N, o co-doped carbon-coated cobalt oxide composite catalyst with hollow structure, preparation method and application thereof

Abstract

The application discloses an N, O co-doped carbon-coated cobalt trioxide composite catalyst with a hollow structure and a preparation method and application thereof. The Co3O4@N, O-C material is obtained by converting carbon contained in ZIF-67 and simultaneously doping nitrogen and oxygen, and converting Co contained in ZIF-67 to obtain N, O co-doped carbon-coated cobalt trioxide. The Co3O4@N, O-C has a hollow structure, and the coating layer is a porous structure. The ZIF-67 precursor is placed in a continuous flow Ar and O2 atmosphere, and ZIF-67 is irradiated by laser focusing to obtain the Co3O4@N, O-C. The Co3O4@N, O-C is prepared by one-step action of laser, and the material is difficult to obtain by using traditional high-temperature calcination. The Co3O4@N, O-C has two types of multiple activation sites, namely, adsorption sites for separating pollutants on the surface of the catalyst and activation sites for persulfate, so that the catalytic performance and practicability of the catalyst are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically to a hollow N,O co-doped carbon-encapsulated cobalt tetroxide composite catalyst, its preparation method, and its application. Background Technology

[0002] With the rapid development of human society, environmental issues have gradually attracted everyone's attention, and water pollution has become increasingly serious. As an indispensable part of the ecological cycle, the water cycle allows pollutants in water bodies to permeate all aspects of human life. Recalcitrant organic pollutants have stable structures in water and soil, making them difficult to degrade naturally. Therefore, how to remove residual organic pollutants from water and soil has become an urgent problem to be solved.

[0003] Advanced oxidation processes (AOPs) are catalytic processes that decompose oxides to generate free radicals and non-free radicals with high oxidation potentials, which then attack pollutants, directly mineralizing them into small molecules such as CO2 and H2O or converting them into less toxic substances. As a simple and complete method for pollutant removal, AOPs have gained popularity. In recent years, heterogeneous catalysts commonly used in AOPs have included metal-based catalysts, carbon-based catalysts, and composite catalysts. Metal-based catalysts, such as CuO and Fe2O3, exhibit excellent catalytic performance, activating persulfate to generate reactive oxygen species with high redox potentials in a very short time. However, they often suffer from metal ion leaching, which burdens the environment. Carbon-based catalysts, such as porous carbon, N-doped carbon, and S-doped carbon, are generally relatively stable and can be used to construct various active sites through heteroatom doping technology. However, they often suffer from low catalytic performance due to electron deficiency. Recent studies have demonstrated that the electron distribution of the carbon layer can be controlled by constructing a metal@carbon core-shell structure, thereby improving the catalytic activity of carbon and protecting the metal core from corrosion. This approach ensures both excellent activity and good material stability. For example, Co@NC catalysts, obtained by calcining ZIF-67 in an inert atmosphere, are porous catalysts. However, the active sites on Co@NC catalysts are singular, making it difficult to efficiently activate PMS (potassium persulfate) for pollutant oxidation and degradation. Therefore, it is necessary to oxidize Co@NC catalysts to obtain catalysts with more stable activity points. However, the traditional method of preparing O-doped carbon by oxidizing Co@NC is technically difficult and it is hard to control the amount of O doping. If the calcination (oxidation) temperature is too high, C will be lost. Low-temperature oxidation can only oxidize Co to obtain Co3O4, and O cannot be doped into C. When activating PMS, the N-doped C active sites are responsible for both pollutant adsorption and persulfate activation, resulting in active site competition. That is, the adsorption of pollutant molecules on the catalyst surface generally occupies a portion of the active sites, and the active sites used for persulfate molecule activation will be greatly reduced, thus affecting the overall pollutant removal efficiency. Therefore, a new method is needed to prepare Co3O4@N,OC, which allows O to be doped into C, forming multiple active sites with N and O doping. These two types of active sites can serve as adsorption sites for pollutants and activation sites for persulfate on the catalyst surface, respectively. One type of site is responsible for the adsorption of pollutants, while the other type is responsible for the activation of persulfate. This not only avoids the problem of competition among active sites but also shortens the migration distance from active substances to pollutants, which will greatly improve the catalytic performance and practicality of the catalyst. Summary of the Invention

[0004] To address the aforementioned limitations of existing technologies, the present invention aims to provide a hollow N,O co-doped carbon-encapsulated cobalt tetroxide composite catalyst, its preparation method, and its applications. This invention enables the one-step laser-assisted preparation of Co3O4@N,OC, a material with a unique hollow structure, which is difficult to achieve with oxygen-doped carbon using traditional calcination methods. The Co3O4@N,OC prepared by this invention possesses adsorption sites for contaminants and activation sites for persulfate on the catalyst surface. One type of site is responsible for contaminant adsorption, while the other type is responsible for persulfate activation, significantly improving the catalyst's catalytic performance and practicality.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a Co3O4@N,OC material, wherein the Co3O4@N,OC material is obtained by simultaneously doping the carbon contained in ZIF-67 with nitrogen and oxygen, and by converting the Co contained in ZIF-67 to obtain N,O co-doped carbon encapsulating cobalt tetroxide.

[0007] Preferably, the Co3O4@N,OC material has a hollow structure and its coating layer has a porous structure.

[0008] Preferably, the atomic doping amount of N in the Co3O4@N,OC material is 2.01% to 21.81%, and the atomic doping amount of O is 12.59% to 35.22%.

[0009] Preferably, the preparation method of the Co3O4@N,OC material is as follows:

[0010] The ZIF-67 precursor was placed in a continuously flowing O2-containing gas atmosphere, and the ZIF-67 precursor was irradiated with a focused laser to obtain Co3O4@N,OC.

[0011] Preferably, the O2-containing gas atmosphere may also contain Ar; the volume ratio of Ar to O2 is 0-80%: 20-100%.

[0012] Preferably, the volume ratio of Ar to O2 is 80%:20%, 70%:30%, 50%:50%, 30%:70%, or 0%:100%.

[0013] Preferably, the gas flow rate of the O2-containing atmosphere is 190–210 sccm.

[0014] Preferably, the wavelength of the laser is 1064nm, the laser power is 20W, and the scan speed is 100mm / s.

[0015] In a second aspect, the present invention provides the use of Co3O4@N,OC material as a catalyst in the catalytic degradation of organic pollutants by PMS.

[0016] Preferably, the organic pollutant is Orange II, Rhodamine B, Methyl Orange, Propranolol, Tetracycline, Chloramphenicol, or p-Nitrophenol.

[0017] The beneficial effects of this invention are:

[0018] (1) This invention employs laser carbonization of ZIF-67, where the laser-irradiated area rapidly heats up and reacts directly with the gas in the reactor, successfully incorporating N and O elements into the carbon layer, thus achieving the successful preparation of Co3O4@N,OC. Laser irradiation enables instantaneous heating, significantly shortening the carbonization time. The high-energy laser beam emitted by the laser gives the resulting Co3O4@N,OC a unique hollow structure. The formation of this hollow structure increases the specific surface area of ​​the material, further enhancing its catalytic performance.

[0019] (2) The Co3O4@N,OC prepared by this method has the effect of efficiently activating PMS, enabling the activated PMS to have a high removal rate for various organic pollutants in water. Co3O4@N,OC exhibits long-term catalytic stability in a large-volume continuous flow reaction system. Attached Figure Description

[0020] Figure 1 The XRD patterns of Co3O4@N,OC and its precursor ZIF-67 prepared in Example 1 of this invention are shown below.

[0021] Figure 2 This is a SEM image of Co3O4@N,OC obtained in Example 1 of the present invention;

[0022] Figure 3 The BET plot of Co3O4@N,OC obtained in Example 1 of this invention;

[0023] Figure 4 The N1s high-resolution XPS spectrum of Co3O4@N,OC prepared in Example 1 of this invention;

[0024] Figure 5 The O1s high-resolution XPS spectrum of Co3O4@N,OC prepared in Example 1 of this invention;

[0025] Figure 6 The graphs show the degradation effects of Co3O4@N,OC-0.5 prepared in Example 1 of this invention and Co@NC and Co3O4@NC prepared in Comparative Examples 1-2 on tetracycline.

[0026] Figure 7The degradation effect of Co3O4@N,OC samples prepared in Examples 1-5 of this invention on tetracycline is shown in the figure.

[0027] Figure 8 The image shows the degradation effect of the Co3O4@N,OC sample prepared in Example 1 of this invention on various dyes and antibiotics.

[0028] Figure 9 The image shows the degradation effect of the Co3O4@N,OC sample prepared in Example 1 of this invention on tetracycline after being reused five times.

[0029] Figure 10 The image shows the degradation effect of the Co@NC sample prepared in Comparative Example 1 of this invention on tetracycline after being reused three times.

[0030] Figure 11 This is a physical diagram of the apparatus used to assemble Co3O4@N,OC obtained in Example 1 of the present invention into a 3D catalyst for use in a large-volume continuous flow reactor.

[0031] Figure 12 The Co3O4@N,OC prepared in Example 1 of this invention was assembled into a 3D catalyst for long-term catalytic stability in a large-volume continuous flow reactor. Detailed Implementation

[0032] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0033] As described in the background section, the reaction process in the activation of persulfate (PMS) by a heterogeneous catalyst generally consists of three main steps. First, the persulfate is activated by the catalyst to generate an active substance (such as SO4· ... - (And ·OH, etc.). The second step involves the migration of active substances towards the target pollutant. The third step involves the oxidative decomposition of the target pollutant by the active substances. Existing catalysts have single active sites, and their ability to activate PMS needs improvement, resulting in low efficiency in the oxidative decomposition of the target pollutant by the active substances, and consequently, insufficient ability to degrade organic pollutants.

[0034] Based on this, the purpose of this invention is to provide a hollow N,O co-doped carbon-encapsulated cobalt tetroxide composite catalyst, its preparation method, and its applications. This invention utilizes laser one-step carbonization to prepare Co3O4@N,OC. By introducing a certain proportion of Ar and O2 mixed gas during laser treatment, N,O co-doped carbon-encapsulated cobalt tetroxide can be prepared. With the introduction of O, the subsequent catalytic performance of the material is further enhanced. Because the precursor ZIF-67 itself does not contain O, in the traditional high-temperature calcination process, ① without introducing O2 in the calcination atmosphere, the obtained material is Co@NC; ② with introducing O2 in the calcination atmosphere, the obtained material is Co3O4. The unique rapid heating and cooling characteristics of lasers allow the C structure to be largely preserved even with the introduction of O2, and successfully incorporate O into the C to form Co3O4. Furthermore, the N and O content in Co3O4@N,OC can be controlled by adjusting the proportion of gases in the Ar and O2 mixed gas, achieving controllable preparation. Thanks to the high-energy laser beam emitted by the laser, the obtained Co3O4@N,OC has a unique hollow structure; while traditional high-temperature calcination will retain the blocky structure of the precursor; the formation of the hollow structure will increase the specific surface area of ​​the material itself, thereby further improving the catalytic performance.

[0035] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0036] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0037] Example 1:

[0038] (1) Preparation of ZIF-67 precursor:

[0039] A. Dissolve 5 mmol of Co(NO3)2·6H2O in 50 mL of methanol solution and label it as solution ①; dissolve 40 mmol of dimethylimidazole in 50 mL of methanol solution and label it as solution ②;

[0040] B. Mix solution ① and solution ② and stir for at least 10 minutes, then let stand for at least 24 hours, and then filter and wash to obtain ZIF-67.

[0041] (2) After spreading ZIF-67 evenly on a quartz sheet, press another quartz sheet on top.

[0042] (3) Place (2) in the self-made reactor, cover it with a light-transmitting window, and ensure that the light-transmitting window is sealed at the contact point with the reactor; introduce a continuous flow of Ar and O2 mixed gas (50% O2 and 50% Ar) from the reactor inlet at a flow rate of 200 sccm, ensure that the gas outlet is smooth, and continuously ventilate for more than 20 minutes to ensure that the atmosphere in the reactor is the set mixed gas ratio;

[0043] (4) Set laser parameters: Use a fiber laser with an output wavelength of 1064nm, set the laser power to 20W, and the scan speed to 100mm / s;

[0044] (5) Laser carbonization: The laser is activated to emit a laser beam. The laser beam is focused through the quartz window of the reactor and irradiates ZIF-67. The laser scans repeatedly 5 times to carbonize ZIF-67.

[0045] (7) After laser carbonization, the collected powder was soaked in 0.5M H2SO4 solution for more than 24 hours, then washed with deionized water 3 times, centrifuged to collect the product, and dried in an oven at 80℃ for 24 hours; the obtained Co3O4@N,OC was recorded as Co3O4@N,OC-0.5.

[0046] like Figure 1 As shown, X-ray powder diffraction analysis revealed that the peak of the precursor ZIF-67 disappeared, and was replaced by peaks of Co3O4 and C.

[0047] The Co3O4@N,OC prepared in this embodiment was tested using a field emission scanning electron microscope (SEM), as shown below. Figure 2 As shown, Co3O4@N,OC exhibits a hollow structure. According to... Figure 3 It can be seen that the specific surface area of ​​this material can reach 661.47 m². 2 / g, which greatly increases the specific surface area of ​​the catalyst.

[0048] X-ray photoelectron spectroscopy (XPS) was performed on the Co3O4@N,OC prepared in this embodiment, as follows: Figure 4 As shown, nitrogen (N) is doped into carbon in three forms: pyridine N, graphitic N, and pyrrole N; Figure 5 As shown, the O element is doped into C in the form of C=O and CO.

[0049] Example 2

[0050] The difference between this invention and Example 1 is that the ratio of the continuously flowing Ar and O2 mixed gas in step (3) is 20% O2 and 80% Ar; the obtained Co3O4@N,OC is denoted as Co3O4@N,OC-0.2.

[0051] Example 3

[0052] The difference between this invention and Example 1 is that the proportion of the continuously flowing Ar and O2 mixed gas in step (3) is 30% O2 and 70% Ar; the obtained Co3O4@N,OC is denoted as Co3O4@N,OC-0.3.

[0053] Example 4

[0054] The difference between this invention and Example 1 is that the proportion of the continuously flowing Ar and O2 mixed gas in step (3) is 70% O2 and 30% Ar; the obtained Co3O4@N,OC is denoted as Co3O4@N,OC-0.7.

[0055] Example 5

[0056] The difference between this invention and Example 1 is that the proportion of the continuously flowing Ar and O2 mixed gas in step (3) is 100% O2; the obtained Co3O4@N,OC is denoted as Co3O4@N,OC-1.

[0057] The nitrogen and oxygen doping content (atoms) of carbon in Examples 1-5 was measured using XPS, and the results are shown in Table 1.

[0058] Table 1

[0059]

[0060]

[0061] It can be seen that in the Co3O4@N,OC materials prepared in Examples 1 to 5, N and O are doped into C in multiple forms, which can provide more types of sites for activating PMS and promote catalytic reactions.

[0062] Comparative Example 1

[0063] Following the method disclosed in *Non-radical-dominated catalytic degradation of bisphenol A by ZIF-67-derived nitrogen-doped carbon nanotube frameworks in the presence of peroxymonosulfate* (Chemical Engineering Journal 336(2018)721-731), Co-MOF was calcined at 700 °C for 2 h under an inert atmosphere to obtain Co@NC.

[0064] Comparative Example 2

[0065] Following the method disclosed in Tunable synthesis of cage-like Co3O4 / NC composite and nest-like Co3O4 for oxidative degradation of Bisphenol A (Journal of Solid State Chemistry 304(2021)122550): Co-MOF was calcined at 330℃ for 2 hours in air atmosphere to obtain Co3O4@NC.

[0066] Application Example 1

[0067] Tetracycline degradation experiments were conducted using Co3O4@N,OC from Examples 1-5 and Comparative Examples 1-2. The procedure was as follows: Tetracycline was dissolved in pure water to prepare a 20 mg / L tetracycline solution. 100 mL of this 20 mg / L solution was placed in each beaker. Subsequently, 10 mg of the catalyst prepared in Examples 1-5 and Comparative Examples 1-2, along with 40 mg of PMS (catalyst concentration 0.1 g / L, PMS concentration 0.65 mM), were added simultaneously. The reaction was continuously stirred. As the degradation process progressed, the remaining tetracycline content gradually decreased. The catalysts prepared in Examples 1 and 3 showed the fastest degradation rate, completely degrading the tetracycline within 8 minutes. Figure 6 and Figure 7 As shown, the Co3O4@N,OC catalyst prepared in this invention can effectively activate PMS and rapidly degrade tetracycline.

[0068] Application Example 2

[0069] The Co3O4@N,OC catalyst from Example 1 was subjected to degradation experiments for Orange II, Rhodamine B, Methyl Orange, Propranolol, Tetracycline, Chloramphenicol, and p-Nitrophenol, respectively. Experimental conditions: Co3O4@N,OC catalyst concentration was 0.1 g / L, PMS concentration was 0.65 mM, and pollutant concentration was 20 mg / L (experimental methods were the same as in Application Example 1). Figure 8 As shown, the prepared Co3O4@N,OC catalyst can effectively activate PMS and rapidly degrade various dyes and antibiotics in solution.

[0070] Application Example 3

[0071] The catalysts prepared in Example 1 and Comparative Example 1 (since the catalytic effect of the catalyst prepared in Comparative Example 2 was significantly lower than that of Comparative Example 1, this experiment was not conducted in Comparative Example 2) were subjected to stability tests. The tetracycline degradation experiment was repeated five times under the same reaction conditions (experimental conditions and methods as in Application Example 1). After the first experiment, the catalyst was recovered. Using the recovered catalyst as raw material, the second tetracycline degradation experiment was conducted under the same reaction conditions as the first repeated experiment. The subsequent three experiments were conducted in the same manner. Figure 9 As shown, after five degradation tests, the tetracycline removal efficiency of the catalyst prepared in Example 1 remained at the initial level, indicating that Co3O4@N,OC still exhibits good activation performance over long-term operation. Figure 10 As shown, the catalyst prepared in Comparative Example 1 gradually decreased its catalytic ability in multiple tetracycline removal experiments.

[0072] Application Example 4

[0073] A 3D catalyst was prepared by immobilizing Co3O4@N,OC from Example 1 in melamine foam, and a structure was constructed as follows: Figure 11 The large-volume continuous flow reactor shown consists of a cylindrical body. Three melamine foams loaded with the catalyst prepared in Example 1 are arranged sequentially from top to bottom within the cylinder, forming a three-stage 3D catalyst structure. A beaker on the left side of the reactor contains a solution of 3 mM PMS and 20 mg / L tetracycline, while a beaker on the right side collects the liquid after the catalytic reaction. A peristaltic pump pumps the tetracycline solution containing PMS from the bottom of the cylinder upwards, and after the catalytic reaction, it flows out from the top of the reactor and is collected in the beaker on the right side. During operation, the container containing the contaminant is continuously replenished with solution (tetracycline is a colorless solution; this is to facilitate differentiation of the effects before and after treatment). Figure 11 Orange-Yellow II was used as a demonstration, and the actual experiment was a tetracycline degradation experiment conducted in a large-volume flow reactor.

[0074] Tetracycline degradation experiments were conducted in a large-volume flow reactor, such as... Figure 12 As shown, after the reaction system operated continuously for 48 hours, there was no significant performance degradation.

[0075] Based on the above tests, it can be seen that the hollow structure of Co3O4@N,OC was successfully prepared by doping N and O elements into the carbon layer using the high-energy effect of laser. The prepared Co3O4@N,OC has good stability and reusability, and exhibits stable and long-term catalytic degradation performance in a large-volume continuous flow reaction system, which can be well applied in actual water treatment.

[0076] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A Co3O4@N,OC material, characterized in that, The Co3O4@N,OC material is obtained by converting the carbon contained in ZIF-67 and simultaneously achieving nitrogen and oxygen doping, and by converting the Co contained in ZIF-67 to obtain N,O co-doped carbon encapsulating cobalt tetroxide; The Co3O4@N,OC material has a hollow structure, and its coating layer has a porous structure. The atomic doping amount of N in the Co3O4@N,OC material is 2.01%~21.81%, and the atomic doping amount of O is 12.59%~35.22%. The preparation method of the Co3O4@N,OC material includes: The ZIF-67 precursor was placed in a continuously flowing atmosphere containing O2 gas, and the ZIF-67 precursor was irradiated with a focused laser to obtain Co3O4@N,OC; The O2-containing gas atmosphere also contains Ar; the volume ratio of Ar to O2 is 30-80%: 20-70%; The gas flow rate in the O2-containing atmosphere is 190~210 sccm; The laser has a wavelength of 1064 nm, a power of 20 W, and a scan speed of 100 mm / s.

2. The Co3O4@N,OC material according to claim 1, characterized in that, The volume ratio of Ar to O2 is 80%:20%, 70%:30%, 50%:50%, or 30%:70%.

3. The use of the Co3O4@N,OC material as a catalyst in the catalytic degradation of organic pollutants by PMS, as described in claim 1 or 2.

4. The use according to claim 3, characterized in that, The organic pollutants are Orange II, Rhodamine B, Methyl Orange, Propranolol, Tetracycline, Chloramphenicol, or p-Nitrophenol.

Images