Nanofiber applications in microbial fuel cells for enhanced energy generation: a mini review.

Microbial fuel cells (MFCs) represent simple devices that harness the metabolic activities of microorganisms to produce electrical energy from diverse sources such as organic waste and sustainable biomass. Because of their unique advantage to generate sustainable energy, through the employment of biodegradable and repurposed waste materials, the development of MFCs has garnered considerable interest. Critical elements are typically the electrodes and separator. This mini-review article presents a critical assessment of nanofiber technology used as electrodes and separators in MFCs to enhance energy generation. In particular, the review highlights the application of nanofiber webs in each part of MFCs including anodes, cathodes, and membranes and their influence on energy generation. The role of nanofiber technology in this regard is then analysed in detail, focusing on improved electron transfer rate, enhanced biofilm formation, and enhanced durability and stability. In addition, the challenges and opportunities associated with integrating nanofibers into MFCs are discussed, along with suggestions for future research in this field. Significant developments in MFCs over the past decade have led to a several-fold increase in achievable power density, yet further improvements in performance and the exploration of cost-effective materials remain promising areas for further advancement. This review demonstrates the great promise of nanofiber-based electrodes and separators in future applications of MFCs.

Chemical Cleaning Process of Polymeric Nanofibrous Membranes.

Membrane fouling is one of the most significant issues to overcome in membrane-based technologies as it causes a decrease in the membrane flux and increases operational costs. This study investigates the effect of common chemical cleaning agents on polymeric nanofibrous membranes (PNM) prepared by polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyamide 6 (PA6) nanofibers. Common alkaline and acid membrane cleaners were selected as the chemical cleaning agents. Membrane surface morphology was investigated. The PAN PNM were selected and fouled by engine oil and then cleaned by the different chemical cleaning agents at various ratios. The SEM results indicated that the use of chemical agents had some effects on the surface of the nanofibrous membranes. Moreover, alkaline cleaning of the fouled membrane using the Triton X 100 surfactant showed a two to five times higher flux recovery than without using a surfactant. Among the tested chemical agents, the highest flux recovery rate was obtained by a binary solution of 5% sodium hydroxide + Triton for alkaline cleaning, and an individual solution of 1% citric acid for acidic cleaning. The results presented here provide one of the first investigations into the chemical cleaning of nanofiber membranes.

Electrospun Poly(ethylene Terephthalate)/Silk Fibroin Composite for Filtration Application.

In this study, fibrous membranes from recycled-poly(ethylene terephthalate)/silk fibroin (r-PSF) were prepared by electrospinning for filtration applications. The effect of silk fibroin on morphology, fibers diameters, pores size, wettability, chemical structure, thermo-mechanical properties, filtration efficiency, filtration performance, and comfort properties such as air and water vapor permeability was investigated. The filtration efficiency (FE) and quality factor (Qf), which represents filtration performance, were calculated from penetration through the membranes using aerosol particles ranging from 120 nm to 2.46 µm. The fiber diameter influenced both FE and Qf. However, the basis weight of the membranes has an effect, especially on the FE. The prepared membranes were classified according to EN149, and the most effective was assigned to the class FFP1 and according to EN1822 to the class H13. The impact of silk fibroin on the air permeability was assessed. Furthermore, the antibacterial activity against bacteria S. aureus and E. coli and biocompatibility were evaluated. It is discussed that antibacterial activity depends not only on the type of used materials but also on fibrous membranes' surface wettability. In vitro biocompatibility of the selected samples was studied, and it was proven to be of the non-cytotoxic effect of the keratinocytes (HaCaT) after 48 h of incubation.

Fouling and Chemical Cleaning of Microfiltration Membranes: A Mini-Review.

Membrane fouling is one of the main drawbacks encountered during the practical application of membrane separation processes. Cleaning of a membrane is important to reduce fouling and improve membrane performance. Accordingly, an effective cleaning method is currently of crucial importance for membrane separation processes in water treatment. To clean the fouling and improve the overall efficiency of membranes, deep research on the cleaning procedures is needed. So far, physical, chemical, or combination techniques have been used for membrane cleaning. In the current work, we critically reviewed the fouling mechanisms affecting factors of fouling such as the size of particle or solute; membrane microstructure; the interactions between membrane, solute, and solvent; and porosity of the membrane and also examined cleaning methods of microfiltration (MF) membranes such as physical cleaning and chemical cleaning. Herein, we mainly focused on the chemical cleaning process. Factors affecting the chemical cleaning performance, including cleaning time, the concentration of chemical cleaning, and temperature of the cleaning process, were discussed in detail. This review is carried out to enable a better understanding of the membrane cleaning process for an effective membrane separation process.

Modified Nanofibrous Filters with Durable Antibacterial Properties.

The main aims of the research were to produce efficient nanofibrous filters with long-term antibacterial properties and to confirm the functionality of samples under real filtration conditions. A polyurethane solution was modified by micro- or nanoparticles of copper oxide in order to juxtapose the aggregation tendency of particles depending on their size. Modified solutions were electrospun by the Nanospider technique. The roller spinning electrode with a needle surface and static wire electrode were used for the production of functionalized nanofibers. The antibacterial properties of the modified nanofibrous layers were studied under simulated conditions of water and air filtration. Particular attention was paid to the fixation mechanism of modifiers in the structure of filters. It was determined that the rotating electrode with the needle surface is more efficient for the spinning of composite solutions due to the continuous mixing and the avoidance of particle precipitation at the bottom of the bath with modified polyurethane. Moreover, it was possible to state that microparticles of copper oxide are more appropriate antimicrobial additives due to their weaker aggregation tendency but stronger fixation in the fibrous structure than nanoparticles. From the results, it is possible to conclude that nanofibers with well-studied durable antibacterial properties may be recommended as excellent materials for water and air filtration applications.

Reuse of Textile Waste to Production of the Fibrous Antibacterial Membrane with Filtration Potential.

Wasted synthetic fabrics are a type of textile waste source; the reuse of them brings environmental protection and turns waste into a valuable material. In this work, the used nylon (polyamide) stockings were transmuted into a fine fibrous membrane via an electrospinning process. In addition, the safety antibacterial agent, monoacylglycerol (MAG), was incorporated into a recycled fibrous membrane. The results revealed that the neat, recycled polyamide (rPA) fibers with a hydrophobic surface could be converted into hydrophilic fibers by blending various amounts of MAG with rPA solution prior to electrospinning. The filtration efficiency and air/water vapor permeability of the two types of produced membranes, neat rPA, and rPA/MAG, were tested. Their filtration efficiency (E100) was more than 92% and 96%, respectively. The membranes were classified according to Standard EN1822, and therefore, the membranes rPA and rPA/MAG were assigned to the classes E10 and E11, respectively. The air permeability was not affected by the addition of MAG, and water vapor permeability was slightly enhanced. Based on the obtained data, prepared rPA/MAG fibrous membranes can be evaluated as antifouling against both tested bacterial strains and antimicrobial against S. aureus.

Surface-Modified Nanofibrous PVDF Membranes for Liquid Separation Technology.

Preparing easily scaled up, cost-effective, and recyclable membranes for separation technology is challenging. In the present study, a unique and new type of modified polyvinylidene fluoride (PVDF) nanofibrous membrane was prepared for the separation of oil-water emulsions. Surface modification was done in two steps. In the first step, dehydrofluorination of PVDF membranes was done using an alkaline solution. After the first step, oil removal and permeability of the membranes were dramatically improved. In the second step, TiO2 nanoparticles were grafted onto the surface of the membranes. After adding TiO2 nanoparticles, membranes exhibited outstanding anti-fouling and self-cleaning performance. The as-prepared membranes can be of great use in new green separation technology and have great potential to deal with the separation of oil-water emulsions in the near future.

Effect of Laminating Pressure on Polymeric Multilayer Nanofibrous Membranes for Liquid Filtration.

In the new century, electrospun nanofibrous webs are widely employed in various applications due to their specific surface area and porous structure with narrow pore size. The mechanical properties have a major influence on the applications of nanofiber webs. Lamination technology is an important method for improving the mechanical strength of nanofiber webs. In this study, the influence of laminating pressure on the properties of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) nanofibers/laminate was investigated. Heat-press lamination was carried out at three different pressures, and the surface morphologies of the multilayer nanofibrous membranes were observed under an optical microscope. In addition, air permeability, water filtration, and contact angle experiments were performed to examine the effect of laminating pressure on the breathability, water permeability and surface wettability of multilayer nanofibrous membranes. A bursting strength test was developed and applied to measure the maximum bursting pressure of the nanofibers from the laminated surface. A water filtration test was performed using a cross-flow unit. Based on the results of the tests, the optimum laminating pressure was determined for both PAN and PVDF multilayer nanofibrous membranes to prepare suitable microfilters for liquid filtration.