Inhibiting the concentration polarization of FO membranes based on the wettable microporous supporting layer and the enhanced dense skin layer

Abstract

A novel thin film composite‐type forward osmosis (FO) membrane with inhibited concentration polarization phenomenon and expectant separation performance was prepared by continuous interfacial polymerization method. The nylon‐6,6 microfiltration membrane with the average pore size of 5 μm and the self‐wetting property was for the first time used as the supporting layer of the FO membranes, which decreased the mass transfer resistance in the porous supporting layer. The skin layer was prepared via the continuous interfacial polymerization of polyamide as a relatively dense layer, with the reverse salt flux of less than 1 g/m−2 h−1. The mass transfer resistance and the reverse salt flux of the prepared FO membranes were remarkably reduced due to the functional design of the double‐layer structure, which effectively enhanced the separation selectivity and restrain the concentration polarization of the FO membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45133.

Thin Film Composite Forward Osmosis Membrane with Single-Walled Carbon Nanotubes Interlayer for Alleviating Internal Concentration Polarization

“…The lowest S value of only 88 µm was appeared on TFC5 membrane, which represented the weakest ICP effect supporting the highest water flux. Notably, the S value of prepared TFC membrane was lower than those reported in most literature [21,[50][51][52], demonstrating that the SWCNTs interlayer was of great significance to prepare high-flux Membrane structure parameter (S) is a direct characterization of ICP effect, which has units of length and can be thought as the distance that a solute particle must travel from the bulk draw solution to the membrane active layer [36]. In Figure 7c, all the TFC membranes with the SWCNTs interlayer presented the lower S value compared to the TFC 0 membrane, attributing that the interconnected SWCNTs with ultrahigh length-to-diameter ratio endowed the low tortuosity.…”

“…The lowest S value of only 88 µm was appeared on TFC 5 membrane, which represented the weakest ICP effect supporting the highest water flux. Notably, the S value of prepared TFC membrane was lower than those reported in most literature [21,[50][51][52], demonstrating that the SWCNTs interlayer was of great significance to prepare high-flux FO membrane. The variation trend of the time-dependent normalized water flux can also show the effect of ICP on separation performance of FO membrane [49].…”

Thin-Film Nanocomposite Forward-Osmosis Membranes on Hydrophilic Microfiltration Support with an Intermediate Layer of Graphene Oxide and Multiwall Carbon Nanotube

“…In terms of reducing the ICP in the support substrates of FO membranes, one strategy is to use supports with large pore size, such as microfiltration (MF) membranes for FO membrane synthesis. Large pores can significantly facilitate the diffusion of salts in the porous support so that ICP is alleviated. − For example, Huang et al applied a microfiltration nylon substrate as forward-osmosis support and then prepared a membrane possessing a higher flux and selectivity. , Zhao et al also reported that a supporting layer with larger pore size is beneficial to inhibit the ICP and improve FO membrane performance . Furthermore, Ren et al investigated the relationship between osmosis performance and support layer pore size and found larger pores led to higher selective layer roughness and thus higher flux .…”

“…Furthermore, Ren et al investigated the relationship between osmosis performance and support layer pore size and found larger pores led to higher selective layer roughness and thus higher flux . Although these previous studies showed that MF substrates are good for the synthesis of FO membranes, unfortunately, it is still difficult to form a polyamide layer with low reverse salt flux and satisfactory membrane integrity on MF substrates by normal interfacial polymerization reaction. ,, …”

Surface-Initiated Passing-through Zwitterionic Polymer Brushes for Salt-Selective and Antifouling Materials

“…The difference in salt permeation when the active layer is either upstream or downstream is observed with other asymmetric thin-film composite (TFC) membranes. − In the most common TFC membranes, a thin layer of the dense polymer serves as the selective layer on one side, while a thicker porous support layer makes up the other side of the membrane. While our system is also asymmetric, as the brush layer is only present on one side, both components of the membrane (cellulose and the PSB brush) are dense nonporous polymers, and salt permeation proceeds by the solution-diffusion model for both materials.…”