Iron and nitrogen co-doped biochar for remediation of Cd-As combined pollution, preparation method and application thereof

Abstract

The application relates to the technical field of water and soil pollution control, and discloses an iron-nitrogen co-doped biochar for Cd-As composite pollution remediation, a preparation method and application, which comprises the following raw materials: biomass material, potassium ferrate and melamine. The iron-nitrogen co-doped biochar can realize the synergistic and efficient removal of Cd(II) and As(III), and the adsorption capacity of the biochar for As(III) in a Cd-As composite pollution system reaches 28.96 mg / g, which is 5.18 times higher than that in a single As(III) pollution system.

Description

Technical Field

[0001] This invention relates to the field of water and soil pollution control technology, and in particular to an iron-nitrogen co-doped biochar for the remediation of Cd-As composite pollution, its preparation method, and its application. Background Technology

[0002] In non-ferrous metal mining areas and surrounding farmland systems, cadmium (Cd) and arsenic (As) often coexist at high concentrations. Since Cd(II) exists as a cation while As(III) exists primarily as neutral molecules or anions, the significant differences in their chemical forms and environmental behaviors make synergistic and efficient removal a technical challenge. Biochar, due to its wide availability, tunable pore structure, abundant surface functional groups, and low cost, is considered a highly promising heavy metal adsorbent. To improve the adsorption performance of biochar for heavy metals, scholars both domestically and internationally have extensively explored modifications through metal loading (such as Fe, Mn, etc.) or non-metal doping (such as N, S, etc.). However, existing modified biochars are mostly effective against single heavy metals, and no biochar material capable of synergistically and efficiently removing Cd-As composite pollution has yet been developed, making it difficult to meet the actual remediation needs of Cd-As composite pollutants in water and soil environments. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides an iron-nitrogen co-doped biochar for the remediation of Cd-As complex pollution, which can achieve synergistic and efficient removal of Cd(II) and As(III).

[0004] The first specific technical solution of the present invention is: an iron-nitrogen co-doped biochar for the remediation of Cd-As composite pollution, comprising the following raw materials: biomass materials, potassium ferrate and melamine.

[0005] This invention uses potassium ferrate (K2FeO4), a strong oxidizing iron source, which can spontaneously decompose in aqueous solution and gradually release Fe. 3+During pyrolysis, it is further transformed into Fe3O4 / γ-Fe2O3 nanoparticles, which synergistically form stable Fe-NC active sites with melamine nitrogen source. This directly constructs the iron-based active sites required for iron-nitrogen co-doping, eliminating the need for additional reducing agents to regulate the iron valence state and avoiding side reactions, impurity residues, and operational risks introduced by reducing agents. At the same time, the oxidizing gas released during K2FeO4 pyrolysis will etch the rice straw char matrix, forming a well-developed pore structure to increase the specific surface area of ​​biochar. Furthermore, the iron species decomposed from it can be uniformly loaded on the pore surface, constructing highly dispersed active sites. This achieves simultaneous completion of pore-forming modification, iron source loading, and active site construction, simplifying the process while improving the adsorption performance of biochar. The iron-nitrogen co-doped biochar of this invention achieves rapid cadmium immobilization through surface complexation and electrostatic adsorption via nitrogen-containing functional groups at Fe-NC sites and hydroxyl groups on the surface of Fe3O4 / γ-Fe2O3 nanoparticles. Utilizing the oxidative activity of Fe-NC sites, combined with the oxidative properties of Fe3O4 / γ-Fe2O3 nanoparticles, highly toxic As(III) is synergistically oxidized to less toxic As(V), enhancing the stability and adsorption capacity of arsenic. The oxidized As(V) undergoes a co-precipitation reaction with the adsorbed Cd(II) at the material interface, forming a stable Cd-As-Fe ternary complex, which not only significantly increases the adsorption capacity of As(III) but also further enhances the immobilization effect of Cd(II). Furthermore, the uniform dispersion of Fe3O4 / γ-Fe2O3 nanoparticles in the carbon matrix forms a complementary and synergistic composite active center with the Fe-NC sites, achieving synergistic and efficient removal of Cd(II) and As(III), thus overcoming the industry challenge of simultaneous remediation of heavy metals by anionic and cationic composites.

[0006] Optionally, the biomass material is rice straw powder.

[0007] Optionally, the mass ratio of the biomass material powder, potassium ferrate, and melamine is 10:2~4:2~4.

[0008] Optionally, the mass ratio of the biomass powder, potassium ferrate, and melamine is 10:3:3.

[0009] The second specific technical solution of the present invention is: a method for preparing iron-nitrogen co-doped biochar for the remediation of Cd-As composite pollution, comprising the following steps: (1) Mix biomass materials, potassium ferrate and melamine in an aqueous solution, and dry to obtain a mixed material; (2) The mixed materials were subjected to vacuum pyrolysis to obtain iron-nitrogen co-doped biochar.

[0010] Optionally, in step (1), the biomass material is a 50-60 mesh powder.

[0011] Optionally, in step (1), the drying temperature is 45~55℃.

[0012] Optionally, in step (1), the mixing time is 20-26 h.

[0013] Optionally, in step (2), the temperature of the vacuum pyrolysis is 600~800℃ and the time is 2~3 h.

[0014] Optionally, after step (2), the iron-nitrogen co-doped biochar is activated by soaking it in a 0.5-1 mol / L K2CO3 solution for 2-4 h, then washing it with water until neutral, and drying it to obtain the activated iron-nitrogen co-doped biochar.

[0015] Slight etching of the biochar surface reduces pore blockage, increases the exposure of Fe-NC active sites on iron oxide sites, and increases its contact area with pollutants. At the same time, a small amount of alkaline functional groups are introduced to help improve the electrostatic adsorption capacity for Cd(II). In addition, the weakly alkaline environment promotes the formation of an extremely thin and dense oxide passivation film on the surface of Fe3O4 / γ-Fe2O3 nanoparticles, improving their anti-agglomeration and stability in water.

[0016] The third specific technical solution of the present invention is: the application of the above-mentioned iron-nitrogen co-doped biochar in the remediation of Cd-As composite polluted water and soil environments.

[0017] Compared with the prior art, the present invention has at least the following advantages: (1) Based on the resource utilization of agricultural waste rice straw, this invention addresses the technical difficulties of simultaneous removal of Cd(II) and As(III) complex heavy metal pollution in water bodies by adopting a dual precursor co-doping strategy of potassium ferrate and melamine. Iron-nitrogen co-doped biochar (FeNBC) is prepared by a one-step high-temperature pyrolysis method. The strong oxidizing, self-decomposing and pore-forming properties of potassium ferrate are utilized, combined with the nitrogen-rich characteristics of melamine, to achieve integrated preparation of carbon matrix pore formation, uniform loading of Fe3O4 / γ-Fe2O3 nanoparticles, and in-situ construction of Fe-NC active sites. By controlling the pyrolysis temperature to optimize the physicochemical properties of the material, a multifunctional biochar material with cadmium complexation and fixation, arsenic oxidation-adsorption-co-precipitation is constructed, ultimately achieving efficient and simultaneous remediation of water bodies polluted by complex heavy metals. This invention overcomes the process drawbacks of traditional iron-nitrogen co-doped biochar preparation, which requires the addition of reducing agents (such as sodium borohydride) to regulate the iron valence state and the need for pore-forming agents to modify the pore structure. This invention achieves a dual breakthrough of process simplification and cost reduction. (2) In the Cd-As composite pollution system, the adsorption capacity of the iron-nitrogen co-doped biochar of the present invention for As(III) was greatly increased from 5.59 mg / g in the single system to 28.96 mg / g, an increase of up to 5.18 times. This fully demonstrates that there is a significant positive synergistic adsorption effect between Cd(II) and As(III), which can effectively overcome the problems of competitive adsorption and decreased removal efficiency that are easy to occur in the composite pollution system of traditional adsorption materials. The iron-nitrogen co-doped biochar of the present invention has strong synchronous adsorption capacity, high adsorption capacity and good stability in Cd(II) and As(III) composite polluted water, showing extremely excellent synergistic and efficient removal performance and practical engineering application potential. Attached Figure Description

[0018] Figure 1 These are SEM images of BC-1, FeNBC-1, BC-2, and FeNBC-2; Figure 2 These are TEM photos and mapping images of FeNBC-2; Figure 3 These are the FTIR spectra of BC-1, FeNBC-1, BC-2, and FeNBC-2; Figure 4 These are the XPS total spectra of BC-1, FeNBC-1, BC-2, and FeNBC-2. Detailed Implementation

[0019] The present invention will now be described through specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0020] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used in this invention are conventional in the art and can be obtained through conventional commercial means; unless otherwise specified, the methods used in this invention are conventional methods in the art. In this invention, Cd(II), As(III), and As(V) represent: Cd(II) represents divalent cadmium, which exists primarily as a hydrated cation in natural water bodies; arsenic (As) is a metalloid element; As(III) represents trivalent arsenic, which does not exist as a simple cation in aqueous solution but primarily as arsenous acid (H3AsO3); As(V) represents pentavalent arsenic, which exists primarily as arsenic acid (H3AsO4) and its dissociated anions in aqueous solution.

[0021] In this invention, the vacuum pyrolysis furnace selected is the SXZC-5-13C type vacuum pyrolysis furnace manufactured by Hangzhou Lantian Instrument Co., Ltd.

[0022] Example 1: The present invention provides an iron-nitrogen co-doped biochar for the remediation of Cd-As composite pollution, which comprises the following raw materials by weight: 10 parts rice straw powder, 3 parts potassium ferrate and 3 parts melamine.

[0023] The preparation method of the above-mentioned iron-nitrogen co-doped biochar includes the following steps: Collected rice straw is washed with tap water to remove surface impurities such as mud and dust. It is then dried at 60°C to constant weight, pulverized, and passed through a 60-mesh sieve to obtain rice straw powder. 10.0 g of rice straw powder, 3.0 g of K₂FeO₄, and 3.0 g of melamine are placed in a beaker, and 100 mL of deionized water is added. The mixture is stirred on a magnetic stirrer for 24 h. After stirring, it is dried in an oven at 50°C to constant weight. After drying, the obtained material is placed in a vacuum pyrolysis furnace and pyrolyzed at 600°C for 2 h. After pyrolysis, it is rinsed three times with deionized water, dried, and passed through a 100-mesh sieve to obtain iron-nitrogen co-doped biochar. The iron-nitrogen co-doped biochar was soaked in 1 mol / L K2CO3 solution for 2 h, then washed with water until neutral, and dried to obtain the activated iron-nitrogen co-doped biochar sample, labeled as FeNBC-1.

[0024] Example 2: The present invention provides an iron-nitrogen co-doped biochar for the remediation of Cd-As composite pollution, which comprises the following raw materials by weight: 10 parts rice straw powder, 3 parts potassium ferrate and 3 parts melamine.

[0025] The preparation method of the above-mentioned iron-nitrogen co-doped biochar includes the following steps: Collected rice straw is washed with tap water to remove surface impurities such as mud and dust. It is then dried at 60°C to constant weight, pulverized, and passed through a 60-mesh sieve to obtain rice straw powder. 10.0 g of rice straw powder, 3.0 g of K₂FeO₄, and 3.0 g of melamine are placed in a beaker, and 100 mL of deionized water is added. The mixture is stirred on a magnetic stirrer for 24 h. After stirring, it is dried in an oven at 50°C to constant weight. After drying, the obtained material is placed in a vacuum pyrolysis furnace and pyrolyzed at 800°C for 2 h. After pyrolysis, it is rinsed three times with deionized water, dried, and passed through a 100-mesh sieve to obtain iron-nitrogen co-doped biochar. The iron-nitrogen co-doped biochar was soaked in 1 mol / L K2CO3 solution for 2 h, then washed with water until neutral, and dried to obtain the activated iron-nitrogen co-doped biochar sample, labeled as FeNBC-2.

[0026] Example 3: The present invention provides an iron-nitrogen co-doped biochar for the remediation of Cd-As composite pollution, which comprises the following raw materials by weight: 10 parts rice straw powder, 2 parts potassium ferrate and 2 parts melamine.

[0027] The preparation method of the above-mentioned iron-nitrogen co-doped biochar includes the following steps: Collected rice straw is washed with tap water to remove surface impurities such as mud and dust. It is then dried at 60℃ to constant weight, pulverized, and passed through a 50-mesh sieve to obtain rice straw powder. 10.0 g of rice straw powder, 2.0 g of K₂FeO₄, and 2.0 g of melamine are placed in a beaker, and 100 mL of deionized water is added. The mixture is stirred on a magnetic stirrer for 24 h. After stirring, it is dried in an oven at 45℃ to constant weight. After drying, the obtained material is placed in a vacuum pyrolysis furnace and pyrolyzed at 600℃ for 3 h. After pyrolysis, it is rinsed three times with deionized water, dried, and passed through a 100-mesh sieve to obtain iron-nitrogen co-doped biochar. The iron-nitrogen co-doped biochar is soaked in a 0.5 mol / L K₂CO₃ solution for 4 h, washed with water until neutral, and dried to obtain an activated iron-nitrogen co-doped biochar sample.

[0028] Example 4: The present invention provides an iron-nitrogen co-doped biochar for the remediation of Cd-As composite pollution, comprising the following raw materials by weight: 10 parts rice straw powder, 4 parts potassium ferrate and 4 parts melamine.

[0029] The preparation method of the above-mentioned iron-nitrogen co-doped biochar includes the following steps: Collected rice straw is washed with tap water to remove surface impurities such as mud and dust. It is then dried at 60℃ to constant weight, pulverized, and passed through a 60-mesh sieve to obtain rice straw powder. 10.0 g of rice straw powder, 4.0 g of K₂FeO₄, and 4.0 g of melamine are placed in a beaker, and 100 mL of deionized water is added. The mixture is stirred on a magnetic stirrer for 24 h. After stirring, it is dried in an oven at 55℃ to constant weight. After drying, the obtained material is placed in a vacuum pyrolysis furnace and pyrolyzed at 800℃ for 3 h. After pyrolysis, it is rinsed three times with deionized water, dried, and passed through a 100-mesh sieve to obtain iron-nitrogen co-doped biochar. The iron-nitrogen co-doped biochar is soaked in a 0.5 mol / L K₂CO₃ solution for 4 h, washed with water until neutral, and dried to obtain an activated iron-nitrogen co-doped biochar sample.

[0030] Comparative Example 1: Straw powder was placed in a vacuum pyrolysis furnace and pyrolyzed at a pyrolysis temperature of 600 °C for 2 h. After pyrolysis was completed, it was rinsed three times with deionized water, dried, and passed through a 100-mesh sieve to obtain a biochar sample, labeled as BC-1.

[0031] Comparative Example 2: Straw powder was placed in a vacuum pyrolysis furnace and pyrolyzed at a pyrolysis temperature of 800 ℃ for 2 h. After pyrolysis was completed, it was rinsed three times with deionized water, dried, and passed through a 100-mesh sieve to obtain a biochar sample, labeled as BC-2.

[0032] The microstructures of BC-1, FeNBC-1, BC-2, and FeNBC-2 were analyzed, and the results are as follows: Figure 1 As shown in the figure, FeNBC-1, compared to BC-1, and FeNBC-2, compared to BC-2, introduce particulate deposits on the surface, proving that the present invention successfully loads iron and nitrogen elements onto the surface of biochar through co-doping. The particulate deposits are Fe-NC active centers and Fe3O4 / γ-Fe2O3 nanoparticles formed during the iron-nitrogen doping process. The carbonization temperature and iron-nitrogen co-doping have a significant impact on the microstructure of biochar. Compared to BC-1 and FeNBC-1, BC-2 and FeNBC-2 have more developed pore networks. Among them, the surface particles of FeNBC-2 are more uniformly dispersed and more tightly bound to the carbon matrix. This may be due to the high temperature enhancing the decomposition and diffusion of metal precursors. The above phenomena indicate that the pyrolysis temperature of 800℃ can enable iron-nitrogen co-doped biochar to have a larger specific surface area and more surface active sites, and have a strong adsorption capacity for Cd(II) and As(III).

[0033] The microstructure and elemental distribution of FeNBC-2 were further characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), as shown in Figure 2. TEM images revealed a large number of high-contrast nanoparticles uniformly embedded in the carbon matrix, directly demonstrating the successful introduction and high dispersion of iron species within the biochar matrix. EDS elemental surface scanning results showed that C, N, O, and Fe elements exhibited a uniform and diffuse distribution within the selected region. In particular, the spatial distributions of Fe and N elements showed a strong correlation, and no obvious macroscopic metal agglomeration was observed. This high dispersion characteristic suggests that during high-temperature carbonization, the introduction of nitrogen atoms may effectively anchor iron species by forming Fe-N coordination bonds, inhibiting their sintering at high temperatures, thereby promoting the in-situ construction and high exposure of Fe-NC active sites.

[0034] FTIR analysis results are as follows Figure 3 As shown in the figure, with increasing pyrolysis temperature, the characteristic signals of oxygen-containing functional groups OH and C=O / C=C on the biochar surface significantly weaken. This phenomenon is mainly due to the high-temperature environment promoting the aromatization of biochar and accelerating the removal of surface polar functional groups. At ~466 cm⁻¹ -1A distinct Fe-O characteristic absorption peak appeared at [a specific location], a direct observation demonstrating that the iron-nitrogen co-doping treatment successfully introduced iron species into the surface and interior of the biochar. Furthermore, the modification treatment significantly altered the chemical bonding environment in the wavenumber region of the biochar; compared to unmodified biochars BC-1 and BC-2, FeNBC-1 and FeNBC-2 showed significantly improved wavenumbers at ~1087 cm⁻¹. -1 The nearby characteristic peaks show significant changes and shift towards lower wavenumbers. This peak shape change is likely due to the formation of CN bonds or the recombination of the CO / N bond structure, indicating that nitrogen has been successfully incorporated into the carbon framework of biochar. The above FTIR characterization results provide direct evidence that iron-nitrogen co-doping modification significantly alters the chemical structure of biochar, further confirming the effectiveness of the co-doping modification strategy of this invention and providing chemical structural support for the excellent synergistic adsorption performance of iron-nitrogen co-doped biochar.

[0035] XPS analysis results are as follows: Figure 4 As shown in the figure, with increasing pyrolysis temperature, the C 1s intensity increases while the O 1s signal decreases, indicating progressive deoxidation, aromatization, and carbon enrichment. These are typical characteristics of higher-temperature heat treatment promoting structural stability and graphitization of biomass-derived carbon materials. Furthermore, iron-nitrogen co-doping modification introduces a significant Fe 2p peak in the FeNBC sample and significantly enhances the N 1s signal compared to the original BC sample, confirming the effective doping of iron and nitrogen. The enhanced retention of nitrogen in the modified sample indicates that Fe plays a stabilizing role during pyrolysis. The elemental chemical state analysis results of the XPS spectra of the biochar samples are shown in Table 1.

[0036] Table 1. Elemental chemical state analysis results of biochar samples based on XPS spectra: ;

[0037] In Table 1, Pyridinic N represents pyridine nitrogen, Pyrrolic N represents pyrrolic nitrogen, Graphitic N represents graphitic nitrogen, Oxidized N represents oxidized nitrogen, C=O / Lattice O represents carbonyl oxygen / lattice oxygen, and OC=O / Adsorbed H2O represents carboxyl oxygen / adsorbed water oxygen. Table 1 shows that as the pyrolysis temperature increases from 600℃ to 800℃, the CC / C=C content of both BC and FeNBC samples exhibits a decreasing trend. This may be attributed to the deep reorganization of the carbon skeleton and the relative change in the proportion of oxygen-containing functional groups at high temperatures. At 600℃, Fe-N co-modification significantly increased the proportion of pyridine nitrogen, jumping from 28.62% in BC-1 to 41.59% in FeNBC-1. This phenomenon indicates that the introduction of Fe effectively promotes the transformation of edge nitrogen to a pyridine-type structure, potentially providing more catalytic active sites. However, as the temperature increased to 800℃, the proportion of graphitic nitrogen in FeNBC-2 increased from 33.44% to 42.08%, confirming the thermodynamic stability of graphitic nitrogen under high-temperature conditions. The C=O / Lattice O ratio in the FeNBC sample was much higher than that in the original BC sample (19.07% and 18.52%), which directly proves the successful construction of iron oxides or metal-oxygen bonds on the biochar surface.

[0038] Isothermal adsorption experiments were conducted on four types of biochar: BC-1, FeNBC-1, BC-2, and FeNBC-2, in single solutions of Cd(II), single solutions of As(III), and Cd-As composite solutions. The experimental procedure was as follows: 50 mL of single solutions of Cd(II) (25–250 mg / L), single solutions of As(III) (0.5–15 mg / L), and Cd-As composite solutions (Cd(II) concentration 50 mg / L, As(III) concentration 5–50 mg / L) were measured into 100 mL polyethylene bottles. The initial pH of each solution was adjusted to 5.0. The four types of biochar were added to each solution at a dosage of 1.0 g / L. The polyethylene bottles were placed in a constant temperature shaker at 25 ℃ and shaken at 180 rpm for 24 h until adsorption equilibrium was reached. After the reaction was completed, the adsorption was measured using a 0.45 μm filter. The solution was filtered through a membrane, and the filtrate was collected and the equilibrium concentrations of Cd(II) and As(III) were determined. The equilibrium adsorption capacity of biochar for heavy metals was calculated based on the initial and equilibrium concentrations. The experimental data were fitted and analyzed using the Freundlich adsorption isotherm model, and the relevant parameters obtained from the fitting are shown in Table 2.

[0039] Table 2. Results of the isothermal adsorption experiment: ;

[0040] In Table 2, Freundlich isotherm refers to the Freundlich adsorption isotherm model (or, the Freundlich adsorption isotherm model). In the Freundlich adsorption isotherm model, K... F R is the adsorption capacity parameter; a larger value indicates a stronger adsorption capacity of the adsorbent. 1 / n is the adsorption strength parameter; a smaller value (closer to 0) indicates easier adsorption and stronger adsorption affinity. 2 The correlation coefficient is denoted as α, and a value closer to 1 indicates a better fit of the model to the experimental data. Table 1 shows that iron-nitrogen co-doping significantly improved the adsorption capacity of biochar for Cd(II), and the Ki of FENBC-1 and FENBC-2... F It is 34 to 113 times that of BC-1 and BC-2; iron-nitrogen co-doping also significantly improves the adsorption capacity for As(III), and the K of FENBC-1 and FENBC-2 is 34 to 113 times that of BC-1 and BC-2. F It is 5 to 30 times that of BC-1 and BC-2; data from the Cd-As composite solution system show that FeNBC-2 has a higher K-value for As(III) than BC-1 and BC-2. F The concentration of FeNBC-1 increased dramatically from 0.426 in the single system to 7.708, an increase of about 18 times. FeNBC-1 increased from 0.225 to 4.076, an increase of about 18 times, which is much higher than that in the single system. This directly confirms that there is a significant positive synergistic adsorption effect between Cd and As. The essence of this effect is the synergistic effect of Fe-NC active sites and Fe3O4 / γ-Fe2O3 nanoparticles in oxidizing As(III) to As(V), as well as the synergistic effect of subsequent co-precipitation of Cd-As-Fe ternary complex.

[0041] To verify the maximum adsorption capacity of the Cd-As composite system, this study set up two control systems: a single As(III) solution (0.5~15 mg / L) and a Cd-As composite solution (Cd(II) concentration 50 mg / L, As(III) concentration 5~50 mg / L). Under the same experimental conditions (temperature 25℃, pH=5.0, dosage 1.0 g / L), the adsorption performance of FeNBC-2 on As(III) was compared and evaluated. The experimental results are shown in Table 3.

[0042] Table 3. Experimental results of maximum adsorption capacity: ;

[0043] In Cd-As composite pollution solutions, the maximum adsorption capacity of FeNBC-2 for As(III) was significantly increased to 28.96 mg / g, which is about 5.18 times higher than that of 5.59 mg / g in single As(III) solutions. This result indicates that, under saturated adsorption conditions, the ultimate adsorption capacity of iron-nitrogen co-doped biochar for As(III) in the composite system is much higher than that in the single system, which fully demonstrates its ability to simultaneously and efficiently remediate actual composite polluted water bodies.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An iron-nitrogen co-doped biochar for the remediation of Cd-As complex pollution, characterized in that, The raw materials include: biomass materials, potassium ferrate, and melamine.

2. The iron-nitrogen co-doped biochar for Cd-As composite pollution remediation according to claim 1, characterized in that, The biomass material is rice straw powder.

3. The iron-nitrogen co-doped biochar for Cd-As composite pollution remediation according to claim 1, characterized in that, The mass ratio of the biomass powder, potassium ferrate, and melamine is 10:2~4:2~4.

4. The iron-nitrogen co-doped biochar for Cd-As composite pollution remediation according to claim 3, characterized in that, The mass ratio of the biomass powder, potassium ferrate, and melamine is 10:3:

3.

5. A method for preparing iron-nitrogen co-doped biochar for the remediation of Cd-As composite pollution, characterized in that, Includes the following steps: (1) Mix biomass materials, potassium ferrate and melamine in an aqueous solution, and dry to obtain a mixed material; (2) The mixed materials were subjected to vacuum pyrolysis to obtain iron-nitrogen co-doped biochar.

6. The method for preparing iron-nitrogen co-doped biochar for Cd-As composite pollution remediation according to claim 5, characterized in that, In step (1), the biomass material is a 50-60 mesh powder.

7. The method for preparing iron-nitrogen co-doped biochar for Cd-As composite pollution remediation according to claim 5, characterized in that, In step (1), the drying temperature is 45~55℃.

8. The method for preparing iron-nitrogen co-doped biochar for Cd-As composite pollution remediation according to claim 5, characterized in that, In step (2), the temperature of the vacuum pyrolysis is 600~800℃ and the time is 2~3h.

9. A method for preparing iron-nitrogen co-doped biochar for Cd-As composite pollution remediation according to any one of claims 5 to 8, characterized in that, After step (2), the iron-nitrogen co-doped biochar is activated by soaking it in 0.5-1 mol / L K2CO3 solution for 2-4 hours, then washing it with water until neutral, and drying it to obtain the activated iron-nitrogen co-doped biochar.

10. The application of iron-nitrogen co-doped biochar as described in any one of claims 1 to 4 in the remediation of Cd-As co-polluted water and soil environments.

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