Preparation method and application of titanium defect titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst

Abstract

The invention belongs to the technical field of photocatalytic materials, and particularly relates to a preparation method and application of a titanium defect titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst. The preparation method comprises the following steps: 1) placing urea in a crucible with a cover, and calcining to obtain graphite phase carbon nitride; and 2) uniformly dispersing the graphite phase carbon nitride into a mixed solution of tetrabutyl titanate, absolute ethyl alcohol and glycerol, obtaining an intermediate by using a hydrothermal method, washing the intermediate with absolute ethyl alcohol, drying, grinding, putting into a crucible with a cover, and calcining to obtain the titanium defect titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst. The formation of the heterojunction can greatly improve the activity of the graphite-phase carbon nitride in photocatalytic reduction of carbon dioxide.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic materials, and specifically relates to a preparation method and application of a titanium-defective titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst. Background Art

[0002] Fossil fuels account for the vast majority of global energy consumption, leading to excessive carbon dioxide emissions and a serious greenhouse effect. At the same time, the consumption of large amounts of fossil fuels has also put humans in the face of energy shortages. Photocatalytic carbon dioxide reduction uses solar energy as the only energy source, directly converting carbon dioxide gas into carbon monoxide and hydrocarbon fuels, which can solve both environmental and energy crises. Graphitic carbon nitride (g-C3N4) has become one of the most promising carbon dioxide reduction photocatalysts due to its non-toxicity, simple synthesis, and high chemical stability. However, g-C3N4 also has obvious defects, such as small specific surface area, rapid recombination of photogenerated carriers, and poor adsorption capacity for carbon dioxide.

[0003] Both titanium dioxide and carbon nitride are easy to prepare, have excellent photochemical stability and environmental friendliness, and have a wide range of photocatalytic applications. Constructing defective titanium dioxide / graphite-phase carbon nitride nanosheet heterojunctions can increase their specific surface area. The heterojunction can significantly inhibit the recombination of photogenerated carriers to provide more active sites, which can significantly improve the photocatalytic performance, thereby achieving the purpose of improving the photocatalytic activity of graphite-phase carbon nitride. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst and its application in the photocatalytic reduction of carbon dioxide. The method is simple, convenient, low-cost, mild in conditions, and conducive to large-scale production. The obtained titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction catalyst has good photocatalytic reduction activity of carbon dioxide.

[0005] The technical solution adopted by the present invention is:

[0006] A method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst comprises the following steps:

[0007] 1) placing urea in a covered crucible and calcining to obtain graphite phase carbon nitride;

[0008] 2) The graphite phase carbon nitride is uniformly dispersed in a mixed solution of tetrabutyl titanate, anhydrous ethanol and propylene glycol, an intermediate is obtained by a hydrothermal method, and then the intermediate is washed with anhydrous ethanol, dried, ground, and then placed in a covered crucible. After calcination, a titanium-defective titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst is obtained.

[0009] Furthermore, in the above-mentioned method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst, in step 1), the calcination temperature is 550° C. and the calcination time is 2-6 hours.

[0010] Furthermore, in the above-mentioned method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst, in step 2), tetrabutyl titanate: anhydrous ethanol: glycerol = 1.5-2.5 g: 55-65 mL: 25-35 mL.

[0011] Furthermore, in the above-mentioned method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst, in step 2), the mass ratio of tetrabutyl titanate to graphite-phase carbon nitride is 1.5-2.5:0.5-1.5.

[0012] Furthermore, in the above-mentioned method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst, in step 2), the hydrothermal temperature is 160-200° C., and the hydrothermal time is 18-30 hours.

[0013] Furthermore, in the above-mentioned method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst, in step 2), the drying temperature is 40-80° C. and the drying time is 8-16 hours.

[0014] Furthermore, in the above-mentioned method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst, in step 2), the grinding time is 30-60 minutes.

[0015] Furthermore, in the above-mentioned method for preparing a titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst, in step 2), the calcination temperature is 450-500° C., and the calcination time is 0.5-2 h.

[0016] Application of the titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst described in any one of the above items in the photocatalytic reduction of carbon dioxide.

[0017] Furthermore, the above application method is as follows: under visible light irradiation, the titanium-defect titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst is placed in a closed space filled with carbon dioxide gas to reduce the carbon dioxide gas to carbon monoxide gas.

[0018] The present invention utilizes the construction of titanium-defect titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction to improve the separation efficiency of carriers, thereby achieving the purpose of improving the photocatalytic activity of graphite-phase carbon nitride. The beneficial effects of this method can be attributed to two aspects:

[0019] 1. The construction of composite materials can increase the specific surface area of ​​the material, provide more surface active sites, and enhance the adsorption of carbon dioxide.

[0020] 2. The construction of the heterojunction forms an internal electric field, which improves the separation efficiency of photogenerated carriers and holes. In addition, the preparation method provided by the present invention has cheap raw materials, simple operation, greatly reduces the cost, and is pollution-free to the environment, realizing green chemistry, and can effectively reduce carbon dioxide. Under visible light irradiation, the carbon monoxide yield of the titanium-defective titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst for reducing carbon dioxide can reach 11.28861μmol h -1 g -1 , which is 3.8 times that of graphite phase carbon nitride. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD patterns of g-C3N4, Ti-Defected TiO2 and CDT2.

[0022] Figure 2 XRD patterns of CDT1, CDT2 and CDT3.

[0023] Figure 3 Fourier transform infrared spectra of g-C3N4, Ti-Defected TiO2 and CDT2.

[0024] Figure 4 Fluorescence spectra of g-C3N4, CDT1, CDT2 and CDT3.

[0025] Figure 5 This is the SEM image of g-C3N4.

[0026] Figure 6 This is the SEM image of Ti-Defected TiO2.

[0027] Figure 7 This is the SEM image of CDT2.

[0028] Figure 8 This is a comparison chart of the photocatalytic reduction of carbon dioxide activity of g-C3N4, Ti-Defected TiO2 CDT1, CDT2 and CDT3.

[0029] Fig. 9 This is a comparison chart of the photocatalytic reduction of carbon dioxide reactions of g-C3N4, Ti-Defected TiO2 CDT1, CDT2 and CDT3.

[0030] Fig.10 Figure 2 is the photocatalytic mechanism diagram of CDT2. DETAILED DESCRIPTION

[0031] Example 1 A titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst (the mass ratio of tetrabutyl titanate to graphite-phase carbon nitride is 2:0.8)

[0032] The preparation method is as follows:

[0033] 1) 20 g of urea was placed in a covered crucible, calcined at 550° C. for 2 hours in an air environment, and then cooled to ambient temperature to obtain graphite carbon nitride (denoted as g-C3N4).

[0034] 2) Dissolve 2 g of tetrabutyl titanate in a mixed solution of 60 mL of anhydrous ethanol and 30 mL of propylene glycol, stir for 30 minutes, put the solution into a 100 mL stainless steel high-pressure reactor, and heat at 180°C for 24 hours. Finally, cool the solution naturally to room temperature, filter, wash, and dry in an oven at 60°C for 12 hours to obtain an intermediate; then place the intermediate in a covered crucible, calcine at 470°C for 1 hour in an air environment, and cool to ambient temperature to obtain titanium-defective titanium dioxide (referred to as Ti-DefectedTiO2).

[0035] 3) 0.8 g g-C3N4 and 2 g tetrabutyl titanate were dissolved in a mixed solution of 60 mL anhydrous ethanol and 30 mL propylene glycol, stirred for 30 minutes, placed in a 100 mL stainless steel high-pressure reactor, and heated at 180°C for 24 hours. Finally, the solution was naturally cooled to room temperature, filtered, washed, and dried in an oven at 60°C for 12 hours to obtain an intermediate. The intermediate was then ground for 30 minutes and then placed in a covered crucible. It was calcined at 470°C for 1 hour in an air environment and cooled to ambient temperature to obtain a titanium-defective titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst (denoted as CDT1).

[0036] The CDT1 prepared in this example was subjected to XRD test, and the test results are as follows: Figure 2 As shown in the figure, it can be seen that the typical characteristic peaks of g-C3N4 and Ti-Defected TiO2 were detected in CDT1, indicating the successful preparation of CDT1.

[0037] Example 2 Photocatalytic reduction of carbon dioxide using CDT1 photocatalyst

[0038] The CDT1 photocatalyst prepared in Example 1 was subjected to a photocatalytic reduction of carbon dioxide experiment. The test process was as follows: using a 300W xenon lamp as a light source, 0.03g g-C3N4, Ti-Defected TiO2 and CDT1 prepared above were directly placed in a reaction container, evacuated and filled with carbon dioxide gas, and then reduced carbon dioxide under visible light irradiation. Figure 8It can be seen that the titanium-defective titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst prepared in Example 1 exhibits good photocatalytic activity, and the carbon monoxide generation rate of the CDT1 photocatalyst reaches 3.70765 μmol h -1 g -1 , while the carbon monoxide generation rate of g-C3N4 is only 2.9021 μmol h -1 g -1 .

[0039] Example 3 A titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst (the mass ratio of tetrabutyl titanate to graphite-phase carbon nitride is 2:1.1)

[0040] The preparation method is as follows:

[0041] 1) 20 g of urea was placed in a covered crucible, calcined at 550° C. for 2 hours in an air environment, and then cooled to ambient temperature to obtain graphite carbon nitride (denoted as g-C3N4).

[0042] 2) Dissolve 2 g of tetrabutyl titanate in a mixed solution of 60 mL of anhydrous ethanol and 30 mL of propylene glycol, stir for 30 minutes, put the solution into a 100 mL stainless steel high-pressure reactor, and heat at 180°C for 24 hours. Finally, cool the solution naturally to room temperature, filter, wash, and dry in an oven at 60°C for 12 hours to obtain an intermediate; then place the intermediate in a covered crucible, calcine at 470°C for 1 hour in an air environment, and cool to ambient temperature to obtain titanium-defective titanium dioxide (referred to as Ti-DefectedTiO2).

[0043] 3) 1.1 g g-C3N4 and 2 g tetrabutyl titanate were dissolved in a mixed solution of 60 mL anhydrous ethanol and 30 mL propylene glycol, stirred for 30 minutes, placed in a 100 mL stainless steel high-pressure reactor, and heated at 180°C for 24 hours. Finally, the solution was naturally cooled to room temperature, filtered, washed, and dried in an oven at 60°C for 12 hours to obtain an intermediate. The intermediate was then ground for 30 minutes and then placed in a covered crucible. It was calcined at 470°C for 1 hour in an air environment and cooled to ambient temperature to obtain a titanium-defective titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst (denoted as CDT2).

[0044] The g-C3N4, Ti-Defected TiO2 and CDT2 prepared in this example were subjected to XRD tests. The test results are as follows: Figure 1 and Figure 2 As shown, it can be seen from the figure that the typical characteristic peaks of g-C3N4 and Ti-Defected TiO2 were detected in CDT2, indicating the successful preparation of CDT2.

[0045] The Fourier transform infrared spectrum of the CDT2 photocatalyst prepared in Example 3 was measured. Figure 3 As shown, the key peaks of g-C3N4 are 1220–1640 and 3050–3280 cm -1 , for Ti-deficient TiO2, the key peaks are 1645 and 3100–3500 cm -1 , in the CDT2 composite material, the main characteristic peaks of g-C3N4 and Ti-deficient TiO2 are still clearly visible. This indicates that the prepared composite material has been successfully combined to successfully form a heterojunction.

[0046] Figure 5 Figure 2 is the SEM image of g-C3N4. g-C3N4 exhibits a multilayer stacked block structure due to a simple direct polymerization method. Figure 6 The SEM image of Ti-Defective TiO2 is shown in Figure 2. Ti-Defective TiO2 exhibits a spiky ball shape due to the crystal arrangement of the material. The CDT2 prepared in Example 3 was subjected to SEM testing. Figure 7 As shown, the surface of g-C3N4 was uniformly covered by Ti-Defected TiO2, indicating that g-C3N4 and Ti-Defected TiO2 were successfully combined.

[0047] Example 4 Photocatalytic reduction of carbon dioxide using CDT2 photocatalyst

[0048] The CDT2 photocatalyst prepared in Example 3 was subjected to a photocatalytic reduction of carbon dioxide experiment. The test process was as follows: using a 300W xenon lamp as a light source, 0.03g g-C3N4, Ti-Defected TiO2 and CDT2 prepared above were directly placed in a reaction container, evacuated and filled with carbon dioxide gas, and then reduced carbon dioxide under visible light irradiation. Figure 8 It can be seen that the titanium-defective titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst prepared in Example 3 exhibits good photocatalytic activity, and the carbon monoxide generation rate of the CDT2 photocatalyst reaches 11.28861 μmol h -1 g -1 , while the carbon monoxide generation rate of g-C3N4 is only 2.9021 μmol h -1 g -1 .

[0049] Example 5 A titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst (the mass ratio of tetrabutyl titanate to graphite-phase carbon nitride is 2:1.4)

[0050] The preparation method is as follows:

[0051] 1) 20 g of urea was placed in a covered crucible, calcined at 550° C. for 2 hours in an air environment, and then cooled to ambient temperature to obtain graphite carbon nitride (denoted as g-C3N4).

[0052] 2) Dissolve 2 g of tetrabutyl titanate in a mixed solution of 60 mL of anhydrous ethanol and 30 mL of propylene glycol, stir for 30 minutes, put the solution into a 100 mL stainless steel high-pressure reactor, and heat at 180°C for 24 hours. Finally, cool the solution naturally to room temperature, filter, wash, and dry in an oven at 60°C for 12 hours to obtain an intermediate; then place the intermediate in a covered crucible, calcine at 470°C for 1 hour in an air environment, and cool to ambient temperature to obtain titanium-defective titanium dioxide (referred to as Ti-DefectedTiO2).

[0053] 3) 1.4 g g-C3N4 and 2 g tetrabutyl titanate were dissolved in a mixed solution of 60 mL anhydrous ethanol and 30 mL propylene glycol, stirred for 30 minutes, placed in a 100 mL stainless steel high-pressure reactor, and heated at 180°C for 24 hours. Finally, the solution was naturally cooled to room temperature, filtered, washed, and dried in an oven at 60°C for 12 hours to obtain an intermediate. The intermediate was then ground for 30 minutes and then placed in a covered crucible. It was calcined at 470°C for 1 hour in an air environment and cooled to ambient temperature to obtain a titanium-defective titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst (denoted as CDT3).

[0054] The CDT3 prepared in this example was subjected to XRD test, and the test results are as follows: Figure 2 As shown in the figure, it can be seen that the typical characteristic peaks of g-C3N4 and Ti-Defected TiO2 were detected in CDT3, indicating the successful preparation of CDT3.

[0055] The fluorescence spectra of the CDT1 photocatalyst prepared in Example 1, the CDT2 photocatalyst prepared in Example 3, and the CDT3 photocatalyst prepared in Example 5 were measured. Figure 4 As shown, the photoluminescence spectrum (PL) with an excitation wavelength of 274nm was measured. The intensity of PL depends on the recombination of electrons and holes. The higher the intensity, the more recombination. For example, the emission peak of g-C3N4 is the strongest. After g-C3N4 and Ti-Defective TiO2 are compounded in different proportions, the intensity of the composite photocatalyst is significantly reduced. This shows that the heterojunction structure can effectively separate electrons and holes, allowing more active sites to be used in the photocatalytic reaction process and improving the photocatalytic yield. Example 6 CDT3 photocatalyst for photocatalytic reduction of carbon dioxide

[0056] The CDT3 photocatalyst prepared in Example 5 was subjected to a photocatalytic reduction of carbon dioxide experiment. The test process was as follows: using a 300W xenon lamp as the light source, 0.03g g-C3N4, Ti-Defected TiO2 and CDT2 prepared above were directly placed in a reaction container, evacuated and filled with carbon dioxide gas, and then reduced carbon dioxide under visible light irradiation. Figure 8 It can be seen that the titanium-defective titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst prepared in Example 5 exhibits good photocatalytic activity, and the carbon monoxide generation rate of the CDT3 photocatalyst reaches 6.3218 μmol h -1 g -1 , while the carbon monoxide generation rate of g-C3N4 is only 2.9021 μmol h -1 g -1 .

[0057] Fig. 9 The gas production of g-C3N4, Ti-Defected TiO2, CDT1, CDT2 and CDT3 over time. The results show that the gas production of all materials increases with time, among which CDT2 increases the most.

[0058] Fig.10 A possible charge transfer path diagram of the pn heterojunction of titanium-defective titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst is shown. The band gap of g-C3N4 is 2.69eV, the band gap of Ti-Defected TiO2 is 3.1eV, the valence band energy levels of g-C3N4 and Ti-Defected TiO2 are 1.90eV and 1.18eV, and the conduction band energy levels are -0.79eV and -1.92eV, respectively. Therefore, g-C3N4 combines with Ti-Defected TiO2 to form a pn heterojunction, and electrons flow from g-C3N4 to Ti-Defected TiO2, and holes flow in the opposite direction until the system reaches Fermi level equilibrium. An intrinsic electric field is generated near the pn heterojunction interface, which accelerates the transfer of electrons and holes and suppresses the recombination of carriers.

[0059] It is worth noting that the titanium-defective titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst has a high photocatalytic carbon dioxide reduction activity. However, as can be seen from the above, the photocatalytic activity of CDT1, CDT2 and CDT3 gradually increases with the increase of the amount of graphite-phase carbon nitride, and the CO generation rate reaches the highest value at CDT2. Subsequently, with the further increase of the dosage, the CO generation rate gradually decreases. This may be because the excessive loading of graphite-phase carbon nitride shields the composite material from the absorption of incident light, and the high content of graphite-phase carbon nitride may inhibit the movement of photogenerated carriers to the surface of the material, thereby inhibiting the photocatalytic carbon dioxide reduction activity.

Claims

1. A titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst, characterized in that: The preparation method thereof comprises the following steps: 1) placing urea in a covered crucible and calcining to obtain graphite phase carbon nitride; 2) The graphite phase carbon nitride is uniformly dispersed in a mixed solution of tetrabutyl titanate, anhydrous ethanol and propylene glycol, an intermediate is obtained by a hydrothermal method, and then the intermediate is washed with anhydrous ethanol, dried, ground, and then placed in a covered crucible. After calcination, a titanium-defective titanium dioxide / graphite phase carbon nitride nanosheet heterojunction photocatalyst is obtained.

2. The titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst according to claim 1, characterized in that: In step 1), the calcination temperature is 550° C. and the calcination time is 2-6 hours.

3. The titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst according to claim 1, characterized in that: In step 2), tetrabutyl titanate: anhydrous ethanol: propylene glycol = 1.5-2.5 g: 55-65 mL: 25-35 mL.

4. The titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst according to claim 1, characterized in that: In step 2), the mass ratio of tetrabutyl titanate to graphite phase carbon nitride is 1.5-2.5:0.5-1.

5.

5. The titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst according to claim 1, characterized in that: In step 2), the hydrothermal temperature is 160-200° C. and the hydrothermal time is 18-30 hours.

6. The titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst according to claim 1, characterized in that: In step 2), the drying temperature is 40-80° C. and the drying time is 8-16 hours.

7. The titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst according to claim 1, characterized in that: In step 2), the grinding time is 30-60 min.

8. The titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst according to claim 1, characterized in that: In step 2), the calcination temperature is 450-500° C. and the calcination time is 0.5-2 h.

9. Use of the titanium-deficient titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst according to any one of claims 1 to 8 in photocatalytic reduction of carbon dioxide.

10. The use according to claim 9, characterized in that: The method is as follows: under visible light irradiation, a titanium-defect titanium dioxide / graphite-phase carbon nitride nanosheet heterojunction photocatalyst is placed in a closed space filled with carbon dioxide gas to reduce the carbon dioxide gas to carbon monoxide gas.

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