Nitrogen-doped carbon dots modified carbon nitride and preparation method and application thereof

Abstract

The application discloses nitrogen-doped carbon dot modified carbon nitride and a preparation method and application thereof, and comprises the following steps: preparing carbon nitride material: firstly, a precursor is cracked by a high-temperature cracking method to prepare carbon nitride material, and the obtained carbon nitride material is washed by deionized water and ethanol; nitrogen-doped carbon dot modified carbon nitride: a carbon source and a passivation agent are dispersed by a solvent to obtain a first dispersion liquid, then the carbon nitride material is added into the first dispersion liquid to uniformly disperse a second dispersion liquid, the second dispersion liquid is synthesized by a hydrothermal-solvothermal method, finally, the nitrogen-doped carbon dot modified carbon nitride photocatalyst is obtained by washing, suction filtering and drying with a deionized water and ethanol solution. The method can utilize green and pollution-free solar energy as an energy source, can treat waste plastics, can produce green energy hydrogen gas, can produce high-value-added chemicals, and has good application prospect due to good catalyst performance and stability.

Description

A nitrogen-doped carbon dot modified carbon nitride, its preparation method and application Technical Field

[0001] This invention relates to the field of photoreforming technology, and in particular to a nitrogen-doped carbon dot modified carbon nitride, its preparation method, and its application. Background Technology

[0002] Plastics are widely used in our production and daily life due to their simple manufacturing process and low cost. However, the pollution caused by discarded plastics can seriously affect human life and health. Current methods for treating waste plastics mainly include incineration, landfill, mechanical treatment, thermal treatment, and photocatalysis. Photocatalysis technology can utilize renewable solar energy to produce clean energy while also generating high-value-added products, and it offers mild reaction conditions and high selectivity. Therefore, photocatalysis is a very promising method for treating waste plastics. There are four main strategies for treating waste plastics in photocatalysis: photodegradation, photoreforming, photothermal catalysis, and artificial photosynthesis. Among these, photoreforming has the advantage of selectivity, producing clean energy and high-value-added chemicals. Therefore, photoreforming is the most advantageous waste plastic conversion method in photocatalysis. However, the biggest challenge in photocatalytic waste plastic treatment is its low efficiency. Therefore, improving photocatalytic efficiency is crucial for the practical application of photoreforming in waste plastic treatment. The key research lies in the construction of highly efficient photocatalysts, expanding light absorption, promoting charge separation, and surface redox reactions.

[0003] In current photochemical reforming of waste plastics, photocatalysts play a crucial role. Current photocatalysts mainly include cadmium sulfide (CdS)-based photocatalysts and metal / MOF material-based photocatalysts. Professor Erwin Reisner's team first used CdS / CdO in 2018. x Quantum dots are used in the field of photo-reforming, and their performance in producing hydrogen through photo-reforming is also quite excellent. (Energy Environ. Sci. Plastic waste as a feedstock for solar-driven H2 generation. 2018, 11, 2853.). In 2021, Professor Morio Nagata's team in Japan constructed CdO. x The CdS / SiC photocatalytic system is used in the field of photo-reforming. (ACS Appl. Mater. Photoreforming of organic waste into hydrogen using a thermally radiative CdO) x / CdS / SiC photocatalyst interfaces 2021, 13, 47511-47519.). Professor Qiu Bocheng's team constructed a molybdenum disulfide-supported cadmium sulfide tip photocatalytic system in 2022, applying it to the field of photo-reforming. (ACS Catalysis, Trash totreasure: Pho-toreforming of plastic waste into commodity chemicals and hydrogen over MoS2-tipped CdS nanorods 2022, 12, 12823-12832.). Recently, Professor Qiao Shizhang's team constructed a defect-rich nickel thiophosphate (d-NiPS3) coupled CdS photocatalyst system (d-NiPS3 / CdS) using plasma technology in 2023. Applying it to the field of photo-reforming, its hydrogen production performance reached a new high, and the yield of high-value-added products per unit time was also quite excellent. (J. Am. Chem. Soc. Boosted photoreforming of plastic waste via defect-rich NiPS3 nanosheets 2023, 145, 6410.). In addition to the cadmium sulfide system, Professor Qiu Bocheng's team constructed a copper indium sulfide (CIS) photocatalytic system in 2023 and applied it to the field of photoreforming waste plastics. (Green Chemsitry. Upgrading polyethylene terephthalate plastic into commodity chemicals paired with hydrogen evolution over apartially oxidized CuIn5S8 nanosheet photocatalyst. 2023, 25, 9818-9825.).

[0004] In the previous field of photoreforming waste plastic conversion, the main photocatalysts used were still cadmium sulfide and its composite photocatalysts. Although their photoreforming performance was excellent, the serious toxicity and instability of cadmium sulfide-based photocatalysts hindered their use in the field of photoreforming. Meanwhile, composite photocatalysts based on MOF structures have a high content of metal elements, resulting in high application costs in the field of photoreforming, which also hinders their development.

[0005] Therefore, the search for and development of new matrix photocatalysts is of great significance. Among them, carbon nitride materials are widely used in the field of photoreforming due to their advantages such as a wide absorption range, ease of modification, extremely low cost, and high safety. In 2019, Professor Erwin Reisner constructed a carbon nitride / nickel phosphide photocatalyst system by combining carbon nitride materials with nickel phosphide (J. Am. Chem. Soc. Photoreforming of nonrecyclable plastic waste over a carbon nitride / nickel phosphide catalyst. 2019, 141, 15201.). In 2022, Professor Zheng Zhaoke constructed a photocatalytic system by connecting carbon nanotubes to carbon nitride and NiMo metal bridges (Applied Catalysis B: Environmental. Photoreforming of plastic waste poly(ethylene terephthalate) via in-situ derived CN-CNTs-NiMo hybrids. 2022, 307, 121143.). In 2022, Professor Huang Jianhua's team constructed Ni using carbon nitride as the substrate material. x Co 1-x The P / rGO / CN photocatalytic system is applied in the field of photo-reforming. (Chemosphere. Synergistic poly(lactic acid) photoreforming and H2 generation over ternary Ni x Co 1-x P / reduced graphene Oxide / g-C3N4composite 2022, 286, 131905.). However, the key scientific challenges facing the field of modified carbon nitride photoreforming for upgrading and recycling waste plastics are its low photocatalytic efficiency and poor selectivity. Summary of the Invention

[0006] The purpose of this invention is to provide a nitrogen-doped carbon dot modified carbon nitride, its preparation method, and its application. It can utilize green and pollution-free solar energy as an energy source, process waste plastics, and generate green energy hydrogen. It can also produce high-value-added chemicals, and has good catalyst performance and stability, showing great application prospects.

[0007] To achieve the above objectives, this invention provides a nitrogen-doped carbon dot modified carbon nitride, its preparation method, and its application, comprising the following steps:

[0008] S1. Preparation of carbon nitride materials: First, carbon nitride materials are prepared by high-temperature pyrolysis of the precursor. The obtained carbon nitride materials are washed with deionized water and ethanol.

[0009] S2, Nitrogen-doped carbon dot modified carbon nitride: The carbon source and passivator are dispersed in a solvent to obtain a first dispersion. Then, the carbon nitride material obtained in step S1 is added to the first dispersion and dispersed evenly to form a second dispersion. The second dispersion is synthesized using a hydrothermal-solvothermal method. Finally, the carbon nitride photocatalyst is obtained by washing, filtering and drying with deionized water and ethanol solution.

[0010] Preferably, in step S1, the precursor includes one or more of melamine, urea, dicyandiamide, and cyanamide.

[0011] Preferably, in step S1, the reaction conditions for high-temperature pyrolysis are: a temperature range of 400~600℃, a heating rate of 0.5~20℃ / min, and a heating time of 1~24h.

[0012] Preferably, in step S2, the carbon source includes one or more of o-phenylenediamine, lactose, fructose, glucose, citric acid, ascorbic acid, catechol, cellulose, biphenyl, glyceraldehyde, cyclodextrin, and levulinic acid.

[0013] Preferably, in step S2, the passivating agent includes one or more of ethylenediamine, triethylamine, pyridine, p-nitroaniline, pyrrolidine, urea, p-aminobenzaldehyde, p-aminoacesulfame, p-nitrophenol, ethyleneimine, and p-aminobenzonitrile.

[0014] Preferably, in step S2, the solvent includes one or more of the following: water, methanol, ethanol, isopropanol, diethyl ether, ethylene glycol, glycerol, n-pentanol, dimethyl sulfoxide, dimethylacetamide, acetone, dichloromethane, cyclohexane, cyclohexanol, n-hexane, benzyl alcohol, toluene, oleylamine, dioxane, benzene, and n-butanol.

[0015] Preferably, in step S2, the mass ratio of carbon nitride material: carbon source: passivating agent is 1000~1:50~1:1~50.

[0016] Preferably, in step S2, the reaction conditions for hydrothermal-solvothermal synthesis are: a temperature range of 100~240℃ and a holding time of 4~72h.

[0017] A method for preparing nitrogen-doped carbon dot modified carbon nitride yields a type of nitrogen-doped carbon dot modified carbon nitride.

[0018] Application of nitrogen-doped carbon dot modified carbon nitride in the photo-reforming process for upgrading and converting waste plastics.

[0019] Therefore, the present invention employs the above-mentioned nitrogen-doped carbon dot modified carbon nitride, its preparation method, and its application, and its technical effects are as follows:

[0020] (1) It was first applied to the upgrading and conversion of waste plastics through photo-reforming, and its highest hydrogen production performance reached 2.3 mmol / g. -1 h -1 Furthermore, its selectivity for organic acids can reach 100%, especially for high-value-added chemicals such as acetic acid, with a performance of up to 1.9 mmol / g. -1 d -1 .

[0021] (2) It can utilize green and pollution-free solar energy as an energy source, and can also process waste plastics. In addition, it generates green energy hydrogen and can produce high-value-added chemicals. The catalyst has good performance and stability and has a good application prospect.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 shows the TEM images of nitrogen-doped carbon dot modified carbon nitride materials; Figure 1(a) is the TEM image of nitrogen-doped carbon dot modified carbon nitride at 50 nm; Figure 1(b) is the TEM image of nitrogen-doped carbon dot modified carbon nitride at 10 nm; Figure 1(c) is the particle size distribution histogram of nitrogen-doped carbon dot modified carbon nitride in the TEM images.

[0024] Figure 2 shows the XRD pattern of nitrogen-doped carbon dot modified carbon nitride material;

[0025] Figure 3 shows the FTIR of nitrogen-doped carbon dot modified carbon nitride materials;

[0026] Figure 4 shows the EDS test results of nitrogen-doped carbon dot modified carbon nitride materials; Figure 4(a) is the HADDF image of nitrogen-doped carbon dot modified carbon nitride; Figure 4(b) shows the carbon element distribution in the HADDF image; Figure 4(c) shows the nitrogen element distribution in the HADDF image; Figure 4(d) shows the oxygen element distribution in the HADDF image; Figure 4(e) shows the sulfur element distribution in the HADDF image.

[0027] Figure 5 shows the photo-reforming performance characterization of nitrogen-doped carbon dot modified carbon nitride materials; Figure 5(a) shows the hydrogen production performance of nitrogen-doped carbon dot, carbon nitride, and nitrogen-doped carbon dot modified carbon nitride; Figure 5(b) shows the distribution of high-value-added products of nitrogen-doped carbon dot, carbon nitride, and nitrogen-doped carbon dot modified carbon nitride; Figure 5(c) shows the five-cycle stability test of nitrogen-doped carbon dot modified carbon nitride; Figure 5(d) shows the NMR spectra of high-value-added products of nitrogen-doped carbon dot modified carbon nitride; Figure 5(e) shows the NMR spectrum of formic acid, a high-value-added product of nitrogen-doped carbon dot modified carbon nitride; Figure 5(f) shows the NMR spectra of glycolic acid and acetic acid, high-value-added products of nitrogen-doped carbon dot modified carbon nitride. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0030] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0031] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0032] It should also be understood that the specific embodiments described above are only used to explain the present invention, and the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0033] Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0034] All prior art documents cited in this specification are incorporated herein by reference in their entirety and are therefore part of the disclosure of this invention.

[0035] Example 1

[0036] This invention provides a method for preparing nitrogen-doped carbon dot modified carbon nitride, comprising the following steps:

[0037] S1. Dicyandiamide was selected as the precursor and a high-temperature pyrolysis method was adopted. The preparation temperature was controlled at 450℃, the heating rate was maintained at 2.5℃ / min, the heating time was maintained at 12h, and the product was washed with deionized water to obtain CN-1.

[0038] S2. Using 2 mmol citric acid as the carbon source and 5 mmol ethylenediamine as the passivating agent, the catalyst was dispersed in 50 mL ethanol. 1 g CN-1 was added, and the mixture was heated to 220 °C and kept at this temperature for 24 h. The catalyst was then washed with deionized water and ethanol, and subsequently dried. This yielded the nitrogen-doped carbon dot-modified carbon nitride (R-CDs-CN-1) photocatalyst.

[0039] Example 2

[0040] This invention provides a method for preparing nitrogen-doped carbon dot modified carbon nitride, comprising the following steps:

[0041] S1. Melamine was selected as the precursor, and a high-temperature pyrolysis method was used. The preparation temperature was controlled at 500℃, the heating rate was maintained at 0.5℃ / min, and the heating time was maintained at 16h. The product was then washed with deionized water to obtain CN-2.

[0042] S2. Using 3 mmol of glucose as the carbon source and 10 mmol of diethylamine as the passivating agent, the catalyst was dispersed in 100 mL of methanol. 2 g of CN-2 was added, and the mixture was heated to 220 °C and kept at that temperature for 24 h. The catalyst was then washed with deionized water and ethanol, and subsequently dried. This yielded the nitrogen-doped carbon dot-modified carbon nitride (R-CDs-CN-2) photocatalyst.

[0043] Example 3

[0044] This invention provides a method for preparing nitrogen-doped carbon dot modified carbon nitride, comprising the following steps:

[0045] S1. Dicyandiamide was selected as the precursor, and a high-temperature pyrolysis method was used. The preparation temperature was controlled at 550℃, the heating rate was maintained at 1℃ / min, and the heating time was maintained at 2h. The product was then washed with deionized water to obtain CN-3.

[0046] S2. Using 2 mmol ascorbic acid as the carbon source and 10 mmol urea as the passivating agent, the catalyst was dispersed in 100 mL of N,N-dimethylformamide. 1 g of CN-3 was added, and the mixture was heated to 180 °C and maintained at this temperature for 24 h. The catalyst was then washed with deionized water and ethanol, followed by drying. This yielded the nitrogen-doped carbon dot-modified carbon nitride (R-CDs-CN-3) photocatalyst.

[0047] Example 4

[0048] This invention provides a method for preparing nitrogen-doped carbon dot modified carbon nitride, comprising the following steps:

[0049] S1. Urea was selected as the precursor, and a high-temperature pyrolysis method was used. The preparation temperature was controlled at 520℃, the heating rate was maintained at 10℃ / min, and the heating time was maintained at 4h. The product was then washed with deionized water to obtain CN-4.

[0050] S2. Using 1 mmol of glucose as the carbon source and 5 mmol of pyrrolidine as the passivating agent, the catalyst was dispersed in 100 mL of ethanol. 2 g of CN-4 was added, and the mixture was heated to 220 °C and kept at this temperature for 24 h. The catalyst was then washed with deionized water and ethanol, and subsequently dried. This yielded the nitrogen-doped carbon dot-modified carbon nitride (R-CDs-CN-4) photocatalyst.

[0051] Example 5

[0052] This invention provides a method for preparing nitrogen-doped carbon dot modified carbon nitride, comprising the following steps:

[0053] S1. Cyanamine was selected as the precursor, and a high-temperature pyrolysis method was used. The preparation temperature was controlled at 550℃, the heating rate was maintained at 5℃ / min, and the heating time was maintained at 8h. The product was then washed with deionized water to obtain CN-5.

[0054] S2. Using 1 mmol of glucose as the carbon source and 10 mmol of p-aminoacesulfame as the passivating agent, the catalyst was dispersed in 100 mL of ethanol. 2 g of CN-5 was added, and the mixture was heated to 220 °C and kept at that temperature for 24 h. The catalyst was then washed with deionized water and ethanol and dried. This yielded the nitrogen-doped carbon dot modified carbon nitride (R-CDs-CN-5) photocatalyst.

[0055] Example 6

[0056] This invention provides a method for preparing nitrogen-doped carbon dot modified carbon nitride, comprising the following steps:

[0057] S1. Melamine was selected as the precursor, and a high-temperature pyrolysis method was used. The preparation temperature was controlled at 550℃, the heating rate was maintained at 5℃ / min, and the heating time was maintained at 8h. The product was then washed with deionized water to obtain CN-6.

[0058] S2. Using 1 mmol glucose as the carbon source and 10 mmol ethyleneimine as the passivating agent, the catalyst was dispersed in 100 mL of ethanol. 2 g CN-6 was added, and the mixture was heated to 220 °C and maintained at this temperature for 24 h. The catalyst was then washed with deionized water and ethanol, and subsequently dried. This yielded the nitrogen-doped carbon dot-modified carbon nitride (R-CDs-CN-6) photocatalyst.

[0059] Application Example 1

[0060] The catalyst material R-CDs-CN-2 from Example 3 was applied to the photo-reforming of plastics, as detailed below:

[0061] S1. Polyethylene terephthalate (PET) treated with NaOH is hydrolyzed and then centrifuged to obtain its supernatant.

[0062] S2. Then, take 80 mg of R-CDs-CN-3 and add 1.8% Pt co-catalyst. Simultaneously, use full-spectrum light with an intensity of 400 mW / cm². -2 .

[0063] S3, through testing with a 6A Labsolar and GC combination, yielded a hydrogen production performance of 1.8 mmol / g. -1 h -1 Quantitative analysis by proton nuclear magnetic resonance spectroscopy revealed that 0.99 mmol / L of acetic acid, 0.88 mmol / L of glycolic acid, and 1.2 mmol / L of formic acid were produced after 24 hours of photo-reforming.

[0064] Application Example 2

[0065] The catalyst material R-CDs-CN-6 from Example 5 was applied to the photo-reforming of plastics, as detailed below:

[0066] S1. Polyethylene terephthalate (PET) treated with NaOH is hydrolyzed and then centrifuged to obtain its supernatant.

[0067] S2. Then take 50 mg of R-CDs-CN-5 and add 0.2% Pt co-catalyst. Simultaneously, use an AM1.5G filter with a light intensity of 500 mW / cm². -2 .

[0068] S3, through testing using a 6A Labsolar and GC combination, yielded a hydrogen production performance of 2.10 mmol / g. -1 h -1 Quantitative analysis by proton nuclear magnetic resonance spectroscopy revealed that 0.68 mmol / L of acetic acid, 0.92 mmol / L of glycolic acid, and 0.92 mmol / L of formic acid were produced after 24 hours of photo-reforming.

[0069] Figure 1 shows TEM characterization, demonstrating that carbon dots are uniformly distributed within the carbon nitride catalyst. Figure 2 shows XRD, and Figure 3 shows FTIR, confirming that the obtained carbon dot-modified carbon nitride photocatalyst retains its basic carbon nitride structure intact. Figure 4 shows HADFF and mapping tests, indicating that the composite photocatalyst contains carbon, nitrogen, and oxygen. These data fully demonstrate that this invention successfully prepared a nitrogen-doped carbon dot-modified carbon nitride photocatalyst. Figure 5 shows the photoreforming performance characterization of the nitrogen-doped carbon dot-modified carbon nitride material.

[0070] Therefore, this invention employs the above-mentioned nitrogen-doped carbon dot modified carbon nitride, its preparation method, and its application to improve its photocatalytic performance, and applies it to the photo-reforming treatment of plastic waste for upgrading and conversion, generating green energy hydrogen while obtaining high-value-added chemicals.

[0071] 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. The application of nitrogen-doped carbon dot modified carbon nitride in the photo-reforming treatment of waste plastics for upgrading and conversion, characterized in that, Includes the following steps: S1. Preparation of carbon nitride material: First, carbon nitride material is prepared from the precursor by high-temperature pyrolysis. The obtained carbon nitride material is washed with deionized water and ethanol. S2. Nitrogen-doped carbon dot modified carbon nitride: The carbon source and passivator are dispersed in a solvent to obtain a first dispersion. Then, the carbon nitride material obtained in step S1 is added to the first dispersion and dispersed evenly to obtain a second dispersion. The second dispersion is synthesized by hydrothermal or solvothermal method. Finally, the carbon nitride photocatalyst is obtained by washing with deionized water and ethanol solution, filtration, and drying. In step S1, the precursor includes one or more of melamine, urea, dicyandiamide, and cyanamide; in step S1, the high-temperature pyrolysis reaction conditions are: a temperature range of 400~600℃, a heating rate of 0.5~20℃ / min, and a heating time of 1~24h; in step S2, the carbon source includes one or more of o-phenylenediamine, lactose, fructose, glucose, citric acid, ascorbic acid, catechol, cellulose, biphenyl, glyceraldehyde, cyclodextrin, and levulinic acid; in step... In step S2, the passivating agent includes one or more of the following: ethylenediamine, triethylamine, pyridine, p-nitroaniline, pyrrolidine, urea, p-aminobenzaldehyde, p-aminoacesulfame, p-nitrophenol, ethyleneimine, and p-aminobenzonitrile; in step S2, the mass ratio of carbon nitride material: carbon source: passivating agent is (1000~1):(50~1):(1~50); in step S2, the reaction conditions for hydrothermal or solvothermal synthesis are: temperature range of 100~240℃, and holding time of 4~72h.

2. The application of nitrogen-doped carbon dot modified carbon nitride according to claim 1 in the photo-reforming treatment of waste plastics for upgrading and conversion, characterized in that, In step S2, the solvent includes one or more of the following: water, methanol, ethanol, isopropanol, diethyl ether, ethylene glycol, glycerol, n-pentanol, dimethyl sulfoxide, dimethylacetamide, acetone, dichloromethane, cyclohexane, cyclohexanol, n-hexane, benzyl alcohol, toluene, oleylamine, dioxane, benzene, and n-butanol.

Images