Preparation method of water-based polyurethane-humic acid cross-linked biomass porous material and application thereof in methylene blue adsorption

Abstract

The application provides a preparation method of a water-based polyurethane-humic acid cross-linked biomass porous material, which comprises the following steps: dissolving modified humic acid in a water-based polyurethane emulsion, adjusting the pH to 7.5-8.5, adding a cross-linking agent ethylenediamine, stirring until gelation, stopping stirring, continuing to mature for 55-65 minutes, then immersing the obtained gel in anhydrous ethanol until no impurities are precipitated, immersing in deionized water to remove the anhydrous ethanol, and then performing freeze-drying to obtain the water-based polyurethane-humic acid cross-linked biomass porous material. The water-based polyurethane-humic acid cross-linked biomass porous material is prepared by taking the non-toxic and environment-friendly water-based polyurethane as a base material and the biomass material humic acid as a functional material, and is applied to the adsorption of a methylene blue solution, and the removal rate of the methylene blue is 82.62-92.82%.

Description

Technical Field

[0001] This invention relates to the preparation of a waterborne polyurethane-humic acid crosslinked biomass porous material and its adsorption of methylene blue, belonging to the field of adsorption separation. Background Technology

[0002] Water is one of the most important material resources for human survival and development. However, with the rapid development of the synthetic dye and textile industries, large amounts of industrial wastewater containing dyes are constantly being discharged into the environment. These dye molecules, characterized by complex structures, high color intensity, high toxicity, and recalcitrant degradation, are causing increasingly serious pollution and harm to ecosystems and human health. Therefore, how to better treat dye wastewater is an urgent problem to be solved.

[0003] In recent years, aerogels, nanoscale porous solid materials formed by replacing the liquid phase in a gel with gas through a specific drying method, have shown promising applications in wastewater treatment due to their high specific surface area, high porosity, and excellent chemical stability, making them an important research topic. Therefore, developing an environmentally friendly and high-performance porous adsorbent to mitigate the harm of dye wastewater to the ecological environment and human health has become a crucial research area in water treatment.

[0004] Waterborne polyurethane has become a research hotspot in recent years due to its advantages such as environmental friendliness, low cost, and non-toxicity. Waterborne polyurethane-based porous materials not only contain numerous functional groups found in waterborne polyurethane, which can interact with adsorbates including dye molecules to remove adsorbate molecules from water, but their porous structure and high specific surface area also expose abundant adsorption sites, making it easy for ions and molecules to enter the material interior, thereby greatly improving removal efficiency.

[0005] However, the adsorption capacity of waterborne polyurethane-based porous materials is relatively low, leaving considerable room for improvement. Therefore, modifying waterborne polyurethane using its functional groups to further enhance the water pollution treatment performance of waterborne polyurethane-based porous adsorbents is of significant research importance.

[0006] Humic acid is a macromolecular organic compound widely found in nature. Its structure contains oxygen-containing active functional groups such as carboxyl, carbonyl, and hydroxyl groups, giving it properties such as hydrophilicity, acidity, complexing ability, adsorption, and dispersibility. It has significant application prospects in environmental protection materials, adsorbent materials, and functional materials. However, the high water solubility of humic acid itself limits its practical applications. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing waterborne polyurethane-humic acid crosslinked biomass porous materials and their application in methylene blue adsorption, achieving the following objectives:

[0008] The prepared waterborne polyurethane-humic acid crosslinked biomass porous material exhibits excellent adsorption performance and reusability for methylene blue cationic dye, and can be used for dye wastewater treatment, thereby reducing costs.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] A method for preparing a waterborne polyurethane-humic acid crosslinked biomass porous material, wherein the preparation method comprises dissolving modified humic acid in a waterborne polyurethane emulsion, adjusting the pH to 7.5-8.5, adding the crosslinking agent ethylenediamine and stirring until gel is formed, then stopping the stirring and continuing to mature for 55-65 minutes, then immersing the resulting gel in anhydrous ethanol until no more impurities precipitate, then soaking in deionized water to remove the anhydrous ethanol, and finally freeze-drying to obtain the waterborne polyurethane-humic acid crosslinked biomass porous material.

[0011] The freeze-drying time is 47-49 hours.

[0012] The mass ratio of the modified humic acid to the aqueous polyurethane emulsion is 1:16-32; the mass ratio of the modified humic acid to ethylenediamine is 5-8:1.

[0013] The modified humic acid is prepared by adding humic acid and triethylamine to dichloromethane in an ice-water bath, then adding methacrylamide chloride, stirring for 23-25 ​​hours, and then washing and drying to obtain the modified humic acid.

[0014] The stirring speed is 380-420 r / min.

[0015] The mass ratio of humic acid to triethylamine is 1.5-1.7:1; the mass-to-volume ratio of humic acid to dichloromethane is 1g:4.5-5.5mL; the mass ratio of humic acid to methacryloyl chloride is 1.5-1.7:1; and the methacryloyl chloride is added over a period of 18-22 minutes.

[0016] The preparation method of the aqueous polyurethane emulsion includes polymerization reaction, chain extension reaction, end-capping reaction, neutralization and salt formation, and shear dispersion.

[0017] The polymerization reaction is carried out by mixing isophorone diisocyanate and polytetramethylene ether glycol, adding bismuth ethylhexanoate catalyst, and reacting at a constant temperature of 87-89℃ for 1.4-1.6 h to obtain a prepolymer; the mass ratio of isophorone diisocyanate to polytetramethylene ether glycol is 1:2.9-3.1; the mass-volume ratio of isophorone diisocyanate to bismuth ethylhexanoate is 20-22 g:1 mL.

[0018] The chain extension reaction is carried out by adding 2,2-dimethylolpropionic acid and bismuth ethylhexanoate catalyst to the prepolymer and performing the chain extension reaction at 87-89℃ for 1.8-2.2h; the mass ratio of isophorone diisocyanate to 2,2-dimethylolpropionic acid is 3.5-4:1; the mass-volume ratio of 2,2-dimethylolpropionic acid to the bismuth ethylhexanoate catalyst added in the chain extension reaction is 2.5-3g:1mL.

[0019] The method for the end-capping reaction is as follows: the product of the chain extension reaction is cooled to 58-62℃, hydroxyethyl methacrylate is added as an end-capping agent, and then bismuth hexanoate catalyst is added. The reaction is carried out at 58-62℃ for 2.8-3.2 h. The mass ratio of isophorone diisocyanate to hydroxyethyl methacrylate is 3.4-3.8:1. The mass-to-volume ratio of hydroxyethyl methacrylate to bismuth hexanoate catalyst added in the end-capping reaction is 2.7-3 g:1 mL.

[0020] The method for neutralization and salt formation involves cooling the temperature to 49-51°C, adding triethylamine, and reacting for 18-22 minutes; the mass ratio of isophorone diisocyanate to triethylamine is 4.8-5.2:1.

[0021] The shear dispersion method involves adding the neutralized salt-forming reaction solution to deionized water and shear dispersing it for 29-31 minutes to obtain an aqueous polyurethane emulsion; the mass ratio of isophorone diisocyanate to deionized water is 1:10.5-11.

[0022] The application of the aforementioned waterborne polyurethane-humic acid crosslinked biomass porous material in methylene blue adsorption.

[0023] The technical route of this invention is as follows: First, a prepolymer is synthesized using polytetrahydrofuran ether as the polyol component and isophorone diisocyanate as the isocyanate component. Then, an aqueous polyurethane emulsion is synthesized using 2,2-dimethylolpropionic acid as a chain extender, hydroxyethyl methacrylate as a capping agent, and triethylamine as a neutralizing agent. Next, humic acid is modified with methacryloyl chloride to obtain HA2. Finally, the aqueous polyurethane and HA2 are crosslinked with ethylenediamine to form a porous adsorbent material.

[0024] Compared with the prior art, the present invention achieves the following beneficial effects:

[0025] (1) This invention uses non-toxic and environmentally friendly waterborne polyurethane as the matrix material and biomass material humic acid as the functional material to prepare waterborne polyurethane-humic acid crosslinked biomass porous material, which is applied to the adsorption of methylene blue solution and has a removal rate of 82.62-92.82% for methylene blue.

[0026] (2) The present invention extracts humic acid from weathered coal to modify waterborne polyurethane, which reduces the modification cost of polyurethane and is beneficial to the mass production of industrial products in the future.

[0027] (3) The waterborne polyurethane-humic acid crosslinked biomass porous material prepared by the present invention has good regeneration performance. After the third cycle of adsorption and desorption, the removal rate of methylene blue is 72-78.26%.

[0028] (4) The waterborne polyurethane-humic acid crosslinked biomass porous material prepared by the present invention has excellent three-dimensional porous structure, green sustainability, adsorption and regeneration performance and significant environmental benefits. It is a green, environmentally friendly and low-cost adsorption material, which is of great significance for the purification of dye wastewater. Attached Figure Description

[0029] Figure 1 Synthesis process of WPU

[0030] Figure 2 The particle size distribution diagram of the WPU prepared in Example 1;

[0031] Figure 3 Infrared spectra of HEMA used in Example 1, WPU prepared in Example 1, and WPU-HA2-3 prepared in Example 6;

[0032] Figure 4 X-ray photoelectron spectra of HA prepared in Example 2 and HA2 prepared in Example 3;

[0033] Figure 5 BET specific surface area curves of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 prepared for this invention;

[0034] Figure 6 Thermogravimetric analysis (TGA) curves of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 prepared for this invention;

[0035] Figure 7 Scanning electron microscope (SEM) images of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 prepared for this invention;

[0036] in Figure 7 (a) is a scanning electron microscope (SEM) image of WPU-HA2-1; Figure 7 (b) is a scanning electron microscope (SEM) image of WPU-HA2-2; Figure 7 (c) is a scanning electron microscope (SEM) image of WPU-HA2-3;

[0037] Figure 8The adsorption performance of WPU-HA2-3 in dye solutions with different pH values ​​is shown in the graph.

[0038] Figure 9 The adsorption performance of WPU-HA2-3 in dye solutions at different temperatures is shown in the graph.

[0039] Figure 10 The graph shows the dye adsorption performance of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 at different adsorption times.

[0040] Figure 11 The adsorption performance of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 in dye solutions with different initial concentrations is shown in the figure.

[0041] Figure 12 Bar chart showing the adsorption efficiency of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3;

[0042] Figure 13 The curves of the pseudo-first-order kinetic model for WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 are shown.

[0043] Figure 14 The graphs are for the pseudo-second-order kinetic models of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3.

[0044] Figure 15 The graphs show the intraparticle diffusion model curves for WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3.

[0045] Figure 16 The adsorption isotherms are for WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the above technical route and accompanying drawings. This description is only intended to illustrate the invention and is not intended to limit the scope of protection of the invention. Any non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0047] Example 1: Preparation of WPU

[0048] (1) Add 8.34 g of isophorone diisocyanate (IPDI) and 25 g of polytetramethylene ether glycol (PTMEG) to a three-necked flask, add 0.4 mL of bismuth ethylhexanoate (BiR3) catalyst, and react at 88 °C for 1.5 h.

[0049] (2) Keep the reaction temperature (88 °C) unchanged and add 2.19 g of 2,2-dihydroxymethylpropionic acid (DMPA) and 0.8 mL of BiR3 catalyst to carry out chain extension reaction for 2 h.

[0050] (3) Cool down to 60 °C. At 60 °C, add 2.28 g of hydroxyethyl methacrylate (HEMA) as a capping agent to the reaction system, and then add 0.8 mL of BiR3 catalyst. The reaction time is 3 h.

[0051] (4) Cool down to 50 °C, add 1.65 g of triethylamine (TEA) to neutralize and form a salt, and the reaction time is 20 min.

[0052] (5) The reaction solution was dispersed into 90 g of deionized water under the action of a shear press and dispersed for 30 minutes to obtain an aqueous polyurethane emulsion (WPU). The particle size distribution is shown in the attached figure. Figure 2 As shown, the average Z-diameter of the waterborne polyurethane emulsion is 66.00 nm, and the polydispersity index is 0.365.

[0053] Example 2: Extraction of HA

[0054] (1) Prepare 0.1 mol·L⁻¹ NaOH solid solution from 25 g NaOH solid. –1 NaOH solution.

[0055] (2) Dissolve 100 g of weathered coal in NaOH solution, centrifuge to remove insoluble solid precipitate, and retain the supernatant.

[0056] (3) Using 0.1 mol·L –1 Acidify the supernatant with HCl solution to pH=3, let it stand, then centrifuge at 5000 rpm for 20 min, discard the supernatant and keep the lower precipitate.

[0057] (4) Wash the lower precipitate repeatedly with deionized water by centrifugation until Cl is no longer present. – until.

[0058] (5) Place the precipitate in a petri dish and dry it at 30 °C. Then grind it finely to obtain the final humic acid product (purity > 90%, particle size 1-6 mm), abbreviated as HA.

[0059] Example 3: Preparation of HA2

[0060] (1) In an ice-water bath, add 3 g HA and 1.82 g triethylamine (TEA) to 15 mL of dichloromethane.

[0061] (2) Add 1.88 g of methacryloyl chloride (MAC) to the reaction system within 20 min using a syringe, and then stir continuously at 400 r / min at room temperature for 24 h.

[0062] (3) The precipitate was washed with dichloromethane to remove unreacted MAC and impurities, and dried to obtain the product modified humic acid (abbreviated as HA2).

[0063] Example 4: Preparation of WPU-HA2-1

[0064] (1) Dissolve 0.16 g HA2 in 5 g WPU at room temperature, and use 0.1 mol·L⁻¹ –1 The pH of the system was adjusted to 8 using NaOH solution.

[0065] (2) At room temperature, add 0.03 g of crosslinking agent EDA (ethylenediamine) and stir until the system gels, then stop stirring and continue to mature for 60 min.

[0066] (3) Immerse the obtained gel in anhydrous ethanol until no more impurities precipitate out, and then soak it in deionized water until no anhydrous ethanol remains.

[0067] (4) Freeze-dry for 48 h to obtain WPU-HA2-1.

[0068] Example 5: Preparation of WPU-HA2-2

[0069] 1) Dissolve 0.24 g HA2 in 5 g WPU at room temperature, and use 0.1 mol·L⁻¹ –1 The pH of the system was adjusted to 8 using NaOH solution.

[0070] (2) At room temperature, add 0.03 g of crosslinking agent EDA and stir until the system gels, then stop stirring and continue to mature for 60 min.

[0071] (3) Immerse the obtained gel in anhydrous ethanol until no more impurities precipitate out, and then soak it in deionized water until no anhydrous ethanol remains.

[0072] (4) Freeze-dry for 48 h to obtain WPU-HA2-2.

[0073] Example 6: Preparation of WPU-HA2-3

[0074] (1) Dissolve 0.31 g HA2 in 5 g WPU at room temperature, and use 0.1 mol·L⁻¹ –1 The pH of the system was adjusted to 8 using NaOH solution.

[0075] (2) At room temperature, add 0.04 g of crosslinking agent EDA and stir until the system gels, then stop stirring and continue to mature for 60 min.

[0076] (3) Immerse the obtained gel in anhydrous ethanol until no more impurities precipitate out, and then soak it in deionized water until no anhydrous ethanol remains.

[0077] (4) Freeze-dry for 48 h to obtain WPU-HA2-3.

[0078] Experimental Example 1: Infrared Spectroscopy Measurement

[0079] The infrared spectra of HEMA used in Example 1, WPU prepared in Example 1, and WPU-HA2-3 prepared in Example 6 were measured, as shown in the appendix. Figure 3 ;

[0080] Appendix Figure 3 As can be seen, the FT-IR spectrum of WPU is at 3335 cm⁻¹. -1 and 1541 cm -1 The peak at 1708 cm⁻¹ shows characteristic peaks related to the tensile and deformational vibrations of NH₄⁺ in -NHCOO⁻. -1 The characteristic peak observed at [location] can be attributed to the stretching vibration of the C=O bond during the reaction of -NHCOO-, HEMA, and -COOH with TEA. Furthermore, -NCO [value] at 2270 cm⁻¹ -1 The complete disappearance of the characteristic peak at the location indicates that WPU was successfully synthesized.

[0081] The spectrum of WPU-HA2-3 is at 1634 cm⁻¹ -1 No characteristic absorption peaks related to the C=C junction of HEMA were observed, indicating that HEMA has been successfully incorporated into the adsorbent. Simultaneously, only minor differences were observed between the characteristic peaks of the FT-IR spectra of WPU-HA2-3 and WPU. This can be explained by the fact that the functional groups of HA are essentially the same as those of the reactants used in the synthesis of WPU. Therefore, the introduction of HA had minimal impact on the FT-IR spectrum of the original WPU, indirectly confirming that HA has been successfully grafted onto the WPU molecular chain.

[0082] Experimental Example 2: Determination of X-ray photoelectron spectroscopy

[0083] X-ray photoelectron spectroscopy (XPS) spectra of HA prepared in Example 2 and HA2 prepared in Example 3 were measured, and the results are shown in the appendix. Figure 4 ;

[0084] From the appendix Figure 4 It can be seen that the O element content of HA2 increased significantly after modification, indicating that methacryloyl chloride has been successfully grafted onto HA.

[0085] Experimental Example 3: Determination of BET Specific Surface Area

[0086] The specific surface area of ​​WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 prepared in Examples 4-6 was measured, and the results are shown in the appendix. Figure 5 ;

[0087] The specific surface areas of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 are 0.8319 m², respectively. 2 ·g –1 1.6188 m 2 ·g –1 3.0352 m 2 ·g –1 .

[0088] Experimental Example 4: Thermogravimetric Analysis (TGA) Curve Determination

[0089] Thermogravimetric analysis (TGA) curves of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 prepared in Examples 4-6 were determined, and the results are shown in the appendix. Figure 6 ;

[0090] From the appendix Figure 6 It can be seen that the thermogravimetric analysis (TGA) curves of WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 have a high degree of overlap. The thermal decomposition process can be divided into five stages: the first stage of weight loss is from about 30 ºC to about 150 ºC, which mainly corresponds to the evaporation of water in the sample; the second stage is from about 150 ºC to about 200 ºC, which may be attributed to the contribution of carboxyl groups in HA; the third stage is from 200 ºC to about 360 ºC, when the sample reaches the third equilibrium, which may be due to the cracking of the hard segment of WPU; the fourth stage is from about 360 °C to about 440 °C, where the weight loss may be due to the thermal decomposition of the soft segment of WPU; the fifth stage is from 440 °C to 600 °C, where as the temperature continues to rise, the various aromatic nuclei of HA begin to thermally decompose until the mass remains constant.

[0091] Experimental Example 5: Determination of Scanning Electron Microscopy (SEM) Images

[0092] The WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 prepared in Examples 4-6 were analyzed by scanning electron microscopy (SEM). The results are shown in the appendix. Figure 7 ;

[0093] From the appendix Figure 7It can be seen that the three adsorbent materials have good porous structures. The pore sizes of WPU-HA2-1, WPU-HA2-2 and WPU-HA2-3 are 41 nm, 64 nm and 4 nm, respectively, which is beneficial to the binding of methylene blue to the adsorption sites.

[0094] Experimental Example 6: Effect of Solution pH on the Adsorption Performance of WPU-HA2-3

[0095] To test the adsorption capacity of WPU-HA2-y, methylene blue was used as a representative pollutant in the adsorption experiment.

[0096] 30 mg of adsorbent WPU-HA2-3 and 40 ml of methylene blue solution were weighed into a 100 ml beaker for adsorption experiments. The initial concentration of the methylene blue solution was 10 mg·L⁻¹. –1 The methylene blue solution was adjusted to different pH values, the adsorption time was 12 hours, and the adsorption temperature was room temperature. The adsorption results are shown in the appendix. Figure 8 ;

[0097] As attached Figure 8 As shown, when the pH of the methylene blue solution is 7, the adsorption capacity of WPU-HA2-3 for MB is 9.03 mg·g. –1 The removal rate was 85.94%, which showed the best adsorption effect. Therefore, the pH of the methylene blue solution was chosen to be 7 for subsequent experiments.

[0098] Experimental Example 7: Effect of Adsorption Temperature on the Adsorption Performance of WPU-HA2-3

[0099] An adsorption experiment was conducted by weighing 30 mg of adsorbent WPU-HA2-3 and 40 mL of methylene blue solution in a 100 mL beaker. The initial concentration of the methylene blue solution was 10 mg·L⁻¹. –1 The adsorption time was 12 h, the solution pH was 7, and adsorption experiments were conducted at different adsorption temperatures. The results are shown in the appendix. Figure 9 .

[0100] From the appendix Figure 9 It can be seen that at an adsorption temperature of 50 ℃, the adsorption capacity of WPU-HA2-3 for methylene blue is 12.05 mg·g⁻¹. –1 The adsorption capacity and removal rate (92.82%) reached their highest values. As the temperature continued to rise, the adsorption capacity and removal rate showed a significant downward trend. Therefore, the optimal adsorption temperature for methylene blue by the adsorbent was 50 °C.

[0101] Experimental Example 8: Effect of Adsorption Time on the Adsorption Performance of WPU-HA2-3

[0102] An adsorption experiment was conducted by weighing 30 mg of adsorbent WPU-HA2-3 and 40 mL of methylene blue solution in a 100 mL beaker. The initial concentration of the methylene blue solution was 10 mg·L⁻¹. –1 The effect of adsorption time on adsorption performance was studied under the conditions of solution pH 7 and adsorption temperature 50 ℃. The results are shown in the appendix. Figure 10 .

[0103] Experimental Example 9: Effect of the initial concentration of methylene blue solution on adsorption performance

[0104] Adsorption experiments were conducted by weighing 30 mg of adsorbent WPU-HA2-3 and 40 mL of methylene blue solution in a 100 mL beaker. Different initial concentrations of methylene blue solution were set, the solution pH was 7, the adsorption temperature was 50 ℃, and the adsorption time was 12 h. The effect of the initial concentration of methylene blue solution on the adsorption performance was investigated. The results are shown in the appendix. Figure 11 .

[0105] from Figure 10 and Figure 11 It can be seen that the adsorption capacity of the adsorbent for methylene blue increases with the increase of adsorption time and initial concentration, and WPU-HA2-3 shows excellent adsorption effect throughout the adsorption process.

[0106] Experimental Example 10: Adsorption Performance Test of Three Adsorbent Materials

[0107] 30 mg of adsorbent to 40 mL of initial concentration of 10 mg·L –1 Adsorption was performed using methylene blue solution for 12 hours at a pH of 7 and at a temperature of 50 °C. Figure 12 As shown, the removal rates of MB by WPU-HA2-1, WPU-HA2-2, and WPU-HA2-3 were 82.62%, 83.99%, and 92.82%, respectively. Therefore, it can be seen that WPU-HA2-3 had the best removal effect on methylene blue.

[0108] Experimental Example 11 Adsorption Kinetics Determination

[0109] At 50 ℃, 40 ml of solution at pH=7 has a concentration of 10 mg·L⁻¹. –1 The adsorption kinetics of the adsorbent were tested in a methylene blue solution, and the results are as follows: Figure 13-15 And as shown in Table 1, the R of the pseudo-second-order dynamic model 2 The higher and more closely aligned adsorption rate of methylene blue indicates that the chemical reaction is the main factor controlling the adsorption rate. Furthermore, the adsorption rate constant k is always less than 1, which suggests that the adsorption process is rapid and easy to carry out.

[0110] Table 1 Characteristic parameters of the adsorption kinetics model

[0111] .

[0112] Experimental Example 12: Determination of Adsorption Isotherms

[0113] The adsorption isotherm of the adsorbent was analyzed after adsorption in 40 ml of methylene blue solution at 50 ℃ for 12 h. The results are as follows: Figure 16 As shown in Table 2, the experimental data best fit the Langmuir model, with R0... 2 The highest value indicates that the adsorption process of methylene blue is mainly monolayer chemisorption. However, R 2 The differences between the two models were not significant, indicating that multiple processes control the adsorption of methylene blue, with electrostatic attraction and ion exchange also having some influence on the adsorption process; furthermore... k L and 1 / n f The fact that both parameters are always less than 1 indicates that the adsorption process of methylene blue by the adsorbent is easy to carry out.

[0114] Table 2. Characteristic parameters of the adsorption isotherm model

[0115] .

[0116] Test Example 13: Determination of Adsorbent Regeneration Performance

[0117] To investigate the regeneration performance of the adsorbent, 30 mg of adsorbent WPU-HA2-3 and 40 mL of methylene blue solution were weighed into a 100 mL beaker for adsorption experiments. The initial concentration of the methylene blue solution was 10 mg·L⁻¹. –1 The adsorption time was 12 h, the solution pH was 7, the adsorption temperature was 50 ℃, and after adsorption was completed, 50 ml of 0.5 mg·L⁻¹ solution was used. –1 The adsorbent was repeatedly desorbed using an eluent with a 1:1 volume ratio of HCl and anhydrous ethanol until no more MB precipitated. The desorbed adsorbent was then freeze-dried, and the samples were collected for repeated adsorption and desorption steps. Testing revealed that the dye removal rate decreased gradually with each cycle, from an initial 92.82%, but still reached 78.26% after the third cycle, indicating that the adsorbent has a certain degree of reusability. Comparison of the above data shows that WPU-HA2-3 exhibits the best overall performance in this invention, representing an environmentally friendly biomass adsorbent material with a three-dimensional porous structure, green sustainability, and excellent performance.

Claims

1. A method for preparing an aqueous polyurethane-humic acid crosslinked biomass porous material for adsorbing methylene blue, characterized in that: The preparation method involves dissolving modified humic acid in an aqueous polyurethane emulsion, adjusting the pH to 7.5-8.5, adding the crosslinking agent ethylenediamine and stirring until gel is formed, then stopping the stirring and continuing to mature for 55-65 minutes. The resulting gel is then immersed in anhydrous ethanol until no more impurities precipitate out, and then soaked in deionized water to remove the anhydrous ethanol. Finally, the gel is freeze-dried to obtain an aqueous polyurethane-humic acid crosslinked biomass porous material. The modified humic acid is prepared by adding humic acid and triethylamine to dichloromethane in an ice-water bath, then adding methacrylamide chloride, stirring for 23-25 ​​hours, and then washing and drying to obtain the modified humic acid. The mass ratio of humic acid to triethylamine is 1.5-1.7:1; the mass-to-volume ratio of humic acid to dichloromethane is 1g:4.5-5.5mL; the mass ratio of humic acid to methacryloyl chloride is 1.5-1.7:1; and the methacryloyl chloride is added over a period of 18-22 minutes.

2. The method of claim 1, wherein: The mass ratio of the modified humic acid to the aqueous polyurethane emulsion is 1:16-32; the mass ratio of the modified humic acid to ethylenediamine is 5-8:

1.

3. The method of claim 1, wherein: The preparation method of the aqueous polyurethane emulsion includes polymerization reaction, chain extension reaction, end-capping reaction, neutralization and salt formation, and shear dispersion.

4. The method of claim 3, wherein: The polymerization reaction is carried out by mixing isophorone diisocyanate and polytetramethylene ether glycol, adding bismuth ethylhexanoate catalyst, and reacting at a constant temperature of 87-89℃ for 1.4-1.6h to obtain a prepolymer; the mass ratio of isophorone diisocyanate to polytetramethylene ether glycol is 1:2.9-3.1; the mass-volume ratio of isophorone diisocyanate to bismuth ethylhexanoate is 20-22g:1mL.

5. The method of claim 4, wherein: The chain extension reaction is carried out by adding 2,2-dimethylolpropionic acid and bismuth ethylhexanoate catalyst to the prepolymer and performing the chain extension reaction at 87-89℃ for 1.8-2.2h; the mass ratio of isophorone diisocyanate to 2,2-dimethylolpropionic acid is 3.5-4:1; the mass-volume ratio of 2,2-dimethylolpropionic acid to the bismuth ethylhexanoate catalyst added in the chain extension reaction is 2.5-3g:1mL.

6. The method of claim 5, wherein: The method for the end-capping reaction is as follows: the product of the chain extension reaction is cooled to 58-62℃, hydroxyethyl methacrylate is added as an end-capping agent, and then bismuth hexanoate catalyst is added. The reaction is carried out at 58-62℃ for 2.8-3.2 h. The mass ratio of isophorone diisocyanate to hydroxyethyl methacrylate is 3.4-3.8:

1. The mass-to-volume ratio of hydroxyethyl methacrylate to bismuth hexanoate catalyst added in the end-capping reaction is 2.7-3 g:1 mL.

7. The preparation method according to claim 5, characterized in that: The neutralization and salt formation method involves cooling the temperature to 49-51℃, adding triethylamine, and reacting for 18-22 minutes; the mass ratio of isophorone diisocyanate to triethylamine is 4.8-5.2:1; the shear dispersion method involves adding the neutralized and salt-formed reaction solution to deionized water and shear dispersing for 29-31 minutes to obtain an aqueous polyurethane emulsion; the mass ratio of isophorone diisocyanate to deionized water is 1:10.5-11.

8. The application of the aqueous polyurethane-humic acid crosslinked biomass porous material prepared by the preparation method of claim 1 in the adsorption of methylene blue.

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