Beta-cyclodextrin coagulant aid as well as preparation method and application thereof

Abstract

The invention provides a beta-cyclodextrin coagulant aid as well as a preparation method and application thereof, and belongs to the technical field of environment and chemistry. The preparation method of the beta-cyclodextrin coagulant aid comprises the following steps: adding beta-cyclodextrin and acrylic acid into a first solvent for esterification reaction to obtain a first polymer; adding the first polymer and dimethyl diallyl ammonium chloride into a second solvent, and adding an initiator for polymerization reaction to obtain a second polymer; and adding the second polymer, sodium trifluoromethanesulfinate and sodium bromate into a third solvent, and carrying out nucleophilic substitution reaction to obtain the beta-cyclodextrin coagulant aid.

Description

Technical Field

[0001] The invention belongs to the field of environment and chemical technology, and particularly relates to a beta-cyclodextrin coagulant aid, a preparation method and an application thereof. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are attracting increasing attention due to their bioaccumulation, long-range transport, toxicity, and persistence in the environment. Worldwide, surveys show widespread contamination of groundwater, surface water, seawater, and even drinking water with PFAS. Currently, various methods are available for removing PFAS from drinking water, with adsorption being one of them. However, long-term use of activated carbon can lead to a decrease in adsorption efficiency, compromising its removal effectiveness. Therefore, it is necessary to optimize and upgrade conventional processes to enhance their PFAS removal capabilities and ensure drinking water safety.

[0003] Coagulation is a commonly used water treatment process, offering advantages such as low cost, ease of operation, and high water purification efficiency. Coagulants are crucial to coagulation effectiveness. However, conventional coagulants, when used to treat PFAS pollution, suffer from low removal efficiency and high dosage requirements, making them inadequate for the treatment of PFAS-contaminated waters. Therefore, the development of coagulants that can effectively remove PFAS is of great practical significance. Summary of the Invention

[0004] In response to the above technical problems, the present invention provides a β-cyclodextrin coagulant aid and its preparation method and application, in order to at least partially solve the above technical problems. The specific technical solutions provided by the present invention are as follows.

[0005] As a first aspect of the present invention, a method for preparing a β-cyclodextrin coagulant is provided, comprising: adding β-cyclodextrin and acrylic acid to a first solvent for an esterification reaction to obtain a first polymer; adding the first polymer and dimethyldiallylammonium chloride to a second solvent, and adding an initiator for a polymerization reaction to obtain a second polymer; and adding the second polymer, sodium trifluoromethanesulfinate, and sodium bromate to a third solvent for a nucleophilic substitution reaction to obtain a β-cyclodextrin coagulant.

[0006] As a second aspect of the present invention, a β-cyclodextrin coagulant aid is provided, which is prepared using the above method.

[0007] As a third aspect of the present invention, there is provided a use of the above-mentioned β-cyclodextrin coagulant aid in sewage treatment.

[0008] In an embodiment of the present invention, olefin groups, amino groups, and fluoride ions are introduced into β-cyclodextrin through step-by-step reactions. The olefin groups are introduced into β-cyclodextrin through an esterification reaction between β-cyclodextrin and acrylic acid to obtain a first polymer. The introduction of the olefin groups provides active sites for subsequent polymerization reactions, allowing β-cyclodextrin to undergo further chemical reactions with other reactants. The amino groups are introduced into β-cyclodextrin through a polymerization reaction between the first polymer and dimethyldiallylammonium chloride to obtain a second polymer. The introduction of the amino groups into β-cyclodextrin is achieved by polymerizing the olefin groups introduced into β-cyclodextrin with the olefin groups in dimethyldiallylammonium chloride. The introduction of the amino groups not only increases the charge density of the β-cyclodextrin coagulant, but also enhances its ability to interact with charged particles, thereby improving the flocculation effect of the β-cyclodextrin coagulant. Fluoride ions are introduced into β-cyclodextrin through a nucleophilic substitution reaction between the second polymer and sodium trifluoromethanesulfinate or sodium bromate. The introduction of fluoride ions can further enhance the stability and hydrophobicity of β-cyclodextrin coagulants, allowing them to maintain good performance in complex water treatment environments. β-cyclodextrin is a natural polymer compound with good biocompatibility and biodegradability. The amino groups and fluoride ions introduced by chemical modification are both common chemical groups and will not introduce new toxic substances. Therefore, the β-cyclodextrin coagulant has low toxicity and is environmentally friendly. The preparation method of this β-cyclodextrin coagulant introduces olefin groups, amino groups and fluoride ions through step-by-step reactions, making the structure of the β-cyclodextrin coagulant more compact and easy to generate a network structure macromolecular substance with a higher degree of polymerization, thereby significantly improving the flocculation effect, stability and environmental friendliness of the β-cyclodextrin coagulant. The preparation method of the β-cyclodextrin coagulant provided by the present invention is simple to operate, has a controllable process, is suitable for large-scale promotion, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The infrared spectra of β-CD, β-CD-AA, β-CD-AA-DMDAAC, and β-CD-AA-DMDAAC-CF3 in Comparative Examples 1-3 and Example 1 are shown;

[0010] Figure 2 The figure shows the treatment effect of the composite coagulant in Comparative Examples 1-3 and Example 1 on wastewater containing anionic perfluorinated compounds;

[0011] Figure 3 This is a diagram showing the treatment effect of the composite coagulant in Example 2-4 on wastewater containing anionic perfluorinated compounds;

[0012] Figure 4 This is a diagram showing the treatment effect of the composite coagulant in Example 2-4 on wastewater containing non-ionic perfluorinated compounds;

[0013] Figure 5 This is a diagram showing the treatment effect of the composite coagulant in Example 2-4 on wastewater containing cationic perfluorinated compounds;

[0014] Figure 6 The figure shows the treatment effect of the composite coagulant and the PAC coagulant on the wastewater containing anionic perfluorinated compounds in Example 2 and Comparative Example 4;

[0015] Figure 7 The figures are as follows: the treatment effect of the composite coagulant and the PAC coagulant on wastewater containing non-ionic perfluorinated compounds in Example 2 and Comparative Example 4;

[0016] Figure 8 The figure shows the treatment effect of the composite coagulant and the PAC coagulant on the wastewater containing cationic perfluorinated compounds in Example 2 and Comparative Example 4;

[0017] Figure 9 The figures are the treatment effects of the composite coagulant on the wastewater containing anionic perfluorinated compounds in Example 2, Comparative Example 5 and Comparative Example 6;

[0018] Figure 10 The figures are the treatment effects of the composite coagulant on wastewater containing non-ionic perfluorinated compounds in Example 2, Comparative Example 5 and Comparative Example 6;

[0019] Figure 11 The figures are the treatment effects of the composite coagulant on the wastewater containing cationic perfluorinated compounds in Example 2, Comparative Example 5 and Comparative Example 6;

[0020] Figure 12 The treatment effect of the composite coagulant in Example 1 on wastewater containing anionic perfluorinated compounds under different pH conditions is shown in FIG.

[0021] Figure 13 The treatment effect of the composite coagulant in Example 1 on wastewater containing non-ionic perfluorinated compounds under different pH conditions is shown;

[0022] Figure 14 This is a diagram showing the treatment effect of the composite coagulant in Example 1 on wastewater containing cationic perfluorinated compounds under different pH conditions. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0024] Recent studies have found that the hydrophilic exterior and hydrophobic interior of β-cyclodextrin (β-CD) make it suitable for applications based on host-guest chemistry. Hydrophobic guests favorably partition from polar aqueous media into the cyclodextrin cavity. Due to their hydrophobic tails and hydrophilic head groups, organic matter can be partitioned into the cyclodextrin cavity. The functional head groups can be solvated by aqueous solutions and interact with hydroxyl groups on the cyclodextrin through hydrogen bonds, offering significant advantages in removing organic matter from water. β-CD is widely available, environmentally friendly, and inexpensive. Using β-CD as the primary raw material for the preparation of organic coagulant aids not only saves raw material costs but also opens up new avenues for the large-scale production and application of β-CD as a coagulant.

[0025] Therefore, the present invention uses β-CD as the main raw material and adopts a simple and effective synthesis strategy to introduce olefin groups, amino groups and trifluoromethyl groups respectively, thereby regulating the microstructure and surface properties of β-CD to obtain a β-cyclodextrin coagulant, thereby enhancing its removal effect on perfluoroalkyl and polyfluoroalkyl substances (PFAS) in wastewater.

[0026] Specifically, as the first aspect of the present invention, a method for preparing a β-cyclodextrin coagulant is provided, comprising: adding β-cyclodextrin and acrylic acid to a first solvent for an esterification reaction to obtain a first polymer; adding the first polymer and dimethyldiallylammonium chloride to a second solvent, and adding an initiator for a polymerization reaction to obtain a second polymer; adding the second polymer, sodium trifluoromethanesulfinate, and sodium bromate to a third solvent for a nucleophilic substitution reaction to obtain a β-cyclodextrin coagulant.

[0027] In an embodiment of the present invention, olefin groups, amino groups, and fluoride ions are introduced into β-cyclodextrin through step-by-step reactions. The olefin groups are introduced into β-cyclodextrin through an esterification reaction between β-cyclodextrin and acrylic acid to obtain a first polymer. The introduction of the olefin groups provides active sites for subsequent polymerization reactions, allowing β-cyclodextrin to undergo further chemical reactions with other reactants. The amino groups are introduced into β-cyclodextrin through a polymerization reaction between the first polymer and dimethyldiallylammonium chloride to obtain a second polymer. The introduction of the amino groups into β-cyclodextrin is achieved by polymerizing the olefin groups introduced into β-cyclodextrin with the olefin groups in dimethyldiallylammonium chloride. The introduction of the amino groups not only increases the charge density of the β-cyclodextrin coagulant, but also enhances its ability to interact with charged particles, thereby improving the flocculation effect of the β-cyclodextrin coagulant. Fluoride ions are introduced into β-cyclodextrin through a nucleophilic substitution reaction between the second polymer and sodium trifluoromethanesulfinate or sodium bromate. The introduction of fluoride ions can further enhance the stability and hydrophobicity of β-cyclodextrin coagulants, allowing them to maintain good performance in complex water treatment environments. β-cyclodextrin is a natural polymer compound with good biocompatibility and biodegradability. The amino groups and fluoride ions introduced by chemical modification are both common chemical groups and will not introduce new toxic substances. Therefore, the β-cyclodextrin coagulant has low toxicity and is environmentally friendly. The preparation method of this β-cyclodextrin coagulant introduces olefin groups, amino groups and fluoride ions through step-by-step reactions, making the structure of the β-cyclodextrin coagulant more compact and easy to generate a network structure macromolecular substance with a higher degree of polymerization, thereby significantly improving the flocculation effect, stability and environmental friendliness of the β-cyclodextrin coagulant. The preparation method of the β-cyclodextrin coagulant provided by the present invention is simple to operate, has a controllable process, is suitable for large-scale promotion, and has broad application prospects.

[0028] According to an embodiment of the present invention, the molar ratio of β-cyclodextrin to acrylic acid is 1:3-5. The introduction of an appropriate amount of acrylic acid groups provides the subsequently produced β-cyclodextrin coagulant with abundant active functional groups, such as carboxyl groups. These carboxyl groups can bind to metal ions and positively charged colloidal particles in water through complexation and electrostatic attraction, helping to improve the β-cyclodextrin coagulant's ability to adsorb and aggregate pollutants, enhancing the flocculation effect. The esterification reaction temperature is 70-90°C. This relatively mild reaction temperature ensures a smooth reaction while avoiding side reactions caused by excessively high temperatures. The esterification reaction duration is 8-12 hours. If the reaction time is too short, the reaction will be incomplete, and the resulting first polymer will contain a large amount of unreacted raw materials or intermediates, which will affect the subsequent polymerization reaction and the performance of the final β-cyclodextrin coagulant. Excessive reaction time can lead to unnecessary degradation or other side reactions in the product, which are also detrimental to the stability and improvement of the β-cyclodextrin coagulant's performance.

[0029] According to an embodiment of the present invention, the mass ratio of the first polymer to dimethyldiallylammonium chloride is 1:1-2. The first polymer is obtained by the esterification reaction of β-cyclodextrin and acrylic acid and contains groups such as carboxyl groups. Dimethyldiallylammonium chloride is a cationic monomer with a positive charge. Controlling their mass ratio to 1:1-2 ensures that the resulting second polymer achieves a good balance in structure and charge. The first polymer provides hydrophilic groups and a certain spatial structure, while dimethyldiallylammonium chloride provides cationic charge. This optimal ratio of the two allows the β-cyclodextrin-based coagulant to better adsorb and agglomerate negatively charged colloidal particles and pollutants. The polymerization reaction temperature is 40-50°C. This relatively mild reaction temperature helps maintain the chemical stability of the reactants and products. The polymerization reaction time is 4-6 hours. If the reaction time is too short, the polymerization reaction may be incomplete, resulting in a polymer with a low molecular weight and poor performance that cannot meet application requirements. However, if the reaction time is too long, it will not only reduce production efficiency and increase production costs, but also cause polymer aging and degradation, affecting polymer performance.

[0030] According to an embodiment of the present invention, the initiator is a persulfate-sulfite initiator. Persulfate-sulfite belongs to a redox initiation system. This initiation system can generate free radicals at relatively low temperatures (40-50°C), thereby initiating the polymerization reaction of the first polymer and dimethyldiallylammonium chloride. Persulfate-sulfite initiators include any of ammonium persulfate-sodium bisulfite, potassium persulfate, and sodium sulfite. The mass ratio of persulfate to sulfite is 1.5-2.5:1. The ratio of the initiator mass to the total mass of the first polymer and dimethyldiallylammonium chloride is 1:25-30.

[0031] According to an embodiment of the present invention, adding a second polymer, sodium trifluoromethanesulfinate, and sodium bromate to a third solvent for a nucleophilic substitution reaction includes the following steps: adding the second polymer, sodium trifluoromethanesulfinate, and sodium bromate to the third solvent, activating the second polymer with sodium bromate, and attacking the activated second polymer with sodium trifluoromethanesulfinate as a nucleophilic reagent, resulting in a nucleophilic substitution reaction. The mass ratio of the second polymer, sodium trifluoromethanesulfinate, and sodium bromate is 1:0.8-1.2:0.3-0.8. Sodium trifluoromethanesulfinate can introduce fluorinated groups into the second polymer during the nucleophilic substitution reaction. When the mass ratio of the second polymer to sodium trifluoromethanesulfinate is controlled at 1:0.8-1.2, the polymer can achieve an appropriate degree of fluorinated substitution. Fluorinated groups have properties such as strong hydrophobicity, high chemical stability, and low surface energy. The appropriate introduction of fluorinated groups can impart enhanced surface activity to β-cyclodextrin-based coagulants, making them more easily enriched at the water-pollutant interface and enhancing their adsorption and agglomeration capabilities. If the amount of sodium trifluoromethanesulfinate used is too small, insufficient fluorinated groups will be introduced, and the performance of the β-cyclodextrin coagulant will not be significantly improved. If used in excessive amounts, the polymer structure will undergo significant changes, affecting its dispersibility and stability in water. The temperature of the nucleophilic substitution reaction is 70-90°C. Nucleophilic substitution reactions require a certain amount of energy to overcome the activation energy of the reaction, making the reactant molecules more active. This can accelerate the frequency of intermolecular collisions and the reaction rate, achieving a high reaction conversion rate in a shorter time, and improving production efficiency. The nucleophilic substitution reaction time is 2-4 hours. If the reaction time is too short, the reaction will be incomplete, resulting in a large amount of unreacted raw materials remaining in the product, affecting the performance of the β-cyclodextrin coagulant. If the reaction time is too long, it will not only reduce production efficiency but also cause some adverse changes in the product, such as product aging and structural damage.

[0032] According to an embodiment of the present invention, the first solvent and the third solvent each independently include at least one of N,N-dimethylformamide and dimethyl sulfoxide; the second solvent includes at least one of water, methanol and dimethyl sulfoxide.

[0033] As a second aspect of the present invention, a β-cyclodextrin coagulant aid is provided, which is prepared using the above method.

[0034] As a third aspect of the present invention, there is provided a use of the above-mentioned β-cyclodextrin coagulant aid in sewage treatment.

[0035] According to an embodiment of the present invention, the use of the β-cyclodextrin coagulant in sewage treatment includes compounding the β-cyclodextrin coagulant with an inorganic coagulant to treat perfluoroalkyl and polyfluoroalkyl substances in sewage. The inorganic coagulant includes at least one of polyaluminum chloride, aluminum sulfate, polyferric sulfate, and ferric chloride.

[0036] In an embodiment of the present invention, an inorganic coagulant is dissolved in water, and then a β-cyclodextrin coagulant aid is added to the aqueous solution for reaction. Through the interaction between the inorganic coagulant and the β-cyclodextrin coagulant aid, the charge neutralization ability can be significantly improved, the coagulation efficiency can be enhanced, and thus the removal effect of PFAS can be improved.

[0037] In the embodiments of the present invention, the introduction of amino groups and fluoride ions makes the structure of the β-cyclodextrin coagulant more compact, and it is easy to generate a network structure macromolecular substance with a high degree of polymerization. By compounding with an inorganic coagulant, the removal efficiency of perfluoroalkyl substances and polyfluoroalkyl substances is improved. Under the premise of ensuring the effective removal of PFAS, the dosage of the inorganic coagulant is reduced, so that the concentration of aluminum or iron in the effluent is significantly lower than that of the inorganic coagulant alone. The composite coagulant obtained by compounding the β-cyclodextrin coagulant with the inorganic coagulant has a significantly improved coagulation efficiency compared to the use of the inorganic coagulant alone, and can maintain a better effect under a wider pH range. The composite coagulant obtained by compounding the β-cyclodextrin coagulant and the inorganic coagulant provided by the present invention can significantly improve the removal efficiency of perfluoro compounds, can be widely used in fields such as water treatment, and has a good water treatment effect.

[0038] Specifically, taking polyaluminium chloride as an inorganic coagulant as an example, a polyaluminium chloride solution is prepared: sodium carbonate (Na2CO3) and aluminum chloride (AlCl3) are added to water at a predetermined alkalinity and mechanically stirred for 12-48 hours to obtain the polyaluminium chloride solution. The predetermined alkalinity can be 1.5. Next, a β-cyclodextrin coagulant solution is prepared: a β-cyclodextrin coagulant is added to water and mechanically stirred for 12-48 hours to obtain the β-cyclodextrin coagulant solution. Finally, for wastewater treatment applications, the polyaluminium chloride solution and the β-cyclodextrin coagulant solution are diluted. The concentration of polyaluminium chloride in the wastewater is preferably 2-12 mg / L, for example, 2 mg / mL, 4 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, or 12 mg / mL; the concentration of the β-cyclodextrin coagulant is preferably 1-3 mg / L, for example, 1 mg / mL, 2 mg / mL, or 3 mg / mL. The pH value of the sewage is 5-10, for example, it can be 5, 6, 7, 8, 9, 10, preferably 6-8.

[0039] The present invention is further illustrated below by examples and related test experiments. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is obvious that one or more embodiments can also be implemented without these specific details. Moreover, in the case of no conflict, the details in the following embodiments can be arbitrarily combined into other feasible embodiments. All instruments, consumables and reagents in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0040] In order to explore the effect of combining β-cyclodextrin coagulants with inorganic coagulants to remove perfluorinated compounds in sewage, the present invention prepared the composite coagulants in Comparative Examples 1 to 3 and Example 1 and applied them in wastewater treatment.

[0041] In the following examples and comparative examples, the wastewater used was a simulated water sample (humic acid concentration of 10 mg / L, perfluorinated compound concentration of 100 μg / L). The different composite coagulants prepared in the examples were applied to the simulated water sample containing perfluorinated compounds to study their effectiveness in removing perfluorinated compounds.

[0042] Comparative Example 1

[0043] In this comparative example 1, unmodified β-cyclodextrin (β-CD) is compounded with an inorganic coagulant to obtain a composite coagulant, wherein the inorganic coagulant used is polyaluminum chloride, and the resulting composite coagulant can be expressed as PAC-β-CD. The specific preparation method is as follows.

[0044] Weigh 7.3594g of sodium carbonate and 22.3546g of AlCl3·6H2O into 250ml of ultrapure water and stir mechanically for 12h until all chemicals are completely dissolved to prepare 10g / L (as Al 3+ Polyaluminium chloride (PAC) solution.

[0045] 1 g of β-CD was weighed and added to 1 L of ultrapure water, mixed evenly, and mechanically stirred for 12 h to prepare a 1 g / L β-CD solution.

[0046] PAC solution and β-CD solution were weighed separately and added to wastewater containing perfluorinated compounds at a concentration of 100 μg / L, so that the concentration of PAC in the wastewater was 10 mg / L and the concentration of β-CD was 1 mg / L, and the wastewater was treated.

[0047] Comparative Example 2

[0048] In this comparative example 2, β-cyclodextrin was modified with acrylic acid, and the modified β-cyclodextrin was compounded with the polyaluminium chloride solution in comparative example 1 to obtain a composite coagulant (which can be expressed as PAC-β-CD-AA). The specific method is as follows.

[0049] 5.6820 g of β-CD was weighed and dissolved in 30 mL of N,N-dimethylformamide (DMF), and then 1.8015 g of AA was added to obtain a mixed solution; the mixture solution was heated at 80°C for 10 hours under vigorous stirring; after the reaction was completed, the reactant was cooled to room temperature and then poured into 30 mL of dichloromethane, the white precipitate was filtered and washed with ethanol at least three times, and finally dried in a vacuum oven at 60°C for 48 hours to obtain the first polymer, namely β-CD-AA.

[0050] Weigh 1 g of β-CD-AA and add it to 1 L of ultrapure water, mix well, and mechanically stir for 12 h to prepare a 1 g / L β-CD-AA solution.

[0051] PAC solution and β-CD-AA solution were weighed separately and added to wastewater containing perfluorinated compounds at a concentration of 100 μg / L, so that the concentration of PAC in the wastewater was 10 mg / L and the concentration of β-CD-AA was 1 mg / L, and the wastewater was treated.

[0052] Comparative Example 3

[0053] In Comparative Example 2, β-CD-AA was modified with dimethyldiallylammonium chloride, and the modified β-CD-AA was compounded with the polyaluminium chloride solution in Comparative Example 1 to obtain a composite coagulant (which can be expressed as PAC-β-CD-AA-DMDAAC). The specific method is as follows.

[0054] 0.8 g of β-CD-AA and 1.2 g of DMDAAC were weighed and dissolved in distilled water, and then 0.0495 g of ammonium persulfate was added; after removing oxygen by bubbling with nitrogen for 15 minutes, 0.0226 g of sodium bisulfite (SBS) dissolved in 2 mL of distilled water was added via syringe; the polymerization reaction was carried out at 45°C for 5 hours, and the reactants were cooled to room temperature and poured into 30 mL of anhydrous ethanol. The white precipitate was filtered and washed with ethanol at least three times, and then dried in a vacuum oven at 60°C for 48 hours to obtain a second polymer, namely β-CD-AA-DMDAAC.

[0055] 1 g of β-CD-AA-DMDAAC was weighed and added to 1 L of ultrapure water, mixed evenly, and mechanically stirred for 12 h to prepare a 1 g / L β-CD-AA-DMDAAC solution.

[0056] PAC solution and β-CD-AA-DMDAAC solution were weighed separately and added to wastewater containing perfluorinated compounds at a concentration of 100 μg / L, so that the concentration of PAC in the wastewater was 10 mg / L and the concentration of β-CD-AA-DMDAACA was 1 mg / L, and the wastewater was treated.

[0057] Example 1

[0058] In Example 1, a β-cyclodextrin coagulant was prepared using the β-CD-AA-DMDAAC in Comparative Example 3. The β-cyclodextrin coagulant was then compounded with the polyaluminium chloride solution in Comparative Example 1 to produce a composite coagulant (which can be expressed as PAC-β-CD-AA-DMDAAC-CF3). The specific method is as follows.

[0059] 1.60 g of sodium bromate (NaBrO3) and 1.60 g of sodium trifluoromethanesulfinate were weighed into a reaction tube, 0.8 g of β-CD-AA-DMDAAC was dissolved in 10 mL of DMF, and the mixture was reacted at 80°C under a nitrogen atmosphere for 3 h. After the reaction was completed, the reactant was cooled to room temperature and then poured into 30 mL of chloroform. The white precipitate was filtered and washed with ethanol for at least three times, and finally dried in a vacuum oven at 60°C for 48 h to obtain a β-cyclodextrin coagulant, namely β-CD-AA-DMDAAC-CF3.

[0060] Weigh 1 g of β-CD-AA-DMDAAC-CF3 and add it to 1 L of ultrapure water, mix well, and mechanically stir for 12 h to prepare a 1 g / L β-CD-AA-DMDAAC-CF3 solution.

[0061] PAC solution and β-CD-AA-DMDAAC-CF3 solution were weighed separately and added to wastewater containing perfluorinated compounds at a concentration of 100 μg / L, so that the concentration of PAC in the wastewater was 10 mg / L and the concentration of β-CD-AA-DMDAAC-CF3 was 1 mg / L, and the wastewater was treated.

[0062] In order to detect the morphology of β-CD, β-CD-AA, β-CD-AA-DMDAAC, and β-CD-AA-DMDAAC-CF3, four-dimensional infrared spectroscopy (FTIR) was performed.

[0063] Figure 1 The infrared spectra of β-CD, β-CD-AA, β-CD-AA-DMDAAC, and β-CD-AA-DMDAAC-CF3 in Comparative Examples 1-3 and Example 1 are shown.

[0064] Depend on Figure 1 It can be seen that compared with β-CD, β-CD-AA has a -1 A new peak appeared at 1639 cm -1 The peak position generated by stretching vibration indicates that the hydroxyl group -OH of β-CD and the carboxyl group -COOH of AA have successfully reacted with each other and introduced C=C. Compared with β-CD-AA, β-CD-AA-DMDAAC has a peak at 1261cm -1The bending vibration absorption peak of the methyl group of ammonium appeared, which verified that DMDAAC and β-CD-AA had undergone free radical copolymerization. Compared with β-CD-AA-DMDAAC, β-CD-AA-DMDAAC-CF3 had a peak at 1141 cm -1 The peak produced by stretching vibration appears at 620cm -1 Bending vibration peaks were generated, indicating that the hydroxyl group (-OH) of β-CD and the carboxyl group (-COOH) of AA had successfully esterified, and CF3 was introduced. Furthermore, β-CD, β-CD-AA, β-CD-AA-DMDAAC, and β-CD-AA-DMDAAC-CF3 all exhibited absorption bands at approximately the same wavenumber, indicating that the structural characteristics of β-cyclodextrin were well preserved.

[0065] Figure 2 The figures are the treatment effects of the composite coagulants in comparative examples 1-3 and Example 1 on wastewater containing anionic perfluorinated compounds. Among them, a is the treatment effect of the composite coagulants in comparative examples 1-3 and Example 1 on wastewater containing perfluorooctane sulfonic acid (PFOS), and the concentration of PFOS in the wastewater is 100μg / L; b is the treatment effect of the composite coagulants in comparative examples 1-3 and Example 1 on wastewater containing perfluorooctanoic acid (PFOA), and the concentration of PFOA in the wastewater is 100μg / L; c is the treatment effect of the composite coagulants in comparative examples 1-3 and Example 1 on wastewater containing perfluorobutyric acid (PFBA ) is a treatment effect diagram of wastewater containing perfluorobutane sulfonic acid (PFBS) by the composite coagulant in Comparative Examples 1-3 and Example 1, and the concentration of PFBS in the wastewater is 100 μg / L; e is a treatment effect diagram of wastewater containing hexafluoropropylene oxide dimer acid (GenX) by the composite coagulant in Comparative Examples 1-3 and Example 1, and the concentration of GenX in the wastewater is 100 μg / L.

[0066] Depend on Figure 2 (ae) It can be seen that the β-cyclodextrin coagulant that is coupled with polyaluminium chloride and simultaneously introduces olefin groups, amino groups and fluoride ions has the highest removal efficiency for the five anionic perfluorinated compounds, and has the best removal effect on long-chain PFOS, indicating that the introduction of amino groups and fluoride ions makes the structure of the modified β-cyclodextrin tighter, and easily generates high-polymerization network-structured macromolecular substances, thereby improving the removal efficiency of anionic perfluorinated compounds, among which the PFOS removal rate increased by nearly 20%, the PFOA removal rate increased by 28%, the PFBA and PFBS removal rates increased by 24% and 15% respectively, and the GenX removal rate increased by 29%.

[0067] In order to explore the effects of polyaluminium chloride concentration and β-cyclodextrin coagulant concentration on the fluoride removal effect of the composite coagulant, the present invention applied the composite coagulants in Examples 2 to 4 in wastewater treatment.

[0068] Example 2

[0069] The composite coagulant used in this Example 2 is the same as that in Example 1, except that the concentrations of PAC in the wastewater are 2 mg / mL, 4 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, and 12 mg / mL, and the concentration of β-CD-AA-DMDAAC-CF3 is 1 mg / L, and the wastewater treatment is carried out.

[0070] Example 3

[0071] The composite coagulant used in this Example 3 is the same as that in Example 1, except that the concentrations of PAC in the wastewater are 2 mg / mL, 4 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, and 12 mg / mL, and the concentration of β-CD-AA-DMDAAC-CF3 is 2 mg / L, respectively, for wastewater treatment.

[0072] Example 4

[0073] The composite coagulant used in this Example 4 is the same as that in Example 1, except that the concentrations of PAC in the wastewater are 2 mg / mL, 4 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, and 12 mg / mL, and the concentration of β-CD-AA-DMDAAC-CF3 is 3 mg / L, and the wastewater treatment is carried out.

[0074] Figure 3 This is a diagram showing the treatment effect of the composite coagulant in Example 2-4 on wastewater containing anionic perfluorinated compounds. Among them, a is a treatment effect diagram of the composite coagulant in Example 2-4 on wastewater containing perfluorooctane sulfonic acid (PFOS), and the concentration of PFOS in the wastewater is 100μg / L; b is a treatment effect diagram of the composite coagulant in Example 2-4 on wastewater containing perfluorooctanoic acid (PFOA), and the concentration of PFOA in the wastewater is 100μg / L; c is a treatment effect diagram of the composite coagulant in Example 2-4 on wastewater containing perfluorobutyric acid (PFBA), and the concentration of PFBA in the wastewater is 100μg / L; d is a treatment effect diagram of the composite coagulant in Example 2-4 on wastewater containing perfluorobutane sulfonic acid (PFBS), and the concentration of PFBS in the wastewater is 100μg / L; e is a treatment effect diagram of the composite coagulant in Example 2-4 on wastewater containing hexafluoropropylene oxide dimer acid (GenX), and the concentration of GenX in the wastewater is 100μg / L.

[0075] Figure 4Figures 2-4 illustrate the treatment effects of the composite coagulant on wastewater containing non-ionic perfluorinated compounds. Figure a shows the treatment effects of the composite coagulant on wastewater containing perfluorooctanesulfonamide (FOSA) in Example 2-4, with a FOSA concentration of 100 µg / L; and figure b shows the treatment effects of the composite coagulant on wastewater containing perfluorobutanesulfonamide (FBSA) in Example 2-4, with a FBSA concentration of 100 µg / L.

[0076] Figure 5 This is a diagram showing the treatment effect of the composite coagulant in Example 2-4 on wastewater containing cationic perfluorinated compounds, wherein the cationic perfluorinated compound is perfluorooctanesulfonamide alkylammonium salt (PFOSAmS), and the concentration of PFOSAmS in the wastewater is 100 μg / L.

[0077] Depend on Figure 3 (ae), Figure 4 (ab) and Figure 5 It can be seen that when treating perfluorinated compound wastewater (100µg / L), β-cyclodextrin coagulants have a significant effect on PFAS removal, and as the concentration of polyaluminum chloride increases, it provides more available surface area for PFAS adsorption or capture, resulting in an increase in PFAS removal efficiency with increasing polyaluminum chloride concentration. In addition, by comparing the effect of polyaluminum chloride concentration on PFAS removal, it was found that when the polyaluminum chloride concentration in Example 3 was 12mg / mL and the β-CD-AA-DMDAAC-CF3 concentration was 2mg / mL, the removal effect was better than that of the composite coagulant at other ratios, with the highest PFOS removal rate of 72.41%, the highest PFOA removal rate of 55.69%, the highest PFBA removal rate of 22.32%, the highest PFBS removal rate of 39.32%, the highest GenX removal rate of 60.01%, the highest FOSA removal rate of 75.34%, the highest FBSA removal rate of 63.68%, and the highest PFOSAmS removal rate of 81.46%.

[0078] In order to explore the effect of β-CD after the simultaneous introduction of amino groups and fluoride ions on the removal of perfluorinated compounds, the present invention applied the composite coagulant in Comparative Example 4 in wastewater treatment.

[0079] Comparative Example 4

[0080] The composite coagulant used in this comparative example 4 is the same as that in comparative example 1, except that the concentrations of PAC in the wastewater are 2 mg / mL, 4 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, and 12 mg / mL, and the concentration of β-CD is 2 mg / L, and the wastewater treatment is carried out.

[0081] Figure 6The figures are as follows: the treatment effect diagram of the composite coagulant and PAC coagulant in Example 2 and Comparative Example 4 on the wastewater containing anionic perfluorinated compounds. Among them, a is the treatment effect diagram of the composite coagulant and PAC coagulant in Example 2 and Comparative Example 4 on the wastewater containing perfluorooctane sulfonic acid (PFOS), and the concentration of PFOS in the wastewater is 100μg / L; b is the treatment effect diagram of the composite coagulant and PAC coagulant in Example 2 and Comparative Example 4 on the wastewater containing perfluorooctanoic acid (PFOA), and the concentration of PFOA in the wastewater is 100μg / L; c is the treatment effect diagram of the composite coagulant and PAC coagulant in Example 2 and Comparative Example 4 on the wastewater containing perfluorobutyric acid (PF d is a diagram showing the treatment effect of the composite coagulant and the PAC coagulant on wastewater containing perfluorobutane sulfonic acid (PFBS) in Example 2 and Comparative Example 4, and the concentration of PFBS in the wastewater is 100 μg / L; e is a diagram showing the treatment effect of the composite coagulant and the PAC coagulant on wastewater containing hexafluoropropylene oxide dimer acid (GenX) in Example 2 and Comparative Example 4, and the concentration of GenX in the wastewater is 100 μg / L.

[0082] Figure 7 The figures show the treatment effects of the composite coagulant and the PAC coagulant in Example 2 and Comparative Example 4 on wastewater containing non-ionic perfluorinated compounds. Figure a shows the treatment effects of the composite coagulant and the PAC coagulant in Example 2 and Comparative Example 4 on wastewater containing perfluorooctanesulfonamide (FOSA), with a FOSA concentration of 100 μg / L; and figure b shows the treatment effects of the composite coagulant and the PAC coagulant in Example 2 and Comparative Example 4 on wastewater containing perfluorobutanesulfonamide (FBSA), with a FBSA concentration of 100 μg / L.

[0083] Figure 8 The figure shows the treatment effect of the composite coagulant and the PAC coagulant on the wastewater containing cationic perfluorinated compounds in Example 2 and Comparative Example 4, wherein the cationic perfluorinated compound is perfluorooctanesulfonamide alkylammonium salt (PFOSAmS), and the concentration of PFOSAmS in the wastewater is 100 μg / L.

[0084] Depend on Figure 6 (ae), Figure 7 (ab) and Figure 8It can be seen that when treating PFAS-containing wastewater (100µg / L), the composite coagulant significantly improved the PFAS removal efficiency compared to the PAC coagulant. Furthermore, compared to unmodified β-CD, the composite coagulant of Example 2 achieved the highest PFAS removal efficiency. Among them, the highest PFOS removal rate was 72.41%, the highest PFOA removal rate was 55.69%, the highest PFBA removal rate was 22.32%, the highest PFBS removal rate was 39.32%, the highest GenX removal rate was 60.01%, the highest FOSA removal rate was 75.34%, the highest FBSA removal rate was 63.68%, and the highest PFOSAmS removal rate was 81.46%.

[0085] In order to explore the effect of combining with other organic coagulants on the removal of PFAS from composite coagulants, the present invention prepared the aluminum salt coupled cationic polyacrylamide composite coagulant (PAC-CPAM) of comparative example 5 and the aluminum salt coupled anionic polyacrylamide composite coagulant (PAC-APAM) of comparative example 6, and applied them in wastewater treatment.

[0086] Comparative Example 5

[0087] The organic coagulant used in Comparative Example 5 is cationic polyacrylamide (CPAM). First, a CPAM solution is prepared: 1 g of CPAM is weighed and added to 1 L of ultrapure water, mixed evenly, and mechanically stirred for 12 h to obtain a 1 g / L CPAM solution.

[0088] The PAC solution in Comparative Example 1 and the CPAM solution in Comparative Example 5 were respectively weighed and added to wastewater containing a perfluorinated compound concentration of 100 μg / L, so that the concentrations of PAC in the wastewater were 2 mg / mL, 4 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, and 12 mg / mL, and the concentration of CPAM was 1 mg / L, and the wastewater treatment was carried out.

[0089] Comparative Example 6

[0090] The difference between Comparative Example 6 and Comparative Example 5 is that the organic coagulant aid used is anionic polyacrylamide (APAM).

[0091] Figure 9The figures are the treatment effects of the composite coagulant in Example 2, Comparative Example 5 and Comparative Example 6 on wastewater containing anionic perfluorinated compounds. Among them, a is the treatment effect of the composite coagulant in Example 2, Comparative Example 5 and Comparative Example 6 on wastewater containing perfluorooctane sulfonic acid (PFOS), and the concentration of PFOS in the wastewater is 100μg / L; b is the treatment effect of the composite coagulant in Example 2, Comparative Example 5 and Comparative Example 6 on wastewater containing perfluorooctanoic acid (PFOA), and the concentration of PFOA in the wastewater is 100μg / L; c is the treatment effect of the composite coagulant in Example 2, Comparative Example 5 and Comparative Example 6 on wastewater containing perfluorobutyric acid (PFB a) is a diagram showing the treatment effect of wastewater, in which the concentration of PFBA in the wastewater is 100 μg / L; d is a diagram showing the treatment effect of the composite coagulant in Example 2, Comparative Example 5 and Comparative Example 6 on wastewater containing perfluorobutane sulfonic acid (PFBS), in which the concentration of PFBS in the wastewater is 100 μg / L; e is a diagram showing the treatment effect of the composite coagulant in Example 2, Comparative Example 5 and Comparative Example 6 on wastewater containing hexafluoropropylene oxide dimer acid (GenX), in which the concentration of GenX in the wastewater is 100 μg / L.

[0092] Figure 10 The figures show the treatment effects of the composite coagulants in Example 2, Comparative Example 5, and Comparative Example 6 on wastewater containing non-ionic perfluorinated compounds. Figure a shows the treatment effects of the composite coagulants in Example 2, Comparative Example 5, and Comparative Example 6 on wastewater containing perfluorooctanesulfonamide (FOSA), where the concentration of FOSA in the wastewater is 100 μg / L; and figure b shows the treatment effects of the composite coagulants in Example 2, Comparative Example 5, and Comparative Example 6 on wastewater containing perfluorobutanesulfonamide (FBSA), where the concentration of FBSA in the wastewater is 100 μg / L.

[0093] Figure 11 The figures show the treatment effects of the composite coagulant on wastewater containing cationic perfluorinated compounds in Example 2, Comparative Example 5 and Comparative Example 6, wherein the cationic perfluorinated compound is perfluorooctanesulfonamide alkylammonium salt (PFOSAmS), and the concentration of PFOSAmS in the wastewater is 100 μg / L.

[0094] Depend on Figure 9 (ae), Figure 10 (ab) and Figure 11 It can be seen that when treating PFAS-containing wastewater (100µg / L), the composite coagulant in Example 2 has a better effect on PFAS removal than PAC-CPAM and PAC-APAM; among them, the removal rates of anionic PFOS, PFOA, PFBA, PFBS, and GenX are the highest, which are 70.93%, 51.95%, 22.91%, 38.93%, and 52.81%, respectively; the removal rates of non-ionic FOSA and FBSA are the highest, which are 74.29% and 61.8%, and the removal rate of cationic PFOSAmS is the highest, which is 88.95%.

[0095] In order to explore the effect of pH value of wastewater containing perfluorinated compounds on the removal of different ionic perfluorinated compounds, the composite coagulant in Example 1 was applied to wastewater containing perfluorinated compounds at different pH values ​​with a concentration of 100 μg / L, wherein the concentration of PAC in the wastewater was 10 mg / L and the concentration of β-CD-AA-DMDAAC-CF3 was 1 mg / L.

[0096] Figure 12 The treatment effect of the composite coagulant in Example 1 on wastewater containing anionic perfluorinated compounds under different pH conditions is shown in FIG. Figure 13 The treatment effect of the composite coagulant in Example 1 on wastewater containing non-ionic perfluorinated compounds under different pH conditions is shown; Figure 14 This is a diagram showing the treatment effect of the composite coagulant in Example 1 on wastewater containing cationic perfluorinated compounds under different pH conditions.

[0097] Depend on Figure 12-14 It can be seen that under acidic conditions (pH < 7), β-cyclodextrin-based coagulants with both amino groups and fluoride ions are more effective in removing anionic perfluorinated compounds. However, when pH is > 7, β-cyclodextrin-based coagulants with both amino groups and fluoride ions are less effective in removing anionic perfluorinated compounds. This shows that composite coagulants are much more effective in removing PFAS under acidic conditions than under alkaline conditions.

[0098] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a β-cyclodextrin coagulant aid, comprising: adding β-cyclodextrin and acrylic acid into a first solvent to carry out an esterification reaction to obtain a first polymer; adding the first polymer and dimethyldiallylammonium chloride into a second solvent, and adding an initiator to carry out a polymerization reaction to obtain a second polymer; The second polymer, sodium trifluoromethanesulfinate and sodium bromate are added into a third solvent to carry out a nucleophilic substitution reaction to obtain a β-cyclodextrin coagulant aid.

2. The method according to claim 1, wherein The molar ratio of β-cyclodextrin to acrylic acid is 1:3-5; The temperature of the esterification reaction is 70-90° C., and the time of the esterification reaction is 8-12 hours.

3. The method according to claim 1, wherein The mass ratio of the first polymer to dimethyldiallylammonium chloride is 1:1-2; The polymerization reaction temperature is 40-50° C., and the polymerization reaction time is 4-6 hours.

4. The method according to claim 3, wherein: The initiator is a persulfate-sulfite initiator; The persulfate-sulfite initiator includes any one of ammonium persulfate-sodium bisulfite, potassium persulfate and sodium sulfite; The mass ratio of the persulfate to the sulfite is 1.5-2.5:1; The ratio of the mass of the initiator to the total mass of the first polymer and dimethyldiallylammonium chloride is 1:25-30.

5. The method according to claim 1, wherein The mass ratio of the second polymer, sodium trifluoromethanesulfinate, and sodium bromate is 1:0.8-1.2:0.3-0.8; The temperature of the nucleophilic substitution reaction is 70-90° C., and the time of the nucleophilic substitution reaction is 2-4 hours.

6. The method according to claim 5, wherein: The step of adding the second polymer, sodium trifluoromethanesulfinate, and sodium bromate into a third solvent to perform a nucleophilic substitution reaction comprises: The second polymer, sodium trifluoromethanesulfinate and sodium bromate are added to a third solvent. The sodium bromate activates the second polymer. The sodium trifluoromethanesulfinate acts as a nucleophilic reagent to attack the activated second polymer, causing a nucleophilic substitution reaction.

7. The method according to claim 1, wherein The first solvent and the third solvent each independently include at least one of N,N-dimethylformamide and dimethyl sulfoxide; The second solvent includes at least one of water, methanol, and dimethyl sulfoxide.

8. A β-cyclodextrin coagulant aid prepared by the method according to any one of claims 1 to 7.

9. Use of the β-cyclodextrin coagulant aid according to claim 8 in sewage treatment.

10. The use according to claim 9, wherein: The application includes: compounding the β-cyclodextrin coagulant aid with an inorganic coagulant to treat perfluoroalkyl substances and polyfluoroalkyl substances in sewage; The inorganic coagulant includes at least one of polyaluminium chloride, aluminium sulfate, polyferric sulfate and ferric chloride.

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