CN120888301A

CN120888301A - A method for preparing coal tar pitch-based modified carbon quantum dots in a methanol-water mixed solvent system

Info

Publication number: CN120888301A
Application number: CN202511416874.XA
Authority: CN
Inventors: 王清风; 徐熠; 张瀚; 翁继; 张志敏; 刘萍; 樊立强; 刘志英
Original assignee: Xingtai Risun Coal Chemical Industry Co ltd
Current assignee: Xingtai Risun Coal Chemical Industry Co ltd
Priority date: 2025-09-30
Filing date: 2025-09-30
Publication date: 2025-11-04

Abstract

The invention relates to a method for preparing coal tar pitch-based modified carbon quantum dots in a methanol-water mixed solvent system, which comprises the steps of uniformly mixing coal tar pitch powder with a mixed solvent of methanol and water and an oxidant, and then heating and reacting to prepare the carbon quantum dots; cooling the reaction liquid, filtering, regulating the pH value of the filtrate, and adding a surface modifier for surface modification to obtain the modified carbon quantum dots. The method solves the problem of uneven dispersion of each reaction component in the traditional solvent. The method uses coal pitch as a raw material, improves the dispersibility of the pitch, increases solid-liquid two-phase contact, improves the reactivity, and improves the fluorescence intensity, fluorescence quantum yield and the like of the carbon quantum dots by improving the reaction conditions.

Description

Method for preparing coal tar pitch-based modified carbon quantum dots in methanol-water mixed solvent system

Technical Field

The invention relates to the technical field of preparation of coal tar pitch-based carbon quantum dots, in particular to a method for preparing modified carbon quantum dots by using a mixed solvent of methanol and water.

Background

Carbon Quantum Dots (CQDs) are zero-dimensional nano materials with remarkable fluorescence performance, and have the advantages of excellent optical properties, good water solubility, low toxicity, wide raw material sources, good biocompatibility, high chemical stability and the like, so that the carbon quantum dots have wide application prospects in various fields such as biomedicine, energy storage, environmental monitoring and agriculture.

Coal is considered an ideal precursor for the production of CQDs as a rich natural carbonaceous material due to the large number of carbon crystals inherent in its structure. However, coal pitch is less useful, and compared with coal, pitch has a denser fused ring structure, and aromatic rings are more tightly connected, forming a larger, more stable conjugated system.

The preparation method of the coal-based carbon quantum dots is various and mainly comprises a chemical oxidation method, an electrochemical method, a solvothermal method and the like. The reactivity cannot be further improved due to poor asphalt dispersibility in conventional reaction solvent water.

Disclosure of Invention

In view of the problems of the prior art, the present inventors have studied various factors affecting the preparation of carbon quantum dots, including raw material particle size, reaction temperature, oxidizing agent, reaction solvent, modifier, etc., and have finally found that high-yield synthesis of carbon quantum dots can be achieved by a combination of specific conditions, and fluorescence intensity and fluorescence amount of carbon quantum dots are improved, thereby providing a method for preparing carbon quantum dots using coal pitch in a mixed solvent. The method solves the problem of uneven dispersion of each reaction component in the traditional solvent. The method uses coal pitch as a raw material, improves the dispersibility of the pitch, increases solid-liquid two-phase contact, improves the reactivity, and improves the fluorescence intensity, fluorescence quantum yield and the like of the carbon quantum dots by improving the reaction conditions.

In one aspect, the present invention provides a method of preparing a modified carbon quantum dot, comprising:

s1, uniformly mixing coal tar pitch powder, a mixed solvent of methanol and water and an oxidant, and then heating for reaction to prepare carbon quantum dots;

s2, cooling the reaction liquid, filtering, and adjusting the pH value of the filtrate;

and S3, adding a surface modifier to react for surface modification to obtain the modified carbon quantum dot.

The following is a detailed description.

Step S1

In some embodiments, the coal pitch refers to tar distillation residues of high-temperature carbonization (1000+/-50 ℃) of coal, ash content is less than or equal to 0.1%, and softening point is 175-178 ℃.

In some embodiments, the pitch powder mesh number is not less than 200 mesh. Within this size range, it is advantageous for the reaction system to disperse uniformly, whereas if it exceeds this range, it may result in poor dispersibility of the reaction system, which is disadvantageous for uniform reaction.

There is no particular limitation on how to obtain the coal tar pitch powder, and it may be a commercially available product or may be prepared from coal tar pitch by a conventional method. In some embodiments, the coal pitch may be obtained by crushing and grinding coal pitch.

According to the invention, the mixed solvent of methanol and water is used, so that the strong polarity of the methanol can be used for improving the dispersibility of coal tar pitch powder and the solubility of water to an oxidant, and the contact area of solid-liquid two phases in a reaction system is increased, thereby solving the problem of uneven dispersion of each reaction component in the traditional solvent and improving the reaction activity.

In some embodiments, the volume ratio of methanol to water in the mixed solvent of methanol and water is 1:1-3.5, for example 1:1.5, 1:2, 1:2.5, 1:3, preferably 1:1.5-3, more preferably 1:2-3, and particularly preferably 2:5. When the proportion of methanol is too large, the dissolution of the oxidant is not facilitated, so that the oxidation is inhibited, and when the proportion of water is too large, the dispersibility of the coal tar pitch powder is affected, the coal tar pitch powder is agglomerated, agglomerated and the like, so that the oxidation is also not facilitated.

In the present invention, the oxidizing agent is a substance having strong oxidizing property. In some embodiments, the oxidizing agent is one or more selected from the group consisting of H ₂SO₄、Na₂S₂O₈、K₂S₂O₈, but is not limited thereto, preferably Na ₂S₂O₈. The invention uses strong oxidant to oxidize and shear the condensation polymerization structure of coal pitch, to etch the coal pitch structure, and to form oxygen-containing functional groups on the surface of coal pitch.

In some embodiments, the mass ratio of coal pitch to oxidant is 1:2-20, e.g., 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, etc., preferably 1:5-15, more preferably 1:8-14, particularly preferably 1:10. Too much oxidant is unfavorable for post-treatment and leads to increased cost, while too little oxidant is used, so that the oxidation effect is not obvious.

In some embodiments, the oxidant mass concentration in the reaction solution may be 0.1-1.0g/mL, e.g., 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.10g/mL, etc. The oxidant concentration is too high, the oxidizing property of the system is too strong, the aromatic skeleton is easy to excessively fracture, a large number of small molecules are generated, the yield of the carbon quantum dots is reduced, excessive oxygen-containing functional groups can be possibly introduced, the fluorescence quantum efficiency is weakened, the oxidation depth is insufficient, the compact polycyclic aromatic hydrocarbon is difficult to sufficiently peel and edge functionalization, and the carbon core size is larger.

The manner of mixing the coal tar pitch powder with the mixed solvent of methanol and water and the oxidizing agent is not particularly limited as long as the mixing and the reduction of the agglomeration of the coal tar pitch powder can be achieved. In some embodiments, blending may be accomplished by sonication or by homogenizer treatment. In particular, the mixing is accomplished by sonication for more than 30 minutes. The ultrasonic treatment time is too short, and the coal pitch and the oxidant may be unevenly dispersed.

In some embodiments, the reaction is performed with stirring. By stirring, agglomeration of coal tar pitch powder can be reduced and the reaction can be promoted to proceed uniformly.

In some embodiments, in S1, the reaction temperature may be 40-80 ℃, e.g., 40, 45, 50, 55, 60, 65, 70, 75, 80 ℃, preferably 60-80 ℃. The energy required by the reaction cannot be reached when the reaction temperature is too low, the oxidation effect is not obvious, and the energy consumption is increased when the temperature is too high.

The reaction time is not particularly limited as long as the target product is obtained in a reasonable yield. In general, the reaction time is affected by the reaction temperature, the concentration of the reactants, and the like. In some embodiments, the reaction time may be 4 hours or more, 6 hours or more, or 8 hours or more. The upper limit of the reaction time is not particularly limited, but too long a time increases the reaction cost, and thus may be 24 hours or less, 20 hours or less, or the like.

Step S2

In some embodiments, the reaction solution is cooled to room temperature, but the present invention is not limited thereto.

In some embodiments, the cooled reaction solution is filtered through a 0.20-0.45 μm filter, but the present invention is not limited thereto. Impurities in the reaction solution can be removed by filtration.

In some embodiments, the filtrate pH is adjusted to neutral, e.g., 6-8, e.g., 6-7. Sodium hydroxide solution may be used for the adjustment, but is not limited thereto.

In some embodiments, step S2 further comprises a step of concentrating the filtrate. Concentration may be performed by rotary evaporation to remove a large amount of water in the solution, but is not limited thereto.

Step S3

In S3, the purpose of adding the surface modifier for modification is to access functional groups with different characteristics on the surface of the carbon quantum dot, and introduce more lone pair electrons through hetero atoms, so that the fluorescence characteristic of the carbon quantum dot is improved.

In some embodiments, the surface modifying agent is a reagent containing N, S, P or other heteroatoms. Reagents containing N, S, P or other heteroatoms include, but are not limited to, o-phenylenediamine, p-phenylenediamine, phosphoric acid, monoammonium phosphate, thiourea and the like, with o-phenylenediamine being preferred.

In some embodiments, in S3, the reaction temperature may be 180-200 ℃, e.g., 180, 185, 190, 195, 200 ℃, etc., but is not limited thereto. Too low a temperature, insufficient reactivity, and too high a temperature may damage the surface structure of the carbon quantum dots. The reaction time may be adjusted according to the reaction temperature, the concentration of the reactants, and the like.

In some embodiments, the reaction time may be 4 hours or more, 6 hours or more, or 8 hours or more. The upper limit of the reaction time is not particularly specified, but too long a time does not significantly increase the yield and increases the reaction cost, and thus may be 20 hours or less, 15 hours or less, 12 hours or less, or the like.

Step S3 may further include a purification step to purify the resulting carbon quantum dots.

In some embodiments, the purification is performed by filtering the reaction solution and dialyzing.

The filtering may be performed using the same conditions as in step S2. Dialysis can be performed using 3500Da dialysis bags, but is not limited thereto.

Step S3 may further include a drying step to obtain solid carbon quantum dots.

Another method of the present invention provides a carbon quantum dot prepared by the method according to the present invention.

The invention also provides application of the carbon quantum dots in hydrogen production by decomposing water.

Advantageous effects

According to the invention, a solid-liquid two-phase reaction system is constructed by using methanol and water as mixed solvents, so that the problems of poor asphalt dispersibility and poor oxidant solubility are solved, and the overall yield is improved. Based on the method, an optimal experimental system is realized, the reaction activity is exerted to the optimal, the heteroatom is used for improving the surface activity of the carbon quantum dot, and finally the modified carbon quantum dot with high fluorescence performance is prepared.

Unless explicitly stated otherwise, numerical ranges throughout this application include any subrange therein and any numerical value incremented by the smallest subunit in which a given value is present. Unless explicitly stated otherwise, numerical values throughout this application represent approximate measures or limits to include minor deviations from the given value and ranges of embodiments having about the stated value and having the exact value noted. Except in the operating examples provided last, all numerical values of parameters (e.g., amounts or conditions) in this document (including the appended claims) should be construed in all cases as modified by the term "about" whether or not "about" actually appears before the numerical value. "about" means that the recited value allows for slight imprecision (with some approximation to the exact value; approximately or reasonably close to the value; approximated). "about" as used herein at least means variations that can be produced by ordinary methods of measuring and using these parameters if the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning. For example, "about" may include a change of less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

This document provides an overview of various implementations or examples of the technology described in this disclosure, and is not a comprehensive disclosure of the full scope or all of the features of the technology disclosed.

Drawings

Fig. 1 is a fluorescence absorption spectrum of the modified carbon quantum dot prepared in example 1.

Fig. 2 is an ultraviolet-visible light absorption spectrum of the modified carbon quantum dot prepared in example 1.

Fig. 3 is a graph showing four catalytic hydrolysis hydrogen evolution effects of the modified carbon quantum dots prepared in example 1 under the visible light condition.

Detailed Description

The following describes the embodiments of the present invention in further detail with reference to examples. However, the following examples are provided only for easier understanding of the present invention, and the scope of the present invention is not limited thereto.

Unless otherwise indicated, all materials, reagents, methods and the like used in the examples are those conventionally used in the art.

Reagent:

coal tar pitch (softening point 175 ℃), xingtai Xu yang coal chemical industry Co., ltd., was ground thoroughly with a 200 mesh screen and dried for use.

Methanol is an analytically pure grade (99.5% or more, AR) reagent purchased from Tianjin metallocene chemical reagent plant.

Sodium persulfate is an analytical grade (. Gtoreq.98.0%, AR) reagent available from Albumin Biotechnology Co., ltd.

The experimental method comprises the following steps:

fluorescence absorption intensity and fluorescence quantum yield were measured and calculated as follows.

Fluorescence spectroscopy measurement was performed by scanning with a irinotef-7100 fluorescence spectrophotometer (excitation/emission slit=5 nm, photomultiplier voltage=700V) at room temperature, scanning speed 1200 nm min ^-1.

Fluorescence quantum yield (Φ) was measured by the integrating sphere method using quinine sulfate (Φ=0.54, 0.1m H ₂SO₄) as a reference. The calculation formula is as follows:

Φ_S= Φ_R× (I_S/I_R) × (A_R/A_S) × (n_S ²/n_R ²)

Wherein the subscript S denotes the sample, R denotes the reference, I is the integrated fluorescence intensity, a is the absorbance at the excitation wavelength (a < 0.1), and n is the solvent refractive index (methanol/water=1.329).

Example 1

(1) 2G of asphalt powder was weighed into a flask, 50mL of a mixed solvent of methanol and water (volume ratio of methanol to water: 2:5) was added, and 20g (0.4 g/mL) of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 60 ℃ for 12h.

(3) After the reaction was completed, after the reaction system was cooled to room temperature, filtered using a 0.45 μm filter membrane, the pH of the solution was adjusted to between 6 and 7 by adding NaOH solution, and then concentrated to 2mL by rotary evaporation.

(4) To the concentrated solution was added 2g of o-phenylenediamine and stirred at 200℃for 10 hours.

(5) Filtering the solution after reaction with a 0.45 μm filter membrane, loading into a regenerated cellulose dialysis bag (3500 Da), dialyzing until the electric conductivity of the dialysate is lower than 50 mu s/cm, collecting the modified carbon quantum dot solution in the dialysis bag, and drying. The modified carbon quantum dot with high fluorescence performance is prepared, the fluorescence absorption intensity is about 18000, the fluorescence quantum yield is 23.8%, and the yield is 74.6%.

Fluorescence absorption spectrometry

The modified carbon quantum dot prepared in example 1 is measured on a Hitachi F-7100 fluorescence spectrophotometer to obtain fluorescence absorption spectrum, and the fluorescence absorption peak is 320-350nm and corresponds to the position of the fluorescence absorption peak of the modified carbon quantum dot as shown in FIG. 1.

Ultraviolet-visible absorption spectrum

The modified carbon quantum dot prepared in example 1 is measured on an Shimadzu UV-2600 spectrophotometer to obtain an ultraviolet-visible absorption spectrum, and the result is shown in fig. 2, wherein the obvious absorption peak of the modified carbon quantum dot at 239nm corresponds to the transition of C=O and N-H groups in amide on the surface of the modified carbon quantum dot, and two absorption peaks at 267nm and 274nm correspond to the transition of aromatic hydrocarbon and a multi-conjugated system pi-pi in the skeleton of the modified carbon quantum dot, so that the ultraviolet absorption characteristic of the modified carbon quantum dot is met.

Experimental example 1

The modified carbon quantum dots prepared in example 1 are subjected to water decomposition under the condition of visible light to prepare hydrogen, and the specific operation is as follows.

50Mg modified carbon quantum dots are weighed and dispersed in 100 mL aqueous solution containing 10% of triethanolamine, and ultrasonic dispersion ensures that a light source can uniformly penetrate through the whole suspension. H ₂PtCl₆ was added and dissolved in the suspension, and 3.0wt% Pt was supported on carbon quantum dots by illuminating a 300W xenon lamp containing a filter (lambda >420 nm) for 1H directly above the reactor with a reducing promoter. Impurity gas in the system was removed by vacuum suction before the start of illumination. During the whole catalysis process, gas is collected every 30min, and the gas components and the gas content are detected by a gas chromatograph (GC-7920) with a TCD detector.

As shown in FIG. 3, the modified carbon quantum dot has better photon absorption capacity, can provide electron-hole and is beneficial to electron transfer.

Example 2

(1) 2G of asphalt powder was weighed into a flask, 50mL of a mixed solvent of methanol and water (volume ratio of methanol to water: 2:5) was added, and 10g (0.2 g/mL) of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 60 ℃ for 12h.

(4) To the concentrated solution was added 2g of p-phenylenediamine and stirred at 200℃for 10 hours.

(5) Filtering the solution after reaction by using a 0.45 mu m filter membrane, filling the solution into a regenerated cellulose dialysis bag (3500 Da), dialyzing until the electric conductivity of the dialysate is lower than 50 mu s/cm, collecting the modified carbon quantum dot solution in the dialysis bag, and drying to obtain the modified carbon quantum dot, wherein the fluorescence absorption intensity is about 13000, the quantum yield is 21.6%, and the yield is 71.9%.

Example 3

(1) 2G of asphalt powder was weighed into a flask, 50mL of a mixed solvent of methanol and water (volume ratio of methanol to water: 2:5) was added, and 40g (0.8 g/mL) of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 60 ℃ for 12h.

(4) To the concentrated solution was added 2g of o-phenylenediamine and stirred at 180℃for 10 hours.

(5) Filtering the solution after the reaction by using a 0.45 mu m filter membrane, filling the solution into a regenerated cellulose dialysis bag (3500 Da), dialyzing until the electric conductivity of the dialysate is lower than 50 mu s/cm, collecting a modified carbon quantum dot solution in the dialysis bag, and drying to obtain the modified carbon quantum dot, wherein the fluorescence absorption intensity is about 16000, the quantum yield is 22.3%, and the yield is 70.8%.

Example 4

(1) 2G of asphalt powder was weighed into a flask, 100mL of a mixed solvent of methanol and water (volume ratio of methanol to water: 2:5) was added, and 20g (0.2 g/mL) of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 80 ℃ for 12h.

(4) To the concentrated solution was added 2g of monoamine phosphate and stirred at 180℃for 14h.

(5) Filtering the solution after reaction by using a 0.45 mu m filter membrane, filling the solution into a regenerated cellulose dialysis bag (3500 Da), dialyzing until the electric conductivity of the dialysate is lower than 50 mu s/cm, collecting the modified carbon quantum dot solution in the dialysis bag, and drying to obtain the modified carbon quantum dot, wherein the fluorescence absorption intensity is about 14000, the quantum yield is 23.1%, and the yield is 72.2%.

Comparative example 1

(1) 2G of asphalt powder was weighed into a flask, 50mL of water was added, and 20g of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 60 ℃ for 12h.

(5) Filtering the solution after reaction by using a 0.45 mu m filter membrane, filling the solution into a regenerated cellulose dialysis bag (3500 Da), dialyzing until the electric conductivity of the dialysate is lower than 50 mu s/cm, collecting the modified carbon quantum dot solution in the dialysis bag, and drying to obtain the modified carbon quantum dot, wherein the fluorescence absorption intensity is 3200, the quantum yield is 12.8%, and the yield is 36.9%.

Comparative example 2

(1) 2G of asphalt powder was weighed into a flask, 50mL of methanol was added, and 20g of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 60 ℃ for 12h.

(3) After the reaction was completed, after the reaction system was cooled to room temperature, filtered using a 0.45 μm filter membrane, the pH of the solution was adjusted to between 6 and 7 by adding NaOH solution, and then concentrated to 10mL by rotary evaporation.

A large amount of white solid is precipitated in the concentrated solution, and the experiment cannot be continued. It is suspected that sodium persulfate cannot be dissolved in methanol, so that the solid-liquid reaction is changed into solid-solid reaction, and the reactivity is greatly reduced.

Comparative example 3

(1) 2G of asphalt powder was weighed into a flask, 50mL of a mixed solvent of tetrahydrofuran and water (tetrahydrofuran: water volume ratio: 1:4) was added, and 20g of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 60 ℃ for 12h.

(3) After the reaction was completed, the reaction system was cooled to room temperature and filtered through a 0.45 μm filter membrane. The oily substance formed by more asphalt light components in the reaction liquid is difficult in the filtering process, the filtering step can not be completed, and the experiment can not be continued.

Comparative example 4

(1) 2G of asphalt powder was weighed into a flask, 50mL of a mixed solvent of methanol and water (volume ratio of methanol to water: 1:4) was added, and 20g of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 60 ℃ for 12h.

(5) Filtering the solution after reaction by using a 0.45 mu m filter membrane, filling the solution into a regenerated cellulose dialysis bag (3500 Da), dialyzing until the electric conductivity of the dialysate is lower than 50 mu s/cm, collecting the modified carbon quantum dot solution in the dialysis bag, and drying to obtain the carbon quantum dot, wherein the fluorescence absorption intensity is 5800, the quantum yield is 16.3%, and the yield is 53.9%.

Comparative example 5

(1) 2G of asphalt powder was weighed into a flask, 50mL of a mixed solvent of methanol and water (volume ratio of methanol to water: 2:1) was added, and 20g of sodium persulfate was added. Suspending ultrasonic for 30min to uniformly disperse asphalt in the solution to form suspension.

(2) The flask was transferred to a water bath and stirred at 60 ℃ for 12h.

A small amount of white solid is separated out from the concentrated solution, and after the concentrated solution is filtered by a 0.45 mu m filter membrane again, naOH solution is added to adjust the pH value of the solution to be between 6 and 7.

(5) Filtering the solution after reaction by using a 0.45 mu m filter membrane, filling the solution into a regenerated cellulose dialysis bag (3500 Da), dialyzing until the electric conductivity of the dialysate is lower than 50 mu s/cm, collecting the modified carbon quantum dot solution in the dialysis bag, and drying to obtain the modified carbon quantum dot, wherein the fluorescence absorption intensity is 900, the quantum yield is 8.6%, and the yield is 22.6%.

As can be seen from comparison of the data of all examples and comparative examples, the invention solves the problems of poor asphalt dispersibility and poor oxidant solubility by using the mixed solvent of methanol and water in a specific proportion range to construct a solid-liquid two-phase reaction system, improves the overall yield and the reaction activity, and the prepared carbon quantum dot has the fluorescence absorption intensity of 12000 or more, the quantum yield of 20 or more and the yield of 70 or more. In comparative example 1, water alone was used as a solvent, the solid-liquid two-phase contact was insufficient, and the fluorescence yield of the modified carbon quantum dots was only 12.8%, and the yield was only 36.9%. Comparative example 2 using methanol alone as a solvent and comparative example 3 using a mixed solvent of tetrahydrofuran and water, the experiment could not be completed. Comparative examples 4 and 5 used a mixed solvent of methanol and water which was not within the range of the present invention, wherein the water content in comparative example 4 was too high, and the methanol content in comparative example 5 was too high, and the quantum yield and yield were not ideal. The modified carbon quantum dot prepared by the preparation method for preparing the modified carbon quantum dot with high fluorescence performance in the mixed solvent with the specific proportion range has higher fluorescence characteristic and yield.

The foregoing is only a few embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think about changes or substitutions within the technical scope of the present invention, and these changes or substitutions are all covered by the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method of preparing a modified carbon quantum dot, comprising:

S1, uniformly mixing coal tar pitch powder, a mixed solvent of methanol and water and an oxidant, and then heating for reaction to prepare carbon quantum dots, wherein the volume ratio of the methanol to the water in the mixed solvent of the methanol and the water is 1:1-3.5, the oxidant is one or more selected from H ₂SO₄、Na₂S₂O₈、K₂S₂O₈, the mass concentration of the oxidant is 0.1-1.0g/mL, the mass ratio of the coal tar pitch to the oxidant is 1:2-20, and the reaction temperature is 40-80 ℃;

s2, cooling the reaction solution, filtering the reaction solution through a 0.20-0.45 mu m filter membrane, regulating the pH value of the filtrate to 6-8, and concentrating the filtrate;

and S3, adding a surface modifier to react for surface modification to obtain the modified carbon quantum dot, wherein the surface modifier is selected from o-phenylenediamine, p-phenylenediamine, phosphoric acid, monoammonium phosphate and thiourea, and the surface modification reaction temperature is 180-200 ℃.

2. The method according to claim 1, wherein, in S1,

The mesh number of the asphalt powder is not less than 200 meshes;

the volume ratio of the methanol to the water is 1:1.5-3;

The mass ratio of the coal pitch to the oxidant is 1:5-15;

the mixing is completed by ultrasonic treatment or by homogenizer treatment;

the reaction is carried out under stirring;

The reaction temperature is 60-80 ℃;

The reaction time is 4h or more and 24h or less.

3. The method of claim 2, wherein the step of determining the position of the substrate comprises,

The volume ratio of the methanol to the water is 1:2-3;

The mass ratio of the coal pitch to the oxidant is 1:8-14;

The mixing is completed by ultrasonic treatment for more than 30 min;

the reaction time is 6h or more and 20h or less.

4. The method according to claim 2, wherein, in S1,

The volume ratio of the methanol to the water is 2:5;

the mass ratio of the coal pitch to the oxidant is 1:10;

The mixing is completed by ultrasonic treatment for more than 30 min;

The reaction time is 8h or more and 20h or less.

5. The method according to claim 1, wherein, in S2,

Cooling the reaction solution to room temperature;

regulating the pH value of the filtrate to 6-7;

the concentration was carried out by rotary evaporation.

6. The method according to claim 1, wherein, in S3,

The surface modifier is o-phenylenediamine;

the reaction time is 4h or more and 20h or less.

7. The method of claim 6, wherein the reaction time is greater than 6 hours and less than 15 hours.

8. The method according to claim 1, wherein step S3 further comprises a purification step;

Wherein the purification is carried out by filtering the reaction solution and dialyzing.

9. The method according to claim 8, wherein the purification is carried out by filtering the reaction solution through a 0.20-0.45 μm filter membrane and the dialysis is carried out using 3500Da dialysis bags.

10. The method according to claim 1, wherein step S3 further comprises a drying step.

11. A carbon quantum dot prepared by the method of any one of claims 1-10.

12. Use of the carbon quantum dot according to claim 11 for hydrogen production by water decomposition.