Nitrogen-doped carbon-coated hollow porous strontium titanate and its preparation method

Abstract

The present invention discloses a preparation method of nitrogen-doped carbon-coated hollow porous strontium titanate, which specifically includes the following steps: dissolving tetrabutyl titanate in ethylene glycol to obtain solution A; dissolving strontium acetate in deionized water to obtain solution B; under magnetic stirring, dropwise adding solution A into solution B until uniformly dispersed, adding NaOH and hexamethylenetetramine into the above solution, stirring until completely dissolved, then carrying out hydrothermal reaction in a reaction kettle, then cooling to room temperature, washing and drying, and finally calcining the product in a tube furnace at 900-1200 °C. By a simple hydrothermal method, a nitrogen-doped carbon-coated hollow porous strontium titanate photocatalyst with uniform size, high performance and high stability is successfully prepared, with simple operation and novel structure; the introduction of hexamethylenetetramine effectively improves the specific surface area, sunlight utilization rate and carrier transport performance of strontium titanate; after nitrogen-doped carbon grows on the surface of strontium titanate, the structural stability is improved and the sunlight utilization rate is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and particularly relates to a nitrogen-doped carbon-coated hollow porous strontium titanate and a preparation method thereof.

[0002] The present invention belongs to the 3.1 New Functional Materials Industry under the 3 New Materials Industry in the Strategic Emerging Industry Catalog, and is under the key direction of 3.1.12 New Catalytic Materials and Auxiliaries - New Photocatalytic Materials and Other Auxiliaries. Background Art

[0003] Energy and environment are the two major themes in the development of the world today and are the basis for the steady development of science and technology and the survival of mankind. Since the 21st century, the problems of energy shortage and environmental pollution have become increasingly serious. Developing environmentally friendly renewable energy is an effective measure to alleviate the energy and environmental crises. As a new technology that has rapidly developed in recent years and can utilize solar energy for environmental purification and energy conversion, photocatalysis has great application potential in efficiently removing various low-concentration organic pollutants in water and energy conversion due to its advantages of environmental friendliness, cleanliness, low toxicity, rich raw materials, good repeatability, and full utilization of renewable resources. Photocatalysts are the core of catalytic reactions, and the development of highly efficient and stable photocatalysts is the focus of research by scholars.

[0004] In recent years, strontium titanate has unique advantages in the field of photocatalysis due to its unique perovskite alternating layer structure, relatively high oxidation potential (higher than •OH radicals), and easy-to-control morphology. However, problems such as low utilization rate of sunlight, easy recombination of photo-generated carriers, and lack of reactive sites have led to unsatisfactory photocatalytic efficiency of single SrTiO3 materials, which has also become a bottleneck in the practical development of this material in the field of photocatalysis. It is reported that ideal photocatalytic materials need to have the following characteristics: (1) a relatively high utilization rate of sunlight to facilitate the generation of abundant photo-generated carriers; (2) abundant surface active sites to promote redox reactions on the catalyst surface; (3) good carrier transport performance to improve the utilization rate of electrons and holes. The design of a hollow porous structure and the construction of a heterojunction are one of the best methods to synergistically improve the above properties.

[0005] The porous structure can increase the specific surface area and reactive sites of the catalyst, and the construction of a heterojunction can improve the carrier transport performance and optimize the utilization rate of sunlight. However, the strontium titanate with a porous structure is unstable during the photocatalytic process and is prone to collapse, and the preparation process of porous strontium titanate is cumbersome, usually requiring the use of templates and consuming a high amount of energy. Therefore, it is of great significance to improve the photocatalytic performance and stability of porous strontium titanate by a simple method.

[0006] In recent years, due to the advantages of good structural stability, abundant raw materials, and low price, nitrogen-doped carbon materials have broad application prospects in the field of photocatalysis. After in-situ constructing a layer of nitrogen-doped carbon on the surface of strontium titanate, the nitrogen-doped carbon can form a heterojunction with strontium titanate, and the construction of the heterojunction can promote the efficient transport of carriers. In addition, nitrogen-doped carbon has excellent structural stability. After coating on the surface of strontium titanate, it can optimize the structure of strontium titanate by using the electrostatic adsorption and surface tension between ions, and improve the structural stability of porous strontium titanate. However, there is no relevant report on the design of a heterojunction of nitrogen-doped carbon-coated hollow porous strontium titanate at present.

[0007] Chinese Patent No. 201810751895.0 discloses an N-SrTiO3 / activated carbon treatment material, which uses activated carbon as a carrier and N-SrTiO3 photocatalyst as an active component. A certain amount of photocatalyst is loaded on the activated carbon by microwave method to prepare an NSrTiO3 / activated carbon composite. This new material has the advantages of high efficiency, cheap and easily available raw materials, easy separation, recyclability, and no secondary pollution in the treatment of heavy metals and COD in electroplating wastewater. In addition, the high specific surface area of the N-SrTiO3 / activated carbon treatment material is obtained by using activated carbon with a high specific surface area as the carrier of the photocatalyst. Summary of the Invention

[0008] In view of the above problems existing in the prior art, the present invention provides a nitrogen-doped carbon-coated hollow porous strontium titanate with uniform size, high performance, and high stability, and a preparation method thereof.

[0009] The purpose of the present invention is achieved in the following way:

[0010] A preparation method of nitrogen-doped carbon-coated hollow porous strontium titanate specifically includes the following steps:

[0011] a. Dissolve 0.5 - 1.0 mL of tetrabutyl titanate in 15 - 35 mL of ethylene glycol to obtain solution A;

[0012] b. Dissolve 3 - 7 mmol of strontium acetate in 15 - 35 mL of deionized water to obtain solution B;

[0013] c. Under magnetic stirring, slowly add solution A dropwise to solution B, stir until solution A is uniformly dispersed in solution B, add 0.10 - 0.30 g of NaOH and 40 - 160 mg of hexamethylenetetramine to the above solution, stir until completely dissolved, then place the mixed solution in a reaction kettle and hydrothermal react at 150 - 180 °C for 6 - 30 h, then cool to room temperature, wash and dry, and finally calcine the product in a tube furnace at 900 - 1200 °C.

[0014] Step c cleaning is to clean with deionized water and ethanol for 2 - 3 times each.

[0015] In step c, if NaOH and hexamethylenetetramine are not sufficiently stirred and dissolved, ultrasonic treatment is carried out for 10 - 90 min.

[0016] The drying temperature in step c is 60 - 80 °C.

[0017] The calcination time in step c is 1 - 3 hours.

[0018] Strontium titanate with a nitrogen - doped carbon - coated hollow porous structure prepared by the above method.

[0019] Compared with the prior art, the present invention successfully prepares a nitrogen - doped carbon - coated hollow porous strontium titanate photocatalyst with uniform size, high performance and high stability through a simple hydrothermal method. The operation is simple and the structure is novel. The introduction of hexamethylenetetramine effectively increases the specific surface area of strontium titanate, the sunlight utilization rate and the carrier transport performance. In addition, the porous strontium titanate structure is unstable and is prone to collapse during the photocatalysis process. After growing nitrogen - doped carbon on the surface, the strontium titanate is transformed from a porous structure into a hollow porous structure. This hollow porous structure can realize multiple reflections of sunlight inside the catalyst, improving the sunlight utilization rate. In addition, after nitrogen - doped carbon coating, the stability of the porous strontium titanate structure is also improved. Therefore, the photocatalytic CO2 reduction activity is significantly improved, the structural stability of the catalyst is good, and it has the advantages of being green, environmentally friendly, low - consumption, highly efficient and having good industrial prospects. Description of the Drawings

[0020] Figure 1 Scanning and transmission electron microscope photos of porous strontium titanate and nitrogen - doped carbon - coated hollow porous strontium titanate.

[0021] Figure 2 XRD curves and XPS diagrams of porous strontium titanate and nitrogen - doped carbon - coated hollow porous strontium titanate with different hexamethylenetetramine contents.

[0022] Figure 3 Performance and stability test diagrams of porous strontium titanate and nitrogen - doped carbon - coated hollow porous strontium titanate. Among them, (a) CO generation efficiency diagram of porous strontium titanate and nitrogen - doped carbon - coated hollow porous strontium titanate; (b) performance stability test diagram; (c) XRD diagram of nitrogen - doped carbon - coated hollow porous strontium titanate before and after photocatalytic test; (d) transmission electron microscope diagram of nitrogen - doped carbon - coated hollow porous strontium titanate after photocatalytic test; (e) transmission electron microscope diagram of porous strontium titanate after photocatalytic test.

[0023] Figure 4It is the schematic diagram of the improved photocatalytic activity of strontium titanate with porous structure and nitrogen-doped carbon-coated hollow porous strontium titanate. (a) Solar absorption spectrum; (b) Nitrogen adsorption and desorption curve; (c) Solid fluorescence spectrum; (d) Transient photocurrent curve; (e) Linear cyclic voltammetry curve; (f) Electrochemical impedance curve.

[0024] Figure 5 It is the schematic diagram of the improved solar energy utilization rate of nitrogen-doped carbon-coated hollow porous strontium titanate. Specific implementation mode

[0025] Example 1

[0026] Preparation method of nitrogen-doped carbon-coated hollow porous strontium titanate: a. 0.9 mL of tetrabutyl titanate is dissolved in 25 mL of ethylene glycol to obtain solution A; b. 4.9 mmol (1.0080 g) of strontium acetate is dissolved in 25 mL of deionized water to obtain solution B; c. Under magnetic stirring, solution A is added dropwise to solution B. After stirring for 30 min, 0.20 g of NaOH and 80 mg of hexamethylenetetramine are added to the above solution, stirred for 30 min, ultrasonically treated for 30 min, and then the mixed solution is placed in a reaction kettle for hydrothermal treatment at 160 °C for 20 h. After cooling to room temperature, it is washed alternately with deionized water and ethanol 2-3 times and dried at 80 °C; finally, the product is calcined in a tubular furnace at 1100 °C for 2 h. Nitrogen-doped carbon-coated hollow porous strontium titanate is prepared.

[0027] Example 2

[0028] The specific preparation method and process parameters of nitrogen-doped carbon-coated hollow porous strontium titanate are the same as those in Example 1, except that the amount of hexamethylenetetramine (HMTA) is 160 mg.

[0029] Example 3

[0030] The specific preparation method and process parameters of nitrogen-doped carbon-coated hollow porous strontium titanate are the same as those in Example 1, except that the amount of hexamethylenetetramine (HMTA) is 40 mg.

[0031] Example 4

[0032] Preparation method of nitrogen-doped carbon-coated hollow porous strontium titanate: a. Dissolve 1.2 mL of tetrabutyl titanate in 35 mL of ethylene glycol to obtain solution A; b. Dissolve 6 mmol of strontium acetate in 40 mL of deionized water to obtain solution B; c. Under magnetic stirring, slowly add solution A dropwise to solution B. After stirring for 30 min, add 0.20 g of NaOH and 80 mg of hexamethylenetetramine to the above solution, stir for 30 min, perform ultrasonic treatment for 30 min, then place the mixed solution in a reaction kettle and hydrothermally react at 160 °C for 20 h. After cooling to room temperature, wash it alternately with deionized water and ethanol 2-3 times, and dry it at 80 °C; finally, calcine the product in a tubular furnace at 1100 °C for 2 h. Nitrogen-doped carbon-coated hollow porous strontium titanate.

[0033] Example 5

[0034] a. Dissolve 0.5 mL of tetrabutyl titanate in 15 mL of ethylene glycol to obtain solution A; b. Dissolve 3 mmol of strontium acetate in 15 mL of deionized water to obtain solution B; c. Under magnetic stirring, slowly add solution A dropwise to solution B. Stir until solution A is evenly dispersed in solution B. Add 0.10 g of NaOH and 80 mg of hexamethylenetetramine to the above solution, stir until completely dissolved. If it is not fully dissolved, ultrasonic treatment can be performed for 10-90 min. Then place the mixed solution in a reaction kettle and hydrothermally react at 150 °C for 6 h. After cooling to room temperature, wash and dry it. Finally, calcine the product in a tubular furnace at 900 °C for 3 hours. Nitrogen-doped carbon-coated hollow porous strontium titanate.

[0035] Example 6

[0036] a. Dissolve 1.0 mL of tetrabutyl titanate in 35 mL of ethylene glycol to obtain solution A; b. Dissolve 7 mmol of strontium acetate in 35 mL of deionized water to obtain solution B; c. Under magnetic stirring, slowly add solution A dropwise to solution B. Stir until solution A is evenly dispersed in solution B. Add 0.30 g of NaOH and 160 mg of hexamethylenetetramine to the above solution, stir until completely dissolved. If it is not fully dissolved, ultrasonic treatment can be performed for 10-90 min. Then place the mixed solution in a reaction kettle and hydrothermally react at 180 °C for 30 h. After cooling to room temperature, wash and dry it. Finally, calcine the product in a tubular furnace at 1200 °C for 1 hour. Nitrogen-doped carbon-coated hollow porous strontium titanate.

[0037] Comparative example

[0038] Preparation of strontium titanate with porous structure: 0.9 mL of tetrabutyl titanate was dissolved in 25 mL of ethylene glycol to obtain solution A; 4.9 mmol (1.0080 g) of strontium acetate was dissolved in 25 mL of deionized water to obtain solution B; under magnetic stirring, solution A was added dropwise to solution B. After stirring for 30 min, 0.20 g of NaOH was added to the above solution, stirred for 30 min, sonicated for 30 min, and then the mixed solution was placed in a reaction kettle for hydrothermal treatment at 160 °C for 20 h. After cooling to room temperature, it was washed alternately with deionized water and ethanol 2-3 times and dried at 80 °C; finally, the product was calcined in a tube furnace at 1100 °C for 2 h. Strontium titanate with porous structure was prepared.

[0039] Scanning electron microscope and transmission electron microscope photos of the strontium titanate with porous structure prepared in the comparative example and the nitrogen-doped carbon-coated hollow porous strontium titanate prepared in Example 1 are as Figure 1 shown. Among them, a-c are the scanning and transmission electron microscope photos of the strontium titanate with porous structure. It can be seen from a-c in the figure that the size of the strontium titanate with porous structure is 100-300 nm, and its lattice fringe of 0.276 nm corresponds to the (110) crystal plane of strontium titanate. As shown in 1d-f are the scanning and transmission electron microscope photos of the nitrogen-doped carbon-coated hollow porous strontium titanate. From Figure 1 d, it can be seen that after adding hexamethylenetetramine, the surface of the sample becomes rough, which helps to increase the specific surface area and reactive active sites; it can be seen from the transmission electron microscope photo in 1e that a nitrogen-doped carbon ring appears on the surface of the hollow porous strontium titanate, and the thickness of the ring is within 100 nm. This hollow ring structure has good stability and is not easy to collapse. In the high-resolution transmission electron microscope, it can be clearly identified that the outer layer is the lattice fringe of distorted nitrogen-doped carbon, and the inner layer lattice fringe of 0.275 nm corresponds to the (110) crystal plane of strontium titanate. The close contact between the two lattices confirms the formation of a high-quality heterojunction between strontium titanate and nitrogen-doped carbon, which can effectively improve the carrier transport performance. In addition, due to the high stability of nitrogen-doped carbon, the strontium titanate wrapped by it helps to improve the structural stability of strontium titanate.

[0040] Figure 2 XRD pictures and XPS spectra of the nitrogen-doped carbon-coated hollow porous strontium titanate photocatalysts prepared in Examples 1-3 above and the strontium titanate photocatalysts with porous structure prepared in the comparative example. From Figure 2 a, it can be seen that after adding nitrogen-doped carbon, the diffraction peaks of strontium titanate basically remain unchanged, which may be due to the poor crystallinity of nitrogen-doped carbon. From Figure 2As can be seen from b-f, Sr, Ti, O, C, and N elements are simultaneously detected in the composite. Among them, compared with pure strontium titanate (i.e., strontium titanate with a porous structure), the diffraction peak positions of Sr, Ti, and O are all shifted, indicating that there is a charge transfer between the nitrogen-doped carbon and strontium titanate, which further confirms the formation of a high-quality heterojunction between the two.

[0041] Photocatalysis experiment

[0042] 20 mg each of the strontium titanate photocatalyst with nitrogen-doped carbon-coated hollow porous structure prepared in the above Examples 1-3 and the strontium titanate photocatalyst with a porous structure prepared in the comparative example were respectively added to a quartz reaction cell, ultrasonically dispersed evenly, then 50 mL of deionized water was added respectively, evacuated for 30 min, and finally 20 mL of CO2 gas was added. The 300 W xenon lamp was turned on, and the CO production was detected by on-line photocatalytic chromatography. The results are shown in Figure 3 . As can be seen from Figure 3 a, after adding hexamethylenetetramine, the photocatalytic efficiency is significantly improved. When the content of hexamethylene is 80 mg, the CO generation efficiency is the highest, reaching 134 μmol / g / h, which is 2.4 times that of the strontium titanate photocatalyst with a porous structure, and has the best CO selectivity (91.1%). Further exploration of the photocatalytic stability and structural stability of the strontium titanate with a porous structure and the strontium titanate with a nitrogen-doped carbon-coated hollow porous structure is as follows Figure 3 As shown in b, after 5 photocatalytic cycles (25 hours), the activity of pure strontium titanate decreases significantly, but the photocatalytic activity of the strontium titanate with a nitrogen-doped carbon-coated hollow porous structure does not decrease significantly, indicating that the introduction of nitrogen-doped carbon successfully improves the photocatalytic stability of the catalyst. In addition, through Figure 3 c XRD and Figure 3 d TEM to explore the structural stability of the strontium titanate with a nitrogen-doped carbon-coated hollow porous structure before and after photocatalysis, it is found that before and after photocatalysis, the diffraction peak positions and numbers of XRD do not change significantly, and the hollow structure remains intact, while the structure of strontium titanate collapses significantly after photocatalysis (see Figure 3 e), indicating that the introduction of nitrogen-doped carbon successfully improves the structural stability of strontium titanate.

[0043] Figure 4 is the schematic diagram of the improvement of the photocatalytic activity of the strontium titanate with a porous structure and the strontium titanate with a nitrogen-doped carbon-coated hollow porous structure. Among them, Figure 4 a is the solar light absorption spectrum of the strontium titanate with a nitrogen-doped carbon-coated hollow porous structure prepared in Example 1 and the strontium titanate with a porous structure prepared in the comparative example. As can be seen from the figure, the solar light utilization rate of the strontium titanate with a nitrogen-doped carbon-coated hollow porous structure is higher than that of the strontium titanate with a porous structure.

[0044] As can be seen from Figure 5It can be seen that the hollow porous structure can promote multiple reflections of sunlight inside the catalyst, thereby effectively improving the utilization rate of sunlight.

[0045] Figure 4 b is the nitrogen adsorption-desorption isotherm of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon prepared in Example 1 and strontium titanate with a porous structure prepared in the comparative example, used to detect the specific surface area of the catalyst. It can be seen from the figure that the specific surface area of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon is also significantly increased compared with that of strontium titanate with a porous structure. When the addition amount of hexamethylenetetramine is 40 mg, 80 mg, and 160 mg, the specific surface area increases from 13.5 m 2 / g to 17.0 m 2 / g, 40.2 m 2 / g, and 38.8 m 2 / g.

[0046] Figure 4 c is the fluorescence spectrum of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon prepared in Example 1 and strontium titanate with a porous structure prepared in the comparative example. It can be seen from the figure that the fluorescence intensity of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon is significantly weaker than that of strontium titanate. Since fluorescence is generated by the recombination of electrons and holes, the weaker fluorescence intensity of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon proves its better carrier separation performance.

[0047] Figure 4 d is the photocurrent curve of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon prepared in Example 1 and strontium titanate with a porous structure prepared in the comparative example. The photocurrent intensity is determined by the number of carriers generated by photoexcitation. The more carriers, the greater the photocurrent intensity. It can be seen from the figure that the photocurrent of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon is stronger, indicating that it has more carriers, which is consistent with the Figure 4 conclusion in c.

[0048] Figure 4 e is the linear cyclic voltammetry curve of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon prepared in Example 1 and strontium titanate with a porous structure prepared in Comparative Example 1. It can be seen from the figure that under the same voltage conditions, the photocurrent of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon is stronger, proving its better carrier separation efficiency.

[0049] Figure 4 f is the impedance curve of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon prepared in Example 1 and strontium titanate with a porous structure prepared in Comparative Example 1. It can be seen from the figure that the impedance of strontium titanate with a hollow porous structure coated with nitrogen-doped carbon is much lower than that of strontium titanate with a porous structure, and the carrier transport performance is improved.

Claims

1. Preparation method of nitrogen-doped carbon-coated hollow porous strontium titanate, characterized in that: Specifically, it includes the following steps: a. Dissolve 0.5 - 1.0 mL of tetrabutyl titanate in 15 - 35 mL of ethylene glycol to obtain solution A; b. Dissolve 3 - 7 mmol of strontium acetate in 15 - 35 mL of deionized water to obtain solution B; c. Under magnetic stirring, slowly add solution A dropwise to solution B, and stir until solution A is uniformly dispersed in solution B. Then add 0.10 - 0.30 g of NaOH and 40 - 160 mg of hexamethylenetetramine to the above solution, stir until completely dissolved, and then place the mixed solution in a reaction kettle for hydrothermal treatment at 150 - 180 °C for 6 - 30 h. Then cool to room temperature, wash and dry. Finally, calcine the product in a tube furnace at 900 - 1200 °C.

2. The preparation method of the nitrogen-doped carbon-coated hollow porous strontium titanate according to claim 1, characterized in that: In step c, the washing is carried out 2 - 3 times each with deionized water and ethanol.

3. The preparation method of the nitrogen-doped carbon-coated hollow porous strontium titanate according to claim 1, wherein: In step c, if NaOH and hexamethylenetetramine are not fully dissolved after stirring, perform ultrasonic treatment for 10 - 90 min.

4. The preparation method of the nitrogen-doped carbon-coated hollow porous strontium titanate according to claim 1, wherein: The drying temperature in step c is 60 - 80 °C.

5. The preparation method of the nitrogen-doped carbon-coated hollow porous strontium titanate according to claim 1, characterized in that: The calcination time in step c is 1 - 3 hours.

6. Strontium titanate with a nitrogen-doped carbon-coated hollow porous structure prepared by the method according to any one of claims 1 - 5.

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