A polydopamine-modified cerium-based metal organic framework chitosan gel sphere and its preparation method and application

Abstract

The present invention belongs to the technical field of water pollution treatment, and specifically relates to a polydopamine-modified cerium-based metal organic framework chitosan gel sphere and a preparation method and application thereof. The polydopamine-modified cerium-based metal organic framework chitosan gel sphere provided by the present invention comprises a cerium-based metal organic framework, a chitosan spherical shell covering the cerium-based metal organic framework, and polydopamine loaded on the surface and pores of the chitosan spherical shell; the cerium in the cerium-based metal organic framework is Ce. 3+ It has excellent adsorption properties for phosphate in water, and the coated gel balls have good water shock resistance and are easy to recycle.

Description

Technical Field

[0001] The invention belongs to the technical field of water pollution treatment, and specifically relates to a polydopamine-modified cerium-based metal organic framework chitosan gel sphere and a preparation method and application thereof. Background Art

[0002] Phosphorus is one of the basic elements for the survival of organisms. It is not only an important component of DNA and human bones, but also participates in energy transfer and maintains acid-base balance during metabolism. However, due to industrial and agricultural activities, excessive phosphates are released into aquatic ecosystems, causing algae to multiply in large numbers and ultimately leading to eutrophication. According to GB18918-2002, the concentration of phosphorus in discharged wastewater is limited to less than 0.5 mg / L. However, studies have shown that the deterioration of water quality can only be effectively inhibited when the concentration of phosphorus is reduced to no more than 0.02 mg / L. Therefore, traditional biotechnology can no longer meet new requirements due to its unsatisfactory phosphorus removal effect. Although chemical precipitation can remove phosphorus to a lower concentration, it requires the addition of more coagulants, which on the one hand leads to higher costs and on the other hand produces a large amount of sludge. In contrast, the adsorption method has the advantages of low operating cost, simple preparation, and high efficiency of phosphorus capture at low concentrations.

[0003] In recent years, great progress has been made in the research of adsorbents. Through the modification of functional groups and the optimization of porous structures, a series of adsorbents, including carbon, metal, organic polymers and other materials, have shown great adsorption capacity for phosphate. Among them, metal-based adsorbent materials have attracted much attention due to their excellent selectivity for phosphate. Rare earth metal cerium, especially trivalent cerium, has been shown to have the ability to efficiently capture phosphate due to its strong attraction to phosphate, especially for low-concentration phosphate. At the same time, by introducing metal-organic frameworks (MOFs), metal-based adsorbents also have the advantages of excellent porosity, high specific surface area and easy functionalization. It can be seen that cerium-based materials have good potential in phosphorus removal. However, considering the crystalline nature of MOFs, their fine powder nature makes them have the disadvantages of poor reusability and secondary pollution in the solid-liquid separation process. This makes them face bottlenecks in large-scale industrial applications, especially under continuous flow conditions. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a polydopamine modified cerium-based metal organic framework chitosan gel sphere and a preparation method and application thereof. The polydopamine modified cerium-based metal organic framework chitosan gel sphere provided by the present invention has excellent adsorption performance for phosphate in water, good water shock resistance and easy recovery.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The invention provides a polydopamine modified cerium-based metal organic framework chitosan gel sphere, comprising a cerium-based metal organic framework, a chitosan spherical shell covering the cerium-based metal organic framework, and polydopamine loaded on the surface and pores of the chitosan spherical shell; the cerium in the cerium-based metal organic framework is Ce. 3+ .

[0007] Preferably, the particle size of the polydopamine-modified cerium-based metal-organic framework chitosan gel spheres is 2 to 3 mm.

[0008] The present invention also provides a method for preparing the polydopamine modified cerium-based metal organic framework chitosan gel spheres described in the above technical solution, comprising the following steps:

[0009] The trivalent cerium salt, the organic ligand and the organic solvent are mixed and subjected to a solvothermal reaction to obtain a cerium-based metal organic framework;

[0010] The cerium-based metal organic framework, chitosan and acetic acid aqueous solution are mixed and ultrasonicated to obtain a mixed solution;

[0011] The mixed solution is mixed with an alkaline alcohol solution, and solidified to obtain chitosan-loaded cerium-based metal organic framework gel spheres;

[0012] The chitosan-loaded cerium-based metal organic framework gel spheres and a dopamine hydrochloride buffer solution are mixed, the dopamine hydrochloride undergoes in-situ self-polymerization, and the obtained product is sequentially washed and dried to obtain polydopamine-modified cerium-based metal organic framework chitosan gel spheres.

[0013] Preferably, the trivalent cerium salt includes ammonium cerium nitrate and / or cerium nitrate; the organic ligand includes phthalic acid and / or trimesic acid; and the molar ratio of the trivalent cerium salt to the organic ligand is 1:1-2.

[0014] Preferably, the temperature of the solvent thermal reaction is 150-180° C., and the time is 12-72 hours.

[0015] Preferably, the mass ratio of the cerium-based metal organic framework to chitosan is 1-5:1-5.

[0016] Preferably, the alkaline alcohol solution comprises sodium hydroxide, ethanol and water; the mass concentration of sodium hydroxide in the alkaline alcohol solution is 10-15%; the mass concentration of ethanol in the alkaline alcohol solution is preferably 20-25%.

[0017] Preferably, the curing is static curing; and the curing time is 12 to 24 hours.

[0018] Preferably, the dopamine hydrochloride buffer solution comprises dopamine hydrochloride, tris(hydroxymethylaminomethane) and water; the mass concentration of dopamine hydrochloride in the dopamine hydrochloride buffer solution is 2 mg / mL, and the molar concentration of tris(hydroxymethylaminomethane) is 10 mmol / L; and the pH value of the dopamine hydrochloride buffer solution is 8.5-9.0.

[0019] The present invention also provides the use of the polydopamine-modified cerium-based metal organic framework chitosan gel spheres described in the above technical solution or the polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared by the preparation method described in the above technical solution in adsorbing phosphate in water.

[0020] The invention provides a polydopamine modified cerium-based metal organic framework chitosan gel sphere, comprising a cerium-based metal organic framework, a chitosan spherical shell covering the cerium-based metal organic framework, and polydopamine loaded on the surface and pores of the chitosan spherical shell; the cerium in the cerium-based metal organic framework is Ce. 3+ The polydopamine modified cerium-based metal organic framework chitosan gel sphere provided by the present invention contains Ce 3+ , it can form a strong interaction relationship with phosphate in water for chemical adsorption, so that it has higher sensitivity, faster reaction rate and larger adsorption capacity for capturing phosphate; moreover, the cerium-based metal organic framework has excellent porosity, specific surface area and three-dimensional pore structure, and has excellent adsorption and catalytic ability for phosphate in water. The chitosan spherical shell coated on the outside of the cerium-based metal organic framework can prevent the cerium-based metal organic framework from easily flocculating in water due to the effect of surface tension, weakening its adsorption effect, or causing secondary pollution to water; and the chitosan spherical shell also has a porous structure, which can ensure the smooth mass transfer process of the solution. Chitosan itself also has multiple groups such as amino and hydroxyl groups, and also has a certain adsorption effect on phosphate; coating the surface of the chitosan-loaded cerium-based metal organic framework gel ball with polydopamine material can, on the one hand, improve the mechanical properties of the gel ball and further enhance the impact resistance of the particles in continuous flow water treatment; on the other hand, it uses the reducing ability of dopamine to ensure that Ce, which is easy to change its valence in alkaline solution, 3+ The stable existence of valence state makes most of the cerium ions in the polydopamine-modified cerium-based metal organic framework chitosan gel spheres remain in the original trivalent state, thereby making the polydopamine-modified cerium-based metal organic framework chitosan gel spheres have a large amount of Ce 3+ active sites, thereby greatly improving its phosphate removal efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a macroscopic morphology of the polydopamine-modified cerium-based metal organic framework chitosan gel sphere obtained in Example 1 of the present invention;

[0022] Figure 2This is a diagram showing the adsorption effect of chitosan, chitosan-loaded cerium-based metal organic framework gel spheres, polydopamine-modified cerium-based metal organic framework chitosan gel spheres, and polydopamine-coated chitosan on phosphorus solution in Example 1 of the present invention;

[0023] Figure 3 The scanning electron microscope images of the polydopamine-modified cerium-based metal organic framework chitosan gel spheres obtained in Example 1 of the present invention before and after the adsorption of phosphate, wherein A is before the adsorption of phosphate, and B is after the adsorption of phosphate;

[0024] Figure 4 This is an isothermal adsorption curve of phosphate adsorbed by polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in an embodiment of the present invention;

[0025] Figure 5 This is an adsorption kinetics curve of phosphate adsorbed by polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in an embodiment of the present invention;

[0026] Figure 6 This is a histogram of phosphorus adsorption of polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in an embodiment of the present invention at different initial pH values;

[0027] Figure 7 A bar chart showing the phosphorus adsorption of polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in an embodiment of the present invention under different competing ions, wherein the abscissa represents different competing ion states and the ordinate represents the adsorption capacity of phosphorus adsorption under different ions;

[0028] Figure 8 This is a graph showing the adsorption capacity of polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared with different ratios of chitosan and cerium-based metal organic framework in the present invention. DETAILED DESCRIPTION

[0029] The invention provides a polydopamine modified cerium-based metal organic framework chitosan gel sphere, comprising a cerium-based metal organic framework, a chitosan spherical shell covering the cerium-based metal organic framework, and polydopamine loaded on the surface and pores of the chitosan spherical shell; the cerium in the cerium-based metal organic framework is Ce. 3+ .

[0030] In the present invention, the particle size of the polydopamine-modified cerium-based metal organic framework chitosan gel spheres is preferably 2 to 3 mm, more preferably 2 to 2.5 mm.

[0031] In the present invention, the organic ligand of the cerium-based metal organic framework in the polydopamine-modified cerium-based metal organic framework chitosan gel sphere is preferably terephthalic acid and / or trimesic acid, more preferably terephthalic acid; 3+The molar ratio of the cerium-based metal organic framework to the organic ligand is preferably 1:1-2, more preferably 1:2; the mass ratio of the cerium-based metal organic framework to chitosan is preferably 1-5:1-5, more preferably 1-4:1-4.

[0032] In the present invention, the specific surface area of ​​the polydopamine-modified cerium-based metal organic framework chitosan gel sphere is preferably 40 m 2 / g.

[0033] The present invention also provides a method for preparing the polydopamine modified cerium-based metal organic framework chitosan gel spheres described in the above technical solution, comprising the following steps:

[0034] The trivalent cerium salt, the organic ligand and the organic solvent are mixed and subjected to a solvothermal reaction to obtain a cerium-based metal organic framework;

[0035] The cerium-based metal organic framework, chitosan and acetic acid aqueous solution are mixed and ultrasonicated to obtain a mixed solution;

[0036] The mixed solution is mixed with an alkaline alcohol solution, and solidified to obtain chitosan-loaded cerium-based metal organic framework gel spheres;

[0037] The chitosan-loaded cerium-based metal organic framework gel spheres and a dopamine hydrochloride buffer solution are mixed, the dopamine hydrochloride undergoes in-situ self-polymerization, and the obtained product is sequentially washed and dried to obtain polydopamine-modified cerium-based metal organic framework chitosan gel spheres.

[0038] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used in the preparation, and commercially available products known to those skilled in the art can be used.

[0039] The invention mixes cerium ammonium nitrate, phthalic acid and an organic solvent, and performs a solvent thermal reaction to obtain a cerium-based metal organic framework.

[0040] In the present invention, the trivalent cerium salt preferably includes ammonium cerium nitrate and / or cerium nitrate, more preferably ammonium cerium nitrate; when the trivalent cerium salt is ammonium cerium nitrate and cerium nitrate, the present invention has no special limitation on the ratio of the ammonium cerium nitrate and cerium nitrate, and any ratio may be used.

[0041] In the present invention, the organic ligand preferably includes phthalic acid and / or trimesic acid, more preferably phthalic acid; when the organic ligand is phthalic acid and trimesic acid, the present invention has no special limitation on the ratio of the phthalic acid and / or trimesic acid, and any ratio may be used.

[0042] In the present invention, the molar ratio of the trivalent cerium salt to the organic ligand is preferably 1:1-2, more preferably 1:2.

[0043] In the present invention, the organic solvent is preferably N,N-dimethylformamide (DMF); the ratio of the mass of the cerium ammonium nitrate to the volume of the organic solvent is preferably 1 g: (12-20) mL, more preferably 1 g: 15 mL.

[0044] In the present invention, the temperature of the solvothermal reaction is preferably 150-180° C., more preferably 150° C., and the time is preferably 12-72 h, more preferably 12-36 h; the equipment used for the solvothermal reaction is preferably a reactor.

[0045] In the present invention, the mixing of the trivalent cerium salt, phthalic acid and the organic solvent is to dissolve the trivalent cerium salt and phthalic acid in the organic solvent.

[0046] In the present invention, the trivalent cerium salt and phthalic acid undergo a solvothermal reaction to generate a cerium-based metal organic framework through coordination bonds.

[0047] After the solvent thermal reaction, the present invention preferably washes and dries the product obtained by the solvent thermal reaction in sequence; the washing is preferably washed with N,N-dimethylformamide for 3 times. The drying is preferably vacuum drying; the drying temperature is preferably 40 to 60°C, more preferably 40°C; the drying time is preferably 24 to 36 hours, more preferably 24 hours; the vacuum degree of the vacuum drying is not particularly limited in the present invention, and can be selected according to actual needs.

[0048] The present invention uses trivalent cerium MOF material to prepare gel balls, mainly because compared with Ce 4+ , Ce 3+ The capture of phosphate has higher sensitivity, faster reaction rate and larger adsorption capacity. This is mainly due to the Ce 3+ The strong interaction between Ce and phosphate is chemical adsorption, so the attraction between them is much greater than that of Ce which is mainly electrostatic attraction. 4+ At the same time, because the MOF structure has excellent porosity, specific surface area and three-dimensional pore structure, it has excellent adsorption and catalytic capabilities. The present invention can achieve Ce by designing the MOF structure. 3+ Optimization of active sites ensures maximum efficiency of phosphate adsorption.

[0049] After obtaining the cerium-based metal organic framework, the present invention mixes the cerium-based metal organic framework, chitosan and an acetic acid aqueous solution, and performs ultrasonic treatment to obtain a mixed solution.

[0050] In the present invention, the mass ratio of the cerium-based metal-organic framework and chitosan is preferably 1-5:1-5, more preferably 1-4:1-4; in an embodiment of the present invention, the mass ratio of the cerium-based metal-organic framework and chitosan is specifically preferably 1:1, 4:1, 2:1, 1:2 or 1:4; the mass concentration of the acetic acid aqueous solution is preferably 5-8%, more preferably 5%; the ratio of the mass of the cerium-based metal-organic framework to the volume of the acetic acid aqueous solution is preferably 1g:(50-75)mL, more preferably 1g:50mL.

[0051] Before mixing the cerium-based metal organic framework, chitosan and acetic acid aqueous solution, the present invention preferably crushes the cerium-based metal organic framework to obtain cerium-based metal organic framework powder; the crushing method is preferably grinding; the present invention has no special limitation on the particle size of the cerium-based metal organic framework powder obtained by crushing, which can be selected according to actual needs.

[0052] The present invention has no special limitation on the mixing process of the cerium-based metal organic framework, chitosan and acetic acid aqueous solution, and the materials can be evenly mixed using a mixing process well known in the art.

[0053] In the present invention, the temperature of the ultrasound is preferably 25° C.; the power of the ultrasound is preferably 400-800 W, more preferably 600 W, and the time is preferably 3-6 min, more preferably 5 min.

[0054] The invention uses ultrasound to uniformly dissolve the cerium-based metal organic framework and chitosan in an acetic acid aqueous solution until there are no bubbles, thereby obtaining a mixed solution.

[0055] After obtaining the mixed solution, the present invention mixes the mixed solution with an alkaline alcohol solution and solidifies the mixture to obtain chitosan-loaded cerium-based metal organic framework gel balls.

[0056] In the present invention, the alkaline alcohol solution preferably comprises sodium hydroxide, ethanol and water; the mass concentration of sodium hydroxide in the alkaline alcohol solution is preferably 10-15%, more preferably 10%; the mass concentration of ethanol in the alkaline alcohol solution is preferably 20-25%, more preferably 23%.

[0057] In the present invention, the mixing of the mixed solution and the alkaline alcohol solution is preferably performed by dropping the mixed solution into the alkaline alcohol solution.

[0058] In the present invention, the curing is preferably static curing; the curing time is preferably 12 to 24 hours, more preferably 12 hours.

[0059] In the present invention, after the mixed solution containing chitosan and cerium-based metal organic framework contacts the alkaline alcohol solution, chitosan precipitates under alkaline conditions to form a chitosan spherical shell, and the cerium-based metal organic framework is coated in the chitosan spherical shell, thereby forming a chitosan-loaded cerium-based metal organic framework gel sphere.

[0060] After the solidification, the present invention preferably washes the gel spheres obtained by the solidification. In the present invention, the reagent used for the washing is preferably water. The present invention preferably washes until the washing liquid after the washing is neutral.

[0061] Chitosan is used as a carrier to anchor MOF in the present invention, mainly because although MOF has excellent phosphorus removal ability, its powder form is used in water treatment and is prone to secondary pollution, and nano powder is easily precipitated in water due to the effect of surface tension, which also weakens its adsorption effect. Therefore, the present invention uses the load of gel balls to solve the leakage and precipitate problems of particles. At the same time, chitosan, as a natural macromolecule, has high biocompatibility and avoids the possibility of self-pollution to water bodies. The present invention uses freeze-drying technology to well retain the pore structure of chitosan gel balls and ensure the smoothness of the solution mass transfer process. And chitosan itself also has multiple groups such as amino and hydroxyl groups, and has a certain adsorption effect for phosphate, so the present invention can strengthen the adsorption effect of cerium-based MOF by loading the cerium-based metal organic framework on chitosan.

[0062] After obtaining the chitosan-loaded cerium-based metal organic framework gel spheres, the present invention preferably mixes the chitosan-loaded cerium-based metal organic framework gel spheres with a dopamine hydrochloride buffer solution, and then sequentially washes and dries the mixture to obtain polydopamine-modified cerium-based metal organic framework chitosan gel spheres.

[0063] In the present invention, the dopamine hydrochloride buffer solution preferably comprises dopamine hydrochloride, tris(hydroxymethylaminomethane) and water; the mass concentration of dopamine hydrochloride in the dopamine hydrochloride buffer solution is preferably 2 mg / mL, and the molar concentration of tris(hydroxymethylaminomethane) is preferably 10 mmol / L; the pH value of the dopamine hydrochloride buffer solution is preferably 8.5-9.0, more preferably 8.5.

[0064] In the present invention, the mixing of the chitosan-loaded cerium-based metal-organic framework gel spheres and the dopamine hydrochloride buffer solution is preferably performed by placing the chitosan-loaded cerium-based metal-organic framework gel spheres in the dopamine hydrochloride buffer solution and shaking; the equipment used for the shaking is preferably a shaker; the shaking rate is preferably 100 to 150 rpm, more preferably 150 rpm; the shaking time is preferably 12 to 24 h, more preferably 12 to 20 h; and the stirring is preferably performed at room temperature.

[0065] During the stirring process, dopamine hydrochloride undergoes self-polymerization under aerobic conditions to generate polydopamine, which is attached to the surface and pores of the chitosan-loaded cerium-based metal organic framework gel balls.

[0066] In the present invention, the cleaning is preferably performed by washing with deionized water and ethanol three times respectively.

[0067] In the present invention, the drying equipment is preferably a freeze dryer; the drying preferably includes pre-freezing and vacuum drying performed in sequence; the pre-freezing time is preferably 2 to 4 hours, more preferably 2 hours; the pre-freezing temperature is preferably -20 to -80°C, more preferably -80°C; the vacuum drying time is preferably 12 to 24 hours, more preferably 12 to 20 hours; the vacuum drying temperature is preferably -20 to -40°C, more preferably -40°C.

[0068] The invention coats the surface of the chitosan-loaded cerium-based metal organic framework gel ball with polydopamine material, which can improve the mechanical properties of the gel ball and further enhance the impact resistance of the particles in continuous flow water treatment; on the other hand, the reduction ability of dopamine is utilized to ensure that Ce, which is easily variable in valence in alkaline solution, is 3+ The stable existence of valence state makes most of the cerium ions in the polydopamine-modified cerium-based metal organic framework chitosan gel spheres remain in the original trivalent state, thereby making the polydopamine-modified cerium-based metal organic framework chitosan gel spheres have a large amount of Ce 3+ active sites, thereby greatly improving its phosphate removal efficiency.

[0069] The gel ball adsorbent in the water body of the present invention has a regular micro-nano microstructure and also has a macrostructure of about 2 cm. The spherical particles have good integrity, hydrophilicity and stability. Compared with general nanomaterials, it has excellent liquid-solid separation characteristics and is suitable for repeated use in continuous flow water bodies.

[0070] The present invention also provides the use of the polydopamine-modified cerium-based metal organic framework chitosan gel spheres or the polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared by the above preparation method in adsorbing phosphate in water.

[0071] The present invention has no special limitation on the application mode of the polydopamine-modified cerium-based metal organic framework chitosan gel spheres in adsorbing phosphate in water, and the application mode can be selected according to actual needs.

[0072] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0073] Example 1

[0074] Weigh 1 g of ammonium cerium nitrate and 0.6 g of H2BDC (benzoic acid) and dissolve them in 15 mL of DMF (N,N-dimethylformamide), then transfer them to a reactor and perform a solvothermal reaction at 150 °C for 12 h. The resulting precipitate is washed three times with DMF and then dried in vacuum at 40 °C for 24 h to obtain a cerium-based metal organic framework (Ce-BDC / 2).

[0075] After the cerium-based metal-organic framework is ground into powder on an agate mortar, 1.5 g of chitosan and 1.5 g of Ce-BDC / 2 powder are dissolved in an acetic acid aqueous solution (containing 50 mL of deionized water and 2.5 mL of glacial acetic acid), and ultrasonicated at 25° C. with a power of 600 W for 5 min until there are no bubbles, to obtain a mixed solution; the mixed solution is placed in a 5 mL syringe and then slowly dripped into a mixed aqueous solution of sodium hydroxide and ethanol with a mass concentration of 10% (containing 10 g of sodium hydroxide, 30 mL of ethanol and 70 mL of water) to form gel balls, and the mixture is allowed to stand and solidify for 12 h. After the solidification is completed, it is repeatedly washed with deionized water until it is neutral to obtain gel balls;

[0076] All the gel balls were added into 400 mL of dopamine hydrochloride buffer solution (containing 10 mM Tris, 2 mg / mL dopamine hydrochloride, pH=8.5) and shaken at 150 rpm for 12 h. After coating, they were washed three times with deionized water and ethanol respectively, transferred to a freeze dryer and pre-frozen at -80°C for 2 h, and then vacuum dried at -40°C for 12 h to obtain polydopamine-modified cerium-based metal organic framework chitosan gel balls.

[0077] Example 2

[0078] Weigh 1 g of ammonium cerium nitrate and 0.6 g of H2BDC (benzoic acid) and dissolve them in 15 mL of DMF (N,N-dimethylformamide), then transfer them to a reactor and perform a solvothermal reaction at 150 °C for 12 h. The resulting precipitate is washed three times with DMF and then dried in vacuum at 40 °C for 24 h to obtain a cerium-based metal organic framework (Ce-BDC / 2).

[0079] The cerium-based metal organic framework was ground into powder on an agate mortar, the total mass of chitosan and Ce-BDC / 2 was fixed to 3 g, the mass ratio of chitosan and Ce-BDC / 2 was changed to 4:1, 2:1, 1:2 and 1:4, and they were dissolved in an acetic acid aqueous solution (containing 50 mL of deionized water and 2.5 mL of glacial acetic acid), respectively, and ultrasonicated at 25° C. with a power of 600 W for 5 min until there were no bubbles, to obtain a mixed solution; the mixed solution was placed in a 5 mL syringe and then slowly dripped into a mixed aqueous solution of sodium hydroxide and ethanol with a mass concentration of 10% (containing 10 g of sodium hydroxide, 30 mL of ethanol and 70 mL of water) to form gel balls, and the mixture was allowed to stand and solidify for 12 h. After the solidification was completed, the mixture was repeatedly washed with deionized water until neutral to obtain gel balls;

[0080] All the gel balls were added into 400 mL of dopamine hydrochloride buffer solution (containing 10 mM Tris, 2 mg / mL dopamine hydrochloride, pH=8.5) and shaken at 150 rpm for 12 h. After coating, they were washed three times with deionized water and ethanol respectively, transferred to a freeze dryer and pre-frozen at -80°C for 2 h, and then vacuum dried at -40°C for 12 h to obtain polydopamine-modified cerium-based metal organic framework chitosan gel balls.

[0081] Performance Testing

[0082] (1) The morphology and structure of the polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in Example 1 were observed. The results are as follows: Figure 1 shown.

[0083] from Figure 1 It can be seen that the polydopamine modified metal organic framework chitosan gel spheres obtained in the present invention are spherical in macroscopic view, and the diameter is about 2 to 3 mm, so that they can be easily recovered after adsorbing phosphorus.

[0084] (2) The chitosan, chitosan-loaded cerium-based metal organic framework gel spheres, polydopamine-modified cerium-based metal organic framework chitosan gel spheres and polydopamine-coated chitosan in Example 1 of the present invention were used to adsorb phosphorus solution at an initial phosphorus concentration of 500 mg / L. The results are as follows: Figure 2 shown.

[0085] Depend on Figure 2 It can be seen that the polydopamine modified cerium-based metal organic framework chitosan gel sphere prepared by the present invention has the highest phosphorus adsorption amount, and the adsorption capacity reaches 120 mg / g. This shows that the polydopamine modified cerium-based metal organic framework chitosan gel sphere prepared by the present invention has excellent phosphorus adsorption effect.

[0086] (3) The microstructure of the polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in Example 1 before and after adsorption of phosphate (initial phosphorus concentration of 500 mg / L) was tested using a scanning electron microscope. The results are as follows: Figure 3 As shown, A is before phosphate adsorption and B is after phosphate adsorption.

[0087] from Figure 3 As can be seen in Figure A, before the adsorption of phosphate, the internal pores of the polydopamine-modified cerium-based metal organic framework chitosan gel sphere prepared by the present invention present an obvious honeycomb network structure at the microscopic level. This is because the pores formed in the wet gel state contain a large amount of water, and the water is directly sublimated after rapid low-temperature freezing, so that the pore structure is retained. These pore structures are conducive to the diffusion and capture of phosphate anions. Figure 3 As can be seen in B, after the adsorption of phosphate, many typical needle-like nanorod structures appeared on the inner surface of the pores of the polydopamine-modified cerium-based metal-organic framework chitosan gel spheres. This is because the cerium phosphate generated by the reaction of phosphate and trivalent cerium is deposited on the surface of the spheres.

[0088] (4) Isothermal adsorption test: 14 groups of 0.025 g polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in Example 1 were weighed and placed in a 50 mL stoppered conical flask. 50 mL of 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 75 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 300 mg / L, 400 mg / L, 500mg / L, 750mg / L, 1000mg / L potassium dihydrogen phosphate (KH2PO4) solution, each conical flask corresponds to a potassium dihydrogen phosphate (KH2PO4) concentration; then the stoppered conical flask was placed in a 25℃ constant temperature shaker at a speed of 125r / min and shaken for 18h for adsorption test. After the end, the phosphorus concentration in each conical flask was measured respectively, and the Langmuir and Freundlich isotherm models were used to fit the test structure. The results are shown in Figure 4 shown.

[0089] from Figure 4 It can be seen that the adsorption amount of phosphorus by the polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in Example 1 of the present invention increases with the increase of the initial concentration, and the adsorption equilibrium is basically reached after 18 hours. The Langmuir isotherm model shows that the saturated adsorption amount of phosphorus is 130.04 mg / g. The fitting constant n is 3.773, which is between 2 and 10, indicating that the polydopamine-modified cerium-based metal organic framework chitosan gel spheres have good adsorption capacity for phosphate.

[0090] (5) Adsorption kinetics test: 0.025 g of the polydopamine-modified cerium-based metal organic framework chitosan gel sphere prepared in Example 1 was weighed and placed in a 50 mL stoppered conical flask, and 50 mL of 500 mg / L potassium dihydrogen phosphate (KH2PO4) solution was added to the stoppered conical flask; the stoppered conical flask was then placed in a 25°C constant temperature shaker at a speed of 125 r / min and shaken for 5 min, 10 min, 15 min, 30 min, 60 min, 120 min, 180 min, 240 min, 300 min, 3 A certain amount of solution was taken out from the conical flask at 60min, 420min, 480min, 540min, 600min, 660min, 720min, 780min, 840min, 900min, 960min, 1020min, 1080min, 1140min, 1200min, 1260min, 1320min, 1380min, and 1440min to measure its residual concentration. The adsorption capacity corresponding to different reaction times was calculated and fitted with pseudo-first-order and pseudo-second-order kinetics. The results are shown in Figure 5 shown.

[0091] from Figure 5 It can be seen that the adsorption capacity of the polydopamine-modified cerium-based metal-organic framework chitosan gel spheres prepared in Example 1 of the present invention under the pseudo-second-order kinetic model is 130.787 mg / g, and the adsorption force is relatively strong.

[0092] (6) Experiment on the influence of environmental pH: 10 groups of 0.025 g polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in Example 1 were weighed and placed in 50 mL stoppered conical flasks. 50 mL of 500 mg / L potassium dihydrogen phosphate (KH2PO4) solution was added to the stoppered conical flasks. The pH of the solution was adjusted to 3-11. Each conical flask corresponded to a pH. The conical flasks were placed in a constant temperature shaker at 25°C at a speed of 125 r / min and shaken for 24 h for adsorption test. The phosphorus concentrations in the conical flasks corresponding to different initial pH values ​​were measured. The results are shown in FIG. Figure 6 shown.

[0093] from Figure 6 It can be seen that the adsorption amount reaches the maximum value at pH=3, reaching more than 250 mg / g. When the pH value is >5, the adsorption capacity decreases significantly. On the whole, the phosphorus removal performance of the polydopamine-modified cerium-based metal-organic framework chitosan gel sphere decreases with the increase of pH value. This shows that the polydopamine-modified cerium-based metal-organic framework chitosan gel sphere obtained by the present invention can maintain a high adsorption level in the range of pH=3 to 5, while under weak acid to alkaline conditions, the adsorption capacity decreases, which may be related not only to the deprotonation of the amino group but also to the ionization ability of metal cerium.

[0094] (7) Competitive ion experiment: First, 8 groups of 0.025 g of polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared in Example 1 were weighed and placed in 50 mL stoppered conical flasks, and 50 mL of 100 mg / L potassium dihydrogen phosphate (KH2PO4) solution was added to each stoppered conical flask; then 0.1 M F - , Cl - 、NO3 - 、SO4 2- 、CO3 2- , Ca 2+ Mg 2+ Each conical flask corresponds to one ion, and the remaining conical flask is used as a control test without competing ions; finally, the stoppered conical flask is placed in a 25℃ constant temperature shaker at a speed of 125r / min, and the adsorption test is carried out after shaking for 24 hours. After the test, the concentration of phosphorus in each conical flask is measured respectively. The results are as follows Figure 7 shown.

[0095] from Figure 7 It can be seen that the competing ion (concentration of 0.1 mol / L) Cl - 、NO3 - Mg 2+ The presence of these three ions did not have much effect on the adsorption capacity of phosphate, while CO3 2- 、SO4 2- and F- have a significant weakening effect on the adsorption of phosphate. 2- and SO4 2- Because they have a similar ionic structure to phosphates, their addition will 2- Competition for active sites occurs, thus inhibiting the material's adsorption of phosphate. - The phosphorus removal effect of the material is affected because it can compete with phosphorus for the active sites on the adsorbent surface through ligand exchange, generating CeF3 precipitation that is deposited on the material surface. However, due to the solubility product constant (K sp =1.0×10 -23 ) is much smaller than CeF3(K sp =8×10 -16 ), so phosphorus still dominates in the coexistence system. In fact, the anions in water are mainly Cl - 、NO3 - 、SO4 2- Mainly, CO3 2- The content of CO3 is much lower. 2-The presence of has little effect on actual water treatment. In this case, the excellent selectivity of polydopamine-modified cerium-based metal-organic framework chitosan gel spheres for phosphate makes them more suitable for actual water treatment.

[0096] (8) Compare the adsorption capacity of phosphate by polydopamine-modified cerium-based metal organic framework chitosan gel spheres prepared with different chitosan and Ce-BDC / 2 ratios in Example 1 and Example 2, specifically: weigh 0.025 g of the above-mentioned polydopamine-modified cerium-based metal organic framework chitosan gel spheres and place them in a 50 mL stoppered conical flask, add 50 mL of 500 mg / L potassium dihydrogen phosphate (KH2PO4) solution to the stoppered conical flask; then place the stoppered conical flask in a 25°C constant temperature shaker and shake at a speed of 125 r / min until the maximum adsorption capacity is reached, measure the residual concentration, and calculate the adsorption capacity corresponding to different ratios. The results are shown in FIG. Figure 8 shown.

[0097] Depend on Figure 8 As shown in the figure, with the decrease of the mass ratio of chitosan and Ce-BDC / 2, the adsorption capacity shows a trend of first increasing and then decreasing. When the mass ratio is 1:1, the adsorbent has the best phosphorus removal effect. After that, whether increasing or decreasing the mass ratio within the experimental range, the phosphorus adsorption capacity has a certain degree of decrease. When the mass ratio is 4:1, the phosphorus removal effect is the worst. In addition, due to the high chitosan content, the viscosity of the mixed solution is large, resulting in irregular morphology of some generated gel balls and weak mechanical properties. When the proportion of chitosan as an adhesive is small, the solution viscosity is too low and the material is not easy to form balls. In summary, whether from the perspective of improving the mechanical properties of the adsorbent or the adsorption effect, the mass ratio of chitosan and Ce-BDC / 2 is 1:1, which is the best ratio for preparing gel ball composite materials.

[0098] In summary, the polydopamine modified cerium-based metal organic framework chitosan gel sphere prepared by the present invention is an adsorption material that can maintain a high adsorption level in the pH range of 3 to 5, has good recyclability, high stability, excellent adaptability, and has good adsorption performance for orthophosphate in actual water bodies.

[0099] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. Application of polydopamine modified cerium-based metal organic framework chitosan gel spheres in adsorbing phosphate, characterized in that: The polydopamine modified cerium-based metal organic framework chitosan gel sphere comprises a cerium-based metal organic framework, a chitosan spherical shell covering the cerium-based metal organic framework, and polydopamine loaded on the surface and pores of the chitosan spherical shell; the cerium in the cerium-based metal organic framework is Ce. 3+ ; The organic ligand of the cerium-based metal organic framework in the polydopamine-modified cerium-based metal organic framework chitosan gel sphere is terephthalic acid and / or trimesic acid; The specific surface area of ​​the polydopamine-modified cerium-based metal organic framework chitosan gel sphere is 40 m 2 / g; The particle size of the polydopamine-modified cerium-based metal organic framework chitosan gel sphere is 2 to 3 mm; The preparation method of the polydopamine modified cerium-based metal organic framework chitosan gel sphere comprises the following steps: The cerium salt, the organic ligand and the organic solvent are mixed and subjected to a solvothermal reaction to obtain a cerium-based metal organic framework; The cerium-based metal organic framework, chitosan and acetic acid aqueous solution are mixed and ultrasonicated to obtain a mixed solution; The mixed solution is mixed with an alkaline alcohol solution, and solidified to obtain chitosan-loaded cerium-based metal organic framework gel spheres; The chitosan-loaded cerium-based metal organic framework gel spheres and a dopamine hydrochloride buffer solution are mixed, the dopamine hydrochloride undergoes in-situ self-polymerization, and the obtained product is sequentially washed and dried to obtain polydopamine-modified cerium-based metal organic framework chitosan gel spheres.

2. The use according to claim 1, characterized in that: The cerium salt comprises ammonium cerium nitrate and / or cerium nitrate; during the preparation process, the molar ratio of the cerium salt to the organic ligand is 1:(1-2).

3. The use according to claim 1 or 2, characterized in that: The temperature of the solvent thermal reaction is 150-180° C. and the time is 12-72 hours.

4. The use according to claim 1, characterized in that: During the preparation process, the mass ratio of the cerium-based metal organic framework to chitosan is (1-5):(1-5).

5. The use according to claim 1, characterized in that: The alkaline alcohol solution comprises sodium hydroxide, ethanol and water; the mass concentration of sodium hydroxide in the alkaline alcohol solution is 10-15%; the mass concentration of ethanol in the alkaline alcohol solution is 20-25%.

6. The use according to claim 1, characterized in that: The curing is static curing; the curing time is 12 to 24 hours.

7. The use according to claim 1, characterized in that: The dopamine hydrochloride buffer solution comprises dopamine hydrochloride, tris(hydroxymethyl)aminomethane) and water; the mass concentration of dopamine hydrochloride in the dopamine hydrochloride buffer solution is 2 mg / mL, the molar concentration of tris(hydroxymethyl)aminomethane is 10 mmol / L; and the pH value of the dopamine hydrochloride buffer solution is 8.5-9.0.

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