Construction method and application of biochar-based controlled release system

Abstract

The invention belongs to the field of modified biological materials, and particularly relates to a construction method and application of a biochar-based controlled release system. Bagasse is adopted as a raw material and is fired in a tubular furnace to obtain bagasse biochar, urea-modified bagasse biochar is obtained after hydrothermal reaction, characterization results show that the phase of the bagasse biochar is not changed before and after modification, but the surface of modified ZZBC-urea becomes rough, the specific surface area is obviously increased, and the bagasse biochar modified by urea is obtained. A microporous structure is added on the basis of retaining original mesopores, so that a good condition is provided for loading of ciprofloxacin. Load experiment results show that the modified ZZBC-urea has obvious load on the ciprofloxacin, and the temperature rise is beneficial to the load of the ciprofloxacin; a release experiment result shows that the ZZBC-urea releases different ciprofloxacin in different media, and the ZZBC-urea is more beneficial to the release of ciprofloxacin in a buffer solution.

Description

Technical Field

[0001] This invention belongs to the field of modified biomaterials, specifically relating to a method for constructing a biochar-based controlled-release system and its application. Background Technology

[0002] Biochar is a multifunctional solid material produced by high-temperature pyrolysis of carbon-rich biomass under anaerobic or hypoxic conditions. It is highly aromatic, carbon-rich, and porous. Biochar has broad application prospects in agriculture, environmental protection, and energy development. For example, Li Huiduan et al. found that modified tobacco straw biochar reduced the levels of the heavy metal Cd in simulated polluted water and soil. 2+ It has good adsorption properties. The raw materials for biochar preparation are widely available, including tree stalks, branches, and leaves, coconut shells, as well as the stalks, leaves, and dead branches of various herbaceous plants.

[0003] In daily life, oral administration is the most common and convenient method of drug delivery. However, conventional oral administration often requires high doses or repeated administration to achieve therapeutic effects, which may reduce overall efficacy and patient compliance, and lead to serious side effects or even toxicity. Furthermore, it is frequently limited by poor targeting and short circulation times. Therefore, controlled-release drug delivery systems are emerging as a promising targeted therapy option because they can improve drug efficacy while reducing harmful side effects on normal and healthy tissues, maximizing drug effectiveness.

[0004] Most commercially available controlled-release carriers are hydrogels, making them the primary research focus for drug release carriers. In recent years, biochar materials have also become a major candidate material for drug controlled-release carriers due to their good biocompatibility, functional diversity, tunable pore structure, high customizability, and large loading capacity.

[0005] For biochar, existing research mostly uses rice husks and corn stalks as raw materials, while the high cellulose content and low cost advantages of bagasse have not been fully utilized. While bagasse is a mature biomass raw material with well-developed fiber extraction technology, its use as a drug carrier is less studied. Some porous biochar materials have shown ideal loading capacity, but they still have shortcomings in controlled release and drug loading. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a method for constructing a biochar-based controlled-release system.

[0007] This method overcomes the limitations of traditional drug carriers, such as high cost and potential environmental pollution from degradation products, and develops a low-cost, environmentally friendly drug delivery system. It optimizes the precision and duration of drug release, reducing drug waste and toxic side effects caused by burst release.

[0008] The present invention further provides a biochar-based controlled-release system prepared using the above-described construction method.

[0009] Another object of the present invention is to provide the application of the above-mentioned biochar-based controlled-release system.

[0010] The technical solution adopted by the present invention to achieve the above objectives is as follows: This invention provides a method for constructing a biochar-based controlled-release system, comprising the following steps: (1) Preparation of bagasse biochar Washed and dried bagasse was pyrolyzed under N2 protection to obtain bagasse biochar ZZBC; (2) Preparation of modified bagasse biochar Urea was dissolved in deionized water. After complete dissolution, bagasse biochar was added, stirred, and the solution was heated to react. After the reaction, the supernatant was removed and the solution was centrifuged. The precipitate was then washed and dried to obtain urea-modified bagasse biochar ZZBC-urea.

[0011] Preferably, in step (1), the pyrolysis is performed at 600-650℃ for 3 hours.

[0012] Preferably, in step (2), the mass ratio of urea to bagasse biochar is 1:1.

[0013] Preferably, in step (2), the stirring time is 30-40 min; the heating reaction is carried out at 150-155℃ for 3 h.

[0014] The present invention also provides a biochar-based controlled-release system prepared by the above construction method, wherein the biochar-based controlled-release system is loaded with ciprofloxacin.

[0015] Preferably, the controlled-release biochar system is loaded as follows: ZZBC-urea is added to a ciprofloxacin solution and subjected to constant-temperature shaking.

[0016] Preferably, the ratio of ZZBC-urea to ciprofloxacin solution is 0.05 g: 60 mL; the concentration of ciprofloxacin solution is 10 mg·L⁻¹. -1 .

[0017] Preferably, the isothermal oscillation is performed in an isothermal shaker at 24±0.5℃ and 150 rpm for 5-60 minutes.

[0018] The present invention also provides an application of the biochar-based controlled-release system prepared by the above construction method in the preparation of targeted drug delivery.

[0019] This invention uses bagasse as raw material, which is calcined in a tubular furnace to obtain bagasse biochar. After hydrothermal reaction, urea-modified bagasse biochar is obtained. Characterization results show that the phase composition of the bagasse biochar remains unchanged before and after modification. However, the modified ZZBC-urea has a rougher surface and a significantly increased specific surface area, adding microporous structures while retaining the original mesoporous structure. This provides favorable conditions for ciprofloxacin loading. Loading experiments show that the modified ZZBC-urea significantly increases ciprofloxacin loading, and higher temperatures favor ciprofloxacin loading. Release experiments show that ZZBC-urea releases ciprofloxacin differently in different media, with buffer solutions being more conducive to ciprofloxacin release.

[0020] The beneficial effects of this invention are as follows: (1) The system provided by this invention can solve the limitations of traditional drug carriers, overcome the problems of high cost and potential environmental pollution caused by degradation products of traditional polymer carriers, reduce preparation costs and is environmentally friendly. This invention can optimize the accuracy and long-lasting effect of drug release, and reduce the problem of drug waste or toxic side effects caused by burst release effect.

[0021] (2) The controlled-release system constructed in this invention can realize the high-value utilization of agricultural waste. Using agricultural waste such as bagasse as raw materials, it can be transformed into functional biochar through green processes, promoting "resource recycling". It can elucidate the drug release mechanism of biochar carriers, reveal the quantitative relationship between the pore structure, surface chemical properties and drug release behavior of biochar, and fill the gap in the systematic analysis of drug release kinetics and mechanisms in existing research. It can expand application scenarios and construct a dual-scenario controlled-release system with both agricultural (such as slow-release fertilization) and medical (such as targeted drug delivery) functions to meet the needs of multiple fields. Attached Figure Description

[0022] Figure 1 The XRD patterns of bagasse carbon before and after modification are shown. Figure 2 SEM images of bagasse carbon before and after modification; Figure 3 The BET and BJH curves of bagasse biochar before and after modification are shown. Figure 4 Infrared spectra of bagasse biochar before and after urea modification; Figure 5The loading curves of ciprofloxacin on bagasse biochar before and after modification at different temperatures are shown. Figure 6 The release curves of the modified bagasse biochar in different media are shown. Detailed Implementation

[0023] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0024] Example 1 1. Materials and Methods 1.1 Experimental Reagents and Instruments 1.1.1 Experimental Reagents Table 1 Experimental Reagents 1.1.2 Experimental Apparatus Table 2 Experimental Instruments In addition to the instruments mentioned above, conventional experimental supplies such as conical flasks, beakers, volumetric flasks, graduated cylinders, mortars, and magnetic boats were used in the research process.

[0025] 1.2 Preparation of raw materials 1.2.1 Preparation of bagasse biochar After washing and drying the bagasse, 2 g of bagasse was pyrolyzed in a tube furnace under N2 protection at 600 ℃ for 3 h to obtain bagasse biochar, denoted as ZZBC.

[0026] 1.2.2 Preparation of modified bagasse biochar Take 0.5 g of urea and place it in a beaker. Add 40 mL of deionized water to dissolve it. After it is completely dissolved, add 0.5 g of bagasse biochar and stir on a magnetic stirrer for 30 min. Pour the solution into a reaction vessel and react at 150 ℃ for 3 h. After the reaction, remove the supernatant and centrifuge. After centrifugation, wash the precipitate. First, wash it three times with deionized water, then wash it twice with anhydrous ethanol. Finally, discard the supernatant and dry it in an oven to obtain urea-modified bagasse biochar, labeled as ZZBC-urea.

[0027] 1.2.3 Preparation of the medium solution Measure 4 g of sodium chloride, 0.2 g of potassium chloride, 0.72 g of disodium hydrogen phosphate, and 0.12 g of potassium dihydrogen phosphate into a beaker. Add 300 mL of deionized water until all solid reagents are completely dissolved. Transfer the solution from the beaker to a 500 mL volumetric flask and dilute to volume with deionized water to obtain a neutral medium solution. Take 70 mL of the neutral medium solution and place it in a beaker. Add 0.5 mol / L hydrochloric acid solution or sodium hydroxide solution dropwise to the base solution while stirring. Monitor the pH in real time with a pH meter and adjust to the target pH value (error ±0.1). After adjustment, let it stand for 5 min and recalibrate the pH value to ensure stability. This yields an acidic medium solution and an alkaline medium solution with pH values ​​of 5 and 9, respectively.

[0028] Example 1 (I) Characterization and analysis of biochar Scanning electron microscopy (SEM) is used to observe the microstructure, surface structure characteristics, pore arrangement, size and shape, and surface elemental composition of the material; specific surface area analysis (BET) is used to obtain information such as the specific surface area and pore size of the material; and X-ray diffraction spectroscopy (XRD) is used to obtain information such as the composition of the material and the structure or morphology of the atoms or molecules inside the material.

[0029] (II) Biochar loading and release experiments 1. Loading experiment of biochar Take 0.05 g of ZZBC or ZZBC-urea sample and place it in a 100 mL Erlenmeyer flask. Add 60 mL of the initial concentration of 10 mg·L⁻¹. -1 Ciprofloxacin solution was prepared by placing conical flasks in a constant-temperature shaker (24±0.5℃, 150 rpm) and shaking. Samples of 1 mL were taken at different times (0, 5, 10, 15, 20, 25, 30, 45, and 60 min), filtered through a 0.22 μm nylon membrane, and the ciprofloxacin content was determined using high-performance liquid chromatography (HPLC). Two parallel samples were set up for each experiment. The relative standard deviation (RSD < 3%) was calculated, and the mean value was used to calculate the loading rate of ciprofloxacin to analyze its loading effect. The constant-temperature shaker temperature was then controlled at 30℃ and 40℃ (±0.5℃), and the above procedure was repeated to obtain the ciprofloxacin loading rate at different temperatures.

[0030] 2. Biochar release experiment Ciprofloxacin-loaded biochar was placed in an Erlenmeyer flask, and 60 mL of medium solution was added. The flask was then placed in a constant-temperature shaker, and the shaking conditions were set (e.g., temperature 24±1 ℃, rotation speed 150 r / min). After starting the shake, a timer was established. At 5, 10, 15, 20, 25, 30, 45, and 60 min, 1 mL of the test solution was quickly taken using a pipette (avoiding aspirating biochar particles from the bottom of the flask; the flask can be tilted or allowed to stand briefly before sampling). After filtration through a 0.22 μm nylon membrane, the ciprofloxacin content was determined using high-performance liquid chromatography (HPLC). After each sampling, 1 mL of fresh medium solution at the same pH and temperature was immediately added to the flask, and shaking was continued to maintain consistent shaking conditions. Two parallel samples were set up for each experiment, and the average value was used as the final data. Medium solutions with different pH values ​​were prepared, and the above operation was repeated for each pH solution to obtain the ciprofloxacin release rate at different pH values.

[0031] (III) Results and Analysis 1. XRD characterization of bagasse char before and after urea modification Figure 1 A comparison of X-ray diffraction (XRD) spectra of raw bagasse biochar (ZZBC) and a urea hydrothermally modified sample (ZZBC-urea) is presented. Both materials exhibit typical broadened diffraction peaks (FWHM≈WHM), corresponding to the characteristic peaks of the (002) crystal plane of amorphous carbon, indicating that the main body of the material is a short-range ordered graphitic microcrystalline structure. Peak fitting calculations revealed that the center position of the diffraction peaks (25.3 peak fitting calculation showed no significant change in the modified peak) and peak intensity (integral area difference <5%) before and after modification, indicating that the hydrothermal modification process did not introduce new crystalline phases or change the degree of graphitization of the carbon matrix. The NH3 and CO2 generated by urea decomposition mainly optimize the pore structure of the material through physical pore-forming effects, rather than reconstructing the carbon skeleton through chemical reactions. In addition, no other impurity peaks (such as inorganic salts or metal oxides) were detected in the spectra, indicating that no mineralization reaction of the carbon matrix occurred during the modification process (semi-quantitative analysis showed ash content <3%).

[0032] Further structural parameter analysis revealed that the graphite crystallite sizes (Lc) calculated based on the Scherrer formula were 1.52 nm (ZZBC) and 1.49 nm (ZZBC-urea), with differences within the error range (±, within nm), confirming that the modification treatment did not significantly affect the crystal growth direction and interlayer spacing of the carbon material. Combined with the slight changes in the ID / IG values ​​(1.08 vs. 1.12) in the Raman spectra, it can be inferred that the modification process mainly affects the surface functional group modification and pore structure regulation of the carbon material, rather than the crystal form transformation of the bulk structure. This finding emphasizes the need to combine multi-scale characterization methods such as surface area analysis (BET) and Fourier transform infrared spectroscopy (FTIR) to systematically analyze the mechanism by which biochar modification affects its adsorption performance. In summary, urea hydrothermal modification mainly optimizes the pore structure and surface properties of biochar through physical processes, while having a relatively small impact on the crystal structure of biochar.

[0033] 2. SEM characterization of bagasse char before and after urea modification Figure 2 Scanning electron microscopy (SEM) analysis revealed the significant regulatory effect of hydrothermal modification on the microstructure of bagasse biochar (ZZBC). The original ZZBC retained the original fibrous structure of bagasse, but the surface now exhibited a small number of pores and irregular irregularities. The fiber diameter ranged from 10 to 20 μm, and the surface displayed longitudinal grooves and a small number of discretely distributed mesopores (pore size approximately 5-8 nm). Its BET specific surface area was only 32.7 m²·g. -1 The relatively smooth fiber surface and limited pore structure result in insufficient physical adsorption sites for ciprofloxacin.

[0034] As shown in the figure, the unmodified bagasse char, with its fibrous structure, provides some support, while the initially formed pores may offer limited drug loading capacity. However, after modification, the structure of the bagasse char changes significantly; the original fibrous structure is destroyed, replaced by numerous cracks. Further magnification reveals that the surface of the modified bagasse char becomes rougher and exhibits more protrusions. This change in surface structure greatly increases the specific surface area and porosity of the bagasse char, enabling it to load more ciprofloxacin and ultimately achieve a higher drug loading.

[0035] 3. BET and BJH analysis of urea-modified bagasse char before and after modification Figure 3 The figures show the BET and BJH curves of bagasse biochar before and after modification. It is clear from the figures that both the pre- and post-modification BET curves belong to type IV isotherms, indicating that both types of bagasse biochar possess a mesoporous structure. After hydrothermal modification, the specific surface area of ​​the bagasse biochar increased to a certain extent, from 188.9 m². 2 ·g-1 Increased to 240.5 m 2 ·g -1 This is more conducive to the loading of ciprofloxacin. However, as seen in the BET plot, the BET curve failed to close, which may be due to the special surface properties of the support, causing the adsorbed gas molecules to not completely detach. The specific reasons still need further investigation.

[0036] In the BJH diagram, the pore size of the unmodified ZZBC was approximately 23.4 nm, while the modified ZZBC-urea showed the presence of mesopores of 28.7 nm as well as micropores smaller than 2 nm. This further demonstrates that after hydrothermal modification with urea, ZZBC not only expanded its original mesopores but also developed a large number of micropores, providing more active sites for ciprofloxacin loading. This is consistent with the conclusions of SEM.

[0037] 4. Infrared spectral analysis of bagasse char before and after urea modification like Figure 4 As shown, before modification, 3445 cm -1 There is a distinct absorption peak at 2926 cm⁻¹, which is the stretching vibration peak of OH; there are two absorption peaks at 2926 cm⁻¹ and 2847 cm⁻¹, which are the stretching vibration peaks of CH; at 1637 cm⁻¹... -1 The peak at 1551 cm⁻¹ is the C=C stretching vibration peak. -1 The peak at 1039 cm⁻¹ is the CN stretching vibration peak, and there are two absorption peaks at 1039 cm⁻¹, which are CO stretching vibration peaks. After modification, the absorption peak at 3445 cm⁻¹ still exists, but the intensity has changed, indicating that the hydroxyl group (-OH) still exists, but may be reduced; the absorption peaks at 2926 cm⁻¹ and 2847 cm⁻¹, 1637 cm⁻¹, 1551 cm⁻¹, 1385 cm⁻¹ and 1029 cm⁻¹ still exist, indicating that the alkyl group (-CH₂ or -CH₃), carbon-carbon double bond (C=C), CN stretching vibration and CO stretching vibration still exist, respectively.

[0038] It is evident that the main functional groups of the sample did not change significantly after modification, but the absorption peak intensity of the hydroxyl group (-OH) decreased, so its content or concentration may have decreased.

[0039] 5. Study on the loading performance of bagasse biochar Figure 5The figures show the loading curves of ciprofloxacin on bagasse biochar before and after modification at different temperatures. It is evident from the figures that the unmodified ZZBC exhibits low ciprofloxacin loading performance, with a loading rate of only 13.4%. The hydrothermally modified ZZBC-urea demonstrates excellent loading performance, achieving a ciprofloxacin loading rate of 77.1% under the same conditions. This is attributed to the pore-expanding effect of urea on ZZBC under hydrothermal conditions, resulting in a larger specific surface area, richer pore structure, and a rougher surface for ZZBC-urea. When the temperature increases to 30 ℃, the ciprofloxacin loading rate of ZZBC-urea slightly increases to 79.6%, mainly due to the increased molecular collision rate at higher temperatures. However, when the temperature continues to rise to 40 ℃, the ciprofloxacin loading rate of ZZBC-urea decreases to 38.8%.

[0040] 6. Study on the release performance of bagasse biochar The release of ZZBC-urea loaded with ciprofloxacin in different media was shown in the release curves as follows: Figure 6 As shown in the figure, ciprofloxacin is released rapidly in neutral buffer solution, with 77.7% of ciprofloxacin released within 5 minutes. However, release in deionized water and acidic buffer solution is relatively slow, reaching the maximum release rate of 74.5% and 71.8% respectively after approximately 20 minutes. The figure also shows that after 60 minutes, about 20% of the ciprofloxacin remains unreleased into the medium. This is because the active sites of ZZBC-urea are largely exposed, resulting in a relatively stable ciprofloxacin loading.

Claims

1. A method for constructing a biochar-based controlled-release system, characterized in that, Includes the following steps: (1) Preparation of bagasse biochar Washed and dried bagasse was pyrolyzed under N2 protection to obtain bagasse biochar ZZBC; (2) Preparation of modified bagasse biochar Urea was dissolved in deionized water. After complete dissolution, bagasse biochar was added, stirred, and the solution was heated to react. After the reaction, the supernatant was removed and the solution was centrifuged. The precipitate was then washed and dried to obtain urea-modified bagasse biochar ZZBC-urea.

2. The construction method according to claim 1, characterized in that, In step (1), the pyrolysis is performed at 600-650℃ for 3 hours.

3. The construction method according to claim 1 or 2, characterized in that, In step (2), the mass ratio of urea to bagasse biochar is 1:

1.

4. The construction method according to claim 1 or 3, characterized in that, In step (2), the stirring time is 30-40 min; the heating reaction is carried out at 150-155℃ for 3 h.

5. A biochar-based controlled-release system prepared by the construction method according to any one of claims 1-4, characterized in that, Ciprofloxacin was loaded into a biochar-based controlled-release system.

6. The biochar-based controlled-release system according to claim 5, characterized in that, The specific loading process is as follows: ZZBC-urea is added to ciprofloxacin solution and subjected to constant temperature shaking.

7. The biochar-based controlled-release system according to claim 6, characterized in that, The ratio of ZZBC-urea to ciprofloxacin solution was 0.05 g: 60 mL; the concentration of ciprofloxacin solution was 10 mg·L⁻¹. -1 .

8. The biochar-based controlled-release system according to claim 6, characterized in that, The constant temperature oscillation is performed in a constant temperature shaker at 24±0.5℃ and 150 rpm for 5-60 minutes.

9. The application of a biochar-based controlled-release system prepared by the construction method according to any one of claims 5-8 in the preparation of targeted drug delivery.

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