Synthesis and Water Treatment Applications of Nanofibers by Electrospinning

Abstract

In the past few decades, the role of nanotechnology has expanded into environmental remediation applications. In this regard, nanofibers have been reported for various applications in water treatment and air filtration. Nanofibers are fibers of polymeric origin with diameters in the nanometer to submicron range. Electrospinning has been the most widely used method to synthesize nanofibers with tunable properties such as high specific surface area, uniform pore size, and controlled hydrophobicity. These properties of nanofibers make them highly sought after as adsorbents, photocatalysts, electrode materials, and membranes. In this review article, a basic description of the electrospinning process is presented. Subsequently, the role of different operating parameters in the electrospinning process and precursor polymeric solution is reviewed with respect to their influence on nanofiber properties. Three key areas of nanofiber application for water treatment (desalination, heavy-metal removal, and contaminant of emerging concern (CEC) remediation) are explored. The latest research in these areas is critically reviewed. Nanofibers have shown promising results in the case of membrane distillation, reverse osmosis, and forward osmosis applications. For heavy-metal removal, nanofibers have been able to remove trace heavy metals due to the convenient incorporation of specific functional groups that show a high affinity for the target heavy metals. In the case of CECs, nanofibers have been utilized not only as adsorbents but also as materials to localize and immobilize the trace contaminants, making further degradation by photocatalytic and electrochemical processes more efficient. The key issues with nanofiber application in water treatment include the lack of studies that explore the role of the background water matrix in impacting the contaminant removal performance, regeneration, and recyclability of nanofibers. Furthermore, the end-of-life disposal of nanofibers needs to be explored. The availability of more such studies will facilitate the adoption of nanofibers for water treatment applications.

Sustainable Applications of Nanofibers in Agriculture and Water Treatment: A Review

“…Physically, the surface area and pore volume of nanofibers are key parameters determining the fiber adsorption capacity and, therefore, water treatment performance. This mechanism was confirmed by many researchers, such as Agrawal et al [102] and Uddin et al [103]. Many recent reviews were published on the removing of hazardous pollutants (i.e., both organic and inorganic materials) from water/wastewater using nanofibers such as Chen et al [104], Cui et al [35], Ibrahim et al [105], Jahan and Zhang [106], Marinho et al [107], Sakib et al [80], Sjahro et al [108], and El-Aswar et al [109].…”

Multifunctional Membranes—A Versatile Approach for Emerging Pollutants Removal

“…Nanofibers exhibit new and advanced properties that can be enhanced by their functionalization. For example, due to their high specific surface area, nanoparticles, nanorods, nanowires, nanotubes, nanosheets, zeolites, and metal-organic frameworks can be immobilized, allowing the high-selectivity removal of water contaminants [140]. The functionalization can be performed through the direct electrospinning of the nanofibers using self-assembly techniques.…”

“…Some disadvantages, such as long-term health and environmental impacts due to their toxicity, nonbiodegradability, and disposal, have to be noted. In terms of waste minimization, there is an urgent need to replace them with recyclable and biodegradable green materials [140,162,163].…”

“…Cyclodextrin (CD) enhances the removal capacity of PAN nanofibers (91.46% for atrazine) and polyethersulfone (PES) nanofibers (for steroid hormones), and has also been investigated in combination with triglycidyl ether and triphenylmethane triglycidyl ether as crosslinkers (95% for estradiol). It was observed that when the diameter is decreased from 557 nm to 497 nm, in the case of CD-PAN, the specific surface area increases [140]. Additionally, the synergistic effect of hydrophobic interaction and hydrogen bonding influences the removal process in the case of CD-PES [181][182][183].…”

“…This type of material, as a composite, was tested for the degradation of emerging pollutants. Good results were achieved for BPA degradation using a UV light source, with an efficiency of about 63-85% [140,216]. Additionally, the electrospinning method was applied for the preparation of ZnO-carbon composite nanofibers, using PAN, polystyrene (PS) and polyvinyl pyrrolidone (PVP) as precursors for caffeine (80.4%) and diclofenac (79.5%) removal under photocatalytic degradation [217].…”