Preparation method of phosphoric acid modified cotton hull biochar for treating antibiotic wastewater

Abstract

The invention belongs to the technical field of preparation of functional environment-friendly materials, and discloses a preparation method of phosphoric acid modified cotton hull biochar for treating antibiotic wastewater. And carrying out high-temperature calcination in a nitrogen atmosphere to prepare the modified biochar material with rich pore structures and phosphorus-containing functional groups. The material has extremely high adsorption capacity to ciprofloxacin, the maximum adsorption capacity can reach 572.8 mg / g, and the material has a good removal effect and coexistence interference resistance to ciprofloxacin in actual wastewater. The adsorption mechanism mainly comprises electrostatic interaction, pi-pi interaction, hydrogen-bond interaction, surface complexation and the like. The material is simple in preparation process, low in cost, good in reproducibility and suitable for treatment of water bodies containing antibiotic pollutants such as pharmaceutical wastewater and aquaculture wastewater. The method fills the technical blank of high-value recycling of the cotton hull waste and cooperative treatment of antibiotic pollution, and has important environmental application prospects and industrial popularization values.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of functional environmentally friendly materials, and in particular relates to a method for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater. Background Art

[0002] In recent years, antibiotic contamination of water bodies has become increasingly serious. Ciprofloxacin, a broad-spectrum antimicrobial drug, is widely used in healthcare and aquaculture. Its residues in water bodies pose a serious threat to ecosystems and human health. Existing treatment methods such as ozone oxidation, Fenton oxidation, and membrane separation, while effective, suffer from high costs, high energy consumption, and a high risk of byproducts. In contrast, adsorption methods offer greater potential for industrialization due to their high efficiency, ease of operation, and lack of toxic byproducts.

[0003] Current research has attempted to improve biochar performance through chemical modification, but commonly used modifiers pose challenges such as high corrosiveness, environmental unfriendliness, and high cost. Furthermore, research on the use of phosphoric acid-modified biochar for ciprofloxacin removal remains limited, particularly with a lack of systematic exploration of the microscopic relationship between functional group configuration and adsorption mechanisms. Therefore, there is an urgent need to develop a green, safe, and industrially applicable phosphoric acid modification method and to clarify the relationship between its structural characteristics and adsorption mechanisms.

[0004] Through the above analysis, the problems and defects of the existing technology are as follows:

[0005] (1) At present, some studies have attempted to improve the performance of biochar through chemical modification, but the commonly used modifiers have problems such as strong corrosiveness, environmental unfriendliness, or high cost.

[0006] (2) There is still a lack of research on the removal of ciprofloxacin by phosphate-modified biochar, especially the lack of systematic exploration of the microscopic relationship between functional group configuration and adsorption mechanism. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater.

[0008] The present invention is achieved by providing a method for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater, comprising:

[0009] Step 1: Select dried biomass, grind it, and pass it through an 80-mesh sieve for later use; take cotton shell powder and place it in a beaker, add H3PO4 solution, and stir with a glass rod at room temperature for 15 minutes to fully infiltrate and achieve preliminary phosphoric acid impregnation;

[0010] Step 2: Transfer the mixed cotton shell slurry into a graphite crucible, seal it, and place it in a muffle furnace for calcination to complete the carbonization activation process;

[0011] Step 3: The calcined solid is repeatedly washed with deionized water until the pH of the washing liquid is neutral (about 7.0), dried, ground and sieved to obtain phosphoric acid-modified cotton hull biochar.

[0012] Furthermore, it is characterized in that, in step 1, the biomass is natural cotton hulls; and the cotton hull powder is 10 g.

[0013] Furthermore, it is characterized in that in step 1, the volume of the H3PO4 solution added is 15 mL and the mass fraction is 30%.

[0014] Furthermore, it is characterized in that in step 2, the seal is placed in a muffle furnace and calcined into a three-layer aluminum foil wrapped seal.

[0015] Furthermore, it is characterized in that, in the step 2, the calcination temperature is 600°C.

[0016] Furthermore, it is characterized in that in the step 2, the drying temperature is 70° C. and the sieving screen is 200 mesh.

[0017] Another object of the present invention is to provide a system for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater, comprising:

[0018] The impregnation module is used to select dried biomass, grind it and pass it through an 80-mesh sieve for later use; take cotton hull powder and place it in a beaker, add H3PO4 solution, and stir with a glass rod at room temperature for 15 minutes to fully infiltrate and achieve preliminary phosphoric acid impregnation;

[0019] The calcination module is used to transfer the mixed cotton shell slurry into a graphite crucible, seal it, and place it in a muffle furnace for calcination to complete the carbonization activation process;

[0020] The washing module is used to repeatedly wash the calcined solid with deionized water until the pH of the washing liquid is neutral (about 7.0), and then grind and sieve it after drying to obtain phosphoric acid-modified cotton hull biochar.

[0021] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0022] The method for preparing phosphate-modified cotton hull biochar proposed in the present invention is simple, green and efficient. It systematically reveals for the first time the dominant role of the phosphate functional group in the adsorption process of ciprofloxacin, significantly improves the specific surface area, pore volume and polar functional group content of the biochar, fills the gaps in the existing technology in green modification and microscopic mechanism identification, and has good practical application prospects and promotion value.

[0023] (1) The maximum adsorption capacity of the prepared cotton hull biochar for ciprofloxacin under optimized conditions reached 572.8 mg / g, which is much higher than that of most conventional biochars and commercial activated carbons, and has significant adsorption advantages;

[0024] (2) A large number of oxygen-containing functional groups such as O–P, C–P–O, and C=O were introduced through phosphoric acid modification. Among them, O–P was confirmed for the first time to be the main binding site of ciprofloxacin, which improved the affinity of the material for polar organic pollutants;

[0025] (3) Phosphoric acid-modified cotton shell biochar not only has excellent adsorption performance for ciprofloxacin, but also shows a removal rate of more than 85% when treating other common organic pollutants (such as tetracycline, acetaminophen, Orange G, etc.), showing wide practicality and indicating that the material has prospects for industrial treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a method for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater provided by an embodiment of the present invention.

[0027] Figure 2 This is a structural block diagram of a system for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater provided by an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the preparation process of phosphoric acid-modified biochar provided in an embodiment of the present invention.

[0029] Figure 4 1 is a scanning electron microscope image of biochar provided by an embodiment of the present invention; b is the N2 adsorption-desorption isotherm of biochar; and c is the pore size distribution curve of biochar.

[0030] Figure 5 3 is a diagram showing the effect of adsorbing ciprofloxacin by different systems provided in the embodiments of the present invention.

[0031] Figure 6 This is a 3DEEM comparison chart of actual wastewater provided by an embodiment of the present invention before and after adsorption by phosphoric acid-activated biochar. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] like Figure 1 As shown, the embodiment of the present invention provides a method for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater, comprising the following steps:

[0034] S101, selecting dried biomass, grinding it, and passing it through an 80-mesh sieve for later use; placing cotton hull powder in a beaker, adding H3PO4 solution, and stirring with a glass rod at room temperature for 15 minutes to fully infiltrate and achieve preliminary phosphoric acid impregnation;

[0035] S102, transferring the mixed cotton shell slurry into a graphite crucible, sealing it, and calcining it in a muffle furnace to complete the carbonization activation process;

[0036] S103, the calcined solid is repeatedly washed with deionized water until the pH of the washing liquid is neutral (about 7.0), dried, ground and sieved to obtain phosphoric acid-modified cotton hull biochar.

[0037] The present invention provides a method for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater. To address the problems in the prior art such as insufficient adsorption performance of biochar, complex or high-cost modification methods, and poor reusability of adsorption materials, a method is proposed that uses renewable agricultural waste cotton hulls as raw materials and combines a simple process flow with phosphoric acid modification to achieve efficient adsorption and resource utilization of antibiotic pollutants.

[0038] First, existing unmodified cotton hull biochar has an underdeveloped pore structure and a small surface area, limiting its physical adsorption capacity for antibiotic molecules. This new method introduces a phosphoric acid modification step before preparation. By leveraging phosphoric acid's dehydrating effect and its ability to promote the formation of a porous structure during carbonization, it effectively improves the pore structure of the carbonized cotton hull material, significantly increasing the specific surface area of the final product and providing more adsorption sites for antibiotic molecules.

[0039] Second, to address the shortcomings of traditional physical activation methods (such as water vapor and carbon dioxide), such as strong dependence on equipment, poor controllability, and high cost, the present invention adopts phosphoric acid chemical activation, which is a mild process, simple to operate, and does not require a high-energy gas activation atmosphere. It only relies on phosphoric acid itself as a modifier, achieving a cost-controlled and environmentally friendly activation path, while avoiding the problem of structural collapse caused by high-temperature treatment.

[0040] Third, traditional modified biochar often exhibits insufficient adsorption selectivity when adsorbing polar pollutants (such as sulfonamide antibiotics), resulting in limited treatment efficiency. Phosphoric acid modification not only introduces surface acidic groups (such as –OH and –PO4), but also enhances the hydrophilicity and polar compatibility of the material surface, thereby strengthening its electrostatic adsorption and hydrogen bonding with polar antibiotic molecules, thereby improving the ability of the material surface to accumulate antibiotics.

[0041] Fourth, biochar products often face challenges in practical water treatment applications, such as insufficient stability and elemental leaching from water. This invention optimizes the washing and drying processes to ensure that residual phosphoric acid in the final product is fully removed, maintaining the material's stability in wastewater environments and preventing the introduction of secondary contamination. It also effectively ensures the structural integrity and adsorption performance of the biochar throughout multiple adsorption and regeneration cycles.

[0042] Fifth, existing modification methods often neglect the controllability and industrial adaptability of the modification process itself, resulting in good laboratory results but difficulty in scaling up. The present invention utilizes standardized phosphoric acid impregnation time and concentration ratios, combined with a sealed muffle furnace calcination process, making the entire carbonization process repeatable and scalable, meeting the requirements for mass production of wastewater treatment materials in industrial applications.

[0043] Sixth, in order to make the prepared phosphate-modified cotton shell biochar have long-term application value in actual antibiotic wastewater treatment, the present invention pays special attention to the control of carbonization temperature and holding time to ensure that the material has good mechanical strength and structural stability; and through the final pH neutralization washing, it has environmentally neutral chemical properties to ensure that it will not have a negative impact on the wastewater treatment system, thereby improving the overall application reliability and environmental friendliness of the material in actual water treatment scenarios.

[0044] In S101 provided in the embodiment of the present invention, the biomass is natural cotton hulls; and the cotton hull powder is 10 g.

[0045] In S101 provided in the embodiment of the present invention, the volume of the added H3PO4 solution is 15 mL, and the mass fraction is 30%.

[0046] In S102 provided in an embodiment of the present invention, the seal is placed in a muffle furnace and calcined into a three-layer aluminum foil wrapped seal.

[0047] In S102 provided in the embodiment of the present invention, the calcination temperature is 600°C.

[0048] In S102 provided in the embodiment of the present invention, the drying temperature is 70° C. and the sieving screen is 200 mesh.

[0049] like Figure 2 As shown, an embodiment of the present invention provides a system for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater, comprising:

[0050] The impregnation module is used to select dried biomass, grind it and pass it through an 80-mesh sieve for later use; take cotton hull powder and place it in a beaker, add H3PO4 solution, and stir with a glass rod at room temperature for 15 minutes to fully infiltrate and achieve preliminary phosphoric acid impregnation;

[0051] The calcination module is used to transfer the mixed cotton shell slurry into a graphite crucible, seal it, and place it in a muffle furnace for calcination to complete the carbonization activation process;

[0052] The washing module is used to repeatedly wash the calcined solid with deionized water until the pH of the washing liquid is neutral (about 7.0), and then grind and sieve it after drying to obtain phosphoric acid-modified cotton hull biochar.

[0053] Example 1

[0054] Step 1: Select dried cotton hulls, grind them, and pass them through an 80-mesh sieve for later use. Place 10g of cotton hull powder in a beaker, add 15mL of a 30% H3PO4 solution, and stir with a glass rod at room temperature for 15 minutes to fully soak and achieve initial phosphoric acid impregnation.

[0055] Step 2: Transfer the mixed cotton shell slurry into a graphite crucible, wrap it with aluminum foil and seal it for heat treatment. Set the muffle furnace heating rate at 5°C / min, heat it to 600°C and keep it at this temperature for 2 hours to complete the carbonization activation process.

[0056] Step 3: The calcined solid was repeatedly washed with deionized water until the pH of the washing solution was neutral (about 7.0), and then dried at 70°C for 24 hours. The dried material was ground and passed through a 200-mesh sieve to obtain phosphoric acid-modified cotton hull biochar.

[0057] The morphology, specific surface area and pore size of the phosphoric acid modified cotton hull biochar prepared by this method are as follows: Figure 3 As shown in the figure, the particle distribution on the surface of the modified biochar is more uniform. In the relative pressure range of 0.45 to 0.9, the modified biochar presents a type IV isotherm and an H4 hysteresis loop. The pore size distribution curve shows that the modified biochar has a typical mesoporous structure (2 to 50 nm) and a specific surface area of 316.1 m2 / g, which is much higher than that of the original biochar, which is conducive to the removal of pollutants. Figure 4 Compared to the original biochar, the total pore volume of the modified biochar increased from 0.19 cm³ / g to 0.45 cm³ / g. This is likely due to the fact that H₃PO₄ inhibited the collapse and fragmentation of the carbon skeleton during pyrolysis, thereby increasing the pore volume of the biochar. The number of micropores and mesopores nearly doubled, indicating a distinct hierarchical pore structure. These results indicate that H₃PO₄ activation is beneficial for increasing the pore volume and specific surface area of the biochar.

[0058] Example 2 (Adsorption Experiment of Phosphoric Acid-Modified Biochar in Different Systems)

[0059] Step 1: prepare 250 mL of each of 80 mg / L, 60 mg / L, 40 mg / L, 20 mg / L, and 10 mg / L solutions of typical organic pollutants such as acetaminophen (APAP), orange G (OG), and tetracycline (TC);

[0060] Step 2: 0.1 g / L of the phosphoric acid-modified biochar prepared in Example 1 was added to each of the above systems, the pH was adjusted to 6.0, and the mixture was shaken in a constant temperature oscillator at 200 rpm and 25°C for 6 hours. After adsorption, samples were taken to detect the concentrations of APAP, OG, and TC.

[0061] The experimental results show that for pollutants with a concentration of less than 40 mg / L, the removal rate can reach at least 85%. The results show that phosphoric acid modified biochar has excellent universality in practical applications ( Figure 5 ).

[0062] Example 3 (Application of Phosphoric Acid-Modified Biochar in Actual Pharmaceutical Wastewater)

[0063] Step 1: Collect wastewater samples from the outlet of a pharmaceutical factory. The initial COD concentration is 486.45 mg / L, the TOC concentration is 71.63 mg / L, and the ciprofloxacin concentration is 11.4 mg / L. The pH is 6.3, and no adjustment is required.

[0064] Step 2: Add the phosphoric acid-modified biochar prepared in Example 1 (dosage: 1 g / L) to 250 mL of the wastewater sample, place the mixture in a shaker, and shake at 25° C. for 4 hours with the shaker speed controlled at 200 rpm;

[0065] Step 3: After the treatment, 5 ml of the solution was filtered through a 0.45 μm filter membrane, and the COD, TOC, and ciprofloxacin concentrations in the filtrate were determined. Changes in the fluorescence intensity of the solution were observed using a three-dimensional fluorescence spectrometer.

[0066] The experimental results showed that after treatment, COD in the wastewater dropped to 50.14 mg / L, TOC dropped to 21.33 mg / L, and the CIP removal rate reached 91.6%. The fluorescence intensity decreased significantly, indicating that the phosphoric acid-modified biochar had a good removal effect on ciprofloxacin and other organic impurities in actual wastewater, and was suitable for the actual removal of CIP in complex water bodies ( Figure 6 ).

[0067] Example 4: Preparation conditions of phosphoric acid concentration 10% and carbonization temperature 500°C

[0068] Select dried cotton hulls, grind them, and pass them through an 80-mesh sieve. Take 20g of cotton hull powder and add it to 200mL of a 10% phosphoric acid solution. Stir continuously with a glass rod at room temperature for 15 minutes to complete the infiltration. The infiltrated cotton hull slurry is placed in a sealed graphite crucible, placed in a muffle furnace, and carbonized at a constant temperature of 500°C for 90 minutes. Remove the cooled solid and wash it with deionized water until the pH of the washing solution is approximately 7.0. Then dry, grind, and sieve to obtain the target biochar material.

[0069] The BET specific surface area test of the sample showed that its specific surface area reached 592m 2 / g, with pore sizes primarily distributed between 2–10nm, indicating a mesoporous material. Infrared spectroscopy characterization results indicate that its surface is rich in oxygen-containing functional groups such as –OH and –PO4. In static adsorption experiments, using 10mg / L sulfamethoxazole (SMX) as a model pollutant, the adsorption rate reached 94.2% within 24 hours, demonstrating excellent adsorption performance.

[0070] Example 5: Preparation conditions of phosphoric acid concentration 20% and carbonization temperature 600°C

[0071] Weigh 20g of pretreated cotton hull powder and add it to 200mL of a 20% phosphoric acid solution. Stir at room temperature for 15 minutes and let it sit for 2 hours to enhance phosphoric acid wetting. The mixture was transferred to a sealed graphite crucible, placed in a muffle furnace, and calcined at 600°C for 60 minutes. After cooling, the mixture was repeatedly washed with deionized water until the pH of the washings reached neutrality. The mixture was then dried, ground, and sieved to obtain the phosphoric acid-modified biochar sample.

[0072] The sample has a higher micropore density and its BET specific surface area reaches 703m 2 / g. XPS test results indicate that the surface phosphorus content is higher than in Example 1. It is speculated that phosphoric acid further promotes the development of a porous structure and the formation of surface functional groups under high temperature conditions. In an adsorption experiment for 20mg / L SMX removal, the adsorption rate was significantly faster than in Example 1 within 2 hours, with a final 24-hour removal rate of 96.7%, demonstrating a more significant adsorption kinetic advantage within a short period of time.

[0073] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing phosphoric acid-modified cotton hull biochar for treating antibiotic wastewater, characterized in that: The following steps are involved: Step 1: Grind and sieve the dried cotton hulls; mix the obtained cotton hull powder with a phosphoric acid solution and stir evenly; Step 2: Transfer the mixture into a graphite crucible, seal it, and calcine it in a muffle furnace; Step three: the calcined product is washed, dried and sieved to obtain the target material.

2. The method according to claim 1, wherein the mass of the cotton hull powder is set to 10 grams and the sieve particle size is 80 meshes.

3. The method of claim 1, wherein the volume of the phosphoric acid solution is 15 ml and the mass fraction is 30%.

4. The method according to claim 1, wherein the calcination process is sealed by wrapping with three layers of aluminum foil.

5. The method of claim 1, wherein the temperature of the muffle furnace calcination is set to 600 degrees Celsius and the duration is set to 60 minutes.

6. The method of claim 1, wherein the drying temperature is set at 70 degrees Celsius and the sieve particle size is set at 200 meshes.

7. A system for preparing phosphoric acid-modified cotton hull biochar, comprising: Impregnation module, used to complete the mixing treatment of cotton hull powder with phosphoric acid solution; Calcination module, used to complete the heat treatment process of the mixture in a sealed state; The washing module is used to wash, dry and screen the carbonized products.

8. The preparation system according to claim 7, wherein the impregnation module comprises a stirring container and a liquid adding structure.

9. The preparation system of claim 7, wherein the calcination module comprises a graphite crucible, a muffle furnace, and a sealing assembly.

10. The preparation system according to claim 7, wherein the washing module comprises a multi-stage filtering device and a temperature-controlled drying device.

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