A water-retaining phosphorus-absorbing hydrogel as well as a preparation method and application thereof

Abstract

The application belongs to the technical field of hydrogel materials, and particularly relates to a water-retaining and phosphorus-absorbing hydrogel as well as a preparation method and application thereof. The water-retaining and phosphorus-absorbing hydrogel provided by the application comprises a synthetic polymer hydrogel grafted with cellulose and chitosan and a metal organic framework loaded on the surface and inner surface of holes of the synthetic polymer hydrogel. The synthetic polymer hydrogel comprises a polyacrylic acid hydrogel and / or a polyacrylamide hydrogel. The cellulose and chitosan are grafted on carbon atoms of the synthetic polymer hydrogel through hydroxyl groups, and the water-retaining and phosphorus-absorbing hydrogel has high water-retaining performance, high phosphorus-absorbing performance and is friendly to natural water bodies.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel materials technology, specifically relating to a water-retaining and phosphorus-absorbing hydrogel, its preparation method, and its application. Background Technology

[0002] Currently, large quantities of different types of fertilizers, especially phosphorus-containing fertilizers, are applied to farmland and dissolved in irrigation water. However, this irrigation water flows out of the farmland through osmosis and farmland drainage, eventually ending up in natural water bodies. This not only causes phosphorus fertilizer loss but also leads to a surge in phosphorus concentrations in natural water bodies. Excessively high phosphorus levels in water bodies result in eutrophication and a series of serious ecological and environmental problems.

[0003] Traditional phosphorus removal methods include biological, ecological, and chemical methods. Chemical phosphorus removal methods include crystallization, ion exchange, and chemical adsorption. Chemical phosphorus removal is more efficient and robust than biological phosphorus removal. Among these, chemical adsorption is widely used due to its advantages such as simple operation, high cost-effectiveness, simple procedures, availability of raw materials, and mild treatment conditions. Currently common phosphorus adsorbents include resin adsorbents, carbon-based adsorbents, magnetic metal oxide adsorbents, and metal-organic framework (MOF) adsorbents. However, most phosphorus adsorbents cannot meet the requirements of actual water bodies due to insufficient adsorption performance. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a water-retaining and phosphorus-absorbing hydrogel, its preparation method and application, wherein the water-retaining and phosphorus-absorbing hydrogel has a strong adsorption capacity for phosphorus.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a water-retaining and phosphorus-absorbing hydrogel, comprising a synthetic polymer hydrogel grafted with cellulose and chitosan and a metal-organic framework loaded on the surface of the synthetic polymer hydrogel and the inner surface of its pores.

[0007] The polymeric hydrogel includes polyacrylic acid hydrogel and / or polyacrylamide hydrogel;

[0008] The cellulose and chitosan are grafted onto the carbon atoms of the synthetic polymer hydrogel via hydroxyl groups.

[0009] Preferably, the cellulose is microcrystalline cellulose; the metal-organic framework is one or more of the MIL series and ZIL series.

[0010] Preferably, the water-retaining and phosphorus-absorbing hydrogel contains 80-86% synthetic polymer hydrogel, 1.8-6.7% cellulose, 1.8-6.7% chitosan, and 5-10% metal-organic framework.

[0011] This invention also provides a method for preparing the water-retaining and phosphorus-absorbing hydrogel described in the above technical solution, comprising the following steps:

[0012] Chitosan solution, cellulose solution, metal-organic framework, organic monomer containing carbon-carbon double bonds, crosslinking agent and free radical initiator are mixed, and the resulting mixture is subjected to crosslinking polymerization reaction to obtain the water-retaining and phosphorus-absorbing hydrogel.

[0013] The organic monomers containing carbon-carbon double bonds include acrylic acid and / or acrylamide.

[0014] Preferably, the free radical initiator is ammonium persulfate.

[0015] Preferably, the crosslinking agent is 2-mercaptobenzoic acid and / or N,N'-methylenebisacrylamide.

[0016] Preferably, the temperature of the crosslinking polymerization reaction is 50–70°C; and the time of the crosslinking polymerization reaction is 3–5 hours.

[0017] The present invention also provides the application of the water-retaining and phosphorus-absorbing hydrogel described in the above technical solution or the water-retaining and phosphorus-absorbing hydrogel prepared by the preparation method described in the above technical solution in water absorption and phosphorus absorption.

[0018] The present invention also provides a method for removing phosphorus from water, comprising the following steps: adding a phosphorus adsorbent to the water for adsorption;

[0019] The phosphorus adsorbent is the water-retaining and phosphorus-absorbing hydrogel described in the above technical solution or the water-retaining and phosphorus-absorbing hydrogel prepared by the preparation method described in the above technical solution.

[0020] Preferably, the phosphorus concentration in the water body is 5–400 mg / L; and the dosage of the phosphorus adsorbent in the water body is 0.02–1 g / L.

[0021] This invention provides a water-retaining and phosphorus-absorbing hydrogel, comprising a synthetic polymeric hydrogel grafted with cellulose and chitosan, and a metal-organic framework supported on the surface and inner pore surfaces of the synthetic polymeric hydrogel; the polymeric hydrogel includes polyacrylic acid hydrogel and / or polyacrylamide hydrogel; the cellulose and chitosan are grafted onto the carbon atoms of the synthetic polymeric hydrogel via hydroxyl groups. The water-retaining and phosphorus-absorbing hydrogel provided by this invention has a network porous structure. Water molecules hydrate with carboxylic acid ions dissociated from the network structure, creating strong osmotic pressure, thereby giving the hydrogel a strong water absorption capacity. The grafting of chitosan and cellulose increases the number of oxygen-containing functional groups (such as hydroxyl groups), which can coordinate with phosphorus and selectively adsorb phosphorus. The numerous amino groups in the chitosan structure can perform ion exchange adsorption of phosphorus, thereby increasing the amount of phosphorus adsorbed. The water-retaining and phosphorus-absorbing hydrogel provided by this invention has high water absorption and high phosphorus adsorption performance. It is friendly to natural water bodies. Within the pH range of natural water bodies (6-8), its phosphorus absorption and water absorption performance remain almost unchanged. It can be used as a reference material for water and phosphorus regulation in agricultural ecosystems. Attached Figure Description

[0022] Figure 1 Characterization diagrams of the biomass-supported MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1.

[0023] Figure 2 FTIR and thermogravimetric analysis results of the biomass-supported MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1.

[0024] Figure 3 XPS spectra of C1s (a), O1s (b), and N1s (c) of the hydrogel (CMP) loaded with MIL-100 (Fe) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1, and the Fe2p XPS spectrum (d) of F-CMP.

[0025] Figure 4 Phosphorus adsorption results of the biomass-supported MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) prepared in Example 1 for different phosphorus concentrations;

[0026] Figure 5 A comparison of phosphorus adsorption results in a 100 mg / L phosphorus solution between the biomass-supported MIL-100 (Fe) hydrogel (F-CMP) prepared in Example 1 and the hydrogel (CMP) in Comparative Example 1.

[0027] Figure 6The water absorption properties (b) and water stability (c) of the biomass-loaded MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) prepared in Example 1 are shown. Detailed Implementation

[0028] This invention provides a water-retaining and phosphorus-absorbing hydrogel, comprising a synthetic polymer hydrogel grafted with cellulose and chitosan and a metal-organic framework loaded on the surface of the synthetic polymer hydrogel and the inner surface of its pores.

[0029] The polymeric hydrogel includes polyacrylic acid hydrogel and / or polyacrylamide hydrogel;

[0030] The cellulose and chitosan are grafted onto the carbon atoms of the synthetic polymer hydrogel via hydroxyl groups.

[0031] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0032] In one embodiment, the polymeric hydrogel includes polyacrylic acid hydrogel and / or polyacrylamide hydrogel, with polyacrylamide hydrogel being a specific example; the cellulose is microcrystalline cellulose; the metal-organic framework is one or more of the MIL series and ZIL series, with MIL-100(Fe) being a specific example. Metal ions such as Fe or Al can act as coordinating atoms in the metal-organic framework. Fe is chosen as a coordinating atom because its Fe-O bond can adsorb phosphorus, and Fe has a relatively small environmental impact.

[0033] In one embodiment, the mass percentage of the synthetic polymer hydrogel in the water-retaining and phosphorus-absorbing hydrogel is 80-86%, specifically 80-85% in this embodiment; the mass percentage of cellulose is 1.8-6.7%, specifically 2-5% in this embodiment; the mass percentage of chitosan is 1.8-6.7%, specifically 2-5% in this embodiment; and the mass percentage of the metal-organic framework is 5-10%, specifically 6-8% in this embodiment.

[0034] In one embodiment, the water absorption rate of the water-retaining and phosphorus-absorbing hydrogel is 100-200 g / g, specifically 150-190 g / g in this embodiment, and the phosphorus adsorption capacity is 90-170 mg / g, specifically 120-160 mg / g in this embodiment.

[0035] Polyacrylamide can absorb water molecules and undergo a hydration reaction with the polar groups (such as carboxyl groups) of the cross-linked polymer, causing the polymer chains to extend and the entire network structure to expand. Water molecules hydrate with carboxylic acid ions dissociated from the network structure, creating strong osmotic pressure, thus giving polyacrylamide a strong water absorption capacity. Grafting chitosan and cellulose adds a large number of oxygen-containing functional groups (such as hydroxyl groups). These oxygen-containing functional groups can coordinate with phosphorus, selectively adsorbing it. Furthermore, polyacrylamide and chitosan structures contain a large number of amino groups, and since amino groups do not participate in the synthesis reaction during polymerization and grafting, they can perform ion exchange adsorption of phosphorus. MIL-100(Fe) can adsorb phosphorus through the coordination of oxygen-containing groups with phosphorus and through ligand exchange to form Fe-OP.

[0036] This invention also provides a method for preparing the water-retaining and phosphorus-absorbing hydrogel described in the above technical solution, comprising the following steps:

[0037] Chitosan solution, cellulose solution, metal-organic framework, organic monomer containing carbon-carbon double bonds, crosslinking agent and free radical initiator are mixed, and the resulting mixture is subjected to crosslinking polymerization reaction to obtain the water-retaining and phosphorus-absorbing hydrogel.

[0038] The organic monomers containing carbon-carbon double bonds include acrylic acid and / or acrylamide.

[0039] In one embodiment, the concentration of chitosan in the chitosan solution is 2.5–10 g / L, specifically 3–5 g / L in this embodiment; the chitosan solution is prepared by mixing chitosan and an acidic solution and stirring to dissolve them; the acidic solution includes one or more of acetic acid solution, formic acid solution, and ionic liquid solution, specifically acetic acid solution in this embodiment; the mass concentration of the acidic solution is 1–5%, specifically 2–3% in this embodiment; the stirring speed is 100–500 rpm, specifically 200–300 rpm in this embodiment; the stirring time is 10–20 min, specifically 15 min in this embodiment; the stirring device is a magnetic stirrer.

[0040] In one embodiment, the concentration of cellulose in the cellulose solution is 2.5–10 g / L, specifically 3–5 g / L in this embodiment. The cellulose solution is prepared by mixing cellulose and a solvent system and then refrigerating the mixture. The solvent system is a NaOH / urea / aqueous solution. The mass ratio of NaOH, urea, and water in the NaOH / urea / aqueous solution is 1:1–3:8–16, or 1:1.5–2:10–15 in another embodiment, specifically 7:12:81 in this embodiment. The refrigeration temperature is -4°C, and the refrigeration time is 20–60 min, specifically 30–40 min in this embodiment. The NaOH / urea / aqueous solution can effectively dissolve cellulose.

[0041] As one embodiment, the preparation method of the metal-organic framework includes the following steps: mixing a metal salt, an organic ligand, and water; subjecting the resulting mixture to a hydrothermal reaction; washing and drying the solid obtained after solid-liquid separation to obtain the metal-organic framework; the metal salt is ferric nitrate nonahydrate and / or aluminum chloride hexahydrate, specifically ferric nitrate nonahydrate in this embodiment; the organic ligand is 1,3,5-pyromellitic acid; the molar ratio of the metal salt to the organic ligand is 1-3:1-4, another embodiment is 1.2-2:1-2, specifically 7.4:9.6 or 12.4:9.6 in this embodiment; the mass ratio of the metal salt to water is 2-5:100, specifically 3-4:100 in this embodiment; the mixing is carried out under stirring conditions; the stirring rate is 100-300 rpm, specifically 150-200 rpm in this embodiment; the stirring time is 1 minute. The hydrothermal reaction time is 0–20 min, specifically 15 min in this embodiment; the hydrothermal reaction temperature is 150–170 °C, specifically 155–160 °C in this embodiment; the hydrothermal reaction time is 12–20 h, specifically 14–16 h in this embodiment; the hydrothermal reaction is carried out under stirring conditions; the stirring speed is 100–300 rpm, specifically 150–200 rpm in this embodiment; the solid-liquid separation is vacuum filtration; the equipment used for vacuum filtration is a vacuum filter; the washing involves sequentially rinsing with deionized water and rinsing with alcohol; the number of times the deionized water is rinsed is 2–5 times, specifically 3–4 times in this embodiment; the number of times the alcohol is rinsed is 2–5 times, specifically 3–4 times in this embodiment; the drying temperature is 60–80 °C, specifically 60–70 °C in this embodiment; the drying time is 1–3 days, specifically 2 days in this embodiment.

[0042] In one embodiment, the organic monomer containing carbon-carbon double bonds includes acrylic acid and / or acrylamide, with acrylamide being a specific example; the free radical initiator is ammonium persulfate; and the crosslinking agent is 2-mercaptobenzoic acid (MBA) and / or N,N'-methylenebisacrylamide, with N,N'-methylenebisacrylamide being a specific example.

[0043] Under the action of free radical initiators, organic monomers polymerize to form organic polymers as hydrogel matrices. Crosslinking agents can crosslink long chains of organic polymers. After crosslinking, the long chains of organic polymers are linked together to form a three-dimensional structure, forming a network pore structure, which improves the porosity and specific surface area of ​​the water-retaining and phosphorus-absorbing hydrogel, thereby increasing its water absorption rate and phosphorus adsorption capacity.

[0044] In one embodiment, the mass ratio of chitosan in the chitosan solution to cellulose in the cellulose solution is 2.5–10:2.5–10, another embodiment is 3–5:3–5, and a specific embodiment is 1:1; the mass ratio of chitosan to metal-organic framework in the chitosan solution is 0.075–0.3:1, and a specific embodiment is 0.1–0.3:1; the mass ratio of chitosan to organic monomer in the chitosan solution is 0.075–0.3:10–16, another embodiment is 0.2–0.3:10–16, and a specific embodiment is 0.3:12–13; the mass ratio of crosslinking agent to organic monomer is 0.02–0.06:10–16, and a specific embodiment is 0.03–0.06:12–13; the mass ratio of free radical initiator to organic monomer is 0.02–0.06:10–16, and a specific embodiment is 0.03–0.06:12–13.

[0045] In one embodiment, chitosan solution, cellulose solution, metal-organic framework, organic monomer containing carbon-carbon double bonds, crosslinking agent, and free radical initiator are mixed as follows: After a first mixing of chitosan solution and metal-organic framework, cellulose solution is added for a second mixing; then a free radical initiator is added for a third mixing; then an organic monomer containing carbon-carbon double bonds is added for a fourth mixing; and finally, a crosslinking agent is added for a fifth mixing. The first, second, third, fourth, and fifth mixing processes are carried out under stirring conditions; the stirring is magnetic stirring; the stirring speed is 400–600 rpm, specifically 500 rpm in this embodiment; the present invention does not have a special limitation on the stirring time, as long as it is sufficient to achieve uniform stirring.

[0046] In one embodiment, the temperature of the crosslinking polymerization reaction is 50-70°C, and in a specific embodiment it is 60°C; the time of the crosslinking polymerization reaction is 3-5 hours, and in a specific embodiment it is 4 hours; the crosslinking polymerization reaction is carried out under water bath heating.

[0047] The purpose of water bath heating is to create the necessary chemical conditions for the cross-linking polymerization reaction. During the stirring process, the synthesized polymer hydrogel has already undergone a free radical cross-linking polymerization reaction through the free radical initiator. The addition of the cross-linking agent enables the chain-like polymer to link together to form a three-dimensional network structure, thereby forming the final product.

[0048] In one embodiment, after the crosslinking polymerization reaction, the process further includes: solid-liquid separation of the product obtained from the crosslinking polymerization reaction; washing the obtained solid and then sequentially freezing and vacuum freeze-drying; the washing is performed by rinsing with deionized water; the freezing temperature is -28 to -56°C, specifically -28°C in this embodiment; the freezing time is 24 to 48 hours, specifically 48 hours in this embodiment; the vacuum freeze-drying temperature is -10 to -66.5°C, specifically -30 to -66.5°C in this embodiment; the vacuum freeze-drying pressure is 10 to 30 Pa, specifically 15 to 30 Pa in this embodiment; and the vacuum freeze-drying time is 1 to 3 days, specifically 2 days in this embodiment.

[0049] This invention utilizes a graft copolymerization method to link twin materials (cellulose and chitosan) at the ends of an organic polymer, forming a double-grafted framework. Cellulose and chitosan can provide a large number of hydroxyl and amino groups to adsorb phosphorus, and the twin material solutions have opposite acidity and alkalinity, allowing them to precipitate simultaneously during the blending process, resulting in a more uniform loading of the organic polymer.

[0050] The preparation method provided by this invention has a simple synthesis process, the synthesis conditions are easy to achieve, and the raw materials used are low in cost and readily available on the market.

[0051] The present invention also provides the application of the water-retaining and phosphorus-absorbing hydrogel described in the above technical solution or the water-retaining and phosphorus-absorbing hydrogel prepared by the preparation method described in the above technical solution in water absorption and phosphorus absorption.

[0052] As one implementation method, the water-retaining and phosphorus-absorbing hydrogel is used in water bodies and / or soil for water and phosphorus absorption.

[0053] The present invention also provides a method for removing phosphorus from water, comprising the following steps: adding a phosphorus adsorbent to the water for adsorption;

[0054] The phosphorus adsorbent is the water-retaining and phosphorus-absorbing hydrogel described in the above technical solution or the water-retaining and phosphorus-absorbing hydrogel prepared by the preparation method described in the above technical solution.

[0055] In one embodiment, the phosphorus concentration in the water is 5–400 mg / L, in another embodiment it is 50–400 mg / L, and in a specific embodiment it is 50–200 mg / L; the pH value of the water is 3–11, in another embodiment it is 6–8, and in a specific embodiment it is 7; the dosage of the phosphorus adsorbent in the water is 0.02–1 g / L, in another embodiment it is 0.2–0.8 g / L, and in a specific embodiment it is 0.4–0.8 g / L.

[0056] In one embodiment, the adsorption temperature is 25–45°C, specifically 25–40°C in this embodiment; the adsorption is carried out at room temperature; the adsorption is carried out under oscillation conditions; the oscillation rate is 100–300 rpm, specifically 200 rpm in this embodiment; the adsorption time is 12–36 h, specifically 24 h in this embodiment.

[0057] In one embodiment, after adsorption, the process further includes: separating the adsorbed water into solid and liquid phases to obtain a phosphorus adsorbent; the solid-liquid separation is performed by filtration; and the filtration is carried out using a 0.45 μm filter membrane.

[0058] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0059] The N,N-methylenebisacrylamide used in the following examples was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd.; microcrystalline cellulose, chitosan, and urea were purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium hydroxide and 1,3,5-benzenetricarboxylic acid were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; ferric nitrate nonahydrate, acrylic acid, ammonium persulfate, and other materials were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; and N,N-methyleneacrylamide, acrylic acid, and other materials were purchased from Xi'an Chemical Reagent Factory, China. All chemical reagents were analytical grade and did not require further purification before use.

[0060] Example 1

[0061] Preparation of MIL-100(Fe): 3g of ferric nitrate nonahydrate and 2.01g of 1,3,5-pyromellitic acid were dissolved together in 100g of water. After stirring at 200rpm for 15min, the mixture was subjected to hydrothermal reaction at 160℃ and 200rpm for 16h in a micro reactor. After the reaction, the mixture was filtered by a vacuum filter, washed 3 times with deionized water, rinsed 3 times with alcohol, and dried at 60℃ for 2d.

[0062] Preparation of chitosan solution: Add 1g of chitosan to 100mL of 1wt% acetic acid solution and stir at 500rpm for 15min on a magnetic stirrer to dissolve, so as to obtain a 10g / L chitosan solution.

[0063] Preparation of microcrystalline cellulose solution: Add 1g of microcrystalline cellulose to 100mL of NaOH / urea / water solution with a mass ratio of 7:12:81, and refrigerate at -4℃ for 30min until the solution is completely clear to obtain a 10g / L microcrystalline cellulose solution.

[0064] Measure 30 mL of the above chitosan solution and add 1 g of MIL-100(Fe). Stir evenly on a magnetic stirrer at 500 rpm. Then add 30 mL of the above microcrystalline cellulose solution and stir evenly. Add 0.06 g of ammonium persulfate and stir for 0.5 h. Add 12 mL (1.02 g / mL) of acrylamide and stir for 0.5 h. Add 0.06 g of N,N′-methylenebisacrylamide and stir for 1 h. Then place it in a mold and heat it in a water bath at 60 °C for 4 h. After molding, rinse the surface impurities with deionized water and freeze it in a freezer at -28 °C for 48 h. Then freeze-dry it in a freeze dryer at 30 Pa and -66.5 °C for 2 days to obtain a water-retaining and phosphorus-absorbing hydrogel (F-CMP) loaded with bimethane and MIL-100(Fe).

[0065] Example 2

[0066] The difference from Example 1 is that the acrylamide is replaced with 12g of granular acrylamide, and the rest is the same as in Example 1.

[0067] Example 3

[0068] The difference from Example 1 is that ferric nitrate nonahydrate is replaced with aluminum chloride hexahydrate, and the rest is the same as in Example 1.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that MIL-100(Fe) was not added, but the rest is the same as in Example 1. The resulting hydrogel is denoted as CMP.

[0071] Comparative Example 2

[0072] The difference from Example 1 is that microcrystalline cellulose was not added; otherwise, the contents are the same as in Example 1.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that chitosan was not added; all other contents are the same as in Example 1.

[0075] Comparative Example 4

[0076] The difference from Example 1 is that microcrystalline cellulose and chitosan were not added, but the rest of the contents are the same as in Example 1.

[0077] Application Example 1

[0078] Weigh 0.02 g of the biomass-loaded MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) prepared in Example 1, add it to a 100 mL centrifuge tube containing 50 mL of 100 mg / L phosphorus solution, adjust the pH to 7, shake in a shaker at 25 °C and 200 rpm for 24 h, and then filter it through a 0.45 μm filter membrane to obtain phosphorus-adsorbed F-CMP.

[0079] Comparative Application Example 1

[0080] The difference from Application Example 1 is that the biomass-loaded MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) in Application Example 1 is replaced with the hydrogel (CMP) of Comparative Example 1. All other contents are the same as Application Example 1.

[0081] Performance testing

[0082] (1) The water-retaining and phosphorus-absorbing hydrogel (F-CMP) of bicellular biomass-loaded MIL-100(Fe) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1 were characterized by SEM electron microscopy. The results are as follows: Figure 1 As shown, (a) is a scanning electron microscope (SEM) image of the hydrogel CMP of Comparative Example 1 at 100 μm, (b) is a scanning electron microscope (SEM) image of the F-CMP of Example 1 at 100 μm, (c) is a scanning electron microscope (SEM) image of the CMP of Comparative Example 1 at 30 μm, (d) is a scanning electron microscope (SEM) image of the F-CMP of Example 1 at 30 μm, (e) is a scanning electron microscope (SEM) image of the F-CMP of Example 1 after phosphorus adsorption at 100 μm, and (f) to (j) are EDS surface scan analysis images of the F-CMP of Example 1, where (f) corresponds to the SEM mapping image of the surface scan analysis, (g) corresponds to the EDS surface scan C element distribution image, (h) corresponds to the EDS surface scan N element distribution image, (i) corresponds to the EDS surface scan O element distribution image, and (j) corresponds to the EDS surface scan Fe element distribution image.

[0083] Depend on Figure 1 In (a), it can be observed that the surface of CMP material is relatively flat and no porous structure is observed.

[0084] Depend on Figure 1 In (b), it can be observed that the F-CMP surface is rough and the pore structure is unevenly distributed. The overall structure is a spherical mesoporous structure. The material surface is rough, and crystalline substances are attached to the macropores and the material surface. Small pores also appear inside the pores, which are also attached with crystals. This crystallization may be due to the presence of MIL-100(Fe) on the material surface through loading.

[0085] Depend on Figure 1 As can be observed in (c), the CMP surface remains a smooth surface even at higher magnifications.

[0086] Depend on Figure 1 In the middle (d) image, more crystals and a more pronounced pore structure can be observed on the F-CMP surface.

[0087] Depend on Figure 1 As can be observed in (e), after F-CMP adsorbs phosphorus, most of the pore structures on its surface are blocked, and the crystalline substances are either covered or disappear.

[0088] Depend on Figure 1 As can be observed in (f) to (j), based on the image structure of F-CMP, the distribution of C, N, and O elements is closely related to the F-CMP structure. The distribution of Fe in F-CMP is also mainly on the surface, but not related to the distribution of C, N, and O. This verifies that the addition of MIL-100 (Fe) is mainly due to free loading.

[0089] (2) FTIR and thermogravimetric analyses were performed on the biomass-supported MIL-100(Fe) hydrogel (F-CMP) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1. The results are as follows: Figure 2 As shown, (a) is the FTIR result of F-CMP and CMP, and (b) is the TG curve and TGA curve of F-CMP obtained by thermogravimetric analysis.

[0090] according to Figure 2 The Fourier transform infrared (FTIR) spectrum shown in (a) reveals that the overall functional groups showed significant variation after loading MIL-100(Fe), but the absorption peak positions did not change much. This may be because the hygroscopic nature of F-CMP causes water absorption on the sample surface before detection, which reduces the sample detection sensitivity but does not affect the analytical results. Figure 2 The FTIR result shown in (a) can be interpreted as the tensile vibration of OH and NH, 2913 cm. -1 and 2856cm -1 The absorption peak at 1551 cm⁻¹ represents both asymmetric and symmetric stretching of CH₄. -1 The vibration of the C=O bond in the carboxyl salt group is 1625 cm⁻¹. -1 The bending vibration of -NH2, 1404 cm -1 1246cm -1 The peak at 1166 cm⁻¹ is attributed to the bending and tensile vibrations of CN, which proves that chitosan has been successfully incorporated into the material. -1 The absorption peak at 1060 cm⁻¹ can be interpreted as the bending vibration of CO. -1 The peak at 460 cm⁻¹ is due to the C-OH absorption of cellulose and chitosan. The material's F-CMP peak is at 460 cm⁻¹. -1 and 490cm -1Weak characteristic peaks of MIL-100 (Fe) were identified at 759 cm⁻¹, mainly due to the stretching of Fe-O. -1 and 711cm -1 The observation of CH bending vibration of the benzene ring indicates that MIL-100(Fe) was successfully loaded onto the surface of the composite material, but the low Fe content resulted in a low peak intensity at this location. The CMP material itself exhibits a peak intensity at 3358 cm⁻¹. -1 There are a large number of OH absorption peaks at the surface, but after adding MIL-100(Fe), the OH absorption peaks are significantly reduced. This may be because the addition of MIL-100(Fe) occupies a large number of hydroxyl groups on chitosan and cellulose. This also indicates that MIL-100(Fe) is loaded on the surface of the composite material by binding with hydroxyl groups.

[0091] Depend on Figure 2 As shown in (b), to further investigate the material composition of F-CMP, its thermal stability was tested using the TG method. The weight loss process of F-CMP can be divided into four stages. Specifically, the first stage is within 469K, mainly due to the material's strong water absorption properties, which can capture moisture in the air. The moisture evaporates upon heating, resulting in a weight loss of 80%. The second stage is from 469K to 614K, where cellulose and chitosan mainly decompose at high temperatures. This may be due to the breakage of C-C bonds and the decomposition of -COOH, -OH, and other groups on the cellulose chain. The weight loss in this stage is 56%. In the third stage, from 614K to 801K, the weight loss is likely caused by the thermal decomposition of the polymer backbone or cross-linked structure that forms the main matrix. The weight loss in this process is 33%. The fourth stage is after 801K, where the mass loss slows down, mainly because the remaining material after structural decomposition is mainly iron oxide, which has high thermal stability.

[0092] (3) Figure 3 XPS spectra of C1s (a), O1s (b), and N1s (c) of the biomass-loaded MIL-100 (Fe) hydrogel (F-CMP) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1, and the Fe2p XPS spectrum (d) of F-CMP.

[0093] Depend on Figure 3 As can be seen, X-ray photoelectron spectroscopy (XPS) can be used to determine information about individual elements, atomic composition, and valence states. The Fe element content is relatively low, and the Fe 2p peak intensity variation is only about 2.5E+3 counts / s. Compared to the C1s and O1s peaks, the Fe 2p peak has poor visibility in the overall spectrum.

[0094] The XPS elemental fine spectrum was analyzed, and charge calibration was performed using the carbon peak at 284.8 eV. Figure 3In (a), it can be confirmed that the C1s spectra of both CMP and F-CMP show CC / CH (284.8 eV), COC / CN (285.88 eV or 285.91 eV), and CO=C (288.89 eV and 288.57 eV). Figure 3 In (c), it can be confirmed that quaternary ammonium salt peaks (399.86 eV and 399.79 eV) appeared in the N1s spectrum, which also proves that chitosan was successfully incorporated into the material. Figure 3 In (b), the O1s spectra of both materials show CO (532.10 eV) and C=O (533.6 eV). However, the peak intensity of C=O at 533.60 eV is significantly increased in the F-CMP material. This is because the pyromellitic acid in MIL-100(Fe) contains a large number of carboxyl groups. Furthermore, analysis of the fine spectrum of Fe in the F-CMP material... Figure 3 In the middle (d) spectrum, the Fe2p fine spectrum shows two peaks at 710.34 eV and 723.11 eV, respectively, corresponding to Fe2p. 1 / 2 [Fe(III)], Fe2p 3 / 2 [Fe(III)], and two satellite peaks of Fe2p appeared at 717.04 and 731.26 eV, indicating that MIL-100(Fe) was successfully loaded into the material.

[0095] (4) Phosphorus adsorption test:

[0096] All adsorption experiments were conducted in 100 mL centrifuge tubes. 0.02 g of adsorbent (the biomass-supported MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1) was weighed and added to a 100 mL centrifuge tube containing 50 mL of phosphorus solution. The adsorption capacity was measured at different phosphorus concentrations (50–400 mg / L). The pH was adjusted to 7, and the mixture was shaken at 25°C and 200 rpm for 24 h. The mixture was then filtered through a 0.45 μm filter membrane. Phosphorus adsorption was determined using the molybdenum-antimony spectrophotometric method. The absorbance was measured at 770 nm using a UV spectrophotometer, and the results were calculated. The phosphorus adsorption results of F-CMP at different phosphorus concentrations are shown below. Figure 4 As shown, the comparison results of phosphorus adsorption of F-CMP and CMP in 100 mg / L phosphorus solution are as follows: Figure 5 As shown.

[0097] Depend on Figure 4 It can be seen that the phosphorus adsorption performance ranges from 93.33 mg / g at low concentrations to 140.5 mg / g at high concentrations, with the phosphorus removal rate at low concentrations being approximately 75%.

[0098] As Figure 5As shown, F-CMP exhibits certain adsorption capacity for phosphorus, reaching a maximum of 116.94 mg / g. CMP's phosphorus adsorption capacity is only 74.36 mg / g, while F-CMP's adsorption capacity is enhanced to 116.94 mg / g. The addition of MIL-100(Fe) increases the phosphorus adsorption capacity of the CMP material by nearly 50%.

[0099] (5) Swelling rate test: water absorption performance test

[0100] At room temperature, weigh 0.5 g (m1, g) of the dried sample (the biomass-supported MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) prepared in Example 1) into a clean beaker. Add 800 mL of distilled water to the 1 L beaker and let it stand for 24 h to reach water absorption equilibrium. Remove the water-absorbed sample and filter out excess water through a 100-mesh sieve. Weigh the mass of the water-absorbed sample (m2, g). Perform three parallel measurements and take the average value. Calculate the water absorption ratio (Qeq, g / g) according to formula (1).

[0101] Qeq=(m2-m1) / m1 (1)

[0102] Through swelling tests, F-CMP showed an adsorption capacity of up to 199.20 g / g for water. The water adsorption process transformed the initial state from a blocky, hard material into a gel-like substance after 24 hours. The actual effect was as follows... Figure 6 (b)

[0103] Water stability test:

[0104] Weigh 0.5 g of adsorbent (the biomass-supported MIL-100(Fe) water-retaining and phosphorus-absorbing hydrogel (F-CMP) prepared in Example 1), immerse it in a beaker containing 800 mL of distilled water, and observe its structural state monthly. Figure 6 As shown in (c), the gel remained stable after 60 days without disintegration.

[0105] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A water-retaining and phosphorus-absorbing hydrogel, characterized in that, The preparation method of the water-retaining and phosphorus-absorbing hydrogel includes the following steps: Preparation of MIL-100(Fe): 3g of ferric nitrate nonahydrate and 2.01g of 1,3,5-pyromellitic acid were dissolved together in 100g of water. After stirring at 200rpm for 15min, the mixture was subjected to hydrothermal reaction at 160℃ and 200rpm for 16h in a micro reactor. After the reaction, the mixture was filtered by a vacuum filter, washed 3 times with deionized water, rinsed 3 times with alcohol, and dried at 60℃ for 2d. Preparation of chitosan solution: Add 1g of chitosan to 100mL of 1wt% acetic acid solution and stir at 500rpm for 15min on a magnetic stirrer to dissolve, so as to obtain a 10g / L chitosan solution. Preparation of microcrystalline cellulose solution: Add 1g of microcrystalline cellulose to 100mL of NaOH / urea / water solution with a mass ratio of 7:12:81, and refrigerate at -4℃ for 30min until the solution is completely clear to obtain a 10g / L microcrystalline cellulose solution. Measure 30 mL of the above chitosan solution and add 1 g of MIL-100(Fe). Stir evenly on a magnetic stirrer at 500 rpm. Then add 30 mL of the above microcrystalline cellulose solution and stir evenly. Add 0.06 g of ammonium persulfate and stir for 0.5 h. Add 12 mL of 1.02 g / mL acrylamide and stir for 0.5 h. Add 0.06 g of N,N′-methylenebisacrylamide and stir for 1 h. Then place in a mold and heat in a water bath at 60 °C for 4 h. After molding, rinse the surface impurities with deionized water and freeze in a -28 °C freezer for 48 h. Then freeze-dry in a freeze dryer at 30 Pa and -66.5 °C for 2 days to obtain a water-retaining and phosphorus-absorbing hydrogel loaded with bicellular biomass and MIL-100(Fe).

2. The application of the water-retaining and phosphorus-absorbing hydrogel according to claim 1 in water and phosphorus absorption.

3. A method for phosphorus removal from water, characterized in that, Includes the following steps: Phosphorus adsorbents are added to water for adsorption; The phosphorus adsorbent is the water-retaining and phosphorus-absorbing hydrogel as described in claim 1.

4. The method according to claim 3, characterized in that, The phosphorus concentration in the water body is 5~400 mg / L; the dosage of the phosphorus adsorbent in the water body is 0.02~1 g / L.

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