A method for preparing microalgae gel balls for water treatment

Abstract

The application provides a preparation method of microalgae gel balls for water treatment, and relates to the field of water treatment, and comprises the following steps: S1, preparation of a composite suspension; S2, preliminary cross-linking to form balls; S3, secondary cross-linking; S4, in-situ strengthening; and S5, coating. The method is characterized in that the microalgae are modified to obtain gel balls, and then the finished gel balls are obtained through coating. The method not only improves the anti-swelling capacity and mechanical strength of the gel balls, but also avoids the dense gel network and the multi-layer coating structure from hindering the diffusion of nutrients, carbon dioxide and the like in the water body to the microalgae cells, so that the photosynthesis efficiency and the pollution degradation capacity of the microalgae are ensured, and the water treatment efficiency of the microalgae is improved.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and more specifically to a method for preparing microalgae gel spheres for water treatment. Background Technology

[0002] Microalgae are tiny, simple photosynthetic microorganisms widely distributed in marine, freshwater, and soil environments. Their cell diameter typically ranges from a few micrometers to tens of micrometers. Through photosynthesis, they fix carbon dioxide and release oxygen. Simultaneously, microalgae efficiently absorb nitrogen and phosphorus from the water (nitrogen and phosphorus are essential nutrients for microalgae growth and reproduction, forming key components of cell structure, enzymes, and energy substances; therefore, microalgae have evolved highly efficient active absorption and utilization mechanisms), effectively purifying water. However, the tiny size of microalgae (generally 2–20 μm in diameter), low cell density (typically only 0.1–1 g / L under natural cultivation), and negatively charged cell surfaces with alternating stability make them difficult to separate from water bodies, hindering harvesting and isolation. This results in large amounts of algae residue and widespread algal blooms in treated water, even leading to algal blooms and secondary water pollution.

[0003] Immobilized microorganism technology refers to the use of physical or chemical methods to immobilize free microbial cells or enzymes within a specific carrier, allowing the microorganisms to maintain their inherent biological activity and enabling repeated and continuous use. Methods of microbial immobilization include adsorption, encapsulation, cross-linking, and composite immobilization. Among these, encapsulation is the most commonly used method, effectively locking microorganisms within the polymer of the immobilized carrier, preventing their widespread diffusion and thus reducing secondary pollution of water bodies. Currently, existing technologies utilize polyvinyl alcohol (PVA) and sodium alginate (SA) as carrier materials for microalgae encapsulation. However, the poor chemical stability of the carrier material makes the gel spheres prone to disintegration or swelling and rupture (the cross-linking bonds of the gel formed by the cross-linking of polyvinyl alcohol with reagents such as borax and pentanediol are easily hydrolyzed in the aqueous environment. Long-term immersion will cause the gel spheres to swell continuously, resulting in surface softening and rupture, or even complete disintegration; sodium alginate gel spheres have low mechanical strength and are easily damaged by water flow impact and stirring shear force). The polyvinyl alcohol released by the disintegrated gel spheres will increase the COD load of the water body and form secondary pollution. At the same time, the composite gel network composed of polyvinyl alcohol and sodium alginate will form a "mass transfer barrier", which will hinder the exchange of substances necessary for microalgae growth, thereby affecting the photosynthetic efficiency and pollution degradation capacity of microalgae. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a method for preparing microalgae gel spheres for water treatment. This method involves compound modification of microalgae to obtain gel spheres, followed by coating to obtain the finished gel spheres. This not only improves the swelling and cracking resistance and mechanical strength of the gel spheres, but also avoids the dense gel network and multi-layer coating structure from hindering the diffusion of nutrients, carbon dioxide, etc. in the water to the microalgae cells, thus ensuring the photosynthetic efficiency and pollution degradation capacity of the microalgae.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing microalgae gel spheres for water treatment, comprising:

[0007] Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; then add biochar and hollow glass microspheres in sequence and stir at high speed until evenly dispersed; then add organic matrix, stir and add microalgae solution, continue stirring and then add functional reagents in sequence and continue stirring to obtain composite suspension;

[0008] Step S2, Initial cross-linking into spheres: The composite suspension is added dropwise to a calcium chloride solution to obtain initial gel spheres;

[0009] Step S3, Secondary cross-linking: First, add the catalytic enzyme and acetylacetone to deionized water and adjust the pH to 5.5 to obtain an enzymatic cross-linking solution; then immerse the initial gel balls in the enzymatic cross-linking solution and cross-link them by constant temperature oscillation to obtain cross-linked gel balls.

[0010] Step S4, In-situ reinforcement: Immerse the cross-linked gel balls in deionized water, adjust the pH to 8.0 with sodium hydroxide, let them stand at a constant temperature, and then adjust the pH to 7.0 with hydrochloric acid to obtain reinforced gel balls;

[0011] Step S5, Coating: Immerse the enhanced gel balls in the coating solution, and allow them to adsorb and solidify at room temperature to obtain microalgae gel balls.

[0012] Based on further optimization of the above scheme, the solid-liquid ratio (i.e., mass-volume ratio) of sodium alginate, gelatin and deionized water in step S1 is 2.5-3.5g: 0.8-1.2g: 80-120mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 55-65℃ and a stirring rate of 300-500rpm for 35-45min.

[0013] Based on further optimization of the above scheme, the biochar used is orange peel biochar, and its specific preparation steps are as follows:

[0014] Raw material pretreatment: Take fresh or dried orange peel, remove residual pulp, seeds and rotten parts, and rinse repeatedly with deionized water 3-5 times; place fresh orange peel in a forced-air drying oven and dry at 60-80℃ for 12-24 hours until constant weight; dried orange peel does not need to be dried. Crush the dried orange peel with a high-speed pulverizer and pass it through an 80-100 mesh sieve to obtain orange peel powder; add the orange peel powder to a 5%-10% (v / v) ethanol solution, with a solid-liquid ratio (i.e., mass-volume ratio) of 1g:10mL, and stir at a constant temperature of 58-62℃ and a stirring rate of 180-200rpm for 2-3 hours. After filtration, wash with deionized water until neutral, and then dry at 58-62℃ until constant weight;

[0015] Pyrolysis: In a tube furnace under an inert gas atmosphere, the temperature is raised to 600-800℃ at a heating rate of 5-10℃ / min, held for 1-3 hours, and then naturally cooled to room temperature to obtain primary orange peel biochar.

[0016] Activation treatment: The primary orange peel biochar is placed back into the tube furnace, an activation gas is introduced, and the temperature is raised to 700-900℃ at a heating rate of 4.5-5.5℃ / min, and held for 1-2 hours. After cooling, the biochar is collected, washed with deionized water until neutral, and dried at 58-62℃ to constant weight to obtain orange peel biochar.

[0017] Based on further optimization of the above scheme, the activation gas is carbon dioxide, and the flow rate of the activation gas is 90-110 mL / min.

[0018] Based on further optimization of the above scheme, the mass ratio of biochar, hollow glass microspheres and sodium alginate is 1.8-2.2:0.08-0.12:2.5-3.5; the particle size of the hollow glass microspheres is 45-55 μm; before adding biochar and hollow glass microspheres, the temperature is lowered to 32-38℃; the stirring speed of the high-speed stirrer is 1400-1600 rpm, and the stirring time is 18-22 min.

[0019] Based on further optimization of the above scheme, the organic matrix includes a β-cyclodextrin solution and an adamantane-modified carboxymethyl starch solution; wherein, the β-cyclodextrin solution is obtained by adding β-cyclodextrin to deionized water and stirring at 45-55°C and a stirring rate of 200-300 rpm for 28-32 min until completely dissolved, and the solid-liquid ratio (i.e., mass-volume ratio) of β-cyclodextrin to deionized water is 3 g: 50 mL; the adamantane-modified carboxymethyl starch solution is obtained by adamantane-modified carboxymethyl starch... Add the powder to deionized water and stir at 200-300 rpm for 58-62 min at room temperature until completely dissolved. The solid-liquid ratio (i.e., mass-volume ratio) of adamantane-modified carboxymethyl starch to deionized water is 1 g: 25 mL; the mass ratio of β-cyclodextrin, adamantane-modified carboxymethyl starch and sodium alginate is 2:3:15; after adding the β-cyclodextrin solution and the adamantane-modified carboxymethyl starch solution, stir at 250-300 rpm for 13-17 min.

[0020] Based on further optimization of the above scheme, the preparation steps of the adamantane-modified carboxymethyl starch are as follows:

[0021] Carboxymethyl starch treatment: First, add carboxymethyl starch to deionized water at a solid-liquid ratio (i.e., mass-volume ratio) of 1 g: 20 mL. Stir magnetically at a constant temperature of 38–42 °C and a stirring rate of 380–420 rpm for 1.5–2.5 h to obtain a transparent and homogeneous carboxymethyl starch aqueous solution. Then, adjust the pH of the carboxymethyl starch aqueous solution to 7.5–8.0 using 0.1 mol / L sodium hydroxide solution.

[0022] Activation of adamantane: First, add 1-adamantane to dimethylformamide (DMF) at a solid-liquid ratio (i.e., mass-to-volume ratio) of 1-adamantane to DMF of 1 g: 10 mL, and sonicate for 8–12 min until adamantane is completely dissolved. Then, slowly add the adamantane solution dropwise to a pH-adjusted carboxymethyl starch aqueous solution at a mass ratio of 1-adamantane to carboxymethyl starch of 1:5, and stir at a stirring rate of 380–420 rpm for 12–16 min. After that, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) at a mass ratio of 0.8:1 to 1-adamantane, and continue stirring at a stirring rate of 380–420 rpm for 8–12 min.

[0023] Grafting: Heat to 48-52℃, maintain a stirring rate of 380-420 rpm, and reflux for 6-8 hours;

[0024] Purification: First, pour the refluxed reaction solution into anhydrous ethanol at a volume ratio of 3:1, stirring at a speed of 380-420 rpm while pouring. Then, centrifuge the mixture at 7500-8500 rpm for 8-12 minutes to remove the supernatant and collect the white precipitate at the bottom. Finally, wash repeatedly with anhydrous ethanol 3-4 times, each time using half the volume of the initial reaction solution. After washing, stir to disperse and centrifuge to obtain adamantane-modified carboxymethyl starch.

[0025] Based on further optimization of the above scheme, the volume-to-mass ratio of the microalgae solution to sodium alginate is 20-40 mL: 3 g (the biomass of the microalgae solution is ≥2 g / L, generally using Chlorella or Spirulina, obtained by further separation and concentration from purchased algal solutions); after adding the microalgae solution, stir at a stirring rate of 250-300 rpm for 8-12 min.

[0026] Based on further optimization of the above scheme, the functional reagent includes a 0.5 mol / L calcium nitrate solution, a 0.3 mol / L sodium phosphate solution, and ammonium bicarbonate. First, the calcium nitrate solution and sodium phosphate solution are added, with a mass ratio of calcium nitrate, sodium phosphate, and sodium alginate of 2:1:15, and the mixture is stirred at a stirring speed of 180-200 rpm for 4-6 minutes. Then, ammonium bicarbonate is added, with a mass ratio of ammonium bicarbonate to sodium alginate of 1:15, and the mixture is stirred at a stirring speed of 380-420 rpm for 2-4 minutes.

[0027] Based on further optimization of the above scheme, in step S2, the concentration of the calcium chloride solution is 2.4%–2.6% (w / v); the mass ratio of calcium chloride to sodium alginate is 2:3; the specific operation of adding the composite suspension to the calcium chloride solution is as follows: the composite suspension is drawn up with a syringe and added vertically at a distance of 14–16 cm from the surface of the calcium chloride solution, with a dropping rate of 1 drop / second, to obtain initial gel spheres with a diameter of 2–3 mm; the initial gel spheres are kept in the calcium chloride solution to solidify for 28–32 min, during which low-speed stirring at 80–100 rpm is used; finally, the initial gel spheres are taken out of the calcium chloride solution and rinsed with deionized water 2–3 times.

[0028] Based on further optimization of the above scheme, the catalytic enzyme is laccase, with an enzyme activity of 5-10 U / mg. The solid-liquid ratio (i.e., mass-volume ratio) of laccase, acetylacetone, and deionized water is 0.01-0.02 mg: 1 mL: 200-220 mL, and the volume-mass ratio of acetylacetone to sodium alginate is 1 mL: 15 g. After immersing the initial gel balls in the enzymatic cross-linking solution, they are subjected to cross-linking by shaking at a rate of 115-125 rpm for 55-65 min in a constant temperature water bath environment of 28-32℃.

[0029] Based on further optimization of the above scheme, in step S4, the cross-linked gel balls are immersed in 200-250 mL of deionized water and kept at a constant temperature of 33-37°C for 35-45 min.

[0030] Based on further optimization of the above scheme, after obtaining the cross-linked gel spheres in step S3, the spheres are rinsed with deionized water 3 to 5 times; after obtaining the reinforced gel spheres in step S4, the spheres are first rinsed with deionized water 2 to 3 times, and then dried in an oven at 37 to 43°C for 8 to 12 minutes.

[0031] Based on further optimization of the above scheme, the coating solution is a solution in which amino-mesoporous silica nanoparticles are uniformly dispersed in deionized water, the concentration of the coating solution is 1.4-1.6% (w / v), and the pH value of the coating solution is 6.0 (which can be adjusted with hydrochloric acid).

[0032] The preparation method of amino-mesoporous silica nanoparticles is as follows:

[0033] First, CTAB (hexadecyltrimethylammonium bromide) and deionized water are mixed and stirred at room temperature at a stirring rate of 300–500 rpm until the solution becomes transparent and homogeneous. Then, ammonia water is slowly added dropwise while stirring continuously for 15–20 min at a dropping rate of 0.3–0.5 mL / min to obtain a CTAB micelle solution. The solid-liquid ratio (i.e., mass-volume ratio) of CTAB, ammonia water, and deionized water is 0.75–0.85 g : 3.2–3.8 mL : 100–120 mL.

[0034] Then, tetraethyl orthosilicate (TEOS) was added dropwise to the CTAB micelle solution at a rate of 1-2 drops / second, while maintaining constant temperature and stirring rate during the addition process. After the addition was completed, stirring was continued for 20-24 hours to obtain a white emulsion. The volume-to-mass ratio of tetraethyl orthosilicate to CTAB was 3.8-4.2 mL: 0.75-0.85 g.

[0035] Then, 3-aminopropyltriethoxysilane was added dropwise to the white emulsion at a rate of 1-2 drops / second, while maintaining constant temperature and stirring speed during the addition process. After the addition was completed, stirring was continued for 10-14 hours. The mixture was then centrifuged at 9500-10500 rpm for 8-12 minutes to remove the supernatant and collect the white precipitate at the bottom.

[0036] Next, anhydrous ethanol and concentrated hydrochloric acid (36%–38% by mass) were added to the precipitate obtained by centrifugation. The volume-to-mass ratio of anhydrous ethanol, concentrated hydrochloric acid, and CTAB was 75–85 mL: 3.5–4.5 mL: 0.75–0.85 g. The mixture was then refluxed and stirred at 58–62 °C for 5.5–6.5 h. After reflux, the mixture was cooled to room temperature and centrifuged at 9500–10500 rpm for 8–12 min. The precipitate was collected and washed 3–4 times with anhydrous ethanol until the supernatant was nearly neutral (the supernatant was used for testing after each centrifugation).

[0037] Finally, the washed white precipitate was dried in a vacuum drying oven at 55–65°C and a vacuum degree of -0.08 MPa to -0.1 MPa for 11–13 hours to obtain amino-mesoporous silica nanoparticles.

[0038] Based on further optimization of the above scheme, in step S5, the oscillation rate of room temperature oscillation adsorption is 120-140 rpm and the oscillation time is 18-22 min; the curing and shaping are specifically carried out by drying in an oven at 33-37℃ for 14-16 min.

[0039] The following are the effects of the technical solution of the present invention:

[0040] This invention utilizes sodium alginate and calcium chloride to form an initial three-dimensional network framework for gel spheres through ionic cross-linking, rapidly locking microalgae and functional components and increasing the swelling rate. Furthermore, laccase catalyzes covalent cross-linking between acetylacetone and active groups in the initial gel sphere matrix, forming a secondary covalent network on top of the initial ionicly cross-linked network. This dual cross-linking structure enhances the mechanical strength of the gel spheres, preventing structural damage caused by the scouring of highly swollen water bodies. The combined effect of the initial ionic cross-linking and secondary covalent cross-linking reduces network dissociation caused by ion exchange. Meanwhile, the orange peel biochar and hollow glass microspheres uniformly dispersed in the gel matrix not only form the physical framework of the gel matrix and enhance the overall structural resistance to compression and swelling cracking through the physical framework combined with the double cross-linking network, but also utilize the uniformly distributed micropores and mesopores of the biochar and the microcavities of the hollow glass microspheres to form transport channels for nutrients such as N and P and carbon dioxide, reducing the diffusion resistance of nutrients. This avoids problems such as the dense gel network structure and coating structure hindering the diffusion of nutrients (N, P, etc.) and carbon dioxide from the water to the microalgal cells in the gel matrix, thus avoiding the inhibition of microalgal metabolism and the slowed growth or death of microalgae in the gel matrix due to the lack of nutrients or carbon dioxide. Furthermore, the inclusion effect formed by the cyclic structure of β-cyclodextrin and the rigid adamantyl group of adamantane-modified carboxymethyl starch enhance the intermolecular binding force, thereby synergistically improving the strength of the gel network and reducing the decomposition of the gel matrix by microorganisms. Moreover, the interaction between β-cyclodextrin and adamantane-modified carboxymethyl starch forms a reversible cross-linked network, effectively avoiding network densification caused by excessive cross-linking, and further ensuring the diffusion and transport of nutrients and carbon dioxide.

[0041] This invention, by adding functional reagents such as calcium nitrate solution, sodium phosphate solution, and ammonium bicarbonate, not only generates hydroxyapatite nanocrystals around the microalgae inside the gel spheres through in-situ mineralization, thereby forming an interpenetrating network, but also forms micron-sized channels during the gel solidification process, improving the diffusion rate of substances such as nitrogen and phosphorus. This effectively balances the contradiction between stability and mass transfer, ensuring the structural stability of the microalgal gel spheres in dynamic water, avoiding problems such as swelling, breakage, and disintegration, while ensuring that nutrients such as nitrogen and phosphorus, as well as carbon dioxide, can enter the gel spheres for microalgae growth, making the mass transfer efficiency highly efficient and controllable.

[0042] Furthermore, the present invention utilizes an amino-mesoporous silica nanoparticle coating layer to adsorb onto the surface of the gel spheres via electrostatic attraction. This provides pores for the free diffusion of nitrogen and phosphorus while effectively adsorbing phosphorus from the water, thereby improving the purification efficiency of the microalgae spheres. At the same time, it effectively adapts to the mechanical support and biocompatibility requirements of the microalgae gel spheres, avoiding secondary pollution during the water treatment process. Attached Figure Description

[0043] Figure 1 This is a microscope image of the microalgae gel spheres prepared in this embodiment of the invention after long-term immersion.

[0044] Figure 2 Microscopic images of gel spheres prepared using existing technology after long-term immersion. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0046] Example 1:

[0047] A method for preparing microalgae gel spheres for water treatment, comprising:

[0048] Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; wherein, the solid-liquid ratio (i.e., mass-volume ratio) of sodium alginate, gelatin and deionized water is 2.5g:0.8g:80mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 55℃ and a stirring speed of 300rpm for 45min.

[0049] Then, biochar and hollow glass microspheres (made of borosilicate glass) were added sequentially (to the homogeneous colloid) and stirred at high speed until uniformly dispersed; the mass ratio of biochar, hollow glass microspheres and sodium alginate was 1.8:0.08:2.5; the particle size of the hollow glass microspheres was 45-55 μm; the temperature was lowered to 32°C before adding biochar and hollow glass microspheres; the stirring speed was 1400 rpm and the stirring time was 22 min.

[0050] The biochar used is orange peel biochar, and its specific preparation steps are as follows:

[0051] Raw material pretreatment: Take fresh or dried orange peels, remove residual pulp, seeds, and rotten parts, and rinse repeatedly with deionized water three times. Place fresh orange peels in a forced-air drying oven and dry at 60℃ for 24 hours until constant weight. Dried orange peels do not need to be dried. Crush the dried orange peels using a high-speed pulverizer and pass them through an 80-mesh sieve to obtain orange peel powder. Add the orange peel powder to a 5% (v / v) ethanol solution with a solid-liquid ratio (i.e., mass-volume ratio) of 1 g: 10 mL. Stir at a constant temperature of 58℃ and a stirring rate of 180 rpm for 3 hours. After filtration, wash with deionized water until neutral, and then dry at 58℃ to constant weight. Pyrolysis: In a tube furnace under an inert gas atmosphere, heat to 600℃ at a heating rate of 5℃ / min, hold for 3 hours, and then cool naturally to room temperature to obtain primary orange peel biochar. Activation treatment: The primary orange peel biochar was placed back into the tube furnace, and the activation gas - carbon dioxide - was introduced at a flow rate of 90 mL / min. The temperature was increased to 700℃ at a rate of 4.5℃ / min and held for 2 hours. After cooling, the biochar was collected, washed with deionized water until neutral, and dried at 58℃ to constant weight to obtain orange peel biochar.

[0052] Next, a β-cyclodextrin solution and an adamantane-modified carboxymethyl starch solution (i.e., the organic matrix) were added to the colloid after uniform dispersion of orange peel biochar and hollow glass microspheres. The β-cyclodextrin solution was obtained by adding β-cyclodextrin to deionized water and stirring at 200 rpm for 32 minutes at 45°C until completely dissolved, with a solid-liquid ratio (mass-volume ratio) of 3 g:50 mL. The adamantane-modified carboxymethyl starch solution was obtained by adding adamantane-modified carboxymethyl starch to deionized water and stirring at 200 rpm for 62 minutes at room temperature until completely dissolved. The solid-liquid ratio (i.e., mass-volume ratio) of methyl starch to deionized water was 1 g: 25 mL; the mass ratio of β-cyclodextrin, adamantane-modified carboxymethyl starch, and sodium alginate was 2:3:15; after adding the organic matrix, the mixture was stirred at 250 rpm for 17 min, and then the microalgae solution was added. The volume-mass ratio of the microalgae solution to sodium alginate was 20 mL: 3 g (the biomass of the microalgae solution was ≥2 g / L, and generally Chlorella or Spirulina were used, which were obtained by further separation and concentration from purchased algal solutions, for example, Chlorella proteoides purchased from the freshwater algae seed bank of the Institute of Hydrobiology, Chinese Academy of Sciences). The mixture was stirred at 250 rpm for 12 min.

[0053] The preparation steps of adamantane-modified carboxymethyl starch are as follows:

[0054] Carboxymethyl starch treatment: First, carboxymethyl starch was added to deionized water at a solid-liquid ratio (i.e., mass-volume ratio) of 1 g: 20 mL. The mixture was magnetically stirred at a constant temperature of 38℃ and a stirring speed of 380 rpm for 2.5 h to obtain a transparent and homogeneous carboxymethyl starch aqueous solution. Then, the pH of the carboxymethyl starch aqueous solution was adjusted to 7.5 using 0.1 mol / L sodium hydroxide solution. Activation of adamantane: First, 1-adamantane was added to dimethylformamide (DMF) at a solid-liquid ratio (mass-volume ratio) of 1-adamantane to DMF of 1 g: 10 mL. The mixture was sonicated for 8 min until the adamantane was completely dissolved. Then, the adamantane solution was slowly added dropwise to a pH-adjusted carboxymethyl starch aqueous solution at a mass ratio of 1-adamantane to carboxymethyl starch of 1:5. The mixture was stirred at 380 rpm for 16 min. Next, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) was added at a mass ratio of 0.8:1 to 1-adamantane, and the mixture was stirred at 380 rpm for another 12 min. Grafting: The temperature was raised to 48 °C, and the mixture was refluxed at 380 rpm for 8 h. Purification: First, pour the refluxed reaction solution into anhydrous ethanol at a volume ratio of 3:1, stirring at 380 rpm while pouring. Then, centrifuge the mixture at 7500 rpm for 12 minutes, remove the supernatant, and collect the white precipitate at the bottom. Finally, wash the mixture three times with anhydrous ethanol, each time using half the volume of the initial reaction solution. After washing, stir and centrifuge to obtain adamantane-modified carboxymethyl starch.

[0055] Finally, a 0.5 mol / L calcium nitrate solution and a 0.3 mol / L sodium phosphate solution were added sequentially, with a mass ratio of calcium nitrate, sodium phosphate, and sodium alginate of 2:1:15. The mixture was stirred at 180 rpm for 6 min. Then, ammonium bicarbonate was added, with a mass ratio of ammonium bicarbonate to sodium alginate of 1:15. The mixture was stirred at 380 rpm for 4 min to obtain a composite suspension.

[0056] Step S2, Initial Cross-linking into Spheres: The composite suspension is added dropwise to the calcium chloride solution to obtain initial gel spheres; the concentration of the calcium chloride solution is 2.4% (w / v); the mass ratio of calcium chloride to sodium alginate is 2:3; the specific operation of adding the composite suspension to the calcium chloride solution is as follows: the composite suspension is drawn up with a syringe and added vertically at a distance of 14 cm from the surface of the calcium chloride solution, with a dropping rate of 1 drop / second, to obtain initial gel spheres with a diameter of 2-3 mm; the initial gel spheres are kept in the calcium chloride solution for 32 min to solidify, during which low-speed stirring at 80 rpm is used; finally, the initial gel spheres are taken out of the calcium chloride solution and rinsed twice with deionized water.

[0057] Step S3, Secondary cross-linking: First, add laccase and acetylacetone to deionized water. The enzyme activity of laccase is 5 U / mg. The solid-liquid ratio (i.e., mass-volume ratio) of laccase, acetylacetone and deionized water is 0.02mg:1mL:200mL. The volume-mass ratio of acetylacetone and sodium alginate is 1mL:15g. Adjust the pH to 5.5 (using hydrochloric acid for pH adjustment) to obtain the enzymatic cross-linking solution.

[0058] The initial gel spheres were then immersed in the enzymatic cross-linking solution and cross-linked at a rate of 115 rpm for 65 min in a constant temperature water bath at 28°C to obtain cross-linked gel spheres. After obtaining the cross-linked gel spheres, they were rinsed three times with deionized water.

[0059] Step S4, In-situ Reinforcement: Immerse the cross-linked gel balls in 200 mL of deionized water and adjust the pH to 8.0 with sodium hydroxide. After standing at 33°C for 45 min, adjust the pH to 7.0 with hydrochloric acid to obtain reinforced gel balls. After obtaining the reinforced gel balls, rinse them twice with deionized water and then dry them in an oven at 37°C for 12 min.

[0060] Step S5, Coating: Immerse the enhanced gel spheres in the coating solution. The coating solution is a solution in which amino-mesoporous silica nanoparticles are uniformly dispersed in deionized water. The concentration of the coating solution is 1.4 (w / v), and the pH value of the coating solution is 6.0 (which can be adjusted with hydrochloric acid).

[0061] The preparation method of amino-mesoporous silica nanoparticles is as follows:

[0062] First, CTAB (hexadecyltrimethylammonium bromide) and deionized water were mixed and stirred at 300 rpm at room temperature until the solution became clear and homogeneous. Then, ammonia was slowly added dropwise while stirring continuously for 20 min at a dropping rate of 0.3 mL / min to obtain a CTAB micelle solution. The solid-liquid ratio (mass-volume ratio) of CTAB, ammonia, and deionized water was 0.75 g: 3.2 mL: 100 mL. Next, tetraethyl orthosilicate (TEOS) was added dropwise to the CTAB micelle solution at a dropping rate of 1 drop / second, while maintaining constant temperature and stirring rate. After the addition was complete, stirring was continued for 24 h to obtain a white emulsion. The volume-mass ratio of tetraethyl orthosilicate to CTAB was 3.8 mL: 0.75 g. Next, 3-aminopropyltriethoxysilane was added dropwise to the white emulsion at a rate of 1 drop / second, while maintaining constant temperature and stirring rate. After addition, stirring was continued for 14 hours. The mixture was then centrifuged at 9500 rpm for 12 minutes, the supernatant was removed, and the white precipitate at the bottom was collected. Then, anhydrous ethanol and 36% (mass fraction) concentrated hydrochloric acid were added to the precipitate obtained by centrifugation, with a volume-to-mass ratio of anhydrous ethanol:3.5 mL:0.75 g CTAB. The mixture was refluxed at 58°C for 6.5 hours. After reflux, the mixture was cooled to room temperature and centrifuged at 9500 rpm for 12 minutes. The precipitate was collected and washed three times with anhydrous ethanol until the supernatant was nearly neutral (the supernatant was used for testing after each centrifugation). Finally, the washed white precipitate was dried in a vacuum drying oven at 55℃ and a vacuum degree of -0.08MPa for 13 hours to obtain amino-mesoporous silica nanoparticles.

[0063] At room temperature, the microalgae gel spheres were adsorbed by oscillation at 120 rpm for 22 min and then dried in an oven at 33 ℃ for 16 min to complete the curing and shaping process.

[0064] Example 2:

[0065] A method for preparing microalgae gel spheres for water treatment, comprising:

[0066] Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; wherein, the solid-liquid ratio (i.e. mass-volume ratio) of sodium alginate, gelatin and deionized water is 3g:1g:100mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 60℃ and a stirring rate of 400rpm for 40min.

[0067] Then, biochar and hollow glass microspheres (made of borosilicate glass) are added sequentially (to the homogeneous colloid) and stirred at high speed until they are evenly dispersed; the mass ratio of biochar, hollow glass microspheres and sodium alginate is 2:0.1:3; the particle size of hollow glass microspheres is 45-55 μm; before adding biochar and hollow glass microspheres, the temperature is lowered to 35℃; the stirring speed of high speed stirring is 1500 rpm and the stirring time is 20 min.

[0068] The biochar used is orange peel biochar, and its specific preparation steps are as follows:

[0069] Raw material pretreatment: Take fresh or dried orange peels, remove residual pulp, seeds, and rotten parts, and rinse repeatedly with deionized water 4 times. Place fresh orange peels in a forced-air drying oven and dry at 70℃ for 18 hours until constant weight. Dried orange peels do not need to be dried. Crush the dried orange peels using a high-speed pulverizer and pass them through a 90-mesh sieve to obtain orange peel powder. Add the orange peel powder to a 7.5% (v / v) ethanol solution, with a solid-liquid ratio (i.e., mass-volume ratio) of 1 g: 10 mL. Stir at a constant temperature of 60℃ and a stirring rate of 190 rpm for 2.5 hours. After filtration, wash with deionized water until neutral, and then dry at 60℃ to constant weight. Pyrolysis: In a tube furnace under an inert gas atmosphere, heat to 700℃ at a heating rate of 7.5℃ / min, hold at that temperature for 2 hours, and then cool naturally to room temperature to obtain primary orange peel biochar. Activation treatment: The primary orange peel biochar was placed back into the tube furnace, and the activation gas - carbon dioxide - was introduced at a flow rate of 100 mL / min. The temperature was increased to 800℃ at a rate of 5℃ / min and held for 1.5 h. After cooling, the biochar was collected, washed with deionized water until neutral, and dried at 60℃ to constant weight to obtain orange peel biochar.

[0070] Next, a β-cyclodextrin solution and an adamantane-modified carboxymethyl starch solution (i.e., the organic matrix) were added to the colloid after uniform dispersion of orange peel biochar and hollow glass microspheres. The β-cyclodextrin solution was obtained by adding β-cyclodextrin to deionized water and stirring at 250 rpm for 30 minutes at 50°C until completely dissolved, with a solid-liquid ratio (mass-volume ratio) of 3 g:50 mL. The adamantane-modified carboxymethyl starch solution was obtained by adding adamantane-modified carboxymethyl starch to deionized water and stirring at 250 rpm for 60 minutes at room temperature until completely dissolved. The solid-liquid ratio (i.e., mass-volume ratio) of methyl starch to deionized water was 1 g: 25 mL; the mass ratio of β-cyclodextrin, adamantane-modified carboxymethyl starch, and sodium alginate was 2:3:15; after adding the organic matrix, the mixture was stirred at 275 rpm for 15 min, and then the microalgae solution was added. The volume-mass ratio of the microalgae solution to sodium alginate was 30 mL: 3 g (the biomass of the microalgae solution was ≥2 g / L, and Chlorella or Spirulina were generally used, which were obtained by further separation and concentration from purchased algal solutions, for example, Chlorella proteoides purchased from the freshwater algae seed bank of the Institute of Hydrobiology, Chinese Academy of Sciences). The mixture was stirred at 75 rpm for 10 min.

[0071] The preparation steps of adamantane-modified carboxymethyl starch are as follows:

[0072] Carboxymethyl starch treatment: First, carboxymethyl starch was added to deionized water. The solid-liquid ratio (i.e., mass-volume ratio) of carboxymethyl starch to deionized water was 1 g: 20 mL. The mixture was magnetically stirred at a constant temperature of 40℃ and a stirring speed of 400 rpm for 2 h to obtain a transparent and homogeneous carboxymethyl starch aqueous solution. Then, the pH of the carboxymethyl starch aqueous solution was adjusted to 7.7 using 0.1 mol / L sodium hydroxide solution. Activation of adamantane: First, 1-adamantane was added to dimethylformamide (DMF) at a solid-liquid ratio (mass-volume ratio) of 1 g:10 mL. The mixture was sonicated for 10 min until the adamantane was completely dissolved. Then, the adamantane solution was slowly added dropwise to a pH-adjusted carboxymethyl starch aqueous solution at a mass ratio of 1:5. The mixture was stirred at 400 rpm for 14 min. Next, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) was added at a mass ratio of 0.8:1 to 1-adamantane, and the mixture was stirred at 400 rpm for another 10 min. Grafting: The temperature was raised to 50 °C, and the mixture was refluxed at 400 rpm for 7 h. Purification: First, pour the refluxed reaction solution into anhydrous ethanol at a volume ratio of 3:1 while stirring at 400 rpm. Then, centrifuge the mixture at 8000 rpm for 10 minutes, remove the supernatant, and collect the white precipitate at the bottom. Finally, wash the mixture three times with anhydrous ethanol, each time using half the volume of the initial reaction solution. After washing, stir and centrifuge to obtain adamantane-modified carboxymethyl starch.

[0073] Finally, a 0.5 mol / L calcium nitrate solution and a 0.3 mol / L sodium phosphate solution were added sequentially, with a mass ratio of calcium nitrate, sodium phosphate, and sodium alginate of 2:1:15. The mixture was stirred at 190 rpm for 5 min. Then, ammonium bicarbonate was added, with a mass ratio of ammonium bicarbonate to sodium alginate of 1:15. The mixture was stirred at 400 rpm for 3 min to obtain a composite suspension.

[0074] Step S2, Initial Cross-linking into Globules: The composite suspension is added dropwise to the calcium chloride solution to obtain initial gel spheres; the concentration of the calcium chloride solution is 2.5% (w / v); the mass ratio of calcium chloride to sodium alginate is 2:3; the specific operation of adding the composite suspension to the calcium chloride solution is as follows: the composite suspension is drawn up with a syringe and added vertically at a distance of 15 cm from the surface of the calcium chloride solution, with a dropping rate of 1 drop / second, to obtain initial gel spheres with a diameter of 2-3 mm; the initial gel spheres are kept in the calcium chloride solution for 30 min to solidify, during which low-speed stirring at 90 rpm is used; finally, the initial gel spheres are taken out of the calcium chloride solution and rinsed twice with deionized water.

[0075] Step S3, Secondary cross-linking: First, add laccase and acetylacetone to deionized water. The enzyme activity of laccase is 7.5 U / mg. The solid-liquid ratio (i.e., mass-volume ratio) of laccase, acetylacetone and deionized water is 0.015mg:1mL:210mL. The volume-mass ratio of acetylacetone and sodium alginate is 1mL:15g. Adjust the pH to 5.5 (using hydrochloric acid for pH adjustment) to obtain the enzymatic cross-linking solution.

[0076] The initial gel spheres were then immersed in the enzymatic cross-linking solution and cross-linked at a rate of 120 rpm for 60 min in a constant temperature water bath at 30°C to obtain cross-linked gel spheres. After obtaining the cross-linked gel spheres, they were rinsed 4 times with deionized water.

[0077] Step S4, In-situ Enhancement: Immerse the cross-linked gel balls in 225 mL of deionized water and adjust the pH to 8.0 with sodium hydroxide. After standing at a constant temperature of 35°C for 40 min, adjust the pH to 7.0 with hydrochloric acid to obtain the enhanced gel balls. After obtaining the enhanced gel balls, rinse them twice with deionized water and then dry them in an oven at 40°C for 10 min.

[0078] Step S5, Coating: Immerse the enhanced gel spheres in the coating solution. The coating solution is a solution in which amino mesoporous silica nanoparticles are uniformly dispersed in deionized water. The concentration of the coating solution is 1.5% (w / v), and the pH value of the coating solution is 6.0 (which can be adjusted with hydrochloric acid).

[0079] The preparation method of amino-mesoporous silica nanoparticles is as follows:

[0080] First, CTAB (hexadecyltrimethylammonium bromide) and deionized water were mixed and stirred at room temperature at a stirring rate of 400 rpm until the solution became transparent and homogeneous. Then, ammonia water was slowly added dropwise while stirring continuously for 17 min at a dropping rate of 0.4 mL / min to obtain a CTAB micelle solution. The solid-liquid ratio (i.e., mass-to-volume ratio) of CTAB, ammonia water, and deionized water was 0.8 g: 3.5 mL: 110 mL. Next, tetraethyl orthosilicate (TEOS) was added dropwise to the CTAB micelle solution at a dropping rate of 1 drop / second, while maintaining a constant temperature and stirring rate. After the addition was completed, stirring was continued for 22 h to obtain a white emulsion. The volume-to-mass ratio of tetraethyl orthosilicate to CTAB was 4 mL: 0.8 g. Next, 3-aminopropyltriethoxysilane was added dropwise to the white emulsion at a rate of 1 drop / second, while maintaining constant temperature and stirring speed. After addition, stirring was continued for 12 hours. The mixture was then centrifuged at 10,000 rpm for 10 minutes, the supernatant was removed, and the white precipitate at the bottom was collected. Then, anhydrous ethanol and 37% (mass fraction) concentrated hydrochloric acid were added to the precipitate obtained by centrifugation, with a volume-to-mass ratio of anhydrous ethanol:4 mL:0.8 g for CTAB. The mixture was refluxed at 60°C for 6 hours. After reflux, the mixture was cooled to room temperature and centrifuged at 10,000 rpm for 10 minutes. The precipitate was collected and washed three times with anhydrous ethanol until the supernatant was nearly neutral (the supernatant was used for testing after each centrifugation). Finally, the washed white precipitate was dried in a vacuum drying oven at 60℃ and a vacuum degree of -0.09MPa for 12 hours to obtain amino-mesoporous silica nanoparticles.

[0081] At room temperature, the microalgae gel spheres were adsorbed by oscillation at 130 rpm for 20 min and then dried in an oven at 35 ℃ for 15 min to complete the curing and shaping process.

[0082] Example 3:

[0083] A method for preparing microalgae gel spheres for water treatment, comprising:

[0084] Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; wherein, the solid-liquid ratio (i.e. mass-volume ratio) of sodium alginate, gelatin and deionized water is 3.5g:1.2g:120mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 65℃ and a stirring speed of 500rpm for 35min.

[0085] Then, biochar and hollow glass microspheres (made of borosilicate glass) were added sequentially (to the homogeneous colloid) and stirred at high speed until uniformly dispersed; the mass ratio of biochar, hollow glass microspheres and sodium alginate was 2.2:0.12:3.5; the particle size of the hollow glass microspheres was 45-55 μm; the temperature was lowered to 35°C before adding biochar and hollow glass microspheres; the stirring speed was 1600 rpm and the stirring time was 18 min.

[0086] The biochar used is orange peel biochar, and its specific preparation steps are as follows:

[0087] Raw material pretreatment: Take fresh or dried orange peel, remove residual pulp, seeds, and rotten parts, and rinse repeatedly with deionized water 5 times; place fresh orange peel in a forced-air drying oven and dry at 80℃ for 12 hours until constant weight; dried orange peel does not need to be dried. Crush the dried orange peel using a high-speed pulverizer and pass it through a 100-mesh sieve to obtain orange peel powder; add the orange peel powder to a 10% (v / v) ethanol solution, with a solid-liquid ratio (i.e., mass-volume ratio) of 1 g: 10 mL, and stir at a constant temperature of 62℃ and a stirring rate of 200 rpm for 2 hours. After filtration, wash with deionized water until neutral, and then dry at 62℃ to constant weight. Pyrolysis: In a tube furnace under an inert gas atmosphere, heat to 800℃ at a heating rate of 10℃ / min, hold at that temperature for 1 hour, and then cool naturally to room temperature to obtain primary orange peel biochar. Activation treatment: The primary orange peel biochar was placed back into the tube furnace, and the activation gas - carbon dioxide - was introduced at a flow rate of 110 mL / min. The temperature was increased to 900℃ at a rate of 5.5℃ / min and held for 1 h. After cooling, the biochar was collected, washed with deionized water until neutral, and dried at 62℃ to constant weight to obtain orange peel biochar.

[0088] Next, a β-cyclodextrin solution and an adamantane-modified carboxymethyl starch solution (i.e., the organic matrix) were added to the colloid containing uniformly dispersed orange peel biochar and hollow glass microspheres. The β-cyclodextrin solution was obtained by adding β-cyclodextrin to deionized water and stirring at 300 rpm for 28 minutes at 55°C until completely dissolved, with a solid-liquid ratio (mass-volume ratio) of 3 g:50 mL. The adamantane-modified carboxymethyl starch solution was obtained by adding adamantane-modified carboxymethyl starch to deionized water and stirring at 300 rpm for 58 minutes at room temperature until completely dissolved. The solid-liquid ratio (i.e., mass-volume ratio) of methyl starch to deionized water was 1 g: 25 mL; the mass ratio of β-cyclodextrin, adamantane-modified carboxymethyl starch, and sodium alginate was 2:3:15; after adding the organic matrix, the mixture was stirred at 300 rpm for 13 min, and then the microalgae solution was added. The volume-mass ratio of the microalgae solution to sodium alginate was 40 mL: 3 g (the biomass of the microalgae solution was ≥2 g / L, and Chlorella or Spirulina were generally used, which were obtained by further separation and concentration from purchased algal solutions, for example, Chlorella proteoides purchased from the freshwater algae seed bank of the Institute of Hydrobiology, Chinese Academy of Sciences). The mixture was stirred at 300 rpm for 8 min.

[0089] The preparation steps of adamantane-modified carboxymethyl starch are as follows:

[0090] Carboxymethyl starch treatment: First, add carboxymethyl starch to deionized water. The solid-liquid ratio (i.e., mass-volume ratio) of carboxymethyl starch to deionized water is 1g:20mL. Stir magnetically at a constant temperature of 42℃ and a stirring rate of 420rpm for 1.5h to obtain a transparent and homogeneous carboxymethyl starch aqueous solution. Then, adjust the pH of the carboxymethyl starch aqueous solution to 8.0 using 0.1mol / L sodium hydroxide solution. Activation of adamantane: First, 1-adamantane was added to dimethylformamide (DMF) at a solid-liquid ratio (mass-volume ratio) of 1 g:10 mL, and sonicated for 12 min until the adamantane was completely dissolved. Then, the adamantane solution was slowly added dropwise to a pH-adjusted carboxymethyl starch aqueous solution at a mass ratio of 1:5, and stirred at 420 rpm for 12 min. Afterward, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) was added at a mass ratio of 0.8:1 to 1-adamantane, and stirring was continued at 420 rpm for 8 min. Grafting: The temperature was raised to 52 °C, and the mixture was refluxed at 420 rpm for 6 h. Purification: First, pour the refluxed reaction solution into anhydrous ethanol at a volume ratio of 3:1, stirring at 420 rpm while pouring. Then, centrifuge the mixture at 8500 rpm for 8 minutes, remove the supernatant, and collect the white precipitate at the bottom. Finally, wash the mixture four times with anhydrous ethanol, each time using half the volume of the initial reaction solution. After washing, stir and centrifuge to obtain adamantane-modified carboxymethyl starch.

[0091] Finally, a 0.5 mol / L calcium nitrate solution and a 0.3 mol / L sodium phosphate solution were added sequentially, with a mass ratio of calcium nitrate, sodium phosphate, and sodium alginate of 2:1:15. The mixture was stirred at 200 rpm for 4 min. Then, ammonium bicarbonate was added, with a mass ratio of ammonium bicarbonate to sodium alginate of 1:15. The mixture was stirred at 420 rpm for 2 min to obtain a composite suspension.

[0092] Step S2, Initial Cross-linking into Globules: The composite suspension is added dropwise to the calcium chloride solution to obtain initial gel spheres; the concentration of the calcium chloride solution is 2.6% (w / v); the mass ratio of calcium chloride to sodium alginate is 2:3; the specific operation of adding the composite suspension to the calcium chloride solution is as follows: the composite suspension is drawn through a syringe and added vertically at a distance of 16 cm from the surface of the calcium chloride solution, with a dropping rate of 1 drop / second, to obtain initial gel spheres with a diameter of 2-3 mm; the initial gel spheres are kept in the calcium chloride solution for 28 min to solidify, during which low-speed stirring at 100 rpm is used; finally, the initial gel spheres are taken out of the calcium chloride solution and rinsed 3 times with deionized water.

[0093] Step S3, Secondary cross-linking: First, add laccase and acetylacetone to deionized water. The enzyme activity of laccase is 10 U / mg. The solid-liquid ratio (i.e., mass-volume ratio) of laccase, acetylacetone and deionized water is 0.01mg:1mL:220mL. The volume-mass ratio of acetylacetone and sodium alginate is 1mL:15g. Adjust the pH to 5.5 (using hydrochloric acid for pH adjustment) to obtain the enzymatic cross-linking solution.

[0094] The initial gel spheres were then immersed in the enzymatic cross-linking solution and cross-linked at a rate of 125 rpm for 55 min in a constant temperature water bath at 32°C to obtain cross-linked gel spheres. After obtaining the cross-linked gel spheres, they were rinsed 5 times with deionized water.

[0095] Step S4, In-situ Enhancement: Immerse the cross-linked gel balls in 250 mL of deionized water and adjust the pH to 8.0 with sodium hydroxide. After standing at 37°C for 35 min, adjust the pH to 7.0 with hydrochloric acid to obtain the enhanced gel balls. After obtaining the enhanced gel balls, rinse them three times with deionized water and then dry them in an oven at 43°C for 8 min.

[0096] Step S5, Coating: Immerse the enhanced gel spheres in the coating solution. The coating solution is a solution in which amino-mesoporous silica nanoparticles are uniformly dispersed in deionized water. The concentration of the coating solution is 1.6% (w / v), and the pH value of the coating solution is 6.0 (which can be adjusted with hydrochloric acid).

[0097] The preparation method of amino-mesoporous silica nanoparticles is as follows:

[0098] First, CTAB (hexadecyltrimethylammonium bromide) and deionized water were mixed and stirred at 500 rpm at room temperature until the solution became clear and homogeneous. Then, ammonia was slowly added dropwise while stirring continuously for 15 min at a dropping rate of 0.5 mL / min to obtain a CTAB micelle solution. The solid-liquid ratio (mass-volume ratio) of CTAB, ammonia, and deionized water was 0.85 g: 3.8 mL: 120 mL. Next, tetraethyl orthosilicate (TEOS) was added dropwise to the CTAB micelle solution at a dropping rate of 2 drops / second, while maintaining constant temperature and stirring rate. After the addition was complete, stirring was continued for 20 h to obtain a white emulsion. The volume-mass ratio of tetraethyl orthosilicate to CTAB was 4.2 mL: 0.85 g. Next, 3-aminopropyltriethoxysilane was added dropwise to the white emulsion at a rate of 2 drops / second, while maintaining constant temperature and stirring speed. After addition, stirring was continued for 10 hours. The mixture was then centrifuged at 10500 rpm for 8 minutes, the supernatant was removed, and the white precipitate at the bottom was collected. Then, anhydrous ethanol and 38% (mass fraction) concentrated hydrochloric acid were added to the precipitate obtained by centrifugation. The volume-to-mass ratio of anhydrous ethanol, concentrated hydrochloric acid, and CTAB was 85 mL:4.5 mL:0.85 g, and the mixture was refluxed at 62°C for 5.5 hours. After reflux, the mixture was cooled to room temperature and centrifuged at 10500 rpm for 8 minutes. The precipitate was collected and washed four times with anhydrous ethanol until the supernatant was nearly neutral (the supernatant was used for testing after each centrifugation). Finally, the washed white precipitate was dried in a vacuum drying oven at 65°C and a vacuum degree of -0.1MPa for 11 hours to obtain amino-mesoporous silica nanoparticles.

[0099] At room temperature, the microalgae gel spheres were adsorbed by oscillation at 140 rpm for 18 min and then dried in an oven at 37 ℃ for 14 min to complete the curing and shaping process.

[0100] Example 4:

[0101] As another preferred embodiment of the present invention, a microalgae gel ball is prepared by any of the above-described embodiments 1 to 3. The obtained microalgae gel ball is rinsed 3 to 5 times with deionized water to remove residual nanoparticles and reagents on the surface. Finally, the microalgae gel ball is placed in deionized water and stored in an environment of about 4°C.

[0102] Comparative Example 1:

[0103] A method for preparing microalgae gel spheres, comprising:

[0104] Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; wherein, the solid-liquid ratio (i.e. mass-volume ratio) of sodium alginate, gelatin and deionized water is 3g:1g:100mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 60℃ and a stirring rate of 400rpm for 40min.

[0105] Biochar was then added sequentially (to the homogeneous colloid) and stirred at high speed until evenly dispersed. Before adding the biochar, the temperature was lowered to 35°C. The stirring speed was 1500 rpm for 20 minutes. Orange peel biochar was used, and its preparation steps were the same as in Example 2. Next, a β-cyclodextrin solution and an adamantane-modified carboxymethyl starch solution (i.e., the organic matrix) were added, following the same steps as in Example 2. Then, a microalgae solution was added (the steps for adding the microalgae solution were the same as in Example 2). Finally, a 0.5 mol / L calcium nitrate solution, a 0.3 mol / L sodium phosphate solution, and ammonium bicarbonate were added sequentially, following the same steps as in Example 2.

[0106] Step S2, preliminary cross-linking into spheres: consistent with the steps in Example 2.

[0107] Step S3, Secondary Crosslinking: Same as in Example 2.

[0108] Step S4, in-situ enhancement: consistent with the steps in Example 2.

[0109] Step S5, Coating: Same as the steps in Example 2.

[0110] Comparative Example 2:

[0111] A method for preparing microalgae gel spheres, comprising:

[0112] Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; wherein, the solid-liquid ratio (i.e. mass-volume ratio) of sodium alginate, gelatin and deionized water is 3g:1g:100mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 60℃ and a stirring rate of 400rpm for 40min.

[0113] Hollow glass microspheres were then added sequentially (to the homogeneous colloid) and stirred at high speed until uniformly dispersed; the particle size of the hollow glass microspheres was 45–55 μm; the temperature was lowered to 35°C before adding the hollow glass microspheres; the stirring speed was 1500 rpm and the stirring time was 20 min. Next, a β-cyclodextrin solution and an adamantane-modified carboxymethyl starch solution (i.e., the organic matrix) were added, following the same steps as in Example 2, followed by the addition of a microalgae solution (the steps for adding the microalgae solution were the same as in Example 2). Finally, a 0.5 mol / L calcium nitrate solution, a 0.3 mol / L sodium phosphate solution, and ammonium bicarbonate were added sequentially, following the same steps as in Example 2.

[0114] Step S2, preliminary cross-linking into spheres: consistent with the steps in Example 2.

[0115] Step S3, Secondary Crosslinking: Same as in Example 2.

[0116] Step S4, in-situ enhancement: consistent with the steps in Example 2.

[0117] Step S5, Coating: Same as the steps in Example 2.

[0118] Comparative Example 3:

[0119] A method for preparing microalgae gel spheres, comprising:

[0120] Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; wherein, the solid-liquid ratio (i.e. mass-volume ratio) of sodium alginate, gelatin and deionized water is 3g:1g:100mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 60℃ and a stirring rate of 400rpm for 40min.

[0121] Next, biochar and hollow glass microspheres were added sequentially (to the homogeneous colloid), following the same steps as in Example 2. Then, an adamantane-modified carboxymethyl starch solution was added. This adamantane-modified carboxymethyl starch solution was added to deionized water, and the mixture was stirred at 300 rpm for 58 minutes at room temperature until completely dissolved. The solid-liquid ratio (i.e., mass-to-volume ratio) of the adamantane-modified carboxymethyl starch to deionized water was 1 g:25 mL; the mass ratio of the adamantane-modified carboxymethyl starch to sodium alginate was 3:15. After adding the adamantane-modified carboxymethyl starch solution, the mixture was stirred at 300 rpm for 13 minutes, and then a microalgae solution was added (the steps for adding the microalgae solution were the same as in Example 2). The preparation of the adamantane-modified carboxymethyl starch was consistent with Example 2.

[0122] Finally, a calcium nitrate solution with a concentration of 0.5 mol / L, a sodium phosphate solution with a concentration of 0.3 mol / L, and ammonium bicarbonate were added in sequence, following the same steps as in Example 2.

[0123] Step S2, preliminary cross-linking into spheres: consistent with the steps in Example 2.

[0124] Step S3, Secondary Crosslinking: Same as in Example 2.

[0125] Step S4, in-situ enhancement: consistent with the steps in Example 2.

[0126] Step S5, Coating: Same as the steps in Example 2.

[0127] Comparative Example 4:

[0128] A method for preparing microalgae gel spheres, comprising:

[0129] Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; wherein, the solid-liquid ratio (i.e. mass-volume ratio) of sodium alginate, gelatin and deionized water is 3g:1g:100mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 60℃ and a stirring rate of 400rpm for 40min.

[0130] Biochar and hollow glass microspheres were then added sequentially (to the homogeneous colloid), following the same steps as in Example 2. Next, a β-cyclodextrin solution was added, which was obtained by adding β-cyclodextrin to deionized water. The mixture was stirred at 55°C and 300 rpm for 28 minutes until completely dissolved. The solid-liquid ratio (i.e., mass-to-volume ratio) of β-cyclodextrin to deionized water was 3 g: 50 mL; the mass ratio of β-cyclodextrin to sodium alginate was 2:15. After adding the β-cyclodextrin solution, the mixture was stirred at 300 rpm for 13 minutes, and then a microalgae solution was added (the steps for adding the microalgae solution were the same as in Example 2).

[0131] Finally, a calcium nitrate solution with a concentration of 0.5 mol / L, a sodium phosphate solution with a concentration of 0.3 mol / L, and ammonium bicarbonate were added in sequence, following the same steps as in Example 2.

[0132] Step S2, preliminary cross-linking into spheres: consistent with the steps in Example 2.

[0133] Step S3, Secondary Crosslinking: Same as in Example 2.

[0134] Step S4, in-situ enhancement: consistent with the steps in Example 2.

[0135] Step S5, Coating: Same as the steps in Example 2.

[0136] Comparative Example 5:

[0137] A method for preparing microalgae gel spheres, comprising:

[0138] Step S1, Preparation of composite suspension: Same as in Example 2.

[0139] Step S2, preliminary cross-linking into spheres: consistent with the steps in Example 2.

[0140] Step S3, Secondary Crosslinking: Secondary enhanced crosslinking is performed using pentylene glycol, boric acid, etc.

[0141] The initial gel spheres obtained in step S2 were redispersed with phosphate-buffered saline (PBS) at pH 6–8 to prepare a microsphere suspension with a mass concentration of 5%–10%. 1–2 g of boric acid was added to 100 mL of deionized water and magnetically stirred until completely dissolved. The pH was then adjusted to 8–9 with 1 mol / L NaOH solution. 5–15 mL of pentanediol was added to the solution, and the mixture was stirred at 200–300 rpm for 10–15 min to obtain a secondary cross-linking solution. The microsphere suspension was slowly added dropwise to the secondary cross-linking solution (dropping rate 1–2 drops / second), and the mixture was magnetically stirred at 150–200 rpm for 2–6 h at 25–37 °C to obtain cross-linked gel spheres. After obtaining the cross-linked gel spheres, they were washed four times by centrifugation with deionized water (centrifugation speed 3000 rpm, centrifugation time 5 min).

[0142] Step S4, in-situ enhancement: consistent with the steps in Example 2.

[0143] Step S5, Coating: Same as the steps in Example 2.

[0144] Comparative Example 6:

[0145] A method for preparing microalgae gel spheres, comprising:

[0146] Step S1, Preparation of composite suspension: Same as in Example 2.

[0147] Step S2, preliminary cross-linking into spheres: consistent with the steps in Example 2.

[0148] Step S3, Secondary Crosslinking: Same as in Example 2.

[0149] Step S4, Coating: Same as step S5 in Example 2.

[0150] Mechanical strength test: Ten gel spheres prepared in Examples 1-3 and Comparative Examples 1-6 were selected respectively, and the average initial diameter of each group was measured using a microscope and recorded as D0. Then, a single microalgae gel sphere was placed between two glass slides, and a 200g weight (with a base area of ​​1cm²) was placed on top of the slides.2 (Apply pressure evenly) and continue squeezing for 10 seconds. Remove the weights and measure the average diameter D1 of each group after squeezing. Observe whether the material breaks to obtain the diameter deformation rate and breakage rate.

[0151]

[0152] The test results are shown in Table 1 below (the average value is the average of the test values ​​of 10 gel balls in each test group):

[0153]

[0154] As shown in the table above, the microalgae gel spheres prepared using the method of the present invention have a low diameter deformation rate of about 5% and are free from breakage. This proves that the microalgae gel spheres of the present invention form an effective supporting framework network through secondary cross-linking and in-situ strengthening, which significantly improves the extrusion resistance and structural integrity of the microalgae gel spheres.

[0155] Ammonia nitrogen removal rate test in water: Simulated aquaculture wastewater was prepared with an initial concentration of 20 mg / L of ammonia nitrogen in 1 L of wastewater. 20 g of the microalgae gel balls prepared in Examples 1-3 and Comparative Examples 1-6 were added to each wastewater container. The mixture was then cultured under red light for 12 h (1500 lux light intensity, with no light for the remaining 12 h) at room temperature (25±1℃) for 3 days. After 3 days, samples were taken to determine the ammonia nitrogen concentration (Nessler's reagent spectrophotometry was used to determine the ammonia nitrogen concentration of each test group). The results are shown in Table 2 below (the average value is the average of the test values ​​of 10 gel balls in each test group).

[0156]

[0157] As shown in the table above, the secondary cross-linked network structure of this invention, along with in-situ reinforcement using biochar, hollow glass microspheres, and organic matrix, enhances the structural stability of the microalgae gel spheres. This, in turn, promotes the transfer of ammonia nitrogen from the water into the gel spheres and ensures the long-term activity of the microalgae. This enhances the microalgae's ability to absorb and convert ammonia nitrogen, improves the transport capacity of substances within the gel spheres, and avoids problems such as slow growth or even death of microalgae inside the gel spheres due to the obstruction of complex encapsulation structures. Ultimately, this improves the water purification capacity of the microalgae gel spheres.

[0158] 2% sodium alginate microalgae gel balls were prepared using the method mentioned in the literature "Effect of immobilized algae in purifying aquaculture wastewater and optimization of immobilization conditions" (Journal of Shanghai Ocean University, Liu E et al., May 2017). These microalgae gel balls and the microalgae gel balls prepared in Example 2 of this invention were placed in the same dynamic device (device environment: aeration conditions, water temperature 25±1℃, water body is simulated aquaculture wastewater with ammonia nitrogen concentration of 20mg / L) and continuously soaked for 30 days. After 30 days, they were observed under a 4x microscope. Figure 1 The microalgae gel spheres prepared in Example 2 of this invention, such as Figure 1 As shown, after soaking the microalgae gel balls in Example 2 for 30 days, the surface of the balls remained smooth, without obvious damage or deformation, and a clear surface and uniformly distributed microalgae could be observed. Figure 2 Sodium alginate microalgae gel spheres prepared using methods described in the literature, such as... Figure 2 As shown, obvious pits and irregular bumps or depressions appeared on the surface of the sphere, and it was clearly observed that the surface was damaged and even microalgae were leaking.

Claims

1. A method for preparing microalgae gel spheres for water treatment, characterized in that: include: Step S1, Preparation of composite suspension: First, add sodium alginate and gelatin to deionized water and stir to form a homogeneous colloid; Next, biochar and hollow glass microspheres are added sequentially and stirred at high speed until evenly dispersed. Then, an organic matrix is ​​added, stirred, and then a microalgae solution is added. After stirring, functional reagents are added sequentially and stirred to obtain a composite suspension. The functional reagents include calcium nitrate solution, sodium phosphate solution, and ammonium bicarbonate. The biochar used is orange peel biochar, and the hollow glass microspheres are made of borosilicate glass. The organic matrix comprises a β-cyclodextrin solution and an adamantane-modified carboxymethyl starch solution. The β-cyclodextrin solution is obtained by adding β-cyclodextrin to deionized water and stirring at 200-300 rpm for 28-32 minutes at 45-55°C until completely dissolved, with a solid-liquid ratio of 3 g:50 mL. The adamantane-modified carboxymethyl starch solution is obtained by adding adamantane-modified carboxymethyl starch to deionized water and stirring at 200-300 rpm for 58-62 minutes at room temperature until completely dissolved, with a solid-liquid ratio of 1 g:25 mL. The mass ratio of β-cyclodextrin, adamantane-modified carboxymethyl starch, and sodium alginate is 2:3:

15. After adding the β-cyclodextrin solution and the adamantane-modified carboxymethyl starch solution, the mixture is stirred at 250-300 rpm for 13-17 minutes. Step S2, Initial cross-linking into spheres: The composite suspension is added dropwise to a calcium chloride solution to obtain initial gel spheres; Step S3, Secondary Cross-linking: First, add the catalytic enzyme and acetylacetone to deionized water and adjust the pH to 5.

5. Laccase is used as the catalytic enzyme to obtain an enzymatic cross-linking solution. Then, immerse the initial gel balls in the enzymatic cross-linking solution and cross-link them by constant temperature shaking to obtain cross-linked gel balls. Step S4, In-situ reinforcement: Immerse the cross-linked gel balls in deionized water, adjust the pH to 8.0 with sodium hydroxide, let them stand at a constant temperature, and then adjust the pH to 7.0 with hydrochloric acid to obtain reinforced gel balls; Step S5, Coating: Immerse the enhanced gel spheres in a coating solution, which is a solution of amino-mesoporous silica nanoparticles uniformly dispersed in deionized water. The concentration of the coating solution is 1.4-1.6%, and the pH value of the coating solution is 6.

0. Adsorption and curing are performed by room temperature shaking. The shaking rate for room temperature shaking adsorption is 120-140 rpm, and the shaking time is 18-22 min. Curing is performed by drying in an oven at 33-37℃ for 14-16 min. Microalgae gel spheres are obtained.

2. The method for preparing microalgae gel spheres for water treatment according to claim 1, characterized in that: In step S1, the solid-liquid ratio of sodium alginate, gelatin and deionized water is 2.5-3.5g: 0.8-1.2g: 80-120mL; the stirring of sodium alginate, gelatin and deionized water is carried out at a constant temperature of 55-65℃ and a stirring speed of 300-500rpm for 35-45min.

3. The method for preparing microalgae gel spheres for water treatment according to claim 1, characterized in that: The mass ratio of biochar, hollow glass microspheres, and sodium alginate is 1.8–2.2:0.08–0.12:2.5–3.5; the particle size of the hollow glass microspheres is 45–55 μm; the temperature is lowered to 32–38 °C before adding the biochar and hollow glass microspheres; the stirring speed of the high-speed stirrer is 1400–1600 rpm, and the stirring time is 18–22 min.

4. The method for preparing microalgae gel spheres for water treatment according to claim 1, characterized in that: The concentration of calcium nitrate solution in the functional reagent is 0.5 mol / L, and the concentration of sodium phosphate solution is 0.3 mol / L. First, calcium nitrate solution and sodium phosphate solution are added, with a mass ratio of calcium nitrate, sodium phosphate and sodium alginate of 2:1:15, and stirred at a stirring speed of 180-200 rpm for 4-6 min. Then, ammonium bicarbonate is added, with a mass ratio of ammonium bicarbonate and sodium alginate of 1:15, and stirred at a stirring speed of 380-420 rpm for 2-4 min.

5. The method for preparing microalgae gel spheres for water treatment according to claim 1, characterized in that: In step S2, the concentration of the calcium chloride solution is 2.4%–2.6%; the mass ratio of calcium chloride to sodium alginate is 2:3; the specific operation of adding the composite suspension to the calcium chloride solution is as follows: the composite suspension is drawn up with a syringe and added vertically at a distance of 14–16 cm from the surface of the calcium chloride solution, with a dropping rate of 1 drop / second, to obtain initial gel spheres with a diameter of 2–3 mm; the initial gel spheres are kept in the calcium chloride solution to solidify for 28–32 min, during which low-speed stirring at 80–100 rpm is used; finally, the initial gel spheres are taken out of the calcium chloride solution and rinsed with deionized water 2–3 times.

6. The method for preparing microalgae gel spheres for water treatment according to claim 1, characterized in that: The laccase has an enzyme activity of 5–10 U / mg, and the solid-liquid ratio of laccase, acetylacetone, and deionized water is 0.01–0.02 mg: 1 mL: 200–220 mL. The volume-to-mass ratio of acetylacetone to sodium alginate is 1 mL: 15 g. After immersing the initial gel spheres in the enzymatic cross-linking solution, they are subjected to cross-linking by shaking at a rate of 115–125 rpm for 55–65 min in a constant temperature water bath at 28–32 °C.

7. The method for preparing microalgae gel spheres for water treatment according to claim 1, characterized in that: In step S4, the cross-linked gel balls are immersed in 200-250 mL of deionized water and kept at a constant temperature of 33-37°C for 35-45 min.

8. The method for preparing microalgae gel spheres for water treatment according to claim 1, characterized in that: After obtaining the cross-linked gel spheres in step S3, rinse with deionized water 3 to 5 times; after obtaining the reinforced gel spheres in step S4, rinse with deionized water 2 to 3 times, and then dry in an oven at 37 to 43°C for 8 to 12 minutes.

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