**1. Introduction**

Common water pollutants such as toxic micro-organisms and inorganic and organic waste are a serious threat to the health of humans, animals and the aquatic biota. Diverse methods and materials are currently used to treat wastewater in order to overcome the high level of water pollution. However, emerging micropollutants (EMPs) such as hormones, pharmaceuticals, detergents, phenols, fragrances, illicit drugs, endocrine disruptors, steroids and personal care products have proven to be persistent and difficult to remove from aqueous systems [1, 2]. In particular, EMPs are continuously found in trace amounts in waste and treated water. In addition, trace organic pollutants find their way into wastewater after being excreted from human bodies and when disposed to the sewage system [1–3]. Pharmaceutical waste and other trace organic pollutants leave the wastewater treatment plant without being treated because they are present in small amounts, biologically active or thermally and chemically stable [2]. EMPs and their derivatives are of great concern since their fate and behavior is not well understood. Moreover, current treatment methods are not effective in the removal of these EMPs. This has therefore led to the development of diverse technologies including nanotechnology-based technologies to remove EMPs in water systems.

Nanotechnology-based techniques frequently applied in water treatment make use of various nanomaterials including, among others, nanofibers, nanowires, nanotubes, nanorods and nanospheres. These distinct nanomaterials are endowed with several advantageous properties that render them suitable in the removal of micropollutants from aqueous systems. These properties include high porosity, small diameters and high surface area per unit volume. In particular, nanofibers are easy to handle, reusable and recyclable making them ideal candidates for use in water treatment applications [4, 5]. Workers have also applied photocatalytic nanomaterials such as TiO<sup>2</sup> and ZnO and found them to be excellent candidates for use in the photodegradation of most micropollutants using their inherent quantum and surface properties [6]. TiO<sup>2</sup> and ZnO nanomaterials have been applied in various areas, which include textile, wastewater treatment, particulate separation, health care, desalination, energy, liquid filtration and sensors [7, 8]. Hollow-structured nanomaterials such as nanotubes and nanofibers (**Figure 1**) can encapsulate active additives such as photocatalysts, antioxidants and antibacterial agents and then applied in water treatment, food packaging and biotechnology [8, 9]. Photocatalysts have been incorporated with other materials such as the natural polymer cyclodextrins (CDs) for use in water treatment applications [10]. CDs are gaining extensive popularity as adsorbents and as membrane materials due to their toroidal structure and distinct characteristics.

CDs and their derivatives such as methyl-βCD (m-βCD) (**Figure 2**) are known to significantly remove organic pollutants from water systems *via* adsorption and inclusion complexation. They can also be polymerized to form supramolecular structures with high surface areas [12]. The geometry of CDs demonstrates a hydrophobic cavity capable of inclusion complexation with a wide range of pollutants [7, 13]. The ability of CDs to capture and form inclusion complexes with other molecules in solution and their ability to be electrospun with ease as well as other physicochemical properties render them ideal candidates for water treatment applications [7, 12, 14]. The release of water molecules from the hydrophobic cavity, coupled with

hydrogen bonding, charge transfer interactions, hydrophobic interactions, van der Waals interactions, release of conformational strain and electrostatic interactions are the driving forces for inclusion complexation through apolar-apolar interaction of CDs and the guest compounds [12, 15]. It is for this reason that CDs are used in water treatment to remove EMPs and various other pollutants as well as in medicine for drug delivery applications. Besides

**Figure 1.** Microscopic view of hollow-structured nanofibers (a and b) the as-electrospun nanofibers. (c and d) The images of nanotubes at low and high magnification. The inset shows the surface and cross profile of the nanotube. Reproduced

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with permission from [11].

**Figure 2.** Schematic illustration of (a) βCD and (b) m-βCD.

Cyclodextrin-Based Nanofibers and Membranes: Fabrication, Properties and Applications http://dx.doi.org/10.5772/intechopen.74737 137

**Figure 1.** Microscopic view of hollow-structured nanofibers (a and b) the as-electrospun nanofibers. (c and d) The images of nanotubes at low and high magnification. The inset shows the surface and cross profile of the nanotube. Reproduced with permission from [11].

**Figure 2.** Schematic illustration of (a) βCD and (b) m-βCD.

**1. Introduction**

136 Cyclodextrin - A Versatile Ingredient

rials such as TiO<sup>2</sup>

technologies to remove EMPs in water systems.

Common water pollutants such as toxic micro-organisms and inorganic and organic waste are a serious threat to the health of humans, animals and the aquatic biota. Diverse methods and materials are currently used to treat wastewater in order to overcome the high level of water pollution. However, emerging micropollutants (EMPs) such as hormones, pharmaceuticals, detergents, phenols, fragrances, illicit drugs, endocrine disruptors, steroids and personal care products have proven to be persistent and difficult to remove from aqueous systems [1, 2]. In particular, EMPs are continuously found in trace amounts in waste and treated water. In addition, trace organic pollutants find their way into wastewater after being excreted from human bodies and when disposed to the sewage system [1–3]. Pharmaceutical waste and other trace organic pollutants leave the wastewater treatment plant without being treated because they are present in small amounts, biologically active or thermally and chemically stable [2]. EMPs and their derivatives are of great concern since their fate and behavior is not well understood. Moreover, current treatment methods are not effective in the removal of these EMPs. This has therefore led to the development of diverse technologies including nanotechnology-based

Nanotechnology-based techniques frequently applied in water treatment make use of various nanomaterials including, among others, nanofibers, nanowires, nanotubes, nanorods and nanospheres. These distinct nanomaterials are endowed with several advantageous properties that render them suitable in the removal of micropollutants from aqueous systems. These properties include high porosity, small diameters and high surface area per unit volume. In particular, nanofibers are easy to handle, reusable and recyclable making them ideal candidates for use in water treatment applications [4, 5]. Workers have also applied photocatalytic nanomate-

radation of most micropollutants using their inherent quantum and surface properties [6]. TiO<sup>2</sup> and ZnO nanomaterials have been applied in various areas, which include textile, wastewater treatment, particulate separation, health care, desalination, energy, liquid filtration and sensors [7, 8]. Hollow-structured nanomaterials such as nanotubes and nanofibers (**Figure 1**) can encapsulate active additives such as photocatalysts, antioxidants and antibacterial agents and then applied in water treatment, food packaging and biotechnology [8, 9]. Photocatalysts have been incorporated with other materials such as the natural polymer cyclodextrins (CDs) for use in water treatment applications [10]. CDs are gaining extensive popularity as adsorbents and as

CDs and their derivatives such as methyl-βCD (m-βCD) (**Figure 2**) are known to significantly remove organic pollutants from water systems *via* adsorption and inclusion complexation. They can also be polymerized to form supramolecular structures with high surface areas [12]. The geometry of CDs demonstrates a hydrophobic cavity capable of inclusion complexation with a wide range of pollutants [7, 13]. The ability of CDs to capture and form inclusion complexes with other molecules in solution and their ability to be electrospun with ease as well as other physicochemical properties render them ideal candidates for water treatment applications [7, 12, 14]. The release of water molecules from the hydrophobic cavity, coupled with

membrane materials due to their toroidal structure and distinct characteristics.

and ZnO and found them to be excellent candidates for use in the photodeg-

hydrogen bonding, charge transfer interactions, hydrophobic interactions, van der Waals interactions, release of conformational strain and electrostatic interactions are the driving forces for inclusion complexation through apolar-apolar interaction of CDs and the guest compounds [12, 15]. It is for this reason that CDs are used in water treatment to remove EMPs and various other pollutants as well as in medicine for drug delivery applications. Besides their use in nanofiber production, CDs and their derivatives have become popular in membrane technology.

temperature that is dependent on the composition. Polymers can be miscible in melt state and immiscible in solid state due to fast crystallization of one component compared to the other [22]. When blended polymers do not crystalize at the same rate, it results in phase separation, which will affect the final product and their envisaged properties [22]. However, due to the miscibility of the components, they can each reside in the interlamellar and/or interspherulitic

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Immiscible solutions are often referred to as emulsions where one component is dispersed on top of the other as small-sized droplets depending on the quantity of each solution as shown in **Figure 3** [28]. Most polymer blends are immiscible because of the weak interfacial interactions between components and different molecular weight of each component [22]. Immiscible polymer blends also have enhanced properties compared to their separate components [29]. Immiscible polymer blends limit full access of each component properties and application due to their incompatibility. Producing nanofibers through this method requires the use of stabilizing agents such as fillers and metal organic frameworks. Produced fibers are

Compatible polymer blends are immiscible polymer blends that have uniform macroscopically physical properties. Compatible polymer blends are often used to enhance the properties of components such as elastic modulus, crystallinity and glass transition temperature [32, 33]. Polymers often require the use of fillers/compatibilizer to induce compatibility between the components (**Figure 4**). To be effective enough, fillers must have a particle radius of the same order of magnitude as the gyration radius of the polymers used.

Sea or island cross-section conjugation is a type of a conjugate spinning method used to fabricate fibers with diameters of less than 1 μm with a predetermined component arrangement in its cross-section. Two polymer components of a conjugate type are elongated and extruded together from a spinneret. These polymers then combine in the back of a spinning nozzle. The produced conjugate fibers with two components are then split into filaments. This technique involves spinning a bicomponent filament consisting of polyester, polyethylene, nylon or polypropylene used as an island component and a polymer like polystyrene is used as a sea component. The fabric is then exposed to a solvent, thermal or mechanical treatment whereby the immiscible components separate as the polystyrene sea component dissolves in a solvent,

Examples of fillers include ethylene-acrylic acid and ethylene-vinyl alcohol [33, 34].

**Figure 3.** Schematic representation of immiscible polymer solution with varied concentrations of each polymer.

regions of each other during crystallization, thus reducing separation rates [27].

in microscale and requires subsequent polymer matrix extraction [30, 31].

**2.2. Sea/island cross-section conjugation**

Recently, workers prepared electrospun nanofibers using chitosan and incorporated silver and iron nanoparticles for water disinfection processes. These nanofibers were later effectively modified using CDs and cellulose to increase their thermal and chemical stability [16]. Somewhere else, thermally and mechanically stable βCD/cellulose acetate nanofibers were synthesized using an environmentally benign procedure and used for enhanced antimicrobial treatment of water [17]. In membrane technology, Adams et al. utilized CD molecules as modifying agents for the preparation of polysulfone-polyurethane (PSF-PU) composite nanofiltration membranes, which were used for the removal of undesirable salts [18].

In this chapter, electrospun CD-based materials are discussed in view of water treatment, their properties and advantages toward improving current water treatment methods by removing EMPs in waste and treated water. We also critically investigate CD-based membrane techniques in terms of their production and characterization methods with focus placed on their application in water treatment. Other applications of these CD-based nanocomposites such as drug delivery, antimicrobial uses, biomedical uses, filtration, photocatalysis and environmental protection are covered.
