CN113481004A - Carbon dots and preparation method and application thereof - Google Patents
Carbon dots and preparation method and application thereof Download PDFInfo
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- CN113481004A CN113481004A CN202110557337.2A CN202110557337A CN113481004A CN 113481004 A CN113481004 A CN 113481004A CN 202110557337 A CN202110557337 A CN 202110557337A CN 113481004 A CN113481004 A CN 113481004A
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/65—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing carbon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/28—Per-compounds
- C25B1/30—Peroxides
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
- C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
- C25B11/065—Carbon
Abstract
The invention discloses a carbon dot and a preparation method and application thereof, wherein the preparation method of the carbon dot comprises the following steps: citric acid, urea and calcium chloride are used as precursors, and carbon dots can be obtained through subsequent purification after vacuum high-temperature calcination. The carbon dots prepared by the method are applied to the industry of producing hydrogen peroxide by electrochemical selective oxygen reduction for the first time, and the detection of a rotating ring disk electrode and H-shaped electrolytic cell equipment shows that the carbon dots have good selectivity in the hydrogen peroxide produced by electrocatalysis, and are beneficial to the application of further industrialized electrocatalysis in hydrogen peroxide production.
Description
Technical Field
The invention belongs to the technical field of material preparation and application, and particularly relates to a carbon dot and a preparation method and application thereof.
Background
Hydrogen peroxide is an important chemical substance and has wide application in the fields of industry, medicine, environmental protection, war industry, food, environment and the like. It has both oxidizing and reducing properties and no secondary pollution after use, and is defined as a green chemical product. At present, the most mature method for industrially producing hydrogen peroxide on a large scale is the anthraquinone method, but the anthraquinone method not only has complicated steps, but also uses some organic solvents to cause secondary pollution to the environment, so that the green and efficient method for producing hydrogen peroxide is urgently found.
In the electrochemical Oxygen Reduction Reaction (ORR), there are two reaction pathways:
i.e. reaction transfer 2e-Pathway generation of H2O2(formula 1) and reaction transfer 4e-Pathway generation of H2O (formula 2), and the selectivity of the catalyst is one of the key factors determining the reaction pathway. Thus, 2e which promotes the reduction of oxygen with a suitable catalyst is selected-Pathways of producing and accumulating large amounts of H2O2And the aim of efficiently and environmentally producing hydrogen peroxide on a small scale is fulfilled.
Most of the existing high-efficiency catalysts for electrocatalytic oxidation-reduction reaction select a 4 e-way; only noble metals and alloys thereof, monatomic catalysts, carbon-based materials, metal complexes and the like can catalyze and select the 2 e-path, but the price is high, the structure of the catalyst needs to be accurately controlled, and the preparation conditions are harsh. Therefore, research and study are needed for other novel materials, and the carbon dots as a carbon material have a large number of oxygen-containing functional groups on the surface, and the oxygen-containing functional groups can greatly improve the selection of the carbon dots for electrocatalytic hydrogen peroxide generation. And the raw materials for preparing the carbon dots are wide in source and low in price, so that the carbon dots have great application prospect in the field of electrochemical oxygen reduction.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention aims to provide a carbon dot and a preparation method and application thereof.
The preparation method of the carbon dots is characterized in that citric acid, calcium chloride and urea are used as precursors, and the carbon dots can be obtained through subsequent purification after high-temperature calcination.
The preparation method of the carbon dots is characterized by comprising the following steps:
1) citric acid, calcium chloride and urea are taken as precursors, and are dissolved in water and placed in a porcelain boat;
2) and (3) placing the porcelain boat with the precursor in a tube furnace, calcining at high temperature in vacuum, naturally cooling to room temperature after calcination, taking out a product in the porcelain boat, adding ethanol, performing ultrasonic treatment, centrifuging to obtain a supernatant, and performing rotary steaming and drying to obtain the carbon dots.
Further, in the step 2), the three precursors are placed in a tube furnace, and the mass ratio of citric acid to urea to calcium chloride is 1.5: 3: 1.
further, in the step 2), the high-temperature calcination process is as follows: raising the temperature from room temperature to 120 ℃ at a temperature raising rate of 5 ℃/min, maintaining the temperature at 120 ℃ for 0.5h, raising the temperature from 120 ℃ to 190-310 ℃, preferably 250 ℃, at a temperature raising rate of 5 ℃/min, then keeping the temperature for 0.5-1.5 h, preferably 1h, and then naturally cooling.
A carbon dot prepared according to the above method.
The application of the carbon dot in preparing hydrogen peroxide by electrocatalysis.
Further, the application of the carbon dots in preparing hydrogen peroxide through electrocatalysis is characterized in that an electrochemical workstation is used as an electrochemical generating device, a three-electrode measuring system is adopted, the carbon dot material is coated on carbon cloth to serve as a working electrode, a platinum wire is used as a counter electrode, saturated calomel is used as a reference electrode, a KOH aqueous solution is used as an electrolyte, and electrochemical oxygen reduction reaction is carried out to produce hydrogen peroxide.
Further, the concentration of the KOH aqueous solution was 0.1 mol/L.
Furthermore, the preparation method of the working electrode comprises the following steps: and adding the carbon dots into a mixed solution of nafion solution and absolute ethyl alcohol, uniformly dispersing by ultrasonic waves, uniformly dripping the dispersed solution on carbon cloth, and finally drying to obtain the corresponding working electrode.
Compared with the prior art, the invention has the following advantages:
1) the invention takes citric acid, urea and calcium chloride as precursors, directly carries out pyrolysis under vacuum, prepares the non-metallic catalyst with high activity for producing hydrogen peroxide by electrocatalysis by a one-step method, and is beneficial to further exploring the industrial application of the non-metallic catalyst. The precursor of the invention takes water as a solvent, and has the advantages of high yield, convenient operation, large-scale preparation and the like, wherein calcium chloride is added as a calcium source, and when the water in the calcium chloride solution is evaporated in vacuum, a thin-wall structure is formed, which promotes the formation of carbon dots.
2) According to the invention, citric acid, urea and calcium chloride are used as precursors, and pyrolysis is directly carried out under vacuum, so that the carbon dot material is innovatively prepared. By infrared, it can be found that a large number of carboxyl groups and hydroxyl groups are present in the carbon dots produced by pyrolysis in the present invention. The carbon dots are used for researching the electrocatalytic hydrogen peroxide production, the number of transfer electrons of the oxygen reduction reaction is 2.15, and the reaction transfer is 2e-The theoretical values of the approaches are close, which shows that the carbon dots have better catalytic activity in the production of preparing hydrogen peroxide by electrochemical oxygen reduction reaction.
3) The carbon dots prepared by the invention are used as a new carbon material and are firstly applied to the industry of producing hydrogen peroxide by electrochemical selective oxygen reduction, and the detection of a rotating ring disk electrode and an H-shaped electrolytic cell device shows that the carbon dots have good selectivity and yield in the hydrogen peroxide production by electrocatalysis, thereby being beneficial to the application of further preparing hydrogen peroxide by industrial electrocatalysis.
Drawings
FIG. 1 is a TEM image of a carbon dot obtained in example 3;
FIG. 2 is an infrared spectrum of a carbon dot obtained in example 3 of the present invention;
FIG. 3 is an absorption spectrum of a carbon dot obtained in example 3 of the present invention;
FIG. 4 is a summary diagram of the selectivity of carbon dots prepared in examples 1 to 5 of the present invention to hydrogen peroxide solution in a rotating ring disk electrode test;
FIG. 5 is a diagram of the electron transfer number of hydrogen peroxide in a rotating ring disk electrode test by carbon dots prepared in examples 1 to 5 of the present invention;
FIG. 6 is a graph showing the performance of carbon dots prepared in examples 1 to 5 in the production of hydrogen peroxide by electrocatalysis in an H-shaped electrolytic cell;
FIG. 7 is a graph showing the life test (i-t) results of carbon dots prepared in example 3 of the present invention in an application of electrocatalytic hydrogen peroxide production.
Detailed Description
The present invention is further illustrated by the following examples, which should not be construed as limiting the scope of the invention.
Example 1: carbon dots for producing hydrogen peroxide by electrocatalysis
The preparation method comprises the following steps:
0.15g of citric acid, 0.3g of urea and 0.1g of calcium chloride are accurately weighed and added into 1ml of water to be fully dissolved. Placing the obtained solution in a porcelain boat, heating from room temperature to 120 deg.C at a heating rate of 5 deg.C/min under vacuum, calcining at 120 deg.C for 0.5h, and heating from 120 deg.C to 190 deg.C at a heating rate of 5 deg.C/minoAnd C, keeping the temperature of 190 ℃ and calcining for 1 h. And after the mixture is naturally cooled, putting the obtained solid powder into a beaker, adding about 30ml of ethanol, carrying out ultrasonic treatment for about 1 hour, centrifuging, taking supernatant, and drying to obtain the carbon dots.
Example 2: carbon dots for producing hydrogen peroxide by electrocatalysis
The preparation method comprises the following steps:
0.15g of citric acid, 0.3g of urea and 0.1g of calcium chloride are accurately weighed and added into 1ml of water to be fully dissolved. Putting the obtained solution into a porcelain boat, heating from room temperature to 120 ℃ at the heating rate of 5 ℃/min under vacuum, keeping the temperature at 120 ℃ for calcining for 0.5h, then heating from 120 ℃ to 220 ℃ at the heating rate of 5 ℃/min, and keeping the temperature at 220 ℃ for calcining for 1 h. And after the mixture is naturally cooled, putting the obtained solid powder into a beaker, adding about 30ml of ethanol, carrying out ultrasonic treatment for about 1 hour, centrifuging, taking supernatant, and drying to obtain the carbon dots.
Example 3: carbon dots for producing hydrogen peroxide by electrocatalysis
The preparation method comprises the following steps:
0.15g of citric acid, 0.3g of urea and 0.1g of calcium chloride are accurately weighed and added into 1ml of water to be fully dissolved. Placing the obtained solution in a porcelain boat, heating from room temperature to 120 ℃ at a heating rate of 5 ℃/min under vacuum, keeping the temperature at 120 ℃ for calcining for 0.5h, then heating from 120 ℃ to 250 ℃ at a heating rate of 5 ℃/min, and keeping the temperature at 250 ℃ for calcining for 1 h. And after the mixture is naturally cooled, putting the obtained solid powder into a beaker, adding about 30ml of ethanol, carrying out ultrasonic treatment for about 1 hour, centrifuging, taking supernatant, and drying to obtain the carbon dots.
Example 4: carbon dots for producing hydrogen peroxide by electrocatalysis
The preparation method comprises the following steps:
0.15g of citric acid, 0.3g of urea and 0.1g of calcium chloride are accurately weighed and added into 1ml of water to be fully dissolved. Putting the obtained solution into a porcelain boat, heating from room temperature to 120 ℃ at the heating rate of 5 ℃/min under vacuum, keeping the temperature at 120 ℃ for calcining for 0.5h, then heating from 120 ℃ to 280 ℃ at the heating rate of 5 ℃/min, and keeping the temperature at 280 ℃ for calcining for 1 h. And after the mixture is naturally cooled, putting the obtained solid powder into a beaker, adding about 30ml of ethanol, carrying out ultrasonic treatment for about 1 hour, centrifuging, taking supernatant, and drying to obtain the carbon dots.
Example 5: carbon dots for producing hydrogen peroxide by electrocatalysis
The preparation method comprises the following steps:
0.15g of citric acid, 0.3g of urea and 0.1g of calcium chloride are accurately weighed and added into 1ml of water to be fully dissolved. Placing the obtained solution in a porcelain boat, heating from room temperature to 120 ℃ at a heating rate of 5 ℃/min under vacuum, keeping the temperature at 120 ℃ for calcining for 0.5h, then heating from 120 ℃ to 310 ℃ at a heating rate of 5 ℃/min, and keeping the temperature at 310 ℃ for calcining for 1 h. And after the mixture is naturally cooled, putting the obtained solid powder into a beaker, adding about 30ml of ethanol, carrying out ultrasonic treatment for about 1 hour, centrifuging, taking supernatant, and drying to obtain the carbon dots.
Example 6: carbon dots for producing hydrogen peroxide by electrocatalysis
The preparation method comprises the following steps:
0.15g of citric acid, 0.3g of urea and 0.1g of calcium chloride are accurately weighed and added into 1ml of water to be fully dissolved. Placing the obtained solution in a porcelain boat, heating from room temperature to 120 ℃ at the heating rate of 5 ℃/min under vacuum, keeping the temperature at 120 ℃ for calcining for 0.5h, then heating from 120 ℃ to 250 ℃ at the heating rate of 5 ℃/min, and keeping the temperature at 250 ℃ for calcining for 0.5 h. And after the mixture is naturally cooled, putting the obtained solid powder into a beaker, adding about 30ml of ethanol, carrying out ultrasonic treatment for about 1 hour, centrifuging, taking supernatant, and drying to obtain the carbon dots.
Example 7: carbon dots for producing hydrogen peroxide by electrocatalysis
The preparation method comprises the following steps:
0.15g of citric acid, 0.3g of urea and 0.1g of calcium chloride are accurately weighed and added into 1ml of water to be fully dissolved. Placing the obtained solution in a porcelain boat, heating from room temperature to 120 ℃ at the heating rate of 5 ℃/min under vacuum, keeping the temperature at 120 ℃ for calcining for 0.5h, then heating from 120 ℃ to 250 ℃ at the heating rate of 5 ℃/min, keeping the temperature at 250 ℃ for calcining for 1.5 h. And after the mixture is naturally cooled, putting the obtained solid powder into a beaker, adding about 30ml of ethanol, carrying out ultrasonic treatment for about 1 hour, centrifuging, taking supernatant, and drying to obtain the carbon dots.
As can be seen from FIG. 1, the carbon dots prepared in example 3 have various sizes, and the size distribution thereof is from 5nm to 100 nm. FIG. 2 is an infrared image of the carbon dots obtained in example 3, and it can be seen that the surface groups thereof have carboxyl groups, hydroxyl groups, etc. FIG. 3 is an absorption spectrum of a carbon dot obtained in example 3. The electrocatalysis performance of the carbon dots prepared in examples 1-5 was verified respectively:
catalyst slurries were prepared using the carbon dots of examples 1-5 and commercial conductive carbon black XC-72R as catalysts, respectively: the carbon dots of examples 1-5, commercial conductive carbon black XC-72R4.0mg, 100 muL of dupont 5% nafion solution and 900 muL of absolute ethyl alcohol were taken respectively, and dispersed uniformly by ultrasonic treatment for 30min to obtain corresponding catalyst slurries prepared by the carbon dots of examples 1-5 and the commercial conductive carbon black XC-72.
The selectivity test of hydrogen peroxide employs Linear Sweep Voltammetry (LSV): 5 mul of catalyst slurry was coated onto a circular glassy carbon area of a rotating disk electrode and dried to form a working electrode. Using an electrochemical workstation as an electrochemical generating device to be coated with a catalystThe rotating ring disk electrode of the reagent is used as a working electrode, a platinum wire is used as a counter electrode, saturated calomel is used as a reference electrode, and the voltage E of the platinum ring endring=1.3 VRHE(voltage E at platinum Ring terminalringIs a parameter which must be set when a rotating ring disk electrode is used for testing, and the voltage set by a platinum ring is set according to the principle that the oxidation reaction can generate H2O2But is unable to oxidize H present in solution2O, thereby enabling H to be tested2O2Current of oxidation, reaction of production H2O2Selectivity of (ii). Using 0.1M KOH aqueous solution as electrolyte, and continuously introducing oxygen (oxygen flow 60 mL/min) into the electrolyte, wherein the selective oxygen reduction test voltage range is 0.0-1.0VRHEThe sweep rate was 10 mV/s. In the test process, the results of the hydrogen peroxide selectivity when the carbon dots of examples 1 to 5 were used as catalysts are shown in fig. 4. From the results of fig. 4 and 5, the results of selectivity and number of transferred electrons for the corresponding selective oxygen reduction at a specific voltage of 0.4V are summarized in table 2.
An H-shaped electrolytic cell device (for testing the yield of hydrogen peroxide) is adopted: mu.L of the catalyst slurry was coated on a size of 1X1cm2And drying the carbon cloth in an infrared drying lamp for 5min to obtain the corresponding working electrode (the carbon cloth electrode coated with the catalyst). An H-type electrolytic cell is used as a reactor, a cathode cell and an anode cell are separated by a proton exchange membrane, electrolyte of a cathode and electrolyte of an anode are 0.1M KOH solution, the catholyte is stirred at 1500r/min, the whole reaction is at room temperature, and 60mL/min of oxygen is continuously introduced into the cathode cell. The carbon cloth electrode prepared above is used as a working electrode and is placed in a cathode tank, a platinum sheet is used as a counter electrode and is placed in an anode tank, and saturated calomel is used as a reference electrode and is also placed in the cathode tank. The reaction is carried out to keep the voltage at-0.3VRHEThe reaction time is 3 h. During the reaction, the cathode reaction solution was sampled and analyzed, and during the test, the results of the concentrations of hydrogen peroxide in the cathode reaction solutions at different reaction times when the carbon dot materials of examples 1 to 5 and XC-72R were used as catalysts, respectively, are shown in fig. 6.
As can be seen from FIGS. 4-6: the carbon dots prepared in the embodiments 1-5 of the invention have good performance in hydrogen peroxide generated by electrocatalysis, the selection performance reaches 95.00%, the corresponding number of transfer electrons is 2.10, and the maximum hydrogen peroxide yield under the catalyst in the embodiment 3 is 75mg/L when the electrocatalysis is carried out for 3 hours.
From the above reaction results, it can be seen that the carbon dot material of the present invention has good performance in electrocatalytic hydrogen peroxide production, which may be due to: a large number of oxygen-containing functional groups on the surface of the carbon dots, such as carboxyl, hydroxyl and the like, play a role in promoting the formation of hydrogen peroxide.
TABLE 2 results of electrocatalytic hydrogen peroxide production by examples 1-7 and commercial conductive carbon blacks (XC-72R)
| The selectivity of hydrogen peroxide | Number n of transferred electrons | |
| Example 1 | 88.78 | 2.22 |
| Example 2 | 84.38 | 2.31 |
| Example 3 | 95.00 | 2.10 |
| Example 4 | 89.99 | 2.20 |
| Comparative example 5 | 87.03 | 2.26 |
| Comparative example 6 | 74.13 | 2.52 |
| Comparative example 7 | 80.52 | 2.39 |
| Commercial XC-72R | 77.15 | 2.46 |
Table 2 summarizes the selectivity of the catalysts and the commercial conductive carbon black (XC-72R) of examples 1 to 7 to hydrogen peroxide and the number of transferred electrons in the electrocatalytic oxygen reduction test results, and it can be seen from table 2 that the hydrogen peroxide selectivity of the carbon dots prepared in example 3 is the best, reaching 95.00%, and the number of transferred electrons is the smallest, only 2.10, which is very close to the theoretical number of transferred electrons 2. Comparing with commercial conductive carbon black (XC-72R) catalyst, the selectivity of hydrogen peroxide produced by XC-72R is 77.15% (under the condition of specific voltage of 0.4V), and the selectivity of carbon points prepared in example 4 and the like to hydrogen peroxide is far superior to that of commercial conductive carbon black. During the preparation of the catalyst, the pyrolysis temperature is increased (190)oC~310oC) The selectivity of hydrogen peroxide has a volcano-type trend, and the effect of hydrogen peroxide production can be weakened by too high or too low pyrolysis temperature. The time for keeping the synthetic carbon point at high temperature is changed, so that the effect of producing hydrogen peroxide is greatly influenced, and the optimal effect of producing hydrogen peroxide can be achieved when the high temperature is kept for 1 hour.
In conclusion, the calcination temperature of the carbon dot material is changed, the calcination time has great influence on the final electrocatalytic hydrogen peroxide production, an optimal experimental condition can be obtained by regulation, the cost is saved, the hydrogen peroxide selectivity is improved, and the industrial electrocatalytic hydrogen peroxide production technology can be realized.
Application example 1 (test catalyst life):
with the carbon dots of example 3 as catalyst, a catalyst slurry was prepared: the carbon dots of example 3 were taken 4.0mg, 100. mu.L of Dupont 5% nafion solution and 900. mu.L of absolute ethanol, and dispersed uniformly by sonication for 30min to obtain the corresponding catalyst slurry prepared using the carbon dots of example 3.
Life test of hydrogen peroxide (current i-time t): 5 mul of catalyst slurry was coated onto a circular glassy carbon area of a rotating disk electrode and dried to form a working electrode. An electrochemical workstation is adopted as an electrochemical generating device, a rotating ring disk electrode coated with a catalyst is used as a working electrode, a platinum wire is used as a counter electrode, saturated calomel is used as a reference electrode, and the voltage E of the platinum ring endring=1.3 VRHE. A0.1M KOH aqueous solution was used as an electrolyte, and oxygen gas was continuously introduced into the electrolyte (oxygen flow rate: 60 mL/min). The voltage is kept at 0.2V during the testRHEAnd (4) detecting the change of the current i of the electrochemical workstation along with the time t. The decrease in current i may reflect its instability and easy deactivation over a long period of time t-reaction. The results of the lifetime test (current i-time t) in the application of electrocatalytic hydrogen peroxide production are shown in fig. 7, and it can be seen from fig. 7 that: the carbon dots prepared in example 3 have good stability (the 60h life test shows that the carbon dots have almost no current attenuation), and have industrial application prospects.
The statements in this specification merely set forth a list of implementations of the inventive concept and the scope of the present invention should not be construed as limited to the particular forms set forth in the examples.
Claims (9)
1. A preparation method of carbon dots is characterized in that citric acid, urea and calcium chloride are used as precursors, and the carbon dots can be obtained through vacuum high-temperature calcination and subsequent purification.
2. The method for preparing carbon dots according to claim 1, which comprises the following steps:
1) citric acid, calcium chloride and urea are taken as precursors, and are dissolved in water and placed in a porcelain boat;
2) and (3) placing the porcelain boat with the precursor in a tube furnace, calcining at high temperature in vacuum, naturally cooling to room temperature after calcination, taking out a product in the porcelain boat, adding ethanol, performing ultrasonic treatment, centrifuging to obtain a supernatant, and performing rotary steaming and drying to obtain the carbon dots.
3. The method for preparing carbon dots according to claim 2, wherein the three precursors in the tube furnace in the step 2) are placed in a tube furnace, and the mass ratio of citric acid to urea to calcium chloride is 1.5: 3: 1.
4. the method for preparing carbon dots according to claim 2, wherein the high-temperature calcination in step 2) is carried out by: raising the temperature from room temperature to 120 ℃ at a temperature raising rate of 5 ℃/min, maintaining the temperature at 120 ℃ for 0.5h, raising the temperature from 120 ℃ to 190-310 ℃, preferably 250 ℃, at a temperature raising rate of 5 ℃/min, then keeping the temperature for 0.5-1.5 h, preferably 1h, and then naturally cooling.
5. A carbon dot produced by the method according to claims 1 to 4.
6. Use of a carbon dot according to claim 5 for the electrocatalytic production of hydrogen peroxide.
7. The application of the carbon dots in the preparation of hydrogen peroxide through electrocatalysis as claimed in claim 6, which is characterized in that an electrochemical workstation is used as an electrochemical generating device, a three-electrode measuring system is adopted, a carbon dot material is coated on carbon cloth to be used as a working electrode, a platinum wire is used as a counter electrode, saturated calomel is used as a reference electrode, KOH aqueous solution is used as electrolyte, and electrochemical oxygen reduction reaction is carried out to produce hydrogen peroxide.
8. The use of a carbon dot for the electrocatalytic production of hydrogen peroxide as claimed in claim 7, wherein the concentration of the aqueous KOH solution is 0.1 mol/L.
9. The use of carbon dots for the electrocatalytic production of hydrogen peroxide as claimed in claim 7, wherein said working electrode is produced by a method comprising: and adding the carbon dots into a mixed solution of the nation solution and absolute ethyl alcohol, uniformly dispersing by ultrasonic waves, uniformly dripping the dispersed solution on carbon cloth, and finally drying to obtain the corresponding working electrode.
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