Melanin-cellulose composite gel and preparation method thereof

Abstract

The invention provides a preparation method of melanin-cellulose composite gel, which comprises the following steps: respectively dissolving carboxylated cellulose nanofiber and ammoniated micron fiber in a proper amount of water to obtain dispersion liquid; adding amino acid doped noradrenaline nanoparticles and CaCl2 into the dispersion liquid, adding an ethylene and vinyl alcohol copolymer EvOH, and stirring to fully foam, so as to obtain a gel liquid 1; then preparing a part of foaming gel liquid 2 which does not contain amino acid doped noradrenaline nanoparticles; respectively freezing and mixing the gel liquid 1 and the gel liquid 2, and freeze-drying to remove moisture to obtain the aerogel. By preparing the new photo-thermal material, the capturing capacity of the surface of the evaporator on solar energy can be greatly enhanced, and the photo-thermal conversion efficiency can be improved. Meanwhile, due to the design of aerogel, the evaporation performance of the evaporator is also remarkably improved, the problem that the evaporation rate is reduced due to salt accumulation is effectively solved, and good economic and social benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, specifically to a melanin-cellulose composite gel and its preparation method. Background Technology

[0002] With rapid global economic development and explosive population growth, water scarcity has become a pressing global issue. According to the World Health Organization, approximately 30% of the world's population lacks access to sufficient clean water. Therefore, developing an environmentally friendly and sustainable clean water production technology is extremely urgent. The ocean contains 96.5% of the world's water resources. Therefore, extracting potable freshwater from seawater is a very promising approach.

[0003] Currently, the mainstream seawater desalination technologies internationally include the following methods: First, distillation: seawater is heated to 105°C to obtain steam, which is then condensed to obtain distilled water. The disadvantages are high energy consumption and the susceptibility of equipment to corrosion and scaling. Second, electrodialysis: using ion exchange technology, a direct current electric field is applied to selectively permeate anions and cations in seawater through anion and cation exchange membranes, separating fresh water from concentrated brine. Its disadvantages are that the development and manufacturing of novel ion exchange membranes is a bottleneck restricting the application of this technology, and it also has high energy consumption. Third, multi-stage flash evaporation: heated seawater is introduced into a low-pressure space. Because the ambient pressure is lower than the saturated vapor pressure corresponding to the heated seawater temperature, the seawater rapidly partially evaporates to produce steam, which is then condensed to become fresh water. The disadvantages of this method are: increased operating costs due to large-scale seawater circulation and fluid transportation; a larger heat transfer area compared to multi-effect distillation; and the need for integration with a power plant. Fourth, the low-temperature multi-effect method: under conditions where the maximum evaporation water temperature is less than 70℃, a large number of horizontal tube falling film evaporators are connected together and divided into multiple groups, with steam introduced. Distilled water is obtained through multiple evaporations and cooling condensations. Its disadvantages are that it consumes a certain amount of steam compared to reverse osmosis, and the equipment structure is more complex. Fifth, the reverse osmosis method: under pressure, freshwater from seawater passes through a semi-permeable membrane into the low-pressure side of the membrane, while salt is blocked on the high-pressure side and discharged with the concentrated seawater. Its disadvantages are higher equipment costs, higher requirements for seawater pretreatment, and the susceptibility of reverse osmosis membranes to fouling and damage during use, generally requiring replacement every 3-5 years. Sixth, the freezing method: freezing seawater, causing the liquid seawater to turn into solid ice, resulting in salt separation and the extraction of freshwater. Traditional freezing methods include direct contact, vacuum freezing, and indirect freezing. Its disadvantages include high energy consumption, poor-tasting and unusable freshwater, large equipment investment, and high technical difficulty; the seventh method is dew point evaporation: it adopts the principle of carrier gas humidification and dehumidification, utilizing the heat from condensation and dehumidification, with the atmosphere as the main carrier, and seawater to humidify and dehumidify it to produce freshwater. The disadvantages of this technology are that the heat transfer efficiency is affected by the side heat transfer of the gas-water mixture, the technology is still in the development stage, large-scale application is rare, and related equipment and operating costs need to be further reduced and optimized.

[0004] It is a well-known fact that the evaporation performance of mainstream solar evaporators decreases with increasing seawater salt concentration. Therefore, there is an urgent need in this field to develop a material that can overcome the defect of decreasing evaporation rate with increasing seawater salt concentration. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to provide a melanin-cellulose composite gel and its preparation method.

[0006] This invention is achieved through the following technical solution:

[0007] The present invention provides a method for preparing a melanin-cellulose composite gel in a first aspect, comprising the following steps:

[0008] S1: Take carboxylated cellulose nanofibers and aminated microfibers and add them to an appropriate amount of water, disperse them evenly to obtain a dispersion;

[0009] S2: Add amino acid-doped norepinephrine nanoparticles and CaCl2 to the dispersion prepared in S1 above, stir at room temperature, then add 1-5 wt% of the ethylene and vinyl alcohol copolymer EvOH described in S1, stir to fully foam, and obtain gel liquid 1.

[0010] S3: Take another equal amount of carboxylated cellulose nanofibers and aminated microfibers and add them to an appropriate amount of water, then disperse them evenly with a disperser to obtain a dispersion.

[0011] S4: Add CaCl2 to the dispersion prepared in S3 above, stir at room temperature, then add 4-8 wt% of the ethylene and vinyl alcohol copolymer EvOH described in S1, stir to fully foam, and obtain gel liquid 2.

[0012] S5: Freeze gel liquid 1 obtained in S2 and gel liquid 2 obtained in S4 at -10 to 0℃ respectively, mix them, freeze dry to remove water, and then they become aerogel.

[0013] Furthermore, in S1 and S3, the mass ratio of the carboxylated cellulose nanofibers to the aminated microfibers is 1 to 1.5:1; even further, in S1 and S3, the mass ratio of the carboxylated cellulose nanofibers to the aminated microfibers is 1 to 1:1.

[0014] Furthermore, in S1 and S3, the mass ratio of the sum of the masses of carboxylated cellulose nanofibers and ammoniated microfibers to water is 400 to 600:1; even further, in S1 and S3, the mass ratio of the sum of the masses of carboxylated cellulose nanofibers and ammoniated microfibers to water is 500:1.

[0015] Furthermore, in S1 and S3, the preparation method of the ammoniated microfiber includes the following steps: First, weigh an appropriate amount of bleached hardwood pulp, completely disperse it in 4 to 6 times its mass of water, and add NaOH and 2,3-epoxypropyltrimethylammonium chloride sequentially, wherein the mass ratio of bleached hardwood pulp:NaOH:2,3-epoxypropyltrimethylammonium chloride is 1:3:1 to 2, react at 55 to 70°C for 10 to 16 hours, after the reaction is completed, neutralize to neutral with acetic acid, filter, wash with water 1 to 3 times, and dry to obtain the product;

[0016] Furthermore, in S2, the mass ratio of the sum of the mass of carboxylated cellulose nanofibers and ammoniated microfibers to the mass of amino acid-doped norepinephrine nanoparticles is 18–24:1; even further, in S2, the mass ratio of the sum of the mass of carboxylated cellulose nanofibers and ammoniated microfibers to the mass of amino acid-doped norepinephrine nanoparticles is 20:1.

[0017] Furthermore, in S2 and S4, the mass ratio of the sum of the carboxylated cellulose nanofibers and the aminated microfibers to the mass of CaCl2 is 1 to 3:1; furthermore, in S2 and S4, the mass ratio of the sum of the carboxylated cellulose nanofibers and the aminated microfibers to the mass of CaCl2 is 2:1.

[0018] Furthermore, in S2 and S4, the stirring speed is 1000-2000 rpm and the stirring time is 15-30 min;

[0019] Furthermore, in S2, the preparation method of the norepinephrine nanoparticles includes the following steps:

[0020] S21: Add norepinephrine to an appropriate amount of water and stir evenly at room temperature to obtain a norepinephrine aqueous solution; further, in S21, the amount of water added is 0.8 to 1.2 times the amount of norepinephrine.

[0021] S22: Add an appropriate amount of water to the amino acids and stir evenly at room temperature to obtain an amino acid aqueous solution; further, in S22, the amount of water added is 0.8 to 1.2 times the amount of norepinephrine; even further, the amino acids are selected from any one or more of histidine, arginine, and lysine.

[0022] S23: Norepinephrine and amino acids are mixed in a mass ratio of 3 to 5:1. The two solutions prepared in S21 and S22 are mixed, heated to 40 to 60°C, and stirred for 20 to 30 hours. After the reaction is completed, centrifugation is performed to obtain amino acid-doped norepinephrine nanoparticles. Further, the mass ratio of norepinephrine to amino acids is 4:1.

[0023] A second aspect of the present invention provides a melanin-cellulose composite gel, prepared by any of the methods described above;

[0024] A third aspect of the present invention provides the use of the above-mentioned melanin-cellulose composite gel in seawater desalination; Attached Figure Description

[0025] Figure 1 Synthetic route diagram of melanin gel nanoparticles

[0026] Figure 2 TEM images of the three types of melanin gel nanoparticles in Examples 1-3.

[0027] Figure 3 XPS images of three types of melanin nanoparticles

[0028] Figure 4 Schematic diagram of the synthesis of melanin gel nanoparticles

[0029] Figure 5 TEM images of the upper layer, lower layer, and cross-section of the aerogel.

[0030] Figure 6 A schematic diagram illustrating the practical application of aerogels in seawater desalination.

[0031] Figure 7 Figure showing the application performance of aerogel

[0032] Beneficial effects

[0033] This invention, through the development of novel photothermal materials, can significantly enhance the solar energy capture capacity of evaporator surfaces and improve photothermal conversion efficiency. Simultaneously, the aerogel design of this invention also significantly improves the evaporator's evaporation performance. On the one hand, it can provide an ample water supply for the evaporation process; on the other hand, it can accelerate the dissolution and transport of surface salts, maintaining a salt-free state on the evaporator surface and solving the problem of decreased evaporation rate caused by salt accumulation, thus offering significant economic and social benefits. Detailed Implementation

[0034] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0035] Example 1

[0036] HPNE preparation: First, weigh 100 mg of norepinephrine (NE) and add it to 90 mL of water. Stir at room temperature for 10 min. Then, weigh 25 mg of histidine (His) and add it to 10 mL of water. After it is completely dissolved, add it to the reaction mixture. Heat to 50 degrees Celsius and stir for 24 h. After the reaction is complete, centrifuge three times at 12000 rpm to obtain the final histidine-doped HPNE nanoparticles.

[0037] Example 2

[0038] APNE preparation: First, weigh 100 mg of norepinephrine (NE) and add it to 90 mL of water. Stir at room temperature for 10 min. Then, weigh 25 mg of arginine (Arg) and add it to 10 mL of water. After it is completely dissolved, add it to the reaction mixture. Heat to 50 degrees Celsius and stir for 24 h. After the reaction is complete, centrifuge three times at 12000 rpm to obtain the final arginine-doped APNE nanoparticles.

[0039] Example 3

[0040] LPNE preparation: First, weigh 100 mg of norepinephrine (NE) and add it to 90 mL of water. Stir at room temperature for 10 min. Then, weigh 25 mg of lysine (Lys) and add it to 10 mL of water. After complete dissolution, add it to the reaction mixture. Heat to 50 degrees Celsius and stir for 24 h. After the reaction is complete, centrifuge three times at 12000 rpm to obtain the final lysine-doped LPNE nanoparticles.

[0041] like Figure 1 As shown, this invention copolymerized three different nanoparticles using a one-pot method. Figure 1 This is a schematic diagram illustrating the synthesis of three types of melanin nanoparticles;

[0042] Figure 2 TEM images of the three types of melanin nanoparticles in Examples 1-3; Figure 3 XPS images of three types of melanin nanoparticles illustrate the bonding structures of C, N, and O contained in the three amino acids within the melanin nanoparticles, demonstrating the successful doping of the three amino acid small molecules.

[0043] Figure 3 XPS images of three types of melanin nanoparticles are shown. Figure 3a, b, c, and d represent the C1s, N1s, and O1s peaks of the N1s peak and N1s peak, respectively, in the X-ray photoelectron spectroscopy (XPS) spectrum of HPNE. The C1s peak consists of three bonds: CC / C-Hx at 284.74 eV, CO / CN at 286.08 eV, and C=O at 287.86 eV. The N1s peak consists of two bonds: Pyrrolic N at 400.10 eV and NC at 401.48 eV. The O1s peak consists of two bonds: C=O at 531.26 eV and CO at 532.82 eV. Compared to PNE, the CO / CN absorption peak area at 268.08 eV increased from 25.4% to 32.7% in HPNE, demonstrating successful histidine doping and resulting in an increase in CN bond content.

[0044] Figures e, f, g, and h show the C1s, N1s, and N1s-O1s peaks in the XPS spectra of APNE, respectively. Compared to PNE, the CO / CN absorption peak area at 285.92 eV increased from 25.4% to 39.2% in APNE, demonstrating the successful doping of arginine, which led to an increase in the CN bond content.

[0045] Figures i, j, k, and l show the C1s, N1s, and O1s peaks of the XPS spectrum of LPNE, respectively. Compared to PNE, the CO / CN absorption peak area at 285.92 eV for APNE increased from 25.4% to 30.7%, demonstrating the successful doping of lysine, which led to an increase in CN bond content.

[0046] Example 4

[0047] like Figure 4 As shown, the gel consists of two parts, which need to be prepared separately before freeze-drying. All steps before freeze-drying are carried out at room temperature and pressure.

[0048] (1) Preparation method of the upper layer: First, weigh 500mg of carboxylated cellulose nanofibers (commercially available, CAS No.: 9004-34-6) and 500mg of ammoniated microfibers and add them to 20mL of water. Disperse them evenly with a disperser. Then add 50mg of HPNE and 500mg of CaCl2 respectively. Stir at room temperature and 1200rpm for 20min. Then add 2wt% of ethylene and vinyl alcohol copolymer (EvOH) by solvent mass and stir mechanically for 20min to make it fully foamed.

[0049] (2) Preparation method of the lower layer: First, weigh 500mg of carboxylated cellulose nanofibers and 500mg of ammoniated microfibers and add them to 20mL of water. Disperse them evenly with a disperser. Then add 500mg of CaCl2 and stir at room temperature and 1200rpm for 20min. Then add 5wt% of ethylene and vinyl alcohol copolymer (EvOH) by solvent and stir mechanically for 20min to make it fully foamed.

[0050] (3) Aerogel preparation method: The upper and lower layers are frozen in a -4℃ refrigerator at different time intervals to form a whole hydrogel. Then, the water is removed by a freeze dryer to obtain the final aerogel.

[0051] The preparation method of ammoniated microfibers includes the following steps: Weigh 6g of hardwood bleached pulp (commercially available), disperse the hardwood bleached pulp completely in 300mL of water using a disperser, add 18g of NaOH and 7.2g of 2,3-epoxypropyltrimethylammonium chloride (commercially available, CAS: 3033-77-0) in sequence, react at 60℃ for 12h, after the reaction is completed, neutralize the pH to 7 with acetic acid; then filter, wash three times with water to obtain the final ammoniated microfibers.

[0052] Figure 5 This is a TEM image showing the cross-sections of the upper layer, lower layer, and connection point of the final aerogel.

[0053] Example 5: Seawater Evaporation Experiment

[0054] like Figure 6 The diagram illustrates the entire aerogel in a real evaporation environment, with the evaporator's absorbent layer placed in seawater and surrounded by foam as a supporting structure. As evaporation proceeds, water molecules are transported from bottom to top to the evaporation interface, where various metal ions and Cl- from the seawater... - Ions are adsorbed by carboxylated cellulose nanofibers and aminated microfibers, respectively. The strong electrostatic forces between cellulose and ions, as well as the forces between ions, break the solvation shell of metal ions and water molecules, reduce the hydrogen bonds between water molecules, lower the enthalpy of evaporation, and increase the evaporation rate. Due to the presence of these forces, this aerogel evaporator performs better in seawater than in pure water, and its performance increases with the ionic strength in seawater.

[0055] Figure 7 The diagram shows the application performance of aerogel. Figure 7 a is the absorption diagram of the aerogel across the entire solar spectrum (300-2500 nm). Figure 7 b is the surface temperature rise curve of the aerogel during actual operation within 1 hour, which shows that it can reach 31.5℃, which is significantly higher than the room temperature of 21℃ at that time; Figure 7 c is the mass graph of water evaporated from the aerogel. Figure 7d is the evaporation rate graph of the aerogel during operation. The cellulose / EvOH ratio is used as a control group without HPNE. Figure 7 c, 7d shows that the evaporation performance can reach 3.59 kg / m³. 2 / Even in the control group without HPNE: cellulose / EvOH, the evaporation performance reached 1.7 kg / m³. 2 / h, far exceeding the evaporation rate of seawater itself (0.51 kg / m³). 2 / h. This figure illustrates that aerogels have high light absorption across the entire solar wavelength range, thus possessing a strong ability to capture sunlight and a high potential for water vapor evaporation; 7e represents the mass of water evaporated by the aerogel in NaCl solutions of different concentrations. Figure 7 f represents the evaporation rate graph of the aerogel working in NaCl solutions of different concentrations. It can be seen that the evaporation rate increases with the increase of salt concentration, unlike traditional evaporators which decrease with the increase of salt concentration.

[0056] The above description is merely a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in this embodiment. Therefore, any equivalent or modified versions made without departing from the spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. A method for preparing a melanin-cellulose composite gel, characterized in that, Includes the following steps: S1: Take carboxylated cellulose nanofibers and aminated microfibers and add them to an appropriate amount of water, disperse them evenly to obtain a dispersion; S2: Add amino acid-doped norepinephrine nanoparticles and CaCl2 to the dispersion prepared in S1 above, stir at room temperature, then add 1-5 wt% of the ethylene and vinyl alcohol copolymer EvOH described in S1, stir to fully foam, and obtain gel liquid 1. S3: Take another equal amount of carboxylated cellulose nanofibers and aminated microfibers and add them to an appropriate amount of water, then disperse them evenly with a disperser to obtain a dispersion. S4: Add CaCl2 to the dispersion prepared in S3 above, stir at room temperature, then add 4-8 wt% of the ethylene and vinyl alcohol copolymer EvOH described in S1, stir to fully foam, and obtain gel liquid 2. S5: The gel liquid 1 obtained in S2 and the gel liquid 2 obtained in S4 are frozen at -10 to 0℃ respectively, mixed, and freeze-dried to remove water to obtain aerogel.

2. The method for preparing the melanin-cellulose composite gel according to claim 1, characterized in that, In S1 and S3, the mass ratio of carboxylated cellulose nanofibers to aminated microfibers is 1 to 1.5:

1.

3. The method for preparing the melanin-cellulose composite gel according to claim 2, characterized in that, In S1 and S3, the mass ratio of carboxylated cellulose nanofibers to aminated microfibers is 1 to 1:

1.

4. The method for preparing the melanin-cellulose composite gel according to claim 1, characterized in that, In S1 and S3, the mass ratio of the sum of the masses of carboxylated cellulose nanofibers and ammoniated microfibers to water is 400–600:

1.

5. The method for preparing the melanin-cellulose composite gel according to claim 4, characterized in that, In S1 and S3, the sum of the masses of carboxylated cellulose nanofibers and ammoniated microfibers is in a mass ratio of 500:1 to water.

6. The method for preparing the melanin-cellulose composite gel according to claim 1, characterized in that, In S1 and S3, the preparation method of the ammoniated microfiber includes the following steps: First, weigh an appropriate amount of bleached hardwood pulp and completely disperse it in 4 to 6 times its mass of water. Then, add NaOH and 2,3-epoxypropyltrimethylammonium chloride sequentially, wherein the mass ratio of bleached hardwood pulp:NaOH:2,3-epoxypropyltrimethylammonium chloride is 1:3:1-2. React at 55-70℃ for 10-16 hours. After the reaction is completed, neutralize with acetic acid to neutral, filter, wash with water 1-3 times, and dry to obtain the product.

7. The method for preparing the melanin-cellulose composite gel according to claim 1, characterized in that, In S2, the sum of the masses of carboxylated cellulose nanofibers and ammoniated microfibers is 18–24:1 with the mass ratio of amino acid-doped norepinephrine nanoparticles.

8. The method for preparing the melanin-cellulose composite gel according to claim 7, characterized in that, In S2, the sum of the masses of carboxylated cellulose nanofibers and ammoniated microfibers is 20:1 with the mass ratio of amino acid-doped norepinephrine nanoparticles.

9. The method for preparing the melanin-cellulose composite gel according to claim 1, characterized in that, In S2 and S4, the sum of the masses of carboxylated cellulose nanofibers and ammoniated microfibers is in a mass ratio of 1 to 3:1 to CaCl2.

10. The method for preparing the melanin-cellulose composite gel according to claim 9, characterized in that, In S2 and S4, the sum of the masses of carboxylated cellulose nanofibers and ammoniated microfibers is in a mass ratio of 2:1 to CaCl2.

11. The method for preparing the melanin-cellulose composite gel according to claim 1, characterized in that, In S2 and S4, the stirring speed is 1000-2000 rpm and the stirring time is 15-30 min.

12. The method for preparing the melanin-cellulose composite gel according to claim 1, characterized in that, In S2, the preparation method of the norepinephrine nanoparticles includes the following steps: S21: Add norepinephrine to an appropriate amount of water and stir evenly at room temperature to obtain a norepinephrine aqueous solution. S22: Add amino acids to an appropriate amount of water and stir evenly at room temperature to obtain an amino acid aqueous solution. S23: Norepinephrine and amino acids are mixed in a mass ratio of 3 to 5:

1. The two solutions prepared in S21 and S22 are mixed, heated to 40 to 60°C, and stirred for 20 to 30 hours. After the reaction is completed, centrifugation is performed to obtain amino acid-doped norepinephrine nanoparticles.

13. The method for preparing the melanin-cellulose composite gel according to claim 12, characterized in that, In S21, the amount of water added is 0.8 to 1.2 times the amount of norepinephrine.

14. The method for preparing the melanin-cellulose composite gel according to claim 12, characterized in that, In S22, the amount of water added is 0.8 to 1.2 times the amount of norepinephrine.

15. The method for preparing the melanin-cellulose composite gel according to claim 13 or 14, characterized in that, In S22, the amino acid is selected from any one or more of histidine, arginine, and lysine.

16. The method for preparing the melanin-cellulose composite gel according to claim 12, characterized in that, In S23, the norepinephrine to amino acid mass ratio is 4:1.

Images