Preparation and application of photocatalyst for regulating CsPbBr3 electronic structure based on strain engineering

Abstract

The invention discloses preparation and application of a photocatalyst for regulating and controlling a CsPbBr3 electronic structure based on strain engineering.The preparation method comprises the following steps that a series of CsPb1-xCuxBr3 (x = 0, 0.05, 0.1 or 0.2) quantum dots are synthesized through a thermal injection method, due to the structural characteristics of ionic bonds, soft lattices and the like of CsPbBr3, precise lattice compression strain can be achieved through Pb-site equivalent cation substitution, and the CsPbBr3 electronic structure is obtained; specifically, the electronic energy band structure of CsPb0. 9Cu0. 1Br3 is changed by regulating and controlling the distortion of the [PbBr6] 4-octahedron, so that the separation of photon-generated carriers is effectively promoted; due to the introduction of the strain, the central position of a d band of Pb in CsPb0. 9Cu0. 1Br3 is closer to the Fermi level, so that the adsorption strength of CO2 and the desorption process of a key reaction intermediate are enhanced. The research reveals an influence mechanism of strain engineering on photocatalytic CO2 reduction reaction, provides theoretical guidance for designing high-performance photocatalytic materials, and has potential application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of perovskite material preparation, and in particular to a photocatalyst preparation based on strain-regulated CsPbBr3 electronic structure and its application in photocatalytic CO2 reduction. Background Art

[0002] As a new type of optoelectronic functional material, metal halide perovskite has many significant advantages, making it quickly become a research focus in the fields of LEDs, solar cells, photodetection, etc. Due to its advantages such as high absorption coefficient, long carrier diffusion distance and adjustable band gap, it has also demonstrated great potential and application value in the field of photocatalysis. As of now, metal halide perovskite photocatalytic materials also face many challenges, such as insufficient catalytic active sites, weak redox ability, and poor separation of photogenerated carriers, which in turn lead to relatively low photocatalytic efficiency. In order to solve the above problems, methods such as morphology and crystal modification, construction of heterojunctions, metal nano-ion deposition and loading of co-catalysts have been proposed one after another.

[0003] In addition, there are some research examples that have proven that introducing appropriate distortion to construct a strain field within the lattice of semiconductor photocatalytic materials can break their structural symmetry. The strain-induced lattice distortion can adjust the atomic spacing and orbital overlap integral, thereby directly affecting the bonding of the adsorbate and the adsorption energy. It can also adjust the surface electronic structure of the catalytic material, enhance the spatial separation and migration of photogenerated carriers, and significantly improve the photocatalytic efficiency. Secondly, according to the d-band center theory, the catalytic activity is essentially closely related to the position of the d-band center relative to the Fermi level. Through Cu 2+ Substitute part of Pb in the CsPbBr3 lattice 2+ The lattice strain introduced by ions also changes the electronic structure of the Pb d orbitals. Therefore, it is necessary to conduct in-depth research to visually characterize the induced strain in CsPbBr3 and to clarify the relationship between strain and the d-band center, as well as the adsorption and desorption characteristics and photogenerated carrier separation during photocatalytic reactions. Summary of the Invention

[0004] In order to solve the problems of the existing technology, we invented a photocatalyst preparation based on strain engineering to regulate the electronic structure of CsPbBr3 and its application in photocatalytic CO2 reduction. 1-x Cu x Br3 quantum dots, through experimental data and theoretical calculations, have demonstrated that Cu 2+The incorporation of strain produces compressive strain in the lattice. The introduction of strain not only facilitates the separation of photogenerated electrons and holes, but also promotes the adsorption and desorption of intermediates during the subsequent CO2 photocatalytic reduction process. In summary, this invention describes the specific effects of strain regulation on the photocatalytic CO2 reduction reaction and provides theoretical guidance for the design of future high-performance photocatalytic materials. The invention specifically includes the following steps: (1) Preparation of cesium oleate precursor Cs-OA: 1 mmol of Cs2CO3 and 10 mL of oleic acid were added to a three-necked flask and stirred continuously for 30 minutes under a nitrogen atmosphere and heated at 140 °C until the cesium carbonate was completely dissolved; (2) Preparation of CsPbBr3 quantum dots: 0.7 mmol PbBr2, 20 mL octadecene, 1 mL oleylamine and 3 mL oleic acid were added to a three-necked flask and stirred continuously for 30 minutes under a nitrogen atmosphere and heated at 120 °C. The temperature was then raised to 150 °C and stirred vigorously. At this time, 2 mL of cesium oleate precursor Cs-OA solution was quickly injected into the three-necked flask. After reacting for 5-10 seconds, the mixture was immediately transferred to an ice-water bath and cooled to room temperature. The precipitate was then obtained by centrifugation and washed three times with toluene to remove residual organic solvent. The product was finally dried in a vacuum drying oven at 60 °C for 12 h and the powder was collected. (3) CsPb 1-x Cu x Preparation of Br3 (x=0.05, 0.1, 0.2) quantum dots: The amounts of PbBr2 used were 0.66, 0.63, and 0.56 mmol, and the corresponding amounts of CuBr2 used were 0.04, 0.07, and 0.14 mmol, respectively. The rest of the conditions remained consistent with the preparation method of CsPbBr3 quantum dots.

[0005] Compared with the existing technology, the present invention has the following beneficial effects: In order to solve the many challenges faced by metal halide perovskite photocatalytic materials, such as insufficient catalytic active sites, weak redox ability, and poor separation of photogenerated carriers, we proposed a strain engineering strategy. Thanks to the structural properties of CsPbBr3 such as ionic bonds and soft lattice, Cu can be doped into CsPbBr3 quantum dots. 2+ To replace part of Pb 2+ Thus, lattice strain is generated. The generation of compressive strain is first proved by the shift of X-ray diffraction patterns and Raman spectroscopy peak positions, and then the intuitive distribution of compressive strain is obtained by geometric phase analysis of high-resolution transmission electron microscopy images. The characterization of femtosecond transient absorption spectroscopy proves that the generation of strain is not only conducive to the separation of photogenerated carriers; in addition, density functional theory calculations have also obtained CsPb 0.9 Cu0.1 The changes in the Br3 electronic band structure show that the band becomes narrower and the Pb-d band center moves toward the Fermi level. This phenomenon reveals that CsPb 0.9 Cu 0.1 The increase in Br3's adsorption strength for CO2, as well as the CO2 temperature-programmed desorption curve, also confirm the above phenomenon. Overall, the preparation method of the present invention is simple, low-cost, and achieves the production of high-value-added fuels without the addition of any sacrificial agents or co-catalysts, thus possessing broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 The following are the XRD patterns of Examples 1, 2 and 3.

[0007] Figure 2 These are the Raman spectra of Examples 1 and 3.

[0008] Figure 3 These are the HRTEM spectra of Examples 1 and 3, the FFT patterns in the corresponding selected areas, and the images obtained by the geometric phase analysis method.

[0009] Figure 4 These are the femtosecond transient absorption spectra of Examples 1 and 3 and the kinetic parameters obtained by fitting to specific wavelengths.

[0010] Figure 5 PDOS spectra of Pb-d orbitals of Examples 1 and 3.

[0011] Figure 6 These are the CO2 temperature-programmed desorption curves of Examples 1 and 3.

[0012] Figure 7 This is a rate spectrum of photocatalytic CO2 reduction to produce CO and CH4 in Examples 1, 2, 3 and 4.

[0013] Figure 8 Example 3 13 Gas chromatography-mass spectrometry measured under CO2 atmosphere. DETAILED DESCRIPTION

[0014] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to Not limited to the content described.

[0015] Example 1: Preparation and application of a photocatalyst based on strain engineering to regulate the electronic structure of CsPbBr3, the specific steps are as follows: (1) Preparation of cesium oleate precursor Cs-OA: 1 mmol of Cs2CO3 and 10 mL of oleic acid were added to a three-necked flask and stirred continuously for 30 minutes under a nitrogen atmosphere and heated at 140 °C until the cesium carbonate was completely dissolved; (2) Preparation of CsPbBr3 quantum dots: 0.7 mmol PbBr2, 20 mL octadecene, 1 mL oleylamine and 3 mL oleic acid were added to a three-necked flask and stirred continuously for 30 minutes under a nitrogen atmosphere and heated at 120 °C. The temperature was then raised to 150 °C and stirred vigorously. At this time, 2 mL of cesium oleate precursor Cs-OA solution was quickly injected into the three-necked flask. After reacting for 5-10 seconds, the mixture was immediately transferred to an ice-water bath and cooled to room temperature. The precipitate was then obtained by centrifugation and washed three times with toluene to remove the residual organic solvent. The product was finally dried in a vacuum drying oven at 60 °C for 12 hours to collect the powder.

[0016] Example 2: Preparation and application of a photocatalyst based on strain engineering to regulate the electronic structure of CsPbBr3, the specific steps are as follows: Cb 0.95 Cu 0.05 Preparation of Br3 quantum dots: 0.66 mmol PbBr2, 0.04 mmol CuBr2, 20 mL octadecene, 1 mL oleylamine, and 3 mL oleic acid were added to a three-necked flask. Stirring was continued at 120°C under a nitrogen atmosphere for 30 minutes. The temperature was then raised to 120°C while maintaining vigorous stirring. 2 mL of cesium oleate precursor Cs-OA solution was then rapidly injected into the three-necked flask. After reacting for 5-10 seconds, the mixture was immediately transferred to an ice-water bath and cooled to room temperature. The precipitate was then centrifuged and washed three times with toluene to remove residual organic solvent. The product was finally dried in a vacuum oven at 60°C for 12 hours to collect the powder.

[0017] Example 3: Preparation and application of a photocatalyst based on strain engineering to regulate the electronic structure of CsPbBr3, the specific steps are as follows: Cb 0.9 Cu 0.1 Preparation of Br3 quantum dots: 0.63 mmol PbBr2, 0.07 mmol CuBr2, 20 mL octadecene, 1 mL oleylamine and 3 mL oleic acid were added to a three-necked flask, and the remaining steps were consistent with Example 2.

[0018] Example 4: A preparation method and application of CsPbBr3 quantum dots based on strain engineering to control carrier dynamics, the specific steps are as follows: Cb 0.8Cu 0.2 Preparation of Br3 quantum dots: 0.56 mmol PbBr2, 0.07 mmol CuBr2, 20 mL octadecene, 1 mL oleylamine and 3 mL oleic acid were added to a three-necked flask, and the remaining steps were consistent with Example 2. Figure 1 The CsPbBr3, CsPb prepared in Examples 1, 2 and 3 are 0.95 Cu 0.05 Br3 and CsPb 0.9 Cu 0.1 The XRD spectrum of Br3 shows that the positions of the three diffraction peaks are consistent with the standard PDF card. 2+ With the addition of CsPb 0.95 Cu 0.05 Br3 and CsPb 0.9 Cu 0.1 The position of the Br3 diffraction peak shifts slightly toward larger angles. According to the Bragg formula, when the lattice is subjected to compressive strain, the lattice constant becomes smaller, causing the diffraction peak to shift toward higher angles.

[0019] Figure 2 The CsPbBr3 and CsPb prepared in Example 1 and Example 3 are 0.9 Cu 0.1 Raman spectrum of Br3 at 136 cm -1 The peak at 319 cm is the signal generated by the asymmetric stretching vibration of Br-Pb-Br. -1 The peak at is the characteristic peak of CsPbBr3. 0.9 Cu 0.1 The positions of these two peaks were observed to be blue-shifted in the Br3 sample. The reason for the blue shift is that Cu 2+ Replaced Pb 2+ The position of the crystal lattice causes compressive strain.

[0020] Figure 3 The CsPbBr3 and CsPb prepared in Example 1 and Example 3 are 0.9 Cu 0.1 HRTEM spectrum of Br3, FFT pattern in the corresponding selected area and image obtained by geometric phase analysis method. It can be seen from the figure that CsPb 0.9 Cu 0.1 The lattice fringe of the (200) crystal plane of Br3 is 0.316 nm, which is 0.299 nm higher than that of CsPbBr3. According to the formula The calculated strain rate is 5.7%. Furthermore, the ε obtained by geometric analysis in the selected area of ​​HRTEM isxx Quantity Figure 3 d, h, shown by Figure 3 h It can be seen that the strain distribution results obtained by geometric phase analysis along the white arrow part have a more obvious contrast in color, suggesting that CsPb 0.9 Cu 0.1 The generation of lattice compressive strain inside the Br3 lattice.

[0021] Figure 4 The CsPbBr3 and CsPb prepared in Example 1 and Example 3 are 0.9 Cu 0.1 The femtosecond transient absorption spectrum of Br3 and the kinetic parameters obtained by fitting the excited state absorption wavelength. The faster decay τ1 component represents the time it takes for the electrons in the excited state to relax to the bottom of the conduction band. It can be seen that CsPb 0.9 Cu 0.1 The fitted lifetime in Br3 is significantly longer than that in CsPbBr3, indicating that more photogenerated electrons participate in the carrier migration process. The τ2 component represents the time taken by the defect state to capture the carrier. Similarly, CsPb 0.9 Cu 0.1 Br3 exhibits a longer lifetime, which is attributed to Cu 2+ The incorporation of leads to an increase in the defect state density, which allows more carriers to be captured, thereby reducing the probability of recombination of photogenerated electrons and holes. The τ3 component represents the photoluminescence lifetime of the recombination of photogenerated electrons and holes. It can be seen that CsPb 0.9 Cu 0.1 The lifetime of Br3 is shorter than that of CsPb 0.9 Cu 0.1 In summary, the increase of τ1 and τ2 lifetimes and the decrease of τ3 indicate that the generation of strain contributes to the 0.9 Cu 0.1 The transfer of photogenerated carriers at the Br3 interface promotes the subsequent CO2 redox reaction.

[0022] Figure 5 The CsPbBr3 and CsPb prepared in Example 1 and Example 3 are 0.9 Cu 0.1 PDOS spectrum of Pb-d orbital of Br3. The calculation results show that the d-band centers of the two are located at -3.05 eV (CsPbBr3) and -2.09 eV (CsPb 0.9 Cu 0.1 Br3). According to the d-band center theory, the closer the d-band center is to the Fermi level, the more electrons are filled in the bonding orbital, and the stability and strength of the adsorption bond will increase. Therefore, compared with CsPbBr3, CsPb 0.9 Cu 0.1Br3 exhibits stronger surface adsorption ability.

[0023] Figure 6 The CsPbBr3 and CsPb prepared in Example 1 and Example 3 are 0.9 Cu 0.1 CO2 temperature-programmed desorption curve of Br3. Compared with CsPbBr3, CsPb 0.9 Cu 0.1 The integrated area of ​​the Br3 adsorption curve peak and the temperatures corresponding to the two desorption peaks were significantly increased, further proving that the introduction of strain changed the center position of the d band and thus improved the CO2 adsorption capacity.

[0024] Figure 7 The CsPbBr3, CsPb prepared in Examples 1, 2, 3 and 4 are 0.95 Cu 0.05 Br3、CsPb 0.9 Cu 0.1 Br3 and CsPb 0.8 Cu 0.2 Br3 photocatalytic CO2 reduction rate spectrum of photocatalytic CO2 reduction to produce CO and CH4. It can be seen from the figure that when the illumination time reaches 3 h, CsPb 0.9 Cu 0.1 The CO and CH4 yields of Br3 reached the highest values, increasing to 25.84 and 69.75 μmol g, respectively. -1 .CsPb 0.9 Cu 0.1 The high Br3 yield is attributed to the introduction of strain, which leads to stronger photogenerated carrier separation ability and enhanced CO2 adsorption capacity.

[0025] Figure 8 The CsPb prepared in Example 3 0.9 Cu 0.1 Br3 13 Gas chromatography-mass spectrometry under CO2 atmosphere. In order to further verify the carbon source of the reaction product, 13 CsPb under CO2 atmosphere 0.9 Cu 0.1 Br3 was used for isotope labeling photocatalytic experiments. The mass spectrometry results clearly detected that the main reaction product was 13 CO (m / z = 29), which indicates that the carbon products obtained are derived from 13 CO2 gas.

[0026] Finally, it should be noted that the above is only a preferred embodiment of the present invention. For technicians in this field and for subsequent applications and production, some improvements and optimizations can be made without departing from the technical principles of the patented technology of the present invention, which are still considered to be within the scope of protection of the invention patent of this technology.

Claims

1. A photocatalyst preparation and application based on strain engineering to regulate the electronic structure of CsPbBr3, the preparation method comprising the following steps: (1) Preparation of cesium oleate precursor Cs-OA: 1 mmol of Cs2CO3 and 10 mL of oleic acid were added to a three-necked flask and stirred continuously for 30 minutes under a nitrogen atmosphere and heated at 140 °C until the cesium carbonate was completely dissolved; (2) Preparation of CsPbBr3 quantum dots: 0.7 mmol PbBr2, 20 mL octadecene, 1 mL oleylamine and 3 mL oleic acid were added to a three-necked flask and stirred continuously for 30 minutes under a nitrogen atmosphere and heated at 120 °C. The temperature was then raised to 150 °C and stirred vigorously. At this time, 2 mL of cesium oleate precursor Cs-OA solution was quickly injected into the three-necked flask. After reacting for 5-10 seconds, the mixture was immediately transferred to an ice-water bath and cooled to room temperature. The precipitate was then obtained by centrifugation and washed three times with toluene to remove residual organic solvent. The product was finally dried in a vacuum drying oven at 60 °C for 12 h and the powder was collected. (3) CsPb 1-x Cu x Preparation of Br3 (x = 0.05, 0.1, 0.2) quantum dots: The amounts of PbBr2 were 0.66, 0.63 and 0.56 mmol, respectively, and the corresponding amounts of CuBr2 were 0.04, 0.07 and 0.14 mmol, respectively. The other conditions were consistent with the preparation method of CsPbBr3 quantum dots; the reason for choosing CuBr2 is that Cu 2+ The radius is smaller than Pb 2+ , and then introduce compressive strain to achieve the change of the d-band center position, and finally in CsPb 0.9 Cu 0.1 Br3 achieves the best carrier separation efficiency and photocatalytic performance.

2. The preparation and application of a photocatalyst for regulating the electronic structure of CsPbBr3 based on strain engineering according to claim 1, characterized in that: The lattice strain was verified by Raman spectroscopy, high-resolution transmission electron microscopy combined with geometric phase analysis.

3. The preparation and application of a photocatalyst for regulating the electronic structure of CsPbBr3 based on strain engineering according to claim 1, characterized in that: The photogenerated carrier separation efficiency is tested by transient absorption spectroscopy or time-resolved fluorescence spectroscopy, which proves that the separation of photogenerated carriers is promoted while the compressive strain is introduced.

4. The preparation and application of a photocatalyst for regulating the electronic structure of CsPbBr3 based on strain engineering according to claim 1, characterized in that: The CsPb 0.9 Cu 0.1 The center position of the Pb-d band of Br3 moves toward the Fermi level, which promotes the adsorption and desorption process in the subsequent photocatalytic reduction process.

5. The preparation of a photocatalyst based on strain engineering to regulate the electronic structure of CsPbBr3 according to claim 1 and its application in photocatalytic CO2 reduction under visible light irradiation.

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