Preparation method and application of biochar-based redox mediator material

Abstract

The invention discloses a preparation method and application of a biochar-based redox mediator material, and belongs to the technical field of water treatment. The invention relates to application of a biochar-based redox mediator material in degradation of organic pollutants in water by an enhanced chemical oxidation technology. The biochar-based redox mediator material prepared by the method disclosed by the invention has the characteristics of a redox mediator, can be used as an electron channel for mediating electron transfer between an oxidant and pollutants, and also has the advantages of large specific surface area, multiple active sites, high stability, low cost, greenness, no pollution and the like; the method is combined with a chemical oxidation method, so that organic pollutants in water can be quickly removed. The biochar-based redox mediator material prepared by the method has the advantages that the electron transfer rate between organic pollutants and an oxidizing agent is remarkably increased, and the biochar-based redox mediator material is simple to prepare, low in price, convenient to recycle, reusable and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a preparation method and application of a biochar-based redox mediator material. Background Art

[0002] In recent years, water pollution caused by organic pollutants has become increasingly serious. Chemical oxidation technology has shown great potential in controlling water pollution because it can change or completely destroy the structure of organic pollutants. However, the traditional chemical oxidation method has limited oxidation capacity for organic matter. Therefore, enhanced chemical oxidation technology that activates / catalyzes the parent chemical oxidant by adding energy or chemical agents to produce highly active oxidizing species has gradually attracted people's attention. Among the common enhancement methods, the method of adding redox mediators has great advantages. As electron transfer bodies, redox mediators have the characteristics of being reversibly reduced and oxidized. Therefore, they can act as electron carriers in multiple redox reactions, accelerate the transfer of electrons from primary electron donors to ultimate electron acceptors, and ultimately increase the rate of pollutant degradation by chemical oxidation by one to several orders of magnitude.

[0003] The redox mediators involved in current research are mostly present in the solution in a homogeneous form when used. On the one hand, it is difficult to recycle them. On the other hand, once they are loaded by chemical grafting, they face the problem of high cost. Studies have found that solid carbon-based materials such as graphene oxide also have the characteristics of redox mediators, which can significantly increase the electron transfer rate between oxidants and organic pollutants. At the same time, the insolubility of solid carbon-based materials in water helps to recycle them and avoid secondary pollution. However, the high cost of solid carbon-based materials such as graphene oxide limits their large-scale application in practice. Summary of the invention

[0004] The purpose of the present invention is to solve the above technical problems and to provide a preparation method and application of a biochar-based redox mediator material.

[0005] The biochar-based redox mediator material prepared by the method of the present invention has the characteristics of a redox mediator and can serve as an "electron channel" to mediate electron transfer between oxidants and pollutants. At the same time, the material also has the advantages of large specific surface area, many active sites, high stability, low cost and being green and pollution-free. Combining it with chemical oxidation can achieve rapid removal of organic pollutants in water.

[0006] The advantages of the biochar-based redox mediator material prepared by the present invention are that it significantly improves the electron transfer rate between organic pollutants and oxidants, is simple to prepare, low in price, easy to recycle, and reusable.

[0007] A method for preparing a biochar-based redox mediator material is specifically completed by the following steps:

[0008] 1. Washing the biomass and then drying it to obtain washed biomass;

[0009] 2. In a nitrogen atmosphere, the cleaned biomass is heated in a tubular furnace or a muffle furnace, and then pyrolyzed at a pyrolysis temperature. After the heating is completed, the pyrolysis product is cooled to room temperature, taken out, ground, crushed and sieved to obtain a pyrolysis product;

[0010] 3. Add the pyrolysis product to concentrated sulfuric acid, then add sodium nitrate and mix well in an ice bath; add potassium permanganate to the mixed solution and stir at 35° C. for a period of time, then add ultrapure water and stir at 98° C. for a period of time to obtain a reaction product;

[0011] 4. Add ultrapure water and 30% hydrogen peroxide solution to the reaction product to obtain a suspension; centrifuge the suspension, wash the solid after centrifugation with hydrochloric acid and ultrapure water in turn, and freeze-dry the washed solid to obtain a biochar-based redox mediator material.

[0012] The main principles of the present invention are as follows:

[0013] The biochar-based redox mediator material prepared by the present invention has redox properties, and can be used as an electron acceptor or electron donor to store and transfer electrons, thereby increasing the electron transfer rate from organic pollutants to oxidants, and is a good electron shuttle material. In addition, the biochar-based redox mediator material contains abundant active sites such as oxygen-containing functional groups, structural defects, and persistent free radicals, which greatly improves the activation efficiency of the oxidant and promotes the generation of active species; the larger specific surface area and developed pore structure of biochar also make the biochar-based redox mediator material have a certain adsorption capacity.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention uses common biomass in nature as raw materials and prepares biochar-based redox mediators by an oxygen-free high-temperature pyrolysis method, which is in line with the concept of "using waste to treat waste"; the method for preparing the material of the present invention is simple, with few process steps and low cost, and is easy to transport and realize large-scale production. At the same time, no wastewater or waste residue is generated during the material preparation process, thus avoiding secondary pollution or the generation of secondary waste;

[0016] 2. The biochar-based redox mediator material prepared by the present invention has strong electron transfer ability, abundant oxygen-containing functional groups, structural defects, active sites such as persistent free radicals, larger specific surface area and developed pore structure, which has great advantages in improving the utilization efficiency of oxidants;

[0017] 3. The biochar-based redox mediator material prepared by the present invention can effectively realize the efficient removal of organic pollutants by chemical oxidation method, and has a good application prospect in the field of water treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the preparation of the biochar-based redox mediator material in the present invention;

[0019] Figure 2 This is a schematic diagram of the change of diclofenac concentration over time under different working conditions. Figure 2 Herein, Mn(VII) is control example 1, Pine needles is control example 2, and Mn(VII)+Pine needles is example 2. DETAILED DESCRIPTION

[0020] The technical scheme of the present invention is further described in detail below by specific embodiments and in conjunction with the accompanying drawings. It should be understood that the following embodiments are provided only for the purpose of illustration and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0022] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0023] Specific implementation method 1: This implementation method is a method for preparing a biochar-based redox mediator material, which is specifically completed by the following steps:

[0024] 1. Washing the biomass and then drying it to obtain washed biomass;

[0025] 2. In a nitrogen atmosphere, the cleaned biomass is heated in a tubular furnace or a muffle furnace, and then pyrolyzed at a pyrolysis temperature. After the heating is completed, the pyrolysis product is cooled to room temperature, taken out, ground, crushed and sieved to obtain a pyrolysis product;

[0026] 3. Add the pyrolysis product to concentrated sulfuric acid, then add sodium nitrate and mix well in an ice bath; add potassium permanganate to the mixed solution and stir at 35° C. for a period of time, then add ultrapure water and stir at 98° C. for a period of time to obtain a reaction product;

[0027] 4. Add ultrapure water and 30% hydrogen peroxide solution to the reaction product to obtain a suspension; centrifuge the suspension, wash the solid after centrifugation with hydrochloric acid and ultrapure water in turn, and freeze-dry the washed solid to obtain a biochar-based redox mediator material.

[0028] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that: in step 1, deionized water is used to wash the biomass 2 to 4 times; the drying temperature in step 1 is 80°C to 100°C, and the drying time is 4h to 6h; the biomass in step 1 is a mixture of one or more of corn straw, wheat straw, rice straw, glucose, lignin, cellulose, bamboo and pine needles. The other steps are the same as those in specific embodiment 1.

[0029] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that: the heating rate of the heating in step 2 is 2°C / min to 5°C / min; the pyrolysis temperature in step 2 is 200°C to 700°C, and the pyrolysis time is 2h to 4h; the sieving in step 2 is 80-120 mesh sieve. The other steps are the same as those in specific implementation method 1 or 2.

[0030] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that: the mass ratio of the pyrolysis product described in step 3 to the volume of concentrated sulfuric acid is (1g-4g):50mL, and the mass fraction of concentrated sulfuric acid is 98%; the mass ratio of the pyrolysis product described in step 3 to sodium nitrate is 1:(0.5-1); the mass ratio of the pyrolysis product described in step 3 to potassium permanganate is 1:(2-4). The other steps are the same as specific embodiments 1 to 3.

[0031] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: the mass ratio of the pyrolysis product described in step 3 to the volume ratio of ultrapure water is (1g to 4g): (45mL to 180mL); the time for adding potassium permanganate to the mixed solution and stirring at 35°C in step 3 is 1h to 2h; the time for adding ultrapure water and stirring at 98°C in step 3 is 10min to 20min. The other steps are the same as those of specific embodiments 1 to 4.

[0032] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that: the volume ratio of the pyrolysis product described in step 3 to the ultrapure water described in step 4 is (1g-4g):80mL; the volume ratio of the pyrolysis product described in step 3 to the 30% hydrogen peroxide solution described in step 4 is (1g-4g):20mL. The other steps are the same as specific embodiments 1 to 5.

[0033] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that: the centrifugal speed in step 4 is 2000r / min to 4000r / min, and the centrifugal time is 5min to 8min; in step 4, the solid after centrifugation is washed 2 to 4 times with 1.0mol / L hydrochloric acid and ultrapure water respectively; the freeze-drying temperature in step 4 is -50℃ to -60℃, and the freeze-drying time is 40h to 48h. The other steps are the same as those in specific embodiments 1 to 6.

[0034] Specific embodiment eight: This embodiment is an application of a biochar-based redox mediator material in the degradation of organic pollutants in water using enhanced chemical oxidation technology.

[0035] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: a biochar-based redox mediator material is applied to an existing chemical oxidation technology to achieve rapid removal of organic pollutants in water, and the amount of the biochar-based redox mediator material is 25 mg / L to 500 mg / L; the existing chemical oxidation technology is potassium permanganate oxidation, potassium ferrate oxidation, peroxide oxidation or Fenton / Fenton-like oxidation. The other steps are the same as those of specific embodiments 1 to 8.

[0036] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the organic pollutants include one or a mixture of phenols, amines, olefins and sulfonamides, and the concentration of the organic pollutants is 0.005 mmol / L. The other steps are the same as those of specific embodiments 1 to 9.

[0037] The following examples are used to verify the beneficial effects of the present invention:

[0038] Example 1: A method for preparing a biochar-based redox mediator material is specifically completed by the following steps:

[0039] 1. Weigh 2.0 g of pine needles, wash the pine needles with deionized water three times to remove surface impurities, and then dry the washed pine needles in an oven at 100° C. for 6 h to obtain washed biomass;

[0040] 2. In a nitrogen atmosphere, the cleaned biomass was heated to 500°C at a heating rate of 4°C / min using a tubular furnace, and pyrolyzed at 500°C for 2 hours. After the heating was completed, the pyrolysis product was taken out after cooling to room temperature, ground and crushed, and passed through a 100-mesh sieve to obtain a pyrolysis product;

[0041] 3. Add the pyrolysis product obtained in step 2 to 50 mL of 98% concentrated sulfuric acid, then add 1.0 g of sodium nitrate and mix well in an ice bath; add 6.0 g of potassium permanganate to the mixed solution and stir at 35° C. for 120 min, then add 95 mL of ultrapure water and stir at 98° C. for 15 min to obtain a reaction product;

[0042] 4. Add 80 mL of ultrapure water and 20 mL of 30% hydrogen peroxide solution to the reaction product obtained in step 3 to obtain a suspension; centrifuge the suspension, and then wash the solid after centrifugation 4 times with 1.0 mol / L hydrochloric acid and ultrapure water, respectively, and freeze-dry the washed solid to obtain a biochar-based redox mediator material;

[0043] The centrifugal speed in step 4 is 2000 r / min, and the centrifugal time is 8 min;

[0044] The freeze-drying temperature in step 4 is -50°C and the freeze-drying time is 48 hours.

[0045] The schematic diagram of the biochar-based redox mediator material prepared in Example 1 is as follows Figure 1 As shown;

[0046] The biochar-based redox mediator material prepared by the present invention has strong electron transfer ability, abundant oxygen-containing functional groups, structural defects, active sites such as persistent free radicals, a larger specific surface area and a developed pore structure, and plays an important role in promoting electron migration and catalyzing chemical oxidation reactions to achieve efficient degradation of organic pollutants.

[0047] Example 2: Using the biochar-based redox mediator material prepared in Example 1 to enhance the oxidation and degradation of diclofenac by potassium permanganate:

[0048] First, 25 mg of the biochar-based redox mediator material prepared in Example 1 was weighed and dispersed into 5 mL of water to obtain a biochar mother liquor, and then the biochar mother liquor was ultrasonicated for 60 min to fully mix the biochar with the water. The biochar-based redox mediator material prepared in Example 1 and potassium permanganate were added to the water to be treated containing 0.1 mol / L buffer solution and 0.005 mmol / L diclofenac at room temperature, and reacted with diclofenac until complete under stirring conditions. The treatment time was 15 min, wherein the solution pH was 5.0, the buffer solution was acetic acid-sodium acetate solution, the amount of the biochar-based redox mediator material prepared in Example 1 was 100 mg / L, and the amount of potassium permanganate was 0.05 mmol / L.

[0049] The following experimental examples under different working conditions, combined with Example 2, further demonstrate the strengthening effect of the biochar-based redox mediator material prepared by the present invention:

[0050] Comparative Example 1: The experiment of adding potassium permanganate alone to oxidize diclofenac was carried out according to the following steps: potassium permanganate was added to the water to be treated containing 0.1 mol / L buffer solution and 0.005 mmol / L diclofenac at room temperature, and it was reacted with diclofenac until complete under stirring. The treatment time was 15 min, wherein the solution pH was 5.0, the buffer solution was acetic acid-sodium acetate solution, and the addition amount of potassium permanganate was 0.05 mmol / L.

[0051] Control Example 2: The experiment of removing diclofenac by adding the biochar-based redox mediator material prepared in Example 1 alone was carried out according to the following steps: the biochar-based redox mediator material prepared in Example 1 was added to the water to be treated containing 0.1 mol / L buffer solution and 0.005 mmol / L diclofenac at room temperature, and it was reacted with diclofenac until complete under stirring conditions. The treatment time was 15 minutes, wherein the solution pH was 5.0, the buffer solution was acetic acid-sodium acetate solution, and the dosage of the biochar-based redox mediator material prepared in Example 1 was 100 mg / L.

[0052] Figure 2 Schematic diagram of the change of diclofenac concentration over time under different working conditions.

[0053] Figure 2 This is a schematic diagram of the change of diclofenac concentration over time under different working conditions. Figure 2 Herein, Mn(VII) is control example 1, Pine needles is control example 2, and Mn(VII)+Pine needles is example 2.

[0054] Depend on Figure 2 It can be seen that potassium permanganate alone has a slow degradation effect on diclofenac, and 41.1% of diclofenac can be removed within 15 minutes; the adsorption effect of diclofenac on biochar-based redox mediator materials alone is poor, and only 6.1% of diclofenac can be adsorbed and removed within 15 minutes; the use of biochar-based redox mediator materials to enhance potassium permanganate can greatly accelerate the degradation of diclofenac, and 66.9% of diclofenac can be degraded within 15 minutes. The above results show that in the process of enhancing potassium permanganate oxidation by biochar-based redox mediator materials, the removal of diclofenac is not a simple superposition of potassium permanganate oxidation and biochar adsorption, but the biochar-based redox mediator material acts as an electron shuttle, which promotes the transfer of electrons from diclofenac to potassium permanganate, thereby accelerating the degradation and removal of diclofenac.

Claims

1. A method for preparing a biochar-based redox mediator material, characterized in that The preparation method is specifically completed according to the following steps:

1. Washing the biomass and then drying it to obtain washed biomass; 2. In a nitrogen atmosphere, the cleaned biomass is heated in a tubular furnace or a muffle furnace, and then pyrolyzed at a pyrolysis temperature. After the heating is completed, the pyrolysis product is cooled to room temperature, taken out, ground, crushed and sieved to obtain a pyrolysis product; 3. Add the pyrolysis product to concentrated sulfuric acid, then add sodium nitrate and mix well in an ice bath; add potassium permanganate to the mixed solution and stir at 35° C. for a period of time, then add ultrapure water and stir at 98° C. for a period of time to obtain a reaction product; 4. adding ultrapure water and 30% hydrogen peroxide solution to the reaction product to obtain a suspension; The suspension is centrifuged, and the solid after centrifugation is washed with hydrochloric acid and ultrapure water in sequence. The washed solid is freeze-dried to obtain a biochar-based redox mediator material.

2. The method for preparing a biochar-based redox mediator material according to claim 1, characterized in that In step one, the biomass is washed with deionized water for 2 to 4 times; the drying temperature in step one is 80° C. to 100° C., and the drying time is 4 to 6 hours; the biomass in step one is a mixture of one or more of corn straw, wheat straw, rice straw, glucose, lignin, cellulose, bamboo and pine needles.

3. The method for preparing a biochar-based redox mediator material according to claim 1, characterized in that The heating rate of the heating in step 2 is 2°C / min to 5°C / min; the pyrolysis temperature in step 2 is 200°C to 700°C, and the pyrolysis time is 2h to 4h; the screening in step 2 is through a 80-mesh to 120-mesh sieve.

4. The method for preparing a biochar-based redox mediator material according to claim 1, characterized in that The mass ratio of the pyrolysis product described in step 3 to concentrated sulfuric acid is (1g~4g):50mL, and the mass fraction of concentrated sulfuric acid is 98%; the mass ratio of the pyrolysis product described in step 3 to sodium nitrate is 1:(0.5~1); the mass ratio of the pyrolysis product described in step 3 to potassium permanganate is 1:(2~4).

5. The method for preparing a biochar-based redox mediator material according to claim 1, characterized in that The mass ratio of the pyrolysis product described in step 3 to the volume ratio of ultrapure water is (1g~4g):(45mL~180mL); in step 3, potassium permanganate is added to the mixed solution and stirred at 35°C for 1h~2h; in step 3, ultrapure water is added and stirred at 98°C for 10min~20min.

6. The method for preparing a biochar-based redox mediator material according to claim 1, characterized in that The volume ratio of the pyrolysis product described in step 3 to the ultrapure water described in step 4 is (1g-4g):80mL; the volume ratio of the pyrolysis product described in step 3 to the 30% hydrogen peroxide solution described in step 4 is (1g-4g):20mL.

7. The method for preparing a biochar-based redox mediator material according to claim 1, characterized in that The centrifugal speed described in step 4 is 2000r / min~4000r / min, and the centrifugal time is 5min~8min; in step 4, the solid after centrifugation is washed 2~4 times respectively with 1.0mol / L hydrochloric acid and ultrapure water; the freeze-drying temperature described in step 4 is -50℃~-60℃, and the freeze-drying time is 40h~48h.

8. Use of a biochar-based redox mediator material prepared by the preparation method according to claim 1, characterized in that A biochar-based redox mediator material is used in the degradation of organic pollutants in water by enhanced chemical oxidation technology.

9. The use of a biochar-based redox mediator material according to claim 8, characterized in that A biochar-based redox mediator material is applied to an existing chemical oxidation technology to achieve rapid removal of organic pollutants in water, and the dosage of the biochar-based redox mediator material is 25 mg / L to 500 mg / L; the existing chemical oxidation technology is potassium permanganate oxidation, potassium ferrate oxidation, peroxide oxidation or Fenton / Fenton-like oxidation.

10. The use of a biochar-based redox mediator material according to claim 8, characterized in that The organic pollutants include one or a mixture of phenols, amines, olefins and sulfonamides, and the concentration of the organic pollutants is 0.005 mmol / L.

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