Composite phosphorus removal agent and preparation method thereof

Abstract

The application belongs to the technical field of sewage treatment and specifically relates to a composite phosphorus removal agent and a preparation method thereof.The preparation method comprises the following steps: adding a chitosan derivative and sodium alginate into water and stirring until uniform, and then adding modified magnesium-aluminum layered double hydroxide to obtain a mixed solution; and adding the mixed solution into a lanthanum nitrate solution to form gel microspheres, which can be washed and vacuum dried.The modified magnesium-aluminum layered double hydroxide, the chitosan derivative and the sodium alginate are used as raw materials to prepare the composite phosphorus removal agent through lanthanum ion crosslinking.The composite phosphorus removal agent has high selectivity, large adsorption capacity, a wide pH application range and excellent repeated reusability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sewage treatment, and particularly relates to a composite phosphorus removal agent and a preparation method thereof. BACKGROUND

[0002] Water body eutrophication is a current prominent water environment problem, one of important causes of which is that the phosphorus element in water exceeds the standard. Eutrophication can cause the oxygen content in water to decrease sharply, cause aquatic organisms to die due to lack of oxygen, cause the ecosystem to degenerate, cause water quality to deteriorate, and significantly increase the difficulty and cost of sewage treatment. Therefore, effectively removing phosphorus in sewage has important significance for preventing and treating water body eutrophication.

[0003] The commonly used sewage phosphorus removal methods at present mainly include a chemical method, a biological method and an adsorption method. The chemical method forms phosphate salt precipitate by adding metal salt reagent, although the effect is good, but chemical sludge is easy to be produced, secondary pollution is caused, and the applicable pH range is limited; the biological method depends on the phosphorus uptake of phosphorus accumulating organisms, the effect is greatly affected by the microbial activity and the fluctuation of influent water quality, the effluent phosphorus concentration is difficult to stably reach the deep treatment requirement, and the operation control is relatively complex; the adsorption method is concerned due to simple operation, fast phosphorus removal rate, environmental friendliness and wide application range. However, although the natural adsorption materials (such as zeolite, clay and the like) have large specific surface area, they generally have problems of low adsorption capacity, poor selectivity to phosphorus, unstable effect under wide pH conditions and the like, which limit the actual application. Therefore, it is necessary to develop an adsorption material with high selectivity, large adsorption capacity, wide pH application range and good regeneration performance. SUMMARY

[0004] In order to overcome the deficiencies of the prior art, the primary purpose of the present application is to provide a preparation method of a composite phosphorus removal agent, which uses modified magnesium-aluminum layered double hydroxide, chitosan derivative and sodium alginate as raw materials, and prepares the composite phosphorus removal agent through lanthanum ion crosslinking.

[0005] Another purpose of the present application is to provide a composite phosphorus removal agent prepared by the above method, which has high selectivity, large adsorption capacity, wide pH application range and good regeneration performance.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] The present application provides a preparation method of a composite phosphorus removal agent, which comprises the following steps:

[0008] The chitosan derivative and the sodium alginate are added into water and stirred uniformly, and then the modified magnesium-aluminum layered double hydroxide is added to obtain a mixed solution; the mixed solution is added into a lanthanum nitrate solution to form gel microspheres, and after washing and vacuum drying, the composite phosphorus removal agent is obtained.

[0009] The modified magnesium-aluminum layered double hydroxide is prepared by modifying a magnesium-aluminum layered double hydroxide with N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt; the structural formula of the N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt is as follows:

[0010] ;

[0011] The preparation process of the chitosan derivative is as follows:

[0012] (1) 4-azidobenzoic acid, N-hydroxysuccinimide and N,N'-dicyclohexyl carbodiimide are added to 1,4 dioxane to perform a first light-avoiding reaction to obtain activated 4-azidobenzoic acid; a dimethyl sulfoxide solution of the activated 4-azidobenzoic acid is added to an acetic acid / water solution of chitosan to perform a second light-avoiding reaction to obtain azidated chitosan;

[0013] (2) the azidated chitosan is added to an acetic acid / dimethyl sulfoxide mixed solvent, and then yne betaine, sodium ascorbate and a CuSO4 solution are added to perform a reaction to obtain the chitosan derivative;

[0014] The structural formula of the yne betaine is as follows:

[0015] .

[0016] Preferably, in step (1), the molar ratio of the 4-azidobenzoic acid, N-hydroxysuccinimide and N,N'-dicyclohexyl carbodiimide is 1: (1-1.5): (1-1.5); the mass ratio of the chitosan to the activated 4-azidobenzoic acid is 1: (0.5-0.8); the time of the first light-avoiding reaction is 12-18 h; and the time of the second light-avoiding reaction is 2-3 d.

[0017] Preferably, in step (2), the mass ratio of the azidated chitosan, yne betaine, sodium ascorbate and CuSO4 is 1: (0.8-1): (0.4-0.5): (0.17-0.21); and the time of the reaction is 24-48 h.

[0018] Preferably, in step (2), the preparation process of the yne betaine is as follows: propargylamine and N,N-diisopropyl ethylamine are added to dichloromethane, and then a dichloromethane solution of betaine chloride acid chloride is added at 0℃ to perform a reaction to obtain the yne betaine; the molar ratio of the propargylamine, betaine chloride acid chloride and N,N-diisopropyl ethylamine is 1: (1.4-2): (3-4).

[0019] Preferably, the preparation process of the modified magnesium-aluminum layered double hydroxide is as follows:

[0020] (a) adding magnesium nitrate and aluminum nitrate into water to obtain a precursor solution; adding sodium nitrate and sodium hydroxide into water to obtain an alkali solution; adding the precursor solution into the alkali solution at 60-70°C to perform a hydrothermal reaction, and obtaining a magnesium-aluminum layered double hydroxide after post-treatment;

[0021] (b) adding the magnesium-aluminum layered double hydroxide into a N-dodecyl-4- (ethoxycarbonyl) pyridinium-S-acetic acid inner salt solution, stirring to react, and obtaining a modified magnesium-aluminum layered double hydroxide after post-treatment.

[0022] Preferably, in step (a), the concentrations of magnesium nitrate and aluminum nitrate in the precursor solution are 1-2 mol / L and 0.5 mol / L, respectively; the concentrations of sodium nitrate and sodium hydroxide in the alkali solution are 2-3 mol / L and 3-5 mol / L, respectively; the volume ratio of the precursor solution to the alkali solution is 1:1; the temperature of the hydrothermal reaction is 100-120°C, and the time is 12-18 h.

[0023] Preferably, in step (b), the ratio of the amount of the magnesium-aluminum layered double hydroxide to the amount of the N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt solution is 1 g:(100-200) mL; the concentration of the N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt solution is 0.02-0.05 mol / L; and the stirring time is 3-5 h.

[0024] Preferably, the N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt is prepared as follows:

[0025] ① adding ethyl isonicotinate and 12-bromo-1-dodecene into ethanol to reflux to react, and obtaining an intermediate 1 after purification; the structural formula of the intermediate 1 is:

[0026] ;

[0027] ② adding the intermediate 1, mercaptoacetic acid and triethylamine into dichloromethane to react at room temperature, and obtaining the N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt after purification.

[0028] Preferably, in step ①, the molar ratio of ethyl isonicotinate to 12-bromo-1-dodecene is 1:(1-1.5), and the reflux reaction time is 48-60 h; in step ②, the molar ratio of the intermediate 1 to mercaptoacetic acid to triethylamine is 1:(1-1.25):(0.5-0.6), and the reaction time at room temperature is 8-10 h.

[0029] The second aspect of the present application provides a composite phosphorus removal agent prepared by the above preparation method.

[0030] The present application has the following effects relative to the prior art:

[0031] 1. The present application provides a composite phosphorus removal agent, which is a three-dimensional network gel microsphere prepared by cross-linking modified magnesium-aluminum layered double hydroxide, chitosan derivative and sodium alginate with lanthanum ions. The composite phosphorus removal agent has high selectivity, large adsorption capacity, wide pH range of application and excellent repeated reusability.

[0032] 2. The modified magnesium-aluminum layered double hydroxide of the present application is obtained by intercalating N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt into magnesium-aluminum layered double hydroxide. The intercalation structure has three effects: first, it expands the interlayer spacing, significantly reducing the diffusion resistance of phosphate; second, the zwitterion pair formed by pyridinium and carboxylate can enhance the selective recognition of phosphate and inhibit the interference of competitive anions such as sulfate and chloride through electrostatic shielding effect; third, it improves the surface hydrophilicity and the number of ion exchange sites of the material. The three effects work together to significantly improve the selectivity, adsorption capacity and adsorption rate of the phosphorus removal agent.

[0033] 3. The chitosan derivative of the present application is prepared by click chemistry reaction of azidated chitosan and alkynyl betaine, which introduces triazole ring connecting arm and terminal quaternary ammonium group on the chitosan backbone. The quaternary ammonium group of the derivative can efficiently capture phosphate through strong electrostatic interaction in a wide pH range, solving the problem of efficiency decline of traditional adsorbents in alkaline conditions due to the weakening of surface charge; at the same time, the conjugated structure of triazole ring can further strengthen the adsorption of phosphate through π-π stacking and other secondary interactions.

[0034] 4. The quaternary ammonium group and triazole ring in the chitosan derivative of the present application, as well as the pyridinium ion in the intercalating agent, all have strong antibacterial activity, which can effectively inhibit the growth of bacteria on the surface and in the pores of the material, prevent the formation of biofilm, and avoid the blockage of adsorption channels and the inactivation of active sites. This property, combined with the stable gel skeleton, not only ensures the sustained stability of the phosphorus removal efficiency of the phosphorus removal agent in the long-term operation process, but also provides excellent regeneration performance, so that it can maintain a high adsorption capacity in repeated use. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The FT-IR spectra of chitosan, azidated chitosan and chitosan derivative in Preparation Example 4, where a corresponds to chitosan, b corresponds to azidated chitosan, and c corresponds to chitosan derivative;

[0036] Figure 2 SEM image of the composite phosphorus removal agent of Example 1. DETAILED DESCRIPTION

[0037] The technical solutions of the present application are further described below in conjunction with the specific embodiments. However, those skilled in the art should understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the present application. The specific conditions not mentioned in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, if not specifically mentioned, are the conventional products obtained through the market channel.

[0038] Preparation Example 1

[0039] Preparation Example 1 provides an acetylene betaine, which is prepared by the following preparation process:

[0040]

[0041] The propargylamine (3.7 mmol) and N,N-diisopropylethylamine (13.0 mmol) were dissolved in 22 mL of dichloromethane, cooled to 0°C, and a solution of betaine chloride chloride in dichloromethane (6.0 mmol, 20 mL) was added. The reaction was carried out at room temperature for 2 h, concentrated under vacuum, and purified by column chromatography (dichloromethane / methanol=100:1~5:1 gradient elution) to obtain the acetylene betaine; 1 HNMR: (400MHz, DMSO-d6) δ: 3.06-3.10 (t, H), 3.30 (s, 9H), 4.13 (s, 2H), 4.19-4.23 (d, 2H), 8.18 (s, H); MS (ESI) m / z=155.12 [M].

[0042] Preparation Example 2

[0043] Preparation Example 2 provides an acetylene betaine, which is prepared by the following preparation process:

[0044] The propargylamine (3.7 mmol) and N,N-diisopropylethylamine (11.1 mmol) were dissolved in 20 mL of dichloromethane, cooled to 0°C, and a solution of betaine chloride chloride in dichloromethane (5.5 mmol, 20 mL) was added. The reaction was carried out at room temperature for 1 h, concentrated under vacuum, and purified by column chromatography (dichloromethane / methanol=100:1~5:1 gradient elution) to obtain the acetylene betaine; the acetylene betaine 1 The HNMR and MS results are consistent with those of Preparation Example 1.

[0045] Preparation Example 3

[0046] Preparation Example 3 provides an acetylene betaine, which is prepared by the following preparation process:

[0047] Propargylamine (3.7 mmol) and N,N-diisopropylethylamine (14.8 mmol) were dissolved in 25 mL of dichloromethane, cooled to 0 °C, and a solution of betaine chloride chloride (7.4 mmol in 20 mL of dichloromethane) was added. The reaction was allowed to proceed at room temperature for 3 h, concentrated in vacuo, and purified by column chromatography (dichloromethane / methanol = 100:1 to 5:1 gradient elution) to give the betaine alkyne; the betaine alkyne was reacted with the azide group of the azidated chitosan according to the procedure described in Preparation Example 1. 1 HNMR and MS results were consistent with those of Preparation Example 1.

[0048] Preparation Example 4

[0049] Preparation Example 4 provides a chitosan derivative, which is prepared as follows:

[0050] (1) 4-Azidobenzoic acid (10 mmol), N-hydroxysuccinimide (12 mmol), and N,N'-dicyclohexylcarbodiimide (12 mmol) were dissolved in 45 mL of 1,4-dioxane and reacted at room temperature for 15 h in the dark. The reaction mixture was filtered, and the filtrate was concentrated by rotary evaporation to give activated 4-azidobenzoic acid. The activated 4-azidobenzoic acid (0.6 g) was dissolved in dimethyl sulfoxide to prepare a 15 g / L solution of activated 4-azidobenzoic acid. Chitosan (1 g) was dissolved in acetic acid / water (1:99, v / v) to prepare a 4 wt% chitosan solution. The activated 4-azidobenzoic acid solution was added to the chitosan solution, and the reaction was allowed to proceed at room temperature for 2.5 d in the dark. The reaction mixture was dialyzed against deionized water and lyophilized to give azidated chitosan;

[0051] (2) The azidated chitosan (0.1 g) was dissolved in 10 mL of acetic acid / dimethyl sulfoxide (1:99, v / v). The betaine alkyne of Preparation Example 1 (0.09 g), sodium ascorbate (0.045 g), and a CuSO4solution (0.019 g, 1 mol / L) were added, and the reaction was allowed to proceed at room temperature for 36 h. The reaction mixture was dialyzed against deionized water and lyophilized to give the chitosan derivative.

[0052] Preparation Example 5

[0053] Preparation Example 5 provides a chitosan derivative, which is prepared as follows:

[0054] (1) 4-azidobenzoic acid (10 mmol), N-hydroxysuccinimide (10 mmol) and N,N'-dicyclohexylcarbodiimide (10 mmol) were dissolved in 40 mL of 1,4-dioxane, and reacted at room temperature for 12 h in the dark. The filtrate was obtained by filtration and rotary evaporation to obtain activated 4-azidobenzoic acid. The activated 4-azidobenzoic acid (0.5 g) was dissolved in dimethyl sulfoxide to prepare a 15 g / L activated 4-azidobenzoic acid solution. Chitosan (1 g) was dissolved in acetic acid / water solution (1:99, v / v) to prepare a 2 wt% chitosan solution. The activated 4-azidobenzoic acid solution was added to the chitosan solution, and reacted at room temperature for 2 d in the dark. The product was obtained by dialysis with deionized water and freeze-drying to obtain azidated chitosan;

[0055] (2) The azidated chitosan (0.1 g) was dissolved in 10 mL of acetic acid / dimethyl sulfoxide solution (1:99, v / v), and acetylene betaine (0.08 g) of Preparation Example 2, sodium ascorbate (0.04 g) and CuSO4 solution (0.017 g, 1 mol / L) were added. The reaction was carried out at room temperature for 24 h, and the product was obtained by dialysis with deionized water and freeze-drying to obtain a chitosan derivative.

[0056] Preparation Example 6

[0057] Preparation Example 6 provides a chitosan derivative, which is prepared as follows:

[0058] (1) 4-azidobenzoic acid (10 mmol), N-hydroxysuccinimide (15 mmol) and N,N'-dicyclohexylcarbodiimide (15 mmol) were dissolved in 50 mL of 1,4-dioxane, and reacted at room temperature for 18 h in the dark. The filtrate was obtained by filtration and rotary evaporation to obtain activated 4-azidobenzoic acid. The activated 4-azidobenzoic acid (0.8 g) was dissolved in dimethyl sulfoxide to prepare a 15 g / L activated 4-azidobenzoic acid solution. Chitosan (1 g) was dissolved in acetic acid / water solution (1:99, v / v) to prepare a 5 wt% chitosan solution. The activated 4-azidobenzoic acid solution was added to the chitosan solution, and reacted at room temperature for 3 d in the dark. The product was obtained by dialysis with deionized water and freeze-drying to obtain azidated chitosan;

[0059] (2) The azidated chitosan (0.1 g) was dissolved in 10 mL of acetic acid / dimethyl sulfoxide solution (1:99, v / v), and acetylene betaine (0.1 g) of Preparation Example 3, sodium ascorbate (0.05 g) and CuSO4 solution (0.021 g, 1 mol / L) were added. The reaction was carried out at room temperature for 48 h, and the product was obtained by dialysis with deionized water and freeze-drying to obtain a chitosan derivative.

[0060] Preparation Example 7

[0061] Preparation Example 7 provides a preparation process of N-dodecyl-4- (ethoxycarbonyl) pyridinium-S-acetic acid inner salt as follows:

[0062]

[0063] 1) Isonicotinic acid ethyl ester (8 mmol) and 12-bromo-1-dodecene (10 mmol) were dissolved in 40 mL of anhydrous ethanol and reacted under reflux condition for 55 h, and then distilled under reduced pressure to obtain a crude product. The crude product was recrystallized with ethyl acetate, filtered, washed with ethyl acetate, and then naturally dried at room temperature to obtain the intermediate 1; 1 HNMR: (400 MHz, DMSO-d6) δ: 1.24-1.35 (m, 17H), 1.99-2.03 (m, 2H), 2.11-2.15 (m, 2H), 4.28-4.32 (m, 2H), 4.86-4.90 (m, 1H), 4.99-5.03 (t, 2H), 5.11-5.15 (m, 1H), 5.80-5.84 (m, 1H), 8.37-8.41 (d, 2H), 9.14-9.18 (d, 2H); MS (ESI) m / z = 318.24 [M].

[0064] 2) The intermediate 1 (20 mmol), mercaptoacetic acid (22 mmol) and triethylamine (11 mmol) were dissolved in 65 mL of dichloromethane and reacted at room temperature for 9 h, and then filtered to obtain a crude product. The crude product was dissolved in an appropriate amount of ethanol, and then an excess of saturated aqueous sodium bicarbonate solution was slowly added under ice-bath stirring. The mixture was stirred at room temperature for 45 min, and then the product was precipitated by adding ethyl acetate. The mixture was filtered, washed with ethyl acetate, and then dried under vacuum to obtain N-dodecyl-4- (ethoxycarbonyl) pyridinium-S-acetic acid inner salt; 1 HNMR: (400 MHz, DMSO-d6) δ: 1.23-1.35 (m, 17H), 1.40-1.44 (m, 2H), 1.55-1.59 (m, 2H), 1.99-2.03 (m, 2H), 2.40-2.44 (t, 2H), 3.55 (s, 2H), 4.28-4.32 (m, 2H), 4.99-5.03 (t, 2H), 8.37-8.41 (d, 2H), 9.14-9.18 (d, 2H); MS (ESI) m / z = 409.23 [M].

[0065] Preparation Example 8

[0066] Preparation Example 8 provides a preparation process of N-dodecyl-4- (ethoxycarbonyl) pyridinium-S-acetic acid inner salt as follows:

[0067] 1 HNMR and MS results were consistent with those of Preparation Example 1.

[0068] 1 HNMR and MS results were consistent with those of Preparation Example 1.

[0069] Preparation Example 9

[0070] Preparation Example 9 provides a method for preparing N-dodecyl-4- (ethoxycarbonyl) pyridinium-S-acetic acid inner salt, which comprises the following steps:

[0071] 1 HNMR and MS results were consistent with those of Preparation Example 1.

[0072] 1 HNMR and MS results were consistent with those of Preparation Example 1.

[0073] Preparation Example 10

[0074] ​​​​Preparation Example 10 provides a modified magnesium-aluminum layered double hydroxide, which is prepared as follows:

[0075] (a) Magnesium nitrate and aluminum nitrate were added to water so that the concentrations of magnesium nitrate and aluminum nitrate were 1.5 mol / L and 0.5 mol / L, respectively, to obtain a precursor solution; sodium nitrate and sodium hydroxide were added to water so that the concentrations of sodium nitrate and sodium hydroxide were 2.5 mol / L and 4 mol / L, respectively, to obtain an alkali solution; the precursor solution was added dropwise to the alkali solution at a volume ratio of 1:1 at 65°C, and then the mixture was placed in an autoclave and reacted at 110°C for 15 h; after the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed with deionized water, and vacuum dried to obtain a magnesium-aluminum layered double hydroxide;

[0076] (b) The magnesium-aluminum layered double hydroxide (1 g) was added to 150 mL of an N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt aqueous solution with a concentration of 0.03 mol / L, stirred at room temperature for 4 h, centrifuged, and the solid was collected and washed with deionized water; after vacuum oven drying at 60°C, a modified magnesium-aluminum layered double hydroxide was obtained.

[0077] Preparation Example 11

[0078] Preparation Example 11 provides a modified magnesium-aluminum layered double hydroxide, which is prepared as follows:

[0079] (a) Magnesium nitrate and aluminum nitrate were added to water so that the concentrations of magnesium nitrate and aluminum nitrate were 1 mol / L and 0.5 mol / L, respectively, to obtain a precursor solution; sodium nitrate and sodium hydroxide were added to water so that the concentrations of sodium nitrate and sodium hydroxide were 2 mol / L and 3 mol / L, respectively, to obtain an alkali solution; the precursor solution was added dropwise to the alkali solution at a volume ratio of 1:1 at 60°C, and then the mixture was placed in an autoclave and reacted at 100°C for 18 h; after the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed with deionized water, and vacuum dried to obtain a magnesium-aluminum layered double hydroxide;

[0080] (b) The magnesium-aluminum layered double hydroxide (1 g) was added to 100 mL of an N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt aqueous solution with a concentration of 0.05 mol / L, stirred at room temperature for 3 h, centrifuged, and the solid was collected and washed with deionized water; after vacuum oven drying at 60°C, a modified magnesium-aluminum layered double hydroxide was obtained.

[0081] Preparation Example 12

[0082] Preparation Example 12 provides a modified magnesium-aluminum layered double hydroxide, which is prepared as follows:

[0083] (a) adding magnesium nitrate and aluminum nitrate into water so that the concentrations of the magnesium nitrate and the aluminum nitrate are 2 mol / L and 0.5 mol / L respectively to obtain a precursor solution; adding sodium nitrate and sodium hydroxide into water so that the concentrations of the sodium nitrate and the sodium hydroxide are 3 mol / L and 5 mol / L respectively to obtain an alkali solution; adding the precursor solution drop by drop into the alkali solution at a volume ratio of 1:1 at 70°C, and then placing the mixture in an autoclave to react at 120°C for 12 h; after the reaction, cooling to room temperature, centrifugation, deionized water washing, and vacuum drying to obtain a magnesium-aluminum layered double hydroxide;

[0084] (b) adding the magnesium-aluminum layered double hydroxide (1 g) into 200 mL of an N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt aqueous solution with a concentration of 0.02 mol / L, stirring at room temperature for 5 h, centrifugation, collecting the solid and washing with deionized water, and vacuum drying at 60°C to obtain a modified magnesium-aluminum layered double hydroxide.

[0085] Example 1

[0086] Example 1 provides a preparation method of a composite phosphorus removal agent, and the specific process is as follows:

[0087] adding the chitosan derivative of Preparation Example 4 (0.3 g) and sodium alginate (0.5 g) into 55 mL of deionized water to stir uniformly, adding the modified magnesium-aluminum layered double hydroxide of Preparation Example 10 (0.45 g) to mix uniformly, and then adding the above solution into a lanthanum nitrate solution with a concentration of 5 wt% to form gel microspheres, washing with deionized water, and vacuum drying to obtain a composite phosphorus removal agent.

[0088] Example 1 also provides a composite phosphorus removal agent obtained by the above preparation method.

[0089] Example 2

[0090] Example 2 provides a preparation method of a composite phosphorus removal agent, and the specific process is as follows:

[0091] adding the chitosan derivative of Preparation Example 5 (0.6 g) and sodium alginate (0.6 g) into 60 mL of deionized water to stir uniformly, adding the modified magnesium-aluminum layered double hydroxide of Preparation Example 11 (0.45 g) to mix uniformly, and then adding the above solution into a lanthanum nitrate solution with a concentration of 5 wt% to form gel microspheres, washing with deionized water, and vacuum drying to obtain a composite phosphorus removal agent.

[0092] Example 2 also provides a composite phosphorus removal agent obtained by the above preparation method.

[0093] Example 3

[0094] Example 3 provides a preparation method of the composite phosphorus removal agent, and the specific process is as follows:

[0095] The chitosan derivative of Preparation Example 6 (0.4 g) and sodium alginate (0.3 g) were added into 50 mL of deionized water and stirred until uniform, and then the modified magnesium-aluminum layered double hydroxide of Preparation Example 12 (0.45 g) was added and mixed until uniform, and then the above solution was added dropwise into a lanthanum nitrate solution with a concentration of 5 wt% to form gel microspheres, which were washed with deionized water and vacuum dried to obtain the composite phosphorus removal agent.

[0096] Example 3 also provides the composite phosphorus removal agent obtained by the above preparation method.

[0097] Comparative Example 1

[0098] Comparative Example 1 is basically the same as Example 1, except that the chitosan derivative in Example 1 is replaced by chitosan.

[0099] Comparative Example 2

[0100] Comparative Example 2 is basically the same as Example 1, except that the modified magnesium-aluminum layered double hydroxide in Example 1 is replaced by the magnesium-aluminum layered double hydroxide obtained in step (a) of Preparation Example 10.

[0101] Structural characterization

[0102] The chitosan, azidated chitosan, and chitosan derivative obtained in Preparation Example 4 were subjected to FT-IR testing, and the results are shown in Figure 1 Figure 1 In the figure, curve a corresponds to chitosan, curve b corresponds to azidated chitosan, and curve c corresponds to the chitosan derivative. As can be seen from the figure, Figure 1 compared with chitosan, azidated chitosan has a characteristic absorption peak of the azide group at 2130 cm -1 , indicating that the azidated chitosan is successfully prepared; compared with azidated chitosan, the chitosan derivative has characteristic absorption peaks of C=C-N=N and methyl groups on the quaternary ammonium salt at 2520 cm -1 and 1474 cm -1 , indicating that the chitosan derivative is successfully prepared.

[0103] The composite phosphorus removal agent obtained in Example 1 was subjected to scanning electron microscope testing, and the results are shown in Figure 2 .

[0104] Performance testing

[0105] ​(1) Removal rate: 8 mg of the phosphorus removal agent prepared in Examples 1-3 and Comparative Example 1-2 was added to 50 mL of an aqueous solution of phosphate (KH2PO4) having an initial concentration of 30 mg / L, and the mixture was shaken at 25°C until adsorption equilibrium was reached. The supernatant was filtered through a 0.45 μm filter, and the concentration of phosphate in the filtrate was measured. The removal rate of the phosphorus removal agent was calculated according to the following formula: R (%) = (C0-C t ) / C0x 100%, where C0and C t are the concentrations of phosphate in the solution before and after adsorption, respectively, and the unit is mg / L. The results are shown in Table 1.

[0106] (2) Adsorption capacity: 8 mg of the phosphorus removal agent prepared in Examples 1-3 and Comparative Example 1-2 was added to 50 mL of an aqueous solution of phosphate (KH2PO4) having an initial concentration of 30 mg / L, and the mixture was shaken at 25°C until adsorption equilibrium was reached. The supernatant was filtered through a 0.45 μm filter, and the concentration of phosphate in the filtrate was measured. The adsorption capacity of the phosphorus removal agent was calculated according to the following formula: Q e = V (C0-C e ) / m, where Q e represents the adsorption amount of the adsorbent at adsorption equilibrium, the unit is mg / g; V represents the volume of the phosphate solution, the unit is L; C e and C0represent the concentrations of phosphate in the equilibrium solution and the initial solution, respectively, and the unit is mg / L; and m represents the mass of the phosphorus removal agent, the unit is g. The results are shown in Table 1.

[0107] (3) Adsorption performance at different pH values: 50 mL of an aqueous solution of phosphate (KH2PO4) having an initial concentration of 30 mg / L was prepared, and the pH value was adjusted to 3, 5, 7, 9 and 11 using 0.1 mol / L HCl solution and NaOH solution. 8 mg of the phosphorus removal agent prepared in Examples 1-3 and Comparative Example 1-2 was added to the aqueous solution of phosphate having different pH values, respectively, and the mixture was shaken at 25°C until adsorption equilibrium was reached. The filtrate was filtered through a 0.45 μm filter, and the concentration of phosphate in the filtrate was measured. The adsorption rate of the phosphorus removal agent was calculated, and the results are shown in Table 2.

[0108] (4) Reusability test: 8 mg of the phosphorus removal agent prepared in Examples 1-3 and Comparative Example 1-2 was added to 50 mL of an aqueous solution of phosphate (KH2PO4) having an initial concentration of 30 mg / L, and the mixture was shaken at 25°C until adsorption equilibrium was reached. The phosphorus removal agent and the solution were separated by filtration through a 0.45 μm filter. The phosphorus removal agent was then placed in 0.1 mol / L NaOH solution for desorption, and after filtration, it was washed with deionized water until it was neutral. After drying, the above adsorption-desorption cycle was repeated for 10 times. After the end of the 10th cycle, the concentration of residual phosphate in the filtrate was measured again using the molybdenum-antimony anti-spectrophotometric method, and the adsorption rate after 10 cycles was calculated. The results are shown in Table 3.

[0109] (5) Anti-interference performance: 8 mg of the phosphorus removal agent prepared in each of Examples 1-3 and Comparative Examples 1-2 was added into 50 mL of an aqueous solution of phosphate (KH2PO4) with an initial concentration of 30 mg / L, and Na2SO4 (30 mg / L) or NaCl (30 mg / L) was added, respectively, and the mixture was oscillated at 25°C until adsorption equilibrium was reached. The supernatant was filtered through a 0.45 μm filter membrane, the concentration of phosphate in the filtrate was determined, and the removal rate of the phosphorus removal agent was calculated. The results are shown in Table 3.

[0110] Table 1

[0111]

[0112] Table 2

[0113]

[0114] Table 3

[0115]

[0116] From the experimental data in Tables 1-3, it can be seen that the composite phosphorus removal agent prepared in Examples 1-3 has a large adsorption capacity, a wide pH range, high selectivity and good regeneration performance.

[0117] Compared with Example 1, the phosphorus removal agent prepared in Comparative Example 1-2 has a decrease in adsorption capacity, pH range, anti-interference performance and reusability to different extents, indicating that the modified magnesium-aluminum layered double hydroxide and the chitosan derivative of the present application can improve the adsorption effect of the phosphorus removal agent to different extents.

[0118] Specific analysis is made on the above results: ① The modified magnesium-aluminum layered double hydroxide of the application is obtained by intercalating modification of N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt on magnesium-aluminum layered double hydroxide. The intercalation structure has three effects: one is to expand the interlayer spacing, significantly reducing the diffusion resistance of phosphate; two is that the zwitterion pair formed by pyridinium and carboxylate can enhance the selective recognition of phosphate and inhibit the interference of competitive anions such as sulfate and chloride through electrostatic shielding effect; three is to improve the surface hydrophilicity and the number of ion exchange sites of the material. The three effects work together to significantly improve the selectivity, adsorption capacity and adsorption rate of the phosphorus removal agent. ② The chitosan derivative of the application is prepared by click chemistry reaction of azidated chitosan and alkynyl betaine, which introduces triazole ring connecting arm and end group quaternary ammonium group on the chitosan main chain. The quaternary ammonium group of the derivative can efficiently capture phosphate through strong electrostatic interaction in a wide pH range, solving the problem of efficiency reduction of traditional adsorbents in alkaline conditions due to the weakening of surface charge; at the same time, the conjugated structure of the triazole ring can further strengthen the adsorption of phosphate through secondary interactions such as π-π stacking. ③ The quaternary ammonium group and triazole ring in the chitosan derivative, as well as the pyridinium ion in the intercalating agent, all have strong antibacterial activity, which can effectively inhibit the growth of bacteria on the surface and in the pores of the material, prevent the formation of biofilm, and avoid the blockage of adsorption channels and the inactivation of active sites. This feature, combined with the stable gel skeleton, not only ensures the sustained stability of the phosphorus removal agent in the long-term operation process, but also provides excellent regeneration performance, so that it can maintain a high adsorption capacity in repeated use.

[0119] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the application, but not to limit it. The basic principles and main features of the application have been described in the above specific embodiments, and some modifications or replacements can be made on the basis of the application, but these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the application claimed.

Claims

1. A method for preparing a composite phosphorus removal agent, characterized by, The method comprises the following steps: The chitosan derivative and sodium alginate are added into water and stirred uniformly, and then the modified magnesium-aluminum layered double hydroxide is added to obtain a mixed solution; the mixed solution is added into a lanthanum nitrate solution to form gel microspheres, and the gel microspheres are washed and vacuum dried to obtain the composite phosphorus removal agent; The modified magnesium-aluminum layered double hydroxide is prepared by modifying the magnesium-aluminum layered double hydroxide with N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt; the structural formula of the N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt is as follows: ； The preparation process of the chitosan derivative is as follows: (1) 4-azidobenzoic acid, N-hydroxysuccinimide and N,N'-dicyclohexyl carbodiimide are added into 1,4-dioxane to perform a first light-avoiding reaction to obtain activated 4-azidobenzoic acid; a dimethyl sulfoxide solution of the activated 4-azidobenzoic acid is added into an acetic acid / water solution of chitosan to perform a second light-avoiding reaction to obtain azidated chitosan; (2) the azidated chitosan is added into an acetic acid / dimethyl sulfoxide mixed solvent, and then ynyl betaine, sodium ascorbate and a CuSO4 solution are added to perform a reaction to obtain the chitosan derivative; The structural formula of the ynyl betaine is as follows: 。 2. The method of claim 1, wherein the composite phosphorus removal agent is prepared by the steps of: In step (1), the molar ratio of the 4-azidobenzoic acid, N-hydroxysuccinimide and N,N'-dicyclohexyl carbodiimide is 1:(1-1.5):(1-1.5); the mass ratio of the chitosan to the activated 4-azidobenzoic acid is 1:(0.5-0.8); the time of the first light-avoiding reaction is 12-18 h; and the time of the second light-avoiding reaction is 2-3 d.

3. The method of claim 1, wherein the composite phosphorus removal agent is prepared by the steps of: In step (2), the mass ratio of the azidated chitosan, ynyl betaine, sodium ascorbate and CuSO4 is 1:(0.8-1):(0.4-0.5):(0.17-0.21); and the reaction time is 24-48 h.

4. The method of claim 1, wherein the composite phosphorus removal agent is prepared by the steps of: In step (2), the preparation process of the ynyl betaine is as follows: propargylamine and N,N-diisopropylethylamine are added into dichloromethane, and then a dichloromethane solution of betaine chloride acid chloride is added at 0°C to perform a reaction to obtain the ynyl betaine; the molar ratio of the propargylamine, betaine chloride acid chloride and N,N-diisopropylethylamine is 1:(1.4-2):(3-4).

5. The method of claim 1, wherein the composite phosphorus removal agent is prepared by the steps of: The preparation process of the modified magnesium-aluminum layered double hydroxide is as follows: (a) magnesium nitrate and aluminum nitrate are added into water to obtain a precursor solution; sodium nitrate and sodium hydroxide are added into water to obtain an alkali solution; the precursor solution is added into the alkali solution at 60-70°C to perform a hydrothermal reaction, and after treatment, a magnesium-aluminum layered double hydroxide is obtained; (b) the magnesium-aluminum layered double hydroxide is added into a N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt solution, and stirred to perform a reaction, and after treatment, the modified magnesium-aluminum layered double hydroxide is obtained.

6. The method of claim 5, wherein the composite phosphorus removal agent is prepared by the steps of: The concentration of magnesium nitrate and aluminum nitrate in the precursor solution in step (a) is 1-2 mol / L and 0.5 mol / L respectively; the concentration of sodium nitrate and sodium hydroxide in the alkali solution is 2-3 mol / L and 3-5 mol / L respectively; the volume ratio of the precursor solution and the alkali solution is 1:1; the temperature of the hydrothermal reaction is 100-120℃, and the time is 12-18 h.

7. The method for preparing the composite phosphorus removal agent according to claim 5, characterized in that, In step (b), the ratio of the amount of the magnesium-aluminum layered double hydroxide and the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt solution is 1 g:(100-200) mL; the concentration of the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt solution is 0.02-0.05 mol / L; the stirring reaction time is 3-5 h.

8. The method of claim 7, wherein the composite phosphorus removal agent is prepared by the steps of: The preparation process of the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt is as follows: ​ 1) ethyl isonicotinate and 12-bromo-1-dodecene are added to ethanol, and refluxed to obtain intermediate 1; the structural formula of the intermediate 1 is as follows: ； 2) the intermediate 1, mercaptoacetic acid and triethylamine are added to dichloromethane, and reacted at room temperature to obtain the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt.

9. The method of claim 8, wherein the composite phosphorus removal agent is prepared by the steps of: In step 1), the molar ratio of ethyl isonicotinate and 12-bromo-1-dodecene is 1:(1-1.5), and the reflux reaction time is 48-60 h; in step 2), the molar ratio of the intermediate 1, mercaptoacetic acid and triethylamine is 1:(1-1.25):(0.5-0.6), and the reaction time at room temperature is 8-10 h. ​ 10. A composite phosphorus removal agent, characterized by, Prepared by the preparation method of any one of claims 1-9. Prepared by the preparation method of any one of claims 1-9.

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