Fluorine-modified biochar and preparation method and application thereof

Abstract

The application belongs to the technical field of adsorbing materials of perfluorinated compounds, and discloses fluoridation modified biochar as well as a preparation method and application thereof; the preparation method of the fluoridation modified biochar is as follows: taking a fluorine-containing ionic compound as a modifier, uniformly dispersing the fluorine-containing ionic compound in an aqueous solvent to obtain a modified solution; placing biochar in the modified solution and mixing to obtain a mixed solution; then, the mixed solution is sequentially subjected to oscillation treatment and ultrasonic treatment, and is filtered, washed, dried and ground, so that the fluoridation modified biochar is obtained. The biochar is fluoridation modified by using the fluorine-containing ionic compound, so that the process is simple, the operation is convenient, the adsorption capacity of the prepared product is increased, the removal efficiency of pollutants such as perfluorooctanoic acid in water is improved, and the fluoridation modified biochar has good research value and application prospect in the field of environmental pollution control.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adsorption materials of perfluorinated compounds, and particularly relates to a fluorinated modified biochar as well as a preparation method and application thereof. BACKGROUND

[0002] Perfluorinated compounds are a typical new pollutant, which refers to organic compounds in which all hydrogen atoms are replaced by fluorine. Perfluorooctanoic acid (PFOA; C8) is one of the typical representatives of perfluorinated compounds. PFOA contains a high bond energy C-F bond (485 kcal / mol), which is extremely stable and difficult to degrade under normal conditions. In addition, PFOA also contains a hydrophilic charged functional group, so it has both hydrophobic and oleophobic properties. Therefore, it is widely used in many fields, such as waterproof / air-permeable clothing membranes, food contact paper oil-resistant coatings, non-stick coatings on cookware, aviation hydraulic oil, fire extinguishing foam, etc. It is used as a surfactant, emulsifier, etc. in industry. The widespread use of PFOA inevitably leads to its accumulation in sewage treatment plants and ultimately enters the natural environment. It has been reported that PFOA has been frequently detected in sewage treatment plants and natural water bodies around the world. As an environmental pollutant, PFOA has the characteristics of biological toxicity, environmental persistence, and biological accumulation, and its biological accumulation in the food chain is enhanced, and its half-life is longer. The half-life of PFOA in the human body is estimated to be 4-5 years, and the half-life in the environment is 41 years. Exposure to PFOA can have adverse effects on human health, affecting development, reproduction, nervous and immune systems, etc.

[0003] The main removal methods of PFOA in water are advanced oxidation, photocatalytic degradation, and adsorption. However, the first two methods have the disadvantages of high cost, difficult operation, and high difficulty in raw material preparation. Advanced oxidation technology can effectively degrade pollutants through the efficient production of reactive oxygen species (ROS) triggered by light radiation, electrochemical reaction, and catalyst activation. However, advanced oxidation technology still has many problems in the process of treating and degrading pollutants, including the need for acidic conditions or additional reagents during the experiment, the generation of iron-containing waste during the combined Fenton experiment, the generation of highly toxic intermediates during the peroxymonosulfate activation experiment, low energy utilization efficiency during the ultraviolet combined Fenton experiment, high cost, and low mineralization rate. Photocatalytic degradation can remove PFOA under certain operating conditions and with the aid of catalysts, but it is limited by the minimum energy required for the band gap (allowing valence electrons to migrate to the conduction band and generate photo-generated electrons (e - ) and holes (h)), e +- , and h, and has some limitations in removing trace concentrations of PFAS in actual water. In addition to the above shortcomings, when using photocatalysts alone, particles are prone to clumping, resulting in a decrease in specific surface area and active sites, and are easily lost in water, making it difficult to recover and reuse.

[0004] Adsorption is favored for its simplicity, high efficiency and energy saving in the process of purifying contaminated water, but the adsorption efficiency of some adsorption materials (such as montmorillonite and silicon dioxide) used in the existing adsorption method is low, and the adsorption capacity is small, which leads to low removal efficiency of PFOA. In addition, adsorption materials with good removal efficiency such as ion exchange resin also have the disadvantages of high cost and difficulty in obtaining.

[0005] Therefore, the present application provides a fluorinated modified biochar for enhancing adsorption of perfluorinated compounds and a preparation method and application thereof. SUMMARY

[0006] In order to solve the above-mentioned deficiencies in the prior art, the present application provides a fluorinated modified biochar and a preparation method and application thereof. The present application takes biochar with surface oxygen-containing groups as a substrate, and modifies it by fluorination, so that fluorine is connected to the surface carbon of the biochar by replacing oxygen-containing functional groups to form carbon-fluorine bonds (C-F), which can further increase the adsorption capacity and removal efficiency of PFOA by forming [F…H…F] - charge-assisted hydrogen bond (CAHB) to further increase the adsorption capacity and removal efficiency of PFOA, thereby improving the adsorption efficiency of perfluorinated compounds.

[0007] The fluorinated modified biochar and the preparation method and application thereof of the present application are realized by the following technical solutions:

[0008] The first object of the present application is to provide a preparation method of a fluorinated modified biochar, comprising the following steps:

[0009] Step 1: taking a fluorine-containing ionic compound as a modifier, uniformly dispersing it in an aqueous solvent to obtain a modified solution;

[0010] Step 2: taking biochar with surface oxygen-containing groups as a substrate, mixing it uniformly in the modified solution to obtain a mixed solution; then sequentially performing oscillation treatment and ultrasonic treatment on the mixed solution, filtering, washing and drying, to obtain the fluorinated modified biochar.

[0011] Further, the biochar is prepared by the following steps:

[0012] Taking solid waste containing organic matter as a carbon source, pyrolyzing it under an inert atmosphere at 250-350℃ for 1-3h to obtain the biochar with surface oxygen-containing groups;

[0013] Among them, the solid waste is any one of municipal sludge, kitchen garbage, wheat straw and corn straw.

[0014] Further, the fluorine-containing ionic compound can be one or both of ammonium fluoride and sodium fluoride.

[0015] Further, the concentration of the fluorine-containing ionic compound in the modification solution is 5.5-6.5 mol / L.

[0016] Further, the ratio of the use amount of the biochar to the modification solution is 1.5-2.5 g:50 mL.

[0017] Further, the temperature of the oscillation treatment is 24-26 DEG C, and the treatment time is 20-28 h.

[0018] Further, the ultrasonic frequency of the ultrasonic treatment is 40 kHz, and the ultrasonic time is 20-40 min.

[0019] Further, the washing is to wash the solid-phase component obtained after filtration until the pH of the washing liquid is neutral.

[0020] Further, the temperature of the drying is 40-60 DEG C, and the drying time is 6-16 h.

[0021] Further, the particle size of the fluorinated modified biochar obtained by the grinding is ≤100 mu m.

[0022] The second object of the application is to provide a fluorinated modified biochar prepared by the preparation method.

[0023] The third object of the application is to provide an application of the fluorinated modified biochar in removing perfluorinated compounds.

[0024] Compared with the prior art, the application has the following beneficial effects:

[0025] The application uses a fluorine-containing ionic compound as a modifier to perform fluorination modification treatment on biochar, so that fluorine is connected to the carbon on the surface of the biochar by replacing oxygen-containing functional groups to form a carbon-fluorine bond (C-F), and then the fluorine-containing ionic compound forms [F…H…F] - charge-assisted hydrogen bonds (CAHB) with perfluorinated compounds (PFOA) to increase the adsorption capacity of the modified biochar and improve the adsorption removal efficiency. After filtration, washing, drying, and grinding, the structure of the biochar is optimized, for example, ammonium fluoride can dissolve into the interior of the biochar to remove inorganic substances, ash, and the like that hinder the expansion of the pore of the biochar, thereby increasing the pore size of the biochar and creating more mesopore structures. In this process, the micropore does not change, so the specific surface area and the total pore volume increase. In addition, the introduction of F-containing functional groups increases the surface functional groups. The fluorinated modified biochar forms a carbon-fluorine bond on the surface, which plays an important role in the adsorption of PFOA to increase the adsorption capacity and increase the adsorption removal of PFOA. When the fluorine-containing ionic compound in the application is used to adsorb and treat PFOA, [F…H…F] -The mechanism of electrostatically assisted hydrogen bonding plays a major role in the adsorption process.

[0026] The present application uses fluorine ion-containing compounds to modify biochar by fluorination, which not only has a simple process and convenient operation, but also increases the adsorption capacity of the prepared product and improves the removal efficiency of perfluorooctanoic acid and other pollutants in water, showing good research value and application prospect in the field of environmental pollution control. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 FT-IR Fourier transform infrared test full spectrum of BCs prepared for Comparative Example 1, BCs-F1 prepared for Example 1, and BCs-F2 prepared for Comparative Example 2;

[0028] Figure 2 is a partial enlarged view of Figure 1

[0029] Figure 3 XPS test full spectrum of BCs prepared for Comparative Example 1, BCs-F1 prepared for Example 1, and BCs-F2 prepared for Comparative Example 2;

[0030] Figure 4 is a partial enlarged view of Figure 3

[0031] Figure 5 SEM photograph of BCs prepared for Comparative Example 1;

[0032] Figure 6 SEM photograph of BCs-F1 prepared for Example 1;

[0033] Figure 7 SEM photograph of BCs-F2 prepared for Comparative Example 2;

[0034] Figure 8 EDS spectrum of BCs prepared for Comparative Example 1;

[0035] Figure 9 EDS spectrum of BCs-F1 prepared for Example 1;

[0036] Figure 10 EDS spectrum of BCs-F2 prepared for Comparative Example 2;

[0037] Figure 11 Isothermal adsorption experiment results of BCs-F1 prepared for Example 1 and BCs prepared for Comparative Example 1;

[0038] Figure 12 Desorption experiment results after isothermal adsorption experiment of BCs prepared for Comparative Example 1;

[0039] ​​Figure 13 Results of desorption experiments performed after isothermal adsorption experiments of BCs-F1 prepared for Example 1. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below.

[0041] The present application provides a kind of fluorinated modified biochar, and its preparation method is as follows:

[0042] Step 1, with fluorine-containing ionic compound as modifier, it is uniformly dispersed in aqueous solvent, and a modified solution is obtained;

[0043] It should be noted that the present application considers that the mechanism of CAHB is an important mechanism for carbon-based materials to efficiently remove new pollutants, and theoretically, the adsorbent containing fluorine functional groups and PFOA will significantly improve the adsorption removal effect of PFOA by forming [F…H…F] - Charge-assisted hydrogen bond, therefore, a low-cost fluorine-containing ionic compound is preferably used as a modifier for fluorination modification of biochar. The fluorine-containing ionic compound used in the present application can be selected from one or both of ammonium fluoride and sodium fluoride.

[0044] In order to ensure the effect of fluorination modification, the fluorine-containing ionic compound is preferably made into a solution before modifying the biochar. For example, using ammonium fluoride as an example, after being made into a solution, it can ensure that ammonium fluoride is completely dissolved and dissociated into ammonium ions and fluoride ions, and the utilization rate of ammonium fluoride is higher, so as to ensure the fluorination modification effect. The fluorine-containing ionic compound is preferably prepared into a modified solution with a concentration of 5.5-6.5 mol / L using an aqueous solvent.

[0045] Step 2, using biochar as a substrate, mix it in the modified solution to obtain a mixed solution; then the mixed solution is sequentially subjected to oscillation treatment, ultrasonic treatment, filtration, washing, and drying to obtain the fluorination modified biochar.

[0046] It should be noted that in order to further ensure the modification effect of the modified solution on the biochar, the biochar is preferably mixed at a dosage ratio of 1.5-2.5 g:50 mL of biochar to modified solution.

[0047] The mixed solution is first subjected to oscillation treatment at a temperature of 24-26°C for 20-28h to ensure that the biochar and the modified solution are in complete and sufficient contact, and to achieve the purpose of good modification of the fluorination modified biochar.

[0048] The product obtained after oscillation treatment is subjected to ultrasonic treatment to ensure that the biochar is completely dispersed, and through ultrasonic treatment, not only can the impurities in the pores be removed, but also the fluorine ions can be uniformly distributed around the biochar under the action of ultrasonic waves, thereby facilitating the uniform and stable loading of fluorine on the biochar. The ultrasonic frequency of the preferred ultrasonic treatment is 40 kHz, and the ultrasonic time is 20-40 min.

[0049] The product after ultrasonic treatment is filtered, wherein the filter membrane with a pore size of 30-50 μm is preferred for filtering treatment to ensure that the flow rate is stable at a moderate speed, and at the same time, it can also ensure that the modified biochar will not be lost in large quantities due to filtration, and the solid phase component obtained is retained on the filter membrane.

[0050] The obtained solid phase component is subjected to washing treatment, and the washing liquid is washed to neutral pH. Among them, ultrapure water or deionized water is used as a washing agent to remove the ash and residual ammonium fluoride solution on the surface of the biochar material.

[0051] The product obtained after washing treatment is dried to remove the residual washing agent, and the drying temperature is 40-60℃, and the drying time is 6-16h. The product obtained after drying treatment is also subjected to grinding treatment, and the particle size is ≤100 μm to reduce the particle size of the modified biochar and increase its pore structure and specific surface area, so as to further optimize the structure of the material, i.e. to obtain fluorinated modified biochar.

[0052] It should be further pointed out that the biochar used in the present application is prepared by the following steps:

[0053] The solid waste with organic matter is used as a carbon source, and is pyrolyzed at 250-350℃ for 1-3h under an inert atmosphere to obtain the biochar. The solid waste with organic matter is preferably any one of municipal sludge, kitchen garbage, wheat straw and corn straw to ensure that the biochar obtained by pyrolysis of the carbon source is rich in oxygen-containing functional groups on the surface, and then the fluorine ions can replace the oxygen-containing functional groups on the surface of the biochar for surface loading during subsequent fluorination modification treatment, so as to ensure that the fluorinated modified biochar can be obtained.

[0054] Example 1

[0055] The present embodiment provides a fluorinated modified biochar, and its preparation method is as follows:

[0056] 1) Preparation of biochar:

[0057] The corn straw produced in Guanzhong, Shaanxi is selected as raw material, washed and dried, crushed by a plant crusher, and sieved through a 100-mesh sieve. The system is placed in a vacuum tube furnace, nitrogen is introduced for 30 min to exhaust the air in the system, and then the temperature of the system is increased from room temperature to 300℃ at a rate of 10℃ / min, and kept constant for 2 h. After pyrolysis, the system is naturally cooled to room temperature under the protection of nitrogen, and then the obtained product is ground and sieved through a 150-mesh sieve to obtain corn straw biochar with a particle size of ≤100 μm.

[0058] 2) Preparation of modified solution

[0059] The ammonium fluoride is uniformly dispersed in deionized water to prepare an ammonium fluoride solution with a concentration of 6 mol / L, i.e., a modified solution.

[0060] 3) Modification treatment

[0061] 2 g of the above prepared biochar is taken and uniformly mixed in a centrifuge tube containing 50 mL of 6 mol / L ammonium fluoride solution, and then placed in a constant temperature shaking incubator, the shaking temperature is controlled at 25℃, the rotation speed is 180 r / min, and the shaking is performed for 24 h. After the shaking is completed, the centrifuge tube is placed in an ultrasonic device, ultrasonic treatment is performed at an ultrasonic frequency of 40 kHz for 30 min. After the ultrasonic treatment is completed, the biochar is filtered by using a circular medium-speed qualitative filter paper with a diameter of 125 mm (pore size of 30-50 μm), and the filtered precipitate (i.e., solid phase component) is repeatedly washed with ultrapure water until the pH of the filtrate is neutral (pH=7.0). Then, the washed precipitate is placed in a 50℃ oven, dried for 8 h, taken out, ground and sieved through a 150-mesh (≤100 μm) sieve, to obtain a fluorinated modified biochar, which is named as BCs-F1.

[0062] Example 2

[0063] The present embodiment provides a fluorinated modified biochar, and the preparation method is as follows:

[0064] 1) Preparation of biochar:

[0065] The corn straw produced in Guanzhong, Shaanxi is selected as raw material, washed and dried, crushed by a plant crusher, and sieved through a 100-mesh sieve. The system is placed in a vacuum tube furnace, nitrogen is introduced for 30 min to exhaust the air in the system, and then the temperature of the system is increased from room temperature to 300℃ at a rate of 10℃ / min, and kept constant for 2 h. After pyrolysis, the system is naturally cooled to room temperature under the protection of nitrogen, and then the obtained product is ground and sieved through a 150-mesh sieve to obtain corn straw biochar with a particle size of ≤100 μm.

[0066] 2) Preparation of modified solution

[0067] The ammonium fluoride is uniformly dispersed in deionized water to prepare an ammonium fluoride solution with a concentration of 5.5 mol / L, i.e., a modified solution.

[0068] 3) Modification treatment

[0069] 1.5 g of the above-prepared biochar is placed in a centrifuge tube containing 50 mL of the 5.5 mol / L ammonium fluoride solution, mixed uniformly, and then placed in a constant-temperature shaking incubator, with a shaking temperature of 24℃ and a rotation speed of 150 r / min, and shaken for 20 h. After the shaking, the centrifuge tube is placed in an ultrasonic device, and ultrasonic treatment is performed at an ultrasonic frequency of 40 kHz for 20 min. After the ultrasonic treatment, the biochar is filtered using a circular medium-speed qualitative filter paper with a diameter of 125 mm and a pore size of 30-50 μm, and the filtered precipitate (i.e., the solid-phase component) is repeatedly washed with ultrapure water until the filtrate has a neutral pH (pH = 7.0). Then, the washed precipitate is placed in an oven at 40℃, dried for 16 h, and then ground through a 150-mesh (≤100 μm) sieve, to obtain the fluorinated modified biochar.

[0070] Example 3

[0071] This example provides a fluorinated modified biochar, and a preparation method thereof is as follows:

[0072] 1) Preparation of biochar

[0073] In this application, corn stalks produced in the Guanzhong region of Shaanxi Province are selected as raw materials, washed, dried, and then crushed using a plant crusher and passed through a 100-mesh sieve. The crushed corn stalks are placed in a vacuum tube furnace, nitrogen gas is introduced for 30 min to exhaust the air in the system, and then the temperature of the system is increased from room temperature to 350℃ at a rate of 12℃ / min, and maintained at 350℃ for 3 h. After the pyrolysis, the system is naturally cooled to room temperature under the protection of nitrogen gas, and then the obtained product is ground and passed through a 150-mesh sieve to obtain corn stalk biochar with a particle size of ≤100 μm.

[0074] 2) Preparation of modified solution

[0075] The ammonium fluoride is uniformly dispersed in deionized water to prepare an ammonium fluoride solution with a concentration of 6.5 mol / L, i.e., a modified solution.

[0076] 3) Modification treatment

[0077] Take 2.5 g of the above prepared biochar, placed in a centrifuge tube containing 50 mL of 6.5 mol / L ammonium fluoride solution, and then placed in a constant temperature shaking incubator, the shaking temperature is controlled at 26℃, the rotation speed is 200 r / min, and the shaking time is 28 h; after the shaking is completed, the centrifuge tube is placed in an ultrasonic device, and ultrasonic treatment is carried out at an ultrasonic frequency of 40 kHz for 40 min; after the ultrasonic treatment is completed, the biochar is filtered with a circular medium-speed qualitative filter paper with a diameter of 125 mm (pore size of 30-50 μm), and the precipitate (i.e. the solid phase component) after filtration is repeatedly washed with ultrapure water until the pH of the filtrate is neutral (pH=7.0); then the washed precipitate is placed in an oven at 60℃, dried for 6 h, taken out, and ground through a sieve with a mesh size of 150 mesh (≤100 μm), to obtain the fluorinated modified biochar.

[0078] Example 4

[0079] The present embodiment provides a fluorinated modified biochar, and the preparation method is as follows:

[0080] 1) Preparation of biochar:

[0081] In the present embodiment, corn stalks are used as raw materials, washed and dried, crushed with a plant crusher, and then passed through a 100 mesh sieve. The system is placed in a vacuum tube furnace, nitrogen is introduced for 30 min to exhaust the air in the system, and then the temperature of the system is increased from room temperature to 300℃ at a rate of 10℃ / min, and kept constant for 2 h. After pyrolysis, the system is naturally cooled to room temperature under the protection of nitrogen, and then the obtained product is ground and passed through a 150 mesh sieve to obtain corn stalk biochar with a particle size of ≤100 μm.

[0082] 2) Preparation of modified solution

[0083] Sodium fluoride is uniformly dispersed in deionized water to prepare a sodium fluoride solution with a concentration of 6 mol / L, i.e. a modified solution.

[0084] 3) Modification treatment

[0085] Take 2 g of the above prepared biochar, placed in a centrifuge tube containing 50 mL of 6 mol / L sodium fluoride solution, and then placed in a constant temperature shaking incubator, the shaking temperature is controlled at 25℃, the rotation speed is 180 r / min, and the shaking time is 24 h; after the shaking is completed, the centrifuge tube is placed in an ultrasonic device, and ultrasonic treatment is carried out at an ultrasonic frequency of 40 kHz for 30 min; after the ultrasonic treatment is completed, the biochar is filtered with a circular medium-speed qualitative filter paper with a diameter of 125 mm (pore size of 30-50 μm), and the precipitate (i.e. the solid phase component) after filtration is repeatedly washed with ultrapure water until the pH of the filtrate is neutral (pH=7.0); then the washed precipitate is placed in an oven at 50℃, dried for 8 h, taken out, and ground through a sieve with a mesh size of 150 mesh (≤100 μm), to obtain the fluorinated modified biochar.

[0086] Example 5

[0087] The present embodiment provides a fluorinated modified biochar, and its preparation method is as follows:

[0088] 1) Preparation of biochar:

[0089] The present application selects corn stalks produced in Guanzhong, Shaanxi as raw material, washes and dries, grinds with a plant grinder, passes through a 100 mesh sieve, places in a vacuum tube furnace, introduces nitrogen for 30 min to exhaust air in the system, then increases the temperature of the system from room temperature to 300℃ at a rate of 10℃ / min, and keeps constant temperature for 2h. After pyrolysis, the system is naturally cooled to room temperature under the protection of nitrogen, then the obtained product is ground and passed through a 150 mesh sieve to obtain corn stalk biochar with particle size ≤100μm.

[0090] 2) Preparation of modified solution

[0091] Add equimolar ammonium fluoride and sodium fluoride to ionized water, stir at a stirring rate of 150r / min for 30 min to mix uniformly, to prepare a modified solution with a fluorine ion concentration of 6mol / L.

[0092] 3) Modification treatment

[0093] Take 2g of the above prepared biochar, mix uniformly in a centrifuge tube containing 50mL of 6mol / L modified solution, then place in a constant temperature shaking incubator, control the shaking temperature at 25℃, the rotation speed at 180r / min, and shake for 24h; after shaking, place the centrifuge tube in an ultrasonic device, ultrasonic at a frequency of 40kHz for 30min; after ultrasonic, filter the biochar with a circular medium-speed qualitative filter paper with a diameter of 125mm (pore size of 30-50μm), and repeatedly rinse the filtered precipitate (i.e. solid component) with ultrapure water until the filtrate pH is neutral (pH=7.0); then place the washed precipitate in a 50℃ oven, dry for 8h, then take out, grind and pass through a 150 mesh (≤100μm) sieve, to obtain fluorinated modified biochar.

[0094] Comparative Example 1

[0095] The difference between the present comparative example and Example 1 is only:

[0096] The present comparative example does not modify the biochar, i.e. the present comparative example is a blank control, and the material provided is corn stalk biochar, which is named as BCs.

[0097] Comparative Example 2

[0098] The difference between the present comparative example and Example 1 is only:

[0099] The comparative example is subjected to only oscillation treatment without ultrasonic treatment during modification treatment, and is named BCs-F2.

[0100] Experimental section

[0101] (I) FT-IR Fourier Transform Infrared Test

[0102] The BCs-F1 prepared in Example 1, the BCs prepared in Comparative Example 1, and the BCs-F2 prepared in Comparative Example 2 are subjected to FT-IR Fourier Transform Infrared Test, and the test results are shown in Figure 1 and Figure 2 , wherein, Figure 1 is the FT-IR Fourier Transform Infrared Test full spectrum of the BCs-F1 prepared in Example 1, the BCs prepared in Comparative Example 1, and the BCs-F2 prepared in Comparative Example 2; Figure 2 is a partial enlarged view of Figure 1 .

[0103] , and it can be seen from Figure 1 and Figure 2 that the three kinds of biochar materials BCs-F1, BCs and BCs-F2 all have peaks at 3300-3600 cm -1 , which are peaks caused by hydroxyl stretching vibration. The peaks appearing near 1600 cm -1 are peaks caused by C=O stretching vibration (1725-1500 cm -1 ). In addition, it can be seen that the BCs-F1 prepared in Example 1 and the BCs-F2 prepared in Comparative Example 2 have a new peak at 1020-1040 cm -1 compared with the BCs prepared in Comparative Example 1, which is a peak caused by C-F bond stretching vibration, which proves that the corn straw biochar prepared by the method of the embodiment successfully completes fluorination modification.

[0104] (II) XPS Test

[0105] The BCs-F1 prepared in Example 1, the BCs prepared in Comparative Example 1, and the BCs-F2 prepared in Comparative Example 2 are subjected to XPS test, and the test results are shown in Figure 3 and Figure 4 , wherein, Figure 3 is the XPS test full spectrum of the BCs-F1 prepared in Example 1, the BCs prepared in Comparative Example 1, and the BCs-F2 prepared in Comparative Example 2; Figure 4 is a partial enlarged view of Figure 3 .

[0106] , and it can be seen from Figure 3 and Figure 4It can be seen that the three kinds of biochar materials BCs-F1, BCs and BCs-F2 all have peaks at 282.0, 397.0 and 530.0 eV, and the three peaks represent C1s, N1s and O1s respectively. In addition, it can be seen that BCs-F1 prepared in Example 1 and BCs-F2 prepared in Comparative Example 2 have obvious F element signals at 683.0 eV, and no F element signal is found in BCs prepared in Comparative Example 1, which shows that the F element is loaded by fluorination modification.

[0107] (III) SEM test

[0108] The BCs prepared in Comparative Example 1, the BCs-F1 prepared in Example 1 and the BCs-F2 prepared in Comparative Example 2 are taken as examples, and SEM tests are respectively carried out on them, and the test results are shown in Figs. 1, 2 and 3 respectively. Figures 5-7

[0109] And from Figures 5-7 It can be seen that the three kinds of biochar materials BCs, BCs-F1 and BCs-F2 all have obvious pore structures. And by comparing Figure 5 , Figure 6 and Figure 7 It can be found that the pore structures of BCs-F1 prepared in Example 1 and BCs-F2 prepared in Comparative Example 2 are more developed, which shows that the fluorination modification treatment of the present application can obviously improve the pore structure of biochar.

[0110] (IV) EDS spectrum test

[0111] The BCs prepared in Comparative Example 1, the BCs-F1 prepared in Example 1 and the BCs-F2 prepared in Comparative Example 2 are taken as examples, and EDS spectrum tests are respectively carried out on them, and the results are shown in Figs. 4, 5 and 6 respectively. Figures 8-10

[0112] And from Figures 8-10 It can be seen that F element appears obviously on the material surface of BCs-F1 and BCs-F2 compared with BCs, which shows that the fluorination modification treatment of the present application can successfully graft fluorine on the surface of biochar and realize fluorination.

[0113] (V) BET detection

[0114] The BCs prepared in Comparative Example 1, the BCs-F1 prepared in Example 1 and the BCs-F2 prepared in Comparative Example 2 are taken as examples, and BET detection is respectively carried out on them, and the test results are shown in Table 1.

[0115] Table 1 Comparison of specific surface area and pore volume of BCs, BCs-F1 and BCs-F2

[0116] Sample Name Specific surface area (m 2 / g) Pore Size (nm) Pore volume (cm 3 / g) BCs 3.0849 16.4595 0.000322 BCs-F1 10.0957 17.9269 0.001064 BCs-F2 4.1254 10.7476 0.000233 ​​

[0117] And as can be seen from Table 1, the specific surface area of the original biochar BCs is 3.0849m 2 / g, the specific surface area of BCs-F1 of Example 1 is significantly increased to 10.0957m 2 / g, which is more than 3 times the specific surface area of the original biochar before modification. The specific surface area of BCs-F2 of Comparative Example 2 which is not subjected to ultrasonic treatment is 4.1254m 2 / g, which is slightly larger than the original biochar, but is smaller than the fluorinated modified biochar subjected to ultrasonic treatment, indicating that ultrasonic treatment plays an important role in improving the pore structure of the biochar material. In addition, compared with the original biochar BCs of Comparative Example 1, the pore volume of the biochar of Example 1 is increased from 0.000322 to 0.001064cm 3 / g, and the pore volume of the fluorinated modified biochar BCs-F2 which is not subjected to ultrasonic treatment is 0.000233cm 3 / g, which indicates that some mesopores or macropores of the original biochar may be blocked during the oscillation modification process, resulting in a decrease in the pore volume, while ultrasonic treatment can remove impurities from the pores, reduce the impurity content, increase the pore volume, and thus improve the adsorption performance.

[0118] (VI) Adsorption effect

[0119] The present application prepares perfluorooctanoic acid (PFOA) solutions with different concentrations (the concentrations are 0, 1.6681, 2.7826, 4.6416, 7.7426, 12.9155, 21.5443, 35.9381, 59.9484, 100 μg / L) as the target to be treated, and BCs-F1 of Example 1 and BCs of Comparative Example 1 are used as adsorbents to carry out isothermal adsorption experiments at room temperature at the same time, and the experimental results are shown in Table 2. Figure 11

[0120] Test method: 20 mg of adsorbent is taken in an 8 mL glass bottle with a cover, a rotation speed of 180 rpm is set at 25℃, and after oscillation for 48 h, centrifugation is carried out at 3000 rpm for 5 min, and the supernatant is taken for adsorption capacity test (i.e. the amount of PFOA adsorbed by unit mass of adsorbent), and three parallel tests (n=3) are carried out for each sample.

[0121] Adsorption capacity Q e (μg / g) is calculated as follows:

[0122]

[0123] In the formula, C0(μg / L) is the concentration of the standard PFOA solution added, V is the volume of the solution subjected to adsorption (L), C e ​is the concentration of PFOA in the solution after adsorption reaches equilibrium, and M (g) is the mass of the adsorbent when adsorption occurs.

[0124] and by Figure 11 It can be seen that the adsorption efficiency of PFOA of the fluorinated modified biochar BCs-F1 is greatly improved. After fitting by the Langmuir equation, the maximum saturated adsorption amount of BCs-F1 is calculated as 42.61 μg / g, and the saturated adsorption amount of the original biochar BCs is only 4.47 μg / g. The fluorinated modified biochar makes the adsorption amount of PFOA increase by nearly 10 times, which shows that the fluorinated modification treatment of the application can significantly improve the adsorption effect of biochar on PFOA.

[0125] After the isothermal adsorption experiment is completed, half of the supernatant (4 mL) in the original adsorption experiment sample is removed, and then the same volume (4 mL) of background solution is added and diluted to prepare a desorption experiment sample. Then the prepared desorption experiment sample is set at 25℃ with a rotation speed of 180 r / min for oscillation treatment (the sample treated by BCs-F1 is oscillated for 48h, and the sample treated by BCs is oscillated for 4h), sampling, centrifugation, supernatant taking and determination and analysis steps are the same as the adsorption experiment. The steps of the desorption experiment are repeated three times, and each sample is made in triplicate (n=3), and the test results are shown in Figure 12 and Figure 13 .

[0126] Figure 12 The BCs desorption experiment results of Comparative Example 1 are shown in Figure 13 The BCs-F1 desorption experiment results of Example 1 are shown in Figure 12 and Figure 13 It can be seen that the fluorinated modified biochar shows more obvious desorption hysteresis phenomenon for the adsorbed PFOA. This is mainly because when the biochar is not modified, the [O…H…F] - heteronuclear CAHB is formed between the oxygen-containing functional groups on the surface of the biochar and PFOA, and when the biochar is fluorinated and modified to adsorb PFOA, the [F…H…F] -The homonuclear CAHB has the same resonance frequency after hydrogen bonding due to the fact that the electronegative atoms on both sides are F, thereby forming a stronger CAHB and stronger adsorption stability, thereby resulting in more obvious desorption hysteresis. This fully proves that the CAHB plays a key role in the adsorption of perfluorinated compounds by fluorinated modified biochar. And although the fluorinated modified biochar prepared in the application has a certain desorption hysteresis, it can also be desorbed, which shows that the fluorinated modified biochar prepared in the application can be recycled and reused, and after removing the adsorbed substances by desorption, it can continue to be adsorbed, and has certain recyclable performance.

[0127] Obviously, the above-mentioned embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope of protection of the present application.

Claims

1. A method for preparing fluorinated modified biochar, characterized in that, Includes the following steps: Step 1: Using a fluoride ion compound as a modifier, uniformly disperse it in an aqueous solvent to obtain a modified solution; Step 2: Using biochar with oxygen-containing groups on its surface as a matrix, it is placed in the modified solution and mixed to obtain a mixed solution; then the mixed solution is subjected to oscillation treatment, ultrasonic treatment, filtration, washing, drying and grinding in sequence to obtain the fluorinated modified biochar. The biochar is prepared by the following steps: Using solid waste containing organic matter as a carbon source, pyrolyzing it at 250–350°C for 1–3 hours under an inert atmosphere yields the biochar with oxygen-containing groups on its surface. The concentration of fluoride ion compounds in the modified solution is 5.5–6.5 mol / L; The ultrasonic treatment uses an ultrasonic frequency of 40 kHz and an ultrasonic time of 20–40 min.

2. The preparation method according to claim 1, characterized in that, The fluorine-containing compound is one or both of ammonium fluoride and sodium fluoride.

3. The preparation method according to claim 1, characterized in that, The ratio of biochar to modified solution is 1.5–2.5 g: 50 mL.

4. The preparation method according to claim 1, characterized in that, The oscillation treatment is performed at a temperature of 24–26°C for 20–28 hours, with an oscillation speed of 150–200 r / min.

5. The preparation method according to claim 1, characterized in that, The drying temperature is 40–60°C, and the drying time is 6–16 hours.

6. The preparation method according to claim 1, characterized in that, The particle size of the fluorinated modified biochar obtained by grinding is ≤100μm.

7. A fluorinated modified biochar prepared by the preparation method according to any one of claims 1-6.

8. The use of the fluorinated modified biochar of claim 7 for the removal of perfluorinated compounds.

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