Preparation method and application of sulfidized nano zero-valent iron loaded biochar@chitosan gel beads

Abstract

This invention belongs to the field of composite catalytic materials and tetracycline-containing wastewater treatment technology, and discloses a method for preparing and applying sulfidated nano-zero-valent iron supported biochar@chitosan gel microspheres. The method first prepares biochar from straw, then prepares a sulfidated nano-zero-valent iron supported biochar catalyst (S-nZVI@BC) via liquid-phase reduction-sulfidation. Subsequently, the catalyst is dispersed in a chitosan solution, cured with alkali, cross-linked with glutaraldehyde, and freeze-dried to obtain the target gel microspheres. This invention features a simple preparation process, inexpensive and readily available raw materials, and the product has advantages such as uniform particle size, easy separation and recovery, and green and efficient operation. When applied to the degradation of tetracycline-containing wastewater, it achieves a tetracycline degradation rate of 99.05% within 30 minutes, solving the problems of difficult recovery and high secondary pollution risk associated with traditional powdered catalysts, and has broad prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of tetracycline degradation technology, specifically relating to a method for preparing and applying sulfidated nano-zero-valent iron-supported biochar@chitosan gel microspheres. Background Technology

[0002] With the rapid development of the pharmaceutical and aquaculture industries, tetracycline antibiotics are widely used due to their broad-spectrum antibacterial properties. However, due to their strong chemical stability and poor biodegradability, large amounts of unmetabolized tetracycline are discharged into the aquatic environment through wastewater, causing serious water pollution. Currently, advanced oxidation technology based on sulfide nano-zero valent iron (S-nZVI) is attracting much attention due to its high degradation efficiency and strong reactivity.

[0003] Biochar (BC) possesses abundant pore structure and large specific surface area, making it suitable as a carrier for S-nZVI, effectively inhibiting its aggregation. Simultaneously, it enriches pollutants through adsorption, enhancing catalytic degradation efficiency. However, existing S-nZVI@BC composite catalysts are mostly in powder form, presenting challenges in practical wastewater treatment such as difficulty in recovery, easy loss, and high risk of secondary pollution, thus limiting their industrial application.

[0004] Chitosan, as a natural polymer material, possesses advantages such as good biocompatibility, biodegradability, and a surface rich in active functional groups, and is often used in the preparation of gel carriers. Immobilizing S-nZVI@BC catalyst within chitosan gel can form uniformly sized gel spheres, which can be separated and recovered through simple precipitation, while reducing the risk of secondary pollution. Therefore, developing a simple and stable method for preparing sulfide nano-zero-valent iron-supported biochar@chitosan gel spheres is of great significance for promoting the development of wastewater treatment technology. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a simple, stable, and environmentally friendly process for degrading tetracycline using sulfidated nano-zero-valent iron-supported biochar@chitosan gel microspheres.

[0006] Another objective of this invention is to provide a method for preparing the above-mentioned sulfurized nano-zero-valent iron-supported biochar@chitosan gel microspheres and their degradation effect on tetracycline.

[0007] The objective of this invention is achieved through the following technical solution.

[0008] A method for preparing sulfide nano-zero-valent iron supported biochar@chitosan gel microspheres includes six steps: biochar preparation, S-nZVI@BC catalyst preparation, chitosan solution preparation, mixed slurry preparation, gel microsphere molding, crosslinking, and drying. The specific operations are as follows:

[0009] (1) Wash the collected straw thoroughly, and then rinse it at 110°C. o Excessive drying at C. The dried straw is crushed into granules and passed through a 200-mesh sieve. It is then dried in a tubular furnace at 900°C under nitrogen atmosphere. o Biochar was prepared by pyrolysis at C for 4 hours.

[0010] (2) Dissolve 2g of the material obtained in step (1) and 4.96g of FeSO4·7H2O in 70mL of solution (50mL of ultrapure water and 20mL of anhydrous ethanol), add 20mL of NaBH4 dropwise and continue stirring for 30min. Finally, add 0.09g of Na2S to the solution and sonicate for 30min. The resulting metal particles are filtered through filter paper and separated from the liquid phase by sedimentation. The solid is then washed several times with water and ethanol and finally freeze-dried. A sulfide nano-zero-valent iron supported biochar catalyst is obtained.

[0011] (3) Dissolve 3g of chitosan in 180mL of ultrapure water and add 3.5mL of glacial acetic acid dropwise. Stir thoroughly for 30min to prepare a chitosan solution;

[0012] (4) At room temperature, add 2-3g of the material obtained in step (2) to the chitosan solution obtained in step (3) and stir until evenly mixed;

[0013] (5) Using a syringe, the mixed solution obtained in step (4) is added dropwise to a 0.65 mL / L NaOH solution to form uniformly sized gel spheres. After standing for 12 hours, the gel spheres are removed and washed until the pH values ​​before and after are the same.

[0014] (6) The gel microspheres described in step (5) are immersed in a 6% (v / v) glutaraldehyde solution for cross-linking reaction. After 3 hours, they are taken out, washed with ultrapure water, and then placed in a freeze dryer for 48 hours to obtain the final gel microspheres.

[0015] The above-mentioned application of nano-zero-valent iron-supported biochar / chitosan gel microspheres in the efficient degradation of tetracycline.

[0016] In the above technical solution, the nano-zero-valent iron-supported biochar / chitosan gel microspheres achieve a 99.05% degradation rate of tetracycline in 30 minutes.

[0017] In the above technical solution, the degradation method is as follows: the nano-zero-valent iron-supported biochar / chitosan gel microspheres are added to the solution to be degraded, and the reaction is carried out by shaking.

[0018] In the above technical solution, the pH of the solution to be degraded is 3 to 9.

[0019] In the above technical solution, the mass of the nano-zero-valent iron-supported biochar / chitosan gel microspheres added to each 200mL of the solution to be degraded is 5~6g.

[0020] In the above technical solution, the concentration of tetracycline in the solution to be degraded before degradation is 5~50 mg / L.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Raw materials are inexpensive and readily available: agricultural waste straw is used as the raw material for biochar, which is low-cost and enables resource recycling; reagents such as chitosan FeSO4･7H2O are common chemical products that are easy to obtain.

[0023] The process is simple and controllable: the entire preparation process does not require complex equipment, and the parameters of each step are easy to adjust, making it suitable for industrial production.

[0024] The product has high performance: the gel microspheres have uniform particle size (1~5mm) and can be separated and recovered by simple precipitation with a recovery rate of over 95%; the S-nZVI@BC catalyst is uniformly dispersed and has a highly efficient adsorption-degradation synergistic effect on tetracycline, with a degradation rate of 99.05% within 30 minutes.

[0025] The product is environmentally friendly: the chitosan carrier has good biocompatibility and is biodegradable, avoiding secondary pollution.

[0026] With broad application prospects, it can be used to treat tetracycline-containing wastewater generated by industries such as livestock and poultry farming and medical treatment. It can also be extended to the treatment of other organic pollutants or heavy metal wastewater, and has important environmental and economic value. Attached Figure Description

[0027] Figure 1 This is a photograph of the gel microspheres containing sulfide nano-zero-valent iron supported biochar catalyst in Example 1 of the present invention.

[0028] Figure 2 This is an electron microscope image of the gel microspheres containing sulfide nano-zero-valent iron supported biochar catalyst in Example 1 of the present invention.

[0029] Figure 3 The degradation efficiency of tetracycline by gel spheres containing sulfide nano-zero-valent iron supported biochar catalyst in Example 1 of the present invention and gel spheres prepared without S were compared with those prepared by persulfate advanced oxidation technology. Detailed Implementation

[0030] To clearly illustrate the technical solution of the present invention, preferred embodiments of the present invention will be given below through specific methods and in conjunction with the accompanying drawings.

[0031] Example 1

[0032] 1. Take corn stalks, wash them clean, and add 110 ml of water. oDry to constant weight, crush and pass through a 200-mesh sieve. Take 5g of the sieved particles and place them in a tube furnace. Heat at 900°C under a nitrogen atmosphere. o Pyrolysis at C for 4 hours yields biochar.

[0033] 2. Weigh 2g of biochar and 4.96g of FeSO4·7H2O, add 70mL of mixed solvent (50mL of ultrapure water + 20mL of anhydrous ethanol), stir and disperse for 30min, add 20mL of 0.5mol / L NaBH4 solution dropwise, stir for 30min, then add 0.09g of Na2S, sonicate at 200W and 30kHz for 30min, filter, wash and freeze dry to obtain S-nZVI@BC catalyst.

[0034] 3. Add 3g chitosan to 180mL of ultrapure water and 3.5mL of glacial acetic acid, stir for 30min to dissolve, and obtain a chitosan solution.

[0035] 4. Add 2g of S-nZVI@BC catalyst, stir at 400r / min for 70min to form a mixed slurry.

[0036] 5. Using a 0.8mm syringe needle, drop the slurry into a 0.65mol / L NaOH solution, let it stand for 12 hours, and wash until the pH is neutral to obtain primary gel microspheres.

[0037] 6. Immerse the primary microspheres in a 6% glutaraldehyde solution for 3 hours for cross-linking, then wash and rinse at -50°C. o Freeze-dry at 5 Pa for 48 h to obtain gel microspheres with a particle size of 2-3 mm and a catalyst loading of 35 wt%.

[0038] 7. Prepare other undoped S-based gel microspheres using steps 1-6 above.

[0039] 8. Place the prepared gel microspheres of different components into a 20 mg / L tetracycline aqueous solution, and add peroxymonosulfate (PMS). Shake and react for 30 minutes. Take 1 mL of the reaction solution at 5, 10, 15, 20, 25, and 30 minutes after adding PMS. Filter the solution through a 0.22 μm filter into a 1.5 mL brown HPLC vial. Add 0.5 mL of HPLC-grade methanol as a quenching agent to the vial.

[0040] 9. For example Figure 3 The figure shows the degradation efficiency of tetracycline by gel spheres containing sulfide nano-zero-valent iron supported biochar catalyst and gel spheres prepared without S doping under persulfate advanced oxidation technology. Among them, the gel spheres containing sulfide nano-zero-valent iron supported biochar catalyst can achieve a tetracycline degradation rate of 99.05% within 30 minutes based on persulfate advanced oxidation.

Claims

1. A method for preparing sulfide nano-zero-valent iron-supported biochar@chitosan gel microspheres, characterized in that, Includes the following steps: Preparation of biochar: Wash the collected straw and heat it at 110°C. o Excessive drying at C. The dried straw is crushed into granules and passed through a 200-mesh sieve. It is then dried in a tubular furnace at 900°C under nitrogen atmosphere. o Biochar was prepared by pyrolysis at C for 4 hours. Preparation of sulfide nano-zero-valent iron supported biochar catalyst: 2g of the material obtained in step (1) and 4.96g of FeSO4·7H2O were dissolved in 70mL of solution (50mL of ultrapure water and 20mL of anhydrous ethanol). 20mL of NaBH4 was added dropwise and stirring was continued for 30min. Finally, 0.09g of Na2S was added to the solution and sonicated for 30min. The resulting metal particles were filtered through filter paper, precipitated, and separated from the liquid phase. The solid was then washed several times with water and ethanol, and finally freeze-dried. Sulfide nano-zero-valent iron supported biochar catalyst was obtained. Preparation of chitosan solution: Dissolve 3g of chitosan in 180mL of ultrapure water and add 3.5mL of glacial acetic acid dropwise. Stir thoroughly for 30min to prepare a chitosan solution. Preparation of the mixed slurry: At room temperature, add 2-3g of the material obtained in step (2) to the chitosan solution obtained in step (3) and stir until the mixture is homogeneous; Gel microsphere formation: The mixed solution obtained in step (4) was added dropwise to a 0.65 mL / L NaOH solution using a syringe to form gel microspheres with uniform particle size. After standing for 12 hours, the gel microspheres were taken out and washed until the pH value before and after was the same. Crosslinking and drying: The gel microspheres described in step (5) were soaked in a 6% (v / v) glutaraldehyde solution for crosslinking reaction. After 3 hours, they were taken out, washed with ultrapure water, and then placed in a freeze dryer for 48 hours to obtain the final gel microspheres.

2. The sulfurized nano-zero-valent iron-supported biochar@chitosan gel microspheres obtained by the preparation method according to any one of claims 1, characterized in that, The gel microspheres have a particle size of 1-5 mm, a density of 0.8-1.2 g / cm³, and a catalyst loading of 30-40 wt%.

3. The sulfurized nano-zero-valent iron-supported biochar@chitosan gel microspheres prepared according to claims 1 and 2 are applied to the degradation of tetracycline in wastewater using advanced oxidation technology.

4. The application according to claim 3, characterized in that, The sulfurized nano-zero-valent iron-supported biochar / chitosan gel microspheres achieved a degradation rate of 99.05% within 30 minutes.

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