Photo-thermal composite hydrogel solar evaporator and preparation method thereof

Abstract

The invention belongs to the technical field of renewable energy utilization and advanced water treatment, and particularly relates to a photo-thermal composite hydrogel solar evaporator and a preparation method thereof. The photo-thermal composite hydrogel solar evaporator is divided into three parts, namely photochromic photo-thermal hydrogel, an efficient water delivery channel and supporting floating foam. And a solar evaporator device with a high evaporation rate is obtained through mold forming. The solar interface evaporator has excellent reversible color change characteristics and photo-thermal performance, can realize efficient seawater evaporation, and has wide application prospects in the fields of new energy and seawater desalination.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy utilization and advanced water treatment, and particularly relates to a photothermal composite hydrogel solar evaporator and a preparation method thereof. Background Art

[0002] Solar interfacial evaporation technology is a new type of water treatment technology based on photothermal conversion. By directly concentrating solar energy at the gas-liquid interface, efficient water evaporation and clean water production can be achieved. Due to its characteristics of being green, low-carbon, low-energy consumption, and high efficiency, this technology has received extensive attention in recent years.

[0003] Hydrogels with a three-dimensional network structure have good hydrophilicity, porous structures, and large surface areas, which are beneficial for the water absorption, water retention, and water transportation of the evaporator. It has been found that polar groups on the hydrogel network activate water through interaction with water, reducing the evaporation enthalpy of water, which can further promote water evaporation.

[0004] Polyoxometalate photochromic materials are special coordination clusters composed of early transition metal ions such as Mo, W, V, and Nb in their highest oxidation states, and are also called polyoxometalates. However, at present, the photo-generated electrons and photo-generated holes of polyoxometalate photochromic materials are prone to recombination, and the utilization rate of photo-generated electrons is low, resulting in a slow color change speed and poor cyclicity.

[0005] The photocatalytic property of titanium dioxide (TiO2) is one of its most significant functional characteristics, which stems from its semiconductor characteristics and active species generated by photoexcitation. By combining hydrogel, polyoxometalate, and titanium dioxide to prepare a solar evaporation device, under visible light irradiation, photo-generated electrons transfer from titanium dioxide to phosphotungstic acid (PWA), thereby reducing W 6+ in phosphotungstic acid to W 5+ , and the material changes from white to blue-black. When there is no light at night, the dark blue composite nanoparticles are oxidized by oxygen in the air and restored to white to achieve reversible color change and efficient production of fresh water.

[0006] The present invention mainly focuses on directions such as the development of photothermal materials, the design of device structures, and the optimization of interfacial evaporation mechanisms. This invention integrates materials science, chemical engineering, environmental engineering, etc., aiming to desalinate seawater through device innovation to solve the problem of clean water shortage. Summary of the Invention

[0007] The present invention mainly focuses on directions such as the development of photothermal materials, the design of device structures, and the optimization of interfacial evaporation mechanisms. It integrates materials science, chemical engineering, environmental engineering, etc., aiming to desalinate seawater through device innovation to solve the problem of clean water shortage.

[0008] The present invention provides a hydrogel-based solar evaporator composite of one or more hydrogels and one or more polyoxometalates, which has good photochromic properties and efficient and rapid water evaporation performance.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A photothermal composite hydrogel solar evaporator, whose structure is divided into three parts, namely: a circular sheet-shaped photochromic and photothermal hydrogel, a water delivery channel, and a supporting floating material.

[0011] Further, for the above-mentioned photothermal composite hydrogel solar evaporator, the water delivery channel is a carrot flower-shaped polypropylene filament bundle with one end dispersed into a circle.

[0012] Furthermore, for the above-mentioned photothermal composite hydrogel solar evaporator, the supporting floating material is polyethylene foam.

[0013] Further, for the above-mentioned photothermal composite hydrogel solar evaporator, the preparation method of the circular sheet-shaped photochromic and photothermal hydrogel is as follows: Mix the photochromic and photothermal material with the double-network hydrogel solution, and ultrasonically disperse it evenly, then pour it into a circular mold for molding.

[0014] Furthermore, for the above-mentioned photothermal composite hydrogel solar evaporator, the mass fraction of the photochromic and photothermal material is 5%.

[0015] Furthermore, for the above-mentioned photothermal composite hydrogel solar evaporator, the photochromic and photothermal material is titanium dioxide / tungstophosphoric acid or titanium dioxide / molybdophosphoric acid.

[0016] Furthermore, for the above-mentioned photothermal composite hydrogel solar evaporator, the preparation method of the photochromic and photothermal material includes the following steps:

[0017] 1) Take 0.50 g of surfactant P123 and 60 mL of diethylene glycol (DEG), heat and stir to dissolve evenly at 60 °C, then raise the temperature to 80 °C, add 1 mL of TiCl4 and mix evenly, then add 1 mL of deionized water and mix evenly, then raise the temperature to 180 °C and heat for 3 h to obtain a self-doped TiO2 dispersion; 3+ Self-doped TiO2 dispersion;

[0018] 2) Dissolve the polyoxometalate in deionized water to form a polyoxometalate solution, then mix the self-doped TiO2 dispersion with the polyoxometalate solution to obtain a white precipitate, and centrifuge, wash and dry the white precipitate for later use; 3+ Self-doped TiO2 dispersion and the polyoxometalate solution are mixed to obtain a white precipitate, and the white precipitate is centrifuged, washed and dried for later use;

[0019] The polyoxometalate is tungstophosphoric acid or molybdophosphoric acid.

[0020] Furthermore, for the above-mentioned photothermal composite hydrogel solar evaporator, the double-network hydrogel is calcium alginate / polyvinyl alcohol double-network hydrogel or chitosan / agarose double-network hydrogel;

[0021] The preparation method of the calcium alginate / polyvinyl alcohol double-network hydrogel is as follows: Dissolve sodium alginate and polyvinyl alcohol in deionized water, heat to completely dissolve it, and put it into a calcium ion solution after repeated freezing and thawing to obtain the calcium alginate / polyvinyl alcohol double-network hydrogel; the mass ratio of sodium alginate to polyvinyl alcohol is 1:1 to 10;

[0022] The preparation method of the chitosan / agarose double-network hydrogel is as follows: Dissolve chitosan, agarose and sodium dodecyl sulfate in acetic acid in deionized water, heat to completely dissolve it, and form the chitosan / agarose double-network hydrogel after cooling; the mass ratio of chitosan to agarose is 7:1.

[0023] The preparation method of the above-mentioned photothermal composite hydrogel solar evaporator includes the following steps:

[0024] 1) Cover a carrot flower-shaped polypropylene filament bundle with one end dispersed into a circle on a circular sheet of photochromic photothermal hydrogel and wait for the gel to form;

[0025] 2) Cut the polyethylene foam into a circular shape of appropriate size, and make a circular hole in the middle so that the other end of the polypropylene filament bundle just passes through the middle, and assemble it into a photothermal composite hydrogel solar evaporator.

[0026] The application of the photothermal composite hydrogel solar evaporator described in any one of the above in seawater desalination.

[0027] Furthermore, the application method is as follows: The photothermal composite hydrogel solar evaporator uses a photochromic photothermal material as the light absorber, a polypropylene filament bundle as the water transmission device, and a polyethylene foam as the floating support device for self-floating seawater desalination.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. The present invention uses a hydrogel as the carrier of the photochromic photothermal material, combines the hydrogel with the photochromic photothermal material to achieve the purpose of efficient water evaporation, uses a polypropylene filament bundle as the material for transporting water, continuously supplies water to the photothermal hydrogel, realizes continuous evaporation of the device, and uses polyethylene foam as the floating support device to realize self-floating evaporation.

[0030] 2. The device of the present invention is simple to prepare, convenient to operate, and low in cost. Brief Description of the Drawings

[0031] Figure 1 It is a structural diagram of the photothermal composite hydrogel solar evaporator.

[0032] Figure 2 It is a color-changing simulation diagram of a photothermal composite hydrogel solar evaporator.

[0033] Figure 3 It is a comparison diagram of the photothermal composite hydrogel solar evaporator before and after illumination.

[0034] Figure 4 It is a physical diagram of a photothermal composite hydrogel solar evaporator with the mass fractions of sodium alginate and polyvinyl alcohol being 1%:5%, 1%:10%, 2%:5%, and 2%:10% respectively.

[0035] Figure 5 It is an infrared spectrum diagram of titanium dioxide, phosphotungstic acid, and titanium dioxide / phosphotungstic acid composite materials.

[0036] Figure 6 It is an ultraviolet-visible diffuse reflectance spectrum diagram of titanium dioxide, phosphotungstic acid, titanium dioxide / phosphotungstic acid solid before illumination, and titanium dioxide / phosphotungstic acid solid after illumination.

[0037] Figure 7 It is the TEM and HRTEM images of titanium dioxide and titanium dioxide / phosphotungstic acid.

[0038] Figure 8 It is the SEM image of calcium alginate / polyvinyl alcohol double-network hydrogel.

[0039] Figure 9 It is the infrared radiation image of the photothermal composite hydrogel solar evaporator prepared in Example 1 during the solar evaporation test.

[0040] Figure 10 It is a graph showing the relationship between the evaporation mass of water and time of the photothermal composite hydrogel solar evaporator prepared in Example 1 during the solar evaporation test. Detailed implementation manners

[0041] In order to highlight the excellent performance of the present invention, it will be further described below in conjunction with specific embodiments. The following specific embodiments are only for the present invention, and the specific implementation process can also be adjusted according to the understanding of those skilled in the art and the actual situation.

[0042] Example 1 A titanium dioxide / phosphotungstic acid photochromic photothermal solar evaporator based on calcium alginate / polyvinyl alcohol hydrogel (I) Preparation method

[0043] 1) Preparation of calcium alginate / polyvinyl alcohol double-network hydrogel solution: Weigh 2 g of sodium alginate and dissolve it in 98 g of deionized water. Heat and stir at 75 °C for 12 h. After complete dissolution, add 5 g of polyvinyl alcohol to the sodium alginate solution and raise the temperature to 95 °C and continue heating for 1 h. After sufficient dissolution, set it aside for use.

[0044] 2) Preparation of photochromic and photothermal material titanium dioxide / tungstophosphoric acid: Take 0.50 g of surfactant P123 and 60 mL of diethylene glycol (DEG), heat and stir to dissolve evenly at 60 °C, then raise the temperature to 80 °C, add 1 mL of TiCl4 and mix evenly, then add 1 mL of deionized water and mix evenly, and then raise the temperature to 180 °C and heat for 3 h to obtain self-doped TiO2 dispersion. Take 0.5 g of tungstophosphoric acid and dissolve it in 1 mL of deionized water. After fully dissolving, add 1 mL of the above-prepared self-doped TiO2 dispersion dropwise thereto, shake to mix it evenly to obtain a white precipitate. After centrifugation, washing, drying and grinding into powder, the photochromic and photothermal material titanium dioxide / tungstophosphoric acid is obtained. 3+ self-doped TiO2 dispersion. Take 0.5 g of tungstophosphoric acid and dissolve it in 1 mL of deionized water. After fully dissolving, add 1 mL of the above-prepared self-doped TiO2 dispersion dropwise thereto, shake to mix it evenly to obtain a white precipitate. After centrifugation, washing, drying and grinding into powder, the photochromic and photothermal material titanium dioxide / tungstophosphoric acid is obtained. 3+ self-doped TiO2 dispersion, shake to mix it evenly to obtain a white precipitate. After centrifugation, washing, drying and grinding into powder, the photochromic and photothermal material titanium dioxide / tungstophosphoric acid is obtained.

[0045] 3) Assembly of photochromic and photothermal evaporation device: Add 5.53 g of titanium dioxide / tungstophosphoric acid to the prepared calcium alginate / polyvinyl alcohol double-network hydrogel solution to make the mass fraction of titanium dioxide / tungstophosphoric acid 5%, and ultrasonically disperse it evenly. Then take 1 mL of the mixed solution and drop it into a circular mold, and disperse one end of a polypropylene tow (diameter 9 mm, height 25 mm) into a circle with a radius of 16 mm, and the whole is in the shape of a carrot flower. Cover the dispersed end of the polypropylene tow on the mixed solution, freeze at -18 °C for 2 h and then thaw, freeze-thaw 5 times repeatedly, then put the whole into a 5% calcium chloride solution, take it out after 4 h, remove the mold, cut the polyethylene foam into a circle with a diameter of 3.5 cm, and dig a circular hole in the middle so that the other end of the polypropylene tow just passes through the middle to assemble a photothermal composite hydrogel solar evaporator.

[0046] (II) Characterization

[0047] Figure 1 is the structural diagram of the photothermal composite hydrogel solar evaporator. As can be seen from the figure, the evaporator is divided into three parts, namely the photothermal layer (i.e., circular sheet-shaped photochromic and photothermal hydrogel), the water delivery channel and the polyethylene foam.

[0048] Figure 2 is the color change simulation diagram of the photothermal composite hydrogel solar evaporator. Under the irradiation of visible light, the photothermal layer changes from white to dark blue; at night without light, the dark blue composite nanoparticles are oxidized by oxygen in the air and restored to white.

[0049] Figure 3 is the comparison diagram of the photothermal composite hydrogel solar evaporator before and after illumination. As can be seen from the physical diagram, it is white before illumination and dark blue after illumination.

[0050] Figure 4Practical diagrams of photothermal composite hydrogel solar evaporators with the mass fractions of sodium alginate and polyvinyl alcohol being 1%:5%, 1%:10%, 2%:5%, and 2%:10% respectively.

[0051] Figure 5 Infrared spectra of titanium dioxide, phosphotungstic acid, and titanium dioxide / phosphotungstic acid composites. From Figure 1 it can be seen that the successful synthesis and preparation of titanium dioxide / phosphotungstic acid are proven.

[0052] Figure 6 Solid ultraviolet-visible diffuse reflectance spectra of titanium dioxide, phosphotungstic acid, titanium dioxide / phosphotungstic acid before illumination, and titanium dioxide / phosphotungstic acid after illumination. From Figure 2 it can be seen that the light absorption ability of titanium dioxide / phosphotungstic acid after illumination is enhanced in the range of 400 - 800 nm, which is consistent with the color change on the surface of the sample.

[0053] Figure 7 TEM and HRTEM images of titanium dioxide and titanium dioxide / phosphotungstic acid. The lattice spacings correspond to the 101 crystal plane of titanium dioxide and the 311 crystal plane of phosphotungstic acid respectively, proving the successful preparation of the titanium dioxide / phosphotungstic acid composite material.

[0054] Figure 8 SEM image of calcium alginate / polyvinyl alcohol double-network hydrogel. As can be seen from the figure, the calcium alginate / polyvinyl alcohol double-network hydrogel presents a porous network structure, ensuring its water absorption ability and facilitating the escape of water vapor.

[0055] (III) Evaporation performance test

[0056] In the solar evaporation experiment, the evaporator was placed in a beaker filled with seawater, and a xenon lamp was used as a solar simulator to irradiate the evaporator at room temperature (25°C). The wavelength range of the xenon lamp was 200 - 2500 nm, and a light intensity of 1 kW m -2 was equivalent to 1 sun intensity. An infrared thermal imager was used to monitor the temperature changes on the surface of the evaporator and the water. An electronic balance was used to record the water loss. During the 480 s, the surface temperature of the evaporator gradually increased from 8.7°C to a maximum of 52.7°C and then remained unchanged. The mass loss of water was recorded every 300 s. After calculation, the evaporation rate of this evaporator was 3.39 kg m -2 h -1 .

[0057] Figure 9 Surface temperature distribution diagram in the evaporation performance test experiment of the evaporator. The temperature of the evaporation film is relatively high, which is beneficial to accelerating the evaporation rate.

[0058] Figure 10 In the evaporation performance test experiment of the evaporator at 1 kW m-2 Mass loss curve of water under light irradiation. It can be seen that the mass loss is linearly related to time.

[0059] Example 2 A titanium dioxide / tungstophosphoric acid photochromic and photothermal solar evaporator based on chitosan / agarose hydrogel

[0060] 1) Preparation of chitosan / agarose double-network hydrogel solution: Weigh 0.3 g of sodium dodecyl sulfate and dissolve it in 100 g of deionized water. Then add 3.0 g of chitosan to it, and add 2 g of acetic acid and stir for 12 h. After complete dissolution, add 0.43 g of agarose to the solution and continue heating at 80 °C for 2 h. After sufficient dissolution, set it aside for use.

[0061] 2) Preparation of the photochromic and photothermal material titanium dioxide / tungstophosphoric acid: The same as step 2) in Example 1.

[0062] 3) Assembly of the photochromic and photothermal evaporation device: Disperse 5.56 g of titanium dioxide / tungstophosphoric acid into the chitosan / agarose double-network hydrogel solution to make the mass fraction of titanium dioxide / tungstophosphoric acid 5%. Ultrasonically disperse it evenly. Take 1 mL of the above mixture and drop it into a circular mold. Disperse one end of the polypropylene tow (diameter 9 mm, height 25 mm) into a circle with a radius of 16 mm, and the whole is in the shape of a carrot flower. Cover the dispersed end of the polypropylene tow on the mixed solution and let it stand for 24 h. After the gel ages, remove the mold. Cut the polyethylene foam into a circle with a diameter of 3.5 cm, and dig a circular hole in the middle so that the other end of the polypropylene tow just passes through the middle to assemble a photothermal composite hydrogel solar evaporator.

[0063] Example 3 A titanium dioxide / molybdophosphoric acid photochromic and photothermal solar evaporator based on sodium alginate / polyvinyl alcohol hydrogel

[0064] 1) Preparation of sodium alginate / polyvinyl alcohol double-network hydrogel solution: The same as step 1) in Example 1.

[0065] 2) Preparation of the photochromic and photothermal material titanium dioxide / molybdophosphoric acid: Take 0.50 g of surfactant P123 and 60 mL of diethylene glycol (DEG) and heat and stir to dissolve evenly at 60 °C. Then raise the temperature to 80 °C, add 1 mL of TiCl4 and mix evenly, then add 1 mL of deionized water and mix evenly. Then raise the temperature to 180 °C and heat for 3 h to obtain a self-doped TiO2 dispersion. Take 0.32 g of molybdophosphoric acid and dissolve it in 1 mL of deionized water. After sufficient dissolution, drop 1 mL of the above-prepared Ti 3+ into it. 3 +The self-doped TiO2 dispersion is shaken to be fully mixed to obtain a white precipitate, which is then centrifuged, washed, dried, and ground into powder to obtain a photochromic and photothermal material titanium dioxide / phosphomolybdic acid.

[0066] 3) Assembly of photochromic photothermal evaporation device: 5.53 g of titanium dioxide / phosphomolybdic acid was added to the prepared calcium alginate / polyvinyl alcohol double network hydrogel solution to make the mass fraction of titanium dioxide / phosphomolybdic acid 5%, and ultrasonically dispersed it evenly. Then, 1 mL of the mixed solution was dropped into a circular mold, and one end of a polypropylene bundle (9 mm in diameter and 25 mm in height) was dispersed into a circle with a radius of 16 mm, and the whole was in the shape of a carrot flower. The dispersed end of the polypropylene bundle was covered on the mixed solution, frozen at -18°C for 2 h and then thawed. After repeated freezing and thawing 5 times, the whole was placed in a 5% by mass calcium chloride solution. After 4 h, it was taken out, the mold was removed, and the polyethylene foam was cut into a circle with a diameter of 3.5 cm. A small circular hole was dug in the middle so that the other end of the polypropylene bundle just passed through the middle to assemble a photothermal composite hydrogel solar evaporator.

Claims

1. A photothermal composite hydrogel solar evaporator, characterized in that: Its structure is divided into three parts, namely: circular sheet-shaped photochromic and photothermal hydrogel, water delivery channel, and supporting floating material.

2. The photothermal composite hydrogel solar evaporator according to claim 1, characterized in that, The water delivery channel is a carrot flower-shaped polypropylene filament bundle with one end dispersed into a circle.

3. The photothermal composite hydrogel solar evaporator according to claim 2, wherein The supporting floating material is polyethylene foam.

4. The photothermal composite hydrogel solar evaporator according to claim 1, wherein The preparation method of the circular sheet-shaped photochromic and photothermal hydrogel is as follows: Mix the photochromic and photothermal material with the double-network hydrogel solution, and ultrasonically disperse it evenly, then pour it into a circular mold to form.

5. The photothermal composite hydrogel solar evaporator according to claim 4, characterized in that, The mass fraction of the photochromic and photothermal material is 5%.

6. The photothermal composite hydrogel solar evaporator according to claim 4, characterized in that: The photochromic and photothermal material is titanium dioxide / tungstophosphoric acid or titanium dioxide / molybdophosphoric acid.

7. The photothermal composite hydrogel solar evaporator according to claim 6, characterized in that, The preparation method of the photochromic and photothermal material includes the following steps: 1) Take 0.50 g of surfactant P123 and 60 mL of diethylene glycol (DEG), heat and stir to dissolve evenly at 60 °C, then raise the temperature to 80 °C, add 1 mL of TiCl4 and mix evenly, then add 1 mL of deionized water and mix evenly. Then raise the temperature to 180 °C and heat for 3 h to obtain a Ti 3+ self-doped TiO2 dispersion; 2) Dissolve the polyoxometalate in deionized water to form a polyoxometalate solution, and then mix the Ti 3+ self-doped TiO2 dispersion with the polyoxometalate solution to obtain a white precipitate. After centrifuging, washing, and drying the white precipitate, it is ready for use; The polyoxometalate is tungstophosphoric acid or molybdophosphoric acid.

8. The photothermal composite hydrogel solar evaporator according to claim 4, wherein The double-network hydrogel is calcium alginate / polyvinyl alcohol double-network hydrogel or chitosan / agarose double-network hydrogel; The preparation method of the calcium alginate / polyvinyl alcohol double-network hydrogel is: Dissolve sodium alginate and polyvinyl alcohol in deionized water, heat to completely dissolve it, and then put it into a calcium ion solution after repeated freezing and thawing to obtain the calcium alginate / polyvinyl alcohol double-network hydrogel; the mass ratio of sodium alginate to polyvinyl alcohol is 1:1 - 10; The preparation method of the chitosan / agarose double-network hydrogel is: Dissolve chitosan, agarose, and sodium dodecyl sulfate in acetic acid in deionized water, heat to completely dissolve it, and then form the chitosan / agarose double-network hydrogel after cooling; the mass ratio of chitosan to agarose is 7:

1.

9. The preparation method of the photothermal composite hydrogel solar evaporator according to any one of claims 3-8, characterized in that, Including the following steps: 1) Cover the carrot flower-shaped polypropylene filament bundle with one end dispersed into a circle on the circular sheet-shaped photochromic and photothermal hydrogel, and wait for the gel to form; 2) Cut the polyethylene foam into a circular shape with a suitable size, and dig a circular small hole in the middle so that the other end of the polypropylene filament bundle just passes through the middle, and assemble it into a photothermal composite hydrogel solar evaporator.

10. Application of the photothermal composite hydrogel solar evaporator according to any one of claims 1 - 8 in seawater desalination.

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