Preparation method for regulating and controlling photocatalytic carbon dioxide reduction based on dielectric constant and application

Abstract

The invention discloses a preparation method and application of photocatalytic carbon dioxide reduction based on dielectric constant regulation and control, organic-inorganic hybrid perovskite-(PEA) 2PbBr4 and (EOA) 2PbBr4 with different dielectric constants are chemically synthesized at room temperature, and the PEA 2PbBr4 and the (EOA) 2PbBr4 are applied to photocatalytic carbon dioxide reduction for the first time. Compared with (PEA) 2PbBr4, (EOA) 2PbBr4 shows higher catalytic activity, and the result shows that the CO generation rate of the EOA 2PbBr4 reaches 18.69 [mu] mol.g <-1 >. H <-1 >. The results are attributed to the existence of carboxyl in the (EOA) 2PbBr4, so that the positive and negative charge centers of O and H are not overlapped, and larger polarity and dielectric constant are generated. The difference of dielectric constants with an inorganic layer is reduced, the dielectric confinement effect is weakened, and relatively small exciton binding energy is shown, so that the separation of photo-induced electrons and holes is promoted, the photocatalytic carbon dioxide reduction performance is enhanced, and potential application prospects are achieved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of perovskite material preparation, and in particular to a preparation method for regulating photocatalytic carbon dioxide reduction based on dielectric constant and application. BACKGROUND

[0002] Organic-inorganic hybrid perovskite materials have unique advantages such as wide light absorption range, long carrier transport lifetime, adjustable band gap and low preparation cost, and have become potential candidates in the fields of solar cells, photoelectric detectors and light-emitting diodes. At the same time, the use of photocatalytic technology to convert renewable solar energy into chemical energy and high-value fuels is considered to be a green way to solve energy and environmental problems. In recent years, organic-inorganic hybrid perovskites have been widely studied in the fields of photocatalytic water splitting, photocatalytic degradation of organic reactions and photocatalytic reduction of carbon dioxide, and have shown high energy conversion efficiency. The A-site cations in the organic-inorganic hybrid perovskite are replaced by some long-chain organic amine molecules, forming a two-dimensional layered quantum well structure of A2BX4 with an alternating period of organic and inorganic layers. Due to the difference in dielectric constant between the organic layer and the inorganic layer, this structure usually shows a large exciton binding energy, thereby limiting the separation and transport of photo-generated electrons and holes.

[0003] Therefore, adjusting the behavior of photo-generated electrons and holes in organic-inorganic hybrid perovskites can effectively improve the performance of photocatalytic carbon dioxide reduction. According to the dielectric confinement effect, when the electric field lines of photo-generated electrons and holes are located in the surrounding medium with relatively small dielectric constant, the Coulomb force between the electrons and holes will be enhanced, which is not conducive to the separation of photo-generated electrons and holes. That is, using an organic molecule with a larger dielectric constant as the A-site cation will reduce the difference in dielectric constant between the organic layer and the inorganic layer, thereby promoting the separation of photo-generated electrons and holes. However, in the field of photocatalytic reduction of carbon dioxide, the dielectric confinement effect of organic-inorganic hybrid perovskites and the application of (PEA)2PbBr4 and (EOA)2PbBr4 in photocatalytic reduction of carbon dioxide have not been explored. SUMMARY

[0004] In order to solve the problems existing in the prior art, we have invented a preparation method for regulating photocatalytic carbon dioxide reduction based on dielectric constant and application, and prepared two kinds of (PEA)2PbBr4 and (EOA)2PbBr4 perovskite materials with different dielectric constants. Compared with (PEA)2PbBr4, (EOA)2PbBr4 has a larger dielectric constant and a smaller exciton binding energy, which is conducive to the separation and transport of photo-generated electrons and holes, and this is the first time to explore the application of the two in the field of photocatalytic reduction of carbon dioxide. The application specifically includes the following steps: (1) Preparation of PEABr: 5.66 mL of HBr solution was slowly added to a mixture of 6.28 mL phenethylamine and 10 mL ethanol, then stirred thoroughly in an ice water bath at 0 °C, the white precipitate after reaction was centrifuged and washed with isopropanol three times. Finally, put it into a 60 °C vacuum drying oven for 12 h to collect the powder; (2) Preparation of EOABr: 5.66 mL of HBr solution was slowly added to a mixture of 3.05 mL ethanolamine and 10 mL ethanol, then stirred thoroughly in an ice water bath at 0 °C, the white precipitate after reaction was centrifuged and washed with isopropanol three times. Finally, put it into a 60 °C vacuum drying oven for 12 h to collect the powder; (3) Preparation of (PEA)2PbBr4: 0.202 g of PEABr and 0.184 g of PbBr2 were dissolved in 10 mL dimethylformamide and stirred for 0.5 h, then 2 mL of the solution was added to 10 mL toluene at once and stirred for 0.5 h. The precipitate was obtained by centrifugal washing, and the obtained precipitate was dried in a vacuum drying oven to collect the powder; (4) Preparation of (EOA)2PbBr4: 0.142 g of EOABr and 0.184 g of PbBr2 were dissolved in 10 mL dimethylformamide and stirred for 0.5 h, then 2 mL of the solution was added to 10 mL toluene at once and stirred for 0.5 h. The precipitate was obtained by centrifugal washing, and the obtained precipitate was dried in a vacuum drying oven to collect the powder.

[0005] Further, the molar ratio of HBr and phenethylamine in step (1) is 1:1, and the stirring time is 2 h.

[0006] Further, the molar ratio of HBr and ethanolamine in step (2) is 1:1, and the stirring time is 2 h.

[0007] Further, the molar ratio of PEABr and PbBr2 in step (3) is 2:1, the centrifugal condition is 6000 r / min, the centrifugal time is 5 min, the vacuum drying time is 12 h, and the drying temperature is 60 °C.

[0008] Further, the molar ratio of EOABr and PbBr2 in step (4) is 2:1, the centrifugal condition is 6000 r / min, the centrifugal time is 5 min, the vacuum drying time is 12 h, and the drying temperature is 60 °C.

[0009] Further, the washing organic solvent in steps (3) and (4) is toluene solution, and the washing number is three times.

[0010] Compared with the prior art, the present application has the following beneficial effects: In order to solve the problem of dielectric confinement effect enhanced due to the difference in dielectric constant in the organic-inorganic hybrid perovskite, two kinds of (PEA)2PbBr4 and (EOA)2PbBr4 perovskite materials with different dielectric constants are synthesized, the application of the two in the field of photocatalytic carbon dioxide is first explored, and a technical reference is provided for the preparation of other photocatalytic materials based on dielectric engineering regulation. Among them, (EOA)2PbBr4 contains hydroxyl, which causes the positive and negative charge centers of O and H not to overlap, resulting in a larger dielectric constant and a smaller exciton binding energy. In addition, density functional theory calculates that the energy difference between the total DOS of C, H and N in (EOA)2PbBr4 and Pb and Br is smaller, which is conducive to weakening the dielectric confinement effect, promoting the separation of photo-generated electrons and holes, and increasing the yield of photocatalytic carbon dioxide reduction to generate CO carbon. The preparation method of the present application is simple and low in cost, realizes the preparation and production of high-value-added organic matter without adding any sacrificial agent and cocatalyst, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is the XRD pattern of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2.

[0012] Figure 2 is the TEM, HADDF-STEM and EDS pattern of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2.

[0013] Figure 3 is the dielectric constant test pattern of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2.

[0014] Figure 4 is the photoluminescence intensity integral pattern of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2 with temperature change.

[0015] Figure 5 is the PDOS pattern of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2 calculated by density functional theory.

[0016] Figure 6 is the rate of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2 photocatalytic CO2 reduction to generate CO and the gas chromatography-mass spectrometry pattern measured under CO2 atmosphere. 13 CO2 gas atmosphere. DETAILED DESCRIPTION

[0017] The application will be further described in detail in connection with the specific embodiments below, but the scope of protection of the application is not limited to the content The application is not limited to the content.

[0018] Example 1: A preparation method and application for regulating photocatalytic reduction of carbon dioxide based on dielectric constant, the specific steps are as follows: (1) 5.66 mL of HBr solution was slowly added to a mixed solution of 6.28 mL of phenethylamine and 10 mL of ethanol, then fully stirred in an ice water bath at 0 ℃, the white PEABr precipitate obtained after the reaction was centrifuged and washed with isopropyl alcohol three times. Finally, it was placed in a 60 ℃ vacuum drying oven for drying for 12 h to collect the powder; (2) 0.202 g of PEABr and 0.184 g of PbBr2 were dissolved in 10 mL of dimethylformamide and stirred for 0.5 h, then 2 mL of the solution was added to 10 mL of toluene at one time and stirred for 0.5 h. The precipitate was obtained by centrifugal washing, and the obtained precipitate was placed in a 60 ℃ vacuum drying oven for drying for 12 h to collect the powder.

[0019] Example 2: A preparation method and application for regulating photocatalytic reduction of carbon dioxide based on dielectric constant, the specific steps are as follows: (1) 5.66 mL of HBr solution was slowly added to a mixed solution of 6.28 mL of phenethylamine and 10 mL of ethanol, then fully stirred in an ice water bath at 0 ℃, the white PEABr precipitate obtained after the reaction was centrifuged and washed with isopropyl alcohol three times. Finally, it was placed in a 60 ℃ vacuum drying oven for drying for 12 h to collect the powder; (2) 0.202 g of PEABr and 0.184 g of PbBr2 were dissolved in 10 mL of dimethylformamide and stirred for 0.5 h, then 2 mL of the solution was added to 10 mL of toluene at one time and stirred for 0.5 h. The precipitate was obtained by centrifugal washing, and the obtained precipitate was placed in a 60 ℃ vacuum drying oven for drying for 12 h to collect the powder.

[0020] Figure 1 The XRD patterns of (PEA)2PbBr4 and (EOA)2PbBr4 synthesized in Example 1 and Example 2 are shown in the figure, it can be seen from the figure that both have good crystallinity, strong diffraction intensity, and complete correspondence with the simulated standard diffraction peak, indicating that (PEA)2PbBr4 and (EOA)2PbBr4 perovskite materials are successfully synthesized.

[0021] Figure 2are TEM, HADDF-STEM and EDS mapping of (PEA)2PbBr4 and (EOA)2PbBr4 synthesized in Example 1 and Example 2. It can be seen that both of them are in the micron range and present flaky morphology. EDS mapping further confirms the presence of elements such as C, O, Pb and Br.

[0022] Figure 3 are dielectric constant test maps of (PEA)2PbBr4 and (EOA)2PbBr4 synthesized in Example 1 and Example 2. It can be seen from the figure that the relative dielectric constant of (PEA)2PbBr4 and (EOA)2PbBr4 is 12.43 and 28.92 respectively at high frequency.

[0023] Figure 4 are photoluminescence intensity integral maps of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2 as a function of temperature, and the inset is the variable-temperature photoluminescence spectrum of both in the range of 60-270 K. According to the formula Figure 4 , the data of (PEA)2PbBr4 and (EOA)2PbBr4 are fitted to obtain the exciton binding energy of 156.07 and 71.03 meV respectively, indicating that the increase of dielectric constant reduces the exciton binding energy of the material.

[0024] Figure 5 are PDOS maps of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2 calculated by density functional theory. It can be found that the position of the total DOS of C, H and N in (EOA)2PbBr4 is closer to the valence band edge than that in (PEA)2PbBr4. This small energy offset is more conducive to the separation and transport of photo-generated electrons and holes.

[0025] Figure 6 are the rate map of CO produced by photocatalytic reduction of CO2 and the gas chromatography-mass spectrometry map of (PEA)2PbBr4 and (EOA)2PbBr4 prepared in Example 1 and Example 2 under 13 CO2 atmosphere. It can be seen that when the illumination time reaches 4.5 h, the CO yield of (PEA)2PbBr4 and (EOA)2PbBr4 increases to 43.8 and 84.1 μmol g -1 respectively. The high yield of (EOA)2PbBr4 is attributed to its strong photo-generated electron-hole separation ability, which leads to more carriers migrating to the reaction active site to participate in the carbon dioxide reduction reaction. In order to further verify the carbon source of the reaction product, an isotopic labeling photocatalytic experiment was carried out on (EOA)2PbBr4 under 13 CO2 atmosphere. Mass spectrometry analysis results clearly determine that the main reaction product is 13CO (m / z = 29), which indicates that the resulting carbon product is derived from the CO2 gas.

[0026] Finally, it should be noted that the above only is the preferred embodiment of the present application, for the skilled in the art and subsequent application and production, without departing from the principles of the present patent technology, can make some improvements and optimization, still considered the scope of the present technical invention patent.

Claims

1. A preparation method and application of photocatalytic carbon dioxide reduction based on dielectric constant regulation, characterized in that: The steps include: (1) Preparation of PEABr: Slowly add 5.66 mL of HBr solution to a mixed solution of 6.28 mL of phenylethylamine and 10 mL of ethanol, then stir thoroughly in an ice-water bath at 0°C. Centrifuge the white precipitate after the reaction and wash it three times with isopropanol. Finally, dry it in a vacuum drying oven at 60°C for 12 h to collect the powder. (2) Preparation of EOABr: 5.66 mL of HBr solution was slowly added to a mixed solution of 3.05 mL of ethanolamine and 10 mL of ethanol, and then stirred thoroughly in an ice-water bath at 0°C. The white precipitate after the reaction was centrifuged and washed three times with isopropanol. Finally, the powder was collected by drying in a vacuum drying oven at 60°C for 12 h. (3) Preparation of (PEA)2PbBr4: Dissolve 0.202 g of PEABr and 0.184 g of PbBr2 in 10 mL of dimethylformamide and stir for 0.5 h. Then, add 2 mL of this solution to 10 mL of toluene and stir for 0.5 h. Wash the solution by centrifugation and dry the resulting precipitate in a vacuum oven to collect the powder. (4) Preparation of (EOA)2PbBr4: Dissolve 0.142 g of EOABr and 0.184 g of PbBr2 in 10 mL of dimethylformamide and stir for 0.5 h. Then, add 2 mL of this solution to 10 mL of toluene and stir for 0.5 h. Wash the mixture by centrifugation to obtain a precipitate, which is then dried in a vacuum oven to collect the powder.

2. The preparation method and application of the photocatalytic carbon dioxide reduction based on dielectric constant regulation according to claim 1, characterized in that: The molar ratio of HBr to phenylethylamine in step (1) is 1:1, and the stirring time is 2 h.

3. The preparation method and application of the photocatalytic carbon dioxide reduction based on dielectric constant regulation according to claim 1, characterized in that: The molar ratio of HBr to ethanolamine in step (2) is 1:1, and the stirring time is 2 h.

4. The preparation method and application of the photocatalytic carbon dioxide reduction based on dielectric constant regulation according to claim 1, characterized in that: The molar ratio of PEABr to PbBr2 in step (3) is 2:1, the centrifugal conditions are a speed of 6000 r / min, a centrifugal time of 5 min, the vacuum drying time is 12 h, and the drying temperature is 60 °C.

5. The preparation method and application of the photocatalytic carbon dioxide reduction based on dielectric constant regulation according to claim 1, characterized in that: In step (4), the molar ratio of EOABr to PbBr2 is 2:1, the centrifugal conditions are a speed of 6000 r / min, a centrifugal time of 5 min, the vacuum drying time is 12 h, and the drying temperature is 60 °C.

6. The preparation method and application of photocatalytic carbon dioxide reduction based on dielectric constant regulation according to claim 1, characterized in that: The washing organic solvent used in steps (3) and (4) is toluene solution, and the washing times are three times.

7. A photocatalyst obtained according to the preparation method of claims 1-5.

8. A first application of the photocatalyst according to claim 6 in photocatalytic carbon dioxide production.

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