Magnetic modified biochar, preparation method thereof and application of magnetic modified biochar in adsorption of micro-plastics

Abstract

The invention discloses magnetic modified biochar, a preparation method and application of the magnetic modified biochar to adsorption of micro-plastics, and belongs to the technical field of biochar. The method comprises the following steps: pretreating industrial hemp straws, pyrolyzing at 700 DEG C in a nitrogen atmosphere to obtain original biochar, activating with potassium hydroxide, and continuously pyrolyzing in the nitrogen atmosphere to obtain activated biochar powder; soaking the obtained activated charcoal powder in an iron nitrate nonahydrate solution, mixing and stirring, drying and pyrolyzing, washing and drying to obtain the magnetic modified charcoal. Compared with traditional biochar, after the activated biochar is subjected to impregnation-pyrolysis treatment, Fe < 3 + > is introduced into the formed magnetic modified biochar, so that the specific surface area, the pore diameter, the adsorption performance and the magnetism are improved; meanwhile, in the application process of adsorbing the micro-plastics, a magnet can be used for separating the magnetic modified charcoal adsorbent from the micro-plastics, and the effects of recycling and cyclic regeneration are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of biochar, and specifically relates to a magnetically modified biochar, a preparation method and an application of the biochar in adsorbing microplastics. Background Art

[0002] Plastic products are mass-produced and used because of their low price and superior performance. The consumption of plastic is very large, but only a small amount (less than 10%) is recycled. These plastic fragments and fibers will form plastic fibers, particles or films smaller than 5 mm through mechanical action, biodegradation and photo-oxidation degradation. Microplastics in the aquatic environment are easily absorbed by submerged plants, floating plants and floating plants. When microplastics are ingested by aquatic organisms, they will be transferred through the food chain and enriched in the human body, becoming a potential risk to human health. Adsorption is a highly feasible method for removing microplastics because of its effectiveness, cost-effectiveness, design flexibility, low-cost materials and ease of use.

[0003] Biochar has well-developed pores, large specific surface area, high degree of aromatization, porous structure, low cost, no pollution, and recyclability, making it a new type of green and environmentally friendly adsorption material. However, the adsorption capacity of raw biochar is limited, and it is difficult to separate from the aqueous solution after use. Since some pollutants are also adsorbed inside it, if they are not separated, they may pollute the environment again and are not conducive to its repeated use. Therefore, the practical application of raw biochar in microplastic treatment is limited.

[0004] Through magnetic modification, magnetic media is introduced into biochar, and magnetic aggregation is used to achieve effective separation from the solution. At present, there are many methods for preparing magnetic activated carbon, such as co-precipitation method. This technical method is simple and easy to control, and the product obtained is of high purity, but the generated Fe3O4 is unstable and easily converted into Fe 2+ How to improve the specific surface area, magnetic properties and adsorption properties of biochar is of great significance for achieving the degradation of plastic fragments and fibers, reducing the enrichment of microplastics, and reducing the potential risks to human health. Summary of the invention

[0005] The purpose of the present invention is to provide a magnetically modified biochar, a preparation method and its application in the adsorption of microplastics. The magnetically modified biochar prepared by the method provided by the present invention can increase the specific surface area and adsorption performance of the biochar and reduce the pore size, and is easy to separate, recycle and reuse.

[0006] A method for preparing magnetically modified biochar comprises the following steps:

[0007] (1) The industrial hemp straw was rinsed with distilled water, air-dried, crushed, passed through a 100-mesh sieve, dried in an oven at 100°C, transferred to an alumina crucible and placed in a tubular furnace, and thermally cracked under nitrogen to obtain the original biochar BC from the industrial hemp straw;

[0008] (2) mixing the raw biochar of industrial hemp straw obtained in step (1) with potassium hydroxide, transferring the mixture into an alumina crucible and placing it in a tubular furnace, performing secondary thermal cracking under nitrogen conditions, washing and drying to obtain activated industrial hemp straw biochar powder BC-KOH2;

[0009] (3) The industrial hemp straw biochar powder is soaked in a nonahydrate ferric nitrate solution, mixed, stirred, dried, thermally cracked in a tubular furnace, washed, and dried to obtain magnetically modified biochar MBC.

[0010] In an embodiment of the present invention, the temperature of the thermal cracking in steps (1), (2) and (3) is 300-900°C, the heating rate is 5°C / min, and the time is 120min. More preferably, the temperature of the thermal cracking is 650-750°C.

[0011] In an embodiment of the present invention, the mass ratio of the industrial hemp straw raw biomass charcoal to potassium hydroxide is 1:1-1:4.

[0012] In an embodiment of the present invention, the washing in step (2) is 1 mol / L HCl solution and deionized water, and the drying time is 105° C. for 12-24 hours.

[0013] In an embodiment of the present invention, in step (3), the mass ratio of biomass charcoal powder to ferric nitrate nonahydrate is 1:5-1:10, the stirring speed is 1000 rpm, and the stirring time is 12-24 h.

[0014] In an embodiment of the present invention, the concentration of the ferric nitrate nonahydrate solution in step (3) is 0.16-0.20 mol / L.

[0015] The magnetic modified biochar prepared by the present invention has iron nanoparticles uniformly distributed on the surface of the material without obvious agglomeration, as shown by scanning electron microscope images.

[0016] The present invention also provides the application of magnetically modified biochar in adsorbing microplastics.

[0017] The method for adsorbing microplastics by magnetically modified biochar of the present invention comprises adding the magnetically modified biochar to a microplastic solution, and then oscillating the solution at a constant temperature on a shaker for 10 to 300 minutes to complete the adsorption.

[0018] Among them: the shaking temperature of the shaking table is 25-45℃, and the shaking speed of the shaking table is 120-180r·min -1 , the pH value of microplastic solution ranges from 3 to 11.

[0019] The pH value of the solution can affect the formation of functional groups on the surface of the adsorbent or adsorbate, which is a key parameter for determining its environmental applicability and obtaining basic mechanism evaluation. It affects the charge of biochar and affects the morphology of MPs present in the solution, changing the state of functional groups. In the application of magnetic modified biochar adsorption of microplastics, microplastic MPs can be adsorbed by magnetic modified biochar, and the adsorbed MPs are mainly attached to the surface of magnetic modified biochar, indicating that magnetic modified biochar is a better microplastic adsorption carrier and can better adsorb microplastics.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention attempts to use an impregnation-pyrolysis method to immerse industrial hemp straw biochar in a nonahydrate ferric nitrate solution, stir it, and pyrolyze it, so that the metal salt is converted into a magnetic medium at high temperature and loaded on the surface of the biochar, thereby obtaining a magnetic biochar with a large specific surface area, a small pore size, and good adsorption performance.

[0022] (2) The magnetically modified biochar prepared by the present invention is ferroferric oxide-modified biochar. The pore size and specific surface area of ​​the biochar are increased by introducing iron ions, and the adsorption capacity is significantly enhanced. Compared with the unmodified biochar, the specific surface area of ​​the magnetically modified biochar is significantly increased by 428 times, and the adsorption capacity for microplastics is increased by 5.60 times. The modified biochar is magnetic, and a magnet can be used to separate the magnetically modified biochar from microplastics after use, which is convenient for recycling and reuse. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanning electron microscope image of the biochar BC prepared in Comparative Example 1.

[0024] Figure 2 This is a scanning electron microscope image of the magnetically modified biochar MBC prepared in Example 1.

[0025] Figure 3 This is the scanning electron microscope image of MBC-MPs after the magnetically modified biochar MBC adsorbed MPs in Application Example 4.

[0026] Figure 4 Infrared spectra of biochar BC prepared in Comparative Examples 1-2, activated biochar BC-KOH2, magnetically modified biochar MBC prepared in Example 1, and magnetically modified biochar MBC-MPs of application example 1 for adsorbing microplastics.

[0027] Figure 5N2 adsorption-desorption isotherms of the biochar BC prepared in Comparative Example 1 and the magnetically modified biochar MBC prepared in Example 1.

[0028] Figure 6 The adsorption rates of microplastics by biochar BC prepared in Comparative Examples 1-2, activated biochar BC-KOH2 and magnetically modified biochar MBC in Application Example 4. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0030] Example 1

[0031] A method for preparing magnetically modified biochar comprises the following steps:

[0032] (1) The industrial hemp straw was rinsed with distilled water, air-dried, cut into pieces, crushed by a grinder, passed through a 100-mesh sieve, dried in a constant temperature oven at 100°C, placed in an alumina crucible and weighed, placed in a tubular furnace, and thermally cracked for 120 minutes at 700°C under nitrogen conditions to obtain industrial hemp straw biochar.

[0033] (2) After the industrial hemp straw powder pyrolyzed at 700°C in a N2 atmosphere was mixed with KOH in a mass ratio of 1:2, it was pyrolyzed at 700°C in a N2 atmosphere at a heating rate of 5°C / min for 2 h; after cooling, the solid was washed with 1 mol / L HCl to remove impurities, washed with ultrapure water to stabilize the pH of the filtrate to 3-9, and dried in an oven at 105°C overnight to obtain activated biochar.

[0034] (3) 100 mL of 0.18 mol / LFe(NO3)3·9H2O solution and 10 g of activated biochar were mixed, stirred at 1000 rpm for 24 h, and dried in an oven at 105 °C for 12 h. The obtained powder was pyrolyzed at 700 °C for 2 h in a tube furnace with a heating rate of 5 °C / min. The biochar sample in the tube furnace was washed three times with deionized water to remove excess chemicals and dried at 100 °C for 24 h to obtain magnetically modified biochar MBC loaded with ferroferric oxide. Scanning electron microscopy showed that Figure 2 shown.

[0035] Comparative Example 1

[0036] The preparation method of biochar and its application in adsorbing microplastics are as follows:

[0037] The industrial hemp straw was rinsed with distilled water, air-dried, cut into pieces, crushed by a grinder, passed through a 100-mesh sieve, dried at 100°C in a constant temperature oven, placed in an alumina crucible and weighed, placed in a tubular furnace, and pyrolyzed for 120 minutes at 700°C under nitrogen conditions to obtain industrial hemp straw biochar BC. Scanning electron microscopy showed that the BC Figure 1 shown.

[0038] 12 g of biochar was placed in a conical flask, and 20 mL of a 60 mg / L MPs solution was added and mixed. The pH of the MPs solution was adjusted to 3-11. The conical flask was placed in a shaker and shaken at 35 °C and 130 rpm for 180 min. After the experiment, the biochar and microplastic mixed solution was filtered, and the concentration of MPs in the sample was determined by measuring the absorption of the sample at 285 nm using a UV-visible spectrophotometer. Each group of experiments was repeated 3 times. Figure 6 shown.

[0039] Comparative Example 2

[0040] The preparation method of activated biochar and its application in adsorbing microplastics are as follows:

[0041] Industrial hemp straw powder pyrolyzed at 700°C in a N2 atmosphere was mixed with KOH in a mass ratio of 1:2, and then pyrolyzed at 700°C in a N2 atmosphere at a heating rate of 5°C / min for 2h; after cooling, the solid was washed with 1mol / LHCl to remove impurities, washed with ultrapure water to stabilize the pH of the filtrate to 3-9, and dried in an oven at 105°C overnight to obtain potassium hydroxide activated biochar BC-KOH2.

[0042] 12 g of activated biochar was placed in a conical flask, and 20 mL of 60 mg / L MPs solution was added and mixed. The pH of the MPs solution was adjusted to 3-11. The conical flask was placed in a shaker and shaken at 35 °C and 130 rpm for 180 min. After the experiment, the biochar and microplastic mixed solution was filtered, and the concentration of MPs in the sample was determined by measuring the absorption of the sample at 285 nm using a UV-visible spectrophotometer. Each group of experiments was repeated 3 times. Figure 6 shown.

[0043] Application Example 1

[0044] The adsorption of microplastics by magnetically modified biochar at different times is as follows:

[0045] Take 12 g of modified biochar and add 20 mL of 60 mg / L MPs solution in a conical flask, adjust the pH of the MPs solution to 3-11, place the conical flask in a shaker, and shake at 35 °C and 130 rpm. The oscillation time is set to 10 min, 20 min, 40 min, 60 min, 80 min, 120 min, 140 min, 180 min, and 300 min, respectively. After the experiment, the modified biochar is adsorbed by an external magnetic field, and the remaining liquid is collected. The filtrate is used to measure the absorption of the sample at 285 nm using a UV-visible spectrophotometer to determine the concentration of MPs in the sample. Each group of experiments is repeated 3 times.

[0046] Application Example 2

[0047] Application of magnetically modified biochar to adsorb microplastics at different temperatures:

[0048] Weigh 12 g of modified biochar, add 20 mL of 60 mg / L MPs solution into a conical flask, adjust the pH of the MPs solution to 3-11, place the conical flask in a shaker, and shake for 180 min at a constant temperature of 25, 35, and 45 °C and 130 rpm. After the experiment, use an external magnetic field to adsorb the modified biochar, collect the remaining liquid, and use a UV-visible spectrophotometer to measure the absorption of the sample at 285 nm to determine the concentration of MPs in the sample. Each group of experiments was repeated 3 times.

[0049] Application Example 3

[0050] Application of magnetically modified biochar for adsorption of microplastics at different MPs solution pH:

[0051] Weigh 12 g of modified biochar, add 20 mL of 60 mg / L MPs solution into a conical flask, adjust the pH of the MPs solution to 3, 5, 7, 9, and 11, respectively, place the conical flask in a shaker, and shake at 130 rpm for 180 min at a constant temperature of 35 °C. After the experiment, the modified biochar was adsorbed by an external magnetic field, and the remaining liquid was collected. The filtrate was used to measure the light absorption of the sample at 285 nm using a UV-visible spectrophotometer to determine the concentration of MPs in the sample. Each group of experiments was repeated 3 times.

[0052] Application Example 4

[0053] Application of magnetically modified biochar for adsorption of microplastics:

[0054] Take 12g of modified biochar and add 20mL of 60mg / L MPs solution in a conical flask. Adjust the pH of the MPs solution to 3-11. Place the conical flask in a shaker and shake at 35℃ and 130rpm for 180min. After the test, use an external magnetic field to adsorb the modified biochar, collect the remaining liquid, and use a UV-visible spectrophotometer to measure the absorption of the sample at 285nm to determine the concentration of MPs in the sample. Each group of experiments was repeated 3 times. Figure 6 shown.

[0055] Effect example

[0056] 1. Scanning Electron Microscope

[0057] The biochar BC prepared in Comparative Example 1 was characterized by scanning electron microscopy, and the results are as follows: Figure 1 As shown by Figure 1 It can be seen that the biochar cracked at 700°C in a N2 atmosphere has a rich pore structure and the texture gradually deepens into strips, and the pore structure becomes more compact and regular.

[0058] The magnetic modified biochar prepared in Example 1 was characterized by scanning electron microscopy, and the results were as follows: Figure 2 It can be seen that after magnetic modification, iron nanoparticles are evenly distributed on the surface of biochar materials without obvious agglomeration.

[0059] The MBC-MPs obtained by adsorbing microplastic solution with magnetically modified biochar in Application Example 4 were characterized by scanning electron microscopy. Figure 3 It can be seen that MPs can be adsorbed by magnetically modified biochar, and the adsorbed MPs are mainly attached to the surface of magnetically modified biochar, and a small part is "stuck" and "trapped" in the pores. This shows that magnetically modified biochar is a better microplastic adsorption carrier and can better adsorb microplastics.

[0060] 2. Infrared spectroscopy

[0061] Figure 4 Infrared spectra of the magnetically modified biochar MBC prepared in Example 1, the biochar BC and activated biochar BC-KOH2 prepared in Comparative Examples 1-2, and the MBC-MPs after the magnetically modified biochar adsorbed microplastics in Application Example 1. Figure 4 Shows the 500-2000cm -1 and 3000-3800cm -1 The high-intensity characteristic peak between 3415cm -1 The broad band at 1630cm corresponds to the -OH stretching vibration of hydrogen-bonded hydroxyl groups or the stretching vibration caused by Fe-OH. -1 The absorption peaks correspond to the vibrations of C=C and C=O, 1399 cm-1 The absorption peak of -CH2 corresponds to 1005 cm -1 The CO vibration bands of the BC-KOH2 surface are shown in Table 1. This indicates the presence of hydroxyl and carboxylate groups. The presence of -OH and C=O indicates that the surface of BC-KOH2 is rich in oxygen-containing functional groups, and the abundance of -OH increases. The formation mechanism of these functional groups may be that KOH can react with active oxygen-containing species to remove oxygen-containing groups and form vacancies at the same time. The anion OH in KOH - Rapidly enter the vacancy and form new oxygen-containing species such as CO, -OH, C=O, -OC, -trihydroxybenzoic acid and -COOH groups; 3235cm -1 The peak at 500–1000 cm-1 is attributed to the aromatic CH structure of MPs, indicating the adsorption of MPs on the biochar surface. -1 The peak at 880 cm-1 is the intrinsic adsorption band corresponding to the metal oxide and the absorption .... -1 The peaks correspond to the modified biochar MBC, which represent the possible stretching vibration of Fe-O bonds. The appearance of these absorption peaks indicates that the metal-O-PS-MPs complex is formed between the modified biochar and PS-MPs, thereby enhancing the removal of PS-MPs.

[0062] 3. Specific surface area, total pore volume, pore size and adsorption effect

[0063] Figure 5 N2 adsorption-desorption isotherms of industrial hemp straw biochar and magnetically modified biochar, Figure 5 The BC showed a type I isotherm, which indicated that the BC of industrial hemp straw biochar was a microporous structure. On the other hand, according to the IUPAC method, the N2 adsorption / desorption isotherms of all modified magnetic biochars were type IV with an obvious H4 hysteresis loop. Time, temperature and pH of the microplastic solution were also indispensable factors affecting the adsorption of microplastics by magnetic modified biochar, with the best adsorption rate at 180 min, 35 °C and pH 7.

[0064] Figure 6 The adsorption rates of biochar BC, potassium hydroxide activated biochar BC-KOH2 and magnetically modified biochar MBC on microplastics. The specific surface area, total pore volume, pore size and adsorption rates of industrial hemp straw biochar and magnetically modified biochar on microplastics are shown in Table 1.

[0065] Table 1 Specific surface area, total pore volume, pore size and adsorption capacity of industrial hemp straw biochar and magnetic modified biochar

[0066] sample Specific surface area Total pore volume Aperture Adsorption amount of MPs Example 1 MBC <![CDATA[1284.09m 2 / g]]> <![CDATA[0.5482cm 3 / g]]> 1.7077nm 89.97mg / g Comparative Example 1 BC <![CDATA[3.04m 2 / g]]> <![CDATA[0.0105cm 3 / g]]> 13.8640nm 9.63mg / g Comparative Example 2 <![CDATA[BC-KOH2]]> <![CDATA[337.33m 2 / g]]> <![CDATA[0.1521cm 3 / g]]> 1.8031nm 16.07mg / g

[0067] Combining Table 1 and Figure 6The results show that compared with Comparative Examples 1 and 2, the specific surface area, pore size and adsorption performance of magnetic modified biochar in Example 1 are significantly improved. The specific surface areas of BC, BC-KOH2 and MBC are 3.04m 2 / g, 337.33m 2 / g, 1284.09m 2 / g, compared with the specific surface area of ​​BC and potassium hydroxide activated biochar BC-KOH2, the specific surface area of ​​MBC increased significantly by 3.8-428 times; the total pore volume increased and the pore size decreased, the adsorption capacity of biochar BC was only 9.63mg / g, while the adsorption capacity of BC-KOH2 was 16.07mg / g. The adsorption capacity of magnetically modified biochar MBC reached 89.97mg / g, which was 9.34 and 5.60 times higher than that of BC and potassium hydroxide activated biochar BC-KOH2; this shows that iron modification is crucial to improving the adsorption capacity. In summary, it is shown that magnetically modified biochar MBC is a promising adsorbent for MPs treatment.

[0068] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing magnetically modified biochar, characterized in that: The following steps are involved: (1) washing, drying, crushing, sieving and drying the industrial hemp stalks, and thermally cracking the industrial hemp stalks under nitrogen conditions to obtain raw biomass charcoal; (2) mixing the original industrial hemp straw biomass charcoal pretreated in step (1) with a potassium hydroxide solution, performing secondary thermal cracking under nitrogen conditions, and washing and drying to obtain activated industrial hemp straw biomass charcoal powder; (3) The activated biochar powder is immersed in a nonahydrate ferric nitrate solution, mixed and stirred, dried, and then thermally cracked, washed, and dried to obtain magnetically modified biochar.

2. The method for preparing magnetically modified biochar according to claim 1, characterized in that: The temperature of the thermal cracking is 300-900°C, the heating rate is 5°C / min, and the thermal cracking time is 60-120min.

3. The method for preparing magnetically modified biochar according to claim 1, characterized in that: In the step (2), the mass ratio of the original biomass charcoal from industrial hemp straw to potassium hydroxide is 1:1-1:

4.

4. The method for preparing magnetically modified biochar according to claim 1, characterized in that: In the step (3), the mass ratio of the biomass charcoal powder to the ferric nitrate nonahydrate is 1:5-1:10, wherein the concentration of the ferric nitrate nonahydrate solution is 0.16-0.20 mol / L.

5. The method for preparing magnetically modified biochar according to any one of claims 1 to 5 obtains magnetically modified biochar.

6. The use of magnetically modified biochar in adsorbing microplastics according to claim 5, characterized in that: The adsorption temperature is 25-45°C, and the pH value of the microplastic solution is 3-11.

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