A cyclodextrin-based material, a preparation method thereof and application thereof in selective removal of norfloxacin

Abstract

The application discloses a cyclodextrin-based material and a preparation method and application thereof in selective removal of norfloxacin. The material is prepared as follows: providing hollow glass microspheres; stirring and reacting the obtained hollow glass microspheres in a sodium hydroxide solution, and vacuum drying to obtain the hollow glass microspheres pretreated by sodium hydroxide; dissolving beta-cyclodextrin, citric acid and a catalyst in water, adding the hollow glass microspheres and stirring and mixing; heating the obtained mixture to perform crosslinking reaction, and obtaining the cyclodextrin-based material. Through the multiple synergistic mechanisms of host-guest inclusion of the cyclodextrin cavity, electrostatic attraction of the surface carboxyl group, hydrogen bond network and hydrophobic effect, the adsorption selectivity of norfloxacin and the structural stability in actual water bodies are significantly improved. Due to the low density characteristics of the hollow glass microspheres, the adsorbent exhibits excellent self-floating performance, can realize rapid solid-liquid separation and convenient recovery, and provides a sustainable solution for norfloxacin pollution treatment in complex water bodies.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a cyclodextrin-based material, its preparation method, and its application in the selective removal of norfloxacin. Background Technology

[0002] Norfloxacin (NOR), a typical fluoroquinolone antibiotic, is frequently detected in aquaculture and pharmaceutical wastewater. The persistent residues and bioaccumulation of NOR in the food chain significantly increase the risk of antibiotic resistance (ARGs) transmission and pose a serious threat to aquatic ecosystem safety and human health. Current technologies for NOR removal include adsorption, ozone oxidation, and photocatalysis, with adsorption being particularly popular due to its ease of operation, low cost, and adaptability. Although adsorbents such as carbon-based materials, clay minerals, metal oxides, and nanomaterials have been extensively studied, they still face bottlenecks in practical applications, including limited adsorption capacity, insufficient selectivity, regeneration difficulties, and low solid-liquid separation efficiency. Therefore, developing novel materials with high adsorption capacity, excellent selectivity, easy regeneration, and convenient solid-liquid separation capabilities is a core research objective in this field.

[0003] β-Cyclodextrin (β-CD), with its unique hydrophobic cavity structure, can efficiently encapsulate organic pollutants through host-guest recognition, but its high water solubility limits its direct application. Using citric acid (CA) as a crosslinking agent can improve the material's water resistance while introducing abundant carboxyl sites, forming cyclodextrin-based adsorbents that combine porous structure with specific recognition function. However, solid-liquid separation of powdered materials remains a bottleneck in applications. Hollow glass microspheres (HGM), with a density lower than water, can automatically float in water to achieve solid-liquid separation. After alkali activation pretreatment, active Si-OH groups are generated on the surface of hollow glass microspheres, which can react and bind with organic matter. Therefore, they can serve as self-floating carriers for cyclodextrin-based materials, providing a feasible path for integrated adsorption and separation. This invention uses citric acid (CA) as a crosslinking agent to combine β-cyclodextrin (β-CD) with pretreated hollow glass microspheres (PHGM) to obtain a cyclodextrin-based composite material β-CD-CA-PHGM. This material selectively adsorbs norfloxacin antibiotics in water through specific recognition capabilities and achieves rapid recovery and recycling of the adsorbed material through self-floating. This reduces treatment costs and provides a new approach for low-energy and sustainable water treatment technology.

[0004] Related literature includes the study by Liu et al. published in the *Journal of Environmental Chemical Engineering* (2026, Vol. 14, No. 1, 121097), entitled "Polyethylene glycol / citric acid cross-linked framework based on aminated cyclodextrin with enhanced water stability for tetracycline hydrochloride removal." This study synthesized a cross-linked aminated β-CD using polyethylene glycol and citric acid, which possesses a porous structure and abundant surface functional groups, enabling effective adsorption and removal of tetracycline hydrochloride from the aquatic environment. Another relevant study is the study by Gou et al. published in *Carbohydrate Research* (2025, Vol. 557, 109631), entitled "Water-stable PEG2000-modified citric acid crosslinked β-CD MOF for efficient removal of tetracycline hydrochloride: synthesis, adsorption behavior, and mechanism." This study used citric acid and polyethylene glycol as modifiers to crosslink with a potassium-based cyclodextrin metal-organic framework, resulting in a composite material with an adsorption capacity of 221.6 mg / g for tetracycline hydrochloride. A study by Zhang et al., published in the *Journal of Environmental Chemical Engineering* (2023, Vol. 11, No. 6, 111413), entitled "Citric acid modified β-cyclodextrin for the synthesis of water-stable and recoverable CD-MOF with enhanced adsorption sites: Efficient removal of Congo red and copper ions from wastewater," synthesized a citric acid-modified cyclodextrin metal-organic framework (CA-β-CD-MOF) using a chemical grafting method. This CA-β-CD-MOF exhibited adsorption capacities of 900.9 mg / g for the anionic dye Congo red and 287.4 mg / g for copper ions.

[0005] Existing technologies still have some technical problems:

[0006] 1. Defects of solid-liquid separation: Existing cyclodextrin-based adsorbents mainly rely on gravity sedimentation or filtration to achieve solid-liquid separation, resulting in long separation cycles, low separation efficiency, high filtration costs, and affecting subsequent recycling and reuse.

[0007] 2. Selective adsorption defects: The adsorption behavior of existing cyclodextrin-based adsorbents mainly relies on non-specific interactions such as electrostatic attraction, hydrogen bonding and hydrophobic partitioning, lacking a precise recognition mechanism based on molecular size and configuration matching, thus failing to achieve selective capture of specific target antibiotics. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a cyclodextrin-based material, its preparation method, and its application in the selective removal of norfloxacin. Using citric acid (CA) as a green crosslinking agent, this invention crosslinks β-cyclodextrin (β-CD) onto the surface of NaOH-pretreated hollow glass microspheres (PHGM), successfully constructing a novel self-floating adsorbent material, β-CD-CA-PHGM, aimed at achieving highly efficient and selective removal of norfloxacin (NOR) from water. This material significantly improves its adsorption selectivity for NOR and its structural stability in actual water bodies through a multiple synergistic mechanism involving the host-guest inclusion effect of the cyclodextrin cavity, electrostatic attraction of surface carboxyl groups, hydrogen bond network, and hydrophobic effects. Simultaneously, thanks to the low-density characteristics of the hollow glass microspheres, this adsorbent exhibits excellent self-floating performance, enabling rapid solid-liquid separation and convenient recovery, providing a sustainable solution for the treatment of norfloxacin pollution in complex water bodies.

[0009] The first objective of this invention is to provide a method for preparing cyclodextrin-based materials that combine self-floating and selectivity, comprising the following steps:

[0010] A hollow glass microsphere is provided;

[0011] The obtained hollow glass microspheres were placed in a sodium hydroxide solution and stirred to react. The mixture was then dried under vacuum to obtain hollow glass microspheres pretreated with sodium hydroxide.

[0012] β-Cyclodextrin, citric acid, and a catalyst were mixed and dissolved in water. Hollow glass microspheres pretreated with sodium hydroxide were added and stirred. The resulting mixture was heated to carry out a cross-linking reaction to obtain the cyclodextrin-based material β-CD-CA-PHGM.

[0013] In some embodiments of the present invention, the concentration of the sodium hydroxide solution is 0.4~0.6 mol / L.

[0014] In some embodiments of the present invention, the temperature of the stirring reaction is 75~85 °C and the time is 1~2 hours; the temperature of vacuum drying is 55~65 °C and the time is 22~25 hours.

[0015] In some embodiments of the present invention, the mass ratio of the β-cyclodextrin, citric acid, catalyst and hollow glass microspheres is (1~3):(1~4):(0.4~0.6):(0.5~2.5).

[0016] In some embodiments of the present invention, the catalyst is selected from potassium dihydrogen phosphate.

[0017] In some embodiments of the present invention, the temperature of the crosslinking reaction is 120~160 °C and the time is 1~5 hours.

[0018] The second objective of this invention is to provide a cyclodextrin-based material prepared by the aforementioned preparation method, which has a three-dimensional network mesoporous structure and is rich in hydrophobic cavities provided by cyclodextrin and carboxyl functional groups provided by citric acid.

[0019] A third objective of this invention is to provide the application of the cyclodextrin-based material in the selective removal of norfloxacin.

[0020] In some embodiments of the present invention, the concentration of norfloxacin is 5-40 mg / L.

[0021] In some embodiments of the present invention, the amount of cyclodextrin-based material used is 0.05~2.5 g / L.

[0022] The beneficial effects of this invention are:

[0023] 1. Excellent Adsorption Capacity: Using the Langmuir isotherm model, the maximum adsorption capacity of β-CD-CA-PHGM for norfloxacin was 258.29 mg / g at pH 7 and temperature 298 K, significantly higher than PHGM and many other previously reported adsorption materials. Furthermore, the material does not require additional energy consumption for heating / cooling during norfloxacin adsorption, nor does it require acid / alkali reagents to adjust the pH of the water sample, thus effectively reducing practical application costs and improving environmental compatibility.

[0024] 2. Highly efficient selective adsorption performance: Through the synergistic effect of the hydrophobic cavity and surface carboxyl groups of the material, including host-guest inclusion, hydrophobic interaction, electrostatic attraction and hydrogen bonding, β-CD-CA-PHGM exhibits excellent selective adsorption performance for norfloxacin in a competitive system of various antibiotics such as fluoroquinolones, tetracyclines and sulfonamides.

[0025] 3. Excellent anti-interference performance: Under conditions where heavy metal ions (copper, lead, mercury, nickel, cadmium, zinc) and nitrogen and phosphorus nutrients coexist, β-CD-CA-PHGM still maintains a high adsorption capacity for norfloxacin, and an appropriate concentration of Cu 2+It can also promote the adsorption of norfloxacin by β-CD-CA-PHGM through bridging, which fully demonstrates the anti-interference performance and broad application potential of this material in complex aquatic environments.

[0026] 4. Highly efficient self-floating separation: β-CD-CA-PHGM can achieve a self-floating rate of over 90% within 30 minutes, which ensures sufficient contact time between the material and norfloxacin antibiotic during the adsorption process, as well as effective solid-liquid separation and subsequent recycling of the material. Attached Figure Description

[0027] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0028] Figure 1 This is the synthesis process for preparing β-CD-CA-PHGM according to an embodiment of the present invention.

[0029] Figure 2 These are schematic diagrams of β-CD-CA-PHGM obtained in Embodiment 1 and PHGM obtained in Comparative Example 1 of the present invention; wherein, (a) is the self-floating curve and (b) is the β-CD-CA-PHGM that floats stably.

[0030] Figure 3 This is a comparison of the adsorption performance of β-CD-CA-PHGM obtained in Example 1 of the present invention and PHGM obtained in Comparative Example 1 on norfloxacin in different pH environments.

[0031] Figure 4 The effects of different factors on the adsorption of norfloxacin by β-CD-CA-PHGM obtained in Example 1 of this invention are shown; where (ab) are heavy metal ions and (cd) are nitrogen and phosphorus nutrients.

[0032] Figure 5 The adsorption results of β-CD-CA-PHGM obtained in Example 1 of this invention on different antibiotics are shown. Among them, (ac) represents the single antibiotic system with different pH and (d) represents the selective adsorption of norfloxacin in the binary mixed antibiotic system (tetracycline antibiotics: tetracycline hydrochloride TCH, doxycycline hydrochloride DH, oxytetracycline hydrochloride OTC; sulfonamide antibiotics: sulfamethoxazole SMZ, sulfadiazine SD; fluoroquinolone antibiotics: ciprofloxacin CIP, levofloxacin LEV, norfloxacin NOR). Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0034] Example 1

[0035] This embodiment provides a method for preparing cyclodextrin-based materials that combine self-floating and selectivity, comprising the following steps:

[0036] S1. Place 10 g of hollow glass microspheres into a 500 mL beaker, then add 300 mL of 0.5 mol / L sodium hydroxide solution and stir mechanically at 80 °C for 1.5 hours. Wash the resulting white solid repeatedly with deionized water and anhydrous ethanol. Collect the solid by filtration, place it in a vacuum drying oven at 60 °C for 24 hours, and then grind it to obtain NaOH pretreated hollow glass microspheres (PHGM).

[0037] S2. Weigh 1 g of β-cyclodextrin, 2 g of citric acid, and 0.5 g of potassium dihydrogen phosphate (as a catalyst) and dissolve them in 20 mL of deionized water. After complete dissolution, add 1 g of PHGM and stir until fully mixed. Then transfer the mixture to an oven at 140 °C for crosslinking reaction for 3 hours. After the reaction is complete, cool the product to room temperature (25 °C), wash several times with deionized water and anhydrous ethanol, and finally dry at 60 °C for 24 hours to obtain β-CD-CA-PHGM.

[0038] Example 2

[0039] This embodiment provides a method for preparing cyclodextrin-based materials that combine self-floating and selectivity, comprising the following steps:

[0040] S1. Place 10 g of hollow glass microspheres into a 500 mL beaker, then add 300 mL of 0.5 mol / L sodium hydroxide solution and stir mechanically at 80 °C for 1.5 hours. Wash the resulting white solid repeatedly with deionized water and anhydrous ethanol. Collect the solid by filtration, place it in a vacuum drying oven at 60 °C for 24 hours, and then grind it to obtain NaOH pretreated hollow glass microspheres (PHGM).

[0041] S2. Weigh 3 g of β-cyclodextrin, 1 g of citric acid, and 0.5 g of potassium dihydrogen phosphate (as a catalyst) and dissolve them in 20 mL of deionized water. After complete dissolution, add 1 g of PHGM and stir until fully mixed. Then transfer the mixture to an oven at 140 °C for crosslinking reaction for 3 hours. After the reaction is complete, cool the product to room temperature (25 °C), wash several times with deionized water and anhydrous ethanol, and finally dry at 60 °C for 24 hours to obtain β-CD-CA-PHGM.

[0042] Example 3

[0043] This embodiment provides a method for preparing cyclodextrin-based materials that combine self-floating and selectivity, comprising the following steps:

[0044] S1. Place 10 g of hollow glass microspheres into a 500 mL beaker, then add 300 mL of 0.5 mol / L sodium hydroxide solution and stir mechanically at 80 °C for 1.5 hours. Wash the resulting white solid repeatedly with deionized water and anhydrous ethanol. Collect the solid by filtration, place it in a vacuum drying oven at 60 °C for 24 hours, and then grind it to obtain NaOH pretreated hollow glass microspheres (PHGM).

[0045] S2. Weigh 1 g of β-cyclodextrin, 2 g of citric acid, and 0.5 g of potassium dihydrogen phosphate (as a catalyst) and dissolve them in 20 mL of deionized water. After complete dissolution, add 1 g of PHGM and stir until fully mixed. Then transfer the mixture to an oven at 130 °C for crosslinking reaction for 3 hours. After the reaction is complete, cool the product to room temperature (25 °C), wash several times with deionized water and anhydrous ethanol, and finally dry at 60 °C for 24 hours to obtain β-CD-CA-PHGM.

[0046] Comparative Example 1

[0047] This example provides hollow glass microspheres pretreated with sodium hydroxide, comprising the following steps:

[0048] 10 g of hollow glass microspheres were placed in a 500 mL beaker, and then 300 mL of 0.5 mol / L sodium hydroxide solution was added. The mixture was mechanically stirred at 80 °C for 1.5 hours. The resulting white solid was then washed several times with deionized water and anhydrous ethanol. The solid was collected by filtration and placed in a vacuum drying oven at 60 °C for 24 hours. After that, it was ground to obtain NaOH pretreated hollow glass microspheres (PHGM).

[0049] PHGM and β-CD-CA-PHGM were used simultaneously for the adsorption of norfloxacin in aqueous solution. The synergistic effect of the hydrophobic cavity provided by cyclodextrin and the carboxyl functional group provided by citric acid in the adsorption was compared and demonstrated.

[0050] Performance testing

[0051] The self-floating performance of β-CD-CA-PHGM prepared in Example 1 and PHGM prepared in Comparative Example 1 were tested, and the specific steps are as follows:

[0052] 50 mg of β-CD-CA-PHGM or 50 mg of PHGM was thoroughly mixed with 100 mL of deionized water in a cylindrical container (volume: 100 mL, diameter: 35 mm, height: 390 mm). Water samples were collected at a depth of 15 mm below the surface at different time intervals, and turbidity was measured. The turbidity value was used to indirectly reflect the concentration of unfloated material, and this was used to calculate the self-floating rate. Experimental results are as follows: Figure 2 As shown, β-CD-CA-PHGM can achieve a self-floatation rate of over 90% within 30 minutes, which ensures sufficient contact time between the material and norfloxacin antibiotic during the adsorption process, as well as effective solid-liquid separation and subsequent recycling of the material.

[0053] The adsorption performance of norfloxacin was tested on β-CD-CA-PHGM prepared in Example 1 and PHGM prepared in Comparative Example 1. The specific steps are as follows:

[0054] The initial concentration of norfloxacin was 20 mg / L. The pH of the solution was adjusted to 3–11, and the dosages of β-CD-CA-PHGM and PHGM were both 0.05 g / L. After adsorption equilibrium was reached, the concentration of residual norfloxacin in the solution was determined using a UV spectrophotometer, and the adsorption capacity was calculated accordingly. The experimental results are as follows: Figure 3 As shown, at all tested pH values, the adsorption capacity of β-CD-CA-PHGM for norfloxacin was significantly higher than that of PHGM, demonstrating that more active adsorption sites were introduced through the cross-linking reaction with cyclodextrin.

[0055] The β-CD-CA-PHGM prepared in Example 1 was used to test the adsorption performance of norfloxacin in a complex aquatic environment. The specific steps are as follows:

[0056] The adsorption performance of β-CD-CA-PHGM for norfloxacin was analyzed in a complex aquatic environment containing heavy metal ions and nitrogen and phosphorus nutrients. The concentrations of heavy metal ions ranged from 0.2 to 4 mg / L, total phosphorus from 0.3 to 6 mg / L, and total nitrogen from 2 to 18 mg / L. The norfloxacin concentration was 20 mg / L, the solution pH was 7, and the β-CD-CA-PHGM dosage was 0.05 g / L. The experimental results are as follows: Figure 4 As shown, although the adsorption capacity of β-CD-CA-PHGM for norfloxacin decreased to some extent in the presence of heavy metal ions and nitrogen and phosphorus, it maintained good adsorption performance overall. In addition, the appropriate concentration of copper ions promoted the adsorption of norfloxacin, which proved that the adsorbent exhibited strong anti-interference ability and structural stability in complex environments and had the potential for application in actual water bodies.

[0057] Specificity test

[0058] The β-CD-CA-PHGM prepared in Example 1 was used in different types of single antibiotic systems and binary mixed antibiotic systems to perform specific adsorption tests on norfloxacin. The specific steps are as follows:

[0059] In the single antibiotic system, three different pH water environments were set up: acidic (pH=5), neutral (pH=7), and alkaline (pH=9). Three representative fluoroquinolone antibiotics (ciprofloxacin CIP, levofloxacin LEV, norfloxacin NOR), three representative tetracycline antibiotics (tetracycline hydrochloride TCH, doxycycline hydrochloride DH, oxytetracycline hydrochloride OTC), and two representative sulfonamide antibiotics (sulfamethoxazole SMZ, sulfadiazine SD) were selected. The initial concentration of each antibiotic was 20 mg / L, and the dosage of β-CD-CA-PHGM was 0.05 g / L. In a binary antibiotic mixture system, norfloxacin was mixed in pairs with other antibiotics (i.e., NOR+LEV, NOR+CIP, NOR+TCH, NOR+OTC, NOR+DH, NOR+SMZ, NOR+SD), with a solution pH of 7. The initial concentration of each antibiotic was 20 mg / L, and the dosage of β-CD-CA-PHGM was 0.05 g / L. The experimental results are as follows: Figure 5 As shown, β-CD-CA-PHGM exhibits higher adsorption capacity for norfloxacin in both single-antibiotic systems and binary mixed-antibiotic systems, demonstrating its excellent selective adsorption performance.

[0060] The embodiments described above are merely preferred embodiments for fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a cyclodextrin-based material, characterized in that, Includes the following steps: A hollow glass microsphere is provided; The obtained hollow glass microspheres were placed in a sodium hydroxide solution and stirred to react. The mixture was then dried under vacuum to obtain hollow glass microspheres pretreated with sodium hydroxide. β-Cyclodextrin, citric acid, and a catalyst were mixed and dissolved in water. Hollow glass microspheres pretreated with sodium hydroxide were added and stirred. The resulting mixture was heated to carry out a cross-linking reaction to obtain the cyclodextrin-based material.

2. The preparation method according to claim 1, characterized in that, The concentration of the sodium hydroxide solution is 0.4~0.6 mol / L.

3. The preparation method according to claim 1, characterized in that, The stirring reaction is carried out at a temperature of 75-85 ℃ for 1-2 hours; the vacuum drying is carried out at a temperature of 55-65 ℃ for 22-25 hours.

4. The preparation method according to claim 1, characterized in that, The mass ratio of β-cyclodextrin, citric acid, catalyst and hollow glass microspheres is (1~3):(1~4):(0.4~0.6):(0.5~2.5).

5. The preparation method according to claim 1, characterized in that, The catalyst is selected from potassium dihydrogen phosphate.

6. The preparation method according to claim 1, characterized in that, The cross-linking reaction is carried out at a temperature of 120~160 ℃ for 1~5 hours.

7. A cyclodextrin-based material prepared by any one of claims 1 to 6, characterized in that, It has a three-dimensional network mesoporous structure and is rich in hydrophobic cavities provided by cyclodextrin and carboxyl functional groups provided by citric acid.

8. The application of the cyclodextrin-based material according to claim 7 in the selective removal of norfloxacin.

9. The application according to claim 8, characterized in that, The concentration of norfloxacin is 5-40 mg / L.

10. The application according to claim 8, characterized in that, The amount of cyclodextrin-based material used is 0.05~2.5 g / L.

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