Preparation method of carbon dot / silicon carbide composite material as well as product and application of carbon dot / silicon carbide composite material

Abstract

The invention discloses a preparation method of a carbon dot / silicon carbide composite material as well as a product and application thereof, and the preparation method comprises the following steps: (1) taking coal pitch as a raw material, mixing with an oxidizing agent, carrying out oxidation reaction, and then carrying out post-treatment to obtain carbon dots; and (2) mixing the carbon dots and silicon carbide prepared in the step (1) with deionized water, and performing hydrothermal reaction to obtain the carbon dot / silicon carbide composite material. The prepared composite material can improve the light absorption capacity and the photo-generated carrier generation capacity, and the hydrogen peroxide generation rate can be remarkably increased when the composite material is applied to the photocatalytic hydrogen peroxide generation reaction as a catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and in particular to a method for preparing a carbon dot / silicon carbide composite material, a product thereof, and an application of the carbon dot / silicon carbide composite material in photocatalytic preparation of hydrogen peroxide. Background Art

[0002] Hydrogen peroxide (H 2 O 2 ) is not only an environmentally friendly oxidant, but also a liquid fuel, and is considered to be a promising alternative to solve environmental pollution and energy shortage problems. 2 O 2 The main preparation method is the anthraquinone method, but this method is complex and energy-intensive. Photocatalytic technology can use solar energy to drive water and oxygen to produce H under mild conditions. 2 O 2 , the key is to develop efficient photocatalysts.

[0003] Photocatalytic production of H 2 O 2 Commonly used catalysts include TiO 2 Photocatalyst, gC 3 N 4 Although many breakthroughs have been made in material modification, the photocatalytic system itself has its own defects, such as low solar energy utilization, recombination of photogenerated electrons and holes, and photocatalytic preparation of H 2 O 2 And its catalysts still need further research. Silicon carbide is an inorganic semiconductor, known as the next generation of semiconductor materials, with high thermal conductivity, strong thermal stability, good electrical and thermal conductivity, anti-oxidation and corrosion resistance and other properties, can adapt to a variety of complex and harsh environments. In addition. The band gap width of silicon carbide is about 2.4eV, which can utilize a wider range of sunlight and can be used for photocatalytic reactions. At present, carbon dot composite materials with silicon carbide as the carrier have not been reported. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention discloses a method for preparing a carbon dot / silicon carbide composite material. The prepared composite material can improve the ability to absorb light and generate photogenerated carriers. When used as a catalyst in a photocatalytic hydrogen peroxide production reaction, the production rate of hydrogen peroxide can be significantly increased.

[0005] The specific technical solutions are as follows:

[0006] A method for preparing a carbon dot / silicon carbide composite material comprises the following steps:

[0007] (1) Coal tar pitch is used as a raw material, mixed with an oxidant, subjected to an oxidation reaction, and then post-treated to prepare carbon dots;

[0008] (2) The carbon dots and silicon carbide prepared in step (1) are mixed with deionized water, and a carbon dot / silicon carbide composite material is obtained after a hydrothermal reaction.

[0009] In step (1):

[0010] The oxidizing agent is selected from formic acid or a mixture of formic acid and hydrogen peroxide.

[0011] Preferably, the oxidant is selected from a mixture of formic acid and hydrogen peroxide; further preferably, the volume ratio of formic acid to hydrogen peroxide is (5-20):1.

[0012] Preferably, in step (1):

[0013] The mass volume ratio of coal tar pitch to oxidant is (200-600): 33 g / mL;

[0014] More preferably, the mass volume ratio is (200-400):33 g / mL.

[0015] The experiment found that the amount of the two had some influence on the photocatalytic performance of the finally prepared carbon dot / silicon carbide composite material.

[0016] In step (2):

[0017] The mass ratio of the carbon dots to silicon carbide is 1:(1.5-20);

[0018] In the deionized water, the concentration of carbon dots is 0.2-1.6 g / L.

[0019] The temperature of the hydrothermal reaction is 150-200°C and the time is 3-8h; the preferred hydrothermal reaction temperature is 180°C.

[0020] The invention also discloses a carbon dot / silicon carbide composite material prepared according to the method.

[0021] The present invention also discloses a method for preparing hydrogen peroxide by photocatalysis, using the carbon dot / silicon carbide composite material as a photocatalyst, specifically comprising:

[0022] Photocatalyst and solvent were added to the reactor to form a suspension. After adsorption equilibrium, the suspension was irradiated with light under stirring conditions to prepare H 2 O 2 .

[0023] To ensure that the adsorption reaches equilibrium, it is preferably stirred for a period of time in dark conditions, such as 30 minutes.

[0024] The solvent is selected from water, or a mixed solvent consisting of water and isopropanol;

[0025] Preferred:

[0026] When the solvent is selected from a mixed solvent, the isopropanol accounts for 5 to 50 vol%, and more preferably 10 to 50 vol%.

[0027] Preferred:

[0028] In the suspension, the mass proportion of the photocatalyst is 0.1 to 1.0 g / L;

[0029] In the photocatalyst, the carbon dots account for 10 to 40 wt %; preferably, 20 to 40 wt %; more preferably, 30 to 40 wt %; and more preferably, 30 wt %.

[0030] Experiments have shown that as the proportion of the above-mentioned carbon dots is continuously optimized, the rate of photocatalytic production of hydrogen peroxide increases significantly.

[0031] Preferred:

[0032] The light is selected from 420-780nm visible light;

[0033] Light intensity is 100~1000mW / cm 2 .

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention uses coal tar pitch as a raw material to synthesize CDs, and adopts a hydrothermal method to prepare a SiC and CDs composite material as a photocatalyst. The preparation method is simple, the labor cost is low, and the product purity is high. A new composite material is prepared to help clean and efficient use of coal tar pitch;

[0036] (2) In the carbon dot / silicon carbide composite material prepared by the present invention, the CDs and SiC interface interact with each other, promoting the separation of photogenerated electrons and holes, so that the photocatalytic reaction can be carried out under mild conditions;

[0037] (3) The carbon dots / silicon carbide composite material prepared by the present invention is applied to photocatalytic H production 2 O 2 The reaction can be carried out efficiently under visible light irradiation at room temperature. The entire reaction process is green, efficient, and the reaction conditions are very mild. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The transient photocurrent response of the carbon dot / silicon carbide composite material prepared in Example 4, and a single silicon carbide sample is given as a comparison;

[0039] Figure 2The electrochemical impedance spectroscopy (EIS) of the carbon dot / silicon carbide composite material prepared in Example 4 is shown, and a single silicon carbide sample is given as a comparison. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0041] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0042] Example 1

[0043] (1) Mix 200 mg coal tar, 30 mL formic acid and 3 mL 30% hydrogen peroxide solution, ultrasonically shake for 3 minutes, and magnetically stir for 20 hours; then centrifuge at a speed of 10,000 rpm for 25 minutes. Rotate the supernatant at 80°C and 40 r / min, cool to room temperature, pour a small amount of anhydrous ethanol into it, and pour it into a culture dish after all the solids are dissolved in ethanol, wash and dry it to obtain coal tar CDs;

[0044] (2) 190 mg SiC was weighed and dispersed in 50 mL deionized water, 10 mg CDs was added and ultrasonicated for 0.5 h, hydrothermally reacted at 180 °C for 4 h, then centrifuged, washed with deionized water for multiple times, and dried at 60 °C to obtain a carbon dot / silicon carbide composite material with a CDs mass fraction of 5%.

[0045] (3) Weigh 5 mg of the carbon dot / silicon carbide composite material prepared above and place it in 50 mL of an aqueous solution containing 10 vol% isopropanol. Stir for 30 min in the dark. Then, under stirring, use 100 mW / cm 2 The suspension was irradiated with visible light and the reaction time was 1 h.

[0046] The iodine ion calibration method was used to determine H 2 O 2 Solubility, tested by UV-Vis spectrophotometer, in this embodiment H 2 O 2 The production rate is 353 μmol·g -1 ·h -1 .

[0047] Example 2

[0048] The preparation process is basically the same as that of Example 1, except that in step (2):

[0049] The mass of silicon carbide added was replaced with 180 mg, and the mass of CDs was replaced with 20 mg, to prepare a carbon dot / silicon carbide composite material with a CDs mass fraction of 10%.

[0050] After testing, H 2 O 2 The production rate is 710 μmol·g -1 ·h -1 .

[0051] Example 3

[0052] The preparation process is basically the same as that of Example 1, except that in step (2):

[0053] The mass of silicon carbide added was replaced with 160 mg, and the mass of CDs was replaced with 40 mg, to prepare a carbon dot / silicon carbide composite material with a CDs mass fraction of 20%.

[0054] After testing, H 2 O 2 The production rate is 1645 μmol·g -1 ·h -1 .

[0055] Example 4

[0056] The preparation process is basically the same as that of Example 1, except that in step (2):

[0057] The mass of silicon carbide added was replaced with 140 mg, and the mass of CDs was replaced with 60 mg to prepare a carbon dot / silicon carbide composite material with a CDs mass fraction of 30%.

[0058] Figure 1 The transient photocurrent response of the carbon dot / silicon carbide composite material prepared in this embodiment is shown, and a separate silicon carbide sample is given as a comparison. When tested under the same conditions, it can be seen that the photocurrent intensity of the composite material is significantly higher than that of the pure silicon carbide sample, indicating that the composite material has better photogenerated electron and hole separation efficiency.

[0059] Figure 2 The electrochemical impedance spectrum (EIS) of the carbon dot / silicon carbide composite material prepared in this embodiment is shown, and a separate silicon carbide sample is given for comparison. It can be seen from the EIS Nyquist plot that the arc radius of the composite material is smaller than that of pure silicon carbide, indicating that it has a lower charge transfer resistance, which can lead to a faster charge transfer rate, thereby accelerating the separation and migration of photogenerated carriers and promoting the photocatalytic hydrogen peroxide production reaction.

[0060] After testing, H 2 O 2 The production rate is 2980 μmol·g-1 ·h -1 .

[0061] Example 5

[0062] The preparation process is basically the same as that of Example 1, except that in step (2):

[0063] The mass of silicon carbide added was replaced with 120 mg, and the mass of CDs was replaced with 80 mg, to prepare a carbon dot / silicon carbide composite material with a CDs mass fraction of 40%.

[0064] After testing, H 2 O 2 The production rate is 2350 μmol·g -1 ·h -1 .

[0065] Example 6

[0066] The preparation process is basically the same as that of Example 4, except that in step (3):

[0067] The solvent was replaced with 50 mL of deionized water.

[0068] After testing, H 2 O 2 The production rate is 1570 μmol·g -1 ·h -1 .

[0069] Example 7

[0070] The preparation process is basically the same as that of Example 4, except that in step (3):

[0071] The isopropanol content in 50 mL of the isopropanol-containing aqueous solution was replaced to 50 vol%.

[0072] After testing, H 2 O 2 The production rate is 2140 μmol·g -1 ·h -1 .

[0073] Example 8

[0074] The preparation process is basically the same as that of Example 4, except that in step (3):

[0075] Replace the visible light intensity with 200mW / cm 2 .

[0076] After testing, H 2 O 2 The production rate is 6350 μmol·g-1 ·h -1 .

[0077] Example 9

[0078] The preparation process is basically the same as that of Example 4, except that in step (1):

[0079] The added coal tar pitch was replaced with 400 mg.

[0080] After testing, H 2 O 2 The production rate is 2870 μmol·g -1 ·h -1 .

[0081] Comparative Example 1

[0082] The preparation process is basically the same as that of Example 4, except that in step (1):

[0083] The added coal tar pitch was replaced with 100 mg.

[0084] After testing, H 2 O 2 The production rate is 520 μmol·g -1 ·h -1 .

[0085] Comparative Example 2

[0086] The preparation process is basically the same as that of Example 4, except that in step (2):

[0087] The added silicon carbide and CDs are blended and fully ground to obtain a composite material.

[0088] After testing, H 2 O 2 The production rate is 1145 μmol·g -1 ·h -1 .

[0089] Comparative Example 3

[0090] Weigh 5 mg of pure silicon carbide and place it in 50 mL of an aqueous solution containing 10 vol% isopropanol. Stir for 30 min in the dark. Then, under stirring, use 100 mW / cm 2 The suspension was irradiated with visible light and the reaction time was 1 h.

[0091] After testing, H 2 O 2 The production rate is 220 μmol·g -1 ·h -1 .

[0092] The above-mentioned embodiments are preferred embodiments, but the protection scope of the present invention is not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above-mentioned embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a carbon dot / silicon carbide composite material, characterized in that: The steps include: (1) Coal tar pitch is used as a raw material, mixed with an oxidant, subjected to an oxidation reaction, and then post-treated to prepare carbon dots; (2) The carbon dots and silicon carbide prepared in step (1) are mixed with deionized water, and a carbon dot / silicon carbide composite material is obtained after a hydrothermal reaction.

2. The method for preparing the carbon dot / silicon carbide composite material according to claim 1, characterized in that: In step (1): The oxidizing agent is selected from formic acid or a mixture of formic acid and hydrogen peroxide.

3. The method for preparing the carbon dot / silicon carbide composite material according to claim 1, characterized in that: In step (1): The mass volume ratio of coal tar pitch to oxidant is (200-600): 33 g / mL.

4. The method for preparing the carbon dot / silicon carbide composite material according to claim 1, characterized in that: In step (2): The mass ratio of the carbon dots to silicon carbide is 1:(1.5-20); In the deionized water, the concentration of carbon dots is 0.2-1.6 g / L.

5. The method for preparing the carbon dot / silicon carbide composite material according to claim 1, characterized in that: In step (2), the temperature of the hydrothermal reaction is 150-200° C. and the time is 3-8 hours.

6. A carbon dot / silicon carbide composite material prepared by the method according to any one of claims 1 to 5.

7. A method for preparing hydrogen peroxide by photocatalysis, characterized in that: The carbon dot / silicon carbide composite material according to claim 6 is used as a photocatalyst, specifically comprising: A photocatalyst and a solvent are added into a reactor to form a suspension. After adsorption equilibrium has been reached, the suspension is irradiated with light under stirring conditions to prepare H2O2.

8. The method for preparing hydrogen peroxide by photocatalysis according to claim 7, characterized in that: The solvent is selected from water, or a mixed solvent consisting of water and isopropanol; When the solvent is selected from a mixed solvent, the isopropanol accounts for 5 to 50 vol%.

9. The method for preparing hydrogen peroxide by photocatalysis according to claim 8, characterized in that: In the suspension, the mass proportion of the photocatalyst is 0.1 to 1.0 g / L; In the photocatalyst, the carbon dots account for 10 to 40 wt %.

10. The method for preparing hydrogen peroxide by photocatalysis according to claim 8, characterized in that: The light is selected from 420-780nm visible light; Light intensity is 100~1000mW / cm 2 .

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