A method for preparing a low enthalpy-of-evaporation "vacancy-defect Bi2WO6-sodium alginate hydrogel"

Abstract

This invention discloses a method for preparing a low enthalpy of vaporization "vacancy-defect Bi2WO6-sodium alginate hydrogel", comprising the following steps: (1) synthesizing vacancy Bi2WO6 (O v -Bi2WO6); (2) Construct O v -Bi2WO6- Sodium alginate hydrogel (OPH): Sodium alginate is dissolved in deionized water, and O2 is added to the sodium alginate solution. v -Bi2WO6, stir evenly; then put the polyurethane sponge into the mixture, and after complete adsorption, immerse the sponge in CaCl2 aqueous solution for 24 h to form O v -Bi2WO6-sodium alginate hydrogel. The O in this invention v -Bi2WO6 not only regulates the "intermediate water" content but also possesses the ability to "weaken interfacial hydrogen bonds," achieving a synergistic effect between the two; O-type structures built with polyurethane foam as the framework... v -Bi2WO6- sodium alginate hydrogel has excellent mechanical stability.

Description

Technical Field

[0001] This invention relates to the fields of water environment purification and wastewater treatment, and in particular to a method for preparing a low enthalpy of vaporization "vacancy-defect Bi2WO6-sodium alginate hydrogel". Background Technology

[0002] Common seawater desalination methods include reverse osmosis, thermal distillation, and freezing. In recent years, solar-powered seawater desalination has attracted researchers' interest because it utilizes solar energy instead of fossil fuels. However, the enthalpy of vaporization of seawater reaches 2450 J / g, which seriously hinders the improvement of the desalination rate of solar-powered seawater.

[0003] Limited by the high enthalpy of vaporization of seawater, reducing this enthalpy has become a research hotspot. Mechanistically, current research primarily focuses on carriers and photothermal materials. Currently, materials for reducing enthalpy of vaporization are mainly concentrated in hydrogels, aerogels, and semiconductor materials. Based on the properties of water, it can be divided into bound water, free water (FW), and intermediate water (IW), with "intermediate water" having the lowest enthalpy of vaporization. For example, carriers such as hydrogels and aerogels, which have abundant hydrophilic groups, utilize this abundant "intermediate water" to reduce the enthalpy of vaporization. However, relying solely on "intermediate water" or a single mechanism of "weakening interfacial hydrogen bonding" to reduce the enthalpy of vaporization cannot further increase the evaporation rate.

[0004] Zheng et al. constructed a bilayer hydrogel evaporator, with acrylamide / sodium alginate foam hydrogel as the lower layer and Fe3O4@polydopamine-acrylamide-sodium alginate hydrogel as the upper layer, achieving an IW / FW ratio of 1.08. Sun et al. developed a bicrosslinked aerogel through hydrogen bonding and freeze-drying chemical crosslinking, introducing abundant carboxyl, amino, and hydroxyl functional groups, achieving an IW / FW ratio of 0.628 in a 3.5% sodium chloride solution. Unlike hydrogels and aerogel supports, semiconductors have recently been reported to possess the ability to disrupt interfacial hydrogen bonding.

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

[0006] The innovation of this invention lies in solving the following problems: (1) expanding the range of photothermal semiconductors with "weak interfacial hydrogen bonding"; (2) achieving the synergistic effect of "intermediate water regulation" and "weakened interfacial hydrogen bonding"; and (3) obtaining an interfacial evaporator with stable mechanical properties.

[0007] Specifically, this invention relates to a method for preparing a low enthalpy-of-evaporation "vacancy-defect Bi2WO6-sodium alginate hydrogel", comprising the following steps:

[0008] (1) Synthetic vacancy Bi2WO6 (Ov Bi₂WO₆ was prepared by dissolving hexadecyltrimethylammonium bromide and NaWO₄•2H₂O in deionized water. Then, Bi(NO₃)₃•5H₂O was added, and the mixture was stirred at room temperature for 3 h. The mixture was then reacted in a hydrothermal reactor at 120 ºC for 24 h to obtain Bi₂WO₆. The Bi₂WO₆ was placed in a crucible and subjected to vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O₂. v -Bi2WO6, heating rate 5 ºC / min;

[0009] (2) Construct O v -Bi2WO6-Sodium alginate hydrogel (OPH): Sodium alginate is dissolved in deionized water, and O2 is added to the sodium alginate solution. v -Bi2WO6, stir evenly; then put the polyurethane sponge into the mixture, and after complete adsorption, immerse the sponge in CaCl2 aqueous solution for 24 h to form O v -Bi2WO6-sodium alginate hydrogel.

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

[0011] The O obtained by the above preparation method v Application of -Bi2WO6-sodium alginate hydrogel in water environment purification and wastewater 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 to "weaken interfacial hydrogen bonds", thus achieving a synergistic effect between the two.

[0014] (2) O-frame constructed with polyurethane foam as the skeleton v -Bi2WO6-sodium alginate hydrogel exhibits excellent mechanical stability. Attached Figure Description

[0015] Figure 1 Image of OPH-100

[0016] Figure 2 The images are: (a) of OPH-200, (b) stability under ultrasonic conditions, (c) wetting properties, and (d) stress-strain curves.

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

[0018] Figure 4 Images of the control sample without sodium alginate before (a) and after (b) ultrasonic treatment for 1 minute.

[0019] Figure 5 Image of sodium alginate hydrogel supporting melamine sponge.

[0020] Figure 6 The results are as follows: hydrogel Raman spectra of the evaporation rates of each component in the OPH evaporator (a), OPH-0 (b) and OPH-200 (c), and calculation of the evaporation kinetics of pure water (d) and OPH-200 (e). Detailed Implementation

[0021] To demonstrate the essential features and significant advancements of the present invention, the following embodiments further illustrate the implementation methods and effects.

[0022] Hexadecyltrimethylammonium bromide and sodium alginate were supplied by Aladdin Chemical Reagent Co., Ltd. Na₂WO₄•₂H₂O was purchased from Tianjin Kemei Chemical Reagent Co., Ltd. Bi(NO₃)₃•₅H₂O and CaCl₂ were purchased from Maclean Chemical Reagent Co., Ltd.

[0023] Example 1 (OPH-100):

[0024] A method for preparing a low enthalpy-of-evaporation "vacancy-defect Bi2WO6-sodium alginate hydrogel", wherein O v The content of -Bi2WO6 is 100 mg

[0025] a. Dissolve 0.16 g of hexadecyltrimethylammonium 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 reactor at 120 ºC for 24 h to obtain Bi₂WO₆. Place Bi₂WO₆ in a crucible and perform vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O₂. v -Bi2WO6, heating rate 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 sodium alginate solution. v-Bi2WO6, stir well. Then add a 4 cm × 4 cm × 1 cm polyurethane sponge to 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. From Figure 1 As can be seen, OPH-100 appears gray, but this is limited by its water supply capacity. Figure 3 c) Its evaporation rate is only 1.773 kg•m -2 •h -1 ( Figure 6 a).

[0027] Example 2 (OPH-200):

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

[0029] a. Dissolve 0.16 g of hexadecyltrimethylammonium 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 reactor at 120 ºC for 24 h to obtain Bi₂WO₆. Place Bi₂WO₆ in a crucible and perform vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O₂. v -Bi2WO6, heating rate 5 ºC / min;

[0030] b. Construct O v -Bi2WO6-Sodium alginate hydrogel (OPH): Dissolve 3.5 g of sodium alginate in 115 ml of deionized water. Add 200 mg of O to 20 ml of sodium alginate solution. v -Bi2WO6, stir well. Then add a 4 cm × 4 cm × 1 cm polyurethane sponge to 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 As can be seen, the synthesized OPH-200 has a grayish-black appearance, and no powder shedding was observed even after treatment under ultrasonic conditions for 1 minute. Figure 2 (b) When a water droplet contacts the surface of the OPH-200, the 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 method for preparing a low enthalpy-of-evaporation "vacancy-defect Bi2WO6-sodium alginate hydrogel" is disclosed, which, compared with Example 1, only changes the O... v -Bi2WO6 content up to 400 mg.

[0034] a. Dissolve 0.16 g of hexadecyltrimethylammonium 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 reactor at 120 ºC for 24 h to obtain Bi₂WO₆. Place Bi₂WO₆ in a crucible and perform vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O₂. v -Bi2WO6, heating rate 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 to 20 ml of sodium alginate solution. v -Bi2WO6, stir well. Then add a 4 cm × 4 cm × 1 cm polyurethane sponge to 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.

[0036] O was observed from the morphology. v -The presence of Bi2WO6 and sodium alginate ( Figure 3 a). From the perspective of light absorption energy, it contains O v -Bi2WO6 comparison sample compared to pure sponge and 0 mg O v Bi2WO6 has strong light absorption capabilities, with OPH-400 being the best. Figure 3 b).

[0037] Different O v An evaporator containing Bi2WO6 was simultaneously placed in water, and filter paper was placed above the evaporator. The observation showed that the filter paper of the OPH-200 was wetted first, demonstrating the excellent water supply capacity of the OPH-200. Figure 3(c, d). Therefore, the optimal content of OPH-200 was obtained by balancing light absorption capacity and water supply capacity.

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

[0039] a. Dissolve 0.16 g of hexadecyltrimethylammonium 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 reactor at 120 ºC for 24 h to obtain Bi₂WO₆. Place Bi₂WO₆ in a crucible and perform vacuum-assisted heat treatment at 300 ºC for 2.5 h to obtain black O₂. v -Bi2WO6, heating rate 5 ºC / min;

[0040] b. Construct O v -Bi2WO6 directly loaded onto the polyurethane foam skeleton: Add 100 mg, 200 mg, or 400 mg of O to 20 ml of deionized water. v -Bi2WO6, stir until homogeneous. Then add a 4 cm × 4 cm × 1 cm polyurethane sponge to the mixture. After complete adsorption, dry to obtain the sample. From Figure 4 As can be seen from a and b, after 1 minute of ultrasonic treatment, the solution becomes turbid, indicating the presence of O2. v -Bi2WO6 detaches, resulting in instability.

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

[0042] Construction of sodium alginate hydrogel loaded onto a melamine sponge skeleton: 3.5 g of sodium alginate was dissolved in 115 ml of deionized water. A 4 cm × 4 cm × 1 cm polyurethane sponge was placed in 20 ml of sodium alginate solution. After complete adsorption, the sponge was immersed in a 0.45 mol / L CaCl2 aqueous solution for 24 h to form a sodium alginate-polyurethane composite hydrogel.

[0043] from Figure 5 It can be seen that it does not contain O v -Bi2WO6 hydrogel has a pale yellow appearance and from Figure 6 a and Figure 3 b proves that the evaporation rate is low at 1.217 kg•m -2 •h -1 Its light absorption capacity is only higher than that of pure melamine sponge, but lower than that of sponge with added O. v -Bi2WO6 sample.

[0044] Experimental example:

[0045] Verifying the efficiency of OPH: Under the light intensity of one sun (100 mW / cm²) 2 A comparative evaporation experiment was conducted.

[0046] The evaporation rates of pure polyurethane foam and pure water are 0.497 kg•m. -2 •h -1 and 0.412 kg•m -2 •h -1 No O v The OPH evaporation rate of -Bi2WO6 is 1.217 kg•m -2 •h -1 With O v -Bi2WO6 from 100 mg to 200 mg, evaporation rate from 1.773 kg•m -2 •h -1 Increased to 1.81 kg•m -2 •h -1 However, when the concentration was further increased to 400 mg, the rate decreased to 1.567 kg•m. -2 •h -1 .

[0047] Surface temperature analysis showed that the temperature of pure water was 26.9 ºC, and effective evaporation was limited due to heat dissipation throughout the water body. The surface temperature of the pure polyurethane sponge skeleton was 38.8 ºC, but its evaporation rate was limited by insufficient water supply. When O v When the Bi₂WO₆ content increased from 0 to 200 mg, the surface temperature reached 35.5 ºC. When the content continued to increase to 400 mg, the surface temperature did not change, but the excess O₂... v -Bi2WO6 restricts the water supply ( Figure 6 a) OPH contains intermediate water, which makes phase transitions more likely to occur than with free water.

[0048] No O v Raman spectrum of -Bi2WO6 ( Figure 6 b) at 3348.2 cm -1 and 3221.7 cm -1 The peak of free water is visible at 3448.5 cm. -1 and 3570.9 cm -1 The peak at that location belongs to intermediate water. The ratio of intermediate water to free water (I / F) is calculated to be 0.66. In OPH-200 ( Figure 6 In c), 3311.2 cm -1 and 3205.6 cm -1The peak at 3436.7 cm represents free water, while the peak at 3436.7 cm represents free water. -1 and 3577.4 cm -1 The peak at that point corresponds to the intermediate water, and the I / F ratio increases to 1.25.

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

[0050] To further study O v The effect of -Bi₂WO₆ on the enthalpy of vaporization was simulated using molecular dynamics with 1000 water molecules. In pure water, 779 water molecules remained after 800 ps ( Figure 6 d) In O v In the -Bi2WO6 system, only 556 water molecules remain ( Figure 6 e). The blue markings indicating the surface hydrogen bond distribution show that hydrogen bonds exist between water molecules. O v The low hydrogen bond distribution near the Bi2WO6 / water interface demonstrates the material's ability to disrupt hydrogen bond interactions. The above analysis confirms the presence of O... v The high evaporation efficiency of the -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 merely illustrative examples and are not intended to limit the specific implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above examples. It is impossible to provide detailed examples of all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A low enthalpy of vaporization O v The method for preparing -Bi2WO6-sodium alginate hydrogel is characterized by, Includes the following steps: (1) Synthesis of vacancy Bi2WO6: Hexadecyltrimethylammonium 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 reacted in a hydrothermal reactor 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; (2) Construct O v -Bi2WO6-Sodium alginate hydrogel: Sodium alginate is dissolved in deionized water, and O is added to the sodium alginate solution. v -Bi2WO6, sodium alginate solution volume: O v The dosage of Bi₂WO₆ was 1:5 ~ 1:20 ml / mg, and the mixture was stirred until homogeneous. Then, the polyurethane sponge was added to the mixture. After complete adsorption, the sponge was immersed in a CaCl₂ aqueous solution for 24 h to form O₂. v -Bi2WO6-sodium alginate hydrogel.

2. O prepared by the method described in claim 1 v Application of -Bi2WO6-sodium alginate hydrogel in water environment purification and wastewater treatment.

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