Stretchable, electrically conductive and superhydrophobic/superoleophilic nanofibrous membrane with a hierarchical structure for efficient oil/water separation

Fast Solution Blow Spinning of Lotus-Leaf-Inspired SiO2 Nanofiber Sponge for High Efficiency Purification

Massive production of SiO2 nanofibers with both high durability and exceptional performance remains a significant challenge. Herein, a novel approach was introduced to achieve the massive production of SiO2 nanofibers with lotus-leaf-inspired surfaces by combining solution blowing spinning (SBS) and the polymer-derived ceramics method. Based on the SBS technique, three types of precursor nanofiber products were fast spined with methyl silsesquioxane polymer and polymethyl hydrogen siloxane employed as Si sources. The flow rate of the SBS spined Si-based ceramic nanofibers was enhanced to 20 mL·h-1. Furthermore, through the integration of hydrophobic-oleophilic SiO2 nanoparticles into the precursor solution, SiO2 nanofibers with lotus-leaf nanoprotrusion surfaces were fabricated. Nanoparticle-decorated SiO2 fibers demonstrated excellent hydrophobicity (138.3°), compression resilience (∼60%), proficiency in organic pollutant adsorption, high-temperature resistance (∼1100 °C), and outstanding thermal insulation properties (thermal conductivity of 0.0165 W·(m·K)-1).

Recent Advances in Membranes Used for Nanofiltration to Remove Heavy Metals from Wastewater: A Review

The presence of heavy metal ions in polluted wastewater represents a serious threat to human health, making proper disposal extremely important. The utilization of nanofiltration (NF) membranes has emerged as one of the most effective methods of heavy metal ion removal from wastewater due to their efficient operation, adaptable design, and affordability. NF membranes created from advanced materials are becoming increasingly popular due to their ability to depollute wastewater in a variety of circumstances. Tailoring the NF membrane's properties to efficiently remove heavy metal ions from wastewater, interfacial polymerization, and grafting techniques, along with the addition of nano-fillers, have proven to be the most effective modification methods. This paper presents a review of the modification processes and NF membrane performances for the removal of heavy metals from wastewater, as well as the application of these membranes for heavy metal ion wastewater treatment. Very high treatment efficiencies, such as 99.90%, have been achieved using membranes composed of polyvinyl amine (PVAM) and glutaraldehyde (GA) for Cr³⁺ removal from wastewater. However, nanofiltration membranes have certain drawbacks, such as fouling of the NF membrane. Repeated cleaning of the membrane influences its lifetime.

Carbon nanofiber reinforced carbon aerogels for steam generation: Synergy of solar driven interface evaporation and side wall induced natural evaporation

Solar-based interface evaporation (SIE) is a green, efficient and cost-effective technique to harvest fresh water. 3D solar evaporators show their unique advantages in gaining energy from environment and hence possess a higher evaporation rate than 2D evaporators. However, much effort is still required to develop mechanically robust and superhydrophilic 3D evaporators with strong water transportation capability and salt-rejection performance, and at the same time reveal how they gain energy from environment via the natural evaporation. In this work, a novel carbon nanofiber reinforced carbon aerogel (CNFA) is prepared for the SIE. The CNFA has a high light absorption up to 97.2% and outstanding photothermal conversion performance. The heteroatom doping and hierarchically porous structure endow the CNFA with superhydrophilicity and thus powerful water transportation capability and salt rejection performance. Benefiting from synergy of the SIE and side wall induced natural evaporation, the CNFA evaporator exhibits a high evaporation rate and efficiency (as high as 3.82 kg m^-2h^-1 and 95.5%, respectively) with long-term stability and durability. The CNFA can also work normally in high-salinity and corrosive seawater. This study demonstrates a new method to fabricate all-carbon aerogel solar evaporators and provides insights for the effective thermal management during the interface evaporation.

Membranes for Oil/Water Separation: A Review

Recent advancements in separation and membrane technologies have shown a great potential in removing oil from wastewaters effectively. In addition, the capabilities have improved to fabricate membranes with tunable properties in terms of their wettability, permeability, antifouling, and mechanical properties that govern the treatment of oily wastewaters. Herein, authors have critically reviewed the literature on membrane technology for oil/water separation with a specific focus on: 1) membrane properties and characterization, 2) development of various materials (e.g., organic, inorganic, and hybrid membranes, and innovative materials), 3) membranes design (e.g., mixed matrix nanocomposite and multilayers), and 4) membrane fabrication techniques and surface modification techniques. The current challenges and future research directions in materials and fabrication techniques for membrane technology applications in oil/water separation are also highlighted. Thus, this review provides helpful guidance toward finding more effective, practical, and scalable solutions to tackle environmental pollution by oils.

Mechanically robust Janus nanofibrous membrane with asymmetric wettability for high efficiency emulsion separation

Water pollution caused by oil leakage or oily sewage has seriously threatened the ecological environment and human health. It remains a tough task for scientists to develop versatile materials to purify different kinds of oily wastewater. In this study, we propose a facile "carbon nanotubes (CNTs) decoration and nanofibrous membrane integration" method to prepare a mechanical robust Janus membrane (JM) composed of a superhydrophilic nanofiber composite layer and a hydrophobic nanofiber composite layer. The asymmetric wettability can be controlled by tuning the thickness of the hydrophobic layer. The nanofiber composite in both two layers possesses a core-shell structure, guaranteeing the excellent flexibility and stretchability of the JM. In addition, the strong interfacial compatibility between the two layers ensures the stability and durability of the JM even after multiple stretching. More importantly, the JM could realize on-demand separation of different kinds of oily wastewater with high separation flux and separation efficiency, including oil/water mixtures with different oil densities, oil-in-water emulsions and water-in-oil emulsions. Furthermore, the JM exhibits cycling stability and long-term serviceability for the emulsion separation. The mechanically robust and stretchable JM has promising applications in purification of various oil contaminated wastewater.

Superhydrophobic, electrically conductive and multifunctional polymer foam composite for chemical vapor detection and crude oil cleanup

The leakage of chemicals (either vapors or liquids) severely threatens the environment and even people's health. It remains a great challenge to develop multifunctional and durable materials that can not only detect the chemical vapors but also clean up the liquid chemicals especially high viscous crude oil. Here, a superhydrophobic and conductive foam composite (SCFC) is prepared by decorating carbon black nanoparticles (CBNPs) onto the skeleton of the pre-swollen polymer foam under the assistance of ultrasonication. The CBNPs are firmly embedded onto the skeleton surface, exhibiting a strong interfacial adhesion and hence excellent surface stability and durability. The SCFC possesses stable vapor sensing behavior and can detect various chemical vapors with a low detection limit and good cycling performance. When used for oil/water separation, the SCFC has large oil adsorption capacity for different oils with excellent reusability. Also, the outstanding photo-thermal conversion performance of the SCFC can be used to significantly reduce the oil viscosity and hence realize efficient cleanup of the crude oil. The multifunctional SCFC has promising applications in the field of environment protection, flexible electronics, etc.

Interface-engineered reduced graphene oxide assembly on nanofiber surface for high performance strain and temperature sensing

Conductive polymer nanofiber composites (CPNCs) based wearable sensing electronics have aroused great attention of scientists in recent years. However, it is still difficult to obtain CPNCs with good water proof, excellent durability, and multiple sensing performance. Herein, we develop a multifunctional CPNC with a wrinkled reduced graphene oxide (RGO) shell and polymer nanofiber core, which is prepared by ultrasonication induced decoration of RGO onto the pre-stretched polyurethane (PU) nanofibers, followed by the release of the strain. The RGO assembly with a wrinkled structure not only greatly increases the surface roughness and thus the hydrophobicity but also enhances the strain sensing sensitivity (with a gauge factor of 154.8 in the strain range of 85%-100%) of the nanofibrous membrane. The obtained CPNC strain sensor also shows excellent sensing durability (over 1000 cycles) and can be used for body motion monitoring. The CPNC shows a negative temperature coefficient effect, which holds promising applications in high performance temperature sensors.

Superhydrophobic, mechanically durable coatings for controllable light and magnetism driven actuators

Although some groundbreaking work has proved the feasibility of non-contact Marangoni propulsion generated by combination of the superhydrophobicity and photothermal effect, there are still challenges including the strong interfacial adhesion, multifunctional structural design and superior durability. In this paper, a simple two-step spraying method is used to prepare superhydrophobic and multi-functional fluorinated acidified carbon nanotubes (F-ACNTs)/Fe₃O₄ nanoparticles/polydimethylsiloxane (PDMS) coatings. The introduction of Fe₃O₄ nanoparticles and F-ACNTs not merely improve the surface roughness but also endow the coating with the outstanding magnetic property and photothermal conversion performance. The PDMS can reduce the surface energy and also improve the interfacial adhesion between the nanofillers and the substrate (the filter paper). The superhydrophobicity can be maintained when the material experiences abrasion, near-infrared (NIR) light irradiation and acid treatment, exhibiting outstanding durability. The highly stable superhydrophobic coating introduces a thin layer of air to decrease the drag force between the filter paper and the water surface, and can be used for controlled self-propelled light-driven motion and magnetic-driven motion. The movement can be manipulated by adjusting the direction of the incident NIR light and magnetic field. In particular, the superhydrophobic and superoleophilic coating based actuators can be easily driven to the oil-contaminated area on the water surface by using a magnet for high efficiency oil removal. This work provides a simple and universal strategy for developing intelligent and multi-responsive actuators possessing promising applications in various fields such as environmental protection, micro-robots and biomedicine.

Multistructured Electrospun Nanofibers for Air Filtration: A Review

Air filtration materials (AFMs) have gradually become a research hotspot on account of the increasing attention paid to the global air quality problem. However, most AFMs cannot balance the contradiction between high filtration efficiency and low pressure drop. Electrospinning nanofibers have a large surface area to volume ratio, an adjustable porous structure, and a simple preparation process that make them an appropriate candidate for filtration materials. Therefore, electrospun nanofibers have attracted increased attention in air filtration applications. In this paper, first, the preparation methods of high-performance electrospun air filtration membranes (EAFMs) and the typical surface structures and filtration principles of electrospun fibers for air filtration are reviewed. Second, the research progress of EAFMs with multistructures, including nanoprotrusion, wrinkled, porous, branched, hollow, core-shell, ribbon, beaded, nets structure, and the application of these nanofibers in air filtration are summarized. Finally, challenges with the fabrication of EAFMs, limitations of their use, and trends for future developments are presented.

Polyvinylpyrrolidone Assisted Preparation of Highly Conductive, Antioxidation, and Durable Nanofiber Composite with an Extremely High Electromagnetic Interference Shielding Effectiveness

With booming development of electronics, electromagnetic interference (EMI) shielding materials based on conductive polymer composites (CPCs) have received increasing attention. However, it remains challenging to develop flexible and lightweight CPCs with excellent stretchability, breathability, durability, and high EMI shielding effectiveness (EMI SE). Here, we propose a facile polyvinylpyrrolidone (PVP) assisted preparation of highly electrically conductive and durable nanofiber composites for high performance EMI shielding. The PVP layer could not only greatly enhance the interfacial interaction between the Ag nanoparticles (AgNPs) and hence the mechanical properties (both tensile strength, Young's modulus and elongation at break) of the polymer nanofiber membrane but also forms a protection layer preventing the AgNPs from oxidizing. The electrical conductivity of the nanofiber composite can reach up to 245.7 ± 30.6 S/cm, which is, to a large degree, maintained after cyclic stretching, abrasion, and ultrasonic washing. In addition, the nanofiber composite exhibits excellent breathability, antibacterial, and Joule heating performance. When used as the EMI shielding material, the nanofiber composite shows an extremely high SE and SSE of ∼96.9 dB and 169.7 dB cm³/g, respectively, and EMI shielding performance possesses outstanding stability and durability. This multifunctional nanofibrous composite membrane exhibits promising applications in wearable electronics.

Carbon nanofiber based superhydrophobic foam composite for high performance oil/water separation

Oil spill has now been a serious environmental issue, threatening the aquatic ecosystems and even human living environment. It is still challenging to develop absorbents for efficient oil/water emulsion separation and clean-up of viscous crude oil. Here, we propose a facile method to fabricate flexible and superhydrophobic foam composites for high efficiency oil/water separation under different complex environment. Carbon nanofibers (CNFs) with a hollow structure are decorated uniformly onto the skeleton of the polydimethylsiloxane (PDMS) foam with a strong interfacial adhesion. CNFs could not only enhance the surface roughness and thus the hydrophobicity but also be served as numerous capillary tubes, improving the oil adsorption and oil/water separation performance. More importantly, the CNFs network with a strong light absorption endows the foam with superior photo-thermal conversion capability. The obtained foam composite possesses excellent corrosion resistance and can adsorb various kinds of oil with different densities. The foam composite is able to separate the oil from the emulsion with a relatively high separation efficiency. The material surface temperature is able to quickly increase under the light irradiation, which can significantly reduce the oil viscosity and hence achieve the rapid clean-up of the crude oil floating on water surface.

Surface Engineering of Ceramic Nanomaterials for Separation of Oil/Water Mixtures

Oil/water mixtures are a potentially major source of environmental pollution if efficient separation technology is not employed during processing. A large volume of oil/water mixtures is produced via many manufacturing operations in food, petrochemical, mining, and metal industries and can be exposed to water sources on a regular basis. To date, several techniques are used in practice to deal with industrial oil/water mixtures and oil spills such as in situ burning of oil, bioremediation, and solidifiers, which change the physical shape of oil as a result of chemical interaction. Physical separation of oil/water mixtures is in industrial practice; however, the existing technologies to do so often require either dissipation of large amounts of energy (such as in cyclones and hydrocyclones) or large residence times or inventories of fluids (such as in decanters). Recently, materials with selective wettability have gained attention for application in separation of oil/water mixtures and surfactant stabilized emulsions. For example, a superhydrophobic material is selectively wettable toward oil while having a poor affinity for the aqueous phase; therefore, a superhydrophobic porous material can easily adsorb the oil while completely rejecting the water from an oil/water mixture, thus physically separating the two components. The ease of separation, low cost, and low-energy requirements are some of the other advantages offered by these materials over existing practices of oil/water separation. The present review aims to focus on the surface engineering aspects to achieve selectively wettability in materials and its their relationship with the separation of oil/water mixtures with particular focus on emulsions, on factors contributing to their stability, and on how wettability can be helpful in their separation. Finally, the challenges in application of superwettable materials will be highlighted, and potential solutions to improve the application of these materials will be put forward.

Flexible and Superhydrophobic Composites with Dual Polymer Nanofiber and Carbon Nanofiber Network for High-Performance Chemical Vapor Sensing and Oil/Water Separation

Polymer nanofiber composites with superhydrophobicity are promising for the chemical vapor sensing or oil/water separation, but it remains challenging to develop superhydrophobic, anticorrosive, and durable nanofiber composites that can achieve both the organic solvent vapor detection and oil (organic solvent)/water separation with high separation flux and excellent recyclability. Here, a flexible, stretchable, and superhydrophobic/superoleophilic nanofiber composite membrane with excellent photothermal conversion performance is fabricated by decorating carbon nanofibers (CNFs) with a hollow structure onto the polyurethane nanofibers and subsequent polydimethylsiloxane (PDMS) modification. The combination of CNFs and PDMS greatly improves the membrane's tensile strength and Young's modulus without sacrificing its stretchability. The dual polymer nanofiber and CNF network are beneficial to the chemical vapor or liquid diffusion into the membrane and thus can be used for high-performance chemical vapor sensing and oil/water separation. The nanofiber composite is responsive to different organic vapors with a low detection limit and good selectivity. Also, the material can achieve fast oil/water separation with the oil (dichloromethane) permeate flux as high as 6577.3 L m^-2 h^-1. In addition, the separation flux and efficiency remain stable during the 30 separated oil/water separation tests, exhibiting excellent recyclability.

Self-Derived Superhydrophobic and Multifunctional Polymer Sponge Composite with Excellent Joule Heating and Photothermal Performance for Strain/Pressure Sensors

Flexible strain or pressure sensors have potential applications in electronic skin, healthcare, etc. It remains a challenge to explore multifunctional strain or pressure sensors that possess excellent water repellent and heating performance and hence can be used in harsh environments such as high moisture and low-temperature conditions. Here, a self-derived superhydrophobic and multifunctional polymer composite foam is prepared by adsorption of the Ag precursor in tetrahydrofuran (THF) onto the rubber sponge followed by reduction of Ag⁺ to Ag nanoparticles (AgNPs). During the Ag⁺ reduction in hydrazine solution, the swollen rubber sponge by THF is partially precipitated based on the nonsolvent-induced phase separation (NIPS). The NIPS creates a porous structure on the sponge surface and thus a high surface roughness, contributing to the material superhydrophobicity. The precipitated polymer wrapping the AgNPs could enhance the interaction between the individual AgNPs. The obtained conductive sponge composite possesses excellent Joule heating and photothermal performance and can be used as both a strain and pressure sensor. The conductive sponge composite sensor possesses good reliability and durability and can be applied to real-time monitoring of human body movements.

Durable and Multifunctional Superhydrophobic Coatings with Excellent Joule Heating and Electromagnetic Interference Shielding Performance for Flexible Sensing Electronics

Superhydrophobic coatings have wide applications in many fields. However, superhydrophobic and smart coatings with multifunctionality and their applications in flexible sensing electronics are seldom reported. In this work, durable, superhydrophobic, and anticorrosive coatings with excellent Joule heating and electromagnetic interference (EMI) shielding performance are prepared on the basis of Ag precursor reduction and synchronous nonsolvent induced phase separation. Silver nanoparticles (AgNPs) coated with the copolymer (polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene: SEBS) are uniformly distributed on the target substrate, forming mechanically durable conductive network. SEBS could not only endow the surface coating with superhydrophobicity but also improve the interaction among individual Ag nanoparticles and the interfacial adhesion between AgNPs and the substrate. The multifunctional coating possesses excellent anticorrosive, self-cleaning, and deicing properties. The high conductivity endows the coatings with excellent Joule heating and EMI shielding performance. The multifunctional coating can be applied to a variety of different substrates with outstanding surface stability and reliability. The conductivity for the smart coating can reach as high as 107 S/cm with the EMI shielding effectiveness up to 37.8 dB. At a low applied voltage of 1 V, the conductive fabric can be heated up to over 80 °C in 60 s and displays good recyclability during dozens of heating and cooling cycles. The Joule heating-induced temperature increase could be used for efficient surface deicing. When used for the flexible and wearable strain sensors, the multifunctional coating has a very low strain detection limit of 0.5% and large sensitivity (with the gauge factor as high as 1075) and excellent repeatability. In addition, it can be used for precisely monitoring different body motions, including both large and subtle joint movement.