Nanovoid Membranes Embedded with Hollow Zwitterionic Nanocapsules for a Superior Desalination Performance

Abstract

In order to lower the capital and operational cost of desalination and wastewater treatment processes, nanofiltration (NF) membranes need to have a high water permeation and ionic rejection, while also maintaining a stable performance through antifouling resistance. Recently, Turing-type reaction conditions [Science 2018, 360, 518–521] and sacrificed metal organic frame (MOF) nanoparticles [Nat. Commun. 2018, 9, 2004] have been reported to introduce nanovoids into thin-film composite (TFC) polyamide (PA) NF membranes for an improved performance. Herein, we report a one-step fabrication of thin-film nanocomposite membranes (TFNM) with controllable nanovoids in the polyamide layer by introducing hollow zwitterionic nanocapsules (HZNCs) during interfacial polymerization. It was found that embedding HZNCs increases the membrane internal free volume, external surface area, and hydrophilicity, thus enhancing the water permeation and antifouling resistance without trading off the rejection of multivalent ions. For example, water permeation of the NF membranes embedded with about 19.0 wt % of HZNCs (73 L m–2 h–1) increased by 70% relative to the value of the control TFC NF membrane without HZNCs (43 L m–2 h–1). This increase comes while also maintaining 95% rejection of Na2SO4. Further, we also determined the effect of the mass loading of HZNCs on the top surface of the TFC NF membranes on the membrane performance. This work provided a direct and simple route to fabricate advanced desalination membranes with a superior separation performance.

Ultra-permeable polyamide membranes harvested by covalent organic framework nanofiber scaffolds: a two-in-one strategy

“…Benefitting from the increased water permeable areas of the crumpled ultrathin PA layers, the membranes showed unprecedented water permeation. Moreover, other research also verified the contribution of increased permeable areas within membrane separation layers to the permeance enhancement 11,22,24,25. Thinning the PA layers and increasing the permeable areas are both beneficial for elevating water permeance.…”

Effect of Porous and Nonporous Nanostructures on the Permeance of Positively Charged Nanofilm Composite Membranes

“…[9][10][11][12] This is an ingenious strategy to increase the liquid permeance by incorporating porous nanostructures them in the organic phase. [33] The water flux was increased by nearly 70% with hollow zwitterionic nanoparticles compared to the TFC membrane. [33] However, when the zwitterionic nanoparticles were taken in the aqueous phase, the resulting TFN membrane does not show any permeance enhancement.…”

“…Indeed, through introducing voids and interlayer composite structures, high flux composite membranes are also developed recently. [11,33,[46][47][48][49][50][51][52] TFN nanofiltration membranes [53] with a high loading of TiO 2 nanoparticles (0-9 wt%) was developed in the earlier days; however, the nanoparticle loading remains inconclusive as an extremely poor rejection of MgSO 4 (≈95%) was achieved because of less crosslinked polyamide structure formed under 5 wt% loading. Incorporation of cellulose nanocrystals (CNCs) enhanced hydrophilicity and increased permeability.…”

“…Carboxy‐functionalized multi‐walled carbon nanotubes (MWNTs) incorporated membranes also show an increase in water flux with a somewhat decrease in salt rejection. [ 32 ] The fabrication of TFNs often follows the process of inclusion of nanomaterials in the separation layer by dispersing them in the aqueous [ 33–35 ] or the organic phase [ 10,19,33,36,37 ] during interfacial polymerization. However, the surface property of the nanomaterials would restrict their dispersion either in aqueous or in the organic phase.…”

“…[ 39 ] A study by Xue and his co‐workers used hollow zwitterionic nanoparticles and non‐hollow nanoparticles in the separation layer by dispersing them in the organic phase. [ 33 ] The water flux was increased by nearly 70% with hollow zwitterionic nanoparticles compared to the TFC membrane. [ 33 ] However, when the zwitterionic nanoparticles were taken in the aqueous phase, the resulting TFN membrane does not show any permeance enhancement.…”