Water-retaining phosphorus-absorbing hydrogel as well as preparation method and application thereof

Abstract

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

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogel materials, and particularly relates to a water-retaining and phosphorus-absorbing hydrogel, a preparation method thereof, and an application thereof. Background Art

[0002] At present, different types of chemical fertilizers are largely input into farmland, especially phosphorus-containing chemical fertilizers, which are dissolved in farmland through irrigation water. However, the irrigation water will flow out of the farmland through osmosis and farmland drainage, and finally flow into natural water bodies, resulting in the loss of phosphate fertilizers and a sharp increase in the phosphorus concentration in natural water bodies. Excessive phosphorus content in water bodies will cause eutrophication of water bodies and lead to a series of serious ecological and environmental problems.

[0003] Traditional methods for phosphorus removal include biological phosphorus removal, ecological phosphorus removal, and chemical phosphorus removal, etc. Chemical phosphorus removal methods include crystallization, ion exchange, and chemical adsorption. Chemical phosphorus removal is more efficient and robust than biological phosphorus removal. Among them, the chemical adsorption method is widely used due to its advantages such as simple operation, high cost-effectiveness, simple procedure, 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, a preparation method thereof, and an application thereof, and the water-retaining and phosphorus-absorbing hydrogel has a strong adsorption capacity for phosphorus.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a water-retaining and phosphorus-absorbing hydrogel, which includes a synthetic polymer hydrogel grafted with cellulose and chitosan, and a metal-organic framework loaded on the surface and the inner surface of the pores of the synthetic polymer hydrogel;

[0007] The polymer 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 through hydroxyl groups.

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

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

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

[0012] Mix a chitosan solution, a cellulose solution, a metal-organic framework, an organic monomer containing a carbon-carbon double bond, a crosslinking agent, and a radical initiator, and carry out a crosslinking polymerization reaction on the obtained mixed solution to obtain the water-retaining and phosphorus-absorbing hydrogel;

[0013] The organic monomer containing a carbon-carbon double bond includes acrylic acid and / or acrylamide.

[0014] Preferably, the 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; the time of the crosslinking polymerization reaction is 3-5 h.

[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 in water body, which includes the following steps: adding a phosphorus adsorbent into the water body 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; the dosage of the phosphorus adsorbent in the water body is 0.02-1 g / L.

[0021] The present invention provides a water-retaining and phosphorus-absorbing hydrogel, which comprises a synthetic polymer hydrogel grafted with cellulose and chitosan, and a metal-organic framework loaded on the surface and the inner surface of the pores of the synthetic polymer hydrogel; the polymer hydrogel comprises a polyacrylic acid hydrogel and / or a polyacrylamide hydrogel; the cellulose and chitosan are grafted onto the carbon atoms of the synthetic polymer hydrogel through hydroxyl groups. The water-retaining and phosphorus-absorbing hydrogel provided by the present invention has a reticular pore structure, and water molecules are hydrated with carboxylate ions dissociated in the reticular structure to form a strong internal and external osmotic pressure, so that the water-retaining and phosphorus-absorbing hydrogel has a strong water absorption capacity. The grafting of chitosan and cellulose increases a large number of oxygen-containing functional groups (such as hydroxyl groups), and these oxygen-containing functional groups can coordinate with phosphorus to selectively adsorb phosphorus. A large number of amino groups in the chitosan structure can perform ion-exchange adsorption on P, thereby increasing the adsorption amount of phosphorus. The water-retaining and phosphorus-absorbing hydrogel provided by the present invention has high water absorption performance, high phosphorus adsorption performance, is friendly to natural water bodies, and within the natural water body pH range (6-8), the phosphorus absorption performance and water absorption performance are almost unchanged, and it can be used as a reference material for water and phosphorus regulation in agricultural ecosystems. Description of the Drawings

[0022] Figure 1 Characterization diagrams of the water-retaining and phosphorus-absorbing hydrogel (F-CMP) loaded with dual biopolymers of MIL-100(Fe) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1;

[0023] Figure 2 FTIR and thermogravimetric analysis diagrams of the water-retaining and phosphorus-absorbing hydrogel (F-CMP) loaded with dual biopolymers of MIL-100(Fe) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1;

[0024] Figure 3 C1s (a), O1s (b), N1s (c) XPS spectra diagrams of the water-retaining and phosphorus-absorbing hydrogel (F-CMP) loaded with dual biopolymers of MIL-100(Fe) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1, and Fe2p XPS spectra diagram (d) of F-CMP;

[0025] Figure 4 Phosphorus adsorption result diagrams of the water-retaining and phosphorus-absorbing hydrogel (F-CMP) loaded with dual biopolymers of MIL-100(Fe) prepared in Example 1 at different phosphorus concentrations;

[0026] Figure 5 Phosphorus adsorption comparison result diagrams of the water-retaining and phosphorus-absorbing hydrogel (F-CMP) loaded with dual biopolymers of MIL-100(Fe) prepared in Example 1 and the hydrogel (CMP) of Comparative Example 1 in a 100 mg / L phosphorus solution;

[0027] Figure 6Water absorption performance graph (b) and water stability graph (c) of the water-retaining and phosphorus-adsorbing hydrogel (F-CMP) prepared with dual-biomass-loaded MIL-100(Fe) for Example 1. Detailed implementation manners

[0028] The present invention provides a water-retaining and phosphorus-adsorbing hydrogel, which comprises a synthetic polymer hydrogel grafted with cellulose and chitosan, and a metal-organic framework loaded on the surface and the inner surface of the pores of the synthetic polymer hydrogel;

[0029] The polymer hydrogel comprises a polyacrylic acid hydrogel and / or a polyacrylamide hydrogel;

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

[0031] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used, and commercially available products well-known to those skilled in the art can be adopted.

[0032] As an implementation manner, the polymer hydrogel comprises a polyacrylic acid hydrogel and / or a polyacrylamide hydrogel, specifically a polyacrylamide hydrogel in specific embodiments; the cellulose is microcrystalline cellulose; the metal-organic framework is one or more of the MIL series and the ZIL series, specifically MIL-100(Fe) in specific embodiments. Metal ions such as Fe or Al can act as coordination atoms of the metal-organic framework. The reason for Fe to be used as a coordination atom is that its Fe-O bond can adsorb phosphorus, and Fe has less impact on the environment.

[0033] As an implementation manner, the mass percentage content of the synthetic polymer hydrogel in the water-retaining and phosphorus-adsorbing hydrogel is 80-86%, specifically 80-85% in specific embodiments, the mass percentage content of cellulose is 1.8-6.7%, specifically 2-5% in specific embodiments, the mass percentage content of chitosan is 1.8-6.7%, specifically 2-5% in specific embodiments, and the mass percentage content of the metal-organic framework is 5-10%, specifically 6-8% in specific embodiments.

[0034] As an implementation manner, the water absorption rate of the water-retaining and phosphorus-adsorbing hydrogel is 100-200 g / g, specifically 150-190 g / g in specific embodiments, and the phosphorus adsorption amount is 90-170 mg / g, specifically 120-160 mg / g in specific embodiments.

[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 stretch and leading to the expansion of the entire network structure; the water molecules hydrate with the carboxylic acid ions dissociated in the network structure, constituting a strong internal and external osmotic pressure, thereby endowing polyacrylamide with strong water absorption capacity. The grafting of chitosan and cellulose adds a large number of oxygen-containing functional groups (such as hydroxyl groups), and these oxygen-containing functional groups can coordinate with phosphorus for selective adsorption of phosphorus. In addition, there are a large number of amino groups in the structures of polyacrylamide and chitosan, and the amino groups do not participate in the synthesis reaction during polymerization and grafting, so the amino groups can perform ion exchange adsorption on P. MIL-100(Fe) can adsorb phosphorus through the coordination of oxygen-containing groups with P and the formation of Fe-O-P through ligand exchange.

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

[0037] Mix a chitosan solution, a cellulose solution, a metal-organic framework, an organic monomer containing a carbon-carbon double bond, a cross-linking agent, and a radical initiator, and subject the obtained mixture to a cross-linking polymerization reaction to obtain the water-retaining and phosphorus-absorbing hydrogel;

[0038] The organic monomer containing a carbon-carbon double bond includes acrylic acid and / or acrylamide.

[0039] As an implementation manner, the concentration of chitosan in the chitosan solution is 2.5 - 10 g / L, and in specific embodiments, it is 3 - 5 g / L; the preparation method of the chitosan solution is: mix chitosan and an acidic solution, and stir to dissolve; the acidic solution includes one or more of acetic acid solution, formic acid solution, and ionic liquid solution, and in specific embodiments, it is acetic acid solution; the mass concentration of the acidic solution is 1 - 5%, and in specific embodiments, it is 2 - 3%; the rotation speed of the stirring is 100 - 500 rpm, and in specific embodiments, it is 200 - 300 rpm; the stirring time is 10 - 20 min, and in specific embodiments, it is 15 min; the stirring device is a magnetic stirrer.

[0040] As an implementation manner, the concentration of cellulose in the cellulose solution is 2.5 - 10 g / L, and in specific embodiments, it is 3 - 5 g / L; the preparation method of the cellulose solution is: mix cellulose and a solvent system, and refrigerate; the solvent system is NaOH / urea / aqueous solution; the mass ratio of NaOH, urea, and water in the NaOH / urea / aqueous solution is 1:1 - 3:8 - 16, and another implementation manner is 1:1.5 - 2:10 - 15, and in specific embodiments, it is 7:12:81; the refrigeration temperature is -4°C; the refrigeration time is 20 - 60 min, and in specific embodiments, it is 30 - 40 min. The NaOH / urea / aqueous solution can dissolve cellulose well.

[0041] As an implementation manner, the preparation method of the metal-organic framework includes the following steps: mixing a metal salt, an organic ligand, and water, subjecting the obtained mixed solution to a hydrothermal reaction, washing the solid obtained by solid-liquid separation, and then drying to obtain the metal-organic framework; the metal salt is ferric nitrate nonahydrate and / or aluminum chloride hexahydrate, specifically ferric nitrate nonahydrate in a specific embodiment; the organic ligand is 1,3,5-benzenetricarboxylic acid; the molar ratio of the metal salt to the organic ligand is 1 to 3:1 to 4, another implementation manner is 1.2 to 2:1 to 2, specifically 7.4:9.6 or 12.4:9.6 in a specific embodiment; the mass ratio of the metal salt to water is 2 to 5:100, specifically 3 to 4:100 in a specific embodiment; the mixing is carried out under stirring; the stirring rate is 100 to 300 rpm, specifically 150 to 200 rpm in a specific embodiment; the stirring time is 10 to 20 min, specifically 15 min in a specific embodiment; the temperature of the hydrothermal reaction is 150 to 170 °C, specifically 155 to 160 °C in a specific embodiment; the time of the hydrothermal reaction is 12 to 20 h, specifically 14 to 16 h in a specific embodiment; the hydrothermal reaction is carried out under stirring; the stirring rate is 100 to 300 rpm, specifically 150 to 200 rpm in a specific embodiment; the solid-liquid separation is suction filtration; the equipment used for suction filtration is a suction filter; the washing is sequentially carried out by washing with deionized water and rinsing with alcohol; the number of times of washing with deionized water is 2 to 5 times, specifically 3 to 4 times in a specific embodiment; the number of times of rinsing with alcohol is 2 to 5 times, specifically 3 to 4 times in a specific embodiment; the drying temperature is 60 to 80 °C, specifically 60 to 70 °C in a specific embodiment; the drying time is 1 to 3 d, specifically 2 d in a specific embodiment.

[0042] As an implementation manner, the organic monomer containing a carbon-carbon double bond includes acrylic acid and / or acrylamide, specifically acrylamide in a specific embodiment; the radical initiator is ammonium persulfate; the crosslinking agent is 2-mercaptobenzoic acid (MBA) and / or N,N'-methylenebisacrylamide, specifically N,N'-methylenebisacrylamide in a specific embodiment.

[0043] Under the action of the radical initiator, the organic monomer polymerizes to form an organic polymer as a hydrogel matrix. The crosslinking agent can crosslink the long chains of the organic polymer. After crosslinking, the long chains of the organic polymer are linked together to form a three-dimensional structure, forming a network pore structure, improving the porosity and specific surface area of the water-retaining and phosphorus-adsorbing hydrogel, thereby increasing its water absorption rate and phosphorus adsorption capacity.

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

[0045] As an implementation manner, the chitosan solution, the cellulose solution, the metal-organic framework, the organic monomer containing a carbon-carbon double bond, the crosslinking agent, and the radical initiator are mixed as follows: after the chitosan solution and the metal-organic framework are first mixed, the cellulose solution is added for second mixing, then the radical initiator is added for third mixing, the organic monomer containing a carbon-carbon double bond is added for fourth mixing, and finally the crosslinking agent is added for fifth mixing; the first mixing, the second mixing, the third mixing, the fourth mixing, and the fifth mixing are carried out under stirring; the stirring is magnetic stirring; the stirring rate is 400 to 600 rpm, and in a specific embodiment, it is 500 rpm; the present invention has no special limitation on the stirring time, and it can be stirred evenly.

[0046] As an implementation manner, the temperature of the crosslinking polymerization reaction is 50 to 70 °C, and in a specific embodiment, it is 60 °C; the time of the crosslinking polymerization reaction is 3 to 5 h, and in a specific embodiment, it is 4 h; the crosslinking polymerization reaction is carried out under water bath heating.

[0047] The function of water bath heating is to create the required chemical conditions for the crosslinking polymerization reaction. The synthetic polymer hydrogel has undergone a free radical crosslinking polymerization reaction through the radical initiator during the stirring process. The addition of the crosslinking agent causes the polymer chains with a chain structure to form a three-dimensional network structure, thereby forming the final product.

[0048] As an implementation method, after the cross-linking polymerization reaction, it further includes: separating the solid and liquid of the product obtained from the cross-linking polymerization reaction, washing the obtained solid, and then performing freezing and vacuum freeze-drying in sequence; the washing is rinsing with deionized water; the temperature of the freezing is -28 to -56 °C, specifically -28 °C in a specific embodiment; the time of the freezing is 24 to 48 h, specifically 48 h in a specific embodiment; the temperature of the vacuum freeze-drying is -10 to -66.5 °C, specifically -30 to -66.5 °C in a specific embodiment; the pressure of the vacuum freeze-drying is 10 to 30 Pa, specifically 15 to 30 Pa in a specific embodiment; the time of the vacuum freeze-drying is 1 to 3 days, specifically 2 days in a specific embodiment.

[0049] The present invention uses the method of graft copolymerization to link double biopolymers (cellulose, chitosan) at the end of the organic polymer to form a double grafted skeleton; cellulose and chitosan can provide a large number of hydroxyl groups and amino groups to adsorb phosphorus, and the acid-base properties of the double biopolymer solutions are exactly opposite, and they can precipitate synchronously during the blending process, making the loading of the organic polymer more uniform.

[0050] The preparation method provided by the present invention has a simple synthesis process, easy-to-achieve synthesis conditions, and low cost of raw materials used, which can be purchased on the market.

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

[0052] As an implementation method, the application fields of the water-retaining phosphorus-absorbing hydrogel in water absorption and phosphorus absorption include water bodies and / or soil.

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

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

[0055] As an implementation method, the phosphorus concentration in the water body is 5 to 400 mg / L, another implementation method is 50 to 400 mg / L, specifically 50 to 200 mg / L in a specific embodiment; the pH value of the water body is 3 to 11, another implementation method is 6 to 8, specifically 7 in a specific embodiment; the dosage of the phosphorus adsorbent in the water body is 0.02 to 1 g / L, another implementation method is 0.2 to 0.8 g / L, specifically 0.4 to 0.8 g / L in a specific embodiment.

[0056] As an implementation manner, the temperature of the adsorption is 25 to 45 °C, specifically 25 to 40 °C in specific embodiments; it is carried out at room temperature; the adsorption is carried out under shaking conditions; the shaking rate is 100 to 300 rpm, specifically 200 rpm in specific embodiments; the adsorption time is 12 to 36 h, specifically 24 h in specific embodiments.

[0057] As an implementation manner, after the adsorption, it further includes: solid-liquid separation of the adsorbed water body to obtain a phosphorus adsorbent that adsorbs phosphorus; the solid-liquid separation is filtration; the filtration is carried out with a 0.45 μm filter membrane.

[0058] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention, but they cannot be understood as limiting the protection scope of the present invention.

[0059] N,N-methylenebisacrylamide used in the following examples was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd., microcrystalline cellulose, chitosan, and urea were all purchased from Sinopharm Chemical Reagent Co., Ltd., sodium hydroxide and 1,3,5-benzenetricarboxylic acid were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., materials such as iron(III) nitrate nonahydrate, acrylic acid, and ammonium persulfate were purchased from Shanghai Macklin Biochemical Technology Co., Ltd., materials such as N,N-methylenepropenylacrylamide and acrylic acid were all purchased from Xi'an Chemical Reagent Factory, China. All chemical reagents were of analytical reagent grade and did not require further purification before use.

[0060] Example 1

[0061] Preparation of MIL-100(Fe): 3 g of iron(III) nitrate nonahydrate and 2.01 g of 1,3,5-benzenetricarboxylic acid were dissolved in 100 g of water together, stirred at 200 rpm for 15 min, and then subjected to a hydrothermal reaction at 160 °C and 200 rpm in a micro-reactor for 16 h. After the reaction, filtration was carried out by a suction filter, and it was washed 3 times with deionized water and 3 times with alcohol, and then dried at 60 °C for 2 d;

[0062] Preparation of chitosan solution: 1 g of chitosan was added to 100 mL of 1 wt% acetic acid solution and dissolved by stirring at 500 rpm on a magnetic stirrer for 15 min to obtain a 10 g / L chitosan solution;

[0063] Preparation of microcrystalline cellulose solution: 1 g of microcrystalline cellulose was added to 100 mL of an NaOH / urea / water solution with a mass ratio of 7:12:81 and refrigerated in a -4 °C refrigerator for 30 min until the solution was completely clear to obtain a 10 g / L microcrystalline cellulose solution;

[0064] Measure 30 mL of the above chitosan solution, 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, stir for 0.5 h, add 12 mL (1.02 g / mL) of acrylamide, 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, put it in a refrigerator at -28 °C for freezing for 48 h, and then carry out vacuum freeze-drying at 30 Pa and -66.5 °C for 2 d with a freeze dryer to obtain a water-retaining and phosphorus-absorbing hydrogel (F-CMP) loaded with dual biopolymers and MIL-100(Fe).

[0065] Example 2

[0066] The difference from Example 1 is that acrylamide is changed to granular acrylamide and 12 g is put in, and the rest is the same as Example 1.

[0067] Example 3

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

[0069] Comparative Example 1

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

[0071] Comparative Example 2

[0072] The difference from Example 1 is that microcrystalline cellulose is not added, and the rest is the same as Example 1.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that chitosan is not added, and the rest is the same as Example 1.

[0075] Comparative Example 4

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

[0077] Application Example 1

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

[0079] Comparative Application Example 1

[0080] The difference from Application Example 1 is that the water-retaining and phosphorus-adsorbing hydrogel (F-CMP) with dual-biomass loaded MIL-100(Fe) in Application Example 1 is replaced with the hydrogel (CMP) of Comparative Example 1, and the rest is the same as Application Example 1.

[0081] Performance Test

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

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

[0084] From Figure 1 (b), it can be observed that the surface of F-CMP is rough, the pore structure is unevenly distributed, and it generally shows a spherical mesoporous structure. The surface of the material is rough, and crystalline substances are attached inside the large pores and on the surface of the material. There are also small pores inside the pores, and crystals are also attached. This crystal may be due to the presence of MIL-100(Fe) on the material surface through loading.

[0085] From Figure 1 (c), it can be observed that the surface of CMP at a larger magnification is still a smooth surface.

[0086] It can be observed from Figure 1 (d) in that more crystallization is observed on the surface of F-CMP, and the pore structure is more obvious.

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

[0088] It can be observed from Figure 1 (f)–(j) in that according to the picture structure of F-CMP, the distributions of C, N, and O elements are all closely related to the F-CMP structure. The distribution of Fe in F-CMP is also mainly on the surface, but it is not related to the distributions of C, N, and O. This verifies that the addition of MIL-100(Fe) is mainly in the form of free loading.

[0089] (2) Fourier transform infrared (FTIR) and thermogravimetric analyses were carried out on the water-retaining and phosphorus-adsorbing hydrogel (F-CMP) loaded with dual biopolymers and MIL-100(Fe) prepared in Example 1 and the hydrogel (CMP) in Comparative Example 1. The obtained results are as Figure 2 shown, where (a) are the FTIR results of F-CMP and CMP, and (b) are the TG curve and TGA curve of F-CMP obtained by thermogravimetric analysis.

[0090] According to Figure 2 the Fourier transform infrared spectrum (FTIR) shown in (a) in, it was found by comparing the FTIR results that the overall groups changed greatly after loading MIL-100(Fe), but the positions of the absorption peaks changed little. This may be because the water absorption of F-CMP caused the sample surface to absorb water before detection, resulting in poor detection sensitivity of the sample, but it did not affect the analysis results. According to Figure 2 the FTIR results shown in (a) in, it can be interpreted as the stretching vibrations of O-H and N-H. The absorption peaks at 2913 cm -1 and 2856 cm -1 are the asymmetric stretching and symmetric stretching of C-H. The absorption peak at 1551 cm -1 is the vibration of the C=O bond of the carboxylate group, and the absorption peak at 1625 cm -1 is the bending vibration of -NH2. The peaks at 1404 cm -1 and 1246 cm -1 are attributed to the bending vibration and stretching vibration of C-N, which proves that chitosan was successfully compounded in the material. The absorption peak at 1166 cm -1 can be interpreted as the bending vibration of C-O. The absorption peak at 1060 cm -1 is due to the C-OH absorption peaks of cellulose and chitosan. The material F-CMP has absorption peaks at 460 cm -1 and 490 cm -1Weak characteristic peaks of MIL-100(Fe) were identified at these positions. These peaks mainly originated from the stretching of Fe-O, 759 cm -1 and 711 cm -1 The C-H bending vibration of the benzene ring was observed at this position, indicating that MIL-100(Fe) was successfully loaded on the surface of the composite material. However, due to the low Fe content, the peak intensity at this position was not high. There were a large number of O-H absorption peaks in the CMP material itself at 3358 cm -1 After adding MIL-100(Fe), the O-H absorption peaks decreased significantly. This might be because the addition of MIL-100(Fe) occupied a large number of hydroxyl groups on chitosan and cellulose. At the same time, this also indicated that MIL-100(Fe) was loaded on the surface of the composite material by binding with hydroxyl groups.

[0091] From Figure 2 (b) in it, it can be seen that in order to further explore the material components of F-CMP, thermogravimetric (TG) method was used to test its thermal stability. The weight loss process of F-CMP was divided into four stages. Specifically, in the first stage within 469 K, this was mainly due to the strong water absorption performance of the material, which could capture moisture in the air. The moisture evaporated when heated and detached, resulting in a weight loss of 80%. In the second stage at 469 K - 614 K, cellulose and chitosan mainly decomposed at high temperature. This might be due to the breaking of C-C bonds and the decomposition of groups such as -COOH and -OH on the cellulose chain. The weight loss reached 56% in this stage. In the third stage from 614 K to 801 K, it might be caused by the thermal decomposition of the polymer main chain or cross-linked structure as the main matrix. The weight loss reached 33% in this process. The fourth stage was after 801 K. The mass loss slowed down in this stage, mainly because the remaining was mainly iron oxide after the structure decomposition, and it had high thermal stability.

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

[0093] From Figure 3 it can be seen that X-ray photoelectron spectroscopy (XPS) can be used to determine information on individual elements, atomic composition, and valence states. The content of Fe element was relatively low, and the change in the intensity of the Fe2p peak was only about 2.5E+3 counts / s. Compared with the C1s and O1s peaks, the Fe2p peak had a poor display in the total spectrum.

[0094] Analyze the XPS elemental fine spectrum, and perform charge calibration through the carbon peak at 284.8 eV. From Figure 3It can be confirmed from (a) that C-C / C-H (284.8 eV), C-O-C / C-N (285.88 eV or 285.91 eV), and C-O═C (288.89 eV and 288.57 eV) all appear in the C1s spectra of CMP and F-CMP. From Figure 3 It can be confirmed from (c) that quaternary ammonium salt peaks (399.86 eV and 399.79 eV) appear in the N1s spectrum. This evidence can also prove that chitosan has been successfully compounded in the material. And from Figure 3 C-O (532.10 eV) and C═O (533.6 eV) exist in the O1s spectra of (b). However, the difference is that the peak intensity of C═O at 533.60 eV in the F-CMP material is significantly increased, which is due to the large amount of carboxyl groups in trimesic acid in MIL-100(Fe). In addition, by analyzing the fine spectrum of Fe in the F-CMP material ( Figure 3 (d)), the Fe2p fine spectrum shows that two peaks appear at 710.34 eV and 723.11 eV, corresponding to Fe2p 1 / 2 [Fe(III)] and Fe2p 3 / 2 [Fe(III)], respectively. In addition, two satellite peaks of Fe2p also appear at 717.04 and 731.26 eV, indicating that MIL-100(Fe) has been successfully loaded in the material.

[0095] (4) Phosphorus adsorption test:

[0096] All adsorption tests were carried out in 100 mL centrifuge tubes. Weigh 0.02 g of adsorbents (the water-retaining phosphorus-adsorbing hydrogel (F-CMP) loaded with dual biomass and MIL-100(Fe) prepared in Example 1 and the hydrogel (CMP) in Comparative Example 1) respectively, and add them to 100 mL centrifuge tubes containing 50 mL of phosphorus solution. Measure the adsorption amounts at different phosphorus concentrations of 50 - 400 mg / L respectively, adjust the pH = 7, shake at 25 °C and 200 rpm in a shaker for 24 h, then filter with a 0.45 μm filter membrane. The determination of phosphorus adopts the molybdenum-antimony anti-spectrophotometry method, and the absorbance is measured with a UV spectrophotometer at 770 nm for calculation. The phosphorus adsorption results of F-CMP at different phosphorus concentrations are as Figure 4 shown, and the comparison results of phosphorus adsorption between F-CMP and CMP in 100 mg / L phosphorus solution are as Figure 5 shown.

[0097] It can be seen from Figure 4 that the phosphorus adsorption performance ranges from 93.33 mg / g at low concentration to 140.5 mg / g at high concentration, and the removal rate of low-concentration phosphorus is about 75%.

[0098] It can be seen from as Figure 5As shown, F-CMP has a certain phosphorus adsorption performance, with a maximum of 116.94 mg / g. The phosphorus adsorption capacity of CMP is only 74.36 mg / g, while that of F-CMP is enhanced to 116.94 mg / g. The addition of MIL-100(Fe) enhances the phosphorus adsorption of the CMP material by nearly 50%.

[0099] (5) Swelling ratio test: Water absorption performance test

[0100] At room temperature, weigh 0.5 g (m1, g) of the dry sample (the water-retaining phosphorus-adsorbing hydrogel (F-CMP) loaded with dual biomass and MIL-100(Fe) prepared in Example 1) into a clean beaker. Add 800 mL of distilled water to a 1 L beaker and let it stand for 24 h to reach the water absorption equilibrium. Take out the water-absorbed sample and filter off the excess water on a 100-mesh sieve, then weigh the mass of the water-absorbed sample (m2, g). Measure it in parallel 3 times and take the average value. Calculate the water absorption ratio (Qeq, g / g) according to Equation (1).

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

[0102] Through the swelling test, the water adsorption capacity of F-CMP is as high as 199.20 g / g. The water adsorption process starts from a blocky hard material in the initial state and becomes a gel after 24 h of adsorption. The actual effect is as shown in (b) in Figure 6 the figure.

[0103] Water stability test:

[0104] Weigh 0.5 g of the adsorbent (the water-retaining phosphorus-adsorbing hydrogel (F-CMP) loaded with dual biomass and MIL-100(Fe) prepared in Example 1), and immerse it in a beaker containing 800 mL of distilled water. Observe its structural state every month. As shown in (c) in Figure 6 the figure, after 60 days, the gel state is stable and no disintegration occurs.

[0105] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention rather than all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, 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: It comprises 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 the pores; The polymer hydrogel includes polyacrylic acid hydrogel and / or polyacrylamide hydrogel; The cellulose and chitosan are grafted onto the carbon atoms of the synthetic polymer hydrogel via hydroxyl groups.

2. The water-retaining and phosphorus-absorbing hydrogel according to claim 1, characterized in that: The cellulose is microcrystalline cellulose; the metal organic framework is one or more of the MIL series and ZIL series.

3. The water-retaining and phosphorus-absorbing hydrogel according to claim 1 or 2, characterized in that: The mass percentage of synthetic polymer hydrogel in the water-retaining and phosphorus-absorbing hydrogel is 80-86%, the mass percentage of cellulose is 1.8-6.7%, the mass percentage of chitosan is 1.8-6.7%, and the mass percentage of metal organic framework is 5-10%.

4. The method for preparing the water-retaining and phosphorus-absorbing hydrogel according to any one of claims 1 to 3, characterized in that: The following steps are involved: The chitosan solution, the cellulose solution, the metal organic framework, the organic monomer containing the carbon-carbon double bond, the crosslinking agent and the free radical initiator are mixed, and the obtained mixed solution is subjected to a crosslinking polymerization reaction to obtain the water-retaining and phosphorus-absorbing hydrogel; The organic monomer containing a carbon-carbon double bond includes acrylic acid and / or acrylamide.

5. The preparation method according to claim 4, characterized in that: The free radical initiator is ammonium persulfate.

6. The preparation method according to claim 4, characterized in that: The cross-linking agent is 2-mercaptobenzoic acid and / or N,N'-methylenebisacrylamide.

7. The preparation method according to claim 4, characterized in that: The temperature of the cross-linking polymerization reaction is 50-70° C.; the time of the cross-linking polymerization reaction is 3-5 hours.

8. Use of the water-retaining and phosphorus-absorbing hydrogel according to any one of claims 1 to 3 or the water-retaining and phosphorus-absorbing hydrogel prepared by the preparation method according to any one of claims 4 to 7 in absorbing water and phosphorus.

9. A method for removing phosphorus from water, characterized in that: The following steps are involved: Adding a phosphorus adsorbent into a water body for adsorption; The phosphorus adsorbent is the water-retaining and phosphorus-absorbing hydrogel described in any one of claims 1 to 3 or the water-retaining and phosphorus-absorbing hydrogel prepared by the preparation method described in any one of claims 4 to 7.

10. The method according to claim 9, 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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