Superhydrophobic and thermally conductive membranes for oil / water separation

Abstract

Superhydrophobic and thermally conductive membranes useful for oil / water separations and oil absorption, and methods of making and using the same, are described. The superhydrophobic and thermally conductive membranes include a substrate, nanostructures disposed on the substrate, and a hydrophobic agent attached to the nanostructures.

Description

70273-WO-PCT / TECH-2024-30 SUPERHYDROPHOBIC AND THERMALLY CONDUCTIVE MEMBRANES FOR OIL / WATER SEPARATION Inventors: Saketh Merugu, Anju R. Gupta RELATED APPLICATIONS

[0001] This application claims priority to United States Provisional Application No.63 / 689,935 filed under 35 U.S.C. § 111(b) on September, 3, 2024, and to United States Provisional Application No. 63 / 688,510 filed under 35 U.S.C. § 111(b) on August 29, 2024, the entire disclosures of which are each incorporated herein by reference for all purposes. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under Grant No.2002307 awarded by the National Science Foundation. The government has certain rights in this invention. BACKGROUND

[0003] Membranes for ultrafast oil / water separations are useful and necessary in a lot of different fields such as the oil / water separation market, the superhydrophobic membranes / coatings market (SAM), the membrane separation market (TAM), separation technologies, cleaning industries, oil spill remediation, corrosion control, and the hydrophobic membrane market which includes oil and gas industries (oil / water separations), electronics, packaging (weather proofing), clothing (safety gear, personal protection equipment), and waste water treatment. There is a need for ecofriendly, economical, and easily fabricated membranes for ultrafast oil / water separations. Currently, synthetic polymer-based membranes (PVDF, PTFE), foams, and sponges with superhydrophobic coatings are being used as membranes for oil / water separations. However, some issues with these include complex and multistep fabrication, slow separation rates, low absorption capacities, they are non-ecofriendly, and they are expensive. There is a need in the art for new and improved membranes for separating oil and water. SUMMARY

[0004] Provided herein is a superhydrophobic membrane comprising a substrate; nanostructures disposed on the substrate; and a hydrophobic agent attached to the nanostructures.

[0005] In certain embodiments, the substrate is a cellulose-based substrate. In certain embodiments, the substrate comprises an absorbent tissue made of untreated paper with a high wicking ability. In certain embodiments, the substrate comprises a virgin wood pulp-based material. In certain embodiments, the70273-WO-PCT / TECH-2024-30 substrate comprises polysulfone. In certain embodiments, the substrate comprises a cellulose filter, a cotton fabric, or a metallic surface.

[0006] In certain embodiments, the nanostructures are metal nanostructures. In certain embodiments, the nanostructures comprise Cu nanoparticles. In certain embodiments, the nanostructures comprise Ni nanoparticles. In certain embodiments, the nanostructures comprise Zn nanoparticles. In certain embodiments, the nanostructures comprise nanorods, the nanorods having an aspect ratio of 1.2 or higher. In certain embodiments, the nanostructures consist of nanorods, the nanorods having an aspect ratio of 1.2 or higher. In certain embodiments, the nanostructures have an average size in a range of from about 1 nm to about 100 nm. In certain embodiments, the nanostructures comprise copper oxide nanospheres or zinc oxide nanospheres. In certain embodiments, the nanostructures comprise paramagnetic particles. In certain embodiments, the nanostructures comprise piezoelectric particles.

[0007] In certain embodiments, the hydrophobic agent comprises a silane, a fatty acid, a fluoropolymer, a wax, or a combination thereof. In certain embodiments, the hydrophobic agent comprises perfluorodecyltriethoxysilane (FAS-17), stearic acid, or a combination thereof.

[0008] In certain embodiments, the superhydrophobic membrane has a water contact angle of at least 140°.

[0009] In certain embodiments, the substrate comprises a cellulose-based material; the nanostructures comprise Cu or Zn; and the hydrophobic agent comprises perfluorodecyltriethoxysilane (FAS-17) or stearic acid. In particular embodiments, the nanostructures comprise nanorods having an aspect ratio of 1.2 or higher. In particular embodiments, the superhydrophobic membrane has a water contact angle of greater than 145°.

[0010] In certain embodiments, the substrate consists of a cellulose-based material; the nanostructures comprise copper or zinc; and the hydrophobic agent consists of perfluorodecyltriethoxysilane (FAS-17) or stearic acid.

[0011] In certain embodiments, the superhydrophobic membrane is thermally conductive.

[0012] Further provided is a method for conducting a separation, the method comprising immersing a superhydrophobic membrane described herein into a mixture of an organic substance and water; allowing the superhydrophobic membrane to absorb at least some of the organic substance from the mixture; and removing the superhydrophobic membrane from the mixture to separate the absorbed organic substance from the mixture. In certain embodiments, the organic substance comprises octane, coconut oil, n-hexane, or chloroform.

[0013] Further provided is a method of making a superhydrophobic membrane, the method comprising contacting a substrate with a first solution comprising a metal to deposit the metal on the substrate; contacting the substrate with a second solution comprising a reducing agent to form70273-WO-PCT / TECH-2024-30 nanostructures on the substrate; and contacting the substrate with a third solution containing a hydrophobic agent to attach the hydrophobic agent to the nanostructures to form a superhydrophobic membrane. In certain embodiments, the substrate is a cellulose-based substrate. In certain embodiments, the nanostructures comprise copper, nickel, or zinc. In certain embodiments, the third solution comprises stearic acid. In certain embodiments, the third solution comprises 1H,1H,2H,2H- perfluorodecyltriethoxysilane (FAS-17). In certain embodiments, the third solution comprises a fatty acid, wax, or fluoro alkyl silane. In certain embodiments, the reducing agent comprises NaOH. In certain embodiments, the substrate is contacted with a second reducing agent prior to contacting the substrate with the third solution. In particular embodiments, the second reducing agent comprises or NaBH4. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0015] FIG.1: Schematic of the different layers and composition of the superhydrophobic membrane.

[0016] FIG.2: Schematic of superhydrophobic modification of Cu-coated Kimwipes®tissues using stearic acid.

[0017] FIG.3: Schematic of superhydrophobic modification of Cu-coated Kimwipes®tissues using FAS-17.

[0018] FIG.4: Schematic of an oil / water separation test setup.

[0019] FIGS.5A-5B: Scanning electron microscopy (SEM) images of a Kimwipes® tissue (FIG. 5A), and a stearic acid / Cu coated Kimwipes® tissue (FIG.5B).

[0020] FIG.6: Water contact angles of a superhydrophobic membrane made with a stearic acid / Cu coated Kimwipe® tissue.

[0021] FIG.7: Photograph showing the separation of octane (colorless) from water (red).

[0022] FIG.8: Absorption of coconut oil (colorless) from water (red).

[0023] FIG.9: Absorption capacity of stearic acid / Cu superhydrophobic membrane with a Kimwipes® tissue substrate recorded every 5 seconds starting from 10 seconds to 35 seconds.

[0024] FIGS.10A-10B: SEM images of a Kimwipes® tissue (FIG.10A) and a superhydrophobic membrane made from a silane / Cu coated Kimwipes® tissue (FIG.10B).

[0025] FIG.11: Water contact angle of a superhydrophobic membrane made from a silane / Cu coated Kimwipes® tissue.

[0026] FIG.12: Photograph showing the separation of octane (colorless) from water (red) by a70273-WO-PCT / TECH-2024-30 superhydrophobic membrane made from a silane / Cu coated Kimwipes® tissue.

[0027] FIG.13: Absorption capacity of a superhydrophobic membrane made from a silane / Cu coated Kimwipes® tissue recorded every 5 seconds starting from 10 seconds to 35 seconds.

[0028] FIG.14: Illustration of a ~148° water contact angle.

[0029] FIG.15A: Photograph showing a polyurethane foam coated with a membrane.

[0030] FIG.15B: Photograph showing a cotton fabric coated with a membrane.

[0031] FIG.15C: Photograph showing a cellulose wipe coated with a membrane.

[0032] FIG.15D: Photograph showing polysulfone films coated with a membrane.

[0033] FIGS.16A-C: Photographs showing a membrane coated polyurethane foam undergoing an immersion test.

[0034] FIGSs 17A-C: Photographs showing a membrane coated polyurethane foam undergoing a tape test.

[0035] FIGS.18A-C: Photographs showing a membrane coated polyurethane foam undergoing an abrasion test. DETAILED DESCRIPTION

[0036] Throughout this disclosure, various publications, patents, and published patent specifications are referenced by an identifying citation. The disclosures of these publications, patents, and published patent specifications are hereby incorporated by reference into the present disclosure in their entirety to more fully describe the state of the art to which this invention pertains.

[0037] Hydrophobic agents can be used to create water-repellent surfaces and superhydrophobic surfaces. In accordance with the present disclosure, a facile two-step in-situ nanostructure coating followed by a hydrophobic coating using hydrophobic agents can create superhydrophobic articles useful as membranes for separation processes or other applications. The use of cellulosic membranes can provide for ultrafast, ultrahigh absorption of low surface tension liquids and provide an ecofriendly and biodegradable alternative to conventional membranes.

[0038] Referring now to FIG.1, depicted is a membrane 100. The membrane 100 includes a substrate 102, a layer of nanostructures 104 disposed on the substrate 102, and a hydrophobic agent 106 attached to the layer of nanostructures 104. The membrane 100 may be superhydrophobic or hydrophobic, depending on various factors such as the composition of the hydrophobic agent 106, the size and shape of the nanostructures 104, and the uniformity of coverage by the hydrophobic agent 106 over the substrate 102. The term “superhydrophobic” is used herein to refer to something having a water contact angle above 120°. In some embodiments, the membrane 100 has a water contact angle of 140° or higher. In some embodiments, the membrane 100 has a water contact angle of 145° or higher.70273-WO-PCT / TECH-2024-30

[0039] Referring still to FIG.1, the substrate 102 may be any rigid structure capable of supporting the nanostructures 104. The substrate 102 may be any membrane, such as a polymer or cellulose membrane. The substrate 102 should be hydrophobic for the best coating results in terms of the hydrophobicity of the final membrane 100. However, there may be some applications in which the substrate 102 is hydrophobic in some regions and hydrophilic in other regions, or is a hydrophilic substrate. The substrate 102 may be, for example, a cellulose-based substrate such as a paper product. Non-limiting example materials suitable for use as the substrate 102 include cellulose filters, tissue papers, polysulfone membranes, cotton fabrics, metallic surfaces, and hydrophilic membranes. However, any surface capable of supporting the nanostructures 104 can be used as the substrate 102. It is particularly advantageous, though, if the substrate 102 has a high wicking ability, so as to allow for a better ability of the membrane 100 to wick up an oil. One non-limiting example material for the substrate 102 is the product available commercially under the trademark Kimwipes®. Kimwipes® tissues are absorbent tissues made of untreated paper (i.e., a virgin wood pulp-based material) with a high wicking ability. Kimwipes® tissues were used as the substrate in the examples herein to demonstrate the capability of the superhydrophobic membranes 100 because Kimwipes® tissues are readily available, have pores, and have good absorption rates. Kimwipes®tissues are generally used as wipes for delicate cleaning applications due to their high wicking nature. The property of high wicking can be utilized for enabling separations by modifying the Kimwipes®tissues to selectively permit only low surface tension liquids such as oils, octanes, n-hexane, and chloroform to pass through it and prevent wetting by water (permselectivity). Metal nanoparticle coatings on the Kimwipes®tissues enabled the formation of hydrophobic layer on the surface of the Kimwipes®tissues to achieve superhydrophobicity. Polysulfones, in contrast to Kimwipes® tissues, have less absorption capacity, but can nonetheless be used as or in the substrate 102. Similarly, cotton or other fabric materials also work well as or in the substrate 102.

[0040] Referring still to FIG.1, the nanostructures 104 serve not only to attach the hydrophobic agent 106 to the substrate 102 but also to increase the surface roughness of the membrane 100, which increases hydrophobicity. Moreover, the nanostructures 104 react to bond with the hydrophobic agent 106, thereby adhering the hydrophobic agent 106 in place with respect to the substrate 102. The nanostructures 104 can be metallic or non-metallic. For metallic nanostructures 104, any metal which dissociates into ions, such as Cu, Au, Ag, Mn, etc., can be used to create nanostructures 104 as described in more detail below. Non-limiting examples of non-metallic nanostructures 104 are silicon nanorods or carbon nanotubes.

[0041] The nanostructures 104 can be thermally conductive, which is important, for example, for membrane distillation where membranes should be thermally conductive and can be used for water desalination. A lot of chemical separations are temperature-dependent and thermal conductivity helps with the efficiency of these applications. The nanostructures 104 may also or alternatively be electrical70273-WO-PCT / TECH-2024-30 conductors, making the membrane 100 useful for battery applications among other things. The nanostructures 104 may also or alternatively be paramagnetic particles or piezoelectric particles, causing the superhydrophobic membrane 100 to be paramagnetic or piezoelectric.

[0042] The nanostructures 104 may also or alternatively have antimicrobial properties, such as antibacterial or antifungal properties. In such embodiments, the superhydrophobic membrane 100 may have antimicrobial properties, which may be desirable in certain applications. However, this is not strictly necessary.

[0043] Regardless of their composition, the shape of the nanostructures 104 impacts the resulting properties of the membrane 100. In particular, the nanostructures 104 should have the morphology of nanorods for better hydrophobicity. Nanorods have an aspect ratio of 1.2 or higher. The aspect ratio of a nanostructure is the ratio of its length to its width. Advantageously, when the nanostructures 104 have a nanorod morphology, the membrane 100 can be more hydrophobic than when the nanostructures 104 are in the form of spheres or cones. However, the nanostructures 104 may nonetheless be or include nano-spheres and / or nano-cones. In some embodiments, the nanostructures 104 include a mixture of morphologies such as a mixture of nanospheres and nanorods.

[0044] The size of the nanostructures 104 may also impact the hydrophobicity of the membrane 100. In general, as the nanostructures 104 increase in size, the hydrophobicity of the membrane 100 decreases. The nanostructures 104 may have an average size of a largest dimension in the range of from about 1 nm to about 100 nm. However, other sizes are possible and encompassed within the scope of the present disclosure. Increasing the size of the nanostructures 104 may also be done to achieve a multiscale architecture with micro-sized and nano-sized particles. In such an alternative embodiment, the micro-sized particles would not be as hydrophobic, though such an architecture may be desirable for certain application.

[0045] As indicated above, the nanostructures 104 may include paramagnetic particles. Non-limiting examples of paramagnetic nanoparticles include iron oxide nanoparticles in their maghemite (γ-Fe2O3) or magnetite (Fe3O4) forms. The nanostructures 104 may also include piezoelectric particles. Non-limiting examples of piezoelectric nanoparticles include zinc oxide (ZnO) or barium titanate (BaTiO3) nanoparticles. It should be appreciated that it is possible to impart magnetic and / or piezoelectric properties to the superhydrophobic membrane 100 by tailoring the properties and composition of the nanostructures 104.

[0046] Referring still to FIG.1, the hydrophobic agent 106 may be any hydrophobic substance which is capable of adhering to the nanostructures 104 and imparting hydrophobicity to the membrane 100. Suitable hydrophobic agents 106 include, but are not limited to, silanes, fatty acids, fluoropolymers, and waxes. Silanes are organosilicon compounds that form a chemical bond with the nanostructures 104. Fatty acids also form a chemical bond with the nanostructures 104, creating a waxy hydrophobic layer by linking the long chain fatty acids to the nanostructures 104 on the substrate 102. Fluoropolymers are hydrophobic70273-WO-PCT / TECH-2024-30 polymer materials which can be coated onto a substrate 102 covered in nanostructures 104 using, for example, an extrusion process to provide extremely low surface energy. These hydrophobic agents 106 can be either derived naturally or synthetically. Long chain fatty acids are among the most economical and ecofriendly of hydrophobic agents 106 because long chain fatty acids are naturally derived. Non-limiting examples of specific hydrophobic agents 106 include 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS- 17), stearic acid, or a combination thereof. Stearic acid, as one example, is cheap, readily available, and biodegradable. In any event, any hydrophobic substance that can be attached to nanostructures 104 can be the hydrophobic agent 106 used to form the membrane 100.

[0047] There are applications for which a combination of both hydrophobic and hydrophilic surfaces is advantageous. Therefore, in some embodiments, the substrate 102 is not entirely covered with the nanostructures 104, and / or the hydrophobic agent 106 does not make a completely uniform layer over all of the nanostructures 104. It will be appreciated that other alternatives are possible and encompassed within the scope of the present disclosure. Furthermore, although the membrane 100 is depicted in FIG.1 as having a generally linear shape, the shape of the membrane 100 does not need to be linear. For example, as one alternative, the membrane 100 may be in the form of a tubular structure.

[0048] Advantageously, the membrane 100 can be fabricated using biodegradable materials. However, this is not strictly necessary.

[0049] With respect to how the membrane 100 can be made, a chemical reaction can be utilized to grow metal or non-metal nanoparticles directly on the substrate 102, providing strong adhesion and uniform distribution of the nanostructures 104. Unlike traditional coating methods which merely deposit particles on the surface, this process can involve in-situ growth, ensuring the nanostructures 104 are firmly anchored to the substrate 102. This results in a more durable and uniformly distributed layer of nanostructures 104, which is important for maintaining consistent hydrophobic properties over time.

[0050] In-situ nanoparticle growth on various materials using chemical reactions to tune the properties of the substrates surface is effective in producing tailored materials according to the need of the particular application. Instead of depositing nanoparticles, in-situ growth of nanoparticles involves the chemical transformation of precursors into functional nanoparticles. The nanoparticles nucleate and grow on active sites of the macromolecular chains resulting high adhesion of nanoparticles to the polymer surface. The existing traditional coating techniques are complex and non-scalable compared to in-situ nanoparticle growth. The surface properties such as high surface area for hydrophobic compound linking, high surface roughness, thermal conductivity, anti-bacterial, anti-fouling, and multi-hierarchical structures can be tuned with traditional coating techniques. The choice of materials (metals and non-metals) that can be coated using traditional coating methods such as chemical vapor deposition, spray coating, and deposition is also limited compared to in-situ nanoparticle growth.70273-WO-PCT / TECH-2024-30

[0051] The membrane 100 can be prepared from a facile two-step process. The first step involves an in-situ growth of nanoparticles using displacement chemical reactions. Typically, a metal or non-metal is grown on the surface of the substrate 102. In the case of a metal, a metal salt such as a metal sulfate or a metal nitrate reacts with a hydroxide to form metal hydroxide nanostructures. This reaction is as follows: Metal salt (M) + Hydroxide → Metal Hydroxide + sulfate / nitrate (1)

[0052] Examples of reaction (1) include, but are not limited to, the following: Example 1: CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4 Example 2: NiSO4 + 2NaOH → Ni(OH)2 + Na2SO4 Example 3: ZnSO4+ 2NaOH → Zn(OH)2+ Na2SO4Example 4: CuSO4 + 2KOH → Ni(OH)2 + K2SO4 Example 5: NiSO4 + 2NaOH → Ni(OH)2 + Na2SO4 Example 6: Cu(NO3)2+ 2NaOH → Cu(OH)2+ 2Na(NO3)

[0053] In some embodiments, the substrate 102 is first dipped into a 1M metal salt solution for a period of time, such as about 15 minutes, then dipped in a solution of 1M NaOH solution for a period of time, such as about 1 minute, to enable the growth of nanoparticles. Then, the substrate 102 is dried at room temperature to remove moisture. The in-situ nanoparticle growth method involves the direct synthesis of the nanostructures 104 on the substrate 102 by controlling reaction conditions such as the concentration of metal salts, hydroxides, reaction times, and temperatures. This process creates a variety of nanostructures 104 that significantly enhance the properties of the substrate 102 for specific applications.

[0054] One type of nanostructure 104 that can be formed is spherical nanoparticles. Metal oxide nanoparticles, such as copper oxide (CuO) and zinc oxide (ZnO), are easily produced using this method. These nanoparticles are uniformly distributed across the substrate 102, enhancing properties such as catalytic activity and antibacterial effects. For instance, CuSO₄ reacting with NaOH forms Cu(OH)₂ nanoparticles, which can be further processed to CuO. Additionally, one-dimensional structures such as nanorods and nanowires can be synthesized by adjusting reaction parameters. These structures have high aspect ratios and provide increased surface area, which is beneficial for applications in catalysis and sensors.

[0055] In some embodiments, the nanostructures 104 are spherical. For example, when the hydrophobic agent includes one or more silanes, the nanostructures 104 may be spherical nanoparticles (e.g., Cu oxide nanospheres). Silanes can be used in high temperatures and the reaction is different in the sense that the silanes react to the nanostructures 104 when the nanostructures 104 are oxides.

[0056] Two-dimensional structures such as nanoplates and nanosheets can also be formed, offering large surface areas and unique electronic properties. For example, ZnSO₄ reacting with NaOH can produce Zn(OH)₂ nanoplates, which can be converted to ZnO nanosheets, useful in electronic and optical70273-WO-PCT / TECH-2024-30 applications. Hierarchical nanostructures, such as nanoflowers composed of petal-shaped nanoparticles, provide multi-hierarchical surfaces that significantly enhance hydrophobicity and other surface interactions. This complex structure increases surface roughness, which is important for creating superhydrophobic surfaces.

[0057] Specialized nanostructures, such as hollow cylindrical nanotubes, can be formed under specific conditions, offering high surface area and potential for encapsulating other materials. These are useful in applications such as drug delivery and catalysis. Controlled growth can also result in well-defined geometric shapes like nanocubes and nanoprisms, which exhibit specific optical and electronic properties, beneficial for applications requiring precise control over physical properties. Additionally, core-shell structures can be created by sequentially adding different metal salts, combining the properties of both materials. For instance, a core of CuO nanoparticles can be coated with another material to enhance its properties.

[0058] Reacting CuSO4 with NaOH results in the formation of Cu(OH)2 nanoparticles, which can take various forms such as spherical particles, nanorods, or hierarchical nanoflowers. Further processing can convert Cu(OH)2 to CuO, enhancing its catalytic and antibacterial properties. Similarly, NiSO₄ reacting with NaOH forms Ni(OH)2 nanoparticles, which can be tailored into different morphologies by adjusting reaction conditions. These nanoparticles are valuable in energy storage devices such as batteries and supercapacitors due to their high surface area and conductivity. ZnSO4 reacting with NaOH produces Zn(OH)2 nanoparticles and controlling reaction parameters can form structures such as nanoplates or nanosheets, which can then be converted to ZnO. These are useful in photocatalysis, sensors, and electronics due to their excellent optical and electronic properties.

[0059] The versatility of the in-situ nanoparticle growth method allows for the formation of a wide range of nanostructures 104 with tailored properties. This method can be applied to metal salts and extended to non-metal precursors, providing flexibility in synthesizing various nanostructures 104. The ability to control the size, shape, and distribution of nanoparticles directly on substrates makes this method highly valuable for customizing material properties for applications in filtration, catalysis, sensors, electronic devices, and superhydrophobic surfaces. The precise control over nanostructure formation ensures consistent and desirable properties, enhancing the performance of the resulting materials in various industrial and research applications.

[0060] A second step of the process for making the membrane 100 can involve the superhydrophobic modification of the nanostructure-coated substrate using the hydrophobic agents 106. In some embodiments, the dried nanostructure-coated substrate is dipped into a solution of an organic solvent, such as the hydrophobic agent ethanol, for a period of time, such as about 10 minutes. The long chain fatty acids and silanes chemically bond with the nanostructures through hydrolysis, condensation, and siloxane-CuO70273-WO-PCT / TECH-2024-30 bonding. The reactions are as follows: Example 1 (Fatty acid): Cu(OH)2+ 2C17H35COOH → Cu(C17H35COO)2+ 2H2O Example 2 (silane): C8F17C2H4Si(OCH3)3+ 3H2O → C8F17C2H4Si(OH)3+ 3CH3OH (hydrolysis) C8F17C2H4Si(OH)3→(C8F17C2H4SiO2)n+3H2O (condensation) CuO−OH+C8F17C2H4Si(OH)3→CuO−O-Si(C8F17C2H4)n+H2O (siloxane-CuO bonding)

[0061] FIG.2 depicts a non-limiting example method for making superhydrophobic membranes. In this example, a superhydrophobic membrane is formed from the superhydrophobic modification of Cu- coated Kimwipes® tissues using stearic acid. FIG.3 shows another non-limiting example method for making a superhydrophobic membrane. In this example, the superhydrophobic membrane is formed from the superhydrophobic modification of Cu-coated Kimwipes® tissues using FAS-17.

[0062] Changes in concentration of the metal solution do not have any significant effect on the growth of Cu nanoparticles. The minimum concentration of metal salt to ensure the saturation of substrate with metal is 0.1 M. The concentration used in the examples herein to demonstrate the successful growth was 0.5 M, which was ideal to grow nanoparticles uniformly across the substrate. The high concentration led to higher nucleation rate resulting in growth of small nanoparticles whereas low concentration led to the growth of larger nanoparticles.

[0063] Adjusting the concentration of reducing agent (e.g., a hydroxide) can provide the ideal environment for nanoparticle growth. The concentration of hydroxide in the solution is also important for adjusting the pH of the solution for enabling the growth of nanoparticles. Appropriate pH is important to stabilize the nanoparticle growth and prevent agglomeration. In the examples described herein, 1M hydroxide concentration was used and was ideal for uniform growth.

[0064] The concentration of fatty acid or silane to ensure completion of reaction and uniform coating of hydrophobic material on the surface has also been evaluated. It has been found that 0.035 M of fatty acid or silane leads to an efficient and complete reaction. At least 0.02M is important for completing the reaction and ensuring the silane or fatty acid is not the limiting reagent. However, other concentrations are possible and encompassed within the scope of the present disclosure.

[0065] The soaking time in each solution also affects the growth of the nanostructures 104 on the substrate 102. The soaking time of the substrate 102 in the metal solution is dependent on the substrate material, as, for best results, the substates 102 should be dipped in each solution until the solution penetrates completely into the substrate 102. In the case of Kimwipes® tissues or another cellulose-based substrate 102, 10 minutes of soaking time has been found to be sufficient to saturate the substrate 102. The soaking time in the hydroxide solution controls the growth of the layer of nanostructures 104 on the substrate 102. The longer dipping time ensures the complete of reaction and results in uniform growth of the nanostructures 104. It has been found that 3 minutes of dipping time is ideal for uniform and complete70273-WO-PCT / TECH-2024-30 growth of the nanostructures 104. However, other times and procedures are possible and encompassed within the scope of the present disclosure.

[0066] The nanostructure-coated substrate can be dried to remove the water completely to prevent the overgrowth of the layer of hydrophobic agent 106. The presence of water results in a very thick, flaky formation of hydrophobic material. It has been found that an ideal coating of hydrophobic agents 106 can be formed after dipping the dried nanostructure-coated substrate in the hydrophobic agent solution for 10 minutes.

[0067] The method described herein of growing nanostructures on substrates followed by hydrophobic modification involves a carefully controlled two-step process designed to achieve uniform and adherent nanostructure coatings with tailored surface properties. The first step is the in-situ growth of nanoparticles on the substrate using displacement chemical reactions. This involves immersing the substrate in a metal salt solution, such as copper sulfate or nickel sulfate, followed by immersion in a hydroxide solution, typically sodium hydroxide. This reaction forms metal hydroxide nanostructures on the substrate surface. The substrates are initially dipped into a 1 M metal salt solution for 15 minutes, allowing metal ions to adsorb onto the substrate, and then transferred to a 1 M NaOH solution for 1 minute to facilitate the growth of nanoparticles. This process is followed by drying the substrate at room temperature to ensure complete removal of moisture, which is important for achieving a stable and uniform nanoparticle layer.

[0068] The concentration of the reactants plays a significant role in the nanostructure growth process. The correct concentration of metal salts is important to saturate the substrate and promote uniform nanoparticle formation. In this method, a concentration of 0.5 M metal salt solution was found to be ideal, ensuring a high nucleation rate and the growth of small, evenly distributed nanoparticles. However, it is noted that a minimum concentration of 0.1 M is important to achieve saturation. The hydroxide concentration is equally important, with a 1 M NaOH solution providing the ideal pH environment for nanoparticle growth. This concentration helps stabilize the nanoparticles and prevent their agglomeration, ensuring that the particles remain well-dispersed across the substrate.

[0069] Once the nanoparticles are grown and the substrate is dried, the next step involves the hydrophobic modification of the nanoparticle-coated surface. This is achieved by dipping the substrate in a hydrophobic agent solution, typically composed of long-chain fatty acids or silanes dissolved in ethanol. The substrate can be immersed in this solution for about 10 minutes, during which time the hydrophobic agents chemically bond with the nanostructures. For example, stearic acid reacts with copper hydroxide to form copper stearate, a process that imparts a hydrophobic, waxy layer to the surface. Similarly, silanes undergo hydrolysis and condensation reactions to form a stable, hydrophobic siloxane layer. The concentration of the hydrophobic agents is important for this step, with 0.035 M for fatty acids and 0.01 M70273-WO-PCT / TECH-2024-30 for silanes being ideal to ensure a complete and uniform coating. This two-step process offers several advantages over traditional coating methods. The in-situ growth of nanostructures ensures high adhesion and uniform distribution on the substrate, which is important for maintaining the desired surface properties. Traditional methods, such as chemical vapor deposition or spray coating, often result in less uniform coatings and limited material options. Additionally, the use of naturally derived hydrophobic agents, such as long-chain fatty acids, is both economical and environmentally friendly compared to synthetic alternatives. This method not only enhances the superhydrophobic characteristics of the substrate but also provides additional benefits such as increased surface roughness, improved thermal conductivity, and antibacterial properties, making it suitable for a wide range of applications, including filtration, textiles, and medical devices.

[0070] Though it is understood that the membranes described herein can nonetheless be prepared by other processes, the process described herein has numerous advantages. The two-step process of in-situ nanoparticle growth followed by hydrophobic modification ensures strong adhesion and durability of the hydrophobic layer. By growing nanoparticles directly on the substrate, this method achieves strong chemical bonding, resulting in a coating that is more durable and less likely to peel off or wear away compared to traditional surface coatings. This strong adhesion ensures that the hydrophobic properties remain effective over a longer period, even under mechanical stress or environmental exposure, which is a significant improvement over traditional techniques such as spray coating or chemical vapor deposition that often result in weaker adhesion and durability issues.

[0071] The process is effectively a method for growing metal or non-metal nanostructures directly on substrates via in-situ chemical reactions, ensuring strong adhesion and uniform distribution. The two- step process involves in-situ nanoparticle growth followed by applying hydrophobic agents such as long- chain fatty acids (e.g., stearic acid) or silanes (e.g., FAS-17), resulting in superhydrophobic properties. This process is applicable to a wide range of substrates, including cellulose filters, tissue papers, polysulfone membranes, cotton fabrics, and metallic surfaces, making it versatile for various industries like filtration, textiles, construction, and medical devices. The technology achieves significantly higher oil permeation flux, absorption rates, and separation efficiencies compared to conventional membranes. The process utilizes naturally derived hydrophobic agents, making the process more economical and environmentally friendly, with straightforward and scalable steps involving simple immersion and drying.

[0072] The process described herein also allows for the precise control of nanostructure size and density, ensuring a uniform distribution across the substrate. By adjusting the concentration of reactants and immersion times, the process can be tailored to achieve specific surface properties. This level of control is challenging to achieve with traditional methods such as dip-coating or spray coating, which often result in uneven coatings with inconsistent hydrophobic properties. The ability to produce a uniform and70273-WO-PCT / TECH-2024-30 controlled nanostructure layer translates into consistent and reliable performance of the hydrophobic surface.

[0073] The in-situ nanostructure growth process is straightforward and easily scalable, making it suitable for industrial applications. The process involves simple immersion and drying steps that do not require complex equipment or controlled environments, unlike techniques such as chemical vapor deposition. This simplicity allows for easy integration into existing manufacturing workflows and facilitates large-scale production. The scalability and simplicity of this method make it a practical choice for creating hydrophobic surfaces in a cost-effective and efficient manner.

[0074] Overall, the process is characterized by the combination of strong adhesion, uniformity, scalability, multifunctionality, eco-friendliness, and the ability to form tailored nanostructures. These advantages make the process a superior alternative to traditional hydrophobic modification techniques, offering enhanced performance and broader applicability in various fields.

[0075] Using naturally derived hydrophobic agents, such as long-chain fatty acids, this two-step process is both economical and environmentally friendly. These materials are more sustainable and less expensive than synthetic alternatives such as fluoropolymers. Additionally, the process avoids the use of harmful chemicals and excessive energy consumption, reducing its environmental impact. Traditional methods often involve toxic chemicals and high-energy processes, contributing to higher costs and environmental pollution. By contrast, the process described herein can use eco-friendly materials, making it a greener and more cost-effective option for creating hydrophobic surfaces.

[0076] The two-step process of in-situ nanoparticle growth followed by hydrophobic modification can be applied to a wide array of substrates, enhancing their water-repellent properties. Cellulose-based materials such as filters and tissue papers can benefit significantly from this treatment, as it helps maintain their structural integrity and performance in wet conditions. Similarly, polymer membranes, including polysulfone and other types used in filtration and separation processes, can be modified to improve their chemical resistance and durability. Textiles and fabrics, both natural like cotton and synthetic-like polyester, can be made hydrophobic, making them suitable for outdoor clothing, protective gear, and industrial applications.

[0077] In addition to organic substrates, the process described herein is effective on various inorganic materials. Metallic surfaces, including metal sheets, foils, and meshes, can be treated to enhance their resistance to corrosion and water damage, which is particularly useful in construction and automotive industries. Hydrophilic materials such as glass and ceramics can also be modified to repel water, reducing issues like fogging and improving durability. Other substrates such as wood and concrete can be made water-repellent, protecting them from moisture damage and extending their lifespan in outdoor and marine environments. This versatile process provides a practical solution for imparting hydrophobic properties to a70273-WO-PCT / TECH-2024-30 diverse range of materials, making it valuable across multiple industries.

[0078] Various surface characterization techniques can be utilized to evaluate the surface of a hydrophobic article, and therefore to confirm the production of the superhydrophobic membrane as described herein. The strength of the coating’s adhesion to the substrate is typically evaluated using the scotch tape test. This test assesses the coating’s ability to remain adhered to the base surface or substrate. Scanning Electron Microscope (SEM) imaging can be employed to capture surface morphologies. A goniometer can be used to determine various contact angles (static, advancing, and receding) of the coated substrate, which helps assess the hydrophobicity and oleophilicity of the surfaces. Hydrophobicity of a material is defined as its ability to repel water, characterized by a high contact angle where water droplets do not spread out but rather form beads on the surface. Hydrophobic surfaces have a very poor affinity for water. Oleophilicity is the property of a material that describes its affinity for oils. Oleophilic surfaces attract and absorb oils, enabling them to wick oil quickly and efficiently. This characteristic is beneficial in applications such as oil spill cleanup, lubrication, and filtration, where the ability to interact with and retain oils is crucial. A higher oil wicking rate and / or wicked volume of the surfaces result in higher porous and oleophilic surfaces. A higher wicking rate is also indicative of better interconnection and tunnel network among the neighboring pores.

[0079] In some embodiments, the process described herein coats a nanostructure-covered substrate with hydrophobic agents such as fatty acids or silanes, which bond chemically to the nanostructures, imparting superhydrophobic properties. The use of chemical bonding ensures a robust hydrophobic layer that is less likely to degrade or wash away compared to physical coatings. This approach enhances the longevity and effectiveness of the hydrophobic surface, which is important for applications exposed to harsh environments.

[0080] The process described herein may use naturally derived hydrophobic agents such as long- chain fatty acids, making it an economical and eco-friendly alternative to synthetic hydrophobic compounds. The use of naturally derived agents not only reduces costs but also minimizes environmental impact. Unlike synthetic hydrophobic agents, which can be expensive and environmentally harmful, long- chain fatty acids offer a sustainable solution without sacrificing effectiveness.

[0081] The process is straightforward and scalable, involving simple immersion and drying steps that do not require complex equipment or controlled environments. The simplicity of the process makes it suitable for large-scale industrial applications. Unlike techniques such as chemical vapor deposition, which require specialized equipment and controlled conditions, this method can be easily integrated into existing manufacturing processes, reducing setup and operational costs. However, the superhydrophobic membranes can be created through other processes, and such other processes are encompassed within the scope of the present disclosure.70273-WO-PCT / TECH-2024-30

[0082] The membranes described herein achieve an oil permeation flux significantly higher than conventional superhydrophobic membranes, enabling rapid separation of oil from water. The high oil permeation flux means that this technology can separate oil from water much faster than existing superhydrophobic membranes. This makes the membranes highly effective for applications such as oil spill cleanup, where quick and efficient separation is important.

[0083] The membranes also exhibit a high absorption rate for low surface tension liquids, ideal for applications such as oil spill remediation. The superior absorption rate of these membranes means they can absorb large quantities of oil quickly, making them exceptionally effective for environmental cleanup efforts. This contrasts with many conventional hydrophobic membranes, which often have lower absorption capacities and slower rates.

[0084] The membranes demonstrate a separation efficiency greater than other materials for octane / water separations, indicating superior performance in selective permeability. The high separation efficiency ensures that the membrane can effectively filter out oil while allowing water to pass through, making it highly suitable for industrial and environmental applications where precise separation is required. Traditional materials often struggle to achieve such high efficiency rates.

[0085] Furthermore, the Cu-coated membranes described herein exhibit anti-bacterial and anti- biofouling properties, making them suitable for wastewater treatment with high organic content. The addition of anti-bacterial and anti-biofouling properties enhances the functionality of the membranes, making them not only hydrophobic but also resistant to microbial growth. This is particularly important for applications in wastewater treatment, where maintaining cleanliness and preventing biofouling are critical.

[0086] In some embodiments, the superhydrophobic membranes described herein are also biodegradable, offering an environmentally friendly solution compared to plastic-based membranes. The use of biodegradable materials addresses environmental concerns associated with plastic waste. These membranes provide a sustainable alternative that can break down naturally, reducing the long-term environmental impact and offering a green solution for various applications.

[0087] The membranes can be used for a multitude of different applications. The membranes can be used for oil spill remediation, providing rapid and efficient absorption of oil from water, making them ideal for cleaning up oil spills in marine and freshwater environments. The membranes can be used for wastewater treatment, and are effective in treating wastewater with high organic content due to their anti- bacterial and anti-biofouling properties. The membranes can be used for industrial filtration, to separate oil from water in various industrial processes, improving efficiency and reducing environmental impact. The membranes can be used in textiles and fabrics, applied to outdoor clothing and protective gear to make them water-repellant and durable against environmental exposure. The membranes can be used in medical devices, to create medical textiles and filters that are hydrophobic and anti-bacterial, enhancing hygiene and70273-WO-PCT / TECH-2024-30 safety. The membranes can be used in construction materials, applied to metallic surfaces, wood, or concrete to enhance their resistance to moisture and corrosion, extending their lifespan in outdoor and marine environments. The membranes can be used in the automotive industry, on vehicle surfaces and components to prevent corrosion and improve durability against water exposure. The membranes can be used in electronics, making water-repellent surfaces for electronic devices and protecting them from moisture damage. The membranes can be used to create biodegradable membranes for various environmental protection applications and reducing reliance on plastic-based materials. The membranes can also be used in consumer products, applied to everyday items such as wipes, tissues, and filters to enhance their water-repellent properties and performance in household and commercial settings.

[0088] The superhydrophobic membranes are a biodegradable, environmentally friendly solution to plastic based membranes. The superhydrophobic membranes are cost-effective and can be made into oil- absorbing wipes or oil / water filters through a facile process. The entire fabrication process can be environmentally friendly and easily scalable. Furthermore, the superhydrophobic membranes offer ultralow surface tension, excellent liquid absorption, and ultrafast separation.

[0089] EXAMPLES

[0090] Superhydrophobic membranes with ultrafast oil / water separation capacity and high oil absorption capacity were fabricated using facile chemical in-situ metal nanoparticle growth followed by superhydrophobic modification. The fabricated membranes possess extremely fast low surface tension liquid wicking capabilities. The entire fabrication process and the fabricated membranes are environmentally friendly. The fabricated membranes are capable of 99.5% low surface tension liquid / water separation. The metal coatings of superhydrophobic membranes make them thermally conductive, opening up new avenues of applications. The use of Kimwipes®tissues as substrates addresses the issues of low oil permeation flux suffered by superhydrophobic membranes currently available commercially. The existing hydrophobic materials pose high economic challenges due to their limited absorption capacities. The modification of Kimwipes®tissues into superhydrophobic membranes creates opportunities for improved separations especially when dealing with dispersions involving low surface tension liquids and water.

[0091] The superhydrophobic membranes described in these examples are capable of separation efficiency > 99.5% for octane / water separations, n-hexane / water separations, and oil / water separations. Conventional superhydrophobic membranes suffer from low oil permeation flux. The superhydrophobic membranes described in these examples enable extremely fast separations with an oil permeation flux close to 320 L·m-2h-1. The superhydrophobic membranes also have a high absorption rate of low surface tension liquids with high absorption capacities making them ideal candidates for oil spill remediation. The Cu- coated superhydrophobic membranes described in these examples also exhibit anti-bacterial and anti- biofouling properties, making them suitable for wastewater treatment with high organic content. The70273-WO-PCT / TECH-2024-30 superhydrophobic membranes are also biodegradable, making them environmentally friendly.

[0092] Materials and methods

[0093] Gravimetric analysis was performed to measure the absorption capacity and absorption rate of the oleophilic substrate. The absorption capacity was determined by immersing the superhydrophobic membranes in coconut oil and measuring the weight before and after immersion. The absorption capacity ^ ^ ^^was calculated using the formula ^ ^ ^ = ^ ^^ ^^t^ (^^.1), where w is the weight of superhydrophobicmembranes after immersing in oil, and w is the weight of superhydrophobic membrane before immersing0 in oil. Additionally, the absorption capacity in percentage (also referred to as absorption rate) was ^^^^ ^( ) calculated using ^ % = × 100 (^^.2), where w is the weight of the superhydrophobic membranet^ ^^after immersing in oil, and w0is the weight of the superhydrophobic membrane before immersing in oil.

[0094] To determine the absorption rate, the absorption capacity was recorded every 5 seconds from 10 seconds to 35 seconds. The absorption rate was then calculated by finding the slope of the absorption capacity versus time curve. This comprehensive gravimetric analysis allows for a detailed understanding of both the absorption capacity and rate, providing valuable insights into the performance of the oleophilic substrate.

[0095] Separation efficiency is an important parameter for evaluating the performance of superhydrophobic materials in separating low surface tension liquids, such as octane, from other substances. ^^( ) This efficiency is calculated using the formula ^ % = × 100 (^^.3), where m represents the mass of1^ ^^the low surface tension liquid (octane) that has successfully permeated through the superhydrophobic stearic acid / Cu modified membrane, and m denotes the initial mass of the octane. By determining the ratio0 of the permeated mass to the initial mass and converting it to a percentage, this metric provides a clear indication of how effectively the superhydrophobic membrane can separate and allow the passage of octane while repelling water and other contaminants. High separation efficiency reflects the superior performance of the material in applications requiring selective permeability, such as oil spill cleanup, wastewater treatment, and industrial filtration processes.

[0096] The low surface tension liquid permeation flux is an important metric for assessing the efficiency of superhydrophobic materials in separating liquids such as octane from other substances. This ^flux is calculated using the formula ^ = × 100 (^^.4), where V represents the volume of the octane^×^that permeates through the material, A the effective area of the material in contact with theoctane, and t is the time required for the separation process. To measure this flux, a specified volume of octane was allowed to pass through the stearic acid / Cu superhydrophobic membrane, and the volume that permeates was collected and measured over a set period. The effective contact area of the Kimwipes® tissue (i.e., the substrate without nanostructures or the hydrophobic agent) with the octane was also70273-WO-PCT / TECH-2024-30 measured to ensure accurate calculation. The resulting permeation flux indicates how quickly and efficiently the material can separate octane from water. High permeation flux values signify rapid and efficient separation, which is vital for applications in environmental cleanup, such as oil spill recovery, as well as in industrial processes where quick and effective separation of oil from water is necessary. This metric helps in tailoring the design and functionality of superhydrophobic materials for various practical application.

[0097] In these examples, Kimwipes® tissue, a type of cellulosic substrate, was chosen to demonstrate the capability of superhydrophobic coatings. The Kimwipes® tissues were modified by coating them with metal nanoparticles (e.g., copper) followed by hydrophobic modification using stearic acid or FAS-17. The two-step in-situ growth and hydrophobic modification process significantly enhanced the separation efficiency of superhydrophobic materials. The in-situ growth of metal nanoparticles on substrates, followed by hydrophobic modification using agents such as stearic acid or FAS-17, created a highly uniform and strongly adherent hydrophobic layer. This layer selectively permeates low surface tension liquids such as oils while repelling water, achieving high separation efficiency. The modified superhydrophobic substrates exhibit higher permeation flux for low surface tension liquids compared to traditional superhydrophobic membranes. The in-situ growth of metal nanoparticles created a highly porous structure with interconnected pathways, allowing for faster and more efficient oil permeation. This structural modification enhanced the overall permeation flux. The superhydrophobic materials produced by this method have a higher absorption capacity and rate for low surface tension liquids. The uniform coating of nanoparticles and subsequent hydrophobic modification improved the wicking ability and absorption properties of the substrates. This resulted in materials that can absorb larger quantities of oil at a faster rate, making them highly effective for applications such as oil spill remediation.

[0098] A simple gravity filtration system was employed as shown in FIG.4 for testing the separation efficiency. To quantify the separation efficiency, a known volume of oil and water were simultaneously poured into the superhydrophobic membrane as illustrated in FIG.4. The time required to completely separate oil from water was recoded to measure the separation rate, and the quantity of the oil collected was recorded to calculate the separation efficiency. To quantify the absorption capacity, a known volume of oil and water was stored in a beaker. The time required to completely separate oil from water was recorded to measure the separation rate, and the quantity of the oil collected was recorded to calculate the separation efficiency.

[0099] Example 1 – Cu coated Kimwipes with stearic acid superhydrophobic modification

[0100] The membranes were fabricated as shown in FIG.2, which depicts the superhydrophobic modification of Cu-coated Kimwipes®tissues using stearic acid, and the membranes were characterized and tested for separation efficiency, permeation flux, absorption capacity, and absorption rate.70273-WO-PCT / TECH-2024-30

[0101] As shown in FIG.2, a Kimwipes®tissue was dipped in a beaker containing 0.5 M CuSO4·5H2O (FIG.2 (i)). After 10 minutes, the Kimwipes®tissue was transferred and dipped in the second beaker (FIG.2 (ii)) containing 1 M NaOH for just 5 seconds and then dried for 8 hours. The Kimwipes®tissue was then dipped into the third beaker (FIG.2 (iii)) which contained 0.035 M stearic acid / ethanol for 10 minutes. The stearic acid dissolved in the ethanol. This is where the hydrophobic modification using stearic acid happens. The Kimwipes®tissue was then removed from the third beaker and dried for 8 hours. Stearic acid forms a thick layer of wax on the membrane, which is why allowing the Kimwipes®tissue to dry is best. This resulted in the superhydrophobic membrane (FIG.2 (iv)).

[0102] The scanning electron microscopy imaging shown in FIGS.5A-5B, confirms the presence of Cu nanorods grown using the in-situ nanoparticle growing process. FIG.5A shows a SEM image of a Kimwipes® tissue and FIG.5B shows a SEM image of a Cu-coated Kimwipe®tissue. The Cu nanoparticles on the Cu-coated Kimwipe®tissue can be observed in FIG.5B. The nanorods shown in FIG. 5B act as an active reaction site for chemically bonding stearic acid to the surface of the substrate.

[0103] The wetting behavior of the stearic acid modified wipes was confirmed by measuring the water contact angle of the membrane. The water contact angle of the stearic acid modified membrane was 148 °. The water contact angle of 148° confirms the superhydrophobicity of the membrane. FIG.6 shows the water contact angles of a stearic acid / Cu coated superhydrophobic membrane.

[0104] A tape test was performed according to ASTM D3359 to measure the adhesion strength of stearic acid modified membrane, and it was found that even 3 continuous adhesions and peelings of tape did not result in removal of the hydrophobic layer.

[0105] The separation efficiency of the superhydrophobic membrane made from Cu / stearic acid- modified Kimwipes® tissues was estimated using the test setup shown in FIG.4. The membrane successfully separated the red colored water from the colorless low surface tension. The low surface tension liquid (octane) permeated the membrane and collected in the bottom of the beaker with the colored water at the top of the membrane. The separation efficiency calculated using Eq.3 is 95.4% for the stearic acid modified membrane. The oil / water separation is shown in FIG.7. The separation was enabled by the hydrophobic stearic acid coating. The rate of separation for the membrane was measured using Eq.4, and the permeation flux was 328 L.m-2.h-1.

[0106] The absorption of coconut oil by the superhydrophobic membrane is shown in FIG.8. The absorption capacity of the superhydrophobic membrane was measured using Eq.1 and Eq.2. The coconut oil absorption capacity of the superhydrophobic membranes was around 581%. FIG.9 shows the absorption capacity of stearic acid / Cu coated superhydrophobic membrane recorded every 5 seconds starting from 10 secs to 35 secs. The absorption rate of the superhydrophobic membranes was 6.81 g / g at 20 secs which slightly increased to 7.0 g / g at 25 secs and remained constant further. The absorption rate70273-WO-PCT / TECH-2024-30 found by calculating the slope of curve shown in FIG.9 was 0.14 g / sec.

[0107] Example 2 – Cu-coated Kimwipes with FAS-17 superhydrophobic modification

[0108] The membranes were fabricated as shown in FIG.3, which depicts the superhydrophobic modification of Cu-coated Kimwipes® tissues using FAS-17. The membranes were characterized and tested for separation efficiency, permeation flux, absorption capacity, and absorption rate.

[0109] As shown in FIG.3, a Kimwipes®tissue was dipped in a beaker containing 0.5 M CuSO4·5H2O for 10 minutes (FIG.3 (i)). The Kimwipes®tissue was then dipped in a second beaker (FIG. 3 (ii)) which contains 1 M NaOH for 5 seconds and then dried for 8 hours. The Kimwipes®tissue was then dipped in a third beaker (FIG.3 (iii)) containing 0.5 M NaBH4 for 10 minutes. The Kimwipes®tissue was then removed and dried for 8 hours. The Kimwipes®tissue was then dipped in a fourth beaker (FIG.3 (iv)) containing 0.01 M FAS-17 / ethanol for 10 minutes. The Kimwipes®tissue was then removed from the fourth beaker (FIG.3 (iv)) and left to dry for 8 hours. This completed the process and the Kimwipes®tissue had been transformed into a superhydrophobic membrane (FIG.3 (v)).

[0110] The SEM image shown in FIG.10A confirms the presence of Cu nanorods grown using the in-situ nanoparticle growing process. The nanorods seen in the SEM image in FIG.10B act as an active reaction site for chemically bonding stearic acid to the surface of the substrate.

[0111] The wetting behavior of the FAS-17-containing membrane was confirmed by measuring the water contact angle of the membrane. The water contact angle of the FAS-17-containing membrane was about 140°, as shown in FIG.11. The water contact angle of 140° confirms the superhydrophobicity of the membrane.

[0112] A tape test was performed according to ASTM D3359 to measure the adhesion strength of stearic acid modified membrane and it was found that even 5 continuous adhesions and peelings of tape did not result in removal of the hydrophobic layer.

[0113] The separation efficiency of the superhydrophobic membrane was estimated using the test setup shown in FIG.4. The membrane successfully separated the red colored water from the colorless low surface tension. The low surface tension liquid (octane) permeated the membrane and collected in the bottom of the beaker with the colored water at the top of the membrane. The separation efficiency calculated using Eq.3 was 96.2% for the FAS-17 modified membrane. The oil / water separation is shown in FIG.12. The separation was enabled by the hydrophobic FAS-17 coating. The rate of separation for the membrane was measured using Eq.4, and the permeation flux was 348 L.m-2.h-1.

[0114] The absorption capacity of the membrane was measured using Eq.1 and Eq.2. The coconut oil absorption capacity of the superhydrophobic membranes was around 526%. The absorption rate of the membrane is shown in FIG.13. The absorption rate of the superhydrophobic membranes was 6.2 g / g at 20 secs which slightly increased to 6.6 g / g at 25 secs and remained constant further. The absorption rate found70273-WO-PCT / TECH-2024-30 by calculating the slope of curve shown in FIG.13 was 0.15 g / sec.

[0115] The fast separation of 320 Lm-2h-1with 99.5% separation of octane / water and the high absorption capacities of 6.81 gram of oil / gram of membrane provide for extremely high oil / water separation rates and high absorption capacity of low surface tension liquids. The oil permselective absorbance leaving water behind can be very helpful for oil spill remediation and oil clean up while being environmentally friendly biodegradable membranes. The ecofriendly superhydrophobic membranes have excellent anti- bacterial and anti-biofouling properties while being ultrathin with a reduced thickness of around 150 μm and ultralight. This process requires only 2 steps which makes the fabrication easy. The low fabrication and material cost of stearic acid (2.60 $ lb) and silanes (5000 $ lb) are also advantages. The superhydrophobic membranes are compact and have reduced density while being thermally conductive from the metallic particles that are used.

[0116] Example 3 – Two step In-situ Nanoparticle Growth and Superhydrophobic Coating Process

[0117] A variety of different substrates were used in this example. The substrates include a polyurethane foam (FIG.15A), a cotton fabric (FIG.15B), cellulose wipes (FIG.15C), and polysulfone films (FIG.15D). Each of these substrates was coated with a membrane and various tests were performed to evaluate their effectiveness.

[0118] Immersion test of membrane

[0119] The coated substrates were immersed in deionized water for 24 hours according to the procedure reported in ASTM D870-15 (2020) to study the life of the coatings, as illustrated in FIGS.16A- 16B. The coated substrates demonstrated long term hydrophobic effects, even when in contact with water for extended periods. The results showed no signs of blisters, swelling, peeling, or loss of adhesion. This means that the membrane coated substrates are suitable for marine, outdoor, food processing, bathroom, and kitchen applications.

[0120] Tape test of membrane

[0121] The coated substrates were taped and peeled according to the procedure reported in ASTM D3359 to study the adhesion of the membranes as shown in FIGS.17A-17B. The membrane coated substrates demonstrated a strong adhesion of the membrane coating. The results showed no decrease in hydrophobicity, no flaking, no delamination, and improved resistance to mechanical stress. This means that the membrane coated substrates are suitable for normal handling, wiping, and touching.

[0122] Abrasion test of membrane

[0123] The coated substrates were touched by multiple fingers, and abrasion cycles were run using sandpaper according to the procedure reported in ATSM D8380-21 to study the resistance against external stimuli as shown in FIGS.18A, 18B, and 18C. FIG.18A shows the touch test. In this example, the membrane was touched 100 times by fingers. FIG.18B shows the dry abrasion test using sand paper.70273-WO-PCT / TECH-2024-30 FIG.18C shows water droplets on the membrane after abrasion cycles were performed. The membrane coated substrates demonstrated no loss of hydrophobicity and improved resistance to real world handling such as dust, sand, oil, and sweat from frequent touches and rubs.

[0124] Certain embodiments of the compositions and methods disclosed herein are defined in the above examples. It should be understood that these examples, while indicating particular embodiments of the invention, are given by way of illustration only. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this disclosure, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt the compositions and methods described herein to various usages and conditions. Various changes may be made and equivalents may be substituted for elements thereof without departing from the essential scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof.

Claims

70273-WO-PCT / TECH-2024-30 CLAIMS What is claimed is:

1. A superhydrophobic membrane comprising: a substrate; nanostructures disposed on the substrate; and a hydrophobic agent attached to the nanostructures.

2. The superhydrophobic membrane of claim 1, wherein the substrate is a cellulose-based substrate.

3. The superhydrophobic membrane of claim 1, wherein the substrate comprises an absorbent tissue made of untreated paper with a high wicking ability.

4. The superhydrophobic membrane of claim 1, wherein the substrate comprises a virgin wood pulp-based material.

5. The superhydrophobic membrane of claim 1, wherein the substrate comprises polysulfone.

6. The superhydrophobic membrane of claim 1, wherein the substrate comprises a cellulose filter, a cotton fabric, or a metallic surface.

7. The superhydrophobic membrane of claim 1, wherein the nanostructures are metal nanostructures.

8. The superhydrophobic membrane of claim 1, wherein the nanostructures comprise Cu, Ni, or Zn nanoparticles.

9. The superhydrophobic membrane of claim 1, wherein the nanostructures comprise nanorods, the nanorods having an aspect ratio of 1.2 or higher.

10. The superhydrophobic membrane of claim 1, wherein the nanostructures have an average size in a range of from about 1 nm to about 100 nm.70273-WO-PCT / TECH-2024-30 11. The superhydrophobic membrane of claim 1, wherein the nanostructures comprise copper oxide nanospheres or zinc oxide nanospheres.

12. The superhydrophobic membrane of claim 1, wherein the nanostructures comprise paramagnetic particles or piezoelectric particles.

13. The superhydrophobic membrane of claim 1, wherein the hydrophobic agent comprises a silane, a fatty acid, a fluoropolymer, a wax, or a combination thereof.

14. The superhydrophobic membrane of claim 1, wherein the hydrophobic agent comprises perfluorodecyltriethoxysilane (FAS-17), stearic acid, or a combination thereof.

15. The superhydrophobic membrane of claim 1, wherein the superhydrophobic membrane has a water contact angle of at least 140°.

16. A method for conducting a separation, the method comprising: immersing the superhydrophobic membrane of claim 1 into a mixture of an organic substance and water; allowing the superhydrophobic membrane to absorb at least some of the organic substance from the mixture; and removing the superhydrophobic membrane from the mixture to separate the absorbed organic substance from the mixture.

17. The method of claim 16, wherein the organic substance comprises octane, coconut oil, n- hexane, or chloroform.

18. A method of making a superhydrophobic membrane, the method comprising: contacting a substrate with a first solution comprising a metal to deposit the metal on the substrate; contacting the substrate with a second solution comprising a reducing agent to form nanostructures on the substrate; and contacting the substrate with a third solution containing a hydrophobic agent to attach the hydrophobic agent to the nanostructures to form a superhydrophobic membrane.70273-WO-PCT / TECH-2024-30 19. The method of claim 18, wherein the substrate is a cellulose-based substrate.

20. The method of claim 18, wherein the substrate is contacted with a second reducing agent prior to contacting the substrate with the third solution.

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