Preparation method and application of C3N4 / Bi2O2CO3 heterojunction photocatalyst

Abstract

The invention belongs to the technical field of photocatalytic materials, and particularly relates to a preparation method and application of a C3N4 / Bi2O2CO3 heterojunction photocatalyst. Bi2O2CO3 is prepared through a simple thermal solvent method, and then C3N4 successfully grows on the Bi2O2CO3 through a mechanical stirring method. The formation of a heterojunction interface is beneficial to the proceeding of a CO2 reduction reaction, and a gas-solid heterogeneous photocatalytic CO2 reduction result shows that the CO yield of the C3N4 / Bi2O2CO3 heterojunction photocatalyst is remarkably improved compared with that of original C3N4 and Bi2O2CO3. Research finds that the enhanced photocatalytic activity can be attributed to the formed heterojunction, and the formation of the heterojunction accelerates the separation of electron-hole pairs, so that the newly synthesized photocatalyst has larger photocurrent and better light absorption performance, thereby promoting the photocatalytic efficiency and improving the photocatalytic CO2 yield.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and in particular relates to a preparation method and application of a C3N4 / Bi2O2CO3 heterojunction photocatalyst. Background Art

[0002] Nowadays, in order to cope with the increasingly serious energy crisis and environmental problems, converting CO2 into high-value-added chemical raw materials or fuels is one of the goals of modern catalytic technology. Synthesis gas, a mixture of CO and H2, is a useful raw material for the production of liquid fuels and synthetic products. Ideally, CO2 reduction and water splitting reactions can be combined to produce syngas through artificial photosynthesis. However, due to the chemical inertness of CO2 molecules and the high recombination rate of photogenerated carriers in individual semiconductors, most photocatalytic CO2 reduction reactions still rely on sacrificial agents such as methanol and triethanolamine, or use expensive photosensitizers to achieve ideal performance. Although many attempts have been made to carry out CO2 photoreduction reactions without the use of sacrificial agents or photosensitizers, the low conversion efficiency still hinders its practical application.

[0003] Among bismuth-based semiconductors, Bi2O2CO3 has attracted extensive attention from researchers due to its low production cost, safety and environmental protection, high stability, and strong internal electric field. C3N4 has the advantages of suitable band structure and convenient preparation, and has been widely used in the field of photocatalysis. Its rich and uniform coordination sites can serve as active sites to adsorb and activate reactants in photocatalytic reactions. Based on the above characteristics of Bi2O2CO3 and C3N4, this paper used a simple solvothermal method to prepare a new C3N4 / Bi2O2CO3 heterojunction, and successfully grew C3N4 on Bi2O2CO3. In the photocatalytic activity test in a gas-solid heterogeneous phase without the addition of sacrificial agents and photosensitizers, the heterojunction photocatalyst prepared in this paper has higher photocatalytic activity and significantly improved photocatalytic efficiency. Summary of the invention

[0004] The present invention discloses a preparation method and application of a C3N4 / Bi2O2CO3 heterojunction photocatalyst.

[0005] The technical solution adopted by the present invention is: a C3N4 / Bi2O2CO3 heterojunction photocatalyst, and the preparation method comprises the following steps:

[0006] 1) dissolving bismuth nitrate pentahydrate in HNO3 solution, and after it is completely dissolved, adding citric acid to the mixed solution, adding NaOH solution to adjust the pH under stirring, and then putting it into an autoclave for hydrothermal reaction, and finally collecting the white precipitate by centrifugation, and drying to obtain Bi2O2CO3;

[0007] 2) Disperse Bi2O2CO3 in ethanol, then add C3N4, continue stirring in a water bath, collect the sample by centrifugation, and finally dry to obtain a C3N4 / Bi2O2CO3 heterojunction photocatalyst.

[0008] In the above-mentioned C3N4 / Bi2O2CO3 heterojunction photocatalyst, in step 1), the molar ratio of bismuth nitrate pentahydrate to citric acid is 2:1.

[0009] In the above-mentioned C3N4 / Bi2O2CO3 heterojunction photocatalyst, in step 1), the pH is adjusted to 6.

[0010] In the above-mentioned C3N4 / Bi2O2CO3 heterojunction photocatalyst, in step 1), the temperature of the hydrothermal reaction is 180°C and the reaction time is 24h.

[0011] The above-mentioned C3N4 / Bi2O2CO3 heterojunction photocatalyst, the preparation method of C3N4 is as follows: take a certain amount of urea and spread it on the bottom of a porcelain boat, then take an equal amount of melamine and spread it on the urea, wrap it with tin foil, put it in a muffle furnace for calcination, and after natural cooling, transfer it to a tubular furnace for further calcination, and finally obtain a yellow sample C3N4.

[0012] For the above-mentioned C3N4 / Bi2O2CO3 heterojunction photocatalyst, the muffle furnace calcination temperature is 550°C, and the calcination time is 4h; the tubular furnace calcination temperature is 450°C, and the calcination time is 4h.

[0013] In the above-mentioned C3N4 / Bi2O2CO3 heterojunction photocatalyst, in step 2), the mass ratio of Bi2O2CO3:C3N4 is 10:1.

[0014] In the above-mentioned C3N4 / Bi2O2CO3 heterojunction photocatalyst, in step 2), the temperature of the water bath is 40°C.

[0015] Application of the above-mentioned C3N4 / Bi2O2CO3 heterojunction photocatalyst in photocatalytic reduction of CO2.

[0016] The above-mentioned application method is as follows: disperse the C3N4 / Bi2O2CO3 heterojunction photocatalyst described in any one of claims 1-8 in a crucible, then place the crucible in a sealed glass reaction container filled with CO2, and photocatalytically reduce CO2 under visible light irradiation conditions.

[0017] The beneficial effects of the present invention are:

[0018] 1. The C3N4 / Bi2O2CO3 heterojunction photocatalyst prepared by the present invention has a larger specific surface area, higher adsorption and desorption performance, and a band gap width that is more suitable for photocatalytic reactions;

[0019] 2. The C3N4 / Bi2O2CO3 heterojunction photocatalyst prepared by the present invention is simple to prepare, environmentally friendly, and conducive to large-scale production;

[0020] 3. The ultra-thin nature of C3N4 is conducive to the transmission of photogenerated carriers, allowing a large number of photogenerated carriers to participate in the photocatalytic CO2 reduction reaction, thereby improving the photocatalytic performance of the C3N4 / Bi2O2CO3 heterojunction photocatalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 These are the X-ray diffraction patterns of C3N4, Bi2O2CO3, and C3N4 / Bi2O2CO3 heterojunction photocatalysts.

[0022] Figure 2 This is the product yield (CO)-time curve of the photocatalytic reduction of CO2 by C3N4, Bi2O2CO3, and C3N4 / Bi2O2CO3 heterojunction photocatalysts. DETAILED DESCRIPTION

[0023] Example 1 C3N4 / Bi2O2CO3 Heterojunction Photocatalyst

[0024] 1. Preparation of Bi2O2CO3:

[0025] First, 1.5mmol (0.728g) Bi(NO)3·5H2O was dissolved in 30ml of 1.2mol / L HNO3 solution prepared in advance. After the solution was stirred from white turbidity to colorless and transparent, 0.144g of citric acid was added. Then, 8mol / L NaOH solution was slowly added to the solution. The pH value of the solution was measured at the same time. After the pH value of the solution was adjusted to 6, the addition of NaOH solution was stopped. After the above solution was stirred at room temperature for 30min, it was transferred to an 80ml hot reaction container and kept at 180° for 24h. After natural cooling, the precipitate was washed by centrifugation, dried at 60°C, and set aside for use.

[0026] 2. Preparation of C3N4:

[0027] Take 2g of urea and spread it on the bottom of the porcelain boat. After spreading it flat, take an equal amount of melamine and spread it on the urea. After wrapping it with tin foil, put it in a muffle furnace and heat it to 550℃ and calcine it for 4h. After cooling naturally, transfer it to a tubular furnace and heat it to 450℃ and continue calcining for 4h. After cooling naturally, a yellow sample is obtained.

[0028] 3. Preparation of C3N4 / Bi2O2CO3 photocatalyst:

[0029] Take 0.1g Bi2O2CO3 and 0.01g C3N4 and put them into a beaker filled with 30ml ethanol. Stir the mixture continuously for 10h at 40℃, collect the product by centrifugation, and finally dry it at 60℃ to obtain the sample.

[0030] Figure 1 This is the X-ray diffraction pattern of the C3N4 / Bi2O2CO3 heterojunction photocatalyst prepared in Example 1. Characteristic diffraction peaks appear at 2θ=12.9°, 23.9°, 30.2° and 32.7°, corresponding to (002), (011), (013) and (110) and (622) crystal planes, which is consistent with the Bi2O2CO3 PDF standard card (PDF#41-1488). At the same time, when the two are combined, Figure 1 It can be seen that at 2θ=12.9°, the diffraction peak of Bi2O2CO3 shifts significantly, indicating that the two substances are successfully composited.

[0031] Example 2

[0032] At room temperature and pressure, take 40 mg of the prepared photocatalytic sample, place it in a round crucible with a diameter of 20 mm, add a small amount of deionized water and ultrasonically treat it for 5 minutes, then dry the sample, put the dried sample at the bottom of the glass reaction container, and add 0.5 ml of deionized water to the reaction container. Then vacuum the glass reactor, repeatedly evacuate and ventilate it 5 times, and then fill the glass reactor with high-purity CO2. The photocatalytic reduction reaction is carried out under a 300w xenon lamp. The reactor is placed 3 cm away from the xenon lamp light source. Finally, 1 ml of the generated gas is extracted using a micro-syringe and quantitatively analyzed by gas chromatograph (GC-1690).

[0033] Figure 2 This is the product of the photocatalytic reduction of CO2 of the sample: CO production-time curve. It can be seen that after 4 hours of light reaction, the CO production of C3N4 / Bi2O2CO3 is significantly improved.

Claims

1. A C3N4 / Bi2O2CO3 heterojunction photocatalyst, characterized in that: The preparation method comprises the following steps: 1) dissolving bismuth nitrate pentahydrate in HNO3 solution, and after it is completely dissolved, adding citric acid to the mixed solution, adding NaOH solution to adjust the pH under stirring, and then putting it into an autoclave for hydrothermal reaction, and finally collecting the white precipitate by centrifugation, and drying to obtain Bi2O2CO3; 2) Disperse Bi2O2CO3 in ethanol, then add C3N4, continue stirring in a water bath, collect the sample by centrifugation, and finally dry to obtain a C3N4 / Bi2O2CO3 heterojunction photocatalyst.

2. The C3N4 / Bi2O2CO3 heterojunction photocatalyst according to claim 1, characterized in that: In step 1), the molar ratio of bismuth nitrate pentahydrate to citric acid is 2:

1.

3. The C3N4 / Bi2O2CO3 heterojunction photocatalyst according to claim 1, characterized in that: In step 1), the pH is adjusted to 6.

4. The C3N4 / Bi2O2CO3 heterojunction photocatalyst according to claim 1, characterized in that: In step 1), the temperature of the hydrothermal reaction is 180° C. and the reaction time is 24 h.

5. The C3N4 / Bi2O2CO3 heterojunction photocatalyst according to claim 1, characterized in that: The preparation method of C3N4 is as follows: take a certain amount of urea and spread it on the bottom of a porcelain boat. After spreading it flat, take an equal amount of melamine and spread it on the urea. After wrapping it with tin foil, put it in a muffle furnace for calcination. After cooling naturally, transfer it to a tubular furnace for further calcination, and finally obtain a yellow sample C3N4.

6. The C3N4 / Bi2O2CO3 heterojunction photocatalyst according to claim 5, characterized in that: The calcination temperature of the muffle furnace is 550° C., and the calcination time is 4 hours; the calcination temperature of the tubular furnace is 450° C., and the calcination time is 4 hours.

7. The C3N4 / Bi2O2CO3 heterojunction photocatalyst according to claim 1, characterized in that: In step 2), the mass ratio of Bi2O2CO3:C3N4 is 10:

1.

8. The C3N4 / Bi2O2CO3 heterojunction photocatalyst according to claim 1, characterized in that: In step 2), the temperature of the water bath is 40°C.

9. Use of the C3N4 / Bi2O2CO3 heterojunction photocatalyst according to any one of claims 1 to 8 in photocatalytic reduction of CO2.

10. The use according to claim 9, characterized in that: The method is as follows: the C3N4 / Bi2O2CO3 heterojunction photocatalyst described in any one of claims 1 to 8 is dispersed in a crucible, and the crucible is then placed in a sealed glass reaction container filled with CO2, and CO2 is photocatalytically reduced under visible light irradiation conditions.

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