Process for preparing nitrogen-rich anchored iron atom magnetic biochar through low-temperature impregnation and method for adsorbing water pollutants by using nitrogen-rich anchored iron atom magnetic biochar

Abstract

The invention belongs to the technical field of biomass utilization, and particularly relates to a process for preparing nitrogen-rich anchored iron atom magnetic charcoal through low-temperature impregnation and application of the nitrogen-rich anchored iron atom magnetic charcoal in water pollutant adsorption. The method comprises the following steps: mixing biomass wastes with potassium hydroxide, and carrying out nitrogen-rich pyrolysis in ammonia gas and inert gas to form nitrogen-rich biochar. Dipping the nitrogen-rich biochar in a ferric trichloride solution, and finally, performing low-temperature drying, so that iron is firmly anchored on the surface of the biochar by a nitrogen functional group in a monatomic form. Different from a traditional high-temperature pyrolysis method that iron is converted into iron oxide at high temperature, it is ensured that part of iron is distributed in a monatomic form, and the bonding strength between iron and nitrogen and the interaction between the iron and nitrogen and pollutants are greatly improved. The nitrogen-rich anchored iron monatomic magnetic biochar has a developed pore structure and abundant surface functional groups, and can efficiently adsorb organic pollutants and the like in water. The method has the advantages of being short in preparation period, low in energy consumption, capable of being regenerated and recycled and the like, a new solution is provided for water pollutant treatment, and high-value utilization of biomass waste is achieved.

Description

Technical Field

[0001] The present invention relates to the field of biomass utilization, and in particular to a process for preparing nitrogen-rich magnetic biochar anchored with iron atoms by low-temperature impregnation and a method for adsorbing water pollutants thereof. Background Art

[0002] There are many kinds of pollutants in water bodies, including organic pollutants (such as pesticides, dissolved organic matter in industrial wastewater) and inorganic pollutants (such as heavy metal ions, minerals, etc.). These pollutants not only threaten the stability of the ecosystem, but also pose a serious threat to human health. At present, many traditional water treatment technologies, such as ion exchange, photocatalytic degradation, electrocatalytic oxidation, extraction, etc., have been widely used to remove water pollutants. However, these methods generally have problems such as high cost, high energy consumption, complex process, and unstable treatment efficiency. In addition, traditional adsorbents such as metal-organic frameworks, clays, zeolites, etc., although they can remove pollutants in water to a certain extent, their preparation costs are high, and the adsorption capacity and speed of various pollutants often cannot meet the needs of actual applications.

[0003] Biochar, as a low-cost, environmentally friendly adsorption material, has been widely studied and applied. Although biochar prepared by traditional pyrolysis methods has a large specific surface area and rich pore structure, its surface activity and adsorption performance are limited, making it difficult to meet the requirements for efficient removal of water pollutants. Therefore, the study of modified biochar has become a key approach to improving its adsorption performance. In particular, the loading of elements such as nitrogen and iron can significantly improve its adsorption capacity for pollutants in water. Previous studies have attempted to load nitrogen and iron into biochar to enhance its adsorption performance, but most methods still use high-temperature pyrolysis. However, high-temperature pyrolysis often leads to the oxidation of iron, forming iron oxide particles, which not only reduces the catalytic activity of iron but also affects the pore structure and adsorption efficiency of the biochar. Furthermore, the iron oxides loaded on the biochar are easily detached during use, resulting in a loss of performance. Therefore, a new preparation process is urgently needed that can effectively avoid the formation of iron oxides and stably anchor the iron to enhance its interaction with pollutants and adsorption performance. The present invention innovatively prepares nitrogen-rich magnetic biochar anchored to single iron atoms by combining low-temperature impregnation with nitrogen-rich pyrolysis. This method produces biochar at a relatively low temperature, significantly reducing the oxidation of the iron element during high-temperature pyrolysis and ensuring the stability and efficient adsorption capacity of the single iron atoms. This nitrogen-rich magnetic biochar anchored to single iron atoms not only has a well-developed pore structure and abundant surface functional groups, but also can efficiently adsorb a variety of organic and inorganic pollutants in water, providing a new solution for the treatment of water pollutants. Summary of the Invention

[0004] In view of the problems in the prior art that high-temperature pyrolysis leads to the formation of iron oxides, reduced catalytic activity of iron elements and limited adsorption performance, the present invention aims to provide a low-temperature impregnation process for preparing nitrogen-rich iron-anchored single-atom magnetic biochar and a method for efficiently adsorbing water pollutants. This method innovatively prepares magnetic biochar with stable iron single atoms anchored by nitrogen atoms by combining low-temperature nitrogen-rich pyrolysis and low-temperature impregnation processes, significantly improving the catalytic activity of iron and the adsorption performance of biochar. This process is low-cost and simple to operate, and can efficiently prepare large quantities of nitrogen-rich and iron-rich magnetic biochar adsorbents, which can be widely used in the efficient removal of various organic and inorganic pollutants in water bodies. Through the present invention, high-value utilization of biomass waste can be achieved, and a new solution is provided for the economic management of water pollutants.

[0005] To achieve the above objectives, the present invention provides a process for preparing nitrogen-rich, iron-anchored magnetic biochar by low-temperature impregnation and a method for efficiently adsorbing water pollutants, comprising the following steps:

[0006] S1: crushing the biomass waste into particles smaller than 100 mesh and drying them;

[0007] S2: The biomass waste in step S1 is fully mixed with the catalyst potassium hydroxide in a mass ratio of 1:4-4:1, and a nitrogen-enriched pyrolysis reaction is carried out in an atmosphere of ammonia and an inert gas. The mixture is subjected to a rapid catalytic pyrolysis reaction, which greatly promotes the formation of nitrogen-rich functional groups to obtain original nitrogen-rich biochar;

[0008] S3: placing the original nitrogen-enriched biochar from step S2 into a flask, adding ferric chloride hexahydrate and distilled water into the flask, and shaking to mix evenly;

[0009] S4: drying the mixture obtained in step S3 in an oven to obtain iron-nitrogen co-doped biochar before washing;

[0010] S5: The iron-nitrogen co-doped biochar before washing in step S4 is treated by an oscillation washing method, and after filtering and drying steps, nitrogen-anchored iron-rich magnetic biochar having a developed pore structure, enriched nitrogen-containing functional groups and nitrogen-anchored iron single atoms is obtained.

[0011] The concept of the present invention is to significantly improve the adsorption capacity of organic and inorganic pollutants in water bodies by optimizing the structure and surface chemical properties of biochar. First, biomass waste is mixed with the catalyst potassium hydroxide in a specific ratio and subjected to nitrogen-enriched pyrolysis reaction in an atmosphere of ammonia and inert gas to obtain raw biochar rich in nitrogen functional groups. In this process, ammonia, as a nitrogen source, reacts chemically with the biomass, not only introducing a large number of nitrogen-containing functional groups, but also promoting the formation of the biochar pore structure, enhancing its specific surface area and adsorption performance. Next, the nitrogen-enriched biochar is placed in a solution containing ferric chloride hexahydrate for low-temperature impregnation. During the initial impregnation process, the iron ions are gradually reduced to iron single atoms and combined with nitrogen atoms, stably anchored on the biomass surface, forming a structure rich in nitrogen-anchored iron single atoms. Compared with traditional high-temperature pyrolysis methods, this process effectively avoids iron oxidation, ensuring that the iron single atoms are loaded on the biochar surface in a stable form, thereby retaining its excellent catalytic and adsorption activity. Through this method, the interaction between single iron atoms and the abundant nitrogen functional groups on the surface of biochar is enhanced, significantly improving the biochar's adsorption capacity for a variety of organic and inorganic pollutants in water. The resulting magnetic biochar, which is rich in nitrogen and anchored with single iron atoms, not only has a well-developed pore structure and abundant surface functional groups, but is also able to efficiently adsorb pollutants in water, providing an efficient and sustainable solution for the treatment of water pollutants. The process is simple, low-cost, and can be mass-produced. It has good regeneration capacity and can effectively improve the efficiency of high-value utilization and resource application of biomass waste.

[0012] Furthermore, the biomass in step S1 is one or more of bamboo, cotton stalks, rice husks, corn stalks, and wheat straw, and the drying temperature is 100° C.-150° C., and the drying time is 10 h-30 h.

[0013] Furthermore, in step S2, the inert gas is argon or nitrogen, and the total gas flow rate of the inert gas and ammonia is 200 mL / min-500 mL / min, wherein the proportion of ammonia in the total gas is 10%-100%. The biomass catalytic nitrogen-enriched pyrolysis temperature is 400°C-800°C, and the reaction time is 10-60 minutes.

[0014] Furthermore, in step S3, the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate is 1:4-4:1, the mass ratio of the total mass of the original nitrogen-rich biochar and ferric chloride hexahydrate to distilled water is 1:3-1:10, the oscillation temperature is 15°C-35°C, the oscillation amplitude is 100rpm-300rpm, and the oscillation time is 10h-30h.

[0015] Furthermore, the drying temperature in step S4 is 100° C.-150° C., and the drying time is 10 h-30 h.

[0016] Furthermore, in step S5, the mass ratio of the iron-nitrogen co-doped biochar to the washing solution before washing is 1:100-1:200. The oscillation temperature is 15°C-35°C, the oscillation amplitude is 100-300 rpm, and the oscillation time is 10 hours-30 hours. The washing solution can be dilute hydrochloric acid or deionized water.

[0017] Furthermore, the drying temperature in step S5 is 100° C.-150° C., and the drying time is 10 h-30 h.

[0018] Furthermore, the magnetic biochar rich in nitrogen-anchored iron atoms obtained in step S5 has a developed pore structure, is enriched in nitrogen-containing functional groups, and has nitrogen-anchored iron single atoms loaded on the surface.

[0019] Furthermore, the wastewater contains phenol, bisphenol A, copper ions, chromium ions and lead ions as water pollutants.

[0020] Furthermore, the dosage of the nitrogen-enriched iron-anchored magnetic biochar is 10 mg / L-200 mg / L.

[0021] In general, the above technical solutions conceived by the present invention can bring the following beneficial effects compared with the prior art:

[0022] (1) This invention innovatively prepares nitrogen-rich magnetic biochar anchored with single iron atoms by first performing nitrogen-enriched pyrolysis followed by low-temperature impregnation. Compared with traditional high-temperature pyrolysis methods, this method avoids the formation of iron oxides, ensuring that single iron atoms are stably loaded on the biochar surface, thereby retaining the excellent catalytic activity and adsorption properties of iron.

[0023] (2) In the technical solution of the present invention, single iron atoms are anchored to the biochar surface through a low-temperature impregnation method, forming a strong interaction with nitrogen-rich functional groups. The presence of single iron atoms not only improves the adsorption capacity of biochar but also, through synergistic interaction with nitrogen functional groups, further enhances its adsorption performance for various pollutants in water, especially its ability to remove organic pollutants and heavy metal ions.

[0024] (3) During the nitrogen-rich pyrolysis process, the use of potassium hydroxide as a catalyst effectively promoted the formation of microporous and mesoporous structures in the biochar, significantly increasing the specific surface area of ​​the biochar. The multi-level pore structure not only improved the adsorption rate and efficiency, but also enhanced the transport capacity of the biochar, ensuring stable performance during long-term use and avoiding the problem of pore blockage.

[0025] (4) The nitrogen-enriched, iron-anchored magnetic biochar prepared by the present invention can be regenerated through a simple washing and drying step, using deionized water as the washing solution, without the need for hazardous chemical reagents. This regeneration method is not only low-cost, safe, and environmentally friendly, but also significantly reduces long-term operating costs, providing an economic advantage for practical applications.

[0026] (5) The nitrogen-rich, iron-anchored magnetic biochar prepared in this invention not only performs well in water pollutant treatment but also demonstrates broad application potential. Its versatility enables this material to play a role in a variety of fields, including heavy metal ion removal, soil improvement, and electrode material development, offering sustainable development potential for commercial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a fitting diagram of the adsorption isotherm of phenol adsorbed by the magnetic biochar rich in nitrogen and anchored with iron single atoms in Example 1 of the present invention;

[0028] Figure 2 This is a fitting diagram of the adsorption isotherm of phenol adsorbed by the magnetic biochar rich in nitrogen and anchored with iron single atoms in Example 2 of the present invention;

[0029] Figure 3 This is a fitting diagram of the adsorption isotherm of phenol adsorbed by the magnetic biochar rich in nitrogen and anchored with iron single atoms in Example 3 of the present invention;

[0030] Figure 4 This is the fitting diagram of the adsorption isotherm of copper ions adsorbed by the magnetic biochar rich in nitrogen and anchored with iron single atoms in Examples 4-6;

[0031] Figure 5 The nitrogen adsorption and desorption curves of the magnetic biochar with nitrogen-rich iron single atoms anchored in Examples 1-3 are shown;

[0032] Figure 6 XRD pattern of magnetic biochar with nitrogen-rich anchored iron single atoms in Examples 1-3. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0034] The present invention provides a low-temperature impregnation process for preparing nitrogen-rich, iron-anchored magnetic biochar and a method for efficiently adsorbing water pollutants, which specifically includes the following steps:

[0035] (1): Grind the biomass waste into particles smaller than 100 mesh and dry them;

[0036] (2): The biomass waste in step (1) is fully mixed with the catalyst potassium hydroxide in a mass ratio of 1:4-4:1, and a nitrogen-rich pyrolysis reaction is carried out in an atmosphere where ammonia and an inert gas coexist. The mixture is subjected to a rapid catalytic pyrolysis reaction, which greatly promotes the formation of nitrogen-rich functional groups and obtains original nitrogen-rich biochar;

[0037] (3): Place the original nitrogen-rich biochar from step (2) in a flask, add ferric chloride hexahydrate and distilled water into the flask, and shake to mix evenly;

[0038] (4): drying the mixture obtained in step (3) in an oven to obtain iron-nitrogen co-doped biochar before washing;

[0039] (5) The iron-nitrogen co-doped biochar before washing in step (4) is treated by an oscillation washing method, and after filtering and drying steps, a magnetic biochar having a developed pore structure, enriched nitrogen-containing functional groups and nitrogen-anchored iron atoms is obtained.

[0040] (6): The magnetic biochar rich in nitrogen and anchored with iron single atoms obtained in step (5) is used to conduct adsorption kinetics and adsorption isotherm experiments on water pollutants.

[0041] The biomass in step (1) is one or more of bamboo, cotton stalks, rice husks, corn stalks, and wheat straw, and the drying temperature is 100° C.-150° C. and the drying time is 10 h-30 h.

[0042] In step (2), the inert gas is argon or nitrogen, and the total gas flow rate of the inert gas and ammonia is 200 mL / min-500 mL / min, wherein the proportion of ammonia in the total gas is 10%-100%. The temperature of the biomass catalytic nitrogen-enriched pyrolysis is 400°C-800°C, and the reaction time is 10-60 minutes.

[0043] In step (3), the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate is 1:4-4:1, the mass ratio of the total mass of the original nitrogen-rich biochar and ferric chloride hexahydrate to distilled water is 1:3-1:10, the oscillation temperature is 15°C-35°C, the oscillation amplitude is 100rpm-300rpm, and the oscillation time is 10h-30h.

[0044] The drying temperature in step (4) is 100° C.-150° C., and the drying time is 10 h-30 h.

[0045] In step (5), the mass ratio of the iron-nitrogen co-doped biochar to the washing solution before washing is 1:100-1:200. The shaking temperature is 15°C-35°C, the shaking amplitude is 100 rpm-300 rpm, and the shaking time is 10 hours-30 hours. The washing solution can be dilute hydrochloric acid or deionized water. The drying temperature is 100°C-150°C, and the drying time is 10 hours-30 hours.

[0046] In step (6), the concentration of water pollutants is 10-1000 mg / L, and the amount of nitrogen-rich iron-anchored magnetic biochar added is 10 mg-200 mg.

[0047] The conception principle of the above invention is: by optimizing the structure and surface chemical properties of biochar, its adsorption capacity for organic and inorganic pollutants in water bodies can be significantly improved. First, biomass waste is mixed with the catalyst potassium hydroxide in a specific proportion, and a nitrogen-rich pyrolysis reaction is carried out in an atmosphere of ammonia and inert gas to obtain raw biochar rich in nitrogen functional groups. In this process, ammonia as a nitrogen source reacts chemically with biomass, not only introducing a large number of nitrogen-containing functional groups, but also promoting the formation of biochar pore structure, enhancing its specific surface area and adsorption performance. Then, the nitrogen-rich biochar is placed in a solution containing ferric chloride hexahydrate for low-temperature impregnation. During the preliminary impregnation process, iron ions are gradually reduced to iron single atoms and combined with nitrogen atoms, stably anchored on the biomass surface, forming a nitrogen-rich iron single atom anchored structure. Compared with the traditional high-temperature pyrolysis method, this process effectively avoids the oxidation of iron, ensuring that the iron single atoms are loaded on the biochar surface in a stable form, thereby retaining its excellent catalytic and adsorption activity. Through this method, the interaction between single iron atoms and the abundant nitrogen functional groups on the biochar surface is enhanced, significantly improving the biochar's adsorption capacity for a variety of organic and inorganic pollutants in water. The resulting magnetic biochar, rich in nitrogen-anchored iron atoms, not only possesses a well-developed pore structure and abundant surface functional groups, but is also capable of efficiently adsorbing pollutants in water, providing an efficient and sustainable solution for the treatment of water pollutants. The process is simple, low-cost, and can be mass-produced. It has good regeneration capacity and can effectively improve the high-value utilization and resource application of biomass waste.

[0048] In order to illustrate the method of the present invention in more detail, the following further describes Example 1 with reference to specific examples.

[0049] The present invention provides a method for preparing nitrogen-rich magnetic biochar anchored with iron atoms by low-temperature impregnation and a method for efficiently adsorbing water pollutants. The method specifically includes the following steps:

[0050] S1: After crushing bamboo into particles smaller than 100 mesh, drying in an oven at 105°C for 24 hours to obtain bamboo chips;

[0051] S2: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 600°C, take 4 g of the bamboo chips raw material obtained in step S1 and 2 g of potassium hydroxide and mix them thoroughly. The mixture is quickly fed into the middle of the reactor. The reaction time is 30 min to fully pyrolyze the biomass. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 10%, to obtain original nitrogen-rich biochar.

[0052] S3: Place the original nitrogen-rich biochar obtained in step S2 in a 250 mL flask, add ferric chloride hexahydrate, and maintain the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate at 1:1. Then add 200 mL of deionized water, place it in a shaker, and shake it at 150 rpm at a temperature of 25°C for 24 hours to ensure that the iron is evenly distributed in the nitrogen-rich biochar and is completely anchored.

[0053] S4: The mixture obtained in step S3 is placed in an oven for drying at a temperature of 105° C. for 24 hours to obtain iron-nitrogen co-doped biochar before washing.

[0054] S5: Treat the iron-nitrogen co-doped biochar from step S4 by oscillating and washing. Oscillate and wash the biochar at 150 rpm for 24 hours at 25°C. Wash the biochar multiple times with deionized water to remove any unanchored residues. After washing, filter the biochar with filter paper and dry it in an oven at 105°C for 24 hours. This yields a nitrogen-anchored iron-rich magnetic biochar with a well-developed porous structure, enriched nitrogen-containing functional groups, and nitrogen-anchored iron atoms.

[0055] S6: Adsorption experiments were conducted using the nitrogen-enriched iron-anchored magnetic biochar obtained in step S5. First, an adsorption kinetics experiment was conducted using a 100 mg / L phenol solution and 25 mg of the nitrogen-enriched iron-anchored magnetic biochar. Next, an adsorption isotherm experiment was conducted using solutions with phenol concentrations of 20, 50, 80, 100, 150, and 200 mg / L and 25 mg of the nitrogen-enriched iron-anchored magnetic biochar to measure its adsorption performance for phenol.

[0056] The obtained nitrogen-rich magnetic biochar anchored with iron single atoms has a specific surface area of ​​473.05 m 2 / g, and the total pore volume is 0.291cm 3 / g. The nitrogen doping accounted for 2.4%, the iron doping accounted for 7.12%, and the maximum adsorption capacity of phenol was 166.053 mg / g.

[0057] Example 2

[0058] This embodiment is the same as embodiment 1, except that the pyrolysis reaction temperature in step S4 is 700°C.

[0059] The obtained nitrogen-rich magnetic biochar anchored with iron single atoms has a specific surface area of ​​796.05 m 2 / g, and the total pore volume is 0.422cm 3 / g. The nitrogen doping ratio is 3.11%, the iron doping ratio is 7.74%, and the maximum adsorption capacity of phenol is 222.742 mg / g.

[0060] Example 3

[0061] This embodiment is the same as embodiment 1, except that the pyrolysis reaction temperature in step S4 is 800°C.

[0062] The obtained magnetic biochar with nitrogen-rich anchored iron single atoms has a specific surface area of ​​814.19 m 2 / g, and the total pore volume is 0.501cm 3 / g. The nitrogen doping accounted for 3.92%, the iron doping accounted for 8.16%, and the maximum adsorption capacity of phenol was 263.096 mg / g.

[0063] Example 4

[0064] S1: After crushing bamboo into particles smaller than 100 mesh, drying in an oven at 105°C for 24 hours to obtain bamboo chips;

[0065] S2: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 600°C, take 4 g of the bamboo chips raw material obtained in step S1 and 2 g of potassium hydroxide and mix them thoroughly. The mixture is quickly fed into the middle of the reactor. The reaction time is 30 min to fully pyrolyze the biomass. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 10%, to obtain original nitrogen-rich biochar.

[0066] S3: Place the original nitrogen-rich biochar obtained in step S2 in a 250 mL flask, add ferric chloride hexahydrate, and maintain the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate at 1:1. Then add 200 mL of deionized water, place it in a shaker, and shake it at 150 rpm at a temperature of 25°C for 24 hours to ensure that the iron is evenly distributed in the nitrogen-rich biochar and is completely anchored.

[0067] S4: The mixture obtained in step S3 is placed in an oven for drying at a temperature of 105° C. for 24 hours to obtain iron-nitrogen co-doped biochar before washing.

[0068] S5: Treat the iron-nitrogen co-doped biochar from step S4 by oscillating and washing. Oscillate and wash the biochar at 150 rpm for 24 hours at 25°C. Wash the biochar multiple times with deionized water to remove any unanchored residues. After washing, filter the biochar with filter paper and dry it in an oven at 105°C for 24 hours. This yields a nitrogen-anchored iron-rich magnetic biochar with a well-developed porous structure, enriched nitrogen-containing functional groups, and nitrogen-anchored iron atoms.

[0069] S6: Adsorption experiments were conducted using the nitrogen-enriched iron-anchored magnetic biochar obtained in step S5. First, an adsorption kinetics experiment was conducted using a 100 mg / L copper ion solution and 25 mg of the nitrogen-enriched iron-anchored magnetic biochar. Next, an adsorption isotherm experiment was conducted using solutions with copper ion concentrations of 20, 50, 80, 100, 150, and 200 mg / L, and 25 mg of the nitrogen-enriched iron-anchored magnetic biochar was added to measure its copper ion adsorption performance.

[0070] The obtained magnetic biochar with nitrogen-rich anchored iron single atoms has a specific surface area of ​​473.05 m 2 / g, and the total pore volume is 0.291cm 3 / g. The nitrogen element doping accounted for 2.4%, the iron element doping accounted for 7.12%, and the maximum adsorption capacity of copper ions was 8.233 mg / g.

[0071] Example 5

[0072] This embodiment is the same as embodiment 4, except that the pyrolysis reaction temperature in step S4 is 700°C.

[0073] The obtained nitrogen-rich magnetic biochar anchored with iron single atoms has a specific surface area of ​​796.05 m 2 / g, and the total pore volume is 0.422cm 3 / g. The nitrogen element doping accounts for 3.11%, the iron element doping accounts for 7.74%, and the maximum adsorption capacity of copper ions is 13.977mg / g.

[0074] Example 6

[0075] This embodiment is the same as embodiment 4, except that the pyrolysis reaction temperature in step S4 is 800°C.

[0076] The obtained magnetic biochar with nitrogen-rich anchored iron single atoms has a specific surface area of ​​814.19 m 2 / g, and the total pore volume is 0.501cm 3 / g. The nitrogen element doping accounts for 3.92%, the iron element doping accounts for 8.16%, and the maximum adsorption capacity of copper ions is 15.696mg / g.

[0077] Example 7

[0078] This embodiment is the same as embodiment 1, except that the pyrolysis reaction temperature in step S4 is 400°C.

[0079] The obtained nitrogen-rich magnetic biochar anchored with iron single atoms has a specific surface area of ​​410.976 m 2 / g, and the total pore volume is 0.201cm 3 / g, and the maximum adsorption capacity of phenol is 116.403 mg / g.

[0080] Example 8

[0081] This embodiment is the same as embodiment 1, except that the pyrolysis reaction temperature in step S4 is 500°C.

[0082] The obtained magnetic biochar with nitrogen-rich anchored iron single atoms has a specific surface area of ​​423.163 m 2 / g, and the total pore volume is 0.211cm 3 / g, and the maximum adsorption capacity of phenol is 142.373 mg / g.

[0083] Example 9

[0084] This embodiment is the same as embodiment 4, except that the pyrolysis reaction temperature in step S4 is 400°C.

[0085] The obtained nitrogen-rich magnetic biochar anchored with iron single atoms has a specific surface area of ​​410.976 m 2 / g, and the total pore volume is 0.201cm 3 / g, and the maximum adsorption capacity of copper ions is 4.538 mg / g.

[0086] Example 10

[0087] This embodiment is the same as embodiment 4, except that the pyrolysis reaction temperature in step S4 is 500°C.

[0088] The obtained magnetic biochar with nitrogen-rich anchored iron single atoms has a specific surface area of ​​423.163 m 2 / g, and the total pore volume is 0.211cm 3 / g, and the maximum adsorption capacity of copper ions is 6.621 mg / g.

[0089] Example 11

[0090] S1: After crushing rice husks into particles smaller than 100 mesh, drying them in an oven at 105°C for 24 hours to obtain bamboo chips;

[0091] S2: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 800°C, take 2 g of the bamboo chips raw material obtained in step S1 and 1 g of potassium hydroxide and mix them thoroughly. The mixture is quickly fed into the middle of the reactor. The reaction time is 60 min to fully pyrolyze the biomass. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 30%, to obtain original nitrogen-rich biochar.

[0092] S3: Place the original nitrogen-rich biochar obtained in step S2 in a 250 mL flask, add ferric chloride hexahydrate, and maintain the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate at 2:1. Then add 200 mL of deionized water, place it in a shaker, and shake it at 150 rpm at a temperature of 25°C for 24 hours to ensure that the iron is evenly distributed in the nitrogen-rich biochar and is completely anchored.

[0093] S4: The mixture obtained in step S3 is placed in an oven for drying at a temperature of 105° C. for 24 hours to obtain iron-nitrogen co-doped biochar before washing.

[0094] S5: Treat the iron-nitrogen co-doped biochar from step S4 by oscillating and washing. Oscillate and wash the biochar at 150 rpm for 24 hours at 25°C. Wash the biochar multiple times with deionized water to remove any unanchored residues. After washing, filter the biochar with filter paper and dry it in an oven at 105°C for 24 hours. This yields a nitrogen-anchored iron-rich magnetic biochar with a well-developed porous structure, enriched nitrogen-containing functional groups, and nitrogen-anchored iron atoms.

[0095] S6: Adsorption experiments were conducted using the nitrogen-rich, iron-anchored magnetic biochar obtained in step S5. First, an adsorption kinetics experiment was conducted using a 100 mg / L phenol solution and 50 mg of the nitrogen-rich, iron-anchored magnetic biochar. Next, an adsorption isotherm experiment was conducted using solutions with phenol concentrations of 20, 50, 80, 100, 150, and 200 mg / L and 30 mg of the nitrogen-rich, iron-anchored magnetic biochar to measure its adsorption performance for phenol.

[0096] The obtained magnetic biochar with nitrogen-rich anchored iron single atoms has a specific surface area of ​​more than 800m 2 / g, the iron content is 6%, and the phenol removal rate can reach 85%.

[0097] Example 12

[0098] S1: After crushing corn stalks into particles smaller than 100 mesh, drying them in an oven at 105°C for 24 hours to obtain bamboo chips;

[0099] S2: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 700°C, take 2 g of the bamboo chips raw material obtained in step S1 and 1 g of potassium hydroxide and mix them thoroughly. The mixture is quickly fed into the middle of the reactor. The reaction time is 20 min to fully pyrolyze the biomass. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 50%, to obtain original nitrogen-rich biochar.

[0100] S3: Place the original nitrogen-rich biochar obtained in step S2 in a 250 mL flask, add ferric chloride hexahydrate, and maintain the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate at 1:1. Then add 200 mL of deionized water, place it in a shaker, and shake it at 150 rpm at a temperature of 25°C for 24 hours to ensure that the iron is evenly distributed in the nitrogen-rich biochar and is completely anchored.

[0101] S4: The mixture obtained in step S3 is placed in an oven for drying at a temperature of 105° C. for 24 hours to obtain iron-nitrogen co-doped biochar before washing.

[0102] S5: Treat the iron-nitrogen co-doped biochar from step S4 by oscillating and washing. Oscillate and wash the biochar at 150 rpm for 24 hours at 25°C. Wash the biochar multiple times with deionized water to remove any unanchored residues. After washing, filter the biochar with filter paper and dry it in an oven at 105°C for 24 hours. This yields a nitrogen-anchored iron-rich magnetic biochar with a well-developed porous structure, enriched nitrogen-containing functional groups, and nitrogen-anchored iron atoms.

[0103] S6: Adsorption kinetics and adsorption isotherm experiments were conducted on phenol using the nitrogen-rich iron-anchored magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 200 mg / L phenol solution with 20 mg of the nitrogen-rich iron-anchored magnetic biochar added. The adsorption isotherm experiment used 20, 50, 80, and 100 mg / L phenol solutions with 20 mg of the nitrogen-rich iron-anchored magnetic biochar added.

[0104] The obtained magnetic biochar with nitrogen-rich anchored iron single atoms has a specific surface area of ​​more than 650m 2 / g, the iron content is 5%, and the phenol removal rate can reach 80%.

[0105] Example 13

[0106] S1: After crushing corn stalks into particles smaller than 100 mesh, drying them in an oven at 105°C for 24 hours to obtain bamboo chips;

[0107] S2: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 600°C, take 2 g of the bamboo chips raw material obtained in step S1 and 1 g of potassium hydroxide and mix them thoroughly. The mixture is quickly fed into the middle of the reactor. The reaction time is 20 min to fully pyrolyze the biomass. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 50%, to obtain original nitrogen-rich biochar.

[0108] S3: Place the original nitrogen-rich biochar obtained in step S2 in a 250 mL flask, add ferric chloride hexahydrate, and maintain the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate at 1:2. Then add 200 mL of deionized water, place it in a shaker, and shake it at 150 rpm at a temperature of 25°C for 24 hours to ensure that the iron is evenly distributed in the nitrogen-rich biochar and is completely anchored.

[0109] S4: The mixture obtained in step S3 is placed in an oven for drying at a temperature of 105° C. for 24 hours to obtain iron-nitrogen co-doped biochar before washing.

[0110] S5: Treat the iron-nitrogen co-doped biochar from step S4 by oscillating and washing. Oscillate and wash the biochar at 150 rpm for 24 hours at 25°C. Wash the biochar multiple times with deionized water to remove any unanchored residues. After washing, filter the biochar with filter paper and dry it in an oven at 105°C for 24 hours. This yields a nitrogen-anchored iron-rich magnetic biochar with a well-developed porous structure, enriched nitrogen-containing functional groups, and nitrogen-anchored iron atoms.

[0111] S6: Adsorption kinetics and adsorption isotherm experiments were conducted on phenol using the nitrogen-rich iron-anchored magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 200 mg / L phenol solution, with a dosage of 25 mg of the nitrogen-rich iron-anchored magnetic biochar. The adsorption isotherm experiment used 20, 50, 80, and 100 mg / L phenol solutions, with a dosage of 30 mg of the nitrogen-rich iron-anchored magnetic biochar.

[0112] The obtained magnetic biochar with nitrogen-rich anchored iron single atoms has a specific surface area of ​​more than 500m 2 / g, the iron content is 8%, and the phenol removal rate can reach 70%.

[0113] Example 14

[0114] S1: After crushing bamboo into particles smaller than 100 mesh, drying in an oven at 105°C for 24 hours to obtain a biomass raw material;

[0115] S2: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 800°C, take 5 g of the bamboo chips raw material obtained in step S1 and 2.5 g of potassium hydroxide and mix them thoroughly. The mixture is quickly fed into the middle of the reactor. The reaction time is 20 min to fully pyrolyze the biomass. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 50%, to obtain original nitrogen-rich biochar.

[0116] S3: Place the original nitrogen-rich biochar obtained in step S2 in a 250 mL flask, add ferric chloride hexahydrate, and maintain the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate at 1:4. Then add 200 mL of deionized water, place it in a shaker, and shake it at 150 rpm at a temperature of 25°C for 24 hours to ensure that the iron is evenly distributed in the nitrogen-rich biochar and is completely anchored.

[0117] S4: The mixture obtained in step S3 is placed in an oven for drying at a temperature of 105° C. for 24 hours to obtain iron-nitrogen co-doped biochar before washing.

[0118] S5: Treat the iron-nitrogen co-doped biochar from step S4 by oscillating and washing. Oscillate and wash the biochar at 150 rpm for 24 hours at 25°C. Wash the biochar multiple times with deionized water to remove any unanchored residues. After washing, filter the biochar with filter paper and dry it in an oven at 105°C for 24 hours. This yields a nitrogen-anchored iron-rich magnetic biochar with a well-developed porous structure, enriched nitrogen-containing functional groups, and nitrogen-anchored iron atoms.

[0119] S6: Adsorption kinetics and adsorption isotherm experiments were conducted on copper ions using the nitrogen-rich iron-anchored magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 100 mg / L copper ion solution, with 50 mg of the nitrogen-rich iron-anchored magnetic biochar added. The adsorption isotherm experiment used 20, 50, 80, 100, 150, and 200 mg / L phenol solutions, with 50 mg of the nitrogen-rich iron-anchored magnetic biochar added.

[0120] The obtained magnetic biochar with nitrogen-enriched iron atoms has a specific surface area of ​​more than 900 m 2 / g, the iron content is 10%, and the copper ion removal rate can reach 95%.

[0121] Figure 1This figure shows the experimental fitting results of the adsorption isotherm for phenol adsorption on the magnetic biochar enriched with nitrogen-anchored iron atoms in Example 1 of the present invention. The experimental results show that due to the etching effect of ammonia, a large number of nitrogen-containing functional groups are enriched on the biochar. Simultaneously, due to the reduction and anchoring effects, the nitrogen on the biochar also anchors many iron atoms. The fitting curves of the two adsorption models show that the adsorption of phenol by the magnetic biochar enriched with nitrogen-anchored iron atoms is a combination of monolayer and multilayer adsorption, dominated by chemical adsorption, with a maximum adsorption capacity of 166.053 mg / g of phenol.

[0122] Figure 2 This figure shows the experimental fitting results of the adsorption isotherm for phenol adsorption on magnetic biochar enriched with nitrogen-anchored iron atoms, as described in Example 2 of the present invention. The experimental results show that the biochar is enriched with nitrogen-containing functional groups due to the etching effect of ammonia. Simultaneously, the nitrogen on the biochar also anchors many iron atoms due to reduction and anchoring effects. The fitting curves of the two adsorption models indicate that the adsorption of phenol by this magnetic biochar enriched with nitrogen-anchored iron atoms is a combination of monolayer and multilayer adsorption, dominated by chemical adsorption, with a maximum adsorption capacity of 222.742 mg / g.

[0123] Figure 3 This figure shows the experimental fitting results of the adsorption isotherm for phenol adsorption on magnetic biochar enriched with nitrogen-anchored iron atoms, as described in Example 3 of the present invention. The experimental results show that the biochar is enriched with nitrogen-containing functional groups due to the etching effect of ammonia. Simultaneously, the nitrogen on the biochar also anchors many iron atoms due to reduction and anchoring effects. The fitting curves of the two adsorption models indicate that the adsorption of phenol by this magnetic biochar enriched with nitrogen-anchored iron atoms is a combination of monolayer and multilayer adsorption, dominated by chemical adsorption, with a maximum adsorption capacity of 263.096 mg / g.

[0124] Figure 4 Figure 4 shows the experimental fitting results of the adsorption isotherms for copper ions on nitrogen-rich magnetic biochar anchored with single iron atoms, as described in Examples 4-6 of the present invention. The experimental results show that the biochar is enriched with nitrogen-containing functional groups due to the etching effect of ammonia. Simultaneously, the nitrogen on the biochar also anchors many single iron atoms due to reduction and anchoring effects. The fitting curves of the two adsorption models indicate that the adsorption of copper ions on the nitrogen-rich magnetic biochar anchored with single iron atoms is dominated by chemical adsorption, with maximum adsorption capacities of 8.233 mg / g, 13.977 mg / g, and 15.696 mg / g, respectively.

[0125] Figure 5This is the nitrogen adsorption-desorption curve result diagram in Examples 1-3 of the present invention. The experimental results show that the magnetic biochar with nitrogen-rich anchored iron single atoms prepared in the examples has a mixture showing type I / IV isotherms, in which the H4 hysteresis reflects the partial existence of mesopores, indicating that the KOH activation and ammonia etching have caused changes in the pore structure of the biochar, and also improved the adsorption performance of water pollutants.

[0126] Figure 6 The XRD patterns of Examples 1-3 of the present invention are shown below. Experimental results show that through nitrogen doping and iron anchoring, a composite material composed primarily of single iron atoms and a small portion of iron oxides forms on the biochar surface. The iron element exists mostly in a single atomic state and, through synergistic interaction with nitrogen, forms an Fe-N bond structure, significantly enhancing its adsorption performance, particularly for water pollutants.

[0127] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for preparing nitrogen-rich iron-anchored magnetic biochar by low-temperature impregnation and a method for adsorbing water pollutants thereof, characterized in that: The preparation of the nitrogen-rich iron-anchored magnetic biochar comprises the following steps: S1: crushing the biomass waste into particles smaller than 100 mesh and drying them; S2: The biomass waste in step S1 is fully mixed with the catalyst potassium hydroxide in a mass ratio of 1:4-4:1, and a nitrogen-enriched pyrolysis reaction is carried out in an atmosphere of ammonia and an inert gas. The mixture is subjected to a rapid catalytic pyrolysis reaction, which greatly promotes the formation of nitrogen-rich functional groups to obtain original nitrogen-rich biochar; S3: placing the original nitrogen-enriched biochar from step S2 into a flask, adding ferric chloride hexahydrate and distilled water into the flask, and shaking to mix evenly; S4: drying the mixture obtained in step S3 in an oven to obtain iron-nitrogen co-doped biochar before washing; S5: The iron-nitrogen co-doped biochar before washing in step S4 is treated by an oscillation washing method, and after filtering and drying steps, nitrogen-anchored iron-rich magnetic biochar having a developed pore structure, enriched nitrogen-containing functional groups and nitrogen-anchored iron single atoms is obtained.

2. The low-temperature impregnation process for preparing nitrogen-rich iron-anchored magnetic biochar and the method for adsorbing water pollutants thereof according to claim 1 is characterized in that: The biomass in step S1 is one or more of bamboo, cotton stalks, rice husks, corn stalks, and wheat straw, and the drying temperature is 100° C.-150° C., and the drying time is 10 h-30 h.

3. The low-temperature impregnation process for preparing nitrogen-rich iron-anchored magnetic biochar and the method for adsorbing water pollutants thereof according to claim 2 is characterized in that: In step S2, the inert gas is argon or nitrogen, and the total gas flow rate of the inert gas and ammonia is 200 mL / min-500 mL / min, wherein the proportion of ammonia in the total gas is 10%-100%. The temperature of the biomass catalytic nitrogen-enriched pyrolysis is 400°C-800°C, and the reaction time is 10-60 minutes.

4. The low-temperature impregnation process for preparing nitrogen-rich iron-anchored magnetic biochar and the method for adsorbing water pollutants thereof according to claim 3 is characterized in that: In step S3, the mass ratio of the original nitrogen-rich biochar to ferric chloride hexahydrate is 1:4-4:1, the mass ratio of the total mass of the original nitrogen-rich biochar and ferric chloride hexahydrate to distilled water is 1:3-1:10, the oscillation temperature is 15°C-35°C, the oscillation amplitude is 100rpm-300rpm, and the oscillation time is 10h-30h.

5. The low-temperature impregnation process for preparing nitrogen-rich iron-anchored magnetic biochar and the method for adsorbing water pollutants thereof according to claim 4 is characterized in that: The drying temperature in step S4 is 100° C.-150° C., and the drying time is 10 h-30 h.

6. The low-temperature impregnation process for preparing nitrogen-rich iron-anchored magnetic biochar and the method for adsorbing water pollutants thereof according to claim 5 is characterized in that: In step S5, the mass ratio of the iron-nitrogen co-doped biochar to the washing solution before washing is 1:100-1:

200. The shaking temperature is 15°C-35°C, the shaking amplitude is 100-300 rpm, and the shaking time is 10-30 hours. The washing solution can be dilute hydrochloric acid or deionized water.

7. The low-temperature impregnation process for preparing nitrogen-rich iron-anchored magnetic biochar and the method for adsorbing water pollutants thereof according to claim 6 is characterized in that: The drying temperature in step S5 is 100° C.-150° C., and the drying time is 10 h-30 h.

8. The low-temperature impregnation process for preparing nitrogen-rich iron-anchored magnetic biochar and the method for adsorbing water pollutants thereof according to claim 7 is characterized in that: The magnetic biochar rich in nitrogen-anchored iron atoms obtained in step S5 has a developed pore structure, is enriched in nitrogen-containing functional groups, and has nitrogen-anchored iron single atoms loaded on the surface.

9. The method of any one of claims 1 to 8 for adsorbing pollutants in water by using nitrogen-rich iron atoms anchored in magnetic biochar, characterized in that: The wastewater contains phenol, bisphenol A, copper ions, chromium ions and lead ions as water pollutants. The dosage of the nitrogen-enriched iron-anchored magnetic biochar is 10 mg / L-200 mg / L.

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