A lead-free bismuth-based mixed halide perovskite nanosheet and a preparation method and application thereof

Abstract

This invention discloses a lead-free bismuth-based mixed halide perovskite nanosheet, its preparation method, and its applications. The invention uses a simple anti-solvent recrystallization method to prepare Cs3Bi 2‑x Sb x Br9 nanosheets, with the molecular formula Cs3Bi 2‑x Sb x Br9, where 0 < x ≤ 0.4. The introduction of Sb increases the visible light absorption capacity and photogenerated carrier separation efficiency of Cs3Bi2Br9. The good size matching of Sb improves the stability of Cs3Bi2Br9 perovskite material. A small amount of Sb doping promotes C(sp... 3 The )-H bond activates the generation of vacancies in key active species.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nanomaterial preparation and photocatalysis, and in particular to a lead-free bismuth-based mixed halide perovskite nanosheet, a preparation method thereof and application thereof in photocatalytic C(sp 3 )-H bond activation. BACKGROUND

[0002] Selective oxidation of saturated hydrocarbons to produce high value-added products (such as aldehydes, ketones and epoxides, etc.) is one of the most challenging and interesting disciplines in catalytic chemistry. Due to the high bond dissociation energy (70-130 kcal mol 3 )-H bond (70-130 kcal mol -1 ) and unfavorable adsorption, harsh conditions (high temperature and / or high pressure) are usually required. In addition, the conversion rate must be less than <15% to avoid poor selectivity caused by excessive oxidation of products under such harsh conditions. To solve this problem, replacing traditional thermal catalysis with mild photocatalysis is a promising solution. Due to their high stability and easy separation, heterogeneous photocatalytic systems of metal oxides and metal sulfides have now attracted widespread attention from researchers. However, due to the narrow light absorption, low charge separation efficiency and conversion efficiency, the performance of these photocatalysts is still not ideal. All-metal halide perovskite A I Pb II X3 (A = Rb, Cs; B = Ge, Pb, Sn; and X = Cl, Br, I), especially CsPbBr3 and CsPbI3, has been proved to be a promising photocatalytic material due to its suitable band gap, excellent light absorption and high efficient carrier mobility. However, due to the lead toxicity, lower oxidation ability (the valence band top is usually less than 1.4 eV) and chemical stability, its application in the field of photocatalysis is limited. SUMMARY

[0003] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a lead-free bismuth-based mixed halide perovskite nanosheet, a preparation method thereof and application thereof, wherein the Bi / Sb mixed halide perovskite nanosheet is prepared by adjusting the proportion of raw materials and the crystallization time through anti-solvent recrystallization. The Sb doping improves the separation efficiency of photo-generated carriers for visible light absorption of the catalyst and promotes the generation of holes. At the same time, the good size matching of Sb improves the stability of the Cs3Bi2Br9 perovskite material.

[0004] In order to achieve the above technical purpose, the present application adopts the following technical scheme:

[0005] A lead-free bismuth-based mixed halide perovskite nanosheet, the molecular formula of which is Cs3Bi 2-x Sb xBr9, wherein 0 < x ≤ 0.4.

[0006] As preferred, in the formula, 0.1 ≤ x ≤ 0.3; further preferably, x = 0.2.

[0007] The application also provides a preparation method of the above-mentioned lead-free bismuth-based mixed halide perovskite nanosheet, comprising the following steps:

[0008] (1) Dissolving CsBr, BiBr3 and SbBr3 in DMSO according to a set molar ratio to obtain a precursor solution;

[0009] (2) Adding the precursor solution obtained in (1) into isopropanol, crystallizing for 0.5-5 min by an anti-solvent method, and then washing and drying to obtain Cs3Bi 2-x Sb x Br9 nanosheet.

[0010] As preferred, the molar ratio of BiBr3 and SbBr3 in step (1) is 1.7:0.3-1.9:0.1, and the concentration of CsBr in DMSO is 10-20 mM.

[0011] Further preferably, the molar ratio of BiBr3 and SbBr3 is 1.8:0.2.

[0012] As preferred, the volume ratio of the precursor solution and isopropanol in step (2) is 1:20-1:30.

[0013] As preferred, in step (2), chloroform is used for washing, and then drying in a vacuum oven at 60℃ for 10 hours to obtain Cs3Bi 2-x Sb x Br9 nanosheet.

[0014] The application also provides an application of the above-mentioned lead-free bismuth-based mixed halide perovskite nanosheet, which is used for photocatalytic C(sp 3 )-H bond activation reaction.

[0015] In the application, Bi and Sb are used as B-site cations in halide perovskite, wherein Bi is the main element and Sb is the auxiliary element, and the mixed halide perovskite nanosheet is synthesized by an anti-solvent recrystallization method. The inventors find that in the anti-solvent process, the crystallization time needs to be strictly controlled to avoid the formation of large crystal particles and to obtain the nanosheet. In the application, a small amount of Sb is introduced into Cs3Bi2Br9 to replace part of Bi, and Sb doping improves the separation efficiency of photo-generated carriers under visible light and promotes the generation of holes. At the same time, the good size matching of Sb improves the stability of the Cs3Bi2Br9 perovskite material.

[0016] Compared with the prior art, the present application has the advantages of:

[0017] The present application prepared Cs3Bi 2-x Sb x Br9 nanosheets by a simple anti-solvent recrystallization method, the introduction of Sb increases the visible light absorption ability and the separation efficiency of photo-generated carriers of Cs3Bi2Br9. The good size matching of Sb improves the stability of the Cs3Bi2Br9 perovskite material. A small amount of Sb doping promotes the generation of a key active species hole of C(sp 3 )-H bond activation. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The SEM images of the samples Cs3Bi2Br9 (a), Cs3Bi 1.8 Sb 0.2 Br9 (b), Cs3Bi 1.5 Sb 0.5 Br9 (c), Cs3Bi 0.7 Sb 1.3 Br9 (d), Cs3Sb2Br9 (e) prepared for Comparative Example 1, Example 1 and Comparative Examples 2-4.

[0019] Figure 2 The SEM images of the samples prepared for Example 1 (a), Comparative Example 5 (b) and Comparative Example 6 (c).

[0020] Figure 3 The SEM images of the samples prepared for Example 1 (a), Comparative Example 7 (b) and Comparative Example 8 (c).

[0021] Figure 4 The XRD patterns of the samples Cs3Bi2Br9, Cs3Bi 1.8 Sb 0.2 Br9, Cs3Bi 1.5 Sb 0.5 Br9, Cs3Bi 0.7 Sb 1.3 Br9, Cs3Sb2Br9 prepared for Comparative Example 1, Example 1 and Comparative Examples 2-4.

[0022] Figure 5 The performance test of photocatalytic toluene oxidation of the samples Cs3Bi2Br9, Cs3Bi 1.8 Sb 0.2 Br9, Cs3Bi 1.5 Sb 0.5 Br9, Cs3Bi 0.7 Sb 1.3 Br9, Cs3Sb2Br9 prepared for Comparative Example 1, Example 1 and Comparative Examples 2-4.

[0023] Figure 6 Cs3Bi2Br9 and Cs3Bi were prepared for Comparative Example 1 and Example 1. 1.8 Sb 0.2 Stability comparison chart of Br9 samples. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0025] This invention utilizes photocatalysis of C(sp) 3 Evaluation of Cs3Bi by )-H bond activation 2-x Sb x Activity of Br9 nanosheets. First, 10 mg of catalyst was dispersed in 5 mL of reaction substrate; the mixture was magnetically stirred in the dark for 30 min, and oxygen (2 mL min) was added. -1 An adsorption-desorption equilibrium was established by introducing the solution into the bottom of the reaction mixture. A 300W xenon lamp equipped with a filter with a wavelength of λ ≥ 400 nm was used as the light source. Quantitative analysis was performed using gas chromatography with the internal standard method.

[0026] Example 1

[0027] Cs3Bi 1.8 Sb 0.2 Preparation of Br9 nanosheets:

[0028] 0.45 mmol CsBr, 0.075 mmol SbBr3, and 0.225 mmol BiBr3 were dissolved in 30 mL of DMSO to obtain a precursor liquid. Then, 2 mL of the precursor was added to 50 mL of isopropanol under vigorous stirring for 1 minute. The mixture was washed three times with chloroform and dried in a vacuum oven at 60 °C for 10 hours to obtain a yellow Cs3Bi 1.8 Sb 0.2 Br9 nanosheets.

[0029] Comparative Example 1

[0030] Preparation of Cs3Bi2Br9 nanosheets:

[0031] 0.45 mmol CsBr and 0.30 mmol BiBr3 were dissolved in 30 mL of DMSO to obtain a precursor liquid. Then, 2 mL of the precursor was added to 50 mL of isopropanol under vigorous stirring and stirred rapidly for 1 minute. The mixture was washed three times with chloroform and dried in a vacuum oven at 60 °C for 10 hours to obtain yellow Cs3Bi2Br9 nanosheets.

[0032] Comparative Example 2

[0033] Cs3Bi 1.5Sb 0.5 Preparation of Br9 nanosheets:

[0034] 0.45 mmol CsBr, 0.150 mmol SbBr3, and 0.150 mmol BiBr3 were dissolved in 30 mL of DMSO to obtain a precursor liquid. Then, 2 mL of the precursor was added to 50 mL of isopropanol under vigorous stirring for 1 minute. The mixture was washed three times with chloroform and dried in a vacuum oven at 60 °C for 10 hours to obtain a yellow Cs3Bi 1.5 Sb 0.5 Br9 nanosheets.

[0035] Comparative Example 3

[0036] Cs3Bi 0.7 Sb 1.3 Preparation of Br9 nanoparticles:

[0037] 0.45 mmol CsBr, 0.225 mmol SbBr3, and 0.075 mmol BiBr3 were dissolved in 30 mL of DMSO to obtain a precursor liquid. Then, 2 mL of the precursor was added to 50 mL of isopropanol under vigorous stirring for 1 minute. The mixture was washed three times with chloroform and dried in a vacuum oven at 60 °C for 10 hours to obtain a yellow Cs3Bi 0.7 Sb 1.3 Br9 nanoparticles.

[0038] Comparative Example 4

[0039] Preparation of Cs3Sb2Br9 nanoparticles:

[0040] 0.45 mmol CsBr and 0.30 mmol SbBr3 were dissolved in 30 mL of DMSO to obtain a precursor liquid. Then, 2 mL of the precursor was added to 50 mL of isopropanol under vigorous stirring and stirred rapidly for 1 minute. The mixture was washed three times with chloroform and dried in a vacuum oven at 60 °C for 10 hours to obtain yellow Cs3Bi2Br9 nanoparticles.

[0041] Comparative Example 5

[0042] Cs3Bi 1.8 Sb 0.2 Preparation of Br9 nanoparticles:

[0043] A precursor solution was prepared by dissolving 0.45 mmol of CsBr, 0.075 mmol of SbBr3, and 0.225 mmol of BiBr3in 30 mL of DMSO. Then, 2 mL of the precursor solution was added to 50 mL of isopropanol under vigorous stirring and stirred rapidly for 180 min. The product was washed with chloroform three times and dried in a vacuum oven at 60 °C for 10 h to obtain yellow Cs3Bi 1.8 Sb 0.2 Br9nanoparticles.

[0044] Comparative Example 6

[0045] Cs3Bi 1.8 Sb 0.2 Preparation of Cs3Bi

[0046] A precursor solution was prepared by dissolving 0.45 mmol of CsBr, 0.075 mmol of SbBr3, and 0.225 mmol of BiBr3in 30 mL of DMSO. Then, 2 mL of the precursor solution was added to 50 mL of isopropanol under vigorous stirring and stirred rapidly for 720 min. The product was washed with chloroform three times and dried in a vacuum oven at 60 °C for 10 h to obtain yellow Cs3Bi 1.8 Sb 0.2 Br9nanoparticles.

[0047] Comparative Example 7

[0048] Cs3Bi 1.8 Sb 0.2 Preparation of Cs3Bi

[0049] A precursor solution was prepared by dissolving 2.25 mmol of CsBr, 0.375 mmol of SbBr3, and 1.125 mmol of BiBr3in 30 mL of DMSO. Then, 2 mL of the precursor solution was added to 50 mL of isopropanol under vigorous stirring and stirred rapidly for 1 min. The product was washed with chloroform three times and dried in a vacuum oven at 60 °C for 10 h to obtain yellow Cs3Bi 1.8 Sb 0.2 Br9nanoparticles.

[0050] Comparative Example 8

[0051] Cs3Bi 1.8 Sb 0.2 Preparation of Cs3Bi

[0052] A precursor solution was prepared by dissolving 4.5 mmol of CsBr, 0.75 mmol of SbBr3and 2.25 mmol of BiBr3in 30 mL of DMSO. Then, 2 mL of the precursor solution was added into 50 mL of isopropanol under vigorous stirring for 1 min. The mixture was washed with chloroform for three times and dried in a vacuum oven at 60 °C for 10 h to obtain yellow Cs3BiSb9nanoparticles. 1.8 Sb 0.2 Br9nanoparticles.

[0053] Performance evaluation:

[0054] The photocatalytic C(sp 3 )-H bond activation was used as a model reaction to investigate the catalytic activity of the prepared samples.

[0055] 10 mg of the sample was dispersed in 5 mL of toluene. The mixture was magnetically stirred in the dark for 30 min and oxygen (2 mL min -1 ) was introduced into the bottom of the reaction mixture to establish adsorption-desorption equilibrium. A 300 W xenon lamp with a λ≥400 nm filter was used as the light source. The amount of reactants and products was determined by internal standard method using n-decane as the internal standard. Quantification was performed on a Shimadzu GC2010 Plus chromatograph equipped with an FID detector and a WAX capillary column (30 m x 0.25 mm x 0.25 μm).

[0056] The results of the photocatalytic toluene oxidation reaction of the samples prepared in Example 1 and Comparative Examples 1-4 are shown in Table 1.

[0057] Table 1 Results of photocatalytic toluene oxidation reaction of the samples prepared in Example 1 and Comparative Examples 1-4

[0058]

[0059] As can be seen from Table 1, different rates of toluene conversion were obtained under different Bi, Sb molar ratios, wherein the generation rates of benzaldehyde and benzyl alcohol were 4.033 mmol g -1 h -1 and 1.779 mmol g -1 h -1 , respectively, when the Bi, Sb molar ratio was 1.8:0.2, and the photocatalytic effect was the best.

[0060] Table 2 Results of photocatalytic toluene oxidation reaction of the samples prepared in Example 1 and Comparative Examples 5-6

[0061]

[0062] As can be seen from Table 2, different rates of toluene conversion were obtained under different crystallization times, wherein the generation rates of benzaldehyde and benzyl alcohol were 4.033 mmol g-1 h -1 and 1.779 mmol g -1 h -1 The photocatalytic effect is the best.

[0063] Table 3. Results of photocatalytic toluene oxidation of the samples prepared in Example 1 and Comparative Examples 7-8

[0064]

[0065] Table 3 shows that CsBr in DMSO yielded different toluene conversion rates. The rates of benzaldehyde and benzyl alcohol formation at a crystallization time of 1 min were 4.033 mmol g and 4.033 mmol g, respectively. -1 h -1 and 1.779 mmol g -1 h -1 The photocatalytic effect is the best.

[0066] The samples prepared in Example 1 were tested with toluene derivatives containing other substituents, and the results are shown in Table 4:

[0067] Table 4. Results of the photocatalytic oxidation of toluene derivatives in the samples prepared in Example 1.

[0068]

[0069]

[0070] Note: a Reaction conditions: 5 mL substrate, 10 mg Cs3 Bi 1.8 Sb 0.2 Br9 as a photocatalyst, λ≥400nm, O2(2mL·min) -1 The reaction time is 3 hours. b Solid p-nitrotoluene (3.225 g, relative density 1.29 g / mL) -1 Dissolve in 2.5 mL of acetonitrile and react.

[0071] like Figure 1 As shown in figure a, Cs3Bi2Br9 exists in the form of nanosheets with a thickness of approximately 20 nm. A small amount of Sb is used to replace (Cs3Bi2Br9) 1.8 Sb 0.2 Br9 and Cs3Bi 1.5 Sb 0.5 Br9) can maintain a sheet-like structure. Figure 1 (b and 1c). However, further increasing the Sb content, Cs3Bi 0.7 Sb 1.3 Br9 appears as nanoparticles ( Figure 1d), which is consistent with pure Cs3Sb2Br9 Figure 1 e).

[0072] As shown in Fig. Figure 2 , the morphology of Cs3Bi 1.8 Sb 0.2 Br9 varies greatly with different crystallization time. Nanosheets (2a) are obtained with 1 min crystallization, nanoparticles (2b) with 180 min crystallization, and larger nanoparticles (2c) with 700 min crystallization.

[0073] As shown in Fig. Figure 3 , the morphology of Cs3Bi 1.8 Sb 0.2 Br9 varies greatly with different concentration of CsBr in DMSO. Nanosheets (3a) are obtained with 15 mM CsBr, nanoparticles (3b) with 75 mM CsBr, and larger nanoparticles (3c) with 150 mM CsBr.

[0074] As shown in Fig. Figure 4 a, compared with Cs3Bi2Br9, the diffraction peaks of (003), (300) and (220) in Cs3Bi2Br9 gradually decrease in position and disappear in Cs3Sb2Br9 with the increase of Sb content, while the characteristic peaks of (022) and (204) shift to larger angles Figure 4 b).

[0075] As shown in Fig. Figure 5 , the conversion of toluene first increases and then decreases with the increase of Sb 3+ . The Cs3Bi 1.8 Sb 0.2 Br9 nanosheets have the highest conversion, reaching 5813 μmol h -1 g -1 , and the selectivity of benzaldehyde and benzyl alcohol is 69.4% and 30.6%, respectively. The photocatalytic activity of Cs3Bi 1.8 Sb 0.2 Br9 is about 5.1 and 2.1 times that of pure Cs3Sb2Br9 and Cs3Bi2Br9, respectively.

[0076] As shown in Fig. Figure 6 , the recycling experiment shows that Cs3Bi 1.8 Sb 0.2 Br9 retains more than 77% of the original activity after 4 cycles, while Cs3Bi2Br9 retains only 50% of the original activity.

Claims

1. Use of a lead-free bismuth-based hybrid halide perovskite nanosheet, characterized in that, It is used for photocatalytic C sp 3 -H bond activation reactions; The molecular formula of the lead-free bismuth-based mixed halide perovskite nanosheet is Cs3Bi 1.8 Sb 0.2 Br9, and the specific preparation process is: Dissolve 0.45 mmol of CsBr, 0.075 mmol of SbBr3, and 0.225 mmol of BiBr3in 30 mL of DMSO to obtain a precursor liquid; then, under vigorous stirring, add 2 mL of the precursor to 50 mL of isopropyl alcohol, and stir rapidly for 1 minute; Washed with chloroform three times, dried in a vacuum oven at 60 °C for 10 hours to obtain yellow Cs3Bi 1.8 Sb 0.2 Br9 nanosheets.

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