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Porous Membranes with Special Wettabilities: Designed Fabrication and Emerging Application

2020; Chinese Chemical Society; Volume: 3; Issue: 3 Linguagem: Inglês

10.31635/ccschem.020.202000457

2096-5745

Jiancheng Di, Li Li, Qifei Wang, Jihong Yu,

Catalytic Processes in Materials Science

Open AccessCCS ChemistryMINI REVIEW1 Mar 2021Porous Membranes with Special Wettabilities: Designed Fabrication and Emerging Application Jiancheng Di, Li Li, Qifei Wang and Jihong Yu Jiancheng Di State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 , Li Li State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 , Qifei Wang State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 and Jihong Yu *Corresponding author: E-mail Address: [email protected] State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 International Center of Future Science, Jilin University, Changchun 130012 https://doi.org/10.31635/ccschem.020.202000457 SectionsAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Porous materials have become a burgeoning research interest in materials science because of their intrinsic porous characteristics, versatile chemical compositions, and abundant functionalities. Recently, inspired by natural superwetting surfaces originating from the cooperation of surface energy and surface geometry, porous membranes with special wettabilities are finding emerging opportunities associated with a wide variety of environmental and energy-related applications. This review will present an overview of the state-of-the-art research on the designed fabrications and applications of superwetting porous membranes based on zeolites, metal–organic frameworks (MOFs), porous organic materials (POMs), and mesoporous materials. General synthetic strategies for the fabrication of porous membranes (e.g., hydrothermal/solvothermal crystallization, interfacial polymerization, electrospinning, etc.), and principles for tuning the wettability of porous membranes through surface energy modulation are introduced. Furthermore, their emerging applications as oil–water separation membranes, lithium-ionbattery separators, self-cleaning layers, and anticorrosion coatings are demonstrated. Finally, we emphasize on future perspectives regarding the development of superwetting porous membranes for practical applications. Download figure Download PowerPoint Introduction Inspired by the fascinating features of natural plants or animals such as the self-cleaning property of lotus leaves, the lubrication effect of pitcher plants, the underwater oil resistance of fish scales, and others, a great deal of efforts have been devoted to engineering surface wettability of solid materials, which hold promising potentials to address the problems related to energy sources, environmental protection, and human health.1–6 As a fundamental property, the wettability of material surfaces depends on the interfacial interaction in solid–liquid–gas or solid–water–oil system. For a smooth substrate, wettability only relies on the surface chemical composition, which can be elucidated typically by the classic Young's equation.5 However, for rough surfaces, the influence of surface topography on the wettability should be considered; therefore, there are two possible models: Wenzel and Cassie−Baxter models. The Wenzel model theorizes that the solid surfaces are fully wetted by air or liquid, giving rise to the maximum air–solid or liquid–solid contact area,7 while solid surfaces are partially wetted or fully unwetted, the Cassie−Baxter model explains the wetting phenomena.8 According to these wetting models, surface wettability can be modulated by manipulating the surface geometry or controlling the surface energy by coating the existing substrates with chemical layers. In principle, the material surfaces exhibit more affinity to oil along with the successive decrease of surface energy, and the surface wettability changes in turns such as amphiphilicity, hydrophobicity/oleophilicity, and dual lyophobicity in solid–liquid–gas system. Moreover, the lyophilicity or lyophobicity of surfaces is enhanced dramatically by increasing the surface roughness, even achieving superlyophilicity or superlyophobicity. Thus far, most of the reported superwetting membranes are constructed by solid materials (e.g., oxides and polymers), which cannot afford the membranes' additional properties of large surface area and open structure, as well as adsorption ability, ion-exchange performance, ion conductivity, and so forth. Porous materials, including zeolites, mesoporous materials, metal–organic frameworks (MOFs), and porous organic materials (POMs), are an important class of solid materials with large surface areas, regular and well-defined channels, and high chemical/thermal stability (Figure 1a).9–15 They have widespread applications in the fields of petrochemical industry, hazardous substance cleaning, energy storage, and others, and are emerging as ideal hosts for loading ultrasmall metal catalysts in high-efficiency catalytic systems, as well as various drugs or proteins in the biological medicine.16–18 Recently, porous membranes have been fabricated through growing porous layers on rigid substrates or blending porous particles in polymeric matrixes, followed by a shaping process (Figure 1b). Based on the anisotropic morphology of porous materials that are randomly overlaid on top of the membrane, there is no need for sophisticated molding processes such as laser ablation, electrolytic deposition, chemical etching, and so forth, to increase the surface roughness further. More importantly, diverse functional groups can be incorporated into porous membranes during either in situ fabrication or the posttreatment process, which can change the surface energy of the porous membranes effectively, giving rise to modulated wettabilities, including hydrophobicity/oleophilicity in air, hydrophilicity/underwater oleophobicity, underliquid dual lyophobicity, and so forth (Figure 1c). The superwetting porous membranes are finding emerging opportunities in applications such as oil–water membranes, lithium-ion battery separators, self-cleaning layers, and anticorrosion coatings (Figure 1d). Figure 1 | (a) Schematic illustration of the classification of superwetting porous membranes and their advantageous features. (b) General fabrication methods of the porous membranes. (c) Chemical modification approaches for modulating the wettabilities of superwetting porous membranes. (d) Environment and energy-related applications of superwetting porous membranes. Download figure Download PowerPoint In this minireview, we will summarize the recent progress in the designed fabrication of superwetting porous membranes and their emerging applications triggered by the synergistic effect between inherent characteristics of porous materials and their unique surface wettabilities. These porous membranes are classified as zeolite membranes, MOF membranes, POM-based membranes, and mesoporous membranes. In each section, we will outline the fabrication methods based on the type of porous material, displaying the wetting features, and present the emerging applications of such membranes in the environmental and energy-related fields. Finally, we will highlight on the current challenges and prospects for the designed fabrication of superwetting porous membranes to meet the increasing demand of practical applications. Zeolite membranes Zeolites are a type of microporous aluminosilicates composed of interconnected TO4 tetrahedra (T = Si or Al), which have become one of the most important heterogeneous catalysts and adsorbents in the chemical industry because of their open-framework structures with molecule-sized entrance, high surface area, and abundant catalytic active sites.19 The pure zeolite coatings are traditionally prepared on inorganic porous substrates (i.e., metal meshes and alumina disks) via an in situ or seeding-assistant hydrothermal process.20 Owning to the high surface roughness coupled with the multiple surface hydroxyl groups, most zeolite membranes without further modification exhibit superamphiphilicity in air.21–26 For instance, our group fabricated the silicalite-1 [Mobil-type five ( MFI) topological structure = all-silica zeolite containing Si, O, and H in the framework] zeolite membranes on stainless steel meshes known as zeolite-coated mesh films (ZCMFs; Figures 2a and 2b) via a seeding-assistant hydrothermal crystallization, and first extended the application of zeolite membrane in the oil–water separation based on superior wettability. The ZCMFs exhibited superamphiphilicity in air, but they showed strong repulsion to various oils when immersed in water, indicating their underwater superoleophobic property (Figures 2c and 2d). Therefore, water could quickly pass through the pinholes that deliberately remained in ZCMFs; but the trapped water layers blocked oils. The residual oil content in the filtrate was 99%, even achieving the separation of surfactant-stabilized emulsions (Figure 3g). Figure 3 | (a) Schematic diagram of the fabrication of [email protected] nanofibrous membrane, and the oil–water separation mechanism. (b and c) Water and oil contact angles on a PVDF nanofibrous membrane without (left) and (right) the growth of ZIF-8 crystals. (d) Optical photos of the water-in-oil emulsion before and after filtration (left), and the corresponding water rejection and membrane flux of [email protected] nanofibrous membranes (right).51 (e) Illustration of the fabrication of [email protected] membrane for oil–water separation. (f) Water and oil contact angles in air and underliquid contact angles on [email protected] nanofibrous membrane, respectively. (g) Separation process of various oil–water mixtures by [email protected] nanofibrous membrane.59 (h) Preparation procedure of HKUST-1 membrane. (i) Underwater crude oil contact angle, sliding angle, and dynamic adhesion of HKUST-1 membrane. (j) Antifouling test of the HKUST-1 membrane. (k) Illustration of the fabrication of HKUST-1 membrane on a copper substrate, and the corresponding SEM images before and after the growth of HKUST-1 crystals.63 (l–n) Illustration of the oil–water separation processes and the purification efficiencies of HKUST-1 membrane for different oil–water mixtures during five separation-regeneration cycles.42 Reprinted with permission from ref 42. Copyright 2019 Elsevier; ref 51. Copyright 2018 Wiley-VCH; ref 59. Copyright 2017 Elsevier; ref 63. Copyright 2018 Royal Society of Chemistry. SEM, scanning electron microscopy. Download figure Download PowerPoint The Hong Kong University of Science and Technology (HKUST)-1 is a copper-based MOF built up of dimeric metal units, connected by benzene-1,3,5-tri-carboxylate linker molecules to form repeating coordination motives [Cu3(BTC)2] that extend in three-dimensions (3Ds) channel structure, which has high-water stability and unsaturated abundant active sites.64 A recent research indicated that the HKUST-1 powder could selectively capture oil droplets, and the oil removal capacity was about six times that of activated carbon.65 Meanwhile, the oil-adsorbed HKUST-1 crystals would aggregate spontaneously and precipitate when added to the oil–water mixtures; thereby realizing the effective removal of oils. Based on these outstanding characteristics, the as-prepared HKUST-1 crystals were adhered onto the stainless steel meshes by a mussel-inspired method in which dopamine (PDA) not only acted as the organic binder to gather the crystals but also increased the hydrophilicity of the membrane due to the existence of large polar groups (Figure 3h).63 The HKUST-1 membrane with an architecture similar to Chinese yam, has an underwater superoleophobicity/underoil superhydrophilicity, as well as a small sliding angle and low adhesion force to crude oil when immersed in water, hence, it displays excellent self-cleaning ability (Figures 3i and 3j). Consequently, for the separation of surfactant-stabilized oil-in-water emulsions, the water fluxes of the HKUST-1 membrane were >300 L m−2 h−1, and the chemical oxygen demand (COD) values in the filtrates were 99.9% for oil-in-water emulsions. Although different types of water-stable MOFs have been synthesized successfully, most of the as-prepared MOFs still suffer from moisture environment damages. Therefore, researchers are dedicated to increasing the hydrophobicity of MOFs to endure the hydrolytic cleavage of the coordination bonds between metal clusters and ligands, typically achievable in two ways: posthydrophobization of the as-synthesized MOFs and in situ hydrophobization during the MOF synthesis process.73,74 The posthydrophobization process can be carried out by physical coating or chemical grafting of various layers (e.g., hydrophobic polymers and organic molecules with long-chain alkyl or fluorine-containing groups) on the as-prepared MOF membranes to decrease the surface energy. Among them, PDMS is a commonly used hydrophobic coating to increase the water repulsion of MOF membranes. For example, the hydrophilic NH2-MIL-125 (Ti) (Ti-MOF) crystals could be deposited in situ on the cotton fabric via a solvothermal crystallization process, which sustained stability when exposed in the corrosive media and extreme temperature variations. Also, it could even endure the repetitive washing and abrasion processes, and thus, exhibited excellent mechanical and environmental stability.48 The Ti-MOF membrane became hydrophobic after coating by PDMS, displaying desirable repellence to water, milk, and coffee. Meanwhile, the PDMS modified Ti-MOF membranes had a high UV protection factor (UPF) value of 26.7–32.8; therefore, these multifunctional fabrics could be used for outdoor protection in daily life. Besides, the PDMS modified Ti-MOF removal efficiencies for layered oil–water mixtures and surfactant-free oil-in-water emulsions were >98% and >95%, respectively. Based on MOFs' unique features such as abundant coordinative unsaturated metal sites and the exchangeable ligands, the chemical composition of its membrane surface can be modulated by chemically grafting low surface energy organic molecules, thereby changing the surface wettability into hydrophobicity. For example, the pristine ZIF-8 membrane was hydrophilic because of the coordinative unsaturated zinc ions and the MIM on the crystal surface that interacted preferentially with water molecules.75 The surface ligand-exchange process proceeded using 5,6-dimethylbenzimidazole (DMBIM) molecules could substitute the surface MIM molecules effectively without affecting the ZIF-8 crystal morphology, and hence, markedly enhanced the hydrophobicity of the membrane due to the steric hindrance of DMBIM (Figures 4a–4e).43,76 Therefore, the ZIF-8 membranes with and without ligand-exchange processes had the opposite wettability that allowed the selective permeation of oil and water through the membrane, respectively, and achieved on-demand oil–water separation (Figures 4f and 4g). Gao et al.77 developed a universal strategy to graft octadecylamine (OA) molecules onto the activated MOFs such as MIL-101(Cr), UiO-66, ZIF-67, and HKUST-1 that contained abundant coordinative unsaturated metal sites (Figures 4h and 4i). The OA molecules with long alkyl chains effectively decreased the surface energy without blocking the inherent porosity and decreasing crystallinity of MOFs. Taking the OA-modified MIL-101(Cr) as an example, this MOF composite displayed the superhydrophobicity in air with a water contact angle of ∼156°, which possessed the high adsorption capacities for various oils (81–219 wt %). The separation device was fabricated by loading OA-modified MIL-101(Cr) on the commercial filter paper, which allowed selective passage of heavy oil through the membrane, giving rise to a high-separation efficiency of >99%. Figure 4 | (a) Illustration of switching the ZIF-8 membrane's wettability through a surface ligand-exchange process. Water contact angles, SEM images, and oil–water separation process of ZIF-8 membranes (b, d, and f) before and (c, e, and g) after the ligand-exchange process.76 (h) Illustration of the fabrication of surfac