Decorating a Loose Defect‐free Hybrid Selective Layer on a Smooth Intermediary: An Effective Way for Unexpected Performances of Nanofiber‐based Forward Osmosis Membranes

Abstract

A novel composite forward osmosis (FO) membrane was fabricated by introducing a chitosan (CS) sublayer between nanofibers and polyamide (PA) layer, which was beneficial to forming thin and defect‐free PA layer and improved binding strength between substrate and the selective layer. Results exhibited low reverse salt flux (0.73 gMH) while maintained high water flux (85.4 LMH), which were better than that in other reports. In order to further improve permeability of membranes, oxidized multiwall carbon nanotubes (OMWNTs) were added into PA layer based on the optimized sublayer. The crosslinking degree of PA layer was reduced, leading to loose PA layers, which promoted the increase of water flux. After modifying, water flux reached 96.9 LMH without sacrificing salt rejection. It was worth mentioning that PAN/CS composite FO membrane, which could adjust microstructure of support layer and selective layer respectively, may provide a promising way for preparing membranes with anticipated separation performance.

A Comprehensive Review of Performance of Polyacrylonitrile-Based Membranes for Forward Osmosis Water Separation and Purification Process

“…In addition, with the optimal CS concentration (3.5%), the PAN/CS TFC nanofiber membrane has achieved 97 % rejection of NaCl salt, 55.05 LMH water flux, and 0.93 gMH reverse salt flux when it is operated in FO mode using DI as FS and 1.5 M NaCl as DS [143]. In another study, a PAN/CS composite nanofiber membrane achieved a water flux of 85.4 LMH, 0.73 gMH RSF, and 97.4% salt rejection when the CS concentration was 3.8% [23].…”

“…It has been noticed that preparing PAN nanofiber by electrospinning is not suitable for the IP process directly. As a consequence, some researchers have improved the binding strength of PAN nanofibers with a PA selective layer, using a thin chitosan (CS) sublayer that was cast on top of hydrolyzed electrospun PAN nanofiber before carrying out the PA formation [23,143,144]. Besides improving the interfacial strength between the PAN nanofiber mat and active layer, this technique has also successfully improved the mechanical strength of the PAN support, achieving a tensile strength of 28.12 MPa and a Young's modulus of 90.66 [143].…”

“…Moreover, this technique has greatly enhanced the selection properties of the fabricated nanofiber TFN membrane under the FO treatment process by achieving elevated water flux and low reverse salt flux, as illustrated in Table 3. For the effect of NPs on the PA-selective layer, N. Li et al [23] have embedded multi-walled carbon nanotubes (MWCNTs) into the PA layer, which reduces their crosslinking degree on top of the electrospun PAN support layer. The addition of MWCNTs showed higher water flux values without sacrificing RSF.…”

“…Most of the PAN-based porous FO membranes were fabricated at a lab scale mainly via the phase inversion technique [16], and a few membranes were prepared via the electrostatic spinning method [17]. Moreover, these membranes were tested under FO conditions after being modified using nanomaterials as membrane fillers to improve their performance in terms of flux, rejection, and resistance to fouling [18][19][20][21][22][23].…”

Selection of substrate manufacturing techniques of polyamine‐based thin‐film composite membranes for forward osmosis process

“…[ 17,20–22 ] Researchers are increasingly interested nowadays in preparing TFC membranes with integrated sublayers between the substrate and their active layer, using various techniques. [ 23–25 ] This approach has yielded promising improvements in the performance of TFC membranes. The first PA‐TFC membranes were proposed by Cadotte in 1979 and have been made for reverse osmosis (RO).…”