A nitrogen-fluorine co-doped transition metal-free dual site catalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts, and particularly relates to a nitrogen and fluorine co-doped transition metal-free dual-site catalyst as well as a preparation method and application thereof. The preparation method provided by the application comprises the following steps: S1) ultrasonic mixing of montmorillonite, nitrogen-rich carbon precursors and water to obtain a first mixture; S2) ultrasonic mixing of the first mixture and fluorine precursors to obtain a second mixture; and S3) pyrolysis of the second mixture to obtain the nitrogen and fluorine co-doped transition metal-free dual-site catalyst. The preparation method provided by the application can realize uniform and efficient doping of N and F, simultaneously form a large number of N vacancies, introduce two adsorption-catalysis dual sites of F sites with rich electrons and N vacancies with electron deficiency into the catalyst, realize 100% selectivity of an oxidant to generate singlet oxygen, and in-situ strengthen effective utilization of the singlet oxygen, so as to realize a water treatment process with higher pollutant degradation performance and environmental benefits.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to a nitrogen and fluorine co-doped transition metal-free dual-site catalyst and a preparation method and application thereof. BACKGROUND

[0002] The removal of refractory organic pollutants in water is a key problem restricting water quality. The Fenton-like catalysis as a representative of advanced oxidation technology is one of the most effective means to remove refractory organic pollutants in water, and the efficient generation of strong oxidizing active substances is crucial. As a typical non-metallic catalyst, carbon-based catalyst avoids the secondary pollution problem of metal leaching during the use of catalysts, and has broad application prospects in catalytic Fenton reaction. Carbon-based catalysts can effectively activate peroxymonosulfate (PMS) to degrade organic pollutants, and the active substances generated include active radicals and singlet oxygen. Compared with active radicals, singlet oxygen has the advantages of long lifetime, high selectivity, and not easy to be consumed by coexisting substances (such as natural organic matter). However, compared with transition metal catalysts, the activities of various reported metal-free catalysts are often more than one order of magnitude lower. On the other hand, the effective utilization of strong active species is the core reaction in the process of pollutant degradation, but catalysts with only a single active site are difficult to meet the adsorption-catalysis requirements in the complex Fenton reaction, and the ineffective quenching of active species limits the pollutant removal efficiency. Therefore, the design and development of high-efficiency metal-free dual-site catalysts have become one of the scientific problems to be solved in this field.

[0003] Heteroatom (such as N, S, P, B, etc.) doping can significantly improve the catalytic activity and stability of the material. Studies have shown that doping can effectively change the geometric properties and electronic structure of the catalyst surface, introduce various active sites (such as heteroatom sites, vacancies, etc.), and effectively improve the utilization rate of the catalytic active site. Fluorine element has the highest electronegativity, and doping it into carbon materials can improve the electrical conductivity of carbon materials, change the electronic arrangement and atomic structure of carbon atoms and their surrounding atoms, form a carbon structure delocalized conjugated system with sp2 hybridization, and thus improve the catalytic activity of carbon materials. However, there are few studies on fluorine-doped carbon materials, and they have not been applied in the environmental field. The reported fluorine doping strategies often involve complex processes, highly toxic fluorine reagents, and special equipment, which not only have low doping efficiency, but also easily cause secondary pollution and high cost; at the same time, the reaction activity and kinetics of different heteroatom precursors in the pyrolysis process are different, making it difficult to achieve uniform co-doping; in addition, the pyrolysis process of fluorine precursor is easy to release highly reactive HF, which interferes with the reaction process and reduces the doping efficiency. Therefore, it is urgent to develop an efficient fluorine doping strategy to achieve the preparation of excellent metal-free dual-site catalysts. Montmorillonite is known as "universal material" and has wide application of catalytic properties and adsorption neutralization. By using these properties to mediate efficient doping of N and F, a new idea for the synthesis of metal-free dual-site catalysts is expected to be provided. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a nitrogen and fluorine co-doped transition metal-free dual-site catalyst and its preparation method and application. The preparation method provided by the present application can achieve uniform and efficient doping of N and F, and at the same time form a large number of N vacancies, introduce two adsorption-catalysis dual sites of F sites with rich electrons and N vacancies with electron deficiency in the catalyst; achieve 100% selectivity of oxidizing agent activation to generate singlet oxygen, and in-situ strengthen its effective utilization, to realize water treatment process with higher pollutant degradation performance and environmental benefits.

[0005] The present application provides a preparation method of a nitrogen and fluorine co-doped transition metal-free dual-site catalyst, comprising the following steps:

[0006] S1) ultrasonic mixing of montmorillonite, nitrogen-rich carbon precursor and water to obtain a first mixture;

[0007] S2) ultrasonic mixing of the first mixture and fluorine precursor to obtain a second mixture;

[0008] S3) pyrolysis of the second mixture to obtain a nitrogen and fluorine co-doped transition metal-free dual-site catalyst.

[0009] Preferably, the montmorillonite is selected from hydrogen-based montmorillonite and / or sodium-based montmorillonite;

[0010] The nitrogen-rich carbon precursor is selected from one or more of melamine, dicyandiamide and urea;

[0011] The fluorine precursor is selected from polytetrafluoroethylene and / or polyvinylidene fluoride.

[0012] Preferably, the mass ratio of the montmorillonite to the nitrogen-rich carbon precursor is 0.5:(0.5-3).

[0013] The mass ratio of the montmorillonite to water is 0.5:(1-4).

[0014] The mass ratio of the montmorillonite to the fluorine precursor is 0.5:(0.4-2).

[0015] Preferably, in step S1), the ultrasonic blending time is 5-60 min.

[0016] In step S2), the ultrasonic blending time is 5-60 min.

[0017] In step S3), the pyrolysis temperature rising rate is 2-20℃ / min; the pyrolysis temperature rising end point temperature is 450-650℃; and the pyrolysis holding time is 0.5-3 h.

[0018] The application also provides a nitrogen-fluorine co-doped transition metal-free dual-site catalyst, which is prepared by the preparation method described in the above technical solution; the nitrogen-fluorine co-doped transition metal-free dual-site catalyst is a 3D nanosheet structure uniformly doped with N and F, and the catalyst is rich in N vacancies.

[0019] The application also provides the nitrogen-fluorine co-doped transition metal-free dual-site catalyst prepared by the preparation method described in the above technical solution or the application of the nitrogen-fluorine co-doped transition metal-free dual-site catalyst described in the above technical solution in water treatment.

[0020] The application also provides a water treatment method, which comprises the following process:

[0021] The nitrogen-fluorine co-doped transition metal-free dual-site catalyst prepared by the preparation method described in the above technical solution or the nitrogen-fluorine co-doped transition metal-free dual-site catalyst described in the above technical solution removes pollutants in water by catalyzing activation of persulfate.

[0022] Preferably, the ratio of the nitrogen-fluorine co-doped transition metal-free dual-site catalyst to persulfate is 0.2 g:(0.2-5) mmol.

[0023] Preferably, the pollutants include one or more of phenolic pollutants, antibiotic pollutants and other pharmaceutical and personal care products (PPCPs) pollutants; the phenolic pollutants are selected from one or more of bisphenol A, phenol and p-chlorophenol; the antibiotic pollutants are selected from sulfamethoxazole and / or sulfamerazine; and the other pharmaceutical and personal care product pollutants are selected from sulfonamides and / or ofloxacin.

[0024] Preferably, the pH value of the water is 3-11.

[0025] The application provides a nitrogen and fluorine co-doped transition metal-free dual-site catalyst, a preparation method and application thereof. The preparation method comprises the following steps: S1) ultrasonic mixing of montmorillonite, nitrogen-rich carbon precursor and water to obtain a first mixture; S2) ultrasonic mixing of the first mixture and fluorine precursor to obtain a second mixture; and S3) pyrolysis of the second mixture to obtain the nitrogen and fluorine co-doped transition metal-free dual-site catalyst. Compared with the prior art, the application uses montmorillonite as an in-situ template, uniformly disperses the montmorillonite, nitrogen-rich carbon precursor and fluorine precursor by ultrasonic mixing, and then co-pyrolyzes the mixture. The catalytic properties and adsorption neutralization effect of the montmorillonite accelerate the pyrolysis reaction, promote the uniform growth of the carbon material and the uniform and efficient doping of N and F. In addition, the montmorillonite can adsorb and consume hydrogen fluoride generated in the pyrolysis process of the fluorine precursor, thereby relieving the corrosion of the hydrogen fluoride on the carbon material. At the same time, the hydrogen fluoride in-situ etches and removes the montmorillonite template, forming a 3D nanosheet structure with regular morphology. The synthesis strategy can realize uniform and efficient doping of N and F, and introduce two adsorption-catalysis dual sites, i.e., F sites with rich electrons and N vacancies with electron deficiency, into the catalyst. The application has the advantages of high doping efficiency, simple operation, low cost and environmental friendliness. In addition, the dual-site catalyst synthesized by the application is used for catalytic activation of persulfate to remove pollutants in water, has a 100% selectivity for generating singlet oxygen, has high selectivity for removing pollutants, strong anti-interference ability, good catalytic stability, no risk of heavy metal dissolution and a wide pH application range. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the application, and for those skilled in the art, other drawings can be obtained without creative labor based on the provided drawings.

[0027] Figure 1 The preparation process schematic diagram of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst provided by the application is shown in the following figure.

[0028] Figure 2Scanning electron microscope (A) and transmission electron microscope (B) of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst obtained in Example 1 of the present application;

[0029] Figure 3 High-resolution transmission electron microscope (A) and corresponding elemental analysis photo (B) of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst obtained in Example 1 of the present application;

[0030] Figure 4 X-ray absorption spectrum N K-edge spectrum (A) and F K-edge spectrum (B) of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst obtained in Example 1 of the present application;

[0031] Figure 5 Comparison chart (A) of C / N ratio statistics and electron paramagnetic resonance spectrum (B) of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst obtained in Example 1 of the present application and the nitrogen and fluorine doped carbon catalyst prepared in Comparative Example 1;

[0032] Figure 6 Comparison chart of activity of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst obtained in Example 1 and the nitrogen and fluorine doped carbon catalyst prepared in Comparative Example 1 in treating phenol wastewater;

[0033] Figure 7 Chart of degradation ability of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst of the present application in treating various phenolic pollutants, antibiotic pollutants and other pharmaceutical and personal care product (PPCPs) pollutants;

[0034] Figure 8 Chart of treatment ability of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst of the present application on phenol wastewater containing different interfering ions;

[0035] Figure 9 Chart of treatment ability of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst of the present application on phenol wastewater containing humic acid;

[0036] Figure 10 Chart of treatment ability of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst of the present application on phenol wastewater with different pH values. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0038] The application provides a preparation method of a nitrogen and fluorine co-doped transition metal-free dual-site catalyst, comprising the following steps: S1) ultrasonic mixing of montmorillonite, nitrogen-rich carbon precursor and appropriate amount of water to obtain a first mixture; S2) ultrasonic mixing of the first mixture and fluorine precursor to obtain a second mixture; S3) pyrolysis of the second mixture to obtain the nitrogen and fluorine co-doped transition metal-free dual-site catalyst.

[0039] Referring to Figure 1 , Figure 1 The application provides a preparation flowchart of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst.

[0040] In the application, the montmorillonite is used as an in-situ template, and the montmorillonite, the nitrogen-rich carbon precursor and the fluorine precursor are uniformly dispersed by ultrasonic mixing; then, the montmorillonite is co-pyrolyzed, the catalytic characteristics and the adsorption neutralization effect of the montmorillonite are utilized to accelerate the pyrolysis reaction and promote the uniform growth of the carbon material and the uniform and efficient doping of N and F; in addition, the montmorillonite can adsorb and consume hydrogen fluoride generated in the pyrolysis process of the fluorine precursor, thereby relieving the corrosion effect of the hydrogen fluoride on the carbon material, and the hydrogen fluoride in-situ etches and removes the montmorillonite template, thereby forming a 3D nanosheet structure with a regular morphology; the synthesis strategy can realize the uniform and efficient doping of N and F, and at the same time, a large number of N vacancies are formed, thereby introducing two adsorption-catalysis dual sites, i.e., the F site with rich electrons and the N vacancy with a lack of electrons, into the catalyst.

[0041] In the application, the source of all raw materials is not particularly limited and can be commercially available.

[0042] The montmorillonite, the nitrogen-rich carbon precursor and appropriate amount of water are ultrasonic mixed to obtain a first mixture. The montmorillonite is preferably hydrogen-based montmorillonite and / or sodium-based montmorillonite; the nitrogen-rich carbon precursor can be any nitrogen-rich carbon precursor known to those skilled in the art and is not particularly limited, and in the application, preferably includes but is not limited to one or more of dicyandiamide, melamine and urea; the mass ratio of the montmorillonite to the nitrogen-rich carbon precursor is preferably 0.5:(0.5-3), more preferably 0.5:(0.5-2), more preferably 0.5:(0.5-1.5), and most preferably 0.5:(0.5-1); the mass ratio of the montmorillonite to water is preferably 0.5:(1-4), more preferably 0.5:(0.5-3), more preferably 0.5:(0.5-2), and most preferably 0.5:(0.5-1.5); the ultrasonic power of the ultrasonic mixing is preferably 200-600 W, more preferably 300-500 W, and more preferably 400 W; and the ultrasonic mixing time is preferably 5-60 min, more preferably 10-40 min.

[0043] The first mixture is ultrasonically blended with a fluorine precursor to obtain a second mixture. The fluorine precursor is a fluorine precursor known to those skilled in the art, and there is no special limitation, and the present application preferably includes but is not limited to polyvinylidene fluoride and / or polytetrafluoroethylene; the mass ratio of the montmorillonite to the fluorine precursor is preferably 0.5:(0.4-2), more preferably 0.5:(0.5-2), more preferably 0.5:(0.5-1.5), and most preferably 0.5:(0.5-1); the ultrasonic power of the ultrasonic blending is preferably 200-600W, more preferably 300-500W, and more preferably 400W; the ultrasonic blending time is preferably 5-60min, more preferably 10-40min.

[0044] The second mixture is pyrolyzed to obtain a nitrogen and fluorine co-doped dual-site catalyst. The pyrolysis temperature rate is preferably 2-20℃ / min, more preferably 5-20℃ / min, more preferably 8-15℃ / min, and most preferably 10-13℃ / min; the pyrolysis temperature endpoint is preferably 450℃-650℃, more preferably 500℃-600℃, and more preferably 550℃; the pyrolysis time is preferably 0.5-3h, more preferably 0.5-2.5h, more preferably 1-2h, and most preferably 1-1.5h.

[0045] The present application utilizes the in-situ templating effect, catalytic properties and adsorption neutralization of montmorillonite to regulate the uniform and efficient doping of N and F during the synthesis of dual-site catalysts, and prepares a nitrogen and fluorine co-doped transition metal-free dual-site catalyst, which is used to catalyze the activation of persulfate to remove pollutants in water, has a 100% selectivity to generate singlet oxygen, has high selectivity for pollutant removal, strong anti-interference ability, good catalytic stability, no risk of heavy metal leaching, and a wide pH application range. The synthesis strategy provided by the present application can realize uniform and efficient doping of N and F, while forming a large number of N vacancies, introducing two adsorption-catalysis dual sites of F sites with rich electrons and N vacancies with electron deficiency in the catalyst; has the advantages of high doping efficiency, simple operation, low cost and environmental friendliness, and provides a new idea for the synthesis and regulation of high-performance transition metal-free catalysts.

[0046] The present application also provides a nitrogen and fluorine co-doped transition metal-free dual-site catalyst prepared by the above preparation method, which is a 3D nanosheet structure with uniform doping of N and F; and the catalyst is rich in N vacancies.

[0047] The present application also provides a nitrogen and fluorine co-doped transition metal-free dual-site catalyst prepared by the above preparation method or the application of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst in water treatment.

[0048] The application further provides a water treatment method, comprising the following process: a nitrogen and fluorine co-doped transition metal-free dual-site catalyst prepared by the preparation method in the above technical solution or the nitrogen and fluorine co-doped transition metal-free dual-site catalyst in the above technical solution removes pollutants in water by catalyzing persulfate.

[0049] Preferably, the ratio of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst to the persulfate is 0.2 g:(0.2-5) mmol, more preferably 0.2 g:(0.1-1.5) mmol, and even more preferably 0.2 g:(0.1-1.0) mmol. In the embodiments provided in the application, the ratio of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst to the persulfate is specifically 0.2 g:0.65 mmol.

[0050] Preferably, the pollutants are one or more of phenolic pollutants, antibiotic pollutants, and other PPCPs pollutants; preferably, the phenolic pollutants are one or more of bisphenol A, phenol, and p-chlorophenol; preferably, the antibiotic pollutants are sulfamethoxazole and / or sulfamethizole; and preferably, the other PPCPs pollutants are sulfonamides and / or ofloxacin.

[0051] Preferably, the pH value of the water is 3-11; in the embodiments provided in the application, the pH value of the water is specifically 3, 5, 7.1, 8.3, 9.5, or 10.8.

[0052] In order to further illustrate the application, the nitrogen and fluorine co-doped transition metal-free dual-site catalyst provided in the application, the preparation method and application thereof are described in detail below in combination with comparative examples and embodiments.

[0053] The reagents used in the following comparative examples and embodiments are commercially available.

[0054] Comparative Example 1

[0055] Preparation of a nitrogen and fluorine doped carbon catalyst without montmorillonite mediation:

[0056] (1) 0.6 g of melamine was added to 2 ml of deionized water, and then was blended with 0.8 g of polytetrafluoroethylene, and was ultrasonically treated for 35 min (the power of the ultrasonic treatment was 400 W) to obtain a precursor material;

[0057] (2) The precursor material obtained in step (1) was treated by pyrolysis for 1 h (the heating rate was 13℃ / min, and the pyrolysis temperature was 550℃) to obtain a nitrogen and fluorine doped carbon catalyst without montmorillonite mediation.

[0058] Example 1

[0059] Preparation of a nitrogen and fluorine co-doped transition metal-free dual-site catalyst:

[0060] (1) 0.5 g of sodium-based montmorillonite was blended with 0.6 g of melamine, 1.5 ml of deionized water was added, and then 400 W ultrasonic dispersion was performed for 20 min to obtain a first mixture;

[0061] (2) The first mixture obtained in step (1) was blended with 0.8 g of polytetrafluoroethylene, and then 0.5 ml of deionized water was added, and 400 W ultrasonic dispersion was performed for 15 min to obtain a second mixture;

[0062] (3) The second mixture obtained in step (2) was treated by pyrolysis, the pyrolysis heating rate was 13℃ / min, the pyrolysis heating end temperature was 550℃, and the pyrolysis was kept for 1 h to obtain a nitrogen and fluorine co-doped transition metal-free dual site catalyst.

[0063] Referring to Figure 2 , Figure 3 , Figure 4 and Figure 5 . Figure 2 Scanning electron microscope image (A) and transmission electron microscope image (B) of the nitrogen and fluorine co-doped transition metal-free dual site catalyst obtained in Example 1 of the present application; from Figure 2 it can be seen that the synthesized nitrogen and fluorine co-doped transition metal-free dual site catalyst has a 3D nanosheet structure. Figure 3 High-resolution transmission electron microscope image and corresponding element analysis image of the nitrogen and fluorine co-doped transition metal-free dual site catalyst obtained in Example 1 of the present application; from Figure 3 it can be seen that the synthesized dual site catalyst has a high N, F doping content, and N, F elements are uniformly distributed on the carbon carrier. Figure 4 X-ray absorption spectrum N K-edge spectrum (A) and F K-edge spectrum (B) of the nitrogen and fluorine co-doped transition metal-free dual site catalyst obtained in Example 1 of the present application; from Figure 4 it can be seen that N and F elements are bonded with C, and there is a strong electronic interaction between C and F, indicating that N and F are successfully co-doped. Figure 5 C / N ratio statistical result comparison graph (A) and electron paramagnetic resonance spectrum (B) of the nitrogen and fluorine co-doped transition metal-free dual site catalyst obtained in Example 1 of the present application and the nitrogen and fluorine doped carbon catalyst prepared in Comparative Example 1; Figure 5 it can be seen from

[0064] Example 2

[0065] Application of the nitrogen and fluorine co-doped transition metal-free dual site catalyst in the treatment of phenol wastewater by activating persulfate;

[0066] The nitrogen and fluorine co-doped transition metal-free dual site catalyst obtained in Example 1 was added to a solution with 20 mg / L phenol as the removal object (pH value was 7), the addition amount was 0.2 g / L, and ultrasonic dispersion was performed; stirring was performed at 700 rpm for 20 min to establish a pollutant adsorption-desorption balance; then, persulfate (PMS) was added to the solution, the addition amount was 0.65 mM; the stirring speed was maintained at 700 rpm, and 100% of the phenol was removed within 20 min. At the same time, a control group experiment was set, and the catalyst added in the control group experiment was the nitrogen and fluorine doped carbon catalyst without montmorillonite mediation obtained in Comparative Example 1.

[0067] Referring to Figure 6 . Figure 6 The activity comparison chart of the nitrogen and fluorine co-doped transition metal-free dual site catalyst prepared by montmorillonite mediation of the present application and the nitrogen and fluorine doped carbon catalyst without montmorillonite mediation obtained in Comparative Example 1 in the treatment of phenol wastewater; it can be seen from Figure 6 that the activity of the nitrogen and fluorine co-doped transition metal-free dual site catalyst prepared by montmorillonite mediation is increased by one to two orders of magnitude compared with the nitrogen and fluorine doped carbon catalyst without montmorillonite mediation.

[0068] Example 3

[0069] Application of the nitrogen and fluorine co-doped transition metal-free dual site catalyst in the treatment of various phenolic wastewater, antibiotic wastewater and other drug and personal care product (PPCPs) pollutant wastewater:

[0070] The nitrogen and fluorine co-doped transition metal-free dual site catalyst obtained in Example 1 was added to a solution with 20 mg / L different pollutants as the removal object (pH value was 7), the addition amount was 0.2 g / L, and ultrasonic dispersion was performed; stirring was performed at 700 rpm for 20 min to establish a pollutant adsorption-desorption balance; then, persulfate (PMS) was added to the solution, the addition amount was 0.65 mM; the stirring speed was maintained at 700 rpm.

[0071] Referring to Figure 7 , Figure 7 The degradation capacity chart of the nitrogen and fluorine co-doped transition metal-free dual site catalyst of the present application in the treatment of various phenolic pollutants, antibiotic pollutants and other drug and personal care product (PPCPs) pollutants; it can be seen from Figure 7 that the nitrogen and fluorine co-doped transition metal-free dual site catalyst of the present application has excellent catalytic degradation capacity for various different pollutants, 100% of the pollutants can be removed within 20 min for bisphenol A, p-chlorophenol, sulfonamide and sulfamethazine, 70% of the pollutants can be removed within 20 min for sulfamethoxazole, and 94.3% of the pollutants can be removed within 20 min for ofloxacin.

[0072] Example 4

[0073] Application of nitrogen and fluorine co-doped transition metal-free dual site catalyst in removal of phenol wastewater in presence of different interfering ions:

[0074] The nitrogen and fluorine co-doped transition metal-free dual site catalyst obtained in Example 1 was added into a solution containing 40 mM Cl - , NO3 - and SO4 2- , with 20 mg / L of phenol as the removal object (pH value was 7), the adding amount was 0.2 g / L, and ultrasonic dispersion was performed; 20 min of stirring at 700 rpm was performed to establish the pollutant adsorption-desorption balance; then, persulfate (PMS) was added into the solution, the adding amount was 0.65 mM; the stirring speed was maintained at 700 rpm, and 100% of the phenol could be removed within 20 min.

[0075] Referring to Figure 8 , Figure 8 Figure is a treatment capacity diagram of the nitrogen and fluorine co-doped transition metal-free dual site catalyst of the present application on the phenol wastewater containing different interfering ions; it can be seen from the Figure 8 that the nitrogen and fluorine co-doped transition metal-free dual site catalyst of the present application has excellent anti-interference ability on various different high-concentration interfering ions.

[0076] Example 5

[0077] Application of nitrogen and fluorine co-doped transition metal-free dual site catalyst in removal of phenol wastewater in presence of humic acid:

[0078] The nitrogen and fluorine co-doped transition metal-free dual site catalyst obtained in Example 1 was added into a solution containing 20 mg / L of phenol as the removal object, and the humic acid concentration was 5 mg / L (pH value was 7), the adding amount was 0.2 g / L, and ultrasonic dispersion was performed; 20 min of stirring at 700 rpm was performed to establish the pollutant adsorption-desorption balance; then, persulfate (PMS) was added into the solution, the adding amount was 0.65 mM; the stirring speed was maintained at 700 rpm, and 100% of the phenol could be removed within 20 min.

[0079] Referring to Figure 9 , Figure 9 Figure is a treatment capacity diagram of the nitrogen and fluorine co-doped transition metal-free dual site catalyst of the present application on the phenol wastewater containing humic acid; it can be seen from the Figure 9 that the nitrogen and fluorine co-doped transition metal-free dual site catalyst of the present application has excellent anti-interference ability on humic acid.

[0080] Example 6

[0081] Application of nitrogen and fluorine co-doped transition metal-free dual site catalyst in treatment of phenol wastewater under different pH conditions:

[0082] The nitrogen and fluorine co-doped transition metal-free dual-site catalyst obtained in Example 1 was added into a solution with 20 mg / L phenol as the removal object, the pH values of the solution were 3, 5, 7.1, 8.3, 9.5 and 10.8 respectively (0.5M NaOH and 0.5M H2SO4 solution were used to adjust the pH value of the solution), the catalyst dosage was 0.2 g / L, and ultrasonic dispersion was carried out; stirring was carried out at 700 rpm for 20 min to establish the adsorption-desorption equilibrium of the pollutants; then, persulfate (PMS) was added into the solution, and the dosage was 0.65 mM; the stirring speed was maintained at 700 rpm.

[0083] Referring to Figure 10 , Figure 10 Figure is the treatment capacity diagram of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst of the present application for phenol wastewater with different pH values; it can be seen from Figure 10 that the nitrogen and fluorine co-doped transition metal-free dual-site catalyst of the present application has a wide pH application range; when the pH value is 3, 5, 7.1, 8.3 and 9.5, the phenol removal rate can reach 100% within 20 min; when the pH value is 10.8, the phenol removal rate can reach 70% within 20 min.

[0084] In summary, the synthesis and application method of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst provided by the present application has the following advantages:

[0085] 1. The present application utilizes the catalytic properties and adsorption neutralization effect of montmorillonite to accelerate the pyrolysis reaction, realize the uniform growth of carbon materials and the uniform and efficient co-doping of N and F, and at the same time, montmorillonite can adsorb and consume hydrogen fluoride generated in the pyrolysis process of fluorine precursor, thereby relieving the corrosion effect of hydrogen fluoride on carbon materials;

[0086] 2. The montmorillonite-mediated N and F co-doping method of the present application uses montmorillonite as an in-situ template and removes it in-situ during the synthesis process, thereby forming a 3D nanosheet structure with regular morphology, which is beneficial to the exposure of active sites;

[0087] 3. The montmorillonite-mediated synthesis strategy of the present application can introduce two adsorption-catalysis dual sites, i.e. F sites with rich electrons and N vacancies with electron deficiency, into the catalyst, thereby greatly improving the utilization efficiency of oxidizing agents and being beneficial to obtaining high catalytic performance and reducing costs in the process of industrial application;

[0088] 4. The montmorillonite-mediated synthesis strategy of the present application uses inexpensive and widely available montmorillonite, nitrogen-rich carbon precursor and fluorine precursor as raw materials, thereby avoiding the use of highly toxic fluorine reagents and greatly reducing secondary pollution and high costs;

[0089] 5、The nitrogen and fluorine co-doped transition metal-free dual-site catalyst synthesized by the montmorillonite mediation of the application is used for catalyzing and activating persulfate to remove pollutants in water, has the advantages of 100% selectivity of producing singlet oxygen, high selectivity of pollutant removal, strong anti-interference ability, good catalytic stability, no risk of heavy metal dissolution and wide pH application range;

[0090] 6、The nitrogen and fluorine co-doped transition metal-free dual-site catalyst synthesized by the montmorillonite mediation of the application has the advantages of simple preparation technology, strong operability, remarkable effect, obvious economy and wide industrial application prospect in the fields of catalysis and environmental pollution purification.

[0091] The above only describes the preferred embodiments of the application, and it should be noted that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements should also be considered within the protection scope of the application.

Claims

1. A process for the preparation of a nitrogen-fluorine co-doped transition metal-free dual site catalyst, characterized in that, The preparation method comprises the following steps: S1) ultrasonic blending of montmorillonite, nitrogen-rich carbon precursor and water to obtain a first mixture; S2) ultrasonic blending of the first mixture and fluorine precursor to obtain a second mixture; S3) pyrolysis of the second mixture to obtain a nitrogen and fluorine co-doped transition metal-free dual-site catalyst; The montmorillonite is selected from hydrogen-based montmorillonite and / or sodium-based montmorillonite; the fluorine precursor is selected from polytetrafluoroethylene and / or polyvinylidene fluoride; and the mass ratio of the montmorillonite to the fluorine precursor is 0.5:(0.4-2). In step S3), the heating rate of the pyrolysis is 2-20 ℃ / min; the final temperature of the pyrolysis is 450-650 ℃; and the holding time of the pyrolysis is 0.5-3 h.

2. The production method according to claim 1, characterized by, The nitrogen-rich carbon precursor is selected from one or more of melamine, dicyandiamide and urea.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the montmorillonite to the nitrogen-rich carbon precursor is 0.5:(0.5-3). The mass ratio of the montmorillonite to water is 0.5:(1-4).

4. The production method according to claim 1, characterized by, In step S1), the ultrasonic blending time is 5-60 min. In step S2), the ultrasonic blending time is 5-60 min.

5. A nitrogen-fluorine co-doped transition metal-free dual site catalyst characterized in that, Prepared by the preparation method according to any one of claims 1-4; the nitrogen and fluorine co-doped transition metal-free dual-site catalyst is a 3D nanosheet structure uniformly doped with N and F, and the catalyst contains N vacancies.

6. The nitrogen and fluorine co-doped transition metal-free dual-site catalyst prepared by the preparation method according to any one of claims 1-4 or the nitrogen and fluorine co-doped transition metal-free dual-site catalyst according to claim 5 is applied to water treatment.

7. A method of water treatment, characterized by, The preparation method comprises the following processes: The nitrogen and fluorine co-doped transition metal-free dual-site catalyst prepared by the preparation method according to any one of claims 1-4 or the nitrogen and fluorine co-doped transition metal-free dual-site catalyst according to claim 5 is used to remove pollutants in water by catalyzing activation of persulfate.

8. The method of claim 7, wherein, The ratio of the nitrogen and fluorine co-doped transition metal-free dual-site catalyst to persulfate is 0.2 g:(0.2-5) mmol.

9. The method of claim 7, wherein, The pollutants include one or more of phenolic pollutants, antibiotic pollutants and other drug and personal care product pollutants; the phenolic pollutants are selected from one or more of bisphenol A, phenol and p-chlorophenol; the antibiotic pollutants are selected from sulfamethoxazole and / or sulfamethopyrazine; and the other drug and personal care product pollutants are selected from sulfonamides and / or ofloxacin.

10. The method of claim 7, wherein, The pH value of the water is 3-11.

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