CN115608402B - Crystalline phase carbon nitride photocatalyst with ordered-distorted interface - Google Patents

Abstract

The invention discloses a crystalline phase carbon nitride photocatalyst with an ordered-twisted interface, and a preparation method and application thereof, and belongs to the technical field of photocatalytic material preparation. The method is characterized in that cyanuric chloride and sodium thiocyanate are used as precursors, and a carbon nitride photocatalyst with a heptazine ordered-twist interface is synthesized in a high-temperature molten salt environment. The invention has simple process and low cost, meets the actual production requirement, and the prepared photocatalyst has good light absorption performance and hydrogen production activity at a long wavelength, and has higher application potential under the condition that platinum is used as a promoter and triethanolamine is used as a sacrificial agent, wherein the photocatalytic hydrogen production activity is obviously superior to that of single crystal phase carbon nitride.

Description

A crystalline carbon nitride photocatalyst with an ordered-twisted interface

Technical field

The invention belongs to the technical field of photocatalytic material preparation, and specifically relates to a crystalline carbon nitride photocatalyst with an ordered-distorted interface and its preparation method and application.

Background technique

The energy and environmental problems caused by the extensive use of fossil energy in human society have become increasingly prominent. On the one hand, there is an upper limit to the reserves of these fossil energy sources such as oil and natural gas. On the other hand, mining and refining fossil energy sources will cause serious environmental pollution, and the large-scale use of fossil energy sources will also lead to an increase in carbon emissions. Therefore, the development and utilization of clean and sustainable new energy is the future trend of human society. Among them, hydrogen, as a new type of energy, is regarded as an ideal alternative energy due to its advantages such as high energy density, cleanliness and environmental protection. However, hydrogen is currently mainly produced through the cracking of fossil fuels and electrolysis of water. The production processes of these methods are complex and the cost is high. Photocatalytic hydrogen production technology, which converts solar energy into hydrogen energy, has the advantages of simple process, economical and environmental protection, and is considered to be one of the ideal ways to produce hydrogen energy in the future. The core of this technology is the development of efficient photocatalysts.

Most of the currently widely used photocatalysts are metal-inorganic semiconductor photocatalysts. Although this type of photocatalyst shows good photocatalytic performance, the presence of metals and even precious metals in the structure results in high cost and complex synthesis steps, which limits large-scale use. In recent years, organic polymer photocatalysts, especially graphite-phase carbon nitride materials, have aroused widespread interest among researchers due to their advantages such as simple synthesis, economy and environmental protection. However, despite their great development in photolysis of water, reduction of carbon dioxide, and organic photosynthesis, they still can only utilize short-wavelength visible light (less than 450 nm). Therefore, it is extremely important to develop a carbon nitride photocatalyst that is easy to prepare, economical and environmentally friendly, and has long-wavelength visible light absorption.

Contents of the invention

The purpose of the present invention is to provide a crystalline carbon nitride photocatalyst with an ordered-distorted interface and its preparation method and application. The prepared carbon nitride photocatalyst has good long-wavelength sunlight utilization and can achieve high efficiency. Photocatalytic decomposition of water to produce hydrogen.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A crystalline carbon nitride photocatalyst with an ordered-distorted interface, which uses cyanuric chloride and sodium thiocyanate as precursors, autogenous salt sodium chloride and external salt lithium chloride as eutectic salts. Synthesized under high-temperature conditions, it has a heptazine-ordered-twisted interface, a microscopic morphology of nanorods, and an optical absorption wavelength of 300nm~700nm. The ordered structure and twisted structure in the photocatalyst form a good contact interface, which not only improves the light absorption performance of the material, but also promotes the separation of photogenerated charges, thereby enabling efficient long-wavelength visible light-driven water splitting to produce hydrogen.

The preparation method of the crystalline carbon nitride photocatalyst with an ordered-distorted interface includes the following steps:

(1) Grind and mix cyanuric chloride, sodium thiocyanate and lithium chloride evenly in a glove box protected by inert gas at a mass ratio of 185:243:327;

(2) Calculate the mixture obtained in step (1) at 500~650°C for 4 hours under a nitrogen atmosphere to obtain the crystalline carbon nitride photocatalyst.

The crystalline carbon nitride photocatalyst with an ordered-twisted interface can be used to catalyze the decomposition of water to produce hydrogen under long-wavelength visible light. Specifically, while using the crystalline carbon nitride photocatalyst, platinum is used as the As a cocatalyst, triethanolamine is used as a sacrificial agent to photolyze water to produce hydrogen under light conditions with a wavelength of 450nm~700nm.

The significant advantages of the present invention are:

(1) The present invention first uses the precursors melamine chloride and sodium thiocyanate to polymerize to form a twisted carbon nitride structure, and during the polymerization process, the precursors melamine chloride and sodium thiocyanate can react to form sodium chloride , it and lithium chloride can form a eutectic salt system with a higher eutectic point. Combined with the control of calcination temperature, the twisted structure can be transformed into an ordered structure, and finally an ordered-twisted interface can be formed.

(2) The photocatalyst synthesized by the present invention contains two kinds of carbon nitride structures: ordered and twisted. The good contact between the two not only improves the light absorption performance of the material, but also promotes the separation of photogenerated charges, thereby achieving efficient and long-term photocatalysts. Visible light of wavelength drives the splitting of water to produce hydrogen.

(3) The entire preparation process of the present invention is simple and easy to control, has low energy consumption and cost, meets actual production needs, and is conducive to large-scale promotion.

Description of drawings

Figure 1 is a powder X-ray diffraction spectrum of the carbon nitride photocatalyst obtained in Examples 1-4.

Figure 2 is a Fourier transform infrared spectrum of the carbon nitride photocatalyst obtained in Example 3.

Figure 3 is a high-resolution transmission electron microscope image of the carbon nitride photocatalyst obtained in Example 3.

Figure 4 is the ultraviolet-visible light diffuse reflection spectrum of the carbon nitride photocatalyst obtained in Example 3.

Figure 5 shows the steady-state fluorescence spectra of the carbon nitride photocatalysts obtained in Examples 1-4 and Comparative Examples.

Figure 6 is a comparative diagram of the photocatalytic water splitting and hydrogen production activities of the carbon nitride photocatalysts obtained in Examples 1-4 and Comparative Examples.

Detailed ways

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 embodiments, but the present invention is not limited thereto.

Example 1

(1) Grind and mix cyanuric chloride, sodium thiocyanate and lithium chloride with a mass ratio of 185:243:327 in an inert gas-protected glove box;

(2) Calculate the mixture obtained in step (1) at 500°C for 4 hours in a nitrogen atmosphere, cool down, wash with water to remove the molten salt, and then dry to obtain a crystalline carbon nitride photocatalyst.

Example 2

(1) Grind and mix cyanuric chloride, sodium thiocyanate and lithium chloride with a mass ratio of 185:243:327 in an inert gas-protected glove box;

(2) Calculate the mixture obtained in step (1) at 550°C for 4 hours in a nitrogen atmosphere, cool down, wash with water to remove molten salt, and then dry to obtain a crystalline carbon nitride photocatalyst.

Example 3

(1) Grind and mix cyanuric chloride, sodium thiocyanate and lithium chloride with a mass ratio of 185:243:327 in an inert gas-protected glove box;

(2) Calculate the mixture obtained in step (1) at 600°C for 4 hours in a nitrogen atmosphere, cool down, wash with water to remove molten salt, and then dry to obtain a crystalline carbon nitride photocatalyst.

Example 4

(1) Grind and mix cyanuric chloride, sodium thiocyanate and lithium chloride with a mass ratio of 185:243:327 in an inert gas-protected glove box;

(2) Calculate the mixture obtained in step (1) at 650°C for 4 hours in a nitrogen atmosphere, cool down, wash with water to remove molten salt, and then dry to obtain a crystalline carbon nitride photocatalyst.

Comparative ratio

(1) Grind and mix cyanuric chloride, potassium thiocyanate and lithium chloride with a mass ratio of 185:292:183 in an inert gas-protected glove box;

(2) Calculate the mixture obtained in step (1) at 550°C for 4 hours in a nitrogen atmosphere, cool down, wash with water to remove the molten salt, and then dry to obtain a carbon nitride photocatalyst with an unoptimized structure.

Figure 1 is a powder X-ray diffraction spectrum of the carbon nitride photocatalyst obtained in Examples 1-4. It can be found from the figure that the carbon nitride photocatalyst prepared in Example 1 has a twisted structure, while the carbon nitride photocatalyst prepared in Examples 2, 3, and 4 contains two types of carbon nitride structures: heptazine ordered and twisted. , among which, the diffraction peaks at 8° and 14° are attributed to the heptaazine matrix phase carbon nitride, and the broad peak at 27° is attributed to the twisted heptazine matrix phase carbon nitride. This shows that the method of the present invention can first form a twisted carbon nitride structure, and then use the calcination temperature to control the transformation of the twisted structure into an ordered structure to form an ordered-twisted interface. However, there are certain differences in the structure of the photocatalyst prepared in Example 4 compared with Examples 2 and 3, indicating that excessively high calcination temperature will lead to changes in the catalyst structure.

Figure 2 is the Fourier transform infrared spectrum of the carbon nitride photocatalyst obtained in Example 3. It can be found from the figure that the prepared carbon nitride photocatalyst is a heptaazine carbon nitride photocatalyst. Among them, the absorption peak with a wave number greater than 3000 cm ^-1 represents the amino group or hydroxyl group in the sample structure, the absorption peak with a wave number of 2170 cm ^-1 represents the cyano group in the structure, and the remaining absorption peaks are mainly from the heptaazinyl carbon nitride material. Characteristic infrared absorption peak.

Figure 3 is a high-resolution transmission electron microscope image of the carbon nitride photocatalyst obtained in Example 3. The figure further demonstrates the existence of an ordered-twisted structure in the photocatalyst, and the two structures form good contacts.

Figure 4 is the ultraviolet-visible light diffuse reflection spectrum of the carbon nitride photocatalyst obtained in Example 3. It can be seen from the figure that the photocatalyst has good long-wavelength visible light absorption. Among them, the absorption edge located at 450nm represents the ordered (crystal phase) structure, and the absorption between 450-700nm belongs to the twisted structure.

Figure 5 shows the steady-state fluorescence spectra of the carbon nitride photocatalysts obtained in Examples 1-4 and Comparative Examples. It can be found from the figure that the carbon nitride photocatalysts prepared in Examples 2 and 3 exhibit lower steady-state fluorescence intensity than Example 1 (twisted structure) and the comparative example, which illustrates that the ordered-twisted interface effectively improves the improve the photogenerated carrier separation efficiency of the photocatalyst. The photocatalyst prepared in Example 4 has higher steady-state fluorescence intensity, which may be caused by structural changes caused by excessively high calcination temperature.

The hydrogen production activity is a reaction system composed of 50 mg of photocatalyst, 100 ml of triethanolamine aqueous solution containing 10% volume fraction, and 3% mass fraction of Pt (obtained by in-situ photodeposition of Pt with H ₂ PtCl ₆ ) as cocatalyst. It is carried out in a reactor equipped with a 300-watt xenon lamp on the top (using a 450 nm cut-off film and controlling the wavelength of the incident light to be greater than 450 nm).

Figure 6 is a comparative chart of the photocatalytic water decomposition and hydrogen production activities of the carbon nitride photocatalysts obtained in Examples 1-4 and Comparative Examples. It can be found from the figure that the photocatalysts prepared in Examples 2 and 3 have high long-wavelength visible light hydrogen production activity. Among them, the hydrogen production rate of the photocatalyst prepared in Example 3 reaches 80 μmol/h, which is higher than the photocatalyst prepared in other Examples and Comparative Examples.

The above are only preferred embodiments of the present invention, and all equivalent changes and modifications made in accordance with the patentable scope of the present invention shall fall within the scope of the present invention.

Claims (1)

1. A method for preparing a crystalline carbon nitride photocatalyst with an ordered-distorted interface, which is characterized in that the steps are as follows: (1) Grind and mix cyanuric chloride, sodium thiocyanate and lithium chloride with a mass ratio of 185:243:327 in an inert gas-protected glove box; (2) Calculate the mixture obtained in step (1) at 600°C for 4 hours in a nitrogen atmosphere, cool down, wash with water to remove molten salt, and then dry to obtain a crystalline carbon nitride photocatalyst.