Magnetic nanometer micro-bubble generating material and application thereof in sewage treatment

Abstract

The application discloses a magnetic nanometer micro-bubble generating material and application thereof in sewage treatment, and belongs to the technical field of sewage treatment. The nanometer micro-bubble itself has the properties of aeration, mixing, micro-flocculation and air flotation. The surface of the nanometer micro-bubble is coated with amino-bimetallic MOF / ferroferric oxide containing magnetism and photocatalysis through an amidation reaction, so that the amino-bimetallic MOF / ferroferric oxide can be uniformly coated, and the amino-bimetallic MOF / ferroferric oxide is prevented from falling off and agglomerating. The nanometer micro-bubble has multiple functions, overturns the design concept of traditional "aeration-precipitation" separation, and can realize a "purification-recovery" integrated system by using magnetic response, so that precise adsorption and efficient separation are achieved. The magnetic nanometer micro-bubble generating material is directionally delivered to an area with high pollutant concentration in sewage by magnetic action, so that the material is prevented from diffusing with water flow, and the contact efficiency of pollutants and adsorption sites is improved. The application of the magnetic nanometer micro-bubble generating material in sewage treatment can significantly reduce organic pollutants in sewage.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sewage treatment, and particularly relates to a magnetic nano micro-bubble generating material and application thereof in sewage treatment. BACKGROUND

[0002] In the face of the demand for resource utilization of rural domestic sewage, the existing mainstream sewage treatment technology has exposed a series of technical bottlenecks that are difficult to overcome. First, rural domestic sewage generally presents the characteristics of low C / N ratio, which leads to low efficiency of traditional biological denitrification process due to the lack of sufficient carbon source, and it is difficult for total nitrogen to meet the standard. Second, the traditional process relies on high-intensity air blowing aeration, which consumes a lot of energy; at the same time, its multi-unit and long-process design leads to large land occupation and complex operation and management, and for rural areas with weak economic foundation and lack of professional personnel, the operation cost is high. Finally, the sewage discharge amount and water quality in rural areas fluctuate dramatically with season and time period, and the microbial system of the traditional process is fragile and has weak impact load resistance, which makes it difficult to guarantee long-term and stable treatment effect. These deep-rooted problems show that simple repair and improvement cannot meet the demand of rural environmental governance in the new era, and a revolutionary innovation of technical paradigm is urgently needed.

[0003] The emerging nano micro-bubble technology provides a new possibility for solving the above-mentioned problems, because of its unique physical and chemical properties and ultra-high gas-liquid mass transfer efficiency, it can significantly enhance the removal effect of organic pollutants and ammonia nitrogen, and reduce the aeration energy consumption, the hydroxyl radical (·OH) generated when it collapses has strong advanced oxidation ability, which can efficiently degrade refractory organic matter and inactivate pathogens, and its large specific surface area and interface negative charge can enhance micro-flocculation and promote solid-liquid separation.

[0004] The publication No. CN107213883B discloses a kind of graphene oxide-polylactic acid micro-bubble composite material and its preparation method and application, in which graphene oxide is modified on the surface of polylactic acid micro-bubble, the advantages of the two are fully combined, so that the composite material has the characteristics of strong adsorption capacity and large adsorption capacity of graphene oxide, and also has the characteristics of polylactic acid micro-bubble, which is not easy to agglomerate and easy to separate from the solution, but in this scheme, polylactic acid micro-bubbles are coated and modified by electrostatic adsorption, which leads to low bonding strength, easy to cause uneven coating and coating layer falling off, and further agglomeration. SUMMARY

[0005] The purpose of the present application is to provide a kind of magnetic nano micro-bubble generating material and its application in sewage treatment, which utilizes the aeration, mixing, micro-flocculation / air floatation properties of nano micro-bubbles itself, and coats aminoated bimetallic MOF / ferroferric oxide with magnetism and photocatalytic properties on the surface through amidation reaction, so as to have multiple functions, and the amidation reaction can avoid the falling off of aminoated bimetallic MOF / ferroferric oxide, so as to make the coating uniform and avoid agglomeration.

[0006] The object of the present application can be achieved by the following technical solutions:

[0007] A magnetic nanometer microbubble generating material is prepared by the following steps:

[0008] Step one: oxidizing the terminal hydroxyl group of polyvinyl alcohol into a carboxyl group to obtain carboxyl-terminated PVA, and then using carboxyl-terminated PVA and polylactic acid as wall materials to prepare carboxyl-terminated PVA nanometer microbubbles by a double emulsion / solvent evaporation method.

[0009] Step two: using ferroferric oxide as a matrix, hydrothermally synthesizing a bimetallic MOF containing titanium and calcium on the surface of the ferroferric oxide to obtain a bimetallic MOF / ferroferric oxide, and then modifying the bimetallic MOF / ferroferric oxide with gamma-aminopropyltriethoxysilane to obtain an aminated bimetallic MOF / ferroferric oxide.

[0010] Step three: using the carboxyl group of the carboxyl-terminated PVA nanometer microbubbles to react with the amino group of the aminated bimetallic MOF / ferroferric oxide through an amidation reaction, and then filling ozone after freeze-drying to obtain the magnetic nanometer microbubble generating material.

[0011] Further, the carboxyl-terminated PVA is prepared according to the following steps:

[0012] PVA with a molecular weight of 31000 and deionized water are added to a reaction kettle, and stirred at 80-90℃ and 500-600r / min for 30-40min, and then naturally cooled to room temperature, and then the pH value is adjusted to 4-5 with 1mol / L HCI solution, and then sodium periodate is added, and heated to 60-70℃, and then stirred for 7-8h until the PVA is completely oxidized, and then glacial acetic acid is added to adjust the pH value to 3-4, and then sodium chlorite is added, and then the solution is left to react for 4-5h until it changes from colorless to yellow-green, and then the filter cake is washed with deionized water for 2-3 times, and then vacuum dried at 60-80℃ for 1-2h to obtain the carboxyl-terminated PVA.

[0013] Further, the amount ratio of PVA, deionized water, sodium periodate and sodium chlorite is 80-90g: 1-2L: 8-9g: 48-50g.

[0014] Further, the carboxyl-terminated PVA nanometer microbubble is prepared according to the following steps:

[0015] The polylactic acid and dichloromethane are added into a reaction kettle, stirred at 20-25°C and 500-600r / min for 12-15min, then deionized water and emulsifier span80 are added, emulsified for 40-50S to obtain an emulsion; the carboxyl-terminated PVA and deionized water are added into a reaction kettle, stirred at 20-25°C and 500-600r / min for 12-15min, then the emulsion and emulsifier span80 are added, continue to stir for 2-3h, centrifuged at 3000-3200r / min for 10-12min, then 5-6% (mass fraction) mannitol as a cryoprotectant is added, and freeze-dried at-40°C for 24-26h to obtain carboxyl-terminated PVA nanobubbles.

[0016] Further, the amount ratio of polylactic acid, dichloromethane, deionized water and span80 is 1.6-2g: 160-200mL: 400-500mL: 4-8g.

[0017] Further, the amount ratio of carboxyl-terminated PVA, deionized water, emulsion, span80 and mannitol is 18-20g: 400-500mL: 80-90mL: 4-8g: 12-14mL.

[0018] Further, the specific preparation steps of the bimetallic MOF / ferroferric oxide are as follows:

[0019] The 2,5-dihydroxyterephthalic acid, ferroferric oxide and N,N-dimethylformamide are added into a polytetrafluoroethylene-lined autoclave, stirred at 20-25°C and 500-600r / min for 30-40min, then titanium tetrachloride, calcium chloride and ethylene glycol are added, heated to 120-130°C, the pH value is adjusted to 8-9 with a 3-4M NaOH solution, and the reaction is continued for 24-26h, then naturally cooled to room temperature, filtered, the filter cake is washed with anhydrous ethanol and deionized water for 2-3times respectively, and vacuum dried at 60-80°C for 1-2h to obtain the bimetallic MOF / ferroferric oxide.

[0020] Further, the amount ratio of 2,5-dihydroxyterephthalic acid, ferroferric oxide, N,N-dimethylformamide, titanium tetrachloride, calcium chloride and ethylene glycol is 80-90g: 70-75g: 120-140mL: 45-48g: 40-50g: 120-140mL.

[0021] Further, the specific preparation steps of the aminated bimetallic MOF / ferroferric oxide are as follows:

[0022] The bimetallic MOF / magnetite, anhydrous ethanol and deionized water are added into a reaction kettle, stirred at 60-70 DEG C and 500-600 r / min for 10-12 min, then gamma-aminopropyl triethoxysilane is added, the pH value is adjusted to 3-4 by using hydrochloric acid solution, and the stirring reaction is continued for 6-7 h, then the precipitate is filtered, washed with deionized water and anhydrous ethanol for 2-3 times, and vacuum dried at 60-80 DEG C for 1-2 h to obtain the aminated bimetallic MOF / magnetite.

[0023] Further, the use amount ratio of the bimetallic MOF / magnetite, anhydrous ethanol, deionized water and gamma-aminopropyl triethoxysilane is 70-80 g: 1-2 L: 2-3 L: 100-120 mL.

[0024] Further, the specific preparation steps of the magnetic nanobubble generating material are as follows:

[0025] The carboxyl-terminated PVA nanobubbles are suspended in a 2-(N-morpholine)-ethanesulfonic acid buffer solution with a pH value of 5.4-6 and a concentration of 50-60 mmol / L, stirred at 20-25 DEG C and 500-600 r / min for 10-12 min, then 1-ethyl-(3-2 methyl aminopropyl) carbodiimide hydrochloride with a concentration of 0.4-0.5 mg / mL and N-hydroxysuccinimide with a concentration of 0.6-0.7 mg / mL are added for activation, the stirring is continued for 15-20 min, then the aminated bimetallic MOF / magnetite is added, the stirring is continued for 24-26 h, centrifugation is carried out at 3000-3200 r / min for 10-12 min, the filter cake is washed with anhydrous ethanol and deionized water for 2-3 times respectively, and the freeze drying is carried out at-40 DEG C for 24-26 h, ozone is filled at a speed of 4-5 mL / min for 3-4 min to obtain the magnetic nanobubble generating material.

[0026] Further, the use amount ratio of the carboxyl-terminated PVA nanobubbles, 2-(N-morpholine)-ethanesulfonic acid buffer solution, 1-ethyl-(3-2 methyl aminopropyl) carbodiimide hydrochloride, N-hydroxysuccinimide and aminated bimetallic MOF / magnetite is 15-20 g: 120-140 mL: 2-4 g: 1-2 g: 50-60 g.

[0027] The beneficial effects of the present application are as follows:

[0028] 1. The magnetic nanobubble generating material prepared by the present application utilizes the aeration, mixing and micro-flocculation / air floatation properties of nanobubbles, and through an amidation reaction, the surface of the nanobubbles is coated with amino-functionalized bimetallic MOF / magnetite, so as to have multiple functions, avoid the detachment of the amino-functionalized bimetallic MOF / magnetite and cause agglomeration, overturn the design concept of traditional "aeration-precipitation" separation, utilize the magnetic responsiveness to realize the integration of "purification-recovery", and when applied in sewage treatment, can significantly reduce organic pollutants and heavy metals in the sewage.

[0029] 2. The amino-functionalized bimetallic MOF / magnetite of the present application, through the amidation reaction coated on the surface of the PVA nanobubbles, can increase the structural strength, the large specific surface area of the nanobubbles can avoid the agglomeration of the amino-functionalized bimetallic MOF / magnetite, and the magnetic property of the magnetite can endow the nanobubbles with magnetism, so as to be more controllable, realize "precise adsorption + efficient separation", and rely on the magnetic effect to direct the magnetic nanobubble generating material to the area with high concentration of pollutants in the sewage, avoid the diffusion of the material with the water flow, and improve the contact efficiency of the pollutants and the adsorption sites.

[0030] 3. The amino-functionalized bimetallic MOF / magnetite of the present application, the surface of which is further coated with bimetallic MOF, the bimetallic MOF contains titanium-based and calcium-based sites, the titanium sites have photocatalytic activity and can assist in degrading organic pollutants in the sewage by using the photocatalytic property, and the calcium sites can chelate heavy metals in the sewage by chelation, so as to achieve the effect of synergistic pollution removal; and in the carboxyl-terminated PVA nanobubbles, only the 1,2- vicinal diol groups in the "head-to-head" structure generate the carboxyl groups, not all the hydroxyl groups on the PVA main chain, so most of the hydroxyl groups are reserved, and in the process of coating the amino-functionalized bimetallic MOF / magnetite on the carboxyl-terminated PVA nanobubbles, the calcium sites in the bimetallic MOF can participate in the crosslinking of PVA, increase the crosslinking degree of the PVA nanobubbles, and further improve the strength of the PVA nanobubbles. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0032] Embodiment 1: A magnetic nanobubble generating material is prepared by the following steps:

[0033] S1: 80 g of PVA with a molecular weight of 31000 and 1 L of deionized water were added to the reaction kettle, stirred at 80 °C and 500 r / min for 30 min, naturally cooled to room temperature, the pH value was adjusted to 4 with 1 mol / L HCI solution, then 8 g of sodium periodate was added, heated to 60 °C, and stirred for 7 h until the PVA was completely oxidized, then 48 g of sodium chlorite was added, and the solution was yellow-green after standing for 4 h. The filter cake was washed with deionized water twice, and vacuum dried at 60 °C for 1 h to obtain carboxyl-terminated PVA.

[0034] S2: 1.6 g of polylactic acid and 160 mL of dichloromethane were added to the reaction kettle, stirred at 20 °C and 500 r / min for 12 min, then 400 mL of deionized water and 4 g of emulsifier span 80 were added, emulsified for 40 s to obtain an emulsion; 18 g of carboxyl-terminated PVA and 400 mL of deionized water were added to the reaction kettle, stirred at 20 °C and 500 r / min for 12 min, then 80 mL of emulsion and 4 g of emulsifier span 80 were added, and stirred for 2 h, centrifuged at 3000 r / min for 10 min, then 12 mL of mannitol with a mass fraction of 5% as a cryoprotectant was added, and freeze-dried at -40 °C for 24 h to obtain carboxyl-terminated PVA nanobubbles.

[0035] S3: 80 g of 2,5-dihydroxyterephthalic acid, 70 g of ferroferric oxide, and 120 mL of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave, stirred at 20 °C and 500 r / min for 30 min, then 45 g of titanium tetrachloride, 40 g of calcium chloride, and 120 mL of ethylene glycol were added, heated to 120 °C, and the pH value was adjusted to 8 with a 3 M NaOH solution, and the reaction was continued for 24 h, then naturally cooled to room temperature, filtered, and the filter cake was washed with anhydrous ethanol and deionized water twice, and vacuum dried at 60 °C for 1 h to obtain a bimetallic MOF / ferroferric oxide.

[0036] S4: 70 g of bimetallic MOF / ferroferric oxide, 1 L of anhydrous ethanol, and 2 L of deionized water were added to the reaction kettle, stirred at 60 °C and 500 r / min for 10 min, then 100 mL of γ-aminopropyltriethoxysilane was added, and the pH value was adjusted to 3 with a hydrochloric acid solution, and the reaction was continued for 6 h, then filtered, and the precipitate was washed with deionized water and anhydrous ethanol twice, and vacuum dried at 60 °C for 1 h to obtain aminated bimetallic MOF / ferroferric oxide.

[0037] S5: 15 g of carboxyl-terminated PVA nanobubbles were suspended in 120 mL of 2-(N-morpholino)-ethanesulfonic acid buffer with a pH value of 5.4 and a concentration of 50 mmol / L, stirred at 20°C and 500 r / min for 10 min, then 2 g of 1-ethyl-(3-2-methylaminopropyl) carbodiimide hydrochloride with a concentration of 0.4 mg / mL and 1 g of N-hydroxysuccinimide with a concentration of 0.6 mg / mL were added for activation, and stirring was continued for 15 min, then 50 g of amino-functionalized bimetallic MOF / ferroferric oxide was added, and stirring was continued for 24 h, centrifugation was performed at 3000 r / min for 10 min, filtration was performed, the filter cake was washed with anhydrous ethanol and deionized water for 2 times respectively, and the filter cake was placed in a freeze dryer at -40°C for 24 h, ozone was filled at a speed of 4 mL / min for 3 min, and a magnetic nanobubble generating material was obtained.

[0038] Example 2: A magnetic nanobubble generating material was prepared by the following steps:

[0039] S1: 85 g of PVA with a molecular weight of 31000 and 1.5 L of deionized water were added to a reaction kettle, stirred at 85°C and 550 r / min for 35 min, naturally cooled to room temperature, the pH value was adjusted to 4.5 with 1 mol / L HCI solution, then 8.5 g of sodium periodate was added, heated to 65°C, and stirring was continued for 7.5 h until the PVA was completely oxidized, then glacial acetic acid was added to adjust the pH value to 3.5, then 49 g of sodium chlorite was added, and the solution was left to react for 4.5 h, the solution changed from colorless to yellow-green, filtration was performed, the filter cake was washed with deionized water for 2 times, and vacuum drying was performed at 70°C for 1.5 h to obtain carboxyl-terminated PVA.

[0040] S2: 1.8 g of polylactic acid and 180 mL of dichloromethane were added to a reaction kettle, stirred at 22.5°C and 550 r / min for 13.5 min, then 450 mL of deionized water and 6 g of emulsifier span 80 were added, emulsification was performed for 45 s to obtain an emulsion; 19 g of carboxyl-terminated PVA and 450 mL of deionized water were added to a reaction kettle, stirred at 22.5°C and 550 r / min for 13.5 min, then 85 mL of the emulsion and 6 g of emulsifier span 80 were added, stirring was continued for 2.5 h, centrifugation was performed at 3100 r / min for 11 min, 13 mL of mannitol with a mass fraction of 5.5% as a cryoprotectant was added, and freeze drying was performed at -40°C for 25 h to obtain carboxyl-terminated PVA nanobubbles.

[0041] S3: 85 g of 2,5-dihydroxyterephthalic acid, 72.5 g of ferroferric oxide and 130 mL of N,N-dimethylformamide were added into a polytetrafluoroethylene-lined autoclave, stirred at 22.5°C and 550 r / min for 35 min, then 46.5 g of titanium tetrachloride, 45 g of calcium chloride and 130 mL of ethylene glycol were added, heated to 125°C, the pH value was adjusted to 8.5 with a 3.5 M NaOH solution, and the reaction was continued for 25 h, and then naturally cooled to room temperature, filtered, and the filter cake was washed with anhydrous ethanol and deionized water for 2 times respectively, and vacuum dried at 70°C for 1.5 h to obtain a bimetallic MOF / ferroferric oxide.

[0042] S4: 75 g of bimetallic MOF / ferroferric oxide, 1.5 L of anhydrous ethanol and 2.5 L of deionized water were added into a reaction kettle, stirred at 65°C and 550 r / min for 11 min, then 110 mL of γ-aminopropyltriethoxysilane was added, the pH value was adjusted to 3.5 with a hydrochloric acid solution, and the stirring reaction was continued for 6.5 h, then filtered, and the precipitate was washed with deionized water and anhydrous ethanol for 2 times, and vacuum dried at 70°C for 1.5 h to obtain an aminated bimetallic MOF / ferroferric oxide.

[0043] S5: 17.5 g of carboxyl-terminated PVA nanobubbles were suspended in 130 mL of 2-(N-morpholine)-ethanesulfonic acid buffer with a pH value of 5.7 and a concentration of 55 mmol / L, stirred at 22.5°C and 550 r / min for 11 min, then 3 g of 1-ethyl-(3-2-methylaminopropyl) carbodiimide hydrochloride with a concentration of 0.45 mg / mL and 1.5 g of N-hydroxysuccinimide with a concentration of 0.65 mg / mL were added for activation, and the stirring was continued for 17.5 min, then 55 g of aminated bimetallic MOF / ferroferric oxide was added, and the stirring was continued for 25 h, and then centrifuged at 3100 r / min for 11 min, filtered, and the filter cake was washed with anhydrous ethanol and deionized water for 2 times respectively, and then freeze-dried at-40°C for 25 h, and then ozone was filled at a speed of 4.5 mL / min for 3.5 min to obtain a magnetic nanobubble generating material.

[0044] Example 3: A magnetic nanobubble generating material was prepared by the following steps:

[0045] S1: 90 g of PVA with a molecular weight of 31000 and 2 L of deionized water were added to the reaction kettle, stirred at 90 °C and 600 r / min for 40 min, naturally cooled to room temperature, the pH value was adjusted to 5 with 1 mol / L HCI solution, then 9 g of sodium periodate was added, heated to 70 °C, and stirred for 8 h until the PVA was completely oxidized, then ice acetic acid was added to adjust the pH value to 4, then 50 g of sodium chlorite was added, and the solution was left to react for 5 h, the solution changed from colorless to yellow-green, the filter cake was washed with deionized water for 3 times, and vacuum dried at 80 °C for 2 h to obtain carboxyl-terminated PVA.

[0046] S2: 2 g of polylactic acid and 200 mL of dichloromethane were added to the reaction kettle, stirred at 25 °C and 600 r / min for 15 min, then 500 mL of deionized water and 8 g of emulsifier span 80 were added, emulsified for 50 s to obtain an emulsion; 20 g of carboxyl-terminated PVA and 500 mL of deionized water were added to the reaction kettle, stirred at 25 °C and 600 r / min for 15 min, then 90 mL of the emulsion and 8 g of emulsifier span 80 were added, and stirred for 3 h, centrifuged at 3200 r / min for 12 min, then 14 mL of mannitol with a mass fraction of 6% as a cryoprotectant was added, and freeze-dried at -40 °C for 26 h to obtain carboxyl-terminated PVA nanometer microbubbles.

[0047] S3: 90 g of 2,5-dihydroxyterephthalic acid, 75 g of ferroferric oxide and 140 mL of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave, stirred at 25 °C and 600 r / min for 40 min, then 48 g of titanium tetrachloride, 50 g of calcium chloride and 140 mL of ethylene glycol were added, heated to 130 °C, the pH value was adjusted to 9 with a 4 M NaOH solution, and the reaction was continued for 26 h, then naturally cooled to room temperature, filtered, the filter cake was washed with anhydrous ethanol and deionized water for 3 times respectively, and vacuum dried at 80 °C for 2 h to obtain a bimetallic MOF / ferroferric oxide.

[0048] S4: 80 g of bimetallic MOF / ferroferric oxide, 2 L of anhydrous ethanol and 3 L of deionized water were added to the reaction kettle, stirred at 70 °C and 600 r / min for 12 min, then 120 mL of γ-aminopropyltriethoxysilane was added, the pH value was adjusted to 4 with a hydrochloric acid solution, and the reaction was continued for 7 h, then filtered, the precipitate was washed with deionized water and anhydrous ethanol for 3 times, and vacuum dried at 80 °C for 2 h to obtain aminated bimetallic MOF / ferroferric oxide.

[0049] S5: 20 g of carboxyl-terminated PVA nanobubbles were suspended in 140 mL of 2-(N-morpholine)-ethanesulfonic acid buffer with a pH value of 6 and a concentration of 60 mmol / L, stirred at 25°C and 600 r / min for 12 min, then 4 g of 1-ethyl-(3-2-methylaminopropyl) carbodiimide hydrochloride with a concentration of 0.5 mg / mL and 2 g of N-hydroxysuccinimide with a concentration of 0.7 mg / mL were added for activation, and stirring was continued for 20 min, then 60 g of amino-functionalized bimetallic MOF / ferroferric oxide was added, and stirring was continued for 26 h, centrifugation was performed at 3200 r / min for 12 min, filtration was performed, the filter cake was washed with anhydrous ethanol and deionized water for 3 times respectively, and the filter cake was placed in a freeze dryer at -40°C for 26 h, ozone was filled at a speed of 5 mL / min for 4 min, and a magnetic nanobubble generating material was obtained.

[0050] Comparative Example 1: On the basis of Example 3, the carboxyl-terminated PVA in step S2 was replaced by the raw material PVA with a molecular weight of 31000 in step S1, and the remaining steps were unchanged, and a magnetic nanobubble generating material was prepared.

[0051] Comparative Example 2: On the basis of Example 3, titanium tetrachloride in step S3 was removed, and the remaining steps were unchanged, and a magnetic nanobubble generating material was prepared.

[0052] Comparative Example 3: On the basis of Example 3, calcium chloride in step S3 was removed, and the remaining steps were unchanged, and a magnetic nanobubble generating material was prepared.

[0053] 1. Chemical oxygen demand (COD) (%) determination: determined by 5B-3B (VB) spectrophotometer and 5B-1 (VB) COD digester.

[0054] 2. NH4 + - removal rate: determined in accordance with the standard of HJ 536-2009 “Determination of Ammonia Nitrogen in Water Salicylic Acid Spectrophotometric Method”.

[0055] 3. TOC (total organic carbon) removal rate: determined in accordance with the standard of “HJ 501-2009 Determination of Total Organic Carbon in Water Combustion Oxidation-Non-dispersive Infrared Absorption Method”.

[0056] 4. Cl - removal rate: determined in accordance with the standard of GB / T 11896-89 “Determination of Chloride in Water Silver Nitrate Titration Method”.

[0057] 5. Cd 2+ removal rate: determined in accordance with the standard of HJ 757-2015 “Determination of Chromium in Water Flame Atomic Absorption Spectrophotometric Method”.

[0058] The magnetic nanobubble generating materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing, 4 g of the magnetic nanobubble generating material was added to 500 mL of simulated sewage, and each pollutant and heavy metal in the sewage was detected, and the results are shown in Table 1:

[0059] Table 1: Test results of magnetic nanobubble sewage treatment

[0060]

[0061] As can be seen from Table 1, the magnetic nanobubble generating materials prepared in Examples 1-3 applied in sewage treatment can significantly improve the removal rate of organic pollutants and heavy metals.

[0062] In Comparative Example 1, the carboxyl-terminated PVA in step S2 was replaced with the raw material PVA with a molecular weight of 31000 in step S1. The raw material PVA lacks carboxyl-terminated groups and cannot be effectively combined with the amino-functionalized bimetallic MOF / ferroferric oxide through amidation reaction, resulting in easy detachment of MOF particles from the microbubble surface and serious agglomeration.

[0063] In Comparative Example 2, titanium tetrachloride in step S3 was removed. Titanium tetrachloride is the source of titanium-based sites in bimetallic MOF, and titanium sites have photocatalytic activity that can strengthen the degradation of organic pollutants through photocatalytic reaction. After removing titanium tetrachloride, the material only retains physical adsorption and microbubble aeration, lacking the synergistic effect of photocatalysis, and has less impact on the removal rate of heavy metals. Therefore, the removal rate of Cd 2+ only shows a partial decrease, but the removal rate of organic pollutants decreases significantly.

[0064] In Comparative Example 3, calcium chloride in step S3 was removed. Calcium chloride is the source of calcium-based sites in bimetallic MOF, and calcium sites can efficiently remove heavy metals through chelation. After removing calcium chloride, the removal rate of Cd 2+ decreases significantly, and calcium sites also participate in the crosslinking of PVA nanobubbles. After the lack of calcium sites, the crosslinking degree of PVA decreases, and the microbubble structure is easy to collapse, resulting in agglomeration of MOF particles, weakening of the magnetic directional transport ability, and further affecting the adsorption and separation efficiency of organic pollutants.

[0065] Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application.

Claims

1. A magnetic nanobubble generating material, characterized by, It is prepared by the following steps: Step one: oxidizing the terminal hydroxyl group of polyvinyl alcohol into carboxyl group to obtain carboxyl-terminated PVA, and then using carboxyl-terminated PVA and polylactic acid as wall materials to prepare carboxyl-terminated PVA nanobubble by double emulsion / solvent evaporation method; Step two: using ferroferric oxide as a matrix, hydrothermally synthesizing a bimetallic MOF containing titanium and calcium on the surface of the ferroferric oxide to obtain bimetallic MOF / ferroferric oxide, and then modifying the bimetallic MOF / ferroferric oxide by using gamma-aminopropyl triethoxysilane to obtain amino-modified bimetallic MOF / ferroferric oxide; Step three: using the terminal carboxyl group of the carboxyl-terminated PVA nanobubble to react with the amino group of the amino-modified bimetallic MOF / ferroferric oxide through amidation reaction, and then filling ozone after freeze-drying to obtain a magnetic nanobubble generating material. 2.The magnetic nanobubble generating material of claim 1, wherein, The carboxyl-terminated PVA is specifically prepared by the following steps: PVA with a molecular weight of 31000 and deionized water are added to a reaction kettle, stirred at 80-90 DEG C and 500-600 r / min for 30-40 min, naturally cooled to room temperature, the pH value is adjusted to 4-5 by using 1 mol / L HCl solution, then sodium periodate is added, heated to 60-70 DEG C, and continued to stir for 7-8 h until PVA is completely oxidized, then glacial acetic acid is added to adjust the pH value to 3-4, sodium chlorite is added, and the solution is left to react for 4-5 h until it changes from colorless to yellow-green, filtered, washed, and vacuum dried to obtain carboxyl-terminated PVA. 3.The magnetic nanobubble generating material of claim 2, wherein, The amount ratio of PVA, deionized water, sodium periodate and sodium chlorite is 80-90 g: 1-2 L: 8-9 g: 48-50 g. 4.The magnetic nanobubble generating material of claim 1, wherein, The carboxyl-terminated PVA nanobubble is specifically prepared by the following steps: Polylactic acid and dichloromethane are added to a reaction kettle, stirred at 20-25 DEG C and 500-600 r / min for 12-15 min, then deionized water and emulsifier span 80 are added, emulsified for 40-50 s to obtain an emulsion; carboxyl-terminated PVA and deionized water are added to a reaction kettle, stirred at 20-25 DEG C and 500-600 r / min for 12-15 min, then the emulsion and emulsifier span 80 are added, continued to stir for 2-3 h, centrifuged at 3000-3200 r / min for 10-12 min, and then 5-6% (mass fraction) mannitol as a cryoprotectant is added, and freeze-dried at-40 DEG C for 24-26 h to obtain carboxyl-terminated PVA nanobubble; The amount ratio of polylactic acid, dichloromethane, deionized water and span 80 is 1.6-2 g: 160-200 mL: 400-500 mL: 4-8 g; the amount ratio of carboxyl-terminated PVA, deionized water, emulsion, span 80 and mannitol is 18-20 g: 400-500 mL: 80-90 mL: 4-8 g: 12-14 mL. 5.The magnetic nanobubble generating material of claim 1, wherein, The bimetallic MOF / ferroferric oxide is specifically prepared by the following steps: 2,5-dihydroxyterephthalic acid, ferric oxide and N,N-dimethylformamide are added into a polytetrafluoroethylene lined autoclave, stirred at 20-25℃ and 500-600r / min for 30-40min, then titanium tetrachloride, calcium chloride and ethylene glycol are added, heated to 120-130℃, the pH value is adjusted to 8-9 with a 3-4M NaOH solution, and the reaction is continued for 24-26h, then it is naturally cooled to room temperature, filtered, washed and vacuum dried to obtain the bimetallic MOF / ferric oxide. 6.The magnetic nanobubble generating material of claim 5, wherein, The amount ratio of 2,5-dihydroxyterephthalic acid, ferric oxide, N,N-dimethylformamide, titanium tetrachloride, calcium chloride and ethylene glycol is 80-90g:70-75g:120-140mL:45-48g:40-50g:120-140mL. 7.The magnetic nanobubble generating material of claim 1, wherein, The specific preparation steps of the aminated bimetallic MOF / ferric oxide are as follows: The bimetallic MOF / ferric oxide, anhydrous ethanol and deionized water are added into a reaction kettle, stirred at 60-70℃ and 500-600r / min for 10-12min, then γ-aminopropyl triethoxysilane is added, the pH value is adjusted to 3-4 with a hydrochloric acid solution, and the reaction is continued for 6-7h, then it is filtered, the precipitate is washed with deionized water and anhydrous ethanol for 2-3 times, and vacuum dried at 60-80℃ for 1-2h to obtain the aminated bimetallic MOF / ferric oxide. The amount ratio of the bimetallic MOF / ferric oxide, anhydrous ethanol, deionized water and γ-aminopropyl triethoxysilane is 70-80g:1-2L:2-3L:100-120mL. 8.The magnetic nanobubble generating material of claim 1, wherein, The specific preparation steps of the magnetic nanobubble generating material are as follows: The carboxyl-terminated PVA nanobubbles are suspended in a 2-(N-morpholine)-ethanesulfonic acid buffer solution with a pH value of 5.4-6 and a concentration of 50-60mmol / L, stirred at 20-25℃ and 500-600r / min for 10-12min, then 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride with a concentration of 0.4-0.5mg / mL and N-hydroxysuccinimide with a concentration of 0.6-0.7mg / mL are added for activation, and the stirring is continued for 15-20min, then the aminated bimetallic MOF / ferric oxide is added, and the stirring is continued for 24-26h, then it is centrifuged at 3000-3200r / min for 10-12min, filtered, and the filter cake is washed with anhydrous ethanol and deionized water for 2-3 times each, frozen and dried at-40℃ for 24-26h, filled with ozone at a speed of 4-5mL / min for 3-4min to obtain the magnetic nanobubble generating material. 9.The magnetic nanobubble generating material of claim 8, wherein, The amount ratio of the carboxyl-terminated PVA nanobubbles, 2-(N-morpholine)-ethanesulfonic acid buffer solution, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride, N-hydroxysuccinimide and aminated bimetallic MOF / ferric oxide is 15-20g:120-140mL:2-4g:1-2g:50-60g.

10. Use of the magnetic nanobubble generating material according to claim 1 in sewage treatment.

Images