Electrospun nanofiber mats have emerged as advanced materials for filtration applications due to their high surface area, tunable porosity, and controllable fiber morphology. The effectiveness of these mats in air and water filtration depends on three critical design parameters: pore size, fiber density, and mechanical stability. Each parameter influences filtration efficiency, pressure drop, and durability, making their optimization essential for high-performance filtration systems.

Pore size is a fundamental property that determines the filtration efficiency of electrospun nanofiber mats. The pore size distribution must be carefully controlled to balance particle capture and airflow or liquid permeability. For air filtration, nanofiber mats with pore sizes ranging from 100 nm to 1 µm effectively capture particulate matter, including PM2.5 and PM10, while maintaining low-pressure drops. In water filtration, smaller pore sizes, typically below 200 nm, are necessary to remove bacteria, viruses, and colloidal particles. The pore size is influenced by fiber diameter, with thinner fibers generally producing smaller pores. For instance, mats composed of fibers with diameters between 100 nm and 500 nm exhibit pore sizes suitable for fine particulate filtration. Additionally, the randomness of fiber deposition affects pore uniformity, with highly aligned fibers creating more consistent pore structures compared to randomly oriented mats.

Fiber density plays a crucial role in determining both filtration efficiency and the pressure drop across the mat. Higher fiber density increases the probability of particle capture by providing more interception sites but also raises the resistance to fluid flow. A balance must be struck to avoid excessive energy consumption in filtration systems. Studies have shown that an optimal fiber density for air filtration lies between 1 g/m² and 5 g/m², achieving over 99% efficiency for sub-micron particles while maintaining a pressure drop below 50 Pa. For water filtration, denser mats with basis weights of 5 g/m² to 10 g/m² are often employed to ensure sufficient mechanical strength and particle retention. The packing density of fibers also influences the mat’s porosity, with typical values ranging from 70% to 90%. Higher porosity reduces flow resistance but may compromise filtration efficiency if not paired with an appropriate pore size distribution.

Mechanical stability is another critical factor, particularly for applications requiring long-term durability or repeated use. Electrospun nanofiber mats are inherently lightweight and can be fragile, making reinforcement necessary for practical filtration systems. Several strategies enhance mechanical stability without significantly altering filtration performance. One approach involves incorporating polymer blends or composite fibers with higher tensile strength. For example, adding a small percentage of polyvinyl alcohol (PVA) or polyacrylonitrile (PAN) to polyvinylidene fluoride (PVDF) nanofibers can improve their mechanical properties while retaining hydrophobicity for water filtration. Another method is thermal or chemical post-treatment, such as heat pressing or crosslinking, which increases inter-fiber bonding and reduces mat brittleness. Mechanical stability is often quantified by tensile strength and elongation at break, with values varying based on material composition. A well-designed electrospun mat for filtration should exhibit a tensile strength of at least 2 MPa and an elongation at break exceeding 50% to withstand operational stresses.

The interplay between pore size, fiber density, and mechanical stability dictates the overall performance of electrospun nanofiber mats in filtration applications. For instance, a mat designed for high-efficiency particulate air (HEPA) filtration requires small pore sizes and moderate fiber density to capture 99.97% of particles larger than 0.3 µm while maintaining breathability. In contrast, a water filtration mat may prioritize mechanical stability and chemical resistance to endure prolonged exposure to aqueous environments. The choice of polymer also affects these parameters; hydrophobic polymers like PVDF and polytetrafluoroethylene (PTFE) are favored for water filtration due to their resistance to fouling, while hydrophilic polymers like polyamide (PA) and polyurethane (PU) are suitable for air filtration where moisture absorption is less critical.

Processing parameters during electrospinning further influence the final mat properties. Key variables include solution concentration, applied voltage, collector distance, and humidity. Higher polymer concentrations produce thicker fibers, increasing pore size and mechanical strength but potentially reducing porosity. Applied voltage affects fiber alignment, with lower voltages favoring random deposition and higher voltages promoting alignment. Collector distance must be optimized to ensure complete solvent evaporation, preventing fiber fusion and maintaining pore integrity. Ambient humidity can also alter fiber morphology, with high humidity leading to porous or bead-on-string structures that may impact filtration performance.

In summary, the design of electrospun nanofiber mats for air and water filtration requires careful consideration of pore size, fiber density, and mechanical stability. Each parameter must be tailored to the specific application to achieve optimal performance. Pore size determines the size of particles captured, fiber density balances efficiency and pressure drop, and mechanical stability ensures durability under operational conditions. By adjusting material composition, electrospinning parameters, and post-treatment methods, it is possible to engineer nanofiber mats that meet the demanding requirements of modern filtration systems. Future advancements may focus on further enhancing mechanical properties without compromising filtration efficiency, as well as scaling up production techniques to meet industrial demands.