Modified melamine foam with soybean protein isolate and preparation method and application thereof

Abstract

This invention discloses a soybean protein isolate modified melamine foam, its preparation method, and its application. The soybean protein isolate modified melamine foam is prepared through the following steps: S1: At room temperature, melamine foam is reacted in an alkaline solution of dopamine hydrochloride to obtain a preliminary modified melamine foam; S2: The preliminary modified melamine foam is placed in an organic solvent containing epichlorohydrin for activation to obtain activated melamine foam; S3: The activated melamine foam is placed in an alkaline aqueous solution containing soybean protein isolate for grafting reaction. After the reaction is completed, it is washed and dried to obtain soybean protein isolate modified melamine foam. This modified melamine foam utilizes the coordination and chelation between abundant active functional groups on its surface and metal ions to achieve efficient adsorption of heavy metal ions. It can also achieve rapid desorption and regeneration through simple extrusion, showing broad application prospects in the field of heavy metal wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of polymer modified materials technology, specifically to soybean protein isolate modified melamine foam, its preparation method and application. Background Technology

[0002] Currently, methods for removing heavy metals from water bodies mainly include chemical precipitation, ion exchange, adsorption, membrane filtration, and biological methods. Among these, adsorption is considered one of the most promising technologies due to its simple operation, low cost, and high efficiency. Adsorption utilizes adsorbents to adsorb one or more pollutants in wastewater, thereby recovering or removing these pollutants and purifying the wastewater. Traditional adsorbents, such as activated carbon, suffer from high cost, poor adsorption capacity, and weak recirculation capacity, which limits their practical application.

[0003] Melamine foam is a three-dimensional foam material composed of melamine, formaldehyde resin, additives, etc. It has a high specific surface area, rich pore structure, and good flexibility and plasticity, and is considered an ideal carrier for constructing composite adsorption materials. However, the surface of melamine foam skeleton is smooth and slender, with almost no adsorption sites and lacking functional groups for adsorbing heavy metal ions.

[0004] Soy protein isolate is a widely available, inexpensive, and renewable natural polymer material. Its molecular chain is rich in active functional groups such as amino, carboxyl, and hydroxyl groups, which have a strong coordination and chelation ability for heavy metal ions. However, there is currently a lack of technology to combine soy protein isolate with melamine foam. Summary of the Invention

[0005] The purpose of this invention is to provide soy protein isolate modified melamine foam, its preparation method and application. Using melamine foam as a skeleton support material, soy protein isolate is loaded onto the melamine foam skeleton to functionalize and modify the melamine foam, thereby solving the technical problem that melamine foam cannot adsorb heavy metal ions in the prior art.

[0006] According to a first aspect of the present invention, a method for preparing soy protein isolate modified melamine foam is provided, comprising the following steps: S1: At room temperature, melamine foam is placed in an alkaline solution of dopamine hydrochloride to react, so that dopamine undergoes an oxidative self-polymerization reaction on the surface of melamine foam and forms a polydopamine coating with strong adhesion and abundant active groups (such as amino and phenolic hydroxyl groups), thus obtaining the initial modified melamine foam. S2: The pre-modified melamine foam is placed in an organic solvent containing epichlorohydrin to carry out an activation reaction, thereby obtaining activated melamine foam. The purpose of activation is to introduce epoxy active groups onto the pre-modified melamine foam. S3: The activated melamine foam is placed in an alkaline aqueous solution containing soy protein isolate for a grafting reaction. Through the ring-opening reaction of epoxy groups with amino groups in soy protein isolate molecules, soy protein isolate is grafted onto the surface of the melamine foam backbone. After the reaction is completed, the foam is washed and dried to obtain soy protein isolate modified melamine foam.

[0007] In some embodiments, the alkaline solution of dopamine hydrochloride in step S1 is prepared by dissolving dopamine hydrochloride and tris(hydroxymethyl)aminomethane hydrochloride in deionized water and adjusting the pH value to 8.0-9.0.

[0008] In some embodiments, the concentration of dopamine hydrochloride in step S1 is 5–20 g / L.

[0009] In some embodiments, the reaction time in step S1 is 8 to 16 hours.

[0010] In some embodiments, the organic solvent in step S2 is N,N-dimethylformamide.

[0011] In some embodiments, in step S2, the volume fraction of epichlorohydrin in the organic solvent containing epichlorohydrin is 20% to 40%, that is, the volume ratio of epichlorohydrin to organic solvent is 20:80 to 40:60.

[0012] In some embodiments, the activation reaction in step S2 is carried out at a temperature of 25–45°C for 4–8 hours.

[0013] In some embodiments, after the activation reaction in step S2 is completed, the melamine foam is rinsed with acetone and deionized water in sequence to remove unreacted reagents, and then dried to obtain activated melamine foam.

[0014] In some embodiments, the alkaline aqueous solution containing soy protein isolate in step S3 comprises the following components by mass fraction: 2%–6% soy protein isolate, 0.5%–2% sodium hydroxide, and the balance being water.

[0015] In some embodiments, the pH value of the alkaline aqueous solution containing soy protein isolate in step S3 is 12 to 14.

[0016] In some embodiments, the temperature of the grafting reaction in step S3 is 50–70°C, and the reaction time is 2–5 h.

[0017] In some embodiments, before reacting the melamine foam in the alkaline solution of dopamine hydrochloride in step S1, the following steps are further included: cutting the melamine foam to the required specifications, immersing it in an aqueous sodium hydroxide solution with stirring and cleaning, removing it, washing it with deionized water until neutral, and drying it. This pretreatment of the melamine foam can remove surface impurities. The stirring time is 1–2 hours, and the drying temperature is 60°C.

[0018] According to a second aspect of the present invention, a soy protein isolate-modified melamine foam is provided, prepared by the above-described preparation method. This soy protein isolate-modified melamine foam has a three-dimensional porous network structure, and the surface of the backbone is uniformly covered with a soy protein isolate functional layer rich in functional groups such as amino, carboxyl, and hydroxyl groups, exhibiting excellent elasticity and compression resilience.

[0019] According to a third aspect of the present invention, the application of soybean protein isolate modified melamine foam in the preparation of adsorbent materials for wastewater containing heavy metal ions is provided.

[0020] In some embodiments, the heavy metal ions are any one or more of Cu(II), Pb(II), Cd(II), Cr(III), Ni(II), Co(II), Mn(II) and Zn(II).

[0021] The beneficial effects of this invention are as follows: (1) This invention successfully covalently fixes soybean protein isolate from biomass resources onto the three-dimensional framework of melamine foam through a three-step modification strategy of "polydopamine coating - epoxy activation - protein grafting". The resulting soybean protein isolate modified melamine foam has the macroscopic porous structure and excellent compression resilience of melamine foam and the rich active functional groups of soybean protein isolate. In the process of adsorbing heavy metal ions, it exhibits the characteristics of fast adsorption rate and high adsorption capacity. (2) The soybean protein isolate modified melamine foam of the present invention has excellent compressibility. After adsorption saturation, it can be rapidly desorbed and regenerated by simple mechanical extrusion and acid soaking, which simplifies the regeneration process and improves the recycling efficiency. After multiple cycles, the material can still maintain a high adsorption capacity and structural integrity, effectively reducing the cost of use and the risk of secondary pollution, and showing good application potential in complex wastewater systems. (4) The preparation method provided by the present invention is simple and mild, with high raw material utilization rate, and is easy to scale up. Moreover, the raw materials used are all low-cost and environmentally friendly materials, which provides a new way for the application of biomass resources in the field of environmental governance. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation process of soybean protein isolate modified melamine foam in an embodiment of the present invention; Figure 2 This is a comparison chart of the adsorption capacity of soybean protein isolate modified melamine foam for different metal ions in the embodiments of the present invention; Figure 3 This is a graph showing the effect of initial metal ion concentration on the adsorption efficiency of soybean protein isolate modified melamine foam in the embodiments of the present invention; Figure 4This is a graph showing the effect of adsorption time on the Cu(II) adsorption performance of soybean protein isolate modified melamine foam in the embodiments of the present invention; Figure 5 This is a graph showing the effect of solution pH on the Cu(II) adsorption performance of soybean protein isolate modified melamine foam in the embodiments of the present invention; Figure 6 This is a graph showing the effect of adsorption temperature on the Cu(II) adsorption performance of soybean protein isolate modified melamine foam in the embodiments of the present invention; Figure 7 This is a graph showing the test results of the recycling performance of soybean protein isolate modified melamine foam in an embodiment of the present invention; Figure 8 The figures shown are stress-strain curves and cyclic compression curves of soybean protein isolate modified melamine foam under different strains in the embodiments of the present invention. Among them, a and c are the stress-strain curves of MF and MF@SPI under different strains, and b and d are the cyclic stress-strain curves of MF and MF@SPI under 40% strain. Figure 9 The Fourier transform infrared absorption spectra of melamine foam and soy protein isolate modified melamine foam in the embodiments of the present invention are shown below. Figure 10 These are scanning electron microscope (SEM) images of melamine foam and soy protein isolate modified melamine foam in the embodiments of the present invention. In the images, ac represents the scanning result of MF, df represents the scanning result of MF@SPI, gi represents the scanning result of MF@SPI after adsorbing Cu(II), and jl shows the EDS elemental distribution after MF@SPI adsorbs Cu(II). Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The soy protein isolate involved in the following examples has a protein content of 90% to 95%, and all raw materials and reagents, unless otherwise specified, are commercially available.

[0024] Although melamine foam is an ideal carrier for constructing composite adsorbent materials, its smooth and delicate skeleton surface means that untreated melamine foam has almost no adsorption capacity. It needs to be chemically modified to form chemical derivatives or graft polymers on the surface of melamine foam materials, which can endow melamine foam with a large number of chelating heavy metal ions (such as amino and carboxyl groups), thus making it have excellent adsorption properties.

[0025] Figure 1This invention demonstrates a preparation process for a soybean protein isolate-modified melamine foam. Specifically, using melamine foam as a three-dimensional framework substrate, dopamine is first self-polymerized onto the surface of the melamine foam to form a polydopamine coating, which is then activated using epichlorohydrin. Finally, soybean protein isolate rich in amino and carboxyl functional groups is covalently grafted onto the foam framework to prepare a modified melamine foam with both a three-dimensional porous structure and good elasticity. This modified melamine foam utilizes the coordination and chelation between its abundant surface active functional groups and metal ions to achieve efficient adsorption of heavy metal ions, and can be rapidly desorbed and regenerated through simple extrusion, showing broad application prospects in the field of heavy metal wastewater treatment.

[0026] Example 1 This embodiment provides a soybean protein isolate modified melamine foam, the preparation method of which includes the following steps: S0 (Melamine Foam Pretreatment): First, cut commercially available melamine foam into sheets of 2×2×0.5cm³. Take 10 sheets and soak them in 300 mL of deionized water containing 0.3g sodium hydroxide, stirring magnetically for 1 hour. After removing the melamine foam, rinse thoroughly with deionized water until the washing solution is neutral, and then dry it in a 60℃ forced-air oven for 12 hours. S1 (Polydopamine Coating): Prepare a mixed aqueous solution containing 10 g / L dopamine hydrochloride and 10 mmol / L tris(hydroxymethyl)aminomethane hydrochloride. Adjust the pH of the solution to 8.5. Then, immerse the S0-treated melamine foam sheet in this solution and stir at room temperature for 12 hours. After the reaction, thoroughly wash the sample with deionized water and dry it at 60°C to obtain the pre-modified melamine foam (MF@PDA). S2 (Epoxy Activation): Measure 70 mL of N,N-dimethylformamide and 30 mL of epichlorohydrin, mix thoroughly, and immerse the MF@PDA obtained in step S1 into this mixed solution. Stir and react at 45°C for 6 hours. After the reaction is complete, remove the sample and rinse it several times alternately with acetone and deionized water to remove residual N,N-dimethylformamide solvent and unreacted epichlorohydrin. Dry the sample for later use to obtain activated melamine foam. S3 (protein grafting): Prepare an aqueous solution containing 4 wt% soy protein isolate and 1 wt% sodium hydroxide, with a pH of 13. Immerse the activated melamine foam obtained in S2 into this solution and react in a 60°C water bath for 3 hours. After the reaction is complete, thoroughly wash the sample with deionized water and dry it at 60°C to obtain soy protein isolate modified melamine foam (MF@SPI).

[0027] It should be noted that: In some other embodiments, the pH value of the alkaline solution of dopamine hydrochloride can be 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, or 9.0.

[0028] In some other embodiments, the volume fraction of epichlorohydrin in the organic solvent containing epichlorohydrin can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, or 40%.

[0029] In some other embodiments, the mass fraction of soy protein isolate in the alkaline aqueous solution can be 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4.2%, 4.5%, 4.7%, 5%, 5.3%, 5.5%, 5.8%, or 6%, and the mass fraction of sodium hydroxide can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9%, or 2%, with the remainder being water.

[0030] In some other embodiments, the pH value of the alkaline aqueous solution containing soy protein isolate can be 12, 12.1, 12.3, 12.5, 12.6, 12.8, 13.2, 13.4, 13.5, 13.7, 13.9, or 14.

[0031] In some other embodiments, the activation reaction in step S2 can be carried out at 25°C, 27°C, 29°C, 30°C, 32°C, 33°C, 35°C, 36°C, 38°C, 40°C, 41°C, 43°C, or 44°C, and the reaction time can be 4h, 4.5h, 5h, 5.5h, 6.5h, 7h, 7.5h, or 8h.

[0032] In some other embodiments, the temperature of the grafting reaction in step S3 can be 50°C, 52°C, 54°C, 55°C, 57°C, 59°C, 61°C, 63°C, 65°C, 66°C, 68°C, or 70°C, and the reaction time can be 2h, 2.5h, 3.5h, 4h, 4.5h, or 5h.

[0033] Comparative Example 1 This comparative example provides an unmodified melamine foam sheet, the preparation method of which includes the following steps: Commercially available melamine foam was cut into sheets of 2×2×0.5 cm³, soaked in 300 mL of deionized water containing 0.3 g sodium hydroxide and stirred for 1 hour. The sheets were then washed with deionized water until neutral and dried at 60°C to obtain unmodified melamine foam (MF).

[0034] Comparative Example 2 This comparative example provides a method for preparing melamine foam sheets treated only with polydopamine coating, comprising the following steps: Following steps S0 and S1 of Example 1, an MF@PDA sample was obtained.

[0035] Approximately 100 mL of a Cu(II) aqueous solution with a concentration of approximately 1000 mg / L was prepared. About 50 mg of the melamine foam sheet sample prepared above and treated only with polydopamine was added to approximately 20 mL of the Cu(II) aqueous solution for adsorption studies. After adsorption at room temperature for approximately 12 hours, the Cu(II) concentration was measured. The results showed that the Cu(II) concentration remained essentially unchanged, indicating that the adsorption capacity of the sample coated only with polydopamine and not grafted with soy protein isolate was limited.

[0036] To verify the adsorption effect of the soybean protein isolate modified melamine foam prepared in this invention on heavy metal ions, the adsorption performance of the prepared modified melamine foam was studied using Cu(II) as the adsorption model.

[0037] (1) Study on the adsorption capacity of soybean protein isolate modified melamine foam for various heavy metal ions Aqueous solutions of Cu(II), Mn(II), Ni(II), Cr(III), Cd(II), Co(II), and Pb(II) with initial concentrations of approximately 1000 mg / L were prepared. 20 mL of each solution was added, and 50 mg of the MF@SPI sample prepared in Example 1 was added. The solutions were allowed to stand at room temperature for 12 hours for adsorption. The concentrations of each metal ion in the solutions before and after adsorption were determined using inductively coupled plasma atomic emission spectrometry (ICP-OES), and the adsorption capacity was calculated. The results are as follows: Figure 2 As shown, the MF@SPI prepared in Example 1 of this invention exhibits significant adsorption effects on all seven metal ions mentioned above, with particularly outstanding adsorption capacities for Cr(II), Pb(II), and Cu(II).

[0038] (2) Effect of initial concentration of Cu(II) aqueous solution on the adsorption capacity of soybean protein isolate modified melamine foam 100 mL aqueous solutions of Cu(II) with concentrations of 100, 200, 300, 500, 750, 1000, 1250, 1500, and 2000 mg / L were prepared. Approximately 50 mL of each different Cu(II) concentration was taken, and approximately 80 mg of the MF@SPI sample prepared in Example 1 was added to each. Three parallel experiments were conducted simultaneously. After adsorption at room temperature for approximately 12 h, samples were taken to determine the Cu(II) concentration, and the average adsorption capacity of the three parallel experiments was calculated. The specific adsorption results are as follows: Figure 3 As shown.

[0039] from Figure 3 It can be seen that when the initial concentration of Cu(II) aqueous solution is low, the adsorption capacity of the MF@SPI sample increases significantly with increasing concentration. When the concentration increases to 1000 mg / L, the reaction sites of the sample gradually reach saturation, and the adsorption capacity gradually tends to equilibrium. The overall adsorption curve shows a typical L-shaped isotherm, indicating that the ratio of the residual Cu(II) capacity in the solution to the Cu(II) capacity adsorbed by the MF@SPI sample decreases with increasing initial Cu(II) concentration. When the initial concentration of Cu(II) aqueous solution is 1000 mg / L, its adsorption capacity is as high as 61.3 mg / g. Therefore, an initial concentration of 1000 mg / L Cu(II) aqueous solution will be used for subsequent experimental studies.

[0040] (3) Effect of adsorption time on Cu(II) adsorption capacity of soy protein isolate modified melamine foam 100 mL of Cu(II) aqueous solution with a concentration of approximately 1000 mg / L was prepared. Approximately 50 mg of the MF@SPI sample prepared in Example 1 was added to approximately 20 mL of the Cu(II) aqueous solution, and adsorption studies were conducted at room temperature. Samples were taken at adsorption times of 5, 10, 20, 30, 40, 60, 90, 120, 180, 240, 300, 420, 540, and 660 min for Cu(II) concentration determination. Specific adsorption results are shown below. Figure 4 As shown.

[0041] from Figure 4 As can be seen, in the first 420 minutes, the adsorption capacity increased with time, gradually stabilizing at a high level of 60.8 mg / g. Compared with other adsorbents, the soybean protein isolate-modified melamine foam prepared in this invention exhibits higher adsorption efficiency due to the presence of active sites on the adsorbent surface, which facilitate chelation with metal cations. Furthermore, the soybean protein isolate-modified melamine foam prepared in this invention is porous and compressible, both of which are beneficial for the rapid chelation of heavy metal ions.

[0042] (4) Effect of pH of Cu(II) aqueous solution on the adsorption capacity of soy protein isolate modified melamine foam The pH value of the metal ion solution is an important factor affecting the adsorption process. Previous studies found that significant precipitation occurred in Cu(II) aqueous solutions at pH 5.5 or higher; therefore, solutions with a pH below 5.5 were selected for adsorption studies. 400 mL of Cu(II) aqueous solutions with a concentration of approximately 1000 mg / L were prepared at pH values ​​of approximately 2, 3, 4, 4.5, and 5, respectively. Approximately 20 mL of each different pH Cu(II) aqueous solution was taken, and approximately 50 mg of the MF@SPI sample prepared in Example 1 was added to each solution. Three parallel experiments were performed for each group. After adsorption at room temperature for approximately 12 h, samples were taken to measure the Cu(II) concentration, and the average adsorption capacity of the three parallel experiments was calculated. Specific adsorption results are shown below. Figure 5 As shown.

[0043] from Figure 5 It can be seen that the adsorption capacity gradually increases with increasing pH, reaching a maximum adsorption capacity of 64.8 mg / g at pH 4.5. At lower pH, high concentrations of protons compete with metal ions for adsorption sites. Therefore, due to electrostatic repulsion, the MF@SPI sample surface carries a positive charge, making it difficult for metal ions of the same charge to approach the active sites. When the pH increases to 4.5, the proton concentration in the solution decreases, and the MF@SPI sample has sufficient amino groups to chelate with Cu(II), resulting in an increased adsorption capacity.

[0044] (5) Effect of adsorption temperature on Cu(II) adsorption capacity of soy protein isolate modified melamine foam Approximately 500 mL of a Cu(II) aqueous solution with a concentration of approximately 1000 mg / L was prepared. Approximately 50 mg of the MF@SPI sample prepared in Example 1 was added to approximately 20 mL of the Cu(II) aqueous solution, and the solutions were placed in water baths at 20, 25, 30, 35, 40, 45, 50, and 55 °C for adsorption studies. Three parallel experiments were conducted simultaneously. After approximately 12 hours of adsorption in each experiment, samples were taken to determine the Cu(II) concentration, and the average adsorption capacity of the three parallel experiments was calculated. Specific adsorption results are shown below. Figure 6 As shown.

[0045] from Figure 6 The results show that the adsorption capacity of Cu(II) decreases with increasing temperature, indicating that the adsorption process is exothermic. Furthermore, the measured adsorption enthalpy ΔH < 0 confirms that the adsorption of Cu(II) by the soy protein isolate-modified melamine foam is an exothermic process. The negative adsorption entropy ΔS explains the decrease in the randomness of the solid-liquid interface during adsorption, attributed to the substitution of hydrated molecules by metal ions through chelation. The negative adsorption free energy ΔG indicates that the adsorption of Cu(II) by the adsorbent sample is spontaneous.

[0046] (6) Study on the recycling capacity of soybean protein isolate modified melamine foam The MF@SPI sample prepared in Example 1 was subjected to 10 consecutive cycles of adsorption testing. The Cu(II) concentration was measured, and the adsorption capacity and adsorption efficiency were calculated. Adsorption efficiency = adsorption capacity after the nth desorption cycle ÷ initial adsorption capacity, where n is the number of cycles. The results are as follows: Figure 7 As shown, the adsorption capacity of the material decreases slightly with increasing cycle number, indicating that some effective adsorption sites gradually decrease during multiple adsorption-desorption processes. Nevertheless, after 10 cycles, the material still maintains an adsorption efficiency of 85.1%, demonstrating good structural stability, durability, and recyclability potential.

[0047] In summary, the soybean protein isolate modified melamine foam prepared by this invention has a high adsorption capacity for Cu(II). When the soybean protein isolate modified melamine foam prepared by this invention is used to adsorb Cu(II), it exhibits higher adsorption performance when the initial concentration of Cu(II) aqueous solution is 1000 mg / L, the adsorption time is 420 min, the solution pH is 4.5, and the adsorption temperature is 20℃.

[0048] In addition, the products prepared in Example 1 and Comparative Example 1 were characterized in this invention.

[0049] The samples prepared in Example 1 and Comparative Example 1 were subjected to stress-strain curve testing to investigate their mechanical properties. The results are as follows: Figure 8 As shown in figures a and c, all curves exhibit hysteresis loops, indicating that the material's mechanical response during compression is typical of viscoelastic behavior. The closed nature of the stress-strain curves signifies that the sample's structure remains intact during these cycles, demonstrating the good structural stability of the MF@SPI prepared in this invention, which facilitates rapid adsorption of metal ions.

[0050] The samples prepared in Example 1 and Comparative Example 1 were subjected to cyclic stress-strain curve tests at 40% strain, and the results are as follows: Figure 8 As shown in b and d, it is demonstrated that MF@SPI has good elasticity and compressibility, and its mechanical properties did not significantly degrade after modification.

[0051] The samples prepared in Example 1 and Comparative Example 1 were characterized by infrared absorption spectroscopy, and the results are as follows: Figure 9 As shown. Compared to melamine foam, MF@SPI at 1659 cm⁻¹ -1 and 1058 cm -1 New characteristic absorption peaks appeared at 3379 cm⁻¹, which can be attributed to the stretching vibrations of C=O and CN groups, respectively, indicating that new oxygen-containing functional groups have been introduced into the material surface. Meanwhile, MF@SPI showed a peak at 3379 cm⁻¹. -1The broadening and enhancement of the nearby absorption peaks may be related to the superposition of stretching vibration signals of hydroxyl (OH) and amino (NH), indicating an increase in the number of polar functional groups on the material surface. Furthermore, at 2931 cm⁻¹... -1 and 2855 cm -1 The observation of the characteristic stretching vibration peak of -CH2- further proves that soy protein isolate has been successfully grafted onto the surface of melamine foam skeleton.

[0052] The samples prepared in Example 1 and Comparative Example 1 were characterized by scanning electron microscopy, and the results are as follows: Figure 10 As shown. Figure 10 a, b, and c: The original melamine foam exhibits a typical three-dimensional porous framework structure with a relatively uniform pore size distribution and a relatively smooth framework surface. For example... Figure 10 Images d, e, and f, after modification with soy protein isolate, show a clear coating on the surface of the foam skeleton, a denser structure, and increased surface roughness, indicating that soy protein isolate was successfully grafted onto the surface of the foam skeleton. Figure 10 g, h, i and Figure 10 After adsorbing Cu(II), granular deposits appeared on the surface of the material, which should be complexes formed by the coordination of amino groups in soy protein isolate with Cu(II).

[0053] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing soy protein isolate modified melamine foam, characterized in that, Includes the following steps: S1: At room temperature, melamine foam is reacted in an alkaline solution of dopamine hydrochloride to obtain initially modified melamine foam; S2: The pre-modified melamine foam is placed in an organic solvent containing epichlorohydrin to carry out an activation reaction, thereby obtaining activated melamine foam; S3: The activated melamine foam is placed in an alkaline aqueous solution containing soy protein isolate for grafting reaction. After the reaction is completed, it is washed and dried to obtain the soy protein isolate modified melamine foam.

2. The method for preparing soybean protein isolate modified melamine foam according to claim 1, characterized in that, The organic solvent is N,N-dimethylformamide.

3. The method for preparing soybean protein isolate modified melamine foam according to claim 1 or 2, characterized in that, In the organic solvent containing epichlorohydrin, the volume fraction of epichlorohydrin is 20% to 40%.

4. The method for preparing soybean protein isolate modified melamine foam according to claim 1, characterized in that, The alkaline aqueous solution containing soy protein isolate comprises the following components by mass fraction: 2%–6% soy protein isolate, 0.5%–2% sodium hydroxide, and the balance being water.

5. The method for preparing soybean protein isolate modified melamine foam according to claim 1 or 4, characterized in that, The pH value of the alkaline aqueous solution containing soy protein isolate is 12-14.

6. The method for preparing soybean protein isolate modified melamine foam according to claim 1, characterized in that, The alkaline solution of dopamine hydrochloride is prepared by dissolving dopamine hydrochloride and tris(hydroxymethyl)aminomethane hydrochloride in deionized water and adjusting the pH to 8.0-9.

0.

7. Soy protein isolate modified melamine foam, characterized in that, Prepared by the method according to any one of claims 1 to 4.

8. The application of the soybean protein isolate modified melamine foam according to claim 7 in the preparation of adsorbent materials for wastewater containing heavy metal ions.

9. The application according to claim 8, characterized in that, The heavy metal ions are any one or more of Cu(II), Pb(II), Cd(II), Cr(III), Ni(II), Co(II), Mn(II) and Zn(II).

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