A method for preparing a high-efficiency stable self-floating core-shell gel catalyst

Abstract

The application discloses a preparation method of a high-efficiency stable self-floating core-shell gel catalyst, and is prepared through the steps of preparing a hydrogel carrier, fixing beta-FeOOH on the surface of the hydrogel carrier and freeze-drying the hydrogel catalyst in sequence. The application can prepare a more high-efficiency stable gel catalyst at a lower temperature, has mild reaction conditions, simple preparation process, low cost, high repeatability, is convenient for salvage recovery, does not cause secondary pollution, and is suitable for the water purification field.

Description

Technical Field

[0001] This invention belongs to the field of gel catalyst preparation technology, and relates to a method for preparing a highly efficient and stable self-floating core-shell gel catalyst. Background Technology

[0002] With social and industrial development, the discharge of pollutants into the aquatic environment has triggered a series of water crises and ecological problems. Organic pollutants, due to their toxicity and resistance to degradation, have caused water pollution that endangers the ecological environment and human health. Traditional wastewater treatment technologies typically employ a combination of physical, biological, and chemical methods to remove pollutants. Among the various pollutant treatment strategies developed, advanced oxidation technologies (AOTs), characterized by the generation of highly oxidizing hydroxyl radicals (·OH), oxidize large, recalcitrant organic molecules into low-toxicity or non-toxic small molecules under reaction conditions involving high temperature, high pressure, electricity, sound, light irradiation, and catalysts. This technology is considered promising for wastewater treatment and has received increasing attention in the field of environmental governance.

[0003] In recent years, many novel composite materials have been applied to the degradation of water pollutants. However, powdered catalysts in water pollutant degradation are prone to agglomeration, difficult to recover, and pose a risk of secondary environmental pollution, limiting the practical application of nanocatalysts in water treatment. Hydrogels are excellent adsorbents and are widely used for the adsorption of pollutants in water. However, they themselves do not possess degradation capabilities, and the complex desorption process can affect the subsequent treatment efficiency of the adsorbent. Therefore, by combining powdered catalysts with specific hydrogels, the hydrogels can act as carriers, providing favorable reaction conditions for the liquid-phase system. Simultaneously, this promotes the uniform dispersion of nanoparticles on the gel, facilitating recovery. Furthermore, the catalyst on the hydrogel can oxidize a large number of pollutants adsorbed by the hydrogel, thereby reducing the cumbersome desorption process and overcoming the shortcomings of single catalysts or single hydrogels in environmental remediation.

[0004] Currently, nanocatalysts and hydrogels can be composited through encapsulation. When nanocatalysts are encapsulated in hydrogels, the stability of the hydrogel catalyst is much higher than that of powdered catalysts. Furthermore, its performance in treating pollutants does not significantly decrease after multiple cycles of degradation. Compared to powdered catalysts, hydrogel catalysts are also easier to recover, avoiding secondary pollution. However, this hydrogel encapsulation reduces the reaction sites between the catalyst and pollutants, thus decreasing the catalyst's degradation performance. Additionally, after a period of use, the catalyst tends to float with the water flow, requiring manual retrieval to prevent secondary pollution. This process is also difficult to identify, wasting time and manpower.

[0005] Therefore, there is an urgent need to load catalysts onto the surface of hydrogels to prepare a core-shell gel catalyst that can expose more sites for catalyst-pollutant binding, adsorb pollutants while more efficiently degrading pollutants enriched on the surface of the gel catalyst, and facilitate subsequent recycling and salvage operations. Summary of the Invention

[0006] This invention aims to provide a method for preparing a highly efficient and stable self-floating core-shell gel catalyst. The method involves the sequential steps of preparing a hydrogel support, immobilizing β-FeOOH on the surface of the hydrogel support, and freeze-drying the hydrogel catalyst. This invention can prepare a more efficient and stable gel catalyst at a lower temperature, with mild reaction conditions, a simple preparation process, low cost, high reproducibility, and efficient degradation of pollutants enriched on the surface of the gel catalyst, while facilitating subsequent recovery and retrieval.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a highly efficient and stable self-floating core-shell gel catalyst, comprising the following steps in sequence:

[0009] (1) Preparation of hydrogel carrier

[0010] Prepare a hydrogel precursor solution, and then add it dropwise to a calcium chloride solution at a rate of 2 drops / s using a dropper. React for 12 hours. Wash the obtained hydrogel with deionized water 3 to 6 times and set aside for use.

[0011] (2) Immobilization of β-FeOOH on the surface of the hydrogel support

[0012] The above hydrogel was placed in a ferric chloride solution with a pH of 2 and heated in a water bath at 65°C for 12 hours to obtain a core-shell hydrogel catalyst.

[0013] (3) Freeze-drying of hydrogel catalysts

[0014] The above-mentioned core-shell hydrogel catalyst was washed with deionized water 3 to 6 times, then pre-frozen for 2 hours, and then dried in a vacuum freeze dryer for 12 hours to obtain the core-shell hydrogel catalyst.

[0015] As a limitation of the present invention, in step (1), the hydrogel precursor solution includes one or two of sodium alginate aqueous solution and pectin aqueous solution, or a mixture of one or more of sodium alginate aqueous solution or pectin aqueous solution and monomer.

[0016] As a second limitation of the present invention, in step (1), the concentration of the calcium chloride solution is 0.1M, and the mass ratio of the hydrogel precursor solution to the calcium chloride solution is 1:2.

[0017] As a third limitation of the present invention, in step (2), the concentration of the ferric chloride solution is 0.1M, and the mass ratio of the hydrogel to the ferric chloride solution is 1:2.

[0018] This invention involves adding a hydrogel precursor solution dropwise into a calcium chloride solution, Ca... 2+ The complexation reaction with metal ions of the hydrogel precursor aims to transform the hydrogel precursor solution into a gel. The ratio of the two and the dropping rate are important in this process, as they affect the formation of calcium alginate gel microspheres and, consequently, the subsequent fixation of β-FeOOH on the surface of the hydrogel carrier.

[0019] As a fourth limitation of the present invention, in step (3), the pre-freezing temperature is -15°C and the freezing temperature in the vacuum freeze dryer is -40°C.

[0020] During the pre-freezing process, the water in the core-shell gel catalyst is pre-frozen into ice, which provides the basis for the direct sublimation of ice into water vapor during the subsequent vacuum freeze-drying. In vacuum freeze-drying, utilizing the principle of sublimation, the water pre-frozen into ice in the core-shell gel catalyst is removed directly by sublimation under high vacuum without melting. During the drying process, it is not affected by surface tension, allowing the core-shell gel catalyst to retain its original structure without shrinking. This process is the formation period of the self-floating core-shell structure. The freeze-drying temperature and time affect the retention of the original structure of the core-shell gel catalyst, and ultimately influence the formation of the self-floating core-shell structure.

[0021] As a fifth limitation of the present invention, in step (1), the sodium alginate aqueous solution has a mass fraction of 2 wt%, the pectin aqueous solution has a mass fraction of 4 wt%, and the monomer is one or both of acrylic acid and acrylamide.

[0022] In the hydrogel precursor solution, the ratio of hydrogel precursor to water affects the formation of hydrogel microspheres, which in turn affects the subsequent fixation of β-FeOOH on the surface of the hydrogel carrier.

[0023] This invention also specifies that the core-shell gel catalyst has a core diameter of 2 mm, a shell thickness of 8-13 μm, and a spherical morphology. The internal hydrogel core exhibits a three-dimensional porous network structure, while the outer shell is composed of spindle-shaped β-FeOOH nanoparticles. This unique morphology of the catalyst prepared by this invention requires, on the one hand, ensuring that β-FeOOH is fixed on the surface of the hydrogel support, and on the other hand, ensuring that the core-shell gel catalyst retains its original structure without shrinking, forming a self-floating core-shell structure.

[0024] In this invention, due to the Fe in the ferric chloride solution 3+Slow diffusion from the gel surface to the interior, under acidic water bath heating conditions, β-FeOOH nucleates and grows on the hydrogel surface, forming a dense β-FeOOH film, producing a core-shell gel catalyst with a soft core / hard shell structure. The mechanical strength of the hard shell of this special morphology structure is higher than that of the soft core. During the freeze-drying process, the water gradually sublimates, and the internal hydrogel forms a three-dimensional porous network structure. The outer shell has high mechanical strength and is dense, ultimately forming a self-floating core-shell structured gel catalyst.

[0025] The above-mentioned technical solution of the present invention is a whole in which each step is closely related and inseparable, and together they affect the catalytic performance and stability of the final product.

[0026] The technical effects achieved by adopting the above-mentioned technical solution of the present invention are as follows:

[0027] 1. Compared to powdered catalysts, gel catalysts are easier to recycle and more convenient for practical use. They also reduce iron leaching during use and avoid secondary pollution.

[0028] 2. Compared with powdered catalysts, core-shell gel catalysts with catalysts supported on hydrogel surfaces exhibit good performance in degrading tetracycline hydrochloride and excellent cycling stability. In an aqueous environment, it can degrade 100% of 100 mL of tetracycline hydrochloride at a concentration of 20 mg / L in 10 min, and can still maintain good degradation effect after 5 cycles.

[0029] 3. This invention can prepare more efficient and stable gel catalysts at lower temperatures, with mild reaction conditions, simple preparation process, low cost, high reproducibility, and easy promotion and industrial application.

[0030] This invention is applicable to the preparation of highly efficient and stable self-floating core-shell gel catalysts.

[0031] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0032] Figure 1 The effect of the core-shell gel catalyst floating in water in Example 1;

[0033] Figure 2 SEM images of the comparative example powder β-FeOOH and the core-shell gel catalyst in Example 1 of this invention;

[0034] Figure 3 XRD patterns of the comparative example powder β-FeOOH and the core-shell gel catalyst in Example 1 of this invention;

[0035] Figure 4Infrared spectra of the comparative example powder β-FeOOH and the core-shell gel catalyst in Example 1 of this invention;

[0036] Figure 5 Degradation performance diagrams of the comparative example powder β-FeOOH and the core-shell gel catalyst in Example 1 of this invention;

[0037] Figure 6 Cyclic degradation performance diagrams of the comparative example powder β-FeOOH and the core-shell gel catalyst in Example 1 of this invention. Detailed Implementation

[0038] Unless otherwise specified, all reagents used in the following embodiments are commercially available reagents, and all experimental and detection methods used in the following embodiments are existing experimental and detection methods.

[0039] Example 1

[0040] This embodiment prepares a highly efficient and stable self-floating core-shell gel catalyst, which is prepared according to the following steps:

[0041] (1) Preparation of hydrogel carrier

[0042] A 2 wt% sodium alginate aqueous solution (50 g) was added dropwise to 100 mL of 0.1 M calcium chloride solution using a 2 mm diameter dropper (dropping rate of 2 drops / s). The cross-linking reaction was carried out for 12 h. The mass ratio of sodium alginate aqueous solution to calcium chloride solution was 1:2. The resulting hydrogel was washed with deionized water 3 to 6 times to prepare the hydrogel.

[0043] (2) Immobilization of β-FeOOH on the surface of the hydrogel support

[0044] The above hydrogel was placed in 100 mL of 0.1 M ferric chloride solution with a pH of 2 and heated in a water bath. The mass ratio of hydrogel to ferric chloride solution was 1:2. The heating temperature was 65 °C and the heating time was 12 h to obtain a core-shell hydrogel catalyst.

[0045] (3) Freeze-drying of hydrogel catalysts

[0046] The above-mentioned core-shell hydrogel catalyst was washed with deionized water 3 to 6 times, then pre-frozen at -15°C for 2 hours, and finally dried at -40°C for 12 hours in a vacuum freeze dryer to obtain the core-shell hydrogel catalyst.

[0047] A series of performance tests were conducted on the self-floating core-shell gel catalyst prepared in this embodiment, and the specific results are as follows:

[0048] from Figure 1As can be seen from the optical photographs, the core-shell gel catalyst in Example 1 can float in water. SEM, XRD, and infrared spectroscopy tests were performed on the core-shell gel catalyst in Example 1, and the results are as follows: Figure 2 , Figure 3 and Figure 4 As shown in the SEM image, spindle-shaped β-FeOOH is present on the surface of the core-shell gel catalyst, indicating that β-FeOOH grows on the hydrogel surface, and the thickness of the β-FeOOH layer is 8-13 μm. The internal cross-sectional view of the core-shell gel catalyst shows that it has a porous structure. The XRD pattern shows that the core-shell gel catalyst has 7 characteristic peaks at 11.8°, 16.8°, 26.7°, 35.2°, 39.2°, 46.4° and 55.9°, which correspond to the (100), (200), (310), (211), (301), (411) and (521) planes of β-FeOOH (ICSD 31136), respectively. The infrared spectrum shows that the core-shell gel catalyst has a porous structure in the 3300-3450 cm⁻¹ region. -1 The absorption band at this point is attributed to the stretching vibration of the hydroxyl groups. After incorporating β-FeOOH into the hydrogel, the hydroxyl groups shift to lower wavenumbers, indicating a strong interaction between the hydrogel and β-FeOOH via hydrogen bonds. A 689 cm⁻¹ band appears in the core-shell gel catalyst. -1 The new peaks at the point are attributed to the stretching or lattice vibrations of Fe-O and Fe-OH, indicating that β-FeOOH nanoparticles were successfully prepared on the hydrogel surface.

[0049] The core-shell gel catalyst prepared in Example 1 was used to degrade tetracycline hydrochloride in an aqueous environment. The specific experimental procedure was as follows: the core-shell gel catalyst was placed in 100 mL of a 20 mg / L tetracycline hydrochloride solution, 10 mM hydrogen peroxide was added, and then the solution was irradiated under a xenon lamp with a cutoff filter. A 3 mL sample was taken every ten minutes, and a sample of the original tetracycline hydrochloride solution was taken as a control. After 10 minutes, the catalyst prepared in Example 1 was used to degrade the tetracycline hydrochloride solution. The degradation rate reached 100%, and the degradation efficiency remained at 100% after 5 cycles. The results are as follows. Figure 5 As shown.

[0050] Example 2

[0051] This embodiment prepares a highly efficient and stable self-floating core-shell gel catalyst, which is prepared according to the following steps:

[0052] (1) A 4 wt% pectin aqueous solution (50 g) was added dropwise to a 0.1 M, 100 mL calcium chloride solution at a dropping rate of 2 drops / s for cross-linking for 24 h. The mass ratio of the pectin aqueous solution to the calcium chloride solution was 1:2, and a pectin hydrogel was obtained.

[0053] (2) The obtained pectin hydrogel was washed with deionized water 3 to 6 times, and then the hydrogel was soaked in 100 mL of ferric chloride solution with pH 2 and concentration of 0.1 M. The mass ratio of hydrogel to ferric chloride solution was 1:2. The hydrogel was heated in a water bath at 65℃ for 12 h to obtain the core-shell hydrogel catalyst.

[0054] (3) Take out the hydrogel catalyst after the reaction, wash it with deionized water 3 to 6 times, pre-freeze the obtained hydrogel at -15℃ for 2 hours, and finally dry it in a vacuum freeze dryer at -40℃ for 12 hours to obtain the core-shell hydrogel catalyst.

[0055] Example 3

[0056] This embodiment prepares a highly efficient and stable self-floating core-shell gel catalyst, which is prepared according to the following steps:

[0057] (1) Preparation of hydrogel carrier

[0058] In a 2 wt% sodium alginate solution (50 g), monomers (0.6 M, 2.16 g acrylic acid), N,N'-methylenebisacrylamide (0.2 wt% of monomer mass), and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (3 wt% of monomer mass) were added and stirred. The mixture was then added dropwise (2 drops / s) to 100 ml of a 0.1 M calcium chloride solution using a 2 mm diameter dropper for crosslinking for 12 h to obtain a calcium alginate hydrogel. The unpolymerized monomers were then photopolymerized under a UV lamp for 3 h to form a calcium alginate / polyacrylic acid hydrogel. The mass ratio of sodium alginate / polyacrylic acid aqueous solution to calcium chloride solution was 1:2. The resulting hydrogel was washed 3–6 times with deionized water to prepare the hydrogel.

[0059] (2) Immobilization of β-FeOOH on the surface of the hydrogel support

[0060] The above hydrogel was placed in 100 mL of 0.1 M ferric chloride solution with a pH of 2 and heated in a water bath. The mass ratio of hydrogel to ferric chloride solution was 1:2. The heating temperature was 65 °C and the heating time was 12 h to obtain a core-shell hydrogel catalyst.

[0061] (3) Freeze-drying of hydrogel catalysts

[0062] The above-mentioned core-shell hydrogel catalyst was washed with deionized water 3 to 6 times, then pre-frozen at -15°C for 2 hours, and finally dried at -40°C for 12 hours in a vacuum freeze dryer to obtain a self-floating core-shell hydrogel catalyst.

[0063] Example 4

[0064] This embodiment prepares a highly efficient and stable self-floating core-shell gel catalyst, which is prepared according to the following steps:

[0065] (1) Preparation of hydrogel carrier

[0066] A mixture of monomers (1M, 3.55g acrylamide), N,N'-methylenebisacrylamide (0.2wt% of monomer mass), and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (3wt% of monomer mass) was added to a 4wt% pectin solution (50g) and stirred. The mixture was then added dropwise (2 drops / s) to 100ml of a 0.1M calcium chloride solution using a 2mm diameter dropper for crosslinking for 12 hours to obtain a calcium alginate hydrogel. The hydrogel was then irradiated with UV light for 3 hours to photopolymerize the unpolymerized monomers, forming a calcium alginate / polyacrylamide hydrogel. The mass ratio of pectin / polyacrylamide aqueous solution to calcium chloride solution was 1:2. The resulting hydrogel was washed 3–6 times with deionized water to prepare the final hydrogel.

[0067] (2) Immobilization of β-FeOOH on the surface of the hydrogel support

[0068] The above hydrogel was placed in 100 mL of 0.1 M ferric chloride solution with a pH of 2 and heated in a water bath. The mass ratio of hydrogel to ferric chloride solution was 1:2. The heating temperature was 65 °C and the heating time was 12 h to obtain a core-shell hydrogel catalyst.

[0069] (3) Freeze-drying of hydrogel catalysts

[0070] The above-mentioned core-shell hydrogel catalyst was washed with deionized water 3 to 6 times, then pre-frozen at -15°C for 2 hours, and finally dried at -40°C for 12 hours in a vacuum freeze dryer to obtain a self-floating core-shell hydrogel catalyst.

[0071] Comparative Example 1

[0072] In this comparative example, powdered β-FeOOH was prepared and subjected to a series of performance tests. The specific preparation method is as follows:

[0073] 100 mL of a 0.1 M ferric chloride solution with a pH of 2 was heated in a water bath at 65 °C for 12 h. The solution was then centrifuged and washed, and the resulting powder was dried to obtain β-FeOOH powder.

[0074] The β-FeOOH powder prepared in this comparative example was characterized by a series of methods including SEM, XRD, and infrared spectroscopy. The results are as follows: Figure 2 , Figure 3 and Figure 4Therefore, in the SEM image, it can be seen that the powder β-FeOOH exhibits a spindle shape with an average length of ~262nm. Peaks corresponding to β-FeOOH can be found in the XRD and infrared images.

[0075] The powdered β-FeOOH prepared in this comparative example was tested for the degradation of tetracycline hydrochloride in an aqueous environment. The specific experimental procedure was as follows: the powdered β-FeOOH catalyst was placed in 100 mL of a 20 mg / L tetracycline hydrochloride solution, 10 mM hydrogen peroxide was added, and then the solution was irradiated under a xenon lamp with a cutoff filter. Samples were taken every ten minutes, 3 mL each time. An additional sample of the original tetracycline hydrochloride solution was taken as a control. Using the catalyst prepared in Comparative Example 1 of this invention for the degradation of tetracycline hydrochloride solution, the degradation rate reached 92.57% after 50 minutes. The results are as follows. Figure 5 As shown.

[0076] Cyclic degradation experiments were conducted on the powdered β-FeOOH and core-shell gel catalyst of Comparative Example 1 of this invention, and the results are as follows: Figure 6 As shown, it is clear that after 5 cycles of degradation, the degradation effect of powdered β-FeOOH on tetracycline hydrochloride solution is significantly reduced, with the degradation efficiency dropping to 38.31%. However, the core-shell gel catalyst prepared in Example 1 of this invention still maintains a 100% degradation effect, indicating that it has good cyclic degradation performance.

[0077] Comparative Example 2

[0078] In this embodiment, a hydrogel-coated β-FeOOH was prepared, and its properties were subjected to a series of tests and studies. The specific preparation process is as follows.

[0079] (1) Heat 100 mL of 0.1 M ferric chloride solution with pH 2 in a water bath at 65 °C for 12 h, then centrifuge and wash the solution. Dry the resulting powder to obtain β-FeOOH powder.

[0080] (2) Dissolve 300mg of the above powder in 49g of water and sonicate for 10min. Then add 1g of sodium alginate and stir. Use a dropper with a diameter of 2mm to drop it into 100mL of calcium chloride solution with a concentration of 0.1M and crosslink for 12h. The mass ratio of sodium alginate aqueous solution to calcium chloride solution is 1:2. The resulting calcium alginate-encapsulated β-FeOOH hydrogel is washed with deionized water 3 to 6 times to obtain hydrogel-encapsulated β-FeOOH.

[0081] The hydrogel-coated β-FeOOH prepared in this comparative example was tested for the degradation of tetracycline hydrochloride in an aqueous environment. The specific experimental procedure was as follows: 0.1 g of the hydrogel-coated β-FeOOH catalyst was placed in 100 mL of a 20 mg / L tetracycline hydrochloride solution, 10 mM hydrogen peroxide was added, and the solution was then irradiated under a xenon lamp with a cutoff filter. Samples were taken every ten minutes, 3 mL each time. An additional sample of the original tetracycline hydrochloride solution was taken as a control. Using the catalyst prepared in Comparative Example 2 of this invention, the degradation rate of tetracycline hydrochloride solution reached 32.71% after 50 minutes.

[0082] Cyclic degradation experiments were conducted on the hydrogel-coated β-FeOOH of Comparative Example 2 of this invention. After 5 cycles of degradation, the degradation effect of the hydrogel-coated β-FeOOH on tetracycline hydrochloride solution was significantly reduced, with the degradation efficiency dropping to 6.34%. In contrast, the core-shell gel catalyst prepared in Example 1 of this invention still maintained a 100% degradation effect, indicating that it has good cyclic degradation performance.

[0083] Comparative Example 3

[0084] This embodiment prepares a gel catalyst. Unlike Example 1, this process does not involve the addition of calcium chloride for crosslinking. The prepared catalyst is then subjected to performance testing, as detailed below:

[0085] This comparative example uses a catalyst prepared without the addition of calcium chloride for cross-linking, which does not yield a stable core-shell gel catalyst. Observation revealed that the outer β-FeOOH shell structure was loose and easily detached, exhibiting poor stability. The gel catalyst prepared in this comparative example was subjected to a tetracycline hydrochloride degradation test in an aqueous environment. The specific experimental procedure was as follows: the gel catalyst was placed in 100 mL of a 20 mg / L tetracycline hydrochloride solution, 10 mM hydrogen peroxide was added, and then it was irradiated under a xenon lamp with a cutoff filter. A 3 mL sample was taken every ten minutes, and a sample of the original tetracycline hydrochloride solution was also taken as a control. Using the catalyst prepared in Comparative Example 3 of this invention for tetracycline hydrochloride degradation, the degradation rate reached 84.41% after 50 minutes.

[0086] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a self-floating core-shell gel catalyst for degrading tetracycline hydrochloride, characterized in that, Follow these steps in sequence: (1) Preparation of hydrogel carrier A hydrogel precursor solution was prepared and then added dropwise to a calcium chloride solution with a concentration of 0.1 M using a dropper. The mass ratio of the hydrogel precursor solution to the calcium chloride solution was 1:

2. The reaction was carried out for 12 h. The resulting hydrogel was washed with deionized water 3 to 6 times and set aside for use. (2) Immobilization of β-FeOOH on the surface of hydrogel support The above hydrogel was placed in a ferric chloride solution with a pH of 2 and heated in a water bath at 65 °C for 12 h. The concentration of the ferric chloride solution was 0.1 M, and the mass ratio of the hydrogel to the ferric chloride solution was 1:2, thus obtaining a core-shell hydrogel catalyst. (3) Freeze-drying of hydrogel catalysts The above core-shell hydrogel catalyst was washed with deionized water 3 to 6 times, then pre-frozen at −15 ℃ for 2 h, and then dried in a vacuum freeze dryer at −40 ℃ for 12 h to obtain the core-shell hydrogel catalyst. The core-shell gel catalyst has a core diameter of 2 mm and a shell thickness of 8-13 μm. It is spherical in shape and exhibits a porous network structure. The shell is composed of spindle-shaped β-FeOOH nanoparticles.

2. The method for preparing a self-floating core-shell gel catalyst for degrading tetracycline hydrochloride according to claim 1, characterized in that, In step (1), the hydrogel precursor solution includes one or two of sodium alginate aqueous solution and pectin aqueous solution, or a mixture of one or more of sodium alginate aqueous solution and pectin aqueous solution with monomer.

3. The method for preparing a self-floating core-shell gel catalyst for degrading tetracycline hydrochloride according to claim 2, characterized in that, In step (1), the sodium alginate aqueous solution has a mass fraction of 2 wt%, the pectin aqueous solution has a mass fraction of 4 wt%, and the monomer is one or both of acrylic acid and acrylamide.

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