Three-dimensional hydrogel tube photo-thermal conversion solar evaporator and preparation method and application thereof

Abstract

The application discloses a three-dimensional hydrogel tube photothermal conversion solar evaporator and a preparation method and application thereof. The method comprises the following steps: dissolving reduced graphene oxide, sodium alginate and polyvinyl alcohol to obtain a mixed solution; adding the mixed solution into a copper ion solution to cross-link the sodium alginate and the copper ion to obtain a hollow hydrogel tube; cross-linking and reinforcing the hydrogel tube by immersing the hydrogel tube in a glutaraldehyde solution; cutting and bundling the prepared hydrogel tube into a bundle, and then bending the hydrogel tube outward to form a three-dimensional hydrogel tube photothermal conversion solar evaporator with an inverted U-shaped structure for solar seawater desalination. The prepared evaporator has good hydrophilicity and excellent photothermal conversion capacity, the inverted U-shaped structure enables the hydrogel tube to draw water from both ends inserted into water and supply the solution to the top at the same time, the evaporator has the performances of high-efficiency evaporation and long-term inhibition of crystalline salt, and a solar evaporator capable of inhibiting the formation of crystalline salt and realizing long-term stable operation is successfully prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solar seawater desalination, in particular to a three-dimensional hydrogel tube photothermal conversion solar evaporator with long-term stable evaporation and good salt resistance, and a preparation method and application thereof. BACKGROUND

[0002] In today's world, the problem of lack of fresh water resources is becoming more and more serious. In order to solve this situation, seawater desalination technology has gradually attracted widespread attention. Traditional seawater desalination technologies, including membrane separation technology and phase change heat technology, are relatively mature means, but this process may cause large energy consumption. Therefore, there is an urgent need to study seawater desalination methods with lower energy consumption and higher efficiency. In view of this problem, using green clean energy as the energy source of seawater desalination to reduce the energy consumption in the process of seawater desalination has become a research frontier. The sun has huge energy, which is a huge green and environmentally friendly energy source. In the existing seawater desalination technology, the form of light-heat conversion interface heating is mainly used.

[0003] However, solar energy is a highly dispersed, non-centralized and low-density energy. Such characteristics make it difficult to be used efficiently. At the same time, seawater contains a large amount of salt ions. If appropriate measures are not taken, the salt solution will reach the saturation concentration and then condense into salt crystals during evaporation. The crystallized salt will block the internal water supply and surface vapor escape channels of the evaporator, and the crystallized salt covering the surface of the evaporator will affect the light-heat conversion efficiency, thereby reducing the evaporation performance and service life of the evaporator. Therefore, the existing evaporator still has the problem of insufficient evaporation performance. How to improve the evaporation performance of the evaporator is a technical problem that needs to be solved at present. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a three-dimensional hydrogel tube photothermal conversion solar evaporator with long-term stable evaporation and good salt resistance, and a preparation method and application thereof, which aims to solve the problem of insufficient evaporation performance of the existing evaporator.

[0005] The technical scheme of the present application is as follows:

[0006] In a first aspect of the present application, a preparation method of a three-dimensional hydrogel tube photothermal conversion solar evaporator is provided, which comprises the following steps:

[0007] A. mixing sodium alginate, polyvinyl alcohol and reduced graphene oxide, and heating and stirring to obtain a mixed solution;

[0008] B. adding the mixed solution into a CuSO4 solution to make sodium alginate cross-link with Cu 2+ to form a hollow hydrogel tube, and soaking the reaction system in a glutaraldehyde solution to obtain SP-rGO.

[0009] C. cutting, bundling and spreading the SP-rGO to obtain a three-dimensional hydrogel tube photothermal conversion solar evaporator with inverted U-shaped structure.

[0010] Optionally, the solvent of the CuSO4 solution is water, and the mass fractions of the sodium alginate, polyvinyl alcohol and reduced graphene oxide in the solvent water are 4wt%, 1wt% and 0.5wt% respectively.

[0011] Optionally, in step A, the temperature of the heating and stirring is 95℃, and the time is 6h.

[0012] Optionally, step A specifically comprises: mixing 4wt% sodium alginate, 1wt% polyvinyl alcohol and 0.5wt% reduced graphene oxide, and heating and stirring at 95℃ for 6h to obtain a mixed solution.

[0013] Optionally, in step B, the mixed solution is injected into the CuSO4 solution through a needle tube.

[0014] The CuSO4 solution is composed of CuSO4, H2O2, Tris-HCl and water, wherein the concentration of CuSO4 is 2wt%, the concentration of H2O2 is 1ml / 100ml, the concentration of Tris-HCl is 0.05M, and the pH value of Tris-HCl is 8.5.

[0015] Optionally, in step B, the sodium alginate is cross-linked with Cu 2+ to form a hollow hydrogel tube for 9-11min;

[0016] The post-reaction system is soaked in a 50wt% glutaraldehyde solution for 23-25h.

[0017] Optionally, step B specifically comprises: injecting the mixed solution into the CuSO4 solution through a needle tube, cross-linking the SA with Cu 2+ to form a hollow hydrogel tube for 9-11min, soaking the post-reaction system in a 50wt% glutaraldehyde solution for 23-25h, and cleaning with deionized water to obtain SP-rGO.

[0018] Optionally, step C specifically comprises: cutting the SP-rGO into multiple sections, each section of SP-rGO having a length of 9-11cm, bundling the multiple sections of SP-rGO using a plastic ribbon, and spreading the multiple sections of SP-rGO from the middle to the periphery to form a three-dimensional hydrogel tube photothermal conversion solar evaporator with inverted U-shaped structure.

[0019] In a second aspect, the application provides a three-dimensional hydrogel tube photothermal conversion solar evaporator, which is prepared by the method as described in the application.

[0020] In a third aspect of the present application, a three-dimensional hydrogel tube photo-thermal conversion solar evaporator is provided.

[0021] Beneficial effects: The present application adds a mixed solution of sodium alginate, polyvinyl alcohol and reduced graphene oxide into a copper sulfate solution, obtains a hollow hydrogel tube through cross-linking reaction of sodium alginate and copper ions, reinforces the hollow hydrogel tube through cross-linking reaction of glutaraldehyde and polyvinyl alcohol, mixes reduced graphene oxide through adhesion of the hydrogel, and then disperses the bundled hydrogel tubes through special structure design to obtain a three-dimensional hydrogel tube photo-thermal conversion solar evaporator with inverted U-shaped structure. The three-dimensional hydrogel tube photo-thermal conversion solar evaporator prepared by the present application is used for solar seawater desalination. The prepared evaporator has good hydrophilicity and the ability to reduce evaporation enthalpy, the capillary structure generated by the hollow hydrogel tube can effectively draw water, and the three-dimensional hydrogel tube structure has good salt ion exchange capacity to effectively avoid the formation of crystalline salt and can be operated stably for a long time. Therefore, the designed evaporator can inhibit the formation of crystalline salt and realize long-term stable operation of high-efficiency solar seawater desalination. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A preparation method of a long-term stable evaporation and good salt resistance three-dimensional hydrogel tube photo-thermal conversion solar evaporator provided for the embodiment of the present application is shown in the flowchart of the preferred embodiment.

[0023] Figure 2 Another flowchart of a preparation method of a long-term stable evaporation and good salt resistance three-dimensional hydrogel tube photo-thermal conversion solar evaporator provided for the embodiment of the present application is shown in the flowchart of another preferred embodiment.

[0024] Figure 3 The dynamic water contact angle and hydrophilicity of the samples in Example 1 and Comparative Examples 1-2 are shown in Table 1.

[0025] Figure 4 The light absorption rate of the samples in Example 1 and Comparative Examples 1-2 in the full spectrum range is shown in Table 2.

[0026] Figure 5 In Example 1 and Comparative Examples 1-3, the evaporator is placed in water, irradiated for 3h using 1kW / m 2 The light intensity, the mass change of the evaporation system is measured, and the evaporation rate of the evaporator obtained under light and dark conditions is observed.

[0027] Figure 6 In Example 1, the ion concentration and salinity of the actual seawater after desalination by the evaporator.

[0028] Figure 7The evaporation rate obtained from the test of the evaporator in Example 1 in the mode of 12 hours of light irradiation and 12 hours of no light irradiation of the xenon lamp in the salt water for 1 week.

[0029] Figure 8 The surface salt crystallization of the evaporator in Example 1 before and after the long-term operation in the simulated seawater. DETAILED DESCRIPTION

[0030] The application provides a three-dimensional hydrogel tube photothermal conversion solar evaporator with long-term stable evaporation and good salt resistance and a preparation method and application thereof. In order to make the purpose, technical scheme and effects of the application more clear and definite, the application is further described in detail below. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application.

[0031] The ways to improve the performance of the solar evaporator include three aspects: obtaining high-efficiency light-heat conversion capacity, stable water supply capacity and high-efficiency heat energy management. Reduced graphene oxide is a carbon-based material with strong light absorption and heat conversion capacity, and can achieve extremely high absorption rate for the visible band in sunlight. The hydrogel has good hydrophilicity and the advantage of reducing water evaporation enthalpy, and the capillary effect can bring strong water supply performance, and is applied to the preparation of the evaporator. The advantage of the three-dimensional structure can effectively avoid the generation of crystalline salt.

[0032] Based on this, the application provides a preparation method of a three-dimensional hydrogel tube photothermal conversion solar evaporator with long-term stable evaporation and good salt resistance, and a preferred embodiment flow chart is shown in Figure 1 , which comprises the following steps:

[0033] S10, mixing sodium alginate (SA), polyvinyl alcohol (PVA) and reduced graphene oxide (rGO) and heating and stirring to obtain a mixed solution;

[0034] S20, adding the mixed solution into a CuSO4 solution to make the sodium alginate crosslink with Cu 2+ to form a hollow hydrogel tube, and soaking the system after the reaction in a glutaraldehyde (GA) solution to obtain SP-rGO;

[0035] S30, cutting, bundling and spreading the SP-rGO to obtain a three-dimensional hydrogel tube photothermal conversion solar evaporator with an inverted U-shaped structure.

[0036] The embodiment of the present application injects a mixed solution of sodium alginate, polyvinyl alcohol and reduced graphene oxide into a copper sulfate solution through a needle tube, so that the mixed solution has a tubular structure when crosslinking, a hollow hydrogel tube is obtained through crosslinking reaction of sodium alginate and copper ions, the hollow hydrogel tube is reinforced through crosslinking reaction of glutaraldehyde and polyvinyl alcohol, the reduced graphene oxide is mixed into the hydrogel through adhesion, and the hydrogel tube bundled by the special structure is scattered to obtain a three-dimensional hydrogel tube photothermal conversion solar evaporator with an inverted U-shaped structure. The three-dimensional hydrogel tube photothermal conversion solar evaporator prepared by the embodiment of the present application is used for solar seawater desalination. The prepared evaporator has good hydrophilicity and the ability to reduce evaporation enthalpy, the capillary structure generated by the hollow hydrogel tube can effectively draw water, and the three-dimensional hydrogel tube structure has good salt ion exchange capacity, effectively avoiding the formation of crystalline salt and being able to operate stably for a long time, so that the designed evaporator can inhibit the formation of crystalline salt and realize long-term stable operation of high-efficiency solar seawater desalination.

[0037] In an embodiment, the solvent of the CuSO4 solution is water, and the mass fractions of the sodium alginate, polyvinyl alcohol and reduced graphene oxide in the solvent water are 4wt%, 1wt% and 0.5wt% respectively.

[0038] In an embodiment, in step S10, the temperature of the heating and stirring is 95℃, and the time is 6h.

[0039] In an embodiment, step S10 specifically comprises: mixing 4wt% sodium alginate, 1wt% polyvinyl alcohol and 0.5wt% reduced graphene oxide, and heating and stirring at 95℃ for 6h to obtain a mixed solution.

[0040] In an embodiment, in step S20, the mixed solution is injected into the CuSO4 solution through a needle tube.

[0041] The CuSO4 solution is composed of CuSO4, H2O2, Tris-HCl and water, wherein the concentration of CuSO4 is 2wt%, the concentration of H2O2 is 1ml / 100ml, the concentration of Tris-HCl is 0.05M, and the pH value of Tris-HCl is 8.5.

[0042] It should be noted that the crosslinking ion in the embodiment of the present application can be but is not limited to copper ions, and can also be selected from other ions such as calcium ions.

[0043] In an embodiment, in step S20, the sodium alginate is crosslinked with Cu 2+ to form a hollow hydrogel tube for 9-11min (such as 10min);

[0044] The post-reaction system is soaked in a 50wt% glutaraldehyde solution for 23-25h (e.g. 24h).

[0045] In one embodiment, step S20 specifically comprises: injecting the mixed solution into a cross-linking solution (solvent is water) consisting of 2wt% CuSO4, 1ml / 100ml H2O2, 0.05M Tris-HCl pH=8 through a needle tube, so as to make SA cross-link with Cu 2+ The cross-linking reaction is carried out for 10min to form a hollow hydrogel tube, the post-reaction system is soaked in a 50wt% glutaraldehyde solution for 24h, and deionized water is used for cleaning to obtain SP-rGO.

[0046] In one embodiment, step S30 specifically comprises: cutting the SP-rGO into multiple sections, each section of SP-rGO has a length of 9-11cm (e.g. 10cm), and the multiple sections of SP-rGO are bundled using plastic straps and then spread out from the middle to the periphery (spread out from the middle to the periphery), so as to form a three-dimensional hydrogel tube photothermal conversion solar evaporator with an inverted U-shaped structure.

[0047] Specifically, referring to Figure 2 In this embodiment, sodium alginate, polyvinyl alcohol and reduced graphene are first made into a mixed solution, the mixed solution is then injected into a copper sulfate solution through a needle tube, a hollow hydrogel tube structure is obtained by cross-linking reaction of copper ions and sodium alginate, and then glutaraldehyde and polyvinyl alcohol are cross-linked and reinforced, finally, the three-dimensional hydrogel tube photothermal conversion solar evaporator (denoted as ESP-rGO) is obtained through appropriate cutting and bundling and spreading. The three-dimensional hydrogel tube photothermal conversion solar evaporator prepared in this embodiment has good hydrophilicity and excellent photothermal conversion capability, and the inverted U-shaped structure has good water supply capacity, and can maintain high-efficiency evaporation and inhibit the formation of crystalline salt in seawater for a long time.

[0048] The three-dimensional hydrogel tube photothermal conversion solar evaporator is prepared by the method as described in the embodiments of the present application.

[0049] The three-dimensional hydrogel tube photothermal conversion solar evaporator is prepared by the method as described in the embodiments of the present application.

[0050] The present application will be further explained and described by specific embodiments.

[0051] Embodiment 1: A preparation method of a three-dimensional hydrogel tube photothermal conversion solar evaporator with long-term stable evaporation and good salt resistance, the specific steps are as follows:

[0052] (1) 4wt% SA, 1wt% PVA and 0.5wt% rGO were heated and stirred at 95°C for 6h to obtain a mixed solution.

[0053] (2) The mixed solution was injected into a crosslinking solution composed of 2wt% CuSO4, 1ml / 100ml H2O2, 0.05M Tris-HCl pH=8.5 through a needle tube, so that SA and Cu 2+ were crosslinked to form a hollow hydrogel tube for 10min, and then the hydrogel tube was immersed in a 50wt% GA solution for 24h and washed with deionized water to obtain SP-rGO.

[0054] (3) The SP-rGO cut into about 10cm long was bundled into a bundle and then tied with a plastic ribbon, and then spread from the middle to the four sides, and then inserted into a beaker to form a three-dimensional hydrogel tube photothermal conversion solar evaporator (denoted as ESP-rGO) with an inverted U-shaped structure.

[0055] Comparative Example 1:

[0056] The same as Example 1, except that step (1) does not contain rGO, and step (2) produces a hollow hydrogel tube SP, and an evaporator ESP is prepared using SP.

[0057] Comparative Example 2:

[0058] The same as Example 1, except that step (1) does not contain PVA, and step (2) produces a hollow hydrogel tube S-rGO, and an evaporator ES-rGO is prepared using S-rGO.

[0059] Comparative Example 3:

[0060] Natural water body without evaporator.

[0061] The three different hydrogel tubes SP-rGO, SP and S-rGO prepared in Example 1, Comparative Example 1 and Comparative Example 2 were tested for performance. The water contact angle measuring instrument was used to measure the hydrophilicity and hydrophobicity of the above three samples, and the test results are shown in Figure 3 The above three samples were detected for absorbance in the wavelength range of 400-2500nm using a UV-visible near-infrared spectrometer, and the test results are shown in Figure 4 The light absorption rate is given by the formula A=1-R-T (R represents the light reflectivity of the evaporator, and T represents the light transmittance of the evaporator). It can be seen that under the same test conditions, the light absorption rate of SP-rGO can reach 90%, the light absorption rate of S-rGO is 87%, and the light absorption rate of SP is only 60%. It is proved that Example 1 has the best light absorption capacity.

[0062] Figure 5To test the evaporation performance of the three different evaporators ESP-rGO, ESP and ES-rGO prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 pure water. The xenon lamp was used as simulated sunlight, and the light intensity was 1 kW / m 2 . The evaporation rate was obtained by the formula (Δm(kg) represents the mass change of the evaporation system, t(h) represents the evaporation time, S(m 2 ) is the effective evaporation area of the evaporator). It can be seen that under the same test conditions, the evaporation rate of ESP-rGO is 1.51 kg·m -2 ·h -1 , while ESP has a low evaporation rate of only 0.55 kg·m -2 ·h -1 due to the lack of light-heat materials, and ES-rGO has an evaporation rate of 0.68 kg·m -2 ·h -1 due to the lack of hydrophilic groups provided by polyvinyl alcohol, and pure water has a lower evaporation rate, which proves the high evaporation performance of Example 1.

[0063] The simulated seawater running experiment of Example 1 was carried out. The xenon lamp was used as simulated sunlight, and the light intensity was 1 kW / m 2 . The simulated seawater (3.5wt%) was prepared by NaCl (2.75wt%), MgSO4 (0.33wt%), MgCl2 (0.24wt%), CaCl2 (0.11wt%) and KCl (0.07wt%). Figure 5 To Example 1 and Comparative Examples 1-3, the evaporator was placed in water and irradiated for 3h using 1 kW / m 2 light intensity, the mass change of the evaporation system was measured, and the evaporation rate of the evaporator obtained under light and dark conditions was observed. Figure 6 To condense the water evaporated by the evaporator ESP-rGO in the simulated seawater, the inductively coupled plasma emission spectrometer was used to analyze the concentration changes of Na + , Mg 2+ , Ca 2+ and K + , and the desalination result met the international standard. Figure 7 To the evaporator of Example 1 in the simulated seawater, the evaporation rate was tested by using the mode of xenon lamp irradiation for 12 hours and no irradiation for 12 hours for 1 week. Figure 8 To the surface salt crystallization of the evaporator of Example 1 in the simulated seawater before and after long-term running.

[0064] In summary, the application mixes reduced graphene oxide by the adhesion of hydrogel, injects the mixed solution of sodium alginate, polyvinyl alcohol and reduced graphene oxide into a cross-linking liquid through a needle tube, obtains a hollow hydrogel tube by cross-linking of copper ions and sodium alginate, and reinforces the hollow hydrogel tube by cross-linking of glutaraldehyde and polyvinyl alcohol, thereby obtaining a hydrogel tube with a hollow structure and high light absorption and heat conversion capacity. The hydrogel tube prepared by the application is cut, bundled and spread to obtain a hollow hydrogel tube solar evaporator with an inverted U-shaped structure. The inverted U-shaped structure enables the hydrogel tube to draw water from both ends inserted into water and supply the solution to the top at the same time, so that the evaporator has high-efficiency evaporation and long-term crystalline salt inhibition performance. Therefore, the designed evaporator can inhibit the formation of crystalline salt in seawater and realize long-term stable operation to achieve high-efficiency solar seawater desalination.

[0065] It should be understood that the application of the application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the application.

Claims

1. A method for preparing a three-dimensional hydrogel tube photothermal conversion solar evaporator, characterized in that, The method comprises the steps of: A. mixing sodium alginate, polyvinyl alcohol and reduced graphene oxide, and heating and stirring to obtain a mixed solution; B. The mixed solution is added into the CuSO4 solution through a needle tube, so that sodium alginate and Cu 2+ occur cross-linking reaction to form a hollow hydrogel tube, and the system after the reaction is immersed in a glutaraldehyde solution to obtain SP-rGO. C. cutting, bundling and spreading the SP-rGO to obtain a three-dimensional hydrogel tube photothermal conversion solar evaporator with an inverted U-shaped structure.

2. The production method according to claim 1, characterized by, The solvent of the CuSO4 solution is water, and the mass fractions of the sodium alginate, polyvinyl alcohol and reduced graphene oxide in the solvent water are 4 wt%, 1 wt% and 0.5 wt% respectively.

3. The preparation method according to claim 1, characterized in that, In step A, the temperature of the heating and stirring is 95°C, and the time is 6h.

4. The production method according to claim 2, characterized by, Step A specifically comprises: mixing 4 wt% sodium alginate, 1 wt% polyvinyl alcohol and 0.5 wt% reduced graphene oxide, and heating and stirring at 95°C for 6h to obtain a mixed solution.

5. The preparation method according to claim 1, characterized in that, In step B, The CuSO4 solution is composed of CuSO4, H2O2, Tris-HCl and water, wherein the concentration of CuSO4 is 2 wt%, the concentration of H2O2 is 1 ml / 100 ml, the concentration of Tris-HCl is 0.05 mol / L, and the pH value of Tris-HCl is 8.

5.

6. The method of claim 1, wherein, In step B, sodium alginate was reacted with Cu 2+ Cross-linking reaction occurred for 9-11 min to form hollow hydrogel tubes; The post-reaction system is soaked in a 50 wt% glutaraldehyde solution for 23-25h.

7. The preparation method according to claim 1, characterized in that, Step B specifically includes: injecting the mixed solution into the CuSO4 solution through a needle tube, allowing sodium alginate to react with Cu 2+ The hollow hydrogel tube is formed by cross-linking reaction for 9-11 min, the post-reaction system is soaked in a 50 wt% glutaraldehyde solution for 23-25 h, and deionized water is used for cleaning, to obtain SP-rGO.

8. The method of claim 1, wherein, Step C specifically comprises: cutting the SP-rGO into multiple sections, each section of SP-rGO having a length of 9-11 cm, bundling the multiple sections of SP-rGO into a bundle using a plastic ribbon, and then spreading the bundle from the middle to the periphery to form a three-dimensional hydrogel tube photothermal conversion solar evaporator with an inverted U-shaped structure.

9. A three-dimensional hydrogel tube photothermal conversion solar evaporator, characterized in that, The three-dimensional hydrogel tube photothermal conversion solar evaporator is prepared by the method of any one of claims 1-8.

10. Use of a three-dimensional hydrogel tube photothermal conversion solar evaporator, characterized in that, The three-dimensional hydrogel tube photothermal conversion solar evaporator of claim 9 is used for solar seawater desalination.

Images