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

CO2-Responsive Smart Wood Scaffold for Natural Organic Matter Removal without Secondary Pollution

Ensuring drinking water safety remains a critical challenge, particularly when treating complex water sources, due to secondary pollution caused by active chemical additives. Herein, a novel CO2-responsive smart wood scaffold that leverages non-toxic CO2 activation is developed to achieve highly efficient removal of carcinogenic natural organic matter (NOM) and broad-spectrum microbial disinfection without requiring additional chemical agents. Unlike conventional water purification techniques that face a safety-efficacy trade-off, the multi-stage CO2-responsive wood scaffold offers exceptional tunability in NOM abatement across diverse environmental conditions, including variable water chemistry, NOM composition, high salinity, and real-world water sources. The purified water meets stringent drinking water standards (e.g., UV254 reduction, dissolved organic carbon removal, and bacterial elimination). It is found that the highly efficient NOM adsorption mainly originates from the strong and stable CO2-triggered cation-π interaction between the scaffold surface and aromatic NOM groups, as revealed via high-resolution mass spectrometry and direct intermolecular force measurements. This ecofriendly and contamination-free CO2-responsive strategy provides a transformative approach to overcoming secondary pollution challenges in water purification, offering a scalable and sustainable platform for environmental applications and beyond.

Gas-Responsive Smart Membrane Separation

Membrane separation technology is one of the most important techniques in modern separation science. To understand the self-regulation mechanisms of cell membranes and mimic their working principles, a plethora of artificial membranes with responsive abilities to external stimuli have been engineered and prepared, whose smart sieving functions continue to attract attention and are applied in various fields. Among all the known stimuli, gas as a new trigger mode exhibits certain biocompatibility and offer irreplaceable advantages compared to other stimuli, such as cleanliness, ease-of-handling, and nondestructive, which make gas-responsive membranes as one of the most promising, smart separation materials. In this review, we summarize recent breakthroughs in the development of gas-responsive membranes, outline the novel strategies on membrane fabrication, and highlight their advanced applications in controlled cargo release, size-/charge-based substance separation, oil-water separation, and self-cleaning. We also outlook the perspectives on the potential research directions and opportunities in the future.

Adaptive Surfaces with Stimuli-Responsive Wettability: From Tailoring to Applications

Adaptive surfaces with tunable wettability have attracted considerable attention due to their increasing importance in adapting to real applications. By incorporation of stimuli-sensitive materials that enable control over surface chemistry or topographical features, or both, a variety of adaptive surfaces are engineered to exhibit reversible tailoring in wettability. This Review provides a comprehensive review of the development of adaptive surfaces with stimuli-responsive wettability. It begins by outlining the background and significance of the adaptive surfaces. Then, this Review delves into the fundamental theories that govern surface wettability, focusing on the influence of external stimuli on wetting behavior. The discussion then shifts to highlighting various triggers, such as magnetism, photo, temperature, pH, electricity, and gas stimuli, that drive response in wettability, as well as surfaces that respond to dual or multiple stimuli. This Review further explores the primary and leading applications in droplet manipulation, oil-water separation, and water harvesting. To conclude, we encapsulate the challenges, potential solutions, and future directions for improving tunable wettability on these surfaces.

Effective separation of water-in-oil emulsions using an under-medium superlyophilic membrane with hierarchical pores

Separating water-in-oil emulsions is important in terms of environmental protection and resource recovery. To address the challenges posed by the water-oil interface, superwetting materials have been designed to accomplish separation through filtration and adsorption. Superhydrophobic membranes prevent the permeation of water droplets owing to extreme repellence and their size-sieving abilities. However, their use in remediating water-contaminated oil is limited by high oil viscosities. Meanwhile, in-air superhydrophilic sorbents are rarely employed for the separation of water-in-oil emulsions due to the thermodynamic and kinetic limitations of water adsorption in oil. Herein, the integration of an under-medium superlyophilic membrane with the hierarchical porous structure of wood is presented for filtration-driven selective adsorption of water from surfactant-stabilized (10 g/L) water-in-oil emulsions. Compared to filtration through a natural wood membrane or direct adsorption using an under-oil superhydrophilic wood membrane, the under-medium superlyophilic wood membrane demonstrated high separation efficiencies of > 99.95% even when applied to the regeneration of high-viscosity lubricating (6.3 mPa s) and edible (50.5 mPa s) oils, exhibiting viscosity-dependent fluxes and excellent stability. Moreover, the cost of purifying 200 mL of lubricating oil using the modified wood membrane was much lower than the oil's market price and required a low energy consumption of ca. 1.72 kWh. ENVIRONMENTAL IMPLICATION: The ever-growing use of petroleum and industrial/domestic oil products has led to excessive (estimated at a million tons per year) output of waste oils. Because direct discharge of waste oils into the environment causes serious pollution problems, separating water-in-oil emulsions is important in terms of environmental protection and resource recovery. Here filtration-driven water adsorption has been demonstrated to be a feasible method for the remediation of water-contaminated waste oils, even those that are highly viscous.

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.

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.