Abstract
Thin-film nanocomposite membranes have shown great promise in organic solvent nanofiltration. However, it is challenging to acquire high permeation flux without severe swelling, which might do harm to rejection and long-term stability. In this study, we introduced dopamine-modified mesoporous silica nanoparticles into the polyamide (PA) matrix via interfacial polymerization to fabricate a series of thin-film nanocomposite membranes. By using polyethyleneimine (PEI) as the aqueous monomer, the modified nanoparticles are designed to be cross-linked within the PA network, which allows the penetration of PEI into the mesopores, and therefore, the membranes show better resistance to solvent-induced swelling and pressure-induced densification. More importantly, the mesopores of nanoparticles provide additional fast channels for solvents, resulting in an unusual enhancement of solvent flux under reduced membrane swelling. Along with the permeation flux, the rejection performance of the nanocomposite membranes is simultaneously improved, thanks to the controlled swelling arising from the strong interfacial adhesion. Thin-film nanocomposite membranes with optimal filler concentration exhibit a high isopropanol permeance of 8.47 L m–2 h–1 bar–1 as well as a quite low-molecular-weight cutoff of 281 Da.
Highlights
Polymer-based thin-film composite membranes have long been the major candidates for practical membrane separation because of the reliability of production and transportation of large-area membranes.[1−5] The bottleneck of polymeric membranes is the so-called “trade-off” between permeability and selectivity, which is typically observed for gas separation, pervaporation, desalination, and organic solvent nanofiltration.[6−8] In particular, for liquid separation, the solvent-induced membrane swelling usually results in enhanced permeation flux and decreased selectivity or rejection.[9−11] Considering that excessive swelling would increase the concerns on membrane stability, the acquisition of high flux at high degree of membrane swelling is not reasonable
For mMS, this spacing slightly decreases to 3.55 nm, indicating that the dopamine modification process had little impact on the removal of N-cetyltrimethylammonium bromide (CTAB) and the mesoporous structures
The band at 1064 cm−1 for mesoporous silica (MS)-CTAB and MS shifts is found to shift to a higher wavenumber in the spectrum of mMS, hinting that dopamine enables the formation of hydrogen bonds between the oxygen atoms of Si−O−Si and the hydrogen atoms of hydroxyl/amino groups
Summary
Polymer-based thin-film composite membranes have long been the major candidates for practical membrane separation because of the reliability of production and transportation of large-area membranes.[1−5] The bottleneck of polymeric membranes is the so-called “trade-off” between permeability and selectivity, which is typically observed for gas separation, pervaporation, desalination, and organic solvent nanofiltration.[6−8] In particular, for liquid separation, the solvent-induced membrane swelling usually results in enhanced permeation flux and decreased selectivity or rejection.[9−11] Considering that excessive swelling would increase the concerns on membrane stability, the acquisition of high flux at high degree of membrane swelling is not reasonable. Further restrict the full use of the filler channels.[28] As suggested by Ismail and coworkers, the “ideal” case of the interface morphology as desired for the simultaneous enhancement of permeability and selectivity for large-pore fillers falls in the range of the “chain rigidification” or “pore blockage” region for typical microporous fillers.[26] such a theory is developed based on gas permeation data, its availability in liquid separation is worth evaluating. The results show that the asprepared membranes did become more robust and permeable, and a simultaneous increase in selectivity was observed from the decrease in the molecular weight cutoff
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