Nanocomposite Electrospun Nanofiber Membranes for Environmental Remediation

Abstract

Rapid worldwide industrialization and population growth is going to lead to an extensive environmental pollution. Therefore, so many people are currently suffering from the water shortage induced by the respective pollution, as well as poor air quality and a huge fund is wasted in the world each year due to the relevant problems. Environmental remediation necessitates implementation of novel materials and technologies, which are cost and energy efficient. Nanomaterials, with their unique chemical and physical properties, are an optimum solution. Accordingly, there is a strong motivation in seeking nano-based approaches for alleviation of environmental problems in an energy efficient, thereby, inexpensive manner. Thanks to a high porosity and surface area presenting an extraordinary permeability (thereby an energy efficiency) and selectivity, respectively, nanofibrous membranes are a desirable candidate. Their functionality and applicability is even promoted when adopting a nanocomposite strategy. In this case, specific nanofillers, such as metal oxides, carbon nanotubes, precious metals, and smart biological agents, are incorporated either during electrospinning or in the post-processing. Moreover, to meet operational requirements, e.g., to enhance mechanical stability, decrease of pressure drop, etc., nanofibrous membranes are backed by a microfibrous non-woven forming a hybrid membrane. The novel generation of nanocomposite/hybrid nanofibrous membranes can perform extraordinarily well in environmental remediation and control. This reality justifies authoring of this review paper.

Keywords: air filtration; membrane; nanocomposite; nanofiber; nanohybrid; water filtration.

Figure 1.

Water scarcity as a global challenge (more than 50% of the world countries will experience water scarcity by 2025) [2].

Figure 2.

The map presented by the National Aeronautics and Space Administration (NASA) shows the air pollution related mortality rates worldwide (in contrary to the dark brown areas, the blue areas are those where the air quality has been improved and the related death rate has declined) [7].

Figure 3.

A schematic of the electrospinning process of polymer nanofibers [22].

Figure 4.

Different fabrication methods of nanocomposite/hybrid ENMs [–35].

Figure 5.

Different classes of nanocomposite/hybrid ENMs based on their environmental applications and performance.

Figure 6.

PES/PET hybrid ENM [44].

Figure 7.

SEM images showing (A) surface and (B) cross-section views of PAN/PET hybrid ENM after E. coli suspension filtration [49].

Figure 8.

Schematic structure of the UF TFC electropun nanofibrous membrane (left) and representative SEM image of electrospun PVA midlayer (right) [50].

Figure 9.

Capturing of metal nanoparticles through the wetting induced-conformational change of the proteins immobilized onto nanofibers [26].

Figure 10.

(A) Extraordinary retention efficiency of the BSA/PANGMA ENMs for Au nanoparticles and (B) visual comparisons between the feed and permeated samples through the neat (I) and BSA/PANGMA ENMs (II).

Figure 11.

The mechanism of charge separation and photocatalytic activity of the TiO₂/ZnO nanofibers [64].

Figure 12.

TEM images of cellulose acetate nanofibers containing 5 wt% AgNO₃ (A) before UV irradiation and (B) after UV irradiation [70].

Figure 13.

TEM observation of (A) ZrO₂/PES fibers [24] and (B) TiO₂/PES nanofibers (adjacent to a bead with the same composition) (the inset picture implies the superhydrophilicity effect of the composite nanofibrous membrane) [24,25].

Figure 14.

The main aerosol capturing mechanisms of a fibrous filter [89].

Figure 15.

A breathable barrier membrane acting as protective clothing [104].