Polyvinyl alcohol-cellulose nanocrystal composite hydrogel interface evaporator, and preparation method therefor and use thereof

Abstract

A polyvinyl alcohol-cellulose nanocrystal composite hydrogel interface evaporator, and a preparation method therefor and the use thereof. The preparation method for the composite hydrogel interface evaporator comprises the following steps: adding a cellulose nanomicrocrystal, polyvinyl alcohol and an acid liquor to water, mixing same, and heating the mixture to dissolve the polyvinyl alcohol, so as to obtain a hydrogel precursor solution; and adding reduced graphene oxide and a cross-linking agent to the hydrogel precursor solution, uniformly mixing same to obtain a mixed solution, gelatinizing the mixed solution, and then freeze-drying same, so as to obtain a target product. The preparation method is simple to operate, low in terms of cost, and environmentally friendly, and endows the hydrogel with excellent multifunctional properties, including wide spectrum absorption performance, seawater desalination performance, wastewater purification performance, etc.

Description

A polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator and its preparation method and application Technical Field

[0001] The invention belongs to the field of solar interface evaporation materials, and in particular relates to a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator and a preparation method and application thereof. Background Art

[0002] Freshwater scarcity and energy crises have severely impacted the sustainable development of human society. Only 2.5% of the Earth's freshwater resources are available for use. According to statistics, 2.4 billion people worldwide face severe water shortages year-round. With population growth, climate change, and increasing freshwater pollution, nearly 80% of the world's population faces a high level of water security threats. To address this issue, an environmentally friendly, efficient, and rapid method for producing freshwater is urgently needed. Solar energy has become an advanced technology for seawater desalination and sewage treatment. However, solar freshwater production requires a large amount of energy input. Therefore, there is an urgent need to develop an interfacial evaporation material that can be used in conjunction with a light-absorbing material to improve solar thermal conversion efficiency and increase evaporation efficiency.

[0003] Hydrogels are functional materials with three-dimensional network structures that are rich in water due to the cross-linking of polymer molecular chains under physical or chemical effects. The physicochemical properties of hydrogels can be finely tuned by varying the polymer network, cross-linking sites, and preparation methods. In addition, the hydrophilic polymer network of hydrogels gives them excellent water absorption capacity, making them suitable candidates for interfacial evaporants. Hydrogels also have a porous structure that facilitates the transport of water to the evaporation surface. When combined with light-absorbing materials, this structure can convert the absorption of sunlight into heat energy, thereby promoting water evaporation. The hydrogel polymer network simultaneously captures water molecules through electrostatic interactions and hydrogen bonds, regulating the hydrogen bond network and intermolecular forces within the hydrogel, thereby adjusting the state and phase transition behavior of water and reducing the enthalpy of water evaporation.

[0004] Cellulose is one of the most abundant, renewable, and biodegradable natural polymers. Cellulose nanocrystals (CNCs) prepared from cellulose possess abundant hydroxyl groups, which can form hydrogen bonds with a variety of molecules, providing abundant attachment sites for light-absorbing materials. CNCs can also be used as reinforcing agents and rheological modifiers through surface modification, improving the mechanical properties of hydrogels. Although a number of composite hydrogel interfacial evaporators are currently available, they struggle to simultaneously achieve excellent mechanical strength, desalination performance, and wastewater purification capabilities. Summary of the Invention

[0005] Existing hydrogel interfacial evaporators struggle to combine multiple functions, limiting their application. To address these challenges, the present invention develops a CNC composite hydrogel that combines excellent mechanical strength, seawater desalination performance, and wastewater purification capabilities. Furthermore, through a nanocomposite strategy, the introduction of photothermal material, reduced graphene oxide (rGO), imparts the composite hydrogel interfacial evaporator with broad spectral absorption (250-2500 nm).

[0006] The first aspect of the present invention is to provide a method for preparing a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator, comprising the following steps:

[0007] Nanocrystalline cellulose, polyvinyl alcohol, and acid are added to water, mixed, and heated to dissolve the polyvinyl alcohol to obtain a hydrogel precursor solution; preferably, the acid is hydrochloric acid; the heating temperature is 95°C; the concentration of PVA in the hydrogel precursor solution is 8-12 wt%, preferably 10 wt%, and the role of PVA is to give the composite hydrogel a certain mechanical strength; the concentration of nanocrystalline cellulose is 0.15 wt%-0.5 wt%; the nanocrystalline cellulose is configured into a solution of a certain concentration before use, and then emulsified and mixed uniformly before use. Further preferably, the emulsification treatment conditions are: emulsification at room temperature and 12,000 rpm for 30 min; the purpose of the emulsification treatment is to uniformly disperse the nanocrystalline cellulose in water.

[0008] Reduced graphene oxide and a cross-linking agent are added to a hydrogel precursor solution, mixed evenly to obtain a mixed solution, which is then freeze-dried after gelation to obtain a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator. Preferably, ultrasonic treatment can be used to mix the mixed solution to obtain a uniform mixture; the concentration of reduced graphene oxide in the mixed solution is 0.1-1%; the cross-linking agent is an aldehyde (glutaraldehyde), boric acid, epichlorohydrin, or a heavy metal salt that can form a gel through coordination complexation with polyvinyl alcohol; the gelation temperature is 60-80°C and the time is 2-3 hours.

[0009] The second aspect of the present invention is to provide a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator, which is prepared by the preparation method described in the first aspect above.

[0010] The third aspect of the present invention is to provide the use of the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator as described in the second aspect in seawater desalination or wastewater purification.

[0011] The present invention has at least the following beneficial effects:

[0012] (1) The polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator provided by the present invention uses CNC as the physical crosslinking site, PVA as the chemical crosslinking network, and rGO as the light absorbing material. The polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator prepared by using CNC, PVA, and rGO in a cellulose-based hydrogel exhibits multifunctional properties. The polyvinyl alcohol-nanocellulose crystal composite strategy in the preparation method of the present invention, through a simple and low-cost process, produces a polyvinyl alcohol-nanocellulose crystal composite hydrogel with excellent mechanical strength, good recyclability, and salt and acid resistance.

[0013] (2) In the present invention, rGO imparts excellent broad-spectrum absorption and photothermal conversion properties to the composite hydrogel; PVA imparts excellent mechanical strength to the composite hydrogel, and CNC affects the evaporation rate of the product. The present invention prepares a product with excellent comprehensive performance by compounding CNC, PVA, and rGO in specific amounts.

[0014] (3) The present invention utilizes the composite of polyvinyl alcohol and nanocellulose crystals to produce a composite hydrogel that exhibits a stable evaporation rate and salt resistance for seawater of different concentrations; the composite hydrogel also exhibits a stable purification rate for wastewater of different concentrations. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a flow chart of the preparation of a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator provided in Example 1 of the present invention.

[0016] FIG2 is a schematic diagram of the invention providing a hydrogel cross-linked network for reducing water evaporation enthalpy.

[0017] FIG3 is an SEM image of the composite hydrogel interface evaporator provided in Example 2 of the present invention and Comparative Example 1.

[0018] FIG4 is a diagram showing the solar light absorption spectra of the products prepared in the examples and comparative examples of the present invention.

[0019] Figure 5 shows rGO 0.1% , storage modulus (G′) and loss modulus (G″) of PCr2 composite hydrogel.

[0020] Figure 6 shows the Na content of 3.5% seawater simulated solution before and after desalination by PCr2 composite hydrogel + , Mg 2+ , K + , Ca 2+ Changes in the concentrations of the four main ions. Modes for Carrying Out the Invention

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0023] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0024] Example 1

[0025] Referring to FIG1 , a method for preparing a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator comprises the following steps:

[0026] (1) Preparation of hydrogel precursor solution: Nanocrystalline cellulose was prepared into a 0.5 wt% CNC solution and then emulsified. The emulsification conditions were: emulsification at room temperature and 12000 rpm for 30 min, and then mixed evenly and set aside for use. 1 g PVA, 3 mL 0.5 wt% CNC solution, and 7 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0027] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 0.1%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0028] (3) Preparation of polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator: Continue to add 250 μL of glutaraldehyde and mix well to obtain a mixed solution. The mixed solution is gelled at 60°C for 2 h to obtain a hydrogel. The hydrogel is placed in a -25°C refrigerator and frozen for 12 h, and then freeze-dried for 48 h. The obtained hydrogel sample is fully swollen and then subjected to evaporation test. The obtained composite hydrogel is named PCr1.

[0029] Example 2

[0030] A method for preparing a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator comprises the following steps:

[0031] (1) Preparation of hydrogel precursor solution: Nanocrystalline cellulose was prepared into a 0.5 wt% CNC solution and then emulsified. The emulsification conditions were: emulsification at room temperature and 12000 rpm for 30 min, and then mixed evenly and set aside for use. 1 g PVA, 5 mL 0.5 wt% CNC solution, and 5 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0032] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 0.1%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0033] (3) Preparation of polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator: Continue to add 250 μL of glutaraldehyde and mix well to obtain a mixed solution. The mixed solution is gelled at 60°C for 2 h to obtain a hydrogel. The hydrogel is placed in a -25°C refrigerator and frozen for 12 h, and then freeze-dried for 48 h. The obtained hydrogel sample is fully swollen and then subjected to evaporation test. The obtained composite hydrogel is named PCr2.

[0034] Example 3

[0035] A method for preparing a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator comprises the following steps:

[0036] (1) Preparation of hydrogel precursor solution: Prepare 0.5 wt% CNC solution with nanocrystalline cellulose and then emulsify it. The emulsification conditions are: emulsify at room temperature and 12000 rpm for 30 min, mix well and set aside. Mix 1 g PVA and 10 mL 0.5 wt% CNC solution in a glass bottle, add 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0037] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 0.1%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0038] (3) Preparation of polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator: Continue to add 250 μL of glutaraldehyde and mix well to obtain a mixed solution. The mixed solution is gelled at 60°C for 2 h to obtain a hydrogel. The hydrogel is placed in a -25°C refrigerator and frozen for 12 h, and then freeze-dried for 48 h. The obtained hydrogel sample is fully swollen and then subjected to evaporation test. The obtained composite hydrogel is named PCr3.

[0039] Comparative Example 1

[0040] A method for preparing a polyvinyl alcohol composite hydrogel interface evaporator comprises the following steps:

[0041] (1) Preparation of hydrogel precursor solution: 1 g PVA and 10 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0042] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 0.1%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0043] (3) Preparation of polyvinyl alcohol composite hydrogel interface evaporator: Continue to add 250 μL glutaraldehyde and mix well to obtain a mixed solution. The mixed solution is gelled at 60 °C for 2 h to obtain a hydrogel. The hydrogel is placed in a -25 °C refrigerator for 12 h and then freeze-dried for 48 h. The obtained hydrogel sample is fully swollen and then subjected to evaporation test. The obtained composite hydrogel is named rGO 0.1% .

[0044] Comparative Example 2

[0045] A method for preparing a polyvinyl alcohol composite hydrogel interface evaporator comprises the following steps:

[0046] (1) Preparation of hydrogel precursor solution: 1 g PVA and 10 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0047] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 0.2%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0048] (3) Preparation of polyvinyl alcohol composite hydrogel interface evaporator: Continue to add 250 μL glutaraldehyde and mix well to obtain a mixed solution. The mixed solution is gelled at 60 °C for 2 h to obtain a hydrogel. The hydrogel is placed in a -25 °C refrigerator for 12 h and then freeze-dried for 48 h. The obtained hydrogel sample is fully swollen and then subjected to evaporation test. The obtained composite hydrogel is named rGO 0.2% .

[0049] Comparative Example 3

[0050] A method for preparing a polyvinyl alcohol composite hydrogel interface evaporator comprises the following steps:

[0051] (1) Preparation of hydrogel precursor solution: 1 g PVA and 10 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0052] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 0.4%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0053] (3) Preparation of polyvinyl alcohol composite hydrogel interface evaporator: Continue to add 250 μL glutaraldehyde and mix well to obtain a mixed solution. The mixed solution is gelled at 60 °C for 2 h to obtain a hydrogel. The hydrogel is placed in a -25 °C refrigerator for 12 h and then freeze-dried for 48 h. The obtained hydrogel sample is fully swollen and then subjected to evaporation test. The obtained composite hydrogel is named rGO 0.4% .

[0054] Comparative Example 4

[0055] A method for preparing a polyvinyl alcohol composite hydrogel interface evaporator comprises the following steps:

[0056] (1) Preparation of hydrogel precursor solution: 1 g PVA and 10 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0057] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 0.6%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0058] (3) Preparation of polyvinyl alcohol composite hydrogel interface evaporator: Continue to add 250 μL glutaraldehyde and mix well to obtain a mixed solution. The mixed solution is gelled at 60 °C for 2 h to obtain a hydrogel. The hydrogel is placed in a -25 °C refrigerator for 12 h and then freeze-dried for 48 h. The obtained hydrogel sample is fully swollen and then subjected to evaporation test. The obtained composite hydrogel is named rGO 0.6% .

[0059] Comparative Example 5

[0060] A method for preparing a polyvinyl alcohol composite hydrogel interface evaporator comprises the following steps:

[0061] (1) Preparation of hydrogel precursor solution: 1 g PVA and 10 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0062] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 0.8%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0063] (3) Preparation of polyvinyl alcohol composite hydrogel interface evaporator: 250 μL of glutaraldehyde was added and mixed evenly to obtain a mixed solution. The mixed solution was gelled at 60 °C for 2 h to obtain a hydrogel. The hydrogel was placed in a -25 °C refrigerator for 12 h and then freeze-dried for 48 h. The obtained hydrogel sample was fully swollen and then subjected to evaporation test. The obtained composite hydrogel was named rGO. 0.8% .

[0064] Comparative Example 6

[0065] A method for preparing a polyvinyl alcohol composite hydrogel interface evaporator comprises the following steps:

[0066] (1) Preparation of hydrogel precursor solution: 1 g PVA and 10 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0067] (2) Treatment of light-absorbing materials: rGO was added to the hydrogel precursor solution with a mass fraction of 1.0%, and placed in an ultrasonic cleaner for 0.5 h. After taking it out, it was placed in a magnetic stirrer and stirred for 10 min to stir evenly.

[0068] (3) Preparation of polyvinyl alcohol composite hydrogel interface evaporator: Continue to add 250 μL glutaraldehyde and mix well to obtain a mixed solution. The mixed solution is gelled at 60 °C for 2 h to obtain a hydrogel. The hydrogel is placed in a -25 °C refrigerator for 12 h and then freeze-dried for 48 h. The obtained hydrogel sample is fully swollen and then subjected to evaporation test. The obtained composite hydrogel is named rGO 1.0% .

[0069] Comparative Example 7

[0070] A method for preparing a polyvinyl alcohol hydrogel comprises the following steps:

[0071] (1) Preparation of hydrogel precursor solution: 1 g PVA and 10 mL deionized water were mixed in a glass bottle, and 1 mL 1.2 mol·L -1 hydrochloric acid, and placed it in an oil bath at 95 °C for magnetic stirring for 0.5 h until the PVA was completely melted to obtain a hydrogel precursor solution.

[0072] (2) Preparation of polyvinyl alcohol hydrogel: 250 μL of glutaraldehyde was added and mixed evenly to obtain a mixed solution. The mixed solution was gelled at 60°C for 2 h to obtain a hydrogel. The hydrogel was placed in a -25°C refrigerator and frozen for 12 h, and then freeze-dried for 48 h. After the obtained hydrogel sample was fully swollen, an evaporation test was performed. The obtained composite hydrogel was named PVA hydrogel.

[0073] Solar interface evaporation performance test

[0074] A xenon lamp was used to simulate sunlight, and the light intensity on the surface of the composite hydrogel interface evaporator was measured with an optical power meter and maintained at 1 kW m -2 A layer of plastic wrap was then placed on the surface of the evaporator to collect the evaporated water. The performance of the composite hydrogel interface evaporator was then measured using an electronic balance system and an infrared thermal imager.

[0075] Figure 3 shows rGO 0.1% (a) and SEM morphology of PCr2 (b), it can be seen that pores with a diameter of about 20 μm are evenly distributed in the figure. The existence of this porous structure and the fact that CNC contains a large number of hydroxyl groups make the PCr2 composite hydrogel have excellent water absorption and water transport capabilities. Moreover, the pores of the PCr2 composite hydrogel are more uniform, which can provide a more stable water transport capacity and ensure a stable evaporation rate.

[0076] Comparative Example 1: The products prepared in Examples 1-3 were exposed to sunlight at a solar intensity of 1 kW m -2 ) irradiated seawater desalination rates were 1.3 kg m -2 h-1 , 1.40 kg m -2 h -1 , 1.62 kg m -2 h -1 , 1.21 kg m -2 h -1 ,It can be seen that when the CNC concentration is kept at 0.25%, the evaporation rate of the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator is the highest.

[0077] This can also be demonstrated by the effect of polyvinyl alcohol-nanocellulose crystal composite hydrogel on the evaporation enthalpy of water. The hydrogel polymer network captures water molecules through electrostatic effects and hydrogen bonds, regulates the hydrogen bond network and intermolecular forces inside the hydrogel, thereby regulating the state and phase change behavior of water, and thus reducing the evaporation enthalpy of water. There are three types of water under the action of high molecular polymer chains: bound water, free water, and intermediate water, as shown in Figure 2. The hydrophilic groups of the high molecular polymer chain and the water molecules form bound water through strong intermolecular interactions. Free water refers to the part where water molecules are connected to each other through hydrogen bonds. Intermediate water exists between free water and bound water. It is connected to the bound water with weaker hydrogen bonds, and this weak force is lower than the hydrogen bonding between free water molecules, which makes it easier to break away from the constraints of weak hydrogen bonds, ultimately reducing the evaporation enthalpy. The evaporation enthalpy of water of the products prepared in Comparative Example 1 and Examples 1-3 is 1911 J g, respectively. -1 , 1634 J g -1 , 1415 J g -1 , 2392 J g -1 , it can be seen that the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator (PCr2) with a CNC concentration of 0.25% has the lowest evaporation enthalpy and is the easiest to evaporate, so the evaporation rate is the highest.

[0078] The products prepared by the present invention exhibit broad spectral absorption properties, as specifically shown in Figure 4 . Figure 4 shows the average light absorptivity of the products prepared in Example 1 and Comparative Examples 2-6 within the spectral absorption range of 250-2500 nm, which are 95.05%, 95.19%, 94.85%, 94.41%, 94.68%, and 94.74%, respectively. The products prepared in Examples 2-3 and Comparative Example 1, each containing 0.1% reduced graphene oxide, exhibited the same average light absorptivity as in Example 1, at 95.05%.

[0079] Figure 5 shows rGO 0.1% , storage modulus (G′) and loss modulus (G″) of PCr2 composite hydrogel. As can be seen from Figure 5, the composite hydrogel product prepared by the present invention has excellent mechanical strength.

[0080] Application Example 1: Seawater Desalination

[0081] Using seawater to simulate the seawater environment, different concentrations of seawater simulation solutions (3.5%, 10%, and 20%) were poured into beakers and placed on an electronic balance. The PCr2 composite hydrogel was prepared into a circular shape using a mold. After sufficient swelling, it floated in the seawater simulation solutions of different concentrations. The xenon lamp light source system was adjusted to a light intensity of 1 kW·m -2 The balance is connected to a computer, recording mass changes in real time. The evaporated fresh water is collected by a collection device. Analysis of the desalinated seawater obtained by evaporating PCr2 revealed removal rates of up to 99% for sodium, magnesium, potassium, and calcium ions. The test results for a 3.5% concentration of simulated seawater solution are shown in Figure 6, demonstrating that the PCr2 composite hydrogel prepared by the present invention has a good desalination effect on seawater.

[0082] Application Example 2 Wastewater Purification

[0083] Pulping wastewater and concentrated pulping wastewater (2 times, 3 times, and 4 times the original concentration) were poured into a beaker and placed on an electronic balance. The PCr2 composite hydrogel was prepared into a round shape through a mold. After sufficient swelling, it floated in the pulping wastewater. The xenon lamp light source system was adjusted to a light intensity of 1 kW·m -2 The balance is connected to a computer, recording mass changes in real time. The evaporated purified water is collected by a collection device. Analysis shows that the BOD and COD removal rates in the purified water obtained by evaporating different concentrated pulping wastewaters using PCr2 are as high as 99.9%, demonstrating excellent wastewater purification efficiency.

[0084] From the test results of the above two application examples, it can be seen that the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator prepared by the present invention performs excellently in seawater desalination and wastewater purification, and has excellent salt resistance, seawater desalination capacity, and wastewater purification capacity.

[0085] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator, characterized in that: The following steps are involved: Adding nanocrystalline cellulose, polyvinyl alcohol, and acid solution into water, mixing, and heating to dissolve the polyvinyl alcohol to obtain a hydrogel precursor solution; Reduced graphene oxide and a cross-linking agent are added to a hydrogel precursor solution, and the mixture is evenly mixed to obtain a mixed solution. The mixed solution is gelled and then freeze-dried to obtain a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator.

2. The method for preparing the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator according to claim 1, characterized in that: The concentration of nanocrystalline cellulose in the hydrogel precursor solution is 0.15 wt %-0.5 wt %.

3. The method for preparing the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator according to claim 1, characterized in that: The nano-microcrystalline cellulose is prepared into a solution of a certain concentration before use, and then emulsified and mixed evenly before use.

4. The method for preparing the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator according to claim 1, characterized in that: The acid solution is hydrochloric acid.

5. The method for preparing the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator according to claim 1, characterized in that: The concentration of reduced graphene oxide in the mixed solution is 0.1-1%.

6. The method for preparing the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator according to claim 1, characterized in that: The cross-linking agent is aldehydes, boric acid, epichlorohydrin or a heavy metal salt that can form a gel through coordination complexation with polyvinyl alcohol.

7. The method for preparing the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator according to claim 6, characterized in that: The aldehyde is glutaraldehyde.

8. The method for preparing a polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator according to any one of claims 1 to 7, characterized in that: The gelation temperature is 60-80° C. and the gelation time is 2-3 hours.

9. A polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator, characterized by: The invention relates to a novel nanostructured carbon foam, which is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the polyvinyl alcohol-nanocellulose crystal composite hydrogel interface evaporator according to claim 9 in seawater desalination or wastewater purification.

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