A biochar-supported self-doped pyridine nitrogen-confined nZVI material and its preparation method

Abstract

This invention discloses a biochar-supported self-doped pyridine nitrogen-confined nZVI material and its preparation method, relating to the field of wastewater treatment materials technology. Utilizing the self-doped nitrogen properties of chitosan, pore-forming and mechanical strength-enhancing processes are achieved using polyethylene glycol and sodium alginate, respectively. A two-step pyrolysis process forms a nitrogen-doped iron-carbon micro-electrolysis filler. The synergistic effect of multiple nitrogen species, pyridine nitrogen and graphitic nitrogen, optimizes the reaction pathway, thereby increasing NO3- content in nitrate wastewater. ‑ The invention improves the removal rate of -N and the N2 selectivity of the product, and, based on the formation of a microscopic galvanic cell between zero-valent iron and biochar, alleviates the pH limitation of nZVI when used alone, and enhances the nitrate removal rate. The biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in this invention possesses comprehensive advantages, including good dispersibility, abundant active sites, optimized reaction pathways, synergistic dual-function properties, strong anti-interference ability, and recyclability, making it suitable for the efficient remediation of nitrate wastewater and complex polluted water bodies.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment materials technology, specifically to a biochar-supported self-doped pyridine nitrogen-confined nZVI material and its preparation method. Background Technology

[0002] Nitrate is the most stable nitrogen-containing compound formed under aerobic conditions and is the final product of the inorganic decomposition of nitrogen-containing organic matter. With the development of industrial and agricultural production, nitrate pollution in surface water and groundwater has become increasingly serious. Sources of nitrate include, but are not limited to, the use of nitrogen-containing fertilizers, the treatment of domestic sewage and excrement, the discharge of industrial wastewater, and the dry and wet deposition of nitrogen oxides formed from the combustion of fossil fuels. Due to the easy migration and relative stability of nitrate, excessive nitrate can seep into groundwater through the soil, leading to groundwater pollution and a series of health and environmental risks. High-concentration nitrate wastewater entering rivers and lakes can also stimulate rapid algal growth, causing water quality deterioration and eutrophication of aquatic ecosystems. Efficient and in-depth treatment of wastewater with low chemical oxygen demand (COD) to total nitrogen (C / N) ratios, while simultaneously removing recalcitrant organic matter, is currently a research hotspot and challenge in the field of water pollution control.

[0003] Nano-zero valent iron (nZVI) has been widely used in water remediation due to its strong reducing power, abundant raw materials, unique nanoscale effects, and tunable physicochemical properties, showing great potential, especially in the reduction and removal of nitrate nitrogen. However, traditional nZVI materials have inherent technical drawbacks: firstly, nZVI particles have extremely high surface energy and magnetism, making them prone to aggregation and oxidative passivation, leading to a sharp drop in reactivity and a shortened lifespan; secondly, nZVI exhibits poor selectivity in nitrate reduction, often generating large amounts of ammonia nitrogen (NH4). + -N) byproducts cause secondary pollution and make it difficult to achieve deep denitrification; thirdly, its function is singular, mainly relying on the reduction pathway, and its removal effect on coexisting organic pollutants in water bodies is limited, making it difficult to deal with actual wastewater with complex composition.

[0004] In recent years, many studies have focused on exploring ways to reduce the aggregation and oxidation phenomena caused by the high surface activity of nZVI and improve the electron selectivity of its reactions. To alleviate the aggregation problem of nZVI, researchers have developed supported nZVI composite materials, among which porous biochar is widely used as a support due to its large specific surface area and good chemical stability. However, conventional physical loading methods are difficult to achieve atomic-level dispersion and robust stability of nZVI, and iron species tend to migrate and aggregate to form large particles during pyrolysis. In addition, ordinary biochar supports have limited electron conductivity and weak regulation of reaction pathways, failing to effectively solve the problems of poor product selectivity and limited functionality. Although introducing an external nitrogen source for doping can improve the electronic structure of carbon materials, this method is usually cumbersome, costly, and may introduce impurities.

[0005] On the other hand, fillers based on the principle of iron-carbon micro-electrolysis have shown potential in treating a variety of pollutants, but their traditional preparation methods have problems such as insufficient contact between iron and carbon, weak galvanic cell effect, and insufficient filler strength that makes them easy to crush, which limit their large-scale application efficiency and long-term stability.

[0006] Therefore, developing a novel composite packing preparation method that is green and economical, can simultaneously achieve high dispersion and stable loading of nZVI, precisely control the reaction path to improve N2 selectivity, and has both redox functions is of great significance for promoting the practical application of wastewater deep treatment technology. Summary of the Invention

[0007] The purpose of this invention is to provide a biochar-supported self-doped pyridine nitrogen-confined nZVI material and its preparation method, to solve the problems of easy agglomeration and oxidation deactivation of nano-zero valent iron, and the single reaction pathway and low efficiency of traditional fillers in complex water bodies. This invention relies on the self-doped nitrogen and chelating properties of chitosan. Through the complexation of trivalent iron ions with the amino and hydroxyl groups of chitosan, iron is stabilized in iron-chitosan hydrogel beads in the form of iron-nitrogen and iron-oxygen bonds. Then, through freeze-drying and high-temperature pyrolysis, the iron is reduced to nano-zero valent iron, and pyridine nitrogen and graphitic nitrogen structures are formed under high-temperature conditions, confining the nano-zero valent iron in different nitrogen-type structures, improving the dispersibility of the nano-zero valent iron. Furthermore, the synergistic mechanism of pyridine nitrogen and graphitic nitrogen is utilized to enhance electron transfer efficiency, successfully constructing a composite material with both microscopic galvanic cell effect and redox dual function, achieving simultaneous and efficient removal of nitrogen pollutants and organic matter.

[0008] In a first aspect, the present invention provides a method for preparing a biochar-supported, self-doped pyridine nitrogen-confined nZVI material, the specific steps of which are as follows:

[0009] S1. Prepare a ferric chloride solution, add chitosan and ethylenediaminetetraacetic acid, stir for 3-5 hours, add polyethylene glycol and sodium alginate, stir for 2-3 hours to obtain a mixed solution, add the mixed solution dropwise into a sodium hydroxide solution under stirring conditions, let stand for 12-24 hours, centrifuge, wash until neutral, store at -60℃ for 10-14 hours, freeze dry for 48 hours to obtain CS-Fe microbeads;

[0010] S2. The CS-Fe microspheres obtained in S1 are subjected to two pyrolysis processes under a nitrogen atmosphere to obtain biochar-supported self-doped pyridine nitrogen-confined nZVI material.

[0011] As a preferred embodiment of the present invention, the ferric chloride solution is prepared by anhydrous ferric chloride and an aqueous solution of acetic acid, wherein the concentration of ferric chloride in the ferric chloride solution is 0.1-0.3 mol / L, and the mass fraction of acetic acid in the ferric chloride solution is 1-5%.

[0012] As a preferred embodiment of the present invention, the molecular weight of the polyethylene glycol is 31k-50k.

[0013] As a preferred embodiment of the present invention, the concentration of sodium hydroxide in the sodium hydroxide solution is 0.5-2 mol / L.

[0014] As a preferred embodiment of the present invention, the degree of deacetylation of the chitosan is not less than 95%.

[0015] As a preferred embodiment of the present invention, the ratio of the amount of ferric chloride solution, chitosan, ethylenediaminetetraacetic acid, polyethylene glycol and sodium alginate is 250mL:15g:(7.5-15)g:(1-5)g:(1-2)g;

[0016] It should be noted that in S1, chitosan, as a natural polymer, not only provides carbon and nitrogen sources, but its active groups on the molecular chain also coordinate with metal ions; ethylenediaminetetraacetic acid, as a strong chelating agent, pre-forms a stable and soluble complex with iron ions, ensuring the atomic-level dispersion of iron species and laying the foundation for the formation of highly active pyridine nitrogen structures during pyrolysis; polyethylene glycol, as a pore-forming agent, can create rich pore structures in the carbon skeleton; sodium alginate enhances the mechanical strength and structural integrity of the precursor microspheres through ionic cross-linking; sodium hydroxide solution, as a coagulant, promotes the gelation and shaping of droplets, forming a porous microsphere precursor with uniform size that is easy to process in subsequent pyrolysis.

[0017] As a preferred embodiment of the present invention, the two pyrolysis processes are divided into a first pyrolysis and a second pyrolysis.

[0018] As a preferred embodiment of the present invention, the first pyrolysis temperature is 700-900℃, the heating rate is 5-15℃ / min, and the duration is 2-3h.

[0019] As a preferred embodiment of the present invention, the second pyrolysis temperature is 300°C and the duration is 1-2 hours.

[0020] It should be noted that the first high-temperature pyrolysis carbonizes the organic components into a nitrogen-doped biochar framework, while reducing ferric iron to zero-valent nano-iron and confining it in the carbon matrix, effectively inhibiting particle aggregation; the second low-temperature pyrolysis aims to further stabilize the nitrogen configuration in the material, promote the synergistic distribution of pyridine nitrogen and graphitic nitrogen, optimize the defect structure and electron transport capacity of the carbon layer, and enhance the interaction between nZVI and the carbon support, thereby improving the catalytic stability and reactivity of the composite material.

[0021] It should be reiterated that the technical solution of this invention utilizes the self-doped nitrogen properties of chitosan, and uses polyethylene glycol and sodium alginate to improve porosity and strength, forming a nitrogen-doped iron-carbon micro-electrolysis filler through a two-step pyrolysis process. On one hand, by controlling the iron / nitrogen ratio and pyrolysis temperature, the pyridine nitrogen structure achieves "chemical anchoring-physical confinement" dispersion of nZVI on porous biochar, alleviating the oxidation and aggregation of nano-zero-valent iron. Furthermore, the synergistic effect of multiple nitrogen species, pyridine nitrogen and graphitic nitrogen, optimizes the reaction pathway, increasing NO3- content in nitrate wastewater. - -N removal rate and N2 selectivity of products; finally, based on the formation of a microscopic galvanic cell between zero-valent iron and biochar, with biochar acting as the cathode, the Fe2+ is accelerated by accepting electrons. 0 To NO3 - Electron transfer of -N.

[0022] A second aspect of the present invention provides a biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared by the method described above.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention uses chitosan material and high temperature pyrolysis to reduce nano-zero valent iron in the synthesis process, which has significant advantages such as low cost, high stability, easy scalability and eco-friendliness, and is suitable for industrial production of wastewater treatment materials.

[0025] (2) The biochar-supported self-doped pyridine nitrogen confined nZVI material synthesized in this invention achieves the pore distribution and confined dispersion of nano-zero valent iron on the surface and inside of biochar through a high content of pyridine nitrogen structure and polyethylene glycol pore formation, successfully avoiding the agglomeration of nano-zero valent iron and giving full play to its reducing activity.

[0026] (3) The biochar-supported self-doped pyridine nitrogen-confined nZVI material synthesized in this invention becomes a highly active site through the presence of lone pair electrons in the pyridine nitrogen structure, promoting Fe 0With NO3 - Electron transfer between -N makes the material resistant to NO3. - The degradation of -N pollutants is relatively excellent.

[0027] (4) The self-doped pyridine nitrogen-confined nZVI chelated biochar granular packing material synthesized by the invention optimizes the degradation pathway of nitrate through the synergistic effect of multiple nitrogen species, improves the N2 selectivity in the nitrogen pollutant removal process, and reduces NH4. + The formation of -N products.

[0028] (5) Based on the principle of iron-carbon micro-electrolysis, a large number of micro-galvanic cell structures are formed. Under aeration and acidic conditions, the cathode gains electrons to generate H2O2, which reacts with Fe produced by corrosion in the water environment. 2+ It undergoes a Fenton-like reaction (heterogeneous) with H2O2 to produce highly reactive free radicals (·OH), which can then non-selectively degrade coexisting organic pollutants in water.

[0029] (6) Based on the generation of strong oxidizing free radicals, the material transforms from a single reducing material into a material with both reducing and oxidizing functions, simultaneously performing deep denitrification (reduction pathway) and degrading organic pollutants (oxidation pathway). It can create carbon sources (by oxidizing and degrading large organic molecules to produce small organic molecules), breaking the limitation of low C / N ratio. In addition, the free radical oxidation pathway can effectively degrade biofilms or natural organic matter covering the nZVI surface, giving the material self-cleaning ability, significantly extending its service life in real water bodies, and enhancing its resistance to interference.

[0030] (7) The biochar-supported self-doped pyridine nitrogen-confined nZVI material synthesized in this invention has no change in particle morphology before and after the reaction, and can be recovered by magnetic attraction. It has good stability and recyclability, and at the same time improves the compatibility of the filler in different scenarios.

[0031] In summary, the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared by this invention has comprehensive advantages such as good dispersibility, abundant active sites, optimized reaction pathway, synergistic dual-function, strong anti-interference ability, and recyclability. It is suitable for the efficient remediation of nitrate wastewater and water bodies with complex pollution, and has important practical application value and environmental benefits. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0033] Figure 1 a, 1b, and 1c are SEM images of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 of this invention.

[0034] Figure 1d, 1e, 1f, 1g, and 1h are the EDS results of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 of this invention.

[0035] Figure 1 i represents the particle size distribution of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 of this invention.

[0036] Figure 2 a is the XPS nitrogen element spectrum of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 of this invention.

[0037] Figure 2 b is the XPS iron element spectrum of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 of this invention.

[0038] Figure 2 c represents the XRD phase composition analysis of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 of this invention.

[0039] Figure 3 a, 3b, 3c, and 3d represent the denitrification effects of the biochar-supported self-doped pyridine nitrogen-confined nZVI materials prepared in Examples 1-3 of this invention.

[0040] Figure 4 a, 4b, 4c, and 4d represent the denitrification effects of the biochar-supported self-doped pyridine nitrogen-confined nZVI materials prepared in Comparative Examples 1-3 of this invention.

[0041] Figure 5 a, 5b, 5c, and 5d represent the denitrification effects of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 of this invention under different pH and DO conditions. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The sources of some components in the examples and comparative examples are as follows:

[0044] Table 1

[0045]

[0046] Example 1

[0047] A method for preparing a biochar-supported, self-doped pyridine nitrogen-confined nZVI material is as follows:

[0048] S1. Prepare a 0.3 mol / L ferric chloride solution using a 1% (w / w) aqueous acetic acid solution to obtain a mixed solution. Add 15 g of chitosan with a degree of deacetylation of 95% and 7.5 g of ethylenediaminetetraacetic acid to 250 mL of the mixed solution and stir for 4 h. Add 1.5 g of polyethylene glycol with an average molecular weight of 40 kJ and 1.5 g of sodium alginate and stir for 3 h to obtain a mixed solution. Drop the mixed solution into a 0.5 mol / L sodium hydroxide solution under stirring at 500 r / min. Let stand for 12 h, centrifuge, wash until neutral, store at -60℃ for 12 h, and freeze-dry for 48 h to obtain CS-Fe microbeads.

[0049] S2. The CS-Fe microspheres obtained in S1 were subjected to two pyrolysis processes under a nitrogen atmosphere. The first pyrolysis temperature was 800℃, the heating rate was 15℃ / min, and the duration was 3h. The second pyrolysis temperature was 300℃ and the duration was 2h, resulting in biochar-supported self-doped pyridine nitrogen-confined nZVI material. Example

[0050] A method for preparing a biochar-supported, self-doped pyridine nitrogen-confined nZVI material is as follows:

[0051] S1. Prepare a 0.3 mol / L ferric chloride solution using a 1% (w / w) aqueous acetic acid solution to obtain a mixed solution. Add 15 g of chitosan with a degree of deacetylation of 95% and 7.5 g of ethylenediaminetetraacetic acid to 250 mL of the mixed solution and stir for 4 h. Add 1.5 g of polyethylene glycol with an average molecular weight of 40 kJ and 1.5 g of sodium alginate and stir for 3 h to obtain a mixed solution. Drop the mixed solution into a 0.5 mol / L sodium hydroxide solution under stirring at 500 r / min. Let stand for 12 h, centrifuge, wash until neutral, store at -60℃ for 12 h, and freeze-dry for 48 h to obtain CS-Fe microbeads.

[0052] S2. The CS-Fe microspheres obtained in S1 were subjected to two pyrolysis processes under a nitrogen atmosphere. The first pyrolysis was carried out at a temperature of 900℃ and a heating rate of 15℃ / min for 3 hours. The second pyrolysis was carried out at a temperature of 300℃ for 2 hours to obtain biochar-supported self-doped pyridine nitrogen-confined nZVI material. Example

[0053] A method for preparing a biochar-supported, self-doped pyridine nitrogen-confined nZVI material is as follows:

[0054] S1. Prepare a 0.3 mol / L ferric chloride solution using a 1% (w / w) aqueous acetic acid solution to obtain a mixed solution. Add 15 g of chitosan with a degree of deacetylation of 95% and 7.5 g of ethylenediaminetetraacetic acid to 250 mL of the mixed solution and stir for 4 h. Add 1.5 g of polyethylene glycol with an average molecular weight of 40 kJ and 1.5 g of sodium alginate and stir for 3 h to obtain a mixed solution. Drop the mixed solution into a 0.5 mol / L sodium hydroxide solution under stirring at 500 r / min. Let stand for 12 h, centrifuge, wash until neutral, store at -60℃ for 12 h, and freeze-dry for 48 h to obtain CS-Fe microbeads.

[0055] S2. The CS-Fe microspheres obtained in S1 were subjected to two pyrolysis processes under a nitrogen atmosphere. The first pyrolysis temperature was 700℃, the heating rate was 15℃ / min, and the duration was 3h. The second pyrolysis temperature was 300℃ and the duration was 2h, resulting in biochar-supported self-doped pyridine nitrogen-confined nZVI material.

[0056] Comparative Example 1

[0057] A method for preparing a biochar-supported, self-doped pyridine nitrogen-confined nZVI material is as follows:

[0058] S1. Weigh 7.55g of anhydrous ferric chloride, dissolve it in a 1% acetic acid aqueous solution, and bring the volume to 250mL to obtain a ferric chloride mixed solution with a concentration of 0.1862mol / L. Add 15g of chitosan with a degree of deacetylation of 95% and 7.5g of ethylenediaminetetraacetic acid to the 250mL mixed solution, stir for 4h, add 1.5g of polyethylene glycol with an average molecular weight of 40k and 1.5g of sodium alginate, stir for 3h to obtain a mixed solution, drop the mixed solution into a 0.5mol / L sodium hydroxide solution under stirring at 500r / min, let stand for 12h, centrifuge, wash until neutral, store at -60℃ for 12h, freeze dry for 48h to obtain CS-Fe microbeads;

[0059] S2. The CS-Fe microspheres obtained in S1 were subjected to two pyrolysis processes under a nitrogen atmosphere. The first pyrolysis temperature was 800℃, the heating rate was 15℃ / min, and the duration was 3h. The second pyrolysis temperature was 300℃ and the duration was 2h, resulting in biochar-supported self-doped pyridine nitrogen-confined nZVI material.

[0060] In this comparative example, the mass ratio of Fe to N in chitosan is 2.

[0061] Comparative Example 2

[0062] A method for preparing a biochar-supported, self-doped pyridine nitrogen-confined nZVI material is as follows:

[0063] S1. Weigh 12.17g of anhydrous ferric chloride, dissolve it in a 1% acetic acid aqueous solution, and bring the volume to 250mL to obtain a ferric chloride mixed solution with a concentration of 0.3001mol / L. Add 15g of chitosan with a degree of deacetylation of 95% and 7.5g of ethylenediaminetetraacetic acid to the 250mL mixed solution, stir for 4h, add 1.5g of polyethylene glycol with an average molecular weight of 40k and 1.5g of sodium alginate, stir for 3h to obtain a mixed solution, drop the mixed solution into a 0.5mol / L sodium hydroxide solution under stirring at 500r / min, let stand for 12h, centrifuge, wash until neutral, store at -60℃ for 12h, freeze dry for 48h to obtain CS-Fe microbeads;

[0064] S2. The CS-Fe microspheres obtained in S1 were subjected to two pyrolysis processes under a nitrogen atmosphere. The first pyrolysis temperature was 800℃, the heating rate was 15℃ / min, and the duration was 3h. The second pyrolysis temperature was 300℃ and the duration was 2h, resulting in biochar-supported self-doped pyridine nitrogen-confined nZVI material.

[0065] In this comparative example, the mass ratio of Fe to N in chitosan is 3.

[0066] Comparative Example 3

[0067] A method for preparing a biochar-supported, self-doped pyridine nitrogen-confined nZVI material is as follows:

[0068] S1. Weigh 14.81g of anhydrous ferric chloride, dissolve it in a 1% acetic acid aqueous solution, and bring the volume to 250mL to obtain a ferric chloride mixed solution with a concentration of 0.3652mol / L. Add 15g of chitosan with a degree of deacetylation of 95% and 7.5g of ethylenediaminetetraacetic acid to the 250mL mixed solution, stir for 4h, add 1.5g of polyethylene glycol with an average molecular weight of 40k and 1.5g of sodium alginate, stir for 3h to obtain a mixed solution, drop the mixed solution into a 0.5mol / L sodium hydroxide solution under stirring at 500r / min, let stand for 12h, centrifuge, wash until neutral, store at -60℃ for 12h, freeze dry for 48h to obtain CS-Fe microbeads;

[0069] S2. The CS-Fe microspheres obtained in S1 were subjected to two pyrolysis processes under a nitrogen atmosphere. The first pyrolysis temperature was 800℃, the heating rate was 15℃ / min, and the duration was 3h. The second pyrolysis temperature was 300℃ and the duration was 2h, resulting in biochar-supported self-doped pyridine nitrogen-confined nZVI material.

[0070] In this comparative example, the mass ratio of Fe to N in chitosan is 4.

[0071] The biochar-supported self-doped pyridine nitrogen-confined nZVI materials provided in the above embodiments and comparative examples were tested as follows:

[0072] I. Physicochemical Properties Characterization

[0073] (1) The biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 was tested by scanning electron microscopy (SEM).

[0074] The results showed that the biochar-supported self-doped pyridine nitrogen-confined nZVI material had a multi-level pore structure. Figure 1 a) This porous structure is beneficial for the internal and external loading and mass transfer of nZVI, while the surface particles are observed to be highly dispersed. Figure 1 b, 1c) This indicates the successful preparation and dispersion of nano-zero valent iron.

[0075] (2) Energy dispersive X-ray spectroscopy (EDS) was performed on the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1.

[0076] The results showed that the mass percentages of C, N, O, and Fe in the biochar-supported self-doped pyridine nitrogen-confined nZVI material were 64.03%, 2.16%, 19.68%, and 14.73%, respectively. Figure 1 The values ​​d, 1e, 1f, 1g, and 1h indicate a relatively uniform distribution of iron and nitrogen elements in the material. (Particle size distribution diagram) Figure 1 i) indicates that 44.72% of the particles in the biochar-supported self-doped pyridine nitrogen-confined nZVI material have a particle size of 34.7±4.8 nm and 55.28% have a particle size of 54.7±12.6 nm. The overall particle size is small and the specific surface area is large, thereby improving the reaction efficiency.

[0077] (3) X-ray photoelectron spectroscopy (XPS) was performed on the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1.

[0078] The results show that the nitrogen elemental spectrum of the biochar-supported self-doped pyridine nitrogen-confined nZVI material ( Figure 2 a) The 398.31 eV and 400.50 eV peaks correspond to the electronic orbital peaks of pyridine nitrogen and graphitic nitrogen, respectively, in the iron element spectrum ( Figure 2 b) Obvious photoelectron peaks of 704.52 eV, 711.25 eV, and 724.05 eV appear, corresponding to Fe... 0 and Fe 3+ Fe2p 3 / 2 Fe2p 1 / 2 The electron orbital peak indicates the successful preparation of zero-valent iron and polynitrogen species.

[0079] (4) X-ray diffraction (XRD) was performed on the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 to analyze its phase composition.

[0080] The results showed that the iron peaks at 2θ = 44.36° and 65.06° of the biochar-supported self-doped pyridine nitrogen-confined nZVI material matched the nZVI peak values. Figure 2 c) represents the standard diffraction peaks of the (110) and (200) crystal planes of αFe(0), respectively, which further demonstrates the successful formation of crystalline ZVI on the material.

[0081] II. Denitrification Effect Test

[0082] (I) Effect of pyrolysis temperature on denitrification efficiency

[0083] The denitrification experiment was conducted in 250 mL Erlenmeyer flasks. Each flask contained 250 mL of deionized water, 0.5 mL of nitrate solution (0.5 g N / L), and 0.5 g of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Examples 1-3. A 250 mL solution of 10 mg / L NO3 was then added. - In the NH4+ removal experiment, N2 was bubbled through the flask for 5 minutes before the experiment to ensure an anaerobic environment. The pH was adjusted to 7, and the flask was sealed with a sealing film. The sealed conical flask was shaken at 180 rpm for 24 hours at room temperature. Samples were taken periodically, and the supernatant was filtered through a 0.45 μm filter before the NH4+ was determined by UV-Vis spectrophotometry. + -N, NO2 - -N, NO3 - The remaining concentration of -N was determined to study its denitrification effect, and NO3 was calculated. - The removal rate of -N and the conversion rate of gaseous nitrogen at different times are shown in the following formulas. The results are as follows: Figure 3 As shown.

[0084] ;

[0085] Where: C0, C t t represents the concentration of pollutants at time 0 and time t, respectively, in mg / L; t represents time, in h.

[0086] ;

[0087] In the formula: TN and NO3 at time 0, respectively - -N, NO2 - -N, NH4 + The concentration of -N, where TN = NO3 - -N + NO2 —N + NH4 + -N, TN and NO3 at time t, respectively. - -N, NO2 - -N, NH4 + -N concentration, in mg / L; t, in h.

[0088] like Figure 3 As shown in Figure a, CS-BC@nZVI-700 (biochar-supported self-doped pyridine nitrogen-confined nZVI material - Example 3) releases more NH4. + -N (12.70±1.60 mg / L) is significantly higher than that of CS-BC@nZVI-800 / 900 (Examples 1 / 2) (6.32±1.50 mg / L and 4.46 mg / L), which is due to the lower pyrolysis temperature, leading to instability of the chitosan side groups and the release of ammonia nitrogen. Meanwhile, no NO2 was observed during the denitrification process in any of the three groups of experiments in Examples 1-3. - The generation of -N ( Figure 3 b) This indicates that the pyrolysis temperature has a significant impact on the material properties, and the denitrification pathways of materials formed at different temperatures are different, which is beneficial for the wide application of the material. The nitrate removal rates of CS-BC@nZVI-700 / 800 / 900 (Example 3 / 1 / 2) after 24 h were 74.20±2.40%, 94.03±8.39%, and 60.60%, respectively. Figure 3 c) NO3 in the three batches of experiments in Examples 1-3 - All NO3- contaminants were removed, indicating that the biochar-supported self-doped pyridine nitrogen-confined nZVI materials prepared by this method have good NO3-removal properties. - The role of -N is observed, with the material exhibiting optimal removal efficiency at a pyrolysis temperature of 800 °C. Most nZVI reduces NO3. - The main reaction product during the -N process is NH4. + -N, the TN content did not change significantly before and after the reaction, but the gaseous nitrogen conversion rate during the experiment was analyzed ( Figure 3 d) The gaseous nitrogen conversion rates of CS-BC@nZVI-800 / 900 (Examples 1 / 2) after 24 h were 34.0±24% and 23.4±2.1%, respectively, while the gaseous nitrogen conversion rate of CS-BC@nZVI-700 (Example 3) in the denitrification experiment after 24 h was 0. The results indicate that increasing the pyrolysis temperature affects the denitrification pathway of the material in the reaction, increasing the gaseous nitrogen conversion rate of the product. This demonstrates the application of biochar-supported self-doped pyridine nitrogen-confined nZVI material in NO3… - The advantages of -N polluted wastewater treatment and its broad application prospects in the treatment of low carbon-to-nitrogen ratio wastewater.

[0089] (II) Effect of the mass ratio of Fe to N in chitosan on denitrification efficiency

[0090] The denitrification experiment was conducted in 250 mL Erlenmeyer flasks. Each flask contained 250 mL of deionized water, 0.5 mL of nitrate solution (0.5 g N / L), and 0.5 g of biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Comparative Examples 1-3. A 250 mL solution of 10 mg / L NO3 was then added. - In the NH4+ removal experiment, N2 was bubbled through the flask for 5 min before the experiment to ensure an anaerobic environment. The pH was adjusted to 7, and the flask was sealed with a sealing film. The sealed conical flask was shaken at 180 rpm for 24 h at room temperature. Samples were taken periodically, and the supernatant was filtered through a 0.45 μm filter before the NH4+ was determined by UV-Vis spectrophotometry. + -N, NO2 - -N, NO3 - The remaining concentration of -N was determined to study its denitrification effect, and NO3 was calculated. - -N removal rate and gaseous nitrogen conversion rate at different times.

[0091] like Figure 4 As shown in Figure a, in the batch experiment, the NH4+ of CS-BC@nZVI-2 / 3 / 4 (Comparative Example 1 / 2 / 3) was observed to be significantly reduced after 24 h. + The NO3- concentrations were 6.53±0.45 mg / L, 6.32±1.50 mg / L, and 1.34±0.02 mg / L, respectively. - The NO removal rates were 77.53±1.48%, 94.08±8.39%, and 12.64±1.06%, respectively. Furthermore, no NO2 was detected in any of the three batches of experiments. - The formation of -N indicates poor denitrification performance of the material under high Fe / N conditions, while Fe / N ratios of 2 and 3 achieve better denitrification effects. Further analysis of the gaseous nitrogen conversion rates in the three experimental groups revealed that the gaseous nitrogen conversion rates of CS-BC@nZVI-2 / 3 / 4 (comparative examples 1 / 2 / 3) were 11.3 ± 5.9%, 33.98 ± 23.98%, and 6.52%, respectively, indicating that Fe / N affects the conversion of NO3- by nano-zero-valent iron. - The reduction pathway of -N means that higher chitosan content leads to increased levels of pyridine nitrogen, graphitic nitrogen, and other nitrogen species during pyrolysis, in conjunction with NO3. - When -N undergoes a reduction reaction, it optimizes the electron transfer path, shifting the reduction direction towards the formation of gaseous nitrogen, which is beneficial for reducing NH4+. + The formation of -N products promotes the removal of nitrogen pollutants from wastewater.

[0092] (III) Effects of different pH and DO conditions on nitrogen removal efficiency

[0093] (1) The pH experiment was conducted in four 250 ml Erlenmeyer flasks. Each flask contained 250 ml of deionized water, 0.5 ml of nitrate solution (0.5 g N / L), and 0.5 g of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1. A 250 ml solution of 10 mg / L NO3 was then added to each flask. - In the NH4+ removal experiment, N2 was bubbled through the flask for 5 min before the experiment to ensure an anaerobic environment. The pH was adjusted to 3, 5.7, 7.2, and 9.3, respectively, and the flasks were sealed with sealing film. The sealed conical flasks were shaken at 180 rpm for 24 h at room temperature. Samples were taken periodically, and the supernatant was filtered through a 0.45 μm filter before the NH4+ was determined by UV-Vis spectrophotometry. + -N, NO2 - -N, NO3 - The remaining concentration of -N was determined to study its denitrification effect, and NO3 was calculated. - -N removal rate and gaseous nitrogen conversion rate at different times.

[0094] (2) The DO experiment was conducted in three 250 ml Erlenmeyer flasks. Each flask contained 250 ml of deionized water, 0.5 ml of nitrate solution (0.5 g N / L), and 0.5 g of the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1. A 250 ml solution of 10 mg / L NO3 was then added to each flask. - In the NH4+ removal experiment, N2 was introduced before the experiment to ensure that the DO environment in the three conical flasks was anaerobic (0.15 mg / L), anoxic (0.35 mg / L), and aerobic (1.47 mg / L), respectively. The pH was adjusted to 7, and the flasks were sealed with sealing film. The sealed conical flasks were shaken at 180 rpm for 24 h at room temperature. Samples were taken periodically, and the supernatant was filtered through a 0.45 μm filter and the NH4+ was determined by UV-Vis spectrophotometry. + -N, NO2 - -N, NO3 - The remaining concentration of -N was calculated, and the nitrate removal rate of the material at 12h and 24h was evaluated to assess its denitrification effect.

[0095] ;

[0096] Where: C0, C t t represents the concentration of pollutants at time 0 and time t, respectively, in mg / L; t represents time, in h.

[0097] Depend on Figure 5From a and b, it can be seen that under pH conditions of 3, 5, 7, and 9, the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 of this invention can achieve efficient nitrate removal under different pH conditions. It was observed that under acidic and alkaline conditions, the nitrate removal efficiency of the biochar-supported self-doped pyridine nitrogen-confined nZVI material did not show significant fluctuations due to pH changes; the nitrate degradation rate of the material was above 84% after 24 hours at different pH levels. Simultaneously, changes in dissolved oxygen had a relatively small impact on the material. Figure 5 c. As shown in 5d, the biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared in Example 1 exhibited high nitrate removal rates under different dissolved oxygen conditions. Under three dissolved oxygen conditions (anaerobic, anoxic, and aerobic), the nitrate removal rates at 12h and 24h were both above 87%. This demonstrates that the biochar-supported self-doped pyridine nitrogen-confined nZVI material provided by this invention possesses both high nitrate removal rates and broad pH and DO applicability.

Claims

1. A method for preparing a biochar-supported self-doped pyridine nitrogen-confined nZVI material, characterized in that: Specifically, the following steps are included: S1. Prepare a 0.3 mol / L ferric chloride solution using a 1% (w / w) aqueous acetic acid solution to obtain a mixed solution. Add 15 g of chitosan with a degree of deacetylation of 95% and 7.5 g of ethylenediaminetetraacetic acid to 250 mL of the mixed solution and stir for 4 h. Add 1.5 g of polyethylene glycol with an average molecular weight of 40 kJ and 1.5 g of sodium alginate and stir for 3 h to obtain a mixed solution. Drop the mixed solution into a 0.5 mol / L sodium hydroxide solution under stirring at 500 r / min. Let stand for 12 h, centrifuge, wash until neutral, store at -60℃ for 12 h, and freeze-dry for 48 h to obtain CS-Fe microbeads. S2. The CS-Fe microspheres obtained in S1 were subjected to two pyrolysis processes under a nitrogen atmosphere. The first pyrolysis temperature was 800℃, the heating rate was 15℃ / min, and the duration was 3h. The second pyrolysis temperature was 300℃ and the duration was 2h, resulting in biochar-supported self-doped pyridine nitrogen-confined nZVI material.

2. A biochar-supported self-doped pyridine nitrogen-confined nZVI material prepared by the method described in claim 1.

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