Multifunctional composite ball for removing surface water algae and preparation method thereof

Abstract

The present invention discloses a multifunctional composite ball for removing algae from surface water and a preparation method thereof, and relates to the field of water treatment. The preparation method of the multifunctional composite ball for removing algae from surface water comprises the following steps: (1) using a soluble iron salt and a soluble ferrous salt as iron sources and a soluble alkali as a precipitant to coprecipitate magnetic balls in an inert gas atmosphere; (2) forming a titanium dioxide coating on the surface of the magnetic ball; and (3) forming a chitosan coating on the surface of the titanium dioxide coating to obtain the multifunctional composite ball. The present invention can rapidly remove surface algae, reduce the generation of odorous substances, and simultaneously enable rapid recycling, significantly reducing the operating load of drinking water treatment.

Description

Technical Field

[0001] The present invention relates to the field of water treatment, in particular to a multifunctional composite ball for removing algae from surface water and a preparation method thereof. Background Art

[0002] Algal contamination of surface water is a serious problem that affects the ecological balance of aquatic bodies. Human activities create polluted water rich in nutrients like nitrogen and phosphorus, creating favorable conditions for algae growth. Lakes, reservoirs, and other water sources are particularly susceptible to algae contamination during summer. During their metabolism, algal cells in the water release microcystins and odorous substances. Microcystins are known to have "tri-toxic" effects, second only to dioxins in their toxicity. The main odorous substances are 2-methylisoborneol (2-MIB) and geosmin (GSM). Their extremely low odor thresholds mean they can emit strong musty and earthy odors even at very low concentrations. Therefore, two new indicators have been added to the newly released Drinking Water Standard (GB5749-2022): 2-methylisoborneol (2-MIB) and geosmin (GSM) levels should be less than 10 ng / L. Existing methods for removing algae rely on sedimentation and filtration disinfection processes performed in water treatment plants. When algae in surface water cannot be effectively removed by coagulation, sedimentation and filtration processes, the algae enter the disinfection process. In order to kill the algal cells, more disinfectants need to be added, which will lead to the large-scale production of disinfection by-products (THMs), which poses a severe challenge to conventional drinking water treatment processes. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a multifunctional composite ball for removing surface water algae and a preparation method thereof, which can quickly remove surface algae and reduce the generation of odorous substances. At the same time, it can be quickly recycled, greatly reducing the operating load of the drinking water treatment system.

[0004] In order to solve the above technical problems, the present invention provides a method for preparing a multifunctional composite ball for removing algae from surface water, which comprises the following steps:

[0005] (1) Using soluble iron salt and soluble ferrous salt as iron sources and soluble alkali as precipitant, magnetic spheres are prepared by co-precipitation in an inert gas atmosphere;

[0006] (2) forming a titanium dioxide coating on the surface of the magnetic ball;

[0007] (3) A chitosan coating layer is formed on the surface of the titanium dioxide coating to obtain a multifunctional composite ball.

[0008] As an improvement of the above technical solution, the soluble iron salt is selected from one or more of ferric nitrate, ferric sulfate, and ferric chloride; and / or

[0009] The soluble ferrous salt is selected from one or more of ferrous nitrate, ferrous sulfate, and ferrous chloride; and / or

[0010] The precipitant is selected from one or more of sodium hydroxide, ammonia water, and potassium hydroxide; and / or

[0011] The inert gas is one or more of helium, nitrogen and argon; and / or

[0012] The molar ratio of the soluble ferrous salt to the soluble ferric salt is 1:1.5 to 1:3; and / or

[0013] The pH value during the coprecipitation process is controlled at 8.5-12; and / or

[0014] The precipitate obtained by solid-liquid separation after coprecipitation is heat-treated at 100°C to 300°C.

[0015] As an improvement of the above technical solution, the molar ratio of the soluble ferrous salt to the soluble ferric salt is 1:2; and / or

[0016] The precipitant is ammonia water, and its concentration is 10wt%~22wt%; and / or

[0017] Nitrogen is selected as the inert gas; and / or

[0018] The pH value during the coprecipitation process is controlled at 9-11; and / or

[0019] After the coprecipitation, heat treatment is performed at 100°C to 200°C in an inert gas atmosphere.

[0020] As an improvement to the above technical solution, step (1) includes:

[0021] (1.1) Dissolving a soluble iron salt and a soluble ferrous salt in water to obtain a first solution; adding aqueous ammonia dropwise in a nitrogen atmosphere until the pH is 9 to 11, and obtaining a precipitate after solid-liquid separation; wherein the concentration of the soluble iron salt in the first solution is 0.2 mol / L to 0.5 mol / L, and the concentration of the soluble ferrous salt in the first solution is 0.1 mol / L to 0.25 mol / L;

[0022] (1.2) Washing the precipitate with water 3 to 6 times;

[0023] (1.3) Heat-treat the washed precipitate at 100°C to 200°C in an inert gas atmosphere for 2 h to 6 h to obtain magnetic spheres.

[0024] As an improvement to the above technical solution, in step (2), titanium dioxide nanoparticles are prepared by a sol-gel method using tetrabutyl titanate as a titanium source, and the titanium dioxide nanoparticles are mixed with a water-ethanol mixed solvent and then sprayed onto the surface of the magnetic ball to form a titanium dioxide coating;

[0025] Wherein, the particle size of the titanium dioxide nanoparticles is 10nm~50nm.

[0026] As an improvement to the above technical solution, step (2) includes:

[0027] (2.1) Tetrabutyl titanate is added dropwise to a solvent and the pH is adjusted to 2 to 3 to obtain a precursor solution, wherein the volume ratio of the solvent to the tetrabutyl titanate is 2:1 to 5:1;

[0028] (2.2) adding water to the precursor solution and stirring to react to obtain titanium dioxide gel; wherein the volume ratio of water to the precursor solution is 1:1 to 10:1;

[0029] (2.3) aging the titanium dioxide gel and then heat-treating it to obtain titanium dioxide nanoparticles;

[0030] (2.4) Mixing the titanium dioxide nanoparticles with a water-ethanol mixed solvent and dispersing them using ultrasound to prepare a mixed solution with a solid content of 70 wt% to 95 wt%, and spraying the mixed solution onto the surface of the magnetic sphere to form a titanium dioxide coating; wherein the volume ratio of ethanol to water in the water-ethanol mixed solvent is 7:3 to 8:2.

[0031] As an improvement to the above technical solution, the solvent is selected from one or more of ethanol, propanol, butanol, and ethylene glycol; and / or

[0032] In step (2.1), acetic acid or hydrochloric acid is used to adjust the pH; and / or

[0033] In step (2.2), the stirring speed is 400 rpm to 600 rpm, and the stirring reaction time is 1 h to 3 h; and / or

[0034] In step (2.3), the aging time is 24h~48h, and the aging temperature is 15℃~35℃; and / or

[0035] In step (2.3), the heat treatment temperature is 300°C to 550°C, and the heat treatment time is 2h to 5h.

[0036] As an improvement of the above technical solution, in step (3), chitosan is first modified with glycidyl trimethylammonium chloride, and then evenly coated on the magnetic sphere with titanium dioxide coating, and solidified to form a chitosan coating layer.

[0037] As an improvement to the above technical solution, step (3) includes:

[0038] (3.1) Dissolving chitosan in a 0.5 wt% to 3 wt% aqueous acetic acid solution to obtain a second solution, wherein the ratio of chitosan weight to acetic acid volume is 1 g to 5 g: 50 mL to 150 mL;

[0039] (3.2) Dissolving glycidyl trimethylammonium chloride in water to obtain a third solution; wherein the concentration of glycidyl trimethylammonium chloride in the third solution is 10 g / L to 20 g / L;

[0040] (3.3) Add the third solution to the second solution, adjust the pH to 9-11, react at 50-60°C for 4-6 hours, and wash with water to obtain an intermediate solution; wherein the volume ratio of the third solution to the second solution is 1:1-1:2;

[0041] (3.4) Centrifuge the intermediate solution to obtain the supernatant, which is the modified chitosan solution;

[0042] (3.5) Immerse the titanium dioxide-coated magnetic spheres in the modified chitosan solution, remove them after 3 to 5 minutes, and dry them at 70 to 100°C for 1 to 5 hours to form a chitosan coating.

[0043] Correspondingly, the present invention also discloses a multifunctional composite ball for removing algae from surface water, which is prepared by the above-mentioned method for preparing the multifunctional composite ball for removing algae from surface water.

[0044] The implementation of the present invention has the following beneficial effects:

[0045] In a method for preparing multifunctional composite spheres for removing algae from surface water, according to one embodiment of the present invention, magnetic spheres are first prepared, then a titanium dioxide coating is formed on their surface, and finally chitosan coating is applied. Firstly, these multifunctional composite spheres have a large specific surface area, and the chitosan coating can adsorb various pollutants through hydroxyl bonding, chelation, and electrostatic interactions. This allows the multifunctional composite spheres to effectively adsorb free algal cells in the water, causing them to flocculate and inhibit their growth. They also adsorb algal metabolites, achieving the purpose of pollutant removal. Secondly, the adsorbed algae and their metabolites are decomposed by the highly oxidizing free radicals generated by the titanium dioxide nanoparticles under light excitation, inhibiting algal growth and decomposing algal metabolites. Furthermore, the multifunctional composite sphere structure of the present invention removes algae without damaging algal cells, releasing toxins, or causing secondary water pollution. Thirdly, the chitosan coating enhances the adhesion between the layers, resulting in a granular structure that is less likely to decompose into a powder during use and easily recyclable. Furthermore, because the magnetic spheres serve as the core, the multifunctional composite spheres can be recovered after use through an external magnetic field. Depending on the surface condition, they can be re-sprayed and re-wetted for recycling, significantly reducing both their cost of use and water treatment. In summary, the multifunctional composite spheres of this embodiment can pre-treat water bodies affected by algae outbreaks, killing algae and decomposing algae metabolites, significantly reducing the subsequent processing load at water plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a scanning electron microscope image of the multifunctional composite ball prepared in Example 1 of the present invention;

[0047] Figure 2 This is an infrared spectrum of the multifunctional composite ball prepared in Example 1 of the present invention;

[0048] Figure 3 is a microscopic image of the Melospora cells in the water sample before treatment in the experimental example of the present invention;

[0049] Figure 4 This is a microscope image of the Stratum canina cells in a water sample treated with the multifunctional composite ball prepared in Example 1 in a test example of the present invention under lightless conditions. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with specific implementation methods.

[0051] In one embodiment of the present invention, a method for preparing a multifunctional composite ball for removing algae from surface water is provided, which comprises the following steps:

[0052] S1: Using soluble iron salt and soluble ferrous salt as iron sources and soluble alkali as precipitant, magnetic spheres are prepared by co-precipitation in an inert gas atmosphere;

[0053] The soluble iron salt is an iron salt soluble in water or other organic solvents, for example, one or more of water-soluble iron nitrate, iron sulfate, iron chloride, and iron bromide, but not limited thereto. Another example is one or more of ethanol-soluble iron phosphate, iron chloride, and iron nitrate, but not limited thereto. Preferably, in one embodiment, the soluble iron salt is one or more of iron nitrate, iron sulfate, and iron chloride, all of which are soluble in water, have a simple reaction system, and are easy to prepare.

[0054] The soluble ferrous salt is a ferrous salt soluble in water or other organic solvents. For example, the soluble ferrous salt is one or more of ferrous nitrate, ferrous sulfate, ferrous chloride, and ferrous bromide that are soluble in water, but is not limited thereto. Another example is one or more of ferrous chloride, ferrous nitrate, and ferrous bromide that are soluble in ethanol, but is not limited thereto. Preferably, in one embodiment, the soluble ferrous salt is one or more of ferrous nitrate, ferrous sulfate, and ferrous chloride; all of which are soluble in water, have a simple reaction system, and are easy to prepare.

[0055] In order to form magnetic spheres with strong magnetism and uniform particle size distribution, the molar ratio of soluble ferrous salt to soluble ferric salt is controlled to be 1:1.5 to 1:3, illustratively 1:1.8, 1:2, 1:2.3, 1:2.5, or 1:2.7, but not limited thereto. Preferably, it is 1:1.8 to 1:2.5, and more preferably, it is 1:2.

[0056] The precipitant may be one or more of sodium hydroxide, ammonia, and potassium hydroxide, but is not limited thereto. By adding the precipitant, the pH of the coprecipitation system is controlled to 8.5 to 12, thereby precipitating magnetic particles having strong magnetism. Exemplarily, the pH of the coprecipitation system is 9, 9.5, 10, 10.5, or 11, but is not limited thereto. Preferably, the pH is 9 to 11.

[0057] Specifically, to prevent the magnetic particles from being oxidized, the coprecipitation reaction is carried out in an inert gas atmosphere. Specifically, the inert gas can be one or more of helium, nitrogen, and argon, but is not limited thereto. Preferably, the inert gas is nitrogen.

[0058] Furthermore, in order to optimize the magnetism of the magnetic spheres, in one embodiment, the magnetic particles obtained by co-precipitation are heat-treated, which improves the uniformity and crystallinity of the particles and further optimizes their magnetism. Specifically, the heat treatment temperature is 100°C to 300°C, and the heat treatment time is 2h to 8h. More preferably, the heat treatment temperature is 100°C to 200°C, and the heat treatment time is 2h to 6h. In addition, in order to prevent the magnetic particles from oxidizing during the heat treatment process, the heat treatment is also carried out in an inert gas atmosphere. Specifically, the inert gas may be one or more of helium, nitrogen, and argon, but is not limited thereto. Preferably, the inert gas is nitrogen.

[0059] Preferably, in one embodiment of the present invention, step S1 includes:

[0060] S11: dissolving a soluble iron salt and a soluble ferrous salt in water to obtain a first solution; adding aqueous ammonia dropwise in a nitrogen atmosphere until the pH is 9 to 11, and obtaining a precipitate after solid-liquid separation;

[0061] The concentration of the soluble iron salt in the first solution is 0.2 mol / L to 0.5 mol / L, exemplified by 0.25 mol / L, 0.29 mol / L, 0.33 mol / L, 0.39 mol / L or 0.45 mol / L, but not limited thereto.

[0062] The concentration of the soluble ferrous salt in the first solution is 0.1 mol / L to 0.25 mol / L, exemplarily 0.12 mol / L, 0.15 mol / L, 0.18 mol / L or 0.21 mol / L, but not limited thereto.

[0063] Preferably, in one embodiment, in order to promote dissolution and coprecipitation reactions, stirring is performed during the preparation of the first solution and the addition of ammonia water, and the stirring speed is controlled to be 200 rpm to 400 rpm.

[0064] S12: washing the precipitate with water 3 to 6 times;

[0065] By washing, unreacted reactants and generated by-products can be removed.

[0066] S13: The washed precipitate is heat-treated at 100°C to 200°C in an inert gas atmosphere for 2 to 6 hours to obtain magnetic spheres. Based on the above steps, Fe3O4 magnetic spheres with strong magnetism and uniform particle size distribution can be obtained.

[0067] S2: forming a titanium dioxide coating on the surface of the magnetic ball;

[0068] Titanium dioxide particles can be mixed with a dispersant (such as water, ethanol, or a styrene-acrylic emulsion) and then coated onto the surface of the magnetic sphere. To ensure the ability to degrade surface algae, the titanium dioxide particle size is controlled to be between 10 nm and 80 nm, exemplified by, but not limited to, 15 nm, 20 nm, 40 nm, 50 nm, 70 nm, or 75 nm. Preferably, it is between 10 nm and 50 nm.

[0069] Preferably, in some embodiments, tetrabutyl titanate is used as a titanium source, titanium dioxide nanoparticles are prepared by a sol-gel method, and the titanium dioxide nanoparticles are mixed with a water-ethanol mixed solvent and then sprayed onto the surface of the magnetic ball to form a titanium dioxide coating.

[0070] Furthermore, based on this embodiment, step S2 includes:

[0071] S21: adding tetrabutyl titanate dropwise into a solvent and adjusting the pH to 2-3 to obtain a precursor solution;

[0072] The solvent is selected from one or more of ethanol, propanol, butanol, and ethylene glycol, but is not limited thereto. The volume ratio of the solvent to tetrabutyl titanate is 2:1 to 5:1, illustratively 2.5:1, 3:1, 3.5:1, 4:1, or 4.5:1, but is not limited thereto. Preferably, it is 2:1 to 4:1.

[0073] Wherein, acetic acid or hydrochloric acid is used to adjust the pH, but it is not limited thereto. Exemplarily, the pH after adjustment is 2.2, 2.4, 2.6 or 2.8, but it is not limited thereto.

[0074] S22: adding water to the precursor solution and stirring to react to obtain titanium dioxide gel;

[0075] After adding water, a hydrolysis reaction occurs, first forming a sol, and then gradually polymerizing to form a gel. In order for the hydrolysis reaction to proceed smoothly, the volume ratio of water to the precursor solution is controlled to be 1:1 to 10:1, illustratively 2:1, 4:1, 6:1, 7:1 or 9:1, but not limited thereto. Preferably, it is 3:1 to 7:1. At the same time, during the hydrolysis reaction, the reaction system is stirred at a stirring speed of 400 rpm to 600 rpm, and the stirring reaction time is 1 hour to 3 hours.

[0076] S23: aging the titanium dioxide gel and then heat-treating it to obtain titanium dioxide nanoparticles;

[0077] Among them, the aging time is 24h~48h, and the aging temperature is 15℃~35℃.

[0078] The heat treatment temperature of the aged titanium dioxide gel is 300°C to 550°C, and the heat treatment time is 2h to 5h.

[0079] After the above reaction steps, titanium dioxide nanoparticles with strong reactivity and high uniformity of particle size can be obtained, providing a good foundation for the subsequent decomposition of algae and its metabolites. Specifically, the particle size of the titanium dioxide nanoparticles is 10nm to 50nm.

[0080] S24: Mix titanium dioxide nanoparticles with a water-ethanol mixed solvent, and use ultrasound to disperse them to prepare a mixed solution with a solid content of 70 wt% to 95 wt%, and spray the mixed solution onto the surface of the magnetic ball to form a titanium dioxide coating.

[0081] The volume ratio of ethanol to water in the water-ethanol mixed solvent is 7:3 to 8:2. Preferably, in one embodiment, a surfactant may be added to the water-ethanol mixed solvent to prevent particle agglomeration. The surfactant may be, but is not limited to, polyethylene glycol or citric acid, and the amount added is 0.5 to 1 wt%.

[0082] S3: A chitosan coating layer is formed on the surface of the titanium dioxide coating to obtain a multifunctional composite ball.

[0083] The chitosan can be mixed with water to coat the magnetic particles with titanium dioxide coating, or the chitosan aqueous solution can be sprayed onto the magnetic particles with titanium dioxide coating and then dried and solidified to form the chitosan coating layer, but the invention is not limited thereto.

[0084] Preferably, in one embodiment, chitosan is first modified with glycidyl trimethylammonium chloride, then evenly coated onto a titanium dioxide-coated magnetic sphere, and dried and solidified to form a chitosan coating. This modification further enhances the algae removal performance of the multifunctional composite sphere.

[0085] Specifically, based on this embodiment, step S3 includes:

[0086] S31: dissolving chitosan in a 0.5 wt % to 3 wt % acetic acid aqueous solution to obtain a second solution;

[0087] The ratio of the weight of chitosan to the volume of the acetic acid aqueous solution is 1 g to 5 g: 50 mL to 150 mL; illustratively, 1.3 g: 55 mL, 1.7 g: 67 mL, 2.5 g: 87 mL, 3 g: 115 mL, 4 g: 127 mL or 4.8 g: 149 mL, but is not limited thereto.

[0088] S32: dissolving glycidyltrimethylammonium chloride in water to obtain a third solution;

[0089] The concentration of glycidyltrimethylammonium chloride in the third solution is 10 g / L to 20 g / L, illustratively 12 g / L, 14 g / L, 16 g / L or 18 g / L, but not limited thereto.

[0090] It should be noted that there is no particular order for steps S31 and S32. Step S31 may be performed first, and then step S32; step S32 may be performed first, and then step S31; or both may be performed simultaneously.

[0091] S33: adding the third solution to the second solution, adjusting the pH to 9-11, reacting at 50° C.-60° C. for 4-6 hours, and washing with water to obtain an intermediate solution;

[0092] The volume ratio of the third solution to the second solution is 1:1 to 1:2, illustratively 1:1.2, 1:1.4, 1:1.6 or 1:1.8, but not limited thereto.

[0093] The pH of the reaction system may be adjusted using an alkaline solution, for example, sodium hydroxide solution, potassium hydroxide solution, ammonia water, etc., but is not limited thereto.

[0094] After the reaction is completed, the unreacted glycidyl trimethylammonium chloride and other by-products can be removed by washing with a large amount of water.

[0095] Preferably, in order to optimize the modification speed, in one embodiment, stirring is performed with a stirring speed of 200 rpm to 400 rpm.

[0096] S34: centrifuging the intermediate solution to obtain a supernatant as a modified chitosan solution;

[0097] S35: Immersing the magnetic ball with the titanium dioxide coating into the modified chitosan solution, taking it out after 3 minutes to 5 minutes, and drying it at 70° C. to 100° C. for 1 hour to 5 hours to form a chitosan coating layer.

[0098] Correspondingly, one embodiment of the present invention also discloses a multifunctional composite ball for removing surface water algae, which is prepared by the above method and can be used to remove common algae, such as green algae, blue algae, diatoms, etc., but is not limited thereto.

[0099] The present invention will be described below with specific embodiments:

[0100] Example 1

[0101] This embodiment provides a multifunctional composite ball for removing algae from surface water, and the preparation method thereof is as follows:

[0102] S1: Weigh 1.52g of ferrous sulfate and 3.25g of ferric chloride into a three-necked flask, add 100mL of deionized water, and stir thoroughly with a magnetic stirrer at 250rpm to form an iron salt solution. After purging with nitrogen, slowly add aqueous ammonia dropwise until the pH reaches 9. The iron salt precipitates as Fe₃O₄. Wash the precipitate five times with deionized water. Heat-treat the washed particles at 110°C in a nitrogen atmosphere for 3h to obtain magnetic spheres.

[0103] S2: Ethanol was added to a beaker, followed by the slow dropwise addition of tetrabutyl titanate (at a volume ratio of 2:1). Hydrochloric acid was slowly added at room temperature to adjust the pH to 2, yielding a precursor solution. Deionized water was then added to the precursor solution at a volume ratio of 3:1. The mixture was stirred at 420 rpm for 3 hours. As the hydrolysis reaction proceeded, a sol gradually formed, followed by polymerization to form a gel. The gel was aged at room temperature for 28 hours and then heat-treated at 320°C for 5 hours to produce 47 nm titanium dioxide nanoparticles. The prepared titanium dioxide nanoparticles were then mixed with a water-ethanol mixture (8:2) to yield a mixed solution with a solid content of 85 wt%. The mixed solution was sprayed onto the surface of the magnetic spheres to form a titanium dioxide coating.

[0104] S3: Dry the chitosan powder in a 70°C forced air drying oven. Remove the dried chitosan powder and weigh 1.5 g of chitosan powder. Add it to a beaker containing 100 mL of 1 wt% acetic acid solution. Add a magnetic stirrer and adjust the speed to 200 rpm. Stir until completely dissolved to obtain a chitosan solution. In another beaker, weigh 1.5 g of glycidyltrimethylammonium chloride (GTMAC) and dissolve it in 100 mL of water. Slowly add this to the chitosan solution. Add a magnetic stirrer and adjust the speed to 200 rpm. Simultaneously, add sodium hydroxide solution dropwise to adjust the pH to 11. Incubate at 50°C for 5 h. After the reaction is completed, the solution is cooled to room temperature, and the precipitate is washed with a large amount of water to remove unreacted GTMAC and other by-products. The precipitate is placed in a high-speed centrifuge (10,000 rpm) and centrifuged for 5 minutes. The supernatant is taken to obtain a cationic modified chitosan solution. The magnetic ball coated with titanium dioxide is immersed in the cationic modified chitosan solution for 5 minutes to form a uniform outer layer. The outer layer is dried and solidified at 70°C to obtain a multifunctional composite ball.

[0105] Example 2

[0106] This embodiment provides a multifunctional composite ball for removing algae from surface water, and the preparation method thereof is as follows:

[0107] S1: Weigh 1.52g of ferrous sulfate and 3.25g of ferric chloride into a three-necked flask, add 100mL of deionized water, and stir thoroughly with a magnetic stirrer at 250rpm to form an iron salt solution. After purging with nitrogen, slowly add aqueous ammonia dropwise until the pH reaches 10. The iron salt precipitates as Fe₃O₄. Wash the precipitate five times with deionized water. Heat-treat the washed particles at 150°C in a nitrogen atmosphere for 4h to obtain magnetic spheres.

[0108] S2: Add ethanol to a beaker, then slowly add tetrabutyl titanate dropwise at a volume ratio of 3:1. Hydrochloric acid is slowly added at room temperature to adjust the pH to 2 to obtain a precursor solution. Deionized water is then added to the precursor solution at a volume ratio of 5:1. The mixture is stirred at 400 rpm for 2 hours. As the hydrolysis reaction proceeds, a sol gradually forms, followed by polymerization to form a gel. The gel is aged at room temperature for 36 hours and then heat-treated at 327°C for 5 hours to produce 42 nm titanium dioxide nanoparticles. The prepared titanium dioxide nanoparticles are then mixed with a water-ethanol mixture (7:3) to obtain a mixed solution with a solid content of 80 wt%. The mixed solution is sprayed onto the surface of the magnetic sphere to form a titanium dioxide coating.

[0109] S3: Dry the chitosan powder in a 70°C forced air drying oven. Remove the dried chitosan powder and weigh 2 g of chitosan powder. Add it to a beaker containing 100 mL of 1 wt% acetic acid aqueous solution. Add a magnetic stirrer and adjust the speed to 200 rpm. Stir until completely dissolved to obtain a chitosan solution. In another beaker, weigh 2.0 g of glycidyltrimethylammonium chloride (GTMAC) and dissolve it in 100 mL of water. Slowly add this to the chitosan solution. Add a magnetic stirrer and adjust the speed to 250 rpm. Simultaneously, add sodium hydroxide solution dropwise to adjust the pH to 11. Incubate the mixture at 58°C for 6 h. After the reaction is completed, the solution is cooled to room temperature, and the precipitate is washed with a large amount of water to remove unreacted GTMAC and other by-products. The precipitate is placed in a high-speed centrifuge (10,000 rpm) and centrifuged for 5 minutes. The supernatant is taken to obtain a cationic modified chitosan solution. The magnetic ball coated with titanium dioxide is immersed in the cationic modified chitosan solution for 5 minutes to form a uniform outer layer. The outer layer is dried and solidified at 80°C to obtain a multifunctional composite ball.

[0110] Example 3

[0111] This embodiment provides a multifunctional composite ball for removing algae from surface water, and the preparation method thereof is as follows:

[0112] S1: Weigh 1.52g of ferrous sulfate and 3.25g of ferric chloride into a three-necked flask, add 100mL of deionized water, and stir thoroughly with a magnetic stirrer at 250rpm to form an iron salt solution. After purging with nitrogen, slowly add aqueous ammonia dropwise until the pH reaches 11. The iron salt precipitates as Fe₃O₄. Wash the precipitate five times with deionized water. Heat-treat the washed particles at 200°C in a nitrogen atmosphere for 2h to obtain magnetic spheres.

[0113] S2: Add ethanol to a beaker, then slowly add tetrabutyl titanate dropwise at a volume ratio of 4:1. Hydrochloric acid is slowly added at room temperature to adjust the pH to 2 to obtain a precursor solution. Deionized water is then added to the precursor solution at a volume ratio of 7:1. The mixture is stirred at 450 rpm for 3 hours. As the hydrolysis reaction proceeds, a sol gradually forms, followed by polymerization to form a gel. The gel is aged at room temperature for 48 hours and then heat-treated at 465°C for 5 hours to produce 38 nm titanium dioxide nanoparticles. The prepared titanium dioxide nanoparticles are then mixed with a water-ethanol mixture (8:2) to obtain a mixture with a solid content of 75 wt%. The mixture is sprayed onto the surface of the magnetic sphere to form a titanium dioxide coating.

[0114] S3: Dry the chitosan powder in a 70°C forced air drying oven. Remove the dried chitosan powder and weigh 4 g of chitosan powder. Add the chitosan powder to a beaker containing 100 mL of 1 wt% aqueous acetic acid. Add a magnetic stirrer and adjust the speed to 200 rpm. Stir until completely dissolved to obtain a chitosan solution. In a separate beaker, weigh 1.2 g of glycidyltrimethylammonium chloride (GTMAC) and dissolve it in 100 mL of water. Slowly add the solution to the chitosan solution and place a magnetic stirrer in the beaker. Set the speed to 300 rpm. Add sodium hydroxide solution dropwise to adjust the pH to 11. Incubate at 55°C for 4 h. After the reaction is completed, the solution is cooled to room temperature, and the precipitate is washed with a large amount of water to remove unreacted GTMAC and other by-products. The precipitate is placed in a high-speed centrifuge (10,000 rpm) and centrifuged for 5 minutes. The supernatant is taken to obtain a cationic modified chitosan solution. The magnetic ball coated with titanium dioxide is immersed in the cationic modified chitosan solution for 5 minutes to form a uniform outer layer. The outer layer is dried and solidified at 90°C to obtain a multifunctional composite ball.

[0115] Comparative Example 1

[0116] This comparative example provides a method for preparing a multifunctional composite ball, which differs from Example 1 in that step S3 is not included, that is, a chitosan coating layer is not formed, and the rest is the same as Example 1.

[0117] Comparative Example 2

[0118] This comparative example provides a method for preparing a multifunctional composite ball, which differs from Example 1 in that step S2 is not included, that is, a titanium dioxide coating is not formed, and the rest is the same as Example 1.

[0119] Comparative Example 3

[0120] This comparative example provides a method for preparing a multifunctional composite ball, which differs from Example 1 in that steps S2 and S3 are not included, that is, the titanium dioxide coating layer and the chitosan wrapping layer are not formed, and the rest are the same as Example 1.

[0121] Test example

[0122] The multifunctional composite balls obtained in the embodiments and comparative examples were tested, and the specific experimental methods are as follows:

[0123] Source water from the algae outbreak at Foshan Water Plant X in July and August was placed in a beaker at a dosage of 20 g / L. The beaker was then placed in a ZR4-6 six-way agitator and subjected to a series of stirring cycles: rapid stirring (250 rpm, 1 min), slow stirring (40 rpm, 10 min), and quiescent stirring (0 rpm, 10 min). The experiments were conducted under both sunlight (with light) and darkness (without light).

[0124] The OD values ​​of the water before and after treatment were measured using an ultraviolet spectrophotometer (Shimadzu UV-2600). 680 、UV 254 The indicators were measured; the turbidity index of the water before and after treatment was measured using a turbidimeter (HACH-2100Q); the content of 2-MIB and GSM in the water before and after treatment was measured using a gas chromatography-mass spectrometer (GC-MS), and the removal rate was calculated. The removal rate was calculated as follows:

[0125] OD 680 Removal rate = (A0-A) / A×100%;

[0126] Where A0 is the OD before treatment 680 Numerical value, A is the OD after processing 680 Numeric value.

[0127] UV 254 Removal rate = (G0-G) / G0×100%;

[0128] Where G0 is the UV before processing 254 Numeric value, G is the processed UV 254 Numeric value.

[0129] 2-MIB removal rate = (C0-C0) / C0×100%;

[0130] Where C0 is the 2-MIB concentration before treatment (ng / L), and C is the 2-MIB concentration after treatment (ng / L).

[0131] GSM removal rate = (D0-D) / D0×100%;

[0132] Where D0 is the GSM concentration before treatment (ng / L), and D is the GSM concentration after treatment (ng / L).

[0133] The data obtained from the specific examples and comparative examples are shown in the following table:

[0134]

[0135] As can be seen from the above table, the multifunctional composite ball of the present invention can achieve OD 680 、UV 254 , 2-MIB, and GSM, which are key indicators of algae outbreaks, can be efficiently removed. In addition, from the comparison of Example 1, Comparative Example 1, and Comparative Example 2 under dark conditions, it can be seen that the removal of algae cells mainly relies on the adsorption effect of the multifunctional composite ball. From the microscopic morphology of algae cells before and after the test under light conditions in Example 1, it can be seen that although the algae cells are damaged to a certain extent, they remain intact ( Figure 3 、 Figure 4 ).

[0136] Furthermore, the multifunctional composite ball obtained in Example 1 was tested, and the results were as follows: Figure 1~Figure 2 As shown. Figure 1 It can be seen that the multifunctional composite ball forms a good wrapping. Figure 2 It can be seen that Fe-O-Ti covalent bonds are formed in the multifunctional composite ball, indicating that titanium dioxide is well sprayed on the surface of the magnetic ball; -1 New characteristic peaks appeared in the region, further illustrating that GTMAC was connected to chitosan and well retained the characteristic peaks belonging to chitosan, which showed that chitosan was successfully modified and the positive charge on the modified surface could effectively enhance the adsorption capacity of algae.

[0137] The above is a preferred embodiment of the invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a multifunctional composite ball for removing algae from surface water, characterized in that: The following steps are involved: (1) Using soluble iron salt and soluble ferrous salt as iron sources and soluble alkali as precipitant, magnetic spheres are prepared by co-precipitation in an inert gas atmosphere; (2) using tetrabutyl titanate as a titanium source, preparing titanium dioxide nanoparticles by a sol-gel method, mixing the titanium dioxide nanoparticles with a water-ethanol mixed solvent and spraying the mixed solvent onto the surface of the magnetic sphere to form a titanium dioxide coating; wherein the particle size of the titanium dioxide nanoparticles is 10 nm to 50 nm; (3) Chitosan was modified with glycidyl trimethylammonium chloride and then evenly coated on a magnetic sphere with a titanium dioxide coating, and solidified to form a chitosan coating layer, thereby obtaining a multifunctional composite sphere.

2. The method for preparing the multifunctional composite ball for removing algae from surface water according to claim 1, wherein: The soluble iron salt is selected from one or more of ferric nitrate, ferric sulfate, and ferric chloride; and / or The soluble ferrous salt is selected from one or more of ferrous nitrate, ferrous sulfate, and ferrous chloride; and / or The precipitant is selected from one or more of sodium hydroxide, ammonia water, and potassium hydroxide; and / or The inert gas is one or more of helium, nitrogen and argon; and / or The molar ratio of the soluble ferrous salt to the soluble ferric salt is 1:1.5 to 1:3; and / or The pH value during the coprecipitation process is controlled at 8.5-12; and / or The precipitate obtained by solid-liquid separation after coprecipitation is heat-treated at 100°C to 300°C.

3. The method for preparing the multifunctional composite ball for removing algae from surface water according to claim 1, wherein: The molar ratio of the soluble ferrous salt to the soluble ferric salt is 1:2; and / or The precipitant is ammonia water, and its concentration is 10wt%~22wt%; and / or Nitrogen is selected as the inert gas; and / or The pH value during the coprecipitation process is controlled at 9-11; and / or After the coprecipitation, heat treatment is performed at 100°C to 200°C in an inert gas atmosphere.

4. The method for preparing the multifunctional composite ball for removing algae from surface water according to claim 1, characterized in that: Step (1) includes: (1.1) Dissolving a soluble iron salt and a soluble ferrous salt in water to obtain a first solution; adding aqueous ammonia dropwise in a nitrogen atmosphere until the pH is 9 to 11, and obtaining a precipitate after solid-liquid separation; wherein the concentration of the soluble iron salt in the first solution is 0.2 mol / L to 0.5 mol / L, and the concentration of the soluble ferrous salt in the first solution is 0.1 mol / L to 0.25 mol / L; (1.2) Washing the precipitate with water 3 to 6 times; (1.3) Heat-treat the washed precipitate at 100°C to 200°C in an inert gas atmosphere for 2 h to 6 h to obtain magnetic spheres.

5. The method for preparing the multifunctional composite ball for removing algae from surface water according to claim 1, characterized in that: Step (2) includes: (2.1) Tetrabutyl titanate is added dropwise to a solvent and the pH is adjusted to 2 to 3 to obtain a precursor solution, wherein the volume ratio of the solvent to the tetrabutyl titanate is 2:1 to 5:1; (2.2) adding water to the precursor solution and stirring to react to obtain titanium dioxide gel; wherein the volume ratio of water to the precursor solution is 1:1 to 10:1; (2.3) aging the titanium dioxide gel and then heat-treating it to obtain titanium dioxide nanoparticles; (2.4) Mixing the titanium dioxide nanoparticles with a water-ethanol mixed solvent and dispersing them using ultrasound to prepare a mixed solution with a solid content of 70 wt% to 95 wt%, and spraying the mixed solution onto the surface of the magnetic sphere to form a titanium dioxide coating; wherein the volume ratio of ethanol to water in the water-ethanol mixed solvent is 7:3 to 8:

2.

6. The method for preparing the multifunctional composite ball for removing algae from surface water according to claim 5, wherein: In step (2.1), the solvent is selected from one or more of ethanol, propanol, butanol, and ethylene glycol; and / or In step (2.1), acetic acid or hydrochloric acid is used to adjust the pH; and / or In step (2.2), the stirring speed is 400 rpm to 600 rpm, and the stirring reaction time is 1 h to 3 h; and / or In step (2.3), the aging time is 24h~48h, and the aging temperature is 15℃~35℃; and / or In step (2.3), the heat treatment temperature is 300°C~550°C, and the heat treatment time is 2h~5h.

7. The method for preparing the multifunctional composite ball for removing algae from surface water according to claim 1, characterized in that: Step (3) includes: (3.1) Dissolving chitosan in a 0.5 wt% to 3 wt% aqueous acetic acid solution to obtain a second solution, wherein the ratio of chitosan weight to acetic acid volume is 1 g to 5 g: 50 mL to 150 mL; (3.2) Dissolving glycidyl trimethylammonium chloride in water to obtain a third solution; wherein the concentration of glycidyl trimethylammonium chloride in the third solution is 10 g / L to 20 g / L; (3.3) Add the third solution to the second solution, adjust the pH to 9-11, react at 50-60°C for 4-6 hours, and wash with water to obtain an intermediate solution; wherein the volume ratio of the third solution to the second solution is 1:1-1:2; (3.4) Centrifuge the intermediate solution to obtain the supernatant, which is the modified chitosan solution; (3.5) Immerse the titanium dioxide-coated magnetic spheres in the modified chitosan solution, remove them after 3 to 5 minutes, and dry them at 70 to 100°C for 1 to 5 hours to form a chitosan coating.

8. A multifunctional composite ball for removing algae from surface water, characterized in that: The multifunctional composite ball for removing surface water algae is prepared by the preparation method of any one of claims 1 to 7.

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