CoFe2O4-charcoal adsorption material as well as preparation method and application thereof

Abstract

The invention discloses a CoFe2O4-charcoal adsorption material as well as a preparation method and application thereof. The preparation method comprises the steps of aldolization, amine-rich modification reaction, sulfydryl reaction, hydrothermal synthesis and the like. The preparation method comprises the following steps: sequentially carrying out acid activation to enable the surface of a biochar pore to have active hydroxyl, carrying out acetal modification on the biochar pore surface by adopting dialdehyde so as to introduce an aldehyde group into the surface of the biochar pore, grafting PEI rich in amino groups by utilizing a Schiff base reaction, and finally generating sulfimide-S-N-through sulfydryl and-C = N-by utilizing cysteine with sulfydryl. A plurality of functional groups such as amido, phosphoryloxy, carboxyl, hydroxyl and dynamic sulfydryl are successfully introduced into the surface of the novel adsorption material, a multi-synergistic adsorbent system is formed, and heavy metal ions in different forms can be efficiently complexed or electrostatically adsorbed; the adsorption material has the characteristics of high adsorption capacity, good universality to various heavy metal ions, excellent anti-interference performance, easiness in separation, strong reusability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a CoFe2O4-biochar adsorption material and a preparation method and application thereof. Background Art

[0002] Cadmium (Cd) is a heavy metal pollutant with strong toxicity and bioaccumulation characteristics, and its environmental presence poses a major public health risk. Initial exposure can cause typical symptoms of poisoning, such as headaches, nausea, respiratory dysfunction, and decreased motor function; long-term exposure can cause organic damage to the respiratory system and kidneys, and in extreme cases, can develop into irreversible pulmonary fibrosis and even organ failure. In addition, Cd has significant harm to the skeletal system and can easily induce fractures and osteomalacia. Lead (Pb), as a typical harmful heavy metal, can be absorbed by plants into the food chain and then accumulated in the human body, causing irreversible damage to the heart, kidneys, and nervous system [5]. Lead can be ingested through various routes, including skin contact, digestive tract absorption, and respiratory inhalation, and has a profound impact on the neurological development of children, leading to lifelong health risks.

[0003] Currently, the main technologies for removing heavy metals from coal-fired power plant wastewater include chemical precipitation, flocculation, membrane separation, and adsorption. Chemical precipitation and flocculation methods suffer from high cost, high energy consumption, and the production of numerous byproducts. In contrast, adsorption offers the greatest potential due to its ease of operation, low treatment costs, wide applicability, and environmental friendliness. However, traditional adsorbent materials such as activated carbon, metal-organic frameworks (MOFs), chitosan, graphene, and layered double hydroxides generally suffer from limited adsorption capacity and high preparation costs. Biochar is a widely available, low-cost, renewable, and green carbon material. However, due to its small particle size, low density, and strong dispersibility, raw biochar is difficult to separate and recover efficiently after adsorption. Furthermore, pore clogging is common in the treatment of high-turbidity wastewater, impacting its adsorption efficiency and service life.

[0004] Spinel ferrite (MFe2O4) has been widely studied due to its excellent magnetic responsiveness, chemical stability, simple preparation process, and effective solid-liquid separation. Although nano-ferrites represented by CoFe2O4 have good magnetic separation properties, they are prone to agglomeration due to high surface energy, which reduces their specific surface area and adsorption activity. In addition, there are some anions in sewage, such as dichromate (CrO4 2- ) is different from heavy metal cations. If carbon-based adsorbents are used directly, multiple adsorption and separation methods are required during adsorption, which is costly.

[0005] In summary, the proposal of a new composite biochar with easy separation, high adsorption performance and a wide range of adsorbed ion types is of great significance to this field. Summary of the Invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a CoFe2O4-biochar adsorption material and its preparation method and application.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention first proposes a method for preparing a CoFe2O4-biochar adsorption material, comprising the following steps: 1) Acetal reaction Reference Figure 3 , acid-activated biochar and ether were mixed in a weight ratio of 1:10, ultrasonically mixed for 1 hour, acetic acid was added dropwise to adjust the pH to 4-6, glutaraldehyde was added, and the mixture was transferred to a three-necked flask equipped with a reflux condenser, heated to 60°C, and refluxed under stirring for 2-3 hours. After filtering and drying, aldehyde-modified biochar with aldehyde groups grafted on the surface and pore surface was obtained; 2) Rich amine modification reaction Reference Figure 4 , add aldehyde-treated biochar and polyethyleneimine into tetrahydrofuran, reflux at 40-50°C for 30-60 minutes, wash with water and filter after the reaction to generate amine-rich biochar with polyethyleneimine membrane rich in amino groups on the surface and in the pores; utilize the aldehyde group to react with the primary amino group of polyethyleneimine (PEI) to undergo Schiff base reaction, and covalently graft the PEI polymer chains rich in amino groups to the biochar surface, greatly increasing the density of amino groups; 3) Thiol reaction Reference Figure 5 Cysteine ​​and -C=N- in amine-rich biochar were added to the trivalent cobalt solution in a molar ratio of 1:1. The weight ratio of amine-rich biochar to trivalent cobalt solution was 1:1.5-2. The mixture was stirred at 0°C for 30 minutes, heated to 60-80°C, and stirred for 1-2 hours. The solution changed from dark brown to pink green, and the cysteine ​​concentration in the solution decreased sharply to a constant level of ≤0.5wt%, indicating that Co 3+ Reduced to Co 2+ , obtaining a suspension of sulfonimide-modified biochar; By Cr 3+ The mild oxidation reaction of sulfhydryl and -C=N- generates sulfonimide -SN-, eliminating the instability defect of -C=N-. At the same time, -SN- is a weak dynamic covalent bond, which is easy to break for a long time and release cysteine. It is sensitive to light metals (such as Na + , K + , Ca 2+ etc.) has no complexing effect, but has a strong adsorption effect on heavy metal ions, which will further improve the adsorption efficiency of heavy metals; and the reduced Cr 2+ complexed with amino groups on the surface and pores of biochar (part of Cr2+ with the primary amine group to form a cage complex), followed by Fe 3+ Perform in situ reactions; 4) Hydrothermal synthesis Reference Figure 6 , Fe(NO3)3·9H2O was added to the suspension of sulfonimide-modified biochar, with the Fe to Co molar ratio controlled at 2:1, and ammonia water accounting for 15-20% of the total weight of the system was added, with the mass fraction of ammonia in the ammonia water being 30%; Stir for 30 min (to make Fe 3+ After complexation and adsorption on the surface and pores of biochar, it is transferred to a high-pressure reactor and hydrothermally reacted at 180-220°C for 1-2 hours. The product is filtered and washed alternately with water and ethanol 2-3 times, and vacuum dried at 60°C and 1kPa for 5 hours to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorption material.

[0008] The present invention uses Co complexed on biochar 2+ and the subsequent addition of Fe 3+ As the metal source, CoFe2O4 nanoparticles were in situ generated on the surface and in the pores of biochar by a hydrothermal method, and finally a magnetic composite material was obtained.

[0009] Preferably, the acid-activated biochar is prepared by the following steps: Biochar was put into deionized water, and an H3PO4 aqueous solution with a mass fraction of 85wt% was added. After ultrasonic dispersion, the mixture was reacted with magnetic stirring at 60-80℃ for 2-5h. The H3PO4 aqueous solution has the functions of chemical activation and introduction of functional groups (mainly phosphorus oxygen groups), introducing hydroxyl groups or phosphorus oxygen groups on the pore surface of biochar. H3PO4 erodes the carbon skeleton through dehydration, cross-linking, oxidation and other effects. The corrosiveness is relatively mild and will not excessively corrode the carbon skeleton. At the same time, groups such as CO-PO3 are introduced, which significantly increases the specific surface area and surface acidity. After filtration and drying, acid-activated biochar was obtained.

[0010] Furthermore, the weight ratio of the biochar, deionized water, and H3PO4 aqueous solution is 1:7:3-5.

[0011] Furthermore, the biochar is prepared by the following steps: First, 20 g of dried corn straw powder was weighed and mixed with 20 g of zinc chloride (ZnCl2) in a mass ratio of 1:1. 200 mL of deionized water was added and placed in a magnetic stirrer. After adding a magnet, the mixture was stirred and immersed at a speed of 1000 r / min for 6 h. After the impregnation is completed, the mixture is divided into Petri dishes and placed in a drying oven at 80 °C to dry to constant weight; The dried sample was ground into a uniform powder in an agate mortar and then placed in a tubular furnace. It was heated to 950°C at a heating rate of 10°C / min under a nitrogen protective atmosphere and kept at this temperature for 2 h. The nitrogen flow rate was maintained at 200 mL / min to complete the carbonization process and obtain biochar. The obtained biochar was ground and sealed for storage.

[0012] Preferably, the weight ratio of the acid-activated biochar to glutaraldehyde in 1) is 5:1.

[0013] Preferably, the weight ratio of the aldehyde-modified biochar, polyethyleneimine and tetrahydrofuran in 2) is 1:0.2-0.4:10.

[0014] Preferably, the preparation process of the trivalent cobalt solution in 3) is as follows: Co(NO3)2·6H2O and 30wt% H2O2 aqueous solution were mixed at a weight ratio of 1:3-5 and reacted at room temperature for 15-20min. The solution turned dark brown, indicating that Co 2+ Oxidized to Co 3+ , cooled to 0℃ in an ice water bath, Co 3+ Difficult to be reduced to Co 2+ , a trivalent cobalt solution is obtained. This solution is unstable at room temperature and needs to be used immediately after preparation.

[0015] Preferably, before the hydrothermal reaction, the high-pressure reactor should be vacuumed and flushed with nitrogen to a nitrogen atmosphere pressure of 1 bar to avoid 2+ is oxidized to ensure that the product is pure phase CoFe2O4.

[0016] The present invention also proposes a CoFe2O4-biochar adsorption material prepared by the above-mentioned preparation method, characterized in that it has the paramagnetism of CoFe2O4, and the biochar pores are saturated with amino groups, phosphate groups, carboxyl groups, hydroxyl groups and a small amount of sulfonimide-SN-, which can easily complex and adsorb various heavy metal ions and resist the adsorption or precipitation interference of light metal ions. At the same time, after the sulfonimide-SN- adsorbs heavy metals, the dynamic equilibrium moves towards the direction of forming SN bond breakage to form -SH, further improving the adsorption of heavy metal ions; in addition, in a slightly acidic environment with a pH of 5-7, the amino group is easily protonated, and can also adsorb some heavy metal high-valent anion salts (such as CrO4 2- wait).

[0017] Finally, the present invention also applies the aforementioned CoFe2O4-biochar adsorption material to the adsorption of Pb in coal-fired power plant wastewater. 2+ 、Cd 2+ 、CrO4 2- , including the following steps: S1. Adsorption The CoFe2O4-biochar adsorption material described in claim 9 was used as an adsorbent, and the adsorbent dosage was fixed at 0.5 g / L wastewater. The system was shaken at 100 rpm at room temperature for 24 hours to ensure sufficient contact with heavy metal ions. The pH was controlled at 2-8. The initial concentration of each metal ion in the wastewater was 100 mg / L, and the adsorption efficiency was tested; The adsorption capacity (Q) and removal efficiency (η) of heavy metals on biochar were obtained by formulas (1) and (2): (1) (2) Where Q is the adsorption capacity, η is the adsorption efficiency, C0 represents the initial concentration of the element to be measured, C e represents the concentration of the element to be measured when it reaches equilibrium (mg / L), V is the volume of the liquid to be measured (mL), and M represents the mass of the adsorbent used for adsorption (mg); S2. Adsorbent regeneration Pb will be adsorbed 2+ 、Cd 2+ or CrO4 2- The CoFe2O4-biochar adsorption material was reacted with a 1 mol / L NaOH solution at room temperature (about 25°C) and 100 rpm for 12 h to promote the effective release of heavy metal ions. After desorption, the adsorbent was separated from the alkaline desorption solution by magnetic separation, and the adsorbent was washed with deionized water and anhydrous ethanol in sequence to remove residual desorbent and impurities, and then dried at 80°C for later use. The regeneration performance and reuse effect of CFO-BC were systematically evaluated by conducting five consecutive adsorption-desorption cycle experiments.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention sequentially activates the biochar pore surface with active hydroxyl groups through acid activation, then uses dialdehyde to perform acetal modification, thereby introducing aldehyde groups on the biochar pore surface, and then uses Schiff base reaction to graft PEI rich in amino groups. Finally, cysteine ​​with a thiol group is used to react the thiol group with -C=N- to form sulfonimide -SN-, thereby obtaining a new adsorption material with multiple functional groups such as amino groups, phosphoxy groups, carboxyl groups, hydroxyl groups and dynamic thiol groups successfully introduced on the surface, forming a multiple synergistic adsorbent system that can efficiently complex or electrostatically adsorb heavy metal ions in different forms.

[0019] 2. The product of the present invention has high adsorption capacity and good universality for a variety of heavy metal ions, especially under certain pH (4-6) conditions, it can be used to protonate CrO4 2- Ion adsorption is carried out to remove Pb2+ 、Cd 2+ 、CrO4 2- The adsorption performance is good, and the present invention is the first to achieve a universal adsorption treatment effect for both anionic and cation heavy metal ions.

[0020] 3. The sulfonimide bond (-SN-) introduced in the present invention is a dynamic covalent bond that eliminates the lack of stability of -C=N-. At the same time, -SN- is a weak dynamic covalent bond that is easily broken over a long period of time and releases cysteine. It is sensitive to light metal ions (such as Na + , K + , Ca 2+ ) has no complexation effect, but when encountering Pb 2+ 、Cd 2+ When it encounters heavy metal ions, it will intelligently break and release the strong complexing group thiol (-SH), thereby achieving selective and preferential adsorption of heavy metal ions. The product has strong selective adsorption capacity and excellent anti-interference performance, which gives it a huge advantage in treating actual wastewater with complex components.

[0021] 4. The process of the present invention has high functional group modification efficiency and stable structure. Through the step-by-step covalent grafting strategy of acid activation-acetal reaction-Schiff base reaction, the PEI polymer chains are firmly fixed on the surface and in the pores of biochar with high density, avoiding the disadvantage of easy loss by physical impregnation method. Through functional group complexation, the in situ hydrothermal synthesis method of CoFe2O4 is promoted, avoiding the use of high-temperature nano-preparation methods. The method of the present invention ensures that the magnetic particles are small in size, uniformly dispersed, and firmly bonded to the carbon matrix. It not only provides strong paramagnetism (high saturation magnetization) to facilitate rapid separation and recovery in an external magnetic field, but also avoids the problems of pore blockage and performance degradation caused by physical mixing.

[0022] 5. The present invention successfully prepared a high-performance CoFe2O4-biochar (CFO-BC) magnetic adsorption material through a multi-step precision molecular design and in situ synthesis strategy. The material also has excellent regeneration performance and strong reusability. This also indirectly demonstrates the stability of the product structure and the reversibility of the functional groups of the present invention. The excellent regeneration performance greatly reduces the long-term use cost of the material, laying a solid foundation for its practical engineering application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the adsorption SEM image of the product of Comparative Example 4 of the present invention, wherein Figure 1 (a) is the SEM of BC-CFO before adsorption in Comparative Example 4, Figure 1 (b) is the SEM of BC-CFO of comparative example 4 after adsorption of Pb2+, Figure 1 (c) is the SEM of BC-CFO of comparative example 4 after adsorption of Pb2+, Figure 1(d) is the SEM of BC-CFO of comparative example 4 after adsorption of CrO42-, the adsorption pH is 6; Figure 2 This is the adsorption SEM image of the product of Example 2 of the present invention, wherein Figure 2 (a) is the SEM of BC-CFO before adsorption in Example 2, Figure 2 (b) is the SEM of BC-CFO after adsorption of Pb2+ in Example 2. Figure 2 (c) is the SEM of BC-CFO after adsorption of Pb2+ in Example 2. Figure 2 (d) is the SEM of BC-CFO after adsorption of CrO42- in Example 2, with an adsorption pH of 6; Figure 3 is a mechanism diagram of the acetal reaction in the present invention; Figure 4 is a mechanism diagram of the rich amine modification reaction in the present invention; Figure 5 Figure 2 is a diagram showing the mechanism of sulfhydryl reaction in the present invention; Figure 6 Schematic diagram of the hydrothermal synthesis mechanism of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the existing known technologies. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] Preparation Example 1 The biochar is prepared by the following steps: First, 20 g of dried corn straw powder was weighed and mixed with 20 g of zinc chloride (ZnCl2) in a mass ratio of 1:1. 200 mL of deionized water was added and placed in a magnetic stirrer. After adding a magnet, the mixture was stirred and immersed at a speed of 1000 r / min for 6 h. After the impregnation is completed, the mixture is divided into Petri dishes and placed in a drying oven at 80 °C to dry to constant weight; The dried sample was ground into a uniform powder in an agate mortar and then placed in a tubular furnace. It was heated to 950°C at a heating rate of 10°C / min under a nitrogen protective atmosphere and kept at this temperature for 2 h. The nitrogen flow rate was maintained at 200 mL / min to complete the carbonization process and obtain biochar. The obtained biochar was ground and sealed for storage.

[0026] Preparation Example 2 The acid-activated biochar is prepared by the following steps: The biochar prepared in Preparation Example 1 was added to deionized water, and an H3PO4 aqueous solution with a mass fraction of 85 wt% was added. After ultrasonic dispersion, the mixture was reacted at 60-80°C with magnetic stirring for 2-5 hours. The H3PO4 aqueous solution has the functions of chemical activation and introduction of functional groups (mainly phosphorus oxygen groups), introducing hydroxyl groups or phosphorus oxygen groups on the pore surface of the biochar. H3PO4 erodes the carbon skeleton through dehydration, cross-linking, oxidation and other actions, and its corrosiveness is relatively mild, and the carbon skeleton will not be excessively corroded. At the same time, groups such as CO-PO3 are introduced, which significantly increases the specific surface area and surface acidity. After filtration and drying, acid-activated biochar is obtained.

[0027] Wherein, the weight ratio of the biochar, deionized water and H3PO4 aqueous solution is 1:7:3.

[0028] Preparation Example 3 The same as Preparation Example 2, except that the weight ratio of biochar, deionized water, and H3PO4 aqueous solution is 1:7:4.

[0029] Preparation Example 4 The same as Preparation Example 2, except that the weight ratio of biochar, deionized water, and H3PO4 aqueous solution is 1:7:5.

[0030] Comparative Preparation Example 1 The same as Preparation Example 2, except that the weight ratio of biochar, deionized water, and H3PO4 aqueous solution is 1:7:2.

[0031] Comparative Preparation Example 2 The same as Preparation Example 2, except that the weight ratio of biochar, deionized water, and H3PO4 aqueous solution is 1:7:7. Example

[0032] The preparation method of CoFe2O4-biochar adsorption material comprises the following steps: 1) Acetal reaction The acid-activated biochar prepared in Preparation Example 2 and ether were mixed in a weight ratio of 1:10, ultrasonically mixed for 1 hour, acetic acid was added dropwise to adjust the pH to 4-6, glutaraldehyde was added, and the mixture was transferred to a three-necked flask equipped with a reflux condenser. The mixture was heated to 60°C and refluxed for 3 hours under stirring. After filtration and drying, the aldehyde-modified biochar with aldehyde groups grafted on the surface and pore surface was obtained. 2) Rich amine modification reaction The aldehyde-modified biochar and polyethyleneimine were added to tetrahydrofuran and refluxed at 40°C for 60 minutes. After the reaction, the biochar was washed with water and filtered to produce an amine-rich biochar with a polyethyleneimine membrane rich in amino groups on the surface and in the pores. 3) Thiol reaction Cysteine ​​and -C=N- in amine-rich biochar were added to trivalent cobalt solution in a molar ratio of 1:1, and the weight ratio of amine-rich biochar to trivalent cobalt solution was 1:1.5. The mixture was stirred at 0°C for 30 minutes, heated to 80°C, and stirred for 1 hour. The solution changed from dark brown to pink green, and the cysteine ​​concentration in the solution decreased sharply to a constant level of ≤0.5wt%, indicating that Co 3+ Reduced to Co 2+ , obtaining a suspension of sulfonimide-modified biochar; 4) Hydrothermal synthesis Fe(NO3)3·9H2O was added to the suspension of sulfonimide-modified biochar, with the Fe / Co molar ratio controlled at 2:1. Ammonia water was added at a concentration of 20% by weight of the total system and a mass fraction of 30% ammonia. Stir for 30 min (to make Fe 3+ After complexation and adsorption on the surface and pores of biochar, it was transferred to a high-pressure reactor and hydrothermally reacted at 180°C for 2 hours. The product was filtered and washed alternately with water and ethanol three times, and vacuum dried at 60°C and 1kPa for 5 hours to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorption material.

[0033] Among them, 1) the weight ratio of neutral acid activated biochar and glutaraldehyde is 5:1.

[0034] Among them, the weight ratio of formaldehyde-treated biochar, polyethyleneimine and tetrahydrofuran in 2) is 1:0.4:10.

[0035] The preparation process of the trivalent cobalt solution in 3) is as follows: Co(NO3)2·6H2O and 30wt% H2O2 aqueous solution were mixed at a weight ratio of 1:3 and reacted at room temperature for 20 min. The solution turned dark brown, indicating that Co 2+ Oxidized to Co 3+ , cooled to 0℃ in an ice water bath, Co 3+ Difficult to be reduced to Co 2+ , a trivalent cobalt solution is obtained. This solution is unstable at room temperature and needs to be used immediately after preparation. Example

[0036] The preparation method of CoFe2O4-biochar adsorption material comprises the following steps: 1) Acetal reaction The acid-activated biochar prepared in Preparation Example 3 and ether were mixed in a weight ratio of 1:10 under ultrasonication for 1 hour, acetic acid was added dropwise to adjust the pH to 4-6, glutaraldehyde was added, and the mixture was transferred to a three-necked flask equipped with a reflux condenser. The mixture was heated to 60°C and refluxed under stirring for 2.5 hours. After filtration and drying, the aldehyde-modified biochar with aldehyde groups grafted on the surface and pore surface was obtained; 2) Rich amine modification reaction The aldehyde-modified biochar and polyethyleneimine were added to tetrahydrofuran and refluxed at 45°C for 45 minutes. After the reaction, the biochar was washed with water and filtered to produce an amine-rich biochar with a polyethyleneimine membrane rich in amino groups on the surface and in the pores. 3) Thiol reaction Cysteine ​​and -C=N- in amine-rich biochar were added to trivalent cobalt solution in a molar ratio of 1:1. The weight ratio of amine-rich biochar to trivalent cobalt solution was 1:1.8. The mixture was stirred at 0°C for 30 minutes, heated to 70°C, and stirred for 1.5 hours. The solution changed from dark brown to pink green, and the cysteine ​​concentration in the solution decreased sharply to a constant level of ≤0.5wt%. This indicated that Co 3+ Reduced to Co 2+ , obtaining a suspension of sulfonimide-modified biochar; 4) Hydrothermal synthesis Fe(NO3)3·9H2O was added to the suspension of sulfonimide-modified biochar, with the Fe / Co molar ratio controlled at 2:1. Ammonia water was added at a concentration of 18% by weight of the total system and a mass fraction of 30% ammonia. Stir for 30 min (to make Fe 3+ After complexation and adsorption on the surface and pores of biochar, it was transferred to a high-pressure reactor and hydrothermally reacted at 200°C for 1.5 hours. The product was filtered and washed twice alternately with water and ethanol, and vacuum dried at 60°C and 1kPa for 5 hours to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorption material.

[0037] Among them, 1) the weight ratio of neutral acid activated biochar and glutaraldehyde is 5:1.

[0038] Among them, the weight ratio of formaldehyde-treated biochar, polyethyleneimine and tetrahydrofuran in 2) is 1:0.3:10.

[0039] The preparation process of the trivalent cobalt solution in 3) is as follows: Co(NO3)2·6H2O and 30wt% H2O2 aqueous solution were mixed at a weight ratio of 1:4 and reacted at room temperature for 18 min. The solution turned dark brown, indicating that Co 2+ Oxidized to Co 3+ , cooled to 0℃ in an ice water bath, Co 3+ Difficult to be reduced to Co 2+ , a trivalent cobalt solution is obtained. This solution is unstable at room temperature and needs to be used immediately after preparation. Example

[0040] The preparation method of CoFe2O4-biochar adsorption material comprises the following steps: 1) Acetal reaction The acid-activated biochar prepared in Preparation Example 4 and ether were mixed in a weight ratio of 1:10 under ultrasonication for 1 hour, acetic acid was added dropwise to adjust the pH to 4-6, glutaraldehyde was added, and the mixture was transferred to a three-necked flask equipped with a reflux condenser. The mixture was heated to 60°C and refluxed under stirring for 2 hours. After filtration and drying, the aldehyde-modified biochar with aldehyde groups grafted on the surface and pore surface was obtained. 2) Rich amine modification reaction The aldehyde-modified biochar and polyethyleneimine were added to tetrahydrofuran and refluxed at 50°C for 30 minutes. After the reaction, the biochar was washed with water and filtered to produce an amine-rich biochar with a polyethyleneimine membrane rich in amino groups on the surface and in the pores. 3) Thiol reaction Cysteine ​​and -C=N- in amine-rich biochar were added to trivalent cobalt solution in a molar ratio of 1:1, and the weight ratio of amine-rich biochar to trivalent cobalt solution was 1:2. The mixture was stirred at 0°C for 30 minutes, heated to 60°C, and stirred for 2 hours. The solution changed from dark brown to pink green, and the cysteine ​​concentration in the solution decreased sharply to a constant level of ≤0.5wt%, indicating that Co 3+ Reduced to Co 2+ , obtaining a suspension of sulfonimide-modified biochar; 4) Hydrothermal synthesis Fe(NO3)3·9H2O was added to the suspension of sulfonimide-modified biochar, with the Fe:Co molar ratio controlled at 2:1. Ammonia water was added at a concentration of 15% by weight of the total system and a mass fraction of 30% ammonia. Stir for 30 min (to make Fe 3+ After complexation and adsorption on the surface and pores of biochar, it was transferred to a high-pressure reactor and hydrothermally reacted at 220°C for 1 hour. The product was filtered and washed alternately with water and ethanol three times, and vacuum dried at 60°C and 1kPa for 5 hours to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorption material.

[0041] Among them, 1) the weight ratio of neutral acid activated biochar and glutaraldehyde is 5:1.

[0042] Among them, the weight ratio of formaldehyde-treated biochar, polyethyleneimine and tetrahydrofuran in 2) is 1:0.2:10.

[0043] The preparation process of the trivalent cobalt solution in 3) is as follows: Co(NO3)2·6H2O and 30wt% H2O2 aqueous solution were mixed at a weight ratio of 1:5 and reacted at room temperature for 15 min. The solution turned dark brown, indicating that Co 2+ Oxidized to Co 3+ , cooled to 0℃ in an ice water bath, Co 3+ Difficult to be reduced to Co2+ , a trivalent cobalt solution is obtained. This solution is unstable at room temperature and needs to be used immediately after preparation.

[0044] Comparative Example 1 The method is basically the same as Example 2, except that the acid-activated biochar from Comparative Preparation Example 1 was used. Due to incomplete acidification and subsequent acetalization, the residual aldehyde content in the system was high, resulting in a lower pore amino modification rate and, in turn, a lower adsorption efficiency.

[0045] Comparative Example 2 The method is basically the same as Example 2, except that the acid-activated biochar of Comparative Preparation Example 1 is used. The biochar skeleton is severely corroded, and the surface activity of the product is reduced.

[0046] Comparative Example 3 This was essentially the same as Example 2, except that the acid-activated biochar from Preparation Example 1 was used directly in place of the acid-activated biochar in Example 2. This biochar had insufficient surface hydroxyl groups and contained high levels of ash and impurities, resulting in incomplete acetalization and a high residual aldehyde content. This reduced the subsequent pore amino modification rate and, consequently, lowered adsorption efficiency. Furthermore, its surface activity was significantly lower than that of Example 2.

[0047] Comparative Example 4 Steps 1) to 3) in Example 2 were omitted, and the biochar prepared in Preparation Example 1 was directly used to replace the sulfonimide-modified biochar in Example 2. The biochar does not contain amine groups in its pores.

[0048] Comparative Example 5 Step 3 in Example 2 is omitted) and amine-rich biochar is directly used to replace sulfonimide-modified biochar, which does not contain sulfonimide bonds and has reduced adsorption and selectivity for heavy metal ions.

[0049] Comparative Example 6 Step 2 of Example 2 was omitted, and only the hydroformylation step 1) was performed. Step 2 was then skipped and Step 3 was performed directly. However, due to the absence of PEI and the absence of -C=N- bonds, the cysteine ​​could not be grafted in Step 3, and only physical mixing was performed. The subsequent hydrothermal steps were the same as in Example 1. The results demonstrated the critical role of the amine groups introduced by PEI and the subsequent sulfonyl imide bonds formed in the performance.

[0050] Comparative Example 7 Step 4 in Example 2 was omitted), and no CoFe2O4 was loaded. Steps 1, 2, and 3 were performed to obtain sulfonimide-modified biochar. Step 4, hydrothermal synthesis, was omitted, and the biochar was directly filtered and dried. The results demonstrated the magnetic function of CoFe2O4 nanoparticles and their possible synergistic effect on adsorption.

[0051] Comparative Example 8 Commercial CoFe2O4 nanopowder (20-30 nm cobalt ferrite soft magnetic material, Qinghe County Ruijiang Metal Materials Co., Ltd.) was purchased and physically mixed with the biochar of Preparation Example 1 according to the theoretical loading ratio of the final product of Example 2.

[0052] Performance testing: The adsorption materials obtained in Examples 1-3 and Comparative Examples 1-8 were used to adsorb Pb in wastewater from coal-fired power plants. 2+ 、Cd 2+ 、CrO4 2- , Ca in wastewater 2+ , Pb 2+ 、Cd 2+ 、CrO4 2- The concentration of each was 100 mg / L, and the following steps were included: S1. Adsorption The CoFe2O4-biochar adsorption material described in claim 9 was used as an adsorbent, and the adsorbent dosage was fixed at 0.5 g / L wastewater. The system was shaken at 100 rpm at room temperature for 24 hours to ensure sufficient contact with heavy metal ions. The pH was controlled at 6, and the adsorption efficiency was tested; The adsorption capacity (Q) and removal efficiency (η) of heavy metals on biochar were obtained by formulas (1) and (2): (1) (2) Where Q is the adsorption capacity, η is the adsorption efficiency, C0 represents the initial concentration of the element to be measured, C e represents the concentration of the element to be measured when it reaches equilibrium (mg / L), V is the volume of the liquid to be measured (mL), and M represents the mass of the adsorbent used for adsorption (mg); S2. Adsorbent regeneration Pb will be adsorbed 2+ 、Cd 2+ or CrO4 2- The CoFe2O4-biochar adsorption material (CFO-BC) was reacted with a 1 mol / L NaOH solution at room temperature (about 25°C) and 100 rpm for 12 h to promote the effective release of heavy metal ions. After desorption, the adsorbent was separated from the alkaline desorption solution by magnetic separation, and the adsorbent was washed with deionized water and anhydrous ethanol in sequence to remove residual desorbent and impurities, and then dried at 80°C for later use. The regeneration performance and reuse effect of CFO-BC were systematically evaluated by conducting five consecutive adsorption-desorption cycle experiments.

[0053] See Table 1 for details: Table 1. Adsorption performance under slightly acidic conditions

[0054] Data Analysis: 1. Influence of acid activation degree As can be seen from Table 1, when comparing Examples 1-3 with Comparative Examples 1-3, Example 2 exhibits the highest adsorption performance. The phosphoric acid activation effect in this formula is optimal. It can not only create a rich pore structure through mild corrosion, significantly increase the specific surface area, but also introduce a maximum amount of surface acidic oxygen-containing functional groups (such as CO-PO3, -COOH, -OH). These functional groups serve as anchor points for subsequent acetal reactions and also provide direct complexation sites for heavy metal ions.

[0055] However, the surface activation of the biochar in Comparative Example 1 was insufficient, and the amount of phosphoric acid used was insufficient, resulting in incomplete activation of the biochar and a limited number of reactive functional groups on the surface. This reduced the subsequent formaldehyde and amination grafting rates, reduced the total adsorption sites, and significantly decreased the adsorption performance.

[0056] In contrast, the surface of the biochar in Comparative Example 2 was over-activated, and the strong corrosiveness of the excess phosphoric acid destroyed the carbon skeleton structure, causing some micropores to collapse, and the total specific surface area decreased. Although the surface acidity was strong, the damaged structure limited its adsorption capacity.

[0057] However, the surface of the biochar in Comparative Example 3 was not activated, the original biochar had few surface functional groups, the pore structure was not optimized, and it contained more ash and impurities, lacked effective chemical adsorption sites, and mainly relied on limited physical adsorption.

[0058] 2. The key role of functional group modification Comparing Example 2 with Comparative Examples 4-6, Comparative Example 4 has no modification and serves as the adsorption baseline of the blank test, and its performance is extremely low, which confirms the absolute necessity of chemical modification. Figure 1 and Figure 2 In comparison, the crystal phase distribution on the surface of BC-CFO modified with ammonia loading is more uniform, and the crystal destruction rate after adsorption is less, indicating that chemical complex adsorption or anion and cation adsorption is the dominant factor. At the same time, the adsorption rate is higher and the regeneration of the adsorbent is easier to handle.

[0059] Comparative Example 5 has no sulfhydryl reaction and its 2+ 、Cd 2+ The adsorption capacity of CrO4 is significantly lower than that of Example 2. 2- The adsorption of Pb was less affected by the loss of the sulfonimide bond (-SN-) and its dynamically released sulfhydryl group (-SH). 2+ 、Cd 2+Soft acid metal ions have strong complexing ability, and the loss of these sites directly leads to a decrease in cationic adsorption capacity. 2- Mainly depends on the protonated amine group (-NH3 + ), so the impact is not significant.

[0060] Comparative Example 6 has no PEI modification, and the performance is greatly reduced, especially for CrO4 2- The adsorption of amines is almost ineffective. This shows that polyethyleneimine provides a large number of primary and secondary amine groups. These amine groups: ① are the basis for the formation of Schiff base bonds and subsequent sulfonyl imide bonds; ② are excellent complexing groups themselves; ③ are protonated (-NH3 + ), the anion CrO4 is efficiently and specifically adsorbed through electrostatic attraction 2- This comparative example proves that the amino group is the adsorbent of CrO4 2- The leading functional group.

[0061] 3. Influence of CoFe2O4 loading method Comparing Example 2 with Comparative Examples 7-8, Comparative Example 7 has no CoFe2O4 loading and its adsorption performance is slightly reduced, indicating that the amino-modified biochar still has a certain adsorption effect, but the role of CoFe2O4 cannot be ignored, and CoFe2O4 nanoparticles also provide magnetic separation function.

[0062] Comparative Example 8 uses physical blending, but the CoFe2O4 nanoparticles easily agglomerate, severely blocking the biochar's pores and hindering the mass transfer and diffusion of heavy metal ions. Furthermore, their contact with the carbon matrix is ​​limited to physical contact, preventing any synergistic effects. The advantages of in-situ hydrothermal synthesis include: ① small particle size and excellent dispersibility; ② strong bonding with the carbon matrix without disrupting the pore structure; and ③ the potential for some metal sites to participate in surface complexation.

[0063] 4. Regeneration performance analysis Test the regeneration cycle performance of the product in Example 2, and use Example 2 to adsorb Pb 2+ For example, see Table 2: Table 2. Regeneration cycle performance of the products of the present invention

[0064] After five adsorption-desorption cycles, Example 2 still maintained 91.1% of its initial adsorption capacity, demonstrating the material's excellent stability and reusability. This may be due to the following advantages of Example 2: ① The covalently grafted PEI chains and in situ grown CoFe2O4 particles are firmly bonded to the carbon matrix and are not easily detached; ② The main adsorption sites (amine, carboxyl, phosphate, etc.) are stable in acidic and alkaline environments; ③ The reversibility of the dynamic covalent bond -SN- enables the material to restore its active structure after alkaline desorption.

[0065] 5. Effect of pH on adsorption performance The adsorption conditions of Example 2 were adjusted to pH 2-8, and the performance test results are shown in Table 3 below: Table 3. Effect of pH on adsorption performance

[0066] It shows that as pH decreases, CrO4 2- The adsorption performance of CrO4 increases first and then decreases; but with the increase of pH, 2- The adsorption performance of CrO4 2- In addition, excessive acidity may cause the degradation of CoFe2O4 particles, thereby reducing the adsorption of Pb 2+ 、Cd 2+ The adsorption performance of Pb 2+ 、Cd 2+ The results showed that the alkali salt precipitation was beneficial to the adsorption of heavy metal ions.

[0067] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a CoFe2O4-biochar adsorption material, characterized in that: The following steps are involved: 1) Acetal reaction Acid-activated biochar and ether were mixed in a weight ratio of 1:10, ultrasonically mixed for 1 hour, acetic acid was added dropwise to adjust the pH to 4-6, glutaraldehyde was added, and the mixture was transferred to a three-necked flask equipped with a reflux condenser. The mixture was heated to 60°C and refluxed under stirring for 2-3 hours. After filtering and drying, the aldehyde-modified biochar with aldehyde groups grafted on the surface and pore surface was obtained. 2) Rich amine modification reaction The aldehyde-modified biochar and polyethyleneimine are added to tetrahydrofuran and refluxed at 40-50°C for 30-60 minutes. After the reaction, the biochar is washed with water and filtered to produce an amine-rich biochar with a polyethyleneimine membrane rich in amino groups on the surface and in the pores. 3) Thiol reaction Cysteine ​​and -C=N- in amine-rich biochar are added to a trivalent cobalt solution at a molar ratio of 1:1, and the weight ratio of amine-rich biochar to trivalent cobalt solution is 1:1.5-2. The mixture is stirred at 0°C for 30 minutes, heated to 60-80°C, and stirred for 1-2 hours to obtain a suspension of sulfonimide-modified biochar. 4) Hydrothermal synthesis Fe(NO3)3·9H2O was added to the suspension of sulfonimide-modified biochar, with the Fe to Co molar ratio controlled at 2:

1. Ammonia water was added at a concentration of 15-20% of the total weight of the system, with a mass fraction of 30% ammonia in the ammonia water. After stirring for 30 minutes, the mixture was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 180-220°C for 1-2 hours. The product was filtered and washed alternately with water and ethanol 2-3 times, and vacuum dried at 60°C and 1 kPa for 5 hours to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorption material.

2. The method for preparing the CoFe2O4-biochar adsorption material according to claim 1, characterized in that: The acid-activated biochar is prepared by the following steps: The biochar was added into deionized water and an 85 wt% H3PO4 aqueous solution was added. After ultrasonic dispersion, the mixture was reacted at 60-80°C with magnetic stirring for 2-5 hours. After filtration and drying, the acid-activated biochar was obtained.

3. The method for preparing the CoFe2O4-biochar adsorption material according to claim 2, characterized in that: The weight ratio of the biochar, deionized water and H3PO4 aqueous solution is 1:7:3-5.

4. The method for preparing the CoFe2O4-biochar adsorption material according to claim 2, characterized in that: The biochar is prepared by the following steps: First, 20 g of dried corn straw powder was weighed and mixed with 20 g of zinc chloride in a mass ratio of 1:

1. 200 mL of deionized water was added and placed in a magnetic stirrer. After adding a magnet, the mixture was stirred at a speed of 1000 r / min and immersed for 6 h. After the impregnation is completed, the mixture is divided into Petri dishes and placed in a drying oven at 80 °C to dry to constant weight; The dried sample was ground into a uniform powder in an agate mortar and then placed in a tubular furnace. It was heated to 950°C at a heating rate of 10°C / min under a nitrogen protective atmosphere and kept at this temperature for 2 h. The nitrogen flow rate was maintained at 200 mL / min to complete the carbonization process and obtain biochar. The obtained biochar was ground and sealed for storage.

5. The method for preparing the CoFe2O4-biochar adsorption material according to claim 1, characterized in that: The weight ratio of the acid-activated biochar to glutaraldehyde in 1) is 5:

1.

6. The method for preparing the CoFe2O4-biochar adsorption material according to claim 1, characterized in that: The weight ratio of the aldehyde-modified biochar, polyethyleneimine and tetrahydrofuran in the above 2) is 1:0.2-0.4:

10.

7. The method for preparing the CoFe2O4-biochar adsorption material according to claim 1, characterized in that: The preparation process of the trivalent cobalt solution in 3) is as follows: Mix Co(NO3)2·6H2O and 30wt% H2O2 aqueous solution in a weight ratio of 1:3-5, react at room temperature for 15-20 minutes, and cool to 0°C in an ice-water bath to obtain a trivalent cobalt solution, which needs to be used immediately.

8. The method for preparing the CoFe2O4-biochar adsorption material according to claim 1, characterized in that: Before the hydrothermal reaction, the high-pressure reactor must be evacuated and flushed with nitrogen to a nitrogen atmosphere pressure of 1 bar.

9. The CoFe2O4-biochar adsorption material prepared according to the preparation method according to any one of claims 1 to 8.

10. The CoFe2O4-biochar adsorption material according to claim 9 is used to adsorb Pb in wastewater from coal-fired power plants 2+ 、Cd 2+ 、CrO4 2- The application is characterized in that The following steps are involved: S1. Adsorption The CoFe2O4-biochar adsorption material described in claim 9 was used as an adsorbent, and the adsorbent dosage was fixed at 0.5 g / L wastewater. The system was shaken at 100 rpm at room temperature for 24 hours to ensure sufficient contact with heavy metal ions. The pH was controlled at 2-8. The initial concentration of each metal ion in the wastewater was 100 mg / L, and the adsorption efficiency was tested; The adsorption capacity and removal efficiency of heavy metals on biochar are obtained by formulas (1) and (2): （1） （2） Where Q is the adsorption capacity, η is the adsorption efficiency, C0 represents the initial concentration of the element to be measured, C e It represents the concentration of the element to be measured when it reaches equilibrium, V is the volume of the liquid to be measured, and M represents the mass of the adsorbent used for adsorption; S2. Adsorbent regeneration Pb will be adsorbed 2+ 、Cd 2+ or CrO4 2- The CoFe2O4-biochar adsorption material was reacted with a 1 mol / L NaOH solution at room temperature and 100 rpm for 12 h to promote the effective release of heavy metal ions. After desorption, the adsorbent was separated from the alkaline desorption solution by magnetic separation, and the adsorbent was washed with deionized water and anhydrous ethanol in sequence to remove residual desorbent and impurities, and then dried at 80°C for later use. The regeneration performance and reuse effect of CFO-BC were systematically evaluated by conducting five consecutive adsorption-desorption cycle experiments.

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