Multifunctional Superwettable Material with Smart pH Responsiveness for Efficient and Controllable Oil/Water Separation and Emulsified Wastewater Purification

Controllable lubricant-infused wrinkled surface for light-manipulated droplet climbing/pinning on inclined surfaces

Stimuli-responsive droplet transport on solid surfaces holds significant importance in various engineering domains; however, achieving accurate and robust manipulation of droplets, particularly their climbing and pinning on inclined surfaces, remains an unresolved challenge. This study proposes a novel light-responsive surface that integrates wrinkle structure with a lubricant-infused photothermal film, enabling flexible light-controlled movement of droplets even on inclined surfaces. The key to constructing this surface lies in fine control of the lubricant infusion amount onto a wrinkled Fe3O4/polydimethylsiloxane (PDMS) composite film, where wrinkles were "half covered, half exposed". Thus, a droplet placed on this controllable lubricant-infused wrinkled surface (CLWS) comes into contact with both the lubricant and the raised parts of wrinkles. In the absence of light, the droplet pins onto the inclined surface, displaying a large sliding angle up to 50°. Upon exposure to external light, the droplet exhibits climbing ability on inclined surfaces with a tilt angle larger than 15°. This behavior is primarily attributed to the Marangoni effect generated by photothermal conversion, which not only provides the driving force for climbing but also alters the distribution of lubricant to mitigate the resistance. The proposed CLWS demonstrates its suitability for various droplets including water, glycol and glycerol, while enabling complex operations such as directional movement, Z-shape turning, and multi-droplet fusion on inclined or curved surfaces. We believe that our proposed CLWS, designed for light-induced droplet climbing/pinning on inclined surfaces, significantly augments the versatility and application potential in the realm of droplet manipulation techniques.

Carboxymethyl cellulose and sodium alginate-enhanced hydrogel for carbon dots loading: A novel platform for pH sensing and sensitive detection of Al3+ and Ag. Int J Biol Macromol 2025;307:141955. [PMID: 40074127 DOI: 10.1016/j.ijbiomac.2025.141955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

To address the challenges associated with the storage and application of traditional carbon dot (CDs) solutions, this study introduces a cyan fluorescent carbon dot-based hydrogel (CDs-SCH). The hydrogel was synthesized by integrating cyan fluorescent CDs, derived from penicillamine and m-phenylenediamine, with carboxymethylcellulose (CMC) and sodium alginate (SA), which was then mixed with acrylamide (AM). The resulting CDs-SCH hydrogel was extensively characterized, focusing on its morphology, chemical structure, and fluorescence behavior. The fluorescence intensity of the hydrogel was enhanced by 3.23 times compared to the original CDs. The fluorescence response of the CDs-SCH hydrogel to pH variations was examined, demonstrating its capability to visually monitor the freshness of aquatic products such as fish and shrimp. Furthermore, Al3+ and Ag+ ions were found to significantly modulate the fluorescence, with Al3+ enhancing and Ag+ quenching the fluorescence, displaying reliable detection limits and linearity. The hydrogel's ability to detect glutathione (GSH) via Ag+ reduction to Ag was also explored. Additionally, the hydrogel exhibited stable Al3+ adsorption, with the process following pseudo-second-order kinetics and the Langmuir adsorption model. As a versatile and responsive material, the CDs-SCH hydrogel holds potential for applications in intelligent food packaging and environmental ion detection.

Preparation, characterization, and applications of kaolin/kaolin-based composite membranes in oily wastewater treatment: Recent developments, challenges, and opportunities

Rapid industrialization and the accompanying generation of significant amounts of oily wastewater pose major environmental challenges, which necessitate efficient treatment technologies. Kaolin-based membranes have emerged as a promising option due to their availability, affordability, and effective filtration performance. This review comprehensively analyzes the potential of kaolin for the treatment of oily wastewater. The focus is on the main manufacturing methods such as uniaxial pressing, slip casting, tape casting, phase inversion, and extrusion, as well as modifications that improve the structural integrity of the membrane, and its surface wettability to enhance separation performance. In addition, characterization techniques to evaluate membrane properties such as mechanical strength, thermal and chemical stability, antifouling behavior etc. are discussed. Basically, kaolin can be used as a supporting substrate, as a primary separation layer or as an additive in non-kaolin membranes. In evaluating the oil-water separation performance of kaolin-based membranes, this review highlights important metrics such as oil separation rate, flux, flux recovery, antifouling behavior, and resistance to harsh physical and chemical environments. Articles selected for the review were retrieved from major databases such as EBSCOhost, Scopus, ScienceDirect, Web of Science, and Google Scholar using relevant keywords. Based on the data from these studies, the main advances, challenges, and prospects are highlighted. Although still in the early stages of commercial application, kaolin membranes show significant potential to improve filtration efficiency, mechanical and chemical resistance, and reduce operating costs in industrial oily wastewater treatment systems.

Strategies to improve the mass transfer in the CO2 capture process using immobilized carbonic anhydrase

High carbon dioxide (CO₂) concentration in the atmosphere urgently requires eco-friendly mitigation strategies. Carbonic anhydrase (CA) is a high-quality enzyme protein, available from a wide range of sources, which has an extremely high catalytic efficiency for the hydration of CO₂ compared with other catalytic CO₂ conversion systems. While free CA is costly and weakly stable, CA immobilization can significantly improve its stability and allow enzyme recycling. However, gaseous CO₂ is significantly different from traditional liquid substrates. Additionally, due to the presence of enzyme carriers, there is limited mass transfer between CO₂ and the active center of immobilized CA. Most of the available reviews provide an overview of the improvement in catalytic activity and stability of CA by different immobilization methods and substrates. However, they do not address the limited mass transfer between CO₂ and the active center of immobilized CA. Therefore, by focusing on the mass transfer process, this review presents CA immobilization strategies that are more efficient and of greater environmental tolerance by categorizing the methods of enhancing the mass transfer process at each stage of the enzymatic CO₂ capture reaction. Such improvements in this green and environmentally friendly biological carbon capture process can increase its efficiency for industrial applications.

Multiple strategies to control the hydrophilic-hydrophobic balance of P(DMA-co-DMAEMA-co-QDMAEMA) coatings

The regulation of the hydrophilic-hydrophobic balance of polymers has an important influence not only on their aggregation behavior in aqueous solution, but also on their adhesion properties on the surface of substrates and the applications of the modified surfaces. Based on this, a random copolymer poly(dopamine methacrylamide-co-2-(dimethylamino)ethyl methacrylate) (P(DMA-co-DMAEMA)) was synthesized as a starting polymer to generate P(DMA-co-DMAEMA-co-QDMAEMA) (PDDQ) derivatives by a programmable quaternization of the DMAEMA precursor. By adjusting the pH or temperature, both the aggregation behavior in aqueous solutions and the surface adhesive behavior on the substrate surfaces of PDDQ copolymers were regulated due to the hydrophilic-hydrophobic balance. Specifically, the surface adsorption of PDDQ copolymers on surfaces was enhanced by the increased hydrophobicity of PDDQ. Stainless steel meshes (SSM) modified with the PDDQ0 copolymer without quaternization showed a superoleophobicity in acidic aqueous media, which endowed it with improved oil-water separation performance. In addition, the hydrophilic-hydrophobic balance of PDDQs and their coatings could also be tuned by changing the ratio of DMAEMA to QDMAEMA in the copolymer. From PDDQ0 to PDDQ100, by increasing the hydrophilic QDMAEMA component of PDDQ copolymers, anti-protein properties and oil/water separation efficiency of the modified surfaces were also enhanced gradually. The results provided a reference for designing P(DMA-co-DMAEMA-co-QDMAEMA) coatings in different application environments.

Smart surfaces with reversibly switchable wettability: Concepts, synthesis and applications

As a growing hot research topic, manufacturing smart switchable surfaces has attracted much attention in the past a few years. The state-of-the-art study on reversibly switchable wettability of smart surfaces has been presented in this systematic review. External stimuli are brought about to render the alteration in chemical conformation and surface morphology to drive the wettability switch. Here, starting from the fundamental theories related to the surfaces wetting principles, highlights on different triggers for switchable wettability, such as pH, light, ions, temperature, electric field, gas, mechanical force, and multi-stimuli are discussed. Different applications that have various wettability requirement are targeted, including oil-water separation, droplets manipulation, patterning, liquid transport, and so on. This review aims to provide a deep insight into responsive interfacial science and offer guidance for smart surface engineering. It ends with a summary of current challenges, future opportunities, and potential solutions on smart switch of wettability on superwetting surfaces.

NaOH-Induced Fabrication of a Superhydrophilic and Underwater Superoleophobic Styrene-Acrylate Copolymer Filtration Membrane for Effective Separation of Emulsified Light Oil-Polluted Water Mixtures

Oil-polluted water mixtures are difficult to separate, and thus, they are considered as a global challenge. A superior superhydrophilic and low-adhesive underwater superoleophobic styrene-acrylate copolymer filtration membrane is constructed using a salt (NaOH)-induced phase-inversion approach. The as-fabricated filtration membrane provides a hierarchical-structured surface morphology and three-dimensional high density open-rough porous geometry with a special chemical composition including highly accessible hydrophilic -COO^- agents, which all are of great importance for long-term usage of immiscible/emulsified (light) oil-polluted wastewater separation. The separation is performed with a high efficiency and a high flux under either a gravity-driven force or a small applied pressure of 0.1 bar. The filtration membrane indicates an excellent anti-fouling property and is easily recycled during multiple cycles. The outstanding performance of the filtration membrane in separating oil-polluted water mixtures and the cost-effective synthetic approach as well as commercially scaled-up initial materials all highlight its potential for practical applications.

Development of Janus Cellulose Acetate Fiber (CA) Membranes for Highly Efficient Oil-Water Separation

A new type of Janus cellulose acetate (CA) fiber membrane was used to separate oil–water emulsions, which was prepared with plasma gas phase grafting by polymerizing octamethylcyclotetrasiloxane (D4) onto a CA fiber membrane prepared by centrifugal spinning. The Janus–CA fiber membrane was described in terms of chemical structure using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) analysis, energy dispersive X-ray spectroscopy (EDX) analysis and morphology by field emission scanning electron microscopy (FESEM). In this contribution, we examine the influence of spinning solution concentration, spinning speed and nozzle aperture on the centrifugal spinning process and the fiber morphology. Superhydrophobic/hydrophilic Janus–CA fiber membrane was used to separate water and 1,2-dibromoethane mixture and Toluene-in-water emulsion. Unidirectional water transfer Janus–CA fiber membrane was used to separate n-hexane and water mixture. The separation for the first-time interception rate was about 98.81%, 98.76% and 98.73%, respectively. Experimental results revealed that the Janus cellulose acetate (CA) fiber membrane gave a permeate flux of about 43.32, 331.72 and 275.27 L/(m²·h), respectively. The novel Janus–CA fiber membrane can potentially be used for sustainable W/O emulsion separation. We believe that this is a facile strategy for construction of filtration materials for practical oil–water separation.

Randomly heterogeneous oleophobic/pH-responsive polymer coatings with reversible wettability transition for multifunctional fabrics and controllable oil-water separation

Stimuli-responsive surfaces with wettability change between superhydrophilic and superhydrophobic are susceptible to oil contamination which often ruins the surface. Herein, a coating with pH-switchable wettability transition between superamphiphobic and superhydrophilic-superoleophobic is achieved by rationally designing oleophobic/pH-responsive polymer heterogeneous chemistry. Fabrics modified with this coating show repellency to both water and oils, while upon exposure to acidic water (pH = 1) the fabrics change to be superhydrophilic-superoleophobic within a short response time of <5 s. More importantly, the superamphiphobicity of the fabric can be restored under mild alkaline condition (pH = 10), and the transition is reversible for many cycles. The effective in situ or ex situ wettability change under acidic/alkaline water treatment makes the coated fabric capable of separating oil-water mixture or even some mixtures of immiscible organic solvents. In addition, the coated fabric is also demonstrated to be promising as a new class of functional fabrics that provide protection against water and many oils in one condition, and can change to be hygroscopic, anti-static, oil-repellent and anti-oil-fouling in the other condition for improved wear comfort and self-cleaning.

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System

Thermochromic metal-organic frameworks (MOFs) are promising functional materials for a wide range of applications due to their ability to exhibit color variation under external temperature stimuli, yet the development of them with high cyclability and efficient regeneration processes remains challenging. Here, presented is a rare example of an ultrastable Ni(II)-MOF exhibiting an unprecedented reversible four-step color change between two complementary colors in a wide temperature range, which could be repeated for at least 500 cycles without losing crystallinity and thermochromic performance. Notably, the regeneration can be achieved within 1 min by simply letting the crystals cool naturally in the air, facilitated by the unique nature of the channels' inner surface. The reversible thermochromic behavior is owing to a series of reversible crystal structure changes with temperature, including the stepwise dehydration/rehydration process, and structural changes. This work facilitates the future development of more MOF-based reversible thermochromic materials with excellent performance and improved practical applicability.

Starch-based nanospheres modified filter paper for o/w emulsions separation and contaminants removal

There is a pressing need around the world to develop novel functional biodegradable materials to separate oil/water mixtures and emulsions completely. Recently, superhydrophilicity and underwater superoleophobicity materials have been attracted attention due to their high efficiency in oil/water separation. However, it is still a challenge to prepare materials that combine oil/water separation and water purification in an environment-friendly way. In this work, biodegradable starch-based nanospheres (SNPs) coated filter paper was prepared in a low-cost, simple, and environmentally friendly manner. The SNPs coating could not only help to change the wettability of the substrate material but also build the hierarchical micro and nano structures which are conducive to separation and purification process. After modification by coating SNPs, the filter paper exhibited excellent performance in a wide range of oil/water mixtures or emulsions separation and the wettability of the filter paper could be regulated by adjusting the pH value. The modified filter paper presented good recyclability after several separation process. Furthermore, the as-prepared filter paper could also remove water-soluble contaminants during the oil/water separation process, thus realizing to combine separation and purification process in one single step. This biodegradable starch-based separating material with good separation performance, stability and recyclability has significant application potential in practical separation and purification process.

Ultrafast Fabrication of Metal-Organic Framework-Functionalized Superwetting Membrane for Multichannel Oil/Water Separation and Floating Oil Collection

Traditional methods for oil/water separation suffer from many tricky problems such as low efficiency, high energy consumption, and difficulties in recycling and reusing. To address these hurdles, we developed a metal-organic framework-coated superwetting membrane for multichannel oil/water separation and collection of floating oils. The dip-coating method adopted in this paper is extremely flexible in manipulation and can be completed within 1 h under a low temperature without any assistance of high pressure. Interestingly, the strategy of fabricating superwetting membrane mainly includes introducing vital interlayers of Cu(OH)₂ nanowires, which not only construct the favorable hierarchical structures but also act as partly sacrificed templates for further growth of hydrophilic MOF nanowhiskers. In virtue of the high flexibility of the as-prepared mesh, this superwetting membrane can be applied for multichannel oil/water separation including gravity-driven oil/water separation, continuous oil/water separation, and floating oil collection. Moreover, the separation efficiency and flux of the superwetting membrane keep high and stable under multiple separation cycles. This study paves the way for a fast and facile preparation of a superwetting membrane with high applicability for multiple oil/water separation.

Superhydrophobic Nickel-Electroplated Carbon Fibers for Versatile Oil/Water Separation with Excellent Reusability and High Environmental Stability

Superhydrophobic filtrating materials have been widely developed for rapid removal or collection of oils from oil/water mixture due to the increasing water pollution caused by oil spills and oil-contaminated wastewater. However, poor reusability, superhydrophobic failure in harsh environments, and that only heavy oil or light oil was separated from water seriously restricted their practical application. Herein, superhydrophobic carbon fibers were first fabricated using a novel nickel electroplating for versatile oil/water separation with excellent reusability and high environmental stability. The interconnected nanometer-scale nickel grains formed on the micrometer-scale fibers and fluoroalkylsilane molecules enabled the fibers to be superhydrophobic with the water contact angle (CA) of ∼159.1° and superoleophilic with the oil CA of ∼0°. The nickel coating contributed to the improvement of the bonding strength, tensile strength, and oxidation resistance of the fibers. The as-prepared fibers could be applied for the separation of heavy or light oil/water mixtures with separation efficiencies above 99.1%, during which the oil content in the separated water all remained below 78 ppm. The fibers also realized the highly efficient separation of dichloromethane and various harsh environmental solutions such as hot water, acid, alkali, and salt. The superhydrophobicity of the fluorinated nickel-coated carbon fibers still remained even after 100 cycles of separation and 24 months of storage in air, demonstrating outstanding durability of the fibers. These novel superhydrophobic carbon fibers had promising potentials for versatile oil/water separation in practical applications.

Hydrophobic Magnetic Porous Material of Eichhornia crassipes for Highly Efficient Oil Adsorption and Separation

Many oil adsorption materials are composed of nonrenewable raw materials, and their disposal can increase resource consumption and cause new environmental pollution. In this paper, the carbonized Eichhornia crassipes (CEC) were immobilized with Fe₃O₄ magnetic nanoparticles and modified with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (PFOS) to prepare an oil adsorption material, referred to here as CEC/Fe₃O₄/PFOS. The magnetic and mechanical strength of the CEC was enhanced by adding Fe₃O₄ magnetic particles, which enable it efficient to dispose the oil/water solution. CEC/Fe₃O₄/PFOS shows high porosity (83.53%), low skeletal density (0.487 g/cm³), excellent magnetism, ultrahigh oil absorption capacity (49.94-140.90 g/g), hydrophobic performances with a water contact angle of 150.1 ± 2.3°, and a sliding angle of 10.5°. It is worth noting that the material can be recycled, and the absorbed oil is obtained by distillation. Therefore, this work may provide a candidate for solving the problem of oil pollution using E. crassipes.

Fine Switching between Underwater Superoleophilicity and Underwater Superoleophobicity while Maintaining Superhydrophobicity

Switching between superhydrophobicity/underwater superoleophilicity and superhydrophilicity/underwater superoleophobicity has been widely designed. Recently, superwettability is subdivided into multiple extreme wetting states for oil, water, and air as wetting and medium phases. However, fine switching among the multiple superwettability is rare. Here, a pH-responsive case is presented to demonstrate the fine switching between underwater superoleophilicity and underwater superoleophobicity while maintaining superhydrophobicity. The surface chemistry of silver-roughened copper coatings is elaborately manipulated by water-repellent perfluoroalkyl and alkyl chains and the smart terminal carboxyl group. By adjusting the pH value of water, the completely opposite extreme wetting states for oil in water are precisely controlled. Simultaneously, the extreme repellence for water in the air can be kept owing to the fairly low surface energy of the perfluoroalkyl chain. This discovery accelerates the subdivision of superwettability and the achievement of unusual superwetting switching.

Intelligent Cellulose Nanofibers with Excellent Biocompatibility Enable Sustained Antibacterial and Drug Release via a pH-Responsive Mechanism

Novel nanosized biomass-based pH-responsive cellulose nanofibers (CNF-PEI) with excellent biocompatibility were tailored by grafting polyethylenimine (PEI) onto carboxylated cellulose nanofibers (CNF-COOH); the active site (-COOH, 0.96 mmol/g) was anchored on cellulose nanofibers (CNFs) to introduce PEI with a high density (10.57 mmol/g) of amino groups. The as-prepared CNF-PEI not only maintained the good properties of CNFs but also possessed excellent biocompatibility and pH-responsive properties, offering interesting possibilities for pH-induced sustained drug release and medical dressing. The CNF-PEI showed rapid wettability conversion from hydrophilic, underwater superoleophobic (WCA = 20.7°, OCA = 159.3°) to hydrophobic, superoleophilic (WCA = 129.6°, OCA = 29.7°) in response to pH change from acidic conditions to alkaline conditions. The antibacterial activity of CNF-PEI toward Escherichia coli and Listeria monocytogenes was 100% and 94.6% under acidic conditions, respectively. Furthermore, the pH-responsive mechanism of CNF-PEI was revealed by XPS, ¹³C NMR, ¹H NMR, and AFM analyses.

Functionalized Superwettable Fabric with Switchable Wettability for Efficient Oily Wastewater Purification, in Situ Chemical Reaction System Separation, and Photocatalysis Degradation

In view of the increasing serious water environmental and human health issues caused by oily wastewater, functional superwetting materials with controllable wettability, high durability, and scale preparation methods are highly desired for efficient oil/water separation. In this respect, a pH-responsive multifunctional fabric with switchable surface wettability, favorable mechanical durability, and self-repairing property has been developed via decorating the modified TiO₂ nanoparticles of special surface compositions onto the fabric surface. By virtue of the intelligent surface wettability, the resulted superwettable fabric can be used for controllable separation of multiple oil/water mixtures, particularly the complicated oil/water/oil ternary mixtures, showing excellent separation efficiency and high filtration flux even under extreme pH conditions, which is comparable to most of the commercial and currently reported functionalized membranes. Simultaneously, the negative pressure-driven, continuous, high-speed, and highly efficient in situ purification of large volumes of oily wastewater is successfully achieved based on the resulted superwettable fabric. More importantly, with the as-prepared superwettable fabric as the filtration membrane, the continuous in situ separation of the synthetic oily product from the corresponding chemical reaction systems is well performed without interruption of the reaction, demonstrating outstanding merits of simplifying procedures, saving operation time, and increasing product yield. In addition, it is worth noting that the alkali-treated superhydrophilic fabric presents superior photocatalysis self-cleaning performance for various water-soluble organic pollutants. These unique advantages of the functionalized smart superwettable fabric ensure that it can be competent in multifarious relevant challenging settings, indicating a broad prospect for diverse practical applications, especially the oily wastewater treatment and multiple industrial operation optimizations.

Durable superamphiphobic coatings from one-step electrostatic dusting

Superamphiphobic coatings are fabricated via electrostatic dusting using modified silica particles and polymethyl methacrylate resin particles on conductive substrates (metal and conductive glass). The obtained translucent superamphiphobic coatings show excellent durability and chemical robustness even after exposure to strong acids and bases. Importantly, the coatings maintain hydrophobicity even after 100 cycles of abrasion testing and 1000 cycles of finger wiping. In addition, the fabricated coatings are superoleophobic after finger wiping, tape peeling and oil immersion. This facile strategy may provide researchers in related fields with new avenues for improving powder coatings in practical applications.