CoFe2O4-biochar adsorbent materials, their preparation methods and applications

Abstract

This invention discloses a CoFe2O4-biochar adsorbent material, its preparation method, and its applications. The preparation method includes steps such as acetal reaction, amine-rich modification reaction, thiol reaction, and hydrothermal synthesis. The invention sequentially activates the biochar pores with acid to introduce active hydroxyl groups, then modifies them with dialdehyde to introduce aldehyde groups onto the biochar pore surface. Next, it grafts amine-rich PEI onto the surface using a Schiff base reaction. Finally, it utilizes cysteine ​​with thiol groups to react with -C=N- to generate sulfonamide -S-N-, resulting in a novel adsorbent material with multiple functional groups, including amine, phosphoroxy, carboxyl, hydroxyl, and dynamic thiol groups, successfully introduced onto its surface. This forms a multi-functional synergistic adsorbent that can efficiently complex or electrostatically adsorb different forms of heavy metal ions. This adsorbent material features high adsorption capacity, good universality for various heavy metal ions, excellent anti-interference performance, easy separation, and strong reusability.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to CoFe2O4-biochar adsorbent materials, their preparation methods, and applications. Background Technology

[0002] Cadmium (Cd) is a heavy metal pollutant with strong toxicity and bioaccumulation characteristics, and its environmental presence poses a significant public health risk. Initial exposure can lead to typical poisoning symptoms such as headache, nausea, respiratory dysfunction and decreased motor function; long-term exposure can cause organic damage to the respiratory system and kidneys, and in extreme cases, it 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) is a typical harmful heavy metal that can be absorbed by plants into the food chain and then accumulate 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 absorption and inhalation, and has a particularly profound impact on the neurodevelopment of children, leading to lifelong health risks.

[0003] Currently, the main technical means for removing heavy metals from wastewater from coal-fired power plants include chemical precipitation, flocculation, membrane separation, and adsorption. Among these, chemical precipitation and flocculation methods have disadvantages such as high cost, high energy consumption, and numerous byproducts. In contrast, adsorption has become one of the most promising technologies due to its simple operation, low treatment cost, wide applicability, and environmental friendliness. However, traditional adsorption 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, inexpensive, and renewable green carbon material. However, raw biochar, due to its small particle size, low density, and strong dispersibility, is difficult to achieve efficient separation and recovery after adsorption, and it is prone to pore blockage in the treatment of high-turbidity wastewater, affecting its adsorption efficiency and service life.

[0004] Spinel ferrites (MFe₂O₄) have been widely studied due to their excellent magnetic responsiveness, chemical stability, and simple preparation process, enabling effective solid-liquid separation. While nano-ferrites, represented by CoFe₂O₄, possess good magnetic separation properties, their high surface energy easily leads to agglomeration, thus reducing their specific surface area and adsorption activity. Additionally, wastewater contains anions such as dichromate (CrO₄⁻). 2- The adsorption mechanism of carbon-based adsorbents differs from that of heavy metal cations. For example, directly using carbon-based adsorbents requires multiple adsorption and separation methods, which is costly.

[0005] In summary, the proposed novel composite biochar, which is easy to separate, has high adsorption performance, and can adsorb a wide range of ions, is of great significance to this field. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing CoFe2O4-biochar adsorbent materials, their preparation methods, and applications.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention first proposes a method for preparing CoFe2O4-biochar adsorbent material, comprising the following steps:

[0009] 1) Acetal reaction

[0010] Reference Figure 3 Acid-activated biochar and diethyl ether were mixed at a weight ratio of 1:10 and ultrasonicated 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 temperature was raised to 60°C, and the mixture was refluxed for 2-3 hours with stirring. After filtration and drying, aldehyde-based biochar with aldehyde groups grafted on the surface and pores was obtained.

[0011] 2) Amine-rich modification reaction

[0012] Reference Figure 4 Aldehyde-modified biochar and polyethyleneimine were added to tetrahydrofuran and refluxed at 40-50°C for 30-60 min. After the reaction, the biochar was washed with water and filtered to generate amine-rich biochar with a polyethyleneimine film rich in amine groups on the surface and in the pores. The amine-rich PEI polymer chains were covalently grafted onto the surface of the biochar by the Schiff base reaction between the aldehyde groups and the primary amine groups of polyethyleneimine (PEI), which greatly increased the amine group density.

[0013] 3) Thiol reaction

[0014] Reference Figure 5 Cysteine ​​and -C=N- from amine-rich biochar were added to a trivalent cobalt solution at a molar ratio of 1:1, with the weight ratio of amine-rich biochar to trivalent cobalt solution being 1:1.5-2. The mixture was stirred at 0℃ for 30 min, then heated to 60-80℃ and stirred for 1-2 h. The solution changed from dark brown to pinkish-green, and the cysteine ​​concentration in the solution decreased sharply to a constant level of ≤0.5 wt%, indicating that Co... 3+ Reduced to Co 2+ A suspension of sulfonylimide-modified biochar was obtained;

[0015] Through Cr 3+ The mild oxidation reaction causes the thiol group to react with -C=N- to form sulfonamide -SN-, eliminating the instability defect of -C=N-. Simultaneously, -SN- is a relatively weak dynamic covalent bond, which is easily broken over time and releases cysteine, thus improving its stability against light metals (such as Na). + K +Ca 2+ (etc.) It has no complexing effect, but it has a very strong adsorption effect on heavy metal ions, which will further improve the heavy metal adsorption efficiency; while the reduced Cr 2+ Cr complexes with amino groups on the surface and pores of biochar (partially Cr) 2+ (forming a cage-like complex with primary amine groups), followed by Fe 3+ In-situ reaction;

[0016] 4) Hydrothermal synthesis

[0017] Reference Figure 6 Fe(NO3)3·9H2O was added to the suspension of sulfonamide-modified biochar, the molar ratio of Fe to Co was 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%.

[0018] Stir for 30 minutes (to allow Fe to be stirred) 3+ After complexation and adsorption on the surface and pores of biochar, the product is transferred to a high-pressure reactor and hydrothermally reacted at 180-220℃ for 1-2 hours. After filtration, the product is washed 2-3 times alternately with water and ethanol and then vacuum dried at 60℃ and 1kPa for 5 hours to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorbent material.

[0019] This invention uses Co complexed on biochar 2+ and the Fe added later 3+ Using a metal source, CoFe2O4 nanoparticles were generated in situ on the surface and within the pores of biochar via a hydrothermal method, ultimately yielding a magnetic composite material.

[0020] Preferably, the acid-activated biochar is prepared by the following steps:

[0021] Biochar was added to deionized water, followed by an 85 wt% H3PO4 aqueous solution. After ultrasonic dispersion, the mixture was magnetically stirred at 60-80℃ for 2-5 hours. The H3PO4 aqueous solution served both as a chemical activator and as a functional group (mainly phospho groups), introducing hydroxyl or phospho groups onto the surface of the biochar pores. H3PO4 eroded the carbon skeleton through dehydration, cross-linking, and oxidation, exhibiting relatively mild corrosiveness and avoiding excessive corrosion of the carbon skeleton. At the same time, the introduction of CO-PO3 and other groups significantly increased the specific surface area and surface acidity. After filtration and drying, acid-activated biochar was obtained.

[0022] Furthermore, the weight ratio of the biochar, deionized water, and H3PO4 aqueous solution is 1:7:3-5.

[0023] Furthermore, the biochar is prepared by the following steps:

[0024] First, weigh 20g of dried corn stalk powder and mix it with 20g of zinc chloride (ZnCl2) at a mass ratio of 1:1. Add 200mL of deionized water, place it in a magnetic stirrer, add a magnetic stir bar, and stir and soak at a speed of 1000r / min for 6h.

[0025] After impregnation, the mixture was dispensed into petri dishes and dried in a drying oven at 80°C until constant weight.

[0026] The dried sample was ground into a uniform powder using an agate mortar and then placed in a tube furnace. Under a nitrogen protective atmosphere, the sample was heated to 950°C at a heating rate of 10°C / min and held at this temperature for 2 hours while maintaining a nitrogen flow rate of 200 mL / min to complete the carbonization process and obtain biochar. The obtained biochar was then ground and sealed for later use.

[0027] Preferably, the weight ratio of acid-activated biochar and glutaraldehyde in step 1) is 5:1.

[0028] Preferably, the weight ratio of aldehyde-based biochar, polyethyleneimine, and tetrahydrofuran in step 2) is 1:0.2-0.4:10.

[0029] Preferably, the preparation process of the trivalent cobalt solution in step 3) is as follows:

[0030] When Co(NO3)2·6H2O is mixed with a 30wt% aqueous solution of H2O2 at a weight ratio of 1:3-5 and reacted at room temperature for 15-20 minutes, the solution turns dark brown, indicating that Co... 2+ Oxidized to Co 3+ Cooled to 0°C in an ice water bath, Co at 0°C 3+ Difficult to be reduced to Co 2+ A trivalent cobalt solution is obtained. This solution is unstable at room temperature and must be prepared and used immediately.

[0031] Preferably, before the hydrothermal reaction, the high-pressure reactor needs to be evacuated and purged with nitrogen until the nitrogen atmosphere pressure is 1 bar to avoid Co. 2+ It is oxidized to ensure that the product is pure phase CoFe2O4.

[0032] This invention also proposes a CoFe2O4-biochar adsorbent prepared by the aforementioned method, characterized in that it possesses the paramagnetism of CoFe2O4, and the biochar pores are saturated with amino groups, phosphate groups, carboxyl groups, hydroxyl groups, and a small amount of sulfonylimide-SN-, which readily complexes and adsorbs various heavy metal ions and can resist the adsorption or precipitation interference of light metal ions. Furthermore, after adsorbing heavy metals, the sulfonylimide-SN- exhibits a dynamic equilibrium that shifts towards the formation of SN bonds and the breaking of SN bonds to form -SH, further enhancing the adsorption of heavy metal ions. Additionally, in a slightly acidic environment with a pH of 5-7, the amino groups are easily protonated, allowing the adsorption of some high-valence heavy metal anions (such as CrO4). 2- wait).

[0033] Finally, this invention also applies the aforementioned CoFe2O4-biochar adsorbent material to adsorb Pb from wastewater from coal-fired power plants. 2+ Cd 2+ CrO4 2- This includes the following steps:

[0034] S1, Adsorption

[0035] The CoFe2O4-biochar adsorbent material described in claim 9 was used as the adsorbent. The adsorbent dosage was fixed at 0.5 g / L of wastewater. The system was shaken at 100 rpm for 24 hours at room temperature 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. The adsorption efficiency was tested.

[0036] The adsorption capacity (Q) and removal efficiency (η) of heavy metals on biochar were obtained by formulas (1) and (2):

[0037] (1)

[0038] (2)

[0039] Where Q is the adsorption capacity, η is the adsorption efficiency, C0 represents the initial concentration of the analyte, and C e V represents the concentration of the analyte at equilibrium (mg / L), V is the volume of the test liquid (mL), and M represents the mass of the adsorbent used for adsorption (mg).

[0040] S2, Adsorbent Regeneration

[0041] Pb adsorbed 2+ Cd 2+ or CrO4 2- The CoFe2O4-biochar adsorbent material was reacted with a NaOH solution with a molar concentration of 1 mol / L at room temperature (about 25°C) and shaken at 100 rpm for 12 h to promote the effective release of heavy metal ions.

[0042] After desorption, the adsorbent is separated from the alkaline desorption solution by magnetic separation. The adsorbent is then thoroughly washed with deionized water and anhydrous ethanol in sequence to remove residual desorbent and impurities. Finally, it is dried at 80°C and stored for later use.

[0043] The regeneration performance and reuse efficiency of CFO-BC were systematically evaluated by conducting five consecutive adsorption-desorption cycle experiments.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1. This invention sequentially activates the biochar pores with acid to introduce active hydroxyl groups, then modifies them with dialdehyde to introduce aldehyde groups onto the biochar pore surface. Next, it grafts PEI rich in amino groups using a Schiff base reaction. Finally, it uses cysteine ​​with thiol groups to generate sulfonamide-SN- by reacting the thiol groups with -C=N-. This results in a novel adsorbent material with multiple functional groups such as amino groups, phosphoroxy groups, carboxyl groups, hydroxyl groups, and dynamic thiol groups successfully introduced onto its surface. This forms a multi-synergistic adsorbent that can efficiently complex or electrostatically adsorb heavy metal ions in different forms.

[0046] 2. The product of this invention has high adsorption capacity and good universality for a variety of heavy metal ions, especially under certain pH conditions (4-6), utilizing amine protonation to adsorb CrO4. 2- Ion adsorption is performed to obtain Pb 2+ Cd 2+ CrO4 2- The adsorption performance is good, and this invention is the first to achieve universal adsorption treatment effect for both anionic and cationic heavy metal ions.

[0047] 3. The sulfonamide bond (-SN-) introduced in this invention is a dynamic covalent bond, eliminating the instability defect of -C=N-. Simultaneously, -SN- is a relatively weak dynamic covalent bond, easily broken over time and releasing cysteine, which is beneficial for light metal ions (such as Na+). + K + Ca 2+ There is no chelation, but it does not interact with Pb. 2+ Cd 2+ When heavy metal ions are present, the product intelligently breaks down and releases a 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 real wastewater with complex composition.

[0048] 4. The functional group modification process of this invention is highly efficient and structurally stable. Through a stepwise covalent grafting strategy of acid activation-acetal reaction-Schiff base reaction, high-density and firm fixation of PEI polymer chains on the surface and in the pores of biochar is achieved, avoiding the disadvantage of easy loss in physical impregnation methods. 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 this 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), which is convenient for rapid separation and recovery by external magnetic field, but also avoids the problems of pore blockage and performance degradation caused by physical mixing.

[0049] 5. This 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. It also has the characteristics of excellent regeneration performance and strong reusability, which also proves the stability of the product structure and the reversibility of functional groups. The excellent regeneration performance greatly reduces the long-term use cost of the material and lays a solid foundation for its practical engineering application. Attached Figure Description

[0050] Figure 1 This is a SEM image of the adsorption of the product in Comparative Example 4 of the present invention, wherein... Figure 1 (a) is a SEM image of BC-CFO before adsorption in Comparative Example 4. Figure 1 (b) is a SEM image of BC-CFO after Pb2+ adsorption in Comparative Example 4. Figure 1 (c) is a SEM image of BC-CFO after Pb2+ adsorption in Comparative Example 4. Figure 1 (d) is a SEM image of BC-CFO after adsorption of CrO42- in Comparative Example 4, with an adsorption pH of 6;

[0051] Figure 2 This is a SEM image of the product adsorption in Example 2 of the present invention, wherein... Figure 2 (a) is a SEM image of BC-CFO before adsorption in Example 2. Figure 2 (b) is a SEM image of BC-CFO after Pb2+ adsorption in Example 2. Figure 2 (c) is a SEM image of BC-CFO after Pb2+ adsorption in Example 2. Figure 2 (d) is a SEM image of BC-CFO after adsorption of CrO42- in Example 2, with an adsorption pH of 6;

[0052] Figure 3 This is a schematic diagram of the acetal reaction mechanism in this invention;

[0053] Figure 4 This is a schematic diagram of the mechanism of the amine-rich modification reaction in this invention;

[0054] Figure 5 This is a schematic diagram of the mechanism of the thiol reaction in this invention;

[0055] Figure 6 This is a schematic diagram of the hydrothermal synthesis mechanism in this invention. Detailed Implementation

[0056] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0057] Preparation Example 1

[0058] The biochar is prepared by the following steps:

[0059] First, weigh 20g of dried corn stalk powder and mix it with 20g of zinc chloride (ZnCl2) at a mass ratio of 1:1. Add 200mL of deionized water, place it in a magnetic stirrer, add a magnetic stir bar, and stir and soak at a speed of 1000r / min for 6h.

[0060] After impregnation, the mixture was dispensed into petri dishes and dried in a drying oven at 80°C until constant weight.

[0061] The dried sample was ground into a uniform powder using an agate mortar and then placed in a tube furnace. Under a nitrogen protective atmosphere, the sample was heated to 950°C at a heating rate of 10°C / min and held at this temperature for 2 hours while maintaining a nitrogen flow rate of 200 mL / min to complete the carbonization process and obtain biochar. The obtained biochar was then ground and sealed for later use.

[0062] Preparation Example 2

[0063] The acid-activated biochar is prepared by the following steps:

[0064] The biochar prepared in Example 1 was added to deionized water, followed by an 85 wt% H3PO4 aqueous solution. After ultrasonic dispersion, the mixture was magnetically stirred at 60-80°C for 2-5 hours. The H3PO4 aqueous solution has both chemical activation and functional group introduction (mainly phospho groups) effects, introducing hydroxyl or phospho groups onto the surface of the biochar pores. H3PO4 erodes the carbon skeleton through dehydration, cross-linking, and oxidation, exhibiting relatively mild corrosiveness and avoiding excessive corrosion of the carbon skeleton. At the same time, it introduces CO-PO3 and other groups, significantly increasing the specific surface area and surface acidity. After filtration and drying, acid-activated biochar was obtained.

[0065] The weight ratio of the biochar, deionized water, and H3PO4 aqueous solution is 1:7:3.

[0066] Preparation Example 3

[0067] Similar to Preparation Example 2, except that the weight ratio of biochar, deionized water, and H3PO4 aqueous solution is 1:7:4.

[0068] Preparation Example 4

[0069] Similar to Preparation Example 2, except that the weight ratio of biochar, deionized water, and H3PO4 aqueous solution is 1:7:5.

[0070] Comparative Preparation Example 1

[0071] Similar to Preparation Example 2, except that the weight ratio of biochar, deionized water, and H3PO4 aqueous solution is 1:7:2.

[0072] Comparative Preparation Example 2

[0073] Similar to Preparation Example 2, except that the weight ratio of biochar, deionized water, and H3PO4 aqueous solution is 1:7:7. Example

[0074] The preparation method of CoFe2O4-biochar adsorbent material includes the following steps:

[0075] 1) Acetal reaction

[0076] The acid-activated biochar and diethyl ether prepared in Example 2 were mixed at a weight ratio of 1:10 and sonicated 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 temperature was raised to 60°C, and the mixture was refluxed for 3 hours with stirring. After filtration and drying, aldehyde-based biochar with aldehyde groups grafted on the surface and pore surface was obtained.

[0077] 2) Amine-rich modification reaction

[0078] Aldehyde-modified biochar and polyethyleneimine were added to tetrahydrofuran and refluxed at 40°C for 60 min. After the reaction, the mixture was washed with water and filtered to produce amine-rich biochar with a polyethyleneimine film rich in amine groups on the surface and in the pores.

[0079] 3) Thiol reaction

[0080] Cysteine ​​and -C=N- from amine-rich biochar were added to a trivalent cobalt solution at a molar ratio of 1:1, with a weight ratio of amine-rich biochar to trivalent cobalt solution of 1:1.5. The mixture was stirred at 0°C for 30 min, then heated to 80°C and stirred for 1 h. The solution changed from dark brown to pinkish-green, and the cysteine ​​concentration in the solution decreased sharply to a constant level of ≤0.5 wt%, indicating that Co... 3+ Reduced to Co 2+ A suspension of sulfonylimide-modified biochar was obtained;

[0081] 4) Hydrothermal synthesis

[0082] Fe(NO3)3·9H2O was added to the suspension of sulfonamide-modified biochar, the molar ratio of Fe to Co was controlled at 2:1, and ammonia water accounting for 20% of the total weight of the system was added, with the mass fraction of ammonia in the ammonia water being 30%.

[0083] Stir for 30 minutes (to allow Fe to be stirred) 3+ After complexation and adsorption on the surface and pores of biochar, the product is transferred to a high-pressure reactor and hydrothermally reacted at 180℃ for 2 hours. After filtration, the product is washed three times alternately with water and ethanol and then vacuum dried at 60℃ and 1kPa for 5 hours to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorbent material.

[0084] Among them, 1) the weight ratio of acid-activated biochar and glutaraldehyde is 5:1.

[0085] In 2), the weight ratio of aldehyde-based biochar, polyethyleneimine, and tetrahydrofuran is 1:0.4:10.

[0086] The preparation process of the trivalent cobalt solution in section 3) is as follows:

[0087] When Co(NO3)2·6H2O was mixed with a 30wt% aqueous solution of H2O2 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°C in an ice water bath, Co at 0°C 3+ Difficult to be reduced to Co 2+ A trivalent cobalt solution is obtained. This solution is unstable at room temperature and must be prepared and used immediately. Example

[0088] The preparation method of CoFe2O4-biochar adsorbent material includes the following steps:

[0089] 1) Acetal reaction

[0090] The acid-activated biochar and diethyl ether prepared in Example 3 were mixed at a weight ratio of 1:10 and ultrasonically 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 temperature was raised to 60°C, and the mixture was refluxed for 2.5 hours with stirring. After filtration and drying, aldehyde-based biochar with aldehyde groups grafted on the surface and pore surface was obtained.

[0091] 2) Amine-rich modification reaction

[0092] Aldehyde-modified biochar and polyethyleneimine were added to tetrahydrofuran and refluxed at 45°C for 45 min. After the reaction, the mixture was washed with water and filtered to produce amine-rich biochar with a polyethyleneimine film rich in amine groups on the surface and in the pores.

[0093] 3) Thiol reaction

[0094] Cysteine ​​and -C=N- from amine-rich biochar were added to a trivalent cobalt solution at a molar ratio of 1:1 (weight ratio of amine-rich biochar to trivalent cobalt solution was 1:1.8). The mixture was stirred at 0°C for 30 min, then heated to 70°C and stirred for 1.5 h. The solution changed from dark brown to pinkish-green, and the cysteine ​​concentration in the solution decreased sharply to a constant level of ≤0.5 wt%, indicating that Co... 3+ Reduced to Co 2+ A suspension of sulfonylimide-modified biochar was obtained;

[0095] 4) Hydrothermal synthesis

[0096] Fe(NO3)3·9H2O was added to the suspension of sulfonamide-modified biochar, the molar ratio of Fe to Co was controlled at 2:1, and ammonia water accounting for 18% of the total weight of the system was added, with the mass fraction of ammonia in the ammonia water being 30%.

[0097] Stir for 30 minutes (to allow Fe to be stirred) 3+ After complexation and adsorption on the surface and pores of biochar, the product is transferred to a high-pressure reactor and hydrothermally reacted at 200℃ for 1.5h. After filtration, the product is washed twice with water and ethanol alternately, and then vacuum dried at 60℃ and 1kPa for 5h to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorbent material.

[0098] Among them, 1) the weight ratio of acid-activated biochar and glutaraldehyde is 5:1.

[0099] In 2), the weight ratio of aldehyde-based biochar, polyethyleneimine, and tetrahydrofuran is 1:0.3:10.

[0100] The preparation process of the trivalent cobalt solution in section 3) is as follows:

[0101] When Co(NO3)2·6H2O was mixed with a 30wt% aqueous solution of H2O2 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°C in an ice water bath, Co at 0°C 3+ Difficult to be reduced to Co 2+ A trivalent cobalt solution is obtained. This solution is unstable at room temperature and must be prepared and used immediately. Example

[0102] The preparation method of CoFe2O4-biochar adsorbent material includes the following steps:

[0103] 1) Acetal reaction

[0104] The acid-activated biochar and diethyl ether prepared in Example 4 were mixed at a weight ratio of 1:10 and ultrasonically 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 temperature was raised to 60°C, and the mixture was refluxed for 2 hours with stirring. After filtration and drying, aldehyde-based biochar with aldehyde groups grafted on the surface and pore surface was obtained.

[0105] 2) Amine-rich modification reaction

[0106] Aldehyde-modified biochar and polyethyleneimine were added to tetrahydrofuran and refluxed at 50°C for 30 min. After the reaction, the mixture was washed with water and filtered to produce amine-rich biochar with a polyethyleneimine film rich in amine groups on the surface and in the pores.

[0107] 3) Thiol reaction

[0108] Cysteine ​​and -C=N- from amine-rich biochar were added to a trivalent cobalt solution at a molar ratio of 1:1, with a weight ratio of amine-rich biochar to trivalent cobalt solution of 1:2. The mixture was stirred at 0°C for 30 min, then heated to 60°C and stirred for 2 h. The solution changed from dark brown to pinkish-green, and the cysteine ​​concentration in the solution decreased sharply to a constant level of ≤0.5 wt%, indicating that Co... 3+ Reduced to Co 2+ A suspension of sulfonylimide-modified biochar was obtained;

[0109] 4) Hydrothermal synthesis

[0110] Fe(NO3)3·9H2O was added to the suspension of sulfonamide-modified biochar, the molar ratio of Fe to Co was controlled at 2:1, and ammonia water accounting for 15% of the total weight of the system was added, with the mass fraction of ammonia in the ammonia water being 30%.

[0111] Stir for 30 minutes (to allow Fe to be stirred) 3+ After complexation and adsorption on the surface and pores of biochar, the product is transferred to a high-pressure reactor and hydrothermally reacted at 220℃ for 1 hour. After filtration, the product is washed three times alternately with water and ethanol and then vacuum dried at 60℃ and 1kPa for 5 hours to obtain biochar loaded with CoFe2O4, namely CoFe2O4-biochar adsorbent material.

[0112] Among them, 1) the weight ratio of acid-activated biochar and glutaraldehyde is 5:1.

[0113] In 2), the weight ratio of aldehyde-based biochar, polyethyleneimine, and tetrahydrofuran is 1:0.2:10.

[0114] The preparation process of the trivalent cobalt solution in section 3) is as follows:

[0115] When Co(NO3)2·6H2O was mixed with a 30wt% aqueous solution of H2O2 at a weight ratio of 1:5 and reacted at room temperature for 15 minutes, the solution turned dark brown, indicating that Co... 2+ Oxidized to Co 3+ Cooled to 0°C in an ice water bath, Co at 0°C 3+ Difficult to be reduced to Co 2+ A trivalent cobalt solution is obtained. This solution is unstable at room temperature and must be prepared and used immediately.

[0116] Comparative Example 1

[0117] The process was essentially the same as in Example 2, except that the acid-activated biochar from Comparative Preparation Example 1 was used. The acidification was incomplete, leading to an incomplete acetal reaction and a high residual aldehyde content in the system. This resulted in a lower pore amine modification rate, and consequently, a decrease in adsorption efficiency.

[0118] Comparative Example 2

[0119] The preparation was essentially the same as in Example 2, except that the acid-activated biochar from Comparative Preparation Example 1 was used. The biochar framework was more severely corroded, resulting in reduced surface activity of the product.

[0120] Comparative Example 3

[0121] The process is essentially the same as in Example 2, except that the biochar from Preparation Example 1 is used to directly replace the acid-activated biochar in Example 2. Its surface hydroxyl groups are insufficient, and it contains more ash and impurities, resulting in incomplete acetal reaction and a higher residual aldehyde group content in the system. This leads to a decrease in the subsequent pore amine group modification rate, and consequently, a decrease in adsorption efficiency. Furthermore, its surface activity is significantly lower than that of Example 2.

[0122] Comparative Example 4

[0123] Steps 1)-3) in Example 2 are omitted, and the biochar prepared in Example 1 is used directly to replace the sulfonylimide-modified biochar in Example 2. Its pores do not contain amine groups.

[0124] Comparative Example 5

[0125] (Step 3 in Example 2 is omitted) Amino-rich biochar is used directly to replace sulfonylimide-modified biochar. Since it does not contain sulfonylimide bonds, its adsorption and selectivity for heavy metal ions are reduced.

[0126] Comparative Example 6

[0127] Step 2 of Example 2 is omitted, and only step 1) of aldehyde alkylation is performed. Then, step 2 is skipped, and step 3 is performed directly. However, because there is no PEI and no -C=N- bond, cysteine ​​cannot be grafted in step 3, and only physical mixing occurs. The subsequent hydrothermal steps are the same as in Example 1. The results demonstrate the key role of the amine group introduced by PEI and the sulfonylimide bond subsequently formed in performance.

[0128] Comparative Example 7

[0129] (Step 4 in Example 2 is omitted). Without CoFe2O4 loading, steps 1, 2, and 3 are performed to obtain sulfonylimide-modified biochar. The hydrothermal synthesis in step 4 is omitted, and the biochar is directly filtered and dried. The results demonstrate the magnetic function of CoFe2O4 nanoparticles and their possible synergistic effect on adsorption.

[0130] Comparative Example 8

[0131] Commercial CoFe2O4 nanopowder (20-30nm 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.

[0132] Performance testing:

[0133] The adsorption materials obtained in Examples 1-3 and Comparative Examples 1-8 were applied to adsorb Pb from 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 sample is 100 mg / L, and the process includes the following steps:

[0134] S1, Adsorption

[0135] The CoFe2O4-biochar adsorbent material described in claim 9 was used as the adsorbent, and the adsorbent dosage was fixed at 0.5 g / L of wastewater. The system was shaken at 100 rpm for 24 hours at room temperature to ensure sufficient contact with heavy metal ions. The pH was controlled at 6, and the adsorption efficiency was tested.

[0136] The adsorption capacity (Q) and removal efficiency (η) of heavy metals on biochar were obtained by formulas (1) and (2):

[0137] (1)

[0138] (2)

[0139] Where Q is the adsorption capacity, η is the adsorption efficiency, C0 represents the initial concentration of the analyte, and Ce V represents the concentration of the analyte at equilibrium (mg / L), V is the volume of the test liquid (mL), and M represents the mass of the adsorbent used for adsorption (mg).

[0140] S2, Adsorbent Regeneration

[0141] Pb adsorbed 2+ Cd 2+ or CrO4 2- CoFe2O4-biochar adsorbent material (CFO-BC) was reacted with a NaOH solution with a molar concentration of 1 mol / L at room temperature (approximately 25°C) and oscillated at 100 rpm for 12 h to promote the effective release of heavy metal ions.

[0142] After desorption, the adsorbent is separated from the alkaline desorption solution by magnetic separation. The adsorbent is then thoroughly washed with deionized water and anhydrous ethanol in sequence to remove residual desorbent and impurities. Finally, it is dried at 80°C and stored for later use.

[0143] The regeneration performance and reuse efficiency of CFO-BC were systematically evaluated by conducting five consecutive adsorption-desorption cycle experiments.

[0144] See Table 1 for details:

[0145] Table 1. Adsorption performance under slightly acidic conditions

[0146]

[0147] Data Analysis:

[0148] 1. The effect of acid activation degree

[0149] As shown in Table 1, compared with Comparative Examples 1-3, Example 2 exhibits the highest adsorption performance. In this formulation, phosphoric acid has the best activation effect, which can not only create a rich pore structure through mild corrosion and significantly increase the specific surface area, but also introduce the largest amount of surface acidic oxygen-containing functional groups (such as CO-PO3, -COOH, -OH). These functional groups are anchoring sites for subsequent acetal reactions and also provide direct complexation sites for heavy metal ions.

[0150] In contrast, the biochar surface activation in Comparative Example 1 was insufficient, and the amount of phosphoric acid was inadequate, resulting in incomplete activation of the biochar and a limited number of reactive functional groups on the surface. This led to a decrease in the subsequent aldehyde and amino grouping grafting rates, a reduction in the total adsorption sites, and a significant decrease in adsorption performance.

[0151] In contrast, the biochar surface of Comparative Example 2 was over-activated. The strong corrosiveness of excessive phosphoric acid destroyed the carbon skeleton structure, causing some micropores to collapse and the total specific surface area to decrease. Although the surface was highly acidic, the damaged structure limited its adsorption capacity.

[0152] In contrast, the biochar surface of Comparative Example 3 was not activated. The original biochar surface had few functional groups, the pore structure was not optimized, and it contained a lot of ash and impurities. It lacked effective chemical adsorption sites and mainly relied on limited physical adsorption.

[0153] 2. The key role of functional group modification

[0154] Comparing Example 2 with Comparative Examples 4-6,

[0155] Comparative Example 4, without any modification, served as the adsorption baseline for the blank test and exhibited extremely low performance, confirming the absolute necessity of chemical modification. Furthermore, due to... Figure 1 and Figure 2 In comparison, the BC-CFO surface modified with ammonia loading has a more uniform crystal phase distribution and a lower crystal form destruction rate after adsorption, 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.

[0156] Comparative Example 5 showed no thiol reaction, and its reaction with Pb was negative. 2+ Cd 2+ The adsorption capacity was significantly lower than that in Example 2, and the adsorption capacity for CrO4 was also significantly lower. 2- The adsorption effect is relatively small, indicating the absence of the sulfonamide bond (-SN-) and the thiol group (-SH) released in its dynamic response. The thiol group has little effect on Pb adsorption. 2+ Cd 2+ Soft acid metal ions have extremely strong complexing abilities, and the absence of these sites directly leads to a decrease in cation adsorption capacity. However, the adsorption of CrO4... 2- Primarily depends on protonated amine groups (-NH3) + Therefore, the impact is not significant.

[0157] Comparative Example 6, without PEI modification, showed a significant overall decrease in performance, especially for CrO4. 2- The adsorption was almost completely ineffective. This indicates that polyethyleneimine provides a large number of primary and secondary amine groups. These amine groups: ① form the basis for the formation of Schiff base bonds and subsequent sulfonylimide bonds; ② are themselves excellent complexing groups; ③ under acidic conditions, they are protonated (-NH3). + ), and is efficiently and specifically adsorbed by anions CrO4 through electrostatic attraction. 2- This comparative example demonstrates that the amine group is responsible for the adsorption of CrO4. 2- The dominant functional group.

[0158] 3. Effect of CoFe2O4 loading mode

[0159] Comparing Example 2 with Comparative Examples 7-8, Comparative Example 7, which lacks CoFe2O4 loading, showed a slight decrease in adsorption performance, indicating that amino-modified biochar still has a certain adsorption effect. However, the role of CoFe2O4 cannot be ignored, and the CoFe2O4 nanoparticles also provide magnetic separation function.

[0160] Comparative Example 8, using a physical blending method, showed that the CoFe2O4 nanoparticles easily aggregated, severely clogging the pore channels of biochar and hindering the mass transfer and diffusion of heavy metal ions. Furthermore, the contact between the nanoparticles and the carbon matrix was merely physical, failing to create a synergistic effect. In contrast, the advantages of in-situ hydrothermal synthesis are: ① small particle size and excellent dispersibility; ② strong bonding with the carbon matrix without disrupting the pore structure; ③ the potential for some metal sites to participate in surface complexation.

[0161] 4. Regeneration Performance Analysis

[0162] Test the regeneration and recycling performance of the product in Example 2, using the adsorption of Pb in Example 2. 2+ For example, see Table 2:

[0163] Table 2. Recycling performance of the product of the present invention

[0164]

[0165] Example 2, after five adsorption-desorption cycles, still retained 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:

[0166] ① The covalently grafted PEI chains and the in-situ grown CoFe2O4 particles are firmly bonded to the carbon matrix and are not easily detached; ② The main adsorption sites (amine groups, carboxyl groups, phosphate groups, etc.) are stable in acidic and alkaline environments; ③ The reversibility of the dynamic covalent bond -SN- allows the material to recover its active structure after alkaline desorption.

[0167] 5. Effect of pH on adsorption performance

[0168] The adsorption conditions (pH) of Example 2 were adjusted to 2-8, and its performance was tested as shown in Table 3 below:

[0169] Table 3. Effect of pH on adsorption performance

[0170]

[0171] This indicates that as pH decreases, CrO4 2- The adsorption capacity of CrO4 first increases and then decreases; however, as pH increases, the adsorption capacity of CrO4... 2- The adsorption performance of CrO4 decreased significantly, indicating that amine matrix protonation significantly affects the adsorption performance of CrO4. 2-The adsorption performance is crucial; furthermore, excessive acidity may cause degradation of CoFe2O4 particles, thereby reducing Pb. 2+ Cd 2+ The adsorption performance of Pb under alkaline conditions. 2+ Cd 2+ The results all showed an increase, indicating that alkali salt precipitation is beneficial for the adsorption of heavy metal ions.

[0172] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing CoFe2O4-biochar adsorbent material, characterized in that, Includes the following steps: 1) Acetal reaction Acid-activated biochar and diethyl ether were mixed at a weight ratio of 1:10 and sonicated 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 temperature was raised to 60°C, and the mixture was refluxed for 2-3 hours with stirring. After filtration and drying, aldehyde-based biochar with aldehyde groups grafted on the surface and pores was obtained. 2) Amine-rich modification reaction Aldehyde-modified biochar and polyethyleneimine were added to tetrahydrofuran and refluxed at 40-50°C for 30-60 min. After the reaction, the mixture was washed with water and filtered to produce amine-rich biochar with a polyethyleneimine film rich in amine groups on the surface and in the pores. 3) Thiol reaction Cysteine ​​and -C=N- from amine-rich biochar were added to a trivalent cobalt solution at 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℃ for 30 min, then heated to 60-80℃ and stirred for 1-2 h to obtain a suspension of sulfonamide-modified biochar. 4) Hydrothermal synthesis Fe(NO3)3·9H2O was added to the suspension of sulfonamide-modified biochar, the molar ratio of Fe to Co was 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%. After stirring for 30 minutes, the mixture was transferred to a high-pressure reactor and hydrothermally reacted at 180-220℃ for 1-2 hours. The product was filtered and washed 2-3 times alternately with water and ethanol. It was then vacuum dried at 60℃ and 1kPa for 5 hours to obtain CoFe2O4-loaded biochar, i.e., CoFe2O4-biochar adsorbent material.

2. The method for preparing CoFe2O4-biochar adsorbent material according to claim 1, characterized in that, The acid-activated biochar is prepared by the following steps: Biochar was added to deionized water, followed by an 85 wt% H3PO4 aqueous solution. After ultrasonic dispersion, the mixture was magnetically stirred at 60-80℃ for 2-5 hours. After filtration and drying, acid-activated biochar was obtained.

3. The method for preparing CoFe2O4-biochar adsorbent 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 CoFe2O4-biochar adsorbent material according to claim 2, characterized in that, The biochar is prepared by the following steps: First, weigh 20g of dried corn stalk powder and mix it with 20g of zinc chloride at a mass ratio of 1:

1. Add 200mL of deionized water, place it in a magnetic stirrer, add a magnetic stir bar, and stir and soak at a speed of 1000r / min for 6 hours. After impregnation, the mixture was dispensed into petri dishes and dried in a drying oven at 80°C until constant weight. The dried sample was ground into a uniform powder using an agate mortar and then placed in a tube furnace. Under a nitrogen protective atmosphere, the sample was heated to 950°C at a heating rate of 10°C / min and held at this temperature for 2 hours while maintaining a nitrogen flow rate of 200 mL / min to complete the carbonization process and obtain biochar. The obtained biochar was then ground and sealed for later use.

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

1.

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

10.

7. The method for preparing the CoFe2O4-biochar adsorbent material according to claim 1, characterized in that, The preparation process of the trivalent cobalt solution in 3) is as follows: Co(NO3)2·6H2O is mixed with a 30wt% H2O2 aqueous solution at a weight ratio of 1:3-5 and reacted at room temperature for 15-20 min. The mixture is then cooled to 0℃ in an ice-water bath to obtain a trivalent cobalt solution, which should be prepared and used immediately.

8. The method for preparing the CoFe2O4-biochar adsorbent material according to claim 1, characterized in that, Before the hydrothermal reaction, the high-pressure reactor needs to be evacuated and purged with nitrogen until the nitrogen atmosphere pressure is 1 bar.

9. CoFe2O4-biochar adsorbent material prepared by any one of the preparation methods according to claims 1-8.

10. The CoFe2O4-biochar adsorbent material according to claim 9 in the adsorption of Pb in wastewater from coal-fired power plants 2+ Cd 2+ CrO4 2- The application is characterized by, Includes the following steps: S1, Adsorption The CoFe2O4-biochar adsorbent material described in claim 9 was used as the adsorbent. The adsorbent dosage was fixed at 0.5 g / L of wastewater. The system was shaken at 100 rpm for 24 hours at room temperature 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. The adsorption efficiency was tested. The adsorption capacity and removal efficiency 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 analyte, and C e V represents the concentration of the element to be tested when equilibrium is reached, V is the volume of the liquid to be tested, and M represents the mass of the adsorbent used for adsorption. S2, Adsorbent Regeneration Pb adsorbed 2+ Cd 2+ or CrO4 2- The CoFe2O4-biochar adsorbent 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 is separated from the alkaline desorption solution by magnetic separation. The adsorbent is then thoroughly washed with deionized water and anhydrous ethanol in sequence to remove residual desorbent and impurities. Finally, it is dried at 80°C and stored for later use. The regeneration performance and reuse efficiency of CFO-BC were systematically evaluated by conducting five consecutive adsorption-desorption cycle experiments.

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