Highly Hydrophobic and Superoleophilic Nanofibrous Mats with Controllable Pore Sizes for Efficient Oil/Water Separation

Asymmetric Robust Superhydrophobic/Superhydrophilic Janus Membranes for the Moisture Proofing of Oil and Purification of Water

The performance degradation of oil caused by moisture and water pollution induced by the infiltration of oil can result in huge losses for society. This is especially true of stable emulsified mixtures of oil and water, which are difficult to separate and urgently require a processing method. In this work, a robust Janus membrane prepared by combining simple electrodeposition and spraying processes was used to separate water-in-transformer oil/lubricating oil emulsions and various oil-in-water emulsions. The membrane with outstanding separation efficiency was also endowed high flux to emulsions, even after 10 separation cycles and 100 sand impact tests, indicating that separation ability was retained. Furthermore, the excellent resistance to acidic and alkaline liquids of the superhydrophobic side groups of the membrane increased the possibility of its service in harsh environments. This study's findings reveal great potential regarding the expansion and application of oil-water separation materials.

Functionalized non-woven surfaces for combating the spread of the COVID-19 pandemic

The worldwide outbreak of SARS-CoV-2 infection has necessitated mandatory use of face masks, personal protective equipment and intake of a healthy diet for immunity boosting. As per WHO's recommendation, continuous use of masks has been proven effective in decreasing the SARS-CoV-2 infection rate. The present study reports on the bacterial filtration efficacy (BFE) of a novel 4-ply functionalized non-woven face mask. We synthesized a polypropylene-based fabric with inner layers of melt-blown fine fibres coated with polylactic acid and immune-boosting herbal phytochemicals. Experimental studies on the synthesized face mask demonstrated a BFE of greater than 99% against Staphylococcus aureus (a bacterium species frequently found in mammalian respiratory tract). A thorough computational analysis using LibDock algorithm demonstrated an effective docking performance of herbal phytochemicals against harmful virus structures. More importantly, the face mask also showed sufficient and stable breathability as per regulatory standards. A breathing resistance of 30 Pa at an aerosol flow rate of 30 l h⁻¹ was reported under standard temperature and pressure conditions, indicating a high potential for real-world applications.

Mussel-Inspired and In Situ Polymerization-Modified Commercial Sponge for Efficient Crude Oil and Organic Solvent Adsorption

Oil spills and pollution of oily wastewater from the industrial field have not only caused serious economic losses but also imposed a huge threat to human beings. To solve these issues, the development of advanced materials and technologies for the purification of oily wastewater has garnered great concern and become a central topic. Hence, a superhydrophobic polyurethane (PU) sponge adsorbent is designed via mussel-inspired coatings by double bonds to PU sponge, followed by in situ polymerization with 1-hexadecene. The prepared PU sponge adsorbent (PU@DB@16ene sponge) showed outstanding mechanical properties including low density, high porosity, and compression recovery ability. Moreover, the prepared PU@DB@16ene sponge showed excellent adsorption of oils and organic solvents (up to 187 g g^-1) and exhibited superior recyclability. Particularly, when the PU@DB@16ene sponge was applied in the continuous and rapid separation of oils and organic solvents, it still showed desired properties at a rapid velocity of 8.3 L m^-3 s^-1. Additionally, the PU@DB@16ene sponge could not only adsorb organic solvents in laboratories but also adsorb crude oil and industrial waxy oil in practice. Therefore, we proposed a simple and convenient method to construct PU sponge absorbents with great application prospects, which would be highly valuable for crude oil and organic solvents cleanup.

A pre-wetting induced superhydrophilic/superlipophilic micro-patterned electrospun membrane with self-cleaning property for on-demand emulsified oily wastewater separation

In this work, a pre-wetting induced superhydrophilic/superlipophilic micro-patterned membrane with surface-loaded BiVO₄ nanoparticles (Bi/PDA@PT) was successfully prepared by electrospinning and polydopamine (PDA) surface modification technology for highly efficient emulsified oily wastewater separation. The results showed that the as-prepared membranes exhibited micro hole-patterned structures and the BiVO₄ nanoparticles were uniformly deposited on the surfaces of fibers to construct hierarchical porous structures by using PDA as an adhesive polymeric bridge. During the separation process of emulsified oily wastewater, the hierarchical porous structures in membranes significantly improved the separation flux, which was nearly 2-3 times than that of the non-patterned membranes. Based on the existence of PDA, the membranes exhibited prewetting-induced superoleophobicity under water and superhydrophobicity under oil, which made it possible for them to separate both water-in-oil and oil-in-water emulsified oily wastewater selectively and efficiently. Moreover, the BiVO₄ nanoparticles loaded on the membranes could degrade the oily contaminants adsorbed on the membranes (nearly 100%) under visible light. All these attractive features demonstrate that the Bi/PDA@PT membranes show a great potential for sustainable and efficient emulsified oily wastewater separation.

Amphipathic Pentiptycene-Based Water-Resistant Cu-MOF for Efficient Oil/Water Separation

Creating novel and practical materials to separate oil/water mixtures with high efficacy is in urgent demand. Herein, we demonstrate an amphipathic pentiptycene-based copper metal-organic framework (Cu-MOF; UPC-29) to satisfy this purpose. UPC-29 exhibits a efficient separation performance for mixtures of naphtha/water, gasoline/water, and diesel/water. Furthermore, materials under loose-packed and tight-pressed forms exhibit opposite hydrophilic-hydrophobic phenomena. This unique feature of UPC-29 provides a new avenue for the application of MOF materials.

An oil/water separation nanofibrous membrane with a 3-D structure from the blending of PES and SPEEK

A new nanofibrous membrane (NFM) was prepared by blending polyethersulfone (PES) and sulfonated poly(ether ether ketone) (SPEEK) via electrospinning. The membrane exhibits good thermal stability and high mechanical strength. The hydrophilicity of the membrane could be controlled by adjusting the mass ratio of PES to SPEEK. PES acts as the backbone fiber and provides high mechanical strength, while SPEEK provides hydrophilic functional groups due to the strong hydrophilicity of the sulfonic group. The test results show that the composite NFM integrates the advantages of the two polymers. Simple adjustment of the weight ratios of the two polymers can enable an adjustable flux so that the membrane can be used for different kinds of oil/water separation. The results show that NFMs can not only separate immiscible oil/water systems but also separate oil-in-water emulsions. The immiscible oil/water separation process was driven only by gravity and had a high flux of 1119.63 Lm−2 h−1. This separation process conserves energy, which is beneficial for environmental protection. The separation flux of the oil-in-water emulsion was 758.71 Lm−2 h−1 bar−1 based on measurements under different pressures, and the separation purity total organic carbon was below 50 ppm. This work indicates that a membrane comprised of PES and SPEEK has excellent performance and can be used in different fields.

Rational design of materials interface at nanoscale towards intelligent oil-water separation

Oil-water separation is critical for the water treatment of oily wastewater or oil-spill accidents. The oil contamination in water not only induces severe water pollution but also threatens human beings' health and all living species in the ecological system. To address this challenge, different nanoscale fabrication methods have been applied for endowing biomimetic porous materials, which provide a promising solution for oily-water remediation. In this review, we present the state-of-the-art developments in the rational design of materials interface with special wettability for the intelligent separation of immiscible/emulsified oil-water mixtures. A mechanistic understanding of oil-water separation is firstly described, followed by a summary of separation solutions for traditional oil-water mixtures and special oil-water emulsions enabled by self-amplified wettability due to nanostructures. Guided by the basic theory, the rational design of interfaces of various porous materials at nanoscale with special wettability towards superhydrophobicity-superoleophilicity, superhydrophilicity-superoleophobicity, and superhydrophilicity-underwater superoleophobicity is discussed in detail. Although the above nanoscale fabrication strategies are able to address most of the current challenges, intelligent superwetting materials developed to meet special oil-water separation demands and to further promote the separation efficiency are also reviewed for various special application demands. Finally, challenges and future perspectives in the development of more efficient oil-water separation materials and devices by nanoscale control are provided. It is expected that the biomimetic porous materials with nanoscale interface engineering will overcome the current challenges of oil-water emulsion separation, realizing their practical applications in the near future with continuous efforts in this field.

Polyaniline Nanofibers: Their Amphiphilicity and Uses for Pickering Emulsions and On-Demand Emulsion Separation

The wetting property of nanomaterials is of great importance to both fundamental understanding and potential applications. However, the study on the intrinsic wetting property of nanomaterials is interfered by organic capping agents, which are often used to lower the surface energy of nanomaterials and avoid their irreversible agglomeration. In this work, the wetting property of the nanostructured polyaniline that requires no organic capping agents is investigated. Compared to hydrophilic granular particulates, polyaniline nanofibers are amphiphilic and have an excellent capability of creating Pickering emulsions at a wide range of pH. It is suggested that polyaniline nanofibers can be easily wetted by water and oil. Furthermore, the amphiphilic polyaniline nanofibers as building blocks can be used to construct filtration membranes with a small pore size. The wetting layer of the continuous phase of emulsions in the porous nanochannels efficiently prevents the permeation of the dispersed phase, realizing high-efficiency on-demand emulsion separation.

Treatment and reclamation of hydrocarbon-bearing oily wastewater as a hazardous pollutant by different processes and technologies: a state-of-the-art review

Hydrocarbon-containing oily wastewater generated by various industries creates a major environmental problem all over the world since petroleum products are commonly used as energy sources and raw materials in various industries. In case of offshore/coastal oil recovery operations, produced water is discharged through either shore side outfalls or coastal rim releases. In many cases, current disposal practices leads to severe environmental pollution by contamination of petroleum hydrocarbon to the surface, ground, and coastal waterways. Therefore, it is necessary to evaluate the performance of various processes for the recovery of petroleum hydrocarbons from wastewater. In this paper, a detailed review on the different separation/treatment processes of oily wastewater is presented. Previous and recent research works are reviewed in the area of oil-water separation from wastewater and also highlight the new developments in these areas. Various separation processes and technologies such as gravity separation, flotation process, membrane process, adsorption process, biological treatment, freeze/thaw process, and photocatalytic oxidation process (PoPs)/advanced oxidation processes (AoPs) are discussed and reviewed. The adsorption properties of a wide variety of porous sorbent materials in oily wastewater treatment, particularly in the area of oil spill cleanup, are also reviewed. The advantages and disadvantages of each process are critically discussed and compared.

Highly Efficient and Robust Oil/Water Separation Materials Based on Wire Mesh Coated by Reduced Graphene Oxide

We develop a simple approach for the preparation of oil/water separation material based on the reduced graphene oxide. First, the graphene oxide (GO) is coated on the commercially available wire mesh. The treatment of O₂ plasma is exploited to open the pores from the back side using the wire mesh as a ready-made mask, and the GO-coated mesh is subjected to the thermal annealing at 200 °C for 2 h to form stable superhydrophobic reduced graphene oxide (RGO) coating. The as-prepared mesh has excellent stability and reusability and the separation selectivity is above 98% for a variety of mixtures of oil and water. Meanwhile, the as-prepared RGO@mesh-300 shows stable and robust superhydrophobic properties including the stability of long-term storage, the resistance to high temperatures, high humidities, and mechanical abrasion. It is expected that this method of fabricating superhydrophobic materials can find more practical applications, especially in the oil/water separation.

Surface Design of Separators for Oil/Water Separation with High Separation Capacity and Mechanical Stability

A convection heat treatment that can replace existing chemical oxidation methods was developed for the preparation of hierarchically oxidized Cu meshes with various surface morphologies, representing a very simple and green route that does not involve toxic chemicals. Three types of Cu meshes [bumpy-like (BL) and short and long needle-like (NL) structures] exhibited similar separation efficiencies of 95-99% over 20 separation cycles, as indicated by their similar water contact angles (WCAs; 147-150°). However, these Cu meshes exhibited different flux behaviors. Excessively rough and excessively smooth surfaces of the Cu mesh resulted in increased resistance to flow and to a decrease of the penetration of oil. A surface with intermediate smoothness, such as the BL-Cu mesh, was necessary for high flux over a broad range of oil viscosities. Furthermore, a less rough surface was more suitable for the separation of highly viscous oil. Computational fluid dynamics (CFD) simulations were carried out to support our experimental results. The BL-Cu meshes also showed outstanding mechanical stability because of their low resistance to the flow of fluids.

Stable Superwetting Meshes for On-Demand Separation of Immiscible Oil/Water Mixtures and Emulsions

Oil-water separation is of great importance for the treatment of oily wastewater, including immiscible light/heavy oil-water mixtures, oil-in-water, or water-in-oil emulsions. Recently, interfacial materials (especially filtration membranes) with special wettability have been broadly developed to solve the environmental problems by virtue of their advantages in energy saving, high flux, and good selectivity. However, the given wetting property (superhydrophilicity or superhydrophobicity) and pore size and poor stability of filtration membranes limit their widespread applications, which is far from meeting a wide variety of oil-polluted water. Here polypyrrole-coated meshes with underwater superoleophobicity and underoil superhydrophobicity as well as controllable pore size were prepared by adopting cyclic voltammetry. It is found that the surface micro/nanohierarchical structures play a critical role in the formation of underwater superoleophobicity and underoil superhydrophobicity. HCl is advantageous to the construction of highly rough surface rather than H₂SO₄ and H₃PO₄. The obtained filtration membranes can be used for the on-demand separation of oil-water mixtures, showing outstanding stability in harsh conditions, such as high temperature (80 °C), low temperature (0 °C), salt (0.5 M NaCl), and acid (1 M HCl), except for alkali (1 M NaOH).

Chemical and Equipment-Free Strategy To Fabricate Water/Oil Separating Materials for Emergent Oil Spill Accidents

Oil spill accidents normally have two important features when considering practical cleanup strategies: (1) unexpected occurrence in any situations possibly without specific equipment and chemicals; (2) emergency to be cleaned to minimize the influences on ecosystems. To address these two practical problems regarding removal of spilt oil, we have proposed an in situ, rapid, and facile candle-soot strategy to fabricate water/oil separating materials based on superhydrophobicity/superoleophilicity. The one-step fabrication method is independent of any chemicals or equipment and can be ready for use through short smoking processes within 5 min by using raw materials available in daily life such as textiles. The as-prepared materials perform good durability for repeated separation test and high recovery rate of various oils from water/oil mixtures. This strategy provides possibility of rapid response to sudden oil spill accidents, especially in cases without any equipment or chemicals and in poor countries/areas those could hardly afford transportation and storage of expensive separating materials.