Yttrium monatomic in-situ co-doped carbon nitride as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalyst preparation, and relates to yttrium monatomic in-situ co-doped carbon nitride as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, preparing an yttrium-containing carbon nitride precursor from melamine, cyanuric acid, an organic carbon source and yttrium nitrate hexahydrate as raw materials by adopting a precipitation method; s2, performing thermal polymerization reaction on the yttrium-containing carbon nitride precursor under an inert gas condition to obtain a crude product; and S3, ultrasonically dispersing the crude product in a nitric acid solution for etching, and then washing and drying to obtain the yttrium monatomic in-situ co-doped carbon nitride Y-C-C3N4. The yttrium monatomic in-situ co-doped carbon nitride prepared by the method has high catalytic activity and high stability, and the photocatalytic reduction capacity of carbon dioxide is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and relates to yttrium single-atom in-situ co-doped carbon nitride, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, the photothermal catalytic CO2 conversion technology has received extensive attention due to its mild reaction conditions and environmental friendliness. Photocatalysis uses light energy to excite a catalyst, enabling carbon dioxide to undergo a reduction reaction on the surface of the catalyst to generate organic substances such as methane and carbon monoxide. Common photocatalysts include homogeneous catalysts and heterogeneous catalysts, such as titanium dioxide (TiO2), doped graphitic carbon nitride (g-C3N4), etc. However, the conversion rate of these photocatalysts for CO2 is not high, so it is necessary to search for new catalysts.

[0003] Single-atom catalysts (SACs) have the advantages of high atomic utilization rate, high reaction activity, low material cost, recyclability, and stronger stability, and are applied in more and more photothermal catalysis. More importantly, single-atom catalysts have a unique electronic structure and unsaturated coordination sites, endowing them with excellent catalytic activity and selectivity.

[0004] In recent years, the research on rare-earth single atoms by researchers has increased. Among them, rare-earth elements on different carriers usually can exhibit different catalytic properties. For example, Wang Guofeng found through research that by combining the characteristics of rare-earth single atoms and the advantages of heterojunctions, a rare-earth single-atom composite photocatalyst was prepared. Specifically, using Er atoms to bridge g-C3N4 and Zn2GeO4 provided an efficient electron transfer path and active sites, thereby promoting carrier separation and CO2 activation. This indicates that not only traditional transition metals can serve as active sites to promote the progress of photocatalytic CO2 reduction, but rare earths also have the potential to photocatalytically convert CO2 into chemicals. Summary of the Invention

[0005] Aiming at the technical problems in the prior art that g-C3N4 lacks effective active sites as a photocatalyst and the separation efficiency of photo-generated carriers is insufficient, etc., the present invention proposes yttrium single-atom in-situ co-doped carbon nitride, a preparation method thereof, and an application thereof.

[0006] The present invention first prepares a yttrium-containing carbon nitride precursor, and then uses thermal polymerization and nitric acid etching to prepare yttrium single-atom in-situ co-doped carbon nitride, which has high catalytic activity and high stability, and improves the ability of photocatalytic reduction of carbon dioxide.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A preparation method of yttrium single-atom in-situ co-doped carbon nitride, comprising the following steps:

[0009] S1. Preparation of yttrium-containing carbon nitride precursor

[0010] Using the precipitation method, a yttrium-containing carbon nitride precursor is prepared from melamine, cyanuric acid, barbituric acid and yttrium nitrate hexahydrate as raw materials;

[0011] S2. Thermal polymerization

[0012] The above-mentioned yttrium-containing carbon nitride precursor is subjected to a thermal polymerization reaction under an inert gas condition to obtain a crude product;

[0013] S3. Nitric acid etching

[0014] The crude product is ultrasonically dispersed in a nitric acid solution for etching, and then washed and dried to obtain yttrium single-atom in-situ co-doped carbon nitride Y-C-C3N4. In the Y-C-C3N4, the doping amount of C is 10wt% - 30wt%, and the doping amount of Y is 1wt% - 7wt%.

[0015] Further defined, the specific process of preparing the yttrium-containing carbon nitride precursor in step S1 is as follows:

[0016] S1.1. Melamine, cyanuric acid and barbituric acid are respectively dissolved in water, heated to 75°C - 80°C and ultrasonically treated to obtain a melamine solution, a cyanuric acid solution and a barbituric acid solution;

[0017] S1.2. Yttrium nitrate hexahydrate is added to the melamine solution; then the cyanuric acid solution and the barbituric acid solution are added to form a white precipitate; the white precipitate is centrifuged, washed and dried to obtain the yttrium-containing carbon nitride precursor.

[0018] Further defined, in step S2, the conditions of the thermal polymerization reaction are: the heating rate is 2.5°C / min - 5°C / min, the temperature is 540°C - 560°C, and the reaction time is 4h - 4.5h.

[0019] Further defined, in step S3, the concentration of the nitric acid solution is 0.5mol / L - 1mol / L, and the etching time is 20min - 60min.

[0020] Yttrium single-atom in-situ co-doped carbon nitride prepared by the method for preparing yttrium single-atom in-situ co-doped carbon nitride.

[0021] Application of the yttrium single-atom in-situ co-doped carbon nitride as a photocatalyst in photothermal carbon dioxide reduction.

[0022] Further defined, when the photocatalyst performs photothermal catalytic reduction on carbon dioxide, the highest yield of methane reaches 97.37μmol·g -1 ·h -1 , and the selectivity is as high as 93.69%.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The present invention first prepares a yttrium-containing carbon nitride precursor, and then uses thermal polymerization and nitric acid etching to prepare yttrium single-atom in-situ co-doped carbon nitride, which has high catalytic activity and high stability, and improves the ability of photocatalytic reduction of carbon dioxide.

[0025] 2. The yttrium single-atom in-situ co-doped carbon nitride prepared by the present invention has strong stability, ensures the isolated existence of yttrium atoms during pyrolysis, and is easy to recycle and reuse.

[0026] 3. The present invention adopts a method combining precipitation method, thermal polymerization and nitric acid etching to prepare the target product. The synthesis process is simple and reasonable, suitable for large-scale industrial production, with low preparation cost; and the raw materials are non-toxic and harmless, and the catalyst is more environmentally friendly.

[0027] 4. When the yttrium single-atom in-situ co-doped carbon nitride prepared by the present invention is used as a photocatalyst for the photothermal catalytic reduction of carbon dioxide, the yield of methane reaches up to 97.37 μmol·g -1 ·h -1 , and the selectivity reaches 93.69%. It can be seen that the yttrium single-atom in-situ co-doped carbon nitride has good selectivity for carbon dioxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the XRD pattern of g-C3N4 catalysts with different yttrium single-atom doping amounts;

[0029] Figure 2 is the XRD pattern of g-C3N4 catalysts with different yttrium single-atom and carbon doping amounts;

[0030] Figure 3 are the scanning and transmission electron microscope images of the 7% Y-C3N4 catalyst;

[0031] Figure 4 is for the scanning and transmission electron microscope images of the 7% Y-C 0.3 -C3N4 catalyst;

[0032] Figure 5 is the photoluminescence spectrum of the catalyst under different Y doping amounts;

[0033] Figure 6 is the photoluminescence spectrum of the catalyst under different doping elements;

[0034] Figure 7 is the comparison result of the photocatalytic CO2 reduction activity of different test samples;

[0035] Figure 8Comparison of photocatalytic CO2 reduction activities of test samples under different treatment steps. Detailed implementation mode

[0036] The technical solution of the present invention will be further described in combination with the embodiments, but the present invention is not limited to the following implementation cases.

[0037] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those with ordinary skills in the field to which the present invention belongs.

[0038] For technologies, methods and equipment known to those of ordinary skill in the relevant field, they may not be discussed in detail, but in appropriate cases, the said technologies, methods and equipment should be regarded as part of the specification.

[0039] It should also be understood that the above-mentioned specific embodiments are only used to explain the present invention, and the protection scope of the present invention is not limited thereto. Any person skilled in the technical field, within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention / invention.

[0040] The present invention provides a preparation method of yttrium single-atom in-situ co-doped carbon nitride, including the following steps:

[0041] S1. Prepare a yttrium-containing carbon nitride precursor

[0042] Using the precipitation method, a yttrium-containing carbon nitride precursor is prepared with melamine, cyanuric acid, barbituric acid and yttrium nitrate hexahydrate as raw materials.

[0043] The specific process of preparing the yttrium-containing carbon nitride precursor in step S1 of the present invention is as follows:

[0044] S1.1. Dissolve melamine, cyanuric acid and barbituric acid in water respectively, heat them to 75°C - 80°C and perform ultrasonic treatment to obtain a melamine solution, a cyanuric acid solution and a barbituric acid solution respectively;

[0045] S1.2. Add yttrium nitrate hexahydrate to the melamine solution; then add the cyanuric acid solution and the barbituric acid solution to form a white precipitate; centrifuge to obtain the white precipitate, and obtain the yttrium-containing carbon nitride precursor after washing and drying.

[0046] S2. Thermal polymerization

[0047] Perform a thermal polymerization reaction on the above-mentioned yttrium-containing carbon nitride precursor under an inert gas condition to obtain a crude product; the conditions of the thermal polymerization reaction are: the heating rate is 2.5°C / min - 5°C / min, the temperature is 540°C - 560°C, and the reaction time is 4h - 4.5h.

[0048] S3. Nitric acid etching

[0049] The crude product is ultrasonically dispersed in a nitric acid solution for etching, and then yttrium single-atom in-situ co-doped carbon nitride Y-C-C3N4 is obtained through washing and drying.

[0050] In Y-C-C3N4, the doping amount of C is 10wt% - 30wt%, and the doping amount of Y is 1wt% - 7wt%.

[0051] The concentration of the nitric acid solution is 0.5mol / L - 1mol / L (denoted as 0.5M - 1M), and the etching time is 20min - 60min.

[0052] The yttrium single-atom in-situ co-doped carbon nitride prepared by the preparation method of yttrium single-atom in-situ co-doped carbon nitride of the present invention. In its XRD pattern, the diffraction peak intensity decreases significantly.

[0053] The application of the yttrium single-atom in-situ co-doped carbon nitride prepared above as a photocatalyst in the photo-thermal reduction of carbon dioxide has high catalytic activity and high stability, can improve the yield of carbon dioxide to methane, and is easy to recycle.

[0054] In the technical solution adopted by the present invention, barbituric acid, cyanuric acid, and melamine are selected as the raw materials for carbon nitride g-C3N4 because the structures of barbituric acid and cyanuric acid are very similar and both can react with melamine; at the same time, only one N in barbituric acid is replaced by C, so it can be used as a material for adjusting the doping of carbon elements. The introduction of carbon elements can not only enhance the absorption of visible light but also increase the specific surface area and form a large delocalized π bond. Further, yttrium is added as a single atom to carbon nitride. Since yttrium is one of the three rare earth elements including lanthanum and scandium that do not have 4f orbitals, its influence on the electronic structure of carbon nitride is relatively easy; in addition, due to the oxygen affinity of yttrium metal, it has a strong adsorption ability for the O atom in CO2 and has potential CO2 activation ability. Loading the yttrium single atom on the carbon element-doped carbon nitride not only has a simple preparation method but also the components act synergistically, making the formed yttrium single-atom in-situ co-doped carbon nitride have good photo-thermal catalytic activity.

[0055] The above technical solutions of the present invention will be described in detail below through several preferred embodiments.

[0056] It should be noted that unless otherwise specified, the chemical reagents, drugs, etc. used in the following embodiments are all existing known products purchased from the market.

[0057] It should be noted that unless otherwise specified, the operations used in the following embodiments are all conventional operations in the art. For example, if the temperature and pressure are not specified, they are all normal temperature and pressure.

[0058] Example 1

[0059] The preparation method of yttrium single-atom in-situ co-doped carbon nitride provided in this example includes the following steps:

[0060] S1. Prepare a yttrium-containing carbon nitride precursor

[0061] Using the precipitation method, a yttrium-containing carbon nitride precursor is prepared from melamine, cyanuric acid, an organic carbon source, and yttrium nitrate hexahydrate as raw materials.

[0062] S1.1. Add melamine (1.193 g, 9.46 mmol), cyanuric acid (0.855 g, 6.62 mmol), and barbituric acid (0.363 g, 2.84 mmol) to 45, 38.5, and 16.5 mL of deionized water respectively, and heat the three groups of substances to 75 °C and ultrasonically dissolve them to obtain three groups of colorless and transparent solutions.

[0063] S1.2. Subsequently, add yttrium nitrate hexahydrate (0.051 g, 0.136 mmol) to the melamine solution, and then mix the three groups of solutions to immediately form a large amount of white precipitate. The obtained white precipitate is centrifuged and washed 3 times with deionized water to remove possible unreacted substances. Finally, the white precipitate is placed in a vacuum oven and dried overnight to obtain the yttrium-containing carbon nitride precursor.

[0064] S2. Thermal polymerization

[0065] Perform a thermal polymerization reaction on the above yttrium-containing carbon nitride precursor under an inert gas condition to obtain a crude product.

[0066] Specifically, place the yttrium-containing carbon nitride precursor in a tubular furnace, heat it to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere, and keep it warm for 4 h. The obtained product is a brownish-yellow powder, which is the crude product.

[0067] S3. Nitric acid etching

[0068] Ultrasonically disperse the crude product in a nitric acid solution for etching, and then obtain yttrium single-atom in-situ co-doped carbon nitride through washing and drying.

[0069] Specifically, ultrasonically disperse the crude product in 40 mL of HNO3 (1 M) solution, stir at room temperature for 1 h to etch and remove Y2O3 that may be generated during the calcination process. Finally, wash it alternately with deionized water and ethanol until the supernatant is neutral, and place the product in a vacuum oven for overnight drying to obtain yttrium single-atom in-situ co-doped carbon nitride Y-C-C3N4, where yttrium doping is 1%, and carbon doping is 30% (i.e., 0.3), denoted as 1%Y-C 0.3 -C3N4.

[0070] Example 2

[0071] The preparation method of yttrium single-atom in-situ co-doped carbon nitride provided by this embodiment includes the following steps:

[0072] S1. Prepare a yttrium-containing carbon nitride precursor

[0073] Using the precipitation method, a yttrium-containing carbon nitride precursor is prepared with melamine, cyanuric acid, an organic carbon source, and yttrium nitrate hexahydrate as raw materials.

[0074] S1.1. Respectively add melamine (1.193 g, 9.46 mmol), cyanuric acid (0.855 g, 6.62 mmol), and barbituric acid (0.363 g, 2.84 mmol) to 45, 38.5, and 16.5 mL of deionized water, and heat the three groups of substances to 75 °C and ultrasonically dissolve them to obtain three groups of colorless transparent solutions.

[0075] S1.2. Add yttrium nitrate hexahydrate (0.207 g, 0.54 mmol) to the melamine solution, and then mix the three groups of solutions to immediately form a large amount of white precipitate. Centrifuge the obtained white precipitate and wash it 3 times with deionized water to remove possible unreacted substances. Finally, place the white precipitate in a vacuum oven and dry it overnight to obtain the yttrium-containing carbon nitride precursor.

[0076] S2. Thermal polymerization

[0077] Perform a thermal polymerization reaction on the above yttrium-containing carbon nitride precursor under an inert gas condition to obtain a crude product.

[0078] Specifically, place the yttrium-containing carbon nitride precursor in a tubular furnace, heat it to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere, and keep it warm for 4 h. The obtained product is a brown-yellow powder, which is the crude product.

[0079] S3. Nitric acid etching

[0080] Ultrasonically disperse the crude product in a nitric acid solution for etching, and then obtain yttrium single-atom in-situ co-doped carbon nitride after washing and drying.

[0081] Specifically, ultrasonically disperse the crude product in 40 mL of HNO3 (1 M) solution, stir it at room temperature for 1 h to etch and remove Y2O3 that may be generated during the calcination process. Finally, wash it alternately with deionized water and ethanol until the supernatant is neutral, and place it in a vacuum oven and dry it overnight to obtain yttrium single-atom in-situ co-doped carbon nitride Y-C-C3N4, where the yttrium doping is 4% and the carbon doping is 30%, denoted as 4% Y-C 0.3 -C3N4.

[0082] Example 3

[0083] The preparation method of yttrium single-atom in-situ co-doped carbon nitride provided by this embodiment includes the following steps:

[0084] S1. Prepare a yttrium-containing carbon nitride precursor

[0085] Using the precipitation method, a yttrium-containing carbon nitride precursor is prepared from melamine, cyanuric acid, an organic carbon source, and yttrium nitrate hexahydrate as raw materials.

[0086] S1.1. Add melamine (1.193 g, 9.46 mmol), cyanuric acid (0.855 g, 6.62 mmol), and barbituric acid (0.363 g, 2.84 mmol) to 45, 38.5, and 16.5 mL of deionized water respectively, and heat the three groups of substances to 75 °C and ultrasonically dissolve them to obtain three groups of colorless and transparent solutions.

[0087] S1.2. Add yttrium nitrate hexahydrate (0.362 g, 0.95 mmol) to the melamine solution, and then mix the three groups of solutions to immediately form a large amount of white precipitate. Centrifuge the obtained white precipitate and wash it 3 times with deionized water to remove possible unreacted substances. Finally, place the white precipitate in a vacuum oven and dry it overnight to obtain the yttrium-containing carbon nitride precursor.

[0088] S2. Thermal polymerization

[0089] Perform a thermal polymerization reaction on the above yttrium-containing carbon nitride precursor under an inert gas condition to obtain a crude product.

[0090] Specifically, place the yttrium-containing carbon nitride precursor in a tube furnace, heat it to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere, and keep it for 4 h. The obtained product is a brownish-yellow powder, which is the crude product.

[0091] S3. Nitric acid etching

[0092] Ultrasonically disperse the crude product in a nitric acid solution for etching, and then obtain yttrium single-atom in-situ co-doped carbon nitride after washing and drying.

[0093] Specifically, ultrasonically disperse the crude product in 40 mL of HNO3 (1 M) solution, stir it at room temperature for 1 h to etch and remove Y2O3 that may be generated during the calcination process. Finally, wash it alternately with deionized water and ethanol until the supernatant is neutral, and place it in a vacuum oven and dry it overnight to obtain yttrium single-atom in-situ co-doped carbon nitride, in which yttrium is doped at 7% and carbon is doped at 30%, denoted as 7%Y-C 0.3 -C3N4.

[0094] Example 4

[0095] The preparation method of yttrium single-atom in-situ co-doped carbon nitride provided by this embodiment includes the following steps:

[0096] S1. Preparation of yttrium-doped carbon nitride precursor

[0097] The yttrium-doped carbon nitride precursor was prepared by a precipitation method using melamine, cyanuric acid, organic carbon source and yttrium nitrate hexahydrate as raw materials.

[0098] S1.1. Melamine (1.193 g, 9.46 mmol), cyanuric acid (0.855 g, 6.62 mmol) and barbituric acid (0.363 g, 2.84 mmol) were separately added to 45, 38.5 and 16.5 mL of deionized water, and the three groups of substances were heated to 75 °C and ultrasonically dissolved to obtain three groups of colorless transparent solutions.

[0099] S1.2. Yttrium nitrate hexahydrate (0.517 g, 1.357 mmol) was added to the melamine solution, and then the three groups of solutions were mixed to immediately form a large amount of white precipitate. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove possible unreacted substances, and finally the white precipitate was placed in a vacuum oven and dried overnight to obtain the yttrium-doped carbon nitride precursor.

[0100] S2. Thermal polymerization

[0101] The above yttrium-doped carbon nitride precursor was subjected to a thermal polymerization reaction under an inert gas condition to obtain a crude product.

[0102] Specifically, the yttrium-doped carbon nitride precursor was placed in a tube furnace and heated to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere and then held for 4 h. The obtained product was a brownish-yellow powder, which was the crude product.

[0103] S3. Nitric acid etching

[0104] The crude product was ultrasonically dispersed in a nitric acid solution for etching, and then obtained yttrium single-atom in-situ co-doped carbon nitride after washing and drying.

[0105] Specifically, the crude product was ultrasonically dispersed in 40 mL of HNO3 (1 M) solution and stirred at room temperature for 1 h to etch and remove Y2O3 that might be generated during the calcination process. Finally, it was washed alternately with deionized water and ethanol until the supernatant was neutral, and the product was placed in a vacuum oven and dried overnight to obtain yttrium single-atom in-situ co-doped carbon nitride, where the yttrium doping was 10% and the carbon doping was 30%, denoted as 10%Y-C 0.3 -C3N4.

[0106] In the above Examples 1 to 4, the carbon doping amount can also be replaced with 10%, 20% or 40%.

[0107] Several groups of yttrium single-atom in-situ co-doped carbon nitride were selected from the above examples for performance testing. At the same time, in order to show the advantages of the materials prepared by the present invention, the following comparative examples were also set up.

[0108] Comparative Example 1

[0109] This comparative example provides a method for preparing a photocatalyst, including the following steps:

[0110] S1. Prepare g-C3N4 supramolecular precursor

[0111] Melamine (1.193 g, 9.46 mmol) and cyanuric acid (1.221 g, 9.46 mmol) were respectively added to 45 and 55 mL of deionized water. Then the two groups of substances were heated to 75 °C and ultrasonicated until melamine and cyanuric acid were completely dissolved to form a colorless transparent solution.

[0112] The two solutions were mixed to form a large amount of white precipitate. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove part of the unreacted Y 3+ and other substances. Finally, the precursor was placed in a vacuum oven and dried overnight to obtain the g-C3N4 supramolecular precursor.

[0113] S2. Thermal polymerization

[0114] The g-C3N4 supramolecular precursor was placed in a tube furnace and heated to 550 °C at a heating rate of 2.5 °C / min under N2 atmosphere and held for 4 h.

[0115] S3. Nitric acid etching

[0116] The obtained product was similar to g-C3N4 as a pale yellow powder. The product was ultrasonically dispersed in 40 mL of HNO3 (1 M) solution and stirred at room temperature for 1 h to etch the material surface. Finally, it was washed alternately with deionized water and ethanol until the supernatant was neutral, and the product was placed in a vacuum oven and dried overnight to obtain g-C3N4.

[0117] Comparative Example 2

[0118] This comparative example provides a method for preparing a photocatalyst, including the following steps:

[0119] S1. Prepare yttrium-containing supramolecular precursor

[0120] Melamine (1.193 g, 9.46 mmol) and cyanuric acid (1.221 g, 9.46 mmol) were respectively added to 45 and 55 mL of deionized water. Then the two groups of substances were heated to 75 °C and ultrasonicated until melamine and cyanuric acid were completely dissolved to form a colorless transparent solution. At this time, yttrium nitrate hexahydrate (0.517 g, 1.357 mmol) was added to the melamine solution. Then the two solutions were mixed to form a large amount of white precipitate. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove part of the unreacted Y 3+Substances such as these, and finally the precursor was placed in a vacuum oven and dried overnight to obtain a yttrium-containing supramolecular precursor.

[0121] S2, Thermal polymerization

[0122] The yttrium-containing supramolecular precursor was placed in a tube furnace and heated to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere and then held for 4 h to obtain a pale yellow powder.

[0123] S3, Nitric acid etching

[0124] The pale yellow powder was ultrasonically dispersed in 40 mL of HNO3 (1 M) solution and stirred at room temperature for 1 h to etch and remove Y2O3 that might be formed during the calcination process. Finally, it was washed alternately with deionized water and ethanol until the supernatant was neutral, and the product was placed in a vacuum oven and dried overnight to obtain Y-C3N4 containing 10% yttrium.

[0125] Comparative Example 3

[0126] This comparative example provides a method for preparing a photocatalyst, including the following steps:

[0127] S1, Preparation of yttrium-containing supramolecular precursor

[0128] Melamine (1.193 g, 9.46 mmol) and cyanuric acid (1.221 g, 9.46 mmol) were respectively added to 45 and 55 mL of deionized water. Then the two groups of substances were heated to 75 °C and ultrasonically treated until melamine and cyanuric acid were completely dissolved to form a colorless transparent solution. At this time, yttrium nitrate hexahydrate (0.362 g, 0.95 mmol) was added to the melamine solution, and then the two solutions were mixed to form a large amount of white precipitate. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove part of the unreacted Y 3+ Substances such as these, and finally the precursor was placed in a vacuum oven and dried overnight to obtain a yttrium-containing supramolecular precursor.

[0129] S2, Thermal polymerization

[0130] The yttrium-containing supramolecular precursor was placed in a tube furnace and heated to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere and then held for 4 h to obtain a pale yellow powder.

[0131] S3, Nitric acid etching

[0132] The pale yellow powder was ultrasonically dispersed in 40 mL of HNO3 (1 M) solution and stirred at room temperature for 1 h to etch and remove Y2O3 that might be formed during the calcination process. Finally, it was washed alternately with deionized water and ethanol until the supernatant was neutral, and the product was placed in a vacuum oven and dried overnight to obtain Y-C3N4 containing 7% yttrium.

[0133] Comparative Example 4

[0134] This comparative example provides a method for preparing a photocatalyst, which includes the following steps:

[0135] S1. Prepare a yttrium-containing supramolecular precursor

[0136] Melamine (1.193 g, 9.46 mmol) and cyanuric acid (1.221 g, 9.46 mmol) were separately added to 45 and 55 mL of deionized water. Then, the two groups of substances were heated to 75 °C and sonicated until melamine and cyanuric acid were completely dissolved to form a colorless transparent solution. At this time, yttrium nitrate hexahydrate (0.207 g, 0.543 mmol) was added to the melamine solution, and then the two solutions were mixed to generate a large amount of white precipitate. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove some unreacted Y 3+ and other substances. Finally, the precursor was placed in a vacuum oven and dried overnight to obtain a yttrium-containing supramolecular precursor.

[0137] S2. Thermal polymerization

[0138] The yttrium-containing supramolecular precursor was placed in a tube furnace and heated to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere and then held for 4 h to obtain a pale yellow powder.

[0139] S3. Nitric acid etching

[0140] The pale yellow powder was ultrasonically dispersed in 40 mL of HNO3 (1 M) solution and stirred at room temperature for 1 h to etch and remove Y2O3 that might be formed during the calcination process. Finally, it was washed alternately with deionized water and ethanol until the supernatant was neutral, and the product was placed in a vacuum oven and dried overnight to obtain Y-C3N4 containing 4% yttrium.

[0141] Comparative Example 5

[0142] This comparative example provides a method for preparing a photocatalyst, which includes the following steps:

[0143] S1. Prepare a yttrium-containing supramolecular precursor

[0144] Melamine (1.193 g, 9.46 mmol) and cyanuric acid (1.221 g, 9.46 mmol) were separately added to 45 and 55 mL of deionized water. Then, the two groups of substances were heated to 75 °C and sonicated until melamine and cyanuric acid were completely dissolved to form a colorless transparent solution. At this time, yttrium nitrate hexahydrate (0.052 g, 0.136 mmol) was added to the melamine solution, and then the two solutions were mixed to generate a large amount of white precipitate. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove some unreacted Y 3+ and other substances. Finally, the precursor was placed in a vacuum oven and dried overnight to obtain a yttrium-containing supramolecular precursor.

[0145] S2, Thermal polymerization

[0146] Place the yttrium-containing supramolecular precursor in a tube furnace, heat it to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere, and keep it for 4 h to obtain a pale yellow powder.

[0147] S3, Nitric acid etching

[0148] Ultrasonically disperse the pale yellow powder in 40 mL of HNO3 (1 M) solution, stir at room temperature for 1 h to etch and remove Y2O3 that may be formed during the calcination process. Finally, wash it alternately with deionized water and ethanol until the supernatant is neutral, and place the product in a vacuum oven to dry overnight to obtain Y-C3N4 containing 1% yttrium.

[0149] Comparative Example 6

[0150] This comparative example provides a method for preparing a photocatalyst, including the following steps:

[0151] S1, Preparation of precursor

[0152] Add melamine (1.193 g, 9.46 mmol), cyanuric acid (0.855 g, 6.62 mmol) and barbituric acid (0.363 g, 2.84 mmol) to 45, 38.5 and 16.5 mL of deionized water respectively, heat the three groups of substances to 75 °C and ultrasonically dissolve them to obtain three groups of colorless transparent solutions. Then mix the three groups of solutions and a large amount of white precipitate will be formed immediately. Centrifuge the obtained white precipitate and wash it 3 times with deionized water to remove possible unreacted substances. Finally, place the white precipitate in a vacuum oven to dry overnight to obtain the precursor.

[0153] S2, Thermal polymerization

[0154] Place the precursor in a tube furnace, heat it to 550 °C at a heating rate of 2.5 °C / min under a N2 atmosphere and keep it for 4 h. The obtained product is a brownish-yellow powder.

[0155] S3, Nitric acid etching

[0156] Ultrasonically disperse the brownish-yellow powder in 40 mL of HNO3 (1 M) solution, stir at room temperature for 1 h to etch the material surface. Finally, wash it alternately with deionized water and ethanol until the supernatant is neutral, and place the product in a vacuum oven to dry overnight to obtain C 0.3 -C3N4 doped with 30% carbon.

[0157] Comparative Example 7

[0158] This comparative example provides a method for preparing a photocatalyst, including the following steps:

[0159] S1. Preparation of precursor

[0160] Melamine (1.193 g, 9.46 mmol), cyanuric acid (0.855 g, 6.62 mmol) and barbituric acid (0.121 g, 0.95 mmol) were separately added to 45, 38.5 and 16.5 mL of deionized water, and the three groups of substances were heated to 75 °C and ultrasonically dissolved to obtain three groups of colorless transparent solutions; then the three groups of solutions were mixed and a large amount of white precipitate was immediately formed. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove possible unreacted substances, and finally the white precursor was placed in a vacuum oven and dried overnight to obtain the precursor.

[0161] S2. Thermal polymerization

[0162] The precursor was placed in a tube furnace and heated to 550 °C at a heating rate of 2.5 °C / min under N2 atmosphere and then held for 4 h to obtain a product as a yellowish-brown powder.

[0163] S3. Nitric acid etching

[0164] The yellowish-brown powder was ultrasonically dispersed in 40 mL of HNO3 (1 M) solution, stirred at room temperature for 1 h to etch the material surface, and finally washed alternately with deionized water and ethanol until the supernatant was neutral, and the product was placed in a vacuum oven and dried overnight to obtain 10% carbon-doped C 0.1 -C3N4.

[0165] Comparative Example 8

[0166] This comparative example provides a method for preparing a photocatalyst, including the following steps:

[0167] S1. Preparation of precursor

[0168] Melamine (1.193 g, 9.46 mmol), cyanuric acid (0.855 g, 6.62 mmol) and barbituric acid (0.242 g, 1.89 mmol) were separately added to 45, 38.5 and 16.5 mL of deionized water, and the three groups of substances were heated to 75 °C and ultrasonically dissolved to obtain three groups of colorless transparent solutions, and then the three groups of solutions were mixed and a large amount of white precipitate was immediately formed. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove possible unreacted substances, and finally the white precursor was placed in a vacuum oven and dried overnight to obtain the precursor.

[0169] S2. Thermal polymerization

[0170] The precursor was placed in a tube furnace and heated to 550 °C at a heating rate of 2.5 °C / min under N2 atmosphere and then held for 4 h to obtain a product as a yellowish-brown powder.

[0171] S3, Nitric acid etching

[0172] The yellowish-brown powder was ultrasonically dispersed in 40 mL of HNO3 (1 M) solution, stirred at room temperature for 1 h to etch the material surface, and finally washed alternately with deionized water and ethanol until the supernatant was neutral. The product was placed in a vacuum oven and dried overnight to obtain C-doped 20% C 0.2 -C3N4.

[0173] Comparative Example 9

[0174] This comparative example provides a method for preparing a photocatalyst, which includes the following steps:

[0175] S1, Preparation of the precursor

[0176] Melamine (1.193 g, 9.46 mmol), cyanuric acid (0.855 g, 6.62 mmol) and barbituric acid (0.484 g, 3.80 mmol) were respectively added to 45, 38.5 and 16.5 mL of deionized water, and the three groups of substances were heated to 75 °C and ultrasonically dissolved to obtain three groups of colorless transparent solutions. Then the three groups of solutions were mixed and a large amount of white precipitate was immediately formed. The obtained white precipitate was centrifuged and washed 3 times with deionized water to remove possible unreacted substances. Finally, the white precursor was placed in a vacuum oven and dried overnight to obtain the precursor.

[0177] S2, Thermal polymerization

[0178] The precursor was placed in a tubular furnace and heated to 550 °C at a heating rate of 2.5 °C / min under N2 atmosphere and then held for 4 h. The obtained product was a yellowish-brown powder.

[0179] S3, Nitric acid etching

[0180] The yellowish-brown powder was ultrasonically dispersed in 40 mL of HNO3 (1 M) solution, stirred at room temperature for 1 h to etch the material surface, and finally washed alternately with deionized water and ethanol until the supernatant was neutral. The product was placed in a vacuum oven and dried overnight to obtain C-doped 40% C 0.4 -C3N4.

[0181] For the materials prepared in the above examples and comparative examples, their performance tests are as follows.

[0182] 1. XRD test

[0183] Take the g-C3N4 of Comparative Example 1, 7% Y-C3N4 of Comparative Example 3, C 0.3 -C3N4 of Comparative Example 6 and 7% Y-C 0.3 -C3N4 of Example 3, and perform XRD tests respectively. The results are as Figure 1 and Figure 2 shown.

[0184] Figure 1 XRD comparison charts of Comparative Example 1 and Comparative Example 3. It can be seen from Figure 1 them that the positions of the XRD diffraction peaks remain the same before and after the introduction of single yttrium atoms, and only the weakening of the peak intensity indicates that the introduction of single yttrium atoms does not change the unit cell size of g-C3N4.

[0185] Figure 2 XRD comparison charts of Comparative Example 1, Comparative Example 6 and Example 3. Introducing 30% of barbituric acid on the basis of g-C3N4 to increase the carbon content of the catalyst does not cause obvious changes in the XRD of the material. When yttrium is introduced as a single atom into the catalyst, the intensity of its diffraction peak drops significantly, which indicates that the introduction of yttrium changes the microscopic arrangement of the catalyst and also proves the successful compounding of yttrium.

[0186] 2. Morphology analysis

[0187] Take 7% Y-C3N4 of Comparative Example 3 and 7% Y-C 0.3 -C3N4 of Example 3 to test their SEM, TEM and element distribution maps respectively. The results are as Figure 3 and Figure 4 shown.

[0188] Figure 3 SEM, TEM and element distribution maps of 7% Y-C3N4. Among them, (a)-(e) are SEM images at different magnifications. It can be seen that it is nanosheet-like, and there are many holes of different sizes on the material surface, which are the holes occupied by the etched Y2O3. (f) is a TEM image, from which obvious lattice fringes can be observed, corresponding to the 002 plane of the catalyst. (g-f) are element distribution maps, and it can be seen that C, N and Y are evenly distributed on the material surface.

[0189] Figure 4 SEM, TEM and element distribution maps of 7% Y-C 0.3 -C3N4. Among them, (a)-(e) are SEM images at different magnifications. From them, it can be seen that holes of different sizes are distributed on the material surface, and the morphology changes from a thinner sheet-like structure to a thicker sheet-like structure with wrinkles in the center. (f) is a TEM image and (g-f) are element distribution maps. It can be seen that C, N and Y are evenly distributed on the material surface.

[0190] 3. Photoluminescence spectrum

[0191] Take g-C3N4 of Comparative Example 1, 10% Y-C3N4 of Comparative Example 2, 7% Y-C3N4 of Comparative Example 3, 4% Y-C3N4 of Comparative Example 4, 1% Y-C3N4 of Comparative Example 5, C of Comparative Example 6 0.3-C3N4 and 7% Y-C of Example 3 0.3 -C3N4 were respectively tested for photoluminescence spectra, and the results are as Figure 5 and Figure 6 shown.

[0192] From Figure 5 and Figure 6 it can be seen that for the g-C3N4 doped with single Y atoms, its fluorescence intensity gradually decreases as the yttrium doping amount increases, and the fluorescence intensity is the lowest when the yttrium doping amount is 7%, and the fluorescence intensity further increases when the Y doping amount increases to 10%. This indicates that when the yttrium doping amount is 7%, the material has the lowest electron-hole recombination rate, and the material at this time is conducive to the photothermal catalytic reduction of carbon dioxide. Similarly, in the material co-doped with yttrium and carbon, 7% Y-C 0.3 -C3N4 has the optimal electron recombination rate, which is conducive to the photothermal catalytic reduction of carbon dioxide at this time. Therefore, it can be seen that when the yttrium doping amount is 7%, it has good luminescence characteristics; in g-C3N4, C and Y can effectively reduce the photogenerated electron-hole recombination rate of g-C3N4, and when C and Y are introduced simultaneously, the photogenerated electron-hole recombination rate of g-C3N4 can be maximally increased.

[0193] 4. Photocatalytic reduction performance

[0194] The photocatalysts prepared in Comparative Examples 1 to 9 and the yttrium single-atom in-situ co-doped carbon nitride prepared in Examples 1 to 4 were taken as test samples, and the photocatalytic CO2 reduction reaction tests were respectively carried out using the above test samples.

[0195] The photocatalytic CO2 reduction reaction test was carried out in a reaction kettle with a transparent quartz top window and heating, and the products were analyzed by gas chromatography.

[0196] Specifically, 5 mg of the catalyst was added to a 100 mL quartz reactor, and then 20 mL of a mixed solution of deionized water (10 mL) and triethanolamine (10 mL) was added. After ultrasonic dispersion, it was placed in the reaction device and stirred at a speed of 300 r / min. Then the reaction system was evacuated, and the reaction system was purged with CO2 gas to ensure that the air in the reaction device was completely removed. Finally, the pressure in the reactor was maintained at about 1 atm.

[0197] The photocatalytic light source used was a 300 W xenon lamp with a 420 nm cut-off filter. After the reaction for 1 h, 2 mL of the gas in the reactor was taken, and the product type and content were analyzed by gas chromatography. The selectivities of Product 1 (CH4) and Product 2 (CO) were calculated respectively by the following formulas:

[0198]

[0199]

[0200] Among them: S 产物1 represents the selectivity of Product 1, and S 产物2 represents the selectivity of Product 2, and R 产物1 represents the reaction rate of Product 1, and K1 represents the number of electrons transferred corresponding to Product 1; R 产物2 represents the reaction rate of Product 2, and K2 represents the number of electrons transferred corresponding to Product 2. K1 = 8, K2 = 2.

[0201] The test results of the photocatalytic CO2 reduction reaction are shown in Table 1, and the catalytic results of some test samples are as Figure 7 shown.

[0202] Table 1 Test Results of the Photocatalytic CO2 Reduction Reaction of Each Test Sample

[0203]

[0204] From Table 1 and Figure 7 the data, it can be seen that the doping of Y and C effectively improves the ability of g-C3N4 to photocatalytically reduce CO2 to produce CH4. Especially when the doping amount of Y is 7% and the doping amount of C is 0.3, the photocatalytic CO2 reduction effect is more significant, and the rate of CH4 reaches 97.37 μmol·g -1 ·h -1 , and finally the calculated selectivity of CH4 reaches 93.69%.

[0205] Further, in Example 3, the yttrium-containing carbon nitride precursor obtained in step S1 and the crude product after thermal polymerization in step S2 are used as test samples, and their photocatalytic CO2 reduction effects are tested with reference to the above method, and the results are as Figure 8 shown.

[0206] From Figure 8 it can be seen that the yttrium-containing carbon nitride precursor without thermal polymerization and etching has almost no effect on the photocatalytic CO2 reduction reaction; while the crude product after thermal polymerization has a rate of CH4 reaching 80 μmol·g -1 ·h -1 , and the rate of producing CO is about 18 μmol·g -1 ·h -1 ; comparing with the photocatalytic CO2 reduction ability of the yttrium single-atom in-situ co-doped carbon nitride after etching in Table 1, it shows that the synergistic effect of thermal polymerization and etching on the yttrium-containing carbon nitride precursor can promote the ability of photocatalytic CO2 reduction to produce CH4.

[0207] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments. Those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent substitutions, and these modifications or equivalent substitutions cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing yttrium single atom in-situ co-doped carbon nitride, characterized in that: The following steps are involved: S1. Preparation of yttrium-containing carbon nitride precursor The yttrium-containing carbon nitride precursor is prepared by using melamine, cyanuric acid, barbituric acid and yttrium nitrate hexahydrate as raw materials by using a precipitation method. S2. Thermal polymerization The yttrium-containing carbon nitride precursor is subjected to a thermal polymerization reaction under an inert gas condition to obtain a crude product; S3, nitric acid etching The crude product is ultrasonically dispersed in a nitric acid solution and etched, and then washed and dried to obtain yttrium single atom in-situ co-doped carbon nitride YC-C3N4, in which the doping amount of C is 10wt% to 30wt%, and the doping amount of Y is 1%wt to 7wt%.

2. The method for preparing yttrium single atom in-situ co-doped carbon nitride according to claim 1, characterized in that: The specific process of preparing the yttrium-containing carbon nitride precursor in step S1 is: S1.1, dissolving melamine, cyanuric acid and barbituric acid in water respectively, heating them to 75°C-80°C and ultrasonically treating them, to obtain melamine solution, cyanuric acid solution and barbituric acid solution respectively; S1.2, yttrium nitrate hexahydrate is added to melamine solution; then cyanuric acid solution and barbituric acid solution are added to generate white precipitate; the white precipitate is collected by centrifugation, and after washing and drying, a yttrium-containing carbon nitride precursor is obtained.

3. The method for preparing yttrium single atom in-situ co-doped carbon nitride according to claim 1, characterized in that: In the step S2, the conditions for the thermal polymerization reaction are: a heating rate of 2.5°C / min-5°C / min, a temperature of 540°C-560°C, and a reaction time of 4h-4.5h.

4. The method for preparing yttrium single atom in-situ co-doped carbon nitride according to claim 1, characterized in that: In step S3, the concentration of the nitric acid solution is 0.5 mol / L-1 mol / L, and the etching time is 20 min-30 min.

5. Yttrium single atom in-situ co-doped carbon nitride prepared by the preparation method of yttrium single atom in-situ co-doped carbon nitride according to claim 1.

6. Use of the yttrium single atom in-situ co-doped carbon nitride as claimed in claim 5 as a photocatalyst in photothermal carbon dioxide reduction.

7. The use according to claim 6, characterized in that: When the photocatalyst performs photothermal catalytic reduction of carbon dioxide, the methane yield reaches a maximum of 97.37 μmol·g -1 ·h -1 , the selectivity is as high as 93.69%.

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