Robust super-hydrophobic/super-oleophilic sandwich-like UIO-66-F4@rGO composites for efficient and multitasking oil/water separation applications

Photocatalytic PAN Nanofibrous Membrane through Anchoring a Nanoflower-Branched CoAl-LDH@PANI Heterojunction for Organic Hazards Degradation and Oil-Containing Emulsified Wastewater Separation

The synergistic treatment of oily wastewater containing organic hazards and emulsified oils remains a big challenge for membrane separation technology. Herein, the photocatalytic membrane, which combined the physical barrier and catalytic oxidation-driven degradation functionality, was fabricated via anchoring a nanoflower-branched CoAl-LDH@PANI Z-scheme heterojunction onto a porous polyacrylonitrile mat and using tannic acid as an adhesive. The assembly of such a Z-scheme heterojunction offered the superior photocatalytic degradation performance of soluble dyes and tetracycline (up to 94.3%) to the membrane with the improved photocatalytic activity of 2.33 times compared with the CoAl-LDH@pPAN membrane. Quenching experiments suggested that the •O2- was the most reactive oxygen species in the catalytic reaction system of the composite membrane. The greatly enhanced photocatalytic activity was attributed to the effective inhibition of photogenerated hole-electron combination using PANI as a carrier, with charge transferring from LDH to PANI. The possible photocatalytic degradation mechanism was proposed based on VB-XPS, electron spin resonance spectroscopy, and DRS technologies, which was confirmed by density functional theory calculation. Meanwhile, benefiting from the superhydrophilic/oleophobic feature and low oil adhesion, the membrane exhibited high permeability for isooctane emulsion (3990.39 L·m-2·h-1), high structure stability, and satisfactory cycling performance. This work provided a strategy to develop superwetting and photocatalytic composite membranes for treating complex multicomponent pollutants in the chemical industry.

Recent advances in functional micro/nanomaterials for removal of crude oil via thermal effects

Crude oil is one of the most widely used energy and industrial raw materials that is crucial to the world economy, and is used to produce various petroleum products. However, crude oil often spills during extraction, transportation and use, causing negative impacts on the environment. Thus, there is a high demand for products to remediate leaked crude oil. Among them, oleophilic and hydrophobic adsorbents can absorb crude oil through thermal effects and are research hotspots. In this review, we first present an overview of wettability theory, the heating principles of various thermal effects, and the theory of reducing crude oil viscosity by heating. Then we discuss adsorbents based on different heating methods including the photothermal effect, Joule heating effect, alternating magnetic field heating effect, and composite heating effect. Preparation methods and oil adsorption performance of adsorbents are summarized. Finally, the advantages and disadvantages of various heating methods are briefly summarized, as well as the prospects for future research.

Design and Machine Learning Prediction of In Situ Grown PDA-Stabilized MOF (UiO-66-NH2) Membrane for Low-Pressure Separation of Emulsified Oily Wastewater

Significant progress has been made in designing advanced membranes; however, persistent challenges remain due to their reduced permeation rates and a propensity for substantial fouling. These factors continue to pose significant barriers to the effective utilization of membranes in the separation of oil-in-water emulsions. Metal-organic frameworks (MOFs) are considered promising materials for such applications; however, they encounter three key challenges when applied to the separation of oil from water: (a) lack of water stability; (b) difficulty in producing defect-free membranes; and (c) unresolved issue of stabilizing the MOF separating layer on the ceramic membrane (CM) support. In this study, a defect-free hydrolytically stable zirconium-based MOF separating layer was formed through a two-step method: first, by in situ growth of UiO-66-NH2 MOF into the voids of polydopamine (PDA)-functionalized CM during the solvothermal process, and then by facilitating the self-assembly of UiO-66-NH2 with PDA using a pressurized dead-end assembly. A stable MOF separating layer was attained by enriching the ceramic support with amines and hydroxyl groups using PDA, which assisted in the assembly and stabilization of UiO-66-NH2. The PDA-s-UiO-66-NH2-CM membrane displayed air superhydrophilicity and underwater superoleophobicity, demonstrating its oil resistance and high antifouling behavior. The PDA-s-UiO-66-NH2-CM membrane has shown exceptionally high permeability and separation capacity for challenging oil-in-water emulsions. This is attributed to numerous nanochannels from the membrane and its high resistance to oil adhesion. The membranes showed excellent stability over 15 continuous test cycles, which indicates that the developed MOFs separating layers have a low tendency to be clogged by oil droplets during separation. Machine learning-based Gaussian process regression (GPR) models as nonparametric kernel-based probabilistic models were employed to predict the performance efficiency of the PDA-s-UiO-66-NH2-CM membrane in oil-in-water separation. The outcomes were compared with the support vector machine (SVM) and decision tree (DT) algorithm. This efficiency includes various metrics related to its separation accuracy, and the models were developed through feature engineering to identify and utilize the most significant factors affecting the membrane's performance. The results proved the reliability of GPR optimization with the highest prediction accuracy in the validation phase. The average percentage increase of the GPR model compared to the SVM and DT model was 6.11 and 42.94%, respectively.

Applications of graphene oxide (GO) in oily wastewater treatment: Recent developments, challenges, and opportunities

The treatment of oily wastewater has become a serious environmental challenge, for which graphene oxide has emerged as a promising material in solving the problem. The ever-growing utilization of graphene oxide (GO) in the treatment of oily wastewater necessitates a constant review. This review article employs a comprehensive literature survey methodology, systematically examining peer-reviewed articles, focusing on, but not entirely limited to, the last five years. Major databases such as EBSCOhost, Scopus, ScienceDirect, Web of Science and Google Scholar were searched using specific keywords related to GO and oily wastewater treatment. The inclusion criteria focused on studies that specifically address the application, efficiency, and mechanisms of GO in treating oily wastewater. The data extracted from these sources were then synthesized to highlight the most important developments, challenges, and prospects in this field. As far as oily wastewater treatment is concerned, the majority of the studies revolve around the use of GO in mitigating fouling in membrane processes, improving the stability, capacity and reusability of sorbents, and enhancing photodegradation by minimizing charge recombination.

Tunable zirconium-based metal organic frameworks synthesis for dibutyl phthalate efficient removal: An investigation of adsorption mechanism on macro and micro scale

The tunable porous structure of metal organic frameworks (MOFs) plays a crucial role in determining their adsorption performance. In this study, we developed and employed a strategy involving monocarboxylic acid assistance to synthesize a series of zirconium-based MOFs (UiO-66-F4) for the removal of aqueous phthalic acid esters (PAEs). The adsorption mechanisms were investigated by combining batch experiments, characterization and theoretical simulation. By adjusting the affecting factors (i.e., initial concentration, pH values, temperature, contact time and interfering substance), the adsorption behavior was confirmed as a spontaneous and exothermic chemisorption process. The Langmuir model provided a good fit, and the maximum expected adsorption capacity of di-n-butyl phthalate (DnBP) on UiO-66-F4(PA) was calculated to be 530.42 mg·g-1. Besides, through carrying out the molecular dynamics (MD) simulation, the multistage adsorption process in the form of DnBP clusters was revealed on a microcosmic scale. The independent gradient model (IGM) method showed the types of weak interactions of inter-fragments or between DnBP and UiO-66-F4. Furthermore, the synthesized UiO-66-F4 displayed excellent removal efficiency (>96 % after 5 cycles), satisfactory chemical stability and reusability in the regeneration process. Hence, the modulated UiO-66-F4 will be regarded as a promising adsorbent for PAEs separation. This work will provide referential significance in tunable MOFs development and actual applications of PAEs removal.

Light-Propelled Super-Hydrophobic Sponge Motor and its Application in Oil-Water Separation

Self-propelled separation materials, that is, motor, are one of the keys to realizing smart oil-water separation. Although three-dimensional sponges such as commercial melamine sponge (MS) exhibit excellent oil-water separation ability, they cannot move by themselves on water. Aiming at solving this problem, a polydimethylsiloxane (PDMS) and molybdenum disulfide (MoS2) modified MS motor (PDMS@MS/MoS2) with an asymmetric multilayer structure was prepared, in which the photothermal layer MoS2 provided the propelling force for the motor under infrared light irradiation, and the middle layer PDMS was used as the superhydrophobic modified agent and adhesive agent between commercial MS and MoS2 powder. PDMS coated MS (PDMS@MS) as the superhydrophobic layer showed good superhydrophobic ability (153.1°) and oil-water separation capacity (52.33 g/g to liquid paraffin). Furthermore, the introduction of MoS2 made the speed of the sponge motor reach 8.27 mm s-1 with a removal quantity of 12.20 g/g for cyclohexane. After recycling 8 times, the contact angle, cyclohexane capturing amount, and average velocity of the motor were 150.3°, 11.40 g/g, and 8.41 mm/s, respectively. Meanwhile, PDMS@MS/MoS2 kept a similar light-propelling velocity (∼8 mm) at different pH values and in simulated seawater, demonstrating that the light-propelling motor possessed a good cycle and practical performance, which provides a possibility for the directional light propulsion of a sponge motor in oil-water separation.

Design and assembly of Ag-decorated Bi2O3 @ 3D MXene Schottky heterojunction for the highly permeable and multiple-antifouling of fibrous membrane in the purification of complex emulsified oil pollutants

Membrane separation technology has potential for purifying emulsified oily wastewater. However, the oils, soluble organic substances, and microorganisms can cause complex membrane fouling problems, thereby reducing the separation efficiency and service life. Herein, a highly permeable and multiple-antifouling composite membrane was prepared using porous PAN fibrous mat as support backbone for the assembly of Ag-decorated Bi₂O₃ @ 3D MXene Schottky heterojunction and hydrophilic TA as the adhesive. The unique arrangement of 3D MXene heterojunction and hydrophilic functionalization effectively broke through the limitation of separation flux and synergistically enhanced the anti-fouling performance of membrane. Such fibrous composite membrane achieved an exceedingly high permeability (2717-3328 L·m^-2·h^-1) for various emulsified oils, while ensuring excellent oil/water emulsion retention rate (99.59%) and good cycle stability. Meanwhile, the composite membrane displayed favorable photocatalytic degradation performance toward degrading MeB (96.1%) and antibacterial ability. Furthermore, the MD simulation and free radical trapping experiments were carried out to unravel the molecular interactions during the separation process and the photocatalytic mechanism of composite membrane, respectively. Overall, the combination of photocatalytic self-cleaning, anti-oil adhesion, and antibacterial effect renders the membrane high permeability and multiple-antifouling performance, which provides a new strategy for dealing with complex oily wastewater in petrochemical industry.

Near-Infrared Light Responsive Surface with Switchable Wettability in Microstructure and Surface Chemistry

Intelligent surfaces with reversibly switchable wettability have recently drawn considerable attention. One typical strategy to obtain such a surface is to change the surface chemistry or the microstructure. Herein, we report a new smart surface for which the wettability was controlled by both the surface chemistry and microstructure. Various wetting states were reversibly and precisely controlled through heating, pressing, NIR irradiation, and oxygen plasma treatment. The excellent shape memory characteristics of shape memory polyurethane (SMPU) and the controlled release of hydrophobic/hydrophilic oxygen-containing functional groups contributed to this ability. Microcapsules were used to design these smart surfaces. They controlled the release of a fluorinated alkyl silane (FAS) through shell melting, changed the surface composition, and played a decisive role in protecting the FAS against hydrolysis and evaporation to ensure that the surface's wettability is recyclable. Controlling of the surface chemistry or microstructure was repeated for at least 19 or 16 cycles, respectively, which indicated excellent repeatability compared to other smart surfaces. Based on the excellent controllability, the surface exhibited multiple functions, such as liquid directional transport and coefficient of friction control. In addition, it maintained this extraordinary ability under harsh environments owing to the great stability of the SMPU and adequate protection of the FAS by the microcapsules. With switchable wettability based on the surface chemistry and microstructure, this work provides a new principle for designing smart surfaces with wettability controlled in two ways.

Robust Superhydrophobic PDMS@SiO2@UiO66-OSiR Sponge for Efficient Water-in-Oil Emulsion Separation

A major challenge in oil/water separation is the processing of surfactant-stabilized emulsions from the water medium. One of the feasible schemes of emulsion separation is the porous melamine sponge coupled with functional particles. Here, we proposed a novel superhydrophobic metal-organic framework (MOF)-based sponge for water-in-oil emulsion separation. The porous melamine sponge was combined with poly(dimethylsiloxane) (PDMS)-coated hydrophobic SiO₂ and UiO66-OSiR particles were prepared for demulsification via the one-step dipping method for the first time. The PDMS@SiO₂@UiO66-OSiR sponge revealed excellent superhydrophobicity at a water contact angle of 160.7° and superlipophilicity at an oil contact angle of 0°. Compared with the pristine melamine sponge, the size-controllable PDMS@SiO₂@UiO66-OSiR sponge could separate stabilized water-in-oil emulsions with ultrahigh separation efficiency (>98.64%) and high flux (e.g., 970 L·m^-2·h^-1). Meanwhile, the PDMS@SiO₂@UiO66-OSiR sponge exhibited superior durability and mechanical reusability. Under harsh conditions such as strong acid and alkali, organic solvent corrosion, etc., all water contact angles of the PDMS@SiO₂@UiO66-OSiR sponge were over 152°. Furthermore, the stress decreased by 5% when the sponge was subjected to 10 loading/unloading compression cycles at a constant strain of 60%. These results demonstrate that the PDMS@SiO₂@UiO66-OSiR sponge can efficiently separate water-in-oil emulsions through its adjustable porous structure coupled with demulsification and hydrophobic particles. This study provides a step forward in developing a feasible strategy for the MOF-based sponge for emulsion separation.

Eco-Friendly Fluorine Functionalized Superhydrophobic/Superoleophilic Zeolitic Imidazolate Frameworks-Based Composite for Continuous Oil-Water Separation

Superhydrophobic metal-organic framework (MOF)-based sponges have received increasing attention in terms of treating oil-water mixtures. However, highly fluorinated substances, commonly used as modifiers to improve the hydrophobicity of MOFs, have aroused much environmental concern. Developing a green hydrophobic modification is crucial in order to prepare superhydrophobic MOF-sponge composites. Herein, we report the preparation of a porous composite sponge via a polydopamine (PDA)-assisted growth of zeolitic imidazolate frameworks (ZIF-90) and eco-friendly hydrophobic short-chain fluorinated substances (trifluoroethylamine) on a melamine formaldehyde (MF) sponge. The composite sponge (F-ZIF-90@PDA-MF) exhibited superhydrophobicity (water contact angle, 153°) and superoleophilicity (oil contact angle, 0°), which is likely due to the combination of the low surface energy brought on by the grafted CF₃ groups, as well as the rough surface structures that were derived from the in situ growth of ZIF-90 nanoparticles. F-ZIF-90@PDA-MF showed an excellent adsorption capacity of 39.4-130.4 g g^-1 for the different organic compounds. The adsorbed organic compounds were easily recovered by physical squeezing. Continuous and selective separation for the different oil-water mixtures was realized by employing the composite sponge as an absorbent or a filter. The separation efficiency and flux reached above 99.5% and went up to 7.1 ×10⁵ L m^-2 h^-1, respectively. The results illustrate that the superhydrophobic and superoleophilic F-ZIF-90@PDA-MF sponge has potential in the field of water-oil separation, especially for the purposes of large-scale oil recovery in a water environment.

Preparation of a Superhydrophobic Surface by a One-Step Powder Pressing Method with Liquid Silicone Rubber As the Carrier

The preparation methods of the superhydrophobic surface play an important role in its application, but most of the existing preparation methods are complicated in operation, high in cost, and polluting to the environment. In order to find a simple, rapid, low-cost, and nonenvironmentally polluting preparation method of the superhydrophobic surface, this paper used liquid silicone rubber as the carrier. Before the liquid silicone rubber was nearly cured, it was evenly covered with a layer of silicon dioxide powder, and then 5 N weight was used to compact the powder on the rubber surface, so that the superhydrophobic surface was quickly formed on its surface. The wettability, bouncing performance, self-cleaning performance, and bending durability of liquid silicone rubber before and after treatment were compared. The results show that the static contact angle and rolling angle of the liquid silicone rubber after powder pressing were 158.22 ± 2.01° and 1.00 ± 0.50°, respectively. Moreover, the superhydrophobic surface formed by the powder pressing method had good self-cleaning performance, high temperature resistance, bending resistance, and excellent droplet bounce performance. The strategy of preparing a superhydrophobic surface by a one-step powder pressing method may be applied to the preparation of the superhydrophobic surface on a large scale.

Preparation of 2D Materials and Their Application in Oil-Water Separation

The problems of environmental pollution are increasingly severe. Among them, industrial wastewater is one of the primary sources of pollution, so it is essential to deal with wastewater, especially oil and water mixtures. At present, biomimetic materials with special wettability have been proven to be effective in oil-water separation. Compared with three-dimensional (3D) materials, two-dimensional (2D) materials show unique advantages in the preparation of special wettable materials due to their high specific surface area, high porosity, controlled structure, and rich functional group rich on the surface. In this review, we first introduce oil-water mixtures and the common oil-water separation mechanism. Then, the research progress of 2D materials in oil-water separation is presented, including but not limited to their structure, types, preparation principles, and methods. In addition, it is still impossible to prepare 2D materials with large sizes because they are powder-like, which greatly limits the application in oil-water separation. Therefore, we provide here a review of several ways to transform 2D materials into 3D materials. In the end, the challenges encountered by 2D materials in separating oil-water are also clarified to promote future applications.

Global research trends in petrochemical wastewater treatment from 2000 to 2021

Petrochemical wastewater (PWW) is a huge industrial contaminant that generates a wide range of resistive and poisonous organic pollutants that harm animals and plants in natural water bodies when discharged untreated or partially treated. Therefore, it is vital to develop technologies that are simple, efficient, and profitable for the treatment of oily wastewater. Although much study has been undertaken on the treatment of PWW, there has not been any recent work on bibliometric analysis of global research trends on this issue. A bibliometric analysis will help current and future researchers figure out where the gaps are and how to fill them. The present study's focus is to examine the characteristics and trends of research on oily wastewater treatment with an emphasis on the treatment of PWW. This research was performed on five important aspects, including characterization of research publications, countries' performances and collaborations, an analysis of the best papers with the most citations, keyword analysis (including frequency distribution of the keyword analysis, the transformation of the keyword combination across time, and exploration of changes in rank over time), and journal analysis, according to the 2457 papers in the Science Citation Index Expanded using the Web of Science (WoS) database from 2000 to 2021. For further analysis, the contingency matrix, bump diagram, and inter-temporal network stream were employed.

Graphene-Based Metal-Organic Framework Hybrids for Applications in Catalysis, Environmental, and Energy Technologies

Current energy and environmental challenges demand the development and design of multifunctional porous materials with tunable properties for catalysis, water purification, and energy conversion and storage. Because of their amenability to de novo reticular chemistry, metal-organic frameworks (MOFs) have become key materials in this area. However, their usefulness is often limited by low chemical stability, conductivity and inappropriate pore sizes. Conductive two-dimensional (2D) materials with robust structural skeletons and/or functionalized surfaces can form stabilizing interactions with MOF components, enabling the fabrication of MOF nanocomposites with tunable pore characteristics. Graphene and its functional derivatives are the largest class of 2D materials and possess remarkable compositional versatility, structural diversity, and controllable surface chemistry. Here, we critically review current knowledge concerning the growth, structure, and properties of graphene derivatives, MOFs, and their graphene@MOF composites as well as the associated structure-property-performance relationships. Synthetic strategies for preparing graphene@MOF composites and tuning their properties are also comprehensively reviewed together with their applications in gas storage/separation, water purification, catalysis (organo-, electro-, and photocatalysis), and electrochemical energy storage and conversion. Current challenges in the development of graphene@MOF hybrids and their practical applications are addressed, revealing areas for future investigation. We hope that this review will inspire further exploration of new graphene@MOF hybrids for energy, electronic, biomedical, and photocatalysis applications as well as studies on previously unreported properties of known hybrids to reveal potential "diamonds in the rough".

Superhydrophobic nanofibrous sponge with hierarchically layered structure for efficient harsh environmental oil-water separation

Oil leakage has posed serious threat to the environment, but still remain a great challenge to be solved especially for harsh environmental conditions. Herein, robust superhydrophobic nickel hydroxide grown by hydrothermal method and stearic acid modification on a blow-spun polyacrylonitrile (PAN)/Al₂O₃ nanofibrous sponge was proposed, so that the nickel hydroxide-modified polyacrylonitrile sponge (NPAS) was successfully obtained for efficient oil-water separation. The porous NPAS with a distinctive hierarchically layered structure, which exhibited excellent separation efficiency and mechanical elasticity. Due to its superhydrophobic and high porosity, the absorption capacity of NPAS could reach as high as 45 g g^-1. It could not only separate a series of oil-water mixture with a high steady flux of 12,413 L m^-2 h^-1 (dichloromethane-water), but also separate stabilized emulsions with a superior flux 2032 L m^-2 h^-1 (water-in-dichloromethane) under gravity, all of that with above 99.92% separation efficiencies, which was higher than that of the most reported sponges. Most importantly, its strong acid/alkali resistance enable it is suitable for hazardous materials treatment applications in harsh environmental conditions. This novel NPAS via facile large-scale blow-spinning provide an efficient strategy for oil-containing wastewater treatment and environmental protection.

A comprehensive review on water remediation using UiO-66 MOFs and their derivatives

Metal-organic frameworks (MOFs) are a versatile class of porous materials offering unprecedented scope for chemical and structural tunability. On account of their synthetic versatility, tunable and exceptional host-guest chemistry they are widely utilized in many prominent water remediation techniques. However, some of the MOFs present low structural stabilities specifically in aqueous and harsh chemical conditions which impedes their potential application in the field. Among the currently explored MOFs, UiO-66 exhibits structural robustness and has gained immense scientific popularity. Built with a zirconium-terephthalate framework, the strong Zr-O bond coordination contributes to its stability in aqueous, chemical, and thermal conditions. Moreover, other exceptional features such as high surface area and uniform pore size add to the grand arena of porous nanomaterials. As a result of its stable nature, UiO-66 offers relaxed admittance towards various functionalization, including synthetic and post-synthetic modifications. Consequently, the adsorptive properties of these highly stable frameworks have been modulated by the addition of various functionalities. Moreover, due to the presence of catalytically active sites, the use of UiO-66 has also been extended towards the degradation of pollutants. Furthermore, to solve the practical handling issues of the crystalline powdered forms, UiO-66 has been incorporated into various membrane supports. The incorporation of UiO-66 in various matrices has enhanced the rejection, permeate flux, and anti-fouling properties of membranes. The combination of such exceptional characteristics of UiO-66 MOF has expanded its scope in targeted purification techniques. Subsequently, this review highlights the role of UiO-66 in major water purification techniques such as adsorption, photocatalytic degradation, and membrane separation. This comprehensive review is expected to shed light on the existing developments and guide the inexhaustible futuristic scope of UiO-66 MOF.

Fabrication of superhydrophobic Enteromorpha-derived carbon aerogels via NH4H2PO4 modification for multi-behavioral oil/water separation

Hydrophobic and oleophilic biomass-based block materials are considered to be highly promising candidates used for oil/water separation. However, the crucial hydrophobic modification process often involves various toxic and hazardous organic substances or requires high energy inputs. Inspired by the flame retardant principle of phosphorus-containing flame retardants, herein, an Enteromorpha-derived carbon (ADP-EP) aerogel with a water contact angle of 144.2° was prepared by successive freeze-shaping, freeze-drying and low-temperature carbonization treatment (300 °C), using NH₄H₂PO₄ (ADP) as a modifier. The results demonstrated that the introduction of NH₄H₂PO₄ could largely facilitate the removal of oxygenated groups from the pristine EP aerogels and enhance their surface roughness, thereby achieving surface hydrophobic modification. Featuring intrinsic low density, rich porosity and strong lipophilicity, the as-fabricated ADP-EP aerogels exhibited exceptional performance in both oil spill adsorption (~140 g/g) and water-in-oil emulsion separation. Moreover, the good reusability for oil uptake was also realized thanks to its robust mechanical compressibility and thermal stability. This work provides a facile, economical and eco-friendly route to obtain a desirable hydrophobic/oleophilic surface.

Superhydrophobic polyurethane sponge based on sepiolite for efficient oil/water separation

Massive oil leakage accidents and illegal discharge of oily wastewater have not just destroyed the sustainability of the ecological environment but caused permanent damage to marine ecosystems, which makes it urgent to handle it. In this paper, by means of sol-gel, micro-nan silica that grew from the surface of fibrous sepiolite was organically modified with 1 H, 1 H, 2 H, 2 H-perfluorodecyltriethoxysilane (PFDS). The superhydrophobic sepiolite/silica firmly attached to the surface of polyurethane sponge under the action of oily epoxy resin with strong adhesion. The sponge exhibited superhydrophobicity and excellent selective oil adsorption capacity (19.98-40 times of their own weight). More importantly, besides the effective separation of immiscible oil-water mixtures (the separation rate reached 98.72%), it could also efficiently separate oil with water and oil with salt solution emulsions. In addition, the sponges kept hydrophobic even after floating in extremely corrosive liquids for 20 h, showing a strong resistance to strong acidic as well as alkaline liquids. After 100 times of mechanical compression, the three-dimensional structure of sponge held still and the water contact angle was greater than 144°, demonstrating an excellent mechanical stability, which provided a reference for its practical application in oil-water separation.

Structured sludge derived multifunctional layer for simultaneous separation of oil/water emulsions and anions contaminants

The effective treatment of complex oily wastewater is of great significance but still a considerable challenge, since single-function, expensive reagents, and complicated process have emerged as shackles for practical applications. Herein, with the objective to waste-control-waste, we proposed a facile and sustainable strategy to fabricate a low-cost multifunctional layer from hazardous waste aluminum sludge (WAS) for complex oily wastewater management. The as-designed layered double oxides/WAS (LDOs/WAS) layer with three-dimensional (3D) hierarchical rough surface exhibited excellent underwater superoleophobicity even under corrosive conditions and low adhesion to oil without any chemical modification reagent treatment. Significantly, the layer can be applied to gravity-directed simultaneous efficient oil-in-water emulsions and anions (taking phosphate as an example) separation with a separation efficiency for emulsion and phosphate up to 99.4% and 99.1%, respectively, and a high separation flux of above 2585 L m^-2 h^-1. Notably, the flux can be controlled simply and flexibly by adjusting the thickness of the layer. Furthermore, the layer also displayed excellent thermal stability, chemical stability, durability and recyclability. Therefore, this work not only presents a promising approach to design sludge-based multifunctional materials for complex oily wastewater remediation, but also shows great potential and value in environmental pollutions reduction and industrial applications.

Electrospun UiO-66-F4/polyacrylonitrile nanofibers for efficient extraction of perfluoroalkyl and polyfluoroalkyl substances in environmental media

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a family of emerging contaminants which are widely present in environment. In this work, novel UiO-66-F₄/polyacrylonitrile (UiO-66-F₄/PAN) hybrid nanofibers were firstly prepared via blend electrospinning or in-situ growth method for the pipette-tip solid phase extraction of PFASs. Characterizations demonstrate the as-synthesized UiO-66-F₄/PAN nanofibers have good chemical and thermal stability, possess large surface area (248 m²/g) and mesoporous framework structure. Several extraction factors including the amount of adsorbent, pH and ionic strength of sample solution, extraction time and eluent were investigated and the optimum conditions are 20 mg of the selected sorbent, adjusting to pH 5 and adding 4% w/v NaCl to sample solution, extraction for 12 min (3 min × 4). The good adsorption affinity of UiO-66-F₄/PAN for PFASs can be attributed to the extensive adsorption sites and multiple interactions including hydrophobic interaction, hydrogen bonding and F-F interaction. Low limit of detection (0.008-0.076 µg/L), limit of quantification (0.010-0.163 µg/L) and recoveries (70.84-113.57%) for 9 PFASs with relative standard deviations < 15% were achieved. When applied in the analysis of target PFASs in lake water, tap water, beverage, and shrimp muscle samples, this method could achieve robust and accurate results with sufficient sensitivity for nine PFASs.

Novel fabrication of hydrophobic/oleophilic human hair fiber for efficient oil/water separation through one-pot dip-coating synthesis route

Frequent oil spill accidents and industrial wastewater discharge has always been one of the most severe worldwide environmental problems. To cope with this problem, many fluorine-containing and high-cost materials with superwettability have been extensively applied for oil-water separation, which hinders its large-scale application. In this work, a novel human hair fiber (HHF)-polymerized octadecylsiloxane (PODS) fiber was fabricated with a facile one-pot dip-coating synthesis approach, inspired by the self-assembly performance and hydrophobicity of OTS modification. The benefits of prominent hydrophobic/lipophilic behavior lie in the low surface energy, and a rough PODS coating was rationally adhered on the surface of HHF. Driven solely by gravity and capillary force, the HHF-PODS showed excellent oil/water separation efficiency (> 99.0%) for a wide range of heavy and light oil/water mixtures. In addition, HHF-PODS demonstrated durability toward different harsh environments like alkaline, acid, and salty solutions.

Bi-functional super-hydrophilic/underwater super-oleophobic 2D lamellar Ti3C2Tx MXene/poly (arylene ether nitrile) fibrous composite membrane for the fast purification of emulsified oil and photodegradation of hazardous organics

Developing the multi-functional membranes including oil/water emulsion separation and removal of hazardous organic pollutants is essential to the purification of the complicated wastewater. However, it remains a daunting challenge to combine these intended functions while maintaining high separation efficiency. Herein, we developed a new 2D lamellar MXene/poly (arylene ether nitrile) (PEN) fibrous composite membrane through the self-assembly of TiO₂ nanoparticles intercalated MXene nanosheets onto the porous PEN nanofibrous mats and bioinspired polydopamine triggered chemical-crosslinking with polyethyleneimine (PEI). Such nano-intercalation and mussel-inspired crosslinking could effectively regulate the interlayer spacing of the MXene nanosheet skin layer and surface wettability of the composite membrane, which also further contributed to the fast separation and unique bifunctional feature. It was found that the MXene@TiO₂/PEN fibrous composite membrane exhibited low oil-adhesion and superhydrophilic (WCA = 0°)/underwater superoleophobic (UOCA > 155°) properties, which could efficiently separate various surfactant-stabilized oil-in-water emulsions under low pressure of 0.04 MPa while keeping good stability (Under 1 M HCl and 2 M NaOH solutions) and recyclability. Interestingly, the fibrous composite membrane achieved favorable permeation flux of 908-1003 Lm^-2h^-1 (2270-2507.5 Lm^-2h^-1bar^-1) in comparison to other reported MXene based multifunctional composite membranes. Moreover, owing to the synergistic effect of MXene nanosheets and TiO₂ nanoparticles, the MXene@TiO₂/PEN membrane showed excellent photocatalytic degradation performance for various dyes under visible light, i.e. the photocatalytic degradation efficiency for 15 ppm MB, MO, CV, and MeB solutions achieved 92.31%, 93.50%, 98.06%, and 99.30% within 60 min, respectively. Such 2D MXene bio-functional composite membranes with outstanding oil/water emulsions separation and photocatalytic degradation of dyes pave an avenue for treating complicated oily wastewater.

Advancing interfacial properties of carbon cloth via anodic-induced self-assembly of MOFs film integrated with α-MnO2: A sustainable electrocatalyst sensing acetylcholine

The metal organic frameworks (MOFs) with tunable composition, modified structure, and morphologically controlled nanoarchitectures are quite imperative to improve the electrochemical (EC) performances of sensing platforms. Herein, EC control over the fabrication of HKUST-1 (Cu-MOFs) nanocrystals is achieved via anodic-induced electrodeposition approach following the mixing of Cu²⁺ salt precursor in the vicinity of benzene-1,3,5-tricarboxylate (BTC^3-) ligands. The problem of controlled mass transfer and slow dispersal of MOFs is resolved by EC deposition of pyramidal-octagonal MOFs on a highly conductive and flexible carbon substrate (activated carbon cloth, ACC) wrapped with rGO layers (ACC-rGO@Cu(BTC). Further, α-MnO₂ is integrated on ACC-rGO@Cu(BTC) to achieve the synergistic effect of ternary structure interfaces. The novel ACC-rGO@Cu(BTC)@MnO₂ based flexible electrode exhibits striking EC performance toward non-enzymatic sensing of acetylcholine (ACh) including wide linear range (0.1 µM - 3 mM), lowest detection limit (5 nM, S/N = 3), high selectivity, and long-term stability. Moreover, the developed sensing system has been applied for real-time detection of ACh efflux released from three different cell lines and biological matrices. Our work unlocks a new prospect of precisely structured MOFs with extensive functionalities and scaled-up fabrication methods via selection of nanoscale reaction centers to develop flexible sensing devices.

Ion cross-linking assisted synthesis of ZIF-8/chitosan/melamine sponge with anti-biofouling activity for enhanced uranium recovery

A ZIF-8/chitosan/melamine sponge (CMZ8) uranium adsorbent was prepared using chitosan and zinc ions as adjuvants to achieve the integration of anti-fouling, adsorption and separation properties.

Ultrasonic assisted rapid preparation of superhydrophobic stainless steel surface and its application in oil/water separation

The preparation of superhydrophobic (SH) surface on stainless steel by chemical etching method is challenging due to the good corrosion resistance of the material. In this work, SH surface with water contact angle (WCA) as high as 163.21° was accomplished on 304 stainless steel surface by a rapid ultrasonic-assisted chemical etching method within 7 min and a low-cost fluorine-free modification treatment. The mechanism of ultrasonic field on the etching process was explored by detecting the cavitation and oscillation energy in the reactor. It is the first time to found that the ultrasonic cavitation effect enhanced the etching process by both chemical and physical facilitation resulting in hierarchical lamellar micro-structures, "mountain-like" micro-structure clusters and "coral-reef-like" nano-scale structures on the surface. With the ultrasonic power increasing, the ultrasonic cavitation effect not only enhanced the superhydrophobicity of sample surface, but also improved the uniformity of surface wettability. The samples also showed excellent performance of oil/water separation for various organics (all separation efficiencies up to 96%) and remarkable mechanical stability.

A dual-functional layer modified GO@SiO2 membrane with excellent anti-fouling performance for continuous separation of oil-in-water emulsion

As the most significant target of membrane separation, the inadequacy of permeability and anti-fouling frequently constrain the application of the membrane in actual oily wastewater. Herein, a novel concept of membrane surface construction was proposed to mitigate this intractable problem, using SiO₂ as the support layer and graphene oxide (GO) as the isolation layer. The best co-localization proportion of the support layer (56 mg/L) and isolation layer (3.5 mg/L) was determined by the separation performance of the modified membranes for the simulated emulsion. The thin GO layer could effectively prevent contaminants from entering the membrane pores without affecting its roughness. Based on the synergistic action of the isolation layer and support layer, the GO@SiO₂ membrane could well implement emulsion purification with a stable permeability (654.11 LMHB) and high separation efficiency (99.41%). The superior anti-fouling performance of the membrane ensures its long-term cycling stability, with the permeability recovery rate of 89.75% (low-density oil) and 90.41% (high-density oil) after 10 repeated cycles. The storage stability also indirectly increases its value in practical applications. More importantly, the GO@SiO₂ membrane also shows great potential for industrial emulsion treatment with excellent purification and cycling stability (permeability recovery rate of 84.01%).

Fabrication of visible-light response cadmium sulfide modified superhydrophobic surface for water resource remediation

Widespread concern has been attached to the frequent occurrence of pollution by oil slicks and water-soluble pollutants in recent years. The semiconductor photocatalysis is applied to sewage treatment owing to the advantages of energy-conserving and environmental protection. However, its application is limited by the defects of not solving oil slicks and the hard recyclability. In this paper, the high specific surface area and rod-shaped CdS were prepared using template and alkali-treated methods. Next, the alkylated SiO₂and alkali-treated CdS were deposited on pure fabric by physical deposition to prepare the multifunctional superhydrophobic fabric. The specific surface area and morphology of alkali-treated CdS were tested by BET specific surface area test and field emission scanning electron microscope. Besides, oil/water separation, water contact angle, and stability test experiments were performed to determine the superhydrophobic performance. Photocatalysis degradation efficiency and cycle degradation stability of multifunctional fabric were characterized by photocatalysis degradation Rh B experiment. Consequently, the alkali-treated CdS displays a high specific surface up to 343 m²g^-1. The multifunctional fabric presents excellent superhydrophobic performance with the water contact angle up to 155°. Meanwhile, the water contact angle of multifunctional fabric is always over 150° under various circumstances (acid-base corrosion, soaking time at 100 °C and frictional numbers), indicating that the multifunctional fabric has excellent superhydrophobic stability. Moreover, the fabric also exhibits outstanding photocatalysis performance (the degradation efficiency is 94% after 3 cycles). Our work provides a feasible method for addressing oil slicks on water surface and degrading water-soluble pollutants with extensive application prospects in water resource remediation.

One-Step Fabrication of a Micro/Nanosphere-Coordinated Dual Stimulus-Responsive Nanofibrous Membrane for Intelligent Antifouling and Ultrahigh Permeability of Viscous Water-in-Oil Emulsions

Membrane fouling is a major challenge for long-term oil/water separation. The incomplete degradation of organic pollutants or membrane damage exists in the common methods of membrane regeneration. Herein, a dual-responsive nanofibrous membrane with high water-in-oil emulsion separation efficiency and smart cleaning properties is reported, which shows complete restoration of its original separation performance. The pH-responsive and upper critical solution temperature (UCST)-type thermoresponsive nanofibrous membrane with a micro/nanosphere structure was developed via a one-step-blending electrospinning strategy. The membrane displays high hydrophobicity/oleophilicity at pH 7 and 25 °C and hydrophilicity/oleophobicity at pH 3 and 55 °C. As a result, it exhibits an ultrahigh permeability of 60528.76 L m^-2 h^-1 bar^-1 and a separation efficiency of 99.5% for water-in-D5 emulsions at room temperature (25 °C). Moreover, the contaminated membranes could be easily reclaimed by being rinsed with warm acidic water (pH 3 and 55 °C). The membrane maintained high separation performance after being used for multiple cycles, indicating its scalable application for purifying emulsified oil. This study provides a facial method of constructing membranes with multiscale hierarchical structures and a new idea for the design of recyclable oil/water separation membranes.

Durable, magnetic-responsive melamine sponge composite for high efficiency,in situoil-water separation

The development of durable and high-performance absorbents forin situoil-water separation is of critical importance for addressing severe water pollution in daily life as well as for solving accidental large-scale oil spillages. Herein, we demonstrate a simple and scalable approach to fabricate magnetic-responsive superhydrophobic melamine sponges byin situdeposition of PDA coatings and Fe₃O₄nanoparticles, followed by surface silanization with low surface energy 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PTOS) layer. The prepared melamine sponge composite (PTOS-Fe₃O₄@PDA/MF) not only exhibits a very high water contact angle of 165 ± 1.5° and an excellent ability to uptake a variety of oils and organic solvents (e.g. up to 141.1 g/g for chloroform), but also shows robust durability and superior recyclability. The PTOS-Fe₃O₄@PDA/MF sponge can also efficiently separate oils (or organic solvents) and water, as demonstrated by different model systems including immiscible oil-water solution mixture and miscible water-oil (W/O) emulsion (stabilized by surfactants). Furthermore, the PTOS-Fe₃O₄@PDA/MF sponge is able toin siturecover organics from water using a peristaltic pump, which gives it significant advantages over other traditional batch processes for oil-water separation. We believe that the PTOS-Fe₃O₄@PDA/MF sponge provides a very promising material solution to address oil-water separation, especially for the large-scale problems that have been long-time challenges with conventional sorption methods.

Multifunctional Photothermal Conversion Nanocoatings Toward Highly Efficient and Safe High-Viscosity Oil Cleanup Absorption

Efficient and safe cleanup for the high-viscosity heavy oil spill has been a worldwide challenge due to its sluggish flowability, while classic absorption methods by electric/solar heating are seriously limited by low efficiency and high fire hazards during heating of highly flammable oil. Facing this dilemma, we reported a novel flame-retardant photothermal conversion nanocoating to endow commercial foams with highly efficient and safe heavy oil cleanup absorption. This multifunctional nanocoating consisting of nano-Fe₃O₄ and reduced graphene oxide (rGO) that both showed photothermal conversion ability and non-flammable nature can be firmly deposited on the polymer foam skeletons via facile coprecipitation and dip-coating processes. The composite foam showed a tough morphology with high hydrophobicity and low density, thus leading to selective high absorption for various oils and organic solvents. Due to the double photothermal conversion effects of nano-Fe₃O₄ and rGO, the temperature of the foam can be rapidly heated at a rate of ∼103.5 °C/min (the fastest rate ever) under 1 sun irradiation. Consequently, the foam with a high absorption capacity of 75.1 times its weight demonstrated a rapid absorption rate of 9000 g m^-2 min^-1 for large-viscosity oil under 1 sun irradiation, which was 3 times faster than previously reported. Furthermore, benefitting from high flame retardancy, elasticity, and magnetism, the foam can be safely and repeatedly used for magnetically controllable oil cleanup absorption, which effectively avoids oil spill hazards.

Modeling oil-water separation with controlled wetting properties

Several oil-water separation techniques have been proposed to improve the capacity of cleaning water. With the technological possibility of producing materials with antagonist wetting behavior, for example, a substrate that repels water and absorbs oil, the understanding of the properties that control this selective capacity has increased with the goal of being used as the mechanism to separate mixed liquids. Besides the experimental advance in this field, less is known from the theoretical side. In this work, we propose a theoretical model to predict the wetting properties of a given substrate and introduce simulations with a four-spin cellular Potts model to study its efficiency in separating water from oil. Our results show that the efficiency of the substrates depends both on the interaction between the liquids and on the wetting behavior of the substrates itself. The water behavior of the droplet composed of both liquids is roughly controlled by the hydrophobicity of the substrate. Predicting the oil behavior, however, is more complex because the substrate being oleophilic does not guarantee that the total amount of oil present on the droplet will be absorbed by the substrate. For both types of substrates considered in this work, pillared and porous with a reservoir, there is always an amount of reminiscent oil on the droplet, which is not absorbed by the substrate due to the interaction with the water and the gas. Both theoretical and numerical models can be easily modified to analyze other types of substrates and liquids.

Advanced applications of Zr-based MOFs in the removal of water pollutants

The global water pollution is caused by the increase of industrial and agricultural activities, which have produced various toxic pollutants. Pollutants in water generally consist of metal ions, pharmaceuticals and personal care products (PPCPs), oil spills, organic dyes, and other organic pollutants. Amongst the adsorbents that have been developed to deal with pollutants in water, Zr-based metal-organic frameworks (MOFs) have drawn scientists' great attention due to their excellent stability and adjustable functionalization. Herein, the present review article introduces the synthetic methods of functionalized Zr-based MOFs and summarizes their applications in water pollution treatment. It also clarifies the interactions and removal mechanisms between pollutants and Zr-based MOFs. The use of these MOFs with eminent adsorption ability and recycling performance have been discussed in detail. Zr-based MOFs also face some challenges such as high cost, lack of real water environment applications, selective removal of pollutants, and low ability to remove composite pollutants. Future research should focus on addressing these issues. Although there is still a blank of the practical utility of Zr-based MOFs on a commercial scale, the research reported to date clearly shows that they are very promising materials for the water treatment.