A nitrogen-doped carbon nanotube-coated cobalt composite material, its preparation method and application

Abstract

This invention provides a nitrogen-doped carbon nanotube-coated cobalt composite material, its preparation method, and its application, belonging to the field of nanocatalytic materials technology. The preparation method of the nitrogen-doped carbon nanotube-coated cobalt composite material provided by this invention includes the following steps: mixing melamine, graphitic carbon nitride, and inorganic cobalt salt to obtain a mixed raw material; calcining the mixed raw material in a protective atmosphere to obtain a calcined material; and sequentially washing and drying the calcined material to obtain the nitrogen-doped carbon nanotube-coated cobalt composite material. The nitrogen-doped carbon nanotube-coated cobalt composite material provided by this invention exhibits good catalytic stability and high catalytic ozone oxidation activity.

Description

Technical Field

[0001] This invention relates to the field of nanocatalytic materials technology, and in particular to a nitrogen-doped carbon nanotube-coated cobalt composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of modern industry, water pollution has become increasingly serious. Ozone, as a strong oxidant, is increasingly used in the treatment of organic wastewater. However, due to its oxidative selectivity and low ozone utilization rate, the widespread application of ozone oxidation technology in water treatment has been limited. Catalytic ozone oxidation technology utilizes catalysts to promote the decomposition of ozone to generate more potent reactive oxygen species (such as hydroxyl radicals and surface-adsorbed reactive oxygen species), accelerating the degradation of organic pollutants in water. Therefore, it has attracted widespread attention from researchers in recent years.

[0003] Nanocatalysts are key to improving the catalytic oxidation performance of ozone, among which transition metal catalysts and carbon catalysts have attracted widespread attention. Transition metal catalysts, where the transition metal exists primarily as nano- or micro-particles, exhibit high catalytic activity but suffer from poor catalytic stability and are prone to metal leaching, causing secondary pollution. Carbon catalysts, composed mainly of carbon nanotubes or graphene with a structure primarily of nano- or micro-particles, offer advantages such as good stability, excellent electron transport, and no metal pollution; however, their catalytic ozone oxidation activity still needs improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a nitrogen-doped carbon nanotube-coated cobalt composite material, its preparation method and application. The nitrogen-doped carbon nanotube-coated cobalt composite material provided by this invention has good catalytic stability and high catalytic ozone oxidation activity.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a nitrogen-doped carbon nanotube-coated cobalt composite material, comprising the following steps:

[0007] Melamine, graphitic carbon nitride, and inorganic cobalt salt are mixed to obtain a mixed raw material;

[0008] The mixed raw materials are calcined in a protective atmosphere to obtain calcined material;

[0009] The calcined material was washed and dried sequentially to obtain the nitrogen-doped carbon nanotube-coated cobalt metal composite material.

[0010] Preferably, the inorganic cobalt salt includes one or more of cobalt chloride, cobalt nitrate, and cobalt sulfate.

[0011] Preferably, the mass ratio of melamine, graphitic carbon nitride, and inorganic cobalt salt is 10:6 to 10:3 to 5.

[0012] Preferably, the calcination includes a first calcination and a second calcination in sequence; the temperature of the first calcination is 500-600℃ and the holding time is 2-4h; the temperature of the second calcination is 700-900℃ and the holding time is 1-2h.

[0013] Preferably, the washing includes sequential acid washing and water washing; the acid reagent used for acid washing includes hydrochloric acid and / or sulfuric acid, the concentration of the acid reagent is 0.5-1 mol / L, and the acid washing time is 1-2 h; the drying temperature is 60-80℃, and the drying time is 4-6 h.

[0014] The present invention provides a nitrogen-doped carbon nanotube-coated cobalt composite material prepared by the preparation method described above, comprising nitrogen-doped carbon nanotubes and cobalt nanoparticles dispersed in the cavities of the nitrogen-doped carbon nanotubes, wherein cobalt and nitrogen are bonded to form a heterostructure in the nitrogen-doped carbon nanotube-coated cobalt composite material.

[0015] Preferably, the cobalt nanoparticles have a particle size of 20–30 nm.

[0016] Preferably, the cobalt content in the nitrogen-doped carbon nanotube-coated cobalt composite material is 1-5 wt%, and the nitrogen content is 3-8 wt%.

[0017] This invention provides the application of the nitrogen-doped carbon nanotube-coated cobalt composite material described above as an ozone oxidation catalyst in the catalytic ozone oxidation degradation of organic pollutants.

[0018] Preferably, the organic pollutant includes methylene blue.

[0019] This invention provides a method for preparing a nitrogen-doped carbon nanotube-coated cobalt composite material, comprising the following steps: mixing melamine, graphitic carbon nitride, and inorganic cobalt salt to obtain a mixed raw material; calcining the mixed raw material in a protective atmosphere to obtain a calcined material; and washing and drying the calcined material sequentially to obtain the nitrogen-doped carbon nanotube-coated cobalt (Co@N-CNT) composite material. The Co@N-CNT composite material prepared by the method provided by this invention includes nitrogen-doped carbon nanotubes and cobalt nanoparticles dispersed within the cavities of the nitrogen-doped carbon nanotubes. In the nitrogen-doped carbon nanotube-coated cobalt composite material, cobalt and nitrogen are bonded to form a heterostructure. The use of inorganic cobalt salt helps ensure the excellent catalytic activity of the Co@N-CNT composite material, improves metal composite efficiency, and reduces costs, which is beneficial for the large-scale preparation and application of this composite material. The Co@N-CNT composite material provided by this invention has a core-shell structure of nitrogen-doped carbon nanotubes encapsulating cobalt nanoparticles. Because the catalytically active metal element is encapsulated within the shell formed by the nitrogen-doped carbon nanotubes, the stability and dispersibility of the metal element are significantly improved, avoiding the aggregation of cobalt nanoparticles and the dissolution of cobalt. This results in good structural stability, long service life, and environmental friendliness. Simultaneously, the cobalt and nitrogen bonds in the Co@N-CNT composite material to form a heterostructure, which accelerates electron transfer and thus enhances catalytic activity. Therefore, the Co@N-CNT composite material provided by this invention, as an ozone oxidation catalyst, exhibits high catalytic activity, effectively promoting the generation of active free radicals in the ozone oxidation reaction, catalyzing the degradation of organic pollutants, and improving the degradation efficiency of organic pollutants. Furthermore, the Co@N-CNT composite material provided by this invention is prepared using a simple solid-phase pyrolysis method, which is simple in process and low in cost, and has certain application value in the field of catalytic ozone oxidation degradation of organic pollutants. Attached Figure Description

[0020] Figure 1 Transmission electron microscopy image of sample 1# prepared in Example 1;

[0021] Figure 2 X-ray diffraction pattern of sample 1# prepared in Example 1;

[0022] Figure 3 The X-ray photoelectron spectrum of sample 1# prepared in Example 1. Detailed Implementation

[0023] This invention provides a method for preparing a nitrogen-doped carbon nanotube-coated cobalt composite material, comprising the following steps:

[0024] Melamine, graphitic carbon nitride, and inorganic cobalt salt are mixed to obtain a mixed raw material;

[0025] The mixed raw materials are calcined in a protective atmosphere to obtain calcined material;

[0026] The calcined material was washed and dried sequentially to obtain the nitrogen-doped carbon nanotube-coated cobalt metal composite material.

[0027] Unless otherwise specified, all raw materials used in this invention are commercially available products well known to those skilled in the art.

[0028] This invention mixes melamine, graphitic carbon nitride (g-C3N4), and inorganic cobalt salt to obtain a mixed raw material. In this invention, the inorganic cobalt salt preferably includes one or more of cobalt chloride, cobalt nitrate, and cobalt sulfate, more preferably cobalt chloride, cobalt nitrate, or cobalt sulfate. Compared to organic cobalt salts, the use of inorganic cobalt salts in this invention significantly improves the catalytic activity of the resulting nitrogen-doped carbon nanotube-coated cobalt composite material, and also improves metal composite efficiency and reduces costs, which is beneficial for the large-scale preparation and application of this composite material. In this invention, the mass ratio of melamine, graphitic carbon nitride, and inorganic cobalt salt is preferably 10:6 to 10:3 to 5, more preferably 10:7 to 10:4 to 5, and even more preferably 10:8 to 9:4.5 to 5. In this invention, melamine provides a carbon source, which is beneficial for generating uniform and dispersed carbon nanotubes; graphitic carbon nitride provides a nitrogen source, which is beneficial for the efficient doping of nitrogen. In this invention, the mixing is preferably a grinding mixture. This invention does not have any special limitations on the specific operating conditions for the grinding mixture, as long as sufficient grinding can be achieved.

[0029] After obtaining the mixed raw materials, the present invention calcines the mixed raw materials in a protective atmosphere to obtain calcined material. In the present invention, the protective atmosphere is preferably a nitrogen atmosphere. In the present invention, the calcination preferably includes sequentially performing a first calcination and a second calcination. In the present invention, the temperature of the first calcination is preferably 500–600°C, specifically 500°C, 550°C, or 600°C; the holding time is preferably 2–4 hours, specifically 2 hours, 3 hours, or 4 hours; the heating rate from room temperature to the temperature of the first calcination is preferably 1.5–2.5°C / min, more preferably 2°C / min. In the present invention, the temperature of the second calcination is preferably 700–900°C, specifically 700°C, 750°C, 800°C, 850°C, or 900°C; the holding time is preferably 1–2 hours, specifically 1 hour, 1.5 hours, or 2 hours; the heating rate from the temperature of the first calcination to the temperature of the second calcination is preferably 4.5–5.5°C / min, more preferably 5°C / min. In the first calcination process of this invention, the organic matter in the mixed raw materials begins to decompose, and the cobalt in the inorganic cobalt salt is reduced to metallic cobalt. In the second calcination process, the carbon-nitrogen mixture generated after the first calcination forms nitrogen-doped carbon nanotubes (i.e., carbon nanotubes doped with nitrogen) under the catalytic action of metallic cobalt. Simultaneously, cobalt and nitrogen bond to form a heterostructure, and the final calcined material is a black solid powder. In embodiments of this invention, the calcination is preferably carried out in a tube furnace.

[0030] After obtaining the calcined material, the present invention sequentially washes and dries the calcined material to obtain the nitrogen-doped carbon nanotube-coated cobalt composite material. In the present invention, the washing preferably includes sequential acid washing and water washing. In the present invention, the acid reagent used for acid washing preferably includes hydrochloric acid and / or sulfuric acid, the concentration of the acid reagent is preferably 0.5–1 mol / L, the acid washing time is preferably 1–2 hours, and the acid washing is preferably carried out at room temperature; the present invention preferably immerses the calcined material in the acid reagent for acid washing, thereby removing cobalt elements from the surface of the calcined material. In the present invention, the water used for water washing is preferably ultrapure water, and the water washing is based on washing until the solution is neutral. In the present invention, the drying temperature is preferably 60–80°C, specifically 60°C, 70°C, or 80°C; the drying time is preferably 4–6 hours, specifically 4 hours, 5 hours, or 6 hours; the drying is preferably vacuum drying.

[0031] This invention provides a nitrogen-doped carbon nanotube-coated cobalt composite material prepared by the preparation method described above. The composite material includes nitrogen-doped carbon nanotubes and cobalt nanoparticles dispersed within the cavities of the nitrogen-doped carbon nanotubes, wherein cobalt and nitrogen are bonded to form a heterostructure. In this invention, the particle size of the cobalt nanoparticles is preferably 20–30 nm. In this invention, the cobalt content in the nitrogen-doped carbon nanotube-coated cobalt composite material is preferably 1–5 wt%, specifically 1.73 wt%, 2.47 wt%, 3.06 wt%, 3.49 wt%, 4.11 wt%, or 4.86 wt%; the nitrogen content is preferably 3–8 wt%, specifically 3.28 wt%, 4.75 wt%, 5.52 wt%, 6.13 wt%, 6.91 wt%, or 7.76 wt%.

[0032] This invention provides the application of the nitrogen-doped carbon nanotube-coated cobalt composite material described above as an ozone oxidation catalyst in the catalytic ozone oxidation degradation of organic pollutants. In this invention, the organic pollutants preferably originate from organic wastewater; the organic pollutants preferably include methylene blue. The method for catalytically degrading organic pollutants in organic wastewater using the nitrogen-doped carbon nanotube-coated cobalt composite material described in this invention as an ozone oxidation catalyst preferably includes the following steps:

[0033] Organic wastewater is mixed with an ozone oxidation catalyst, and ozone is introduced into the resulting mixture for degradation.

[0034] In this invention, the concentration of organic pollutants in the organic wastewater is preferably 20-50 mg / L, more preferably 30 mg / L; the ratio of organic wastewater to ozone oxidation catalyst is preferably 500 mL: 5-20 mg, more preferably 500 mL: 10 mg; the ozone flow rate is preferably 3-10 mg / min, more preferably 5 mg / min. In this invention, the degradation is preferably carried out at room temperature. In an embodiment of this invention, when degradation is carried out under the aforementioned conditions for 10 min, the removal rate of organic pollutants can reach 99.0-99.8%.

[0035] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0036] Example 1

[0037] 1g of melamine, 1g of g-C3N4, and 0.5g of cobalt sulfate were weighed and thoroughly ground in an agate mortar. The ground mixture was transferred to a tube furnace and heated to 600℃ for 2h at a rate of 2℃ / min under a nitrogen atmosphere, and then heated to 800℃ for 2h at a rate of 5℃ / min to obtain a black powder. The black powder was immersed in 1mol / L hydrochloric acid for acid washing for 1h, filtered, and the filter cake was repeatedly washed with ultrapure water until the solution was neutral. It was then transferred to a vacuum drying oven and dried at 60℃ for 6h to obtain a nitrogen-doped carbon nanotube-coated cobalt metal (Co@N-CNT) composite catalyst, designated as sample 1#. The cobalt metal content in sample 1# was 4.11wt%, and the nitrogen content was 6.91wt%.

[0038] Figure 1 The transmission electron microscope image of sample 1# prepared in Example 1 shows that sample 1# has a tubular structure in which black cobalt nanoparticles are coated with carbon nanotubes and the cobalt nanoparticles are uniformly dispersed with a particle size of 20-30 nm.

[0039] Figure 2 The X-ray diffraction pattern of sample 1# prepared in Example 1 shows a diffraction peak at 2θ = 26°, which corresponds to the (002) crystal plane diffraction peak of graphitic carbon, indicating that sample 1# contains sp. 2 The hybrid carbon structure; diffraction peaks corresponding to the (111), (200) and (220) crystal planes of metallic cobalt appeared at 2θ of 44°, 52° and 76°.

[0040] Figure 3 The X-ray photoelectron spectrum of sample 1# prepared in Example 1 shows that a peak of cobalt-nitrogen bonding structure appears in sample 1#.

[0041] Example 2

[0042] 1g of melamine, 0.8g of g-C3N4, and 0.4g of cobalt chloride were weighed and thoroughly ground in an agate mortar. The ground mixture was transferred to a tube furnace and heated to 500℃ at a rate of 2℃ / min for 3h under a nitrogen atmosphere, and then heated to 900℃ at a rate of 5℃ / min for 1h to obtain a black powder. The black powder was immersed in 0.5mol / L sulfuric acid for 2h, filtered, and the filter cake was repeatedly washed with ultrapure water until the solution was neutral. It was then transferred to a vacuum drying oven and dried at 80℃ for 4h to obtain a nitrogen-doped carbon nanotube-coated cobalt (Co@N-CNT) composite catalyst, designated as sample 2#. The cobalt content in sample 2# was 3.06wt%, and the nitrogen content was 6.13wt%.

[0043] Example 3

[0044] 1g of melamine, 0.6g of g-C3N4, and 0.3g of cobalt nitrate were weighed and thoroughly ground in an agate mortar. The ground mixture was transferred to a tube furnace and heated to 550℃ at a rate of 2℃ / min for 4h under a nitrogen atmosphere, and then heated to 700℃ at a rate of 5℃ / min for 3h to obtain a black powder. The black powder was immersed in 0.8mol / L hydrochloric acid for 1h, filtered, and the filter cake was repeatedly washed with ultrapure water until the solution was neutral. It was then transferred to a vacuum drying oven and dried at 70℃ for 5h to obtain a nitrogen-doped carbon nanotube-coated cobalt (Co@N-CNT) composite catalyst, designated as sample 3#. The cobalt content in sample 3# was 1.73wt%, and the nitrogen content was 4.75wt%.

[0045] Example 4

[0046] 1g of melamine, 0.8g of g-C3N4, and 0.5g of cobalt sulfate were weighed and thoroughly ground in an agate mortar. The ground mixture was transferred to a tube furnace and heated to 600℃ at a rate of 2℃ / min for 2h under a nitrogen atmosphere, and then heated to 800℃ at a rate of 5℃ / min for 2h to obtain a black powder. The black powder was immersed in 0.6mol / L sulfuric acid for 2h, filtered, and the filter cake was repeatedly washed with ultrapure water until the solution was neutral. It was then transferred to a vacuum drying oven and dried at 60℃ for 6h to obtain a nitrogen-doped carbon nanotube-coated cobalt (Co@N-CNT) composite catalyst, designated as sample 4#. The cobalt content in sample 4# was 4.86wt%, and the nitrogen content was 5.52wt%.

[0047] Example 5

[0048] 1g of melamine, 0.6g of g-C3N4, and 0.4g of cobalt chloride were weighed and thoroughly ground in an agate mortar. The ground mixture was transferred to a tube furnace and heated to 500℃ at a rate of 2℃ / min for 3h under a nitrogen atmosphere, and then heated to 700℃ at a rate of 5℃ / min for 3h to obtain a black powder. The black powder was immersed in 0.6mol / L hydrochloric acid for 1h, filtered, and the filter cake was repeatedly washed with ultrapure water until the solution was neutral. It was then transferred to a vacuum drying oven and dried at 80℃ for 4h to obtain a nitrogen-doped carbon nanotube-coated cobalt (Co@N-CNT) composite catalyst, designated as sample 5#. The cobalt content in sample 5# was 3.49wt%, and the nitrogen content was 3.28wt%.

[0049] Example 6

[0050] 1g of melamine, 1g of g-C3N4, and 0.4g of cobalt nitrate were weighed and thoroughly ground in an agate mortar. The ground mixture was transferred to a tube furnace and heated to 550℃ at a rate of 2℃ / min for 4 hours under a nitrogen atmosphere. Then, the temperature was increased to 900℃ at a rate of 5℃ / min and held for 1 hour to obtain a black powder. The black powder was immersed in 0.8mol / L sulfuric acid for 2 hours for acid washing. After filtration, the filter cake was repeatedly washed with ultrapure water until the solution was neutral and then transferred to a vacuum drying oven and dried at 70℃ for 5 hours to obtain a nitrogen-doped carbon nanotube-coated cobalt (Co@N-CNT) composite catalyst, designated as sample 6#. The cobalt content in sample 6# was 2.47wt%, and the nitrogen content was 7.76wt%.

[0051] Comparative Example 1

[0052] Following the method of Example 1, except that g-C3N4 was omitted, a nitrogen-doped nano-cobalt (Co-N) composite catalyst was finally prepared, designated as Sample 7#; the cobalt content in Sample 7# was 4.66 wt%, and the nitrogen content was 6.25 wt%.

[0053] Comparative Example 2

[0054] Following the method of Example 6, except that cobalt nitrate was omitted, a nitrogen-doped carbon nanotube (CNT-N) composite catalyst was finally prepared, designated as Sample 8#; the cobalt content in Sample 8# was 0 wt%, and the nitrogen content was 7.92 wt%.

[0055] Comparative Example 3

[0056] The procedure was followed according to Example 1, except that cobalt sulfate was replaced with cobalt acetylacetone. The final product was a nitrogen-doped carbon nanotube-coated cobalt (Co@N-CNT) composite catalyst, designated as sample 9#. The cobalt content in sample 9# was 0.84 wt%, and the nitrogen content was 7.12 wt%.

[0057] Comparative Example 4

[0058] The procedure was followed according to Example 1, except that cobalt sulfate was replaced with cobalt acetylacetonate and the amount of cobalt acetylacetonate was increased to 1.5g. The nitrogen-doped carbon nanotube-coated cobalt (Co@N-CNT) composite catalyst was finally prepared and was designated as sample 10#. The cobalt content in sample 10# was 2.53wt% and the nitrogen content was 7.94wt%.

[0059] Test Example 1

[0060] The composite catalysts prepared in the examples and comparative examples were used to treat simulated organic wastewater by ozone catalytic oxidation. The specific steps are as follows: 10 mg of the composite catalyst was added to 500 mL of simulated organic wastewater with an initial methylene blue concentration of 30 mg / L. After stirring evenly with magnetic force, ozone gas with a flow rate of 5 mg / min was introduced at room temperature (25℃). The concentration change of methylene blue was analyzed at regular intervals. The experimental results are shown in Table 1. As can be seen from Table 1, the Co@N-CNT composite material prepared in the examples of this invention has high catalytic activity as an ozone oxidation catalyst. It can effectively promote the generation of active free radicals in the ozone oxidation reaction, catalyze the degradation of organic pollutants by ozone oxidation, and improve the degradation efficiency of organic pollutants. It has significant advantages compared with the composite material prepared in the comparative example.

[0061] Table 1. Performance test results of the composite catalysts prepared in the examples and comparative examples for degrading methylene blue.

[0062]

[0063]

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon nanotube-coated cobalt composite material, comprising the following steps: Melamine, graphitic carbon nitride, and inorganic cobalt salt are mixed to obtain a mixed raw material; the mass ratio of melamine, graphitic carbon nitride, and inorganic cobalt salt is 10:6~10:3~5. The mixed raw materials are calcined in a protective atmosphere to obtain calcined material; The calcined material is washed and dried sequentially to obtain the nitrogen-doped carbon nanotube-coated cobalt composite material. The nitrogen-doped carbon nanotube-coated cobalt composite material includes nitrogen-doped carbon nanotubes and cobalt nanoparticles dispersed in the cavities of the nitrogen-doped carbon nanotubes, and cobalt and nitrogen are bonded to form a heterostructure in the nitrogen-doped carbon nanotube-coated cobalt composite material. The particle size of the cobalt nanoparticles is 20~30 nm. The cobalt content in the nitrogen-doped carbon nanotube-coated cobalt composite material is 1~5 wt%, and the nitrogen content is 3~8 wt%.

2. The preparation method according to claim 1, characterized in that, The inorganic cobalt salt includes one or more of cobalt chloride, cobalt nitrate, and cobalt sulfate.

3. The preparation method according to claim 1, characterized in that, The calcination includes a first calcination and a second calcination in sequence; the temperature of the first calcination is 500~600 ℃ and the holding time is 2~4 h; the temperature of the second calcination is 700~900 ℃ and the holding time is 1~2 h.

4. The preparation method according to claim 1, characterized in that, The washing process includes sequential acid washing and water washing; the acid reagent used for acid washing includes hydrochloric acid and / or sulfuric acid, the concentration of the acid reagent is 0.5~1 mol / L, and the acid washing time is 1~2 h; the drying temperature is 60~80 ℃, and the drying time is 4~6 h.

5. The nitrogen-doped carbon nanotube-coated cobalt composite material prepared by the preparation method according to any one of claims 1 to 4, comprising nitrogen-doped carbon nanotubes and cobalt nanoparticles dispersed in the cavities of the nitrogen-doped carbon nanotubes, wherein cobalt and nitrogen are bonded to form a heterostructure in the nitrogen-doped carbon nanotube-coated cobalt composite material; the particle size of the cobalt nanoparticles is 20 to 30 nm; and the cobalt content in the nitrogen-doped carbon nanotube-coated cobalt composite material is 1 to 5 wt%, and the nitrogen content is 3 to 8 wt%.

6. The application of the nitrogen-doped carbon nanotube-coated cobalt composite material of claim 5 as an ozone oxidation catalyst in the catalytic ozone oxidation degradation of organic pollutants.

7. The application according to claim 6, characterized in that, The organic pollutant includes methylene blue.

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