A mineral-based photo-thermal composite hydrogel as well as a preparation method and application thereof

Abstract

The present application relates to the technical field of hydrogel, especially relates to a mineral-based photo-thermal composite hydrogel and a preparation method and application thereof.The preparation method comprises the following steps: S1, growing ZIF-67 particles in situ on the surface of montmorillonite; calcining and carbonizing to obtain ZIF-67 derived porous carbon / montmorillonite composite material; S2, adding acetic acid solution to a mixed solution of polyvinyl alcohol and chitosan, and then performing ultrasonic stirring and dispersion after rapid stirring and crosslinking, and performing physical circulation freezing-melting for several times.The ZIF-67 derived porous carbon / montmorillonite composite material prepared by the present application has the advantages of simple preparation process and high photo-thermal conversion capacity, can promote the formation of a complex crosslinking network of the hydrogel, obviously improves the mechanical strength, improves the recycling capacity, environmental tolerance and structural stability of the hydrogel, and the water evaporation rate of the hydrogel under continuous light conditions can reach 2.2 kg m ‑2 h ‑1 , and the desalination capacity is more than 98%.

Description

Technical Field

[0001] This invention relates to the field of hydrogel technology, and in particular to a mineral-based photothermal composite hydrogel, its preparation method, and its application. Background Technology

[0002] Composite-doped hydrogels refer to hydrogels in which one or more composite materials with unique properties are doped into them, and the composite materials can be uniformly dispersed in the hydrogel; these are also called composite hydrogels. These gels can exhibit special properties such as tensile strength, electrical conductivity, cell affinity, and photothermal properties, and can also improve the mechanical properties of the gel to a certain extent, making them suitable for applications in electrical devices, biopharmaceuticals, seawater desalination, and other fields.

[0003] Photothermal materials are materials that can efficiently convert solar energy into thermal energy, and are an important part of the efficient and comprehensive utilization of solar energy. Common photothermal conversion materials include metal nanoparticles, carbon-based materials, and metal oxides, and their preparation methods are relatively mature. Metal nanoparticles are commonly prepared by chemical reduction and photochemical methods. The former uses a reducing agent to reduce metal ions into nanoparticles, while the latter uses a photosensitizer for reduction under light. Carbon-based materials, such as carbon nanotubes and graphene, are mostly prepared by chemical vapor deposition and solvothermal methods. The former involves the pyrolysis of hydrocarbon gases under the action of a high-temperature catalyst, while the latter involves the reaction in a high-temperature and high-pressure solvent to generate porous carbon. Metal oxides, such as iron oxide and titanium oxide, are commonly prepared by sol-gel and hydrothermal methods. The former involves the hydrolysis and condensation of metal-organic precursors, while the latter involves the reaction in a high-temperature and high-pressure aqueous solution to generate nanoparticles. However, these preparation methods are usually accompanied by high production costs and energy consumption.

[0004] Furthermore, existing technologies incorporate photothermal materials into hydrogels to form composite photothermal evaporators, but these composite photothermal evaporators suffer from problems such as low strength, low light absorption, low evaporation rate, and high enthalpy of evaporation. For example, Chinese patent CN111171340A discloses a photothermal evaporation material based on PVA hydrogel, with an evaporation rate of 1.4 kg / m³. 2 *h. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a mineral-based photothermal composite hydrogel, its preparation method, and its applications.

[0006] The present invention discloses a method for preparing a mineral-based photothermal composite hydrogel, comprising the following steps:

[0007] S1. Preparation of ZIF-67-derived porous carbon / montmorillonite composite materials

[0008] Take an appropriate amount of montmorillonite, cobalt nitrate hexahydrate and 2-methylimidazole and place them in a methanol solution to grow ZIF-67 particles in situ on the surface of montmorillonite; then calcine and carbonize the composite material to obtain ZIF-67 derived porous carbon / montmorillonite composite material.

[0009] S2, Preparation of photothermal gel

[0010] An acetic acid solution was added to a mixed solution of polyvinyl alcohol and chitosan. After rapid stirring and crosslinking, the ZIF-67-derived porous carbon / montmorillonite composite material was dispersed by ultrasonic stirring. Finally, the solution was poured into a mold and subjected to several cycles of physical freeze-thaw.

[0011] Furthermore, the mass ratio of montmorillonite, cobalt nitrate hexahydrate, and 2-methylimidazole is 1-3:1:1.

[0012] Furthermore, the calcination and carbonization temperature is 550-950℃, and the time is 2-4 hours.

[0013] Furthermore, the heating rate for calcination and carbonization is 10℃ / min.

[0014] Furthermore, in step S2, the mass of ZIF-67 derived porous carbon / montmorillonite is 1-4 wt% of the total mass of the solution.

[0015] Furthermore, the mass ratio of ZIF-67 derived porous carbon / montmorillonite, polyvinyl alcohol, and chitosan is 1-3:1-2:3-4.

[0016] Furthermore, the freeze-thaw cycle is repeated three times.

[0017] Furthermore, the concentration of the acetic acid solution is 1 wt%.

[0018] A mineral-based photothermal composite hydrogel prepared by the method described above.

[0019] An application of a mineral-based photothermal composite hydrogel as described above in seawater desalination and wastewater treatment.

[0020] Beneficial effects:

[0021] 1. The ZIF-67-derived porous carbon / montmorillonite composite material prepared by this invention has a simple and easy preparation process and high photothermal conversion capacity, with an absorbance exceeding 90% across the entire spectrum. While ensuring stable absorbance, the production efficiency of the ZIF-67-derived porous carbon / montmorillonite composite material far exceeds that of ZIF-67-derived porous carbon. After calcination, the organic ligands of ZIF-67 decompose, leaving nitrogen-doped porous carbon material. This process causes mass loss and agglomeration of porous carbon, thus affecting light absorption and production efficiency. By loading the same mass of ZIF-67 onto montmorillonite and then carbonizing it, the structural control during the carbonization process is enhanced, the dispersion of particulate porous carbon is improved, and large-scale, efficient preparation is achieved.

[0022] 2. The introduction of ZIF-67-derived porous carbon / montmorillonite composite material can promote the formation of complex cross-linked networks in hydrogels. Compared with photothermal hydrogels prepared by ZIF-67-derived porous carbon, the mechanical strength is significantly improved, enhancing its recyclability, environmental tolerance, and structural stability.

[0023] 3. The photothermal gel provided by this invention can be applied to seawater desalination, achieving a water evaporation rate of up to 2.2 kg / m³ under continuous light irradiation. -2 h -1 Its desalination capacity exceeds 98%.

[0024] 4. A hydrogel with a stable structure and rich pore structure was obtained by rationally combining ZIF-67-derived porous carbon / montmorillonite composite material, polyvinyl alcohol and chitosan. Attached Figure Description

[0025] Figure 1 Photograph of the ZIF-67-derived porous carbon hydrogel prepared for Comparative Example 1;

[0026] Figure 2 Photograph of the ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 1;

[0027] Figure 3 The light absorption effects of ZIF-67, ZIF-67-derived porous carbon prepared in Comparative Example 1, and ZIF-67-derived porous carbon / montmorillonite prepared in Example 6;

[0028] Figure 4 Microstructure of ZIF-67-derived porous carbon / montmorillonite prepared for ZIF-67 and Example 6;

[0029] Figure 5 The ZIF-67-derived porous carbon prepared in Comparative Example 1 and the ZIF-67-derived porous carbon / montmorillonite N2 adsorption-desorption isotherms prepared in Example 6;

[0030] Figure 6The pore size distribution of ZIF-67-derived porous carbon prepared in Comparative Example 1 and ZIF-67-derived porous carbon / montmorillonite prepared in Example 6;

[0031] Figure 7a and Figure 7b The microstructure of the ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6;

[0032] Figure 8 The desalination effect of the ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6;

[0033] Figure 9 The effect of reducing the enthalpy of vaporization of the ZIF-67-derived porous carbon hydrogel prepared in Comparative Example 1 and the ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6 was investigated.

[0034] Figure 10 The light absorption effect of the ZIF-67-derived porous carbon / montmorillonite hydrogels prepared in Examples 4 and 6;

[0035] Figure 11 The ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6 was used to improve the evaporation rate of seawater desalination. Detailed Implementation

[0036] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0037] Example 1: Preparation of ZIF-67-derived porous carbon / montmorillonite hydrogel

[0038] (1) Preparation of ZIF-67-derived porous carbon / montmorillonite composite material: 1g of cobalt nitrate hexahydrate was dissolved in 10ml of methanol, 1g of 2-methylimidazole was dissolved in another 40ml of methanol, and 2g of montmorillonite was dispersed in 50ml of methanol. After dissolving each, the cobalt nitrate hexahydrate-methanol solution was added dropwise to the montmorillonite-methanol solution. After stirring at room temperature for 1h, 2-methylimidazole was slowly poured into the above mixed solution in a straight line. After stirring at room temperature for 1h, it was allowed to stand for 24h to obtain a bright purple precipitate, which is montmorillonite / ZIF-67. The montmorillonite / ZIF-67 was placed in a tube furnace under an argon atmosphere at a heating rate of 10℃ / min and held at 550℃ for 3h to obtain the ZIF-67-derived porous carbon / montmorillonite composite material.

[0039] (2) Preparation of photothermal hydrogel: 0.80 g chitosan and 2.40 g polyvinyl alcohol were dispersed in a beaker containing 40 ml of pure water and heated and stirred at 90 °C for 3 h to obtain a mixed solution. After cooling the mixed solution to room temperature, 1 wt% acetic acid solution was added, and the mixture was rapidly stirred and crosslinked for 30 min. Then, 1 wt% ZIF-67-derived porous carbon / montmorillonite composite material was dispersed by ultrasonic stirring. Finally, the solution was poured into an acrylic mold with a diameter of 3 cm and a height of 2 cm, solidified at -25 °C for 6 h, and then thawed at room temperature. This process was repeated three times.

[0040] Example 2: Preparation of ZIF-67-derived porous carbon / montmorillonite hydrogel

[0041] (1) Preparation of ZIF-67-derived porous carbon / montmorillonite composite material: 1g of cobalt nitrate hexahydrate was dissolved in 10ml of methanol, 1g of 2-methylimidazole was dissolved in another 40ml of methanol, and 2g of montmorillonite was dispersed in 50ml of methanol. After dissolving each, the cobalt nitrate hexahydrate-methanol solution was added dropwise to the montmorillonite-methanol solution. After stirring at room temperature for 1h, 2-methylimidazole was slowly poured into the above mixed solution in a straight line. After stirring at room temperature for 1h, it was allowed to stand for 24h to obtain a bright purple precipitate, which is montmorillonite / ZIF-67. The montmorillonite / ZIF-67 was placed in a tube furnace under an argon atmosphere at a heating rate of 10℃ / min and held at 750℃ for 3h to obtain the ZIF-67-derived porous carbon / montmorillonite composite material.

[0042] Step (2) is the same as in Example 1.

[0043] Example 3: Preparation of ZIF-67-derived porous carbon / montmorillonite hydrogel

[0044] (1) Preparation of ZIF-67-derived porous carbon / montmorillonite composite material: 1g of cobalt nitrate hexahydrate was dissolved in 10ml of methanol, 1g of 2-methylimidazole was dissolved in another 40ml of methanol, and 2g of montmorillonite was dispersed in 50ml of methanol. After dissolving each, the cobalt nitrate hexahydrate-methanol solution was added dropwise to the montmorillonite-methanol solution. After stirring at room temperature for 1h, 2-methylimidazole was slowly poured into the above mixed solution in a straight line. After stirring at room temperature for 1h, it was allowed to stand for 24h to obtain a bright purple precipitate, which is montmorillonite / ZIF-67. The montmorillonite / ZIF-67 was placed in a tube furnace under an argon atmosphere, heated at a rate of 10℃ / min, and held at 950℃ for 3h to obtain the ZIF-67-derived porous carbon / montmorillonite composite material.

[0045] Step (2) is the same as in Example 1.

[0046] Example 4: Preparation of ZIF-67-derived porous carbon / montmorillonite hydrogel

[0047] Step (1) is the same as in Example 2.

[0048] (2) Preparation of photothermal hydrogel: 0.80 g chitosan and 2.40 g polyvinyl alcohol were dispersed in a beaker containing 40 ml of pure water and heated and stirred at 90 °C for 3 h to obtain a mixed solution. After cooling the mixed solution to room temperature, 1 wt% acetic acid solution was added, and the mixture was rapidly stirred and crosslinked for 30 min. Then, 2 wt% ZIF-67-derived porous carbon / montmorillonite composite material was dispersed by ultrasonic stirring. Finally, the solution was poured into an acrylic mold with a diameter of 3 cm and a height of 2 cm, solidified at -25 °C for 6 h, and then thawed at room temperature. This process was repeated three times.

[0049] Example 5: Preparation of ZIF-67-derived porous carbon / montmorillonite hydrogel

[0050] Step (1) is the same as in Example 2.

[0051] (2) Preparation of photothermal hydrogel: 0.80 g chitosan and 2.40 g polyvinyl alcohol were dispersed in a beaker containing 40 ml of pure water and heated and stirred at 90 °C for 3 h to obtain a mixed solution. After cooling the mixed solution to room temperature, 1 wt% acetic acid solution was added, and the mixture was rapidly stirred and crosslinked for 30 min. Then, 3 wt% ZIF-67-derived porous carbon / montmorillonite composite material was dispersed by ultrasonic stirring. Finally, the solution was poured into an acrylic mold with a diameter of 3 cm and a height of 2 cm, solidified at -25 °C for 6 h, and then thawed at room temperature. This process was repeated three times.

[0052] Example 6: Preparation of ZIF-67-derived porous carbon / montmorillonite hydrogel

[0053] Step (1) is the same as in Example 2.

[0054] (2) Preparation of photothermal hydrogel: 0.80 g chitosan and 2.40 g polyvinyl alcohol were dispersed in a beaker containing 40 ml of pure water and heated and stirred at 90 °C for 3 h to obtain a mixed solution. After cooling the mixed solution to room temperature, 1 wt% acetic acid solution was added, and the mixture was rapidly stirred and crosslinked for 30 min. Then, 4 wt% ZIF-67-derived porous carbon / montmorillonite composite material was dispersed by ultrasonic stirring. Finally, the solution was poured into an acrylic mold with a diameter of 3 cm and a height of 2 cm, solidified at -25 °C for 6 h, and then thawed at room temperature. This process was repeated three times.

[0055] Comparative Example 1: Preparation of ZIF-67-derived porous carbon gel

[0056] (1) Preparation of ZIF-67-derived porous carbon composite material: 1g of cobalt nitrate hexahydrate was dissolved in 10ml of methanol, and 1g of 2-methylimidazole was dissolved in another 40ml of methanol. After dissolving, the 2-methylimidazole was slowly poured into the cobalt nitrate hexahydrate-methanol solution in a straight line. After stirring at room temperature for 1h, the mixture was allowed to stand for 24h to obtain a bright purple precipitate, which was ZIF-67. ZIF-67 was placed in a tube furnace under an argon atmosphere and heated at 750℃ for 3h at a rate of 10℃ / min to obtain ZIF-67-derived porous carbon.

[0057] (2) Preparation of photothermal hydrogel: 0.80 g chitosan and 2.40 g polyvinyl alcohol were dispersed in a beaker containing 40 ml of pure water and heated and stirred at 90 °C for 3 h to obtain a mixed solution. After cooling the mixed solution to room temperature, 1 wt% acetic acid solution was added, and the mixture was rapidly stirred and crosslinked for 30 min. Then, 4 wt% ZIF-67-derived porous carbon was dispersed by ultrasonic stirring. Finally, the solution was poured into an acrylic mold with a diameter of 3 cm and a height of 2 cm, solidified at -25 °C for 6 h, and then thawed at room temperature. This process was repeated three times.

[0058] Figure 1 The image shows a photograph of the ZIF-67-derived porous carbon hydrogel prepared for Comparative Example 1. As can be seen from the image, the hydrogel exhibits low mechanical strength, and its surface is not smooth enough after demolding, showing surface damage.

[0059] Figure 2 The image shows the ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6. Due to the introduction of the ZIF-67-derived porous carbon / montmorillonite composite material, the crosslinking sites of the long polymer chains are enriched. In addition, the ZIF-67-derived porous carbon / montmorillonite composite material has strong mechanical stability. The synergistic effect of the two improves the crosslinking density and mechanical strength. After demolding, the surface of the hydrogel is smooth and the structure is intact.

[0060] Figure 3 The light absorption effects of ZIF-67, ZIF-67-derived porous carbon prepared in Comparative Example 1, and ZIF-67-derived porous carbon / montmorillonite prepared in Example 6 are shown. The light absorption capacity of ZIF-67 is significantly improved after calcination to become porous carbon. As shown in the inset, the light absorption rate is also improved after loading ZIF-67 onto MMT and then calcining. This is due to the microscopic regulation of porous carbon by MMT, which alters light absorption and scattering, thereby increasing the light absorption rate, which exceeds 90% across the entire spectrum.

[0061] Figure 4 Microstructure of ZIF-67-derived porous carbon / montmorillonite prepared in Example 6: ZIF-67 exhibits an aggregated cubic morphology, and after being calcined with montmorillonite, it exhibits a separated porous spherical carbon morphology.

[0062] Figure 5The images show the N2 adsorption-desorption isotherms of ZIF-67-derived porous carbon prepared in Comparative Example 1 and ZIF-67-derived porous carbon / montmorillonite prepared in Example 6. The specific surface area of ​​ZIF-67-derived porous carbon / montmorillonite is higher than that of ZIF-67-derived porous carbon.

[0063] Figure 6 The pore size distribution of ZIF-67-derived porous carbon prepared in Comparative Example 1 and ZIF-67-derived porous carbon / montmorillonite prepared in Example 6 is shown. ZIF-67-derived porous carbon / montmorillonite has a richer pore structure than ZIF-67-derived porous carbon.

[0064] Figure 7a and Figure 7b The image shows the microstructure of the ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6. The ZIF-67-derived porous carbon / montmorillonite hydrogel exhibits a porous network structure.

[0065] Desalinated seawater ion concentration test: The hydrogel was placed between a transparent glass cover and a transparent glass plate. 1 mL of desalinated distilled water from step (5) and 1 mL of undesalinated seawater were collected and subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES). The measured ion was Na+. + K + Ca 2+ Mg 2+ .

[0066] Figure 8 The desalination effect of the ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6 was demonstrated by applying the ZIF-67-derived porous carbon / montmorillonite hydrogel to seawater desalination via interfacial evaporation. By collecting distilled water during the desalination process, it was shown that the hydrogel can effectively remove metal ions from seawater (Yellow Sea), with a metal ion interception rate of up to 98% and a desalination capacity of over 98%.

[0067] Figure 9 The ZIF-67-derived porous carbon hydrogel prepared in Comparative Example 1 and the ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6 were used to reduce the enthalpy of evaporation. The ZIF-67-derived porous carbon / montmorillonite hydrogel (MMT / ZIF-67-CH) was applied to the interfacial evaporation desalination of seawater and could effectively reduce the enthalpy of evaporation to 1360 J / g.

[0068] Figure 10 The light reflection effect of the ZIF-67-derived porous carbon / montmorillonite hydrogels prepared in Examples 4 and 6 is shown in the figure. Figure 10 It can be seen that the ZIF-67-derived porous carbon / montmorillonite hydrogel has low light reflectivity and good photothermal effect.

[0069] Water evaporation capacity test: The hydrogel was placed in a beaker containing fresh water, and a xenon lamp was used as the solar energy source. The functional density of the solar energy was measured using a power meter, and the mass change of water during the solar-driven evaporation process was monitored using an electronic balance. The ambient temperature and humidity were 26℃ and 50%, respectively. Figure 11 The ZIF-67-derived porous carbon / montmorillonite hydrogel prepared in Example 6 was applied to the evaporation rate of seawater desalination, such as... Figure 11 As shown, under continuous sunlight exposure, the water evaporation rate can reach 2.2 kg / m³. -2 h -1 .

[0070] For any points not covered above, existing technologies shall apply.

[0071] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a mineral-based photo-thermal composite hydrogel, characterized in that, The method comprises the following steps: S1, preparing ZIF-67 derived porous carbon / montmorillonite composite material An appropriate amount of montmorillonite, cobalt nitrate hexahydrate and 2-methyl imidazole are placed in a methanol solution to grow ZIF-67 particles in situ on the surface of the montmorillonite; then the composite material is calcined and carbonized to obtain the ZIF-67 derived porous carbon / montmorillonite composite material; S2, preparing a photothermal hydrogel An acetic acid solution is added to a mixed solution of polyvinyl alcohol and chitosan, and after rapid stirring and crosslinking, the ZIF-67 derived porous carbon / montmorillonite composite material is dispersed by ultrasonic stirring, and finally the solution is poured into a mold and subjected to physical cycle freezing-thawing for several times; The mass ratio of montmorillonite, cobalt nitrate hexahydrate and 2-methyl imidazole is 1-3:1:

1.

2. The production method according to claim 1, wherein The calcination and carbonization temperature is 550-950 ℃, and the time is 2-4h.

3. The production method according to claim 1, characterized by, The heating rate of calcination and carbonization is 10 ℃ / min.

4. The production method according to claim 1, characterized by, In step S2, the mass of ZIF-67 derived porous carbon / montmorillonite is 1-4 wt% of the total mass of the solution.

5. The production method according to claim 4, wherein The mass ratio of ZIF-67 derived porous carbon / montmorillonite, polyvinyl alcohol and chitosan is 1-3:1-2:3-4.

6. The production method according to claim 1, wherein The number of freezing-thawing is 3 times.

7. The production method according to claim 1, characterized by, The concentration of the acetic acid solution is 1 wt%.

8. A mineral-based photothermal composite hydrogel prepared by the preparation method of any one of claims 1-7.

9. The use of the mineral-based photothermal composite hydrogel of claim 8 in desalination of seawater and sewage treatment.

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