Perovskite quantum dot-based graded heterojunction photocatalyst and preparation method and application thereof

Abstract

The application provides a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst and a preparation method and application thereof. The preparation method is that perovskite quantum dots are anchored on the surface of TPA-COFS nanosheets, specifically, TPA-COFS nanosheets are prepared by a solvothermal method; perovskite quantum dots are prepared by a hot injection method; the perovskite quantum dots are anchored on the TPA-COFS nanosheets by an electrostatic self-assembly method, and finally, the ladder-shaped heterojunction photocatalyst is obtained. In the catalyst system, the COFs is an oxidation-type photocatalyst, and the perovskite quantum dots are reduction-type photocatalysts, which not only make the photo-generated electrons and holes with weak reduction-oxidation ability recombine, but also make the photo-generated carriers with strong reduction-oxidation ability highly separated; and the TPA-COFS can effectively enhance the chemical adsorption and activation of acidic CO2 molecules, and the catalyst shows enhanced CO2 reduction activity under the irradiation of ultraviolet visible light.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthesis and application of photocatalytic materials, and particularly relates to a perovskite quantum dot-based ladder-type heterojunction photocatalyst and a preparation method and application thereof. BACKGROUND

[0002] The overconsumption of fossil fuels and the continuous emission of exhaust gases have led to a continuous increase in the concentration of carbon dioxide (CO2) in the atmosphere, exacerbating the problems of energy shortage and greenhouse effect. Solar energy is an inexhaustible clean energy, and the use of efficient photocatalytic technology to convert CO2 into high-value storable energy is one of the effective strategies to alleviate the above problems and achieve the double carbon goal.

[0003] Covalent organic framework materials (COFs) are a new type of porous polymer formed by light elements (C, O, N, B, etc.) connected by covalent bonds, and have a large specific surface area, high porosity and crystallinity, and are star materials in the field of photocatalysis. In particular, Schiff base COFs condensed by Schiff base reaction of aldehyde and amine have significant crystallinity, excellent chemical stability, a narrow band gap and a controllable energy band structure, and are a high-quality photocatalyst with strong reduction ability and visible light absorption. Benefiting from the large specific surface area, unique pore structure and rich weak basic nitrogen elements of Schiff base COFs, acidic CO2 molecules can be efficiently adsorbed and activated on the surface thereof, thereby promoting photocatalytic CO2 reduction. However, the photo-generated electrons and holes in a single COF are prone to recombination, resulting in low photocatalytic efficiency.

[0004] CsPbBr3 is a typical halide perovskite material with a tunable band gap, a narrow band gap and excellent quantum size effect. Compared with COFs, the conduction band position of CsPbBr3 quantum dots is higher, showing stronger reduction ability.

[0005] How to make good use of the intrinsic properties and advantages of COFs and CsPbBr3, couple them into a heterojunction composite photocatalyst through a simple strategy, realize efficient separation of photo-generated carriers with strong reduction and oxidation ability, and promote photocatalytic reduction of CO2 to improve the photocatalytic CO2 reduction activity of single Schiff base COF and CsPbBr3, and help achieve the goal of “carbon peak and carbon neutralization”, is a technical problem that needs to be solved at present. SUMMARY

[0006] The purpose of the present application is to provide a perovskite quantum dot-based ladder-type heterojunction photocatalyst and a preparation method and application thereof to solve the above problems of the prior art.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] The first object of the present application is to provide a preparation method of a perovskite quantum dot-based ladder heterojunction photocatalyst, comprising the following specific steps:

[0009] Step S1, synthesis of TPA-COFs: dissolve amine monomers and aldehyde monomers in a mixed solution composed of o-dichlorobenzene and anhydrous ethanol, then add an appropriate amount of acetic acid, perform liquid nitrogen freezing, vacuum pumping, remove air in the reactor, and then react in an oven at a certain temperature for several days; after washing, centrifuging and drying, brown TPA-COFs solid powder is obtained;

[0010] Step S2, preparation of CsPbBr3 perovskite quantum dot precursor solution: dissolve cesium source in a mixed solution composed of octadecene and oleic acid, and obtain cesium oleate solution by first oil bath reaction under vacuum conditions; dissolve lead source in a mixed solution composed of octadecene, oleylamine and oleic acid, and obtain lead-containing solution by second oil bath reaction under vacuum conditions;

[0011] Step S3, synthesis of CsPbBr3 perovskite quantum dots: inject the lead-containing solution obtained in step S2 into the cesium oleate solution obtained in step S2 at a certain temperature, quickly stir the reaction, and then quickly cool to obtain a bright green precipitate; the upper solution collected after centrifuging and washing is the CsPbBr3 perovskite quantum dot solution;

[0012] Step S4, synthesis of COFs / CsPbBr3 perovskite quantum dot-based ladder heterojunction photocatalyst: disperse the TPA-COFs solid powder obtained in step S1 in an organic solvent, then add the CsPbBr3 perovskite quantum dot solution obtained in step S3 dropwise and stir, and dry to obtain the COFs / CsPbBr3 perovskite quantum dot-based ladder heterojunction photocatalyst.

[0013] Further, in step S1, the amine monomer is tri(4-aminophenyl)amine or N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine, and the aldehyde monomer is tri(4-formylphenyl)amine or 4,4',4'',4'''-(1,4-phenylenebis(azatriyl)) tetrakisbenzaldehyde.

[0014] Further, in step S1, the volume ratio of o-dichlorobenzene to anhydrous ethanol is 2:1 to 6:1, and the volume ratio of acetic acid to o-dichlorobenzene is 1:10 to 1:30; the TPA-COFs synthesis temperature is 80 to 160℃, and the time condition is 1 to 5 days.

[0015] Further, in step S2, the cesium source is cesium carbonate or cesium chloride or cesium bromide, the volume ratio of octadecene and oleic acid solution is 5:1-20:1; the lead source is lead bromide or lead chloride, the volume ratio of octadecene, oleylamine and oleic acid solution is 5:1:1-15:1:1; the reaction temperature of the first oil bath and the second oil bath is 90-150 DEG C, and the reaction time is 0.5-3h.

[0016] Further, in step S3, the temperature of the lead-containing solution is 130-180 DEG C, the volume ratio of cesium oleate added to the lead-containing solution is 1:5-1:30, and the rapid stirring time is 2-10s.

[0017] Further, in step S4, the mass ratio of CsPbBr3 perovskite quantum dots to TPA-COFs is (50-200):100, and the stirring time is 1-4h.

[0018] The second object of the present application is to provide a perovskite quantum dot-based gradient heterojunction photocatalyst prepared by the above preparation method.

[0019] Further, the TPA-COFs nanosheet has a size of about 200nm and a thickness of 3-5nm, and the CsPbBr3 perovskite quantum dots have an average particle size of no more than 10nm; the mass ratio of the CsPbBr3 perovskite quantum dots to TPA-COFs is (50-200):100.

[0020] The third object of the present application is to provide an application of the perovskite quantum dot-based gradient heterojunction photocatalyst in catalytic reduction of CO2.

[0021] The fourth object of the present application is to provide a method for catalytic reduction of CO2, in which the perovskite quantum dot-based gradient heterojunction photocatalyst is used to reduce CO2 into CO and CH4 under ultraviolet-visible light.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] (1) The application provides a preparation method of a perovskite quantum dot-based ladder-type heterojunction photocatalyst.

[0024] (2) The perovskite quantum dot-based ladder-type heterojunction photocatalyst provided by the application is used in a COFs / CsPbBr3 perovskite quantum dot-based ladder-type heterojunction photocatalyst system, wherein the COFs is an oxidation-type photocatalyst, and the CsPbBr3 perovskite quantum dot is a reduction-type photocatalyst, which not only makes the photo-generated electrons and holes with weak reduction-oxidation ability recombine, but also makes the photo-generated carriers with strong reduction-oxidation ability be separated efficiently; and the TPA-COFs can effectively enhance the chemical adsorption and activation of acidic CO2 molecules, so that the catalyst exhibits enhanced photocatalytic CO2 reduction activity.

[0025] (3) The method provided by the application is simple in process, convenient to operate, easy to obtain raw materials, does not need complex equipment, and is low in production cost, and is very suitable for large-scale industrial production.

[0026] (4) In the COFs / CsPbBr3 perovskite quantum dot heterojunction material provided by the application, the COFs nanosheet and the CsPbBr3 perovskite quantum dot form a ladder-type heterojunction structure, so that the photo-generated holes with strong oxidation ability on the highest occupied molecular orbital of the COFs and the photo-generated electrons with strong reduction ability on the conduction band of the CsPbBr3 perovskite quantum dot are effectively separated; and the TPA-COFs can effectively enhance the chemical adsorption and activation of acidic CO2 molecules, so that the heterojunction material exhibits excellent photocatalytic CO2 reduction activity and enhanced CH4 selectivity without any molecular catalyst and sacrificial agent, which is of great importance to alleviate the increasingly serious energy shortage and environmental pollution problem, and helps to promote the realization of the 'carbon peak and carbon neutralization' goal. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figures la-lb The field emission scanning electron microscope photos of the TPA-COFs prepared in the application and the transmission electron microscope photos of the CsPbBr3 perovskite quantum dots;

[0028] Figures 2a-2bA transmission electron microscope photo of the COFs / CsPbBr3 perovskite quantum dot-based light catalytic ladder-shaped heterojunction photocatalyst prepared in the application;

[0029] Figure 3 An X-ray diffraction pattern of the material prepared in the application, Example 1 and Comparative Examples 1-3;

[0030] Figure 4 An ultraviolet-visible diffuse emission absorption spectrum of the material prepared in the application, Example 1 and Comparative Examples 1-3;

[0031] Figures 5a-5b A CO2 reduction performance graph of the material prepared in the application, Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0032] In order to make the objects, technical solutions and advantages of the application clearer, the embodiments of the application are described in detail below, and the examples of the embodiments are shown in the drawings, in which the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application.

[0033] Example 1

[0034] The embodiment provides a preparation method of a perovskite quantum dot-based light catalytic ladder-shaped heterojunction photocatalyst.

[0035] The specific steps are as follows:

[0036] Step S1, synthesis of TPA-COFs: dissolve two monomers of tris(4-aminophenyl)amine and tris(4-formylphenyl)amine in a mixed solution composed of o-dichlorobenzene and anhydrous ethanol, the volume ratio of o-dichlorobenzene to anhydrous ethanol is 4:1, then add acetic acid, the volume ratio of acetic acid to o-dichlorobenzene is 1:20; perform liquid nitrogen freezing, vacuum extraction and repeat several times to remove air in the reactor, then react in an oven at 120℃ for 3 days; after washing, centrifugation and drying, brown TPA-COFs solid powder is obtained.

[0037] Step S2, preparation of CsPbBr3 perovskite quantum dot precursor solution: dissolve cesium carbonate in a mixed solution composed of octadecene and oleic acid, the volume ratio of octadecene to oleic acid is 12:1, obtain a transparent cesium oleate solution under vacuum at 120℃ oil bath for 1 hour; at the same time, dissolve lead bromide in a mixed solution composed of octadecene, oleylamine and oleic acid, the volume ratio of octadecene, oleylamine and oleic acid solution is 10:1:1, obtain a lead-containing solution under vacuum at 120℃ oil bath for 0.5 hours.

[0038] Step S3, synthesis of CsPbBr3 perovskite quantum dots: the lead-containing solution obtained in step S2 was further heated to 150-160℃, and then a certain amount of cesium oleate solution obtained in step S2 was quickly injected, the volume ratio of cesium oleate to the lead-containing solution being 1:15, the reaction system was quickly cooled in an ice water bath after stirring for 5 seconds, a bright green precipitate was obtained, and the upper solution was collected after centrifugation and washing, thereby obtaining a CsPbBr3 perovskite quantum dot solution.

[0039] Step S4, synthesis of COFs / CsPbBr3 perovskite quantum dot-based gradient heterojunction photocatalyst: the TPA-COFs solid powder obtained in step S1 was dispersed in n-hexane solution, the CsPbBr3 perovskite quantum dot solution obtained in step S3 was added dropwise and stirred for 2 hours, and a COFs / CsPbBr3 perovskite quantum dot-based gradient heterojunction photocatalyst was obtained by electrostatic self-assembly method, the mass ratio of CsPbBr3 perovskite quantum dots to TPA-COFs being 100:100.

[0040] Example 2

[0041] The embodiment provides a preparation method of a perovskite quantum dot-based gradient heterojunction photocatalyst.

[0042] The embodiment is basically the same as example 1, except that in step S1, N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine and 4,4',4'',4'''-(1,4-phenylenebis(azatriyl)) tetrakisbenzaldehyde are dissolved in a mixed solution composed of o-dichlorobenzene and anhydrous ethanol.

[0043] Example 3

[0044] The embodiment provides a preparation method of a perovskite quantum dot-based gradient heterojunction photocatalyst.

[0045] The embodiment is basically the same as example 1, except that in step S1, the volume ratio of o-dichlorobenzene to anhydrous ethanol is 2:1.

[0046] Example 4

[0047] The embodiment provides a preparation method of a perovskite quantum dot-based gradient heterojunction photocatalyst.

[0048] The embodiment is basically the same as example 1, except that in step S1, the volume ratio of o-dichlorobenzene to anhydrous ethanol is 6:1.

[0049] Example 5

[0050] The embodiment provides a preparation method of a perovskite quantum dot-based gradient heterojunction photocatalyst.

[0051] The procedure was essentially the same as in Example 1, except that in step S1, the volume ratio of acetic acid to o-dichlorobenzene was 1:10.

[0052] Example 6

[0053] The present embodiment provides a preparation method of a perovskite quantum dot-based ladder heterojunction photocatalyst.

[0054] The procedure was essentially the same as in Example 1, except that in step S1, the volume ratio of acetic acid to o-dichlorobenzene was 1:30.

[0055] Example 7

[0056] The present embodiment provides a preparation method of a perovskite quantum dot-based ladder heterojunction photocatalyst.

[0057] The procedure was essentially the same as in Example 1, except that in step S1, the volume ratio of acetic acid to o-dichlorobenzene was 1:30.

[0058] Example 8

[0059] The present embodiment provides a preparation method of a perovskite quantum dot-based ladder heterojunction photocatalyst.

[0060] The procedure was essentially the same as in Example 1, except that in step S1, the volume ratio of acetic acid to o-dichlorobenzene was 1:30.

[0061] Example 9

[0062] The present embodiment provides a preparation method of a perovskite quantum dot-based ladder heterojunction photocatalyst.

[0063] The procedure was essentially the same as in Example 1, except that in step S1, the volume ratio of acetic acid to o-dichlorobenzene was 1:30.

[0064] Example 10

[0065] The present embodiment provides a preparation method of a perovskite quantum dot-based ladder heterojunction photocatalyst.

[0066] The procedure was essentially the same as in Example 1, except that in step S1, the volume ratio of acetic acid to o-dichlorobenzene was 1:30.

[0067] Example 11

[0068] The present embodiment provides a preparation method of a perovskite quantum dot-based ladder heterojunction photocatalyst.

[0069] The procedure was essentially the same as in Example 1, except that in step S2, the cesium source was cesium chloride.

[0070] Example 12

[0071] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0072] The embodiment is basically the same as that of the embodiment 1, except that in step S2, the cesium source is cesium bromide.

[0073] Embodiment 13

[0074] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0075] The embodiment is basically the same as that of the embodiment 1, except that in step S2, the volume ratio of octadecene to oleic acid is 5:1.

[0076] Embodiment 14

[0077] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0078] The embodiment is basically the same as that of the embodiment 1, except that in step S2, the volume ratio of octadecene to oleic acid is 20:1.

[0079] Embodiment 15

[0080] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0081] The embodiment is basically the same as that of the embodiment 1, except that in step S2, the transparent cesium oleate solution is obtained by oil bath at 90 DEG C under vacuum for 1 hour.

[0082] Embodiment 16

[0083] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0084] The embodiment is basically the same as that of the embodiment 1, except that in step S2, the transparent cesium oleate solution is obtained by oil bath at 150 DEG C under vacuum for 1 hour.

[0085] Embodiment 17

[0086] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0087] The embodiment is basically the same as that of the embodiment 5, except that the lead source is lead chloride.

[0088] Embodiment 18

[0089] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0090] The same as example 5, except that: in step S2, the volume ratio of octadecene, oleylamine, and oleic acid solution is 5:1:1.

[0091] Example 19

[0092] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0093] The same as example 5, except that: in step S2, the volume ratio of octadecene, oleylamine, and oleic acid solution is 15:1:1.

[0094] Example 20

[0095] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0096] The same as example 5, except that: in step S2, the volume ratio of octadecene, oleylamine, and oleic acid solution is 15:1:1.

[0097] Example 21

[0098] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0099] The same as example 5, except that: in step S2, the volume ratio of octadecene, oleylamine, and oleic acid solution is 15:1:1.

[0100] Example 22

[0101] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0102] The same as example 5, except that: in step S3, the lead-containing solution obtained in step S2 is further increased to 130 DEG C.

[0103] Example 23

[0104] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0105] The same as example 5, except that: in step S3, the lead-containing solution obtained in step S2 is further increased to 130 DEG C.

[0106] Example 24

[0107] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0108] The same as example 5, except that in step S3, a certain amount of cesium oleate solution obtained in step S2 is quickly injected subsequently, and the volume ratio of cesium oleate to lead-containing solution is 1:5.

[0109] Example 25

[0110] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0111] The same as example 5, except that in step S3, a certain amount of cesium oleate solution obtained in step S2 is quickly injected subsequently, and the volume ratio of cesium oleate to lead-containing solution is 1:30.

[0112] Example 26

[0113] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0114] The same as example 5, except that in step S3, the reaction system is quickly cooled in an ice water bath after being stirred for 10 seconds.

[0115] Example 27

[0116] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0117] The same as example 5, except that in step S4, the CsPbBr3 perovskite quantum dot solution obtained in step S3 is added dropwise and stirred for 4 hours.

[0118] Example 28

[0119] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0120] The same as example 5, except that in step S5, the mass ratio of CsPbBr3 perovskite quantum dots to TPA-COFs is 50:100.

[0121] Example 29

[0122] The embodiment provides a preparation method of a perovskite quantum dot-based ladder-shaped heterojunction photocatalyst.

[0123] The same as example 5, except that in step S5, the mass ratio of CsPbBr3 perovskite quantum dots to TPA-COFs is 200:100.

[0124] Comparative example 1

[0125] The preparation method of the COF nanosheet is as follows:

[0126] Step S1, synthesis of TPA-COFs: dissolve two monomers of tris(4- aminophenyl)amine and tris(4-formylphenyl)amine in a mixed solution consisting of o- dichlorobenzene and anhydrous ethanol, the volume ratio of o-dichlorobenzene to anhydrous ethanol is 4:1, then add acetic acid, the volume ratio of acetic acid to o- dichlorobenzene is 1:20; freeze in liquid nitrogen, vacuumize, and repeat several times to remove air in the reactor, then react in an oven at 120°C for 3 days; after washing, centrifugation and drying, brown TPA-COFs solid powder is obtained.

[0127] Comparative Example 2

[0128] The preparation method of CsPbBr3perovskite quantum dots is as follows:

[0129] Step S1, preparation of CsPbBr3perovskite quantum dot precursor solution: dissolve cesium carbonate in a mixed solution consisting of octadecene and oleic acid, the volume ratio of octadecene to oleic acid is 12:1, obtain transparent cesium oleate solution under vacuum at 120°C oil bath for 1 hour; at the same time, dissolve lead bromide in a mixed solution consisting of octadecene, oleylamine and oleic acid, the volume ratio of octadecene, oleylamine and oleic acid solution is 10:1:1, obtain lead-containing solution under vacuum at 120°C oil bath for 0.5 hours.

[0130] Step S2, synthesis of CsPbBr3perovskite quantum dots: further increase the temperature of the lead-containing solution obtained in step S2 to 150-160°C, then quickly inject a certain amount of cesium oleate solution obtained in step S2, the volume ratio of cesium oleate to lead-containing solution is 1:15, after 5 seconds of rapid stirring, the reaction system is quickly cooled in an ice water bath, a bright green precipitate is obtained, after centrifugation and washing, the upper solution is collected as the CsPbBr3perovskite quantum dot solution.

[0131] Comparative Example 3

[0132] The preparation method of COFs+CsPbBr3perovskite quantum dot physical mixing material is as follows:

[0133] Step S1, synthesis of TPA-COFs: dissolve two monomers of tris(4- aminophenyl)amine and tris(4-formylphenyl)amine in a mixed solution consisting of o- dichlorobenzene and anhydrous ethanol, the volume ratio of o-dichlorobenzene to anhydrous ethanol is 4:1, then add acetic acid, the volume ratio of acetic acid to o- dichlorobenzene is 1:20; freeze in liquid nitrogen, vacuumize, and repeat several times to remove air in the reactor, then react in an oven at 120°C for 3 days; after washing, centrifugation and drying, brown TPA-COFs solid powder is obtained.

[0134] Step S2, preparation of CsPbBr3 perovskite quantum dot precursor solution: dissolve cesium carbonate in a mixed solution composed of octadecene and oleic acid, the volume ratio of octadecene and oleic acid being 12:1, to obtain a transparent cesium oleate solution under vacuum at 120°C for 1 hour; at the same time, dissolve lead bromide in a mixed solution composed of octadecene, oleylamine and oleic acid, the volume ratio of octadecene, oleylamine and oleic acid being 10:1:1, to obtain a lead-containing solution under vacuum at 120°C for 0.5 hours.

[0135] Step S3, synthesis of CsPbBr3 perovskite quantum dots: further increase the temperature of the lead-containing solution obtained in step S2 to 150-160°C, then rapidly inject a certain amount of the cesium oleate solution obtained in step S2, the volume ratio of cesium oleate to the lead-containing solution being 1:15, and after rapid stirring for 5 seconds, place the reaction system in an ice water bath for rapid cooling, to obtain a bright green precipitate, and after centrifugation and washing, collect the upper solution to obtain a CsPbBr3 perovskite quantum dot solution.

[0136] Step S4, synthesis of COFs+CsPbBr3 perovskite quantum dot physical mixture: physically mix the TPA-COFs obtained in step S1 with the quantum dot solution powder obtained in step S3 after drying, to obtain a COFs+CsPbBr3 perovskite quantum dot physical mixture, the mass ratio of CsPbBr3 perovskite quantum dots to TPA-COFs being 100:100.

[0137] In order to better illustrate the performance of the perovskite quantum dot-based ladder-type heterojunction photocatalyst prepared in the present application, the following research was conducted by the present applicant:

[0138] Performance characterization:

[0139] The perovskite quantum dot-based ladder-type heterojunction photocatalyst was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and embodiments 1-29 all had similar micro-morphologies. Taking embodiment 1 as an example, reference is made to Figure la and Figure lb , which are scanning electron micrographs, and from the figures it can be seen that the TPA-COFs present a sheet-like morphology, the nanosheet size being about 200 nm and the thickness being 3-5 nm; the CsPbBr3 perovskite quantum dots present a cubic morphology, the average particle size being less than 10 nm; reference is made to Figure 2a and Figure 2b , which are transmission electron micrographs, and from the figures it can be seen that the CsPbBr3 perovskite quantum dots are anchored on the TPA-COFs nanosheets; from Figure 2a , an energy dispersive X-ray spectrogram (inset) can be observed to confirm the presence of C, N, Cs, Pb and Br elements, confirming the successful synthesis of the COFs / CsPbBr3 perovskite quantum dot-based ladder-type heterojunction photocatalyst.

[0140] ReferenceFigure 3 X-ray diffraction patterns of the materials obtained in Example 1 and Comparative Examples 1-3 were obtained. The diffraction peaks of TPA-COFs corresponded completely to the simulated peaks thereof, and the diffraction peaks of the CsPbBr3perovskite quantum dots corresponded completely to the standard card (PDF #54-0752); in addition to the diffraction peaks of the TPA-COFs, the diffraction peaks of the CsPbBr3perovskite quantum dots appeared in the COFs / CsPbBr3perovskite quantum dot-based ladder-type heterojunction photocatalyst, confirming the successful synthesis of the heterojunction material.

[0141] Reference Figure 4 UV-visible diffuse reflectance absorption spectra of the materials obtained in Example 1 and Comparative Examples 1-3 were obtained. As can be seen from the figure, the absorption band edges of the TPA-COFs and the CsPbBr3perovskite quantum dots were located at about 610 and 550 nm, respectively; after the TPA-COFs were coupled with the CsPbBr3perovskite quantum dots to construct the ladder-type heterojunction photocatalyst, the absorption in the ultraviolet and visible light regions was slightly reduced compared with the pure COFs, confirming the presence of the CsPbBr3perovskite quantum dots in the heterojunction photocatalyst.

[0142] In order to better illustrate the effect of the perovskite quantum dot-based ladder-type heterojunction photocatalyst of the application in the application of catalyzing CO2, the applicant also carried out the following research:

[0143] Photocatalytic activity test: photocatalytic CO2 reduction was carried out in an online gas-closed system equipped with a gas circulation pump, and a 300W xenon lamp was used as the light source. During the experiment, the composite material obtained in Example 1 and Comparative Examples 1-3 was added to the quartz liquid reactor, and 30mL of acetonitrile and a small amount of water were also added. After the reaction system was pumped to a vacuum state, about 60kPa of high-purity CO2 gas (99.999%) was introduced. After adsorption equilibrium, the xenon lamp was turned on to start irradiation. A gas chromatograph (GC-2030, Shimadzu) equipped with a dielectric barrier discharge plasma detector (BID) was used to detect the CO2 reduction products. Standard mixed gas was used to calibrate the retention time value of the gas, so as to determine the types of photocatalytic CO2 reduction products. At the same time, two groups of blank experiments were designed, one group of experiments without the introduction of CO2 gas, and the other group of experiments without the light source, and the results showed that the presence of CO2 and light source were the two most critical factors for photocatalytic CO2 reduction.

[0144] Reference Figures 5a-5b Based on the data shown in Table 1, the photocatalytic CO2 reduction performance comparison chart and data statistics table of the materials prepared in Example 1 and Comparative Examples 1-3 were obtained. As can be seen from the figure, the COFs / CsPbBr3perovskite quantum dot-based ladder-type heterojunction photocatalyst showed the best CO2 reduction activity, in which the generation rate of CO was 41.2μmol g -1, the CH4 generation rate was 13.8 pmol g -1 , the CH4 selectivity reached ~30%, which was much higher than that of pure COFs, pure CsPbBr3 perovskite quantum dots, and COFs physically mixed with CsPbBr3 perovskite quantum dots.

[0145] Table 1.

[0146]

[0147] The above not involved, applicable to the prior art.

[0148] Although some specific embodiments of the present application have been described in detail by way of examples, it should be understood that the above examples are only for illustration and are not intended to limit the scope of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or replace them with similar ways, but without deviating from the direction of the present application or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modification, equivalent replacement, improvement, etc. made to the above embodiments according to the technical essence of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a perovskite quantum dot-based graded heterojunction photocatalyst, characterized in that, Comprise the following specific steps: S1, synthesis of TPA-COFs: dissolve amine monomer and aldehyde monomer in a mixed solution composed of o-dichlorobenzene and anhydrous ethanol, then add appropriate amount of acetic acid, freeze in liquid nitrogen, vacuumize, remove air in the reactor, then react in an oven at a certain temperature for several days; after washing, centrifuging and drying, brown TPA-COFs solid powder is obtained; the amine monomer is tris(4-aminophenyl)amine or N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine, and the aldehyde monomer is tris(4-formylphenyl)amine or 4,4',4'',4'''-(1,4-phenylenebis(azatriyl))tetrakisbenzaldehyde; the volume ratio of o-dichlorobenzene and anhydrous ethanol is 2:1-6:1, and the volume ratio of acetic acid and o-dichlorobenzene is 1:10-1:30; the synthesis temperature of TPA-COFs is 80-160 ℃, and the time condition is 1-5 days; S2, preparation of CsPbBr3 perovskite quantum dot precursor solution: dissolve cesium source in a mixed solution composed of octadecene and oleic acid, and obtain cesium oleate solution by first oil bath reaction under vacuum condition; dissolve lead source in a mixed solution composed of octadecene, oleylamine and oleic acid, and obtain lead-containing solution by second oil bath reaction under vacuum condition; the cesium source is cesium carbonate or cesium chloride or cesium bromide, and the volume ratio of octadecene and oleic acid solution is 5:1-20:1; the lead source is lead bromide or lead chloride, and the volume ratio of octadecene, oleylamine and oleic acid solution is 5:1:1-15:1:1; S3, synthesis of CsPbBr3 perovskite quantum dot solution: quickly inject the lead-containing solution obtained in step S2 into the cesium oleate solution obtained in step S2 at a certain temperature, quickly stir and react, then quickly cool to obtain bright green precipitate, and the upper solution collected after centrifuging and washing is the CsPbBr3 perovskite quantum dot solution; the temperature of the lead-containing solution is 130-180 ℃, and the volume ratio of the added cesium oleate solution to the lead-containing solution is 1:5-1:30; S4, synthesis of COFs / CsPbBr3 perovskite quantum dot-based gradient heterojunction photocatalyst: disperse the TPA-COFs solid powder obtained in step S1 in an organic solvent, then add dropwise the CsPbBr3 perovskite quantum dot solution obtained in step S3 and stir, and dry to obtain the COFs / CsPbBr3 perovskite quantum dot-based gradient heterojunction photocatalyst; the mass ratio of CsPbBr3 perovskite quantum dot to TPA-COFs is (50-200):

100.

2. The production method according to claim 1, characterized by, In step S2, the reaction temperature of the first oil bath and the second oil bath is 90-150 ℃, and the time condition is 0.5-3 h.

3. The production method according to claim 1, characterized by, In step S3, the quick stirring time condition is 2-10 s.

4. The production method according to claim 1, characterized by, In step S4, the stirring time is 1-4 h.

5. A perovskite quantum dot-based gradient heterojunction photocatalyst prepared by the preparation method of any one of claims 1-4.

6. The perovskite quantum dot-based graded heterojunction photocatalyst of claim 5, wherein, TPA-COFs nanosheet and CsPbBr3 perovskite quantum dots anchored on the surface thereof, the TPA-COFs nanosheet has a size of 200 nm and a thickness of 3-5 nm, and the CsPbBr3 perovskite quantum dots have an average particle size of no more than 10 nm; and the mass ratio of the CsPbBr3 perovskite quantum dots to the TPA-COFs is (50-200):

100.

7. Use of the perovskite quantum dot-based gradient heterojunction photocatalyst according to claim 5 or 6 in photocatalytic reduction of CO2.

8. A method of catalytic reduction of CO2, characterized by, Under ultraviolet-visible light, the perovskite quantum dot-based gradient heterojunction photocatalyst according to claim 5 or 6 is used to reduce CO2 into CO and CH4.

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