Process for preparing magnetic biochar rich in nitrogen / iron oxide through rapid pyrolysis activation and method for efficiently adsorbing phenol by using magnetic biochar

Abstract

The invention belongs to the technical field of biomass utilization, and particularly relates to a process for preparing magnetic charcoal rich in nitrogen / iron oxide through rapid pyrolysis activation and a method for efficiently adsorbing phenol through the magnetic charcoal. The method comprises the following steps: by taking biomass as a raw material, crushing, cleaning and drying, impregnating with a ferric trichloride solution, drying at a low temperature to prepare an iron-containing precursor, and then quickly pyrolyzing in an ammonia gas atmosphere to generate nitrogen / iron oxide-rich magnetic biochar which has a developed pore structure and loaded iron oxide and ferroferric oxide particles. The adsorbent is short in preparation period, low in energy consumption and high in efficiency, and the specific surface area and surface functional group distribution are further improved by optimizing pyrolysis conditions, so that the adsorption rate and capacity of phenol are remarkably enhanced. The prepared iron-nitrogen co-doped biochar is low in cost, efficient and renewable, a new path is provided for organic pollutant treatment, and high-value utilization of biomass waste and economic treatment of water pollution are achieved.

Description

Technical Field

[0001] The invention relates to the field of biomass utilization, and in particular to a process for preparing magnetic biochar rich in nitrogen / iron oxides by rapid pyrolysis and activation and a method for efficiently adsorbing phenol. Background Art

[0002] The generation of anthropogenic wastewater during the industrialization process has led to the persistent deterioration of the aquatic environment. A large part of these wastewaters are water-soluble and volatile organic compounds. Phenol is a very common soluble organic pollutant in wastewater in the fields of fossil energy, agriculture, fine chemicals, etc. It can accumulate in organisms and has the harm of causing human deformities and cancer. Due to its high biological hazard and persistence, it is difficult to remove phenol pollutants in wastewater. Therefore, removing phenol from wastewater has become a huge challenge. There are already methods including ion exchange, extraction, photocatalytic degradation, and electrocatalytic oxidation to remove phenol from water. Metal organic frameworks, clays, zeolites, etc. have also been used as adsorbents to remove phenol. Most adsorbents are expensive to prepare, and their adsorption capacity for phenol is not satisfactory. Therefore, it is necessary to study ways to improve the physical and chemical properties of biochar, so as to improve its adsorption capacity and speed for phenol.

[0003] The biochar obtained by the original pyrolysis method has poor adsorption effect and needs to be loaded with other elements to improve the adsorption performance. The preparation of magnetic biochar rich in nitrogen / iron oxides is difficult to load iron and nitrogen at the same time, which is affected by many process flows and parameters, and the reagents used in some preparation processes are expensive. At present, no one has studied the comparison of the adsorption level of phenol by different preparation methods of Fe-N co-doped biochar and post-treatment methods. It is urgent to explore a process for preparing magnetic biochar rich in nitrogen / iron oxides by rapid pyrolysis and activation and its efficient adsorption of phenol, which meets the requirements of simple operation, low cost, and efficient preparation of high-performance adsorbents. Summary of the invention

[0004] In view of the above defects and improvement needs, the present invention aims to propose a process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis and activation and a method for efficiently adsorbing phenol, so as to realize the pyrolysis of biomass waste to prepare high-performance phenol adsorbent, thereby improving the utilization value of biomass waste. The method has low cost and simple process, and can continuously and efficiently prepare a large amount of biochar loaded with nitrogen-containing functional groups and iron oxide particles, greatly reducing the removal cost of phenol pollutants in wastewater.

[0005] To achieve the above object, the present invention provides a process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis and activation and a method for efficiently adsorbing phenol, comprising the following steps:

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

[0007] S2: placing the biomass waste from step S1 in a flask, adding ferric chloride hexahydrate and distilled water into the flask, and shaking and mixing them evenly;

[0008] S3: drying the mixture obtained in step S2 in an oven to obtain iron-doped biomass waste before pyrolysis;

[0009] S4: the iron-doped biomass waste in step S3 is fully mixed with the catalyst potassium hydroxide in a mass ratio of 1:4-4:1, and a nitrogen-rich pyrolysis reaction is carried out in an atmosphere where ammonia and an inert gas coexist, and the mixture is subjected to a rapid catalytic pyrolysis reaction, which greatly promotes the formation of nitrogen-rich functional groups, and obtains original nitrogen / iron-rich biochar;

[0010] S5: The original nitrogen / iron-rich biochar after pyrolysis in step S4 is treated by an oscillation washing method, and after filtering and drying steps, nitrogen / iron-rich magnetic biochar with a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface is obtained.

[0011] The conception principle of the above invention is: to improve the adsorption capacity of phenol by optimizing the structure and surface chemical properties of biochar. By pre-treating biomass waste with ferric chloride hexahydrate, iron ions are embedded in the biomass material during the initial impregnation process to form a basic co-doping structure. In the subsequent nitrogen-rich pyrolysis reaction, ammonia, as a nitrogen source, reacts chemically with iron-doped biomass under high temperature conditions, not only introducing a large number of nitrogen-containing functional groups, but also promoting the formation of the pore structure of biochar. The use of catalyst potassium hydroxide further enhances the porosity and surface area of ​​the material, which is conducive to the adsorption and transmission of phenol molecules. In addition, the active nitrogen-containing functional groups formed in the nitrogen-rich environment significantly enhance the interaction between biochar and phenol. At the same time, the iron oxide particles loaded on the surface can catalyze the degradation and surface complexation reaction of phenol, thereby improving the adsorption efficiency. The final nitrogen-rich / iron oxide magnetic biochar not only has a developed pore structure, but also improves the adsorption capacity and regeneration performance of phenol because of the rich nitrogen-containing functional groups and iron oxide particles on the surface. This functional material can be used for water pollution control, providing an efficient and sustainable solution and achieving high-value transformation and resource utilization of biomass waste.

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

[0013] Furthermore, in step S2, the mass ratio of biomass waste to ferric chloride hexahydrate is 1:4-4:1, the mass ratio of the total mass of biomass waste and ferric chloride hexahydrate to the added distilled water is 1:3-1:10, the oscillation temperature is 15°C-35°C, the oscillation amplitude is 100rpm-300rpm, and the oscillation time is 10h-30h.

[0014] Furthermore, the drying temperature in step S3 is 100° C. to 150° C., and the drying time is 10 h to 30 h.

[0015] Furthermore, in step S4, the inert gas is argon or nitrogen, the total gas flow of the inert gas and ammonia is 200 mL / min to 500 mL / min, wherein the proportion of ammonia in the total gas is 10% to 100%. The biomass catalytic nitrogen-enriched pyrolysis temperature is 400° C. to 800° C., and the reaction time is 10 to 60 min.

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

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

[0018] Furthermore, the magnetic biochar obtained in step S5 is nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, rich in nitrogen-containing functional groups and rich in iron oxide and ferrosoferric oxide particles loaded on the surface.

[0019] Furthermore, the obtained nitrogen / iron oxide-rich magnetic biochar is used to adsorb phenol in water, requiring that the wastewater contains phenol as an organic pollutant.

[0020] Furthermore, nitrogen / iron oxide-rich magnetic biochar is used to adsorb phenol in water, with a dosage of 10 mg / L-100 mg / L.

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

[0022] (1) In the method of the present invention, biomass waste and ferric chloride hexahydrate are treated under specific mixing and shaking conditions so that iron ions are evenly distributed in the biomass. In the subsequent nitrogen-rich pyrolysis process, ammonia is used as a nitrogen source to introduce a large number of nitrogen-containing functional groups, which not only enhance the chemical adsorption capacity of phenol, but also enhance the physical adsorption performance of the material through synergistic action with iron oxide particles.

[0023] (2) During the catalytic pyrolysis process, potassium hydroxide was used as an activator to effectively promote the formation of micropores and mesopores in biochar. This multi-level pore structure greatly increases the specific surface area, provides more channels for the transmission and adsorption of phenol molecules, and improves the adsorption speed and efficiency. In addition, the more complex pore structure can also effectively prevent pore blockage and maintain long-term high-efficiency adsorption function.

[0024] (3) The unique chemical composition of the nitrogen / iron oxide-rich magnetic biochar obtained in the present invention can be regenerated by simple washing and drying steps after use. The use of dilute hydrochloric acid or deionized water eliminates the need for the use of harmful chemical reagents, achieving a low-cost, safe, and environmentally friendly regeneration process, thereby significantly reducing long-term operating costs.

[0025] (4) The biochar obtained in the present invention has iron oxide and ferroferric oxide particles loaded on the surface of the biochar, which gives the material a certain catalytic degradation ability. This enables the material to not only adsorb phenol, but also partially achieve catalytic degradation of phenol, reduce secondary pollution problems, and improve the overall purification effect.

[0026] (5) The entire preparation process of the present invention avoids the use of strong acids and bases, and the product properties can be controlled by adjusting the ammonia concentration and reaction conditions. This flexible process design simplifies the operation steps and reduces the environmental burden, meeting the requirements of sustainable development.

[0027] (6) The nitrogen / iron oxide-rich magnetic biochar of the present invention not only performs well in water pollution control, but can also be applied to other fields such as heavy metal ion removal, soil quality improvement, electrode material development, etc., demonstrating good versatility and commercial potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a fitting diagram of the adsorption isotherm of phenol adsorbed by the magnetic biochar rich in nitrogen / iron oxide in Example 1 of the present invention;

[0029] Figure 2 This is a fitting diagram of the adsorption isotherm of phenol adsorbed by the magnetic biochar rich in nitrogen / iron oxide in Example 2 of the present invention;

[0030] Figure 3 This is a fitting diagram of the adsorption isotherm of phenol adsorbed by the magnetic biochar rich in nitrogen / iron oxide in Example 3 of the present invention;

[0031] Figure 4 The nitrogen adsorption and desorption curves of the magnetic biochar rich in nitrogen / iron oxide in Examples 1-3;

[0032] Figure 5is the pore size distribution diagram of the nitrogen / iron oxide-rich magnetic biochar in Example 1-3;

[0033] Figure 6 XRD patterns of nitrogen / iron oxide-rich magnetic biochars in Examples 1-6. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] The present invention provides a process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis and activation and a method for efficiently adsorbing phenol, which specifically comprises the following steps:

[0036] (1) crushing the biomass waste into particles smaller than 100 mesh and drying them;

[0037] (2) placing the biomass waste from step (1) in a flask, adding ferric chloride hexahydrate and distilled water into the flask, and shaking and mixing them uniformly;

[0038] (3): drying the mixture obtained in step (2) in an oven to obtain iron-doped biomass waste before pyrolysis;

[0039] (4): The iron-doped biomass waste in step (3) is fully mixed with the catalyst potassium hydroxide in a mass ratio of 1:4-4:1, and a nitrogen-rich pyrolysis reaction is carried out in an atmosphere where ammonia and an inert gas coexist. The mixture is subjected to a rapid catalytic pyrolysis reaction, which greatly promotes the formation of nitrogen-rich functional groups, thereby obtaining original nitrogen / iron-rich biochar;

[0040] (5) The original nitrogen / iron-rich biochar after pyrolysis in step (4) is treated by an oscillation washing method, and after filtering and drying steps, a nitrogen / iron-rich magnetic biochar having a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface is obtained.

[0041] (6): The nitrogen / iron oxide-rich magnetic biochar obtained in step (5) is used to conduct adsorption kinetics and adsorption isotherm experiments on phenol.

[0042] The biomass in step (1) is one or more of bamboo, cotton stalks, rice husks, corn stalks, and wheat stalks. The drying temperature is 100°C to 150°C, and the drying time is 10h to 30h.

[0043] In step (2), the mass ratio of biomass waste to ferric chloride hexahydrate is 1:4-4:1, the mass ratio of the total mass of biomass waste and ferric chloride hexahydrate to the added distilled water is 1:3-1:10, the oscillation temperature is 15°C-35°C, the oscillation amplitude is 100rpm-300rpm, and the oscillation time is 10h-30h.

[0044] The drying temperature in step (3) is 100° C. to 150° C., and the drying time is 10 h to 30 h.

[0045] In step (4), the inert gas is argon or nitrogen, and the total gas flow rate of the inert gas and ammonia is 200 mL / min to 500 mL / min, wherein the proportion of ammonia in the total gas is 10% to 100%, the biomass catalytic nitrogen-enriched pyrolysis temperature is 400° C. to 800° C., and the reaction time is 10 to 60 min.

[0046] In step (5), the mass ratio of the original nitrogen / iron-rich biochar to the washing solution is 1:100-1:200. The shaking temperature is 15°C-35°C, the shaking amplitude is 100rpm-300rpm, and the shaking time is 10h-30h. The washing solution can be dilute hydrochloric acid or deionized water. The drying temperature is 100°C-150°C, and the drying time is 10h-30h.

[0047] In step (6), the concentration of phenol is 20-200 mg / L, and the amount of nitrogen / iron oxide-rich magnetic biochar added is 20 mg-50 mg.

[0048] The conception principle of the above invention is: to improve the adsorption capacity of phenol by optimizing the structure and surface chemical properties of biochar. By pre-treating biomass waste with ferric chloride hexahydrate, iron ions are embedded in the biomass material during the initial impregnation process to form a basic co-doping structure. In the subsequent nitrogen-rich pyrolysis reaction, ammonia, as a nitrogen source, reacts chemically with iron-doped biomass under high temperature conditions, not only introducing a large number of nitrogen-containing functional groups, but also promoting the formation of the pore structure of biochar. The use of catalyst potassium hydroxide further enhances the porosity and surface area of ​​the material, which is conducive to the adsorption and transmission of phenol molecules. In addition, the active nitrogen-containing functional groups formed in the nitrogen-rich environment significantly enhance the interaction between biochar and phenol. At the same time, the iron oxide particles loaded on the surface can catalyze the degradation and surface complexation reaction of phenol, thereby improving the adsorption efficiency. The final nitrogen-rich / iron oxide magnetic biochar not only has a developed pore structure, but also improves the adsorption capacity and regeneration performance of phenol because of the rich nitrogen-containing functional groups and iron oxide particles on the surface. This functional material can be used for water pollution control, providing an efficient and sustainable solution and achieving high-value transformation and resource utilization of biomass waste.

[0049] In order to explain the method of the present invention in more detail, the following further describes Example 1 in conjunction with specific examples.

[0050] The embodiment of the present invention describes a process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis activation and a method for efficiently adsorbing phenol, and the method specifically comprises the following steps:

[0051] S1: crush the bamboo into particles smaller than 100 mesh, put it into an oven at 105°C and dry it for 24 hours to obtain a biomass raw material;

[0052] S2: 20 g of the bamboo chips obtained in step S1 was placed in a 250 mL flask, and 20 g of ferric chloride hexahydrate was added at the same time, and then 200 mL of deionized water was added, and the mixture was placed in a shaker, and shaken at a speed of 150 rpm for 24 h at a temperature of 25° C. to make it shake and mix evenly;

[0053] S3: drying the mixture obtained in step S2 in an oven at 105° C. for 24 hours to obtain an iron-doped biomass raw material before pyrolysis;

[0054] S4: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 600°C, take 4 g of the iron-doped bamboo chips raw material in step S3 and 2 g of potassium hydroxide and mix them thoroughly. Quickly send the mixture into the middle of the reactor. The reaction time is 30 min. The biomass is fully pyrolyzed. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 10%, to obtain magnetic biochar rich in nitrogen / iron oxides without post-treatment;

[0055] S5: Place the nitrogen / iron oxide-rich magnetic biochar after pyrolysis in step S4 but without post-treatment into a 100 mL conical flask, add 100 g of deionized water, and wash it in a shaker at 25°C and 150 rpm for 24 hours, filter it with filter paper, and dry it in an oven at 105°C for 24 hours to obtain nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface.

[0056] S6: Adsorption kinetics and adsorption isotherm experiments were performed on phenol using the nitrogen / iron oxide-rich magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 100 mg / L phenol solution, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 30 mg. The adsorption isotherm experiment used 20, 50, 80, 100, 150 and 200 mg / L phenol solutions, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 25 mg.

[0057] The specific surface area of ​​the obtained nitrogen / iron oxide-rich magnetic biochar is 423.163 m 2 / g, and the total pore volume is 0.211cm 3 / g. The proportion of nitrogen doping is 3.57%, the proportion of iron doping is 3.53%, and the maximum adsorption amount of phenol is 219.065mg / g.

[0058] Example 2

[0059] This embodiment is the same as embodiment 1, except that the pyrolysis reaction temperature in step S4 is 700°C.

[0060] The specific surface area of ​​the obtained nitrogen / iron oxide-rich magnetic biochar is 688.507 m 2 / g, and the total pore volume is 0.347cm 3 / g, the nitrogen element doping accounts for 3.34%, the iron element doping accounts for 3.00%, and the maximum adsorption capacity of phenol is 212.659mg / g.

[0061] Example 3

[0062] This embodiment is the same as embodiment 1, except that the pyrolysis reaction temperature in step S4 is 800°C.

[0063] The specific surface area of ​​the obtained nitrogen / iron oxide-rich magnetic biochar is 824.697 m 2 / g, and the total pore volume is 0.436cm 3 / g, the nitrogen element doping accounts for 3.67%, the iron element doping accounts for 1.48%, and the maximum adsorption capacity of phenol is 200.104mg / g.

[0064] Example 4

[0065] S1: crush the bamboo into particles smaller than 100 mesh, put it into an oven at 105°C and dry it for 24 hours to obtain a biomass raw material;

[0066] S2: 20 g of the bamboo chips obtained in step S1 was placed in a 250 mL flask, and 20 g of ferric chloride hexahydrate was added at the same time, and then 200 mL of deionized water was added, and the mixture was placed in a shaker, and shaken at a speed of 150 rpm for 24 h at a temperature of 25° C. to make it shake and mix evenly;

[0067] S3: drying the mixture obtained in step S2 in an oven at 105° C. for 24 hours to obtain an iron-doped biomass raw material before pyrolysis;

[0068] S4: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 600°C, take 4 g of the iron-doped bamboo chips raw material in step S3 and 2 g of potassium hydroxide and mix them thoroughly. Quickly send the mixture into the middle of the reactor. The reaction time is 30 min. The biomass is fully pyrolyzed. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 10%, to obtain magnetic biochar rich in nitrogen / iron oxides without post-treatment;

[0069] S5: The nitrogen / iron oxide-rich magnetic biochar after pyrolysis in step S4 but not post-treated is placed in a 100 mL conical flask, 100 g of 1 mol / L dilute hydrochloric acid is added, and the biochar is placed in a shaker and washed at 25°C and 150 rpm for 24 hours. The biochar is filtered with filter paper and dried in an oven at 105°C for 24 hours to obtain nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface.

[0070] S6: Adsorption kinetics and adsorption isotherm experiments were performed on phenol using the nitrogen / iron oxide-rich magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 100 mg / L phenol solution, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 30 mg. The adsorption isotherm experiment used 20, 50, 80, 100, 150 and 200 mg / L phenol solutions, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 25 mg.

[0071] The specific surface area of ​​the obtained nitrogen / iron oxide-rich magnetic biochar is 599.448 m 2 / g, and the total pore volume is 0.332cm 3 / g, the nitrogen element doping accounts for 5.5%, the iron element doping accounts for 2.28%, and the maximum adsorption capacity of phenol is 145.287mg / g.

[0072] Example 5

[0073] This embodiment is the same as embodiment 4, except that the pyrolysis reaction temperature in step S4 is 700°C.

[0074] The specific surface area of ​​the obtained nitrogen / iron oxide-rich magnetic biochar is 1464.716 m 2 / g, and the total pore volume is 0.762cm 3 / g, nitrogen element incorporation accounts for 7.42%, iron element incorporation accounts for 1.76%, and the maximum adsorption capacity of phenol is 144.596mg / g.

[0075] Example 6

[0076] This embodiment is the same as embodiment 4, except that the pyrolysis reaction temperature in step S4 is 800°C.

[0077] The specific surface area of ​​the obtained nitrogen / iron oxide-rich magnetic biochar is 1740.527 m 2 / g, and the total pore volume is 0.917cm 3 / g, the nitrogen element doping accounts for 6.71%, the iron element doping accounts for 0.28%, and the maximum adsorption capacity of phenol is 179.477mg / g.

[0078] Example 7

[0079] This embodiment is the same as embodiment 1, except that the pyrolysis reaction temperature in step S4 is 400°C.

[0080] The obtained nitrogen / iron oxide-rich magnetic biochar has a specific surface area of ​​18.642 m 2 / g, and the total pore volume is 0.052cm 3 / g, and the maximum adsorption capacity of phenol is 29.861mg / g.

[0081] Example 8

[0082] This embodiment is the same as embodiment 1, except that the pyrolysis reaction temperature in step S4 is 500°C.

[0083] The specific surface area of ​​the obtained nitrogen / iron oxide-rich magnetic biochar is 304.915 m 2 / g, and the total pore volume is 0.171cm 3 / g, and the maximum adsorption amount of phenol is 76.514 mg / g.

[0084] Example 9

[0085] This embodiment is the same as embodiment 4, except that the pyrolysis reaction temperature in step S4 is 400°C.

[0086] The obtained nitrogen / iron oxide-rich magnetic biochar has a specific surface area of ​​77.737 m 2 / g, and the total pore volume is 0.138cm 3 / g, and the maximum adsorption capacity of phenol is 33.502mg / g.

[0087] Example 10

[0088] This embodiment is the same as embodiment 4, except that the pyrolysis reaction temperature in step S4 is 500°C.

[0089] The specific surface area of ​​the obtained nitrogen / iron oxide-rich magnetic biochar is 420.890 m 2 / g, and the total pore volume is 0.248cm 3 / g, and the maximum adsorption capacity of phenol is 65.602mg / g.

[0090] Embodiment 11

[0091] S1: crush the rice husk into particles smaller than 100 mesh, put it into an oven at 105°C and dry it for 24 hours to obtain a biomass raw material;

[0092] S2: Place 20 g of the raw material obtained in step S1 in a 250 mL flask, add 40 g of ferric chloride hexahydrate, and then add 200 mL of deionized water, place in a shaker, and shake at 25° C. and 150 rpm for 24 hours to make it shake and mix evenly;

[0093] S3: drying the mixture obtained in step S2 in an oven at 105° C. for 24 hours to obtain an iron-doped biomass raw material before pyrolysis;

[0094] S4: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 600°C, take 4 g of the iron-doped biomass raw material in step S3 and 2 g of potassium hydroxide and mix them thoroughly. Quickly feed the mixture into the middle of the reactor. The reaction time is 30 min. The biomass is fully pyrolyzed. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 10%, to obtain magnetic biochar rich in nitrogen / iron oxides without post-treatment;

[0095] S5: The nitrogen / iron oxide-rich magnetic biochar after pyrolysis in step S4 but not post-treated is placed in a 100 mL conical flask, 100 g of 1 mol / L dilute hydrochloric acid is added, and the biochar is placed in a shaker and washed at 25°C and 150 rpm for 24 hours. The biochar is filtered with filter paper and dried in an oven at 105°C for 24 hours to obtain nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface.

[0096] S6: Adsorption kinetics and adsorption isotherm experiments were performed on phenol using the nitrogen / iron oxide-rich magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 150 mg / L phenol solution, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 50 mg. The adsorption isotherm experiment used 20, 50, 80, 100, 150 and 200 mg / L phenol solutions, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 30 mg.

[0097] The obtained nitrogen / iron oxide-rich magnetic biochar has a specific surface area of ​​more than 400 m 2 / g, the iron content is 3%, and the phenol removal rate can reach 80%.

[0098] Example 12

[0099] S1: After the corn is crushed into particles smaller than 100 mesh, it is placed in an oven at 105°C and dried for 24 hours to obtain a biomass raw material;

[0100] S2: Place 20 g of the raw material obtained in step S1 in a 250 mL flask, add 20 g of ferric chloride hexahydrate, and then add 200 mL of deionized water, place in a shaker, and shake at 25° C. and 150 rpm for 24 hours to make it shake and mix evenly;

[0101] S3: drying the mixture obtained in step S2 in an oven at 105° C. for 24 hours to obtain an iron-doped biomass raw material before pyrolysis;

[0102] S4: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 800°C, take 4 g of the iron-doped biomass raw material in step S3 and 4 g of potassium hydroxide and mix them thoroughly. Quickly feed the mixture into the middle of the reactor. The reaction time is 30 min. The biomass is fully pyrolyzed. The total flow rate of argon and ammonia is 300 mL / min, of which the proportion of ammonia is 40%, to obtain magnetic biochar rich in nitrogen / iron oxides without post-treatment;

[0103] S5: The nitrogen / iron oxide-rich magnetic biochar after pyrolysis in step S4 but not post-treated is placed in a 100 mL conical flask, 100 g of 1 mol / L deionized water is added, and the biochar is placed in a shaker and washed at 25°C and 150 rpm for 24 hours. The biochar is filtered with filter paper and dried in an oven at 105°C for 24 hours to obtain nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface.

[0104] S6: Adsorption kinetics and adsorption isotherm experiments were performed on phenol using the nitrogen / iron oxide-rich magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 200 mg / L phenol solution, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 20 mg. The adsorption isotherm experiment used 20, 50, 80, and 100 mg / L phenol solutions, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 20 mg.

[0105] The obtained nitrogen / iron oxide-rich magnetic biochar has a specific surface area of ​​more than 800 m 2 / g, the iron content is 4%, and the phenol removal rate can reach 80%.

[0106] Example 13

[0107] S1: After the corn stalks are crushed into particles smaller than 100 mesh, they are placed in an oven at 105°C and dried for 24 hours to obtain a biomass raw material;

[0108] S2: 20 g of the raw material obtained in step S1 was placed in a 250 mL flask, and 30 g of ferric chloride hexahydrate was added at the same time, and then 200 mL of deionized water was added, and the mixture was placed in a shaker, and shaken at 300 rpm for 24 h at a temperature of 35° C. to make it shake and mix evenly;

[0109] S3: drying the mixture obtained in step S2 in an oven at 105° C. for 24 hours to obtain an iron-doped biomass raw material before pyrolysis;

[0110] S4: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 200°C, take 4 g of the iron-doped biomass raw material in step S3 and 2 g of potassium hydroxide and mix them thoroughly. Quickly send the mixture into the middle of the reactor. The reaction time is 60 min. The biomass is fully pyrolyzed. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 20%, to obtain magnetic biochar rich in nitrogen / iron oxides without post-treatment;

[0111] S5: The nitrogen / iron oxide-rich magnetic biochar after pyrolysis in step S4 but not post-treated is placed in a 100 mL conical flask, 100 g of 1 mol / L deionized water is added, and the biochar is placed in a shaker and washed at 25°C and 150 rpm for 24 hours. The biochar is filtered with filter paper and dried in an oven at 105°C for 24 hours to obtain nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface.

[0112] S6: Adsorption kinetics and adsorption isotherm experiments were performed on phenol using the nitrogen / iron oxide-rich magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 150 mg / L phenol solution, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 25 mg. The adsorption isotherm experiment used 10, 20, 50, 150 and 200 mg / L phenol solutions, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 30 mg.

[0113] The obtained nitrogen / iron oxide-rich magnetic biochar has a specific surface area of ​​more than 350 m 2 / g, the iron content is 3%, and the phenol removal rate can reach 70%.

[0114] Embodiment 14

[0115] S1: crush the bamboo into particles smaller than 100 mesh, put it into an oven at 105°C and dry it for 24 hours to obtain a biomass raw material;

[0116] S2: 20 g of the raw material obtained in step S1 was placed in a 250 mL flask, and 30 g of ferric chloride hexahydrate was added at the same time, and then 200 mL of deionized water was added, and the mixture was placed in a shaker, and shaken at 200 rpm for 24 h at a temperature of 25° C. to make it shake and mix evenly;

[0117] S3: drying the mixture obtained in step S2 in an oven at 105° C. for 24 hours to obtain an iron-doped biomass raw material before pyrolysis;

[0118] S4: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 700°C, take 4 g of the iron-doped biomass raw material in step S3 and 4 g of potassium hydroxide and mix them thoroughly. Quickly send the mixture into the middle of the reactor. The reaction time is 60 min. The biomass is fully pyrolyzed. The total flow rate of argon and ammonia is 300 mL / min, of which the proportion of ammonia is 80%, to obtain magnetic biochar rich in nitrogen / iron oxides without post-treatment;

[0119] S5: The nitrogen / iron oxide-rich magnetic biochar after pyrolysis in step S4 but not post-treated is placed in a 100 mL conical flask, 100 g of 1 mol / L deionized water is added, and the biochar is placed in a shaker and washed at 25°C and 150 rpm for 24 hours. The biochar is filtered with filter paper and dried in an oven at 105°C for 24 hours to obtain nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface.

[0120] S6: Adsorption kinetics and adsorption isotherm experiments were performed on phenol using the nitrogen / iron oxide-rich magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 100 mg / L phenol solution, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 30 mg. The adsorption isotherm experiment used 20, 50, 80, 100, 150 and 200 mg / L phenol solutions, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 25 mg.

[0121] The obtained nitrogen / iron oxide-rich magnetic biochar has a specific surface area of ​​more than 700 m 2 / g, the iron content is up to 4.5%, and the phenol removal rate can reach 85%.

[0122] Embodiment 15

[0123] S1: After the corn stalks are crushed into particles smaller than 100 mesh, they are placed in an oven at 105°C and dried for 24 hours to obtain a biomass raw material;

[0124] S2: Place 20 g of the raw material obtained in step S1 in a 250 mL flask, add 20 g of ferric chloride hexahydrate, and then add 200 mL of deionized water, put it in a shaker, and shake it at 150 rpm for 24 hours at a temperature of 15°C to make it shake and mix evenly;

[0125] S3: drying the mixture obtained in step S2 in an oven at 105° C. for 24 hours to obtain an iron-doped biomass raw material before pyrolysis;

[0126] S4: Use a fixed bed reactor with a diameter of 45 mm and a length of 60 mm for pyrolysis. After heating the reactor to a specified temperature of 500°C, take 4 g of the iron-doped biomass raw material in step S3 and 2 g of potassium hydroxide and mix them thoroughly. Quickly send the mixture into the middle of the reactor. The reaction time is 30 min. The biomass is fully pyrolyzed. The total flow rate of argon and ammonia is 200 mL / min, of which the proportion of ammonia is 50%, to obtain magnetic biochar rich in nitrogen / iron oxides without post-treatment;

[0127] S5: The nitrogen / iron oxide-rich magnetic biochar after pyrolysis in step S4 but not post-treated is placed in a 100 mL conical flask, 100 g of 1 mol / L dilute hydrochloric acid is added, and the biochar is placed in a shaker and washed at 25°C and 150 rpm for 24 hours. The biochar is filtered with filter paper and dried in an oven at 105°C for 24 hours to obtain nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, enriched nitrogen-containing functional groups and rich iron oxide particles on the surface.

[0128] S6: Adsorption kinetics and adsorption isotherm experiments were performed on phenol using the nitrogen / iron oxide-rich magnetic biochar obtained in step S5. The adsorption kinetics experiment used a 250 mg / L phenol solution, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 40 mg. The adsorption isotherm experiment used 100, 150, 200, 300, 400 and 500 mg / L phenol solutions, and the amount of nitrogen / iron oxide-rich magnetic biochar added was 40 mg.

[0129] The obtained nitrogen / iron oxide-rich magnetic biochar has a specific surface area of ​​more than 450 m 2 / g, the iron content is up to 2.5%, and the phenol removal rate can reach 75%.

[0130] Figure 1This is a graph showing the experimental fitting results of the adsorption isotherm of phenol adsorbed by the nitrogen / iron oxide-rich magnetic biochar in Example 1 of the present invention; the experimental results show that due to the etching effect of ammonia and the role of nitrogen atoms anchoring iron atoms, more nitrogen-containing functional groups are enriched on the biochar, and a large number of iron oxide particles are also loaded. The results of the fitting curves of the two adsorption models show that the adsorption of phenol by the nitrogen / iron oxide-rich magnetic biochar is a combination of single-layer and multi-layer adsorption dominated by chemical adsorption, and the maximum adsorption amount of phenol can reach 219.065 mg / g.

[0131] Figure 2 This is a graph showing the experimental fitting results of the adsorption isotherm of phenol adsorbed by the nitrogen / iron oxide-rich magnetic biochar in Example 2 of the present invention; the experimental results show that due to the etching effect of ammonia and the role of nitrogen atoms anchoring iron atoms, more nitrogen-containing functional groups are enriched on the biochar, and a large number of iron oxide particles are also loaded. The results of the fitting curves of the two adsorption models show that the adsorption of phenol by the nitrogen / iron oxide-rich magnetic biochar is a combination of single-layer and multi-layer adsorption dominated by chemical adsorption, and the maximum adsorption amount of phenol can reach 212.659 mg / g.

[0132] Figure 3 This is a graph showing the experimental fitting results of the adsorption isotherm of phenol adsorbed by the nitrogen / iron oxide-rich magnetic biochar in Example 3 of the present invention; the experimental results show that due to the etching effect of ammonia and the role of nitrogen atoms anchoring iron atoms, more nitrogen-containing functional groups are enriched on the biochar, and a large number of iron oxide particles are also loaded. The results of the fitting curves of the two adsorption models show that the adsorption of phenol by the nitrogen / iron oxide-rich magnetic biochar is a combination of single-layer and multi-layer adsorption dominated by chemical adsorption, and the maximum adsorption amount of phenol can reach 200.104 mg / g.

[0133] Figure 4 It is a graph showing the nitrogen adsorption-desorption curve results in Examples 1-3 of the present invention; the experimental results show that the nitrogen / iron oxide-rich magnetic biochar prepared in the examples has a mixture showing type I / IV isotherms, in which the H4 hysteresis reflects the partial existence of mesopores, indicating that the KOH activation and ammonia etching have caused changes in the pore structure of the biochar, and also improved the adsorption performance of phenol.

[0134] Figure 5 The pore size distribution curves of Examples 1-3 of the present invention are shown in the experimental results. The micropores and mesopores act as transmission channels to form a hierarchical pore structure. KOH produces micropores, FeCl3 produces mesopores, and the nitrogen source promotes the formation of porous biochar by generating gas molecules to destroy the carbon structure. Iron plays a role in reducing carbon shrinkage during pyrolysis and also acts as a catalyst in the formation of pore structure. The newly generated iron oxide loaded on the surface of biochar can also produce more pore structures. This further promotes the adsorption of phenol.

[0135] Figure 6 The XRD diagram of Examples 1-6 of the present invention is shown in Figure 1. The experimental results show that iron and nitrogen elements are successfully loaded on biochar. There are more Fe3O4 and Fe2O in the nitrogen / iron oxide-rich magnetic biochar. 3， Fe-N modification can induce more Fe atoms to penetrate into the carbon matrix. The additional defects formed by the loading of iron oxides and the defect sites generated on the carbon surface by alkali corrosion further promote the entry and fixation of phenol, thereby enhancing the adsorption performance.

[0136] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

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

2. According to claim 1, a process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis activation and a method for efficiently adsorbing phenol are characterized in that: The biomass in step S1 is one or more of bamboo, cotton stalks, rice husks, corn stalks, and wheat stalks. The drying temperature is 100° C. to 150° C., and the drying time is 10 h to 30 h.

3. A process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis and activation and a method for efficiently adsorbing phenol according to claim 2, characterized in that: In step S2, the mass ratio of biomass waste to ferric chloride hexahydrate is 1:4-4:1, the mass ratio of the total mass of biomass waste and ferric chloride hexahydrate to the added distilled water is 1:3-1:10, the oscillation temperature is 15°C-35°C, the oscillation amplitude is 100rpm-300rpm, and the oscillation time is 10h-30h.

4. A process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis and activation and a method for efficiently adsorbing phenol according to claim 3, characterized in that: The drying temperature in step S3 is 100° C. to 150° C., and the drying time is 10 h to 30 h.

5. A process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis and activation and a method for efficiently adsorbing phenol according to claim 4, characterized in that: In step S4, the inert gas is argon or nitrogen, and the total gas flow of the inert gas and ammonia is 200 mL / min to 500 mL / min, wherein the proportion of ammonia in the total gas is 10% to 100%. The biomass catalytic nitrogen-enriched pyrolysis temperature is 400° C. to 800° C., and the reaction time is 10 to 60 min.

6. The method for preparing magnetic biochar rich in nitrogen / iron oxides for efficient adsorption of phenol in water according to claim 5, characterized in that: In step S5, the mass ratio of the original nitrogen / iron-rich biochar to the washing solution is 1:100-1:

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

7. A process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis and activation and a method for efficiently adsorbing phenol according to claim 6, characterized in that: The drying temperature in step S5 is 100° C. to 150° C., and the drying time is 10 h to 30 h.

8. The process for preparing nitrogen / iron oxide-rich magnetic biochar by rapid pyrolysis and activation and the method for efficiently adsorbing phenol according to claim 7, characterized in that: The magnetic biochar obtained in step S5 is nitrogen / iron oxide-rich magnetic biochar with a developed pore structure, rich in nitrogen-containing functional groups, and rich in iron oxide and ferrosoferric oxide particles loaded on the surface.

9. The method for adsorbing phenol in water by using magnetic biochar rich in nitrogen / iron oxide according to any one of claims 1 to 8, characterized in that: The wastewater contains phenol as an organic pollutant.

10. The adsorption method according to claim 9, characterized in that: The dosage of nitrogen / iron oxide-rich magnetic biochar is 10mg / L-100mg / L.

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