A seawater desalination device and a super-hydrophobic surface preparation method thereof

Abstract

The application discloses a seawater desalination device and a preparation method of a super-hydrophobic surface thereof, and the super-hydrophobic surface can be used durably and efficiently in the field of seawater desalination under the existence of temperature difference. The preparation method comprises the following steps: (1) preparation of a microstructure; (2) preparation of a nanostructure; (3) coordinated preparation of a micro-nano composite structure; and (4) preparation of a micro-nano composite super-hydrophobic structure. The application reduces the adhesion of condensed droplets in the microstructure by combining nano sheets or fractal nano structures inside and outside the micro cavity with small holes; the small holes at the top of the microstructure and the fractal nano structure provide stable gas channels, prevent the non-desalinated seawater from communicating with the fresh water and failing, and utilize the synergistic effect of the micro cavity structure to quickly discharge the condensed water, and thus a preparation method of a micro-nano composite structure surface is provided, which can efficiently and lowly consume energy to actively transport the condensed water in the super-hydrophobic surface structure and realize seawater desalination under the existence of temperature difference.

Description

Technical Field

[0001] This invention belongs to the field of superhydrophobic materials technology, specifically relating to a seawater desalination device and a method for preparing its superhydrophobic surface. Background Technology

[0002] Global water scarcity has spurred the need for low-cost and sustainable seawater desalination processes. Membrane distillation desalination can utilize waste-grade heat or renewable energy sources in this regard. Superhydrophobic surfaces have attracted increasing attention due to their superior performance in antifouling, metal corrosion prevention, marine organism adhesion, chemical heat and mass transfer, and biomedicine. In recent years, research on the application of superhydrophobic membranes in seawater desalination has become increasingly widespread. However, most hydrophobic membranes exhibit poor performance stability in transporting condensate droplets, resulting in high energy consumption for condensate transport. Improving the performance of superhydrophobic membranes in seawater desalination has become a major research issue. The key to constructing superhydrophobic surfaces lies in the design of micro / nanostructures and the use of low surface energy materials. Micro / nanostructures provide a specific space for condensate droplet transport (internal gas can exist stably, forming a gas layer), while low surface energy materials prevent liquid from wetting the interior of the structure. Thanks to the development of new materials and iterative structural designs, the mechanical stability of superhydrophobic surfaces (preventing the destruction of micro / nanostructures and loss of droplet transport channels) has made significant progress; however, research on the thermodynamic stability of the gas layer (where the gas layer is replaced by water) is still insufficient. Steam condensation, as a typical phase change process, is widely present in natural phenomena and industrial production. Especially when superhydrophobic membranes are used in seawater desalination environments, the transport of condensate droplets within their high-humidity structure is unavoidable. In this process, the passive transport of condensate droplets consumes a significant amount of energy.

[0003] The above indicates that when superhydrophobic surfaces are used in seawater desalination environments, the non-directional flow of condensed droplets due to their micro-nano structures often leads to the loss of superhydrophobic properties and higher energy consumption due to wetting. A completely new design is needed in seawater desalination environments to ensure the durability and low energy consumption of superhydrophobic surfaces. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a superhydrophobic surface for seawater desalination that actively transports condensate through the synergistic effect between micro and nano structures. By adjusting the rational layout of the micro and nano structures and controlling the design parameters of the nano and micro structures, droplets that nucleate and grow in the nano structure are directionally and actively transported to the micro structure and rapidly discharged into the fresh water. This effectively prevents the connection between undesalinated seawater and fresh water, effectively reduces the energy consumption of condensate droplet transport, and thus improves its seawater desalination performance.

[0005] A method for preparing a superhydrophobic surface for seawater desalination that actively transports condensate through the synergistic effect between micro and nanostructures is disclosed. This method involves combining nanosheets or fractal nanostructures inside and outside a microcavity with pores to reduce the adhesion of condensate droplets within the microstructure; utilizing the pores at the top of the microstructure and the fractal nanostructure to provide stable gas channels to prevent undesalinated seawater from connecting with fresh water and becoming ineffective; and utilizing the synergistic effect with the microcavity structure to rapidly discharge the accumulated condensate.

[0006] To achieve the above objectives, this invention provides a method for preparing an underwater superhydrophobic surface that enables the active and timely discharge of condensate through the synergistic effect between micro and nanostructures, comprising the following steps:

[0007] (1) Preparation of microstructures

[0008] Continuous inverted quadrangular pyramidal structures and strip structures with small holes and certain tilt angles, depths and widths are prepared on different substrates using photolithography or molding processes.

[0009] (2) Preparation of nanostructures

[0010] By using selected polymer or inorganic particles with different shapes as building blocks of nanocoatings, sheet-like or fractal nanostructures with certain height, particle size, and spacing can be prepared on both sides of different surfaces through methods such as spraying, chemical vapor deposition (CVD) or evaporation, or through chemical oxidation or ion beam etching.

[0011] (3) Preparation of micro-nano composite structures

[0012] The microstructured surface prepared in step (1) is used to prepare a micro-nano composite surface using the method in step (2);

[0013] (4) Fabrication of micro / nano composite superhydrophobic structures

[0014] The micro-nano composite surface prepared in step (3) is cleaned and placed in a vacuum environment in which perfluorooctyltrichlorosilane is present at a certain temperature for a period of time.

[0015] Furthermore, the substrate may include metal, alloy, silicon wafer, or glass.

[0016] Furthermore, the molding process includes the following steps: First, preparing a PDMS mixture of soft materials for molding; second, preparing a PDMS microstructure template; and third, obtaining the target microstructure with small pores.

[0017] Furthermore, the etching steps include: cleaning, pre-baking, spin coating, post-baking, exposure, development, buffer oxide etching, and wet etching. Cleaning refers to 30 minutes in a plasma cleaner; buffer oxide etching time is 3-4 minutes; the wet etching time varies with the etching size, angle, and depth.

[0018] Furthermore, the tilt angle of the microstructure is 40~80°; the depth is 80~300μm; and the width of the microstructure is 120~500μm. Among them, the diameter of the pores is 5-20μm.

[0019] Furthermore, the nanostructure has a particle size of 20-120 nm, a spacing of 10-60 nm, and a depth of 100-400 nm.

[0020] Further, chemical oxidation involves placing both ends of the sample on the outer flame of a candle and moving them rapidly and uniformly for approximately 0.5 minutes (the exact time depends on the sample area). The sample is then placed in a vacuum environment at room temperature containing 4 ml of ammonia and 4 ml of tetraethyl orthosilicate for 20–24 hours. Finally, the sample is transferred to a muffle furnace and calcined at 550 °C for 2 hours at a rate of 5 °C / min, after which it is allowed to cool naturally to room temperature before being removed.

[0021] Furthermore, the coordination of the micro-nano composite structure lies in the fact that the thickness of the nanostructure is 5~20μm on the side with the tilt angle and 30μm on the side with the planar angle.

[0022] Furthermore, the cleaning method in step (4) is as follows: the surface prepared in step (3) is placed in a plasma cleaner for 10-15 minutes.

[0023] Furthermore, in step (4), the amount of perfluorooctyltrichlorosilane used is 300~400μL, the temperature is 60 ℃, and the time is 2h.

[0024] An underwater superhydrophobic surface capable of actively and promptly draining condensate through the synergistic effect between micro and nano structures was prepared by adopting a method that enables the active and timely drainage of condensate through the synergistic effect between micro and nano structures.

[0025] In summary, the present invention has the following advantages:

[0026] The main function of micron structures is to provide a stable gas-liquid interface and gas layer. At the same time, micron structures of appropriate size are conducive to timely contact between the merged condensate droplets and the gas-liquid interface and rapid discharge into the freshwater area.

[0027] The main function of nanostructures is to control the nucleation and growth process of condensed droplets, and to ensure that the condensed droplets remain on the top of the structure after they grow, thus maintaining their stable Cassie state and low adhesion properties.

[0028] The small pores at the top of the microstructure serve to provide a channel for gas from the seawater region to enter the microstructure, ensuring that, under conditions of temperature difference, the liquid in the seawater region transforms into freshwater through a gas-liquid phase change from the micro-nano composite structure with the small pore channels and enters the freshwater region.

[0029] By combining sheet-like or fractal nanostructures within and on the surface of the microstructure cavity, the adhesion of condensate droplets inside and outside the microstructure is reduced; a single-concave continuous hydrophobic microstructure is used to provide a stable gas-liquid interface and sufficient cavitation to prevent the mixing of liquids in the seawater and freshwater regions due to the failure of the surface superhydrophobicity; and the synergistic effect with the micro-nano composite structure is used to rapidly discharge condensate droplets generated by the gas-liquid phase change into the freshwater region. A method for preparing a superhydrophobic surface for seawater desalination that actively transports condensate through the synergistic effect between micro-nano structures is proposed. Attached Figure Description

[0030] Figure 1 A schematic diagram of the side structure of a micro / nano composite superhydrophobic surface for seawater desalination.

[0031] Figure 2 SEM image of a micro / nano composite superhydrophobic surface for seawater desalination;

[0032] Figure 3 A schematic diagram of the gas-liquid interface changes and gas layer detachment caused by condensation within microstructures and micro-nano composite superhydrophobic surface structures.

[0033] Figure 4 Metallurgical microscopic image of a silicon-based inverted square pyramid with microstructures and small pores;

[0034] Figure 5 A schematic diagram of the contact angles on both sides of the superhydrophobic surface of a micro / nano composite structure for seawater desalination;

[0035] Figure 6 Metallographic micrograph of the vapor in the seawater region of the micro-nano composite structure for seawater desalination turning into condensed droplets, which then nucleate and discharge into the freshwater region. Detailed Implementation

[0036] The principles and features of the present invention are described below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, specific conditions or manufacturer-recommended conditions should be followed in the embodiments. Reagents or instruments whose manufacturers are not specified are all commercially available products. Example

[0037] A seawater desalination device includes a substrate, a fractal nanostructure, and a microstructure. One side of the substrate has a concave structure, and the microstructure is located on the inner surface of the concave structure. The fractal nanostructure is located on the other side of the substrate. A small hole for condensate to pass through is provided between the fractal nanostructure and the microstructure. One side of the fractal nanostructure is a seawater region, and the other side of the microstructure is a freshwater region. A temperature difference exists between the seawater and freshwater regions.

[0038] In one embodiment, the temperature of the seawater zone is 35°C, and the temperature of the freshwater zone is 25°C. Condensate is transported from the seawater zone to the freshwater zone through small pores and a micron-sized structure via evaporation, thereby achieving seawater desalination. Example

[0039] This embodiment provides a method for preparing a superhydrophobic surface for seawater desalination that actively transports condensate through the synergistic effect between micro and nanostructures, including the following steps:

[0040] (1) Preparation of microstructures

[0041] Photolithography was used to fabricate continuous inverted quadrangular pyramidal structures and strip structures with small holes and certain tilt angles, depths, and widths on different silicon wafers.

[0042] The microstructures have an inclination angle of 40–80°, a depth of 80–300 μm, and a width of 120–500 μm. The pores have a diameter of 5–20 μm.

[0043] (2) Preparation of micro-nano composite structures

[0044] Conical nanostructures with a certain height, particle size, and spacing were prepared on different surfaces in step (1) by ion beam etching.

[0045] The nanostructures have a particle size of 20-120 nm, a spacing of 10-60 nm, a depth of 100-400 nm, and a thickness of 5-20 μm on the side with the tilt angle and 30 μm on the side with the plane.

[0046] (3) Fabrication of micro / nano composite superhydrophobic structures

[0047] The micro-nano composite surface prepared in step (2) is cleaned and placed in a vacuum environment in which perfluorooctyltrichlorosilane is present at a certain temperature for a period of time.

[0048] The cleaning method specifically involves placing the prepared surface in a plasma cleaner for 10-15 minutes; using 300-400 μL of perfluorooctyltrichlorosilane at a temperature of 60 °C for 2 hours. Example 3

[0049] This embodiment provides a method for preparing a superhydrophobic surface for seawater desalination that actively transports condensate through the synergistic effect between micro and nanostructures, including the following steps:

[0050] Preparation of microstructures

[0051] Photolithography will be used to fabricate continuous inverted quadrangular pyramidal structures and strip structures with small holes and certain tilt angles, depths, and widths on different silicon wafers.

[0052] The microstructures have an inclination angle of 40–80°, a depth of 80–300 μm, and a width of 120–500 μm. The pores have a diameter of 5–20 μm.

[0053] (2) Preparation of micro-nano composite structures

[0054] Using candle ash nanoparticles, conical or fractal nanostructures of a certain height, particle size, and spacing are prepared on different surfaces in step (1) by chemical vapor deposition.

[0055] The nanostructures have a particle size of 20-120 nm, a spacing of 10-60 nm, a depth of 100-400 nm, and a thickness of 5-20 μm on the side with the tilt angle and 30 μm on the side with the plane.

[0056] (3) Fabrication of micro / nano composite superhydrophobic structures

[0057] The micro-nano composite surface prepared in step (2) is cleaned and placed in a vacuum environment in which perfluorooctyltrichlorosilane is present at a certain temperature for a period of time.

[0058] The cleaning method specifically involves placing the prepared surface in a plasma cleaner for 10-15 minutes; using 300-400 μL of perfluorooctyltrichlorosilane at a temperature of 60 °C for 2 hours. Example

[0059] This embodiment provides a method for preparing a superhydrophobic surface for seawater desalination that actively transports condensate through the synergistic effect between micro and nanostructures, including the following steps:

[0060] (1) Preparation of microstructures

[0061] Using soft material reshaping, continuous inverted quadrangular pyramidal structures and strip structures with small holes and certain tilt angles, depths and widths are fabricated on polymer SU-8 photoresist substrates;

[0062] The microstructures have an inclination angle of 40–80°, a depth of 80–300 μm, and a width of 120–500 μm. The pores have a diameter of 5–20 μm.

[0063] (2) Preparation of micro-nano composite structures

[0064] Using silica nanoparticles of different sizes, fractal nanostructures with certain height, particle size, and spacing are prepared on different surfaces in step (1) by spraying.

[0065] The nanostructures have a particle size of 20-120 nm, a spacing of 10-60 nm, a depth of 100-400 nm, and a thickness of 5-20 μm on the side with the tilt angle and 30 μm on the side with the plane.

[0066] (3) Fabrication of micro / nano composite superhydrophobic structures

[0067] The micro-nano composite surface prepared in step (2) is cleaned and placed in a vacuum environment in which perfluorooctyltrichlorosilane is present at a certain temperature for a period of time.

[0068] The cleaning method specifically involves placing the prepared surface in a plasma cleaner for 10-15 minutes; using 300-400 μL of perfluorooctyltrichlorosilane at a temperature of 60 °C for 2 hours.

Claims

1. A method for preparing a superhydrophobic surface for a seawater desalination device, characterized in that, The seawater desalination device includes a substrate, nanostructures, and microstructures. The nanostructures are located on both sides of the substrate, and one side of the substrate has a single concave structure. There are small holes between the nanostructures on the planar side and the nanostructures on the inner surface of the single concave structure to allow condensate to pass through. The method for preparing superhydrophobic surfaces for seawater desalination devices includes the following steps: S1. Using photolithography or molding processes, a continuous inverted quadrangular pyramid structure or strip structure with small holes and a certain tilt angle, depth and width is prepared on the substrate; S2. Using polymer or inorganic particles with different shapes as building blocks of nano-coatings, sheet-like or fractal nanostructures with certain height, particle size, and spacing are prepared on both sides of different surfaces by spraying, chemical vapor deposition, evaporation, chemical oxidation, or ion beam etching. S3. The micron-structured surface prepared in step S1 is used to prepare a micro-nano composite surface using the method in step S2. S4. Clean the micro-nano composite surface prepared in step S3 and place it in a vacuum environment containing perfluorooctyltrichlorosilane at a certain temperature for a period of time.

2. The method for preparing the superhydrophobic surface of the seawater desalination device as described in claim 1, characterized in that, Molding includes the following steps: The first step is to prepare a PDMS mixture as a molding soft material; the second step is to prepare a PDMS microstructure template; the third step is to obtain a microstructure with pores, wherein the diameter of the pores is 5-20 μm.

3. The method for preparing the superhydrophobic surface of the seawater desalination device as described in claim 1, characterized in that, The tilt angle of the microstructure is 40~80°; the depth is 80~300 μm; and the width of the microstructure is 120~500 μm.

4. The method for preparing the superhydrophobic surface of the seawater desalination device as described in claim 1, characterized in that, The nanostructures have a particle size of 20-120 nm, a spacing of 10-60 nm, and a depth of 100-400 nm.

5. The method for preparing the superhydrophobic surface of the seawater desalination device as described in claim 1, characterized in that, The chemical oxidation refers to placing both ends of the sample on the outer flame of a candle and moving them rapidly and uniformly for 0.2 to 0.8 minutes. Then, the sample is placed in a vacuum room temperature environment containing ammonia and tetraethyl orthosilicate for 20 to 24 hours. Finally, the sample is transferred to a muffle furnace and calcined at 550 °C for 2 hours at a rate of 5 °C / min, and then allowed to cool naturally to room temperature before being removed.

6. The method for preparing the superhydrophobic surface of the seawater desalination device as described in claim 1, characterized in that, The structural coordination of the micro-nano composite is that the thickness of the nanostructure is 5~20 μm on the side with the tilt angle, and the thickness of the nanostructure is 30 μm on the planar side.

7. The method for preparing the superhydrophobic surface of the seawater desalination device as described in claim 1, characterized in that, The cleaning method in step S4 is as follows: place the surface prepared in step S3 in a plasma cleaner for 10-15 minutes.

8. The method for preparing the superhydrophobic surface of the seawater desalination device as described in claim 1, characterized in that, In step S4, the amount of perfluorooctyltrichlorosilane used is 300~400 μL, the temperature is 60 ℃, and the time is 2 h.

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