Preparation process of modifier-doped iron-containing magnetic biochar and method for adsorbing organic pollutants by using modifier-doped iron-containing magnetic biochar

Abstract

The invention belongs to the field of biochar material preparation technology and application, and discloses a preparation process of modifier-doped ferromagnetic biochar and a method for adsorbing organic pollutants by using the modifier-doped ferromagnetic biochar. Aiming at the problems of complex modification process, low adsorption efficiency, difficulty in recovery and the like of the existing biochar, the scheme comprises the following steps: mixing corncob serving as a raw material with ferric nitrate and carbonate / bicarbonate according to a mass ratio of 2: 1: 1, grinding, calcining for 2-4 hours in an inert atmosphere at 600-700 DEG C, and cleaning and drying to obtain the magnetic biochar. According to the process, through the synergistic effect of double modifiers, carbonate is decomposed at high temperature to form pores to increase the specific surface area, ferric nitrate is pyrolyzed to generate Fe3O4 to endow the magnetic recovery performance, and structure optimization and function enhancement are synchronously achieved. When being applied to adsorption, the biochar treats organic pollutants according to the dosage of 10-15 mg / 100 mL under the conditions that the pH value is equal to 7 and the temperature is 20-30 DEG C, efficient adsorption is achieved through pore filling, the conjugation effect and the iron complexing effect, and the magnet can be separated and recycled within 30 seconds. The method is suitable for environmental treatment of various organic pollutants.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation and application of biochar materials, and particularly relates to a preparation process of iron-containing magnetic biochar doped with a modifier and a method for adsorbing organic pollutants. Background Art

[0002] In the context of the accelerating global industrialization and agricultural modernization, due to the persistence, bioaccumulation, mobility, and toxicity diversity of organic pollutants, their emissions and accumulations have become key issues seriously threatening the ecological environment and human health. Common organic pollutants include antibiotics, polycyclic aromatic hydrocarbons, pesticides, etc. The adsorption method can separate pollutants from the environmental medium through the interaction between the adsorbent and organic pollutants, providing an important way to solve the problem of organic pollutants. Facing the many challenges of organic pollutant treatment, the adsorption method is highly favored in the field of environmental governance due to its unique advantages.

[0003] Common adsorbents such as activated carbon, zeolite, metal-organic frameworks, etc. are expensive to prepare. As a potential new type of adsorption material, biochar has been increasingly studied in the environmental field in recent years. It has the characteristics of wide sources, relatively low cost, adjustable adsorption performance, etc., providing a new solution for the treatment of organic pollutants. The preparation materials of biochar are rich and diverse, and common ones include crop straws, forestry wastes, livestock and poultry manure, etc. Although biochar itself has certain adsorption performance, in the real environment, affected by various factors such as acidity and alkalinity, biomass, and competing ions, the adsorption effect will decline. To further improve its adsorption capacity for organic pollutants, it is often necessary to modify it, usually by loading other elements to improve the adsorption performance. The preparation of iron-modified magnetic biochar is affected by many technological processes and parameters, and some of the reagents used in the preparation process are expensive. Summary of the Invention

[0004] Aiming at the problems and disadvantages of the existing technology, the present invention aims to propose a process for rapidly pyrolyzing and activating iron-containing magnetic biochar doped with a double modifier and a method for efficiently adsorbing organic pollutants. Using agricultural waste corncobs as raw materials, after directly doping and grinding with the double modifier, iron-modified biochar materials are prepared by co-calcination in a nitrogen atmosphere. The cost is low and the method is simple, and a large amount of magnetic biochar can be prepared efficiently and continuously. It can not only efficiently adsorb organic pollutants in water bodies, but also be recovered by using a magnet to avoid secondary environmental pollution, and has good application potential.

[0005] The object of the present invention is to provide a preparation process of iron-containing magnetic biochar doped with a modifier in view of the problems existing in the prior art, which includes the following steps: crushing agricultural waste corn cobs into particles below 80 mesh and performing a drying treatment; soaking the dried corn cob powder in a 0.5 - 1 mol / L HCl solution for 20 - 30 min, washing it with deionized water until neutral, then immersing it in a 1 - 1.5 mol / L urea solution for 1 - 2 h, washing it with deionized water until neutral and then drying to obtain modified corn cob powder; mixing the modified corn cob powder with iron nitrate and bicarbonate or carbonate in a mass ratio of 2:1:1 and grinding them evenly; under an inert atmosphere, heating to 600 - 700 °C and calcining for 2 - 4 hours; after the calcined product is cooled, washing it with deionized water until neutral, and then drying at 90 - 100 °C for 9 - 10 hours to obtain the iron-containing magnetic biochar doped with the modifier.

[0006] Furthermore, the preparation process of the iron-containing magnetic biochar doped with a modifier includes the following steps: crushing agricultural waste corn cobs into particles below 80 mesh and performing a drying treatment; soaking the dried corn cob powder in a 1 mol / L HCl solution for 30 min, washing it with deionized water until neutral, then immersing it in a 1.5 mol / L urea solution for 2 h, washing it with deionized water until neutral and then drying to obtain modified corn cob powder; mixing the modified corn cob powder with iron nitrate and bicarbonate or carbonate in a mass ratio of 2:1:1 and grinding them evenly; under an inert atmosphere, heating to 700 °C and calcining for 4 hours; after the calcined product is cooled, washing it with deionized water until neutral, and then drying at 100 °C for 10 hours to obtain the iron-containing magnetic biochar doped with the modifier.

[0007] Further, the heating to 700 °C is carried out at a rate of 5 °C / min.

[0008] Further, an oxygen-free environment is maintained during the calcination process.

[0009] Further, the mass ratio of the corn cob powder, iron nitrate and bicarbonate or carbonate is 2:1:1.

[0010] Further, the bicarbonate is selected from: sodium bicarbonate and / or potassium bicarbonate.

[0011] Further, the carbonate is selected from: sodium carbonate and / or potassium carbonate.

[0012] A method for the iron-containing magnetic biochar doped with a modifier to adsorb organic pollutants includes the following steps: adding the iron-containing magnetic biochar doped with the modifier into an aqueous solution containing organic pollutants; performing adsorption under the oscillation conditions of 20 - 30 °C and 160 - 190 r / min; after the adsorption is completed, separating the iron-containing magnetic biochar doped with the modifier from the solution by using a magnet.

[0013] Furthermore, the organic pollutant is at least one of tetracycline, polycyclic aromatic hydrocarbons, and atrazine.

[0014] Furthermore, the pH value of the aqueous solution is 7.

[0015] Furthermore, the dosage of the magnetic biochar is 10 - 15 mg / 100 mL of the solution.

[0016] Furthermore, the magnet separation is completed within 30 seconds.

[0017] The raw material pretreatment removes metal cations in the corncob through hydrochloric acid and hydrolyzes hemicellulose to form pore channels; urea impregnation introduces amino groups, generating nitrogen-containing functional groups during high-temperature pyrolysis, enhancing the surface electron cloud density and π-π electron donor ability. In the synergistic activation of double modifiers, carbonate (NaHCO 3 ) generates CO 2 gas during pyrolysis, forming three-dimensional through pores, significantly improving the specific surface area and pore volume of the biochar; iron oxide (Fe 3 O 4 ) is in-situ generated above 600 °C, having a high magnetization intensity and enabling rapid magnetic separation. High-temperature calcination promotes the carbonization of cellulose to form a graphene-like structure, and Raman spectroscopy shows a highly defective sp 2 hybrid carbon skeleton, significantly enhancing the electron transfer ability.

[0018] The adsorption mechanism of the present invention is based on multi-component synergistic action. By constructing a hierarchical pore structure, a molecular sieve effect is achieved, and size-matched adsorption of tetracycline is generated. In surface chemical action, the aromatic ring of the biochar forms a π-π conjugate stack with the benzotetracycline structure of tetracycline, and the surface hydroxyl groups of Fe 3 O 4 form a hydrogen bond network with the pollutant -OH / -NH. Fe 3+ forms an octahedral chelate with the ketone group of tetracycline. Fe 3 O 4 grains are uniformly dispersed in the carbon matrix, forming a magnetic-carbon heterojunction, and under an external magnetic field, high-efficiency magnetic separation with a recovery rate > 99% within 30 seconds is achieved through gradient magnetic force.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. The raw material of the biochar is selected from waste crops, which has a wide source, low cost, and is environmentally friendly. The present invention prepares the modified biochar by directly mixing and grinding the modifier with the raw material, which is simple in operation; the pyrolysis time is short, the preparation process is short, and the production efficiency is greatly improved;

[0021] 2. The porous structure of biochar can rapidly and efficiently adsorb organic pollutants under the action of pore filling. The aromatic ring structure in biochar and organic pollutants can produce a conjugation effect, and the hydroxyl groups in organic pollutants can form hydrogen bonds with biochar. These effects accelerate the adsorption process;

[0022] 3. Improve its adsorption capacity for organic pollutants by optimizing the biochar structure and surface chemical properties. The modifier NaHCO 3 Generate bubbles to create pores on the biochar surface to increase the porosity of biochar and improve its specific surface area, which can increase the adsorption sites of biochar. Fe(NO 3 ) 3 functions to load iron onto the biochar. Not only does the biochar become magnetic and can be recovered by a magnet, but during the adsorption process, iron can have a complexation reaction with organic pollutants. Compared with before modification, the adsorption effect is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the removal rate of tetracycline (TC) by the biochar prepared in Example 1, Comparative Example 1 - Comparative Example 3 of the present invention.

[0024] Figure 2 This is the XRD (X-ray diffraction) pattern of the crystal structure analysis of the biochar prepared in Example 1, Comparative Example 1 - Comparative Example 3 of the present invention.

[0025] Figure 3 This is the VSM (Vibrating Sample Magnetometer) test diagram of the magnetic regression line of the biochar prepared in Example 1 and Comparative Example 3 of the present invention.

[0026] Figure 4 This is the adsorption diagram of the biochar prepared in Example 1 of the present invention for different concentrations of the antibiotic tetracycline (TC).

[0027] Figure 5 This is the adsorption of the biochar prepared in Example 1 of the present invention for different concentrations of the polycyclic aromatic hydrocarbon naphthalene (Nap).

[0028] Figure 6 This is the adsorption of the biochar prepared in Example 1 of the present invention for different concentrations of the organic pesticide atrazine (ATZ).

[0029] Figure 7 . This is the SEM (Scanning Electron Microscopy) scanning imaging of the biochar prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0031] Example 1

[0032] Preparation of iron-doped magnetic biochar with a dopant modifier: Crush agricultural waste corn cobs into particles smaller than 80 mesh and perform a drying treatment; soak the dried corn cob powder in 1 mol / L HCl solution for 30 min, wash it with deionized water until neutral, then soak it in 1.5 mol / L urea solution for 2 h, wash it with deionized water until neutral and then dry it to obtain modified corn cob powder; mix the modified corn cob powder with iron nitrate and bicarbonate or carbonate in a mass ratio of 2:1:1 and grind them evenly; under an inert atmosphere, heat up to 700 °C and calcine for 4 hours; after the calcined product is cooled, wash it with deionized water until neutral, and then dry it at 100 °C for 10 hours to obtain the iron-doped magnetic biochar with the dopant modifier.

[0033] Comparative Example 1

[0034] Preparation of a biochar: Crush the corn cob raw material into particles smaller than 80 mesh and then perform a drying treatment. Place 2 g of corn cob powder into a tubular furnace and prepare a raw biochar material through anaerobic calcination under a nitrogen atmosphere. Set the heating rate at 5 °C / min and calcine at 700 °C for 2 h. After cooling, wash it with deionized water until neutral, and then put it into an oven. Set the temperature at 90 °C and dry it for 9 h to obtain a biochar.

[0035] Comparative Example 2

[0036] Preparation of a biochar: Crush the corn cob raw material into particles smaller than 80 mesh and then perform a drying treatment. Mix 2 g of corn cob powder with 1 g of NaHCO 3 After doping and grinding evenly, use a tubular furnace to prepare an iron-modified biochar material through anaerobic co-calcination under a nitrogen atmosphere. Set the heating rate at 5 °C / min and calcine at 700 °C for 2 h. After cooling, wash it with deionized water until neutral, and then put it into an oven. Set the temperature at 90 °C and dry it for 9 h to obtain a biochar.

[0037] Comparative Example 3

[0038] Crush the corn cob raw material into particles smaller than 80 mesh and then perform a drying treatment. Mix 2 g of corn cob powder with 1 g of Fe(NO 3 ) 3 、1 g of NaHCO3 After doping and grinding evenly, an iron-modified biochar material was prepared by anoxic co-calcination in a nitrogen atmosphere using a tube furnace. The heating rate was set at 5 °C / min, and it was calcined at 700 °C for 2 h. After cooling, it was washed with deionized water until neutral, and then placed in an oven at a temperature of 90 °C and dried for 9 h to obtain a biochar.

[0039] Performance test:

[0040] 1. Adsorption performance test for tetracycline: Prepare 100 mL of tetracycline (TC) solution with an initial concentration of 10 mg / L in a glass volumetric flask. The pH value of the solution is 7. After adding 10 mg of different biochars (Example 1, Comparative Example 1 - Comparative Example 3), seal it with a rubber stopper and place it in a constant temperature shaker. Set the rotation speed to 180 r / min and the temperature to 25 °C. At reaction times of 5, 10, 15, 20, 30, 40, 50, and 60 min, draw the solution with a 10 mL syringe, filter it through a 0.22 μm filter membrane, and measure the remaining concentration with a UV spectrophotometer to calculate the adsorption capacity q of TC t and the removal rate Q.

[0041] The results are as Figure 1 shown. The data of Example 1 are better than those of Comparative Example 1 - Comparative Example 3. Experiments show that the synergistic effect of the double modifiers (ferric nitrate + sodium bicarbonate) significantly improves the adsorption efficiency: the removal rate of Example 1 reaches nearly 80% or more within 60 minutes, much higher than that of unmodified and only NaHCO 3 modified biochar. The mechanism is that NaHCO 3 decomposes at high temperature to produce CO 2 , forming a porous structure to increase the specific surface area; ferric nitrate pyrolyzes to generate magnetic Fe 3 O 4 , endowing magnetic recovery ability and undergoing a complexation reaction with pollutants.

[0042] 2. XRD patterns of the crystal structures of the biochars prepared in Example 1, Comparative Example 1 - Comparative Example 3 are as Figure 2 shown. Diffraction peaks of elemental iron and iron carbide were detected in the biochar added with Fe(NO 3 ) 3 , indicating that iron was loaded on the biochar.

[0043] 3. VSM tests of the magnetic regression lines of the biochars prepared in Example 1 and - Comparative Example 3 are as Figure 3 shown. Added with Fe(NO 3 ) 3The biochar exhibits superparamagnetism. As shown in the figure, the biochar can be separated from water within 30 s using a magnet. In practical applications, the iron-modified biochar can be separated from an aqueous solution by a magnet, and it can quickly return to its original state after the magnet is removed.

[0044] 4. Adsorb different concentrations of the antibiotic tetracycline (TC) using the biochar prepared in Example 1: Prepare 100 mL of TC solutions with a pH of 7 and different concentrations (5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L) in volumetric flasks. Add 15 mg of the adsorbent to the solutions and place them in a constant-temperature shaker. Set the rotation speed to 180 r / min and the temperature to 25 °C. The test results are as Figure 4 shown. In the 10 mg / L TC solution, the removal rate reaches 99.15% and the adsorption capacity reaches 661.0 mg / g, with the best comprehensive effect. It has a good adsorption effect on antibiotic organic pollutants.

[0045] 5. Adsorb different concentrations of the polycyclic aromatic hydrocarbon naphthalene (Nap) using the biochar prepared in Example 1: Prepare 100 mL of TC solutions with a pH of 7 and different concentrations (2 mg / L, 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L) in volumetric flasks. Add 15 mg of the adsorbent to the solutions and place them in a constant-temperature shaker. Set the rotation speed to 180 r / min and the temperature to 25 °C. The test results are as Figure 5 shown. In the 5 mg / L TC solution, the removal rate reaches 95.62% and the adsorption capacity reaches 478.10 mg / g, with the best comprehensive effect. It has a good adsorption effect on polycyclic aromatic hydrocarbon organic pollutants.

[0046] 6. Adsorb different concentrations of the organic pesticide atrazine (ATZ) using the biochar prepared in Example 1: Prepare 100 mL of TC solutions with a pH of 7 and different concentrations (2 mg / L, 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L) in volumetric flasks. Add 15 mg of the adsorbent to the solutions and place them in a constant-temperature shaker. Set the rotation speed to 180 r / min and the temperature to 25 °C. The test results are as Figure 6 shown. In the 5 mg / L TC solution, the removal rate reaches 94.19% and the adsorption capacity reaches 470.95 mg / g, with the best comprehensive effect. It has a good adsorption effect on organic pesticides.

[0047] 8. Figure 7 Shows the scanning electron microscope (SEM) image of the biochar prepared in Example 1. The image shows that the biochar surface has a rich porous structure and rough texture, and these features mainly come from sodium bicarbonate (NaHCO 3)The gas decomposed during the high-temperature calcination process, thereby forming pores and increasing the specific surface area. At the same time, some granular substances are distributed on the surface, for iron oxides (such as Fe 3 O 4 ), and these particles endow the biochar with magnetism. The porous and rough surface structure and the distribution of iron particles make the iron-containing magnetic biochar doped with modifiers exhibit excellent performance in adsorbing organic pollutants.

[0048] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing iron-containing magnetic biochar doped with a modifier, characterized in that: The following steps are involved: The agricultural waste corn cobs are crushed into particles below 80 mesh and dried; the dried corn cob powder is first soaked in a 0.5-1 mol / L HCl solution for 20-30 minutes, washed with deionized water until neutral, then immersed in a 1-1.5 mol / L urea solution for 1-2 hours, washed with deionized water until neutral, and then dried to obtain modified corn cob powder; The modified corn cob powder is mixed with ferric nitrate and bicarbonate or carbonate in a mass ratio of 2:1:1 and ground evenly; in an inert atmosphere, the temperature is raised to 600-700°C and calcined for 2-4 hours; after the calcined product is cooled, it is washed with deionized water to neutrality, and then dried at 90-100°C for 9-10 hours to obtain the iron-containing magnetic biochar doped with the modifier.

2. The process for preparing the iron-containing magnetic biochar doped with a modifier according to claim 1, characterized in that: An oxygen-free environment is maintained during the calcination process.

3. The process for preparing the iron-containing magnetic biochar doped with a modifier according to claim 1, characterized in that: The mass ratio of the corncob powder, ferric nitrate and bicarbonate or carbonate is 2:1:

1.

4. The process for preparing the iron-containing magnetic biochar doped with a modifier according to claim 1, characterized in that: The bicarbonate is selected from sodium bicarbonate and / or potassium bicarbonate.

5. The process for preparing the iron-containing magnetic biochar doped with a modifier according to claim 1, characterized in that: The carbonate is selected from sodium carbonate and / or potassium carbonate.

6. A method for adsorbing organic pollutants by a magnetic biochar doped with an iron-containing modifier obtained in the preparation process of a magnetic biochar doped with an iron-containing modifier according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: adding the iron-containing magnetic biochar doped with the modifier into an aqueous solution containing organic pollutants; The adsorption is carried out under the oscillation conditions of 20-30° C. and 160-190 r / min; after the adsorption is completed, the iron-containing magnetic biochar doped with the modifier is separated from the solution by using a magnet.

7. The method for adsorbing organic pollutants by iron-containing magnetic biochar doped with a modifier according to claim 6, characterized in that: The organic pollutant is at least one of tetracycline, polycyclic aromatic hydrocarbons and atrazine.

8. The method for adsorbing organic pollutants by iron-containing magnetic biochar doped with a modifier according to claim 6, characterized in that: The pH value of the aqueous solution is neutral.

9. The method for adsorbing organic pollutants by iron-containing magnetic biochar doped with a modifier according to claim 6, characterized in that: The dosage of the magnetic biochar is 10-15 mg / 100 mL solution.

10. The method for adsorbing organic pollutants by iron-containing magnetic biochar doped with a modifier according to claim 6, characterized in that: The magnet separation was completed within 30 seconds.

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