A method for degrading organic pollutants in water by using nitrogen-sulfur co-doped biochar
Through the combined effect of nitrogen-sulfur co-doped biological carbon and permonosulfate prepared by calcining under a nitrogen atmosphere, the problems of difficult degradation of organic pollutants in water and metal catalyst pollution are solved, and efficient degradation and resource reuse are achieved, achieving Degradation rate of more than 95%.
Patent Information
- Application Number
- CN202310198627.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-03-03
- Publication Date
- 2024-12-27
- Estimated Expiration
- 2043-03-03
AI Technical Summary
The prior art is difficult to effectively degrade organic pollutants that are not easily degraded in water, and the environmental pollution caused by ion leaching and heavy metal toxicity is not effectively utilized.
Nitrosulfide co-doped biological carbon is prepared by calcining the oil tea shell under a nitrogen atmosphere and applying it to the degradation method of organic pollutants in water. Through joint action with persulfate, efficient degradation is achieved.
The efficient degradation rate of organic pollutants is achieved, reaching more than 95%, solving the environmental pollution problem of metal doped catalysts, and converting agricultural waste such as oil tea shells into efficient catalysts to achieve resource reuse.
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Figure CN116510762B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of material technology and waste biomass resource utilization, and specifically relates to nitrogen-sulfur co-doped biochar and a method for using the nitrogen-sulfur co-doped biochar to degrade organic pollutants in water. Background Art
[0002] Camellia oleifera is a woody oil crop widely planted in southern my country. The camellia oleifera husk is composed of cellulose, hemicellulose, lignin and other substances. It is the main by-product in the camellia oleifera production process, accounting for 54% of the total weight of the camellia oleifera fruit and is usually discarded as biological waste.
[0003] Industrial production and people's daily life will bring various organic pollutants into the environment, causing serious pollution and threatening the ecosystem and human health. The molecules of many organic pollutants are very stable and not easily degraded by light, chemicals, biology and other reagents. The commonly used methods for treating such organic pollutants that are not easily degraded include adsorption, heating, alkaline water immersion, etc. However, these methods are not ideal for the degradation of organic pollutants. They can only slightly reduce the residues and cannot achieve the effect of truly degrading them into "green products".
[0004] Advanced oxidation technologies (AOPs) are the most studied wastewater treatment methods in recent years. For example, photocatalytic oxidation, electrochemical oxidation, and ozone oxidation have been used to remove organic pollutants. However, these methods also have some disadvantages. For example, photocatalytic oxidation is sensitive to turbidity and difficult to scale up; ozone oxidation uses ozone, which is a strong oxidant with low solubility in water, thus limiting the ozonation process; in the electrochemical oxidation process, the active anode is easily passivated due to the formation of an organic film on the anode surface during the degradation of pollutants. Studies have found that among the active oxygen produced by advanced oxidation technologies, SO4 ·- It has a high redox potential (E°=2.5~3.1V), high reactivity in a wide pH range (2~8), a long life cycle and high oxidation selectivity, and can efficiently and quickly degrade organic pollutants. ·- It is mainly produced by peroxymonosulfate (PMS) and peroxydisulfate (PS). Compared with PS, PMS has an asymmetric structure and is easier to activate. Common methods for activating PMS include heating, ultraviolet rays, ultrasound, transition metals and their oxides, etc. Heating, ultraviolet rays, and ultrasound activation of PMS require higher energy, which limits its use in large-scale treatment of organic wastewater; transition metals and their oxides and PMS have limited application scope in homogeneous catalytic systems, and the dissolved metals are highly toxic, which is not conducive to the actual treatment of organic wastewater.
[0005] Transition metals such as cobalt, nickel, copper, and iron have been widely reported to be used for the degradation of organic pollutants due to their high activity. However, while degrading pollutants, metal ion leaching and toxicity limit their practical application. The introduction of heavy metal ions into water, and the content of each metal cannot exceed the national standard for discharged water, will cause secondary pollution to the environment; in addition, pure carbon materials have a weak ability to activate persulfate, which usually manifests as adsorption, and also cannot achieve the purpose of degradation. Therefore, non-metal-doped biochar is considered to be a substitute for the above materials. Summary of the invention
[0006] The purpose of the present invention is to provide a nitrogen-sulfur co-doped biochar to address the problem of recycling tea oil shells and the environmental pollution problem caused by ion leaching and heavy metal toxicity of metal-doped catalysts. It not only solves the resource waste existing in the prior art, but also applies it to the degradation method of organic pollutants in water, thereby solving the problems of environmental pollution and difficulty in degrading organic pollutants.
[0007] The technical solution adopted by the present invention is:
[0008] A nitrogen-sulfur co-doped biochar is prepared by calcining tea oil shell at 600-650° C. in a nitrogen atmosphere to obtain a carbon matrix, then using urea as a nitrogen source and thiourea as a sulfur source, heating the mixture to 500-550° C. in a nitrogen atmosphere and maintaining the mixture for 1-1.5 hours, and then quenching the mixture at 800-850° C. for 1.5-2 hours to obtain the nitrogen-sulfur co-doped biochar.
[0009] Another object of the present invention is to provide a method for preparing the nitrogen-sulfur co-doped biochar, comprising the following steps:
[0010] Step (1), drying the camellia oleifera shell into powder, placing it in a tube furnace, heating it to 600-650° C. in a nitrogen atmosphere and calcining it for 2-3 hours to form a carbon matrix;
[0011] Step (2), fully grinding the carbon matrix, urea and thiourea, putting them into a tubular furnace, heating them to 500-550° C. and maintaining them for 1-1.5 hours under a nitrogen atmosphere, and then heating them to 800-850° C. and calcining them for 1.5-2 hours to obtain nitrogen-sulfur co-doped biochar.
[0012] In step (1), the nitrogen flow rate is 4 to 6 cm 3 / min, preferably 5cm 3 / min.
[0013] The heating rate is 3-6°C / min.
[0014] Preferably, the dried camellia oleifera shell is ground into powder, put into a tube furnace, and calcined at 600° C. at a heating rate of 3° C. / min for 3 h in a nitrogen atmosphere to form a carbon matrix;
[0015] In step (2), the mass ratio of the carbon substrate, urea and thiourea is 1:5:(5-10), preferably 1:5:(7.5-10), and more preferably 1:5:10.
[0016] Nitrogen flow rate is 4-6 cm 3 / min, preferably 5cm 3 / min.
[0017] The heating rates for the first and second heating are both 3-6°C / min.
[0018] Preferably, the carbon matrix, urea and thiourea are fully ground, put into a tubular furnace, and in a nitrogen atmosphere, first heated to 500-525°C at a heating rate of 3°C / min and maintained for 1 hour, and then heated to 800°C at a heating rate of 3°C / min and calcined for 2 hours to obtain nitrogen-sulfur co-doped biochar.
[0019] Another object of the present invention is to provide a method for applying the nitrogen-sulfur co-doped biochar to the degradation of organic pollutants in water, comprising: adding the nitrogen-sulfur co-doped biochar to wastewater, first stirring to adsorption equilibrium, then adding peroxymonosulfate, and stirring at room temperature to degrade the organic pollutants.
[0020] The dosage of the nitrogen-sulfur co-doped biochar catalyst is 300-450 mg / L, preferably 300 mg / L; the dosage of the peroxymonosulfate is 0.90-1.35 mM, preferably 0.90 mM; and the pH is 5-7, preferably 5.
[0021] The organic pollutants are 2,4-dichlorophenol, ofloxacin, sulfamethoxazole, atrazine and glyphosate.
[0022] The method for degrading organic pollutants in water by using nitrogen-sulfur co-doped biochar according to the present invention also includes: when the wastewater contains CO3 2- When adding calcium chloride, CO3 2- It is converted into calcium carbonate precipitate, and then nitrogen-sulfur co-doped biochar is added to the wastewater, first stirred to adsorption equilibrium, and then peroxymonosulfate is added and stirred at room temperature to degrade organic pollutants.
[0023] Beneficial effects of the present invention:
[0024] The invention uses cheap and readily available agricultural waste materials such as camellia oleifera shells, urea and thiourea as raw materials, has a simple preparation method, forms a nitrogen-sulfur doped biocarbon catalyst, and can be widely used in the degradation of organic pollutants.
[0025] When preparing the carbon matrix, calcination in a nitrogen atmosphere can prevent oxygen from reacting with biochar at high temperature to generate carbon dioxide. Constant heating rate can ensure that the tar in the oil tea shell is slowly released to avoid tar clogging the instrument due to too fast heating. Constant calcination at 600-650°C ensures that the oil tea shell generates more biochar and maximizes the removal of tar to improve efficiency. If the calcination temperature is too low, tar will be loaded on the surface of biochar, blocking the pores of biochar and affecting the subsequent nitrogen and sulfur doping. When preparing nitrogen-sulfur co-doped biochar, calcination in a nitrogen atmosphere can also prevent oxygen from reacting with biochar at high temperature to generate carbon dioxide. Constant heating rate can avoid nitrogen and sulfur elements agglomerating on the surface of the carbon matrix due to too fast heating. Constant heating rate is first used to 500-550°C, and then to 800-850°C, which is conducive to urea and thiourea to generate more graphite nitrogen and thiophene sulfur on the surface of biochar, which are beneficial to the degradation of organic matter.
[0026] The invention realizes the recycling of oil tea shells and turns waste into treasure, which is an effective way to save resources, protect the environment and maximize economic benefits, and is very important for environmental protection and economic sustainable development.
[0027] The nitrogen-sulfur co-doped biochar of the present invention is used as a catalyst for the degradation of organic pollutants in water, solving the environmental pollution problem caused by ion leaching and heavy metal toxicity of metal-doped catalysts. Non-metallic atom doping can adjust the electronic characteristics of biochar orbital hybridization, increase active sites, accelerate electron transfer, and effectively degrade organic pollutants in water. The nitrogen-sulfur co-doped biochar of the present invention has a more superior degradation effect on organic pollutants, with a degradation rate of more than 95%, and the degradation rate of some organic pollutants even reaches 100%. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 These are the scanning electron microscope images and transmission electron microscope images of each element.
[0029] Figure 2 The voltammograms and impedance diagrams of carbon matrix (BC) and nitrogen-sulfur co-doped biocarbon (NSBC).
[0030] Figure 3 The degradation effect of 2,4-dichlorophenol was catalyzed by nitrogen-sulfur co-doped biochar prepared from camellia oleifera shells, walnut shells and lotus leaves.
[0031] Figure 4 X-ray electron energy spectra of 2,4-dichlorophenol before (a) and after (b) degradation catalyzed by nitrogen-sulfur co-doped biochar NSBC.
[0032] Figure 5 The degradation effect of 2,4-dichlorophenol catalyzed by different non-metal-doped biochars.
[0033] Figure 6The degradation effect of 2,4-dichlorophenol catalyzed by nitrogen-sulfur co-doped biochar prepared with different nitrogen and thiourea addition amounts.
[0034] Figure 7 This is the effect of nitrogen-sulfur co-doped biochar dosage, permonosulfate dosage, solution pH and anions in water on the degradation of 2,4-dichlorophenol.
[0035] Figure 8 This is a diagram showing the degradation effect of nitrogen-sulfur co-doped biochar NSBC on other organic pollutants.
[0036] Fig. 9 This is the cycle test diagram of nitrogen-sulfur co-doped biocarbon NSBC. DETAILED DESCRIPTION
[0037] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.
[0038] Example 1
[0039] A nitrogen-sulfur co-doped biochar is prepared from a carbon matrix made from oil tea shells, urea (as a nitrogen source), and thiourea (as a sulfur source), and comprises the following steps:
[0040] Step (1), drying fresh camellia oleifera shells, grinding them into powder using a grinder, placing them in a tube furnace, and heating them in a nitrogen atmosphere (nitrogen flow rate 5 cm 3 / min) at a heating rate of 3°C / min to 600°C and calcined for 3h to form a carbon matrix (BC);
[0041] Step (2), weigh 1g of carbon matrix, 5g of urea and 10g of thiourea, grind them thoroughly in a mortar, put them in a tube furnace, and simmer them in a nitrogen atmosphere (nitrogen flow rate 5cm 3 / min), the temperature was first increased to 500 °C at a heating rate of 3 °C / min and maintained for 1 h, and then increased to 800 °C at the same rate of 3 °C / min and calcined for 2 h to form nitrogen-sulfur co-doped biochar (NSBC).
[0042] The structural characteristics of the material were explored through scanning electron microscopy and transmission electron microscopy. Figure 1 shown. Figure 1 a is the SEM image of the carbon matrix without N and S addition, and it can be seen that the carbon surface has an uneven porous structure; Figure 1 b is the scanning electron microscopy image of nitrogen-sulfur co-doped biochar with added N and S elements, indicating that the N and S elements are evenly distributed on the surface of the carbon matrix. Figure 1 d-1g is the content of each element in nitrogen-sulfur co-doped biochar under transmission electron microscopy, representing C, N, O, and S elements, respectively, indicating that N and S elements were successfully loaded on the surface of the carbon matrix. Figure 1 h means Figure 1c The content of each element of C, N, O, and S. In addition, through the specific surface area (BET) test, it was found that the BET of the carbon matrix is 17.2886 m 2 / g, while NSBC's BET=425.9288m 2 / g, indicating that the addition of N and S elements increases the specific surface area of nitrogen-sulfur co-doped biochar and provides more active sites for the degradation of organic pollutants.
[0043] The inventors tested the electrochemical characteristics of BC and NSBC ( Figure 2 ). The voltammetric characteristic curve and impedance curve show that NSBC has a larger current area and a smaller curve radius, and has a faster electron transfer ability during the degradation process, which is beneficial to improving the degradation rate of organic pollutants.
[0044] Investigation of catalytic degradation of organic pollutants: Weigh 40 mg of 2,4-chlorophenol into a 1L volumetric flask, titrate to the mark with deionized water to obtain a 2,4-dichlorophenol solution with a concentration of 40 mg / L, and adjust the pH of the 2,4-dichlorophenol solution to 7 with 0.1 mmol / L sulfuric acid and 0.1 mmol / L sodium hydroxide. Take 100 mL of 2,4-dichlorophenol solution in a 100 mL volumetric flask, add 30 mg of nitrogen-sulfur co-doped biochar prepared in Example 1, Comparative Example 1, and Comparative Example 2 as catalysts, stir for 20 min until adsorption equilibrium, then add 0.9 mM permonosulfate (2KHSO5·KHSO4·K2SO4), stir at room temperature, take out about 2 mL of solution with a syringe every 10 min, filter with a 0.22 μm polyethersulfone filter membrane, and quench the remaining free radicals with 0.5 mL of methanol. The concentration of 2,4-dichlorophenol was detected at 280 nm using a high performance liquid chromatography (HPLC) UV-visible detector, a reverse phase chromatography column C18 column (5 μm, 4.6 mm × 250 mm), water and methanol (30%: 70%) as the mobile phase, and the flow rate was 1 mL / min. The peak areas of the solution before and after degradation were tested by high performance liquid chromatography, and the ratio of the two was calculated to obtain the degradation rate.
[0045] Depend on Figure 3 It can be seen that without adding PMS in the first 20 minutes, when the catalyst reaches adsorption equilibrium (sampling is taken every 5 minutes, and the concentrations before and after are tested by high performance liquid chromatography, and the closeness of the last few groups of values indicates adsorption equilibrium), after adding peroxymonosulfate (PMS), the degradation rate of nitrogen-sulfur co-doped biochar made from tea oil shells reaches 100% within 20 minutes. Under the same conditions, the degradation effects of nitrogen-sulfur co-doped biochar made from walnut shells and lotus leaves were not significant, with degradation rates of 83% and 87%, respectively.
[0046] The inventors tested the X-ray electron spectroscopy (XPS) of NSBC before and after degradation. Figure 4It can be seen that the peak values of graphite N and thiophene S in NSBC after degradation are significantly reduced, indicating that graphite N and thiophene S provided by N and S doping are the main active sites for activating PMS and play a leading role in the degradation of 2,4-dichlorophenol.
[0047] Comparative Example 1
[0048] The camellia oleifera shells were replaced with walnut shells, and the preparation method was the same as that in Example 1 to obtain nitrogen-sulfur co-doped biochar, which was recorded as NSBC-1.
[0049] Comparative Example 2
[0050] The camellia oleifera shell was replaced with lotus leaf, and the preparation method was the same as that in Example 1 to obtain nitrogen-sulfur co-doped biochar, which was recorded as NSBC-2.
[0051] Example 2
[0052] Based on Example 1, tea oil shell was determined as the carbon matrix, and referring to Example 1 "Investigation of catalytic degradation of organic pollutants", the degradation effect of biocarbon doped with different non-metallic elements (boric acid represents B, phosphoric acid represents P, thiourea represents S, and urea represents N) on 2,4-dichlorophenol (40 mg / L) was investigated.
[0053] Catalyst S (N) is the nitrogen-sulfur co-doped biochar (NSBC) prepared in Example 1.
[0054] Catalyst B (N): except that 10 g of thiourea in Example 1 is replaced by 10 g of boric acid, the preparation method is the same as that in Example 1.
[0055] Catalyst P(N): except that 10 g of thiourea in Example 1 was replaced by 10 g of phosphoric acid, the preparation method was the same as that in Example 1.
[0056] Catalyst S: The method for preparing nitrogen-sulfur co-doped biochar (NSBC) was followed as in Example 1, but only 10 g of thiourea was added instead of urea.
[0057] Catalyst N: The method for preparing nitrogen-sulfur co-doped biochar (NSBC) was followed as in Example 1, but only 10 g of urea was added without adding thiourea.
[0058] from Figure 5 It can be seen that after adsorption equilibrium, the degradation rates of peroxymonosulfate (PMS) are added, and the order from large to small is: S(N)>B(N)>S>P(N)>N, indicating that the degradation effect of nitrogen-sulfur co-doped biochar is better than that of other non-metal-doped biochars.
[0059] Example 3
[0060] The effects of the addition of nitrogen and thiourea on the degradation of 2,4-dichlorophenol (40 mg / L) were screened, biochar: urea: thiourea = 1g: 1g: 1g, 1g: 5g: 5g, 1g: 5g: 7.5g, 1g: 5g: 10g, except for the addition of nitrogen and thiourea, the preparation method was the same as Example 1. Referring to Example 1 "Investigation of catalytic degradation of organic pollutants", the degradation effect of nitrogen-sulfur co-doped biochar prepared with different addition amounts of nitrogen and thiourea on 2,4-dichlorophenol (40 mg / L) was investigated.
[0061] from Figure 6 It can be seen that the nitrogen-sulfur co-doped biochar prepared by biochar: urea: thiourea = 1g:5g:10g and 1g:5g:7.5g has significantly better degradation effect on 2,4-dichlorophenol than the other two ratios, and the nitrogen-sulfur co-doped biochar prepared by biochar: urea: thiourea = 1g:5g:10g has the fastest degradation rate within 10 minutes and the highest degradation rate within 40 minutes, reaching 100%.
[0062] Example 5
[0063] After determining that the oil tea shell is used as the carbon matrix and the mass ratio of biochar: urea: thiourea is 1g: 5g: 10g, referring to Example 1 "Investigation of catalytic degradation of organic pollutants", the amount of catalyst (Example 1 nitrogen and sulfur co-doped biochar) (0, 150, 300, 450 mg / L), the amount of permonosulfate (0, 0.45, 0.90, 1.35 mM), the solution pH (0.1 mmol / L sulfuric acid and 0.1 mmol / L sodium hydroxide were used to adjust the solution pH to 3, 5, 7, 9, 11, respectively) and the anion (CO3 2- , Cl - 、NO3 - , humic acid, CO3 2- , Cl - 、NO3 - Effects of adding potassium carbonate, potassium chloride and potassium nitrate respectively on the degradation of 2,4-dichlorophenol (40 mg / L).
[0064] Results Figure 7 When the catalyst amount = 300-450 mg / L, the peroxymonosulfate amount = 0.90-1.35 mM, and the pH = 5-7, the degradation rate of 2,4-dichlorophenol reached 100%. Considering the effective utilization of resources, the degradation efficiency of 2,4-dichlorophenol was best when the catalyst amount = 300 mg / L, the peroxymonosulfate amount = 0.90 mM, and the pH = 5.
[0065] Common anions in natural water or wastewater - 、NO3 - 、CO3 -and natural organic matter - humic acid, Cl - 、NO3 - and humic acid had little effect on degradation, but CO3 2- It has a strong inhibitory effect on the degradation of 2,4-dichlorophenol, and the removal rate is only 62% within 40 minutes. 2- When adding a small amount of calcium chloride, CO3 2- Converted into calcium carbonate precipitate.
[0066] Example 6
[0067] Deionized water was used to prepare solutions of ofloxacin (12 mg / L), sulfamethoxazole (12 mg / L), atrazine (12 mg / L), and glyphosate (50 mg / L), respectively. Referring to Example 1 "Investigation of catalytic degradation of organic pollutants", the degradation effect of the catalyst (Example 1 nitrogen and sulfur co-doped biochar, catalyst dosage 300 mg / L, peroxymonosulfate 0.90 mM, pH = 7) on organic pollutants was investigated.
[0068] The experimental results are as follows Figure 8 As shown, within 60 minutes, the removal rates of ofloxacin (12 mg / L), sulfamethoxazole (12 mg / L), atrazine (12 mg / L), and glyphosate (50 mg / L) reached 98.5%, 97.7%, 96.3%, and 100%, respectively, indicating that the nitrogen-sulfur co-doped biochar of the present invention has good applicability for the degradation of organic pollutants.
[0069] Example 7
[0070] Referring to Example 1 "Investigation of catalytic degradation of organic pollutants", the ability of the catalyst (Example 1 nitrogen-sulfur co-doped biochar) to cyclically catalyze the degradation of 2,4-dichlorophenol solution (40 mg / L) was tested. After standing for about 1 hour after each degradation, the catalyst was filtered, placed in an oven at 80°C for 3 hours, and the catalyst was recovered and continued to degrade 40 mg / L of 2,4-dichlorophenol solution. The removal rate of 2,4-dichlorophenol by the catalyst recovered for the third time reached 95.1%, indicating that the NSBC prepared by the invention has good cyclicity and stability.
Claims
1. A method for degrading organic pollutants in water by using nitrogen-sulfur co-doped biochar, characterized in that: include: Nitrogen-sulfur co-doped biochar was added to wastewater, stirred until adsorption equilibrium was reached, and then peroxymonosulfate was added and stirred at room temperature to degrade organic pollutants; The nitrogen-sulfur co-doped biochar is prepared by first calcining the oil tea shell at 600-650°C in a nitrogen atmosphere to obtain a carbon matrix, then using urea as a nitrogen source and thiourea as a sulfur source, heating the mixture to 500-550°C in a nitrogen atmosphere for 1-1.5 hours, and then quenching the mixture at 800-850°C for 1.5-2 hours to obtain the nitrogen-sulfur co-doped biochar. The mass ratio of the carbon matrix, urea and thiourea is 1:5:(7.5-10); The organic pollutants are 2,4-dichlorophenol, ofloxacin, sulfamethoxazole, atrazine and glyphosate.
2. A method for degrading organic pollutants in water by using nitrogen-sulfur co-doped biochar, characterized in that: include: When wastewater contains CO3 2- When adding calcium chloride, CO3 2- Converted into calcium carbonate precipitation, then nitrogen-sulfur co-doped biochar is added to the wastewater, first stirred until adsorption equilibrium, then peroxymonosulfate is added, and stirred at room temperature to degrade organic pollutants; The nitrogen-sulfur co-doped biochar is prepared by first calcining the oil tea shell at 600-650°C in a nitrogen atmosphere to obtain a carbon matrix, then using urea as a nitrogen source and thiourea as a sulfur source, heating the mixture to 500-550°C in a nitrogen atmosphere for 1-1.5 hours, and then quenching the mixture at 800-850°C for 1.5-2 hours to obtain the nitrogen-sulfur co-doped biochar. The mass ratio of the carbon matrix, urea and thiourea is 1:5:(7.5-10); The organic pollutants are 2,4-dichlorophenol, ofloxacin, sulfamethoxazole, atrazine and glyphosate.
3. The method for degrading organic pollutants in water using nitrogen-sulfur co-doped biochar according to claim 1 or 2, characterized in that: The dosage of the nitrogen-sulfur co-doped biochar is 300-450 mg / L; the dosage of the peroxymonosulfate is 0.90-1.35 mM; and the pH is 5-7.
4. The method for degrading organic pollutants in water using nitrogen-sulfur co-doped biochar according to claim 3, characterized in that: The amount of the nitrogen-sulfur co-doped biochar is 300 mg / L; the amount of the peroxymonosulfate is 0.90 mM; and the pH is 5.