Preparation method and application of lignin-based hydrogel for adsorbing nitrogen and phosphorus ions

Abstract

This invention relates to a method for preparing a lignin-based hydrogel that adsorbs nitrogen and phosphorus ions and its application, belonging to the field of functional materials. The hydrogel of this invention uses lignin sulfonate as a raw material, methacryloyloxyethyltrimethylammonium chloride and acrylic acid as monomers, potassium persulfate as an initiator, and N,N-methylenebisacrylamide as a crosslinking agent, undergoing a free radical polymerization reaction to obtain a lignin-based hydrogel. Subsequently, the above lignin-based hydrogel is mixed with an aqueous solution of nitrogen and / or phosphorus ions for adsorption, and then filtered. The resulting solid sample is the lignin-based hydrogel after adsorbing nitrogen and phosphorus ions. This invention not only provides a new pathway for the high-value utilization of lignin in industrial applications, but also produces a lignin-based hydrogel with extremely strong adsorption capacity for nitrogen and phosphorus ions in water. Furthermore, the hydrogel after adsorbing nitrogen and phosphorus ions can be developed into a slow-release fertilizer for application in hydroponic rice cultivation.

Description

Technical Field

[0001] This invention relates to a method for preparing a lignin-based hydrogel that adsorbs nitrogen and phosphorus ions and its application, belonging to the field of functional materials. Background Technology

[0002] Resource scarcity and environmental pollution are global problems facing humanity today. Phosphorus is an essential nutrient for the survival of all living organisms in nature. However, with the rapid development of related industries, large amounts of nitrogen and phosphorus-containing wastewater are discharged into runoff systems, causing severe eutrophication of water bodies and posing a serious threat to ecological balance. Therefore, effectively controlling nitrogen and phosphorus pollutants in water bodies and alleviating eutrophication has become one of the most urgent problems to be solved.

[0003] Currently, numerous technologies have been applied to remove nitrogen and phosphorus pollutants from water bodies. Among them, adsorption not only boasts advantages such as low cost, simple operation, and rapid efficiency, but also allows for the recovery of nitrogen and phosphorus from the water and the recycling of the adsorbent through a simple desorption process, making it considered one of the technologies with the greatest potential for industrial application. The key to treating nitrogen and phosphorus-containing wastewater using adsorption lies in developing inexpensive, efficient, green, and pollution-free adsorption materials. Compared to common activated carbon, carbon nanotubes, porous microspheres, ion exchange resins, and metal-organic frameworks, biomass-based materials are made from inexpensive, readily available, and renewable raw materials, making them a highly promising adsorption material for industrial application. Lignin, in particular, is a very abundant renewable biomass resource in nature. It is widely sourced, plentiful, renewable, and environmentally compatible, and possesses abundant oxygen-containing functional groups. It can be developed into various green and efficient lignin-based adsorbents, showing great application potential in wastewater treatment. Currently, based on the type of ions that impart functional groups, lignin-based adsorbents are generally classified into cationic and anionic adsorbents.

[0004] Lignin-based anion exchange adsorbents are typically prepared by transferring sulfonic acid or carboxyl groups from lignin to lignin via sulfonation, carboxymethylation, or graft polymerization. Current research reports on lignin adsorbents for the adsorption of cationic methylene blue, Congo red, Cr(VI), and Cd in wastewater. 2+The removal efficiency of lignin-based cationic adsorbents is studied. Lignin-based cationic adsorbents are generally prepared by introducing cationic amines or quaternary amino groups onto lignin. The amination of lignin has been extensively studied through the Mannich reaction, which transfers amine groups (e.g., primary, secondary, and tertiary amines) onto lignin. Various other amines, including diethylenetriamine (DETA), polyethyleneimine (PEI), and ethylenediamine, have also been used in this reaction. However, the amination process requires formaldehyde as a cross-linking agent, which is unfriendly to both the environment and humans. Quaternary ammonium groups are typically introduced into lignin through free radical polymerization or etherification. The etherification of lignin is usually accomplished by reacting the hydroxyl groups in lignin with glycidyltrimethylammonium chloride or 3-chloro-hydroxypropyltrimethylammonium chloride under alkaline conditions, allowing the reaction to proceed in a homogeneous system. Free radical polymerization of lignin typically uses vinyl monomers containing quaternary ammonium groups as monomers; commonly used monomers include dimethyl diallyl ammonium chloride (DADMAC) or methallyloxyethyltrimethylammonium chloride (METAC). Methacryloxyethyltrimethylammonium chloride can polymerize with numerous free radical sites on the benzene ring of lignin, thereby enhancing the adsorption capacity of the adsorbent. However, free radical polymerization reactions are usually carried out under acidic conditions. Since ordinary lignin is insoluble in acidic solutions, these reactions are typically conducted in heterogeneous systems, which affects the reaction efficiency. Furthermore, it has been confirmed that eutrophic wastewater usually contains both anionic and cationic pollutants. Lignin-based gel adsorbents containing only one type of ionic group cannot remove all ionic pollutants, failing to meet practical application needs. Based on this, this invention, starting from the structure of lignin itself and utilizing its abundant oxygen-containing functional groups, prepares a lignin-based hydrogel capable of adsorbing anions and cations through free radical polymerization for the efficient removal and recovery of nitrogen and phosphorus ions in water. This hydrogel is then applied to the field of rice hydroponics to explore the feasibility of using lignin-based hydrogels as slow-release fertilizer carriers. Summary of the Invention

[0005] This invention addresses the shortcomings of existing nitrogen and phosphorus ion adsorption materials by providing a method for preparing and applying a lignin-based hydrogel that adsorbs nitrogen and phosphorus ions. Using lignin sulfonate as a raw material, methacryloyloxyethyltrimethylammonium chloride and acrylic acid as monomers, potassium persulfate as an initiator, and N,N-methylenebisacrylamide as a crosslinking agent, a lignin-based hydrogel is prepared via free radical polymerization. This hydrogel then adsorbs nitrogen and phosphorus ions, yielding a lignin-based hydrogel with adsorbed nitrogen and phosphorus ions, which is finally applied in hydroponic rice cultivation. This invention not only provides a new pathway for the high-value utilization of lignin in industrial applications, but also demonstrates that the prepared lignin-based hydrogel exhibits extremely strong adsorption capacity for nitrogen and phosphorus ions in water, and can simultaneously adsorb both nitrogen and phosphorus ions. Furthermore, the lignin-based hydrogel after adsorbing nitrogen and phosphorus ions can be developed into a slow-release fertilizer for hydroponic rice cultivation, showing promising application prospects.

[0006] A method for preparing a lignin-based hydrogel that adsorbs nitrogen and phosphorus ions includes the following steps:

[0007] Step 1: Mix lignin sulfonate and deionized water evenly, then add methacryloyloxyethyltrimethylammonium chloride, acrylic acid, N,N-methylenebisacrylamide, and potassium persulfate in sequence, stir evenly, and purge air with nitrogen to obtain a mixed solution;

[0008] Step 2: Transfer the mixed solution obtained in Step 1 to a sealed container for free radical polymerization reaction. Soak the resulting product in deionized water to obtain lignin-based hydrogel.

[0009] Step 3: Mix the lignin-based hydrogel with an aqueous solution of nitrogen and / or phosphorus ions and adsorb them in a shaker. After the adsorption is complete, filter the mixture. The resulting solid sample is the lignin-based hydrogel after adsorbing nitrogen and phosphorus ions.

[0010] The lignin-based hydrogels that adsorb nitrogen and phosphorus ions described in this invention can be divided into three types: first, lignin-based hydrogels that adsorb nitrogen ions; second, lignin-based hydrogels that adsorb phosphorus ions; and third, amphoteric lignin-based hydrogels that simultaneously adsorb nitrogen and phosphorus ions.

[0011] Preferably, the lignin-based hydrogel is an amphoteric lignin-based hydrogel that simultaneously adsorbs nitrogen and phosphorus ions.

[0012] In the above technical solution, the amphoteric fingers in the amphoteric lignin-based hydrogel can simultaneously adsorb anions and cations.

[0013] In the method of the present invention, in step 1, the ratio of lignin sulfonate to deionized water is 0.2g:5-15mL.

[0014] Preferably, in step 1, the ratio of lignin sulfonate to deionized water is 0.2g:7mL.

[0015] In the method of the present invention, in step 1, the ratio of lignosulfonate, methacryloyloxyethyltrimethylammonium chloride, acrylic acid, N,N-methylenebisacrylamide, and potassium persulfate is 0.2g:1.0-3.0g:1.0-3.0g:0.01-0.05g:0.01-0.05g.

[0016] Preferably, in step 1, the ratio of lignosulfonate, methacryloyloxyethyltrimethylammonium chloride, acrylic acid, N,N-methylenebisacrylamide, and potassium persulfate is 0.2g:2.5g:2.5g:0.03g:0.03g.

[0017] In the method of the present invention, in step 1, the stirring conditions are magnetic stirring at 200-600 rpm for 10-30 minutes.

[0018] In the method of the present invention, in step 2, the free radical polymerization reaction conditions are 40-80°C for 1-3 hours.

[0019] Preferably, in step 2, the temperature of the free radical polymerization reaction is 60°C and the time is 2 hours.

[0020] In the method of the present invention, in step 2, the product is soaked in deionized water for 20 to 40 hours.

[0021] Preferably, the product is soaked in deionized water for 24 hours.

[0022] In the method of the present invention, in step 2, the free radical polymerization reaction is carried out in an oven.

[0023] In the method of the present invention, in step 3, the adsorption conditions are adsorption at 20-40°C and 50-150 rpm for 10-600 min.

[0024] Preferably, in step 3, the adsorption conditions are adsorption at 25°C and 100 rpm for 300 min.

[0025] In the method of the present invention, in step 3, the nitrogen ion aqueous solution is one or more of ammonium chloride solution, ammonium sulfate solution and ammonium nitrate solution.

[0026] In the method of the present invention, in step 3, the phosphate ion aqueous solution is one or more of potassium dihydrogen phosphate solution, dipotassium hydrogen phosphate solution, and sodium dihydrogen phosphate solution.

[0027] Preferably, the nitrogen ion aqueous solution is an ammonium chloride solution.

[0028] Preferably, the phosphorus ion aqueous solution is a potassium dihydrogen phosphate solution.

[0029] Preferably, the mixed aqueous solution of nitrogen and phosphorus ions is a mixture of ammonium chloride solution and potassium dihydrogen phosphate solution.

[0030] In the method of the present invention, in step 3, the concentration of the nitrogen ion aqueous solution is 10-200 mg N / L.

[0031] Preferably, the concentration of the nitrogen ion aqueous solution is 100 mg N / L.

[0032] In the method of the present invention, in step 3, the concentration of the phosphate ion aqueous solution is 10-200 mg P / L.

[0033] Preferably, the concentration of the phosphate ion aqueous solution is 200 mg P / L.

[0034] In the method of the present invention, in step 3, the nitrogen and phosphorus ion mixed solution is obtained by dissolving ammonium chloride and potassium dihydrogen phosphate in deionized water and stirring until homogeneous.

[0035] In the method of the present invention, in step 3, the concentration of nitrogen ions in the nitrogen-phosphorus ion mixed solution is 10-200 mg N / L, and the concentration of phosphorus ions is 10-200 mg P / L.

[0036] Preferably, the concentration of nitrogen ions in the nitrogen-phosphorus ion mixed solution is 100 mg N / L and the concentration of phosphorus ions is 100 mg P / L.

[0037] In the method of the present invention, the ratio of the lignin-based hydrogel to the aqueous solution of nitrogen and / or phosphorus ions is 0.015 g: 10-50 mL.

[0038] Preferably, the ratio of the lignin-based hydrogel to the aqueous solution of nitrogen and / or phosphorus ions is 0.015 g: 30 mL.

[0039] Another object of the present invention is to provide a lignin-based hydrogel that adsorbs nitrogen and phosphorus ions prepared by the above method.

[0040] Another object of the present invention is to provide the application of the above-mentioned lignin-based hydrogel that adsorbs nitrogen and phosphorus ions as a slow-release fertilizer in the field of hydroponic rice cultivation.

[0041] The lignin-based hydrogel that adsorbs nitrogen and phosphorus ions described in this invention is used as a slow-release fertilizer in the field of hydroponic rice cultivation. The application process is as follows: the lignin-based hydrogel that has adsorbed nitrogen and phosphorus ions is freeze-dried and then thoroughly pulverized, crushed, or mashed to obtain a slow-release fertilizer. It is then placed in deionized water to obtain an aqueous solution containing the slow-release fertilizer. Germinated rice seedlings are dispersed in the above aqueous solution to conduct rice seedling growth experiments.

[0042] In the above technical solution, the freeze-drying temperature is -50 to -60°C, and the time is 40 to 50 hours.

[0043] Preferably, the freeze-drying temperature is -50°C and the time is 48 hours.

[0044] In the above technical solution, the ratio of the lignin-based hydrogel after adsorbing nitrogen and phosphorus ions to deionized water is 0.1g:10-30mL.

[0045] Preferably, the ratio of the lignin-based hydrogel after adsorbing nitrogen and phosphorus ions to deionized water is 0.1g:10mL.

[0046] In the above technical solution, the germinated rice seedlings are pretreated rice seedlings. The pretreatment method is as follows: weigh a certain amount of rice seeds, soak them in deionized water for 20-40 hours, then sow 10-200 seeds in a pre-humidified petri dish, and cultivate them at a temperature of 20-40℃ and a humidity of 50-70% for 1-5 days to obtain germinated rice seedlings.

[0047] Preferably, the soaking time in deionized water is 48 hours.

[0048] Preferably, 5 to 20 rice seeds are selected for cultivation, and more preferably 10 seeds are selected.

[0049] Preferably, the rice seed cultivation temperature is 30℃, the humidity is 60%, and the cultivation time is 7 days.

[0050] In the above technical solution, the rice seedling growth experiment process is as follows: the seedlings are cultured for 5 to 10 days under environmental conditions of 20 to 40°C and 50 to 70% humidity.

[0051] Preferably, the rice seedling growth experiment process is as follows: the seedlings are cultured for 7 days under environmental conditions of 30°C and 60% humidity.

[0052] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0053] 1. The raw material used in this invention is lignin sulfonate, a byproduct of the pulping and papermaking process. This raw material is not only widely available, abundant, renewable, and environmentally compatible, but also has rich oxygen-containing functional groups, making it suitable for large-scale industrial use.

[0054] 2. The hydrogel prepared by this invention contains abundant nitrogen and phosphorus ion adsorption sites, thus it has a strong adsorption capacity for nitrogen and phosphorus ions and can adsorb nitrogen and phosphorus ions simultaneously.

[0055] 3. This invention is the first to use lignin hydrogel after adsorbing nitrogen and phosphorus ions in the preparation of slow-release fertilizer. The resulting nitrogen and phosphorus-rich lignin-based hydrogel can be developed into a slow-release fertilizer for application in the field of hydroponic rice cultivation.

[0056] 4. This invention utilizes industrial lignin to prepare hydrogels and applies them to the fields of nitrogen and phosphorus ion adsorption and slow-release fertilizers. This not only makes full use of lignin, an industrial waste, providing a new avenue for its high-value utilization, but also the prepared hydrogels exhibit extremely strong adsorption capacity for nitrogen and phosphorus ions in water. Furthermore, the hydrogels after adsorbing nitrogen and phosphorus ions can be used to prepare slow-release fertilizers to promote the growth of rice seedlings. Therefore, it has promising application prospects. Attached Figure Description

[0057] Figure 1 Images of lignin-based hydrogel samples obtained in Examples 1, 2, and 3.

[0058] Figure 2 The images are SEM images of the lignin-based hydrogels obtained in Examples 1, 2 and 3 at different magnifications.

[0059] Figure 3 The lignin-based hydrogel obtained in Example 1 in a binary system with NH4 + and H2PO4 - Ion competition adsorption data.

[0060] Figure 4 NH4+ of the lignin-based hydrogels obtained in Examples 2 and 3 + and H2PO4 - Ion adsorption data.

[0061] Figure 5 The lignin-based hydrogels obtained in Examples 1, 2, and 3 adsorb NH4 + and H2PO4 - A diagram illustrating the promotion of rice seedling growth. Detailed Implementation

[0062] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0063] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0064] Example 1

[0065] A method for preparing an amphoteric lignin-based hydrogel that adsorbs nitrogen and phosphorus ions includes the following steps:

[0066] Step 1: Mix 0.2g of lignin sulfonate with 7mL of deionized water to obtain a homogeneous lignin sulfonate solution. Then, add 2.5g of methacryloyloxyethyltrimethylammonium chloride, 2.5g of acrylic acid, 0.03g of potassium persulfate, and 0.03g of N,N-methylenebisacrylamide in sequence. Stir magnetically at 400rpm for 20min to completely dissolve the lignin sulfonate and remove air with N2 to obtain a mixed solution.

[0067] Step 2: Transfer the mixed solution obtained in Step 1 to a sealed container and place it in a 60°C oven for 3 hours for free radical polymerization. The resulting product is then soaked in deionized water for 24 hours to obtain lignin-based hydrogel (ALH) (see...). Figure 1 and Figure 2 ).

[0068] Step 3: Weigh 0.015g of the ALH hydrogel obtained in Step 2 into a 100mL Erlenmeyer flask, then add 30mL of a mixed solution of ammonium chloride (100mg N / L) and potassium dihydrogen phosphate (100mg P / L). (The mixed solution is prepared by simultaneously weighing 0.0382g of ammonium chloride and 0.0439g of potassium dihydrogen phosphate into 100mL of deionized water and mixing thoroughly to obtain NH4+.) + Concentration of 100 mg N / L and H2PO4 - A mixed solution with a concentration of 100 mg P / L was prepared. Finally, the conical flask was sealed and placed in a constant temperature shaker. The mixture was shaken at 25°C and 100 rpm for 5 hours. Then, it was filtered through a 0.22 μm filter membrane. The resulting solid sample was the lignin-based hydrogel after adsorbing nitrogen and phosphorus ions, denoted as ALH-N&P.

[0069] Lignin-based hydrogels (ALH) for the removal of NH4 in water + and H2PO4 - Ion adsorption:

[0070] Based on the NH4 in the aqueous solution before and after adsorption + and H2PO4 - The nitrogen and phosphorus ion adsorption capacity of the lignin-based hydrogel was calculated based on the ion concentration (results are shown in...). Figure 3 ), of which NH4 in the filtrate + and H2PO4 - Ion concentrations were determined by Nessler's reagent method and ammonium molybdate colorimetric method, respectively.

[0071] The above-mentioned preparation simultaneously adsorbs NH4 + and H2PO4 - An experiment was conducted to use ionized lignin-based hydrogels (ALH-N&P) as slow-release fertilizers to promote rice seedling growth, including the following steps:

[0072] (1) After freeze-drying ALH-N&P hydrogel and ALH hydrogel (drying at -50℃ for 48h), weigh 0.1g of each, put them into a mortar and grind them thoroughly, and then put the resulting solids into test tubes containing 10mL of deionized water.

[0073] (2) Weigh a certain amount of rice seeds, soak them in deionized water for 24 hours, and then sow 200 seeds in a pre-humidified culture dish. Cultivate them for 3 days at a temperature of 30℃ and a humidity of 60%. After the rice seeds germinate, take 10 germinated rice seedlings from each plant and disperse them in the test tubes obtained in step (1) to conduct seedling growth experiments.

[0074] (3) After 7 days, observe the growth of the rice seedlings in step (2) at a temperature of 30℃ and a humidity of 60%, and measure the stem length, root length, diameter and dry weight of the rice seedlings (see results). Figure 5 (and Table 1).

[0075] Example 2

[0076] A method for preparing a lignin-based hydrogel that adsorbs nitrogen ions includes the following steps:

[0077] Step 1: Mix 0.2g of lignin sulfonate with 7mL of deionized water to obtain a homogeneous lignin sulfonate solution. Then, add 2.5g of methacryloyloxyethyltrimethylammonium chloride, 2.5g of acrylic acid, 0.03g of potassium persulfate, and 0.03g of N,N-methylenebisacrylamide in sequence. Stir magnetically at 400rpm for 20min to completely dissolve the lignin sulfonate and remove air with N2 to obtain a mixed solution.

[0078] Step 2: Transfer the mixed solution obtained in Step 1 to a sealed container and place it in a 60°C oven for 3 hours for free radical polymerization. The resulting product is then soaked in deionized water for 24 hours to obtain lignin-based hydrogel (ALH) (see...). Figure 1 and Figure 2 ).

[0079] Step 3: Weigh 0.015g of the ALH hydrogel obtained in Step 2 into a 100mL Erlenmeyer flask, then add 30mL of ammonium chloride solution (weigh 0.0382g of ammonium chloride in 100mL of deionized water to obtain NH4+). + An ammonium chloride solution with a concentration of 100 mg N / L was prepared. The conical flask was then sealed and placed in a constant temperature shaker. The mixture was shaken at 25°C and 100 rpm for 5 hours. The sample was then filtered through a 0.22 μm filter membrane. The resulting solid sample was the lignin-based hydrogel after adsorbing nitrogen ions, denoted as ALH-N.

[0080] Lignin-based hydrogels (ALH) for the removal of NH4 in water + Ion adsorption:

[0081] Based on the NH4 in the aqueous solution before and after adsorption + The nitrogen ion adsorption capacity of the lignin-based hydrogel was calculated from the concentration (results are shown in [reference]). Figure 4 ), of which NH4 in the filtrate + Ion concentrations were determined using the Nessler reagent method.

[0082] The adsorbed NH4 obtained above + An experiment was conducted to use ionized lignin-based hydrogel (ALH-N) as a slow-release fertilizer to promote rice seedling growth, including the following steps:

[0083] (1) After freeze-drying the ALH-N hydrogel (drying at -50℃ for 48h), weigh 0.1g, put it into a mortar and grind it thoroughly, and then put the resulting solid into a test tube containing 10mL of deionized water.

[0084] (2) Weigh a certain amount of rice seeds, soak them in deionized water for 24 hours, and then sow 200 seeds in a pre-humidified petri dish. Cultivate them for 3 days at a temperature of 30℃ and a humidity of 60%. After the rice seeds germinate, take 10 germinated rice seedlings and disperse them in the test tubes obtained in step (1) to carry out seedling growth experiments.

[0085] (3) After cultivating the rice seedlings for 7 days at a temperature of 30℃ and a humidity of 60%, observe the growth of the rice seedlings in step (2), and measure the stem length, root length, diameter and dry weight of the rice seedlings (see results). Figure 5 (and Table 1).

[0086] Example 3

[0087] A method for preparing a lignin-based hydrogel that adsorbs phosphorus ions includes the following steps:

[0088] Step 1: Mix 0.2g of lignin sulfonate with 7mL of deionized water to obtain a homogeneous lignin sulfonate solution. Then, add 2.5g of methacryloyloxyethyltrimethylammonium chloride, 2.5g of acrylic acid, 0.03g of potassium persulfate, and 0.03g of N,N-methylenebisacrylamide in sequence. Stir magnetically at 400rpm for 20min to completely dissolve the lignin sulfonate and remove air with N2 to obtain a mixed solution.

[0089] Step 2: Transfer the mixed solution obtained in Step 1 to a sealed container and place it in a 60°C oven for 3 hours for free radical polymerization. The resulting product is then soaked in deionized water for 24 hours to obtain lignin-based hydrogel (ALH) (see...). Figure 1 and Figure 2 ).

[0090] Step 3: Weigh 0.015g of the ALH hydrogel obtained in Step 2 into a 100mL Erlenmeyer flask, then add 30mL of potassium dihydrogen phosphate solution (weigh 0.0878g of potassium dihydrogen phosphate in 100mL of deionized water, mix well to obtain H2PO4). - A potassium dihydrogen phosphate solution with a concentration of 200 mg P / L was prepared. The conical flask was then sealed and placed in a constant temperature shaker. The mixture was shaken at 25°C and 100 rpm for 5 hours. The sample was then filtered through a 0.22 μm filter membrane. The resulting solid sample was the lignin-based hydrogel after adsorbing phosphorus ions, denoted as ALH-P.

[0091] Lignin-based hydrogels (ALH) for H2PO4 in water - Ion adsorption:

[0092] Based on the H2PO4 in the aqueous solution before and after adsorption - The phosphorus ion adsorption capacity of the lignin-based hydrogel was calculated from the concentration (results are shown in...). Figure 3 ), of which, the filtrate contains H2PO4 - Ion concentration was determined by the ammonium molybdate colorimetric method.

[0093] The adsorbed H2PO4 prepared above - An experiment was conducted to use ionized lignin-based hydrogel (ALH-P) as a slow-release fertilizer to promote rice seedling growth, including the following steps:

[0094] (1) After freeze-drying the ALH-P hydrogel (drying at -50℃ for 48h), weigh 0.1g, put it into a mortar and grind it thoroughly, and then put the resulting solid into a test tube containing 10mL of deionized water.

[0095] (2) Weigh a certain amount of rice seeds, soak them in deionized water for 24 hours, and then sow 200 seeds in a pre-humidified petri dish. Cultivate them for 3 days at a temperature of 30℃ and a humidity of 60%. After the rice seeds germinate, take 10 germinated rice seedlings and disperse them in the test tubes obtained in step (1) to carry out seedling growth experiments.

[0096] (3) After 7 days, observe the growth of the rice seedlings in step (2) at a temperature of 30℃ and a humidity of 60%, and measure the stem length, root length, diameter and dry weight of the rice seedlings (see results). Figure 5 (and Table 1).

[0097] Table 1. Statistical data on the effects of lignin-based hydrogels under different treatments on rice seedling growth.

[0098]

[0099] Figure 1 These are images of lignin-based hydrogel samples obtained in Examples 1, 2, and 3 of this invention.

[0100] Figure 2 These are SEM images of the lignin-based hydrogels obtained in Examples 1, 2, and 3 of this invention at different magnifications. As can be seen from the images, the lignin-based hydrogels possess a typical three-dimensional porous structure of dry polymer gels. The honeycomb-like pores are distributed relatively regularly, and the porous channels and loose network structure on the surface and inside increase the specific surface area of ​​the hydrogel material, which is beneficial for exposing more active sites and making the adsorption process easier.

[0101] Figure 3 The lignin-based hydrogel obtained in Example 1 of this invention is in a binary system with NH4 + and H2PO4 -Ion competition adsorption data. The graph shows that increasing the NH4+ concentration in the binary solution... + and H2PO4 - The concentration of ions can lead to a decrease in the equilibrium adsorption capacity of lignin-based hydrogels for another type of ion.

[0102] Figure 4 The NH4+ of the lignin-based hydrogels obtained in Examples 2 and 3 of this invention + and H2PO4 - Ion adsorption data. The graph shows that as the amount of lignin-based hydrogel increased from 0.25 g / L to 0.50 g / L, its adsorption capacity for NH4+ increased. + and H2PO4 - The equilibrium adsorption capacity of ions all reached their maximum values.

[0103] Figure 5 The lignin-based hydrogels obtained in Examples 1, 2, and 3 of this invention adsorb NH4 + and H2PO4 - The figure shows the effect of lignin-based hydrogels adsorbing nitrogen and phosphorus ions on rice seedling growth. Table 1 shows the statistical data on the effect of lignin-based hydrogels adsorbing nitrogen and phosphorus ions on rice seedling growth. It can be seen that the dry weight, stem length, diameter and root length of seedlings grown in ALH-N&P, ALH-N and ALH-P are all higher than those grown in ALH. This proves that the adsorption of NH4+ ions promotes the growth of rice seedlings. + and / or H2PO4 - Ionic lignin-based hydrogels are beneficial for biomass accumulation, thereby promoting the growth of rice seedlings.

Claims

1. A method for preparing a lignin-based hydrogel that adsorbs nitrogen and phosphorus ions, characterized in that: Includes the following steps: Step 1: Mix lignin sulfonate and deionized water evenly, then add methacryloxyethyltrimethylammonium chloride, acrylic acid, N,N-methylenebisacrylamide, and potassium persulfate sequentially, stir evenly, and purge air with nitrogen to obtain a mixed solution; wherein, the ratio of lignin sulfonate to deionized water is 0.2 g : 5~15 mL, and the ratio of lignin sulfonate, methacryloxyethyltrimethylammonium chloride, acrylic acid, N,N-methylenebisacrylamide, and potassium persulfate is 0.2 g : 1.0~3.0 g : 1.0~3.0 g : 0.01~0.05 g : 0.01~0.05 g; Step 2: Transfer the mixed solution obtained in Step 1 to a sealed container for free radical polymerization reaction. Soak the resulting product in deionized water to obtain lignin-based hydrogel. Step 3: Mix the lignin-based hydrogel with a mixed aqueous solution of nitrogen and phosphorus ions, and adsorb the mixture in a shaker. After the adsorption is complete, filter the mixture. The resulting solid sample is the lignin-based hydrogel after adsorbing nitrogen and phosphorus ions. The adsorption conditions are as follows: adsorption at 20-40℃ and 50-150 rpm for 10-600 min; the concentration of the mixed aqueous solution of nitrogen and phosphorus ions is 10-200 mg N(P) / L; and the ratio of the lignin-based hydrogel to the mixed aqueous solution of nitrogen and phosphorus ions is 0.015 g : 10-50 mL.

2. The preparation method according to claim 1, characterized in that: In step 2, the free radical polymerization reaction is carried out at 40-80°C for 1-3 hours; the product is soaked in deionized water for 20-40 hours.

3. The method according to claim 1, characterized in that: In step 3, the nitrogen and phosphorus ion mixed aqueous solution is a mixture of ammonium chloride solution and potassium dihydrogen phosphate solution.

4. The preparation method according to any one of claims 1 to 3 yields a lignin-based hydrogel that adsorbs nitrogen and phosphorus ions.

5. The application of the lignin-based hydrogel according to claim 4 as a slow-release fertilizer in the field of hydroponic rice cultivation.

6. The application according to claim 5, characterized in that: The lignin-based hydrogel that has adsorbed nitrogen and phosphorus ions is freeze-dried and then thoroughly pulverized, crushed, or pounded to obtain a slow-release fertilizer. This fertilizer is then placed in deionized water to obtain an aqueous solution containing the slow-release fertilizer.

7. The application according to claim 6, characterized in that: The freeze-drying temperature is -50~-60℃, and the time is 40~50 h; the ratio of the lignin-based hydrogel after adsorption of nitrogen and phosphorus ions to deionized water is 0.1 g : 10~30 mL.

Images