Soil carbon sequestration synergistic organic pollutant degradation method based on iron-modified oxygen-carrying biochar material

Abstract

The invention relates to the technical field of biochar materials, in particular to a soil carbon sequestration synergistic organic pollutant degradation method based on an iron-modified oxygen-carrying biochar material. According to the preparation method of the iron-modified oxygen-carrying biochar, iron modification and nano oxygen loading modification are combined, micropores of the prepared iron-modified oxygen-carrying biochar are obviously increased, the opening degree of the pores is increased, and the specific surface area and the number of surface active sites of the material are remarkably increased; the modified biochar material has very excellent performance in the aspects of promoting fixation of organic carbon in soil and adsorbing and degrading antibiotics, and has a relatively good application prospect in soil carbon fixation and emission reduction and pollutant degradation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biochar materials, and particularly relates to a soil carbon sequestration and organic pollutant degradation method based on iron modified oxygen-carrying biochar materials. BACKGROUND

[0002] Soil carbon pool is the largest terrestrial carbon pool, and the soil organic carbon (SOC) storage is about 1550 Pg, which is twice that of the atmospheric carbon pool. SOC, as a key medium, plays a crucial role in the exchange of greenhouse gases between the soil surface and the atmosphere. Paddy soil is one of the most common types of agricultural cultivated soil, and paddy field emission reduction is an important way to achieve carbon neutralization. However, the annual carbon fixation of paddy fields is lower than the carbon emission, resulting in a high level of net carbon emission in paddy fields. Soil extracellular enzymes, as key catalysts for microbial decomposition of organic matter, play an important role in soil carbon cycle. Extracellular enzymes such as β-glucosidase (BG), β-N-acetylglucosaminidase (NAG) and acid phosphatase (ACP) directly affect the mineralization rate and carbon pool stability of soil organic carbon by catalyzing the decomposition of cellulose, chitin and organic phosphorus. Enzyme stoichiometry studies have shown that enzyme activity ratios (such as BG:NAG:ACP) can effectively reflect the carbon, nitrogen and phosphorus limitation of soil microorganisms, and thus affect the decomposition and sequestration of soil organic carbon. In addition, the formation of iron-organic matter complex (Fe-SOC) is an important mechanism for soil carbon sequestration. Iron oxides significantly improve the stability of soil organic carbon and reduce its decomposition rate through physical protection, chemical complexation and biochemical action, thereby enhancing the carbon sequestration capacity of soil. On the other hand, long-term excessive application of livestock manure in paddy fields leads to a large amount of tetracycline antibiotics (TCs) residues, which poses a potential risk to the stability of the ecosystem. Therefore, it is urgent to develop an economic and efficient and environmentally friendly soil carbon sequestration and emission reduction and antibiotic pollution removal technology.

[0003] Studies have shown that the application of biochar and other soil amendments in paddy fields is an easy-to-operate and long-term ecological benefit measure for paddy field carbon sequestration. Biochar can improve the carbon sequestration capacity of paddy soil through affecting extracellular enzyme activity, soil aggregate formation and other pathways. At the same time, biochar is widely used in the remediation of heavy metal, organic pollutant and other environmental problems due to its porous structure, high specific surface area and rich surface functional groups. Traditional biochar can reduce the bioavailability of pollutants through physical adsorption, charge effect and complexation. However, in the face of structurally stable and difficult to degrade antibiotic pollutants, single adsorption often fails to achieve complete removal. SUMMARY

[0004] This invention provides a method for preparing iron-modified oxygen-carrying biochar and its application, as well as a method for soil carbon sequestration and synergistic degradation of organic pollutants based on iron-modified oxygen-carrying biochar materials.

[0005] This invention loads nano-oxygen bubbles into iron-modified biochar materials, which, while retaining the original adsorption properties of biochar, further endow it with oxidation and pollutant degradation properties, significantly improving the effect of biochar materials in promoting soil organic carbon fixation and the degradation of antibiotics such as tetracycline.

[0006] Specifically, the present invention provides the following technical solutions.

[0007] In a first aspect, the present invention provides a method for preparing iron-modified oxygen-carrying biochar, the method comprising: modifying biochar with iron to obtain iron-modified biochar, and then loading nano-oxygen onto the iron-modified biochar. The iron modification includes: acid washing biochar to obtain acid-washed biochar; mixing the acid-washed biochar with an iron source to obtain Fe-impregnated biochar; mixing the Fe-impregnated biochar with a nitrogen source to obtain an Fe-N precursor mixture; and pyrolyzing the Fe-N precursor mixture to obtain pyrolysis products.

[0008] The above preparation method combines iron modification with nano-oxygen loading modification to prepare iron-modified oxygen-carrying biochar. The synergistic effect of iron modification and nano-oxygen loading modification significantly improves the performance of biochar materials. The micropores of biochar materials are significantly increased and the degree of pore opening is increased, which significantly improves the specific surface area and the number of surface active sites, thereby enhancing the oxygen carrying capacity and adsorption performance of the materials. The modified biochar material is significantly better than iron modification and nano-oxygen loading modification alone in promoting soil organic carbon fixation and promoting the degradation of antibiotics such as tetracycline.

[0009] This invention employs an optimized impregnation method to prepare iron-modified biochar. The biochar is impregnated in an iron source solution and mixed with a nitrogen source to prepare an Fe-N precursor mixture. In the pyrolysis step, iron ions react with the biochar at high temperature to form iron-modified biochar.

[0010] In the preparation of iron-modified biochar, the introduction of nitrogen source and the preparation of Fe-N precursor mixture are beneficial to the formation and stabilization of iron active sites, the increase of biochar specific surface area, and the improvement of oxygen carrying capacity.

[0011] In the above method, the pyrolysis preferably includes performing a first pyrolysis and a second pyrolysis in sequence; wherein, the first pyrolysis is performed at a constant temperature of 450-550℃ for 1.5-2.5h, and the second pyrolysis is performed at a constant temperature of 650-750℃ for 0.8-1.5h.

[0012] Preferably, the first pyrolysis is carried out at a constant temperature of 490-510℃ for 1.8-2.2 hours, and the second pyrolysis is carried out at a constant temperature of 690-710℃ for 0.8-1.2 hours.

[0013] The pyrolysis temperature affects the performance of iron-modified biochar. At low temperatures, the biochar has a low degree of graphitization, incomplete pore structure development, and weak interaction between iron ions and biochar. While high temperatures can increase graphitization and porosity, excessively high temperatures can cause the biochar structure to collapse and iron atoms to aggregate. This invention discovers that a two-step gradient pyrolysis method—first isothermal at 450-550℃ for 1.5-2.5 h, then isothermal at 650-750℃ for 0.8-1.5 h—can significantly improve the interaction between iron and biochar, promote iron loading in the biochar, increase the iron loading capacity, and thus improve the adsorption and other properties of iron-modified biochar.

[0014] Preferably, the biochar is straw biochar or rice husk biochar. The above-described pyrolysis method is particularly suitable for straw biochar and rice husk biochar.

[0015] Preferably, in the first pyrolysis, the temperature is 3-20℃ min. -1 Raise the temperature to 450-550℃. After the first pyrolysis, reduce the temperature by 3-20℃ per minute. -1 The temperature is raised to 650-750℃ for a second pyrolysis.

[0016] Preferably, in the first pyrolysis, the temperature is 3-8℃ min. -1 Raise the temperature to 490-510℃. After the first pyrolysis, reduce the temperature by 3-8℃ min. -1 The temperature is raised to 690-710℃ for a second pyrolysis. Preferably, the pyrolysis is carried out under an inert gas atmosphere. The inert gas may be nitrogen.

[0017] Preferably, after pyrolysis, unstable iron species are removed from the pyrolysis products to obtain iron-modified biochar. The removal of unstable iron species can be achieved using conventional methods such as acid washing, for example, by treating with 0.8-2M H₂SO₄ at 75-85℃ for 1-3 hours.

[0018] In the preparation of iron-modified biochar, the iron source includes one or more selected from ferric nitrate, ferric chloride, ferrous acetate, ferrous sulfate, and ferrous oxalate. The nitrogen source includes one or more selected from urea, pyrrole, and imidazole.

[0019] In some embodiments of the present invention, the iron source is ferric nitrate. Preferably, the acid-washed biochar is impregnated in an iron source solution. Preferably, the concentration of Fe ions in the iron source solution is 0.1-0.2 M. Preferably, the acid-washed biochar and the iron source are mixed under stirring conditions for 1-3 hours. After stirring, the mixture is dried to obtain Fe-impregnated biochar.

[0020] In some embodiments of the present invention, the nitrogen source is urea or imidazole.

[0021] Preferably, the ratio of the iron source to the acid-washed biochar is 1-5 mmol: 5g.

[0022] Preferably, the mass ratio of the Fe-impregnated biochar to the nitrogen source is 1:(3-5).

[0023] In the preparation of iron-modified biochar, the main role of acid washing is to optimize the physical structure and surface chemical properties of the biochar, creating more favorable conditions for subsequent iron loading.

[0024] The acid used for pickling can be any acid commonly used in the pickling step of biochar modification, preferably a strong acid or a medium-strong acid.

[0025] Preferably, the acid used for pickling includes one or more selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids.

[0026] In some embodiments of the present invention, the acid is hydrochloric acid. Preferably, the concentration of the hydrochloric acid is 0.8-2M.

[0027] Preferably, after acid washing, the biochar is dried, then washed with water, filtered, and then dried again to obtain clean acid-washed biochar for subsequent reactions.

[0028] In the above method, the drying can be carried out at 70-90℃.

[0029] In the above method, the loading of nano-oxygen includes: (1) vacuuming iron-modified biochar; (2) mixing the vacuumed iron-modified biochar with oxygen under high pressure to load nano-oxygen.

[0030] Preferably, the high-pressure condition is 0.18-0.25 MPa (more preferably 0.18-0.22 MPa). The nano-oxygen loading is performed by mixing with oxygen under high-pressure conditions for 20-500 min.

[0031] Preferably, the vacuuming process involves maintaining a negative pressure vacuum for 2-8 hours under a pressure of -0.08 to -0.15 MPa.

[0032] Preferably, the above operations (1) and (2) are repeated 1-2 times to obtain iron-modified oxygen-carrying biochar.

[0033] In some embodiments of the present invention, the iron-modified biochar is subjected to a negative pressure vacuum maintained at a pressure of -0.08 to -0.15 MPa for 4-5 hours, followed by the introduction of oxygen at 0.18-0.22 MPa and maintenance of this pressure for 20-40 minutes. Then, a negative pressure vacuum is applied again at a pressure of -0.08 to -0.15 MPa for 1-3 hours, followed by the introduction of oxygen at 0.18-0.22 MPa and high-pressure oxygen loading for 5-7 hours.

[0034] Preferably, the purity of the oxygen is 99-100%.

[0035] Secondly, the present invention provides an iron-modified oxygen-carrying biochar, which is prepared by the iron-modified oxygen-carrying biochar preparation method described in the first aspect above.

[0036] The iron-modified oxygen-carrying biochar is loaded with both iron and nano-oxygen.

[0037] Thirdly, the present invention provides a method for preparing the iron-modified oxygen-carrying biochar described above, or any of the following applications of the iron-modified oxygen-carrying biochar: (1) Application in promoting soil carbon sequestration; (2) Application in promoting soil carbon reduction; (3) Application in promoting antibiotic degradation in the environment.

[0038] The promotion of soil carbon sequestration or promotion of soil carbon emission reduction includes inhibiting soil extracellular enzyme activity, increasing soil carbon limitation, inhibiting organic carbon decomposition, and / or increasing the content of iron-bound organic carbon in the soil.

[0039] The antibiotic is preferably tetracycline. The environment is preferably a soil environment.

[0040] In this invention, the soil is preferably paddy field soil.

[0041] Fourthly, the present invention provides a method for soil carbon sequestration and / or degradation of organic pollutants, the method comprising: applying the iron-modified oxygen-carrying biochar described above to the soil.

[0042] Preferably, the organic compound is an antibiotic.

[0043] The beneficial effects of this invention include at least the following: The iron-modified oxygen-carrying biochar preparation method provided by this invention combines iron modification with nano-oxygen loading modification to prepare iron-modified oxygen-carrying biochar, which significantly increases the micropores and the degree of pore opening, thereby significantly improving the specific surface area and the number of surface active sites of the material, thus enhancing the oxygen carrying capacity and adsorption performance of the material. This modified biochar material performs very well in promoting soil organic carbon fixation and adsorbing and degrading antibiotics, and has good application prospects in soil carbon sequestration and emission reduction and pollutant degradation. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the preparation process of iron-modified oxygen-carrying biochar in Example 1 of the present invention.

[0046] Figure 2 The images are scanning electron microscope (SEM) images of unmodified biochar (BC), iron-modified oxygen-carrying biochar (FeOC) of Example 1, nano-oxygen biochar (BOC) of Comparative Example 1, and iron-modified biochar (FeC) of Comparative Example 2 in the experimental examples of this invention.

[0047] Figure 3 The results of oxygen carrying capacity determination of different biochars in the experimental examples of this invention are shown. Among them, a is a comparison between iron-modified oxygen-carrying biochar (FeOC) of Example 1 and unmodified biochar (BC), and modified biochar (BOC, FeC) prepared in Comparative Examples 1 and 2. b is a comparison between iron-modified oxygen-carrying biochar (FeOC) of Example 2 and unmodified biochar (BC), and modified biochar (BOC, FeC) prepared in Comparative Examples 3 and 4.

[0048] Figure 4 The results of soil extracellular enzyme activity determination using different treatments of iron-modified oxygen-carrying biochar (FeOC) from Example 1, unmodified biochar (BC), and modified biochar (BOC, FeC) prepared in Comparative Examples 1 and 2 are presented in the experimental examples of this invention. In the examples, (a): BG represents β-1,4-glucosidase; (b): CBH represents cellobiose hydrolase; (c): NAG represents β-1,4-N-acetylglucosidase; (d): LAP represents leucine aminopeptidase; and (e): ACP represents acid phosphatase. Significant differences between treatments (P<0.05) are represented by different letters.

[0049] Figure 5The stoichiometric regression analysis of the activities of carbon, nitrogen, and phosphorus capture enzymes under different treatments in the experimental examples of this invention includes: (a) the relationship between the relative activities of carbon capture enzymes and nitrogen capture enzymes; (b) the relationship between the relative activities of carbon capture enzymes and phosphorus capture enzymes; (c) the relationship between the relative activities of nitrogen capture enzymes and phosphorus capture enzymes; and (d) linear regression analysis to determine the relationship between microbial C limitation and microbial N / P limitation.

[0050] Figure 6 The figures represent the content of bound organic carbon during the tillering stage of different treatments of iron-modified oxygen-carrying biochar (FeOC) from Example 1, unmodified biochar (BC), and modified biochar (BOC, FeC) prepared in Comparative Examples 1 and 2, respectively. Significant differences (P<0.05) between different treatments are represented by different letters.

[0051] Figure 7 The adsorption kinetic curves are for the iron-modified oxygen-carrying biochar (FeOC) of Example 1, the unmodified biochar (BC), and the modified biochar (BOC, FeC) prepared in Comparative Examples 1 and 2, respectively, used in the experimental examples of this invention.

[0052] Figure 8 The figures represent the removal rates of tetracycline by different biochar materials in the experimental examples of this invention (24h). Among them, a is a comparison between the iron-modified oxygen-carrying biochar (FeOC) of Example 1 and the unmodified biochar (BC), and the modified biochar (BOC, FeC) prepared in Comparative Examples 1 and 2; b is a comparison between the iron-modified oxygen-carrying biochar (FeOC) of Example 2 and the unmodified biochar (BC), and the modified biochar (BOC, FeC) prepared in Comparative Examples 3 and 4. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] The common straw biochar used in the following examples and comparative examples is corn straw biochar purchased from Henan Lize Environmental Protection Technology Co., Ltd.

[0055] Example 1 This embodiment provides a method for preparing iron-modified oxygen-carrying biochar (FeOC), which includes the following steps (the preparation process is as follows). Figure 1 (as shown) (1) Preparation of iron-modified biochar: Weigh an appropriate amount of corn stalk biochar that has been ground through a 60-mesh sieve and place it in a 2L beaker. Add 1 mol·L⁻¹ -1 Hydrochloric acid was used to completely submerge the biochar. After thorough stirring, the mixture was placed in an oven and the temperature was adjusted to 80°C. Once no moisture remained in the beaker, acid-washed straw biochar was obtained. This was then washed with water, filtered, and dried further in the oven to obtain clean acid-washed straw biochar. 2.75 mmol (1.11 g) of Fe(NO3)3·9H2O was dissolved in 20 mL of deionized water, and 5 g of clean acid-washed straw biochar was added. The mixture was stirred thoroughly on a magnetic stirrer for 2 hours and then dried in an oven at 80°C. Afterward, it was mixed evenly with 20 g of urea in a mortar to obtain an Fe-N precursor mixture (i.e., iron-nitrogen-doped biochar). This mixture was placed in a quartz boat and heated in a tube furnace under nitrogen protection at 5°C / min. -1 Heat to 500°C and hold for 2 hours, then increase the temperature by 5°C / min. -1 The temperature was raised to 700°C and held for 1 hour. After cooling, the pyrolysis product was treated with 1.0 M H2SO4 at 80°C for 2 hours to remove unstable iron species, thus obtaining iron-modified biochar.

[0056] (2) Iron-modified biochar loaded with nano-oxygen: The iron-modified biochar obtained above was subjected to high-pressure oxygen loading as follows: The iron-modified biochar was transferred to a vacuum flask and vacuumed for 6 hours at a pressure of -0.1 MPa. The biochar material in the vacuum flask was transferred to a high-pressure sealed device, and 99.99% pure oxygen was introduced at a pressure of 0.2 MPa and maintained at this pressure for 30 minutes. After the device naturally depressurized to atmospheric pressure, the biochar material was removed from the high-pressure device and placed back into the vacuum flask. Vacuuming was performed for 2 hours at a pressure of -0.1 MPa. After the vacuuming was completed, the biochar material was transferred back to the high-pressure device and 99.99% pure oxygen was introduced at a pressure of 0.2 MPa for 6 hours. After the high-pressure device naturally depressurized until the internal pressure was equal to the external atmospheric pressure, the biochar material was removed, and iron-modified oxygen-loaded biochar was obtained.

[0057] This embodiment also provides iron-modified oxygen-carrying biochar prepared by the above method.

[0058] Example 2 This embodiment provides a method for preparing iron-modified oxygen-carrying biochar (FeOC), which includes the following steps: (1) Preparation of iron-modified biochar: Weigh an appropriate amount of rice husk biochar that has been ground through a 60-mesh sieve and place it in a 2L beaker. Add 1 mol·L⁻¹ -1Hydrochloric acid was used to completely submerge the biochar. After thorough stirring, the mixture was placed in an oven and the temperature was adjusted to 80°C. Once the beaker was free of moisture, acid-washed straw biochar was obtained. It was then washed with water, filtered, and dried further in the oven to obtain clean acid-washed straw biochar. 2.75 mmol (1.11 g) of Fe(NO3)3·9H2O was dissolved in 20 mL of deionized water, and 5 g of clean acid-washed straw biochar was added. The mixture was stirred thoroughly on a magnetic stirrer for 2 hours and then dried in an oven at 80°C. Afterward, it was mixed evenly with 20 g of imidazole in a mortar to obtain an Fe-N precursor mixture. This mixture was placed in a quartz boat and heated in a tube furnace under nitrogen protection at 7°C·min. -1 Heat to 500°C and hold for 2 hours, then increase the temperature by 7°C / min. -1 The temperature was raised to 700°C and held for 1 hour. After cooling, the pyrolysis product was treated with 1.0 M H2SO4 at 80°C for 2 hours to remove unstable iron species, thus obtaining iron-modified biochar.

[0059] (2) Iron-modified biochar loaded with nano-oxygen: The iron-modified biochar obtained above was subjected to high-pressure oxygen loading as follows: The iron-modified biochar was transferred to a vacuum flask and vacuumed for 6 hours at a pressure of -0.15 MPa. The biochar material in the vacuum flask was transferred to a high-pressure sealed device, and 99.99% pure oxygen was introduced at a pressure of 0.22 MPa and maintained at this pressure for 30 minutes. After the device naturally depressurized to atmospheric pressure, the biochar material was removed from the high-pressure device and placed back into the vacuum flask. Vacuuming was performed for 2 hours at a pressure of -0.15 MPa. After the vacuuming was completed, the biochar material was transferred back to the high-pressure device and 99.99% pure oxygen was introduced at a pressure of 0.22 MPa for 6 hours. After the high-pressure device naturally depressurized until the internal pressure was equal to the external atmospheric pressure, the biochar material was removed, and iron-modified oxygen-loaded biochar was obtained.

[0060] This embodiment also provides iron-modified oxygen-carrying biochar prepared by the above method.

[0061] Comparative Example 1 This comparative example provides a method for preparing nano-oxygen biochar (BOC), the steps of which are as follows: Weigh an appropriate amount of corn stalk biochar (same as in Example 1) that has passed through a 60-mesh sieve, transfer it to a vacuum flask, and maintain a vacuum at -0.1 MPa for 6 hours. Transfer the biochar material in the vacuum flask to a high-pressure sealed device, and purge with 99.99% pure oxygen at 0.2 MPa for 30 minutes. After the device naturally depressurizes to atmospheric pressure, remove the biochar material from the high-pressure device, place it back into the vacuum flask, and vacuum it at -0.1 MPa for 2 hours. After vacuuming, transfer the biochar material back to the high-pressure device, purge with 99.99% pure oxygen at 0.2 MPa, and maintain high-pressure oxygen loading for 6 hours. After the high-pressure device naturally depressurizes until the internal pressure equals the external atmospheric pressure, remove the biochar material to obtain nano-oxygen biochar material.

[0062] This comparative example also provides nano-oxygen biochar materials prepared using the above method.

[0063] Comparative Example 2 This comparative example provides a method for preparing iron-modified biochar (FeC), the steps of which are as follows: Weigh an appropriate amount of corn stalk biochar (same as in Example 1) that has been ground through a 60-mesh sieve and place it in a 2L beaker, add 1 mol·L⁻¹ -1 Hydrochloric acid was used to completely submerge the biochar. After thorough stirring, the mixture was placed in an oven and the temperature was adjusted to 80°C. Once the beaker was free of moisture, acid-washed straw biochar was obtained. It was then washed with water, filtered, and dried further in the oven to obtain clean acid-washed straw biochar. 2.75 mmol (1.11 g) of Fe(NO3)3·9H2O was dissolved in 20 mL of deionized water, and 5 g of clean acid-washed straw biochar was added. The mixture was stirred thoroughly on a magnetic stirrer for 2 hours, then dried in an 80°C oven. Afterward, it was mixed evenly with 20 g of urea in a mortar, placed in a quartz boat, and heated in a tube furnace under nitrogen protection at 5°C / min. -1 Heat to 500°C and hold for 2 hours, then increase the temperature by 5°C / min. -1 The temperature was raised to 700°C and held for 1 hour. After cooling, the pyrolysis product was treated with 1.0 M H2SO4 at 80°C for 2 hours to remove unstable iron species, thus obtaining iron-modified biochar.

[0064] This comparative example also provides iron-modified biochar prepared using the above method.

[0065] Comparative Example 3 This comparative example provides a method for preparing nano-oxygen biochar (BOC), the steps of which are as follows: Weigh an appropriate amount of rice husk biochar (same as in Example 2) that has passed through a 60-mesh sieve, transfer it to a vacuum flask, and maintain a vacuum at -0.15 MPa for 6 hours. Transfer the biochar material in the vacuum flask to a high-pressure sealed device, and purge with 99.99% pure oxygen at 0.22 MPa, maintaining this pressure for 30 minutes. After the device naturally depressurizes to atmospheric pressure, remove the biochar material from the high-pressure device, place it back into the vacuum flask, and vacuum at -0.15 MPa for 2 hours. After vacuuming, transfer the biochar material back to the high-pressure device, and purge with 99.99% pure oxygen at 0.22 MPa for 6 hours. After the high-pressure device naturally depressurizes until the internal pressure equals the external atmospheric pressure, remove the biochar material to obtain iron-modified oxygen-carrying biochar.

[0066] This comparative example also provides nano-oxygen biochar materials prepared using the above method.

[0067] Comparative Example 4 This comparative example provides a method for preparing iron-modified biochar (FeC), the steps of which are as follows: Weigh an appropriate amount of rice husk biochar (same as in Example 2) that has been ground through a 60-mesh sieve and place it in a 2L beaker, add 1 mol·L⁻¹ -1 Hydrochloric acid was used to completely submerge the biochar. After thorough stirring, the mixture was placed in an oven and the temperature was adjusted to 80°C. Once no moisture remained in the beaker, acid-washed straw biochar was obtained. This was then washed with water, filtered, and dried further in the oven to obtain clean acid-washed straw biochar. 2.75 mmol (1.11 g) of Fe(NO3)3·9H2O was dissolved in 20 mL of deionized water, and 5 g of clean acid-washed straw biochar was added. The mixture was stirred thoroughly on a magnetic stirrer for 2 hours, then dried in an oven at 80°C. Afterward, it was mixed evenly with 20 g of imidazole in a mortar to obtain an Fe-N precursor mixture. This mixture was placed in a quartz boat and heated in a tube furnace under nitrogen protection at 7°C·min. -1 Heat to 500°C and hold for 2 hours, then increase the temperature by 7°C / min. -1 The temperature was raised to 700°C and held for 1 hour. After cooling, the pyrolysis product was treated with 1.0 M H2SO4 at 80°C for 2 hours to remove unstable iron species, thus obtaining iron-modified biochar.

[0068] This comparative example also provides iron-modified biochar prepared using the above method.

[0069] Experimental Example Based on the above embodiments and comparative examples, indoor tetracycline removal experiments and pot experiments were conducted to detect the oxygen carrying capacity, tetracycline adsorption effect, quantitative measurement of carbon limitation by soil extracellular enzyme activity, and carbon fixation effect of iron-organic matter complex related to rhizosphere iron-carbon coupling mechanism of different biochar materials. The effects of different biochar materials on the organic carbon content and tetracycline degradation of paddy soil were analyzed.

[0070] Five treatments were set up for the indoor tetracycline removal experiment and the pot experiment: blank control (CK), ordinary straw biochar addition (BC), nano oxygen biochar addition (BOC, comparative example 1 or comparative example 3), iron modified biochar (FeC, comparative example 2 or comparative example 4) addition, and iron modified oxygen-carrying biochar (FeOC, example 1 or example 2) addition. The specific experimental methods and results are as follows.

[0071] 1. Experimental materials Soil: The soil used in the experiment was taken from paddy field soil of the control (CK) in the Qingpu Modern Agricultural Park to ensure a consistent soil background and reduce the impact of soil differences on the experimental results. The basic physicochemical properties of the soil before the experiment were: total nitrogen 1.70 g·kg⁻¹ -1 Total phosphorus 0.95 g·kg -1 0.11 g·kg of readily available potassium -1 Organic matter 29.60 g·kg -1 The pH value is 7.02.

[0072] 2. Potted plant experiment steps Rice seedling cultivation: Select plump, undamaged rice seeds of the Qingxiang Ruanjing variety. Soak the rice seeds in deionized water for 48 hours, then soak them in 10% H2O2 for 10 minutes with constant stirring. After soaking, rinse four times with deionized water. After screening and sterilization, spread the seeds evenly in petri dishes and cover with plastic wrap (with holes punched in the wrap). Place the petri dishes in the dark for 72 hours to germinate. After germination, place the seeds on a ceramic dish lined with two layers of gauze and keep them moist. Set the photoperiod to 14 hours daytime and 10 hours nighttime, and the temperature to 23℃. After two weeks of cultivation (when the seedlings grow to 5-7cm), place three seedlings in each 50mL centrifuge tube for further cultivation (wrapped and secured with sterile absorbent cotton). First, place them in deionized water for one day to acclimatize, then place them in 40mL nutrient solution for one week (changing the solution every 2-3 days).

[0073] White plastic buckets with a bottom diameter of 13.5 cm and a height of 16 cm were used for the pot experiment. The soil was taken from paddy fields in Qingpu Modern Agricultural Park. The fresh soil was manually removed of residues, air-dried, and sieved through a 20-mesh sieve. Each bucket contained 1.5 kg of sieved dry soil. Different biochar materials (ordinary straw biochar (BC), nano-oxygen biochar (BOC), iron-modified biochar (FeC), and iron-modified oxygen-carrying biochar (FeOC)) were mixed with the soil at a ratio of 1% and then placed into the bucket.

[0074] One day after watering, rice seedlings were transplanted, with three seedlings per hole in each pot. The relevant parameters in the smart climate chamber were set as follows: daytime temperature 28℃, nighttime temperature 25℃, average humidity 70%, daytime duration 14 hours, and nighttime duration 10 hours. Base fertilizer was applied on the same day as transplanting the rice seedlings on December 24, 2022, including 150 kg·hm² of fertilizer. -2 N, 60kg·hm -2 P2O5, 60 kg·hm -2 K2O. Tillering fertilizer was applied on January 14, 2023, including 90 kg·hm². -2 N. Topdressing fertilizer was applied on February 12, 2023, including 60 kg·hm². -2 N. Topdressing fertilizer for seedling growth was applied on June 27, 2023, including 60 kg·hm². -2 N, 30kg·hm -2 P2O5, 30 kg·hm -2 K2O. The nitrogen fertilizer is urea, the phosphorus fertilizer is superphosphate, and the potassium fertilizer is potassium chloride. No drainage is required during the growing season; the water level should always be maintained at 1-3 cm. The rice growth should be observed regularly, and pests and diseases should be controlled by spraying imidacloprid, acetamiprid, and pyridaben.

[0075] Based on the rice growth, three replicates were randomly selected from nine replicates in each treatment at the tillering, heading, and maturity stages for destructive sampling.

[0076] 3. Indoor tetracycline removal test procedure Prepare 5 mg·L -1Tetracycline solution of a certain concentration was prepared, and 50 mg of iron-modified oxygen-carrying biochar (FeOC), iron-modified biochar (FeC), nano-oxygen biochar (BOC), and ordinary straw biochar (BC) were added to conical flasks, respectively, with a system volume of 100 mL. The samples were placed in a constant-temperature shaker (25℃, 200 rpm), and 1 mL of the reaction solution was collected at 0.1 h, 1 h, 2 h, 4 h, and 24 h. After filtration through a 0.22 μm organic filter membrane, the samples were analyzed by HPLC. All samples were measured in triplicate, and the average value was taken. The adsorption kinetic equations were fitted using pseudo-first-order kinetic equations (Equation 1) and pseudo-second-order kinetic equations (Equation 2), and the adsorption behavior of the biochar materials was determined based on the degree of fit.

[0077] 4. Measurement Items and Experimental Methods Determination of oxygen carrying capacity of different biochar materials: Using an oxygen carrying capacity measuring device, nitrogen gas was introduced into the left three-necked flask to purge the air. Different biochar materials to be tested were added and stirred to release oxygen into the right three-necked flask to complete the titration. The actual oxygen carrying capacity was then calculated.

[0078] The specific method is as follows: Add 0.02 mol·L⁻¹ to a 50 mL acid burette. -1 Add acidic KMnO4 to the 0 mark. Add 300 mL of deoxygenated water to the left-hand three-necked flask, and purge the air from the system by introducing nitrogen gas from the left side. When the dissolved oxygen meter reading is stable at 0, add 200 mL of 0.01 mol·L⁻¹ ... -1 Na₂SO₃. Quickly add 0.5g of the biochar to be tested to the left-hand three-necked flask, continuously purge the apparatus with nitrogen gas, and turn on the stirring and heating functions of the magnetic stirrer on the left-hand three-necked flask. When the dissolved oxygen meter reading is stable at 0, use 0.02mol·L⁻¹... -1 KMnO4 titration of 0.01 mol·L⁻¹ in the three-necked flask on the right -1 Na2SO3 until the solution turns light red and does not recover within 30 seconds. Record the titration endpoint and calculate the oxygen-carrying capacity of the oxygen-carrying biochar according to the following formula.

[0079] Where M represents the total amount of biochar-supported nano-oxygen added in the determination (mg·g). -1 ); , The concentrations (mol·L⁻¹) of sodium sulfite and acidic potassium permanganate solutions, respectively. -1 ), and The values ​​represent the volumes (L) used for sodium sulfite and acidic potassium permanganate, respectively, and m(biochar) represents the mass (g) of biochar added during the test.

[0080] Soil SOC: Determined using flow analysis. Weigh 0.2000–0.3000 g of air-dried soil sample (passed through a 100-mesh sieve) into a 100 mL digestion tube, add 5 mL of concentrated sulfuric acid and shake well, then add 10 drops of perchloric acid and shake well again. Place a small funnel over the mouth of the tube and heat to 120 °C in a digestion oven until the solution turns white and becomes transparent, then continue digestion for another 20 minutes. Rinse the cooled digested solution with small amounts of water several times into a 500 mL volumetric flask. After cooling, dilute to 500 mL with water, filter or clarify, and then prepare for analysis. Perform a sample blank simultaneously. After obtaining the digested solution, select the assay program and perform the analysis.

[0081] Soil extracellular enzyme activity: Five soil extracellular enzymes belonging to the hydrolytic enzyme class were selected for assay, including carbon-acquired enzymes: β-1,4-glucosidase (BG) and cellobiase (CBH); nitrogen-acquired enzymes: β-N-acetylglucosidase (NAG) and leucine aminopeptidase (LAP); and phosphorus-acquired enzyme: acid phosphatase (ACP). All assays were performed using a 96-well microplate fluorescence assay. Absorbance values ​​were measured at specific wavelengths using a multi-functional microplate reader (Synergy 2 Microplate Reader, Biotek, USA). All kits used for measuring soil extracellular enzyme activity were purchased from Sangon Biotech (Shanghai) Co., Ltd.

[0082] The main functions of various extracellular enzymes are shown in Table 1.

[0083] Table 1. Detailed information on soil extracellular enzymes

[0084] Soil iron-bound organic carbon: Treatment group: 0.5g of soil was added to 15mL of a 0.27M trisodium citrate-0.1M sodium bicarbonate solution, mixed, and heated in a water bath to 80℃. 0.25g of sodium dithionite was added, and the mixture was heated in a water bath for 15min. Control group: 0.5g of soil was added to 15mL of a 1.6M sodium chloride-0.1M sodium bicarbonate solution, mixed, and heated in a water bath to 80℃. 0.22g of sodium chloride was added, and the mixture was heated in a water bath for 15min. The mixture was centrifuged at 3000g for 20min. The supernatant from the treatment group was stored in a separate centrifuge tube. The supernatant from the control group was discarded, and the residue was rinsed multiple times with 5mL of deionized water. The deionized water was discarded, and the residue in the tubes was freeze-dried. The organic carbon content was measured using a total organic carbon analyzer. The iron-bound organic carbon content was calculated based on the difference between the organic carbon content of the control and treatment groups.

[0085] 5. Results Scanning electron micrographs of different biochars are shown below. Figure 2As shown, the results indicate that ordinary straw biochar exhibits typical porous characteristics. After oxygen loading treatment, the pores expand and become loose, increasing the open structure. Iron modification causes the collapse of the original macropores but forms more micropores, increasing the specific surface area. Iron-modified oxygen-loaded biochar combines the two modification methods. On the basis of iron-induced pore collapse and the formation of micropores, the oxygen loading process further expands and loosens the pores. Although this dual modification causes the collapse of some macropores, the increase in micropores and the opening of pores significantly improve the specific surface area and the number of surface active sites, thereby enhancing the oxygen loading capacity and adsorption performance. It can show higher potential in applications such as pollutant removal and oxidation reactions.

[0086] Depend on Figure 3 As can be seen from a, both unloaded ordinary straw biochar (BC) and iron biochar (FeC) have low oxygen loading capacities, at 3.98 mg·g⁻¹. -1 and 2.21 mg·g -1 Among them, the oxygen loading capacity of FeC was even lower than that of BC, possibly because the introduction of iron atoms occupied some oxygen-containing functional groups under oxygen-free conditions, leading to a decrease in the overall surface oxygen content. However, after loading nano-oxygen bubbles, the oxygen loading capacity was significantly improved. The oxygen loading capacity of BOC increased to 14.02 mg·g⁻¹. -1 It is about 3.5 times that of BC. The oxygen carrying capacity of FeOC reaches 18.06 mg·g. -1 The oxygen content was the highest among all samples, exceeding that of oxygen-loaded BOC and iron-modified FeC. This indicates that the presence of iron facilitates the binding of oxygen to the biochar material, allowing the material to load more oxygen. Figure 3 As shown in b, the rice husk biochar used in Example 2, after iron-modified oxygen loading treatment, obtained similar results to those in Example 1, wherein the oxygen loading capacity of FeOC was significantly higher than that of BC, FeC and BOC.

[0087] Figure 4 The results show the results of soil extracellular enzyme measurements obtained from the rhizosphere soil of rice plants in pots during the destructive selection period (tillering stage). The activities of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosidase (NAG), leucine aminopeptidase (LAP), and acid phosphatase (ACP) in the BOC treatment were significantly lower than those in the CK treatment (P<0.05). The activities of BG, LAP, and ACP in the FeOC treatment were significantly lower than those in the CK treatment (P<0.05), and the activities of BG, LAP, and ACP were also lower than those in the FeC treatment.

[0088] Depend on Figure 5 From a and b, it can be seen that the synergistic relationship between the activities of carbon-acquired enzymes and nitrogen and phosphorus-acquired enzymes is weak among different treatments, and the activities of nitrogen-acquired enzymes and phosphorus-acquired enzymes are also relatively independent. Figure 5(c) This indicates a decoupling phenomenon between the activities of different hydrolases, suggesting heterogeneous nutrient limitation. Figure 5 As can be seen from d, compared to the CK treatment, the BOC treatment is farther from the origin of the coordinate system, which indicates that it exhibits a higher carbon limitation, thereby inhibiting the decomposition of organic carbon by microorganisms and increasing the soil organic carbon content. Furthermore, all treatments show that phosphorus limitation is dominant (the central point clusters are all located above the diagonal line between the starting point of the drawing and the 1:1 position). In other words, the nutrient limitation pattern is often complex, and different treatments may be subject to multiple nutrient limitations.

[0089] Depend on Figure 6 It can be seen that the FeOC treatment significantly increased the content of iron-bound organic carbon in the soil compared with other treatments, with an iron-bound organic carbon content of 0.21%, which is twice that of the CK treatment. The increase in iron-bound organic carbon content can improve the stability of soil organic carbon and reduce its decomposition rate, thereby enhancing the soil's carbon sequestration capacity.

[0090] like Figure 7 As shown, the fitting results of the adsorption kinetic curves of the four materials exhibit significant differences. The pseudo-first-order model fitting goodness (R²=0.953) of ordinary biochar is higher than that of the pseudo-second-order model (R²=0.872), indicating that its adsorption process is dominated by physical diffusion, which is related to the rich pore structure of the surface. The pseudo-second-order model fitting goodness of the three modified materials (BOC, FeC, and FeOC) is higher than that of the pseudo-first-order model, indicating that chemisorption is the dominant mechanism, but physical adsorption still participates in adsorption. Among them, the pseudo-second-order model fitting of FeOC is the best (R²=0.995), and its possible mechanism for tetracycline removal is that oxygen-containing functional groups enrich pollutants through complexation and remove pollutants through redox reactions, making its equilibrium adsorption capacity 1.79, 1.26, and 1.12 times that of BC, BOC, and FeC, respectively. The initial adsorption rate of the modified materials is significantly increased (2.3-3.8 times), while BC reaches adsorption equilibrium rapidly within 60 min due to insufficient surface active sites. BOC and FeC exhibited a secondary adsorption plateau during the equilibrium phase (90-150 min), indicating that the adsorption process of this material involves both physical filling and chemical adsorption stages.

[0091] Depend on Figure 8 As shown in section a, the removal rates of tetracycline by the four materials BC, BOC, FeC, and FeOC reached 50.9%, 75.0%, 56.6%, and 76.8% respectively after 24 hours. Among them, FeOC and BOC showed significantly higher removal rates of tetracycline than BC and FeC, indicating that both ordinary biochar oxygen-carrying and iron-modified biochar oxygen-carrying can significantly increase the oxidation performance of biochar materials, thereby efficiently removing tetracycline pollutants. Figure 8As can be seen from b, in Example 2, the treatment with oxygen-loaded oxygen after iron modification using rice husk biochar resulted in a significantly higher tetracycline removal rate than BC and FeC, reaching 82.7% after 24 hours.

[0092] This invention analyzed the effects of applying different biochar materials on tetracycline removal and organic carbon sequestration in paddy field soil through indoor and pot experiments. Furthermore, it elucidated the removal effect and carbon sequestration mechanism from the perspectives of oxygen carrying capacity, adsorption performance, extracellular enzyme activity, carbon-limited production, and the content of iron-bound organic carbon in the soil. The experimental results are summarized and analyzed below.

[0093] (1) Effects of oxygen carrying capacity and adsorption capacity on soil carbon sequestration Different biochar materials exhibit significant differences in oxygen loading capacity. Both unloaded ordinary biochar and iron-modified biochar have low oxygen loading capacities, with iron-modified biochar even lower than ordinary biochar, possibly due to the introduction of iron atoms occupying some oxygen-containing functional groups. Loading with nano-oxygen bubbles significantly increases oxygen loading, with iron-modified oxygen-carrying biochar reaching the highest capacity, indicating that iron facilitates the binding of oxygen to biochar materials. Adsorption kinetics experiments show that ordinary biochar is dominated by physical diffusion, while modified materials are dominated by chemical adsorption. Among these, iron-modified oxygen-carrying biochar exhibits the best adsorption performance; its tetracycline removal mechanism may involve the complexation and enrichment of pollutants by oxygen-containing functional groups, followed by the removal of pollutants by iron sites through redox reactions.

[0094] (2) Iron-modified oxygen-carrying biochar promotes soil carbon sequestration in paddy fields by increasing the carbon limitation of extracellular enzymes in the soil. Experimental results showed that the application of iron-modified oxygen-carrying biochar mainly inhibited the activity of soil extracellular enzymes. This may be because the biochar material has a large specific surface area and porosity, which may lead to the adsorption and separation of soil extracellular enzymes from substrates, resulting in enzymes lacking substrates and thus reducing their activity. The application of iron-modified oxygen-carrying biochar can increase the carbon limitation of paddy field soil, thereby restricting microbial metabolism and inhibiting the decomposition of organic carbon.

[0095] (3) Iron-modified oxygen-carrying biochar promotes soil carbon sequestration in paddy fields by increasing the content of iron-bound organic carbon in the soil. Experimental results show that applying iron-modified oxygen-carrying biochar can promote the increase of iron-bound organic carbon content in soil. On the one hand, it promotes the formation of soil aggregates through physical protection of SOC; on the other hand, it promotes the chemical co-precipitation of iron oxides and organic carbon to form closed-state organic matter, thereby reducing the bioavailability of SOC and improving the stability of SOC, thus promoting carbon sequestration in paddy soil.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing iron-modified oxygen-carrying biochar, characterized in that, The method includes: modifying biochar with iron to obtain iron-modified biochar, and then loading nano-oxygen onto the iron-modified biochar. The iron modification includes: acid washing biochar to obtain acid-washed biochar; mixing the acid-washed biochar with an iron source to obtain Fe-impregnated biochar; mixing the Fe-impregnated biochar with a nitrogen source to obtain an Fe-N precursor mixture; and pyrolyzing the Fe-N precursor mixture to obtain pyrolysis products.

2. The method for preparing iron-modified oxygen-carrying biochar according to claim 1, characterized in that, The pyrolysis includes sequentially performing a first pyrolysis and a second pyrolysis; wherein the first pyrolysis is performed at a constant temperature of 450-550℃ for 1.5-2.5 hours, and the second pyrolysis is performed at a constant temperature of 650-750℃ for 0.8-1.5 hours.

3. The method for preparing iron-modified oxygen-carrying biochar according to claim 2, characterized in that, In the first pyrolysis, at 3-20℃ min -1 Heat to 450-550℃; And / or, after the first pyrolysis, at 3-20℃ min -1 The temperature is raised to 650-750℃ for a second pyrolysis.

4. The method for preparing iron-modified oxygen-carrying biochar according to any one of claims 1 to 3, characterized in that, The iron source includes one or more selected from ferric nitrate, ferric chloride, ferrous acetate, ferrous sulfate, and ferrous oxalate. And / or, the nitrogen source includes one or more selected from urea, pyrrole, and imidazole.

5. The method for preparing iron-modified oxygen-carrying biochar according to claim 4, characterized in that, The ratio of the iron source to the acid-washed biochar is 1-5 mmol: 5g; And / or, the mass ratio of the Fe-impregnated biochar to the nitrogen source is 1:(3-5).

6. The method for preparing iron-modified oxygen-carrying biochar according to any one of claims 1 to 3 and 5, characterized in that, The acid used for pickling includes one or more selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids.

7. The method for preparing iron-modified oxygen-carrying biochar according to any one of claims 1 to 3 and 5, characterized in that, The supported nano-oxygen comprises: (1) Vacuum treatment of iron-modified biochar; (2) The iron-modified biochar after vacuuming was mixed with oxygen under high pressure to carry nano-oxygen loading; Preferably, the high pressure condition is 0.18-0.25 MPa.

8. An iron-modified oxygen-carrying biochar, characterized in that, It is prepared using the method for preparing iron-modified oxygen-carrying biochar as described in any one of claims 1 to 7.

9. The method for preparing the iron-modified oxygen-carrying biochar according to any one of claims 1 to 7, or any one of the following applications of the iron-modified oxygen-carrying biochar according to claim 8: (1) Application in promoting soil carbon sequestration; (2) Application in promoting soil carbon reduction; (3) Application in promoting antibiotic degradation in the environment.

10. A method for soil carbon sequestration and / or organic pollutant degradation, characterized in that, The method includes applying the iron-modified oxygen-carrying biochar of claim 8 to the soil.

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