Endogenous single-atom iron supported biochar, and preparation method and application thereof

Abstract

The application discloses endogenous single-atom iron loaded biochar as well as a preparation method and application thereof, and belongs to the technical field of environmental functional materials. The application is characterized in that: the Eichhornia crassipes seedlings are placed in an iron-containing nutrient solution for culture, so that the roots of the seedlings are endogenously enriched with iron; after washing, drying, crushing and sieving, slow pyrolysis is carried out under an inert atmosphere; and finally, washing and drying are carried out to obtain the endogenous single-atom iron loaded biochar. In the obtained biochar, iron is uniformly dispersed on a carbon base in the form of single atoms to form a stable FeOC coordination structure. The application is characterized in that: the endogenous iron loading avoids the risks of iron agglomeration and secondary pollution caused by exogenous loading, and the preparation process is simple. The prepared biochar has excellent electron storage and transmission capacity, can directly provide electrons for denitrifying microorganisms, promotes the complete conversion of N2O to N2, significantly reduces soil N2O emission, optimizes soil microbial community structure, up-regulates the expression of denitrification functional genes, and has good environmental benefits and application prospect.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, specifically relating to an endogenous single-atom iron-supported biochar, its preparation method, and its application. Background Technology

[0002] Agricultural soils are a significant source of nitrogen (N2O) emissions, primarily driven by nitrogen fertilizer application-induced microbial nitrification and denitrification processes. Biochar, a porous carbon-rich material, is widely used for soil carbon sequestration and greenhouse gas emission reduction. While traditional iron-modified biochar can regulate denitrification and reduce N2O emissions, the exogenously loaded iron is prone to aggregation and uneven distribution, posing a risk of secondary pollution. Existing technologies disclose methods for preparing iron-loaded biochar by endogenously enriching iron in hyperaccumulating plants. However, the iron in this biochar is mainly in the form of oxide particles such as Fe2O3 and Fe3O4, failing to achieve atomic-level dispersion. Furthermore, it requires strong alkali ash removal treatment, which damages some surface functional groups and limits electron transfer efficiency. Existing technologies also disclose laser irradiation to improve iron dispersion, but this process is complex, costly, and introduces zero-valent iron with uncertain long-term environmental behavior. In addition, the resource utilization of hyperaccumulating plants such as water hyacinth (Eichhornia crassipes) as environmental remediation plants is still insufficient. Therefore, developing a novel biochar material with stable structure, high electron transfer efficiency, low environmental risk, and simple preparation process is of great significance for achieving synergistic effects between the utilization of hyperaccumulating plant resources and the reduction of greenhouse gas emissions from farmland. Summary of the Invention

[0003] To address the aforementioned issues in the prior art, this invention discloses an endogenous single-atom iron-supported biochar, its preparation method, and its applications. This aims to solve the technical problems in existing iron-modified biochar, such as easy agglomeration, poor dispersibility, low electron transfer efficiency, and insufficient utilization of hyperaccumulating plant resources.

[0004] To achieve the above objectives, the technical solution adopted by this invention is: to provide a method for preparing endogenous single-atom iron-supported biochar, which includes the following steps: S1: Place water hyacinth seedlings in an iron-containing nutrient solution with an iron concentration of 4-8 mg / L for cultivation; S2: After culturing for 80-100 days, collect the roots of water hyacinth, and after washing, drying, crushing and sieving, obtain iron-loaded biomass powder; S3: Place the iron-loaded biomass powder in an inert atmosphere, heat it to 500~700℃ at a heating rate of 1℃ / min, and keep it at the temperature for 1~3h to obtain crude biochar. S4: Wash the crude biochar until neutral and dry it to obtain the final product.

[0005] Based on the above solution, the present invention can also be improved in the following ways.

[0006] Furthermore, the iron-containing nutrient solution in step S1 is a Hogrange nutrient solution containing NH4Fe(SO4)2.

[0007] Furthermore, the drying procedure in step S2 is to first dry at 100~110℃ for 28~32 min, and then dry at 55~65℃ for 42~50 h.

[0008] In the above steps, the roots of water hyacinth are first dried at 100-110℃ for 28-32 minutes to quickly kill enzymes, terminate cell physiological metabolism, and prevent the migration or loss of iron. Then, they are dried at 55-65℃ for 42-50 hours to fully remove the bound water inside the biomass at low temperature, ensuring that the roots are completely dry and that the tissue structure is not damaged by high temperature, which facilitates subsequent crushing and maintains the uniform distribution of iron.

[0009] Furthermore, in step S2, the mesh size of the sieve is 0.2~0.3mm.

[0010] Furthermore, in step S4, the drying temperature is 55~65℃ and the drying time is 45~50h.

[0011] This invention also discloses the application of endogenous single-atom iron-supported biochar prepared by the above preparation method in the preparation of N2O emission reduction materials for farmland.

[0012] The beneficial effects of this invention are: 1. This invention uses the hyperaccumulating plant *Eichhornia crassipes* as raw material, utilizing its endogenous iron loading and then preparing biochar through high-temperature pyrolysis. The resulting biochar has iron uniformly dispersed in single-atom form on a carbon substrate, forming a Fe-OC coordination structure, significantly enhancing the biochar's electron storage and transfer capabilities. The preparation method precisely controls the iron concentration (4~8 mg / L) and enrichment time (≥2 months) during the plant cultivation stage, combined with a slow heating rate for pyrolysis. This promotes the in-situ coordination of iron enriched within the plant tissue with oxygen-containing functional groups during the graphitization of the carbon skeleton, spontaneously forming a stable single-atom Fe-OC structure, thus avoiding iron atom aggregation caused by exogenous loading or high-concentration iron enrichment. Compared to the non-single-atom structure formed by rapid pyrolysis, the single-atom structure obtained by slow pyrolysis is more stable, has higher dispersion, and possesses superior electron storage and transfer capabilities.

[0013] 2. The endogenous single-atom iron-supported biochar prepared in this invention can directly provide electrons to denitrifying microorganisms, promoting the complete conversion of N2O to N2. Experimental results show that applying this biochar can reduce soil N2O emissions by more than 60%; it can increase the relative abundance of Bacillus microorganisms in the soil, and directionally optimize the soil microbial community structure; it can upregulate the menC and ribA genes related to electron transport and denitrification functional genes. nosZ-I The expression of these substances increases the activity of cytochrome c, mitochondrial respiratory chain complex I, and complex III, thereby improving soil health. Attached Figure Description

[0014] Figure 1 The image shows the low-magnification morphology of the sample using HAADF-STEM. Figure 2 Atomic-resolution HAADF-STEM image of the sample; Figure 3 For BC, 8BC I and 8BC E XPS total spectrum; Figure 4 8BC I The fine XPS spectrum of O 1s; Figure 5 8BC I Fe 2p 3 / 2 and Fe 2p 1 / 2 XPS spectrum; Figure 6 8BC E Fe 2p 3 / 2 and Fe 2p 1 / 2 XPS spectrum; Figure 7 8BC I 8BC E 4BC I and 4BC E A comparison chart of specific capacitance values; Figure 8 Figure showing the community composition structure analysis results at the classification level of soil microorganisms in each group; Figure 9 Heatmaps of functional genes related to nitrogen metabolism and electron transport in each group of soil samples; Figure 10 A statistical chart of denitrifying enzyme activity in soil samples from each group; Figure 11 A statistical graph showing the relative expression levels of key genes involved in denitrification and the ratio of (nirS+nirK) / nosZ under different exogenous and endogenous single-atom iron-loaded biochar treatments. Detailed Implementation

[0015] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0016] The Hogland nutrient solution used in the examples was purchased from Qingdao High-tech Industrial Park Haibo Biotechnology Co., Ltd., product number: HB8870-1.

[0017] Example 1 An endogenous single-atom iron-supported biochar is prepared by the following steps: S1: Cultivate water hyacinth seedlings in clean water for 2 weeks, then transfer them to Hogland diluted nutrient solution containing 4 mg / L ferric ammonium sulfate for cultivation. The dilution ratio of Hogland diluted nutrient solution is 10%. Replenish nutrient solution and iron source every 7 days to ensure iron content is 4 mg / L. S2: After 90 days of cultivation, the roots of water hyacinth were collected and washed with water. Then the roots were dried at 105℃ for 30 minutes and then dried at 60℃ for 48 hours. Then the roots were crushed and passed through a sieve with a pore size of 0.25 mm to obtain iron-loaded biomass powder. S3: Iron-loaded biomass powder is placed in a tube furnace and heated to 500°C at a heating rate of 1°C / min under N2 atmosphere. The mixture is then kept at this temperature for 2 hours and allowed to cool naturally to obtain crude biochar. S4: Wash the crude biochar repeatedly with deionized water until the conductivity of the washing solution tends to stabilize and the pH is neutral. Then dry it at 60℃ for 48 hours to obtain the product, labeled as 4BC. I .

[0018] The Fe content in the obtained biochar was determined to be 2.34 mg / g using microwave digestion.

[0019] Example 2 An endogenous single-atom iron-supported biochar is prepared by the following steps: S1: Cultivate water hyacinth seedlings in clean water for 2 weeks, then transfer them to Hogland diluted nutrient solution containing 8 mg / L ferric ammonium sulfate for cultivation. The dilution ratio of Hogland diluted nutrient solution is 10%. Replenish nutrient solution and iron source every 7 days to ensure iron content is 8 mg / L. S2: After 90 days of cultivation, the roots of water hyacinth were collected and washed with water. Then the roots were dried at 105℃ for 30 minutes and then dried at 60℃ for 48 hours. Then the roots were crushed and passed through a sieve with a pore size of 0.25 mm to obtain iron-loaded biomass powder. S3: Iron-loaded biomass powder is placed in a tube furnace and heated to 500°C at a heating rate of 1°C / min under N2 atmosphere. The mixture is then kept at this temperature for 2 hours and allowed to cool naturally to obtain crude biochar. S4: Wash the crude biochar repeatedly with deionized water until the conductivity of the washing solution tends to stabilize and the pH is neutral. Then dry it at 60℃ for 48 hours to obtain the product, labeled as 8BC. I .

[0020] The Fe content in the obtained biochar was determined to be 4.19 mg / g using microwave digestion.

[0021] Example 3 An endogenous single-atom iron-supported biochar is prepared by the following steps: S1: Cultivate water hyacinth seedlings in clean water for 2 weeks, then transfer them to Hogland diluted nutrient solution containing 6 mg / L ferric ammonium sulfate for cultivation. The dilution ratio of Hogland diluted nutrient solution is 10%. Replenish nutrient solution and iron source every 7 days to ensure iron content is 6 mg / L. S2: After 80 days of cultivation, the roots of water hyacinth were collected and washed with water. Then the roots were dried at 100℃ for 32 minutes and then dried at 65℃ for 42 hours. Then the roots were crushed and passed through a sieve with a pore size of 0.25 mm to obtain iron-loaded biomass powder. S3: Iron-loaded biomass powder is placed in a tube furnace and heated to 700°C at a heating rate of 1°C / min under N2 atmosphere. The mixture is then kept at this temperature for 1 hour and allowed to cool naturally to obtain crude biochar. S4: Wash the crude biochar repeatedly with deionized water until the conductivity of the washing solution tends to be stable and the pH is neutral, and then dry it at 65℃ for 45 hours to obtain the final product.

[0022] Example 4 An endogenous single-atom iron-supported biochar is prepared by the following steps: S1: Cultivate water hyacinth seedlings in clean water for 2 weeks, then transfer them to Hogland diluted nutrient solution containing 6 mg / L ferric ammonium sulfate for cultivation. The dilution ratio of Hogland diluted nutrient solution is 10%. Replenish nutrient solution and iron source every 7 days to ensure iron content is 6 mg / L. S2: After 100 days of cultivation, the roots of water hyacinth were collected and washed with water. The roots were then dried at 110℃ for 28 minutes and then at 55℃ for 50 hours. The roots were then crushed and passed through a sieve with a pore size of 0.25 mm to obtain iron-loaded biomass powder. S3: Iron-loaded biomass powder is placed in a tube furnace and heated to 600°C at a heating rate of 1°C / min under N2 atmosphere. The mixture is then kept at this temperature for 3 hours and allowed to cool naturally to obtain crude biochar. S4: Wash the crude biochar repeatedly with deionized water until the conductivity of the washing solution tends to be stable and the pH is neutral, and then dry it at 55℃ for 50 hours to obtain the final product.

[0023] Comparative Example 1 A biochar preparation method differs from that in Example 2 in that water hyacinth is cultured in Hogland diluted nutrient solution without NH4Fe(SO4)2 in step S1, and the resulting biochar is labeled as BC.

[0024] Comparative Example 2 An exogenous iron-supported biochar, the preparation method of which includes the following steps: S1: Water hyacinth was cultured in Hogland diluted nutrient solution without NH4Fe(SO4)2. After 90 days of culture, the roots of water hyacinth were collected and washed with water. The roots were then dried at 105℃ for 30 minutes and then at 60℃ for 48 hours. The roots were then crushed and passed through a sieve with a pore size of 0.25 mm to obtain biomass powder. S2: Mix biomass powder with different Fe content 3+ The solution of the concentration was mixed and loaded at 150 rpm for 3 h in a shaker at 25 °C, and then centrifuged and dried (dried at 60 °C for 48 h) to obtain iron-loaded biomass powder. S3: Iron-loaded biomass powder is placed in a tube furnace and heated to 500°C at a heating rate of 1°C / min under N2 atmosphere. The mixture is then kept at this temperature for 2 hours and allowed to cool naturally to obtain crude biochar. S4: Wash the crude biochar repeatedly with deionized water until the conductivity of the washing solution stabilizes and the pH becomes neutral. Then dry it at 60℃ for 48 hours to obtain the final product. (This process involves multiple adjustments and reduction of Fe content.) 3+ The solution concentration range was adjusted multiple times to ensure that the exogenously loaded Fe content in the biochar was consistent with the Fe content in Examples 1 and 2, respectively; these were labeled as 4BC. E and 8BC E ).

[0025] Experimental Example ① The 8BC prepared in Example 2 was examined using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). I Microscopic morphology and atomic-scale structure characterization were performed; the results are as follows: Figures 1-2 As shown, Figure 2 The data shows that Fe single atoms are uniformly dispersed.

[0026] ② Perform X-ray photoelectron spectroscopy (XPS) analysis on the sample. Figure 3 It is BC, 8BC I and 8BC E XPS total spectrum; Figure 4 It is 8BC I XPS fine spectrum of O1s; Figure 5 It is 8BC I Fe 2p 3 / 2 and Fe 2p1 / 2 XPS spectrum; Figure 6 8BC E Fe2p 3 / 2 and Fe 2p 1 / 2 The XPS spectrum shows that iron is uniformly dispersed in single-atom form on the carbon substrate and forms an Fe-O coordination structure with oxygen atoms.

[0027] ③ Investigate the impact of endogenous single-atom iron-supported biochar on N2O emissions. First, the alluvial brown soil was mixed with biochar (2 wt%), and then KNO3 solution was added for anaerobic culture. The biochar corresponding to the five treatment groups were BC, 4BC, and 4BC prepared in the examples and comparative examples, respectively. I 8BC I 4BC E and 8BC E The results showed that 8BC Ⅰ The treatment group exhibited the lowest cumulative N2O emissions, reducing soil N2O emissions by over 60%. Simultaneously, it produced the highest N2 output, with a significantly reduced N2O / (N2O+N2) ratio. Electrochemical testing showed that at 8BC... Ⅰ The specific capacitance is 3.1 F / g, such as Figure 7 As shown, it was significantly higher than the control biochar and exogenous iron-supported biochar.

[0028] ④ Investigate the microbial mechanism of action of biochar supported by endogenous single-atom iron. High-throughput sequencing and quantitative analysis of functional genes of microorganisms were performed on the soil after the culture in step ③ was completed. The results are as follows: Figures 8-11 As shown. Figure 8 The diagram shows the community composition structure analysis results at the classification level of soil microorganisms in each group. It can be seen that, compared with exogenously loaded Fe biochar, endogenously loaded Fe biochar can better increase the relative abundance of Bacillus phylum. Figure 9 The heatmaps of functional genes related to nitrogen metabolism and electron transport in each soil group show that endogenously loaded Fe biochar can regulate genes related to electron transport. menC , ribA Genes and denitrification functional genes nosZI The expression. Figure 10 The statistical chart shows the denitrifying enzyme activity in each soil group. Endogenously loaded Fe biochar can increase the activity of cytochrome c, mitochondrial respiratory chain complex I, and complex III. Figure 11The graph shows the relative expression levels and (nirS+nirK) / nosZ ratio of key genes (nirK, nirS, narG, nosZI, and nosZII) involved in denitrification under different exogenous and endogenous single-atom iron-loaded biochar treatments. It can be seen that the (nirS+nirK) / nosZ ratio is reduced in soil treated with endogenous single-atom iron-loaded biochar during denitrification, promoting the complete reduction of N2O to N2.

[0029] In summary, compared with exogenously loaded Fe biochar, endogenously loaded Fe biochar is more effective in increasing the relative abundance of Bacillus species, the relative expression levels of electron transport-related genes such as menC and ribA, and the denitrification functional gene nosZI, as well as the activities of cytochrome c, complex I, and complex III. Higher endogenous Fe single-atom concentrations are more effective in achieving efficient N2O emission reduction by optimizing microbial community structure, enhancing electron transport, and promoting complete denitrification.

[0030] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for preparing endogenous single-atom iron-supported biochar, characterized in that, Includes the following steps: S1: Place water hyacinth seedlings in an iron-containing nutrient solution with an iron concentration of 4-8 mg / L for cultivation; S2: After culturing for 80-100 days, collect the roots of water hyacinth, and after washing, drying, crushing and sieving, obtain iron-loaded biomass powder; S3: The iron-loaded biomass powder is placed in an inert atmosphere and heated to 500~700℃ at a heating rate of 1℃ / min, and kept at the temperature for 1~3h to obtain crude biochar. S4: Wash the crude biochar until neutral and dry it to obtain the final product.

2. The method for preparing endogenous single-atom iron-supported biochar according to claim 1, characterized in that: The iron-containing nutrient solution mentioned in step S1 is a Hogrange nutrient solution containing NH4Fe(SO4)2.

3. The method for preparing endogenous single-atom iron-supported biochar according to claim 1, characterized in that: The drying procedure in step S2 is to first dry at 100~110℃ for 28~32 min, and then dry at 55~65℃ for 42~50 h.

4. The method for preparing endogenous single-atom iron-supported biochar according to claim 1, characterized in that: In step S2, the mesh size of the sieve is 0.2~0.3mm.

5. The method for preparing endogenous single-atom iron-supported biochar according to claim 1, characterized in that: In step S4, the drying temperature is 55~65℃ and the drying time is 45~50h.

6. Endogenous single-atom iron-supported biochar prepared by the preparation method according to claims 1 to 5.

7. The application of the endogenous single-atom iron-supported biochar according to claim 6 in the preparation of N2O emission reduction materials for farmland.

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