Preparation method and application of hydrophilic composite hydrogel-hydrophobic PVDF membrane
By preparing a hydrophilic composite hydrogel-hydrophobic PVDF membrane, the stability and environmental sustainability issues of photocatalysts were solved, enabling efficient water collection in the morning and long-term hydrogen production during the day. This improved hydrogen production efficiency and total output, and solved the problems of resource waste and environmental pollution associated with traditional hydrogen production technologies.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG SCI-TECH UNIV
- Filing Date
- 2023-11-10
- Publication Date
- 2026-07-07
AI Technical Summary
In existing hydrogen production technologies, photocatalysts lack performance stability and environmental sustainability, and traditional methods consume large amounts of fossil energy, resulting in resource waste and environmental pollution. Therefore, a more efficient and clean hydrogen production method is needed.
A hydrophilic composite hydrogel-hydrophobic PVDF membrane was prepared by forming a hydrophobic PVDF membrane on the surface of the hydrophilic composite hydrogel using electrospinning technology. A photocatalyst was uniformly dispersed in the hydrogel to achieve efficient water collection in the morning and long-term hydrogen production during the day.
It achieves efficient water collection and long-term hydrogen production in an anhydrous environment, increases the hydrogen production rate and total amount, prolongs the retention time of water molecules, reduces water molecule evaporation loss, and improves the utilization efficiency of photocatalysts.
Smart Images
Figure CN117654310B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of hydrogen production technology, and in particular to a method for preparing a hydrophilic composite hydrogel-hydrophobic PVDF membrane and its application. Background Technology
[0002] Finding a clean, renewable, and safe energy source to replace traditional fossil fuels is of paramount importance. Hydrogen energy, as a crucial component of "zero-carbon industrial parks," boasts advantages such as high energy density, strong sustainability, abundant reserves, and zero pollution, aligning with national requirements for green, clean, and sustainable development. However, currently, most hydrogen is produced through the steam reforming of fossil fuels. This production route not only consumes vast amounts of fossil fuels but also results in significant resource waste and greenhouse gas emissions.
[0003] Currently, most hydrogen is produced from fossil fuels, consuming vast amounts of non-renewable resources and polluting our environment. Several solar-powered hydrogen production methods exist, such as photoelectrochemical water splitting, but these typically require corrosive electrolytes, limiting their performance stability and environmental sustainability. Among various hydrogen production technologies, photocatalytic hydrogen production, powered by abundant solar energy, addresses energy shortages without causing environmental pollution, and can simply and efficiently convert solar energy into hydrogen. Therefore, a photocatalytic hydrogen production method is needed that can extend the hydrogen production time and efficiently utilize water resources in the natural environment. Summary of the Invention
[0004] To address the aforementioned technical problems, this invention provides a method for preparing a hydrophilic composite hydrogel-hydrophobic PVDF membrane and its application. The hydrophilic composite hydrogel-hydrophobic PVDF membrane prepared by this invention exhibits efficient water collection in the morning and long-lasting hydrogen production during the day, enabling cyclic hydrogen production in an anhydrous environment.
[0005] The specific technical solution of this invention is as follows:
[0006] In a first aspect, a method for preparing a hydrophilic composite hydrogel-hydrophobic PVDF membrane includes the following steps:
[0007] (1) The photocatalyst was dispersed in water, and 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, polyethylene glycol methyl ether methacrylate and N,N'-methylenebisacrylamide were added. After stirring evenly, the mixture was subjected to deoxygenation treatment. Then, an initiator and a promoter were added, and the mixture was heated to polymerize, resulting in a hydrophilic composite hydrogel with the photocatalyst uniformly dispersed inside.
[0008] The ratio of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, polyethylene glycol methyl ether methacrylate, N,N'-methylenebisacrylamide, initiator and accelerator, calculated in mL and mg, is 400-500 mL: 700-800 mL: 10-20 mg: 10-20 mg: 10-20 mg.
[0009] (2) Dissolve polyvinylidene fluoride (PVDF) in an organic solvent, heat and stir to obtain an electrospinning solution.
[0010] (3) Using electrospinning technology, under the conditions of electrospinning parameters of voltage 10-15kV, speed 0.1-0.5mL / h, and distance between receiver and needle 10-15cm, a non-dense hydrophobic PVDF membrane with a thickness of 40-70μm and a porosity of 50-80% is formed on the surface of the hydrophilic composite hydrogel, and the resulting hydrophilic composite hydrogel-hydrophobic PVDF membrane is obtained.
[0011] The hydrophilic composite hydrogel substrate of this invention uses thermosensitive polymers 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester and polyethylene glycol methyl ether methacrylate as raw materials. To better achieve water collection in the morning and water retention during the day, the composite hydrogel substrate needs to be in a hydrophilic state. Therefore, by adjusting the formulation, the phase transition temperature of the resulting composite hydrogel is greater than 45°C. This strategy enables the composite hydrogel to autonomously absorb more dew in its hydrophilic state during the morning and daytime, when the ambient temperature cannot reach this phase transition temperature, thus achieving better water retention.
[0012] The hydrophilic composite hydrogel-hydrophobic PVDF membrane of this invention comprises two parts: a hydrophilic composite hydrogel as a substrate, on which a hydrophobic PVDF membrane is formed directly by electrospinning; and a photocatalyst uniformly dispersed within the hydrophilic composite hydrogel, which is loaded into the hydrogel. The three-dimensional network structure of the hydrogel effectively disperses the photocatalyst, solving the aggregation effect and increasing its specific surface area, thereby improving the hydrogen production rate and total hydrogen production. The hydrophobic PVDF membrane is a porous, non-dense membrane that collects and conducts moisture and provides a channel for hydrogen release.
[0013] The hydrophilic composite hydrogel-hydrophobic PVDF membrane of this invention can be used for photocatalytic hydrogen production from water. The principle is as follows: with the hydrophobic surface of the hydrophilic composite hydrogel-hydrophobic PVDF membrane facing upwards, dew can be collected in the morning. Because this hydrophilic composite hydrogel-hydrophobic PVDF membrane has a hydrophobic upper layer and a hydrophilic lower layer, dew can spontaneously and rapidly conduct from the hydrophobic layer to the hydrophilic layer through the pores, achieving rapid dew collection in the morning. After dew collection, the upper hydrophobic PVDF membrane can also prevent the evaporation of water molecules inside the composite hydrogel, achieving long-term water retention. During the day, under sunlight, the photocatalyst in the hydrophilic composite hydrogel exerts a catalytic effect, spontaneously producing hydrogen using the collected dew as raw material. The generated hydrogen gas automatically passes through the pores of the hydrophobic PVDF membrane and is eventually collected. Therefore, the hydrophilic composite hydrogel-hydrophobic PVDF membrane of this invention has the functions of efficient water collection and long-term hydrogen production.
[0014] This invention reveals that the microstructure and thickness of the hydrophobic PVDF membrane are crucial for the conduction of dew and hydrogen. An ideal hydrophobic PVDF membrane should possess a reasonable pore structure and thickness, enabling rapid conduction of dew to the hydrophilic composite hydrogel while preventing water molecules from escaping and facilitating hydrogen evolution. Regarding pore size, insufficient or no pores prevent water and hydrogen from penetrating the hydrophobic PVDF membrane; excessive pores hinder water retention. Similarly, insufficient thickness results in inadequate hydrophobicity of the hydrophobic surface, hindering rapid water conduction to and absorption by the hydrophilic composite hydrogel, thus impairing water retention; excessive thickness, on the other hand, hinders hydrogen evolution. Ultimately, this invention achieves a hydrophobic PVDF membrane with ideal pore structure and thickness by controlling the electrospinning parameters within the aforementioned range, thus simultaneously possessing the aforementioned effects.
[0015] Preferably, in step (1), the amount of photocatalyst used is 10-15 mg in mL and mg, and the amount of water used is 3-7 mL.
[0016] Preferably, in step (1), the photocatalyst is g-C3N4 / Pt nanosheets; the initiator is ammonium persulfate; and the promoter is N,N,N,N-tetramethylethylenediamine.
[0017] Preferably, in step (1), the dispersion method is ultrasonic dispersion, and the dispersion time is 20-40 min; the deoxygenation treatment is to place it in a N2 atmosphere for 10-20 min; the heating polymerization reaction temperature is 25-35℃, and the time is 5-10 h.
[0018] Preferably, in step (2), the organic solvent is a mixed solution of N,N'-dimethylformamide and acetone.
[0019] Preferably, in step (2), the ratio of the amount of polyvinylidene fluoride, N,N'-dimethylformamide and acetone used in mL and mg is (0.1-0.5)g:(1-3)mL:(1-3)mL.
[0020] Preferably, in step (2), the heating and stirring temperature is 40-50℃, the time is 4-7h, and the stirring speed is 400-500rpm.
[0021] Preferably, in step (3), the electrospinning time is 1-10 min.
[0022] Secondly, a method for producing hydrogen using the aforementioned hydrophilic composite hydrogel-hydrophobic PVDF membrane includes: placing the hydrophilic composite hydrogel-hydrophobic PVDF membrane outdoors with the hydrophobic PVDF membrane facing upwards; collecting dew on the surface of the hydrophobic PVDF membrane in the morning; conducting and collecting the dew in the hydrophilic composite hydrogel; and generating hydrogen gas using the dew as a raw material under the action of a photocatalyst under sunlight during the day; the hydrogen gas passing through the pore structure of the hydrophobic PVDF membrane and finally being collected.
[0023] Compared with the prior art, the present invention has the following technical effects:
[0024] (1) This invention first prepares a hydrophilic composite hydrogel with a uniformly dispersed photocatalyst, and then prepares a hydrophobic PVDF film on the surface of the hydrophilic composite hydrogel using electrospinning technology. Because the hydrophobic PVDF film is hydrophobic, it can effectively prevent the evaporation and escape of water molecules inside the composite hydrogel, achieving good water retention performance, thus providing water molecules for a longer period of time and realizing photocatalytic hydrogen production. Simultaneously, the structure formed by the hydrophobic PVDF film and the hydrophilic composite hydrogel enables the rapid transport of water molecules from the hydrophobic side to the hydrophilic side, thus efficiently collecting surface dew in the morning and achieving long-term hydrogen production by the composite hydrogel. In summary, the hydrophilic composite hydrogel-hydrophobic PVDF film of this invention can achieve efficient water collection (dew absorption) in the morning and long-term hydrogen production (photocatalytic water splitting) during the day, realizing cyclic hydrogen production in a waterless environment.
[0025] (2) The present invention regulates the pore size and thickness of the hydrophobic PVDF membrane by electrospinning parameters, thereby adjusting the water conduction capacity, water retention capacity and hydrogen evolution capacity of the material. Attached Figure Description
[0026] Figure 1The images show surface SEM images of composite hydrogels without PVDF fiber membranes and composite hydrogels with PVDF fiber membranes of different thicknesses prepared in Examples 1, 2, and 3 of this invention; wherein, (a) is the SEM image of the composite hydrogel without PVDF fiber membrane in Example 1; (b) is the surface SEM image of the PVDF fiber membrane (48 μm) and composite hydrogel in Example 2; and (c) is the surface SEM image of the PVDF fiber membrane (65 μm) and composite hydrogel in Example 3.
[0027] Figure 2 The figures show the contact angle changes of the composite hydrogels without PVDF fiber membranes and composite hydrogels with PVDF fiber membranes of different thicknesses prepared in Examples 1, 2, and 3 of this invention. In the figures, (a) and (b) are the contact angles of the composite hydrogel without PVDF fiber membrane in Example 1 at the moment of contact (0s) and after 40 minutes and 37 seconds; (c) and (d) are the contact angles of the PVDF fiber membrane (48 μm) and composite hydrogel in Example 2 at the moment of contact (0s) and after 4 minutes and 56 seconds; (e) and (f) are the contact angles of the PVDF fiber membrane (65 μm) and composite hydrogel in Example 3 at the moment of contact (0s) and after 15 minutes and 52 seconds.
[0028] Figure 3 The graphs show the hydrogen production curves of water splitting for composite hydrogels without PVDF fiber membranes and composite hydrogels with PVDF fiber membranes of different thicknesses prepared in Examples 1, 2, and 3 of this invention. The dotted lines represent the hydrogen production curves of the PVDF fiber membrane (48 μm) and composite hydrogel in Example 2, the triangular lines represent the hydrogen production curves of the PVDF fiber membrane (65 μm) and composite hydrogel in Example 3, and the square lines represent the hydrogen production curve of the composite hydrogel without PVDF fiber membrane in Example 1.
[0029] Figure 4 The graphs show the hydrogen production rates of the composite hydrogels without PVDF fiber membranes and composite hydrogels with PVDF fiber membranes of different thicknesses prepared in Examples 1, 2, and 3 of this invention. The right side shows the hydrogen production rate of the PVDF fiber membrane (48 μm) and composite hydrogel in Example 2, the middle side shows the hydrogen production rate of the PVDF fiber membrane (65 μm) and composite hydrogel in Example 3, and the left side shows the hydrogen production rate of the composite hydrogel without PVDF fiber membrane in Example 1. Detailed Implementation
[0030] The present invention will be further described below with reference to embodiments.
[0031] Example 1
[0032] 10 mg g-C3N4 / Pt was sonicated in 5 mL of deionized water for 30 min to form a suspension. 462 mL of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, 714 mL of polyethylene glycol methyl ether methacrylate, and 14 mg of crosslinking agent N,N'-methylenebisacrylamide were dissolved in the suspension. Then, after incubating the solution under a nitrogen atmosphere for 15 min, 12 mg of initiator ammonium persulfate and 12 mL of accelerator N,N,N,N-tetramethylethylenediamine were added. The reaction was carried out at 30 °C for 6 h. A composite hydrogel containing g-C3N4 / Pt was obtained.
[0033] Example 2
[0034] First, 10 mg of g-C3N4 / Pt was sonicated in 5 mL of deionized water for 30 min to form a suspension. 462 mL of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, 714 mL of polyethylene glycol methyl ether methacrylate, and 14 mg of crosslinking agent N,N'-methylenebisacrylamide were dissolved in the suspension. Then, after incubating the solution under a nitrogen atmosphere for 15 min, 12 mg of initiator ammonium persulfate and 12 mL of accelerator N,N,N,N-tetramethylethylenediamine were added. The reaction was carried out at 30 °C for 6 h. A hydrogel substrate containing g-C3N4 / Pt was obtained.
[0035] Next, 0.2 g of polyvinylidene fluoride (PVDF), 1 mL of N,N'-dimethylformamide (DMF) and 1 mL of acetone were dissolved in a sealed environment at 45°C and 450 rpm for 4 h to obtain an electrospinning solution.
[0036] Finally, the prepared electrospinning solution was electrospinned on the hydrogel substrate for 2 min under the conditions of 10 kV voltage, 0.3 mL / h speed, and 10 cm distance between the receiver and the needle, to obtain a PVDF fiber membrane (48 μm) and a composite hydrogel system.
[0037] Example 3
[0038] First, 10 mg of g-C3N4 / Pt was sonicated in 5 mL of deionized water for 30 min to form a suspension. 462 mL of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, 714 mL of polyethylene glycol methyl ether methacrylate, and 14 mg of crosslinking agent N,N'-methylenebisacrylamide were dissolved in the suspension. Then, after incubating the solution under a nitrogen atmosphere for 15 min, 12 mg of initiator ammonium persulfate and 12 mL of accelerator N,N,N,N-tetramethylethylenediamine were added. The reaction was carried out at 30 °C for 6 h. A hydrogel substrate containing g-C3N4 / Pt was obtained.
[0039] Next, 0.2 g of polyvinylidene fluoride (PVDF), 1 mL of N,N'-dimethylformamide (DMF) and 1 mL of acetone were dissolved in a sealed environment at 45°C and 450 rpm for 4 h to obtain an electrospinning solution.
[0040] Finally, the prepared electrospinning solution was electrospinned on the hydrogel substrate for 5 min at a voltage of 10 kV, a speed of 0.3 mL / h, and a distance of 10 cm between the receiver and the needle, to obtain a PVDF fiber membrane (65 μm) with a Janus structure and a composite hydrogel system.
[0041] Performance testing
[0042] (1) Surface SEM images of the composite hydrogels without PVDF fiber membranes and the composite hydrogels with PVDF fiber membranes of different thicknesses prepared in Examples 1-3 are shown below. Figure 1 As shown in the figure, the PVDF fiber membrane has been successfully spun onto the surface of the composite hydrogel. The PVDF fiber membrane forms a non-dense film with a porosity of 78.9% (48 μm) and 60.7% (65 μm) on the surface of the composite hydrogel, which can ensure the precipitation of H2 in the subsequent photocatalytic water splitting hydrogen production process.
[0043] (2) The contact angle changes of the surfaces of the composite hydrogels without PVDF fiber membranes prepared in Examples 1-3 and the composite hydrogels with PVDF fiber membranes of different thicknesses are as follows: Figure 2 As shown, the composite hydrogel of Example 1, which does not contain a PVDF fiber membrane, although having better surface hydrophilicity (58.45°), requires 40 minutes and 37 seconds to achieve complete water absorption, reducing the contact angle to 0°. In stark contrast, the composite hydrogel of Example 2, with a hydrophobic PVDF fiber membrane (48 μm) on its surface, has a contact angle increased to 86.96°, indicating a decrease in hydrophilicity, but it only requires 4 minutes and 56 seconds to achieve complete water absorption. Example 3 further increases the thickness of the PVDF fiber membrane to 65 μm, and the contact angle continues to increase to 93.86°, indicating a change from hydrophilic to hydrophobic surface, but it still only requires 15 minutes and 52 seconds to achieve complete water absorption. Therefore, it can be concluded that the structure composed of hydrophobic PVDF fiber membrane and hydrophilic composite hydrogel can realize the efficient transport of surface water from the hydrophobic side to the hydrophilic side of the system, and can quickly and efficiently collect morning dew and store it inside the hydrogel, thereby prolonging the photolysis hydrogen production time of the composite hydrogel and increasing the total amount of hydrogen produced.
[0044] (3) The total amount of hydrogen produced by photocatalytic water splitting in the composite hydrogels without PVDF fiber membranes prepared in Examples 1-3 and the composite hydrogels with PVDF fiber membranes of different thicknesses is as follows: Figure 3As shown in the figure, the effect of PVDF fiber membrane thickness on the water retention and total hydrogen production of the composite hydrogel by photocatalytic water splitting was investigated. It can be seen from the figure that the total hydrogen production from photocatalytic water splitting of the composite hydrogels containing PVDF fiber membranes in Examples 2 and 3 is significantly higher than that of the composite hydrogel without PVDF fiber membrane in Example 1. This is because the upper hydrophobic PVDF fiber membrane can effectively prevent the evaporation and dissipation of water molecules inside the composite hydrogel, providing the necessary water molecules for the photocatalysis of g-C3N4 / Pt, thereby greatly extending the photocatalytic water splitting time and increasing the total hydrogen production.
[0045] (4) The photocatalytic hydrogen production rates of the composite hydrogels without PVDF fiber membranes prepared in Examples 1-3 and the composite hydrogels with PVDF fiber membranes of different thicknesses are as follows: Figure 4 As shown, the composite hydrogel without a PVDF fiber membrane in Example 1 had the slowest hydrogen production rate, while the composite hydrogel with a hydrophobic PVDF fiber membrane (48 μm) on its surface in Example 2 had the fastest hydrogen production rate. This is because the composite hydrogel without a PVDF fiber membrane on its surface loses a large amount of water during the photocatalytic water splitting process, and cannot provide sufficient water molecules for hydrogen production in the later stages. Compared to the composite hydrogel with a hydrophobic PVDF fiber membrane (48 μm) on its surface, the composite hydrogel with a hydrophobic PVDF fiber membrane (65 μm) on its surface in Example 3, due to the thicker PVDF fiber membrane, can better prevent the evaporation of internal water, but also hinders the precipitation of H2 generated by photocatalytic water splitting from the inside of the composite hydrogel to the outside.
[0046] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.
[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.
Claims
1. A method for preparing a hydrophilic composite hydrogel-hydrophobic PVDF membrane, characterized in that: Includes the following steps: (1) The photocatalyst was dispersed in water, and 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, polyethylene glycol methyl ether methacrylate and N,N'-methylenebisacrylamide were added. After stirring evenly, the mixture was subjected to deoxygenation treatment. Then, an initiator and a promoter were added, and the mixture was heated to polymerize, resulting in a hydrophilic composite hydrogel with the photocatalyst uniformly dispersed inside. The ratio of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, polyethylene glycol methyl ether methacrylate, N,N'-methylenebisacrylamide, initiator and accelerator, calculated in mL and mg, is 400-500 mL: 700-800 mL: 10-20 mg: 10-20 mg: 0.01-0.02 mL. (2) Dissolve polyvinylidene fluoride in an organic solvent, heat and stir to obtain an electrospinning solution; (3) Using electrospinning technology, under the conditions of electrospinning parameters of voltage 10-15kV, speed 0.1-0.5mL / h, and distance between receiver and needle 10-15cm, a non-dense hydrophobic PVDF membrane with a thickness of 40-70μm and a porosity of 50-80% is formed on the surface of the hydrophilic composite hydrogel, and the resulting hydrophilic composite hydrogel-hydrophobic PVDF membrane is obtained.
2. The preparation method according to claim 1, characterized in that: In step (1), the amount of photocatalyst used is 10-15 mg in mL and mg; the amount of water used is 3-7 mL.
3. The preparation method according to claim 1 or 2, characterized in that: In step (1), The photocatalyst is g-C3N4 / Pt nanosheets; The initiator is ammonium persulfate; the accelerator is N,N,N,N-tetramethylethylenediamine.
4. The preparation method according to claim 1, characterized in that: In step (1), The dispersion method is ultrasonic dispersion, and the dispersion time is 20-40 minutes; The deoxygenation treatment involves placing the sample in an N2 atmosphere for 10-20 minutes. The heating polymerization reaction is carried out at a temperature of 25-35℃ for 5-10 hours.
5. The preparation method according to claim 1, characterized in that: In step (2), the organic solvent is a mixed solution of N,N'-dimethylformamide and acetone.
6. The preparation method according to claim 5, characterized in that: In step (2), the ratio of the amount of polyvinylidene fluoride, N,N'-dimethylformamide and acetone used in mL and mg is (0.1-0.5)g:(1-3)mL:(1-3)mL.
7. The preparation method according to claim 1, characterized in that: In step (2), the heating and stirring temperature is 40-50℃, the time is 4-7h, and the stirring speed is 400-500rpm.
8. The preparation method according to claim 1 or 5, characterized in that: In step (3), the electrospinning time is 1-10 min.
9. The application of the hydrophilic composite hydrogel-hydrophobic PVDF membrane obtained by the preparation method according to any one of claims 1-8 in the photocatalytic hydrogen production using dew and sunlight.
10. A method for hydrogen production using a hydrophilic composite hydrogel-hydrophobic PVDF membrane obtained by the preparation method according to any one of claims 1-8, characterized in that: The hydrophilic composite hydrogel-hydrophobic PVDF membrane is placed outdoors with the hydrophobic PVDF membrane facing upwards. Dew is collected on the surface of the hydrophobic PVDF membrane in the morning. The dew is conducted and collected in the hydrophilic composite hydrogel. Under sunlight during the day, hydrogen gas is generated from the dew as a raw material under the action of a photocatalyst. The hydrogen gas passes through the pore structure of the hydrophobic PVDF membrane and is eventually collected.