CO2-Responsive Nanofibrous Membranes with Switchable Oil/Water Wettability

Multifunctional negatively-charged poly (ether sulfone) nanofibrous membrane for water remediation

Multifunctional materials, which can effectively and simultaneously remove various water-soluble contaminants like dyes and heavy metal ions, and separate oil from water, are urgent to meet increasing challenges on wastewater remediation. Herein, a cross-linked poly (acrylic acid) (PAA) modified poly (ether sulfone) nanofibrous membrane (NFM) was fabricated by a facile in-situ pre-reaction followed by electrospinning. The as-prepared NFM showed excellent hydrophilicity and underwater lipophobicity, therefore expressed excellent water permeability with high water flux (about 5142 L m² h^-1). As a result, under solely driven by gravity, the NFM was capable to separate emulsified oil/water emulsion and a wide range of oil/water mixtures. Moreover, repeating separation tests indicated that the NFM had great long-term sustainability even after ten separation cycles. In addition, due to the introduction of PAA and the large surface-to-volume ratio, the NFM also expressed rapid adsorption capacity for cationic dyes as well as heavy metal ions; thus could simultaneously remove these contaminants during the oil/water separation process. Furthermore, the NFM could be also decorated by Ag NPs to endow the membranes with remarkable antibacterial ability against both E. coli and S. aureus. Our findings strongly suggested that the multifunctional NFM may have great potential in treating complicated wastewater.

High-Flux Oil/Water Separation with Interfacial Capillary Effect in Switchable Superwetting Cu(OH)2@ZIF-8 Nanowire Membranes

Highly ordered architectures with roughness and porous surface are the key challenges toward developing smart superwetting membranes. We prepared switchable superwetting Cu(OH)₂@ZIF-8 core/shell nanowire membranes for high-flux oil/water separation as well as simultaneous heavy-metal ions removal in one step. The well-defined Cu(OH)₂@ZIF-8 core/shell nanowire grown on copper mesh with average length of ca. 15 μm and diameter of ca. 162 nm exhibits high water contact angle (CA) of ca. 153 ± 0.6°. After modified by ethanol, the membrane holds the reverse superwettability with oil (dichloromethane as an example) CA of ca. 155 ± 0.8° underwater. The separation efficiencies of the membranes are higher than that of 97.2% with a remarkable flux rate higher than 90 000 L m^-2 h^-1 for the immiscible oil/water mixture. And the removal efficiency for Cr³⁺ ions at 10 ppb can arrive at 99.2 wt % in the toluene-in-water emulsion. The high performances of the smart superwetting membranes can be attributed to the interfacial capillary effects of the hierarchical Cu(OH)₂@ZIF-8 core/shell nanostructures. This work may provide a new insight into the design of smart superwetting surfaces for oil/water separation and target adsorption in one step.

Renewable boronic acid affiliated glycerol nano-adsorbents for recycling enzymatic catalyst in biodiesel fuel production

Nano-adsorbents composed of poly(4-vinylphenyl boronic acid) shell and silica core efficiently remove residual glycerol from a lipase catalyst layer in biodiesel fuel production, resulting in excellent lipase recycling. The subsequent CO2-acidolysis endows the adsorbents with sustainable renewability.

Continuous in Situ Extraction toward Multiphase Complex Systems Based on Superwettable Membrane with Micro-/Nanostructures

Liquid-phase extraction is widely used in the chemical industry. Traditional extracting routes always involve multiple procedures, need a large floor space, and have long operating time. "Continuous in situ extraction" that can conduct a real-time integration of solutes extraction and solvents separation simultaneously would be of great significance. Superwettable materials offer us a good choice to separate different immiscible solvents; herein, we achieve continuous in situ extraction of multiphase complex systems by using a porous polytetrafluoroethylene membrane with nanostructure-induced superwettability. It realizes a rapid, selective, and efficient real-time removal of various extracting agents during a continuous process due to their wetting differences. Compared with traditional extraction, our route shows a distinct superiority on saving operating time, enhancing liquid recovery, and simplifying procedures, while still retaining high extracting performance. In addition, our membrane possesses excellent durability even after long-term work in harsh chemical environments or under strong mechanical impacts. Thus, we believe that it will provide a potential alternative for current industrial extractions.

Review: Porous Metal Filters and Membranes for Oil-Water Separation

In recent years, oil-water separation has been widely researched to reduce the influences of industrial wastewater and offshore oil spills. A filter membrane with special wettability can achieve the separation because of its opposite wettability for water phase and oil phase. In the field of filter membrane with special wettability, porous metal filter membranes have been much investigated because of the associated high efficiency, portability, high plasticity, high thermal stability, and low cost. This article provides an overview of the research progress of the porous metal filter membrane fabrication and discusses the future developments in this field.

Fabrication of Thermoresponsive Polymer-Functionalized Cellulose Sponges: Flexible Porous Materials for Stimuli-Responsive Catalytic Systems

In this present work, a thermoresponsive and recyclable catalytic system was prepared by grafting poly( N-isopropylacrylamide)- co-poly(glycidyl methacrylate) (PNIPAM- co-PGM) to a cellulose sponge, which was reinforced by polydopamine (PDA) and (3-aminopropyl)triethoxysilane (APTMS). Au nanoparticles (Au NPs) were loaded via in situ reduction of HAuCl₄ with PDA. Fourier transform infrared, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis results revealed that the Au NPs (<10 nm) were homogenously dispersed on the surface of the sponge. Catalytic experiments with sponges prepared without PNIPAM- co-PGM demonstrated an increased reaction rate when the temperature of the reaction medium was elevated. However, in the presence of PNIPAM-i co-PGM in the sponges, the reaction rate was decreased when the reaction temperature was higher than the lower critical solution temperature of the polymer. The sponge could be conveniently separated from the reactions and reused up to 22 cycles.

Controlled Movement of a Smart Miniature Submarine at Various Interfaces

Smart miniaturized aquatic devices have many important applications, but their locomotion at different interfaces remains a challenge. Here, we report a smart miniaturized submarine moving at various air/liquid or oil/water interfaces. The microsubmarine is fabricated by a CO₂-responsive superhydrophobic copper mesh and is driven by the Marangoni effect. The microsubmarine can not only transfer among different interfaces reversibly but also move horizontally at the interfaces freely. The unique locomotion of the device is attributed to a CO₂-triggered switch between superhydrophobicity and underwater superoleophobicity. Moreover, the microsubmarine exhibits good stability and excellent oil repellence at the oil/water interface. Our study provides a strategy for fabricating smart aquatic devices that have potential applications in environment monitoring, water purification, channel-free microfluidics, and so on.

CO2 -Breathing Polymer Assemblies via One-Pot Sequential RAFT Dispersion Polymerization

ABC triblock copolymer assemblies with reversible "breathing" behaviors based on poly[oligo(ethylene glycol) methyl ether methacrylate]-b-poly(benzyl methacrylate)-b-poly[2-(diethylamino)ethyl methacrylate] (POEGMA-b-PBnMA-b-PDEA) are fabricated via one-pot sequential reverisble addition-fragmentation chain transfer dispersion polymerization. Using a POEGMA as the macromolecular chain transfer agent, chain extension with BnMA and DEA is conducted in ethanol, where PBnMA acts as the core-forming block, and the PDEA block endows the solvophilicity and CO₂ -responsiveness. With the increment of the DP of PBnMA, the morphology of the assemblies evolves from spheres to worms, and to vesicles, while it degenerates from conglutinated vesicles to spheres as the DP of PDEA increases. After replacing ethanol with water, the morphologies of these assemblies remain unchanged, while their size decreases due to the collapse of the hydrophobic PDEA chains. Interestingly, due to the protonation and deprotonation of PDEA blocks, both the spheres and vesicles manifest a reversible expansion/shrinkage upon alternative CO₂ /Ar stimulation, exhibiting distinctive breathing feature.

Controlling CO2 -Responsive Behaviors of Polymersomes Self-Assembled by Coumarin-Containing Star Polymer via Regulating Its Crosslinking Pattern

An oligo(ethylene glycol)-based star polymer of N₂ -(OEG-C)₃ with fluorescent coumarin as hydrophobic end groups and dual tertiary amines as the star center is designed and synthesized. Owing to its amphiphilic nature of N₂ -(OEG-C)₃ , it will self-assemble into hollow vesicles with coumarin groups dispersed in the hydrophobic membrane and exhibits CO₂ -responsive behavior due to the protonation of amine centers with CO₂ . More importantly, coumarin moieties can either form non-crosslinking with γ-cyclodextrin via the 2/1 host-guest inclusion, or covalently photodimerized by 365 nm light, offering a tunable crosslinking pattern in the hydrophobic membrane and thus adjusting its CO₂ -stimulated reorganization and disassembly behaviors of these vesicles in aqueous solution.

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

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

Facile Fabrication of CO2-Responsive Nanofibers from Photo-Cross-Linked Poly(pentafluorophenyl acrylate) Nanofibers

CO₂-responsive nanofibers were facilely prepared from photo-cross-linked poly(pentafluorophenyl acrylate) (PPFPA) nanofibers via "amine-active ester" chemical modification. Photo-cross-linked PPFPA nanofibers were modified with histamine under mild conditions to generate cross-linked poly(histamine acrylamide) (PHAAA) nanofibers featuring a CO₂ responsiveness. As expected, the prepared cross-linked PHAAA nanofibers can exhibit a CO₂-responsive behavior to induce a reversible transition from hydrophobic to hydrophilic upon alternating addition and removal of CO₂ on the surface of nanofibrous membranes. Based on this finding, we could demonstrate that cross-linked PHAAA nanofibers can be employed for reversible absorption and release of protein using bovine serum albumin (BSA) as a model.

Nanosecond Laser-Induced Underwater Superoleophobic and Underoil Superhydrophobic Mesh for Oil/Water Separation

Materials with special wettability have drawn considerable attention especially in the practical application for the separation and recovery of the oily wastewater, whereas there still remain challenges of the high-cost materials, significant time, and complicated production equipment. Here, a simple method to fabricate the underwater superoleophobic and underoil superhydrophobic brass mesh via the nanosecond laser ablation is reported for the first time, which provided the micro-/nanoscale hierarchical structures. This mesh is superhydrophilic and superoleophilic in air but superoleophobic under water and superhydrophobic under oil. On the basis of the special wettability of the as-fabricated mesh, we demonstrate a proof of the light or heavy oil/water separation, and the excellent separation efficiencies (>96%) and the superior water/oil breakthrough pressure coupled with the high water/oil flux are achieved. Moreover, the nanosecond laser technique is simple and economical, and it is advisable for the large-area and mass fabrication of the underwater superoleophobic and underoil superhydrophobic mesh in the large-scale oil/water separation.

Dual-Responsive Self-Propulsion Smart Device Steadily Driven by CO2 and H2O2

In this paper, we introduce a kind of tertiary amine-based CO₂-responsive material combining with the H₂O₂-responsive material to develop a dual-responsive self-propulsion smart device which can convert the chemical energy of H₂O₂ into mechanical energy steadily through diving-surfacing cycles. In this dual-responsive device, the CO₂-responsive material is designed as a wettability conversion species, which is wrapped with a strip of platinum to catalyze the decomposition of H₂O₂ to generate gaseous O₂ to realize surfacing. In deionized water, the device floats on the surface of the water initially and can perform a diving-surfacing cycle when CO₂ and H₂O₂ stimuli are alternately applied to the aqueous solution. The cyclic movement of the device can be realized by the generation and release of the inner gas through the hydrophobic cover, leading to a new controllable transition of different kinds of energy.

CO2-Switchable-hydrophilicity membrane (CO2-SHM) triggered by electric potential: faster switching time along with efficient oil/water separation

CO₂-Switchable-hydrophilicity membrane (CO₂-SHM) triggered by electric potential which could be effectively used for oil/water separation.

CO2-Acidolysis of iminoboronate ester based polymersomes

The iminoboronate-terminalized star-like prodrug N₃-(OEG-IBCAPE)₄ was prepared to investigate the CO₂-acidolysis of polymersomes with a tunable release feature of CAPE molecules.

Selective Cooperation with Liquids for Environmentally Friendly and Comprehensive Oil-Water Separation

A hydrophobic 3 D material having smart relationship with oil under water (having both water affinity and water repellency in absence and presence of oil), is developed here using a scalable and facile 1,4-conjugate addition reaction between acrylate and amine groups at ambient conditions without using any catalyst. The material that was soaked with water in air is capable of absorbing both heavy and light oils with an efficiency above 1000 wt %, and the impregnated metastable aqueous phase was spontaneously and selectively ejected out from the material. This unprecedented super-oil-absorbance property remained intact in diverse scenarios, including extremes of temperature (100 and 10 °C), pressure (184.7 mbar), and prolonged (7 days) exposures to extremes of pH (1 and 12), surfactants-contaminated (dodecyltrimethylammonium bromide/sodium dodecyl sulfate, DTAB/SDS, 1 mm) water, artificial sea water, etc. Furthermore, this super-oil-absorbent having outstanding durability was exploited also in demonstrations of comprehensive and facile clean-up of oil from various forms of oil-water mixtures (i.e., floating light-oil, sediment heavy-oil, oil-in-water emulsions, etc.) in extremes and complex settings that are relevant to practical scenarios including marine oil spills, following ecofriendly and energy-efficient selective-absorption/active-filtration principles.

CO2-Switchable Membranes Prepared by Immobilization of CO2-Breathing Microgels

Herein, we report the development of a novel CO₂-responsive membrane system through immobilization of CO₂-responsive microgels into commercially available microfiltration membranes using a method of dynamic adsorption. The microgels, prepared from soap-free emulsion polymerization of CO₂-responsive monomer 2-(diethylamino)ethyl methacrylate (DEA), can be reversibly expanded and shrunken upon CO₂/N₂ alternation. When incorporated into the membranes, this switching behavior was preserved and further led to transformation between microfiltration and ultrafiltration membranes, as indicated from the dramatic changes on water flux and BSA rejection results. This CO₂-regulated performance switching of membranes was caused by the changes of water transportation channel, as revealed from the dynamic water contact angle tests and SEM observation. This work represents a simple yet versatile strategy for making CO₂-responsive membranes.

External-Field-Induced Gradient Wetting for Controllable Liquid Transport: From Movement on the Surface to Penetration into the Surface

External-field-responsive liquid transport has received extensive research interest owing to its important applications in microfluidic devices, biological medical, liquid printing, separation, and so forth. To realize different levels of liquid transport on surfaces, the balance of the dynamic competing processes of gradient wetting and dewetting should be controlled to achieve good directionality, confined range, and selectivity of liquid wetting. Here, the recent progress in external-field-induced gradient wetting is summarized for controllable liquid transport from movement on the surface to penetration into the surface, particularly for liquid motion on, patterned wetting into, and permeation through films on superwetting surfaces with external field cooperation (e.g., light, electric fields, magnetic fields, temperature, pH, gas, solvent, and their combinations). The selected topics of external-field-induced liquid transport on the different levels of surfaces include directional liquid motion on the surface based on the wettability gradient under an external field, partial entry of a liquid into the surface to achieve patterned surface wettability for printing, and liquid-selective permeation of the film for separation. The future prospects of external-field-responsive liquid transport are also discussed.

Highly Porous Poly(high internal phase emulsion) Membranes with "Open-Cell" Structure and CO2-Switchable Wettability Used for Controlled Oil/Water Separation

Polymer membranes with switchable wettability have promising applications in smart separation. Hereby, we report highly porous poly(styrene-co-N,N-(diethylamino)ethyl methacrylate) (i.e., poly(St-co-DEA)) membranes with "open-cell" structure and CO₂-switchable wettability prepared from water-in-oil (W/O) high internal phase emulsion (HIPE) templates. The open-cell porous structure facilitates fluid penetration through the membranes. The combination of CO₂-switchable functionality and porous microstructure enable the membrane with CO₂-switchable wettability from hydrophobic or superoleophilic to hydrophilic or superoleophobic through CO₂ treatment in an aqueous system. This type of membrane can be used for gravity-driven CO₂-controlled oil/water separation, in which oil selectively penetrates through the membrane and separates from water. After being treated with CO₂ switching wettability of the membrane, a reversed separation of water and oil can be achieved. Such a wettability switch is fully reversible, and the membrane could be regenerated through simple removal of CO₂ and oil residual through drying. This facile and cost-effective approach represents the development of the first CO₂-switchable polyHIPE system, which is promising for smart separation in a large volume.

Polypyrrole Whelk-Like Arrays toward Robust Controlling Manipulation of Organic Droplets Underwater

Whelk-like polypyrrole (PPy) arrays film is successfully prepared by electropolymerization of pyrrole in the presence of low-surface-energy tetraethylammonium perfluorooctanesulfonate (TEAPFOS) as dopant. The underwater wettability of PPy whelk-like arrays can be successfully tuned by electrical doping/dedoping of PFOS ions. Interestingly, CCl₄ droplets with microliter-size as a representative sample are gathered together to form a larger droplet underwater at the potential of +0.8 V (vs Ag/AgCl), because PPy is in its PFOS-doped states. Note that CCl₄ droplet can climb uphill successfully on the inclined whelk-like arrays PPy film under the applied potential of -1.0 V (vs Ag/AgCl), which may be attributed to wettability gradient derived from different oxidation states of PPy induced by electrochemical potential. These results may provide a simple strategy for on-demand manipulation of organic droplets underwater at low voltage.

Synthesis of porous polymer/tissue paper hybrid membranes for switchable oil/water separation

The unusually broad physical and chemical property window of ionic liquids allows for a wide range of applications, which gives rise to the recent spring-up of ionic liquid-based functional materials. Via solvothermal copolymerization of a monomeric ionic liquid and divinylbenzene in the presence of a tissue paper in autoclave, we fabricated a flexible porous polymer/paper hybrid membrane. The surface areas of the hybrid membranes depend on the weight fraction of the copolymer impregnated inside the tissue paper. The as-prepared hybrid membrane shows controlled surface wettability in terms of ethanol wetting and ethanol removal by harsh drying condition. This unique property provides the hybrid membrane with switchable oil/water separation function, thus of practical values for real life application.