Preparation method and application of carbon defect synergetic strontium doped g-C3N4 photocatalyst

Abstract

The invention belongs to the technical field of photocatalytic materials, and particularly relates to a preparation method and application of a carbon defect synergistic strontium doped g-C3N4 photocatalyst. According to the preparation method, formaldehyde is used for assisting the thermal shrinkage and process of a strontium chloride hexahydrate-melamine precursor, and high-temperature oxidation etching is used for thermally stripping blocky carbon nitride into ultrathin nanosheets, so that the specific surface area of the carbon nitride is greatly increased. The method can be applied to the field of gas-phase photocatalytic CO2 reduction. Compared with an existing photocatalyst, the strontium-doped carbon defect type g-C3N4 photocatalyst has the advantages that the preparation method is simple, the cost is low, the specific surface area is large, more reaction active sites can be provided, the separation efficiency of current carriers can be further improved through carbon defects, CO2 is more effectively adsorbed in cooperation with strontium atom doping, and photocatalytic CO2 reduction is promoted in cooperation.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to a preparation method and application of a carbon defect synergistic strontium-doped g-C 3 N 4 photocatalyst. Background Art

[0002] The excessive consumption of fossil fuels has led to a significant increase in air pollution and carbon dioxide emissions, which has become the main cause of global warming. Artificially photoreducing carbon dioxide into useful chemical raw materials such as CO, methane, and methanol is a promising and sustainable solution to energy shortage and climate improvement. The photocatalytic carbon dioxide reduction technology provides mild reaction conditions and only relies on the inexhaustible solar energy, and is considered an effective way to sustainably reduce carbon dioxide. However, the chemical inertness of carbon dioxide molecules and the high dissociation energy of the C=O bond pose a major challenge to the catalytic efficiency of photocatalytic carbon dioxide reduction.

[0003] Graphitic carbon nitride is a metal-free organic conjugated polymer photocatalyst, which has been widely used in the field of photocatalysis due to its rich raw material sources, excellent chemical stability, visible light response, controllable composition and molecular structure. However, due to the inherent defects of graphitic carbon nitride, such as serious recombination of photo-generated electron-hole pairs and difficulty in adsorbing and activating carbon dioxide molecules, its carbon dioxide reduction performance is poor. To solve these limitations, the present invention introduces carbon defects and single-atom strontium doping to synergistically promote photocatalytic activity. The specific surface area of carbon nitride is controlled by defects, and more active sites are exposed by increasing the specific surface area, improving the separation efficiency of photo-generated electron-hole pairs, promoting charge transfer, and at the same time introducing single-atom strontium as an active site to enhance the adsorption and activation of carbon dioxide molecules, thereby improving photocatalytic activity; and there is no relevant report on the photocatalyst of strontium-doped carbon defect type graphitic carbon nitride in gas-phase carbon dioxide reduction. Summary of the Invention

[0004] To solve the above problems, the present invention provides a preparation method and application of a carbon defect synergistic strontium-doped g-C 3 N 4 photocatalyst.

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

[0006] A preparation method of a carbon defect synergistic strontium-doped g-C 3 N 4 photocatalyst, comprising the following steps:

[0007] 1) Dissolve strontium chloride hexahydrate in 120 mL of water, stir until dissolved, then add melamine to the strontium chloride solution, and heat and stir until the solution becomes colorless and transparent;

[0008] 2) Add the formaldehyde solution to the colorless and transparent solution obtained in step 1), continue heating and stirring until fully mixed, then place it in an oven for drying, and grind to obtain a white powder;

[0009] 3) Put the white powder obtained in step 2) into a crucible with a lid, place it in a tubular furnace for high-temperature calcination, cool it down, and obtain a massive brown-yellow substance, grind it into powder, and collect it for standby;

[0010] 4) Put the brown-yellow powder obtained in step 3) into the crucible again, place it in a muffle furnace for oxidative etching, and obtain a light-yellow powder, which is the strontium-doped carbon-deficient g-C 3 N 4 photocatalyst, denoted as Sr-CN-V c photocatalyst.

[0011] Further, in the above preparation method, in step 1), the molar ratio of strontium chloride hexahydrate to melamine is 0.001 - 0.04:1, and the amount of melamine used is 3 g.

[0012] Further, in the above preparation method, in step 1), the heating method is water bath heating, and the water bath temperature is 90 °C.

[0013] Further, in the above preparation method, the molar ratio of formaldehyde to melamine is 0.001 - 0.005:1.

[0014] Further, in the above preparation method, in step 2), the heating method is water bath heating, the heating temperature is 90 °C, and the heating and stirring time is 30 minutes.

[0015] Further, in the above preparation method, in step 2), the drying temperature is 60 - 110 °C.

[0016] Further, in the above preparation method, in steps 1) and 2), the stirring method is to use a magnetic stirrer for stirring.

[0017] Further, in the above preparation method, in step 3), the high-temperature calcination temperature is 550 °C, the heating rate is 5 °C / min, the calcination time is 4 h, and the atmosphere in the tubular furnace is a nitrogen atmosphere.

[0018] Further, in the above preparation method, in step 4), the oxidative etching temperature is 510 °C, the heating rate is 5 °C / min, and the etching time is 2 h.

[0019] The Sr-CN-V c photocatalyst prepared by the preparation method described in any one of the above is used in the gas-phase photocatalytic CO 2 reduction.

[0020] Further, for the above application, the method is as follows: Take Sr-CN-V c The photocatalyst is evenly dispersed in 0.5 mL of ethanol and sonicated for 5 minutes; the obtained ethanol dispersion of the photocatalyst is evenly dropped onto a circular crucible piece with a radius of 1 cm and dried; the crucible piece loaded with the sample is placed in a reactor, and then deionized water is added, and the reactor is sealed; after evacuation, carbon dioxide is introduced and repeated three times; under visible light conditions, it is irradiated to catalyze the reduction of carbon dioxide.

[0021] Furthermore, for the above application, Sr-CN-V c The photocatalyst: deionized water = 10 mg: 0.5 mL.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The present invention successfully prepares carbon defect-synergistic strontium-doped g-C 3 N 4 photocatalyst through formaldehyde-assisted thermal shrinkage, which has a large specific surface area, can expose more active sites, enhance the adsorption and activation of carbon dioxide molecules, and enhance the photocatalytic activity.

[0024] 2. The Sr-CN-V c photocatalyst prepared by the present invention has a stronger ability to absorb visible light, which is an effective way to improve the visible light photocatalytic activity.

[0025] 3. The Sr-CN-Vc photocatalyst prepared by the present invention has good photocatalytic carbon dioxide reduction performance, and the method is simple to prepare, environmentally friendly and non-toxic, low-cost, and conducive to large-scale production. Description of the Drawings

[0026] Figure 1 For the X-ray diffraction patterns of CN, CN-V c , 1Sr-CN-V c , 2Sr-CN-V c , 3Sr-CN-V c photocatalysts.

[0027] Figure 2 For the carbon dioxide reduction to carbon monoxide production-time curve graphs of CN, CN-V c , 1Sr-CN-V c , 2Sr-CN-V c , 3Sr-CN-V c photocatalysts. Detailed Embodiments

[0028] Example 1 Sr-CN-V c Photocatalyst

[0029] (I) 3 N 4 Preparation

[0030] Dissolve 3g of melamine in 120mL of deionized water, heat in a water bath to 90℃, and stir magnetically until the solution is clear and transparent. Dry the solution in an oven at 100℃, put the resulting powder into a crucible with a lid, and calcine at 550℃ for 4h in a nitrogen atmosphere tube furnace at a heating rate of 5℃ / min to obtain gC 3 N 4 , denoted as CN.

[0031] (II) CN-V c Preparation

[0032] Dissolve 3g of melamine in 120mL of deionized water, heat to 90℃ in a water bath, and stir magnetically until the solution is clear and transparent. Add 12μL of formaldehyde solution (concentration of 37%) to the transparent solution, and continue to stir magnetically in a 90℃ water bath for 30min. Put the mixed solution into a 100℃ oven to dry, grind the obtained precursor into a covered crucible, and place it in a nitrogen atmosphere tube furnace for calcination at 550℃ for 4h, with a heating rate of 5℃ / min. After natural cooling, grind it again, put it into a muffle furnace for annealing at 510℃ for 2h, with a heating rate of 5℃ / min, and obtain CN-V c .

[0033] (III) 1Sr-CN-V c Preparation

[0034] Dissolve 0.063g of strontium chloride hexahydrate in 120mL of deionized water, then add 3g of melamine to the solution, place the solution in a water bath, heat it to 90°C, and stir it magnetically until the solution becomes clear and transparent. Add 12μL of formaldehyde solution (concentration of 37%) to the transparent solution, and continue to stir it magnetically in a 90°C water bath for 30min. Put the mixed solution into a 100°C oven to dry, put the obtained powder into a crucible with a lid, and place it in a nitrogen atmosphere tube furnace and calcine it at 550°C for 4h, with a heating rate of 5°C / min. After natural cooling, grind the obtained brown-yellow block into powder, put it into a muffle furnace and anneal it at 510°C for 2h to obtain 1Sr-CN-V c .

[0035] (IV) 2Sr-CN-V c Preparation

[0036] Dissolve 0.127g of strontium chloride hexahydrate in 120mL of deionized water, then add 3g of melamine to the solution, place the solution in a water bath, heat the water bath to 90°C, and stir magnetically until the solution becomes clear and transparent. Add 12μL of formaldehyde solution (concentration of 37%) to the transparent solution, and continue to stir magnetically in a 90°C water bath for 30min. Put the mixed solution into a 100°C oven to dry, put the obtained powder into a crucible with a lid, and place it in a nitrogen atmosphere tube furnace for calcination at 550°C for 4h, with a heating rate of 5°C / min. After natural cooling, grind the obtained brown-yellow block into powder, put it into a muffle furnace for annealing at 510°C for 2h, and obtain 2Sr-CN-V c .

[0037] (V) 3Sr-CN-V c Preparation

[0038] Dissolve 0.190g of strontium chloride hexahydrate in 120mL of deionized water, then add 3g of melamine to the solution, place the solution in a water bath, heat it to 90°C, and stir it magnetically until the solution becomes clear and transparent. Add 12μL of formaldehyde solution (concentration of 37%) to the transparent solution, and continue to stir it magnetically in a 90°C water bath for 30min. Put the mixed solution into a 100°C oven to dry, put the obtained powder into a crucible with a lid, and place it in a nitrogen atmosphere tube furnace and calcine it at 550°C for 4h, with a heating rate of 5°C / min. After natural cooling, grind the obtained brown-yellow block into powder, put it into a muffle furnace and anneal it at 510°C for 2h to obtain 3Sr-CN-V c .

[0039] Figure 1 CN and CN-V prepared in Example 1 c , 1Sr-CN-V c 、2Sr-CN-V c 、3Sr-CN-V c X-ray diffraction pattern of the photocatalyst. Characteristic diffraction peaks appear at 2θ=13.1° and 27.6°, corresponding to the (100) and (002) crystal planes, which is consistent with the gC 3 N 4 The diffraction peaks are consistent with those of pure gC 3 N 4 Compared with the samples after doping, the diffraction peak intensity decreased and the peak position shifted. Doping changed the gC 3 N 4 (002) plane and shortened gC 3 N 4 The distance between layers.

[0040] Example 2

[0041] At normal temperature and pressure, 10 mg of the photocatalyst prepared in Example 1 was evenly dispersed in 0.5 mL of absolute ethanol and ultrasonicated for 5 min. The ethanol dispersion of the obtained photocatalyst was dropped onto a crucible piece with a radius of 1 cm and dried in an oven at 60 °C. The dried crucible piece loaded with the sample was placed in a reactor, and then 0.5 mL of deionized water was added to the reactor. The reactor was sealed, evacuated for 2 min, and then carbon dioxide was introduced at a constant flow rate (80 mL / min). The above evacuation and carbon dioxide introduction processes were repeated three times. Then the reactor was irradiated under a xenon lamp. Every 60 min during the photocatalytic reaction, 1000 μL of gas was extracted from the container with a syringe and the carbon monoxide concentration was detected by a gas chromatograph.

[0042] Figure 2 It is the production-time curve of photocatalytic reduction of carbon dioxide to carbon monoxide for the sample. It can be seen that after 4 h of photocatalytic reaction, 2Sr-CN-V c The carbon monoxide production is 112 μmol / g, which is 8 times that of pure g-C 3 N 4 in carbon monoxide production. It shows that the doped and modified 2Sr-CN-V c has a much higher photocatalytic activity than pure g-C 3 N 4 in the gas-phase photocatalytic reduction of carbon dioxide.

Claims

1. A method for preparing a carbon defect-cooperative strontium-doped g-C3N4 photocatalyst, characterized in that: The steps include: 1) Dissolve strontium chloride hexahydrate in 120 mL of water and stir until dissolved, then add melamine to the strontium chloride solution, heat and stir until the solution becomes colorless and transparent; 2) adding the formaldehyde solution to the colorless transparent solution obtained in step 1), continuing heating and stirring until fully mixed, placing in an oven to dry, and grinding to obtain a white powder; 3) putting the white powder obtained in step 2) into a crucible with a cover, placing it in a tube furnace for high-temperature calcination, cooling it down to obtain a blocky brown-yellow substance, grinding it into powder, and collecting it for later use; 4) The brown-yellow powder obtained in step 3) is put into a crucible again and placed in a muffle furnace for oxidation etching to obtain a light yellow powder, which is the strontium-doped carbon-deficient g-C3N4 photocatalyst, denoted as Sr-CN-V c Photocatalyst.

2. The preparation method according to claim 1, characterized in that: In step 1), the molar ratio of strontium chloride hexahydrate to melamine is 0.001-0.04:1, and the amount of melamine used is 3g.

3. The preparation method according to claim 1, characterized in that: In step 1), the heating method is water bath heating, and the water bath temperature is 90°C.

4. The preparation method according to claim 1, characterized in that: The molar ratio of formaldehyde to melamine is 0.001-0.005:

1.

5. The preparation method according to claim 1, characterized in that: In step 2), the heating method is water bath heating, the heating temperature is 90° C., the heating stirring time is 30 minutes; and the drying temperature is 60-110° C.

6. The preparation method according to claim 1, characterized in that: In step 3), the high temperature calcination temperature is 550° C., the heating rate is 5° C. / min, the calcination time is 4 h, and the atmosphere of the tubular furnace is nitrogen.

7. The preparation method according to claim 1, characterized in that: In step 4), the oxidation etching temperature is 510° C., the heating rate is 5° C. / min, and the etching time is 2 h.

8. Sr-CN-V prepared by the preparation method according to any one of claims 1 to 7 c Application of photocatalysts in gas-phase photocatalytic CO2 reduction.

9. The use according to claim 8, characterized in that: The method is as follows: Take Sr-CN-V c The photocatalyst was evenly dispersed in 0.5 mL of ethanol and ultrasonicated for 5 minutes; the obtained ethanol dispersion of the photocatalyst was evenly dropped onto a circular crucible with a radius of 1 cm and dried; the crucible loaded with the sample was placed in a reactor, deionized water was added, and the reactor was sealed; carbon dioxide was introduced after vacuuming, and the process was repeated three times; and catalytic carbon dioxide reduction was performed under visible light conditions.

10. The use according to claim 9, characterized in that: Sr-CN-V c Photocatalyst: deionized water = 10 mg: 0.5 mL.

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