Robust superhydrophobic mesh coated by PANI/TiO2 nanoclusters for oil/water separation with high flux, self-cleaning, photodegradation and anti-corrosion

Modified silica-based double-layered hydrophobic-coated stainless steel mesh and its application for oil/seawater separation

A double-layered hydrophobic-coated stainless steel mesh (CSSM) was successfully prepared by vapor deposition of polydimethylsiloxane (PDMS) to form aerosol silica (SiO2) particles on SSM followed by coating with the in situ modified SiO2 generated in the natural rubber (NR) latex for use in oil/seawater separation. The in situ SiO2 particles were modified with octyltriethoxysilane (OTES) or hexadecyltrimethoxysilane (HDTMS). Transmission electron microscopy, 29Si solid-state nuclear magnetic resonance, and Fourier transform infrared spectroscopy were used to determine the structure of the in situ modified SiO2 generated in the NR latex. Scanning electron microscopy and water contact angle analyses were applied to characterize the morphology and hydrophobicity of the CSSM, respectively. The presence of aerosol SiO2 particles from PDMS and in situ modified SiO2 by OTES (MSi-O) or HDTMS (MSi-H) generated in the NR could enhance the surface roughness and hydrophobicity of the CSSM. The hydrophobic CSSM was then applied for the separation of chloroform/seawater and crude oil/seawater mixtures. A high separation efficiency (up to 99.3%) with the PDMS/NR/MSi-H CSSM was obtained and the mesh was reusable for up to 20 cycles.

Durable underwater super-oleophobic/super-hydrophilic conductive polymer membrane for oil-water separation

Oily sewage has made serious impact on environment and people's life, and its treatment has become a global problem to be urgently solved. Oil-water separation has been considered to be an effective method to treat oily sewage at present. In this work, an underwater super-oleophobic/super-hydrophilic membrane with oil-water separation and self-cleaning properties was fabricated by electrochemical oxidation of sodium lignosulfonate doped polypyrrole. The membrane showed super-hydrophilicity for water-removal in air and super-hydrophilicity for oil-removal underwater in both oxidation and reduction states. The oil-water separation efficiency of the membranes for different organics exceeded 98.44%, no matter in oxidation or reduction state. Moreover, the membrane still exhibited excellent performance in terms of the oil-water separation efficiency and flux after 70 cycles, which were greater than 97.18% and 70.14 L·m-2·h-1, respectively. Simultaneously, through exploration of the mechanism, it was found that the larger anion kept intact in the membrane during the redox process, which made the stability of composition and performance. Thus, the membrane with advantageous properties, including underwater super-oleophobic/super-hydrophilicity, high oil-water separation efficiency, high circulating rate and stability, has significant potential in separation and collection of oily sewage.

Constructing a composite microfiltration carbon membrane by TiO2 and Fe2O3 for efficient separation of oil-water emulsions

Membrane-based separation technology has attracted enormous attention for oil/water emulsion treatment. Here, composite microfiltration carbon membranes (MCMs) were prepared from the precursor of phenolic resin doping with TiO2 and Fe2O3 via the processes of stereotype and pyrolysis. The functional groups, thermal stability, porous structure, microstructure, morphology, and hydrophilicity of the membrane samples were analyzed by Fourier-transform infrared spectroscopy, thermogravimetric analysis, bubble pressure method, X-ray diffraction, scanning electron microscope, and water contact angle, respectively. The effect of dopant amount on the separation performance of MCMs was investigated. The results show that a mixed matrix system is constructed by TiO2 and Fe2O3 in MCMs, which is beneficial for further optimizing the pore size, porosity, and hydrophilicity of MCMs for oily wastewater treatment by varying the dopant amount. The maximum oil rejections are achieved at 98.9% and 99.6% for MCMs with a dopant content of TiO2 and Fe2O3 at 25%, respectively. In brief, this study offers an attractive strategy for improving the separation performance of MCMs for oily wastewater.

Eco-Friendly Approach for the Construction of Superhydrophobic Coating on Stainless Steel Metal Based on Biological Metal-Organic Framework and Its Corrosion Resistance Performance

In this paper, we present a sustainable approach for the creation of superhydrophobic (SP) coating on a stainless-steel substrate based on a biological metal-organic framework (MOF). The MOF was synthesized using aspartic acid as a linker and copper ions as a core metal. Two SP coatings were well constructed on stainless steel utilizing electrodeposition of nickel (Ni) and nickel altered by MOF (Ni@Bio-MOF) coatings followed by soaking in a solution of stearic acid in ethanol. The results of Fourier transform infrared spectroscopy demonstrate that the stearic acid-grafted nickel coating (Ni@SA) and the stearic acid-grafted Ni@Bio-MOF composite (Ni@Bio-MOF@SA), were effectively deposited on the stainless steel. The wettability findings displayed that the water contact angle of Ni@SA and Ni@Cu-As MOF@SA are 160° ± 1.1°, and 168° ± 1.2°, respectively. The prepared SP coating was also found to be chemically and mechanically stable. The results show that the Ni@SA coating maintains SP characteristics in a pH range of 3-11 while the Ni@Cu-As MOF@SA coating retained SP characteristics in a pH range of 1-13. Additionally, the superhydrophobic Ni@SA coating demonstrated SP characteristics up to a length of abrasion equal to 1300 mm, while the Ni@Cu-As MOF@SA coating exhibited SP characteristics up to a length of abrasion equal to 2700 mm. Furthermore, the Ni@SA and Ni@Cu-As MOF@SA coatings exhibited significantly improved corrosion protection in a 0.5 M NaCl solution compared with bare stainless steel, with protection efficiencies of approximately 94% and 99%, respectively. The results of this study demonstrate that the proposed approach is a promising method for the fabrication of eco-friendly and corrosion-resistant SP coatings on stainless steel substrate.

Customization of surface wettability of nano-SiO2 by coating Trimethoxy(vinyl)silane modifier for oil-water separation: Fabrication of metal-based functional superwetting nanomaterial, characterizations and performance evaluation

The wettability of nano-SiO₂ surface was transformed from the inherent hydrophilicity to functional superhyderophobicity by coating Trimethoxy (vinyl)silane modifier, and the resultant surface showed contrasting wettability for water and oil (Superhydrophobic and Superoleophilic), which is a desired characteristic for the membranes used in oil-water separation. Initially Trimethoxy (vinyl)silane coated SiO₂ nanoparticles (TMVS@SiO₂) were synthesized by hydrolysis and poly-condensation reactions, and this nano dispersion was spray coated on the annealed stainless-steel mesh surface, whose resulting hierarchical surface texture brought about the desired wettability, with the water-surface-air (θ_WA) and oil-surface-air (θ_OA) interfacial contact angles of 150° and 0° respectively. In addition to the wettability studies (contact angles), FTIR, morphological, and elemental characterizations of the TMVS@SiO₂ coated surfaces were carried out to understand the alterations that have taken place on the TMVS@SiO₂ surface that in turn rendered superhydrophobicity and superoleophilicity to the surface. The FTIR absorption peaks indicate that after modifying SiO₂ with TMVS, the -OH groups on SiO₂ surface are clearly replaced by -CH₃. The morphological studies indicated that modification of SiO₂ leads to better cross-linking between coating composition and nanoparticles and EDS spectra and elemental mapping of the modified surface showed the presence of Si, O and C elements. Finally, this surface was tested for its efficiency and stability as a membrane in the process of separating oil and water from the oily water using gravity driven method. The oil-water separation efficiency was estimated to be 99% for this membrane and also it was found to be quite stable as the surface effectively retained this oil-water separation efficiency even after 10 cycles of separation process.

Advances in Asymmetric Wettable Janus Materials for Oil–Water Separation

The frequent occurrence of crude oil spills and the indiscriminate discharge of oily wastewater have caused serious environmental pollution. The existing separation methods have some defects and are not suitable for complex oil–water emulsions. Therefore, the efficient separation of complex oil–water emulsions has been of great interest to researchers. Asymmetric wettable Janus materials, which can efficiently separate complex oil–water emulsions, have attracted widespread attention. This comprehensive review systematically summarizes the research progress of asymmetric wettable Janus materials for oil–water separation in the last decade, and introduces, in detail, the preparation methods of them. Specifically, the latest research results of two-dimensional Janus materials, three-dimensional Janus materials, smart responsive Janus materials, and environmentally friendly Janus materials for oil–water separation are elaborated. Finally, ongoing challenges and outlook for the future research of asymmetric wettable Janus materials are presented.

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.

Fabrication of eco-friendly graphene-based superhydrophobic coating on steel substrate and its corrosion resistance, chemical and mechanical stability

Superhydrophobic coatings were successfully fabricated on steel substrates using potentiostatic electrodeposition of Ni and Ni-graphene, Ni-G, coatings followed by immersion in an ethanolic solution of stearic acid, SA. Rice straw, an environmentally friendly biomass resource, was used to synthesize high-quality graphene. The Raman spectra proved the high quality of the produced graphene. The Fourier transform infrared spectroscopy, FTIR, results showed that the Ni coating grafted with stearic acid, Ni-SA, and the Ni-G composite grafted with stearic acid, Ni-G-SA, were successfully deposited on the steel substrate. The scanning electron microscope, SEM, results showed that the prepared superhydrophobic coatings exhibit micro-nano structures. The wettability results revealed that the values of contact angles, CAs, for Ni-SA and Ni-G-SA coatings are 155.7° and 161.4°, while the values of sliding angles, SAs, for both coatings are 4.0° and 1.0°, respectively. The corrosion resistance, chemical stability, and mechanical abrasion resistance of the Ni-G-SA coating were found to be greater than those of the Ni-SA coating.

Superhydrophobic nanohybrid sponges for separation of oil/ water mixtures

The industrial revolution has led to different types of environmental pollution, including frequent leakage of crude oil to marine waters and the contamination of wastewater with immiscible or emulsified oils and organic liquids from various industrial residues. Hence, developing multifunctional materials for oil/water separation is a field of high significance for the remediation of oil-polluted water. Recently, advanced superwetting materials have been employed for oily wastewater treatment. This review summarizes the recent development in fabricating superhydrophobic/superoleophilic nanohybrid polyurethane, melamine, and cellulose sponges for oil/water separation. The use of organic and/or inorganic nanohybrid materials opens the horizon for designing a diverse and wide range of superhydrophobic sponges due to the synergistic effect between the surface roughness and chemical composition. The discussion is organized based on different classes of low surface energy materials including thermoplastics, thermosets, elastomers, fluorinated polymers, conductive polymers, organosilanes, long alkyl chain compounds, and hydrophobic carbon-based materials. Recent examples for the separation of both immiscible and emulsified oil/water mixtures are presented, with a focus on fabrication strategies, separation efficiency, recyclability, mechanical performance, and durability. Currently, most studies did not focus on the mechanical/chemical stability of the fabricated sponges, and hence, future research directions shall address the fabrication of robust and long-term durable superhydrophobic sponges with proper guidelines. Similarly, more research focus is required to design superhydrophobic sponges for the separation of emulsified oil/water mixtures and heavy crude oil samples. Superhydrophobic sponges can be employed for treatment of oily wastewater, emulsion separation, and cleanup of crude oil spills.

Toward Efficient Oil Energy Recovery: Eco-Friendly Fabrication of a Biomimetic Durable Metal Mesh with a Moss-Like Silver Nanocluster Structure

With the purpose of oil energy recovery as well as achieving efficiency of oil/water separation, hydrophobic mesh materials have attracted extensive attention. However, fabrication of the current methods is not environmentally friendly, has high energy consumption, and creates serious pollution. Inspired by lotus leaves and rose petals, a biomimetic superhydrophobic surface was fabricated prepared on a stainless steel mesh by an in situ chemical reduction method with simple operation and mild conditions. The results of SEM, XRD, and XPS demonstrated that the mesh shows a stable and uniform moss-like rough structured surface. The SSM/Ag/ODA mesh, which was modified by moss-like Ag nanoclusters and low surface energy agents, has excellent superhydrophobicity with an excellent oil/water separation efficiency that reached up to 99.8%. The silver mirror phenomenon formed by the Ag nanoclusters further confirmed that silver ions were reduced and attached to the surface of the mesh. Moreover, the mesh can maintain superhydrophobicity under harsh conditions, such as a high concentration of a salty solution, organic solvents, alkaline, acidic solution, and even long-time UV irradiation, etc. More importantly, the modified mesh has excellent physical stability, in which the water contact angle on the mesh can be maintained above 150° after harsh mechanical wear. The hydrophobic mesh showed great potential to be applied for highly efficient oil/water separation and oil energy recovery even under complex and harsh conditions.

One-step in-situ fabrication of carbon nanotube/stainless steel mesh membrane with excellent anti-fouling properties for effective gravity-driven filtration of oil-in-water emulsions

The occurrence of membrane fouling has resulted in limited wastewater treatment applications. The development of superhydrophilic-underwater superoleophobic materials has received significant attention owing to their good anti-fouling properties. However, to fabricate such materials need costly regents and tedious steps. Thus, developing a one-step process to prepare a low-cost material for oil/water separation is still desired. In this study, bio-inspired from an arachnid, inorganic carbon nanotube stainless steel meshes (CNT@SSMs) having superhydrophilic-underwater superoleophobic and excellent anti-fouling properties and a unique fiber structure were fabricated via a one-step thermal chemical vapor deposition method. The CNT@SSMs had a small pore size enabling a high water flux of 10,639 L m^-2h^-1 and the separation of oily wastewater, including various emulsions, at a high rejection ratio of >98.89%. As a result of its excellent chemical stability under high temperatures, a broad pH range, and saline environments, the CNT@SSM has the potential to be used in extreme conditions. In summary, these CNT@SSMs are easy to fabricate and are low-cost as a result of inexpensive reagents involved. Moreover, these novel superwetting membranes are promising candidates for treatment of hazardous oily wastewater.

Advanced Materials with Special Wettability toward Intelligent Oily Wastewater Remediation

Clean water resources are essential to our human society. Oil leakage has caused water contamination, which leads to serious shortage of clean water, environmental deterioration, and even increasing number of deaths. It is of great urgency to solve the oil-polluted water problems worldwide. Efficient oil/water separation, especially emulsified oil/water mixture separation, is widely used to mitigate water pollution issues. Recently, advanced materials with special wettability have been employed for oily wastewater remediation. Moreover, by endowing them with various intelligent functions, smart materials can effectively separate complex oil/water mixtures including extremely stable emulsions. In this review, oil/water separation mechanisms and various fabrication methods of special wettability separation materials are summarized. We highlight the special wettable materials with intelligent functions, including photocatalytic, self-healing, and switchable oil/water separation materials, which can achieve self-cleaning, self-healing, and efficient oily wastewater treatment. In each section, the acting mechanisms, fabricating technologies, representative studies, and separation efficiency are briefly introduced. Lastly, the challenges and outlook for oil/water separation based on the special wettability materials are discussed.

Fabrication of a PAN–PA6/PANI membrane using dual spinneret electrospinning followed by in situ polymerization for separation of oil-in-water emulsions

A polyacrylonitrile–polyamide 6/polyaniline (PAN–PA6/PANI) doped membrane was prepared using dual spinneret simultaneous electrospinning of PAN and PA6 and in situ polymerization of aniline at low temperature.