Preparation and application of amino-rich ordered carbon nitride nanosheet catalyst

Abstract

The invention belongs to the technical field of photocatalytic materials, and particularly discloses a preparation method of an amino-rich ordered carbon nitride nanosheet catalyst and application of the amino-rich ordered carbon nitride nanosheet catalyst in photocatalytic degradation of methyl mercaptan. Aiming at the problems of insufficient surface active sites, high photon-generated carrier recombination rate and the like of an existing carbon nitride material, carbon nitride is subjected to secondary thermal polymerization in an ammonia atmosphere through an ammonia-assisted thermal polymerization reconstruction strategy, and a carbon nitride nanosheet catalyst with high-density surface amino groups and a layered ordered structure is formed through induction. The amino-rich ordered carbon nitride nanosheet catalyst prepared by the invention can realize high-efficiency degradation of methyl mercaptan under the conditions of room temperature and visible light. The technical system has the advantages of low reaction energy consumption, high degradation efficiency, mild operation conditions and the like, and meets the actual production requirements; the catalyst shows excellent photocatalytic activity and stability, is suitable for large-scale industrial production, and has a good industrial application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to the preparation and application of an amino-rich ordered carbon nitride nanosheet catalyst. Background Art

[0002] Methyl mercaptan (CH3SH), as a typical sulfur-containing volatile organic compound, widely exists in the processes of fossil energy development such as coal mining and oil and gas drilling, as well as in chemical production systems. Its harmfulness presents multi-dimensional characteristics: at the level of biosafety, inhalation by humans can cause acute poisoning reactions such as nausea and vomiting, and high-concentration exposure can lead to respiratory paralysis and even death; at the level of industrial applications, gaseous CH3SH is prone to chemically adsorb on the metal surface, corroding equipment and pipelines; at the level of the ecological environment, CH3SH in the atmosphere can generate sulfate aerosols through photooxidation reactions, forming photochemical smog and acid rain. Currently, the removal technologies for CH3SH mainly include physical adsorption methods, biodegradation methods, and catalytic conversion methods (including catalytic oxidation and photocatalytic degradation). Among them, the photocatalytic method is a technology that uses a photocatalyst to generate electron-hole pairs under light irradiation conditions, thereby undergoing oxidation-reduction reactions to remove methyl mercaptan. The key to the industrial application of photocatalytic technology lies in the development of economical and efficient photocatalysts.

[0003] In the photocatalytic system, traditional catalysts such as titanium dioxide (TiO2), transition metal oxides (such as Fe2O3, WO3, Bi2O3), metal sulfides (such as CdS, MoS2, ZnIn2S4, WS2, Cd x Zn 1-x S), and metal-organic framework (MOF) materials have been widely used, but their actual performance is limited by bottlenecks such as a narrow solar spectrum response range, a sharp increase in material costs caused by the dependence on noble metal cocatalysts, easy secondary pollution, and poor structural stability, which greatly limits their large-scale application. To address the above technical challenges, the construction of a new type of photocatalyst with both high desulfurization activity and excellent catalytic stability has become the core research direction for promoting the engineering application of this technology.

[0004] In recent years, carbon nitride, as a new type of non-metallic semiconductor photocatalyst, has shown broad application prospects in the field of environmental photocatalysis due to its low cost, simple preparation process, excellent chemical stability, and strong structural tunability. However, carbon nitride prepared by traditional thermal polymerization methods has problems such as insufficient surface active sites and high recombination rates of photo-generated carriers, making it difficult to deeply oxidize CH3SH to generate SO4 2- . Therefore, it is necessary to construct a carbon nitride catalyst with rich surface active sites and a high photo-generated carrier transfer rate to achieve the deep oxidation of CH3SH. Summary of the Invention

[0005] To solve the drawbacks and deficiencies of the above technologies, the present invention provides a preparation method and application of a photocatalytic degradation catalyst for CH3SH. Through an ammonia-assisted thermal polymerization reconstruction strategy, the present invention performs secondary thermal polymerization of carbon nitride in an ammonia atmosphere to induce the formation of a carbon nitride nanosheet catalyst with a high-density surface amino group and a layered ordered structure; the degree of interlayer order of the catalyst is improved, accelerating the transport rate of photogenerated carriers, and enabling the deep oxidation of CH3SH. At the same time, the catalyst preparation process of the present invention is simple, the raw materials are easily available, and it can be reused, having broad industrial application prospects.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a rich-amino ordered carbon nitride nanosheet catalyst, which performs secondary thermal polymerization of carbon nitride in an ammonia atmosphere through an ammonia-assisted thermal polymerization reconstruction strategy to induce the formation of a carbon nitride nanosheet catalyst with a high-density surface amino group and a layered ordered structure.

[0007] The above preparation method of a rich-amino ordered carbon nitride nanosheet catalyst includes the following steps: (1) Place the nitrogen-containing precursor in an air muffle furnace for calcination, naturally cool to room temperature, and grind to obtain carbon nitride powder; (2) Put the carbon nitride powder into an alumina boat and transfer it to a tube furnace, calcine it in an ammonia atmosphere, naturally cool to room temperature, wash the product with deionized water, then dry and grind to obtain the rich-amino ordered carbon nitride nanosheet catalyst.

[0008] Further, in step (1), the nitrogen-containing precursor includes but is not limited to dicyandiamide, melamine, and urea.

[0009] Further, in step (1), the dosage of the nitrogen-containing precursor is 5-20 g. Preferably, the dosage of the nitrogen-containing precursor is 10 g.

[0010] Further, in step (1), the calcination conditions are: heating to 550 °C at a heating rate of 2-10 °C / min and calcining for 2 h. Preferably, the heating rate is 5 °C / min.

[0011] Further, in step (2), the dosage of the carbon nitride powder is 2-5 g. Preferably, the dosage of the carbon nitride powder is 2.5 g.

[0012] Further, in step (2), the calcination conditions are: heating to 600-620 °C at a heating rate of 2-5 °C / min and calcining for 1-3 h. Preferably, the heating rate is 3 °C / min, the calcination temperature is 600 °C, and the calcination time is 1.5 h.

[0013] Further, in step (2), the flow rate of ammonia gas is 50 - 150 ml / min. Preferably, the flow rate of ammonia gas is 100 ml / min.

[0014] Amino-rich ordered carbon nitride nanosheet catalyst prepared by the above preparation method.

[0015] Application of the above amino-rich ordered carbon nitride nanosheet catalyst in photocatalytic degradation of CH3SH. Specifically, at room temperature and atmospheric pressure, using a xenon lamp or LED lamp as the light source, a continuous flow reactor is used to test the photocatalytic oxidation reaction activity of the amino-rich ordered carbon nitride nanosheet catalyst for CH3SH; the mass of the catalyst used is 20 mg, and the concentration of CH3SH introduced into the reaction system is 100 ppm.

[0016] The beneficial effects of the technical solution of the present invention are as follows: (1) The present invention adopts an ammonia-assisted thermal polymerization reconstruction strategy. First, a nitrogen-containing precursor (such as dicyandiamide, melamine, etc.) is calcined for the first time to prepare carbon nitride powder, and then it is calcined for the second time in an ammonia atmosphere at 600 - 620 °C. In this process, the nitrogen source of NH3 reacts with uncondensed edge sites to generate a high-density surface amino group to enhance the adsorption capacity for CH3SH; at the same time, NH3 etches the weak chemical bonds (such as hydrogen bonds or van der Waals forces) between the carbon nitride layers to peel off and form an ultra-thin nanosheet structure with a thickness < 10 nm, which can shorten the migration distance of photogenerated carriers, thereby promoting charge separation; the finally prepared amino-rich ordered carbon nitride nanosheet catalyst can achieve the deep oxidation of CH3SH (SO4 2- ).

[0017] (2) The preparation method of the catalyst used in the present invention is simple, the raw materials are easy to obtain, it can be reused, and the photocatalytic activity is stable.

[0018] (3) The process of the present invention is simple to operate, green, safe and pollution-free, suitable for large-scale industrial production, and has good industrial application prospects. Description of the Drawings

[0019] Figure 1 Fourier transform infrared spectrum (FT-IR) of the MCN-NH2 catalyst prepared in Example 1 and CN prepared in the comparative example.

[0020] Figure 2 N1s fine spectrum of X-ray photoelectron spectroscopy (XPS) of the MCN-NH2 catalyst prepared in Example 1 and CN prepared in the comparative example.

[0021] Figure 3 X-ray powder diffraction pattern (XRD) of the MCN-NH2 catalyst prepared in Example 1 and CN prepared in the comparative example.

[0022] Figure 4 Transmission electron microscope image (TEM) of the MCN-NH2 catalyst prepared in Example 1.

[0023] Figure 5 Atomic force microscope image (AFM) of the MCN-NH2 catalyst prepared in Example 1.

[0024] Figure 6 Photocatalytic degradation activity comparison chart of the MCN-NH2 catalyst prepared in Example 1 and CN prepared in the comparative example for CH3SH.

[0025] Figure 7 Photocatalytic degradation stability test chart of the MCN-NH2 catalyst prepared in Example 1 for 4 cycles for CH3SH. Detailed implementation manners

[0026] In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific implementation manners, but the present invention is not limited thereto.

[0027] Example 1 First, weigh 10 g of melamine and calcine it in an air muffle furnace at a heating rate of 5 °C / min to 550 °C for 2 h, then naturally cool it to room temperature and grind it to obtain carbon nitride powder. Weigh 2.5 g of carbon nitride powder and put it into an alumina boat, and transfer it to a tubular furnace. Under an ammonia atmosphere, heat it to 600 °C at a heating rate of 3 °C / min and calcine it for 1.5 h, with an ammonia flow rate of 100 ml / min. Naturally cool it to room temperature, wash the product with deionized water, then dry and grind it to obtain an amino-rich ordered carbon nitride nanosheet catalyst (MCN-NH2) synthesized using melamine as a precursor.

[0028] Example 2 First, weigh 10 g of dicyandiamide and calcine it in an air muffle furnace at a heating rate of 5 °C / min to 550 °C for 2 h, then naturally cool it to room temperature and grind it to obtain carbon nitride powder. Weigh 2.5 g of carbon nitride powder and put it into an alumina boat, and transfer it to a tubular furnace. Under an ammonia atmosphere, heat it to 600 °C at a heating rate of 3 °C / min and calcine it for 1.5 h, with an ammonia flow rate of 100 ml / min. Naturally cool it to room temperature, wash the product with deionized water, then dry and grind it to obtain an amino-rich ordered carbon nitride nanosheet catalyst (DCN-NH2) synthesized using dicyandiamide as a precursor.

[0029] Comparative example First, weigh 10 g of melamine and heat it in an air muffle furnace at a heating rate of 5 °C / min to 550 °C for 2 h. Then, cool it naturally to room temperature. Wash the product with deionized water, and then dry and grind it to obtain polymeric carbon nitride (CN).

[0030] Application Example The photocatalytic degradation reaction activity of amino-rich ordered carbon nitride nanosheet catalyst for CH3SH was tested using a continuous flow reactor. The experimental process was as follows: Load 20 mg of the catalyst into a quartz reactor, seal both ends with quartz wool plugs, and then feed CH3SH gas (total gas flow rate of 10 ml / min, CH3SH concentration of 100 ppm, O2 concentration of 50000 ppm, and N2 as the balance gas) into the reactor. After purging for a period of time under dark conditions to reach adsorption equilibrium, irradiate continuously with a xenon lamp or an LED lamp as the light source. A gas chromatograph (FULI-9790Ⅱ) equipped with a flame photometric detector was used to qualitatively and quantitatively analyze the gas-phase products in the system.

[0031] Figure 1 FT-IR spectra of the MCN-NH2 catalyst obtained in Example 1 and CN obtained in the comparative example. It can be seen from the figure that 805 cm -1 belongs to the out-of-plane bending vibration of the heptazine ring, and 1200 - 1630 cm -1 belongs to the stretching vibration of the aromatic CN heterocycle. The range of 3200 cm -1 belongs to the stretching vibration of -NH2 / -NH, confirming that the prepared product is a carbon nitride material. Among them, the infrared peak intensity of -NH2 / -NH in MCN-NH2 is significantly enhanced, indicating an increase in the amino groups of the MCN-NH2 catalyst.

[0032] Figure 2 XPS N1s fine spectra of the MCN-NH2 catalyst obtained in Example 1 and CN obtained in the comparative example. It can be seen from the figure that the peak intensities related to bridging -NH- and terminal amino -NH2 groups increase, further indicating that carbon nitride with a high-density surface amino group can be obtained by introducing ammonia during the calcination process.

[0033] Figure 3 XRD patterns of the MCN-NH2 catalyst obtained in Example 1 and CN obtained in the comparative example. It can be seen from the figure that the (002) diffraction peak of MCN-NH2 is shifted to the right compared with that of CN, reflecting a shortening of the interlayer stacking distance, which is beneficial to the transport of carriers between layers and improves the photocatalytic activity. Compared with CN, the full width at half maximum of the (002) peak of MCN-NH2 is narrower than that of CN, indicating an improvement in the interlayer order of MCN-NH2.

[0034] Figure 4TEM image of the MCN-NH2 catalyst obtained in Example 1. It can be seen from the figure that the clear lattice fringes with an interlayer spacing of 0.32 nm correspond to the (002) plane of MCN-NH2; MCN-NH2 exhibits the characteristics of being thin, transparent, and curly stacked.

[0035] Figure 5 AFM image of the MCN-NH2 catalyst obtained in Example 1. It can be seen from the figure that the prepared MCN-NH2 is an ultrathin nanosheet structure.

[0036] Figure 6 Photocatalytic degradation activity comparison chart of the MCN-NH2 catalyst obtained in Example 1 and CN obtained in the comparative example for CH3SH. It can be seen from the figure that the photocatalytic degradation activity of CN for CH3SH is very low, while the MCN-NH2 catalyst has high photocatalytic degradation activity for CH3SH. In the 10-hour catalytic reaction, the conversion rate of CH3SH reaches 100%, and it has good stability.

[0037] Figure 7 Photocatalytic degradation stability test chart of the MCN-NH2 catalyst obtained in Example 1 for 4 cycles of CH3SH. It can be seen from the figure that no obvious inactivation is observed for the regenerated catalyst after four cycles, and the photocatalytic degradation conversion rate of CH3SH is still 100%, indicating that the MCN-NH2 catalyst has good cycle stability.

[0038] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A preparation method of an amino-rich ordered carbon nitride nanosheet catalyst, characterized in that: Through the ammonia-assisted thermal polymerization reconstruction strategy, carbon nitride is subjected to secondary thermal polymerization in an ammonia atmosphere to induce the formation of a carbon nitride nanosheet catalyst with a high-density surface amino group and a layered ordered structure.

2. The preparation method according to claim 1, characterized in that: It includes the following steps: (1) Calcinate the nitrogen-containing precursor in an air muffle furnace, naturally cool it to room temperature, and grind it to obtain carbon nitride powder; (2) Put the carbon nitride powder into an alumina boat and transfer it to a tubular furnace. Calcinate it in an ammonia atmosphere, naturally cool it to room temperature, wash the product with deionized water, then dry and grind it to obtain the amino-rich ordered carbon nitride nanosheet catalyst.

3. The preparation method according to claim 2, characterized in that: In step (1), the nitrogen-containing precursor includes but is not limited to dicyandiamide, melamine, and urea.

4. The preparation method according to claim 2, characterized in that: In step (1), the dosage of the nitrogen-containing precursor is 5-20 g.

5. The preparation method according to claim 2, characterized in that: In step (1), the calcination conditions are: heat up to 550 °C at a heating rate of 2-10 °C / min and calcine for 2 h.

6. The preparation method according to claim 2, characterized in that: In step (2), the dosage of the carbon nitride powder is 2-5 g.

7. The preparation method according to claim 2, characterized in that: In step (2), the calcination conditions are: heat up to 600-620 °C at a heating rate of 2-5 °C / min and calcine for 1-3 h.

8. The preparation method according to claim 2, characterized in that: In step (2), the flow rate of ammonia is 50-150 ml / min.

9. An amino-rich ordered carbon nitride nanosheet catalyst prepared by the preparation method according to any one of claims 1-8.

10. Application of the amino-rich ordered carbon nitride nanosheet catalyst according to claim 9 in photocatalytic degradation of CH3SH.

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