Carbon nanodots with h-aggregation property and preparation method and application thereof

Abstract

This invention discloses a carbon nanodot with H-aggregation properties, its preparation method, and its applications. Citric acid, p-phenylenediamine, and sodium hydroxide are dissolved in deionized water and stirred until fully dissolved to obtain a mixed solution A. Mixed solution A is then placed in a reaction vessel for a hydrothermal reaction to obtain product B. Finally, product B is naturally cooled and dialyzed to obtain carbon nanodots with H-aggregation properties. The carbon nanodots prepared by this invention are non-toxic, harmless, and can be stored for a long time. The fluorescence intensity and carrier lifetime can be controlled by concentration, making them suitable for photocatalysis.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic hydrogen production materials, and particularly relates to carbon nanodots with H aggregation properties and a preparation method and application thereof. BACKGROUND

[0002] H aggregation refers to a molecular packing or aggregation phenomenon, which is usually the pi-pi stacking interaction of organic conjugated molecules, resulting in molecular orbital overlap, thereby affecting the energy band structure and electronic properties. Generally speaking, H aggregation can cause changes in the absorption spectrum, usually showing a significant blue shift of the absorption peak. At the same time, the fluorescence spectrum of H aggregation molecules is red-shifted, the light-emitting ability is weakened, and the electron lifetime is increased, which means that the ability of the molecules to absorb and release photons changes in the H aggregation state. The weakening of the light-emitting ability means that the non-radiative transition ability is enhanced, and the carrier lifetime is increased, which is suitable for the field of photocatalysis, so H aggregation molecules have great potential for application in photocatalysis. At present, most H aggregation materials are mainly organic conjugated small molecules, but these materials are generally not soluble in water, and inevitably have the shortcomings of complex preparation procedures, toxicity, poor reliability, etc. In addition, these shortcomings greatly hinder the development prospects of H aggregation materials. There are few reports on the use of H aggregation materials in photocatalytic hydrogen production, so it is necessary to develop a new type of photocatalytic material that can form H aggregation.

[0003] Carbon nanodots (CDs) are zero-dimensional nanomaterials with a particle size of less than 10 nm, which have attracted great interest from researchers due to their excellent properties such as easy preparation, low cost, low toxicity, and high optical stability. They are composed of elements such as C, H, and O, and the core is generally composed of sp2 and sp3 hybridized carbon, forming a multi-layer graphite microcrystalline structure. To design CDs that can undergo H aggregation, appropriate precursors need to be selected to ensure that the carbon nanodots can undergo H aggregation. H aggregation usually involves pi-pi stacking interactions between molecules or within molecules, so selecting a precursor with a suitable conjugated structure is key. The precursor should contain conjugated structures such as aromatic rings, conjugated double bonds, or molecules containing pi-electron systems. These structures help promote pi-pi stacking interactions between molecules, thereby facilitating H aggregation. On the other hand, because CDs are photocatalysts, they should be hydrophilic and can introduce functional groups such as amino, carboxyl, and hydroxyl groups. The introduction of functional groups may help enhance the affinity of the precursor and facilitate the formation of H aggregation, promoting pi-pi stacking between molecules. CDs can be prepared by methods such as thermal decomposition, hydrothermal method, and microwave-assisted synthesis, but the specific method parameters and conditions need to be adjusted according to the properties of the precursor. To date, few works have reported CDs that can form H aggregation. SUMMARY

[0004] The technical problems to be solved by the present application are to provide carbon nanodots with H aggregation properties, a preparation method and application thereof, and to solve the technical problems of short carrier lifetime of nano-photocatalysts and complex solutions.

[0005] The present application adopts the following technical solutions:

[0006] The preparation method of the carbon nanodots with H aggregation properties comprises the following steps: dissolving citrazinic acid, p-phenylenediamine and sodium hydroxide in deionized water, stirring to obtain a uniform transparent mixed solution A; subjecting the mixed solution A to hydrothermal reaction at 180-200 DEG C to obtain product B; and cooling the product B, and subjecting it to dialysis to obtain carbon nanodots capable of forming H aggregation.

[0007] Preferably, the mass ratio of citrazinic acid, p-phenylenediamine and sodium hydroxide is (0.15-1.50 g):(0.12-0.32 g):(0.12-0.48 g).

[0008] Preferably, the stirring time is 10-20 min.

[0009] More preferably, a magnetic stirrer is used for stirring.

[0010] More preferably, the stirring temperature is room temperature.

[0011] Preferably, the hydrothermal reaction time is 1-10 hours.

[0012] Preferably, the dialysis time is 12-24 hours.

[0013] Another technical solution of the present application is the carbon nanodots with H aggregation properties, which are prepared according to the preparation method of the carbon nanodots with H aggregation properties.

[0014] Preferably, the diameter of the carbon nanodots is 4.1-10.5 nm, the lattice fringe spacing of the carbon nanodots is 0.21 nm, the excitation wavelength is 310-340 nm, and the emission wavelength is 410-430 nm.

[0015] Another technical solution of the present application is that the carbon nanodots with H aggregation properties are applied to photocatalytic hydrogen production.

[0016] Compared with the prior art, the present application has at least the following beneficial effects:

[0017] The application discloses a preparation method of carbon nanodots with H aggregation properties.

[0018] Further, the mass ratio of citrazinic acid and p-phenylenediamine is set to better control the reaction product, and sodium hydroxide is used to dissolve citrazinic acid, too much sodium hydroxide can oxidize the reactants, and too little sodium hydroxide can not dissolve the sample.

[0019] Further, the stirring time is set to better dissolve citrazinic acid and make the reaction raw materials uniform.

[0020] Further, sodium hydroxide can release a large amount of heat, and stirring at room temperature can protect the sample from oxidation.

[0021] Further, the water hydrolysis reaction time is set to ensure complete reaction.

[0022] Further, the dialysis time is set to remove the reaction raw materials, impurities and the like, so that the sample is more pure.

[0023] The carbon nanodots with H aggregation properties can be aggregated at high concentrations, have stable structures, and can be stored for a long time.

[0024] The carbon nanodots prepared by the application can be used in the field of photocatalytic hydrogen production and have wide application prospects.

[0025] In summary, the application can simply adjust the concentration to inhibit the radiation luminescence of the carbon nanodots, prolong the carrier lifetime, and improve the photocatalytic performance.

[0026] The technical solutions of the application will be further described in detail below with reference to the drawings and examples. DESCRIPTION OF DRAWINGS

[0027] Figure 1 The transmission electron microscope image of the carbon nanodots with H aggregation properties prepared in the application example 1 is shown in the figure;

[0028] Figure 2 The excitation spectrum of the carbon nanodots with H aggregation properties prepared in the application example 1 is shown in the figure;

[0029] Figure 3 The fluorescence emission spectrum of the carbon nanodots with H aggregation properties prepared in the application example 1 under multi-excitation wavelength excitation is shown in the figure;

[0030] Figure 4 The absorption spectrum of the carbon nanodots with H aggregation properties prepared in the application example 1 with concentration change (normalized) is shown in the figure;

[0031] Figure 5 The fluorescence spectrum of the carbon nanodots capable of forming H aggregation prepared in Example 1 of the present application varies with concentration, wherein (a) is the fluorescence spectrum without normalization processing, and (b) is the fluorescence spectrum without normalization processing;

[0032] Figure 6 The fluorescence lifetime spectrum of the carbon nanodots capable of forming H aggregation prepared in Example 1 of the present application varies with concentration.

[0033] Figure 7 The photocatalytic performance spectrum of the carbon nanodots capable of forming H aggregation prepared in Example 1 of the present application varies with concentration. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0035] In the present application, all the embodiments and preferred embodiments mentioned in the present application can be combined to form new technical solutions, if not otherwise specified.

[0036] In the present application, all the technical features and preferred features mentioned in the present application can be combined to form new technical solutions, if not otherwise specified.

[0037] In the present application, percentage (%) or part refers to the weight percentage or weight part of the composition, if not otherwise specified.

[0038] In the present application, all the components or preferred components involved can be combined to form new technical solutions, if not otherwise specified.

[0039] In the present application, unless otherwise specified, the numerical range "a~b" represents a shorthand notation for any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "6~22" represents that all the real numbers between "6~22" have been listed herein, and "6~22" is only a shorthand notation for these numerical combinations.

[0040] The lower limit and upper limit of the range disclosed in the present application can be one or more lower limits and one or more upper limits, respectively.

[0041] In the present application, the term "and / or" used herein means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0042] In the present application, unless otherwise specified, each reaction or operation step can be carried out sequentially or in sequence.

[0043] Unless otherwise specified, the professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to that described can also be applied in the present application.

[0044] The present application provides a kind of carbon nanodots with H aggregation properties and its preparation method and application, citrazinic acid, p-phenylenediamine and sodium hydroxide are dissolved in deionized water, after stirring and fully dissolving, product B is obtained by placing in reaction kettle and carrying out hydrothermal reaction;Finally, product B is naturally cooled and dialyzed, to obtain carbon nanodots with H aggregation properties.The carbon nanodots prepared by the present application are non-toxic and harmless, can be stored for a long time, can control the fluorescence intensity and carrier lifetime by concentration, and can be used in the field of photocatalysis.

[0045] The present application provides a kind of carbon nanodots with H aggregation properties and its preparation method and application, citrazinic acid, p-phenylenediamine and sodium hydroxide are dissolved in deionized water, after stirring and fully dissolving, product B is obtained by placing in reaction kettle and carrying out hydrothermal reaction;Finally, product B is naturally cooled and dialyzed, to obtain carbon nanodots with H aggregation properties.The carbon nanodots prepared by the present application are non-toxic and harmless, can be stored for a long time, can control the fluorescence intensity and carrier lifetime by concentration, and can be used in the field of photocatalysis.

[0046] S1, citrazinic acid, p-phenylenediamine and sodium hydroxide are dissolved in deionized water according to the mass ratio of (0.15-1.50g):(0.12-0.32g):(0.12-0.48g), and stirred at room temperature to fully dissolve, to obtain a uniform transparent mixed solution A;

[0047] Stirring is carried out at room temperature by using a magnetic stirrer, and the stirring time is 10-20 min.

[0048] S2, the mixed solution A is placed in a reaction kettle, and hydrothermal reaction is carried out at 180-200 DEG C for 1-10 hours to obtain product B;

[0049] S3, product B is cooled and dialyzed for 24 hours, to obtain carbon nanodots capable of forming H aggregation.

[0050] A kind of carbon nanodots with H aggregation properties is prepared by the above method, and the yield of carbon nanodots is 5%-20%. The prepared carbon nanodots can aggregate at high concentration (>0.01 mg / mL), have stable structure, and can be stored for a long time.

[0051] The carbon nanodots with H aggregation properties prepared by the present application can be used in the field of photocatalytic hydrogen production.

[0052] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0053] Embodiment 1

[0054] S1, 0.15 g of citrazinic acid, 0.12 g of p-phenylenediamine and 0.12 g of sodium hydroxide were dissolved in deionized water, and a magnetic stirrer was used to stir at room temperature for 10 min to make them fully dissolved, to obtain a mixed solution A;

[0055] S2, the mixed solution A was placed in a reaction kettle to perform a hydrothermal reaction at 180 DEG C for 5 h to obtain a product B;

[0056] S3, the product B was naturally cooled and dialyzed in water for 24 h to obtain carbon nanodots with H aggregation property.

[0057] From Figure 1 It can be seen that the carbon nanodots prepared in the present application have a diameter of 7.5 nm, and the lattice stripe spacing of the carbon nanodots is 0.21 nm, corresponding to the

[100] crystal face of graphite, indicating that the product is a carbon-based material.

[0058] From Figure 2 It can be seen that the optimal excitation wavelength of the carbon nanodots prepared in the present application is 340 nm, and the optimal emission peak position of the sample can be obtained at the optimal excitation wavelength, which is 410 nm.

[0059] From Figure 3 It can be seen that the fluorescence emission peak of the carbon nanodots prepared in the present application has excitation wavelength dependence, and the optimal emission wavelength of the carbon nanodots is 340 nm.

[0060] From Figure 4 It can be seen that with the increase of the concentration of the carbon nanodots, the absorption spectrum of the carbon nanodots is blue-shifted, proving that the carbon nanodots prepared in the present application can form H aggregation.

[0061] From Figure 5(a) It can be seen that the fluorescence intensity of the carbon nanodots prepared in this invention gradually weakens with increasing concentration and exhibits a red shift. (b) The figure shows that its fluorescence peak position has red-shifted from 411 nm to 508 nm. Combined with... Figure 4 The results further prove that the carbon point formed H aggregates at high concentrations.

[0062] Depend on Figure 6 As can be seen, with increasing concentration, the lifetime of the carbon nanodots prepared in this invention increased from 3.1 ns to 5.2 ns under 295 nm excitation. This indicates that the carbon nanodots prepared in this invention form H aggregates at high concentrations.

[0063] Depend on Figure 7 It can be seen that, under simulated solar lamp conditions without the addition of Pt co-catalyst, carbon dots exhibit photocatalytic hydrogen production even as monomers, with a water splitting hydrogen production performance of 3.1 μmol / gh. With increasing carbon dot concentration, the photocatalytic hydrogen production performance is improved, reaching a maximum of 17.5 μmol / gh. Therefore, it is evident that the carbon nanodots prepared in this invention can achieve improved photocatalytic hydrogen production performance simply by increasing their concentration.

[0064] Example 2

[0065] S1. Dissolve 0.30g citric acid, 0.12g p-phenylenediamine and 0.12g sodium hydroxide in deionized water and stir with a magnetic stirrer at room temperature for 20 minutes to fully dissolve them, to obtain mixed solution A.

[0066] S2. Place the mixed solution A in a reaction vessel and carry out a hydrothermal reaction at 190°C for 1 hour to obtain product B;

[0067] S3. After naturally cooling product B, dialyze it in water for 12 hours to obtain carbon nanodots that can form H aggregates.

[0068] The carbon nanodots prepared in this embodiment have a diameter of 4–10 nm, a lattice fringe spacing of 0.21 nm, an optimal excitation wavelength of 320 nm, and an emission wavelength of 412 nm.

[0069] Example 3

[0070] S1. Dissolve 0.30g citric acid, 0.24g p-phenylenediamine and 0.12g sodium hydroxide in deionized water and stir with a magnetic stirrer at room temperature for 10 minutes to fully dissolve them, to obtain mixed solution A.

[0071] S2. Place the mixed solution A in a reaction vessel and carry out a hydrothermal reaction at 200°C for 5 hours to obtain product B;

[0072] S3, after the product B is naturally cooled, dialysis in water for 12h, carbon nanodots with the aggregation property of the travel H are obtained.

[0073] The carbon nanodots prepared in the embodiment have a diameter of 5-8nm, a lattice fringe spacing of 0.22nm, an optimal excitation wavelength of 310nm and an emission wavelength of 408nm.

[0074] Embodiment 4

[0075] S1, 0.30g of citrazinic acid, 0.32g of p-phenylenediamine and 0.24g of sodium hydroxide are dissolved in deionized water, and a magnetic stirrer is used to stir at room temperature for 12min, so that they are fully dissolved to obtain a mixed solution A;

[0076] S2, the mixed solution A is placed in a reaction kettle for hydrothermal reaction at 200℃ for 5h to obtain a product B;

[0077] S3, after the product B is naturally cooled, dialysis in water for 12h, carbon nanodots with the aggregation property of the travel H are obtained.

[0078] The carbon nanodots prepared in the embodiment have a diameter of 4-10nm, a lattice fringe spacing of 0.21nm, an optimal excitation wavelength of 320nm and an emission wavelength of 400nm.

[0079] Embodiment 5

[0080] S1, 0.30g of citrazinic acid, 0.32g of p-phenylenediamine and 0.36g of sodium hydroxide are dissolved in deionized water, and a magnetic stirrer is used to stir at room temperature for 16min, so that they are fully dissolved to obtain a mixed solution A;

[0081] S2, the mixed solution A is placed in a reaction kettle for hydrothermal reaction at 180℃ for 8h to obtain a product B;

[0082] S3, after the product B is naturally cooled, dialysis in water for 18h, carbon nanodots with the aggregation property of the travel H are obtained.

[0083] The carbon nanodots prepared in the embodiment have a diameter of 5-10nm, a lattice fringe spacing of 0.21nm, an optimal excitation wavelength of 330nm and an emission wavelength of 430nm.

[0084] Embodiment 6

[0085] S1, 0.45g of citrazinic acid, 0.32g of p-phenylenediamine and 0.48g of sodium hydroxide are dissolved in deionized water, and a magnetic stirrer is used to stir at room temperature for 17min, so that they are fully dissolved to obtain a mixed solution A;

[0086] S2, the mixed solution A is placed in a reaction kettle for hydrothermal reaction at 190°C for 10h to obtain product B;

[0087] S3, the product B is naturally cooled and dialyzed in water for 15h to obtain carbon nanodots with good dispersion property.

[0088] The carbon nanodots prepared in the embodiment have a diameter of 6-9nm, a lattice fringe spacing of 0.23nm, an optimal excitation wavelength of 340nm and an emission wavelength of 420nm.

[0089] Example 7

[0090] S1, 0.60g of citrazinic acid, 0.32g of p-phenylenediamine and 0.36g of sodium hydroxide are dissolved in deionized water, and a magnetic stirrer is used to stir at room temperature for 20min to make them fully dissolved to obtain a mixed solution A;

[0091] S2, the mixed solution A is placed in a reaction kettle for hydrothermal reaction at 180°C for 4h to obtain product B;

[0092] S3, the product B is naturally cooled and dialyzed in water for 13h to obtain carbon nanodots with good dispersion property.

[0093] The carbon nanodots prepared in the embodiment have a diameter of 4.1-10.5nm, a lattice fringe spacing of 0.22nm, an optimal excitation wavelength of 320nm and an emission wavelength of 418nm.

[0094] Example 8

[0095] S1, 0.75g of citrazinic acid, 0.24g of p-phenylenediamine and 0.36g of sodium hydroxide are dissolved in deionized water, and a magnetic stirrer is used to stir at room temperature for 10min to make them fully dissolved to obtain a mixed solution A;

[0096] S2, the mixed solution A is placed in a reaction kettle for hydrothermal reaction at 200°C for 5h to obtain product B;

[0097] S3, the product B is naturally cooled and dialyzed in water for 18h to obtain carbon nanodots with good dispersion property.

[0098] The carbon nanodots prepared in the embodiment have a diameter of 5-9nm, a lattice fringe spacing of 0.21nm, an optimal excitation wavelength of 340nm and an emission wavelength of 430nm.

[0099] Example 9

[0100] S1, 0.90 g of citrazinic acid, 0.24 g of p-phenylenediamine and 0.48 g of sodium hydroxide were dissolved in deionized water, and a magnetic stirrer was used to stir at room temperature for 14 min to make it fully dissolved to obtain a mixed solution A;

[0101] S2, the mixed solution A was placed in a reaction kettle and hydrothermal reaction was carried out at 190°C for 10 h to obtain product B;

[0102] S3, after natural cooling, product B was dialyzed in water for 20 h to obtain carbon nanodots with H aggregation properties.

[0103] The carbon nanodots prepared in this example have a diameter of 4-10.5 nm, a lattice fringe spacing of 0.21 nm, an optimal excitation wavelength of 330 nm and an emission wavelength of 409 nm.

[0104] Example 10

[0105] S1, 0.90 g of citrazinic acid, 0.24 g of p-phenylenediamine and 0.48 g of sodium hydroxide were dissolved in deionized water, and a magnetic stirrer was used to stir at room temperature for 14 min to make it fully dissolved to obtain a mixed solution A;

[0106] S2, the mixed solution A was placed in a reaction kettle and hydrothermal reaction was carried out at 190°C for 10 h to obtain product B;

[0107] S3, after natural cooling, product B was dialyzed in water for 20 h to obtain carbon nanodots with H aggregation properties.

[0108] The carbon nanodots prepared in this example have a diameter of 4-10.5 nm, a lattice fringe spacing of 0.21 nm, an optimal excitation wavelength of 330 nm and an emission wavelength of 409 nm.

[0109] Example 11

[0110] S1, 0.90 g of citrazinic acid, 0.24 g of p-phenylenediamine and 0.48 g of sodium hydroxide were dissolved in deionized water, and a magnetic stirrer was used to stir at room temperature for 14 min to make it fully dissolved to obtain a mixed solution A;

[0111] S2, the mixed solution A was placed in a reaction kettle and hydrothermal reaction was carried out at 190°C for 10 h to obtain product B;

[0112] S3, after natural cooling, product B was dialyzed in water for 20 h to obtain carbon nanodots with H aggregation properties.

[0113] The carbon nanodots prepared in this example have a diameter of 4-10.5 nm, a lattice fringe spacing of 0.21 nm, an optimal excitation wavelength of 330 nm and an emission wavelength of 409 nm.

[0114] Example 12

[0115] S1. Dissolve 1.35g citric acid, 0.24g p-phenylenediamine and 0.48g sodium hydroxide in deionized water and stir with a magnetic stirrer at room temperature for 10 minutes to fully dissolve them, to obtain mixed solution A.

[0116] S2. Place the mixed solution A in a reaction vessel and carry out a hydrothermal reaction at 190°C for 8 hours to obtain product B;

[0117] S3. After naturally cooling product B, dialyze it in water for 24 hours to obtain carbon nanodots that can form H aggregates.

[0118] The carbon nanodots prepared in this embodiment have a diameter of 5-10 nm, a lattice fringe spacing of 0.23 nm, an optimal excitation wavelength of 330 nm, and an emission wavelength of 416 nm.

[0119] Example 13

[0120] S1. Dissolve 1.50g citric acid, 0.24g p-phenylenediamine and 0.48g sodium hydroxide in deionized water and stir with a magnetic stirrer at room temperature for 10 minutes to fully dissolve them, to obtain mixed solution A.

[0121] S2. Place the mixed solution A in a reaction vessel and carry out a hydrothermal reaction at 180°C for 5 hours to obtain product B;

[0122] S3. After naturally cooling product B, dialyze it in water for 12 hours to obtain carbon nanodots that can form H aggregates.

[0123] The carbon nanodots prepared in this embodiment have a diameter of 6-10 nm, a lattice fringe spacing of 0.21 nm, an optimal excitation wavelength of 320 nm, and an emission wavelength of 421 nm.

[0124] Example 14

[0125] S1. Dissolve 1.35g citric acid, 0.32g p-phenylenediamine and 0.48g sodium hydroxide in deionized water and stir with a magnetic stirrer at room temperature for 10 minutes to fully dissolve them, to obtain mixed solution A.

[0126] S2. Place the mixed solution A in a reaction vessel and carry out a hydrothermal reaction at 180°C for 7 hours to obtain product B;

[0127] S3. After naturally cooling product B, dialyze it in water for 14 hours to obtain carbon nanodots that can form H aggregates.

[0128] The carbon nanodots prepared in this embodiment have a diameter of 4–10 nm, a lattice fringe spacing of 0.21 nm, an optimal excitation wavelength of 330 nm, and an emission wavelength of 430 nm.

[0129] Currently, most reported carbon dots cannot form H aggregates, making it difficult to extend carrier lifetime through concentration. The carbon nanodots prepared in this invention have an absorption peak at 360 nm. When the concentration increases, the absorption peak of the carbon nanodots undergoes a blue shift and the absorption edge undergoes a red shift, increasing the carrier lifetime from 3 ns to 6 ns. At the same time, the photocatalytic hydrogen production efficiency increases from 3.1 μmol / gh to 17.5 μmol / gh.

[0130] Based on spectral characterization, the characteristics of H aggregation are as follows:

[0131] (1) At a sufficiently dilute concentration (0.01 mg / mL), no aggregation occurs. At this concentration, the carbon dots exhibit a characteristic peak at 360 nm. As the concentration increases, the absorption spectrum of the carbon nanodots (CDs) shows a blue shift, with the characteristic peak at 347 nm gradually shifting to 335 nm. This is a significant characteristic of H aggregation. This is because the S1 energy level of H aggregation splits into two peaks, one being a high-energy-level absorption peak with a large dipole moment. A low-level absorption peak with a very small dipole moment (theoretically 0). The intensity of light absorption by a molecule is directly related to the dipole moment of electronic transitions, and is directly reflected in the absorption peaks in the absorption spectrum. A blue shift will occur as the concentration increases.

[0132] (2) As the concentration of carbon nanodots (CDs) increases, the fluorescence intensity of CDs decreases sharply, while their lifetime increases. This is because although electrons are excited to higher energy levels... However, according to Kasha's rule, the electron will eventually return to the lowest energy level. Because the dipole moment of lower energy levels is very small, aggregates are less prone to radiative transitions, thus reducing fluorescence intensity. The lifetime of photogenerated carriers is inversely proportional to the dipole moment of the energy level; therefore, from... Energy level transitions have a long lifetime. The higher the concentration, the larger the size of the resulting H aggregates. The smaller the dipole moment of the energy level, the lower the potential, the lower the fluorescence intensity, and the longer the carrier lifetime; the excitation spectrum as a function of concentration further verifies this. Changes in energy levels.

[0133] In summary, this invention provides a carbon nanodot with H aggregation properties, its preparation method, and its application. By simply adjusting the concentration, radiative luminescence can be suppressed, the lifetime of photogenerated carriers can be extended, and the efficiency of photocatalytic hydrogen production can be effectively improved.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon nanodots having H-aggregation properties, characterized by, Dissolving citrazinic acid, p-phenylenediamine and sodium hydroxide in deionized water, stirring to obtain a uniform transparent mixed solution A; After hydrothermal reaction of the mixed solution A at 180~200℃, product B is obtained; then the product B is cooled and dialyzed to obtain carbon nanodots capable of forming H aggregation.

2. The method of claim 1, wherein the carbon nanodots have H-aggregation properties. The mass ratio of citrazinic acid, p-phenylenediamine and sodium hydroxide is (0.15~1.50 g):(0.12~0.32 g):(0.12~0.48 g).

3. The method of claim 1, wherein the carbon nanodots have H-aggregation properties. The stirring time is 10~20 min.

4. The method of claim 3, wherein the carbon nanodots have H-aggregation properties. The stirring is performed by a magnetic stirrer.

5. The method of claim 3, wherein the carbon nanodots have H-aggregation properties. The stirring temperature is room temperature.

6. The method of claim 1, wherein the carbon nanodots have H-aggregation properties. The hydrothermal reaction time is 1~10 hours.

7. The method of claim 1, wherein the carbon nanodots have H-aggregation properties. The dialysis time is 12~24 hours.

8. Carbon nanodots having H-aggregation properties, characterized in that, The carbon nanodots prepared according to the method of any one of claims 1 to 7 have a diameter of 4.1~10.5 nm, a crystal lattice fringe spacing of 0.21 nm, an excitation wavelength of 310~340 nm and an emission wavelength of 410~430 nm.

9. The carbon nanodots with H aggregation properties according to claim 8 are applied to photocatalytic hydrogen production.

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