Tm / g-c3n4 nanocomposite photocatalyst and preparation method and application thereof

Abstract

The application relates to the technical field of semiconductor photocatalysis, in particular to a Tm / g-C3N4 nano-composite photocatalyst and a preparation method and application thereof. The Tm / g-C3N4 nano-composite photocatalyst is prepared by microwave activation under normal temperature and pressure, g-C3N4 nanosheets are used as a precursor, thulium nitrate is used as raw material, a polar mixed solution of water and acetonitrile is used as a solvent, and dithiothreitol is used as a reducing agent. The Tm / g-C3N4 composite photocatalyst material can be simply and quickly prepared by the method, the microstructure of the obtained Tm / g-C3N4 composite photocatalyst material is a sheet structure, the Tm / g-C3N4 composite photocatalyst material has a light response, and can exhibit excellent photocatalytic hydrogen production activity under visible light.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor photocatalysis, in particular to a Tm / g-C3N4 nano-composite photocatalyst and a preparation method and application thereof. BACKGROUND

[0002] With the development of industrialization, a large amount of fossil energy is consumed to support the process of industrialization, and the energy shortage and environmental problems faced by human society are becoming increasingly serious. Hydrogen energy is considered to be one of the most effective green energies, and large-scale application of hydrogen energy can effectively solve the energy crisis and environmental pollution problems caused by the use of fossil fuels. At present, the technical cost of water electrolysis to produce hydrogen is high, the conversion efficiency of high-temperature pyrolysis of water to produce hydrogen is low, and the energy consumption is large, and there are problems such as secondary emission of greenhouse gases. Therefore, it is necessary to develop clean hydrogen production technology, such as photocatalytic water splitting to produce hydrogen technology, which can convert endless solar energy into hydrogen energy, and is a very potential hydrogen energy utilization technology.

[0003] Among many photocatalytic water splitting catalysts, graphite phase carbon nitride (g-C3N4) is a photocatalyst that is highly efficient, stable and has stable chemical properties, and is highly concerned by people, but the separation efficiency of photo-generated carriers is low, and the photocatalytic performance is difficult to satisfy. Therefore, it is necessary to modify the pure g-C3N4 photocatalyst, for example, depositing noble metal nanoparticles on the surface of g-C3N4 can greatly improve the photocatalytic water splitting performance.

[0004] At present, the method of hydrothermal synthesis is generally used to prepare noble metal deposited graphite phase carbon nitride composite materials, but the hydrothermal method has the disadvantages of high temperature, high pressure and danger. Therefore, developing a simple method for synthesizing metal deposited graphite phase carbon nitride composite photocatalyst is a very meaningful research work for the wide application and popularization of photocatalyst. SUMMARY

[0005] In view of the technical problems of high temperature, high pressure and danger in the hydrothermal synthesis of metal / graphite phase carbon nitride composite photocatalyst, the present application provides a Tm / g-C3N4 nano-composite photocatalyst and a preparation method and application thereof. A polar mixed solution of water and acetonitrile is used as a solvent, dithiothreitol is used as a reducing agent, and a microwave activation method is used at normal temperature and pressure, so that the Tm / g-C3N4 composite photocatalyst material can be simply and quickly prepared. The microstructure of the obtained Tm / g-C3N4 composite photocatalyst material is a sheet structure, which has a light response and can exhibit excellent photocatalytic hydrogen production activity under visible light.

[0006] In a first aspect, the application provides a preparation method of a Tm / g-C3N4 nanocomposite photocatalyst, which comprises the following steps: using g-C3N4 nanosheets as a precursor, thulium nitrate as a raw material, a polar mixed solution of water and acetonitrile as a solvent, dithiothreitol as a reducing agent, and preparing the Tm / g-C3N4 nanocomposite photocatalyst under normal temperature and pressure through microwave activation.

[0007] Further, the specific steps are as follows:

[0008] (1) The water and acetonitrile are uniformly mixed, and the g-C3N4 nanosheets and thulium nitrate are fully dispersed into the polar mixed solution of water and acetonitrile under ultrasonic conditions;

[0009] (2) Then, the dithiothreitol is added into the mixed solution of step (1) and fully dispersed under ultrasonic conditions;

[0010] (3) The mixed solution of step (2) is placed in a microwave reaction instrument for activation reaction;

[0011] (4) After the reaction is completed, the product is washed, and the product is vacuum freeze-dried.

[0012] Further, the molar ratio of water to acetonitrile is 1:1.5-2.5.

[0013] Further, the addition amount of the polar mixed solution of water and acetonitrile is 100-150 mL.

[0014] Further, the addition amount of the g-C3N4 nanosheets is 170-200 mg, the addition amount of the thulium nitrate is 0.01-0.2 mmol, and the addition amount of the dithiothreitol is 0.02-0.035 g.

[0015] Further, the microwave power is 100-150 W, and the reaction time is 2-5 min.

[0016] Further, the vacuum degree of the vacuum freeze-drying is <15 Pa, and the temperature is ≤-50℃.

[0017] In a second aspect, the application provides a Tm / g-C3N4 nanocomposite photocatalyst prepared by the above preparation method.

[0018] In a third aspect, the application provides an application of the above Tm / g-C3N4 nanocomposite photocatalyst in photocatalytic decomposition of water to produce hydrogen.

[0019] The technical principles and beneficial effects of the application are as follows:

[0020] In the present application, the polar mixed solution of water and acetonitrile can adjust the solvent polarity during the reaction process, and the use of dithiothreitol as a reducing agent, combined with the microwave activation method at normal temperature and pressure, can reduce the thulium element with +3 valence into thulium single element and deposit it on the surface of graphite phase carbon nitride nanosheet in situ. At the same time, the microwave activation method used in the present application can uniformly disperse the precursor, prevent excessive growth, and on the other hand, can activate the reaction molecules, reduce the reaction energy barrier, and effectively reduce the preparation temperature. The method of the present application overcomes the problems of high temperature, high pressure, high energy consumption and low performance of the catalyst existing in the preparation of the photocatalyst by the traditional hydrothermal method. In the Tm / g-C3N4 nanocomposite photocatalyst prepared by the method of the present application, the Tm particles are uniform and form smaller nanoparticles, which provide more catalytically active sites and are very beneficial to the improvement of photocatalytic activity. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0022] Figure 1 is the transmission electron microscope image of the 5% Tm / g-C3N4 nanocomposite photocatalyst prepared in Example 1.

[0023] Figure 2 is the XRD image of the Tm / g-C3N4 nanocomposite photocatalyst prepared in Example 1.

[0024] Figure 3 is the infrared spectrum image of the Tm / g-C3N4 nanocomposite photocatalyst prepared in Example 1 and the g-C3N4 nanosheet.

[0025] Figure 4 is the ultraviolet-visible absorption spectrum image of the Tm / g-C3N4 nanocomposite photocatalyst prepared in Example 1 and the g-C3N4 nanosheet.

[0026] Figure 5 is the photocatalytic water decomposition hydrogen production performance image of the Tm / g-C3N4 nanocomposite photocatalyst prepared in Example 2 and the g-C3N4 nanosheet. DETAILED DESCRIPTION

[0027] In the following, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application, so that those skilled in the art can better understand the technical solutions in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work should belong to the protection scope of the present application.

[0028] Embodiment 1

[0029] (1) Water and acetonitrile were uniformly mixed in a molar ratio of 1:2 to obtain a polar mixed solution of water and acetonitrile with a total volume of 120 mL, and 170 mg of g-C3N4 nanosheets and different amounts of Tm(NO3)3 were fully dispersed in the polar mixed solution under ultrasonic conditions;

[0030] (2) Then 0.025 g of dithiothreitol was added as a reducing agent into the mixed solution of step (1) and fully dispersed under ultrasonic conditions;

[0031] (3) The mixed solution of step (2) was placed in a microwave reaction instrument for activation reaction, and the microwave power was 150 W and the reaction time was 3 min;

[0032] (4) After the reaction was completed, the product was washed and dried completely by a vacuum freeze dryer, and the vacuum degree of drying was <15 Pa and the temperature was -50°C.

[0033] According to the different amounts of Tm(NO3)3 added, the product obtained when the amount of Tm(NO3)3 was 0.01 mmol was named 1% Tm / CN, the product obtained when the amount of Tm(NO3)3 was 0.03 mmol was named 3% Tm / CN, the product obtained when the amount of Tm(NO3)3 was 0.05 mmol was named 5% Tm / CN, the product obtained when the amount of Tm(NO3)3 was 0.08 mmol was named 8% Tm / CN, the product obtained when the amount of Tm(NO3)3 was 0.1 mmol was named 10% Tm / CN, and the product obtained when the amount of Tm(NO3)3 was 0.2 mmol was named 20% Tm / CN.

[0034] The prepared 5% Tm / CN nanocomposite photocatalyst was observed by transmission electron microscopy, and the results are shown in Figure 1 . Figure 1The left and right pictures are transmission electron microscope pictures of two different positions of the 5% Tm / g-C3N4 nanocomposite photocatalyst. It can be seen that the overall Tm / g-C3N4 composite material presents a nanosheet structure, and the thulium metal element with a diameter of about 1-5 nm is uniformly deposited on the surface of g-C3N4.

[0035] The prepared Tm / g-C3N4 nanocomposite photocatalyst was characterized by XRD, and the results are shown in Figure 2 As the content of thulium increases, the XRD diffraction peak intensity of g-C3N4 gradually decreases, which indicates that thulium is on the surface of g-C3N4 and has a shielding effect on x-rays, reducing the peak intensity.

[0036] The prepared Tm / g-C3N4 nanocomposite photocatalyst was tested by infrared, and compared with the precursor g-C3N4 nanosheet (marked as CN in the figure), and the results are shown in Figure 3 As the content of thulium increases, the composite material mainly shows the vibration peak characteristics of g-C3N4, and the microframe structure is not changed, which indicates that thulium element is deposited on the surface of g-C3N4.

[0037] The prepared Tm / g-C3N4 nanocomposite photocatalyst was determined by ultraviolet-visible absorption spectrum, and compared with the precursor g-C3N4 nanosheet (marked as CN in the figure), and the results are shown in Figure 4 As the content of thulium increases, the light absorption performance of Tm / g-C3N4 nanocomposite photocatalyst gradually increases, which indicates that thulium is deposited on the surface of g-C3N4, which can significantly increase its light absorption properties.

[0038] Example 2

[0039] (1) Mix water and acetonitrile uniformly according to the molar ratio of 1:2 to obtain a polar mixed solution of water and acetonitrile with a total volume of 120 mL. Under ultrasonic conditions, 200 mg of g-C3N4 nanosheet and different amounts of Tm(NO3)3 are dispersed into the above polar mixed solution;

[0040] (2) Then under ultrasonic conditions, 0.025 g of dithiothreitol as a reducing agent is added to the mixed solution of step (1) and dispersed uniformly;

[0041] (3) The mixed solution of step (2) is placed in a microwave reaction instrument for activation reaction, and the microwave power is 150 W, and the reaction time is 3 min;

[0042] (4) After the reaction is completed, the product is washed, and a vacuum freeze dryer is used to completely dry the product, and the vacuum degree of drying is <15 Pa and the temperature is -50°C.

[0043] According to different amounts of Tm(NO3)3, the product obtained when the amount of substance of Tm(NO3)3 is 0.01 mmol is named 1% Tm / CN', the product obtained when the amount of substance of Tm(NO3)3 is 0.03 mmol is named 3% Tm / CN', the product obtained when the amount of substance of Tm(NO3)3 is 0.05 mmol is named 5% Tm / CN', the product obtained when the amount of substance of Tm(NO3)3 is 0.08 mmol is named 8% Tm / CN', the product obtained when the amount of substance of Tm(NO3)3 is 0.1 mmol is named 10% Tm / CN', and the product obtained when the amount of substance of Tm(NO3)3 is 0.2 mmol is named 20% Tm / CN'.

[0044] The six Tm / g-C3N4 nanocomposite photocatalyst samples prepared in Example 2 were used respectively for photocatalytic water splitting to produce hydrogen, and the precursor g-C3N4 nanosheet (labeled as CN in the figure) was used as a control. The results are shown in Figure 5 As shown in the figure, under visible light, the performance of the Tm / g-C3N4 nanocomposite photocatalyst showed a trend of first increasing and then decreasing. This is mainly because with the increase of thulium content, its effect of inhibiting the recombination of photo-generated carriers is inhibited, and it can promote the transmission of photo-generated carriers and hydrogen evolution. However, excessive deposition of thulium element is not conducive to the improvement of photocatalytic hydrogen production performance.

[0045] Although the present application has been described in detail with reference to the preferred embodiments, the application is not limited to the preferred embodiments. Any modification or replacement of the embodiments of the present application made by those skilled in the art without departing from the spirit and essence of the present application should be within the scope of the present application. Any modification or replacement made by those skilled in the art within the technical scope disclosed in the present application should be within the protection scope of the present application.

Claims

1. The application of a Tm / g-C3N4 nanocomposite photocatalyst in photocatalytic water splitting for hydrogen production, characterized in that, The preparation method of the Tm / g-C3N4 nanocomposite photocatalyst is as follows: using g-C3N4 nanosheets as a precursor, thulium nitrate as a raw material, a polar mixed solution of water and acetonitrile as a solvent, and dithiothreitol as a reducing agent, it is prepared by microwave activation at room temperature and pressure.

2. The application as described in claim 1, characterized in that, The specific steps are as follows: (1) Mix water and acetonitrile evenly, and under ultrasonic conditions, fully disperse g-C3N4 nanosheets and thulium nitrate into a polar mixed solution of water and acetonitrile; (2) Then, under ultrasonic conditions, dithiothreitol is added to the mixed solution of step (1) and dispersed thoroughly; (3) Place the mixed solution from step (2) in a microwave reactor for activation reaction; (4) After the reaction is complete, wash the product and freeze-dry it under vacuum.

3. The application as described in claim 1 or 2, characterized in that, The molar ratio of water to acetonitrile is 1:1.5~2.

5.

4. The application as described in claim 1 or 2, characterized in that, The amount of the polar mixed solution of water and acetonitrile added is 100~150mL.

5. The application as described in claim 1 or 2, characterized in that, The amount of g-C3N4 nanosheets added is 170~200mg, the amount of thulium nitrate added is 0.01~0.2mmol, and the amount of dithiothreitol added is 0.02~0.035g.

6. The application as described in claim 1 or 2, characterized in that, The microwave power is 100~150W, and the reaction time is 2~5min.

7. The application as described in claim 2, characterized in that, Vacuum freeze drying has a vacuum degree of <15Pa and a temperature of ≤-50℃.

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