Preparation method of boron-nitrogen co-doped cobalt monatomic catalyst

Abstract

The invention relates to the technical field of wastewater treatment, and particularly provides a preparation method of a boron-nitrogen co-doped cobalt monatomic catalyst, which comprises the following steps: S1, synthesizing a boron-nitrogen functionalized graphene quantum dot solution based on a graphene quantum dot precursor, an amino precursor and a boron source; and S2, obtaining the boron-nitrogen co-doped cobalt monatomic catalyst based on the boron-nitrogen functionalized graphene quantum dot solution, a cobalt source, a nitrogen source and carbon particles. According to the preparation method disclosed by the embodiment of the invention, cobalt and boron-nitrogen functional groups are subjected to chelation reaction, and cobalt monoatoms are stably and uniformly anchored on the surface of the cobalt monoatoms to improve the dispersity of the monoatoms, so that the purposes of preventing cobalt monoatom aggregation and improving the metal utilization rate are achieved. The prepared cobalt monatomic catalyst not only has high metal loading capacity (the cobalt metal loading capacity in the catalyst can reach 6-10 wt%) and monatomic dispersity, but also has high two-electron oxygen reduction capacity, and the number of active sites and the metal utilization rate in the persulfate activation process are remarkably increased.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly relates to a preparation method of a boron and nitrogen co-doped cobalt single-atom catalyst. Background Art

[0002] The electro-activated persulfate advanced oxidation technology is often used for the treatment of organic wastewater. Its specific principle is that under the action of an electric field, active oxidation species are generated by the electron transfer of persulfate at the cathode to degrade pollutants in the wastewater. However, due to the negative charges of both persulfate and the cathode and the occurrence of cathode side reactions, the efficiency of electro-activating persulfate alone is low. Transition metal single-atom catalysts have been increasingly studied and used in the fields of catalysis and electrocatalysis due to their high metal atom utilization rate, good catalytic activity and selectivity.

[0003] However, the preparation methods of transition metal single-atom catalysts have defects such as low dispersion of metal single atoms and easy agglomeration, which will affect the activation of persulfate and the removal efficiency of pollutants. The single-atom catalyst derived from graphene quantum dots as a carrier can effectively ensure the dispersion and loading amount of metals.

[0004] Therefore, there is an urgent need to provide a metal single-atom catalyst with high dispersion, heteroatom doping, and capable of effectively coupling multiple persulfate activation paths. Summary of the Invention

[0005] Considering that there are multiple persulfate activation paths, such as catalyst activation, electro-activation, alkali activation, and hydrogen peroxide activation. How to design and improve the catalyst to integrate multiple persulfate activation paths and improve the multi-effect synergy of the single-atom catalyst is of great significance.

[0006] Heteroatom-doped metal single-atom catalysts show good development prospects in the multi-effect synergistic activation of persulfate. On the one hand, such heteroatom-doped single-atom catalysts can change the charge distribution around metal atoms, promote electron transfer and increase active sites, and are commonly used for the heterogeneous catalysis of persulfate; on the other hand, heteroatom-doped metal single atoms can also efficiently undergo a two-electron oxygen reduction reaction under the action of an electric field, and the generated hydrogen peroxide and the alkaline environment at the cathode can both effectively activate persulfate.

[0007] The inventor of the present invention has found through repeated research and a large number of experiments that a single-atom catalyst derived from graphene quantum dots can provide sites for the anchoring of a large number of isolated metal single atoms, and has the characteristics of high metal dispersion and loading, which can significantly improve the activation of persulfate and the removal efficiency of pollutants. Further, a metal single-atom catalyst doped with nitrogen and heteroatoms can effectively promote the multi-effect synergistic activation of persulfate. The boron-nitrogen functionalized structure contributes to the adsorption of persulfate and electron transfer, promotes the cleavage of the O-H and O-O bonds of persulfate molecules, and thus is conducive to the generation of reactive oxygen species, realizing the degradation of pollutants through free radical and non-free radical pathways. Moreover, the boron-nitrogen structure can also catalyze the two-electron oxygen reduction reaction, and its products hydrogen peroxide and the alkaline environment at the cathode can further improve the activation efficiency of persulfate. Therefore, the preparation of a cobalt single-atom catalyst co-doped with boron and nitrogen can effectively improve the degradation efficiency of organic substances, and on this basis, the present invention has been completed.

[0008] The object of the present invention is to provide a preparation method of a cobalt single-metal catalyst doped with nitrogen and boron heteroatoms, with high metal single-atom dispersion and loading, and capable of effectively coupling multiple persulfate activation paths.

[0009] According to the preparation method of the boron-nitrogen co-doped cobalt single-atom catalyst of the embodiment of the present invention, it includes:

[0010] Step S1, synthesizing a boron-nitrogen functionalized graphene quantum dot solution based on a graphene quantum dot precursor, an amino precursor, and a boron source;

[0011] Step S2, obtaining a boron-nitrogen co-doped cobalt single-atom catalyst based on the boron-nitrogen functionalized graphene quantum dot solution, a cobalt source, a nitrogen source, and carbon particles.

[0012] In some embodiments of the present invention, the step S1 includes:

[0013] Step S11, generating an amino-functionalized graphene quantum dot solution by using the graphene quantum dot precursor and the amino precursor;

[0014] Step S12, dispersing the boron source in deionized water to obtain a boron precursor solution;

[0015] Step S13, generating the boron-nitrogen functionalized graphene quantum dot solution based on the amino-functionalized graphene quantum dot solution and the boron precursor solution.

[0016] Further, the step S11 includes:

[0017] Step S111, dispersing the graphene quantum dot precursor in deionized water, introducing the amino precursor therein, and performing ultrasonic treatment while stirring and mixing to obtain a first mixture;

[0018] Step S112, placing the first mixed liquid in a hydrothermal reaction kettle, heating it at 180-220° C. for 8-12 hours, and then naturally cooling it to room temperature to obtain a first coolant;

[0019] Step S113, filtering the first cooling liquid through a membrane with a pore size of 0.22 micrometers, and then evaporating and drying to obtain a first concentrated liquid, and then dialyzing the first concentrated liquid in a dialysis bag (4-6 kDa) to obtain an amino-functionalized graphene quantum dot solution;

[0020] Furthermore, in step S111, the graphene quantum dot precursor is one or more of 1,3,6-trinitropyrene, 1,3,6,8-tetranitropyrene, and 9-nitroanthracene, and the amino precursor is one or more of ammonia water and ammonia gas, and the method of introducing the amino precursor is to continuously introduce ammonia gas or add an excess of concentrated ammonia water at one time. Here, the purpose of introducing the amino precursor is to functionalize the graphene quantum dots with amino groups so that the metal can be more easily anchored and attached later.

[0021] Furthermore, in step S12, the boron source is one or more of boric acid and boron oxide.

[0022] Furthermore, the step S13 includes:

[0023] Step S131, mixing the boron precursor solution with the amino-functionalized graphene quantum dot solution, and subjecting the mixture to ultrasonic treatment for 3-5 hours to obtain a second mixed solution;

[0024] Step S132, placing the second mixed liquid in a hydrothermal reaction kettle, heating it at 180-220° C. for 8-12 hours, and then naturally cooling it to room temperature to obtain a second coolant;

[0025] Step S133, placing the second coolant in a dialysis bag for dialysis to obtain the boron-nitrogen functionalized graphene quantum dot solution.

[0026] Furthermore, the power of the ultrasonic treatment in step S131 is 400-800W.

[0027] Furthermore, the specification of the dialysis bag in step S133 is 4-6 kDa.

[0028] In some embodiments of the present invention, step S2 includes:

[0029] Step S21, dispersing the cobalt source into deionized water to obtain a cobalt precursor solution;

[0030] Step S22: Mix the cobalt precursor solution with the boron and nitrogen functionalized graphene quantum dot solution to obtain a cobalt-boron-nitrogen co-doped graphene quantum dot solution. Subsequently, place it in an ice water environment and ultrasonically treat it for 15 - 20 minutes. Freeze-dry the obtained solution for 48 - 72 hours to obtain cobalt-boron-nitrogen co-doped graphene quantum dot powder;

[0031] Step S23: Thoroughly grind the cobalt-boron-nitrogen co-doped graphene quantum dot powder with a nitrogen source, place it in a tube furnace for heating, and mechanically ball-mill the obtained product with carbon particles to obtain the boron and nitrogen co-doped cobalt single-atom catalyst.

[0032] Further, in step S21, the cobalt source is one or more of cobalt sulfate, cobalt acetate, cobalt chloride, and cobalt nitrate.

[0033] In step S22, corresponding to the concentration of cobalt element in the cobalt precursor solution of 0.005 - 0.02 μM, take 0.7 - 1.5 mL of boron and nitrogen functionalized graphene quantum dot solution and mix it with the cobalt precursor solution.

[0034] Even further, step S23 includes:

[0035] Step S231: Mix and grind the cobalt-boron-nitrogen co-doped graphene quantum dot powder with a nitrogen source to obtain a premix;

[0036] Step S232: Place the premix in a tube furnace, heat it to 500 - 600 °C within 1 hour in an argon environment and hold for 1.5 - 2.5 hours, and then naturally cool it to room temperature to obtain a heated product;

[0037] Step S233: Mechanically ball-mill the heated product with carbon particles to obtain the boron and nitrogen co-doped cobalt single-atom catalyst.

[0038] Even further, in step S231, the nitrogen source is one or more of urea and guanidine hydrochloride.

[0039] In the premix, the mass ratio of the cobalt-boron-nitrogen co-doped graphene quantum dot powder to the nitrogen source is 1:(10 - 15).

[0040] Even further, in step S233, the carbon particles are one or more of carbon black, acetylene black, and carbon nanotubes, and the mass ratio of the heated product to the carbon particles is (10 - 15):(15 - 20).

[0041] At least one of the above technical solutions of the present invention has the following beneficial effects:

[0042] According to the preparation method of the embodiments of the present invention, cobalt chelates with the boron-nitrogen functional groups on the graphene quantum dots, enabling cobalt single atoms to be stably and uniformly anchored on their surfaces to improve the single-atom dispersion, thereby achieving the purpose of preventing the aggregation of cobalt single atoms and increasing the metal loading. The prepared cobalt single-atom catalyst not only has a high metal loading (the cobalt metal loading in the catalyst can be as high as 6-10 wt%), but also can synergistically activate persulfate through various paths such as heterogeneous activation, electro-generated hydrogen peroxide activation, and alkali activation, effectively improving the activation efficiency of the single-atom catalyst. Description of the Drawings

[0043] Figure 1 It is the spherical aberration electron microscope image of the finished catalyst obtained in Example 1 of the present invention;

[0044] Figure 2 It is the comparison chart of the degradation effects of the finished catalyst obtained in Example 1 of the present invention and the catalysts of Comparative Examples 1-3 on primidone. Detailed Embodiments

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0046] First, the preparation method of the boron-nitrogen co-doped cobalt single-atom catalyst according to the embodiments of the present invention will be specifically described below.

[0047] The preparation method of the boron-nitrogen co-doped cobalt single-atom catalyst according to the embodiments of the present invention includes:

[0048] Step S1, synthesizing a boron-nitrogen functionalized graphene quantum dot solution based on a graphene quantum dot precursor, an amino precursor, and a boron source;

[0049] Step S2, obtaining a boron-nitrogen co-doped cobalt single-atom catalyst based on the boron-nitrogen functionalized graphene quantum dot solution, a cobalt source, a nitrogen source, and carbon particles.

[0050] That is to say, according to the preparation method of the present invention, first, a boron-nitrogen functionalized graphene quantum dot solution is synthesized. Thereafter, boron-nitrogen co-doping is carried out with cobalt using the boron-nitrogen functionalized graphene quantum dot particles, and after mechanical ball milling with carbon particles, a boron-nitrogen co-doped cobalt single-atom catalyst is obtained.

[0051] According to the method of an embodiment of the present invention, by preparing boron and nitrogen functionalized graphene quantum dots and anchoring cobalt single atoms thereon, a chelation reaction occurs between cobalt and boron and nitrogen functional groups, enabling the cobalt single atoms to be stably and uniformly dispersed on their surface to achieve the purpose of increasing the metal loading amount and preventing the aggregation of cobalt single atoms. The prepared cobalt single atom catalyst not only has a high metal loading amount (the cobalt metal loading amount in the catalyst can be as high as 6-10 wt%), but also has a high single atom dispersion degree, significantly increasing the number of active sites and the metal utilization rate.

[0052] In addition, the boron and nitrogen functionalized structure formed by the doped boron element and nitrogen element not only has good electrical conductivity to promote electron transfer, but also can promote the generation of the 2-electron oxygen reduction reaction. Its product hydrogen peroxide and the alkaline environment of the cathode can further activate persulfate to degrade pollutants, which can not only improve the degradation efficiency of pollutants, but also effectively reduce the degradation cost per unit of pollutants, providing a novel and efficient catalyst for the persulfate advanced oxidation technology.

[0053] Next, a detailed description will be given one by one of the synthesis of the boron and nitrogen functionalized graphene quantum dot solution and the synthesis of the boron and nitrogen co-doped cobalt single atom catalyst.

[0054] (I) Synthesis of the boron and nitrogen functionalized graphene quantum dot solution

[0055] In some embodiments of the present invention, the synthesis of the boron and nitrogen functionalized graphene quantum dot solution may specifically include three steps: the amino functionalization of graphene quantum dots, the preparation of a boron precursor, and the synthesis of the boron and nitrogen functionalized graphene quantum dot solution.

[0056] Specifically, in some embodiments of the present invention, the synthesis of the boron and nitrogen functionalized graphene quantum dot solution includes the following steps:

[0057] Step S11, using the graphene quantum dot precursor and the amino precursor to generate an amino functionalized graphene quantum dot solution.

[0058] That is to say, first, the graphene quantum dot precursor and the amino precursor are used to generate an amino functionalized graphene quantum dot solution.

[0059] More specifically, step S11 may include:

[0060] Step S111, dispersing the graphene quantum dot precursor in deionized water, introducing the amino precursor therein, and performing ultrasonic treatment while stirring and mixing to obtain a first mixed solution.

[0061] In some embodiments of the present invention, the graphene quantum dot precursor may be, for example, one of 1,3,6-trinitropyrene, 1,3,6,8-tetranitropyrene, and 9-nitroanthracene.

[0062] In some embodiments, for example, ammonia gas (as an amino precursor) can be continuously introduced during the ultrasonic process.

[0063] In addition, in some embodiments, aqueous ammonia (as an amino precursor) and graphene quantum dot precursors can also be dispersed in deionized water at one time.

[0064] Step S112: Place the first mixture in a hydrothermal reaction kettle, heat it at a temperature of 180 - 220 °C for 8 - 12 hours, and then naturally cool it to room temperature to obtain a first cooling liquid.

[0065] The graphene quantum dot precursor serves as a carbon source, and graphene quantum dots are generated through a hydrothermal reaction. It has abundant edge sites, which is conducive to the attachment of amino groups derived from the amino precursor. The role of the amino precursor is to provide amino groups so that the amino groups attach to the edges of the graphene quantum dots to obtain amino-functionalized graphene quantum dots.

[0066] Step S113: Filter the first cooling liquid using a membrane with a pore size of 0.22 microns, then evaporate and dry it to obtain a first concentrated liquid. Subsequently, place the first concentrated liquid in a dialysis bag (4 - 6 kDa) for dialysis to obtain an amino-functionalized graphene quantum dot solution.

[0067] Among them, the role of the dialysis bag is to remove contaminants and unreacted small molecules.

[0068] Step S12: Disperse the boron source in deionized water to obtain a boron precursor solution.

[0069] Boric acid will react with the oxygen functional groups on the edges of the amino-functionalized graphene quantum dots in the subsequent hydrothermal reaction to form nitrogen-boron-oxygen bonds (N - B - O), thereby effectively increasing the doping amount of nitrogen and boron elements.

[0070] In some embodiments of the present invention, the boron source can be, for example, one or more of boric acid and boron oxide.

[0071] Step S13: Generate the boron and nitrogen co-functionalized graphene quantum dot solution based on the amino-functionalized graphene quantum dot solution and the boron precursor solution.

[0072] That is to say, after separately preparing amino-functionalized graphene quantum dot particles and a boron precursor solution, these two materials are used to prepare a boron and nitrogen co-functionalized graphene quantum dot solution.

[0073] In some embodiments of the present invention, step S13 includes:

[0074] Step S131: Mix the boron precursor solution with the amino-functionalized graphene quantum dot solution, and perform ultrasonic treatment on it for 3 - 5 hours to obtain a second mixture;

[0075] Step S132: Place the second mixture into a hydrothermal reactor and heat it at a temperature of 180 - 220 °C for 8 - 12 hours, and then naturally cool it to room temperature to obtain the second coolant.

[0076] Step S133: Dialyze the second coolant in a dialysis bag to obtain the boron and nitrogen functionalized graphene quantum dot solution.

[0077] In addition, the power of the ultrasonic treatment is set to 400 - 800 W, for example. Of course, the power of the ultrasonic treatment can be appropriately adjusted according to the operation time and the total amount of the solution.

[0078] In addition, the specification of the dialysis bag in Step S133 can be set to 4 - 6 kDa, for example. There is no strict limitation on the specification of the dialysis bag. For example, it can be comprehensively adjusted by combining the hydrothermal time, temperature, etc.

[0079] It should be noted that the boron and nitrogen co - doping in the catalyst of the present invention can change the electron distribution near the heteroatom, promote the electron to shift from the inside to the outside, that is, from the heteroatom to the nearby carbon atoms, form an electron channel and promote electron transfer. This structure plays two roles in the catalyst. First, the boron and nitrogen co - doping structure is beneficial to weakening the adsorption of the intermediate product hydroxyl radical in the two - electron oxygen reduction reaction, effectively reducing the reaction energy barrier and accelerating the generation rate of hydrogen peroxide, and hydrogen peroxide can be effectively activated to oxidize organic pollutants with persulfate. Second, the boron and nitrogen structure itself has the characteristic of activating persulfate, which can effectively promote the generation of non - radical pathways such as electron transfer, singlet oxygen, and high - valence metals, and play a synergistic role with the radical pathway of cobalt single - atom activating persulfate to achieve the purpose of efficiently degrading pollutants.

[0080] (II) Synthesis of boron and nitrogen co - doped cobalt single - atom catalyst

[0081] In some embodiments of the present invention, the synthesis of the boron and nitrogen co - doped cobalt single - atom catalyst specifically includes three steps, namely: preparation of the cobalt precursor solution, preparation of the cobalt - boron and nitrogen co - doped - graphene quantum dot powder, and full mixing of the cobalt - boron and nitrogen co - doped - graphene quantum dot powder with carbon particles to form the boron and nitrogen co - doped cobalt single - atom catalyst.

[0082] The following will elaborate on each step in detail.

[0083] Step S21: Disperse the cobalt source into deionized water to obtain the cobalt precursor solution.

[0084] That is to say, first prepare the cobalt precursor solution.

[0085] In some embodiments of the present invention, the cobalt source can be selected from one or more of cobalt sulfate, cobalt acetate, cobalt chloride, and cobalt nitrate.

[0086] Step S22: Mix the cobalt precursor solution with the boron and nitrogen functionalized graphene quantum dot solution to form a cobalt-boron-nitrogen co-doped graphene quantum dot solution. Then, place it in an ice water environment for ultrasonic treatment and freeze-dry for 48 - 72 hours to obtain cobalt-boron-nitrogen co-doped graphene quantum dot powder.

[0087] In some embodiments of the present invention, corresponding to the concentration of cobalt element in the cobalt precursor solution being 0.005 - 0.02 μM, take 0.7 - 1.5 mL of boron and nitrogen functionalized graphene quantum dot solution and mix it therewith. Too little cobalt element is likely to reduce the metal loading amount, while too much cobalt element is likely to reduce the single-atom dispersion and increase the probability of forming clusters.

[0088] To mix evenly, it can be placed in an ice water bath for ultrasonic treatment. The power of the ultrasonic treatment can be set, for example, to 400 - 800 w, and the duration of the ultrasonic treatment can be set to 15 - 20 minutes.

[0089] In addition, through freeze-drying, it is possible to well avoid the agglomeration phenomenon that often occurs during heat drying, which helps to improve the particle dispersion.

[0090] In addition, after freeze-drying, it can be ground to obtain cobalt-boron-nitrogen co-doped graphene quantum dot powder with more uniform particle size.

[0091] Step S23: Thoroughly grind the cobalt-boron-nitrogen co-doped graphene quantum dot powder with a nitrogen source, place it in a tube furnace for heating, and mechanically ball-mill the obtained product with carbon particles to obtain the boron-nitrogen co-doped cobalt single-atom catalyst.

[0092] Among them, the carbon particles are one or more of carbon black, acetylene black, and carbon nanotubes.

[0093] The inventors found that the role of the carbon particles not only has the effect of strengthening the anchoring of cobalt single atoms and reducing metal spillage; in addition, the carbon particles themselves have active sites, can catalyze the generation of hydrogen peroxide, and can also enhance the catalytic effect of the two-electron oxygen reduction reaction.

[0094] In some embodiments of the present invention, step S23 may include:

[0095] Step S231: Mix and grind the cobalt-boron-nitrogen co-doped graphene quantum dot powder with a nitrogen source to obtain a premix;

[0096] Step S232: Place the premix in a tube furnace, heat it to 500 - 600 °C within 1 hour in an argon environment and hold for 1.5 - 2.5 hours, and then naturally cool to room temperature to obtain a heated product;

[0097] Step S233: Mechanically ball-mill the heating product and carbon particles to obtain the boron and nitrogen co-doped cobalt single-atom catalyst.

[0098] Among them, the nitrogen source is one or more of urea and guanidine hydrochloride. The role of introducing the nitrogen source is to optimize the nitrogen doping ratio, and by adjusting the doping ratio of boron and nitrogen elements to adjust the boron-nitrogen structure to further improve the activation effect. The role of carbon particles is to further anchor metal single atoms and enhance the electron transfer characteristics of the catalyst, thereby promoting the two-electron oxygen reduction reaction and facilitating the generation of hydrogen peroxide to activate persulfate under the action of an electric field.

[0099] It should be noted here that the purpose of introducing the amino precursor in the process of preparing the boron and nitrogen functionalized graphene quantum dot solution is to achieve the edge functionalization of graphene quantum dots. If too much "nitrogen" is introduced at this time, it will affect the functionalization of graphene quantum dots, thereby affecting the subsequent metal attachment. According to the preparation method of the present invention, "N" is introduced in two steps, that is, the edge functionalization of graphene quantum dots is achieved through the "amino precursor" in the first step, and the nitrogen doping amount is further increased through the "nitrogen source" in the second step. Adjusting the boron-nitrogen ratio and improving the boron-nitrogen structure can achieve a better activation effect.

[0100] In some embodiments of the present invention, in the premix in step S231, the mass ratio of cobalt-boron and nitrogen co-doped-graphene quantum dot powder to the nitrogen source is 1:(10 - 15). In step S233, the mass ratio of the heating product to the carbon particles is (10 - 15):(15 - 20), and the mass ratio is adjusted according to the types of the nitrogen source and carbon particles to obtain the catalyst with the optimal performance.

[0101] In addition, in step S232, the argon flow rate in the tubular furnace can be set to 80 - 120 sccm.

[0102] Through the above preparation method, the boron and nitrogen co-doped cobalt single-atom catalyst is obtained. The catalyst includes carbon particles and boron and nitrogen co-doped cobalt single atoms, and the boron and nitrogen co-doped cobalt single atoms are anchored on the surface of the carbon particles.

[0103] Next, the preparation method of the catalyst of the present invention will be further described in detail through specific examples.

[0104] Example 1

[0105] 1) Preparation of boron and nitrogen functionalized graphene quantum dot solution.

[0106] 1.1) Disperse 1.2 g of 1,3,6-trinitropyrene powder in 220 mL of deionized water, continuously introduce ammonia gas, and use ultrasonic treatment with a power of 600 w for 4 hours while stirring and mixing to obtain a mixed solution;

[0107] 1.2) Place 120 mL of the obtained mixed solution into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, put it into an oven and heat it at 200 °C for 10 hours, and then cool it to room temperature to obtain an amino-functionalized graphene quantum dot solution;

[0108] 1.3) Filter the amino-functionalized graphene quantum dot solution using a membrane with a pore size of 0.22 microns, then evaporate and dry to obtain 90 mL of concentrated solution. Subsequently, place the concentrated solution into a dialysis bag with a specification of 4.5 kDa and dialyze it for 48 hours to obtain a dialysate;

[0109] 1.4) Disperse 0.3 g of boric acid into 30 mL of deionized water to prepare a boron precursor solution;

[0110] 1.5) Mix the boron precursor solution described in 1.4) with the dialysate obtained in 1.3), and ultrasonically treat it with 600 w for 4 hours;

[0111] 1.6) Place 120 mL of the mixed solution obtained in 1.5) into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, put it into an oven and heat it at 200 °C for 20 hours, and then cool it to room temperature;

[0112] 1.7) Dialyze the solution obtained in 1.6) using a dialysis bag with a specification of 4.5 kDa for 48 hours to obtain a boron and nitrogen co-functionalized graphene quantum dot solution.

[0113] 2) Preparation of boron and nitrogen co-doped cobalt single-atom catalyst.

[0114] 2.1) Disperse 1 g of cobalt nitrate into 200 mL of deionized water to prepare a cobalt precursor solution;

[0115] 2.2) Mix the cobalt precursor solution and the boron and nitrogen co-functionalized graphene quantum dot solution according to a volume ratio of 1:10, and then place it in an ice water environment and ultrasonically treat it with a power of 600 w for 15 minutes;

[0116] 2.3) Freeze-dry the solution obtained in 2.2) to obtain cobalt-boron and nitrogen co-doped-graphene quantum dot powder, mix it with urea according to a mass ratio of 1:10 and grind it to obtain a mixture;

[0117] 2.4) Place the mixture obtained in 2.3) into a tube furnace, heat it to 500 °C within 1 hour under an Ar atmosphere of 100 sccm and keep it for 2 hours, and collect the powder after natural cooling to room temperature to obtain a heated product.

[0118] 2.4) Mix the heated product obtained in 2.3) with carbon black according to a mass ratio of 1:1, and make them fully mixed and anchored by mechanical ball milling to obtain a boron and nitrogen co-doped cobalt single-atom catalyst.

[0119] Figure 1The aberration-corrected electron microscopy image of the boron and nitrogen co-doped cobalt single-atom catalyst in Example 1 is shown. It can be seen from Figure 1 that cobalt (i.e., as shown in the circle in the figure) is successfully anchored on the matrix and is dispersed in a single-atom state on the surface of the support.

[0120] Comparative Example 1:

[0121] Referring to Example 1 above, the implementation steps are the same as those in Example 1 except for the following:

[0122] Instead of adding boron element, cobalt single atoms are directly anchored on amino-functionalized graphene quantum dots, and finally a nitrogen-doped cobalt single-atom catalyst is obtained.

[0123] Specifically, steps 1.4), 1.5), 1.6), and 1.7) in Example 1 are not carried out, and the boron and nitrogen-functionalized graphene quantum dot solution used in step 2.2) is replaced with the dialysis solution described in 1.3).

[0124] Comparative Example 2:

[0125] Referring to Example 1, the implementation steps are the same as those in Example 1 except for the following:

[0126] Cobalt single atoms are not loaded (specifically, steps 2.1) and 2.2) are not carried out), and the solution used in step 2.3) is replaced with the boron and nitrogen-functionalized graphene quantum dot solution obtained in step 1.7), and finally a metal-free boron and nitrogen co-doped catalyst is obtained.

[0127] Comparative Example 3:

[0128] Referring to Example 1, the implementation steps are the same as those in Example 1 except for the following:

[0129] Carbon particles are not added (specifically, step 2.4) is not carried out), and a boron and nitrogen co-doped cobalt single-atom catalyst without added carbon particles is obtained.

[0130] In order to study the degradation effect of the catalyst obtained in Example 1, a working electrode was prepared using the boron and nitrogen co-doped cobalt single-atom catalyst obtained in Example 1, and taking PMD (i.e., primidone) as an example, a degradation experiment was carried out to evaluate its degradation effect.

[0131] I. Preparation of the working electrode

[0132] 10 mg of the boron and nitrogen co-doped cobalt single-atom catalyst obtained in Example 1 above, the nitrogen-doped cobalt single-atom catalyst obtained in Comparative Example 1, the metal-free boron and nitrogen co-doped catalyst obtained in Comparative Example 2, and the boron and nitrogen co-doped cobalt single-atom catalyst without added carbon particles obtained in Comparative Example 3 were respectively dispersed in 1 mL of 75% ethanol under ice bath sonication. Subsequently, each slurry was sprayed onto carbon paper using an airbrush and air-dried under natural conditions to obtain the Example 1 electrode, the Comparative Example 1 electrode, the Comparative Example 2 electrode, and the Comparative Example 3 electrode, respectively.

[0133] II. Pollutant degradation experiment.

[0134] Using PMD as the pollutant, a 0.3 mg / L PMD solution was prepared to test the catalytic performance of the boron and nitrogen co-doped cobalt single-atom catalyst, and potassium monohydrogen phosphate and dipotassium hydrogen phosphate composite salts were added to make the concentration 50 mM. An electrolysis experiment was carried out using a three-electrode system, with Ag / AgCl (KCl sat) as the reference electrode, a Pt sheet as the counter electrode, and the electrodes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 above as the working electrodes, respectively. A 10-minute constant potential electrolysis experiment was carried out at a constant potential of -0.3 V vs. RHE.

[0135] The experimental results are shown in Figure 2 . It can be seen from Figure 2 that ten minutes after the start of the experiment, the primidone removal rate of the Example 1 electrode was 96%, while those of Comparative Example 1, Comparative Example 2, and Comparative Example 3 were 80%, 36%, and 76% respectively, indicating that the boron and nitrogen co-doped cobalt single-atom catalyst of Example 1 had the best pollutant degradation ability and stability. This result shows that compared with the nitrogen-doped cobalt single-atom catalyst (i.e., Comparative Example 1), the metal-free boron and nitrogen co-doped catalyst (i.e., Comparative Example 2), and the boron and nitrogen co-doped cobalt single-atom catalyst without added carbon particles (Comparative Example 3), the coupling of cobalt single atoms and boron and nitrogen co-doping effectively improved the pollutant degradation efficiency.

[0136] Example 2:

[0137] Referring to Example 1, the implementation steps were the same as those in Example 1 except for the following content:

[0138] 1.1) 1.2 g of dry 1,3,6-trinitropyrene powder was dispersed in 220 mL of deionized water, mixed with 20 mL of 30% concentrated ammonia water, and sonicated for 4 hours at a power of 600 w while stirring to obtain a mixed solution.

[0139] The experimental results showed that the primidone removal rate in 10 minutes was 92.2%.

[0140] Example 3:

[0141] Referring to Example 1, the implementation steps are the same as it except for the following content:

[0142] 1.1) Disperse 1 g of dry 9-nitroanthracene powder in 220 mL of deionized water, continuously introduce ammonia gas, and while stirring and mixing, use ultrasonic treatment with a power of 600 w for 4 hours to obtain a mixed solution.

[0143] The experimental results show that the primidone removal rate in 10 minutes is 92.7%.

[0144] Example 4:

[0145] Referring to Example 1, the implementation steps are the same as it except for the following content:

[0146] 2.3) Freeze-dry the solution obtained in 2.2) to obtain cobalt-boron-nitrogen co-doped graphene quantum dot powder, and mix it with guanidine hydrochloride in a mass ratio of 1:12 and grind to obtain a mixture;

[0147] The experimental results show that the primidone removal rate in 10 minutes is 93.3%.

[0148] Example 5:

[0149] Referring to Example 1, the implementation steps are the same as it except for the following content:

[0150] 2.4) Mix the heated product obtained in 2.3) with acetylene black in a mass ratio of 1:1, and make them fully mixed and anchored by mechanical ball milling to obtain a boron-nitrogen co-doped cobalt single-atom catalyst.

[0151] The experimental results show that the primidone removal rate in 10 minutes is 91.3%.

[0152] Example 6:

[0153] Referring to Example 1, the implementation steps are the same as it except for the following content:

[0154] 2.1) Disperse 1 g of cobalt sulfate in 200 mL of deionized water to prepare a cobalt precursor solution;

[0155] 2.2) Mix the cobalt precursor solution and the boron-nitrogen functionalized graphene quantum dot solution in a volume ratio of 1:12, and then place it in an ice water environment and use ultrasonic treatment with a power of 600 w for 18 minutes;

[0156] The experimental results show that the primidone removal rate in 10 minutes is 89.7%.

[0157] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a boron and nitrogen co-doped cobalt single-atom catalyst, characterized in that, Including: Step S1: Synthesize a boron and nitrogen functionalized graphene quantum dot solution based on a graphene quantum dot precursor, an amino precursor, and a boron source; Step S2: Obtain a boron and nitrogen co-doped cobalt single-atom catalyst based on the boron and nitrogen functionalized graphene quantum dot solution, a cobalt source, a nitrogen source, and carbon particles.

2. The preparation method according to claim 1, characterized in that, The said Step S1 includes: Step S11: Generate an amino-functionalized graphene quantum dot solution using the graphene quantum dot precursor and the amino precursor; Step S12: Disperse the boron source in deionized water to obtain a boron precursor solution; Step S13: Generate the boron and nitrogen functionalized graphene quantum dot solution based on the amino-functionalized graphene quantum dot solution and the boron precursor solution.

3. The preparation method according to claim 2, characterized in that, The said Step S11 includes: Step S111: Disperse the graphene quantum dot precursor in deionized water, introduce the amino precursor thereto, and perform ultrasonic treatment while stirring and mixing to obtain a first mixture; Step S112: Place the first mixture in a hydrothermal reaction kettle, heat it at a temperature of 180 - 220 °C for 8 - 12 hours, and then naturally cool it to room temperature to obtain a first coolant; Step S113: Filter the first coolant using a membrane with a pore size of 0.22 microns, then evaporate and dry it to obtain a first concentrated solution, and then place the first concentrated solution in a dialysis bag (4 - 6 kDa) for dialysis to obtain the amino-functionalized graphene quantum dot solution.

4. The preparation method according to claim 2, wherein in the said Step S11, the graphene quantum dot precursor is one or more of 1,3,6-trinitropyrene, 1,3,6,8-tetranitropyrene, and 9-nitroanthracene; in the said Step S11, the amino precursor is one or more of ammonia water and ammonia gas; in the said Step S12, the boron source is one or more of boric acid and boron oxide.

5. The preparation method according to claim 2, characterized in that, The said Step S13 includes: Step S131: Mix the boron precursor solution and the amino-functionalized graphene quantum dot solution, and perform ultrasonic treatment thereon for 3 - 5 hours to obtain a second mixture; Step S132: Place the second mixture in a hydrothermal reaction kettle, heat it at a temperature of 180 - 220 °C for 8 - 12 hours, and then naturally cool it to room temperature to obtain a second coolant; Step S133: Place the second coolant in a dialysis bag (4 - 6 kDa) for dialysis to obtain the boron and nitrogen functionalized graphene quantum dot solution.

6. The preparation method according to claim 1, wherein The said Step S2 includes: Step S21: Disperse the cobalt source in deionized water to obtain a cobalt precursor solution; Step S22: Mix the cobalt precursor solution and the boron and nitrogen functionalized graphene quantum dot solution to obtain a cobalt-boron and nitrogen co-doped-graphene quantum dot solution, then perform ultrasonic treatment on it in an ice water environment for 15 - 20 minutes, and freeze-dry the obtained solution for 48 - 72 hours to obtain a cobalt-boron and nitrogen co-doped-graphene quantum dot powder; Step S23: Thoroughly grind the cobalt-boron and nitrogen co-doped-graphene quantum dot powder with the nitrogen source, heat it in a tube furnace, and perform mechanical ball milling on the obtained product with carbon particles to obtain the boron and nitrogen co-doped cobalt single-atom catalyst.

7. The preparation method according to claim 6, wherein in the step S21, the cobalt source is one or more of cobalt sulfate, cobalt acetate, cobalt chloride, and cobalt nitrate, in the step S22, corresponding to the concentration of cobalt element in the cobalt precursor solution being 0.005 - 0.02 μM, 0.7 - 1.5 mL of the boron and nitrogen functionalized graphene quantum dot solution is taken and mixed therewith.

8. The preparation method according to claim 6, characterized in that, The step S23 includes: step S231, mixing and grinding the cobalt - boron and nitrogen co - doped - graphene quantum dot powder with a nitrogen source to obtain a premix; step S232, placing the premix in a tube furnace, heating it to 500 - 600 °C within 1 hour in an argon atmosphere and holding for 1.5 - 2.5 hours, and then naturally cooling to room temperature to obtain a heated product; step S233, mechanically ball - milling the heated product with carbon particles to obtain the boron and nitrogen co - doped cobalt single - atom catalyst.

9. The preparation method according to claim 8, wherein the nitrogen source is one or more of urea and guanidine hydrochloride, in the premix, the mass ratio of the cobalt - boron and nitrogen co - doped - graphene quantum dot powder to the nitrogen source is 1:(10 - 15), in the step S233, the carbon particles are one or more of carbon black, acetylene black, and carbon nanotubes, and the mass ratio of the heated product to the carbon particles is (10 - 15):(15 - 20).

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