Preparation method of low-evaporation-enthalpy vacancy defect Bi2WO6-sodium alginate hydrogel

Abstract

The invention discloses a preparation method of'vacancy defect Bi2WO6-sodium alginate hydrogel 'with low evaporation enthalpy. The preparation method comprises the following steps: (1) synthesizing vacancy Bi2WO6 (Ov-Bi2WO6); (2) construction of Ov-Bi2WO6-sodium alginate hydrogel (OPH): dissolving sodium alginate in deionized water, adding Ov-Bi2WO6 into the sodium alginate solution, and uniformly stirring the solution and the Ov-Bi2WO6 and the deionized water; the preparation method comprises the following steps: mixing the Ov-Bi2WO6 with sodium alginate, then putting polyurethane sponge into a mixture, and after complete adsorption, immersing the sponge into a CaCl2 aqueous solution for 24 hours to form the Ov-Bi2WO6-sodium alginate hydrogel. The Ov-Bi2WO6 in the invention not only can regulate the content of'intermediate water ', but also has'interface hydrogen bond weakening' ability, so that the synergistic effect of the Ov-Bi2WO6 and the intermediate water is realized; the Ov-Bi2WO6-sodium alginate hydrogel constructed by taking the polyurethane sponge as a framework has excellent mechanical stability.

Description

Technical Field

[0001] The present invention relates to the fields of water environment purification and sewage treatment, and particularly to a preparation method of "vacancy defect Bi2WO6-sodium alginate hydrogel" with low evaporation enthalpy. Background Art

[0002] Commonly used seawater desalination methods include reverse osmosis, thermal distillation, freezing method, etc. In recent years, solar seawater desalination has attracted the interest of researchers because it uses solar energy instead of fossil energy. However, the evaporation enthalpy of seawater reaches 2450 J / g, seriously hindering the improvement of the solar seawater desalination rate.

[0003] Limited by the high evaporation enthalpy of seawater, reducing the evaporation enthalpy has become a research hotspot. Analyzing from the mechanism, most of the current research focuses on carriers and photothermal materials. Currently, materials for reducing the evaporation enthalpy mostly focus on hydrogels, aerogels and semiconductor materials. According to the properties of water, water is divided into bound water, free water (FW) and intermediate water (IW), among which the evaporation enthalpy of "intermediate water" is the lowest. For example, carriers such as hydrogels and aerogels with rich hydrophilic groups use the abundant "intermediate water" to reduce the evaporation enthalpy. Whether relying on the single mechanism of "intermediate water" or "weakening the interfacial hydrogen bond interaction" to reduce the evaporation enthalpy, the evaporation rate cannot be further increased.

[0004] Zheng et al. constructed a bilayer hydrogel evaporator, in which foamed acrylamide / sodium alginate hydrogel was used as the lower layer, and Fe3O4@polydopamine-acrylamide-sodium alginate hydrogel was used as the upper layer, and the IW / FW ratio was 1.08. Sun et al. developed a double-crosslinked aerogel through chemical crosslinking of hydrogen bonds and freeze-drying, introducing abundant carboxyl, amino and hydroxyl functional groups. In a 3.5% sodium chloride solution, the IW / FW ratio was 0.628. Different from hydrogel and aerogel carriers, recently reported semiconductors also have the ability to disrupt interfacial hydrogen bond interactions.

[0005] Based on this, the technical solution of the present application is proposed to develop an evaporator that can achieve the synergistic effect of two mechanisms. Summary of the Invention

[0006] The innovation of the solution of the present invention lies in that it can solve the following problems: (1) Expand the range of photothermal semiconductors with "weak interfacial hydrogen bond interaction"; (2) Achieve the synergistic effect of "intermediate water regulation" and "weakening interfacial hydrogen bond interaction"; (3) Obtain an interfacial evaporator with stable mechanical properties.

[0007] Specifically, the present invention relates to a preparation method of "vacancy defect Bi2WO6-sodium alginate hydrogel" with low evaporation enthalpy, including the following steps:

[0008] (1) Synthesize vacant Bi2WO6 (Ov -Bi2WO6); Cetyltrimethylammonium bromide and NaWO4•2H2O were dissolved in deionized water. Then, Bi(NO3)3•5H2O was added and stirred at room temperature for 3 h; the mixture was hydrothermally reacted in a hydrothermal autoclave at 120 ºC for 24 h to obtain Bi2WO6. Bi2WO6 was placed in a crucible and subjected to vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O v -Bi2WO6, heating rate 5 ºC / min;

[0009] (2)Construct O v -Bi2WO6-sodium alginate hydrogel (OPH): Sodium alginate was dissolved in deionized water, and O v -Bi2WO6 was added to the sodium alginate solution and stirred evenly; then the polyurethane sponge was placed in the mixture. After complete adsorption, the sponge was immersed in a CaCl2 aqueous solution for 24 h to form O v -Bi2WO6-sodium alginate hydrogel.

[0010] More preferably, the concentration of the sodium alginate solution described in step (2) is the volume of the added sodium alginate solution (ml): O v -The dosage of Bi2WO6 (mg) is 1:5 ~ 1:20 ml / mg.

[0011] The O v -Bi2WO6-sodium alginate hydrogel prepared by the above preparation method is used in water environment purification and sewage treatment.

[0012] The present invention has the following beneficial effects:

[0013] (1) O v -Bi2WO6 can not only regulate the content of "intermediate water" but also has the ability of "weakening interfacial hydrogen bonds", realizing the synergistic effect of the two;

[0014] (2) The O v -Bi2WO6-sodium alginate hydrogel constructed with a polyurethane sponge as the framework has excellent mechanical stability. Description of the drawings

[0015] Figure 1 For: Picture of OPH-100

[0016] Figure 2 For: Picture of OPH-200 (a), stability under ultrasonic conditions (b), wettability (c) and stress-strain curve (d).

[0017] Figure 3are: the surface morphology of OPH-400 (a), the light absorption capacity of different evaporators (b), and the comparison of water supply capacity (c, d).

[0018] Figure 4 are: pictures of the comparative sample without sodium alginate before (a) and after (b) 1 min of ultrasonic treatment.

[0019] Figure 5 are: pictures of sodium alginate hydrogel-loaded melamine sponges.

[0020] Figure 6 are: the comparative experiment of the evaporation rate of each component of the OPH evaporator (a), the Raman spectra of the hydrogels of OPH-0 (b) and OPH-200 (c), and the calculation of the evaporation kinetics of water molecules of pure water (d) and OPH-200 (e). Specific Embodiments

[0021] In order to show the substantial features and remarkable progress of the present invention, the following embodiments are used to further illustrate the embodiments and effects.

[0022] Cetyltrimethylammonium bromide and sodium alginate were provided by Aladdin Chemical Reagent Co., Ltd. Na2WO4•2H2O was purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. Bi(NO3)3•5H2O and CaCl2 were purchased from Macklin Chemical Reagent Co., Ltd.

[0023] Example 1 (OPH-100):

[0024] A preparation method of "vacancy defect Bi2WO6-sodium alginate hydrogel" with low evaporation enthalpy, where the content of O v -Bi2WO6 is 100 mg

[0025] a. Dissolve 0.16 g of cetyltrimethylammonium bromide and 1.056 g of Na2WO4•2H2O in 250 ml of deionized water. Then, add 3.1 g of Bi(NO3)3•5H2O and stir at room temperature for 3 h. React the mixture in a hydrothermal autoclave at 120 ºC for 24 h to obtain Bi2WO6. Put Bi2WO6 into a crucible and perform vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O v -Bi2WO6, with a heating rate of 5 ºC / min;

[0026] b. Construct O v -Bi2WO6-sodium alginate hydrogel (OPH): Dissolve 3.5 g of sodium alginate in 115 ml of deionized water. Add 100 mg of O to 20 ml of the sodium alginate solution v-Bi2WO6, stir evenly. Then put a 4 cm × 4 cm ×1 cm polyurethane sponge into the mixture. After complete adsorption, immerse the sponge in a 0.45 mol / L CaCl2 aqueous solution for 24 h to form O v -Bi2WO6-sodium alginate hydrogel. Figure 1 It can be seen that OPH-100 appears gray, but is limited by water supply capacity ( Figure 3 c), its evaporation rate is only 1.773 kg•m -2 •h -1 ( Figure 6 a).

[0027] Embodiment 2 (OPH-200):

[0028] A method for preparing a low evaporation enthalpy "vacancy defect Bi2WO6-sodium alginate hydrogel" is provided. Compared with Example 1, only the O v - Bi2WO6 content up to 200 mg.

[0029] a. Dissolve 0.16 g hexadecyltrimethylammonium bromide and 1.056 g Na2WO4•2H2O in 250 ml deionized water. Then, add 3.1 g Bi(NO3)3•5H2O and stir at room temperature for 3 h. React the mixture in a hydrothermal reactor at 120 ºC for 24 h to obtain Bi2WO6. Put Bi2WO6 into a crucible and perform vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O v -Bi2WO6, heating rate 5 ºC / min;

[0030] b. Build O v -Bi2WO6-alginate hydrogel (OPH): 3.5 g of sodium alginate was dissolved in 115 ml of deionized water. 200 mg O v -Bi2WO6, stir evenly. Then put a 4 cm × 4 cm ×1 cm polyurethane sponge into the mixture. After complete adsorption, immerse the sponge in a 0.45 mol / L CaCl2 aqueous solution for 24 h to form O v -Bi2WO6-sodium alginate hydrogel.

[0031] from Figure 2 a It can be seen that the appearance of the synthesized OPH-200 is gray-black, and no powder is observed to fall off even after being treated under ultrasonic conditions for 1 minute ( Figure 2 b), when the water droplet touches the surface of OPH-200, the water droplet spreads completely within 2.4 ms ( Figure 2c). At 30% strain, the maximum stress of OPH-200 reached 0.027 MPa( Figure 2 d).

[0032] Example 3 (OPH-400):

[0033] A preparation method of "vacancy defect Bi2WO6-sodium alginate hydrogel" with low evaporation enthalpy. Compared with Example 1, only the content of O v -Bi2WO6 was changed to 400 mg.

[0034] a. Dissolve 0.16 g of cetyltrimethylammonium bromide and 1.056 g of Na2WO4•2H2O in 250 ml of deionized water. Then, add 3.1 g of Bi(NO3)3•5H2O and stir at room temperature for 3 h. React the mixture in a hydrothermal autoclave at 120 ºC for 24 h to obtain Bi2WO6. Put Bi2WO6 into a crucible and perform vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O v -Bi2WO6, with a heating rate of 5 ºC / min;

[0035] b. Construct O v -Bi2WO6-sodium alginate hydrogel (OPH): Dissolve 3.5 g of sodium alginate in 115 ml of deionized water. Add 400 mg of O v -Bi2WO6 to 20 ml of the sodium alginate solution and stir evenly. Then, put a 4 cm × 4 cm × 1 cm polyurethane sponge into the mixture. After complete adsorption, immerse the sponge in a 0.45 mol / L aqueous CaCl2 solution for 24 h to form O v -Bi2WO6-sodium alginate hydrogel.

[0036] The presence of O v -Bi2WO6 and sodium alginate was observed from the morphology( Figure 3 a). Analyzed from the aspect of light absorption energy, the comparative sample containing O v -Bi2WO6 has stronger light absorption ability than the pure sponge and 0 mg of O v -Bi2WO6, and OPH-400 is the best( Figure 3 b).

[0037] Evaporators with different O v -Bi2WO6 contents were simultaneously placed in water, and a filter paper was placed above the evaporators. It was observed from the phenomenon that the filter paper of OPH-200 was first wetted, proving the excellent water supply ability of OPH-200( Figure 3c, d). Therefore, the optimal content of OPH-200 is obtained under the balance of light absorption ability and water supply ability.

[0038] Comparative Example 1: O v -Bi2WO6 was directly loaded onto melamine sponge

[0039] a. Dissolve 0.16 g of cetyltrimethylammonium bromide and 1.056 g of Na2WO4•2H2O in 250 ml of deionized water. Then, add 3.1 g of Bi(NO3)3•5H2O and stir at room temperature for 3 h. React the mixture in a hydrothermal autoclave at 120 ºC for 24 h to obtain Bi2WO6. Put Bi2WO6 into a crucible and perform vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O v -Bi2WO6, heating rate 5 ºC / min;

[0040] b. Construct O v -Bi2WO6 was directly loaded onto the polyurethane sponge framework: Add 100 mg, 200 mg or 400 mg of O v -Bi2WO6 to 20 ml of deionized water and stir evenly. Then put a 4 cm × 4 cm × 1 cm polyurethane sponge into the mixture. After complete adsorption, dry to obtain the sample. It can be seen from Figure 4 a, b that after ultrasonic treatment for 1 minute, the solution becomes turbid, that is, the loaded O v -Bi2WO6 falls off and has no stability.

[0041] Comparative Example 2: Melamine sponge was only loaded with sodium alginate hydrogel

[0042] Construct sodium alginate hydrogel loaded onto the melamine sponge framework: Dissolve 3.5 g of sodium alginate in 115 ml of deionized water. Put a 4 cm × 4 cm × 1 cm polyurethane sponge into 20 ml of sodium alginate solution. After complete adsorption, immerse the sponge in 0.45 mol / L CaCl2 aqueous solution for 24 h to form sodium alginate-polyurethane composite hydrogel.

[0043] From Figure 5 it can be seen that the hydrogel without O v -Bi2WO6 shows a light yellow appearance, and from Figure 6 a and Figure 3 b it is proved that the evaporation rate is lower, 1.217 kg•m -2 •h -1 , and its light absorption ability is only higher than that of pure melamine sponge and lower than that of the sample added with O v -Bi2WO6.

[0044] Test Example:

[0045] Verify the efficiency of OPH: Conduct a comparative evaporation experiment under the light intensity of one sun (100 mW / cm 2 ).

[0046] The evaporation rates of pure polyurethane sponge and pure water are 0.497 kg•m -2 •h -1 and 0.412 kg•m -2 •h -1 respectively. The evaporation rate of OPH without O v -Bi2WO6 is 1.217 kg•m -2 •h -1 . As the amount of O v -Bi2WO6 increases from 100 mg to 200 mg, the evaporation rate increases from 1.773 kg•m -2 •h -1 to 1.81 kg•m -2 •h -1 , but when it further increases to 400 mg, the rate decreases to 1.567 kg•m -2 •h -1 .

[0047] Surface temperature analysis shows that the temperature of pure water is 26.9 ºC. Since the heat dissipates throughout the water body, it limits the effective evaporation. The surface temperature of the pure polyurethane sponge framework is 38.8 ºC, but its evaporation rate is limited by insufficient water supply. When the content of O v -Bi2WO6 increases from 0 to 200 mg, the surface temperature is 35.5 ºC. When the content continues to increase to 400 mg, the surface temperature does not change, but the excessive O v -Bi2WO6 limits the water supply ( Figure 6 a). There is intermediate water in OPH, which makes the phase change easier to occur than free water.

[0048] The Raman spectrum of OPH without O v -Bi2WO6 ( Figure 6 b) shows peaks of free water at 3348.2 cm -1 and 3221.7 cm -1 . The peaks at 3448.5 cm -1 and 3570.9 cm -1 belong to intermediate water. The ratio of intermediate water to free water (I / F) is calculated to be 0.66. In OPH-200 ( Figure 6 c), the peaks at 3311.2 cm -1 and 3205.6 cm -1The peak at [X] cm represents free water, while the peaks at 3436.7 cm -1 and 3577.4 cm -1 correspond to intermediate water, and the I / F ratio increases to 1.25.

[0049] The above results confirm that O v -Bi2WO6 increases the content of intermediate water.

[0050] To further study the effect of O v -Bi2WO6 on the enthalpy of evaporation, molecular dynamics simulations were performed using 1000 water molecules. In pure water, 779 water molecules remained after 800 ps ( Figure 6 d), while in the O v -Bi2WO6 system, only 556 water molecules remained ( Figure 6 e). It can be seen from the blue markers of the surface hydrogen bond distribution that hydrogen bonds exist between water molecules. There is less hydrogen bond distribution near the O v -Bi2WO6 / water interface, demonstrating the ability of this material to disrupt hydrogen bond interactions. The above analysis confirms that the high evaporation efficiency of the O v -Bi2WO6-sodium alginate hydrogel is due to the synergistic effect of "intermediate water" and "weakened interfacial hydrogen bonds".

[0051] Of course, the above embodiments of the present invention are only examples for illustrating the present invention, and are not limitations on the specific implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above examples. It is not possible to give detailed examples of all implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A preparation method of "vacancy defect Bi2WO6-sodium alginate hydrogel" with low evaporation enthalpy, characterized in that, It includes the following steps: (1) Synthesize vacancy Bi2WO6 (O v -Bi2WO6); (2) Construction of O v -Bi2WO6-sodium alginate hydrogel (OPH): Dissolve sodium alginate in deionized water, and add O v -Bi2WO6 to the sodium alginate solution and stir evenly; then put the polyurethane sponge into the mixture, after complete adsorption, immerse the sponge in the CaCl2 aqueous solution for 24 h to form O v -Bi2WO6-sodium alginate hydrogel.

2. The manufacturing method according to claim 1, characterized in that, Step (2), volume of sodium alginate solution added (ml): 0 v - The dosage of Bi2WO6 (mg) is 1:5 to 1:20 ml / mg.

3. O obtained by the preparation method of claim 1 or 2 v - Application of Bi2WO6 - sodium alginate hydrogel in water environment purification and sewage treatment.

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