CO2-Responsive Nanofibrous Membranes with Switchable Oil/Water Wettability

New Insights on the Chemical Origin of Life: The Role of Aqueous Polymerization of N-carboxyanhydrides (NCA)

At the origin, the emergence of proteins was based on crucial prebiotic stages in which simple amino acids-based building blocks spontaneously evolved from the prebiotic soup into random proto-polymers called protoproteins. Despite advances in modern peptide synthesis, these prebiotic chemical routes to protoproteins remain puzzling. We discuss in this perspective how polymer science and systems chemistry are reaching a point of convergence in which simple monomers called N-carboxyanhydrides would be able to form such protoproteins via the emergence of a protometabolic cycle involving aqueous polymerization and featuring macromolecular Darwinism behavior.

Scalable weaving of resilient membranes with on-demand superwettability for high-performance nanoemulsion separations

This study leverages the ancient craft of weaving to prepare membranes that can effectively treat oil/water mixtures, specifically challenging nanoemulsions. Drawing inspiration from the core-shell architecture of spider silk, we have engineered fibers, the fundamental building blocks for weaving membranes, that feature a mechanically robust core for tight weaving, coupled with a CO2-responsive shell that allows for on-demand wettability adjustments. Tightly weaving these fibers produces membranes with ideal pores, achieving over 99.6% separation efficiency for nanoemulsions with droplets as small as 20 nm. They offer high flux rates, on-demand self-cleaning, and can switch between sieving oil and water nanodroplets through simple CO2/N2 stimulation. Moreover, weaving can produce sufficiently large membranes (4800 cm2) to assemble a module that exhibits long-term stability and performance, surpassing state-of-the-art technologies for nanoemulsion separations, thus making industrial application a practical reality.

Engineering Dual CO2- and Photothermal-Responsive Membranes for Switchable Double Emulsion Separation

Stimulus-responsive membranes demonstrate promising applications in switchable oil/water emulsion separations. However, they are unsuitable for the treatment of double emulsions like oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) emulsions. For efficient separation of these complicated emulsions, fine control over the wettability, response time, and aperture structure of the membrane is required. Herein, dual-coated fibers consisting of primary photothermal-responsive and secondary CO2-responsive coatings are prepared by two steps. Automated weaving of these fibers produces membranes with photothermal- and CO2-responsive characteristics and narrow pore size distributions. These membranes exhibit fast switching wettability between superhydrophilicity (under CO2 stimulation) and high hydrophobicity (under near-infrared stimulation), achieving on-demand separation of various O/W/O and W/O/W emulsions with separation efficiencies exceeding 99.6%. Two-dimensional low-field nuclear magnetic resonance and correlated spectra technique are used to clarify the underlying mechanism of switchable double emulsion separation. The approach can effectively address the challenges associated with the use of stimulus-responsive membranes for double emulsion separation and facilitate the industrial application of these membranes.

Janus Membranes with Asymmetric Superwettability for High-Performance and Long-Term On-Demand Oil/Water Emulsion Separation

Current single-function superwettable materials are typically designed for either oil removal or water removal and are constrained by oil density, limiting their widespread applications. Janus membranes with opposite wettability on their two surfaces have recently emerged and present attractive opportunities for on-demand oil/water emulsion separation. Here, a combination strategy is introduced to prepare a Janus membrane with asymmetric superwettability for switchable oil/water emulsion separation. A mussel-inspired asymmetric interface introduction cooperating with the sequence-confined surface modification not only brings about an asymmetric superwettability Janus interface but also guarantees an outstanding stable interface and remarkable chemical stability surfaces. Specifically, the superhydrophilic surface with underwater superoleophobicity can separate surfactant-stabilized oil-in-water emulsions. Conversely, other surface displays opposite superhydrophobicity and superoleophilicity to treat surfactant-stabilized water-in-oil emulsions. Significantly, this superwettable Janus membrane presents superior long-term on-demand oil/water emulsion separation without obvious flux decline and high recovery ability because of its superwettability and superior stability. Furthermore, the asymmetric superwettability enhances the interfacial floatability at air-water interfaces, enabling the design of advanced interfacial materials. The as-prepared superwettable Janus membrane has established a cooperated separation system, overcoming the monotony of conventional superwettable membranes and expanding the application of these specialized membranes to oily wastewater treatment.

Robust and flexible polyester fiber membrane with under-liquid dual superlyophobicity for efficient on-demand oil-water separation

Functional materials with under-liquid dual superlyophobicity have generated a great deal of concern from researchers due to their switchable separation ability oil-water mixtures and emulsions. Conceptually, under-liquid dual superlyophobicity is a Cassie state achievable under-liquid through the synergy of an under-liquid double lyophobic surface and the construction of a highly rough surface. However, obtaining an under-liquid dual superlyophobic surface remains difficult due to its thermodynamic contradiction and complex surface composition. Herein, we successfully prepared a functional coating by modifying the mixture of cellulose nanocrystals (CNCs) and nano-TiO2 with perfluorooctanoic acid (PFOA) via a simple method, then obtained a polyester fiber membrane with under-liquid dual superlyophobicity by roll coating method. The surface wettability of the polyester (PET) membrane was altered, transforming it from the original under-water oleophobic/under-oil superhydrophilic state to the under-water superoleophobic/under-oil superhydrophobic state after coated. The resulting membrane was applied to separate oil and water on-demand. The coated PET membrane exhibited high separation efficiency (>99 %) and high separation flux, effectively separating immiscible oil-water systems as well as oil-in-water and water-in-oil emulsions. The coated PET membrane also demonstrated the ability to perform alternate separation of oil-water mixtures through wetting, washing, and rewetting cycles, with repeated processes up to 10 times without significant reduction in separation efficiency. Furthermore, compared with the previous works, our approach offers a simpler and more convenient method for constructing under-liquid dual superlyophobic surface, making it more suitable for continuous corporate production. This study may provide inspiration for the production and application in large-scale of under-liquid dual superlyophobic membranes.

A review of stimuli-responsive polymer-based gating membranes

The formation and properties of smart (stimuli-responsive) membranes are reviewed, with a special focus on temperature and pH triggering of gating to water, ions, polymers, nanoparticles, or other molecules of interest. The review is organized in two parts, starting with all-smart membranes based on intrinsically smart materials, in particular of the poly(N-isopropylacrylamide) family and similar polymers. The key steps of membrane fabrication are discussed, namely the deposition into thin films, functionalization of pores, and the secondary crosslinking of pre-existing microgel particles into membranes. The latter may be free-standing and do not necessitate the presence of a porous support layer. The temperature-dependent swelling properties of polymers provide a means of controlling the size of pores, and thus size-sensitive gating. Throughout the review, we highlight "positive" (gates open) or "negative" (closed) gating effects with respect to increasing temperature. In the second part, the functionalization of porous organic or inorganic membranes of various origins by either microgel particles or linear polymer brushes is discussed. In this case, the key steps are the adsorption or grafting mechanisms. Finally, whenever provided by the authors, the suitability of smart gating membranes for specific applications is highlighted.

Versatile CO2-responsive Sponges Decorated with ZIF-8 for Bidirectional Separation of Oil/Water and Controllable Removal of Dyes

The complex wastewater containing water-soluble dyes and water-insoluble oils has given rise to significant environmental concerns that demand urgent remediation. Herein, a novel "smart" multifunctional sponge (ZIF-8@PMS) stepwise decorated with ZIF-8 nanoparticles and CO2-responsive copolymer (poly(2-(diethylamino) ethyl methacrylate-co-3-(trimethoxysilyl)propyl acrylate-co-stearyl methacrylate) was successfully prepared for CO2 controllable oil/water separation and dyes removal. The results revealed that the sponge coated with CO2-responsive copolymer for three cycles (ZIF-8@PMS-3) exhibited optimal comprehensive properties. The ZIF-8@PMS-3 had excellent compressive-resilient characteristics and chemical stability. As expected, it displayed tunable wettability and charged state under the regulation of CO2. Based on these features, ZIF-8@PMS-3 presented highly efficient removal of oil and dyes, even for the dye-containing oil/water emulsions, via a synergistic combination of adsorption and separation methods. The adsorption capacity for oil and various organic solvents ranged from 21.3 to 50 g g-1. The maximum adsorption capacities toward anionic dyes: methyl orange with 1205.89 mg g-1 and methyl blue with 880.00 mg g-1 in the presence of CO2 through electrostatic interaction. In the absence of CO2, it achieved maximum adsorption capacities for cationic dyes, including malachite green with 1246.15 mg g-1 and rhodamine B with 203 mg g-1, primarily driven by π-π interactions. According to distinct adsorption mechanisms, ZIF-8@PMS-3 could selectively adsorb either anionic or cationic dyes by exploiting CO2 as a trigger. Furthermore, the separation efficiencies for both types of oil/water emulsions surpassed 99.9%, with respective fluxes of 1566.99 L m-2 h-1 (water-in-oil emulsion) and 310.37 L m-2 h-1 (oil-in-water emulsion). Additionally, the as-prepared sponges exhibited remarkable antibacterial properties and exceptional recyclability. Therefore, the ZIF-8@PMS-3 holds substantial promise for potential applications in practical industrial wastewater treatment.

Developing aerogel surfaces via switchable-hydrophilicity tertiary amidine coating for improved oil recovery

Blanket aerogels (i.e., Cabot™ Thermal Wrap® (TW) and Aspen™ Spaceloft® (SL)) with surfaces that have controllable wettability are promising advanced materials for oil recovery applications, where high oil uptake during deployment could be coupled with high oil release to enable reusability of recovered oil. The study presented here details the preparation of CO₂-switchable aerogel surfaces through the application of switchable tertiary amidine (i.e., tributylpentanamidine (TBPA)) onto aerogel surfaces using drop casting, dip coating, and physical vapor deposition techniques. TBPA is synthesized via two step processes: (1) synthesis of N, N-dibutylpentanamide, (2) synthesis of N, N-tributylpentanamidine. The deposition of TBPA is confirmed by X-ray photoelectron spectroscopy. Our experiments revealed that surface coating of TBPA onto aerogel blankets was partially successful within limited set of process conditions (e.g., 290 ppm CO₂ and 5500 ppm humidity for PVD, 106 ppm CO₂ and 700 ppm humidity for drop casting and dip coating), but that the post-aerogel modification strategies yielded poor, heterogeneous reproducibility. Overall, more than 40 samples were tested for their switchability in the presence of CO₂ and water vapor, respectively, and the success rate was 6.25 %, 11.7 % and 18 % for PVD, drop casting, and dip coating, respectively. The most likely reasons for unsuccessful coating onto aerogel surfaces are: (1) the heterogeneous fiber structure of the aerogel blankets, (2) poor distribution of the TBPA over the aerogel blanket surface.

Recent developments in the application of membrane separation technology and its challenges in oil-water separation: A review

In the development and production process of domestic and foreign oil fields, large amounts of oil-bearing wastewater with complex compositions containing toxic and harmful pollutants are generated. These oil-bearing wastewaters will cause serious environmental pollution if they are not effectively treated before discharge. Among these wastewaters, the oily sewage produced in the process of oilfield exploitation has the largest content of oil-water emulsion. In order to solve the problem of oil-water separation of oily sewage, the paper summarizes the research of many scholars in many aspects, such as the use of physical and chemical methods such as air flotation and flocculation, or the use of mechanical methods such as centrifuges and oil booms for sewage treatment. Comprehensive analysis shows that among these oil-water separation methods, membrane separation technology has higher separation efficiency in the separation of general oil-water emulsions than other methods and also exhibits a better separation effect for stable emulsions, which has a broader application prospect for future developments. To present the characteristics of different types of membranes more intuitively, this paper describes the applicable conditions and characteristics of various types of membranes in detail, summarizes the shortcomings of existing membrane separation technologies, and offers prospects for future research directions.

Advanced stimuli-responsive membranes for smart separation

Membranes have been extensively studied and applied in various fields owing to their high energy efficiency and small environmental impact. Further conferring membranes with stimuli responsiveness can allow them to dynamically tune their pore structure and/or surface properties for efficient separation performance. This review summarizes and discusses important developments and achievements in stimuli-responsive membranes. The most commonly utilized stimuli, including light, pH, temperature, ions, and electric and magnetic fields, are discussed in detail. Special attention is given to stimuli-responsive control of membrane pore structure (pore size and porosity/connectivity) and surface properties (wettability, surface topology, and surface charge), from the perspective of determining the appropriate membrane properties and microstructures. This review also focuses on strategies to prepare stimuli-responsive membranes, including blending, casting, polymerization, self-assembly, and electrospinning. Smart applications for separations are also reviewed as well as a discussion of remaining challenges and future prospects in this exciting field. This review offers critical insights for the membrane and broader materials science communities regarding the on-demand and dynamic control of membrane structures and properties. We hope that this review will inspire the design of novel stimuli-responsive membranes to promote sustainable development and make progress toward commercialization.

Reduced Graphene Oxide-Doped Porous Thermoplastic Polyurethane Sponges for Highly Efficient Oil/Water Separation

In this paper, a porous polyurethane sponge with excellent hydrophobicity was prepared through thermal phase separation. Preparation condition modified experiments were systematically carried out, and a sponge with a saturated oil absorption capacity (13.3 g g^-1) and a rapid absorption rate (achieving absorption equilibrium within 20 s) was achieved. The thermoplastic polyurethane (TPU) sponge as an oil absorbent is capable of selectively absorbing various oils/organic solvents from oil/water mixtures with a high recovery rate. To further enhance the hydrophobicity and mechanical properties of the porous sponge, 3% reduced graphene oxide was doped to this material. The morphological investigation indicated that the three-dimensional composite sponges have uniformly distributed micropores and nanopores, and the hydrophobicity and mechanical properties were improved. The composite as a whole exhibited remarkable superelasticity, excellent reversible compressibility, and fatigue resistance (strength up to 186 kPa at 80% strain), which allows it to re-absorb oil by simple manual extrusion. The abovementioned properties make this TPU porous material a promising candidate for practical application in water pollution treatment.

Scalable and switchable CO2-responsive membranes with high wettability for separation of various oil/water systems

Smart membranes with responsive wettability show promise for controllably separating oil/water mixtures, including immiscible oil-water mixtures and surfactant-stabilized oil/water emulsions. However, the membranes are challenged by unsatisfactory external stimuli, inadequate wettability responsiveness, difficulty in scalability and poor self-cleaning performance. Here, we develop a capillary force-driven confinement self-assembling strategy to construct a scalable and stable CO₂-responsive membrane for the smart separation of various oil/water systems. In this process, the CO₂-responsive copolymer can homogeneously adhere to the membrane surface by manipulating the capillary force, generating a membrane with a large area up to 3600 cm² and excellent switching wettability between high hydrophobicity/underwater superoleophilicity and superhydrophilicity/underwater superoleophobicity under CO₂/N₂ stimulation. The membrane can be applied to various oil/water systems, including immiscible mixtures, surfactant-stabilized emulsions, multiphase emulsions and pollutant-containing emulsions, demonstrating high separation efficiency (>99.9%), recyclability, and self-cleaning performance. Due to robust separation properties coupled with the excellent scalability, the membrane shows great implications for smart liquid separation.

Facile Approach for the Potential Large-Scale Production of Polylactide Nanofiber Membranes with Enhanced Hydrophilic Properties

Polylactide (PLA) nanofiber membranes with enhanced hydrophilic properties were prepared through electrospinning. As a result of their poor hydrophilic properties, common PLA nanofibers have poor hygroscopicity and separation efficiency when used as oil-water separation materials. In this research, cellulose diacetate (CDA) was used to improve the hydrophilic properties of PLA. The PLA/CDA blends were successfully electrospun to obtain nanofiber membranes with excellent hydrophilic properties and biodegradability. The effects of the additional amount of CDA on the surface morphology, crystalline structure, and hydrophilic properties of the PLA nanofiber membranes were investigated. The water flux of the PLA nanofiber membranes modified with different CDA amounts was also analyzed. The addition of CDA improved the hygroscopicity of the blended PLA membranes; the water contact angle of the PLA/CDA (6/4) fiber membrane was 97.8°, whereas that of the pure PLA fiber membrane was 134.9°. The addition of CDA enhanced hydrophilicity because it tended to decrease the diameter of PLA fibers and thus increased the specific surface area of the membranes. Blending PLA with CDA had no significant effect on the crystalline structure of the PLA fiber membranes. However, the tensile properties of the PLA/CDA nanofiber membranes worsened due to the poor compatibility between PLA and CDA. Interestingly, CDA endowed the nanofiber membranes with improved water flux. The water flux of the PLA/CDA (8/2) nanofiber membrane was 28,540.81 L/m²·h, which was considerably higher than that of the pure PLA fiber membrane (387.47 L/m²·h). The PLA/CDA nanofiber membranes can be feasibly applied as an environmentally friendly oil-water separation material because of their improved hydrophilic properties and excellent biodegradability.

Porous Electrospun Films with Reversible Photoresponsive Microenvironmental Humidity Regulation: A Controllable Hydrogen-Bonding Synergistic Effect Exhibited by Acrylic Acid Segments

Suitable relative humidity is essential for the preservation of cultural relics, food storage, and so on. A special material that can regulate the relative humidity in the microenvironment is particularly important. In this work, several innovative electrospun films with reversible photoresponsive wettability and the ability to regulate microenvironmental relative humidity were prepared. The spiropyran unit of the synthesized copolymer played the most important role in humidity regulation due to its reversible transition between a nonpolar ring-closed state and a polar ring-opened state induced by alternating ultraviolet/visible illumination. More interestingly, the introduction of acrylic acid segments exhibited a controllable hydrogen bond synergistic effect for increasing the range of humidity regulation. The color change and the reversible change ranges of wettability and microenvironmental relative humidity under ultraviolet/visible irradiation are all closely related to the number of acrylic acid segments. Cassie theory, density functional theory (DFT), and interaction region indicator (IRI) analysis were used to characterize this phenomenon. Electrospinning is a promising method to achieve large-scale production that can put such material into practical applications.

Multi-responsive on-demand drug delivery PMMA-co-PDEAEMA platform based on CO2, electric potential, and pH switchable nanofibrous membranes

This study investigated the release characteristics of curcumin (CUR)-loaded switchable poly(methyl methacrylate)-co-poly(N,N-diethylaminoethyl methacrylate) (PMMA-co-PDEAEMA) membranes following the application of various stimuli, as well as the platform's applicability in wound dressing and tissue engineering applications. The free-radical polymerization method was used to synthesize the PMMA-co-PDEAEMA copolymer. The drug-loaded nanofibrous membrane with electric potential (EP)-, CO₂-, and pH-responsive properties was developed by the electrospinning of PMMA-co-PDEAEMA and CUR. The resulted structure was characterized by a scanning electron microscope (SEM) coupled with X-ray energy dispersive spectroscopy and wide-angle X-ray scattering measurements. The release characteristics of the CUR-loaded wound covering were analyzed in various simulated environments at varying voltages, alternated CO₂/N₂ gas bubbling, and at two different pH values; the results demonstrated high drug release controllability. Loaded CUR displayed high stability and better solubility compared with free CUR. The CUR-loaded tissue also exhibited high antibacterial activity against Escherichia coli and staphylococcus aureus bacteria. In addition, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay depicted high biocompatibility of up to 95% in the CUR-loaded membrane. This platform could be a promising candidate for usage in tissue engineering and medical applications such as targeted drug delivery, biodetection, reversible cell capture-and-release systems, and biosensors.

Bioinspired Under-Liquid Dual Superlyophobic Surface for On-Demand Oil/Water Separation

Porous membranes with under-liquid dual superlyophobic properties, which are difficult to achieve because of a thermodynamic contradiction, have attracted considerable interest in the field of switchable oil/water separation. Herein, a bioinspired mesh membrane with alternating hydrophilic and hydrophobic chemical patterns on its surface that endows it with superamphiphilic and under-liquid dual superlyophobic properties is fabricated by a simple liquidus modification process. The as-prepared membrane possesses a combination of under-oil superhydrophobic and under-water superoleophobic characteristics in the absence of external stimuli. Moreover, it can effectively perform the on-demand separation of various oil/water systems, including immiscible oil/water mixtures and oil/water emulsions owing to its under-liquid dual superlyophobic properties.

Collagen Fiber-Based Advanced Separation Materials: Recent Developments and Future Perspectives

Separation plays a critical role in a broad range of industrial applications. Developing advanced separation materials is of great significance for the future development of separation technology. Collagen fibers (CFs), the typical structural proteins, exhibit unique structural hierarchy, amphiphilic wettability, and versatile chemical reactivity. These distinctive properties provide infinite possibilities for the rational design of advanced separation materials. During the past 2 decades, many progressive achievements in the development of CFs-derived advanced separation materials have been witnessed already. Herein, the CFs-based separation materials are focused on and the recent progresses in this topic are reviewed. CFs widely existing in animal skins display unique hierarchically fibrous structure, amphiphilicity-enabled surface wetting behaviors, multi-functionality guaranteed covalent/non-covalent reaction versatility. These outstanding merits of CFs bring great opportunities for realizing rational design of a variety of advanced separation materials that were capable of achieving high-performance separations to diverse specific targets, including oily pollutants, natural products, metal ions, anionic contaminants and proteins, etc. Besides, the important issues for the further development of CFs-based advanced separation materials are also discussed.

Smart Hierarchical Zeolitic Imidazolate Framework-Coated Stainless Steel Meshes with Switchable Wettability for Oil/Water Separation

Selective filtration based on superwetting materials has brought about widespread attention in the field of oil/water separation. In this study, a ZIF-L@8-coated stainless steel mesh (ZIF-L@8-coated SSM) was prepared via in situ growth of two-dimensional leaf-shaped ZIF-L nanosheets on SSM, followed by heterogeneous epitaxial growth of ZIF-8 on a ZIF-L coating. The synthesized ZIF-L@8-coated SSM with a hierarchical micro/nanoscale structure exhibited outstanding switchable wettability between underwater superoleophobicity and underoil superhydrophobicity upon respective prewetting using water and oil without additional external stimuli. It possessed excellent separation performances and stabilities with respect to various types of oil/water mixtures. The switchable wettability mechanism was analyzed and elucidated in detail. The synthesized ZIF-L@8-coated SSM with switchable wettability in this study would have great potential in on-demand oil/water separation.

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.

Carbon Dioxide Chemically Responsive Switchable Gas Valves with Protonation-Induced Liquid Gating Self-Adaptive Systems

Carbon dioxide (CO₂ ) capture and storage technologies are promising to limit CO₂ emission from anthropogenic activities, to achieve carbon neutrality goals. CO₂ capture requires one to separate CO₂ from other gases, and therefore a gas flow system that exhibits discernible gating behaviors for CO₂ would be very useful. Here we propose a self-adaptive CO₂ gas valve composed of chemically responsive liquid gating systems. The transmembrane critical pressures of the liquid gate vary upon the presence of CO₂ , due to the superamphiphiles assembled by poly(propylene glycol) bis(2-aminopropyl ether) and oleic acid in gating liquids that are protonated specifically by CO₂ . It is shown that the valve can perform self-adaptive regulation for specific gases and different concentrations of CO₂ . This protonation-induced liquid gating mechanism opens a potential platform for applications of CO₂ separators, detectors, sensors and beyond.

Stimuli-Responsive Pickering Emulsions Regulated via Polymerization-Induced Self-Assembly Nanoparticles

With the development of reversible deactivated radical polymerization techniques, polymerization-induced self-assembly (PISA) is emerging as a facile method to prepare block copolymer nanoparticles in situ with high concentrations, providing wide potential applications in different fields, including nanomedicine, coatings, nanomanufacture, and Pickering emulsions. Polymeric emulsifiers synthesized by PISA have many advantages comparing with conventional nanoparticle emulsifiers. The morphologies, size, and amphiphilicity can be readily regulated via the synthetic process, post-modification, and external stimuli. By introducing stimulus responsiveness into PISA nanoparticles, Pickering emulsions stabilized with these nanoparticles can be endowed with "smart" behaviors. The emulsions can be regulated in reversible emulsification and demulsification. In this review, the authors focus on recent progress on Pickering emulsions stabilized by PISA nanoparticles with stimuli-responsiveness. The factors affecting the stability of emulsions during emulsification and demulsification are discussed in details. Furthermore, some viewpoints for preparing stimuli-responsive emulsions and their applications in antibacterial agents, diphase reaction platforms, and multi-emulsions are discussed as well. Finally, the future developments and applications of stimuli-responsive Pickering emulsions stabilized by PISA nanoparticles are highlighted.

Mechanical response of surface wettability of Janus porous membrane and its application in oil-water separation

Smart surfaces with switchable wettability are widely studied for environmental application. Although a large number of stimulation routes provide broad prospects for the development of smart surfaces, achieving high sensitivity, fast response and recovery, simple operation, security and good stability is still challenging. Herein, a Janus membrane via electrospinning, chemical bath deposition and heat treatment is constructed. By using the hydrophilic ZIF-L nanosheet to functionalize the hydrophobic thermoplastic polyurethane (TPU) substrate, a smart surface utilizes the ZIF-L crack induced by strain in the hydrophilic layer to control surface wettability is obtained. In the range of 0%-100% strain, the wettability of the smart surface presents an obvious change with stretching, and water contact angle of the surface shows a monotonic increase with a maximum tuning range from 47° to 114°. Due to local fusion of the TPU microfibers and good binding between the ZIF-L layer and the TPU substrate after heat treatment, the prepared Janus membrane exhibits consistent and symmetrical hydrophilic-hydrophobic-hydrophilic transition curves in 50 stretching-releasing cycles. Thanks to the porous and asymmetric architecture, the membrane shows good oil-water separation performance, and the separation flux increases with the increase of strain, while the separation efficiency is always higher than 98%. Because of the excellent structural stability, the robust membrane with 100% strain maintains its oil-water separation property for 50 stretching-releasing cycles. This study provides a new perspective for the development of smart material with stimuli responsive surface for oily wastewater purification.

Turning Waste into Wealth: Remotely NIR Light-Controlled Precious Metal Recovery by Covalently Functionalized Black Phosphorus

It is a great challenge to refine precious metals from e-wastes under mild conditions without hazardous reagents. Herein, black phosphorus (BP) was covalently functionalized with poly(N-isopropylacrylamide) (PNIPAM) to obtain thermo/near-infrared (NIR)-responsive BP-P for precious metal recovery. Precious metals (Au, Ag, and Pd) with higher redox potentials than BP-P could be efficiently recovered by reduction-driven enrichment. Taking Au as an example, the recovery process presented fast kinetics (<15 min), excellent selectivity, and high efficiency (≈98 %). Remote operation with NIR light could generate heat by BP, which induced the hydrophilic-to-hydrophobic transition of PNIPAM, allowing the spontaneous gathering, facile collection, and practical recycle of BP-P following Au extraction. Thanks to the unique features of BP-P, not only could high-quality Au nanoparticles (20-30 nm) be economically extracted (cost: $0.731-1.222 g^-1 Au nanoparticles; 5-6 orders of magnitude lower than the market price), but also the formed BP-P-Au nanocomposites have potential application in hydrogen evolution reaction.

Facile Synthesis of CO2 -Responsive Nano-Objects: Batch versus Semi-Batch RAFT Copolymerization

Precise polymer architecture and self-assembled morphological control are attractive due to their promising applications, such as drug delivery, biosensors, tissue engineering and "smart" optical systems. Herein, starting from the same hydrophilic units poly(ethylene glycol) (PEG), using CO₂ -sensitive monomer N, N-diethylaminoethyl methacrylate (DEAEMA) and hydrophobic monomer benzyl methacrylate (BzMA), a series of well-defined statistical, block, and gradient copolymers is designed and synthesized with similar degree of polymerization but different monomer sequences by batch and semi-batch RAFT polymerization process and their CO₂ -responsive behaviors of these nano-objects is systematically studied. The gradient copolymers are generated by using semi-batch methods with programmed monomer feed rate controlled by syringe pumps, achieving precise control over desired gradient copolymer composition distribution. In aqueous solution, the copolymers could self-assemble into various aggregates before CO₂ stimulus. Upon bubbling CO₂ , the gradient copolymers preferred to form nanosheet-like structures, while the block and statistical copolymers with similar molar mass could only form larger vesicles with thinner membrane thickness or disassemble. The semi-batch strategy to precisely control over the desired composition distribution of the gradient segment presents an emerging trend for the fabrication and application of stimuli-responsive polymers.

Insights into Regional Wetting Behaviors of Amphiphilic Collagen for Dual Separation of Emulsions

Industrial manufacture generates a huge quantity of emulsion wastewater, which causes serious threats to the aquatic ecosystems. Water-in-oil (W/O) and oil-in-water (O/W) emulsions are two major types of emulsions discharged by industries. However, dual separation of W/O and O/W emulsions remains a challenging issue due to the contradictory permselectivity for separating the two emulsions. In the present investigation, the amphiphilicity-derived regional wetting mechanism of water and oil on the amphiphilic collagen fibers was revealed based on the combination of numerous experiments and molecular dynamics (MD) simulations. Electrostatic interactions and van der Waals force were manifested to be the driving forces of regional wetting in the hydrophilic and hydrophobic regions, respectively. The regional wetting endowed amphiphilic collagen fibers with underwater oleophobicity and underoil hydrophilicity, which enabled dual separation of emulsions by selectively retaining the dispersed water phase of W/O emulsions in the hydrophilic regions while the dispersed oil phase of O/W emulsions in the hydrophobic regions. The achieved separation efficiency was higher than 99.98%, and the flux reached 3337.6 L m^-2 h^-1. Initial wetting status significantly affects the regional wetting-enabled dual separation. Based on the MD simulations, amphiphilic intramolecular conformations of tropocollagen were suggested to be the origins of regional wetting on collagen fibers. Our findings may pave the way for developing high-performance dual separation materials that are promising to be utilized for the practical treatment of emulsion wastewater.

A Universal Strategy for the Preparation of Dual Superlyophobic Surfaces in Oil-Water Systems

There are some methods to prepare superwetting surfaces with underwater superoleophobicity (UWSOB) or underoil superhydrophobicity (UOSHB), but it is still thorny to put forward a universal strategy for constructing dual superlyophobic surfaces in oil-water systems due to a thermodynamic contradiction. Herein, a universal strategy was proposed to prepare the dual superlyophobic surfaces in oil-water systems only via delicately controlling surface chemistry, that is, adjusting the ratios of superhydrophilic and superhydrophobic counterparts in the spray solution. Three types of materials, attapulgite (APT), TiO₂, and loess, were chosen to prepare a diverse series of mixed coatings (mass gradient of superhydrophobic counterparts from 0 to 100 wt %). With the proportion of each superhydrophobic counterpart increasing, the underwater oil contact angle (θ_o/w^*) of each mixed coating slightly decreased but still was more than 150°, that is, UWSOB. In contrast, the underoil water contact angle (θ_w/o^*) was significantly improved, realizing the transformation from UOHL (or UOHB) to UOSHB. More importantly, the respective mass ratios of superhydrophobic counterparts in the resulting mixed coatings of APT, TiO₂, and loess were finally determined to be 0.3, 0.4, and 0.2, respectively. Taking APT as a model, a train of mixed APT coatings with different superhydrophobic components were systematically characterized and analyzed. Finally, the prepared superlyophobic separation mesh in oil-water systems was applied to the separation of various surfactant-stabilized oil-water emulsions. We envision that this universal strategy we proposed will show a significant application potential in addressing scientific and technological challenges in the field of interfacial chemistry such as oil-water separation, microfluidics, microdroplet manipulation, antifogging/icing, cell engineering, drag reduction, and so forth.

Simultaneous, efficient and continuous oil-water separation via antagonistically functionalized membranes prepared by atmospheric-pressure cold plasma

For decades, oil and water separation has remained a challenge. Not only oil spills but also industrial oily wastewaters are threatening our environment. Over the years, oil-water separation methods have been developed, however, there are still considerable hurdles to overcome to provide a low cost and efficient process able to treat a large amount of liquid. In this work, we suggest a continuous, simultaneous and effective oil-water separation method based on the antagonistic functionalization of meshes using atmospheric pressure cold plasmas. Using this robust plasma method, superhydrophobic/underwater-superoleophilic or superhydrophilic/underwater-superoleophobic functionalized meshes are obtained. Antagonistically functionalized meshes can simultaneously separate oil and water and show continuous separation flow rates of water (900 L m-2 h-1) and oil (400 L m-2 h-1) with high purities (> 99.9% v/v). This fast, low-cost and continuous plasma-based process can be readily and widely adopted for the selective functionalization of membranes at large scale for oil-spill cleanup and water purification.

Photo-switchable smart superhydrophobic surface with controllable superwettability

An azobenzene-based smart superhydrophobic surface undergoes reversible transformations among multiple bioinspired superwetting states through photo-manipulation, demonstrating promising potential on a rewritable platform for droplet transportation.

Molecular-Structure-Induced Under-Liquid Dual Superlyophobic Surfaces

Surfaces with under-water superoleophobicity or under-oil superhydrophobicity have attractive features due to their widespread applications. However, it is difficult to achieve under-liquid dual superlyophobic surfaces, that is, under-oil superhydrophobicity and under-water superoleophobicity coexistence, due to the thermodynamic contradiction. Herein, we report an approach to obtain the under-liquid dual superlyophobic surface through conformational transitions of surface self-assembled molecules. Preferential exposure of either hydrophobic or hydrophilic moieties of the hydroxythiol (HS(CH₂)_nOH, where n is the number of methylene groups) self-assembled monolayers to the surrounding solvent (water or oil) can be used to manipulate macroscopic wettability. In water, the surfaces modified with different hydroxythiols exhibit under-water superoleophobicity because of the exposure of hydroxyl groups. In contrast, surface wettability to water is affected by molecular orientation in oil, and the surface transits from under-oil superhydrophilicity to superhydrophobicity when n ≥ 4. This surface design can amplify the molecular-level conformational transition to the change of macroscopic surface wettability. Furthermore, on-demand oil/water separation relying on the under-liquid dual superlyophobicity is successfully demonstrated. This work may be useful in developing the materials with opposite superwettability.

Construction of Natural Loofah/Poly(vinylidene fluoride) Core-Shell Electrospun Nanofibers via a Controllable Janus Nozzle for Switchable Oil-Water Separation

Developing microstructure and multifunctional membranes toward switchable oil-water separation has been highly desired in oily wastewater treatment. Herein, a controllable Janus nozzle was employed to innovatively electrospin natural loofah/poly(vinylidene fluoride) (PVDF) nanofibers with a core-shell structure for gravity-driven water purification. By adjusting flow rates of the PVDF component, a core-shell structure of the composite fibers was obtained caused by the lower viscosity and surface tension of PVDF. In addition, a steady laminar motion of fluids was constructed based on the Reynolds number of flow fields being less than 2300. In order to investigate the formation mechanism of the microstructure, a series of Janus nozzles with different lengths were controlled to study the blending of the two immiscible components. The gravity difference between the two components might cause disturbance of the jet motion, and the PVDF component unidirectionally encapsulated the loofah to form the shell layer. Most importantly, the dry loofah/PVDF membranes could separate oil from an oil-water mixture, while the water-wetted membrane exhibited switchable separation that could separate water from the mixtures because of the hydroxyl groups of the hydrophilic loofah hydrogen-bonding with water molecules and forming a hydration layer. The composite fibers can be applied in water remediation in practice, and the method to produce core-shell structures seems attractive for technological applications involving macroscopic core-shell nano- or microfibers.

A CO2-gated anodic aluminum oxide based nanocomposite membrane for de-emulsification

A carbon-dioxide-responsive organic-inorganic nanocomposite membrane based on a through-hole anodic aluminum oxide (AAO) template was constructed. The composite was prepared via a surface-initiated reversible addition-fragmentation chain-transfer (SI-RAFT) polymerization strategy to achieve the grafting of poly(methyl methacrylate-co-2-(diethylamino)ethyl methacrylate) brushes on the AAO membrane. The grafted polymer chain length could be controlled based on the feed ratio between the free chain transfer agent (CTA) and reactive monomer, e.g., methyl methacrylate and 2-(diethylamino)ethyl methacrylate, resulting in a membrane that features adjustable water permeability. Importantly, the membrane pore size and surface wettability could be switched from hydrophobic to hydrophilic upon the introduction of carbon dioxide and nitrogen gases. This allowed for the nanocomposite membrane to be utilized for controlled water flux and oil/water emulsion separation. The simple fabrication methodology as well as sustainable gaseous stimulus will be useful for the construction of future smart membranes.