Superhydrophilic/superoleophobic shell powder coating as a versatile platform for both oil/water and oil/oil separation

Synthesis and demulsification performance of a novel low-temperature demulsifier based on trimethyl citrate

A significant amount of water-in-oil (W/O) emulsion is generated during petroleum extraction. However, the current commercial demulsifiers are expensive to produce and requires high demulsification temperatures, leading to increased energy and economic consumption. To enhance the efficiency of demulsifiers and reduce the cost of demulsifying W/O emulsions, we have successfully developed a novel demulsifier named TCED through a straightforward two-step process. This demulsifier features trimethyl citrate as the hydrophilic core grafted with three hydrophobic chains. Its structure was characterized using EA, FT-IR and 1H NMR spectroscopy, and the demulsification performance was comprehensively evaluated. At a low demulsification temperature of 40 °C, TCED demonstrated a remarkable demulsification efficiency (DE) of 99.06% and 98.74% in emulsions containing water contents of 70% (E70) and 50% (E50), respectively. Especially, a DE of 100% could be obtained in both E70 and E50 emulsions at a concentration of 600 mg/L. Moreover, TCED displayed a high DE even at high salinity levels of 50,000 mg/L and across a wide pH range of 2-10. Additionally, the phase interface was consistently clear after demulsification. To investigate the demulsification mechanism of TCED, various adsorption kinetics experiments were conducted, including measurements of interfacial tension (IFT), surface tension (SFT), interfacial competitive adsorption, and stability of interfacial film. The results obtained from the experiments indicated that TCED possessed remarkable diffusion and replacement capabilities within the emulsions. As a result, it effectively disrupted the original interfacial active substances, such as asphaltenes aggregates found in crude oil. TCED exhibits a high DE at low concentration and temperature. This characteristic highlights its significant potential for low-temperature demulsification applications in the petroleum industry.

A comprehensive review on the inherent and enhanced antifouling mechanisms of hydrogels and their applications

Biofouling remains a persistent challenge within the domains of biomedicine, tissue engineering, marine industry, and membrane separation processes. Multifunctional hydrogels have garnered substantial attention due to their complex three-dimensional architecture, hydrophilicity, biocompatibility, and flexibility. These hydrogels have shown notable advances across various engineering disciplines. The antifouling efficacy of hydrogels typically covers a range of strategies to mitigate or inhibit the adhesion of particulate matter, biological entities, or extraneous pollutants onto their external or internal surfaces. This review provides a comprehensive review of the antifouling properties and applications of hydrogels. We first focus on elucidating the fundamental principles for the inherent resistance of hydrogels to fouling. This is followed by a comprehensive investigation of the methods employed to enhance the antifouling properties enabled by the hydrogels' composition, network structure, conductivity, photothermal properties, release of reactive oxygen species (ROS), and incorporation of silicon and fluorine compounds. Additionally, we explore the emerging prospects of antifouling hydrogels to alleviate the severe challenges posed by surface contamination, membrane separation and wound dressings. The inclusion of detailed mechanistic insights and the judicious selection of antifouling hydrogels are geared toward identifying extant gaps that must be bridged to meet practical requisites while concurrently addressing long-term antifouling applications.

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

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

Under-Oil Superhydrophilic/Superhydrophobic Janus Nanofibrous Membrane for Highly Efficient Separation of Surfactant-Stabilized Water-in-Oil Emulsions

Highly efficient separation of surfactant-stabilized water-in-oil emulsions with both a high separation efficiency and high permeation flux is still challenging. In this work, an under-oil superhydrophilic/superhydrophobic Janus membrane was fabricated by combining an electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane and its modified membrane composited with poly(ethylene glycol) diacrylate (PEGDA). The incorporation of PEGDA is realized by in situ ultraviolet (UV)-initiated polymerization during the electrospinning process, and it endows the upper layer with unique under-oil superhydrophilicity that is very important for the demulsification of water-in-oil emulsions. The under-oil superhydrophobic lower layer serves to block the water and also can promote the permeation flux, because of its oil-absorbing ability. For surfactant-stabilized water-in-n-hexane emulsion (water content of 1 wt %), such a Janus membrane exhibits outstanding separation performance with a separation efficiency of >99.95% and permeation flux of >25 000 L m-2 h-1. Moreover, the Janus membrane shows excellent reusability and high applicability for water-in-diesel, water-in-hexadecane, and water-in-petroleum ether emulsions with separation efficiencies of 99.63%, 99.80% and 99.82%, respectively. These features make the Janus membrane a promising candidate as a separation membrane for surfactant-stabilized water-in-oil emulsions.

Spontaneous Separation of Immiscible Organic Droplets on Asymmetric Wedge Channels with Hierarchical Microchannels

Spontaneous separation of immiscible organic droplets has substantial research implications for environmental protection and resource regeneration. Compared to the widely explored separation of oil-water mixtures, there are fewer reports on separating mixed organic droplets on open surfaces due to the low surface tension differences. Efficient separation of mixed organic liquids by exploiting the rapid spontaneous transport of droplets on open surfaces remains a challenge. Here, through the fusion of inspiration from the fast droplet transport capability of Sarracenia trichome and the asymmetric wedge channel structure of shorebird beaks, this work proposes a spine with hierarchical microchannels and wedge channels (SHMW). Due to the synergistic effect of capillary force and asymmetric Laplace force, the SHMW can rapidly separate mixed organic droplets into two pure phases without requiring additional energy. In particular, the self-spreading of the oil solution on the open channel surface is utilized to amplify the surface energy difference between two droplets, and SHMW achieves the pickup of oil droplets floating on the surface of the organic solution. The maximum separation efficiency on 3-SHMW can reach 99.63%, and it can also realize the antigravity separation of mixed organic droplets with a surface tension difference as low as 0.87 mN·m-1. Furthermore, SHMW performs controllable separation, oil droplet pickup, and continuous separation and collection of mixed organic droplets. It is expected that this cooperative structure composed of hierarchical microchannels and wedge channels will be realized in resource recovery or chemical reactions in industrial production processes.

Biomimetic materials in oil/water separation: Focusing on switchable wettabilities and applications

Clean water resources are crucial for human society, as the leakage and discharge of oily wastewater not only harm the economy but also disrupt our living environment. Therefore, there is an urgent need for efficient oil-water separation technology. Surfaces with switchable superwetting behavior have garnered significant attention due to their importance in both fundamental research and practical applications. This review introduces the fundamental principles of wettability in the oil-water separation process, the basic theory of switchable wettability, and the mechanisms involved in oil-water separation. Subsequently, the review discusses the research progress, challenges, and issues associated with three conventional types of special wettability materials: superhydrophobic/superoleophilic materials, superhydrophilic/superoleophobic materials, and superhydrophilic/underwater superoleophobic materials. Most importantly, it provides a detailed exploration of recent advancements in switchable wettability smart materials, which combine elements of traditional special wettability materials. These include stimulus-responsive smart materials, pre-wetting-induced materials, and Janus materials. The discussion covers key response factors, detailed examples of representative works, design concepts, and fabrication strategies. Finally, the review offers a comprehensive summary of switchable superwetting smart materials, encompassing their advantages and disadvantages, persistent challenges, and future prospects.

Underwater Superoleophobic and Underoil Superhydrophilic Copper Benzene-1,3,5-tricarboxylate (HKUST-1) Mesh for Self-Cleaning and On-Demand Emulsion Separation

Surfaces with underoil superhydrophilic (UOSHL) and underwater superoleophobic (UWOHB) have great potential for on-demand emulsion separation. However, the fabrication of underoil superhydrophilic based on wetting thermodynamic principles is quite challenging. Several previous studies have shown that some sarcocarps are able to spontaneously absorb water to moisturize themselves and have a unique UOSHL ability. By mimicking this unique ability of the sarcocarp, an outstanding UWOHB and UOSHL membrane was prepared. We choose 2300 mesh stainless steel mesh (SSM) as the substrate, then grow Cu and Cu(OH)₂ on SSM by a simple electrochemical method, and finally grow HKUST-1 crystals via a fast in situ growth method. The whole preparation process is simple, low cost, and does not require complex and long-term hydrothermal reactions. By growing HKUST-1 crystals, the prepared surface successfully achieved the required UOSHL and UWOHB properties. When the water droplets come into contact with the membrane under n-hexane, it will diffuse and can completely spread out in 2 s. The as-prepared membrane exhibits outstanding anti-fouling and self-cleaning properties for rapeseed oil and crude oil with high viscosity underwater due to the special wetting. By prewetting the surface with an appropriate amount of the dispersion medium, it can rapidly and efficiently on-demand separate different emulsions. The separation efficiencies of water-in-oil emulsions and oil-in-water emulsions are above 99.00 and 97.00%. With their outstanding performance in self-cleaning, on-demand emulsion separation, low cost, and fast preparation, the as-prepared UOSHL and UWOHB HKUST-1 meshes show excellent potential for treating oily wastewater in practical applications.

Mussel-Inspired Robust Peony-like Cu3(PO4)2 Composite Switchable Superhydrophobic Surfaces for Bidirectional Efficient Oil/Water Separation

To alleviate the economic and environmental damage caused by industrial discharges of oily wastewater, materials applied for efficient oil/water separation are receiving significant attention from researchers and engineers. Among others, switchable wettable materials for bidirectional oil/water separation show great potential for practical applications. Inspired by mussels, we utilized a simple immersion method to construct a polydopamine (PDA) coating on a peony-like copper phosphate surface. Then, TiO₂ was deposited on the PDA coating surface to build a micro-nano hierarchical structure, which was modified with octadecanethiol (ODT) to obtain a switchable wettable peony-like superhydrophobic surface. The water contact angle of the obtained superhydrophobic surface reached 153.5°, and the separation efficiency was as high as 99.84% with a flux greater than 15,100 L/(m²·h) after 10 separation cycles for a variety of heavy oil/water mixtures. Notably, the modified membranes have a unique photoresponsiveness, transforming to superhydrophilic upon ultraviolet irradiation, achieving separation efficiencies of up to 99.83% and separation fluxes greater than 32,200 L/(m²·h) after 10 separation cycles for a variety of light oil/water mixtures. More importantly, this switch behavior is reversible, and the high hydrophobicity can be restored after heating to achieve efficient separation of heavy oil/water mixtures. In addition, the prepared membranes can maintain high hydrophobicity under acid-base conditions and after 30 sandpaper abrasion cycles, and damaged membranes can be restored to superhydrophobicity after a brief modification in the ODT solution. This simple-to-prepare, easy-to-repair, robust membrane with switchable wettability shows great potential in the field of oil/water separation.

Separation of Oil from an Oil/Water Mixed Drop under a Lamb Wave Field: A Review

Oil separation from oil/water mixed drop under a Lamb wave field is one of the emerging acoustofluidic technologies that integrate acoustics and microfluidics. In recent years, this technology has attracted significant attention due to its effective, fast, contactless, and pollution-free. It has been validated in the separation of oil/water mixture on different non-piezoelectric substrates and shows great potential in incompatible liquids applications. Here, we summarize our recent progress in this exciting field and show great potential in different applications. This review introduces the theories and mechanisms of oil/water mixed drop separation induced by Lamb waves, the applications of this technology in the separation of oil/water mixed drop, and discusses the challenges and prospects of this field.

Self-Healing Superwetting Surfaces, Their Fabrications, and Properties

The research on superwetting surfaces with a self-healing function against various damages has progressed rapidly in the recent decade. They are expected to be an effective approach to increasing the durability and application robustness of superwetting materials. Various methods and material systems have been developed to prepare self-healing superwetting surfaces, some of which mimic natural superwetting surfaces. However, they still face challenges, such as being workable only for specific damages, external stimulation to trigger the healing process, and poor self-healing ability in the water, marine, or biological systems. There is a lack of fundamental understanding as well. This article comprehensively reviews self-healing superwetting surfaces, including their fabrication strategies, essential rules for materials design, and self-healing properties. Self-healing triggered by different external stimuli is summarized. The potential applications of self-healing superwetting surfaces are highlighted. This article consists of four main sections: (1) the functional surfaces with various superwetting properties, (2) natural self-healing superwetting surfaces (i.e., plants, insects, and creatures) and their healing mechanism, (3) recent research development in various self-healing superwetting surfaces, their preparation, wetting properties in the air or liquid media, and healing mechanism, and (4) the prospects including existing challenges, our views and potential solutions to the challenges, and future research directions.

Polyphenylene Sulfide Ultrafine Viscous Fibrous Membrane Modified by ZIF-8 for Highly Effective Oil/Water Separation under High Salt or Alkaline Conditions

The oil/water separation in harsh environments has always been a challenging topic all over the world. In this study, the ZIF-8/PPS fiber membranes were fabricated via the combination of hot pressing and in situ growth. The distribution of ZIF-8 in the membranes was adjusted by changing the ZIF-8 in situ growth time, which could control the oil/water separation effect. Due to the hydrophilic nature of the ZIF-8/PPS fiber membranes, the water molecules in the oil-in-water emulsion could quickly penetrate into the fiber membrane under the drive of pressure, gravity, and capillary force, forming a water layer on the surface of the fiber membranes. The coupling of the water layer and the fiber structure prevented direct contact between the oil molecules and the fiber membrane, thereby realizing the separation of the emulsion. The results show that when the ZIF-8 in situ growth time was 10 h, the contact angle, the porosity, and the pure water flux of the ZIF-8/PPS fiber membranes were 72.5°, 52.3%, and 12,351 L/h·m², respectively. More importantly, the separation efficiency of M10 was 97%, and the oil/water separation efficiency reached 95% after 14 cycles. This study provides a novel strategy for preparing MOFs/fiber materials for oil/water separation in harsh environments.

Fabrication of a biological metal-organic framework based superhydrophobic textile fabric for efficient oil/water separation

In response to the industry's difficulty in properly separating oily wastewater discharge, researchers are investigating enhanced oil/water separation materials. In this work, a cost-effective and environmentally friendly superhydrophobic textile fabric was fabricated for effective oil-water mixture and emulsion separation. A biological metal-organic framework consisting of copper as a core metal and aspartic acid as a linker (Cu-Asp MOF) was used to improve the surface roughness of the pristine textile fabric, and stearic acid was used to lower its surface energy. The thermal gravimetric analysis investigated the prepared Cu-Asp MOF's thermal stability. X-ray spectroscopy and Fourier-transform infrared spectroscopy studied the crystal orientation and chemical composition of the Cu-Asp MOF, Cu-Asp MOF@SA, pristine textile fabric, and superhydrophobic textile fabric, respectively. The surface morphology of the pristine and modified textile fabric was studied by scanning electron microscope. The wettability results showed that the prepared superhydrophobic textile fabric has a water contact angle of 158° ± 1.3 and water sliding angle of 2° ± 0.2°. The prepared superhydrophobic textile fabric showed excellent oil-water mixture and emulsion separation performance, oil absorption capacity, chemical stability, mechanical abrasion resistance, and a high flux rate. These outstanding characteristics of the prepared superhydrophobic textile fabric greatly increase the possibility for practical applications.

Asymmetric Robust Superhydrophobic/Superhydrophilic Janus Membranes for the Moisture Proofing of Oil and Purification of Water

The performance degradation of oil caused by moisture and water pollution induced by the infiltration of oil can result in huge losses for society. This is especially true of stable emulsified mixtures of oil and water, which are difficult to separate and urgently require a processing method. In this work, a robust Janus membrane prepared by combining simple electrodeposition and spraying processes was used to separate water-in-transformer oil/lubricating oil emulsions and various oil-in-water emulsions. The membrane with outstanding separation efficiency was also endowed high flux to emulsions, even after 10 separation cycles and 100 sand impact tests, indicating that separation ability was retained. Furthermore, the excellent resistance to acidic and alkaline liquids of the superhydrophobic side groups of the membrane increased the possibility of its service in harsh environments. This study's findings reveal great potential regarding the expansion and application of oil-water separation materials.

Selective Fabrication of Robust and Multifunctional Super Nonwetting Surfaces by Diverse Modifications of Zirconia-Ceria Nanocomposites

The creation of surfaces with various super nonwetting properties is an ongoing challenge. We report diverse modifications of novel synthesized zirconia-ceria nanocomposites by different low surface energy agents to fabricate nanofluids capable of regulating surface wettability of mineral substrates to achieve selective superhydrophobic, superoleophobic-superhydrophilic, and superamphiphobic conditions. Surfaces treated with these nanofluids offer self-cleaning properties and effortless rolling-off behavior with sliding angles ≤7° for several liquids with surface tensions between 26 and 72.1 mN/m. The superamphiphobic nanofluid coating imparts nonstick properties to a solid surface whereby liquid drops can be effortlessly displaced on the coating with a near-zero tilt and conveniently lifted off using a needle tip, leaving no trace. Further, the superamphiphobic surface demonstrates good oil repellency toward ultralow surface tension liquids such as n-hexane and n-heptane. The superoleophobic-superhydrophilic surface repels oil droplets well regardless of whether it is in the air or underwater conditions. In addition, reaping the benefits of the ZrO₂-CeO₂ nanocomposites' photocatalysis feature, the superoleophobic-superhydrophilic coating exhibits self-cleaning ability by the degradation of color dyes. Modification of the wettability of substrates is carried out by a cost-effective and facile solution-immersion approach, which creates surfaces with hierarchical nano-submicron-scaled structures. The multipurpose coated surfaces have outstanding durability and mechanical stability. They also resist well high-temperature-high-pressure conditions, which will provide various practical applications in different fields, including the condensate banking removal in gas reservoirs or the separation of oil/water mixtures.

Biodegradable, biomimetic, and nanonet-engineered membranes enable high-flux and highly-efficient oil/water separation

Porous membranes with fascinating super-wettable surface and tunable porous architecture for oil-water separation have been developed rapidly, however, the serious secondary marine pollution caused by the non-degradable defectiveness of membranes themselves is still a thorny problem. Herein, we create an eco-friendly membrane with biomimetic cobweb-like nanostructure via assembling two-dimensional bacterial cellulose nanonets on the starch nanofibrous membrane on a large scale. The obtained novel composite membranes exhibit integrated properties of sub-micron pore size, ultrahigh porosity, superhydrophilicity, and underwater superoleophobicity, stemming from the synergistic effect of the hydrated nanonet-skin-layer and porous starch matrix. By virtue of the narrow-distributed sub-micron pores, ultrahigh porosity, and ultrathin thickness, the resulting membrane shows outstanding performance of excellent separation efficiency (up to 99.996%), high percolation flux (maximum of 15968 L m^-2 h^-1), well surpassing the conventional microfiltration membranes. More significantly, with the advantage of biodegradability and anti-oil-fouling property, the membrane could serve as the robust platform for long-term wastewater remediation.

Ag/polydopamine-coated textile for enhanced liquid/liquid mixtures separation and dye removal

Engineering a versatile platform that enables to separate both oil/water and oil/oil mixtures and remove dye from water is not easy. To address this challenge, we have developed an Ag/polydopamine-coated textile (Ag/PDA@textile) by chemically depositing Ag particles on the textile surface using polydopamine as the binder layer. The obtained Ag/PDA@textile attracts water but repels oil in the air, underwater, and when immersed into the oil. Exploiting its water-attracting and oil resistance, the Ag/PDA@textile is acted as a separation membrane to separate oil/water mixtures with enhanced separation efficiency. The Ag/PDA@textile also possesses opposite wetting behavior to oils with different polarities, allowing it to separate oil/oil mixtures efficiently. Thanks to the catalytic performance of the Ag particle, organic dyes can be decomposed effectively by our Ag/PDA@textile under UV illustration or in the presence of NaBH₄. Our Ag/PDA@textile may be valuable for applications in water purification and oil sewage treatment.

Robust multifunctional superhydrophobic, photocatalytic and conductive fabrics with electro-/photo-thermal self-healing ability

The fabrication of superhydrophobic and conductive fabrics that can conveniently and repeatedly restore the lost superhydrophobicity, caused by either the surface accumulation of trace organic contaminants or the chemical damage to surface components, remains challenging. Herein, we report a multifunctional superhydrophobic and conductive cotton fabric that integrates not only the photocatalytic activity for cleaning organic contaminants, but also the self-healing ability enabled by either electro-thermal or photo-thermal heating besides convection oven heating. The fabric was fabricated through the polydopamine (PDA)-assisted deposition of photocatalyst Ag/CdS and the subsequent thiol-Ag self-assembly. Either UV or visible light irradiation is able to decompose the surface organic contaminants, and the photocatalysis-induced slight damage on super water-repellency is curable by heating. The Ag layer endows the fabric with antibacterial property and conductivity along with the electro-/photo-thermal conversion ability, which offers relatively convenient ways of heating for curing the surface chemical damages caused by O₂ plasma etching or accelerated washing. Of particular importance is that the fabric still shows super water-repellency even after 18 cycles of accelerated washing, which equals to 90 normal home laundering cycles. The combination of these multiple functions makes this fabric very promising for a wide range of wearable applications.

Fabrication of silver vanadate quantum dots/reduced graphene oxide/graphitic carbon nitride Z-scheme heterostructure modified polyvinylidene fluoride self-cleaning membrane for enhancing photocatalysis and mechanism insight

The enhancement of the self-cleaning ability of photocatalytic membranes and their degradation efficiency over tetracycline (TC) still remains a challenge. In this study, an alternative silver vanadate quantum dots (AgVO₃ QDs) doped reduced graphene oxide (RGO) and graphitic carbon nitride (C₃N₄) nanocomposites modified polyvinylidene fluoride (PVDF) membrane (AgVO₃/RGO/C₃N₄-PVDF) was successfully fabricated to enhance the photocatalytic activity. The AgVO₃/RGO/C₃N₄ nanocomposites were functioned as the active component for the photocatalytic membrane. The unique Z-scheme heterostructure of AgVO₃/RGO/C₃N₄ and the porous PVDF framework synergistically enhanced the separation and transport efficiency of photogenerated carriers and facilitated the interaction between the photocatalyst and the pollutant. As a result, the degradation efficiency of TC for the AgVO₃/RGO/C₃N₄-PVDF reached 88.53% within 120 min, which was higher than those of the binary component membranes (64.8% for RGO/C₃N₄-PVDF and 79.18% AgVO₃/C₃N₄-PVDF). In addition, AgVO₃/RGO/C₃N₄-PVDF exhibited high permeability (1977 L·m^-2·h^-1·bar^-1) and excellent antifouling activity. Under visible-light irradiation, the flux recovery rate (FRR) increased from 92.4% to 99.1%. Furthermore, AgVO₃/RGO/C₃N₄-PVDF could reject 97.4% of Escherichia coli (E. coli) owning to its self-cleaning capacity, and eliminated the E. coli under visible-light irradiation trough the photogeneration of h⁺. This study highlights a highly efficient photocatalytic membrane based on a Z-scheme heterostructure, which may have a great potential application in practical wastewater treatment.

A solar-heated antibacterial sodium alginate aerogel for highly efficient cleanup of viscous oil spills

HYPOTHESIS

Major oil spills highlight the need for environmentally responsible and cost-effective recovery technologies. However, challenges remain for heavy oil spill recovery because of its high viscosity and low fluidity. To achieve this goal, an ecofriendly bio-based aerogel with efficient photothermal conversion ability was developed as a novel absorbent to achieve the fast removal of heavy oil spill by reducing the oil viscosity.

EXPERIMENTS

From the renewable and abundant raw material sodium alginate (SA), hydrophobic and antibacterial SA/graphene oxide/ZIF-8 aerogel (SAGZM) was successfully fabricated via freezing-drying and chemical vapor deposition (CVD) technique. A series of characterization and tests, including aerogel structure, selective wettability, photothermal conversion ability, crude oil removal capability, and antibacterial ability, have been investigated in detail. SAGZM aerogels have rich pore structure, high porosity, excellent mechanical properties, and better photothermal conversion efficiency.

FINDINGS

Under sunlight illumination, the recovery ability of SAGZM for heavy crude oil was investigated through infrared thermal imaging, oil permeability behavior analysis, and the continuous absorption for crude oil. In addition, these results are well supported by the theoretical liquid absorption coefficient. This study indicates that SAGZM is highly efficient in in situ regulating oil viscosity through its remarkably photothermal conversion capability. Importantly, SAGZM possesses an excellent antibacterial ability that is often neglected in the design of environmentally friendly materials in extending its service life. The findings of this work not only provide an eco-friendly bio-based aerogel material but also demonstrate that the photo-responsive SAGZM is efficient in heavy crude oil absorption. The proposed solar-heated SA-based aerogel provides a sustainable approach and material to solve the recovery problem of viscous crude oil spills.

Wettability Improvement in Oil-Water Separation by Nano-Pillar ZnO Texturing

The nanostructure-based surface texturing can be used to improve the materials wettability. Regarding oil−water separation, designing a surface with special wettability is as an important approach to improve the separation efficiency. Herein, a ZnO nanostructure was prepared by a two-step process for sol−gel process and crystal growth from the liquid phase to achieve both a superhydrophobicity in oil and a superoleophobic property in water. It is found that the filter material with nanostructures presented an excellent wettability. ZnO-coated stainless-steel metal fiber felt had a static underwater oil contact angle of 151.4° ± 0.8° and an underoil water contact angle of 152.7° ± 0.6°. Furthermore, to achieve water/oil separation, the emulsified impurities in both water-in-oil and oil-in-water emulsion were effectively intercepted. Our filter materials with a small pore (~5 μm diameter) could separate diverse water-in-oil and oil-in-water emulsions with a high efficiency (>98%). Finally, the efficacy of filtering quantity on separation performance was also investigated. Our preliminary results showed that the filtration flux decreased with the collection of emulsified impurities. However, the filtration flux could restore after cleaning and drying, suggesting the recyclable nature of our method. Our nanostructured filter material is a promising candidate for both water-in-oil and oil-in-water separation in industry.