Covalent triazine quantum dot synthesized based on water-microwave synergistic regulation and control as well as synthesis method and application of covalent triazine quantum dot

Abstract

The invention discloses covalent triazine quantum dots synthesized based on water-microwave synergistic regulation and control and a synthesis method and application of the covalent triazine quantum dots, and belongs to the field of preparation of organic semiconductor nanomaterials. According to the method, amidino monomers and aldehyde monomers are used as precursors, alkali is used as a catalyst, reversible balance of amidino-aldehyde condensation polymerization is dynamically regulated and controlled through water molecules in a water-containing N, N-dimethylformamide solvent system under the microwave-assisted condition, and the covalent triazine framework quantum dots are synthesized. According to the preparation method, the synthesis period is shortened to be within 1 hour through a water-microwave synergistic regulation mechanism, the monodisperse covalent triazine framework quantum dots can be obtained without complex post-treatment, and the obtained CTF-QDs have narrow particle size distribution (2-9 nm), high fluorescence performance and excellent thermal stability and have important industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of organic semiconductor nanomaterial synthesis, and specifically relates to a covalent triazine quantum dot synthesized based on water-microwave synergistic regulation, a synthesis method and an application thereof. Background Art

[0002] In the field of materials science, covalent triazine frameworks (CTFs), a novel material with unique structures and properties, have garnered significant attention in recent years. These porous materials, composed of triazine units, exhibit significant advantages, including high chemical stability, high nitrogen content, and excellent thermal stability. They demonstrate significant potential for applications in a wide range of fields, including gas adsorption and separation, heterogeneous catalysis, and optoelectronics.

[0003] Since 2008, significant progress has been made in the synthesis of covalent triazine frameworks (CTFs) through various methods, such as zinc chloride ion thermal synthesis, trifluoromethanesulfonic acid superacid catalytic synthesis, phosphorus-based catalytic method and low-temperature aldehyde amidine condensation method. Each method provides unique advantages for tailoring the structure and properties of CTFs. However, most existing methods focus on the synthesis of bulk materials rather than quantum dots (QDs). Preparing CTFs in the form of small-sized quantum dots (CTF-QDs) can enhance light absorption, promote charge separation and transport, improve dispersibility and stability, achieve tunable optical and electronic properties, and increase surface active sites, thereby significantly improving their performance and application potential in the fields of photocatalysis and photoelectric conversion. To date, nanoscale CTFs have been synthesized mainly by top-down post-processing techniques to peel off crystalline bulk materials into few-layer functionalized nanosheets. Specifically, there has been a sulfuric acid peeling method ( Chem. Commun. 2019, 55, 1434-1437) and small molecule intercalation and exfoliation ( Cryst. Growth Des. 2023, twenty three , 3349-3356). However, the resulting nanoCTFs typically exist as two-dimensional films that are prone to aggregation and are large in size with poor dispersion, making them unsuitable as functional reagents. Therefore, there is an urgent need to find a simple method for directly synthesizing covalent triazine framework quantum dots. Summary of the Invention

[0004] The present invention provides a covalent triazine quantum dot synthesized based on water-microwave synergistic regulation, a synthesis method and application thereof, and realizes the synthesis of monodisperse covalent triazine framework quantum dots (CTF-QDs). The obtained CTF-QDs have a narrow particle size distribution, strong fluorescence properties and excellent thermal stability.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for synthesizing covalent triazine framework quantum dots (CTF-QDs) based on water-microwave synergistic regulation is provided, comprising the following steps: Using amidine monomers and aldehyde monomers as precursors and base as catalyst, CTF-QDs were synthesized in a water-containing N, N-dimethylformamide (DMF) solvent system under microwave-assisted conditions, by dynamically regulating the reversible equilibrium of the amidine-aldehyde condensation reaction through water molecules.

[0006] According to the above scheme, the aldehyde monomer is at least one of terephthalaldehyde, 2,5-thiophenedicarboxaldehyde, pyridine-2,6-dicarboxaldehyde, and isophthalaldehyde.

[0007] According to the above scheme, the amidine monomer is at least one of terephthalamidine, isophthalamidine, and biphenyldicarboxamidine.

[0008] According to the above scheme, the molar ratio of the aldehyde monomer to the amidine monomer is 1:1.5-2.5.

[0009] According to the above scheme, the molar volume ratio of the amidine monomer and water is 1 mmol:1~5 mL.

[0010] According to the above scheme, the volume ratio of water to N, N-dimethylformamide (DMF) is 1:2~10.

[0011] According to the above scheme, the molar ratio of the amidine monomer to the base catalyst is 1:1~1.5.

[0012] According to the above scheme, the base catalyst is potassium tert-butoxide.

[0013] According to the above scheme, the microwave reaction power is 300~900 W and the reaction time is 5~60 min.

[0014] According to the above scheme, the specific steps of the synthesis method are: 1) dissolving an amidine monomer in water to obtain a homogeneous amidine precursor solution; 2) sequentially adding an aldehyde monomer, a base catalyst, and an N, N-dimethylformamide solvent to the homogeneous amidine precursor solution obtained in step 1), followed by microwave reaction and post-treatment to obtain covalent triazine framework quantum dots.

[0015] According to the above scheme, in step 1), the amidine monomer is dissolved in water at a dissolution temperature of 45-55°C.

[0016] According to the above scheme, in step 2), the post-treatment is as follows: cooling to room temperature after the reaction is terminated, centrifuging, and freeze-drying to obtain a light yellow powder, which is the covalent triazine framework quantum dots.

[0017] Provided are covalent triazine framework quantum dots (CTF-QDs) synthesized by the above method, which have a particle size distribution of 2-9 nm.

[0018] Provided is an application of the covalent triazine framework quantum dots as a functional additive for perovskite solar cells.

[0019] According to the above solution, the perovskite solar cell is a CsPbBr3 perovskite solar cell.

[0020] Preferably, the application is specifically as follows: the covalent triazine framework quantum dots are added as additives to a PbBr2 solution, and a PbBr2 layer containing the covalent triazine framework quantum dots is prepared by spin coating.

[0021] More preferably, the concentration of the covalent triazine framework quantum dots in the PbBr2 solution is 1.8-2.2 mg / L.

[0022] More preferably, the concentration of the PbBr2 solution is 0.9~1.1 mol / L.

[0023] More preferably, the solvent in the PbBr2 solution is DMF.

[0024] The method of the present invention uses amidine monomers and aldehyde monomers as precursors. Under base catalysis, the reversible equilibrium of the amidine-aldehyde condensation reaction is dynamically regulated by water molecules. Combined with the microwave energy field to directionally enhance the polymerization path, the kinetically controllable synthesis of CTF-QDs is achieved in an N, N-dimethylformamide (DMF) solvent system.

[0025] The beneficial effects of the present invention are as follows: 1. The present invention provides a method for synthesizing covalent triazine framework quantum dots. Using amidine and aldehyde monomers as precursors, the method introduces water molecules to regulate the reaction pathway in an N,N-dimethylformamide (DMF) solvent system under base catalysis, accelerating nucleation kinetics. This promotes rapid crystal nucleation, inhibits Ostwald ripening, and promotes the formation of quantum dots with smaller particle sizes. Furthermore, the method combines microwave energy field-directed enhancement of the reaction pathway, successfully overcoming the bottleneck of the difficulty in coordinating the polycondensation rate and selectivity in traditional quantum dot synthesis, and achieving the preparation of monodisperse CTF-QDs. Due to their good dispersibility and abundant surface active sites, the prepared CTF-QDs can significantly improve the photoelectric conversion efficiency of perovskite solar cells by up to 27% when used as a functional additive.

[0026] 2. The present invention uses a water-microwave synergistic regulation mechanism to control the CTF-QDs synthesis cycle to less than 1 hour. The synthesis time is short and the efficiency is high. Monodisperse quantum dots CTF-QDs can be obtained without complex post-processing, which has important industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FT-IR spectrum (a) and CP / MAS 13C solid-state NMR spectrum (b) of the covalent triazine framework quantum dots prepared in Example 1-4.

[0028] Figure 2 TEM images (inset: fluorescence photograph) (a is Example 1, c is Example 2, e is Example 3, g is Example 4) and HR-TEM images (inset: lattice fringe images) (b is Example 1, d is Example 2, f is Example 3, h is Example 4) of the covalent triazine framework quantum dots prepared in Examples 1-4.

[0029] Figure 3 Fluorescence images of the covalent triazine framework quantum dots prepared in Examples 1-4 (a) (CTF-QD-1~4 from left to right) and PL images of different quantum dots (b).

[0030] Figure 4 Thermogravimetric analysis (a) and XRD patterns (b) of the covalent triazine framework quantum dots prepared in Example 1-4.

[0031] Figure 5 JV curves and cell parameter diagrams of CsPbBr3 perovskite solar cells doped with covalent triazine framework quantum dots prepared in Examples 1, 2, and 4 after solar simulator testing. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to specific implementation examples.

[0033] Example 1 A method for synthesizing covalent triazine framework quantum dots (CTF-QD-1) based on water-mediated dynamic equilibrium regulation and microwave-assisted synergy is provided, comprising the following steps: 1.0 mmol of terephthalamidine was dissolved in 3 mL of deionized water and stirred at 50°C until completely dissolved, forming a homogeneous amidine precursor solution. The amidine precursor solution, 0.5 mmol of terephthalaldehyde, and 1.1 mmol of potassium tert-butoxide catalyst were added sequentially to a 50 mL round-bottom flask. 10 mL of DMF was then added and stirred. The mixture was reacted in a 400 W microwave reactor for 55 min, where the condensation / hydrolysis equilibrium was dynamically controlled by water molecules to obtain a colloidal solution of CTF-QD-1. After the reaction was terminated, the mixture was cooled to room temperature, centrifuged (10,000 rpm for 3 min), and freeze-dried to obtain a pale yellow powder (yield 27.6%), which is the covalent triazine framework quantum dot, designated CTF-QD-1.

[0034] FT-IR and ¹³C NMR confirmed the triazine ring (C=N 1515 cm -1 , 170 ppm) and residual aldehyde groups (C=O 1673 cm -1 , 195.6 ppm) coexist ( Figure 1 ). FE-TEM ( Figure 2 ab) show monodispersed spherical quantum dots (average particle size 2.6 nm), with lattice fringes (crystallinity) visible through HR-TEM. Fluorescence images (a) and PL images (b) of the colloidal solution obtained by dispersing covalent triazine framework quantum dots in ethanol are shown in Figure 1. Figure 3 shown. Figure 3 It can be seen that the CTF-QD-1 quantum dot colloidal solution exhibits green fluorescence characteristics. CTF-QD-1 quantum dots have long-range disorder ( Figure 4 b) It has excellent thermal stability and does not decompose at 300°C in a nitrogen environment ( Figure 4 a).

[0035] CTF-QD-1 modified CsPbBr3 perovskite solar cell performance: The FTO (fluorine-doped tin oxide) substrate was cleaned sequentially with detergent, acetone, isopropanol, ethanol, and deionized water, followed by UV-ozone treatment for 30 minutes to ensure surface decontamination. Next, a SnO2 quantum dot electron transport layer (ETL) was uniformly spin-coated (2000 rpm, 30 seconds) on the FTO substrate and thermally cured at 200°C for 1 hour under ambient conditions. The CTF-QD-1 prepared in Example 1 was added to a PbBr2 solution in DMF to a CTF-QD-1 concentration of 2 mg / L. A 1M PbBr2 solution in DMF, preheated to 80°C, was then spin-coated at 2000 rpm for 30 seconds on the FTO / ETL substrate and annealed at 90°C for 30 minutes. Next, a 0.07M CsBr methanol solution was spin-coated on the PbBr2 layer at 2000 rpm for 30 seconds and then sintered at 250°C for 5 minutes. This sequential coating and annealing cycle was repeated 9 times to obtain the desired perovskite film. Finally, a carbon electrode was prepared on the FTO / ETL / CsPbBr3 stack by doctor blade coating to complete the device preparation. Then, the photoelectric conversion efficiency was tested by a solar simulator to be 9.27%, which was 9.3% higher than the blank (without CTF-QD-1) of 8.41%. Figure 5 ).

[0036] Example 2 A method for synthesizing covalent triazine framework quantum dots (CTF-QD-2) based on water-mediated dynamic equilibrium regulation and microwave-assisted synergy is provided, comprising the following steps: 1.0 mmol of m-phthalamidine was dissolved in 1 mL of deionized water and stirred at 50°C until completely dissolved, forming a homogeneous amidine precursor solution. The amidine precursor solution, 0.67 mmol of 2,5-thiophenedicarbaldehyde, and 1.3 mmol of potassium tert-butoxide catalyst were added to a 50 mL round-bottom flask. 10 mL of dimethylformamide (DMF) was then added and stirred. The mixture was reacted in a 900 W microwave reactor for 5 min, where the condensation / hydrolysis equilibrium was dynamically controlled by water molecules to obtain a colloidal solution of CTF-QD-2. After the reaction was terminated, the mixture was cooled to room temperature, centrifuged (10,000 rpm for 3 min), and freeze-dried to obtain a pale yellow powder (yield 28.3%), which is the covalent triazine framework quantum dot, designated CTF-QD-2.

[0037] FT-IR and ¹³C NMR confirmed the triazine ring (C=N 1516 cm -1 , 170 ppm) and residual aldehyde groups (C=O 1673 cm -1 , 195.6 ppm) coexist ( Figure 1 ). FE-TEM ( Figure 2 cd) show monodispersed spherical quantum dots (average particle size 2.0 nm), with lattice fringes (crystallinity) visible through HR-TEM. Fluorescence images (a) and PL images (b) of the colloidal solution obtained by dispersing covalent triazine framework quantum dots in ethanol are shown in Figure 1. Figure 3 shown. Figure 3 It can be seen that the CTF-QD-2 quantum dot colloidal solution exhibits yellow fluorescence characteristics. CTF-QD-2 quantum dots have long-range disorder ( Figure 4 b) It has excellent thermal stability and does not decompose at 300°C in a nitrogen environment ( Figure 4 a).

[0038] CTF-QD-2 modified CsPbBr3 perovskite solar cells: The FTO (fluorine-doped tin oxide) substrate was cleaned sequentially with detergent, acetone, isopropanol, ethanol, and deionized water, followed by UV-ozone treatment for 30 minutes to ensure surface decontamination. Next, a SnO2 quantum dot electron transport layer (ETL) was uniformly spin-coated (2000 rpm, 30 seconds) on the FTO substrate and thermally cured at 200°C for 1 hour under ambient conditions. CTF-QD-2 was added to a PbBr2 solution in DMF to a CTF-QD-2 concentration of 2 mg / L. A 1 M PbBr2 solution in DMF, preheated to 80°C, was then spin-coated at 2000 rpm for 30 seconds on the FTO / ETL substrate and annealed at 90°C for 30 minutes. Next, a 0.07M CsBr solution in methanol was spin-coated on the PbBr2 layer at 2000 rpm for 30 seconds, followed by sintering at 250°C for 5 minutes. This sequential coating and annealing cycle was repeated nine times to obtain the desired perovskite film. Finally, a carbon electrode was prepared on the FTO / ETL / CsPbBr3 stack by doctor blade coating to complete the device fabrication. The device was then tested using a solar simulator, demonstrating a photoelectric conversion efficiency of 10.67%, a 27% increase compared to the blank's 8.41%. Figure 5 ).

[0039] Example 3 A method for synthesizing covalent triazine framework quantum dots (CTF-QD-3) based on water-mediated dynamic equilibrium regulation and microwave-assisted synergy is provided, comprising the following steps: 1.0 mmol of terephthalamidine was dissolved in 5 mL of deionized water and stirred at 50°C until completely dissolved, forming a homogeneous amidine precursor solution. The amidine precursor solution, 0.4 mmol of pyridine-2,6-dicarboxaldehyde, and 1.5 mmol of potassium tert-butoxide catalyst were added sequentially to a 50 mL round-bottom flask. 10 mL of DMF was then added and stirred. The mixture was reacted in a 300 W microwave reactor for 60 min, where the condensation / hydrolysis equilibrium was dynamically controlled by water molecules to obtain a CTF-QD-3 colloidal solution. After the reaction was terminated, the mixture was cooled to room temperature, centrifuged (10,000 rpm for 3 min), and freeze-dried to obtain a pale yellow powder (yield 27.3%), which is the covalent triazine framework quantum dot, designated CTF-QD-3.

[0040] FT-IR and ¹³C NMR confirmed the triazine ring (C=N 1516 cm -1 , 170 ppm) and residual aldehyde groups (C=O 1673 cm -1 , 195.6 ppm) coexist ( Figure 1 ). FE-TEM ( Figure 2Figures ef) show monodispersed spherical quantum dots (average particle size 9.0 nm) with visible lattice fringes (crystallinity) by HR-TEM. Fluorescence images (a) and PL images (b) of the colloidal solution obtained by dispersing covalent triazine framework quantum dots in ethanol are shown in Figure ef. Figure 3 shown. Figure 3 It can be seen that the CTF-QD-3 colloidal solution exhibits green fluorescence characteristics. CTF-QD-3 quantum dots have long-range disorder ( Figure 4 b) It has excellent thermal stability and does not decompose at 300°C in a nitrogen environment ( Figure 4 a).

[0041] Example 4 A method for synthesizing covalent triazine framework quantum dots (CTF-QD-4) based on water-mediated dynamic equilibrium regulation and microwave-assisted synergy is provided, comprising the following steps: 1.0 mmol of biphenyldicarboxamidine was dissolved in 5 mL of deionized water and stirred at 50°C until completely dissolved, forming a homogeneous amidine precursor solution. The amidine precursor solution, 0.5 mmol of m-phthalaldehyde, and 1.4 mmol of potassium tert-butoxide catalyst were added sequentially to a 50 mL round-bottom flask. 10 mL of DMF was then added and stirred. The mixture was reacted in a 500 W microwave reactor for 35 min, where the condensation / hydrolysis equilibrium was dynamically controlled by water molecules to obtain a colloidal solution of CTF-QD-4. After the reaction was terminated, the mixture was cooled to room temperature, centrifuged (10,000 rpm for 3 min), and freeze-dried to obtain a pale yellow powder (yield 28.8%), which is the covalent triazine framework quantum dot, designated CTF-QD-4.

[0042] FT-IR and ¹³C NMR confirmed the triazine ring (C=N 1516 cm -1 , 170 ppm) and residual aldehyde groups (C=O 1673 cm -1 , 195.6 ppm) coexist ( Figure 1 ). FE-TEM ( Figure 2 gh) shows monodispersed spherical quantum dots (average particle size 5.4 nm), with lattice fringes (crystallinity) visible by HR-TEM. Fluorescence image (a) and PL image (b) of the colloidal solution obtained by dispersing covalent triazine framework quantum dots in ethanol are shown in Figure 3 shown. Figure 3 It can be seen that the CTF-QD-3 colloidal solution exhibits green fluorescence characteristics. The CTF-QD-4 quantum dots have long-range disorder ( Figure 4 b) It has excellent thermal stability and does not decompose at 300°C in a nitrogen environment ( Figure 4 a).

[0043] CTF-QD-4 modified CsPbBr3 perovskite solar cells: The FTO (fluorine-doped tin oxide) substrate was cleaned sequentially with detergent, acetone, isopropanol, ethanol, and deionized water, followed by UV-ozone treatment for 30 minutes to ensure surface decontamination. Next, a SnO2 quantum dot electron transport layer (ETL) was uniformly spin-coated (2000 rpm, 30 seconds) on the FTO substrate and thermally cured at 200°C for 1 hour under ambient conditions. CTF-QD-4 was added to a PbBr2 solution in DMF to a CTF-QD-4 concentration of 2 mg / L. A 1 M PbBr2 solution in DMF, preheated to 80°C, was then spin-coated at 2000 rpm for 30 seconds on the FTO / ETL substrate and annealed at 90°C for 30 minutes. Next, a 0.07 M CsBr solution in methanol was spin-coated on the PbBr2 layer at 2000 rpm for 30 seconds, followed by sintering at 250°C for 5 minutes. This sequential coating and annealing cycle was repeated nine times to obtain the desired perovskite film. Finally, a carbon electrode was prepared on the FTO / ETL / CsPbBr3 stack by doctor blade coating to complete the device fabrication. The device was then tested using a solar simulator, demonstrating a photoelectric conversion efficiency of 9.87%, a 17.4% increase compared to the blank's 8.41%. Figure 5 ).

[0044] Characterization of the samples from Examples 1-4 above demonstrated that the synthesized materials were all monodisperse quantum dots. Characterization revealed that the quantum dots were successfully prepared, exhibiting a fragmented structure with triazine rings connected to aldehyde groups, and possessed a small particle size. When used as functional additives in perovskite solar cells, they can significantly improve the cell's photoelectric conversion efficiency.

[0045] The foregoing is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for synthesizing covalent triazine framework quantum dots based on water-microwave synergistic regulation, characterized in that: The following steps are involved: Using amidine monomers and aldehyde monomers as precursors and base as catalyst, in a water-containing N, N-dimethylformamide solvent system and under microwave-assisted conditions, the reversible equilibrium of the amidine-aldehyde condensation reaction was dynamically regulated by water molecules to synthesize covalent triazine framework quantum dots.

2. The method according to claim 1, characterized in that The aldehyde monomer is at least one of terephthalaldehyde, 2,5-thiophene dicarboxaldehyde, pyridine-2,6-dicarboxaldehyde, and isophthalaldehyde; the amidine monomer is at least one of terephthalamidine, isophthalamidine, and biphenyl dicarboxamidine.

3. The method according to claim 1, characterized in that The molar ratio of the aldehyde monomer to the amidine monomer is 1:1.5-2.

5.

4. The method according to claim 1, wherein The molar volume ratio of the amidine monomer to water is 1 mmol: 1-5 mL; the volume ratio of water to N, N-dimethylformamide is 1: 2-10.

5. The method according to claim 1, wherein The molar ratio of the amidine monomer to the base catalyst is 1:1 to 1.

5.

6. The method according to claim 1, characterized in that The base catalyst is potassium tert-butoxide.

7. The method according to claim 1, characterized in that The microwave reaction power was 300-900 W, and the reaction time was 5-60 min.

8. The method according to claim 1, characterized in that The specific steps of the synthesis method are: 1) dissolving terephthalamidine in water to obtain a homogeneous amidine precursor solution; 2) terephthalaldehyde, a base catalyst, and N, N-dimethylformamide solvent are sequentially added to the homogeneous amidine precursor solution obtained in step 1), followed by microwave reaction and post-treatment to obtain covalent triazine framework quantum dots.

9. A covalent triazine framework quantum dot synthesized by the method according to any one of claims 1 to 8, characterized in that: The particle size distribution of the covalent triazine framework quantum dots is 2-9 nm.

10. Use of the covalent triazine framework quantum dots according to claim 9 as a functional additive for perovskite solar cells.

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