Preparation method and application of composite hydrogel based on soybean protein and sodium alginate

Abstract

The invention relates to the technical field of hydrogen production, and discloses a preparation method and application of composite hydrogel based on soybean protein and sodium alginate, and the preparation method comprises the following steps: (1) respectively dissolving sodium alginate and soybean protein nanofiber in water to respectively obtain an SA solution and an SPN solution; the preparation method comprises the following steps: preparing an SPN / SA hydrogel bead, mixing the SPN / SA hydrogel bead and the CaCl2 solution according to a ratio, dropwise adding the mixed solution into the CaCl2 solution through an injector for crosslinking, and cleaning with deionized water after gelation is finished to obtain the SPN / SA hydrogel bead; (2) uniformly dispersing a photocatalyst in a sodium alginate solution, then adding the SPN / SA hydrogel beads into the dispersion liquid, and uniformly stirring; and adding the solution into a CaCl2 solution for crosslinking to finally obtain the composite hydrogel. The SPN / SA hydrogel beads are embedded into the sodium alginate hydrogel to obtain the composite hydrogel, high light absorption and long water-retaining property are realized by virtue of refractive index difference and intermolecular hydrogen bonds, and the hydrogen production efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen production, and more particularly relates to a preparation method and application of a composite hydrogel based on soy protein and sodium alginate. Background Art

[0002] The development of hydrogen production technology is crucial for promoting global energy transformation, reducing dependence on fossil fuels, protecting the environment, and enhancing energy security. As a clean and efficient energy carrier, hydrogen energy can not only compensate for the intermittency and instability of renewable energy sources such as wind and solar energy, but also reduce greenhouse gas emissions and combat global climate change. In addition, the key role of hydrogen in industrial applications and its potential to provide zero-emission solutions in the transportation sector indicate that the hydrogen energy industry will create new job opportunities and drive economic growth. With the advancement of technological innovation, the progress of hydrogen production technology will reduce costs, improve efficiency, and promote energy cooperation and sustainable development globally. Therefore, investing in and developing hydrogen production technology has far-reaching implications for achieving energy sustainable development, environmental protection, economic diversification, and international cooperation, and is an indispensable part of the future energy structure.

[0003] Current hydrogen production technologies, especially traditional fossil fuel-based hydrogen production methods such as methane reforming and water-gas shift reactions, although widely used in industry, have significant environmental problems. These methods not only consume large amounts of fossil energy, but also emit large amounts of carbon dioxide and other greenhouse gases during hydrogen production, exacerbating the problem of global climate change. In addition, these technologies may also produce toxic gases and oil vapors, posing a threat to the environment and human health. Therefore, it has become particularly urgent to develop more environmentally friendly hydrogen production technologies. Photocatalytic water splitting for hydrogen production is a process that uses solar energy to decompose water into hydrogen and oxygen, which produces no harmful by-products and is a completely clean energy conversion method. Compared with traditional hydrogen production methods, photocatalytic water splitting for hydrogen production technology has significant environmental advantages. It can not only reduce dependence on fossil fuels and lower greenhouse gas emissions, but also effectively utilize solar energy, an inexhaustible energy source. Therefore, based on the above discussion, there is an urgent need to develop a method based on photocatalytic hydrogen production that can efficiently utilize the energy in the natural environment to enhance hydrogen conversion. Summary of the Invention

[0004] The main object of the present invention is to address the above problems by providing a preparation method and application of a composite hydrogel based on soy protein and sodium alginate. By embedding SPN / SA hydrogel beads into the sodium alginate composite hydrogel, due to the difference in refractive index between the sodium alginate composite hydrogel and the soy protein SPN / SA hydrogel beads, and the inhomogeneity of the internal structure of the hydrogel beads, the SPN / SA hydrogel beads can serve as light scattering centers in the sodium alginate composite hydrogel, thereby greatly improving the light absorption capacity of the sodium alginate composite hydrogel. At the same time, the -COOH and -NH 2 groups in SPN can form hydrogen bonds and electrostatic interactions with water molecules, reducing the water evaporation rate and improving the water retention performance, providing an adequate water environment for photocatalytic water splitting to produce hydrogen. Loading the photocatalyst inside the sodium alginate hydrogel can achieve effective dispersion using the three-dimensional network structure, avoiding the aggregation effect, and thus improving the hydrogen production efficiency. Therefore, the composite hydrogel embedded with SA / SPN hydrogel beads can be placed in areas with sufficient sunlight but water shortage such as grasslands and deserts to improve the hydrogen production efficiency by enhancing the light absorption capacity and water retention performance.

[0005] To achieve the above object, the present invention is realized through the following technical solutions:

[0006] One of the technical solutions of the present invention: A preparation method of a composite hydrogel based on soy protein and sodium alginate, comprising the following steps:

[0007] (1) Dissolve sodium alginate and soy protein nanofibers in water respectively to obtain SA solution and SPN solution; mix the two in proportion, and then drop the mixed solution into CaCl 2 solution for crosslinking. After the gelation is completed, wash with deionized water to obtain SPN / SA hydrogel beads;

[0008] (2) Uniformly disperse the photocatalyst in water, add sodium alginate to dissolve to obtain a dispersion; then add the SPN / SA hydrogel beads to the dispersion and stir evenly; then add this solution to CaCl 2 solution for crosslinking to finally obtain a composite hydrogel.

[0009] The composite hydrogel in the present invention achieves high light absorption and long water retention by means of the refractive index difference and intermolecular hydrogen bonds between soy protein and sodium alginate. It uses sodium alginate as a raw material and is prepared by physical crosslinking. Ca 2+ forms crosslinking points with -COOH in sodium alginate, resulting in an inhomogeneous porous structure in the hydrogel, which can effectively separate the photocatalyst and prevent its aggregation. At the same time, the porous structure is also beneficial to the effective transmission of hydrogen.

[0010] By regulating the cross-linking time of sodium alginate composite hydrogel, the hydrogel can be promoted to form a porous structure that is conducive to hydrogen transmission. 2 The longer the solution is, the longer the cross-linking time is, which will cause the network structure of the hydrogel to become more compact. This compact network structure will greatly affect the effective transmission of hydrogen. 2 If the solution is stored for too short a time, it will lead to insufficient cross-linking, and the hydrogel will not be able to form a stable structure. In the subsequent photocatalytic hydrolysis process to produce hydrogen, it will not be able to reach the ideal state, which will also affect the service life.

[0011] The amount of photocatalyst and soy protein nanofibers used also plays a vital role in improving the hydrogen production capacity. The amount of photocatalyst used determines the total amount of hydrogen produced. If the photocatalyst content is too low, there will be too few photocatalytic sites, and photocatalytic hydrolysis hydrogen production cannot be carried out; if the photocatalyst content is too high, it will cause a large number of agglomerations inside the sodium alginate hydrogel, the surface area will be reduced, the light utilization rate will be reduced, and the hydrogen production effect will be reduced. At the same time, in the process of preparing SPN / SA hydrogel beads, appropriate SPN can improve the water retention performance of sodium alginate composite hydrogel, provide sufficient water environment for photocatalytic hydrogen production, and help to quickly collect hydrogen produced by photocatalysis. If the SPN content is too low, the light absorption and water retention performance cannot be improved, and the hydrogen production efficiency decreases; if the SPN content is too high, the hydrogel beads cannot be formed, which is not conducive to subsequent photocatalytic hydrogen production.

[0012] Further preferably, in step (1), the method for preparing soybean protein nanofibers comprises the following steps: dispersing soybean protein isolate in water and adjusting the pH to 2-4, and hydrating overnight; obtaining the supernatant of the solution by centrifugation, and removing undissolved large particles through a filter membrane; subsequently heating and stirring the solution, and then rapidly cooling and adjusting the pH to neutral; and finally freeze-drying the solution to obtain soybean protein nanofibers.

[0013] Further preferably, the soy protein isolate is dispersed in water at a ratio of 4-6 g:100 mL; the overnight hydration is placed at 2-6°C; the centrifugal speed is 8000-10000 rpm, and the time is 20-30 min; the heating and stirring temperature is 70-90°C, and the heating time is 8-10 h.

[0014] Further preferably, in step (1), the concentration of the SA solution is 1-1.5wt%; the concentration of the SPN solution is 1-1.5wt%; and the volume ratio of the SA solution to the SPN solution is (1-3):(1-3).

[0015] Further preferably, in step (1), the CaCl 2The concentration of the solution is 1 - 1.5 wt%; the volume ratio of the mixed solution to the CaCl 2 solution is 15 - 20:20; the crosslinking time is 24 - 48 h.

[0016] Further preferably, in step (2), the photocatalyst is g-C 3 N 4 / Pt nanosheets; the concentration of the sodium alginate solution is 1 - 1.5 wt%.

[0017] g-C 3 N 4 responds to visible light, has a low price, is simple to synthesize and prepare, and has good stability, so it is widely used in the field of hydrogen production. However, pure g-C 3 N 4 photocatalyst has limited photocatalytic performance due to low carrier separation efficiency and serious charge recombination. To improve its photocatalytic activity, g-C 3 N 4 is modified with Pt to achieve efficient water splitting for hydrogen production and CO 2 efficient activation and conversion. The addition of Pt can promote the rapid transfer of photo-generated electrons produced by g-C 3 N 4 , reduce the recombination of electron-hole pairs, and thus improve the photocatalytic efficiency. In addition, the high dispersion of Pt nanoparticles also helps to increase the surface area and active sites of the photocatalyst, further enhancing its photocatalytic performance.

[0018] Further preferably, in step (2), the dosage ratio of the photocatalyst, sodium alginate and water is 2 - 5 mg: 0.1 g: 10 mL; the dispersion method is ultrasonic dispersion, and the dispersion time is 20 - 40 min.

[0019] Further preferably, in step (2), the dosage ratio of the SPN / SA hydrogel beads to the dispersion liquid is 0.5 - 0.8 g: 10 - 15 mL.

[0020] Further preferably, in step (2), the concentration of the CaCl 2 solution is 1 - 1.5 wt%; the volume ratio of the dispersion liquid to the CaCl 2 solution is 10 - 15:20.

[0021] Further preferably, in step (2), the crosslinking time is 24 - 48 h.

[0022] The second technical solution of the present invention: an application of the composite hydrogel obtained by the above preparation method in photocatalytic hydrogen production.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) First, the SPN / SA hydrogel beads are prepared in the present invention, and then they are embedded inside the sodium alginate hydrogel to obtain a composite hydrogel. By virtue of the refractive index difference and intermolecular hydrogen bonds between soy protein and sodium alginate, high light absorption and long water retention are achieved. Due to the different refractive indices of sodium alginate and soy protein nanofibers, the SPN / SA hydrogel beads can serve as light scattering centers, and the multiple scattering of incident light improves the light absorption ability, thereby improving the hydrogen production efficiency. At the same time, the -COOH and -NH 2 groups of the SPN / SA hydrogel beads can form hydrogen bonds and electrostatic interactions with water molecules, reducing the evaporation rate of water molecules inside the hydrogel and enhancing the water retention, providing an adequate water environment for photocatalytic water splitting for hydrogen production.

[0025] (2) By loading the photocatalyst inside the sodium alginate hydrogel in the present invention, effective dispersion can be achieved by utilizing the three-dimensional network structure, avoiding the aggregation effect, and thus improving the hydrogen production efficiency. Description of the Drawings

[0026] Figure 1 are the cross-sectional SEM images of the sodium alginate composite hydrogel without hydrogel beads prepared in Comparative Example 1 of the present invention and the composite hydrogel embedded with SPN / SA hydrogel beads prepared in Example 2; among them, (a) is the cross-sectional SEM image of the composite sodium alginate hydrogel without hydrogel beads in Comparative Example 1; (b) is the cross-sectional SEM image of the composite hydrogel embedded with SPN 2 / SA 1 hydrogel beads in Example 2;

[0027] Figure 2 are the light absorption diagrams of the sodium alginate composite hydrogel without hydrogel beads and the composite hydrogel embedded with SPN / SA hydrogel beads prepared in Examples 1, 2 and Comparative Example 1 of the present invention;

[0028] Figure 3 are the water retention performance diagrams of the sodium alginate composite hydrogel without hydrogel beads and the composite hydrogel embedded with SPN / SA hydrogel beads prepared in Examples 1, 2 and Comparative Example 1 of the present invention; in the three-column bar charts for each time period, the left column is the water loss rate of the composite sodium alginate hydrogel without hydrogel beads in Comparative Example 1, the middle column is the water loss rate of the composite hydrogel embedded with SPN 1 / SA 1 hydrogel beads in Example 1, and the right column is the water loss rate of the composite hydrogel embedded with SPN 2 / SA 1 hydrogel beads in Example 2;

[0029] Figure 4Hydrogen production total amount graphs of the sodium alginate composite hydrogels without hydrogel beads and the composite hydrogels embedded with SPN / SA hydrogel beads prepared in Example 1, Example 2 and Comparative Example 1 of the present invention. Detailed implementation manners

[0030] The above content of the present invention will be further described in detail through the following examples. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. Any technology implemented based on the above content of the present invention belongs to the scope of the present invention.

[0031] Comparative Example 1

[0032] Ultrasonically treat 2 mg g-C 3 N 4 / Pt in 10 mL of deionized water for 15 min to form a suspension. Dissolve 0.1 g of sodium alginate (SA) in the above suspension. Then, crosslink the solution in 20 mL of a 1 wt% CaCl 2 solution for 24 h to obtain a composite hydrogel. Subsequently, soak the composite hydrogel in deionized water for 12 h to remove undissolved impurities, and obtain a sodium alginate composite hydrogel.

[0033] Example 1

[0034] (1) Uniformly disperse 5 g of soy protein isolate (SPI) in 100 mL of deionized water, and adjust the pH value to 2.0 with HCl. Stir the solution at room temperature for 2 h and then store it at 4 °C overnight. Subsequently, centrifuge the hydrated solution at 10000 rpm for 30 min, and filter the obtained supernatant through a filter membrane. Then, continuously stir the solution at 85 °C for 12 h, cool it with ice water, and adjust the pH to neutral with NaOH. After freeze-drying the solution, soy protein nanofibers (SPN) are obtained.

[0035] (2) Dissolve sodium alginate and soy protein nanofibers in water respectively to obtain an SA solution and an SPN solution; take 10 mL of a 1 wt% SA solution and 10 mL of a 1 wt% SPN solution and mix them, and stir at a speed of 600 rmp at room temperature for 4 h. Drop the mixed solution into 20 mL of a 1 wt% CaCl 2 solution for crosslinking for 6 h, and maintain the rotation speed at 300 rpm during this period. Subsequently, wash the obtained SPN 1 / SA 1 hydrogel beads 3 times with deionized water to remove impurities on the surface.

[0036] (3) Ultrasonically treat 2 mg g-C 3 N 4 / Pt was ultrasonically treated in 10 mL of deionized water for 15 min to form a suspension. 0.1 g of sodium alginate (SA) was dissolved in the above suspension to obtain a dispersion. Subsequently, 0.5 g of SPN 1 / SA 1 hydrogel beads were added to the dispersion. And the solution was cross-linked in 20 mL of a 1 wt% CaCl 2 solution for 24 h. The resulting gel was washed with deionized water to obtain a composite hydrogel. Subsequently, the composite hydrogel was soaked in deionized water for 12 h to remove undissolved impurities. A composite hydrogel embedded with SPN 1 / SA 1 hydrogel beads was obtained.

[0037] Example 2

[0038] (1) 5 g of soy protein isolate (SPI) was uniformly dispersed in 100 mL of deionized water, and the pH value was adjusted to 2.0 with HCl. After stirring the solution at room temperature for 2 h, it was stored overnight at 4 °C. Subsequently, the hydrated solution was centrifuged at 10000 rpm for 30 min, and the resulting supernatant was filtered through a filter membrane. Then the solution was continuously stirred at 85 °C for 12 h, cooled with ice water, and the pH was adjusted to neutral with NaOH. After freeze-drying the solution, soy protein nanofibers (SPN) were obtained.

[0039] (2) Sodium alginate and soy protein nanofibers were respectively dissolved in water to obtain an SA solution and an SPN solution; 5 mL of a 1 wt% SA solution and 10 mL of a 1 wt% SPN solution were mixed and stirred at a speed of 600 rmp at room temperature for 4 h. The mixed solution was dropped into 20 mL of a 1 wt% CaCl 2 solution for cross-linking for 6 h, and the rotation speed was maintained at 300 rpm during this period. Subsequently, the obtained SPN 2 / SA 1 hydrogel beads were washed 3 times with deionized water to remove surface impurities.

[0040] (3) 2 mg of g-C 3 N 4 / Pt was ultrasonically treated in 10 mL of deionized water for 15 min to form a suspension. 0.1 g of sodium alginate (SA) was dissolved in the above suspension to obtain a dispersion. Subsequently, 0.5 g of SPN 2 / SA 1 hydrogel beads were added to the dispersion. And the solution was in 20 mL of a 1 wt% CaCl 2After crosslinking in the solution for 24 h, the obtained gel was washed with deionized water to obtain a composite hydrogel. Subsequently, the composite hydrogel was immersed in deionized water for 12 h to remove undissolved impurities. A composite hydrogel embedded with SPN 2 / SA 1 hydrogel beads was obtained.

[0041] Example 3

[0042] (1) 5 g of soy protein isolate (SPI) was uniformly dispersed in 100 mL of deionized water, and the pH value was adjusted to 2.0 with HCl. After stirring the solution at room temperature for 2 h, it was stored overnight at 4 °C. Subsequently, the hydrated solution was centrifuged at 10000 rpm for 30 min, and the obtained supernatant was filtered through a filter membrane. Then, after continuously stirring the solution at 85 °C for 12 h, it was cooled with ice water, and the pH was adjusted to neutral with NaOH. After freeze-drying the solution, soy protein nanofibers (SPN) were obtained.

[0043] (2) Sodium alginate and soy protein nanofibers were respectively dissolved in water to obtain SA solution and SPN solution; 10 mL of 1 wt% SA solution and 10 mL of 1 wt% SPN solution were taken and mixed, and stirred at a speed of 600 rpm at room temperature for 4 h. The mixed solution was dropped into 20 mL of 1 wt% CaCl 2 solution for crosslinking for 6 h, and the rotation speed was maintained at 300 rpm during this period. Subsequently, the obtained SPN 1 / SA 1 hydrogel beads were washed 3 times with deionized water to remove surface impurities.

[0044] (3) 2 mg of g-C 3 N 4 / Pt was ultrasonically treated in 10 mL of deionized water for 15 min to form a suspension. 0.1 g of sodium alginate (SA) was dissolved in the above suspension to obtain a dispersion. Subsequently, 0.5 g of SPN 1 / SA 1 hydrogel beads were added to the dispersion. And after crosslinking the solution in 20 mL of 1 wt% CaCl 2 solution for 72 h, the obtained gel was washed with deionized water to obtain a composite hydrogel. Subsequently, the composite hydrogel was immersed in deionized water for 12 h to remove undissolved impurities. A composite hydrogel embedded with SPN 1 / SA 1 hydrogel beads was obtained.

[0045] Example 4

[0046] (1) 5 g of soy protein isolate (SPI) was uniformly dispersed in 100 mL of deionized water, and the pH value was adjusted to 2.0 with HCl. After stirring the solution at room temperature for 2 h, it was stored overnight at 4 °C. Subsequently, the hydrated solution was centrifuged at 10,000 rpm for 30 min, and the obtained supernatant was filtered through a membrane filter. Then, the solution was continuously stirred at 85 °C for 12 h, cooled with ice water, and the pH was adjusted to neutral with NaOH. After freeze-drying the solution, soy protein nanofibers (SPN) were obtained.

[0047] (2) Sodium alginate and soy protein nanofibers were dissolved in water respectively to obtain SA solution and SPN solution; 10 mL of 1 wt% SA solution and 10 mL of 1 wt% SPN solution were taken and mixed, and stirred at a speed of 600 rmp at room temperature for 4 h. The mixed solution was dropped into 20 mL of 1 wt% CaCl 2 solution for crosslinking for 6 h, and the rotation speed was maintained at 300 rpm during this period. Subsequently, the obtained SPN 1 / SA 1 hydrogel beads were washed 3 times with deionized water to remove impurities on the surface.

[0048] (3) 2 mg of g-C 3 N 4 / Pt was ultrasonically treated in 10 mL of deionized water for 15 min to form a suspension. 0.1 g of sodium alginate (SA) was dissolved in the above suspension to obtain a dispersion. Subsequently, 0.5 g of SPN 1 / SA 1 hydrogel beads were added to the dispersion. And the solution was crosslinked in 20 mL of 1 wt% CaCl 2 solution for 0.5 h, and the obtained gel was washed with deionized water to obtain a composite hydrogel. Subsequently, the composite hydrogel was soaked in deionized water for 12 h to remove undissolved impurities. A composite hydrogel embedded with SPN 1 / SA 1 hydrogel beads was obtained.

[0049] Example 5

[0050] (1) 5 g of soy protein isolate (SPI) was uniformly dispersed in 100 mL of deionized water, and the pH value was adjusted to 2.0 with HCl. After stirring the solution at room temperature for 2 h, it was stored overnight at 4 °C. Subsequently, the hydrated solution was centrifuged at 10,000 rpm for 30 min, and the obtained supernatant was filtered through a membrane filter. Then, the solution was continuously stirred at 85 °C for 12 h, cooled with ice water, and the pH was adjusted to neutral with NaOH. After freeze-drying the solution, soy protein nanofibers (SPN) were obtained.

[0051] (2) Dissolve sodium alginate and soy protein nanofibers in water respectively to obtain SA solution and SPN solution; take 10 mL of 1 wt% SA solution and 10 mL of 1 wt% SPN solution and mix them, and stir at a speed of 600 rmp at room temperature for 4 h. Drop the mixed solution into 20 mL of 1 wt% CaCl 2 solution for crosslinking for 6 h, and keep the rotation speed at 300 rpm during this period. Subsequently, the obtained SPN 1 / SA 1 hydrogel beads are washed 3 times with deionized water to remove impurities on the surface.

[0052] (3) Ultrasonically treat 0.5 mg g-C 3 N 4 / Pt in 10 mL of deionized water for 15 min to form a suspension. Dissolve 0.1 g of sodium alginate (SA) in the above suspension to obtain a dispersion. Subsequently, add 0.5 g of SPN 1 / SA 1 hydrogel beads into the dispersion. After crosslinking the solution in 20 mL of 1 wt% CaCl 2 solution for 24 h, the obtained gel is washed with deionized water to obtain a composite hydrogel. Subsequently, soak the composite hydrogel in deionized water for 12 h to remove undissolved impurities. Obtain a composite hydrogel embedded with SPN 1 / SA 1 hydrogel beads.

[0053] Example 6

[0054] (1) Uniformly disperse 5 g of soy protein isolate (SPI) in 100 mL of deionized water, and adjust the pH value to 2.0 with HCl. Stir the solution at room temperature for 2 h and then store it at 4 °C overnight. Subsequently, centrifuge the hydrated solution at a speed of 10000 rpm for 30 min, and filter the obtained supernatant through a filter membrane. Then, continuously stir the solution at 85 °C for 12 h, cool it with ice water, and adjust the pH to neutral with NaOH. After freeze-drying the solution, soy protein nanofibers (SPN) are obtained.

[0055] (2) Dissolve sodium alginate and soy protein nanofibers in water respectively to obtain SA solution and SPN solution; take 10 mL of 1 wt% SA solution and 10 mL of 1 wt% SPN solution and mix them, and stir at a speed of 600 rmp at room temperature for 4 h. Drop the mixed solution into 20 mL of 1 wt% CaCl 2 solution for crosslinking for 6 h, and keep the rotation speed at 300 rpm during this period. Subsequently, the obtained SPN 1 / SA 1The hydrogel beads were washed three times with deionized water to remove the impurities on the surface.

[0056] (3) 1 g of g-C 3 N 4 / Pt was ultrasonically treated in 10 mL of deionized water for 15 min to form a suspension. 0.1 g of sodium alginate (SA) was dissolved in the above suspension to obtain a dispersion. Subsequently, 0.5 g of SPN 1 / SA 1 hydrogel beads were added to the dispersion. And the solution was crosslinked in 20 mL of a 1 wt% CaCl 2 solution for 24 h. The resulting gel was washed with deionized water to obtain a composite hydrogel. Subsequently, the composite hydrogel was immersed in deionized water for 12 h to remove the undissolved impurities. A composite hydrogel embedded with SPN 1 / SA 1 hydrogel beads was obtained.

[0057] Example 7

[0058] (1) 5 g of soy protein isolate (SPI) was uniformly dispersed in 100 mL of deionized water, and the pH value was adjusted to 2.0 with HCl. After stirring the solution at room temperature for 2 h, it was stored overnight at 4 °C. Subsequently, the hydrated solution was centrifuged at 10000 rpm for 30 min, and the obtained supernatant was filtered through a filter membrane. Then, after continuously stirring the solution at 85 °C for 12 h, it was cooled with ice water, and the pH was adjusted to neutral with NaOH. After freeze-drying the solution, soy protein nanofibers (SPN) were obtained.

[0059] (2) Sodium alginate and soy protein nanofibers were respectively dissolved in water to obtain an SA solution and an SPN solution; 1 mL of a 1 wt% SA solution and 10 mL of a 1 wt% SPN solution were taken and mixed, and the mixture was stirred at a speed of 600 rmp at room temperature for 4 h. The mixed solution was dropped into 20 mL of a 1 wt% CaCl 2 solution for crosslinking for 6 h, and the rotation speed was maintained at 300 rpm during this period. Subsequently, the obtained SPN 10 / SA 1 hydrogel beads were washed three times with deionized water to remove the impurities on the surface.

[0060] (3) 2 mg of g-C 3 N 4 / Pt was ultrasonically treated in 10 mL of deionized water for 15 min to form a suspension. 0.1 g of sodium alginate (SA) was dissolved in the above suspension to obtain a dispersion. Subsequently, 0.5 g of SPN 10 / SA 1The hydrogel beads were added to the dispersion. The solution was crosslinked in 20 mL of a 1 wt% CaCl 2 solution for 24 h. The resulting gel was washed with deionized water to obtain a composite hydrogel. Subsequently, the composite hydrogel was soaked in deionized water for 12 h to remove undissolved impurities. A composite hydrogel embedded with SPN 10 / SA 1 hydrogel beads was obtained.

[0061] Example 8

[0062] (1) 5 g of soy protein isolate (SPI) was uniformly dispersed in 100 mL of deionized water, and the pH value was adjusted to 2.0 with HCl. After stirring the solution at room temperature for 2 h, it was stored overnight at 4 °C. Subsequently, the hydrated solution was centrifuged at 10,000 rpm for 30 min, and the resulting supernatant was filtered through a membrane filter. Then, the solution was continuously stirred at 85 °C for 12 h, cooled with ice water, and the pH was adjusted to neutral with NaOH. After freeze-drying the solution, soy protein nanofibers (SPN) were obtained.

[0063] (2) Sodium alginate and soy protein nanofibers were respectively dissolved in water to obtain an SA solution and an SPN solution; 10 mL of a 1 wt% SA solution and 1 mL of a 1 wt% SPN solution were taken and mixed, and the mixture was stirred at a speed of 600 rmp at room temperature for 4 h. The mixed solution was dropped into 20 mL of a 1 wt% CaCl 2 solution for crosslinking for 6 h, and the rotation speed was maintained at 300 rpm during this period. Subsequently, the obtained SPN 1 / SA 10 hydrogel beads were washed 3 times with deionized water to remove impurities on the surface.

[0064] (3) 2 mg of g-C 3 N 4 / Pt was ultrasonically treated in 10 mL of deionized water for 15 min to form a suspension. 0.1 g of sodium alginate (SA) was dissolved in the above suspension to obtain a dispersion. Subsequently, 0.5 g of SPN 1 / SA 10 hydrogel beads were added to the dispersion. The solution was crosslinked in 20 mL of a 1 wt% CaCl 2 solution for 24 h. The resulting gel was washed with deionized water to obtain a composite hydrogel. Subsequently, the composite hydrogel was soaked in deionized water for 12 h to remove undissolved impurities. A composite hydrogel embedded with SPN 1 / SA 10 hydrogel beads was obtained.

[0065] Performance test

[0066] (1) The sodium alginate composite hydrogel without hydrogel beads prepared in Comparative Example 1 and the composite hydrogel embedded with SPN 2 / SA 1 hydrogel beads are shown in cross-section as Figure 1 follows. It can be seen from the figure that the cross-sections of the composite hydrogels in Comparative Example 1 and Example 2 both show a porous structure. In contrast, the pores of the composite hydrogel embedded with SPN 2 / SA 1 hydrogel beads in Example 2 are much smaller. This is because there are -COOH and -NH 2 / SA 1 groups in the SPN 2 / SA hydrogel beads, and the electrostatic interaction and hydrogen bond interaction between the hydrogel beads and the sodium alginate composite hydrogel are enhanced. This not only improves the mechanical properties and structural stability of the hydrogel, but also makes the hydrogel network denser and the pore size smaller.

[0067] (2) The ultraviolet-visible absorbance of the sodium alginate composite hydrogel without hydrogel beads prepared in Comparative Example 1 and the composite hydrogels embedded with SPN / SA hydrogel beads prepared in Examples 1-2 was studied using a UV-visible spectrophotometer with an integrating sphere (UV-2600, PerkinElmer, USA). The wavelength range was selected as 200 - 800 nm. The light absorption effects of the sodium alginate composite hydrogel without hydrogel beads prepared in Comparative Example 1 and the composite hydrogels embedded with SPN / SA hydrogel beads prepared in Examples 1-2 are shown in Figure 2 the figure. It can be seen that the light absorption ability of the composite hydrogels embedded with SPN / SA hydrogel beads in Examples 1-2 is significantly improved compared to that of the sodium alginate composite hydrogel without hydrogel beads in Comparative Example 1. This is related to the different refractive indices of SPN and SA. Since the refractive index of SPN is different from that of SA, the SPN / SA hydrogel beads can serve as scattering centers for incident light, which is beneficial to significantly improving the light absorption ability and thus enhancing the photocatalytic hydrogen production ability by water splitting. In addition, the composite hydrogel embedded with SPN2 / SA1 hydrogel beads in Example 2 has a stronger light absorption ability. This is because an increase in the content of soy protein nanofibers will increase the specific surface area of the material and enhance light absorption; at the same time, the more soy protein nanofibers, the more times light is scattered in the fibers, resulting in more light being absorbed.

[0068] (3) The water retention ability was studied by measuring the weight loss of the sodium alginate composite hydrogel without hydrogel beads prepared in Comparative Example 1 and the composite hydrogels embedded with SPN / SA hydrogel beads prepared in Examples 1-2 under infrared light (LP-3B, Beijing Wuke Optoelectronic Technology Co., Ltd.). The water retention performances of the sodium alginate composite hydrogel without hydrogel beads prepared in Comparative Example 1 and the sodium alginate composite hydrogels without hydrogel beads and the composite hydrogels embedded with SPN / SA hydrogel beads prepared in Examples 1-2 are as Figure 3 shown. It can be seen from the figure that the water retention performance of the sodium alginate composite hydrogel without hydrogel beads in Comparative Example 1 is the worst, followed by the composite hydrogel embedded with SPN 1 / SA 1 hydrogel beads in Example 1, and the composite hydrogel with the best water retention performance is the composite hydrogel embedded with SPN 2 / SA 1 hydrogel beads in Example 2. This is because SPN, as a protein, has extremely strong hydrophilicity and can absorb a large number of water molecules and bind to them. The higher the SPN content, the more hydrophilic groups it contains, which is more conducive to the existence of water molecules in the hydrogel and provides an abundant water environment for photocatalytic hydrolysis to produce hydrogen.

[0069] (4) Under the irradiation of a xenon lamp (TCD GC, GC1690, China Coulon Technology Co., Ltd.), a gas chromatograph (TCDGC, GC1690, China Coulon Technology Co., Ltd.) was used to measure photocatalytic hydrogen evolution. The total hydrogen production amounts of the sodium alginate composite hydrogel without hydrogel beads prepared in Comparative Example 1 and the composite hydrogels embedded with SPN / SA hydrogel beads prepared in Examples 1-2 are as Figure 4 shown. The figure shows that the total hydrogen production amount of the composite hydrogel embedded with SPN 2 / SA 1 hydrogel beads in Example 2 is the largest, followed by the composite hydrogel embedded with SPN 1 / SA 1 hydrogel beads in Example 1, and the total hydrogen production amount of the composite sodium alginate without hydrogel beads in Comparative Example 1 is the least. The embedded SPN / SA hydrogel beads, as the scattering centers of the sodium alginate composite hydrogel, can effectively improve the light absorption ability; at the same time, the -COOH and -NH 2 groups in SPN can enhance the hydrogen bond and electrostatic interactions with water molecules, resulting in an improvement in the water retention performance of the sodium alginate composite hydrogel. The combined action of these two aspects significantly improves the hydrogen production efficiency of the composite hydrogel embedded with SPN / SA hydrogel beads.

[0070] Table 1

[0071]

[0072]

[0073] (5) The hydrogen production comparisons of the composite hydrogels embedded with SPN / SA hydrogel beads prepared in Examples 1-8 under different parameters are shown in Table 1. In Example 3, due to the too long soaking time in the CaCl 2 solution, the crosslinking degree of the composite hydrogel was too large, the internal three-dimensional network structure was tighter, and the hydrogen produced by photocatalysis could not be transported. In Example 4, the soaking time in the CaCl 2 solution was too short to form a composite hydrogel, so the subsequent hydrogen production could not be carried out. In Example 5, the content of the photocatalyst was too low, resulting in too few photocatalytic sites and little hydrogen production. In Example 6, due to the too high content of the photocatalyst, a large amount of the photocatalyst agglomerated, reducing the area exposed to light, and thus affecting the hydrogen production rate. In Example 7, the content of SPN in the hydrogel beads was too high, making gelation difficult and unable to form a composite hydrogel, resulting in the inability to carry out the hydrogen production experiment. In Example 8, the content of SPN in the hydrogel beads was too low, resulting in the components of the sodium alginate hydrogel and the hydrogel beads being basically the same, and the light absorption and water retention ability were hardly improved, and the hydrogen production efficiency was similar to that of Comparative Example 1.

[0074] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0075] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a composite hydrogel based on soy protein and sodium alginate, characterized in that: The steps include: (1) Sodium alginate and soybean protein nanofibers are dissolved in water to obtain SA solution and SPN solution respectively; the two are mixed in proportion, and then the mixed solution is dropped into a CaCl2 solution through a syringe for cross-linking, and after the gelation is completed, it is washed with deionized water to obtain SPN / SA hydrogel beads; (2) The photocatalyst is uniformly dispersed in water, and sodium alginate is added to dissolve to obtain a dispersion; SPN / SA hydrogel beads are then added to the dispersion and stirred evenly; the solution is then added to a CaCl2 solution for cross-linking to finally obtain a composite hydrogel.

2. The method for preparing the composite hydrogel based on soy protein and sodium alginate according to claim 1, characterized in that: In step (1), the preparation method of the soybean protein nanofibers comprises the following steps: dispersing the soybean protein isolate in water and adjusting the pH to 2-4, and hydrating overnight; obtaining the supernatant of the solution by centrifugation, and removing the undissolved large particles through a filter membrane; then heating and stirring the solution, and then rapidly cooling and adjusting the pH to neutral; and finally freeze-drying the solution to obtain the soybean protein nanofibers.

3. The method for preparing the composite hydrogel based on soy protein and sodium alginate according to claim 2, characterized in that: The soy protein isolate is dispersed in water at a ratio of 4-6 g:100 mL; the overnight hydration is carried out at 2-6° C.; the centrifugal speed is 8000-10000 rpm, and the time is 20-30 min; the heating and stirring temperature is 70-90° C., and the heating time is 8-10 h.

4. The method for preparing the composite hydrogel based on soybean protein and sodium alginate according to any one of claims 1 to 3, characterized in that: In step (1), the concentration of the SA solution is 1-1.5wt%; the concentration of the SPN solution is 1-1.5wt%; and the volume ratio of the SA solution to the SPN solution is (1-3): (1-3).

5. The method for preparing the composite hydrogel based on soybean protein and sodium alginate according to claim 1, characterized in that: In step (2), the photocatalyst is g-C3N4 / Pt nanosheets; and the concentration of the sodium alginate solution is 1-1.5wt%.

6. The method for preparing the composite hydrogel based on soybean protein and sodium alginate according to claim 1 or 5, characterized in that: In step (2), the amount ratio of the photocatalyst, sodium alginate and water is 2-5 mg: 0.1 g: 10 mL; the dispersion method is ultrasonic dispersion, and the dispersion time is 20-40 min.

7. The method for preparing the composite hydrogel based on soybean protein and sodium alginate according to claim 1 or 5, characterized in that: In step (2), the usage ratio of the SPN / SA hydrogel beads to the dispersion is 0.5-0.8 g: 10-15 mL.

8. The method for preparing the composite hydrogel based on soybean protein and sodium alginate according to claim 1, characterized in that: In step (1) and step (2), the concentration of the CaCl2 solution is 1-1.5wt%.

9. The method for preparing the composite hydrogel based on soybean protein and sodium alginate according to claim 1 or 8, characterized in that: In step (2), the cross-linking time is 24-48 hours.

10. Use of the composite hydrogel obtained by the preparation method according to any one of claims 1 to 9 in photocatalytic hydrogen production.

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