Beyond Symmetry: Exploring Asymmetric Electrospun Nanofiber Membranes for Liquid Separation

Abstract

Composite membranes with asymmetric traits have gained attention in liquid separation, featuring gradient chemical and physical attributes that align or oppose mass transfer direction. Chemically asymmetric configurations harness internal driving forces to heighten separation efficiency, rendering them an appealing option for heightened separation efficiency and fouling prevention. Concurrently, the internal hierarchical structure differences within composite membranes—such as fiber‐based structural adjustments and the gradient density of functional layers—yield the dual benefits of effective liquid repelling and heightened transport efficiency. Unlike conventional phase‐change methods, electrospinning technology possesses advantages in constructing and governing composite fibrous membrane materials with asymmetric chemistry and hierarchical structures, driven by its adaptable stacking methodologies. Notably, the inherent pore structure of electrospun nanofibrous membranes emerges as a proven solution for minimizing transport resistance. In recent times, interest has surged in electrospun nanofibrous membranes endowed with internal asymmetric properties. However, the spotlight has predominantly graced Janus membranes, spotlighting opposite wettability on different sides, leaving other facets of asymmetric membrane enhancement somewhat underexplored. This comprehensive work unveils recent strides in design, fabrication, facilitated transport mechanisms, and real‐world liquid separation applications, all under the aegis of electrospun nanofiber membranes, each endowed with distinct asymmetric properties.

Optimized Polymeric Membranes for Water Treatment: Fabrication, Morphology, and Performance

“…Membranes produced from these synthetic polymers are categorized into the following groups: (1) isotropic or symmetric and (2) anisotropic or asymmetric. This categorization depends on factors like nonporosity, as well as the presence of charged or uncharged polymeric chains (as fabricated through solvent-based or other techniques) [ 49 , 50 ].…”

Buoyancy-Assisted Fabrication of Liquid Diode: Janus Nanofibrous Membrane for Efficient Wastewater Treatment

“…To address the environmental pollution caused by oily wastewater, various technologies have been developed. Traditional methods such as gravity separation, electro-flocculation, bioremediation, demulsification, air flotation, adsorption, coagulation and flocculation, coalescence, centrifugation, and oil skimming have been used. , However, these approaches have limitations such as low separation efficiency (SE ff ), high costs of operation and maintenance, and the production of secondary pollutants, especially when treating different immiscible oil/water emulsions. ,, In this regard, polymeric membrane separation technology is considered the most effective method for separating oily wastewater, due to its inexpensiveness, high separation efficiency, and convenience of use. , Several polymeric membranes, including polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyurethane (PUR), polysulfone (PSU), and polytetrafluoroethylene (PTFE), have been developed for this purpose. , Among these, PVDF-based nanofibrous membranes play a crucial role, providing a strong and stable foundation for the membrane’s structure and performance. ,, PVDF is chosen for its remarkable chemical resistance, mechanical strength, and thermal stability, making it an ideal material for membrane applications. , The fabrication of PVDF nanofibrous membranes typically involves electrospinning (e-spinning), a technique that uses high voltage to create nanoscale fibers from a polymer solution. , This technique offers numerous advantages in the fabrication of PVDF nanofibrous membranes. It facilitates the creation of ultrafine fibers with a large surface area and enables precise control over morphology and pore structure of the fibers, enabling customization of pore size, porosity, and interconnectivity. , Additionally, the uniform distribution of fibers enhances the membranes’ mechanical strength and stability, providing opportunities for further enhancements in performance through modifications. ,, Despite the advantages of polymeric nanofibrous membrane separation technology, traditional membranes with single wettability face significant challenges in effectively separating complex oil–water emulsions. , Most superwetting membranes with singular wettability are only effective to separate specific oil or water mixtures .…”