Electrospun Nanofiber-Based Membranes for Water Treatment

Abstract

Water purification and water desalination via membrane technology are generally deemed as reliable supplementaries for abundant potable water. Electrospun nanofiber-based membranes (ENMs), benefitting from characteristics such as a higher specific surface area, higher porosity, lower thickness, and possession of attracted broad attention, has allowed it to evolve into a promising candidate rapidly. Here, great attention is placed on the current status of ENMs with two categories according to the roles of electrospun nanofiber layers: (i) nanofiber layer serving as a selective layer, (ii) nanofiber layer serving as supporting substrate. For the nanofiber layer's role as a selective layer, this work presents the structures and properties of conventional ENMs and mixed matrix ENMs. Fabricating parameters and adjusting approaches such as polymer and cosolvent, inorganic and organic incorporation and surface modification are demonstrated in detail. It is crucial to have a matched selective layer for nanofiber layers acting as a supporting layer. The various selective layers fabricated on the nanofiber layer are put forward in this paper. The fabrication approaches include inorganic deposition, polymer coating, and interfacial polymerization. Lastly, future perspectives and the main challenges in the field concerning the use of ENMs for water treatment are discussed. It is expected that the progress of ENMs will promote the prosperity and utilization of various industries such as water treatment, environmental protection, healthcare, and energy storage.

Keywords: electrospinning; electrospun nanofiber-based membranes (ENMs); membrane fabrication; nanofiber layer; water treatment.

Figure 1

(a) Preparation and application of ENMs; (b,c) ENMs schematic images of two roles of nanofiber layers: served as selective layer (b) and supporting substrate (c).

Figure 2

Schematic representation of the ES process. Reprinted with permission from Ref. [27]. 2020, Elsevier.

Figure 3

(a) Schematic illustration of PVDF chains crosslinking induced by NH₃·H₂O and the 17-FAS grafting onto PVDF polymer chains; (b) FE-SEM images of PVDF ENMs through a fluorinated, self-roughened process and thermal treatment. Reprinted with permission from Ref. [72]. 2020, Elsevier.

Figure 4

(a) SEM images for the top layer (a1,a4), bottom layer (a2,a5), and cross-section (a3,a6) of the prepared PVDF ENMs; (b) Permeate flux of PVDF ENMs (ESD1–7); (c) Rejection of Cd, Pb, Zn, Cu and Ni (c1–c5). Reprinted with permission from Ref. [73]. 2018, Elsevier.

Figure 5

(a) SEM images of optimized fibers; (b1,b2) Flux data and rejection percentage as a function of time for the commercial and the synthesized membranes; Reprinted with permission from Ref. [82]. 2017, Elsevier. (c1–c3) SEM images of top surface, beads diameter and cross-section of the optimized PVDF/Al₂O₃ ENMs; (d1,d2) SEM images of beads without and with 30 wt% Al₂O₃ nanoparticles. Reprinted with permission from Ref. [83]. 2018, Elsevier.

Figure 6

(a) Schematic diagrams and TEM images of S-PVDF/PVDF/GO nanofibers; (b) Water flux of PVDF ENMs with CNTs in different concentrations. Reprinted with permission from Ref. [101]. 2017, Elsevier.

Figure 7

(a) Schematic illustration of vapor deposition fluorination; (b) Contact angles of DI water and other liquids on PVDF-HFP and PVDF-HFP-F membranes; (c) Conductivity and water flux verses time of the PVDF-HFP-F membrane in DCMD. Reprinted with permission from Ref. [120]. 2020, Elsevier.

Figure 8

(a) Schematic diagram of the fabrication process of dual-layer ENMs; (b) permeance performance of the prepared ENMs; Reprinted with permission from Ref. [126]. 2017, Elsevier. (c) cross section SEM images of the optimized dual-layer ENMs; (d,e) permeating performance and stability test in different conditions of thermal and strain; Reprinted with permission from Ref. [128]. 2020, Elsevier. (f) cross-section SEM images and EDX analysis of the optimized dual-layer ENMs (CENM-5); (g,h) permeating performance of dual-layer ENMs. Reprinted with permission from Ref. [129]. 2017, Elsevier.

Figure 9

(a) Schematic illustration and SEM images of Janus PAN/CNTs ENMs; (b) separation results by two sides of Janus PAN/CNTs₀.₅ ENMs; (c) pure water flux, O/W flux and water rejection by the pure PAN and PAN/CNTs ENMs; (d) spreading behaviors of water and oil droplet on two sides of PAN/CNTs₀.₅ ENMs. Reprinted with permission from Ref. [133]. 2017, Elsevier.

Figure 10

(a) Schematic diagram of TFN C PVDF/PVA ENMs; (b) FESEM images of PVDF/PVA nanofiber layer and TFNC PVDF/PVA ENMs for top surface (b1,b2); (c) FO performance of commercial HTI-CTA (c1) and prepared TFNC PVDF/PVA ENMs (c2). Reprinted with permission from Ref. [148]. 2017, Elsevier.