A carbon nitride homojunction photocatalyst for selective conversion of methane to ethanol and a preparation method and application thereof

Abstract

This invention discloses a carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, its preparation method, and its application, belonging to the field of photocatalysis. The carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol is made of carbon nitride semiconductor CNC. I Axially oxygen-coordinated copper single-atom co-catalyst and carbon nitride semiconductor CN II Composition. Based on carbon nitride semiconductor CN. I The first semiconductor is formed by supramolecular assembly and thermal polymerization, on which an axially oxygen-coordinated copper single-atom co-catalyst and a second semiconductor CN are simultaneously introduced. II The carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, denoted as Cu-CN, was prepared. II / CN I The catalyst used in this invention is made from abundant and inexpensive raw materials, and its preparation route is simple. The prepared catalyst significantly promotes the separation of charge carriers and exhibits excellent catalytic performance in the photocatalytic conversion of methane to ethanol, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, specifically to a carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, its preparation method, and its applications. Background Technology

[0002] Methane is a vital C1 resource with abundant global reserves and diverse sources, including natural gas, shale gas, coalbed methane, combustible ice, and biogas, playing a crucial role in my country's energy and chemical industry system. Currently, the vast majority of methane produced in my country is directly used for combustion heating, residential gas supply, and gas-fired power generation, with only about 10% used as a carbon source for the synthesis of high-value-added chemicals. This not only wastes the value of high-quality carbon-based resources but also exacerbates greenhouse gas emissions. Therefore, promoting the targeted conversion of methane from fuel combustion to high-value-added chemicals is a win-win path to maximizing resource value and controlling carbon emissions.

[0003] However, methane possesses a highly symmetrical tetrahedral structure with a CH bond dissociation energy as high as 434 kJ / mol, exhibiting extremely inert chemical properties. Its selective activation and directional conversion under mild conditions remains a recognized "holy grail" challenge in the field of catalysis. Photocatalytic conversion of methane to liquid fuels and chemicals is considered an ideal pathway for the resource utilization of methane. Methanol, ethanol, and other liquid oxygen-containing compounds not only serve as easily transportable and stored liquid fuels but also as platform molecules for various value-added chemicals, making them ideal products of methane conversion. Therefore, research on the photocatalytic conversion of methane to liquid oxygen-containing compounds, especially methanol, has received significant attention from the academic community. Furthermore, compared to methanol, ethanol has a higher calorific value and greater energy density, and its higher boiling point makes it safer to use. Research on the photocatalytic conversion of methane to ethanol holds broad prospects and enormous potential, and the construction of high-performance photocatalysts is the core key to realizing the industrial application of this technology.

[0004] Graphitic carbon nitride (g-C3N4), as a class of non-metallic polymer semiconductor photocatalytic materials, has become a core catalytic material with great application potential in the field of photocatalytic conversion due to its unique two-dimensional layered structure, tunable electronic band structure, simple preparation process, low raw material cost, and excellent chemical and thermal stability. It has been widely studied and reported in the fields of photocatalytic water splitting to produce hydrogen, photocatalytic synthesis of hydrogen peroxide, and photocatalytic selective oxidation of methane to methanol (Applied Catalysis B: Environmental, 2020, 278, 119342; Carbon Energy, 2024, 6(11); Chinese Journal of Catalysis, 2025, 76 (9): 96-107). In recent years, carbon nitride-based materials have been gradually expanded to be applied in the photocatalytic conversion of methane to ethanol. Existing published research (Energy & Fuels, 2022, 36, 3929-3937; Chemical Communications, 2021, 57 (7): 871-874; Nature Communications, 2019, 10 (1): 506-513) shows that carbon nitride photocatalysts for the photocatalytic conversion of methane to ethanol have demonstrated certain promise. However, the conversion process relies on reactive oxygen species (ROS) such as hydroxyl radicals and superoxide radicals. While ROS can activate the CH4 group of methane to drive its conversion, their strong oxidizing properties easily lead to deep oxidation. This not only wastes methane resources but also reduces ethanol selectivity, significantly increasing the difficulty and cost of subsequent product separation and purification processes, making it difficult to meet the requirements of industrial applications. By controlling the formation of ROS, deep oxidation can be suppressed and selectivity improved to some extent; however, this results in a decrease in ethanol yield. To overcome the trade-off between ethanol yield and selectivity, our research group developed a novel ROS-independent methane activation strategy (CCS Chemistry, 2025, 1-15) through extensive literature review and experimental verification. By constructing an axially oxygen-coordinated single-atom copper-modified carbon nitride catalyst, we achieved a simultaneous increase in ethanol selectivity and yield, with an ethanol selectivity as high as 98%. This addresses the core challenges of deep product oxidation and low selectivity in traditional ROS-dependent pathways, where suppressing ROS generation leads to low yields. However, despite achieving such high ethanol selectivity, the ethanol yield of this catalytic system still does not meet the requirements for industrial applications.

[0005] Therefore, how to overcome the bottleneck of catalytic activity of carbon nitride-based materials in the photocatalytic reaction of methane to ethanol while maintaining high selectivity has become a core technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To overcome the defects and shortcomings of the existing technology, the present invention aims to provide a carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, as well as the preparation method and application of the catalyst.

[0007] In our previous research, we constructed a single-atom copper-modified carbon nitride catalyst with axial oxygen coordination, achieving a simultaneous improvement in the selectivity and yield of methane to ethanol conversion. This solved the core problem of the trade-off between ethanol yield and selectivity commonly found in traditional ROS-dependent pathways. However, due to the inherent defects of carbon nitride photogenerated carriers, such as easy recombination and low separation and migration efficiency, the ethanol yield still falls short of the requirements for industrial applications and urgently needs improvement. Our previous work has demonstrated that constructing band-matched graphitic carbon nitride-based homojunctions can significantly improve carrier separation efficiency, thereby significantly promoting the performance of photocatalytic water splitting for hydrogen production (Applied Catalysis B: Environmental, 2020, 269, 118778). Our group has also developed hollow carbon nitride materials based on melamine, metal salts, and cyanuric acid pre-assembled pyrolytic single-atom metal implantation (Journal of the American Chemical Society, 2018, 140, 16936-16940). To obtain highly efficient heterojunction catalysts, the tight bonding of the two semiconductors is crucial. In our newly developed ROS-independent photocatalytic conversion system for methane to ethanol, the key to solving current technical challenges lies in introducing a tightly bonded second carbon nitride semiconductor to form a carbon nitride homojunction with axial oxygen coordination and copper single-atom coordination. This breakthrough in catalytic activity while maintaining high ethanol selectivity is the core solution to the current technical difficulties.

[0008] Inspired by the phenomenon of carbon adhering to and growing on the surface of pond stones in nature, this invention prepares carbon nitride (CN) by polymerization of nitrogen-carbon sources and carbonyl compounds. I Using melamine, copper salts, and cyanuric acid as the matrix, and mimicking stones in a pond, this study employs a molecular self-assembly thermal polymerization strategy based on carbon nitride-supported single-atom catalytic materials established by our research group. This involves the molecular self-assembly of melamine, copper salts, and cyanuric acid, followed by pyrolysis, within the CN... I In-situ growth of carbon nitride components Cu-CN with embedded copper single-atom sites on the substrate surface II As a moss, and through subsequent controlled reduction and controlled oxidation treatments, a novel, highly efficient carbon nitride homojunction catalyst, Cu-CN, containing an axially oxygen-coordinated copper single-atom co-catalyst, was prepared. II / CN I The prepared axially oxygen-coordinated copper single-atom cocatalyst exhibits excellent catalytic performance in the photocatalytic selective conversion of methane to ethanol.

[0009] The technical solution of the present invention is as follows: A carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, wherein the carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol is composed of carbon nitride semiconductor CN I Axially oxygen-coordinated copper single-atom co-catalyst and carbon nitride semiconductor CN II constitute.

[0010] With carbon nitride semiconductor CN I The first semiconductor is formed by supramolecular assembly and thermal polymerization, on which an axially oxygen-coordinated copper single-atom co-catalyst and a second semiconductor CN are simultaneously introduced. II The carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, denoted as Cu-CN, was prepared. II / CN I .

[0011] In the aforementioned carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, the semiconductor Cu-CN II The mass percentage of the catalyst is 10%~50%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 0.1%~5%.

[0012] A method for preparing a carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, the method comprising the following steps: Step 1: Add the carbon-nitrogen source and carbonyl compound to a mixed solvent of organic solvent and water, adjust the pH value, heat the reaction, and then evaporate the solvent to obtain solid A. Calcine solid A in an air atmosphere in a muffle furnace to obtain carbon nitride semiconductor CN. I ; Step 2: Apply carbon nitride semiconductor CN I Dispersion a was prepared by dispersing melamine and copper salt in DMSO solvent; solution b was prepared by dissolving melamine and copper salt in DMSO; solution b was poured into dispersion a under stirring, and after stirring, dispersion c was obtained; cyanuric acid was dissolved in DMSO solvent to obtain solution d; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, and then filtered, washed, and dried to obtain solid B. Step 3: Calcine solid B under N2 atmosphere to obtain solid C, which is then acid washed, water washed and dried to obtain solid D; Step 4: Solid D is first calcined in a H2 / N2 reducing atmosphere, and then calcined in an O2 / N2 oxidizing atmosphere to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I .

[0013] Further, in step 1, the carbon-nitrogen source is one of urea, melamine, dicyandiamide, and thiourea; the carbonyl compound is one of acetone, glyoxal, benzaldehyde, acetophenone, and terephthalaldehyde; the organic solvent is one of ethanol, methanol, DMSO, and DMF; and the mass ratio of carbon-nitrogen source: carbonyl compound: organic solvent: water is 1:(0.01~0.5):(0.1~5):(0.1~5).

[0014] Furthermore, in step 1, the acid used to adjust the pH value is one of sulfuric acid, nitric acid, or hydrochloric acid, adjusted to a pH value range of 2-7; the heating reaction temperature is 30-80℃, the reaction time is 1-6 h, and the calcination temperature in the muffle furnace is 200-700℃, with a calcination time of 1-6 h.

[0015] Furthermore, in step 2, the carbon nitride semiconductor CN used to prepare dispersion a I The mass ratio of DMSO solvent is 1:10~100; the copper salt used to prepare solution b is one of copper nitrate, copper acetate, copper chloride, copper sulfate, and copper acetylacetonate, and the mass ratio of melamine:copper salt:DMSO solvent is 1:(0.1~5):(50~500); the mass ratio of solution b to dispersion a used to prepare solution c is (0.1~10):1; the mass ratio of cyanuric acid:DMSO solvent used to prepare solution d is 1:(50~500); the mass ratio of solution d to dispersion c used to prepare dispersion e is (0.1~5):1.

[0016] Furthermore, in step 3, the N2 flow rate is 5~200 mL / min, the calcination temperature is 200~700℃, the calcination time is 1~6 h, the acid used for pickling is one of sulfuric acid, nitric acid, or hydrochloric acid, the concentration of the acid solution is 0.1~2.0 wt%, and the mass ratio of solid C to acid is 1:(200~2000).

[0017] Furthermore, in step 4, the volume percentage of H2 in the H2 / N2 mixture is 2% to 50%, the flow rate is 5 to 100 mL / min, the temperature is 50 to 500 °C, and the time is 1 to 6 h.

[0018] Furthermore, in step 4, the volume percentage of O2 in the O2 / N2 mixture is 2% to 50%, the flow rate is 5 to 100 mL / min, the temperature is 50 to 500℃, and the time is 1 to 6 h.

[0019] Furthermore, in steps 2 and 3, the drying temperature is 20~150℃, and the drying time is 1~24 h. The carbon nitride homojunction catalyst prepared in this invention is used for the photocatalytic conversion of methane to ethanol, exhibiting excellent catalytic activity, selectivity, and stability.

[0020] The present invention has the following beneficial effects: (1) The present invention constructs a carbon nitride homojunction containing axially oxygen-coordinated copper single atoms through molecular self-assembly thermal polymerization, which effectively overcomes the core defects of traditional single-structure carbon nitride with high recombination rate of photogenerated carriers and low visible light utilization efficiency, significantly promotes the separation and migration of photogenerated carriers, and greatly improves the catalytic performance of methane photocatalysis to ethanol.

[0021] (2) The Cu-containing carbon nitride homojunction photocatalyst prepared by the present invention has excellent catalytic performance and simultaneously achieves high ethanol yield and selectivity.

[0022] (3) In the preparation of the present invention, the raw materials are widely available and the cost is low. The preparation route is simple and easy to implement. No precious metals are required, and no complicated preparation methods are needed. It is easy to carry out industrial applications on a large scale. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0024] Figure 1 This is a scanning electron microscope image of the carbon nitride homojunction catalyst S1 prepared in Example 1 of the present invention.

[0025] Figure 2 The image shows a scanning electron microscope (SEM) image of the reference sample D1 prepared for Comparative Example 1. This demonstrates that a second semiconductor was successfully introduced into the first semiconductor D1.

[0026] Figure 3 The infrared spectra of the carbon nitride homojunction catalyst S1 prepared in Example 1 and the reference sample D1 prepared in Comparative Example 1 further illustrate that a second semiconductor was successfully introduced based on the first semiconductor D1; wherein, (a) is 3750~2500 cm⁻¹ -1 Infrared spectra of wavenumbers, (b) 2000–750 cm⁻¹ -1 Infrared spectrum of wavenumber.

[0027] Figure 4 The electron paramagnetic resonance (EPR) spectra of the carbon nitride homojunction catalyst S1 prepared in Example 1 of this invention, the reference sample D1 prepared in Comparative Example 1, and the reference sample D2 prepared in Comparative Example 2 further illustrate that a second semiconductor was successfully introduced based on the first semiconductor D1; and that the carbon nitride homojunction prepared in this invention is a type II junction; wherein, (a) is the EPR spectrum of the captured hydroxyl radical, and (b) is the EPR spectrum of the captured superoxide radical. Detailed Implementation

[0028] The present invention will be described below with reference to specific embodiments. Those skilled in the art will understand that these are for illustrative purposes only and do not limit the scope of the invention in any way.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 20 g of urea and 1.18 g of acetone were added to a mixed solvent of 39.45 g of ethanol and 20 g of water. The pH was adjusted to approximately 4.3 with nitric acid. The mixture was heated in an oil bath at 50°C for 3 hours. The solvent was then evaporated to obtain solid A. Solid A was calcined in a muffle furnace at 550°C for 4 hours to obtain carbon nitride semiconductor CN. I ; 150 mg of carbon nitride semiconductor CN I Dispersion a was prepared by dispersing melamine in 9 g of DMSO solvent; solution b was prepared by dissolving 41.7 mg of melamine and 11.3 mg of copper nitrate in 9 g of DMSO; solution b was poured into dispersion a under stirring, and after stirring for a period of time, dispersion c was obtained; solution d was prepared by dissolving 54 mg of cyanuric acid in 9 g of DMSO under stirring; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, then filtered, washed, and dried overnight at 105 °C in an oven to obtain solid B; solid B was calcined under N2 atmosphere at 300 °C for 2 h at a flow rate of 30 mL / min to obtain solid C; 150 mg of solid C was acid-washed with 150 g of 0.5 wt% nitric acid solution for 4 h, washed with water, and dried at 105 °C in an oven to obtain solid D; solid D was calcined at a concentration of 20% and a flow rate of 30 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 300℃ for 2 h and then cooled to room temperature. Subsequently, it was calcined at 200℃ for 2 h in an O2 / N2 atmosphere with a concentration of 20% and a flow rate of 30 mL / min to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I S1. Semiconductor Cu-CN in the catalyst. IIThe mass percentage of the catalyst is 20%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 1.6%.

[0032] Example 2 25 g of urea and 1.68 g of acetone were added to a mixed solvent of 39.55 g of methanol and 20 g of water. The pH was adjusted to approximately 4.8 with nitric acid. The mixture was heated in an oil bath at 50°C for 3 hours. The solvent was then evaporated to obtain solid A. Solid A was calcined in a muffle furnace at 550°C for 4 hours to obtain carbon nitride semiconductor CN. I ; 150 mg of carbon nitride semiconductor CN I Dispersion a was prepared by dispersing melamine in 9 g of DMSO solvent; solution b was prepared by dissolving 41.7 mg of melamine and 11.3 mg of copper chloride in 9 g of DMSO; solution b was poured into dispersion a under stirring, and after stirring for a period of time, dispersion c was obtained; solution d was prepared by dissolving 54 mg of cyanuric acid in 20 g of DMSO under stirring; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, then filtered, washed, and dried overnight at 105 °C in an oven to obtain solid B; solid B was calcined under N2 atmosphere at 300 °C for 2 h at a flow rate of 40 mL / min to obtain solid C; 150 mg of solid C was acid-washed with 150 g of 0.5 wt% nitric acid solution for 6 h, washed with water, and dried at 105 °C in an oven to obtain solid D; solid D was calcined at a concentration of 10% and a flow rate of 40 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 350℃ for 2 h and then cooled to room temperature. Subsequently, it was calcined at 300℃ for 1 h in an O2 / N2 atmosphere with a concentration of 30% and a flow rate of 20 mL / min to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I S2. Semiconductor Cu-CN in the catalyst. II The mass percentage content is 25%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 2.1%.

[0033] Example 3 20 g of dicyandiamide and 1.8 g of benzaldehyde were added to a mixed solvent of 40 g of DMF and 20 g of water. The pH was adjusted to approximately 3.5 with nitric acid. The mixture was heated in an oil bath at 50°C for 3 hours. The solvent was then evaporated to obtain solid A. Solid A was calcined in a muffle furnace at 550°C for 5 hours to obtain carbon nitride semiconductor CN. I ; 150 mg of carbon nitride semiconductor CN IDispersion a was prepared by dispersing melamine in 9 g of DMSO solvent; solution b was prepared by dissolving 41.7 mg of melamine and 11.3 mg of copper chloride in 9 g of DMSO; solution b was poured into dispersion a under stirring, and after stirring for a period of time, dispersion c was obtained; solution d was prepared by dissolving 54 mg of cyanuric acid in 9 g of DMSO under stirring; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, then filtered, washed, and dried overnight at 105 °C in an oven to obtain solid B; solid B was calcined under N2 atmosphere at 350 °C for 2 h at a flow rate of 20 mL / min to obtain solid C; 150 mg of solid C was acid-washed with 150 g of 1.0 wt% nitric acid solution for 4 h, washed with water, and dried at 105 °C in an oven to obtain solid D; solid D was calcined at a concentration of 20% and a flow rate of 50 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 400℃ for 2 h and then cooled to room temperature. Subsequently, it was calcined at 250℃ for 3 h in an O2 / N2 atmosphere with a concentration of 15% and a flow rate of 50 mL / min to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I S3. Semiconductor Cu-CN in the catalyst. II The mass percentage content is 22%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 1.8%.

[0034] Example 4 20 g of melamine and 1.68 g of acetone were added to a mixed solvent of 39.45 g of ethanol and 20 g of water. The pH was adjusted to approximately 5.4 with nitric acid. The mixture was heated in an oil bath at 70°C for 3 hours. The solvent was then evaporated to obtain solid A. Solid A was calcined in a muffle furnace at 550°C for 5 hours to obtain carbon nitride semiconductor CN. I ; 150 mg of carbon nitride semiconductor CN IDispersion a was prepared by dispersing melamine in 12 g of DMSO solvent; solution b was prepared by dissolving 41.7 mg of melamine and 11.3 mg of copper chloride in 9 g of DMSO; solution b was poured into dispersion a under stirring, and after stirring for a period of time, dispersion c was obtained; solution d was prepared by dissolving 54 mg of cyanuric acid in 9 g of DMSO under stirring; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, then filtered, washed, and dried overnight in an oven at 80 °C to obtain solid B; solid B was calcined under N2 atmosphere at 350 °C for 2 h at a flow rate of 40 mL / min to obtain solid C; 150 mg of solid C was acid-washed with 150 g of 1.0 wt% nitric acid solution for 4 h, washed with water, and dried in an oven at 105 °C to obtain solid D; solid D was calcined at a concentration of 20% and a flow rate of 35 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 350℃ for 2 h and then cooled to room temperature. Subsequently, it was calcined at 250℃ for 2 h in an O2 / N2 atmosphere with a concentration of 25% and a flow rate of 10 mL / min to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I S4. Semiconductor Cu-CN in the catalyst. II The mass percentage of copper is 18%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 1.4%.

[0035] Example 5 20 g of urea and 1.18 g of acetophenone were added to a mixed solvent of 40 g of DMSO and 20 g of water. The pH was adjusted to approximately 4.3 with sulfuric acid. The mixture was heated in an oil bath at 50°C for 3 hours. The solvent was then evaporated to obtain solid A. Solid A was calcined in a muffle furnace at 550°C for 4 hours to obtain carbon nitride semiconductor CN. I ; 150 mg of carbon nitride semiconductor CN IDispersion a was prepared by dispersing melamine in 9 g of DMSO solvent; solution b was prepared by dissolving 52 mg of melamine and 11.3 mg of copper sulfate in 9 g of DMSO; solution b was poured into dispersion a under stirring, and after stirring for a period of time, dispersion c was obtained; solution d was prepared by dissolving 66 mg of cyanuric acid in 9 g of DMSO under stirring; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, then filtered, washed, and dried overnight at 105 °C in an oven to obtain solid B; solid B was calcined under N2 atmosphere at 300 °C for 2 h at a flow rate of 40 mL / min to obtain solid C; 150 mg of solid C was acid-washed with 150 g of 0.5 wt% nitric acid solution for 4 h, washed with water, and dried at 105 °C in an oven to obtain solid D; solid D was calcined at a concentration of 30% and a flow rate of 20 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 200℃ for 2 h and then cooled to room temperature. Subsequently, it was calcined at 200℃ for 2 h in an O2 / N2 atmosphere with a concentration of 10% and a flow rate of 60 mL / min to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I S5. Semiconductor Cu-CN in the catalyst. II The mass percentage content is 25%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 1.5%.

[0036] Example 6 20 g of urea and 1.32 g of terephthalaldehyde were added to a mixed solvent of 40 g of ethanol and 20 g of water. The pH was adjusted to approximately 4.3 with hydrochloric acid. The mixture was heated in an oil bath at 50°C for 3 hours, and then the solvent was evaporated to obtain solid A. Solid A was then calcined in a muffle furnace at 550°C for 4 hours to obtain carbon nitride semiconductor CN. I ; 150 mg of carbon nitride semiconductor CN IDispersion a was prepared by dispersing melamine in 9 g of DMSO solvent; solution b was prepared by dissolving 32 mg of melamine and 11.3 mg of copper acetate in 9 g of DMSO; solution b was poured into dispersion a under stirring, and after stirring for a period of time, dispersion c was obtained; solution d was prepared by dissolving 45 mg of cyanuric acid in 9 g of DMSO under stirring; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, then filtered, washed, and dried overnight in an oven at 105 °C to obtain solid B; solid B was calcined under N2 atmosphere at 250 °C for 3 h at a flow rate of 20 mL / min to obtain solid C; 150 mg of solid C was acid-washed with 150 g of 0.8 wt% hydrochloric acid solution for 4 h, washed with water, and dried in an oven at 105 °C to obtain solid D; solid D was calcined at a concentration of 5% and a flow rate of 50 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 400℃ for 2 h and then cooled to room temperature. Subsequently, it was calcined at 250℃ for 2 h in an O2 / N2 atmosphere with a concentration of 15% and a flow rate of 70 mL / min to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I S6. Semiconductor Cu-CN in the catalyst. II The mass percentage of the catalyst is 15%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 2.4%.

[0037] Example 7 30 g of urea and 2.28 g of acetone were added to a mixed solvent of 40 g of ethanol and 20 g of water. The pH was adjusted to approximately 6.2 with hydrochloric acid. The mixture was heated in an oil bath at 70°C for 3 hours. The solvent was then evaporated to obtain solid A. Solid A was calcined in a muffle furnace at 550°C for 5 hours to obtain carbon nitride semiconductor CN. I ; 150 mg of carbon nitride semiconductor CN IDispersion a was prepared by dispersing melamine in 9 g of DMSO solvent; solution b was prepared by dissolving 32 mg of melamine and 11.3 mg of copper sulfate in 9 g of DMSO; solution b was poured into dispersion a under stirring, and after stirring for a period of time, dispersion c was obtained; solution d was prepared by dissolving 45 mg of cyanuric acid in 9 g of DMSO under stirring; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, then filtered, washed, and dried overnight in an oven at 105 °C to obtain solid B; solid B was calcined under N2 atmosphere at 250 °C for 3 h at a flow rate of 50 mL / min to obtain solid C; 150 mg of solid C was acid-washed with 150 g of 0.8 wt% hydrochloric acid solution for 4 h, washed with water, and dried in an oven at 105 °C to obtain solid D; solid D was calcined at a concentration of 10% and a flow rate of 80 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 400℃ for 4 h and then cooled to room temperature. Subsequently, it was calcined at 180℃ for 5 h in an O2 / N2 atmosphere with a concentration of 10% and a flow rate of 60 mL / min to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I This is denoted as S7. The semiconductor Cu-CN in the catalyst... II The mass percentage content is 12%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 2.2%.

[0038] Example 8 20 g of urea and 2 g of acetone were added to a mixed solvent of 40 g of ethanol and 20 g of water. The pH was adjusted to approximately 6.2 with hydrochloric acid. The mixture was heated in an oil bath at 50°C for 3 hours. The solvent was then evaporated to obtain solid A. Solid A was calcined in a muffle furnace at 550°C for 5 hours to obtain carbon nitride semiconductor CN. I ; 150 mg of carbon nitride semiconductor CN IDispersion a was prepared by dispersing melamine in 9 g of DMSO solvent; solution b was prepared by dissolving 32 mg of melamine and 11.3 mg of copper acetylacetonate in 9 g of DMSO; solution b was poured into dispersion a under stirring, and after stirring for a period of time, dispersion c was obtained; solution d was prepared by dissolving 45 mg of cyanuric acid in 9 g of DMSO under stirring; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, then filtered, washed, and dried overnight at 105 °C in an oven to obtain solid B; solid B was calcined under N2 atmosphere at 250 °C for 3 h at a flow rate of 50 mL / min to obtain solid C; 150 mg of solid C was acid-washed with 150 g of 1.5 wt% hydrochloric acid solution for 4 h, washed with water, and dried at 105 °C in an oven to obtain solid D; solid D was calcined at a concentration of 20% and a flow rate of 20 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 350℃ for 3 h and then cooled to room temperature. Subsequently, it was calcined at 250℃ for 3 h in an O2 / N2 atmosphere with a concentration of 25% and a flow rate of 30 mL / min to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I This is denoted as S8. The semiconductor Cu-CN in the catalyst... II The mass percentage content is 16%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 2.0%.

[0039] Comparative Example 1 20 g of urea and 1.18 g of acetone were added to a mixed solvent of 39.45 g of ethanol and 20 g of water. The pH was adjusted to approximately 4.3 with nitric acid. The mixture was heated in an oil bath at 50°C for 3 hours. The solvent was then evaporated to obtain solid A. Solid A was calcined in a muffle furnace at 550°C for 4 hours to obtain carbon nitride semiconductor CN. I ; to use carbon nitride semiconductor CN I Under H2 / N2 conditions with a concentration of 20% and a flow rate of 30 mL / min, the mixture was calcined at 300 °C for 2 h and then cooled to room temperature. Subsequently, it was calcined at 200 °C for 2 h in an O2 / N2 atmosphere with a concentration of 20% and a flow rate of 30 mL / min to obtain D1.

[0040] Comparative Example 2 150 mg of MgO was used as CN. IA template was dispersed in 9 g of DMSO solvent to prepare dispersion f; 41.7 mg of melamine and 11.3 mg of copper nitrate were dissolved in 9 g of DMSO to prepare solution b; under stirring, solution b was poured into dispersion f, and after stirring for a period of time, dispersion g was obtained; 54 mg of cyanuric acid was dissolved in 9 g of DMSO to obtain solution d; under stirring, solution d was poured into dispersion g to obtain dispersion h; dispersion h was assembled under stirring, then filtered, washed, and dried overnight in an oven at 105 °C to obtain solid E; solid E was calcined in a N2 atmosphere at 300 °C for 2 h at a flow rate of 30 mL / min to obtain solid F; 150 mg of solid F was acid-washed in 150 g of 0.5 wt% nitric acid solution for 4 h, washed with water, and dried in an oven at 105 °C to obtain solid G; solid G was calcined at a concentration of 20% and a flow rate of 30 mL / min. Under H2 / N2 conditions, the catalyst was calcined at 300℃ for 2 h and then cooled to room temperature. Subsequently, it was calcined at 200℃ for 2 h in an O2 / N2 atmosphere with a concentration of 20% and a flow rate of 30 mL / min to obtain the carbon nitride catalyst Cu-CN. II , denoted as D2.

[0041] Example 9 The prepared catalysts (S1-8, D1, D2) were placed in a 100 mL single-necked flask and dispersed in 25 mL of water. The dispersion was then transferred to a reactor, and the reaction solution was bubbled with N2 at 30 mL / min to remove oxygen. Subsequently, methane was introduced into the reaction solution at a flow rate of 50 mL / min to obtain a methane-saturated reaction solution. The methane saturation process before the reaction experiment was carried out in darkness, with the reaction solution irradiated by a 300 W xenon lamp. The reactant solution was reacted for 1 h on an instrument equipped with a 420 nm cutoff filter. During the reaction, the temperature of the reactant solution was maintained at 25 °C by a cooling water flow. The methane photocatalytic reaction performance was tested, and the results after 1 h of reaction are listed in Table 1 (from GC analysis results). The table shows that the prepared S1 catalyst exhibits a high ethanol yield and very high selectivity, showing great promise. For S1 and D1, D2, it can be seen that the formation of a carbon nitride homojunction catalyst significantly improves the catalytic activity and selectivity of methane photocatalytic conversion to ethanol compared to the two individual semiconductor catalysts. However, S1 and S2-S8 revealed that differences in the preparation conditions of carbon nitride homojunctions affected the final formation of Cu-CN. II / CN I The catalytic activity is also significantly affected.

[0042] Table 1. Catalytic performance of the catalysts prepared in the above examples in the photocatalytic conversion of methane to ethanol.

Claims

1. A carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, characterized in that, The carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol is made of carbon nitride semiconductor CN. I Axially oxygen-coordinated copper single-atom co-catalyst and carbon nitride semiconductor CN II constitute; With carbon nitride semiconductor CN I The first semiconductor is formed by supramolecular assembly and thermal polymerization, on which an axially oxygen-coordinated copper single-atom co-catalyst and a second semiconductor CN are simultaneously introduced. II The carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, denoted as Cu-CN, was prepared. II / CN I ; In the aforementioned carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol, the semiconductor Cu-CN II The mass percentage of the catalyst is 10%~50%, and the loading of axial oxygen-coordinated copper single-atom co-catalyst is 0.1%~5%.

2. A method for preparing the carbon nitride homojunction photocatalyst for the selective conversion of methane to ethanol as described in claim 1, characterized in that, The preparation method includes the following steps: Step 1: Add the carbon-nitrogen source and carbonyl compound to a mixed solvent formed by organic solvent and water, adjust the pH value, heat the reaction, evaporate the solvent, and obtain solid A; calcine solid A in a muffle furnace under an air atmosphere to obtain carbon nitride semiconductor CN. I ; Step 2: Apply carbon nitride semiconductor CN I Dispersion a was prepared by dispersing melamine and copper salt in DMSO solvent; solution b was prepared by dissolving melamine and copper salt in DMSO; solution b was poured into dispersion a under stirring, and after stirring, dispersion c was obtained; cyanuric acid was dissolved in DMSO solvent to obtain solution d; solution d was poured into dispersion c under stirring to obtain dispersion e; dispersion e was assembled under stirring, and then filtered, washed, and dried to obtain solid B. Step 3: Calcine solid B under N2 atmosphere to obtain solid C, which is then acid washed, water washed and dried to obtain solid D; Step 4: Solid D is first calcined in a H2 / N2 reducing atmosphere, and then calcined in an O2 / N2 oxidizing atmosphere to obtain the carbon nitride homojunction photocatalyst Cu-CN. II / CN I .

3. The method for preparing the carbon nitride homojunction photocatalyst according to claim 2, characterized in that, In step 1, the carbon-nitrogen source is one of urea, melamine, dicyandiamide, and thiourea; the carbonyl compound is one of acetone, glyoxal, benzaldehyde, acetophenone, and terephthalaldehyde; and the organic solvent is one of ethanol, methanol, DMSO, and DMF. The mass ratio of carbon-nitrogen source: carbonyl compound: organic solvent: water is 1:(0.01~0.5):(0.1~5):(0.1~5).

4. The method for preparing the carbon nitride homojunction photocatalyst according to claim 2, characterized in that, In step 1, the acid used to adjust the pH value is one of sulfuric acid, nitric acid, or hydrochloric acid, adjusted to a pH value range of 2-7; the heating reaction temperature is 30-80℃, the reaction time is 1-6 h, and the calcination temperature in the muffle furnace is 200-700℃, with a calcination time of 1-6 h.

5. The method for preparing the carbon nitride homojunction photocatalyst according to claim 2, characterized in that, In step 2, the carbon nitride semiconductor CN used to prepare dispersion a I The mass ratio of DMSO solvent is 1:10~100; the copper salt used to prepare solution b is one of copper nitrate, copper acetate, copper chloride, copper sulfate, and copper acetylacetonate, and the mass ratio of melamine:copper salt:DMSO solvent is 1:(0.1~5):(50~500); the mass ratio of solution b to dispersion a used to prepare solution c is (0.1~10):1; The mass ratio of cyanuric acid to DMSO solvent used to prepare solution d is 1:(50~500), and the mass ratio of solution d to dispersion c used to prepare dispersion e is (0.1~5):

1.

6. The method for preparing the carbon nitride homojunction photocatalyst according to claim 2, characterized in that, In step 3, the N2 flow rate is 5~200 mL / min, the calcination temperature is 200~700℃, the calcination time is 1~6 h, the acid used for pickling is one of sulfuric acid, nitric acid, or hydrochloric acid, the concentration of the acid solution is 0.1~2.0 wt%, and the mass ratio of solid C to acid is 1:(200~2000).

7. The method for preparing the carbon nitride homojunction photocatalyst according to claim 2, characterized in that, In step 4, the volume percentage of H2 in the H2 / N2 mixture is 2% to 50%, the flow rate is 5 to 100 mL / min, the temperature is 50 to 500℃, and the time is 1 to 6 h.

8. The method for preparing the carbon nitride homojunction photocatalyst according to claim 2, characterized in that, In step 4, the volume percentage of O2 in the O2 / N2 mixture is 2% to 50%, the flow rate is 5 to 100 mL / min, the temperature is 50 to 500℃, and the time is 1 to 6 h.

9. The method for preparing the carbon nitride homojunction photocatalyst according to claim 2, characterized in that, In steps 2 and 3, the drying temperature is 20~150℃ and the time is 1~24 h.

10. The application of the carbon nitride homojunction photocatalyst according to claim 1 or the carbon nitride homojunction photocatalyst prepared by the method according to any one of claims 2-9, characterized in that, Used for photocatalytic conversion of methane to ethanol.

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