Dual-scaled porous nitrocellulose membranes with underwater superoleophobicity for highly efficient oil/water separation

The Effect of Electrolyte Properties on Ionic Transport through Solid-State Nanopores: Experiment and Simulation

Nanopore membranes enable versatile technologies that are employed in many different applications, ranging from clean energy generation to filtration and sensing. Improving the performance can be achieved by conducting numerical simulations of the system, for example, by studying how the nanopore geometry or surface properties change the ionic transport behavior or fluid dynamics of the system. A widely employed tool for numerical simulations is finite element analysis (FEA) using software, such as COMSOL Multiphysics. We found that the prevalent method of implementing the electrolyte in the FEA can diverge significantly from physically accurate values. It is often assumed that salt molecules fully dissociate, and the effect of the temperature is neglected. Furthermore, values for the diffusion coefficients of the ions, as well as permittivity, density, and viscosity of the fluid, are assumed to be their bulk values at infinite dilution. By performing conductometry experiments with an amorphous SiO2 nanopore membrane with conical pores and simulating the pore system with FEA, it is shown that the common assumptions do not hold for different mono- and divalent chlorides (LiCl, NaCl, KCl, MgCl2, and CaCl2) at concentrations above 100 mM. Instead, a procedure is presented where all parameters are implemented based on the type of salt and concentration. This modification to the common approach improves the accuracy of the numerical simulations and thus provides a more comprehensive insight into ion transport in nanopores that is otherwise lacking.

An Eco-Friendly Manner to Prepare Superwetting Melamine Sponges with Switchable Wettability for the Separation of Oil/Water Mixtures and Emulsions

Oil/water separation processes have garnered significant global attention due to the quick growth in industrial development, recurring chemical leakages, and oil spills. Hence, there is a significant demand for the development of inexpensive superwetting materials in an eco-friendly manner to separate oil/water mixtures and emulsions. In this study, a superwetting melamine sponge (SMS) with switchable wettabilities was prepared by modifying melamine sponge (MS) with sodium dodecanoate. The as-prepared SMS exhibited superhydrophobicity, superoleophilicity, underwater superoleophobicity, and underoil superhydrophobicity. The SMS can be utilized in treating both light and heavy oil/water mixtures through the prewetting process. It demonstrated fast permeation fluxes (reaching 108,600 L m-2 h-1 for a light oil/water mixture and 147,700 L m-2 h-1 for a heavy oil/water mixture) and exhibited good separation efficiency (exceeding 99.56%). The compressed SMS was employed in separating surfactant-stabilized water-in-oil emulsions (SWOEs), as well as surfactant-stabilized oil-in-water emulsions (SOWEs), giving high permeation fluxes (reaching 7210 and 5054 L m-2 h-1, respectively). The oil purity for SWOEs' filtrates surpassed 99.98 wt% and the separation efficiencies of SOWEs exceeded 98.84%. Owing to their remarkable capability for separating oil/water mixtures and emulsions, eco-friendly fabrication method, and feasibility for large-scale production, our SMS has a promising potential for practical applications.

Point-of-Care Diagnosis on Selenium Nutrition Based on Time-Resolved Fluorometric Glycoaffinity Chromatography

Given the lack of timely evaluation of the well-received selenium fortification, a neat lateral-flow chromatographic solution was constructed here by using the recently identified urinary selenosugar (Sel) as a strongly indicative marker. As there are no ready-made receptors for this synthetic standard, phenylboronic acid (PBA) esterification and Dolichos biflorus agglutinin (DBA) affinity joined up to pinch and pin down the analyte into a sandwich-type glycol complex. Pilot lectin screening on homemade glycan microarrays verified such a new pairing between dual recognizers as PBA-Sel-DBA with a firm monosaccharide-binding constant. To quell the sample autofluorescence, europium nanoparticles with efficient long-life afterglow were employed as conjugating probes under 1 μs excitation. After systematic process optimizations, the prepared Sel-dipstick achieved swift and sensitive fluorometry over the physiological level of the target from 0.1 to 10 μM with a detection limit down to 0.06 μM. Further efforts were made to eliminate matrix effects from both temperature and pH via an approximate formula. Upon completion, the test strips managed to quantify the presence of Sel in not just imitated but real human urine, with comparable results to those in the references. As far as we know, this would be the first in-house prototype for user-friendly and facile diagnosis of Se nutrition with fair accuracy as well as selectivity. Future endeavors will be invested to model a more traceable Se-supplementary plan based on the rhythmic feedback of Sel excretion.

Nanomembranes-Affiliated Water Remediation: Chronology, Properties, Classification, Challenges and Future Prospects

Water contamination has become a global crisis, affecting millions of people worldwide and causing diseases and illnesses, including cholera, typhoid, and hepatitis A. Conventional water remediation methods have several challenges, including their inability to remove emerging contaminants and their high cost and environmental impact. Nanomembranes offer a promising solution to these challenges. Nanomembranes are thin, selectively permeable membranes that can remove contaminants from water based on size, charge, and other properties. They offer several advantages over conventional methods, including their ability to remove evolving pollutants, low functioning price, and reduced ecological influence. However, there are numerous limitations linked with the applications of nanomembranes in water remediation, including fouling and scaling, cost-effectiveness, and potential environmental impact. Researchers are working to reduce the cost of nanomembranes through the development of more cost-effective manufacturing methods and the use of alternative materials such as graphene. Additionally, there are concerns about the release of nanomaterials into the environment during the manufacturing and disposal of the membranes, and further research is needed to understand their potential impact. Despite these challenges, nanomembranes offer a promising solution for the global water crisis and could have a significant impact on public health and the environment. The current article delivers an overview on the exploitation of various engineered nanoscale substances, encompassing the carbonaceous nanomaterials, metallic, metal oxide and metal-organic frameworks, polymeric nano-adsorbents and nanomembranes, for water remediation. The article emphasizes the mechanisms involved in adsorption and nanomembrane filtration. Additionally, the authors aim to deliver an all-inclusive review on the chronology, technical execution, challenges, restrictions, reusability, and future prospects of these nanomaterials.

Recent advances in superwetting materials for separation of oil/water mixtures

Engineering surfaces or membranes that allow an efficient oil/water separation is highly desired in a wide spectrum of applications ranging from oily wastewater discharge to offshore oil spill accidents. Recent advances in biomimetics, manufacturing, and characterization techniques have led to remarkable progress in the design of various superwetting materials with special wettability. In spite of exciting progress, formulating a strategy robust enough to guide the design and fabrication of separating surfaces remains a daunting challenge. In this review, we first present an overview of the wettability theory to elucidate how to control the surface morphology and chemistry to regulate oil/water separation. Then, parallel approaches are considered for discussing the separation mechanisms according to different oil/water mixtures, and three separation types were identified including filtration, adsorption and other separation types. Finally, perspectives on the challenges and future research directions in this research area are briefly discussed.

Fabrication of Epitaxially Grown Mg2Al-LDH-Modified Nanofiber Membranes for Efficient and Sustainable Separation of Water-in-Oil Emulsion

Efficient separation of water-in-oil emulsion is of great importance but remains highly challenging since such emulsion contains stable tiny droplets with a diameter less than 20 μm. Herein, we reported the fabrication of a modular fibrous functional membrane using an "in situ growth and covalent functionalization" strategy. The as-prepared PAN@LDH@OTS (PAN = polyacrylonitrile; LDH = layered double hydroxides; and OTS = octadecyltrichlorosilane) membrane possessed an interlaced rough nanostructured surface with intriguing superhydrophobic/superlipophilic properties. When applied for the separation of surfactant-stabilized water-in-oil emulsion (SSE), the PAN@LDH@OTS membrane exhibited an ultrahigh permeation flux of up to 4.63 × 10⁴ L m^-2 h^-1 with an outstanding separation efficiency of >99.92%, outperforming most of the state-of-the-art membranes. In addition, the membrane can maintain a stable permeation flux and superhydrophobic/superlipophilic properties after 20 times of use. Detailed characterization demonstrated that the demulsification of the SSE process was as follows: first, the droplets can be easily adsorbed to the PAN@LDH@OTS membrane due to the improved intermolecular interactions between OTS and the surfactants (Span 80); second, the droplets can be deformed by the electropositive LDH laminate; and third, the deformed tiny emulsion droplets coalesced into large droplets and floated up, and as a result, efficient separation of SSE can be achieved.

Separate Reclamation of Oil and Surfactant from Oil-in-Water Emulsion with a CO2-Responsive Material

Oil-in-water (O/W) emulsion is one type of oily wastewater produced by many industries. The treatment of and resource recovery from O/W emulsions are very challenging. Unlike bulk or floating oil, which can be successfully abstracted from wastewater by hydrophobic/oleophilic materials, the abstraction of emulsified oil is not easy because of its highly hydrophilic surface composed of dense surfactants. Separate reclamation of miscible oil and surfactant through a green approach is even more difficult. Here, we report that a CO₂-responsive material can abstract emulsified oil and demulsify the oil droplets. Moreover, it can release the abstracted oil and surfactant separately. This material exhibited a very high adsorption capacity for emulsified oil (14 g g^-1). Upon switching the surface wettability of the material under CO₂ or synthetic flue gas sparging, coalesced oil was reclaimed while the surfactant was retained inside the pores. The hydrophobic character of the material was retrieved when CO₂ was purged with nitrogen sparging or air heating. Then, the surfactant was reclaimed by elution with diluted alkali/ethanol. Oil and surfactant were thus separately reclaimed from the O/W emulsion. High rates of oil removal, oil recovery, and surfactant recovery were maintained during repeated adsorption/desorption operations. This work provides a potentially sustainable and green way for O/W emulsion treatment and resource recovery.

Intelligent high-tech coating of natural biopolymer layers

Polymeric materials play a vital role in our daily life, but the growing concern for the environment demands economical and natural biopolymers that can be cross-linked to create technologically innovative lightweight materials. Their cellular matrix with extreme flexibility makes them highly acceptable for application prospects in material science, engineering, and biomedical applications. Furthermore, their biocompatibility, mechanical properties, and structural diversity provide a gateway to research them to form technologically important materials. In the light of the same, the review covers cellulose derivatives. The first section of the study covers the general properties and applications of cellulose and its derivatives. Then, the biopolymers are characterised based on their dielectric properties, crystallinity, rheology, and mechanical properties. An in-depth analysis of the diffuse process of swelling and dissolution followed by a brief discussion on diffusion and diffusion of crosslinking has been done. The review also covers a section on swelling and swelling kinetics of carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC). The examination of all the aforementioned parameters gives an insight into the future aspects of the biopolymers. Lastly, the study briefly covers some preferred choices of cross-linking agents and their effect on the biopolymers.

Piezoelectricity induced by pulsed hydraulic pressure enables in situ membrane demulsification and oil/water separation

Recovering oil from oily wastewater is not only for economic gains but also for mitigating environmental pollution. However, demulsification of oil droplets stabilized with surfactants is challenging because of their low surface energy. Although the widely used oil/water separation membrane technologies based on size screening have attracted considerable attention in the past few decades, they are incapable of demulsification of stabilized oil emulsions and the membrane concentrates often require post-processing. Herein, the piezoelectric ceramic membrane (PCM), which can respond to the inherent transmembrane pressure in the pressure-driven membrane processes, was employed to transform hydraulic pressure pulses into electroactive responses to in situ demulsification. The pulsed transmembrane pressure on the PCM results in the generation of considerable rapid voltage oscillations over 3.2 V and a locally high electric field intensity of 7.2 × 10⁷ V/m, which is capable of electrocoalescence with no additional stimuli or high voltage devices. Negative dielectrophoresis (DEP) force occurred in this membrane process and repelled the large size of oil after demulsification away from the PCM surface, ensuring continuous membrane demulsification and oil/water separation. Overall, PCM provides a further opportunity to develop an environmentally friendly and energy-saving electroresponsive membrane technology for practical applications in wastewater treatment.

Upcycling Waste Pine nut Shell Membrane for Highly Efficient Separation of Crude Oil-in-Water Emulsion

Discharge of oily sewage and frequent oil spills have caused serious harm to human production, life, and ecological environment. Due to the presence of a large number of surfactants in water, these oil-water mixtures are easy to form oil-in-water emulsion, which is difficult to separate by traditional methods. At the same time, the water-soluble pollutants such as dyes and heavy metal ions in oily wastewater also cause great harm to the human body and the environment. A pine nut shell is a kind of common domestic waste material. Herein, an underwater superoleophobic pine nut shell membrane (PNSM) was prepared by the simple pumping filtration method, which realized the separation of oil-in-water emulsion and adsorption of dyes and heavy metal ions. In addition, the filter membrane can be used for separating corrosive emulsions of strong acid, strong alkali, and 3.5% NaCl solutions (simulated seawater). Besides, the PNSM showed excellent toughness and flexibility. Due to the abovementioned performance, this cost-efficient and environmentally friendly membrane can be a promising candidate for multifunctional oily water remediation.

Wood-Inspired Compressible Superhydrophilic Sponge for Efficient Removal of Micron-Sized Water Droplets from Viscous Oils

Efficient micron-sized droplet separation materials have become a new demand for environmental protection and economic development. However, existing separation methods are difficult to be effectively used for micron-sized water droplets surrounded by viscous oil, and common materials have difficulty maintaining hydrophilicity underoil. Here, inspired by the microstructure of tree xylem, we report a cellulose-polyurethane sponge (CP-Sponge) with wood-like pores and underoil superhydrophilicity using directional freeze-casting. The CP-Sponge has an excellent selective water absorption capacity underoil and compression resilience. This preparation strategy can flexibly control the sponge's dimensional morphology. The designed cylindrical CP-Sponge can be easily installed in the silicone tube of a peristaltic pump. During pump operation, with a simple absorption, compression, and recovery process, the CP-Sponge continuously and effectively removes micron-sized water from crude oil and lubricating oil, reducing residual water in the oil to less than 2 ppm. The absorption-saturated sponge can be dried to continue recycling. Eco-friendly, recyclable, and sustainable artificial porous sponges provide new ideas and inspiration for the practical application of deep dehydration of viscous oils.

Emerging Separation Applications of Surface Superwettability

Human beings are facing severe global environmental problems and sustainable development problems. Effective separation technology plays an essential role in solving these challenges. In the past decades, superwettability (e.g., superhydrophobicity and underwater superoleophobicity) has succeeded in achieving oil/water separation. The mixture of oil and water is just the tip of the iceberg of the mixtures that need to be separated, so the wettability-based separation strategy should be extended to treat other kinds of liquid/liquid or liquid/gas mixtures. This review aims at generalizing the approach of the well-developed oil/water separation to separate various multiphase mixtures based on the surface superwettability. Superhydrophobic and even superoleophobic surface microstructures have liquid-repellent properties, making different liquids keep away from them. Inspired by the process of oil/water separation, liquid polymers can be separated from water by using underwater superpolymphobic materials. Meanwhile, the underwater superaerophobic and superaerophilic porous materials are successfully used to collect or remove gas bubbles in a liquid, thus achieving liquid/gas separation. We believe that the diversified wettability-based separation methods can be potentially applied in industrial manufacture, energy use, environmental protection, agricultural production, and so on.

Emulsion-Templated, Magnetic, Hydrophilic-Oleophobic Composites for Controlled Water Removal

Emulsion-templated, hydrophilic-oleophobic porous materials are promising for the removal of a small amount of water from oil-water mixtures, but the maneuver and complete collection of these porous materials are challenging. Herein, we report the fabrication of magnetic, hydrophilic-oleophobic polyHIPE composites from reactive Fe₃O₄ nanoparticle-stabilized high internal phase emulsions through simultaneous bulk polymerization of water-soluble monomers and interface-catalyzed polycondensation of 1H,1H,2H,2H-perfluorooctyltriethoxysilane. The resulting composites were hydrophilic-oleophobic, with water droplets rapidly absorbed (within 20 s), and exhibited designable magnetic responsiveness. The hydrophilicity-oleophobicity enabled water to be removed through selective absorption from oil-water mixtures (including surfactant-stabilized water-in-oil emulsions), with a high separation rate over 99%. The magnetic-responsiveness enabled both the dry and the swollen composites to be maneuvered in a remote and contactless manner and to be fully collected. Therefore, the magnetic, hydrophilic-oleophobic polyHIPE composites are excellent candidates for the removal of water from water-oil mixtures with complete collection.

Cracked-earth-like titanium carbide MXene membranes with abundant hydroxyl groups for oil-in-water emulsion separation

Membrane separation technology is one of the best methods to deal with wastewater released from oil spills and industrial wastewater. Therefore, we designed and prepared hydroxyl-rich titanium carbide MXene materials and filtered them onto a commercial polyvinylidene fluoride substrate membrane to obtain a cracked-earth-like MXene membrane with abundant hydroxyl groups and excellent underwater wettability. The underwater oil contact and sliding angles were approximately 157° and less than 3°, respectively. Moreover, the membrane effectively separated a variety of surfactant-stabilized stable emulsions with a high permeation flux of up to 6385 L m^-2h^-1 bar^-1 and offered adequate performance after five cycles of the separation experiment. Additionally, the membrane exhibited remarkable resistance toward corrosive chemicals without any decrease in its underwater wettability performance. For example, the membrane was used to separate the emulsions containing alkali, salt, and acid. This study provides a new strategy to resolve the oily wastewater disposal problem by fabricating a cracked-earth-like MXene membrane with abundant hydroxyl groups.

Multifunctional filtration membrane with anti-viscous-oils-fouling capacity and selective dyes adsorption ability for complex wastewater remediation

Multifunctional filtration membranes (MFMs), which can both effectively separate oil and selectively remove dyes from polluted aquatic system with robust anti-viscous-oil-fouling capacity, strong chemical/physical resistance, and long cycled stability, are highly required but still a challenge to be realized. Herein, a simple route has been demonstrated to address this challenge aforementioned by decorating both halloysite nanotubes (HNTs) and zwitterionic poly (sulfobetaine methyl methacrylate) (PSBMA) on the microporous polyvinylidene fluoride (PVDF) membrane surface via modified polydopamine (PDA) coating route. The as-prepared membrane exhibits super-hydrophilic/underwater super-oleophobic performance and high water permeation flux (32529 ± 278 L m^-2 h^-1 at 0.85 bar) to purify the diverse viscous oil-in-water emulsions from oily wastewater accompanying with good cycled stability (the recovery rate of permeate flux is close to 100% after 5 cycles). Moreover, the as-prepared MFM possesses not only strong chemical resistance under wide range of pH value (from 1 to 12) and high saline (NaCl: 10 wt%) environment, but also physical resistance against ultrasound bath for 30 min. Given the presence of HNTs, PDA, and PSBMA, our MFM shows enough active sites to adsorb the soluble dyes and metallic ions in wastewater. These excellent properties endow our MFM with great potential for the remediation of complex wastewater.

Bacterial Superoleophobic Fibrous Matrices: A Naturally Occurring Liquid-Infused System for Oil-Water Separation

Nanocellulose fibers bioengineered by bacteria are a high-performance three-dimensional cross-linked network which can confine a dispersed liquid medium such as water. The strong chemical and physical interactions of dispersed water molecules with the entangled cellulosic network allow these materials to be ideal substrates for effective liquid separation. This type of phenomenon can be characterized as green with no equivalent precedent; its performance and sustainability relative to other cellulose-based or synthetic membranes are shown herein to be superior. In this work, we demonstrated that the renewable bacterial nanocellulosic membrane can be used as a stable liquid-infused system for the development of soft surfaces with superwettability and special adhesion properties and thus address intractable issues normally encountered by solid surfaces.

Gravity-Driven Separation of Oil/Water Mixture by Porous Ceramic Membranes with Desired Surface Wettability

Porous Al₂O₃ membranes were prepared through a phase-inversion tape casting/sintering method. The alumina membranes were embedded with finger-like pores perpendicular to the membrane surface. Bare alumina membranes are naturally hydrophilic and underwater oleophobic, while fluoroalkylsilane (FAS)-grafted membranes are hydrophobic and oleophilic. The coupling of FAS molecules on alumina surfaces was confirmed by Thermogravimetric Analysis and X-ray Photoelectron Spectroscopy measurements. The hydrophobic membranes exhibited desired thermal stability and were super durable when exposed to air. Both membranes can be used for gravity-driven oil/water separation, which is highly cost-effective. The as-calculated separation efficiency (R) was above 99% for the FAS-grafted alumina membrane. Due to the excellent oil/water separation performance and good chemical stability, the porous ceramic membranes display potential for practical applications.

2D and 3D Bulk Materials for Environmental Remediation: Air Filtration and Oil/Water Separation

Air and water pollution pose an enormous threat to human health and ecosystems. In particular, particulate matter (PM) and oily wastewater can cause serious environmental and health concerns. Thus, controlling PM and oily wastewater has been a great challenge. Various techniques have been reported to effectively remove PM particles and purify oily wastewater. In this article, we provide a review of the recent advancements in air filtration and oil/water separation using two- and three-dimensional (2D and 3D) bulk materials. Our review covers the advantages, characteristics, limitations, and challenges of air filters and oil/water separators using 2D and 3D bulk materials. In each section, we present representative works in detail and describe the concepts, backgrounds, employed materials, fabrication methods, and characteristics of 2D and 3D bulk material-based air filters and oil/water separators. Finally, the challenges, technical problems, and future research directions are briefly discussed for each section.

Thermally Sensitized Membranes for Crude Oil-Water Remediation under Visible Light

Effective remediation of produced water requires separating crude oil-water mixture and removing the dissolved organic pollutants. Membranes with selective wettability for water over oil enable the gravity-driven separation of an oil-water mixture by allowing water to permeate through while repelling oil. However, these membranes are often limited by their inability to remove the dissolved organic pollutants. In this work, a membrane with in-air superhydrophilic and underwater superoleophobic wettability is fabricated by thermal annealing of a stainless steel mesh. The resulting membrane possesses a hierarchical surface texture covered with a photocatalytic oxide layer composed of iron oxide and chromium oxide. The membrane exhibits chemical and mechanical robustness, which makes it suitable for remediation of crude oil and water mixture. Further, after being fouled by crude oil, the membrane can recover its inherent water-rich permeate flux upon visible light irradiation. Finally, the membrane demonstrates that it can separate surfactant-stabilized crude oil-in-water emulsion under gravity and decontaminate water-rich permeate by photocatalytic degradation of dissolved organic pollutants upon continuous irradiation of visible light.

Simple Amphoteric Charge Strategy to Reinforce Superhydrophilic Polyvinylidene Fluoride Membrane for Highly Efficient Separation of Various Surfactant-Stabilized Oil-in-Water Emulsions

Long-term efficient separation of highly emulsified oily wastewater is challenging. Reported herein is the preparation of a reinforced superhydrophilic, underwater superoleophobic membrane with demulsification properties using active iron nanoparticles in situ generated on a polydopamine (PDA)/polyethylenimine (PEI)-modified polyvinylidene fluoride (PVDF) membrane surface. A stable zwitterionic structure is fabricated on the membrane surface and provides it with an excellent capability of binding a hydration layer, leading to enhanced superhydrophilic/underwater superoleophobic properties. The interaction between the membrane surface and water is quantified using the relaxation time of water. After iron nanoparticles in situ anchoring, the superhydrophilic, underwater superoleophobic PDA/PEI modified PVDF membrane shows more stable flux behaviors, higher oil separation efficiency, demulsification, and excellent antioil-fouling properties for various anionic, nonionic, and cationic surfactant-stabilized oil-in-water emulsions in a crossflow filtration system. The reinforced hydration layer and the amphoteric charged demusification properties of the membrane play important roles in enhancing the membrane separation performance. The reinforced membrane also exhibits excellent cleaning and reusability performance in long-term operations. The outstanding separation performance, as well as the simple and cost-effective fabrication process of the membrane with various favorable properties, highlight its promise in practical emulsified oily water applications.

Robust Bifunctional Compressed Carbon Foam for Highly Effective Oil/Water Emulsion Separation

In this study, we report the pure compressed carbon foam (CCF) that offers a brand-new solution for separating emulsified oil/water mixtures. The CCF was fabricated by low-temperature carbonization of three-dimensional commercial melamine foam, which was then compressed without any further chemical modification. The CCF has amphiphilicity in air, underwater superoleophobicity, and underoil superhydrophobicity; therefore, it has been proved to be successfully utilized in highly emulsified oil-in-water and water-in-oil emulsions with excellent separation efficiencies, and it merely relies on gravity in the absence of external force. The CCF can also maintain its superwetting property under different harsh conditions, including strong acid, alkali, and salt solution conditions; this property offers great opportunities for widespread applications. Importantly, the CCF exhibits excellent permeability, separation efficiency, antifouling, and reusability performance. This novel CCF material has great potential application in handling oily wastewater owing to its low-cost raw materials, easily scaled-up preparation process, excellent antifouling property, and high separation capacity of materials.

Selective Wettability Membrane for Continuous Oil-Water Separation and In Situ Visible Light-Driven Photocatalytic Purification of Water

Membrane-based technologies are attractive for remediating oily wastewater because they are relatively energy-efficient and are applicable to a wide range of industrial effluents. For complete treatment of oily wastewater, removing dissolved contaminants from the water phase is typically followed by adsorption onto an adsorbent, which complicates the process. Here, an in-air superhydrophilic and underwater superoleophobic membrane-based continuous separation of surfactant-stabilized oil-in-water emulsions and in situ decontamination of water by visible-light-driven photocatalytic degradation of dissolved organic contaminants is reported. The membrane is fabricated by utilizing a thermally sensitized stainless steel mesh coated with visible light absorbing iron-doped titania nanoparticles. Post annealing of the membrane can enhance the adhesion of nanoparticles to the membrane surface by formation of a bridge between them. An apparatus that enables continuous separation of surfactant-stabilized oil-in-water emulsion and in situ photocatalytic degradation of dissolved organic matter in the water-rich permeate upon irradiation of visible light on the membrane surface with greater than 99% photocatalytic degradation is developed. The membrane demonstrates the recovery of its intrinsic water-rich permeate flux upon continuous irradiation of light after being contaminated with oil. Finally, continuous oil-water separation and in situ water decontamination is demonstrated by photocatalytically degrading model toxins in water-rich permeate.

Hierarchical Graphene/Metal-Organic Framework Composites with Tailored Wettability for Separation of Immiscible Liquids

Membrane filtration is a promising technology for the separation of organic immiscible liquids. Surface topography has a direct impact on the wettability of membranes, and it remains largely unexplored. Here, we introduce on-demand liquid separation by coating porous graphene/metal-organic framework (MOF) composites with tunable wettability on porous substrates. Our results have shown that polydopamine (PDA) coating mediates the controlled growth of MOF nanostructures and subsequent fluorination on the porous graphene framework. Surface topography of the graphene frameworks strongly depends on the loading content of MOF nanostructures. The concurrent control of surface coverage of MOF and surface chemistry allows tailoring of the trapped air fraction underneath the porous graphene frameworks in the range of 0.97 to 0.8. As a result, the surface energy of the graphene/MOF coatings can be programmed to afford the change in surface properties from superamphiphobicity to lyophobicity and the selective penetration of low-surface-energy (SE) liquids and the interception of high-SE liquids were achieved. The tailored wettability of graphene/MOF coatings allows for the separation of liquid mixtures of different ranges of SE, making it a general strategy for complex liquid treatment and chemical purification.

Highly Flexible and Patternable Multiwalled-Carbon Nanotube/Nitrocellulose Hybrid Conducting Paper Electrodes as Heating Platforms for Effective Ignition of Nanoenergetic Materials

In this study, a highly flexible, patternable multiwalled-carbon nanotube (MWCNT) paper electrode was specially designed and fabricated. The addition of a nitrocellulose (NC) polymer binder at less than the critical amount (≤2 wt %) was found to be effective for maintaining both the flexibility and electrical conductance of the resulting MWCNT paper electrode. The fabricated MWCNT paper electrode was then employed as a heating platform to ignite Al/CuO nanoparticle-based nanoenergetic materials (nEMs). The nEM layer was drop-cast on the surface of the MWCNT paper electrode with specially patterned shapes using a plotter, and its ignition was evaluated by applying various voltages through the MWCNT paper electrode. To increase the adhesion between the nEM layer and MWCNT paper electrode and to decrease the sparking sensitivity of the nEM layer, it was essential to incorporate NC in the nEM matrix. However, the combustion and explosion properties of nEM layers deteriorated with the addition of NC, enabling the estimation of the optimum amount of NC to be incorporated. The fabricated igniter can be employed in various thermal engineering applications, such as in the ignition of explosives and propellants, and in pyrotechnics. To demonstrate this, a compact, flexible, and patternable igniter composed of the NC/nEM layer (NC/nEM = 2:8 wt %) on an MWCNT paper electrode was used to successfully ignite solid propellants for launching a small rocket.

Micro/Nanoscale Structured Superhydrophilic and Underwater Superoleophobic Hybrid-Coated Mesh for High-Efficiency Oil/Water Separation

A novel micro/nanoscale rough structured superhydrophilic hybrid-coated mesh that shows underwater superoleophobic behavior is fabricated by spray casting or dipping nanoparticle–polymer suspensions on stainless steel mesh substrates. Water droplets can spread over the mesh completely; meanwhile, oil droplets can roll off the mesh at low tilt angles without any penetration. Besides overcoming the oil-fouling problem of many superhydrophilic coatings, this superhydrophilic and underwater superoleophobic mesh can be used to separate oil and water. The simple method used here to prepare the organic–inorganic hybrid coatings successfully produced controllable micro-nano binary roughness and also achieved a rough topography of micro-nano binary structure by controlling the content of inorganic particles. The mechanism of oil–water separation by the superhydrophilic and superoleophobic membrane is rationalized by considering capillary mechanics. Tetraethyl orathosilicate (TEOS) as a base was used to prepare the nano-SiO₂ solution as a nano-dopant through a sol-gel process, while polyvinyl alcohol (PVA) was used as the film binder and glutaraldehyde as the cross-linking agent; the mixture was dip-coated on the surface of 300-mesh stainless steel mesh to form superhydrophilic and underwater superoleophobic film. Properties of nano-SiO₂ represented by infrared spectroscopy and surface topography of the film observed under scanning electron microscope (SEM) indicated that the film surface had a coarse micro–nano binary structure; the effect of nano-SiO₂ doping amount on the film’s surface topography and the effect of such surface topography on hydrophilicity of the film were studied; contact angle of water on such surface was tested as 0° by the surface contact angle tester and spread quickly; the underwater contact angle to oil was 158°, showing superhydrophilic and underwater superoleophobic properties. The effect of the dosing amount of cross-linking agent to the waterproof swelling property and the permeate flux of the film were studied; the oil–water separation effect of the film to oil–water suspension and oil–water emulsion was studied too, and in both cases the separation efficiency reached 99%, which finally reduced the oil content to be lower than 50 mg/L. The effect of filtration times to permeate flux was studied, and it was found that the more hydrophilic the film was, the stronger the stain resistance would be, and the permeate flux would gradually decrease along with the increase of filtration times.

Preparation and Photochromic Performance of Homogeneous Phase Nitrocellulose Membrane Grafting Spirooxazine Moieties

The synthesis of 1,3,3-trimethyl-9′-acryloxyspiro[indoline-2,3′(3H)naphtho[2,1-b][l,4]-oxazine] (AISO) was carried out by catalytic esterification of 1,3,3-trimethyl-9′-hydroxyspiro-[indoline-2,3′(3H)naphtho[2,1-b][l,4]oxazine] (SO–OH) and acrylic acid in the presence of 1,3-dicyclohexylcarbodiimide (DCC) and N-dimethylaminopyridine (DMAP). Then, the synthesis of the target copolymer (NC-g-AISO) was was carried out by benzoyl peroxide (BPO)-induced graft copolymerization of the AISO monomer onto nitrocellulose (NC) in a homogeneous methyl isobutyl ketone medium. The structure of NC-g-AISO was characterized by Fourier transform infrared (IR) spectroscopy, 13C Nuclear Magnetic Resonance (NMR) spectra and thermogravimetric (TG) analysis. The photochromic properties of NC-g-AISO were investigated by examining UV–Vis spectra in ethyl acetate solution and solid membrane. Compared with the AISO monomer in ethyl acetate solution, the thermal color decay stability of the colored form of NC-g-AISO in ethyl acetate solution and in solid membrane improved significantly. The thermal color decay reaction rate constants in ethyl acetate solution and membrane at 25 °C were 1.77 × 10–2 and 1.36 × 10–3 s–1, respectively, fitted using the first-order reaction equation. After ten photochromic cycles, the relative absorption intensity of the colored form of NC-g-AISO decreased by 0.85%, indicating that the NC-g-AISO membrane has good reversible photochromic behavior.

A Self-Cleaning Heterostructured Membrane for Efficient Oil-in-Water Emulsion Separation with Stable Flux

Lack of clean water is a major global challenge. Membrane separation technology is an ideal choice for the treatment of industrial, domestic sewage owing to its low energy consumption and cost. However, membranes are highly susceptible to contamination, particularly during wastewater treatment, which has limited their practical applications in this field. Similarly, the flux of the membrane decreases with prolonged use due to its reduced interlayer spacing. Preparation of membranes with anticontamination properties and stable flux is the key to addressing this problem. In this study, a 2D heterostructure membrane with visible-light-driven self-cleaning performance is prepared via a self-assembly process. Notably, the addition of palygorskite increases the interlayer spacing of the graphene and heterojunction structures, which increases the flux of the membrane and avoids a decrease of the interlayer spacing of the membrane under pressure. The presence of a heterojunction with visible light catalytic properties effectively avoids membrane fouling and avoids a sharp decrease of the permeation flux. Importantly, the prepared 2D membrane has excellent separation performance for oil-water emulsions with both high flux and efficiency. These features suggest great potential for the prepared 2D membrane in wastewater treatment applications.

Cellulose acetate monolith with hierarchical micro/nano-porous structure showing superior hydrophobicity for oil/water separation

Eco-friendly cellulose acetate (CA) monolith with novel hierarchical micro/nano-porous structure was successfully fabricated via a simple thermally impacted nonsolvent induced phase separation (TINIPS) method. Based on the unique three-dimensional (3D) hierarchical porous structure, CA monolith revealed a high porosity (92.1%), excellent hydrophobicity (water contact angle of 147°) and superoleophilicity (oil contact angle of 0°). As a result, the porous monolith could selectively and efficiently adsorb various oils and organic solvents from oil/water mixtures with high saturation adsorption capacity (Q_m) of 6.59-15.03 g g^-1. Besides, the monolith exhibited outstanding environmental stability in different pH (1-14), temperature (0-70 °C) and turbulent environments with almost unchanged hydrophobicity and Q_m. Besides, CA monolith also showed a continuous oil/water separation ability to purify the polluted water by using a pump-assisted system, revealing a great potential for controlling ocean oil pollution.

Multifunctional TiO2-Based Superoleophobic/Superhydrophilic Coating for Oil-Water Separation and Oil Purification

Materials that possess distinguishable superwettability toward oil and water have aroused widespread attention for their application in oil-water separation. Among them, a superoleophobic/superhydrophilic material is considered as the ideal candidate because of its antioil-fouling and water-wetting behavior; however, the fabrication is a challenge and there has been insufficient attention given to multipurpose applications in treating intricate mixtures. Herein, for the first time, a multifunctional superoleophobic/superhydrophilic coating integrated with a photocatalysis property was fabricated by the combination of polarity component-enhanced fluorosurfactant and titanium dioxide (TiO₂) nanoparticles. The coating applied on stainless steel mesh preserves the ability to separate immiscible oil-water mixtures, whereas the coated cotton preserves the ability to separate both surfactant-stabilized oil-in-water and water-in-oil emulsions. Notably, benefiting from the photocatalysis property of titanium dioxide, the coating also can be used in liquid purification. Contaminated oil can be separated and purified by a separation-purification process, during which the oil-soluble contamination is degraded under ultraviolet (UV) irradiation. The multipurpose coating provides an alternative solution for oil-water remediations, which has prospects in intricate liquid treatment in industrial and domestic applications.

Dual super-amphiphilic modified cellulose acetate nanofiber membranes with highly efficient oil/water separation and excellent antifouling properties

Along with increasing oily, industrial wastewater and seawater pollution, oil spills-and their clean-up via the separation of oil and water-are still a worldwide challenge. Aiming to fabricate an oil/water separation membrane with excellent comprehensive performance, we report here a new type of multifunctional deacetylated cellulose acetate (d-CA) membrane. The cellulose acetate (CA) nanofiber membranes are fabricated by electrospinning and then deacetylated to obtain the d-CA nanofiber membranes, which are super-amphiphilic in air, oleophobic in water, and super-hydrophilic in oil. The multifunctional d-CA nanofiber membranes can be used as water-removal substances for oil/water mixtures, as well as emulsified oil/water and oil/corrosive aqueous systems, with gravity as the only needed driving force. The d-CA nanofiber membranes possess the highest separation flux, reaching up to 38,000 L/m²·h, and the highest separation efficiency, reaching up to 99.97 % for chloroform/water mixtures under the force of gravity. In fact, the separation flux was several times higher than that of commercial CA (c-CA) membranes. The excellent anti-pollution and self-cleaning abilities endow the membranes with powerful cyclic stability and reusability. The d-CA nanofiber membranes show great application prospects in chemical plants, textile mills, and the food industry, as well as offshore oil spills, to separate oil from water.

Hydrothermal synthesized UV-resistance and transparent coating composited superoloephilic electrospun membrane for high efficiency oily wastewater treatment

As oily wastewater issues continue to grow, the treatment of oily wastewater has become urgent an emergency. However, present solutions are restricted by the limited performance of materials. An UV-resist and transparent coating consisting of PDMS and ZnO decorated on a highly stable and self-standing polyimide is reported in this work as a potential solution. The obtained fibrous membranes not only allow high-efficiency (higher than 99%) oily wastewater separation but also show superior UV-resistant activity. Moreover, the superoleophilicity and hydrophobicity of the composite membrane were confirmed to be stable under harsh conditions, and the transparent coating layer has the potential to be applied in other fields. The design of the UV-resistant, transparent and superoleophilic nanofibrous membrane is very practical, and will be quite promising for reducing oily environmental contaminations from waters.