A bio-based porous cobalt monatomic catalyst, a preparation method and application thereof

Abstract

The present application provides a kind of bio-based porous cobalt monatomic catalyst and its preparation method and application, it is related to wastewater treatment technical field.The present application mixes urea, dicyandiamide, pore-forming agent and precursor silkworm sand in solvent and disperses, then mixes and disperses with cobalt source, after drying and specific calcination treatment, obtain bio-based porous cobalt monatomic catalyst, wherein, pore-forming agent is at least one of bicarbonate, carbonate.The bio-based porous cobalt monatomic catalyst prepared by the present application can efficiently remove pollutants at room temperature and neutral conditions when treating organic pollutants in water body, can effectively overcome the adverse effects of DOC in water, and as a solid-supported particulate catalyst, it is easy to separate and recycle with water, and has good recycling stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, and particularly relates to a biological-based porous cobalt monatomic catalyst as well as a preparation method and application thereof. BACKGROUND

[0002] In recent years, the acceleration of industrialization has led to the discharge of various types of refractory organic pollutants into water environments at an exponential scale, which has become a long-term and severe public health problem. In order to ensure the supply of clean drinking water and eliminate ecological risks, a variety of water treatment technologies have been developed for application in the field of industrial wastewater and municipal sewage treatment to promote environmental sustainable development and protect drinking water safety. These technologies include physical adsorption, biochemical treatment, chemical conversion, Fenton oxidation, PMS activation, and ferrate oxidation. However, due to the complexity and stability of the structure of refractory organic pollutants, the above-mentioned technologies often fail to achieve efficient removal, and there is a common problem of high energy consumption. In addition, the widespread presence of dissolved organic carbon (DOC) in water bodies not only significantly inhibits the degradation process of organic pollutants, but also can promote the generation of harmful by-products, which undoubtedly makes the remediation of organic pollution in actual water bodies face more daunting challenges.

[0003] Recently, scholars have found that cation-pi interactions can promote the generation of electric fields by adjusting the charge rearrangement between metal ions and pi systems or the coordination of surface pollutants. Moreover, the strength of cation-pi interactions depends on the type of cations and the properties of pi systems, which indicates that the adjacent environment involved plays a key role in regulating the strength of the electric field. This provides the possibility of utilizing cation-pi system coordination to generate electric field energy and achieve low-energy and efficient water treatment. In the past, the construction of cation-pi systems often relied on graphene, but the catalyst prepared from graphene is powdery and not suitable for actual water body treatment. Moreover, the high cost of graphene preparation greatly limits its practical application. SUMMARY

[0004] The present application aims to overcome the deficiencies of the prior art and provides a biological-based porous cobalt monatomic catalyst as well as a preparation method and application thereof.

[0005] To achieve the above-mentioned purpose, in a first aspect, the present application provides a preparation method of a biological-based porous cobalt monatomic catalyst, comprising the following steps:

[0006] mixing and dispersing urea, dicyandiamide, a pore-forming agent, and silkworm excrement in a solvent to obtain dispersion liquid A;

[0007] mixing and dispersing a cobalt source with the dispersion liquid A to obtain dispersion liquid B;

[0008] drying the dispersion liquid B to obtain solid particles;

[0009] The solid particles are calcined at 250-600℃ for 2-6h, and then calcined at 650-900℃ for 1-3h to obtain a solid product, i.e. a bio-based porous cobalt monatomic catalyst.

[0010] The pore-forming agent is at least one of a bicarbonate and a carbonate.

[0011] The catalyst synthesized by the above preparation method has monatomic Co sites and a graphenoid (GL) π system, wherein the monatomic Co has a large specific surface area, which is conducive to improving the utilization rate of Co atoms, and the monatomic Co has high spin, which helps to promote the catalytic degradation of organic pollutants and accelerate the transfer of electric charges; compared with carbon nitride, the electron transport capacity of the graphenoid is stronger, so that the catalytic degradation rate of the organic pollutants is higher. At the same time, the monatomic Co is connected to the GL structure through Co-O-C and Co-N-C chemical coordination bonds, the π electrons on the GL are activated and transferred to the periphery of the monatomic Co through these chemical bond bridges, forming an electron high-density region, and an electron low-density region is formed near the GL, thereby forming a strong electric field on the surface of the catalyst. When the obtained catalyst is used for wastewater treatment, the synergistic coordination of the high-spin monatomic Co sites and the GL sites under the DOC-organic pollutants-H2O causes a strong surface charge rearrangement, producing very strong electric field energy, so that the adsorption groups of the organic pollutants undergo continuous oxidation and homolytic cleavage of adjacent chemical bonds, until complete mineralization. In the entire reaction process, the free radicals produced can continuously charge the catalyst function, without the need for external energy assistance, so as to realize low-energy consumption and efficient purification of wastewater, especially composite wastewater.

[0012] Urea is calcined at 250-600℃ to form a carbon nitride network structure through condensation polymerization, and can play a role of a binder in the condensation polymerization process, coating cobalt and silkworm excrement, and at the same time, compounding with dicyandiamide. Since urea and dicyandiamide have different condensation directions in the formation of the carbon nitride network structure, the formed carbon nitride network structure can better coat cobalt and silkworm excrement, promoting better complexation between cobalt and silkworm excrement, and the synthesized catalyst has better stability. In addition, urea and dicyandiamide further carbonize at 650-900℃, acting as a template to make the silkworm excrement directionally grow at high temperature to form a graphenoid structure.

[0013] The preparation method uses at least one of bicarbonate and carbonate as a pore-forming agent, which has two main functions. One is to act as a pore-forming agent, so that the synthesized catalyst has a uniform porous structure. The other is to act as a reducing agent to avoid the formation of cobalt oxide during the reaction calcination process, and to directionally induce the formation of single-atom Co. However, if a pore-forming agent without reducing properties, such as zinc chloride, zinc nitrate, aluminum chloride, etc., is used, although it has strong pore-forming ability and is uniformly dispersed with other raw materials, the pore structure is uniform, but it cannot form single-atom Co, resulting in low efficiency of the catalyst in catalyzing the degradation of organic pollutants. For example, ammonium chloride, which is weakly acidic, is not easy to disperse uniformly with other raw materials, resulting in uneven pore structure, and it cannot form single-atom Co, so the efficiency of the catalyst in catalyzing the degradation of organic pollutants is low.

[0014] The preparation method uses silkworm excrement as a carbon-based precursor to form a graphene-like structure. Compared with graphite, melamine, dicyandiamide, etc., using silkworm excrement as a carbon-based precursor can form a graphene-like structure, which has stronger electron transport capacity, resulting in a higher rate of catalytic degradation of organic pollutants. Compared with wood chips, silkworm excrement can be better coated with Co during the urea and dicyandiamide polycondensation reaction, and can chemically coordinate with Co. At the same time, using graphite, melamine, dicyandiamide, wood chips, etc. as a carbon-based precursor, the synthesized catalyst is powdery, while using silkworm excrement as a carbon-based precursor, the synthesized catalyst is granular, has good processing stability, is suitable for water treatment, is easy to separate and recover, and silkworm excrement contains various heteroatoms, which is conducive to regulating the coordination charge environment of Co single atoms, making the catalyst have stronger catalytic activity, and the cost is low and easy to obtain.

[0015] The preparation method needs to mix and disperse urea, dicyandiamide, pore-forming agent and precursor silkworm excrement in a solvent, and then mix and disperse with a cobalt source. This is conducive to the interaction between urea and dicyandiamide and the precursor silkworm excrement to form a molecular network complex, and the pore-forming agent is uniformly dispersed in it. After adding the cobalt source, the pore-forming agent reacts with the cobalt source to produce gas, which can open the silkworm excrement channels, allowing them to better adsorb cobalt ions and coordinate with them, and the polycondensation of urea and dicyandiamide is more uniform, and the dispersion of metal atoms in the catalyst is more uniform.

[0016] When the catalyst synthesized by the above preparation method is used to treat organic pollutants in water, it can achieve efficient removal of pollutants at room temperature and neutral conditions. Compared with conventional wastewater oxidation treatment methods, it can effectively overcome the adverse effects of natural organic carbon (DOC) in water on pollutant removal. In addition, the catalyst can retain the morphology of the precursor silkworm excrement particles, which is a solid-supported granular catalyst, easy to separate from water, and has good cycle stability.

[0017] Preferably, the mass ratio of the urea, the dicyandiamide, the pore-forming agent and the cocoon is (0.4-0.75):(1-1.9):(0.1-0.45):1, and the mass ratio of the cocoon to the amount of substance of cobalt element in the cobalt source is 1 g:(0.001-0.0019) mol.

[0018] For example, the mass ratio of the urea, the dicyandiamide, the pore forming agent, and the silk cocoon is 0.40:1.0:0.10:1, 0.50:1.2:0.20:1, 0.60:1.5:0.30:1, 0.70:1.7:0.40:1, 0.75:1.9:0.45:1, 0.40:1.2:0.20:1, 0.40:1.5:0.30:1, 0.40:1.7:0.40:1, 0.40:1.9:0.45:1, 0.50:1.0:0.10:1, 0.50:1.5:0.30:1, 0.50:1.7:0.40:1, 0.50:1.9:0.45:1, 0.60:1.0:0.10:1, 0.60:1.2:0.20:1, 0.60:1.7:0.40:1, 0.60:1.9:0.45:1, 0.70:1.0:0.10:1, 0.70:1.2:0.20:1, 0.70:1.5:0.30:1, 0.70:1.9:0.45:1, 0.75:1.0:0.10:1, 0.75:1.2:0.20:1, 0.75:1.5:0.30:1, 0.75:1.7:0.40:1, 0.50:1.0:0.20:1, 0.60:1.0:0.30:1, 0.70:1.0:0.40:1, 0.75:1.0:0.45:1, 0.40:1.2:0.10:1, 0.60:1.2:0.30:1, 0.70:1.2:0.40:1, 0.75:1.2:0.45:1, 0.40:1.5:0.10:1, 0.50:1.5:0.20:1, 0.70:1.5:0.40:1, 0.75:1.5:0.45:1, 0.40:1.7:0.10:1, 0.50:1.7:0.20:1, 0.60:1.7:0.30:1, 0.75:1.7:0.45:1, 0.40:1.9:0.10:1, 0.50:1.9:0.20:1, 0.60:1.9:0.30:1, 0.70:1.9:0.40:1, 0.50:1.2:0.10:1, 0.60:1.5:0.10:1, 0.70:1.7:0.10:1, 0.75:1.9:0.10:1, 0.40:1.0:0.20:1, 0.60:1.5:0.20:1, 0.70:1.7:0.20:1, 0.75:1.9:0.20:1, 0.40:1.0:0.30:1, 0.50:1.2:0.30:1, 0.70:1.7:0.30:1, 0.75:1.9:0.30:1, 0.40:1.0:0.40:1, 0.50:1.2:0.40:1, 0.60:1.5:0.40:1, 0.75:1.9:0.40:1, 0.40:1.0:0.45:1, 0.50:1.2:0.45:1, 0.60:1.5:0.45:1, or 0.70:1.7:0.45:1, etc.

[0019] For example, the mass ratio of the silkworm excrement to the amount of cobalt in the cobalt source is 1g:0.001mol, 1g:0.0011mol, 1g:0.0012mol, 1g:0.0013mol, 1g:0.0014mol, 1g:0.0015mol, 1g:0.0016mol, 1g:0.0017mol, 1g:0.0018mol, or 1g:0.0019mol.

[0020] More preferably, the mass ratio of urea, dicyandiamide, pore-forming agent and silkworm excrement is (0.47~0.58):(1.1~1.5):(0.355~0.395):1, and the mass ratio of silkworm excrement to the molar amount of cobalt in the cobalt source is 1g:(0.0014~0.0015)mol, so as to make the catalyst have higher catalytic activity.

[0021] More preferably, the mass ratio of urea, dicyandiamide, pore-forming agent and silkworm excrement is 0.5:1.25:0.375:1, and the mass ratio of silkworm excrement to the molar amount of cobalt in the cobalt source is 1g:0.00145mol, so as to improve the catalytic activity of the catalyst. The dosages of urea, dicyandiamide, pore-forming agent, silkworm excrement, and cobalt source should be controlled to meet the following requirements: the mass ratio of urea, dicyandiamide, pore-forming agent, and silkworm excrement should be (0.4~0.75):(1~1.9):(0.1~0.45):1, and the mass ratio of silkworm excrement to the molar amount of cobalt in the cobalt source should be 1g:(0.001~0.0019)mol. Specifically, the mass ratio of urea, dicyandiamide, pore-forming agent, and silkworm excrement should be (0.47~0.58):(1.1~1.5):(0.355~0.395):1, and the mass ratio of silkworm excrement to the molar amount of cobalt in the cobalt source should be 1g:(0.0014~0.0015)mol. Furthermore, the mass ratio of urea, dicyandiamide, pore-forming agent, and silkworm excrement should be 0.5:1.25. The ratio of 0.375:1 and the molar ratio of silkworm excrement to cobalt in the cobalt source is 1g: 0.00145 mol, which makes the condensation of urea, dicyandiamide and silkworm excrement more uniform and less prone to carbonization, with a more developed pore structure, more active sites, less cobalt species agglomeration, less surface oxides, and higher catalytic activity.

[0022] In the process of preparing bio-based porous cobalt single-atom catalysts using the solid particles, they need to be calcined at 250~600℃ (e.g., 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃ or 600℃) for 2~6h (e.g., 2h, 3h, 4h, 5h or 6h), and then calcined at 650~900℃ (e.g., 650℃, 680℃, 700℃, 720℃, 750℃, 780℃, 800℃, 820℃, 850℃, 870℃ or 900℃) for 1~3h (e.g., 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h).

[0023] Preferably, the specific steps for calcining the solid particles at 250~600℃ for 2~6h are as follows: calcining the solid particles at 250~400℃ for 1~3h, and then calcining them at 450~600℃ for 1~3h. The solid particles are first calcined at 250-400℃ (e.g., 250℃, 270℃, 300℃, 320℃, 340℃, 360℃, 380℃, or 400℃) for 1-3 hours (e.g., 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, or 3 hours) to induce semi-condensation polymerization. Then, they are calcined at 450-600℃ (e.g., 450℃, 470℃, 500℃, 520℃, 550℃, 570℃, or 600℃) for 1-3 hours (e.g., 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, or 3 hours). h), to allow it to undergo complete condensation polymerization, which makes the condensation polymerization of urea and dicyandiamide more uniform, prevents excessive carbonization, and forms a more complete network structure with a superior electronic structure, thereby making the catalyst more active.

[0024] Preferably, the pore-forming agent includes at least one of sodium bicarbonate, ammonium bicarbonate, sodium carbonate, potassium bicarbonate, and potassium carbonate.

[0025] More preferably, the pore-forming agent includes ammonium bicarbonate. Using ammonium bicarbonate as a pore-forming agent will result in a more potent catalytic activity in the synthesized catalyst.

[0026] Preferably, the cobalt source includes at least one of cobalt chloride hexahydrate, cobalt sulfate, cobalt acetate, cobalt sulfate heptahydrate, cobalt acetate tetrahydrate, and cobalt nitrate hexahydrate.

[0027] Preferably, during calcination, the heating rate is controlled within the range of 2~20℃ / min. This facilitates the elimination of trace adsorbed water in solid product B, allowing its active species to disperse and denature, and then uniformly doped into the graphene-like structure through chemical bonding. The target catalyst particles are uniform and black in color. The heating rates for each stage of calcination are independent and can be the same or different, such as 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min, or 20℃ / min.

[0028] Preferably, the roasting is carried out in a protective atmosphere, which includes at least one of nitrogen and an inert gas.

[0029] Preferably, the material-to-liquid ratio in the dispersion A is: (urea + dicyandiamide + pore-forming agent + silkworm excrement): solvent = 1g: (2~6)mL, such as 1g:2mL, 1g:2.5mL, 1g:3mL, 1g:3.5mL, 1g:4mL, 1g:4.5mL, 1g:5mL, 1g:5.5mL or 1g:6mL.

[0030] Preferably, the solvent in the dispersion A includes water.

[0031] Preferably, the solid product is further cleaned and dried to obtain a bio-based porous cobalt single-atom catalyst. Water can be used as the cleaning agent; the drying temperature can be selected from 60 to 120°C, and the drying time can be selected from 12 to 36 hours.

[0032] Preferably, in the process of mixing and dispersing urea, dicyandiamide, pore-forming agent and silkworm excrement in a solvent to obtain dispersion A, the dispersion is carried out by stirring at a speed of 10-30 rpm for a time of 1-6 hours.

[0033] Preferably, in the process of mixing and dispersing the cobalt source with the dispersion A to obtain dispersion B, the dispersion is carried out by stirring, with a stirring speed of 10~30 rpm and a stirring time of 1~24 h.

[0034] Preferably, during the drying of the dispersion B to obtain solid particles A, the drying temperature is 80~150℃ and the drying time is 12~72h.

[0035] Secondly, the present invention provides a bio-based porous cobalt single-atom catalyst prepared by the method for preparing the bio-based porous cobalt single-atom catalyst.

[0036] Thirdly, the present invention provides the application of the bio-based porous cobalt single-atom catalyst in the degradation of organic pollutants in water.

[0037] Preferably, the organic pollutant includes at least one of quinolones, phenols, and antihistamines.

[0038] Preferably, the quinolones include at least one of ciprofloxacin (CIP), norfloxacin, and tetracycline.

[0039] Preferably, the phenolic compounds include at least one of bisphenol A (BPA), bisphenol B, bisphenol S, bisphenol F, and bisphenol AF.

[0040] Preferably, the antihistamines include at least one of diphenhydramine (DP) and cetirizine.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] I. The catalyst synthesized in this invention utilizes the synergistic coordination of high-spin single-atom Co sites and GL sites to induce strong surface charge rearrangement and generate very strong electric field energy, which causes continuous oxidation of the adsorption groups of organic pollutants and homolytic cleavage of adjacent chemical bonds until complete mineralization. The free radicals generated throughout the reaction process can continuously charge the catalyst, achieving low-energy and high-efficiency purification of wastewater, especially complex wastewater, without the need for external energy assistance.

[0043] Second, when the catalyst synthesized in this invention is used to treat organic pollutants in water, it can achieve efficient removal of pollutants under neutral conditions at room temperature.

[0044] Third, compared with conventional wastewater oxidation treatment methods, the catalyst synthesized in this invention can effectively overcome the adverse effects of DOC in water on pollutant removal.

[0045] Fourth, the catalyst synthesized in this invention is a supported particulate catalyst, which is easy to separate from water and recycle, and has good cycle stability. Attached Figure Description

[0046] Figure 1 Co prepared in Example 1 SA SEM (scanning electron microscope) image of -N2O2-GL;

[0047] Figure 2 Co prepared in Example 1 SA HAADF-STEM (High Angle Annular Dark Field Scanning Transmission Electron Microscopy) image of -N2O2-GL;

[0048] Figure 3 Co prepared in Example 1 SAEPR (electron paramagnetic resonance) plots of NC prepared by -N2O2-GL and Comparative Example 1;

[0049] Figure 4 Co prepared in Example 1 SA Degradation curves of -N2O2-GL for CIP, BPA and DP;

[0050] Figure 5 Co prepared in Example 1 SA -N2O2-GL TOC removal map for CIP, BPA and DP;

[0051] Figure 6 Co prepared in Example 1 SA Degradation curves of CIP in urban sewage and drinking water sources by -N2O2-GL;

[0052] Figure 7 Co prepared in Example 1 SA -N2O2-GL repeat experiment activity evaluation diagram. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0055] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0056] In this invention, there are no particular limitations on the specific dispersion and stirring methods.

[0057] Unless otherwise specified, all reagents or instruments used in this invention are commercially available products.

[0058] Example 1

[0059] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, including the following steps:

[0060] Urea, dicyandiamide, pore-forming agent, and silkworm excrement were added to water and stirred at 20 rpm for 2 hours to obtain dispersion A. The pore-forming agent was sodium bicarbonate, and the mass ratio of urea, dicyandiamide, pore-forming agent, and silkworm excrement was 0.5:1.25:0.375:1. The material-to-liquid ratio in dispersion A was (urea + dicyandiamide + pore-forming agent + silkworm excrement): solvent = 1 g: 3.2 mL.

[0061] The cobalt source was added to dispersion A and stirred at 20 rpm for 4 hours to obtain dispersion B. The cobalt source was cobalt chloride hexahydrate, and the mass ratio of silkworm excrement to the molar amount of cobalt in the cobalt source was 1 g: 0.00145 mol.

[0062] Dispersion B was placed in a 100℃ oven and dried for 24 hours to obtain solid particles A.

[0063] Solid particles A were placed in a tube furnace and calcined under a N2 atmosphere. The temperature was first raised to 350℃ and calcined for 1 hour, then raised to 550℃ and calcined for 1 hour, and then raised to 700℃ and calcined for 2 hours. The heating rate during calcination was 5℃ / minute. After calcination, the temperature was allowed to drop naturally to obtain solid product B.

[0064] Solid product B was washed three times with water and baked in a 60℃ oven for 24 hours to obtain a biomass-based porous cobalt single-atom catalyst, denoted as Co. SA -N2O2-GL.

[0065] Example 2

[0066] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that the mass ratio of urea, dicyandiamide, pore-forming agent and silkworm excrement is 0.47:1.5:0.355:1, and the mass ratio of silkworm excrement to the amount of cobalt in the cobalt source is 1g:0.0014mol.

[0067] Example 3

[0068] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that the mass ratio of urea, dicyandiamide, pore-forming agent and silkworm excrement is 0.58:1.1:0.395:1, and the mass ratio of silkworm excrement to the amount of cobalt in the cobalt source is 1g:0.0015mol.

[0069] Example 4

[0070] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that the mass ratio of urea, dicyandiamide, pore-forming agent and silkworm excrement is 0.4:1.9:0.1:1, and the mass ratio of silkworm excrement to the amount of cobalt in the cobalt source is 1g:0.001mol.

[0071] Example 5

[0072] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that the mass ratio of urea, dicyandiamide, pore-forming agent and silkworm excrement is 0.75:1:0.45:1, and the mass ratio of silkworm excrement to the amount of cobalt in the cobalt source is 1g:0.0019mol.

[0073] Example 6

[0074] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that the pore-forming agent is ammonium bicarbonate.

[0075] Example 7

[0076] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that the cobalt source is cobalt sulfate.

[0077] Example 8

[0078] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 250°C for 3 hours, then raised to 450°C for 3 hours, and then raised to 600°C for 3 hours. The calcination heating rate is 2°C / minute, and after natural cooling, solid product A is obtained.

[0079] Example 9

[0080] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 400°C for 1 hour, then raised to 600°C for 1 hour, and then raised to 900°C for 1 hour. The calcination heating rate is 20°C / minute, and after natural cooling, solid product A is obtained.

[0081] Example 10

[0082] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 350°C for 2 hours, and then raised to 700°C for 2 hours. The calcination heating rate is 5°C / minute. After natural cooling, solid product A is obtained.

[0083] Example 11

[0084] This embodiment provides a method for preparing a bio-based porous cobalt single-atom catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 550°C for 2 hours, and then raised to 700°C for 2 hours. The calcination heating rate is 5°C / minute. After natural cooling, solid product A is obtained.

[0085] Comparative Example 1

[0086] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that a cobalt source is not used; instead, dispersion A is directly stirred at 20 rpm for 4 hours to obtain dispersion B. The catalyst obtained in this comparative example is denoted as NC.

[0087] Comparative Example 2

[0088] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that only urea is used instead of dicyandiamide, and the mass ratio of urea, pore-forming agent and silkworm excrement is 1.75: 0.375:1.

[0089] Comparative Example 3

[0090] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that only dicyandiamide is used instead of urea, and the mass ratio of dicyandiamide, pore-forming agent and silkworm excrement is 1.75: 0.375:1.

[0091] Comparative Example 4

[0092] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that the pore-forming agent is zinc chloride.

[0093] Comparative Example 5

[0094] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that an equal weight of sawdust is used to completely replace silkworm excrement.

[0095] Comparative Example 6

[0096] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, heated to 700°C and calcined for 3 hours, with a calcination heating rate of 5°C / minute, and then allowed to cool naturally after calcination to obtain solid product B.

[0097] Comparative Example 7

[0098] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 200°C for 2 hours, and then raised to 700°C for 2 hours. The calcination heating rate is 5°C / minute. After calcination, the temperature is naturally lowered to obtain solid product B.

[0099] Comparative Example 8

[0100] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 650°C for 2 hours, and then raised to 700°C for 2 hours. The calcination heating rate is 5°C / minute. After calcination, the temperature is naturally lowered to obtain solid product B.

[0101] Comparative Example 9

[0102] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 550°C for 2 hours, and then raised to 600°C for 2 hours. The calcination heating rate is 5°C / minute. After calcination, the temperature is naturally lowered to obtain solid product B.

[0103] Comparative Example 10

[0104] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 550°C and calcined for 2 hours, and then raised to 1000°C and calcined for 2 hours. The calcination heating rate is 5°C / minute. After calcination, the temperature is naturally lowered to obtain solid product B.

[0105] Comparative Example 11

[0106] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 550°C and calcined for 1 hour, and then raised to 700°C and calcined for 2 hours. The calcination heating rate is 5°C / minute. After calcination, the temperature is naturally lowered to obtain solid product B.

[0107] Comparative Example 12

[0108] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 550°C and calcined for 8 hours, and then raised to 700°C and calcined for 2 hours. The calcination heating rate is 5°C / minute. After calcination, the temperature is naturally lowered to obtain solid product B.

[0109] Comparative Example 13

[0110] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 550°C and calcined for 2 hours, and then raised to 700°C and calcined for 0.5 hours. The calcination heating rate is 5°C / minute. After calcination, the temperature is naturally lowered to obtain solid product B.

[0111] Comparative Example 14

[0112] This comparative example provides a method for preparing a catalyst, which differs from Example 1 in that: when solid particles A are placed in a tube furnace and calcined under a N2 atmosphere, the temperature is first raised to 550°C and calcined for 2 hours, and then raised to 700°C and calcined for 4 hours. The calcination heating rate is 5°C / minute. After calcination, the temperature is naturally lowered to obtain solid product B.

[0113] The catalysts prepared in each example and comparative example were subjected to structural analysis by SEM, HAADF-STEM, and EPR. Figure 1 , Figure 2 , Figure 3 The catalyst Co prepared in Example 1 is respectively SA SEM, HAADF-STEM, and EPR images of -N2O2-GL were obtained from... Figure 1 It can be seen that the catalyst Co SA -N2O2-GL has a honeycomb-like porous structure with a pore size of 1~10μm; Figure 2 In the middle, the entire catalyst Co SA The surface of -N2O2-GL has abundant isolated bright spots, which indicate that the ingenious complexation of Co with the graphene-like structure promotes the formation of abundant cobalt atom sites on the catalyst surface; Figure 3 In comparison with NC (i.e., the catalyst obtained in Comparative Example 1), Co... SA The EPR spectrum of -N2O2-GL shows an extremely strong signal peak at g=3.01, confirming the presence of high-spin Co atoms. Furthermore, the introduction of Co induces a polarized distribution of electrons on the catalyst surface, forming a surface micro-electric field.

[0114] Table 1. Co obtained in Example 1 SA Numerical fitting results of Co-order EXAFS oscillations of -N2O2-GL

[0115]

[0116] Table 1 shows that the coordination number of the central Co atom is 4. There are 2.2 directly bonded O atoms in the first coordination layer, and an average of 2.1 N atoms and 1.4 C atoms directly bonded in the second coordination layer. These results confirm that Co... SA The symmetry-breaking configuration of -N2O2-GL effectively improves the interfacial electron transfer capacity and structural stability of the catalyst. Therefore, in Co SA On the -N2O2-GL surface, single-atom Co interacts strongly with the delocalized π orbitals perpendicular to the aromatic ring plane in the graphene-like GL support through Co–O–C and Co–N–C bond bridges.

[0117] Application Experiment 1

[0118] 0.03 g of the catalyst samples prepared in each example and comparative example were added to 50 mL of a 10 mg / L contaminant solution (prepared with the contaminant and ultrapure water UPW, the contaminant being BPA). The solution was kept at a constant temperature of 35°C and continuously magnetically stirred at 35 rpm for 120 min to initiate the degradation reaction. The catalyst was then separated, and the concentration of the contaminant in the resulting solution was measured. The separated catalyst was dried and the contaminant solution was recycled according to the aforementioned process. The contaminant degradation rates after one and six cycles are shown in Table 2. The contaminant degradation rate after one cycle = (initial concentration of contaminant in solution - concentration of contaminant in solution after one cycle) / initial concentration of contaminant in solution × 100%, and the contaminant degradation rate after six cycles = (initial concentration of contaminant in solution - concentration of contaminant in solution after six cycles) / initial concentration of contaminant in solution × 100%. The contaminant degradation of the catalyst prepared in Example 1 after each cycle is shown in Table 2. Figure 7 As can be seen, the catalyst has good stability, can be recycled, and after six consecutive runs, the removal rate of BPA remains above 99.5%, and the release of cobalt is only 0.06 mg / L.

[0119] Table 2

[0120]

[0121] The data above show that the catalysts obtained in each embodiment have good catalytic activity and stability. For example, the BPA degradation rate is above 63.5% after one run and above 60% after six runs.

[0122] Comparative Example 1 did not use a cobalt source, resulting in deviations in the catalytic activity and stability of the obtained catalyst. Comparative Example 2 used only urea, and the highly directional condensation reaction meant that the resulting carbon nitride network structure could not effectively coat cobalt and silkworm excrement, leading to deviations in the catalytic activity and stability of the obtained catalyst. Comparative Example 3 used only dicyandiamide, which does not act as a binder and cannot effectively coat cobalt and silkworm excrement, resulting in deviations in the catalytic activity and stability of the obtained catalyst. Comparative Example 4 used zinc chloride as a pore-forming agent, which lacks reducing properties, causing cobalt to form cobalt oxide during calcination, resulting in deviations in the catalytic activity and stability of the obtained catalyst. Comparative Example 5 used sawdust as a carbon-based precursor, resulting in a catalyst with low activity and a powdery form, making it difficult to recycle. Comparative Example 6 did not use staged calcination, resulting in excessively rapid decomposition of the pore-forming agent, which was not conducive to the formation of single-atom Co, and excessive carbonization of urea and dicyandiamide, leading to excessively low catalyst activity. Comparative Example 7 had an excessively low calcination temperature in the low-temperature stage, making the material prone to agglomeration during calcination and not conducive to the formation of cobalt and silkworm excrement. In Comparative Example 8, the calcination temperature in the low-temperature stage was too high, causing the pore-forming agent to decompose too quickly, which was not conducive to the formation of single-atom Co. Moreover, the excessive carbonization of urea and dicyandiamide resulted in low catalyst activity. In Comparative Example 9, the calcination temperature in the high-temperature stage was too low, making the material prone to agglomeration during the calcination process, resulting in low catalyst activity. In Comparative Example 10, the calcination temperature in the high-temperature stage was too high, causing excessive carbonization of urea, dicyandiamide, and silkworm excrement, resulting in low catalyst activity. In Comparative Example 11, the calcination time in the low-temperature stage was too short, which was not conducive to the condensation of urea and dicyandiamide to form carbon nitride, resulting in low catalyst activity. In Comparative Example 12, the calcination time in the low-temperature stage was too long, which made cobalt species prone to agglomeration, resulting in low catalyst activity. In Comparative Example 13, the calcination time in the high-temperature stage was too short, which was not conducive to the formation of graphene-like structures by silkworms, resulting in low catalyst activity. In Comparative Example 14, the calcination time in the high-temperature stage was too long, causing excessive carbonization of the material, resulting in low catalyst activity.

[0123] As shown in Examples 1-5, when the amounts of urea, dicyandiamide, pore-forming agent, silkworm excrement, and cobalt source meet the following conditions: the mass ratio of urea, dicyandiamide, pore-forming agent, and silkworm excrement is (0.4-0.75):(1-1.9):(0.1-0.45):1, and the mass ratio of silkworm excrement to the molar amount of cobalt in the cobalt source is 1g:(0.001-0.0019)mol, especially when the mass ratio of urea, dicyandiamide, pore-forming agent, and silkworm excrement is (0.47-0.58):(1.1-1.5):(0.355-0.395):1, and the mass ratio of silkworm excrement to the molar amount of cobalt in the cobalt source is 1g:(0.0014-0.0015)mol, especially when the mass ratio of urea, dicyandiamide, pore-forming agent, and silkworm excrement is 0.5:1.25: When the mass ratio of silkworm excrement to cobalt in the cobalt source is 0.375:1 and the molar ratio of cobalt to silkworm excrement in the cobalt source is 1 g: 0.00145 mol, the synthesized catalyst exhibits superior catalytic activity and cycle stability.

[0124] Comparing Examples 1 and 8-11, it can be seen that dividing the low-temperature calcination stage into two stages is as follows: calcining the solid particles at 250-400℃ for 1-3 hours, and then calcining them at 450-600℃ for 1-3 hours, is more conducive to the condensation polymerization of urea and dicyandiamide, resulting in a more complete network structure and a superior electronic structure, thereby improving the catalytic activity of the catalyst.

[0125] Application Experiment 2

[0126] 0.03 g of the catalyst sample prepared in Example 1 was added to 50 mL of a pollutant solution with a concentration of 10 mg / L. The solution was kept at a constant temperature of 35 °C and continuously stirred with magnetic force to start the degradation reaction. The stirring speed was 35 rpm. Samples were taken at different time points and the concentration of pollutants was detected.

[0127] When the contaminant is CIP, BPA, or DP, and the contaminant solution is prepared from the contaminant and ultrapure water (UPW), the test results are shown below. Figure 4 and Figure 5 The pollutant degradation rate is calculated as follows: (initial concentration of pollutants in the solution - concentration of pollutants in the solution after the reaction) / initial concentration of pollutants in the solution × 100%. The TOC (total organic carbon) removal rate is calculated as follows: (initial concentration of TOC in the solution - concentration of TOC in the solution after the reaction) / initial concentration of TOC in the solution × 100%.

[0128] When the contaminant is CIP, and the contaminant solution is prepared by mixing the contaminant with one of ultrapure water (UPW), municipal wastewater (MW), or drinking water source water (RDW), the test results are shown below. Figure 6 .

[0129] from Figure 4 and Figure 5 It can be seen that, without external energy assistance, Co SA -N2O2-GL can completely remove CIP, BPA, and DP through a self-purification process within 120 minutes, with corresponding TOC removal rates as high as 74.0%, 76.1%, and 55.8%, respectively. It is worth noting that when utilizing Co... SA When treating pollutant solutions prepared from municipal wastewater (MW) or drinking water source water (RDW) using -N2O2-GL, 100% removal of CIP can be achieved within just 30 minutes. Figure 6 This indicates that DOC can greatly promote the degradation of BPA, which is completely different from the usual oxidation process.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this article without departing from the essence and scope of the technical solutions of this article.

Claims

1. A method for preparing a bio-based porous cobalt single-atom catalyst, characterized in that, Includes the following steps: Urea, dicyandiamide, pore-forming agent and silkworm excrement are mixed and dispersed in a solvent to obtain dispersion A; The cobalt source is mixed and dispersed with the dispersion A to obtain dispersion B; The dispersion B was dried to obtain solid particles; The solid particles were calcined at 250-600℃ for 2-6 hours, and then calcined at 650-900℃ for 1-3 hours to obtain a solid product, which is a bio-based porous cobalt single-atom catalyst. The pore-forming agent is at least one of bicarbonate and carbonate; The mass ratio of the urea, the dicyandiamide, the pore-forming agent and the silkworm excrement is (0.4~0.75):(1~1.9):(0.1~0.45):1, and the mass ratio of the silkworm excrement to the amount of cobalt in the cobalt source is 1g:(0.001~0.0019)mol.

2. The method for preparing the bio-based porous cobalt single-atom catalyst as described in claim 1, characterized in that, The mass ratio of the urea, the dicyandiamide, the pore-forming agent, and the silkworm excrement is (0.47~0.58):(1.1~1.5):(0.355~0.395):1, and the mass ratio of the silkworm excrement to the molar amount of cobalt in the cobalt source is 1g:(0.0014~0.0015)mol.

3. The method for preparing the bio-based porous cobalt single-atom catalyst as described in claim 2, characterized in that, The mass ratio of the urea, the dicyandiamide, the pore-forming agent, and the silkworm excrement is 0.5:1.25:0.375:1, and the mass ratio of the silkworm excrement to the molar amount of cobalt in the cobalt source is 1g:0.00145 mol.

4. The method for preparing the bio-based porous cobalt single-atom catalyst as described in claim 1, characterized in that, The specific steps for calcining the solid particles at 250~600℃ for 2~6h are as follows: calcining the solid particles at 250~400℃ for 1~3h, and then calcining them at 450~600℃ for 1~3h.

5. The method for preparing the bio-based porous cobalt single-atom catalyst as described in claim 1, characterized in that, The pore-forming agent includes at least one of sodium bicarbonate, ammonium bicarbonate, sodium carbonate, potassium bicarbonate, and potassium carbonate; and / or, The cobalt source is a water-soluble cobalt source, including at least one of cobalt chloride hexahydrate, cobalt sulfate, cobalt acetate, cobalt sulfate heptahydrate, cobalt acetate tetrahydrate, and cobalt nitrate hexahydrate.

6. The method for preparing the bio-based porous cobalt single-atom catalyst as described in claim 1, characterized in that, At least one of the following conditions must be met: S1. During the calcination of solid particles, the heating rate is controlled within the range of 2~20℃ / min; S2. The calcination of solid particles is carried out in a protective atmosphere, which includes at least one of nitrogen and inert gas. S3. The material-to-liquid ratio in the dispersion A is: (urea + dicyandiamide + pore-forming agent + silkworm excrement): solvent = 1g: (2~6)mL; S4. The solvent in dispersion A includes water; S5. The solid product is further cleaned and dried to obtain a bio-based porous cobalt single-atom catalyst.

7. The bio-based porous cobalt single-atom catalyst prepared by the method according to any one of claims 1 to 6.

8. The application of the bio-based porous cobalt single-atom catalyst as described in claim 7 in the degradation of organic pollutants in water.

9. The application as described in claim 8, characterized in that, The organic pollutants include at least one of quinolones, phenols, and antihistamines.

10. The application as described in claim 9, characterized in that, The quinolones include at least one of ciprofloxacin, norfloxacin, and tetracycline; and / or, The phenols include at least one of bisphenol A, bisphenol B, bisphenol S, bisphenol F, and bisphenol AF; and / or, The antihistamines include at least one of diphenhydramine and cetirizine.

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