Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 and application thereof

Abstract

The invention discloses an Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 and application of the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2. The catalyst takes CeO2 modified g-C3N4 as a carrier and is loaded with an active component Eu-Bi3O4Br. According to the preparation method, CeO2 modified g-C3N4 is taken as a carrier, so that photon-generated carriers and electron-hole pairs of the catalyst are improved, Eu-Bi3O4Br improves the electron migration efficiency of the catalyst, Eu-Bi3O4Br is more uniformly distributed on the modified g-C3N4, clustering is prevented, and the utilization rate of Eu-Bi3O4Br is increased. The catalyst shows excellent performance in photocatalytic reduction of CO2, CO2 reduction is efficient and rapid, CO2 can be reduced within a short time, the CO2 concentration can be reduced, the requirement for the environment is friendly, and secondary pollution cannot be generated in the reaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of comprehensive utilization of CO2, and particularly relates to a catalyst for reducing CO2 and a method for photocatalytic reduction of CO2. Background Art

[0002] Energy and environmental problems are the two major problems faced by human survival. With the continuous increase in the concentration of CO2 in the atmosphere, the global temperature is warming, resulting in an increasing number of disastrous weather events year by year. Therefore, how to reduce CO2 emissions and control and utilize it at the source has become a global issue of concern. In the process of continuously exploring CO2 emission reduction technologies, people have found that photocatalytic technology has the advantages of mild reaction conditions, environmental protection and pollution-free, and low energy consumption, thus attracting much attention from scientists.

[0003] Photocatalytic CO2 reduction with water as the reaction medium to produce value-added carbonaceous substances has been considered an attractive method to solve the global warming problem and simultaneously manage the global carbon balance. Although a large number of impressive CO2 reduction photocatalysts have been developed, most still have low photocatalytic activity, poor product selectivity or high requirements for sacrificial agents, which greatly limits their practical applications. Therefore, we hope to design a robust catalyst with high reduction efficiency, high selectivity without using sacrificial reagents.

[0004] The key point of photocatalytic reduction of CO2 lies in the preparation of an efficient photocatalyst. Research shows that Bi3O4Br not only has high photocatalytic activity (strong ultraviolet absorption performance, strong reducibility of photogenerated electrons and oxidizability of holes), but also has the advantages of being cheap, non-toxic, having broad-spectrum applicability, and stable chemical properties (resistant to acid-base and photochemical corrosion), and is considered an excellent photocatalyst. However, the ultraviolet radiation range absorbed by Bi3O4Br is limited, and solar energy cannot be fully utilized; in addition, the recombination probability of photogenerated electrons and holes is very high, resulting in low utilization efficiency of photogenerated carriers of Bi3O4Br. Due to these two defects, to a certain extent, it restricts the practical application of Bi3O4Br photocatalytic technology.

[0005] In recent years, ultrathin two-dimensional (2D) materials with suitable band structures have been proven to have obvious advantages as emerging photocatalysts. The atomic thickness and huge specific surface area allow better absorption of ultraviolet-visible light. Due to the shortened diffusion distance from the inner surface, the ultrathin structure can significantly reduce the possibility of volume recombination of carriers. In addition, the high ratio of coordination-unsaturated surface atoms to bulk atoms can provide more sites to promote interfacial reactions. In particular, a single type of surface atom is beneficial for producing highly selective CO2 reduction products. However, the high surface charge recombination rate and the lack of active sites limit the full utilization of carriers to trigger the photoreduction process. To further improve the reduction efficiency of CO2, adding isolated single atoms to 2D ultrathin nanosheets may be an attractive strategy. Single-atom catalysts have the highest atomic utilization efficiency and unique properties, showing great potential in different catalytic applications. Summary of the Invention

[0006] The object of the present invention is to provide a Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst with high reduction efficiency and high selectivity for photocatalytic reduction of CO2.

[0007] The Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst provided by the present invention uses CeO2-modified g-C3N4 as a carrier and loads the active component Eu-Bi3O4Br. Taking the mass of g-C3N4 as 100%, the content of CeO2 is 0.1% - 2.5%, the content of Eu is 0.5% - 2.5%, and the content of Bi3O4Br is 1.0% - 5.0%; preferably, the content of CeO2 is 1.0% - 2.3%, the content of Eu is 0.5% - 2.0%, and the content of Bi3O4Br is 3.0% - 5.0%.

[0008] The preparation method of the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst of the present invention includes the following steps:

[0009] Step 1: Dissolve cerium nitrate, melamine, and ammonium chloride in deionized water, stir at 15 - 30 °C for 0.5 - 1 h, transfer the obtained mixed solution into a corundum crucible, first dry at 60 - 120 °C in a blast drying oven for 4 - 10 h, then calcine at 350 - 450 °C in a muffle furnace for 1 - 2 h, and then raise the temperature to 550 - 600 °C and calcine for 1 - 3 h. After calcination, cool naturally and grind to obtain g-C3N4 / CeO2;

[0010] Step 2: Add g-C3N4 / CeO2 and lactic acid into ethylene glycol. After stirring for 0.5 - 1 h, add bismuth nitrate and mannitol, denoted as solution A; dissolve potassium bromide and europium nitrate in deionized water, denoted as solution B; dropwise add solution A into solution B, stir at 15 - 30 °C for 0.5 - 2 h, then transfer the obtained mixture into a hydrothermal reactor lined with polytetrafluoroethylene, and react statically in an oven at 120 - 180 °C for 8 - 24 h. After the reaction, centrifuge, wash, and dry to obtain the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst.

[0011] In the above step 1, preferably, the mass ratio of cyanuric acid, cerium nitrate, and ammonium chloride is 1:0.2 - 0.5:0.5 - 1.0.

[0012] In the above step 2, preferably, the mass ratio of g-C3N4 / CeO2, lactic acid, mannitol, and potassium bromide is 1:0.1 - 0.6:0.1 - 0.4:0.03 - 0.05.

[0013] Furthermore, in the above step 2, preferably, transfer the obtained mixture into a hydrothermal reactor lined with polytetrafluoroethylene, and react statically in an oven at 140 - 160 °C for 8 - 12 h.

[0014] The present invention also provides the application of the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst in photocatalytic reduction of CO2. The specific method is as follows: Add Eu-Bi3O4Br / g-C3N4 / CeO2 into absolute ethanol, ultrasonically disperse for 30 - 60 min, then pour the dispersion into a corundum watch glass, dry in a blast drying oven at 60 - 100 °C, put the dried watch glass into a visible high-pressure photocatalytic reactor, add deionized water into the watch glass, then introduce CO2 gas at 0.1 - 0.5 MPa, carry out a dark reaction at 20 - 50 °C for 20 - 50 min, and then irradiate with visible light at a power of 300 - 1400 W for 1 - 4 h.

[0015] In the above application of photocatalytic reduction of CO2, preferably, add Eu-Bi3O4Br / g-C3N4 / CeO2 into absolute ethanol, ultrasonically disperse for 40 - 60 min, then pour the dispersion into a corundum watch glass, dry in a blast drying oven at 80 °C, put the dried watch glass into a visible high-pressure photocatalytic reactor, add deionized water into the watch glass, then introduce CO2 gas at 0.25 - 0.45 MPa, carry out a dark reaction at 30 - 40 °C for 30 - 40 min, and then irradiate with visible light at a power of 500 - 800 W for 2 - 3 h.

[0016] In the above application of photocatalytic reduction of CO2, the concentration of Eu-Bi3O4Br / g-C3N4 / CeO2 in deionized water is 0.5-2.0 g / L, and preferably the concentration of Eu-Bi3O4Br / g-C3N4 / CeO2 in deionized water is 1.0-1.5 g / L.

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

[0018] 1. The catalyst of the present invention uses g-C3N4 modified by CeO2 as a carrier to improve the photocurrent carriers and electron-hole pairs of the catalyst; doping Eu into the catalyst can improve the mechanical strength of the carrier, and the doping of Eu makes the electron migration efficiency of the catalyst increase, achieving a better catalytic effect, improving the service life of the catalyst, and increasing the thermal stability of the catalyst; Bi3O4Br has a large visible light range and a band gap width of 2.84 eV, which can utilize sunlight more efficiently. Bi3O4Br / g-C3N4 / CeO2 is a Z-type heterojunction with a band gap width of 2.63 eV, which can increase more defect sites, making the catalyst have more active sites, and Eu-Bi3O4Br is more evenly distributed on the modified g-C3N4, preventing clustering and increasing the utilization rate of Eu-Bi3O4Br;

[0019] 2. The preparation process of the catalyst of the present invention is simple, takes a short time, the raw materials are rich and easy to obtain, and it can be reused. It shows excellent performance in photocatalytic reduction of CO2, reduces CO2 efficiently and quickly, can reduce the concentration of CO2 in a short time, is friendly to the environment, does not produce secondary pollution during the reaction, and does not require the use of sacrificial reagents in photocatalytic reduction of CO2, greatly reducing the CO2 treatment cost. Description of the Drawings

[0020] Figure 1 is the XRD pattern of Eu-Bi3O4Br / g-C3N4 / CeO2 prepared in Example 1.

[0021] Figure 2 is the SEM image of Eu-Bi3O4Br / g-C3N4 / CeO2 prepared in Example 1.

[0022] Figure 3 is the recycling diagram of Eu-Bi3O4Br / g-C3N4 / CeO2 in Example 4. Detailed Embodiments

[0023] The present invention will be further described in detail below with reference to the drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0024] Example 1

[0025] In the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst of this embodiment, based on the mass of g-C3N4 being 100%, the content of CeO2 is 2.0%, the content of Eu is 0.7%, and the content of Bi3O4Br is 2.3%. The preparation method of the catalyst includes the following steps:

[0026] Step 1: Accurately weigh 3.000 g of cerium nitrate hexahydrate, 10.000 g of cyanuric acid, and 7.500 g of ammonium chloride, dissolve them in 40 mL of deionized water, magnetically stir (400 r / min) at 20 °C for 1 h, transfer the uniformly mixed solution into a 100 mL corundum crucible, first dry it in a blast drying oven at 100 °C for 300 min, then transfer the corundum crucible into a muffle furnace, heat it at a heating rate of 5 °C / min to 400 °C and calcine for 1 h, and then heat it at a heating rate of 5 °C / min to 575 °C and calcine for 2 h. After calcination, cool it naturally and grind it to obtain g-C3N4 / CeO2.

[0027] Step 2: Weigh 10 g of the g-C3N4 / CeO2 obtained in Step 1 and disperse it in 75 mL of ethylene glycol, add 2 g of lactic acid as a structure assistant, stir for 1 h, then add 1.455 g of bismuth nitrate pentahydrate and 1.2 g of mannitol, and record it as Solution A. Dissolve 0.375 g of potassium bromide and 0.2 g of europium nitrate hexahydrate in 20 mL of deionized water, stir for 1 h, and record it as Solution B; drop Solution A into Solution B drop by drop, continue to stir at room temperature for 2 h, then transfer the obtained mixture into a 100 mL hydrothermal autoclave with a polytetrafluoroethylene liner, and react statically for 8 h in an environment of 140 °C in a drying oven. After the reaction, cool it naturally to room temperature, collect the precipitate by centrifugation, then wash it alternately with deionized water and ethanol, and then dry it in an oven at 80 °C to obtain the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst.

[0028] Perform structural characterization on the obtained catalyst. Figure 1 is the XRD pattern of Eu-Bi3O4Br / g-C3N4 / CeO2. It can be seen from the figure that there is a strong diffraction peak at 2θ = 28.3°, corresponding to the (002) crystal plane of g-C3N4 modified by CeO2. There are strong diffraction peaks at 2θ = 30.5°, 31.8°, 33.4°, and 40°, corresponding to the (411), (002), (102), and (512) crystal planes of Bi3O4Br respectively. There are strong diffraction peaks at 2θ = 24.4°, 45.5°, and 55°, corresponding to the (110), (100), and (001) crystal planes of Eu respectively, indicating good crystallization effect. Figure 2 is the SEM image of Eu-Bi3O4Br / g-C3N4 / CeO2. It can be seen from the figure that the obtained catalyst is in a two-dimensional thin layer shape, and Eu-Bi3O4Br is uniformly loaded on the surface of g-C3N4 / CeO2.

[0029] Example 2

[0030] For the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst of this example, based on the mass of g-C3N4 being 100%, the content of CeO2 is 2.0%, the content of Eu is 0.5%, and the content of Bi3O4Br is 3.0%; the preparation method of the catalyst includes the following steps:

[0031] Step 1: Accurately weigh 3.000 g of cerium nitrate hexahydrate, 10.000 g of cyanuric acid, and 7.500 g of ammonium chloride, dissolve them in 40 mL of deionized water, magnetically stir (400 r / min) at 20 °C for 1 h, transfer the uniformly mixed solution into a 100 mL corundum crucible, first dry it in a blast drying oven at 100 °C for 5 h, then transfer the corundum crucible into a muffle furnace, heat it at a heating rate of 5 °C / min to 400 °C and calcine for 1 h, then heat it at a heating rate of 5 °C / min to 575 °C and calcine for 2 h, and naturally cool and grind after calcination to obtain g-C3N4 / CeO2.

[0032] Step 2: Weigh 10 g of the g-C3N4 / CeO2 obtained in Step 1, disperse it in 75 mL of ethylene glycol, add 2 g of lactic acid as a structure assistant, stir for 1 h, then add 1.455 g of bismuth nitrate pentahydrate and 1.2 g of mannitol, and record it as Solution A. Dissolve 0.390 g of potassium bromide and 0.1750 g of europium nitrate hexahydrate in 20 mL of deionized water, stir for 1 h, and record it as Solution B; drop Solution A into Solution B drop by drop, continue to stir at room temperature for 2 h, then transfer the obtained mixture to a 100 mL hydrothermal autoclave with a polytetrafluoroethylene inner lining, and react statically for 10 h in an environment of 160 °C in a drying oven. After the reaction, naturally cool to room temperature, collect the precipitate by centrifugation, then wash it alternately with deionized water and ethanol, and then dry it in an oven at 80 °C to obtain the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst.

[0033] Example 3

[0034] For the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst of this example, based on the mass of g-C3N4 being 100%, the content of CeO2 is 2.0%, the content of Eu is 0.83%, and the content of Bi3O4Br is 2.1%; the preparation method of the catalyst includes the following steps:

[0035] Step 1: Accurately weigh 3.000 g of cerium nitrate hexahydrate, 10.000 g of cyanuric acid, and 7.500 g of ammonium chloride, dissolve them in 40 mL of deionized water, and magnetically stir (400 r / min) at 20 °C for 1 h. Transfer the well-mixed liquid into a 100 mL corundum crucible, first dry it in a forced-air drying oven at 100 °C for 5 h, then transfer the corundum crucible into a muffle furnace, heat it at a heating rate of 5 °C / min to 400 °C and calcine for 1 h, and then heat it at a heating rate of 5 °C / min to 575 °C and calcine for 2 h. After calcination, let it cool naturally and grind to obtain g-C3N4 / CeO2.

[0036] Step 2: Weigh 10 g of the g-C3N4 / CeO2 obtained in Step 1 and disperse it in 75 mL of ethylene glycol, add 2 g of lactic acid as a structure assistant, stir for 1 h, then add 1.455 g of bismuth nitrate pentahydrate and 1.2 g of mannitol, and record it as Solution A. Dissolve 0.350 g of potassium bromide and 0.235 g of europium nitrate hexahydrate in 20 mL of deionized water, stir for 1 h, and record it as Solution B; drop Solution A into Solution B drop by drop, continue to stir at room temperature for 2 h, then transfer the obtained mixture into a 100 mL hydrothermal autoclave with a polytetrafluoroethylene liner, and react statically for 12 h in an environment of 150 °C in a drying oven. After the reaction, let it cool naturally to room temperature, collect the precipitate by centrifugation, then wash it alternately with deionized water and ethanol, and then dry it in an oven at 80 °C to obtain the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst.

[0037] Example 4

[0038] Application of the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst in Example 1 for photocatalytic reduction of CO2

[0039] Add 0.010 g of Eu-Bi3O4Br / g-C3N4 / CeO2 to 5 mL of absolute ethanol, ultrasonically disperse for 60 min, then pour the dispersion into a corundum watch glass, dry it in a forced-air drying oven at 80 °C for 4 h, put the dried watch glass into a visible high-pressure photocatalytic reaction kettle, add 10 mL of deionized water to the watch glass, then introduce 0.40 MPa of CO2 gas, and carry out a dark reaction at 25 °C for 30 min, and then irradiate it with a 500 W cold light source xenon lamp for 2 h. Analyze the gas after the reaction using GC-MS, and calculate the efficiency of the catalyst by calculating the peak area as follows: carbon monoxide: 206 mmol / (g*h), methane: 105 mmol / (g*h).

[0040] Dry and redisperse the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst after the reaction in Example 4 above, and continue to carry out 5 repeated experiments according to the method of Example 4, as Figure 3As shown, the last obtained efficiency is: carbon monoxide: 195.5 mmol / (g*h), methane: 95.6 mmol / (g*h). It can be seen that the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst of the present invention has relatively stable performance and can be recycled multiple times.

Claims

1. An Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2, characterized in that: The catalyst uses CeO2-modified g-C3N4 as a carrier and loads the active component Eu-Bi3O4Br. Taking the mass of g-C3N4 as 100%, the CeO2 content is 0.1% - 2.5%, the Eu content is 0.5% - 2.5%, and the Bi3O4Br content is 1.0% - 5.0%. This catalyst is prepared by the following method: Step 1: Dissolve cerium nitrate, melamine cyanurate, and ammonium chloride in deionized water, stir at 15 - 30 °C for 0.5 - 1 h, transfer the obtained mixed solution into a corundum crucible, first dry at 60 - 120 °C in a blast drying oven for 4 - 10 h, then calcine at 350 - 450 °C in a muffle furnace for 1 - 2 h, then raise the temperature to 550 - 600 °C and calcine for 1 - 3 h. After calcination, cool naturally and grind to obtain g-C3N4 / CeO2; Step 2: Add g-C3N4 / CeO2 and lactic acid into ethylene glycol, stir for 0.5 - 1 h, then add bismuth nitrate and mannitol, denoted as solution A; dissolve potassium bromide and europium nitrate in deionized water, denoted as solution B; dropwise add solution A to solution B, stir at 15 - 30 °C for 0.5 - 2 h, then transfer the obtained mixture to a hydrothermal autoclave with a polytetrafluoroethylene inner lining, and react statically at 120 - 180 °C in a drying oven for 8 - 24 h. After the reaction, centrifuge, wash, and dry to obtain the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst.

2. The Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 according to claim 1, characterized in that: Taking the mass of g-C3N4 as 100%, the CeO2 content is 1.0% - 2.3%, the Eu content is 0.5% - 2.0%, and the Bi3O4Br content is 3.0% - 5.0%.

3. The Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 according to claim 1 or 2, characterized in that: In Step 1, the mass ratio of melamine cyanurate, cerium nitrate, and ammonium chloride is 1:0.2 - 0.5:0.5 - 1.

0.

4. The Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 according to claim 1 or 2, characterized in that: In Step 2, the mass ratio of g-C3N4 / CeO2, lactic acid, mannitol, and potassium bromide is 1:0.1 - 0.6:0.1 - 0.4:0.03 - 0.

05.

5. The Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 according to claim 1 or 2, characterized in that: In Step 2, transfer the obtained mixture to a hydrothermal autoclave with a polytetrafluoroethylene inner lining, and react statically at 140 - 160 °C in a drying oven for 8 - 12 h.

6. Use of the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst according to claim 1 for photocatalytic reduction of CO2, characterized in that: Add Eu-Bi3O4Br / g-C3N4 / CeO2 into absolute ethanol, ultrasonically disperse for 30 - 60 min, then pour the dispersion into a corundum watch glass, dry in a blast drying oven at 60 - 100 °C, put the dried watch glass into a visible light high-pressure photocatalytic reactor, add deionized water to the watch glass, then introduce CO2 gas at 0.1 - 0.5 MPa, carry out a dark reaction at 20 - 50 °C for 20 - 50 min, and then irradiate with visible light at a power of 300 - 1400 W for 1 - 4 h.

7. Use of the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 according to claim 6, characterized in that: Add Eu-Bi3O4Br / g-C3N4 / CeO2 into anhydrous ethanol, ultrasonically disperse it for 40 - 60 min, then pour the dispersion into a corundum petri dish and dry it in a blast drying oven at 80 °C. Place the dried petri dish into a visible-light high-pressure photocatalytic reactor, add deionized water into the petri dish, then introduce CO2 gas at 0.25 - 0.45 MPa and conduct a dark reaction at 30 - 40 °C for 30 - 40 min. After that, irradiate it with visible light at a power of 500 - 800 W for 2 - 3 h.

8. Use of the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 according to claim 6 or 7, characterized in that: The concentration of Eu-Bi3O4Br / g-C3N4 / CeO2 in the deionized water is 0.5 - 2.0 g / L.

9. Use of the Eu-Bi3O4Br / g-C3N4 / CeO2 catalyst for photocatalytic reduction of CO2 according to claim 6 or 7, characterized in that: The concentration of Eu-Bi3O4Br / g-C3N4 / CeO2 in the deionized water is 1.0 - 1.5 g / L.

Images