of the sieving effect of the natural pore size (∼0.4 nm) and the preferential adsorption of polar molecules, ZIF-67 performed well in the separation of azeotrope organic mixtures with large molecular size differences.…”

“…Furthermore, ultrathin (∼180 nm) NU-906 membranes were synthesized. 93 On the basis of the inherent micropore (∼1 nm) and excellent hydrophilicity (water contact angle of 12°), it performed well in the dehydration of 90 wt % n-butanol with a separation factor of 2630 and a total flux of 1.45 kg m −2 h −1 . Continuous PV test results for 10 days showed that the total flux and separation factor remained stable, confirming the excellent stability of the membrane.…”