Photocatalytic Nanofiber Membranes for the Degradation of Micropollutants and Their Antimicrobial Activity: Recent Advances and Future Prospects

Abstract

This review paper systematically evaluates current progress on the development and performance of photocatalytic nanofiber membranes often used in the removal of micropollutants from water systems. It is demonstrated that nanofiber membranes serve as excellent support materials for photocatalytic nanoparticles, leading to nanofiber membranes with enhanced optical properties, as well as improved recovery, recyclability, and reusability. The tremendous performance of photocatalytic membranes is attributed to the photogenerated reactive oxygen species such as hydroxyl radicals, singlet oxygen, and superoxide anion radicals introduced by catalytic nanoparticles such as TiO₂ and ZnO upon light irradiation. Hydroxyl radicals are the most reactive species responsible for most of the photodegradation processes of these unwanted pollutants. The review also demonstrates that self-cleaning and antimicrobial nanofiber membranes are useful in the removal of microbial species in water. These unique materials are also applicable in other fields such as wound dressing since the membrane allows for oxygen flow in wounds to heal while antimicrobial agents protect wounds against infections. It is demonstrated that antimicrobial activities against bacteria and photocatalytic degradation of micropollutants significantly reduce membrane fouling. Therefore, the review demonstrates that electrospun photocatalytic nanofiber membranes with antimicrobial activity form efficient cost-effective multifunctional composite materials for the removal of unwanted species in water and for use in various other applications such as filtration, adsorption and electrocatalysis.

Keywords: antimicrobial properties; micropollutants; nanofiber membranes; photocatalysis; wastewater treatment.

Figure 1

Chemical structures of different types of polymers that are often used in the fabrication of nanofiber membranes. The asterisk (*) indicates that the structure is continuous.

Figure 2

An example of a composite nanofiber membrane consisting of an electrospun polyacrylonitrile (PAN) layer coated with a chitosan layer. Reprinted from [42] with permission from Elsevier.

Figure 3

Fabrication of Polyethersulfone (PES)-TiO₂ nanofiber composite membrane via electrospinning as well as simultaneous adsorption and photodegradation of micropollutants. Reprinted from [44] with permission from Elsevier.

Figure 4

Schematic illustration of how a photocatalytic membrane operates with the photocatalytic layer on top degrading pollutants and membrane filtering the remaining pollutants. Reprinted from [50] with permission from Elsevier.

Figure 5

Structures of commonly used photocatalytic materials. Reprinted from [80] with permission from Elsevier.

Figure 6

Scanning Electron Microscopy (SEM) images of ZnO nanofibers with diverse morphology produced at different temperatures (a) 350 °C, (b) 450 °C, (c) 550 °C, and (d) 650 °C. Reprinted from [83] with permission from Elsevier.

Figure 7

Illustration of the fabrication of ZnO-ABS composite nanofibers membrane with antimicrobial properties tested against E. coli, S. Aureus and selective oil absorption. Reprinted from [88] with permission from Elsevier.

Figure 8

Illustration of simultaneous filtration and photodegradation processes on a photocatalytic-filtration hybrid composite membrane. Reprinted from [92] with permission from Elsevier.

Figure 9

Fabrication process of an antimicrobial TFC membranes used for water treatment. Reprinted from [124] with permission from Elsevier.

Figure 10

Illustration of antimicrobial activity on a surface of an antimicrobial membrane during water filtration. Reprinted from [124] with permission from Elsevier.

Figure 11

Field emission–scanning electron microscope (FE-SEM) images of (a,c) ZnO-nanorods/polyurethane, (b,d) Polydopamine-ZnO-nanorods/polyurethane. Reprinted from [128] with permission from Elsevier.

Figure 12

Transmission electron microscopy (TEM) images of (a) polyacrylonitrile (PAN) and (b) Ag₃PO₄/PAN composite membranes used for photodegradation and antimicrobial studies by Panthi et al. Reprinted from [129] with permission from Elsevier.

Figure 13

Demonstration of the (a) photocatalysis mechanism and process as well as (b) Self-cleaning/antifouling mechanism and process of polyvinylidene fluoride (PVDF)/TiO₂ membrane. Reprinted from [131] with permission from Elsevier.

Figure 14

Preservation of red grape packed in different materials at 37 °C for 6 days: (a) plastic wrap; (b) pure chitosan film; (c) chitosan-TiO₂ film. Reprinted from [133] with permission from Elsevier.

Figure 15

Membrane fouling reduction induced by the addition of TiO₂ coating through photodegradation. Reprinted from [161].

Figure 16

(a) Graphical illustration and (b) reaction schemes for the surface modification of a polysulfone (PSf) base membrane with TiO₂–graphene oxide (GO). Reprinted from [165] with permission from Elsevier.

Figure 17

Step-by-step illustration of the fabrication of a Bi₂Mo₃O₁₂/MoO₃ nano heterostructure photocatalyst by Liu et al. Reprinted from [166] with permission from Elsevier.

Figure 18

Illustration of adsorption, absorption, and rejection of organic micropollutants and arsenic on the surface and within the membrane pores modified with Fe₃O₄ microspheres during a filtration-absorption process. Adapted from [179] with permission from Elsevier.

Figure 19

SEM cross-sectional image of chitosan/PVA/PES-a-Fe₃O₄ dual layer nanofibrous membranes for adsorption-filtration of Cr(VI) and Pd(II). Reprinted from [181] with permission from Elsevier.

Figure 20

Operating principle of different types of electrochemical electrolysis. Reprinted from [193].