A multi-element doped biochar composite material and applications thereof

Abstract

The application discloses a multi-element doped biochar composite material and application thereof, and belongs to the technical field of environmental catalysis and pollutant treatment. The composite material is prepared by co-doping of nitrogen, sulfur and cobalt doping elements, and the carbon base body is Dian polygonatum sibiricum residue, wherein the nitrogen and sulfur source is a single-component nitrogen and sulfur source (thiourea). The single-component nitrogen and sulfur source is used to dope the Co-doped Dian polygonatum sibiricum residue biochar, which can reduce the escape of S elements, avoid poor material repeatability, reduce the leaching amount of Co in the material catalysis process, and improve the stability of the material catalysis performance. In addition, the Dian polygonatum sibiricum residue is used as the carbon source, and the thiourea is used as the nitrogen and sulfur source to co-dope N, S and Co to form a C-Co3S4-N x structure, and the synergistic effect enhances the removal efficiency of carbamazepine.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental catalysis and pollutant treatment, and particularly relates to a multi-element doped biochar composite material and application thereof. Background Art

[0002] In the new era, people's yearning for a better life has prompted them to pay more attention to water pollution issues and has also continuously promoted the exploration of technologies for the efficient removal of difficult-to-degrade organic pollutants. In recent years, advanced oxidation technology based on persulfate has been proven to be a highly efficient technology for the removal of difficult-to-degrade organic pollutants. Current methods for persulfate activation mainly include ultraviolet activation, thermal activation, ultrasonic activation, and over-metal activation. Among them, metallic cobalt species have been shown to be the most effective for persulfate activation. However, the leaching of metallic cobalt during the activation process deserves attention, as excessive cobalt ions can harm the environment and public health.

[0003] In recent years, biochar has been widely used in the removal of organic pollutants due to its excellent physical and chemical properties, environmental friendliness, wide availability and low cost. However, the efficiency of pure biochar in catalytic degradation of organic pollutants is limited. Modification strategies that can overcome this limitation and improve the physical and chemical properties of biochar have been widely studied and applied. Usually, non-metallic heteroatoms or metal species are introduced into the carbon matrix to synthesize carbon-based composite materials with unique physical and chemical properties. For example, sp2 hybridized carbon is formed during the process of metal cobalt being incorporated into the carbon matrix. Compared with the inactive sp3 hybridized carbon, it can more effectively activate persulfate. In order to solve the problem of cobalt leaching, non-metallic species such as N and S are doped on the basis of cobalt to enhance the catalytic activity through interaction with cobalt. At the same time, cobalt species are anchored in the carbon matrix to prevent cobalt leaching.

[0004] In the existing research on nitrogen and sulfur co-doped carbon composites, the nitrogen source and sulfur source are mainly two-component nitrogen-sulfur sources (two substances containing nitrogen or sulfur, respectively). However, the two-component nitrogen-sulfur sources have the phenomenon of sulfur escape during the preparation of the composite materials and the anchoring effect on the cobalt species of Co is poor. In view of this, the present invention explores a doped composite material with stable performance and excellent catalytic performance. Summary of the Invention

[0005] The main purpose of the present invention is to provide a multi-element doped biochar composite material and its application. The present invention makes improvements from the perspectives of carbon source (Polygonatum sibiricum residue) and nitrogen and sulfur source (single-component nitrogen and sulfur source, i.e., organic matter containing both nitrogen and sulfur elements). The prepared nitrogen, sulfur and cobalt co-doped biochar composite material synergistically catalyzes the degradation of carbamazepine with PMS, presenting a more efficient degradation effect.

[0006] To achieve the above-mentioned purpose, the present invention provides a multi-element doped biochar composite material, which is based on biochar made from the residue of Polygonatum dahliae as a carbon source and is obtained by co-doping with nitrogen, sulfur and cobalt doping elements, wherein a single-component nitrogen and sulfur source is used as the raw material for the nitrogen and sulfur doping elements, and the single-component nitrogen and sulfur source is thiourea.

[0007] A method for preparing a multi-element doped biochar composite material comprises the following steps:

[0008] (1) dissolving thiourea and Polygonatum dangshen powder in ethanol, stirring and ultrasonicating the mixture to obtain a mixed solution;

[0009] (2) adding a cobalt salt aqueous solution to the mixed solution and stirring, then evaporating the water and drying to obtain a solid block, grinding the solid block and calcining it in a protective gas;

[0010] (3) The calcined material was ground into powder and soaked in sulfuric acid, then washed, separated, and dried to obtain a nitrogen, sulfur, and cobalt co-doped biochar composite material, denoted as Co@BC-N,S.

[0011] As a further improvement of the present invention, the molar ratio of the cobalt salt to thiourea is 1:(15-30).

[0012] As a further improvement of the present invention, the mass ratio of the cobalt salt to the Yunnan Polygonatum sibiricum residue powder is (1-3):40; more preferably, the mass ratio of the cobalt salt to the Yunnan Polygonatum sibiricum residue powder is 1:20.

[0013] As a further improvement of the present invention, in step (1), the stirring and ultrasonication times are both 1 hour.

[0014] As a further improvement of the present invention, in step (2), the stirring time is 1 hour.

[0015] As a further improvement of the present invention, in step (2), the water is evaporated in a water bath at 60°C.

[0016] As a further improvement of the present invention, in step (2), the protective gas is nitrogen, the nitrogen flow rate is 100 ml / min, the heating rate is 5°C / min, the calcination temperature is 700°C to 900°C, and the constant temperature time is 2h.

[0017] As a further improvement of the present invention, in step (2), the calcination temperature is 700°C.

[0018] As a further improvement of the present invention, in step (3), the concentration of sulfuric acid is 0.1-0.5 mol / L, and the soaking time is 12 hours.

[0019] As a further improvement of the present invention, in step (2), the solid block is ground into 0.3 mm flake solids.

[0020] The present invention also claims protection for the use of the multi-element doped biochar composite material to activate PMS in removing organic pollutants in water bodies.

[0021] The beneficial effects of the present invention are embodied in that: the present invention uses the Polygonatum sibiricum residue as a carbon source and co-dopes nitrogen, sulfur and cobalt doping elements to obtain a multi-element doped biochar composite material, wherein the nitrogen and sulfur sources are divided into a single-component nitrogen and sulfur source (thiourea). The use of a single-component nitrogen and sulfur source doped with Co-doped Polygonatum sibiricum residue biochar can, on the one hand, reduce the escape of the S element to avoid poor material repeatability, and on the other hand, reduce the amount of Co leaching during the material catalysis process, thereby improving the stability of the material's catalytic performance. In addition, Polygonatum sibiricum residue is used as a carbon source and thiourea as a nitrogen and sulfur source to co-dope N, S and Co to form C-Co3S4-N x structure, synergistically enhance the removal efficiency of carbamazepine, and form a stable structure to enhance the catalytic stability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a comparative chart of the activities of the materials prepared in Example 1 and Comparative Examples 1-6 of the present invention as PMS catalysts for degrading the pollutant carbamazepine.

[0023] Figure 2 This is a comparative chart of the adsorption and degradation activities of the pollutant carbamazepine by the materials prepared in Example 1 and Comparative Examples 1-6 of the present invention.

[0024] Figure 3 This is a comparison chart of the activities of the multi-element doped biochar composite material prepared in comparative example 7 of the present invention as a PMS catalyst for degrading the pollutant carbamazepine and the adsorption degradation of the pollutant carbamazepine. In the figure, Co@BC-N,S-500+PMS is the activity curve of the multi-element doped biochar composite material as a PMS catalyst for degrading the pollutant carbamazepine, and the figure Co@BC-N,S-500 is the activity curve of the adsorption degradation of the pollutant carbamazepine.

[0025] Figure 4 This is a comparison chart of the activity of the multi-element doped biochar composite material prepared in Example 2 of the present invention as a PMS catalyst for degrading the pollutant carbamazepine and the adsorption degradation of the pollutant carbamazepine. In the figure, Co@BC-N,S-900+PMS is the activity curve of the multi-element doped biochar composite material as a PMS catalyst for degrading the pollutant carbamazepine, and in the figure, Co@BC-N,S-900 is the activity curve of the adsorption degradation of the pollutant carbamazepine.

[0026] Figure 5 This is a five-cycle degradation diagram of the pollutant carbamazepine using the multi-element doped biochar composite material prepared in Example 1 of the present invention as a PMS catalyst.

[0027] Figure 6 This is a graph showing the concentration of cobalt leached from the multi-element doped biochar composite materials prepared in Examples 1-2 of the present invention and Comparative Example 7 after the reaction. In the figure, 900 is the Co@BC-N,S-900 material prepared in Example 2, 700 is the Co@BC-N,S material prepared in Example 1, and 500 is the Co@BC-N,S-500 material prepared in Comparative Example 7.

[0028] Figure 7 These are the XRD patterns of the materials prepared in Example 1 and Comparative Examples 1-4 of the present invention. Figure (a) is the XRD pattern of the materials prepared in Comparative Examples 1-3; Figure (b) is the XRD pattern of the materials prepared in Comparative Example 4 and Example 1.

[0029] Figure 8 These are XPS graphs of the multi-element doped biochar composite materials prepared in Examples 1 and 2 of the present invention and Comparative Example 7. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing a multi-element doped biochar composite material comprises the following steps:

[0033] (1) Grind the dried Yunnan Polygonatum sibiricum residue with a ball mill and pass it through an 80-mesh sieve to obtain the Polygonatum sibiricum residue powder.

[0034] (2) A certain amount of thiourea was weighed and dissolved in 50 ml of anhydrous ethanol, and then 1 g of the powder of the Polygonatum sibiricum residue was also dissolved therein, followed by magnetic stirring and ultrasonication for 1 h each to obtain a solution.

[0035] (3) Weigh 0.05 g of CoCl2·6H2O and dissolve it in 50 ml of pure water to obtain a cobalt chloride aqueous solution.

[0036] (4) The cobalt chloride aqueous solution obtained in step (3) was added dropwise to the solution obtained in step (2), and magnetic stirring was continued for 1 hour. The obtained mixed solution was then placed in a water bath at 60° C. to evaporate the water content of the solution to obtain a solid agglomerate; the molar ratio of CoCl2·6H2O to thiourea was 1:25.

[0037] (5) The agglomerated solid obtained in step (4) was further dried in a drying oven at 60°C for 24 h. The dried solid was then ground into flakes with a diameter of about 0.3 mm, and then calcined at 700°C for 2 h in a tube furnace under a nitrogen atmosphere with a flow rate of 100 ml / min, with a heating rate of 5°C / min. The calcined material was ground through 200 mesh and then soaked in 0.1 mol / L sulfuric acid for 12 h. It was then filtered and washed with deionized water until neutral and dried in a drying oven at 60°C to obtain a multi-element doped biochar composite material, which was recorded as Co@BC-N,S.

[0038] Example 2

[0039] The only difference between the preparation method of the multi-element doped biochar composite material described in this embodiment and that in Example 1 is that in step (5), the calcination temperature is 900° C., which is recorded as Co@BC-N,S-900.

[0040] Example 3

[0041] A method for preparing a multi-element doped biochar composite material comprises the following steps:

[0042] (1) Grind the dried Yunnan Polygonatum sibiricum residue with a ball mill and pass it through an 80-mesh sieve to obtain the Polygonatum sibiricum residue powder.

[0043] (2) A certain amount of thiourea was weighed and dissolved in 50 ml of anhydrous ethanol, and then 1 g of the powder of the Polygonatum sibiricum residue was also dissolved therein, followed by magnetic stirring and ultrasonication for 1 h each to obtain a solution.

[0044] (3) Weigh 0.075 g of CoCl2·6H2O and dissolve it in 50 ml of pure water to obtain a cobalt chloride aqueous solution.

[0045] (4) The cobalt chloride aqueous solution obtained in step (3) was added dropwise to the solution obtained in step (2), and magnetic stirring was continued for 1 hour. The obtained mixed solution was then placed in a water bath at 60° C. to evaporate the water content of the solution to obtain a solid agglomerate; the molar ratio of CoCl2·6H2O to thiourea was 1:30.

[0046] (5) The agglomerated solid obtained in step (4) was further dried in a drying oven at 60°C for 24 h. The dried solid was then ground into flakes with a diameter of about 0.3 mm, and then calcined at 700°C for 2 h in a tube furnace under a nitrogen atmosphere with a flow rate of 100 ml / min, with a heating rate of 5°C / min. The calcined material was ground through 200 mesh and then soaked in 0.5 mol / L sulfuric acid for 12 h. It was then filtered and washed with deionized water until neutral and dried in a drying oven at 60°C to obtain a multi-element doped biochar composite material, which was recorded as Co@BC-N,S-3.

[0047] Comparative Example 1

[0048] A method for preparing a multi-element doped biochar composite material comprises the following steps:

[0049] (1) Grind the dried Yunnan Polygonatum sibiricum residue with a ball mill and pass it through an 80-mesh sieve to obtain the Polygonatum sibiricum residue powder.

[0050] (2) Dissolve 1 g of Polygonatum sibiricum residue powder in 50 ml of anhydrous ethanol with magnetic stirring and ultrasonic treatment for 1 h each, then place the solution in a 60°C water bath to evaporate the water to obtain agglomerated solids.

[0051] (3) The agglomerated solid obtained in step (2) was further dried in a drying oven at 60°C for 24 h. The dried solid was then ground into flakes with a diameter of about 0.3 mm, and then calcined at 700°C for 2 h in a tube furnace under a nitrogen atmosphere with a flow rate of 100 ml / min, with a heating rate of 5°C / min. The calcined material was ground through 200 mesh and then soaked in 0.1 mol / L sulfuric acid for 12 h. It was then filtered and washed with deionized water until neutral, and then dried in a drying oven at 60°C to obtain the Polygonatum sibiricum residue biochar, which was recorded as BC.

[0052] Comparative Example 2

[0053] The preparation method of the multi-element doped biochar composite material described in this comparative example is different from that in Example 1 only in that no thiourea is added, and is recorded as Co@BC.

[0054] Comparative Example 3

[0055] The preparation method of the multi-element doped biochar composite material described in this comparative example is different from that in Example 1 only in that thiourea is replaced by urea in an equal molar amount, which is recorded as Co@BC-N.

[0056] Comparative Example 4

[0057] The preparation method of the multi-element doped biochar composite material described in this comparative example is different from that in Example 1 only in that thiourea is replaced by diphenyl disulfide with half the molar amount of thiourea (keeping the molar amount of sulfur the same), which is recorded as Co@BC-S.

[0058] Comparative Example 5

[0059] The preparation method of the multi-element doped biochar composite material described in this comparative example is different from that in Example 1 only in that CoCl2·6H2O is not added, and is recorded as BC-N,S.

[0060] Comparative Example 6

[0061] (1) Grind the dried Yunnan Polygonatum sibiricum residue with a ball mill and pass it through an 80-mesh sieve to obtain the Polygonatum sibiricum residue powder.

[0062] (2) Equal moles of urea and diphenyl disulfide were weighed and dissolved in 50 ml of anhydrous ethanol, and then 1 g of Polygonatum sibiricum residue powder was also dissolved therein, followed by magnetic stirring and ultrasonication for 1 h each to obtain a solution.

[0063] (3) Weigh 0.05 g of CoCl2·6H2O and dissolve it in 50 ml of pure water to obtain a cobalt chloride aqueous solution.

[0064] (4) The cobalt chloride aqueous solution obtained in step (3) was added dropwise to the solution obtained in step (2), and magnetic stirring was continued for 1 hour. The obtained mixed solution was then placed in a water bath at 60° C. to evaporate the water content of the solution to obtain agglomerated solids; the molar ratios of CoCl2·6H2O to urea and diphenyl disulfide were 1:25 and 1:12.5, respectively.

[0065] (5) The agglomerated solid obtained in step (4) was further dried in a drying oven at 60°C for 24 h. The dried solid was then ground into flakes with a diameter of about 0.3 mm, and then calcined at 700°C for 2 h in a tube furnace under a nitrogen atmosphere with a flow rate of 100 ml / min, with a heating rate of 5°C / min. The calcined material was ground through 200 mesh and then soaked in 0.1 mol / L sulfuric acid for 12 h. It was then filtered and washed with deionized water until neutral and dried in a drying oven at 60°C to obtain a multi-element doped biochar composite material, which was recorded as Co@BC-NS-1.

[0066] Comparative Example 7

[0067] The only difference between the preparation method of the multi-element doped biochar composite material described in this comparative example and that in Example 1 is that in step (5), the calcination temperature is 500° C., recorded as Co@BC-N,S-500.

[0068] Comparative Example 8

[0069] The only difference between the preparation method of the multi-element doped biochar composite material described in this comparative example and that in Example 1 is that in step (2), the powder of Polygonatum sibiricum residue is replaced with chitosan of the same mass, which is recorded as Co@BC-NS-2.

[0070] Test Example 1

[0071] Test samples: materials prepared in Examples 1-3 and Comparative Examples 1-8.

[0072] The test sample was used as a PMS catalyst to degrade carbamazepine pollutants. The specific steps included: adding 0.01g of the test sample to a 2.5mg / L carbamazepine solution (carbamazepine solution pH ≈ 7), and adding potassium permonosulfate (PMS) at a dosage of 0.3mmol / L. The reaction was then carried out at 25°C under natural light for 40min. Sampling was performed at fixed time intervals, and the degradation effect of carbamazepine was detected by liquid chromatography. The results are shown in FIG. Figure 1-4 and Table 1.

[0073] Test Example 2

[0074] Test samples: materials prepared in Examples 1-3 and Comparative Examples 1-8.

[0075] The test samples were used to adsorb and degrade the model pollutant carbamazepine. The specific steps included: adding 0.01g of the test sample to a 2.5mg / L carbamazepine solution (carbamazepine solution pH ≈ 7), and then reacting for 40min at 25℃ under natural light conditions. Sampling was performed at fixed time intervals, and the adsorption and degradation effect of carbamazepine was detected by liquid chromatography. The results are shown in Figure 1-4 .

[0076] Test Example 3

[0077] Test sample: the material prepared in Example 1.

[0078] The test sample was activated with PMS to degrade carbamazepine for 5 cycles, specifically including the following steps: 0.01 g of the test sample was added to a 2.5 mg / L carbamazepine solution (carbamazepine solution pH ≈ 7), wherein potassium permonosulfate (PMS) was added at the same time in an amount of 0.3 mmol / L, and then reacted for 40 minutes at 25°C under natural light conditions, and samples were taken at fixed time intervals, and the degradation effect of carbamazepine was detected by liquid chromatography; the cyclic degradation experiment was carried out by adding pollutants without recovering the catalyst; specifically, the residual rate of pollutants in the reaction solution was measured based on the last sample of each cycle, and a certain amount of pollutants was added so that the amount of pollutants in the solution was basically the same as at the beginning, and 5 cycles of degradation were carried out, and the results are shown in FIG. Figure 5 .

[0079] Test Example 4

[0080] Test samples: materials prepared in Examples 1, 2 and Comparative Example 7.

[0081] The Co@BC-N,S prepared in Example 1 and Comparative Examples 7 and 8 at different calcination temperatures were used to catalyze the degradation of the model pollutant carbamazepine. 0.01 g of the catalyst was added to a 2.5 mg / L carbamazepine solution (pH ≈ 7), wherein the amount of potassium permonosulfate (PMS) added was 0.3 mmol / L. The reaction was carried out at 25°C under natural light for 40 min. After the reaction was completed, a certain volume of sample was taken and the concentration of leached cobalt was measured by flame atomic absorption spectrometry. The results are shown in FIG. Figure 6 and Table 1.

[0082] Table 1

[0083]

[0084] Figure 1-2 According to the catalytic degradation effects of BC, Co@BC and BC-N,S prepared in Comparative Examples 1, 2 and 5, it can be seen that the catalytic degradation effect of metal-free carbon materials on pollutants is limited, and cobalt doping is crucial to enhance the catalytic activity of the materials. Figure 7 From the XRD diagram, it can be seen that the metallic cobalt in the Co@BC material prepared in Comparative Example 5 is mainly anchored in the biochar matrix in the form of Co metal particles, while the single nitrogen or sulfur doping and nitrogen-sulfur co-doping make the composite material show different catalytic degradation effects of pollutants. This is mainly because the single nitrogen or sulfur doping and nitrogen-sulfur co-doping will induce the cobalt in the biochar matrix to exist in the form of different cobalt species: in the Co@BC-N material prepared in Comparative Example 3, single nitrogen doping makes the cobalt not form an obvious crystalline phase in the carbon matrix, and it may exist mainly in the form of Co-N coordination, thus showing a weaker catalytic degradation effect than Co@BC; in the Co@BC-S material prepared in Comparative Example 4, single sulfur doping causes the cobalt to exist mainly in the crystalline phase of Co9S8 in the carbon matrix, thus showing a better catalytic degradation effect than Co@BC. The catalytic performance of the composite material is shown in Figure 2, which shows that the incorporation of elemental sulfur can significantly improve the catalytic activity of the composite material. In Example 1, the Co@BC-N,S prepared by using a single-component nitrogen and sulfur source, the synergistic effect of nitrogen and sulfur co-doping will induce the Co9S8 generated when sulfur is doped alone to be converted into Co3S4, thereby showing a better catalytic effect. In Comparative Example 6, the catalytic degradation effect of Co@BC-N,S-1 prepared by using a two-component nitrogen and sulfur source is significantly weaker than that of Co@BC-N,S. This is attributed to the fact that during the doping process of the two-component nitrogen and sulfur source, nitrogen and sulfur exist in the composite material as two components, which are easy to escape during the pyrolysis process, while in the doping process of the single-component nitrogen and sulfur source, N and S are bonded to the same carbon atom in the form of single bonds and double bonds, respectively (NC=S), making the anchoring of nitrogen, sulfur and cobalt on the material more stable, and forming C-Co3S4-N xThe structure significantly improves the catalytic performance of the material. As shown in Table 1, compared with Example 1, Comparative Example 8, which uses chitosan as a carbon source, achieves the same 100% removal rate for the synergistic degradation of carbamazepine with potassium monopersulfate. However, the material prepared in Comparative Example 8 suffers from high leaching of metallic cobalt ions during the catalytic degradation of pollutants. Excessive cobalt leaching harms the environment and public health, and cobalt leaching also seriously affects the catalytic stability of the material. In contrast, the material in Example 1 not only has lower cobalt leaching, but also has the ability to efficiently catalyze the degradation of pollutants and stable performance.

[0085] according to Figure 1-4 It can be seen that the calcination temperature significantly affects the physical and chemical properties of the material and thus affects its performance in catalytic degradation of pollutants; with the increase of pyrolysis temperature, the catalytic degradation and adsorption degradation effect of the material also increases. Figure 6 Cobalt leaching of materials at different pyrolysis temperatures and Figure 8 The XPS results in the figure show that as the pyrolysis temperature increases, the nitrogen content in the material gradually decreases; elemental nitrogen can coordinate with metallic cobalt to fix metallic cobalt; the lower nitrogen content and higher cobalt content cause Co@BC-N,S-900 to expose more cobalt species active sites. Although it has extremely high catalytic activity, there will be a high amount of cobalt ion leaching during the catalytic process, which is easy to cause environmental pollution; in contrast, Co@BC-N,S has both excellent catalytic degradation of pollutants and low cobalt ion leaching, so 700℃ is selected as the optimal calcination temperature.

[0086] according to Figure 5 It can be seen that the multi-element doped biochar composite material prepared by the present invention has good stability, and the removal rate of carbamazepine after five cycles is about 80%.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A multi-element doped biochar composite material, characterized by: The biochar is prepared from the residue of Polygonatum yunnanensis as a carbon source and is obtained by co-doping with nitrogen, sulfur and cobalt doping elements, wherein thiourea is used as the raw material for nitrogen and sulfur doping elements; The preparation method of the multi-element doped biochar composite material comprises the following steps: (1) Dissolve thiourea and Polygonatum dangshen powder in ethanol, stir, and ultrasonicate to obtain a mixed solution; (2) Adding the cobalt salt aqueous solution to the mixed solution and stirring, then evaporating the water and drying to obtain a solid block, grinding the solid block and calcining it in a protective gas; the protective gas is nitrogen, the nitrogen flow rate is 100 ml / min, the heating rate is 5 ° C / min, the calcination temperature is 700 ° C ~ 900 ° C, and the calcination constant temperature time is 2 h; (3) The calcined material is ground into powder and soaked in sulfuric acid, then washed, separated, and dried to obtain a nitrogen, sulfur, and cobalt co-doped biochar composite material.

2. The multi-element doped biochar composite material according to claim 1, characterized in that: The molar ratio of the cobalt salt to the thiourea in the cobalt salt aqueous solution is 1:(15-30).

3. The multi-element doped biochar composite material according to claim 1, characterized in that: The mass ratio of the cobalt salt in the cobalt salt aqueous solution to the Yunnan Polygonatum odoratum residue powder is (1-3):

40.

4. The multi-element doped biochar composite material according to claim 1, characterized in that: In the step (2), the calcination temperature is 700°C.

5. The multi-element doped biochar composite material according to claim 1, characterized in that: In step (3), the concentration of sulfuric acid is 0.1-0.5 mol / L, and the soaking time is 12 hours.

6. Use of the multi-element doped biochar composite material according to any one of claims 1 to 5 to activate PMS in removing organic pollutants from water.

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