A method for preparing carbon nitride with high efficiency photocatalytic oxygen production

Abstract

The invention discloses a polyheptazine imino carbon nitride photocatalyst and a preparation method and application thereof, and belongs to the technical field of photocatalytic material preparation. The invention uses melamine as a precursor, rubidium chloride as a high-temperature solvent and a structure-directing agent, and synthesizes a polyheptazine imino carbon nitride photocatalyst having a heptazine crystal phase structure by a thermal polymerization method. The catalyst has a simple synthesis method and a considerable yield. It is a non-metallic photocatalytic oxygen production catalyst with a relatively high efficiency at present, and has the potential to realize photocatalytic total water decomposition and the prospect of large-scale industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic material preparation, and specifically relates to a polyheptazine imino carbon nitride photocatalyst with high photolysis water oxygen production performance, and a preparation method and application thereof. Background Art

[0002] Global industrialization has led to over-exploitation of fossil fuels, exacerbating two major problems: energy crisis and environmental pollution. Therefore, people have proposed carbon neutrality plans and carbon peak targets. Using solar energy to convert hydrogen is currently one of the most ideal and promising green and achievable ways. Photocatalytic water decomposition to produce hydrogen has attracted more and more attention due to its simplicity and low cost. The reaction consists of a hydrogen evolution half-reaction and an oxygen evolution half-reaction. Among them, because the oxygen evolution half-reaction is a four-electron transfer reaction process, it becomes the rate-determining step of the entire reaction. At present, because the conditions of the oxygen evolution half-reaction are more stringent than those of the hydrogen evolution half-reaction, there are very few catalysts that meet the oxygen evolution performance, which seriously restricts the research progress of the entire photocatalytic water decomposition to produce hydrogen.

[0003] Among many photocatalysts, polymer semiconductor photocatalysts, such as carbon nitride and conjugated organic frameworks, have great research potential due to their tunable energy band structures. Among them, carbon nitride is considered to be one of the best photocatalyst candidates due to its advantages such as simple synthesis method, low cost, tunable structure and stable performance. However, carbon nitride photocatalysts are still in their infancy. Therefore, it is extremely important to develop a carbon nitride photocatalyst that is easy to prepare, economical, environmentally friendly and high-performance. Summary of the invention

[0004] The purpose of the present invention is to provide a polyheptazine imino carbon nitride photocatalyst and a preparation method and application thereof. The prepared photocatalyst has a high sunlight utilization rate and can achieve efficient photocatalytic decomposition of water to produce oxygen.

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

[0006] A polyheptazine imino carbon nitride photocatalyst is synthesized by thermal polymerization of melamine and rubidium chloride as a high-temperature solvent and structure-directing agent. It has a heptazine crystal phase structure, a microscopic morphology of hexagonal prism-like flakes, and an optical absorption edge near 460 nm.

[0007] The preparation method of the polyheptazine imino carbon nitride photocatalyst comprises the following steps:

[0008] 1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0009] 2) Grind and mix the polymer carbon nitride and rubidium chloride in a mass ratio of 1:10, then heat to 400°C at a rate of 1°C / min, keep warm for 2 hours, cool to room temperature and evacuate, then heat to 600°C at a rate of 1°C / min, keep warm for 8 hours, to obtain the polyheptazine imino carbon nitride photocatalyst.

[0010] The intrinsic absorption band edge of the polyheptazine imino carbon nitride photocatalyst is improved, so that it has a stronger driving force for oxygen production during the photocatalytic reaction, and can be used for photocatalytic decomposition of water to produce oxygen. The specific application method is to use the polyheptazine imino carbon nitride as a photocatalyst, add AgNO 3 As an electron sacrificial agent, La 2 O 3 As a pH buffer, it photocatalytically decomposes water to produce oxygen under light conditions.

[0011] The significant advantages of the present invention are:

[0012] (1) In the present invention, rubidium chloride is used as a high-temperature solvent and a structure regulator, which can effectively improve the absorption band edge of the catalyst.

[0013] (2) The photocatalyst synthesized by the present invention embeds alkali metal ions rubidium into the carbon nitride framework, which promotes the separation of photogenerated charges, thereby facilitating the photocatalytic decomposition to produce oxygen.

[0014] (3) The preparation process of the present invention is simple and has a considerable yield. It is currently a non-metallic photocatalytic oxygen production catalyst with relatively high efficiency and has the prospect of large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a scanning electron microscope image of the carbon nitride photocatalyst obtained in Example 4.

[0016] Figure 2 The figure is a comparison of the powder X-ray diffraction spectra of the carbon nitride photocatalysts obtained in Examples 1-4.

[0017] Figure 3 This is a comparison chart of the Fourier transform infrared spectra of the carbon nitride photocatalysts obtained in Examples 1-4.

[0018] Figure 4 This is a high-resolution transmission electron microscopy image of the carbon nitride photocatalyst obtained in Example 4.

[0019] Figure 5 This is the UV-visible diffuse reflectance spectrum of the carbon nitride photocatalyst obtained in Example 4.

[0020] Figure 6 This is a comparison chart of the photocatalytic water decomposition and oxygen production activities of the carbon nitride photocatalysts obtained in Examples 1-4.

[0021] Figure 7 This is a comparison chart of the photocatalytic decomposition of water to produce oxygen by the carbon nitride photocatalysts obtained in Example 4 and Comparative Examples 1-4. DETAILED DESCRIPTION

[0022] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0023] Example 1

[0024] (1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0025] (2) The obtained polymer carbon nitride and rubidium chloride were ground and mixed in a mass ratio of 1:10, and then heated to 400°C at a rate of 1°C / min and kept at this temperature for 2 h. After cooling to room temperature, the mixture was evacuated and then heated to 525°C at a rate of 1°C / min and kept at this temperature for 8 h to obtain the carbon nitride photocatalyst.

[0026] Example 2

[0027] (1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0028] (2) The obtained polymer carbon nitride and rubidium chloride were ground and mixed in a mass ratio of 1:10, and then heated to 400°C at a rate of 1°C / min and kept at this temperature for 2 h. After cooling to room temperature, the mixture was evacuated and then heated to 550°C at a rate of 1°C / min and kept at this temperature for 8 h to obtain the carbon nitride photocatalyst.

[0029] Example 3

[0030] (1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0031] (2) The obtained polymer carbon nitride and rubidium chloride were ground and mixed in a mass ratio of 1:10, and then heated to 400°C at a rate of 1°C / min and kept at this temperature for 2 h. After cooling to room temperature, the mixture was evacuated and then heated to 575°C at a rate of 1°C / min and kept at this temperature for 8 h to obtain the carbon nitride photocatalyst.

[0032] Example 4

[0033] (1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0034] (2) The obtained polymer carbon nitride and rubidium chloride were ground and mixed evenly in a mass ratio of 1:10, and then heated to 400°C at a rate of 1°C / min and kept at this temperature for 2 h. After cooling to room temperature, the mixture was evacuated and then heated to 600°C at a rate of 1°C / min and kept at this temperature for 8 h to obtain the carbon nitride photocatalyst.

[0035] Comparative Example 1

[0036] (1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0037] (2) The obtained polymer carbon nitride was heated to 400°C at a rate of 1°C / min and kept at this temperature for 2 h. After cooling to room temperature, the mixture was evacuated and then heated to 600°C at a rate of 1°C / min and kept at this temperature for 8 h to obtain a carbon nitride photocatalyst.

[0038] Comparative Example 2

[0039] (1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0040] (2) The obtained polymer carbon nitride and sodium chloride are ground and mixed evenly in a mass ratio of 1:10, and then the temperature is increased to 400°C at a rate of 1°C / min and kept at this temperature for 2 hours. After cooling to room temperature, the temperature is evacuated, and then the temperature is increased to 600°C at a rate of 1°C / min and kept at this temperature for 8 hours to obtain the carbon nitride photocatalyst.

[0041] Comparative Example 3

[0042] (1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0043] (2) The obtained polymer carbon nitride and potassium chloride are ground and mixed evenly in a mass ratio of 1:10, and then the temperature is increased to 400°C at a rate of 1°C / min and kept at this temperature for 2 h. After cooling to room temperature, the temperature is evacuated, and then the temperature is increased to 600°C at a rate of 1°C / min and kept at this temperature for 8 h to obtain the carbon nitride photocatalyst.

[0044] Comparative Example 4

[0045] (1) placing melamine solid powder in a muffle furnace, heating it to 550°C at a rate of 275°C / h, keeping it at that temperature for 4 hours, and then grinding it evenly to obtain polymer carbon nitride;

[0046] (2) The obtained polymer carbon nitride and cesium chloride were ground and mixed in a mass ratio of 1:10, and then heated to 400°C at a rate of 1°C / min and kept at this temperature for 2 h. After cooling to room temperature, the mixture was evacuated and then heated to 600°C at a rate of 1°C / min and kept at this temperature for 8 h to obtain the carbon nitride photocatalyst.

[0047] Figure 1 This is a scanning electron microscope image of the carbon nitride photocatalyst obtained in Example 4. From the image, it can be observed that the carbon nitride is in the form of hexagonal thin sheets.

[0048] Figure 2 The figure is a comparison of the powder X-ray diffraction spectra of the carbon nitride photocatalysts obtained in Examples 1-4. It can be found from the figure that all catalysts have diffraction peaks at 8° and 28°, which correspond to the repeating unit in the plane and the interlayer stacking distance, respectively, and are typical PHI. In addition, there are some high-angle but relatively low-intensity diffraction peaks, and when the synthesis temperature reaches 600°C, the relative intensity of these high-angle diffraction peaks reaches the highest.

[0049] Figure 3 The Fourier transform infrared spectrum of the carbon nitride photocatalyst obtained in Example 1-4 is shown in FIG. -1 The absorption peak of the wave number is attributed to the amino or hydroxyl groups in the structure, 800cm −1 , 995 and 915 cm -1 The absorption peaks on the left and right correspond to the vibration absorption of the heptazine ring and the stretching vibration of MN, respectively, proving that the obtained product is polyheptazine imino carbon nitride. At the same time, with the increase of synthesis temperature, the intensity of infrared absorption increases consistently, which proves that the Rb ion content increases with temperature, which improves the polymerization degree of the heptazine ring.

[0050] Figure 4 This is a high-resolution transmission electron microscope image of the carbon nitride photocatalyst obtained in Example 4. This image further shows that the obtained photocatalyst has good crystallinity. Among them, the lattice spacing of about 1.0 nanometers represents the periodic repeating unit of the heptazine ring in the plane, and the lattice spacing of about 0.316 nanometers represents the interlayer stacking of the heptazine ring in the two-dimensional plane similar to graphite.

[0051] Figure 5 This is the UV-visible diffuse reflectance spectrum of the carbon nitride photocatalyst obtained in Example 4. It can be seen from the figure that the optical absorption edge of the photocatalyst is near 460 nanometers.

[0052] Oxygen production activity experiment:

[0053] Use 50 mg photocatalyst, 100 ml deionized water, 0.17 g AgNO 3 and 0.2 g La 2 O 3 , a photocatalytic oxygen production reaction is carried out in a reactor equipped with a 300-watt xenon lamp on the top.

[0054] Figure 6 This is a comparison chart of the photocatalytic decomposition of water and oxygen production activity of carbon nitride photocatalysts obtained in Examples 1 to 4. It can be seen from the figure that the photocatalytic oxygen production rate of the catalyst prepared in Example 4 at a synthesis temperature of 600°C reaches 298µmol / h, which is significantly better than the catalysts prepared at other synthesis temperatures.

[0055] Figure 7 The figure is a comparison of the photocatalytic decomposition of water and oxygen production activity of carbon nitride photocatalysts obtained in Example 4 and Comparative Examples 1 to 4. It can be found from the figure that the photocatalytic oxygen production performance of the catalyst prepared using rubidium chloride as a high-temperature solvent and a structure regulator is the best.

[0056] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. An application of a polyheptazine imino carbon nitride photocatalyst in photocatalytic decomposition of water to produce oxygen, characterized in that: The polyheptazine imino carbon nitride photocatalyst has a heptazine crystal phase structure, and its microscopic morphology is a hexagonal prism-like thin sheet; the preparation method thereof comprises the following steps: 1) placing melamine solid powder in a muffle furnace, heating it to a certain temperature at a certain rate, keeping it warm for reaction, and grinding it evenly to obtain polymer carbon nitride; 2) grinding and mixing the polymer carbon nitride and rubidium chloride as a high-temperature solvent and a structure-directing agent, and subjecting the polymer carbon nitride to a thermal polymerization reaction to synthesize the polyheptazine imino carbon nitride photocatalyst; In step 2), the thermal polymerization reaction is carried out by heating to 400°C at a rate of 1°C / min, keeping the temperature for 2 hours, cooling to room temperature, evacuating the temperature, and then heating to 600°C at a rate of 1°C / min and keeping the temperature for 8 hours.

2. The use according to claim 1, characterized in that: The heating rate in step 1) is 275°C / h.

3. The use according to claim 1, characterized in that: Step 1) The temperature of the heat preservation reaction is 550°C and the time is 4 hours.

4. The use according to claim 1, characterized in that: The mass ratio of polymer carbon nitride to rubidium chloride used in step 2) is 1:10.

Images