Facile Covalent Crosslinking of Zeolitic Imidazolate Framework/Polydimethylsiloxane Mixed Matrix Membrane for Enhanced Ethanol/Water Separation Performance

Abstract

The interfacial design is critical in preparing high-performance mixed matrix membranes (MMMs), especially for the separation of larger sized components from mixtures. Herein, a facile and novel strategy was employed to design covalently linked zeolitic imidazolate framework-8-polydimethylsiloxane (ZIF-8@PDMS) MMMs without interfacial defects by a one-step synthesis route for ethanol recovery from ethanol aqueous solution. In this strategy, 3-glycidyloxypropyltrimethoxysilane (GOPTS) worked as the covalent linker of PDMS and amine-functionalized ZIF-8 nanoparticles (AZIF-8) simultaneously. The chemical structures and morphologies of AZIF-8 and AZIF-8@PDMS MMMs were demonstrated by various characterization techniques. The results exhibited that AZIF-8 and the MMMs were successfully prepared and AZIF-8 as the filler displayed better dispersion in the PDMS matrix and compatibility with the PDMS matrix as compared to ZIF-8 or GOPTS-modified ZIF-8 (GZIF-8). Therefore, AZIF-8@PDMS MMMs showed more excellent separation performance than ZIF-8 or GZIF-8-filled MMMs. In particular, AZIF-8@PDMS MMM with 7 wt % AZIF-8 loading exhibited the highest separation factor of 17.7 and a comparable total flux of 585.6 g/m2 h at 40 °C with 5 wt % ethanol aqueous solution, which were improved by 176.6 and 34.5%, respectively, in comparison with the pristine PDMS membrane, breaking the “trade-off” effect between the flux and separation factor. This study might provide some new insights into the fabrication of high-performance MMMs for pervaporation recovery of various organic systems.

A Review on Mixed Matrix Membranes for Solvent Dehydration and Recovery Process

“…Similar results were obtained in other studies too [21,37,40,41,57]. On the other hand, the permeability was found to decrease, mainly due to the reduction in the solubility of the permeant components on the membrane surface, in the case of ethanol-water mixtures [21,44] as well as butanol-water mixtures [55].…”

“…These defects allowed greater mass transfer diffusion for the smaller water molecules, resulting in increased water permeability and decreased butanol permeability and selectivity. The results showed an increase in the total flux with the particle loading, while the separation factor and selectivity first increased, reached a maximum at 1 wt% loading and then began to decrease [44]. Similar behaviour was observed for ZIF-91 loaded PDMS as well, where both the flux and separation factor were increased on increasing the % loading (displaying an anti-trade off phenomenon) up to 20%, while both were found to decrease beyond 20% loading.…”

“…Jin et al [32] observed a decline in PV performance of ZIF-8@PDMS membranes with 8 wt% loading, prepared for phenol separation via drying free process. At high loading, the probability of interaction and collision among the particles increased, severe particle aggregation occurred and large particles were formed, destroying the integrity of the hybrid membrane [37,44]. This increased the likelihood of formation of defects such as voids amongst the particles, as well as between the particles and the membrane, as investigated by Li et al [36], on the PV performance of the O-ZIF-8@PDA/PDMS membranes for butanol pervaporation.…”

“…A novel one-step synthesis technique was employed by Zhu et al [44] to prepare MMMs doped with amine-functionalized ZIF-8. A strong covalent linking was observed among the PDMS, 3-glycidoxypropyltrimethoxysilane (GOPTS) and amine-functionalized ZIF-8 (AZIF-8), rendering a well-dispersed membrane with excellent polymer-filler compatibility, eliminating the interfacial defects.…”

“…In studies conducted by Fan et al [48], for the use of ZIF-8/PDMS membranes for solvent separation, three pathways were suggested for the passage of the solvent molecules through the selective layer: (i) through the polymer dense layer, (ii) through the inner channels of the filler nanoparticles due to their organophilicity and hydrophobicity and (iii) through the filler-polymer interface (gaps) [44]. In the pervaporation process, the permeation flux was greatly improved as the solvent/water mixture preferentially diffused through the inner channels of ZIF-8 nanoparticles and gaps as it offered lower resistance than the dense and nonporous PDMS layer.…”