**4.1 Applications of electrospun fibers in water purification**

Electrospinning is a fabrication technique that involves application of a high electric field to generate nanofibers from a charged polymer solution or melt. it is a useful method for the fabrication of complex structures consisting on continuous fibers. The morphology of electrospun fibers can be controlled by adjusting experimental parameters, such as precursor solution concentration, type of spinneret, voltage and the spinneret-collector distance. Using this technique affords us numerous benefits such non-complicated and inexpensive equipment, easy to modify, ability to carefully monitor the morphology of materials, and as well almost all polymers with even high molecular are applicable in the synthesis [23]. The chemical properties of electrospun fibers are mainly influenced by two factors: hydrophilicity and chemical composition of the fibers. The characterization of the mechanical features is critical for the electrospun nanofibers. It can be stated that the electrospun nanofiber membranes are appropriate for the pressure driven membrane procedures where the target product is mainly the permeate phase, for example, water/wastewater treatments [31]. Water purification is mostly defined by filtration through size exclusion or adsorption. The water purification process is classified according to the average pore size of the materials and applications include microfiltration (MF) (0.1-10 μm), ultrafiltration (UF) (0.001–0.1 μm), nanofiltration (NF) (0.001–0.01 μm), reverse osmosis (RO) (0.0001–0.001 μm), and forward osmosis (FO) (0.0001–0.001 μm) [32]. In a study conducted by Mahadevappa Y et.al, where electrospinning was used to fabricate nanofibrous membranes for MF applications using polyvinyl alcohol. Owing to its cost-effectiveness, stability (thermally and chemically) and non-degradability, poly (vinyl alcohol) was selected as a precursor in the fabrication process [33]. However, the poly (vinyl alcohol) nanofiber membranes, produced from electrospinning process, must be treated with cross-linking agents for preparing a 3-D waterproof system before being utilized as water filters [31]. Liu's team has introduced a nanofiber MF membrane that required doping with copper oxide (CuO) nanosheets (**Figure 3**). The fabricated membrane has a separation efficiency of >99.89% for polystyrene (PS) microspheres with a diameter > 300 nm in water [34]. The introduction of such functional materials can not only achieve the corresponding modification purpose, but also enhance static electricity to improve the strength of individual nanofibers. Stable high porosity, good interconnectivity, and ultra-thin membrane thickness are key major factors responsible for its strong permeate flux and excellent bacteria rejection efficiency [35].

**169**

*Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification…*

Electrospun carbon nanofibers exhibit favorable properties, such as nanometersized diameters, high specific surface areas, and web morphologies, making them highly suitable for an anode material. Electrospinning has been identified as the most promising route for designing novel anode materials and structures, owing to its simple process setup. The electrospinning technique is suitable for the implementation of existing anode material research based on the process being able to mass-produce anodes [36]. In a study conducted by Peng et al. and co-workers, the porous carbon nanofibers were synthesized using a PAN/polymethyl methacrylate (PMMA) precursor solution with the aid of electrospinning technique. PMMA is immiscible with PAN, during the course of preparation macro phase separation was observed and was then thermally treated at high reaction temperature-800°C which caused elimination of PMMA while creating pores on the surface of the fiber. In order to investigate the fiber morphology and the electrochemical performance of carbon nanofibers, the author varied the concentration effect of PMMA in the precursor solution. The variation of PMMA showed that its addition significantly

**4.2 Applications of electrospun fibers in lithium ion batteries**

improves the surface area and pore volume of the prepared fibers.

The morphologies of the electrospun fibers after carbonization are shown in **Figure 4**. In **Figure 4(a)**, the carbon nanofibers prepared using neat PAN exhibited long and bead-free morphology. By contrast, the PAN/PMMA-derived carbon nanofibers were uneven and interconnected, particularly for 5:5 PAN/PMMA-derived carbon nanofibers (**Figure 4(c, e)**). The interconnected structure was attributed to the presence of PMMA. PMMA is a thermally liable polymer, which melts during pyrolysis.

**Figure 4** also provides the inner structure of the nanofibers. As observed in **Figure 4(b)**, neat PAN-derived carbon nanofibers were internally nonporous. The introduction of PMMA in precursor solution facilitated the development of pores and channels inside the carbon nanofibers (**Figure 4(d,f)**). The availability of the fiber morphology consequently resulted to highly efficient discharge capacity compared to counterpart neat PAN-prepared carbon nanofibers. Therefore, the 5:5 PAN/PMMAderived carbon nanofibers exhibited a discharge capacity of 446 mAh/g at a current density of 150 mA/g. They exhibited a discharge capacity of 354 mAh/g after 100 cycles at a current density of 200 mA/g equivalent to 67% retention, demonstrating the favorable cycle stability. The significance of their study was based on the manipulation of morphology of electrospun carbon nanofibers for the use as anode materials for lithium ion batteries application to secure good performance. Therefore, it can be said that the superior electrochemical performance of the PAN/PMMA-derived carbon nanofibers was mainly attributed to the prevalent mesopore volume and the high-specific surface area which earned them desired contact between the fibers and electrolyte and conse-

quently improved the diffusion of electrolyte ions into the material [37].

Electrospun nanofibers are materials of multi-applications, hence have been widely studied in the field of biomedical and tissue engineering owing to their good characteristic properties and suitability to be incorporated into various morphologies to stir the desired influence in them, such as nonwoven form, aligned nanofibers, core–shell structure, and hybrid nanocomposites. The interesting characteristic properties of electrospun nanofibers- loose structure, high porosity, and superb flexibility possess perfect features to mimic the extracellular matrix (ECM) for cells to grow and, therefore, they have been employed in tissue engineering applications [38]. In a study, a composite nanofiber scaffold made of poly (vinyl alcohol)–poly (vinyl acetate) (PVA–PVAc) was manufactured and subsequently

**4.3 Electrospun fibers in biomedical applications**

*DOI: http://dx.doi.org/10.5772/intechopen.94962*

**Figure 3.** *Morphology of PVDF/CuO nanosheet nanofiber MF membrane. Adapted from Ref. [34].*

*Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification… DOI: http://dx.doi.org/10.5772/intechopen.94962*

## **4.2 Applications of electrospun fibers in lithium ion batteries**

Electrospun carbon nanofibers exhibit favorable properties, such as nanometersized diameters, high specific surface areas, and web morphologies, making them highly suitable for an anode material. Electrospinning has been identified as the most promising route for designing novel anode materials and structures, owing to its simple process setup. The electrospinning technique is suitable for the implementation of existing anode material research based on the process being able to mass-produce anodes [36]. In a study conducted by Peng et al. and co-workers, the porous carbon nanofibers were synthesized using a PAN/polymethyl methacrylate (PMMA) precursor solution with the aid of electrospinning technique. PMMA is immiscible with PAN, during the course of preparation macro phase separation was observed and was then thermally treated at high reaction temperature-800°C which caused elimination of PMMA while creating pores on the surface of the fiber. In order to investigate the fiber morphology and the electrochemical performance of carbon nanofibers, the author varied the concentration effect of PMMA in the precursor solution. The variation of PMMA showed that its addition significantly improves the surface area and pore volume of the prepared fibers.

The morphologies of the electrospun fibers after carbonization are shown in **Figure 4**. In **Figure 4(a)**, the carbon nanofibers prepared using neat PAN exhibited long and bead-free morphology. By contrast, the PAN/PMMA-derived carbon nanofibers were uneven and interconnected, particularly for 5:5 PAN/PMMA-derived carbon nanofibers (**Figure 4(c, e)**). The interconnected structure was attributed to the presence of PMMA. PMMA is a thermally liable polymer, which melts during pyrolysis. **Figure 4** also provides the inner structure of the nanofibers. As observed in **Figure 4(b)**, neat PAN-derived carbon nanofibers were internally nonporous. The introduction of PMMA in precursor solution facilitated the development of pores and channels inside the carbon nanofibers (**Figure 4(d,f)**). The availability of the fiber morphology consequently resulted to highly efficient discharge capacity compared to counterpart neat PAN-prepared carbon nanofibers. Therefore, the 5:5 PAN/PMMAderived carbon nanofibers exhibited a discharge capacity of 446 mAh/g at a current density of 150 mA/g. They exhibited a discharge capacity of 354 mAh/g after 100 cycles at a current density of 200 mA/g equivalent to 67% retention, demonstrating the favorable cycle stability. The significance of their study was based on the manipulation of morphology of electrospun carbon nanofibers for the use as anode materials for lithium ion batteries application to secure good performance. Therefore, it can be said that the superior electrochemical performance of the PAN/PMMA-derived carbon nanofibers was mainly attributed to the prevalent mesopore volume and the high-specific surface area which earned them desired contact between the fibers and electrolyte and consequently improved the diffusion of electrolyte ions into the material [37].

#### **4.3 Electrospun fibers in biomedical applications**

Electrospun nanofibers are materials of multi-applications, hence have been widely studied in the field of biomedical and tissue engineering owing to their good characteristic properties and suitability to be incorporated into various morphologies to stir the desired influence in them, such as nonwoven form, aligned nanofibers, core–shell structure, and hybrid nanocomposites. The interesting characteristic properties of electrospun nanofibers- loose structure, high porosity, and superb flexibility possess perfect features to mimic the extracellular matrix (ECM) for cells to grow and, therefore, they have been employed in tissue engineering applications [38]. In a study, a composite nanofiber scaffold made of poly (vinyl alcohol)–poly (vinyl acetate) (PVA–PVAc) was manufactured and subsequently

*Nanofibers - Synthesis, Properties and Applications*

**4.1 Applications of electrospun fibers in water purification**

Electrospinning is a fabrication technique that involves application of a high electric

field to generate nanofibers from a charged polymer solution or melt. it is a useful method for the fabrication of complex structures consisting on continuous fibers. The morphology of electrospun fibers can be controlled by adjusting experimental parameters, such as precursor solution concentration, type of spinneret, voltage and the spinneret-collector distance. Using this technique affords us numerous benefits such non-complicated and inexpensive equipment, easy to modify, ability to carefully monitor the morphology of materials, and as well almost all polymers with even high molecular are applicable in the synthesis [23]. The chemical properties of electrospun fibers are mainly influenced by two factors: hydrophilicity and chemical composition of the fibers. The characterization of the mechanical features is critical for the electrospun nanofibers. It can be stated that the electrospun nanofiber membranes are appropriate for the pressure driven membrane procedures where the target product is mainly the permeate phase, for example, water/wastewater treatments [31]. Water purification is mostly defined by filtration through size exclusion or adsorption. The water purification process is classified according to the average pore size of the materials and applications include microfiltration (MF) (0.1-10 μm), ultrafiltration (UF) (0.001–0.1 μm), nanofiltration (NF) (0.001–0.01 μm), reverse osmosis (RO) (0.0001–0.001 μm), and forward osmosis (FO) (0.0001–0.001 μm) [32]. In a study conducted by Mahadevappa Y et.al, where electrospinning was used to fabricate nanofibrous membranes for MF applications using polyvinyl alcohol. Owing to its cost-effectiveness, stability (thermally and chemically) and non-degradability, poly (vinyl alcohol) was selected as a precursor in the fabrication process [33]. However, the poly (vinyl alcohol) nanofiber membranes, produced from electrospinning process, must be treated with cross-linking agents for preparing a 3-D waterproof system before being utilized as water filters [31]. Liu's team has introduced a nanofiber MF membrane that required doping with copper oxide (CuO) nanosheets (**Figure 3**). The fabricated membrane has a separation efficiency of >99.89% for polystyrene (PS) microspheres with a diameter > 300 nm in water [34]. The introduction of such functional materials can not only achieve the corresponding modification purpose, but also enhance static electricity to improve the strength of individual nanofibers. Stable high porosity, good interconnectivity, and ultra-thin membrane thickness are key major factors responsible

for its strong permeate flux and excellent bacteria rejection efficiency [35].

*Morphology of PVDF/CuO nanosheet nanofiber MF membrane. Adapted from Ref. [34].*

**168**

**Figure 3.**

**Figure 4.**

*SEM micrographs of electrospun fibers carbonized at 800°C. a and b PAN/PMMA = 10:0; c and d PAN/PMMA = 7:3; and e and f PAN/PMMA = 5:5. Adapted from Ref. [37].*

loaded with simvastatin superficial layer to obtain an efficient osteogenesis process by the continuous release of the drug [39]. The use of PVA was attributed to its environmentally benign, elasticity, flexibility, proper mechanical properties, nontoxicity, swelling ability, and biodegradability. PVA is not stable in aqueous state, this instability however creates limitation in its use in drug delivery processes. In order to overcome instability issue, PVA was then crosslinked with biocompatible and biodegradable PVAc that possess hydrolysable groups. Afterward a simvastatin drug was loaded into the blended solution of PVA–PVAc in order to promote the efficiency of bone regeneration. The obtained results revealed good bioactivity, inducing the precipitation of bone-like apatite minerals on its surface and successfully simulating physiological conditions for cell growth [39]. Electrospun nanofibrous dressings have high surface-to-volume ratio, allow gas permeation, help to regulate wound moisture, enhance tissue regeneration, improve removal of exudates, and have high porosity, which qualifies them to be used in wound healing treatment. Previous studies have shown low inflammatory reaction and fast re-epithelization with the use of nanofiber-based wound dressing [38].

Bredigite polymer electrospun nanofibers have been widely investigated to access their suitability in wound-dressing processes. It has been reported as a

**171**

**Figure 5.**

*(b) T-BR nanoparticles. Adapted from [40].*

*Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification…*

scaffold however, results showed that while the bioactivity of the composite nanofibers was improved, and the low dispersibility and high agglomeration of nanoparticles decrease the efficiency of prepared electrospun nanofibers [40]. In another attempt, bredigite (BR) nanoparticles were modified by an organosilane coupling agent in order to increase its dispersibility [40]. The SEM results reveal that the modified BR nanoparticles are widely dispersed in the body of the nanofibers without any agglomeration (**Figure 5**). Moreover, the mechanical and biodegrada-

*Schematic illustration and SEM images of PHBV nanofibers containing 15% of (a) bredigite (BR) and* 

The fabrication of energy device material such as thin film photoelectrode for splitting water into H2 and O2 during photoelectrochemical process and the development of photovoltaic cells, for solar energy conversion is tasking and difficult, requiring a special operational technique. For efficient solar energy capturing and conversion in photovoltaic cells, effective separation electrons and holes in photoelectrode required [41, 42]. This depend on the deposited semiconducting material ultrathin layer, evenly coated and tightly connected to conductive layer. Atomic layer deposition (ALD) as a vapor phase technique is capable of producing thin films of different materials. ALD is applicable in the fabrication of uniform and ratio structures with thickness control to Angstrom level, and tuneable film composition [43]. Due to all this advantages, ALD has emerged as a powerful tool for many

tion rate of the scaffolds dramatically improved after BR modification.

**5. Advance manufacturing methods for energy applications**

*DOI: http://dx.doi.org/10.5772/intechopen.94962*

*Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification… DOI: http://dx.doi.org/10.5772/intechopen.94962*

#### **Figure 5.**

*Nanofibers - Synthesis, Properties and Applications*

loaded with simvastatin superficial layer to obtain an efficient osteogenesis process by the continuous release of the drug [39]. The use of PVA was attributed to its environmentally benign, elasticity, flexibility, proper mechanical properties, nontoxicity, swelling ability, and biodegradability. PVA is not stable in aqueous state, this instability however creates limitation in its use in drug delivery processes. In order to overcome instability issue, PVA was then crosslinked with biocompatible and biodegradable PVAc that possess hydrolysable groups. Afterward a simvastatin drug was loaded into the blended solution of PVA–PVAc in order to promote the efficiency of bone regeneration. The obtained results revealed good bioactivity, inducing the precipitation of bone-like apatite minerals on its surface and successfully simulating physiological conditions for cell growth [39]. Electrospun nanofibrous dressings have high surface-to-volume ratio, allow gas permeation, help to regulate wound moisture, enhance tissue regeneration, improve removal of exudates, and have high porosity, which qualifies them to be used in wound healing treatment. Previous studies have shown low inflammatory reaction and fast

*SEM micrographs of electrospun fibers carbonized at 800°C. a and b PAN/PMMA = 10:0; c and d* 

*PAN/PMMA = 7:3; and e and f PAN/PMMA = 5:5. Adapted from Ref. [37].*

re-epithelization with the use of nanofiber-based wound dressing [38].

Bredigite polymer electrospun nanofibers have been widely investigated to access their suitability in wound-dressing processes. It has been reported as a

**170**

**Figure 4.**

*Schematic illustration and SEM images of PHBV nanofibers containing 15% of (a) bredigite (BR) and (b) T-BR nanoparticles. Adapted from [40].*

scaffold however, results showed that while the bioactivity of the composite nanofibers was improved, and the low dispersibility and high agglomeration of nanoparticles decrease the efficiency of prepared electrospun nanofibers [40]. In another attempt, bredigite (BR) nanoparticles were modified by an organosilane coupling agent in order to increase its dispersibility [40]. The SEM results reveal that the modified BR nanoparticles are widely dispersed in the body of the nanofibers without any agglomeration (**Figure 5**). Moreover, the mechanical and biodegradation rate of the scaffolds dramatically improved after BR modification.

### **5. Advance manufacturing methods for energy applications**

The fabrication of energy device material such as thin film photoelectrode for splitting water into H2 and O2 during photoelectrochemical process and the development of photovoltaic cells, for solar energy conversion is tasking and difficult, requiring a special operational technique. For efficient solar energy capturing and conversion in photovoltaic cells, effective separation electrons and holes in photoelectrode required [41, 42]. This depend on the deposited semiconducting material ultrathin layer, evenly coated and tightly connected to conductive layer. Atomic layer deposition (ALD) as a vapor phase technique is capable of producing thin films of different materials. ALD is applicable in the fabrication of uniform and ratio structures with thickness control to Angstrom level, and tuneable film composition [43]. Due to all this advantages, ALD has emerged as a powerful tool for many

**Figure 6.** *Atomic layer deposition (ALD) reactor. Adapted from Ref. [43].*

#### **Figure 7.**

*Schematic illustration of ALD process schematic of ALD process. (a) Substrate surface has natural functionalization or is treated to functionalize the surface. (b) Precursor a is pulsed and reacts with surface. (c) Excess precursor and reaction by-products are purged with inert carrier gas. (d) Precursor B is pulsed and reacts with surface. (e) Excess precursor and reaction by-products are purged with inert carrier gas. (f) Steps 2–5 are repeated until the desired material thickness is achieved. Adapted from Ref. [45].*

energy research material fabrications. ALD method has been a useful tool for the deposition of ultrathin-layered semiconductors on conductive substrate.

ALD process generally consists of sequential alternating pulses of gaseous chemical precursors that react with the substrate, these individual gas-surface reactions called 'half-reactions' and appropriately make up only part of the materials synthesis. During each half-reaction, the precursor is pulsed into a compartment under vacuum (< 1 Torr) over a selected extent of time to allow the precursor to fully react with the substrate surface through a self-limiting process that leaves no more than one monolayer at the surface [44, 45]. Then, the chamber is purged with an inert carrier gas (typically N2 or Ar) to remove any unreacted precursor or reaction by-products.

**173**

**Author details**

**6. Conclusion**

Amos Adeleke Akande1

and Bonex Wakufwa Mwakikunga5

Industrial Research, Pretoria, South Africa

provided the original work is properly cited.

\*Address all correspondence to: aaakande@csir.co.za

*Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification…*

This is then followed by the counter-reactant precursor pulse and purge, creating up to one layer of the desired material. This process is then cycled until the appropriate

The interdigitated electrode is reported as cost effective method for prototyping gas, chemical and bio sensor and the method is widely used for laboratory research purpose. State of the art techniques such high tech semiconductor deposition instruments, photolithography and electron beam lithography are used for commercial sensors built with printed electronics and Lab-on-a chip. Electrospinning method is highly important in the fabrication of micro and nano porous fibers for the manufacturing of membranes and battery devices. This method has also been identified for designing anode materials suitable for lithium ion battery fabrication. Atomic layer deposition is useful for producing ultrathin layer-layered semiconductors with inherent properties necessary for efficient energy capturing. This deposition technique is very useful in the manufacturing of photovoltaic cells and related

\*, Aderemi Timothy Adeleye2,3, Abraham Abdul Adenle4

1 Next Generation Enterprises and Institutions Cluster, EDT4IR Research Centre,

2 CAS Key Laboratory of Science and Technology on Applied Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China

3 University of Chinese Academy of Sciences, Shijingshan District, Beijing, China

4 State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian National Laboratory for Clean Energy, Dalian, China

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

5 National Centre for Nano-Structured Materials, Council for Scientific and

Council for Scientific and Industrial Research, Pretoria, South Africa

devices for effective separation electrons and holes in photo-electrode.

*DOI: http://dx.doi.org/10.5772/intechopen.94962*

film thickness is achieved (**Figures 6** and **7**).

*Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification… DOI: http://dx.doi.org/10.5772/intechopen.94962*

This is then followed by the counter-reactant precursor pulse and purge, creating up to one layer of the desired material. This process is then cycled until the appropriate film thickness is achieved (**Figures 6** and **7**).
