Silver and sulfur co-doped graphite phase carbon nitride denitration film, preparation method and application thereof

Abstract

This invention belongs to the field of graphitic carbon nitride thin film technology, specifically disclosing a silver-sulfur co-doped graphitic carbon nitride denitrification thin film, its preparation method, and its application. The method includes the following steps: preparing a precursor mixture; placing the precursor mixture into a ceramic crucible, and covering the top of the ceramic crucible with fluorine-doped tin oxide glass; annealing the ceramic crucible covered with fluorine-doped tin oxide glass in a muffle furnace, and naturally cooling to room temperature to obtain the silver-sulfur co-doped graphitic carbon nitride denitrification thin film. This invention utilizes the above-mentioned silver-sulfur co-doped graphitic carbon nitride denitrification thin film, its preparation method, and its application. By proposing a metal-nonmetal co-doping strategy and employing the thermal vapor condensation (TVC) method, a silver-sulfur co-doped graphitic carbon nitride thin film with high photocatalytic activity is prepared, and its ability to degrade NO under light irradiation is confirmed. x The effectiveness of this technology can further promote the industrial application of graphitic carbon nitride films in the field of photocatalytic denitrification.

Description

Technical Field

[0001] This invention belongs to the field of graphite phase carbon nitride thin film technology, specifically relating to silver and sulfur co-doped graphite phase carbon nitride denitrification thin films, their preparation methods, and applications. Background Technology

[0002] Nitrogen oxides (NO) x NO (including approximately 95% NO and 5% NO2) is an unavoidable major pollutant in exhaust gases, harming the human respiratory system, the ozone layer, and atmospheric composition. Therefore, there is an urgent need for cost-effective methods to control NO emissions. x The decomposition of pollutants and the recovery of clean air are key areas of focus. Developing photocatalysts that effectively decompose gaseous pollutants under light irradiation is an ideal solution. The key technology in this field lies in improving the surface catalytic performance of photocatalysts to enhance solar spectrum utilization, suppress carrier recombination rates, and increase surface reactivity. Carbon-based catalysts have attracted widespread attention in the field of denitrification due to their low cost, good stability, and non-toxicity.

[0003] Graphitic carbon nitride (g-CN), as a visible light-responsive semiconductor with a band gap of 2.7 eV, possesses the ability to photodegrade and remove NO. x The possibility of NO removal is limited. However, on pure g-CN, the conversion rate of NO to N2 and O2 was only 0.6% at 450℃, and 8.9% at 550℃. To improve the NO removal efficiency of g-CN... x The catalytic activity of NO can be enhanced by appropriate doping with Zn, Bi, and Group IIA elements (such as Mg, Ca, Sr, and Ba). x The removal rate is significantly improved to 30-69%, especially for Zn and Ba-doped g-CN powders, where the efficiency can reach as high as 69.4% and 62%, respectively. However, the process of synthesizing heteroatom-doped g-CN powder is relatively complex. Traditional powdered g-CN catalysts suffer from problems such as easy agglomeration, difficult recovery, and large pressure drop, making them unsuitable for industrial continuous fluid purification systems. Moreover, although single metal or non-metal doping can partially improve photocatalytic performance, the synergistic effect between dopant elements has not been fully explored.

[0004] In summary, the existing technology has the following shortcomings: (1) Existing powder preparation processes mostly use liquid phase impregnation, which has high industrialization costs; (2) Existing single-metal or non-metal-doped g-CN has insufficient visible light response range extension, high photogenerated carrier recombination rate, low quantum efficiency, and lacks stable reactive sites, making it unsuitable for low concentrations of NO. x The capture and conversion capacity for (<100ppm) is insufficient; (3) Traditional g-CN powder has problems such as easy agglomeration, large pressure drop and difficulty in recovery, and is not suitable for industrial continuous flow gas purification systems.

[0005] Therefore, there is a need in the field to develop a method for preparing doped and modified graphitic carbon nitride denitrification films to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide silver and sulfur co-doped graphitic carbon nitride denitrification films, their preparation methods, and applications. By proposing a metal-nonmetal co-doping strategy and employing thermal vapor condensation (TVC) method, silver and sulfur co-doped graphitic carbon nitride films (Ag,S co-doped g-CN films) with high photocatalytic activity were prepared, and their ability to degrade NO under photoirradiation was demonstrated. x The effectiveness of g-CN films can further promote their industrial application in photocatalytic denitrification.

[0007] To achieve the above objectives, this invention provides a method for preparing silver and sulfur co-doped graphitic carbon nitride denitrification films, synthesized via the TVC method, specifically including the following steps: S1. Weigh solid thiourea, grind it in an agate mortar for 10-20 minutes, then weigh solid melamine and solid silver nitrite, grind them together with solid thiourea in an agate mortar for 10-20 minutes, mix them thoroughly, and obtain a precursor mixture. S2. Polish the edge of the ceramic crucible continuously with 400CW, 800CW, and 1200CW sandpaper. Then, put the precursor mixture into a 200-300ml ceramic crucible and cover the top of the ceramic crucible with fluorine-doped tin oxide (FTO) glass. Place a 300-400g load on top of the FTO glass to minimize leakage of the gaseous thiourea source, gaseous melamine source, and gaseous silver nitrite source. S3. Place the ceramic crucible covered with FTO glass into a muffle furnace for annealing and naturally cool to 20-25℃ to obtain a silver and sulfur co-doped graphite phase carbon nitride denitrification film.

[0008] Preferably, in S1, the mass ratio of solid-phase melamine to solid-phase thiourea is 3:2, and the amount of solid-phase silver nitrite is 1-7% of the sum of the masses of solid-phase melamine and solid-phase thiourea.

[0009] Furthermore, the amount of solid silver nitrite used is 1%, 3%, 5% or 7% of the sum of the mass of solid melamine and solid thiourea.

[0010] Preferably, in S3, the annealing specifically involves heating from 20-25°C to 500-510°C at a heating rate of 2-4°C / minute, and maintaining the temperature at 500-510°C for 3 hours.

[0011] The present invention also provides a method for preparing a silver and sulfur co-doped graphite phase carbon nitride denitrification film.

[0012] This invention also provides the application of silver and sulfur co-doped graphite phase carbon nitride denitrification films in the removal of NO under light irradiation.

[0013] This invention utilizes the aforementioned silver and sulfur co-doped graphite-phase carbon nitride denitrification thin film, its preparation method, and its application, with the following beneficial effects: (1) Overcoming the complexity of the preparation process: The present invention adopts the thermal vapor condensation (TVC) method, which is simple and convenient. It does not involve liquid phase dissolution, washing, separation and other processes. Based on a certain ratio of solid precursor, a micron-thick Ag,S co-doped thin film g-CN can be prepared in one step, which is suitable for large-scale industrial production.

[0014] (2) Overcoming the bottleneck of limited modification effect of single doping: This invention is based on a mixture of three precursors: melamine, thiourea, and silver nitrite. A muffle furnace is used to heat and anneal the precursors to generate a gaseous molecular source for thermal polycondensation. Utilizing the coordination ability of Ag and the bandgap modulation ability of S, the synergistic effect between the two doping elements can fundamentally change the electronic structure of g-CN materials, significantly improving the degree of polymerization of g-CN polymers and narrowing the band gap. Ag,S co-doped g-CN films with high visible light response, high photogenerated carrier separation efficiency, and high reactive sites are successfully applied to NO. x During photodegradation.

[0015] (3) This invention, by combining experimental and computational methods, designed Ag,S co-doped g-CN films to further enhance their photochemical performance and provided a profound understanding of the role mechanism of Ag and S doping in g-CN films, offering a new perspective for the precise control of the electronic structure of widely used g-CN-based photocatalytic materials in the future. A simple photocatalytic denitrification device was also constructed, demonstrating that Ag,S co-doped g-CN films deposited on FTO glass substrates can completely remove 50ppm NO gas flowing at a flow rate of 1L / min under room temperature illumination for 3-4 hours.

[0016] (4) The Ag,S co-doped g-CN photocatalyst prepared in this invention can overcome the defects in the engineering application of powdered catalysts. When the prepared Ag,S co-doped g-CN photocatalyst is made into a coating sprayed on ships or buildings, it is expected to remove NO from the air in a green way using sunlight. x Pollutants.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 The flowchart of preparing Ag,S co-doped g-CN thin films using the TVC method is shown in the embodiments of the present invention, which describes the silver and sulfur co-doped graphitic carbon nitride denitrification thin films, their preparation methods, and applications. Figure 2 Images of Examples 1-4 and Comparative Example 1 of the silver-sulfur co-doped graphite phase carbon nitride denitrification thin film of the present invention, its preparation method and application; in, Figure 2 Image (a) in the diagram is an image of CN-MT from Comparative Example 1. Figure 2 (b) in the example is CN-MTAg from Example 2. 1% The picture Figure 2 (c) in the example is CN-MTAg from Example 3. 3% The picture Figure 2 (d) in the text refers to CN-MTAg from Example 1. 5% The picture Figure 2 (e) in Example 4 refers to CN-MTAg. 7% The image; Figure 3 The images are scanning electron microscope (SEM) images of the silver and sulfur co-doped graphitic carbon nitride denitrification films of the present invention, their preparation methods and applications, and the films of Comparative Example 1. in, Figure 3 Image (a) in the figure is a SEM image of CN-MT from Comparative Example 1. Figure 3 (b) in the example is CN-MTAg from Example 2. 1% SEM image, Figure 3 (c) in the example is CN-MTAg from Example 3. 3% SEM image, Figure 3 (d) in the text refers to CN-MTAg from Example 1. 5% SEM image, Figure 3 (e) in Example 4 refers to CN-MTAg. 7% SEM image; Figure 4 Transmission electron microscope (TEM) images of the silver-sulfur co-doped graphitic carbon nitride denitrification thin film of the present invention, its preparation method and application, and the thin film of Comparative Example 1. in, Figure 4 (a) in the figure is a TEM image of CN-MT in Comparative Example 1. Figure 4 (b) in the example is CN-MTAg from Example 2. 1% TEM image, Figure 4 (c) in the example is CN-MTAg from Example 3. 3% TEM image, Figure 4 (d) in the text refers to CN-MTAg from Example 1.5% TEM image, Figure 4 (e) in Example 4 refers to CN-MTAg. 7% TEM image; Figure 5 Example 1 shows the elemental distribution diagram of the silver-sulfur co-doped graphitic carbon nitride denitrification film of the present invention, its preparation method, and its application. in, Figure 5 (a) in the text is CN-MTAg 5% The distribution diagram of C elements, Figure 5 (b) in the text is CN-MTAg 5% The distribution diagram of N elements, Figure 5 (c) in the text refers to CN-MTAg. 5% Distribution diagram of O element, Figure 5 (d) in the text refers to CN-MTAg. 5% Distribution diagram of S element, Figure 5 (e) in the text refers to CN-MTAg. 5% Distribution map of Ag elements; Figure 6 The X-ray photoelectron spectroscopy (XPS) spectra of the silver-sulfur co-doped graphitic carbon nitride denitrification films of the present invention, their preparation methods and applications, and the films of Comparative Example 1 are shown. in, Figure 6 (a) in the figure is the C 1s XPS plot of the films of Examples 1-4 and Comparative Example 1. Figure 6 (b) in the figure shows the N 1s XPS plots of the films from Examples 1-4 and Comparative Example 1. Figure 6 (c) in the figure is the O 1s XPS plot of the films of Examples 1-4 and Comparative Example 1. Figure 6 In the figure (d), the S 2p XPS plots of the films of Examples 1-4 and Comparative Example 1 are shown. Figure 6 (e) in the figure is the Ag 3d XPS diagram of the films of Examples 1-4 and Comparative Example 1; Figure 7 Fourier transform infrared vibrational spectra (FTIR) and X-ray electron diffraction (XRD) patterns of the silver-sulfur co-doped graphitic carbon nitride denitrification thin films of the present invention, their preparation methods and applications, and Comparative Example 1. in, Figure 7 (a) in the figure is the FTIR spectrum of the thin films of Examples 1-4 and Comparative Example 1. Figure 7 (b) in the figure is the XRD pattern of the thin film of Examples 1-4 and Comparative Example 1; Figure 8 The optical properties of the silver-sulfur co-doped graphitic carbon nitride denitrification thin film of the present invention, its preparation method and application, and the thin film of Comparative Example 1 are shown in the figure. in, Figure 8(a) in the figure is the Tauc plot (derived from UV-Vis absorption spectrum). Figure 8 (b) in the figure is the XPS valence band spectrum. Figure 8 (c) in the diagram is a schematic diagram of the band structure. Figure 8 (d) in the image represents the fluorescence spectrum; Figure 9 This is an atomic structure model diagram of the silver and sulfur co-doped graphitic carbon nitride denitrification thin film, its preparation method, and its application in this invention (gray, blue, white, yellow, and light blue spheres represent carbon (C), nitrogen (N), hydrogen (H), sulfur (S), and silver (Ag) atoms, respectively). in, Figure 9 Image (a) is a top view of the atomic structure model of pure graphitic carbon nitride (CN). Figure 9 Image (b) is a top view of the S-doped graphitic carbon nitride (SCN) structural model. Figure 9 (c) is a top view of the Ag-S co-doped graphitic carbon nitride structure model (AgSCN); Figure 10 The total density of states (TPDOS) curves of CN, SCN, and AgSCN calculated by DFT (ωB97XD / SDD) for the silver and sulfur co-doped graphitic carbon nitride denitrification thin film, its preparation method, and its application in this invention. in, Figure 10 (a) in the figure is the TPDOS curve of CN. Figure 10 (b) in the figure is the TPDOS curve of SCN. Figure 10 (c) in the figure is the TPDOS curve of AgSCN. The inset shows the spatial distribution of the highest occupied molecular orbital (HOMO) (top right corner) and HOMO-1 (bottom left corner). Figure 11 The UV-Vis absorption spectra of CN, SCN, and AgSCN films calculated by TD-DFT (TD-ωB97XD / SDD) for the silver and sulfur co-doped graphitic carbon nitride denitrification films, their preparation methods, and applications in this invention are shown below. in, Figure 11 In the image, (a) is the UV-Vis absorption spectrum of the CN thin film. Figure 11 (b) in the figure is the UV-Vis absorption spectrum of the SCN thin film. Figure 11 (c) in the figure is the UV-Vis absorption spectrum of the AgSCN thin film; the excited states of interest are marked in blue; the inset is the spatial distribution of its charge carriers, where the blue and green isosurfaces represent holes and electrons, respectively (isosurface value = 0.001 eV). D and E These represent the average distance between electrons and holes and the exciton binding energy, respectively. Figure 12In Example 4 of this invention, a photocatalytic gas-solid reactor containing CN-MTAg was used to prepare a silver-sulfur co-doped graphite-phase carbon nitride denitrification thin film, its preparation method, and its application. 5% Top view of the sample after denitrification; Figure 13 In Example 4 of this invention, a photocatalytic gas-solid reactor containing CN-MTAg was used to prepare a silver-sulfur co-doped graphite-phase carbon nitride denitrification thin film, its preparation method, and its application. 5% Side view of the sample after denitrification; Figure 14 This is a graph showing the change in NO concentration in Experiment Example 4 of the present invention, which describes the silver and sulfur co-doped graphite phase carbon nitride denitrification film, its preparation method, and its application. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] Example 1 like Figure 1 As shown, the preparation method of silver and sulfur co-doped graphite phase carbon nitride denitrification thin film includes the following steps: S1. Weigh 4g of solid thiourea and grind it in an agate mortar for 10 minutes. Then weigh 6g of solid melamine and 0.5g of solid silver nitrite and grind them together with solid thiourea in an agate mortar for 10 minutes to mix them thoroughly and obtain a precursor mixture. S2. Polish the edge of the 300ml ceramic crucible with sandpaper of 400CW, 800CW and 1200CW. Then put the precursor mixture into the ceramic crucible, cover the top of the ceramic crucible with FTO glass, and place the 360g load on the top of the FTO glass. S3. Place the ceramic crucible covered with FTO glass into a muffle furnace for annealing. Start from 25°C and heat to 500°C at a rate of 3°C / min. Hold at 500°C for 3 hours, then allow to cool naturally to 25°C to obtain a silver-sulfur co-doped graphite-phase carbon nitride denitrification film, denoted as CN-MTAg. 5% .

[0022] Example 2 A method for preparing silver and sulfur co-doped graphite-phase carbon nitride denitrification films includes the following steps: S1. Weigh 4g of solid thiourea and grind it in an agate mortar for 10 minutes. Then weigh 6g of solid melamine and 0.1g of solid silver nitrite and grind them together with solid thiourea in an agate mortar for 10 minutes to mix them thoroughly and obtain a precursor mixture. S2. Polish the edge of the 300ml ceramic crucible with sandpaper of 400CW, 800CW and 1200CW. Then put the precursor mixture into the ceramic crucible, cover the top of the ceramic crucible with FTO glass, and place the 360g load on the top of the FTO glass. S3. Place the ceramic crucible covered with FTO glass into a muffle furnace for annealing. Start from 25°C and heat to 500°C at a rate of 3°C / min. Hold at 500°C for 3 hours, then allow to cool naturally to 25°C to obtain a silver-sulfur co-doped graphite-phase carbon nitride denitrification film, denoted as CN-MTAg. 1% .

[0023] Example 3 A method for preparing silver and sulfur co-doped graphite-phase carbon nitride denitrification films includes the following steps: S1. Weigh 4g of solid thiourea and grind it in an agate mortar for 10 minutes. Then weigh 6g of solid melamine and 0.3g of solid silver nitrite and grind them together with solid thiourea in an agate mortar for 10 minutes to mix them thoroughly and obtain a precursor mixture. S2. Polish the edge of the 300ml ceramic crucible with sandpaper of 400CW, 800CW and 1200CW. Then put the precursor mixture into the ceramic crucible, cover the top of the ceramic crucible with FTO glass, and place the 360g load on the top of the FTO glass. S3. Place the ceramic crucible covered with FTO glass into a muffle furnace for annealing. Start from 25°C and heat to 500°C at a rate of 3°C / min. Hold at 500°C for 3 hours, then allow to cool naturally to 25°C to obtain a silver-sulfur co-doped graphite-phase carbon nitride denitrification film, denoted as CN-MTAg. 3% .

[0024] Example 4 A method for preparing silver and sulfur co-doped graphite-phase carbon nitride denitrification films includes the following steps: S1. Weigh 4g of solid thiourea and grind it in an agate mortar for 10 minutes. Then weigh 6g of solid melamine and 0.7g of solid silver nitrite and grind them together with solid thiourea in an agate mortar for 10 minutes to mix them thoroughly and obtain a precursor mixture. S2. Polish the edge of the 300ml ceramic crucible with sandpaper of 400CW, 800CW and 1200CW. Then put the precursor mixture into the ceramic crucible, cover the top of the ceramic crucible with FTO glass, and place the 360g load on the top of the FTO glass. S3. Place the ceramic crucible covered with FTO glass into a muffle furnace for annealing. Start from 25°C and heat to 500°C at a rate of 3°C / min. Hold at 500°C for 3 hours, then allow to cool naturally to 25°C to obtain a silver-sulfur co-doped graphite-phase carbon nitride denitrification film, denoted as CN-MTAg. 7% .

[0025] Comparative Example 1 A method for preparing a graphitic carbon nitride thin film includes the following steps: S1. Weigh 4g of solid thiourea, grind it in an agate mortar for 10 minutes, then weigh 6g of solid melamine, grind it together with the solid thiourea in the agate mortar for 10 minutes, mix thoroughly to obtain a precursor mixture. S2. Polish the edge of the 300ml ceramic crucible with sandpaper of 400CW, 800CW and 1200CW. Then put the precursor mixture into the ceramic crucible, cover the top of the ceramic crucible with FTO glass, and place the 360g load on the top of the FTO glass. S3. Place the ceramic crucible covered with FTO glass into a muffle furnace for annealing. Starting from 25°C, heat the crucible to 500°C at a heating rate of 3°C / min. Hold the temperature at 500°C for 3 hours and then allow it to cool naturally to 25°C to obtain a silver and sulfur co-doped graphite phase carbon nitride denitrification film, denoted as CN-MT.

[0026] Experimental Example 1 Physical comparisons were made of the films prepared in Examples 1-4 and Comparative Example 1, and the results are as follows: Figure 2 As shown. From Figure 2 As can be seen, Ag doping affects the color of the film. As the Ag content increases, the film gradually deepens from light yellow to dark yellow.

[0027] Experimental Example 2 To confirm that Ag and S co-doping was achieved in the g-CN thin films synthesized by the TVC method, the structures of the thin films prepared in Examples 1-4 and Comparative Example 1 were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared vibrational spectroscopy (FTIR), X-ray photoelectron diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results are as follows: Figures 3-7 As shown.

[0028] Figure 3 For the SEM image of the thin film, from Figure 3 As can be seen, the overall surface morphology of the film exhibits a curled, flower-like structure, indicating the formation of a well-polymerized g-CN-based film, in which the ordered microstructure preferentially follows the curves. <100> directional growth, forming a larger (002) plane. The flower width gradually increases with increasing Ag content: CN-MT and CN-MTAg1% Similar to each other (4-6 μm), CN-MTAg 3% and CN-MTAg 5% Slightly larger (8-11 μm), CN-MTAg 7% The maximum value (13-17 μm) was reached. The expansion of the micron-sized flowers indicates that silver incorporation promoted polymerization. However, in CN-MTAg 7% The decrease in the number density of micron-sized flower-like structures suggests that further Ag doping may have hindered nucleation growth within g-CN or reached the limit of particle integration.

[0029] CN-MT, CN-MTAg 1% CN-MTAg 3% CN-MTAg 5% and CN-MTAg 7% The film thicknesses were 2.93, 2.74, 3.11, 4.87, and 3.73 μm, respectively. CN-MTAg 5% The thickness is the largest, indicating that the micron flowers stacked on its surface may generate the largest number of photogenerated carriers.

[0030] Figure 4 For TEM images of the thin film, from Figure 4 As can be seen, many nanoscale spherical particles exist on the surface of the micron-sized flowers; these are residual Ag and crystalline Ag₂O nanoparticles. With increasing Ag doping concentration, the aggregation of Ag and Ag₂O nanoparticles becomes more pronounced.

[0031] Figure 5 This is an elemental surface distribution diagram of the thin film in Example 1, from... Figure 5 As can be seen, S and Ag elements are uniformly distributed throughout the sample, indicating that Ag has the opportunity to be embedded in the porous structure of g-CN. The N of the heptaazine ring of g-CN forms a cross-linking network through coordination interaction with Ag, which promotes polymerization.

[0032] Figure 6 XPS images of the thin films from Examples 1-4 and Comparative Example 1, from... Figure 6 As can be seen, the C1s XPS mainly forms two peaks at 284.9 and 288.3 eV, corresponding to the sp in the g-CN structural unit. 2 Hybrid C. In the five samples of Examples 1-4 and Comparative Example 1, the intensities and relative ratios of these two peaks were almost identical, indicating that the chemical bonding environment of C was similar in all samples. N 1s XPS was distributed at three peaks at 398.9, 399.9, and 401.1 eV, which were attributed to the CN=C bond sp. 2 The N in hybridized N, N-(C)3, or HN-(C)2 groups and the N in -NH2. Notably, CN-MTAg 5%The highest peak intensity was observed at 398.9 eV, and the peak ratio relative to 399.9 and 401.1 eV was higher than other samples, indicating a higher abundance of structural units, i.e., an increased degree of polymerization. O 1s XPS consistently showed a main peak at 531.5 eV, attributed to surface-adsorbed hydroxyl groups or physi-adsorbed water molecules, while the smaller peak at 530.7 eV was attributed to O-Ag bonds, providing direct evidence for Ag₂O nanoparticles formed under aerobic annealing conditions. S 2p XPS showed two spin-orbit splitting peaks at 161.9 eV (S 2p³ / 2) and 163.1 eV (S 2p¹ / 2), corresponding to CSC covalent bonds. In CN-MTAg… 5% In Ag, the simultaneous increase in oxygen content leads to the retention of more sulfur, even forming S=O bonds at 169.2 eV. Two main peaks were observed in Ag 3d XPS, located at 367.5 and 373.5 eV, corresponding to the 3d peaks of silver. 5 / 2 and 3D 3 / 2 The binding energy reflects the Ag-Ag bonds present in Ag nanoparticles. CN-MTAg 5% and CN-MTAg 7% The additional small peaks at 376.9 and 378.4 eV are characteristic of plasma loss. Most of the Ag dopant is present within the metal nanoparticles, with a minority in the oxidized state, while trace amounts of silver bound to nitrogen or sulfur are undetectable in all XPS. In CN-MTAg... 5% Among the various types of silver, silver species exhibit the most ideal dispersion and the highest silver content in the g-CN matrix. Therefore, using 5% AgNO2 as a precursor is the optimal dosage for constructing Ag,S co-doped g-CN films.

[0033] Figure 7 The FTIR and XRD patterns of the thin films from Examples 1-4 and Comparative Example 1 are shown below. Figure 7 As can be seen, all FTIR spectra show a high degree of similarity, indicating that the g-CN framework structure is preserved after silver doping. 850 cm⁻¹ -1 The prominent peak at 1200-1700 cm⁻¹ is attributed to the respiratory vibrational pattern of the heptaazine unit. -1 The absorption bands within the region are attributed to the stretching vibrations of the CN / CO / CS structural groups. (3200-3400 cm⁻¹) -1 The broad peaks within the range originate from the NH / OH stretching vibration. No significant vibrational characteristics were observed for Ag-Ag and Ag-O bonds, likely due to the low doping concentration, which has negligible impact on the overall vibrational fingerprint. XRD analysis shows that the peaks located at 2... θThe strong diffraction peaks at 14.87° and 28.21° are attributed to the (100) and (002) planes. The (100) plane is associated with the in-plane periodic stacking of heptaazine units and the development of micron-like flower-like morphology, while the (002) plane reflects the interlayer stacking of conjugated microstructures formed through π–π interactions. The greater intensity of the (100) diffraction peaks compared to the (002) planes indicates that in-plane aggregation of heptaazine units is dominant, rather than vertical stacking. CN-MTAg 5% The sample exhibited the highest peak intensities at (100) and (002), indicating that a 5% AgNO2 precursor loading achieved optimal crystallinity enhancement. This improvement is attributed to the silver dopant linking the heptaazine units through coordination bonds with nitrogen, thereby promoting structural ordering and enhancing the extended π-conjugated network in the silver-sulfur co-doped g-CN film.

[0034] Experimental Example 3 (1) The optical properties and electronic structure of the thin films prepared in Examples 1-4 and Comparative Example 1 were tested, and the results are as follows: Figure 8 As shown.

[0035] from Figure 8 As can be seen from (a) in the figure, from CN-MT, CN-MTAg 1% CN-MTAg 3% To CN-MTAg 5% The band gap of the thin film gradually decreases, until CN-MTAg 7% The values ​​increased further, reaching 2.75 eV, 2.57 eV, 2.41 eV, 2.21 eV, and 2.36 eV respectively, indicating that visible light absorption increases with increasing Ag dopant content, with 5% Ag dopant exhibiting the highest visible light absorption. Figure 8 As can be seen from (b), the VB peak of CN-MT is located at 1.61 eV, and CN-MTAg 5% The VB peak shifts to 1.38 eV, which is generally attributed to the reconstruction and increase of the π conjugated structure.

[0036] Based on the estimated band gap and the measured VB top, the CB bottom of all samples is calculated, thereby constructing a band structure diagram, such as... Figure 8 As shown in (c) of CN-MTAg. 5% It has the smallest band gap, maximizing the absorption of visible light, and its highest VB peak facilitates faster transfer of photogenerated holes. From Figure 8As can be seen in (d), the two emission peaks at 420-440 nm and 450-470 nm in the fluorescence spectra of all samples correspond to the reverse processes of π→π* and n→π* electronic transitions, that is, the recombination of electrons and holes is related to this electronic activity. The atomic radii of S (104 pm) and Ag (172 pm) are much larger than those of C (77 pm) and N (70 pm). The addition of S and Ag to the g-CN lattice causes greater distortion of the (100) plane, thus generating richer electronic transition activities. CN-MTAg 5% and CN-MTAg 7% The low quenching intensity indicates that the recombination of photogenerated charges has been effectively suppressed.

[0037] (2) In order to provide a deeper understanding of the electronic transition and light absorption mechanism in Ag and S co-doped g-CN thin films, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were subsequently performed.

[0038] The above experimental characterization shows that S atoms can bind to the main framework of g-CN, while Ag dopants form Ag-N coordination bonds with six N atoms at the g-CN pore sites. Therefore, a cluster model was constructed to simulate S-doped g-CN (named SCN) derived from melamine and thiourea precursors and Ag / S co-doped g-CN (named AgSCN) derived from melamine, thiourea, and AgNO2. For comparison, a pristine pure g-CN model (named CN) was also constructed. The results are as follows: Figure 9 As shown, the geometries of CN, SCN, and AgSCN were obtained through DFT (ωB97XD / SDD) optimization. Gray, blue, white, yellow, and light blue spheres represent carbon (C), nitrogen (N), hydrogen (H), sulfur (S), and silver (Ag) atoms, respectively. The figure shows C–S bond lengths of 1.8–1.9 Å and Ag–N coordination bond lengths of 2.4–2.7 Å, demonstrating the possibility of chemical bond formation. The binding energies of S occupying N vacancies in the g-CN film and Ag occupying pore sites in g-CN are -2.148 eV and -1.833 eV, respectively, confirming the rationale for S and Ag embedding within the g-CN framework structure.

[0039] Figure 10 Total density of states (TPDOS) plots of CN, SCN, and AgSCN thin films calculated for DFT, from Figure 10 As can be seen, their band gaps gradually decrease, reaching 5.77, 4.73, and 2.93 eV respectively. This is attributed to the insertion of band gap states (ranging from -9 to -5 eV) caused by heteroatom S doping. Furthermore, the more stable molecular energy levels formed after Ag doping indirectly drive the S band gap states to higher energy levels. The total partial state density of AgSCN (… Figure 10(c) indicates that the Ag-N coordinate bond corresponds to the orbital energy level distribution from -12 to -10 eV, indicating that the formation of the Ag-N bond occupies the lower energy level region, thus pushing up the energy level of the non-bonding electronic state originating from S.

[0040] The natural population analysis (NPA) electron distribution data of relevant atoms in AgSCN were obtained by DFT calculation, and the results are shown in Table 1. Table 1 shows that the Ag-N coordination bond mainly contributes from the 5s electrons of Ag and the 2s2p electrons of the N hybrid orbitals of g-CN, forming a stable σ bond, thus occupying a lower energy level region. The chemical bonding characteristics follow... E σ < E π < E n < E π* < E σ* The energy level sequence. Therefore, the σ-bonding orbitals and their σ* antibonding orbitals of Ag-N should be at lower and higher energy levels, respectively, which is consistent with the PDOS distribution characteristics of Ag in AgSCN ( Figure 10 (c) The blue curve matches perfectly.

[0041] Table 1. Electron distribution data from natural population analysis (NPA)

[0042] To elucidate the roles of Ag and S in the optical properties of modulation-modified g-CN thin films, the UV-Vis absorption spectra of CN, SCN, and AgSCN thin films were predicted using TD-DFT (TD-ωB97XD / SDD). The results are as follows: Figure 11 As shown. From Figure 11 As can be seen, the original CN, SCN, and AgSCN films all have an absorption peak at ~290 nm, while the SCN film has another absorption peak at ~460 nm, and AgSCN has an absorption peak at ~550 nm. This indicates that the original CN film has limited utilization of sunlight, while S and Ag doping can extend the light absorption into the visible light region. In particular, the absorption peak of Ag, S co-doped g-CN (i.e., the AgSCN model) shows a redshift of ~90 nm, highlighting the synergistic effect of Ag in further enhancing the visible light response.

[0043] Experiment Example 4 Application of the Ag,S co-doped g-CN thin film prepared in the examples for NO removal under light irradiation.

[0044] Design a simple gas-solid reactor for NOx removal, such as... Figures 12-13As shown. This denitrification device is sealed and made of quartz glass (which has better light transmittance than ordinary glass), measuring 12×12×5cm in length, width, and height. 3 One end is the inlet of a NO (50ppm) gas cylinder, and the other end is the outlet, which is connected to a NO concentration detection device. A 10×10cm sheet is placed at the bottom of the container. 2 The Ag,S co-doped g-CN thin film has a light transmission window at the top, allowing a xenon lamp to vertically irradiate the film from the top. The formula for calculating the NO removal rate (%) is as follows: % In the formula, C 0 and C These represent the NO concentrations in the inlet and outlet gases, respectively.

[0045] The NO inlet flow rate is 1 L / min. A comparison was made between two g-CN thin films (CN-MT and CN-MTAg). 5% Under room temperature and light irradiation, the NO gas concentration ratio before and after the test was compared to determine the NO removal efficiency. The results are as follows: Figure 14 As shown. From Figure 14 As can be seen, the Ag,S co-doped g-CN film has a higher efficiency in removing NO, and can completely remove NO within 176 minutes.

[0046] Therefore, this invention employs the aforementioned silver and sulfur co-doped graphitic carbon nitride denitrification thin films, their preparation methods, and applications. By proposing a metal-nonmetal co-doping strategy and using the thermal vapor condensation (TVC) method, Ag,S co-doped g-CN thin films with high photocatalytic activity are prepared, and their ability to degrade NO under light irradiation is demonstrated. x The effectiveness of g-CN films can further promote their industrial application in photocatalytic denitrification.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a silver- and sulfur-co-doped graphite-phase carbon nitride denitrification film, characterized in that, Includes the following steps: S1. Weigh solid thiourea, grind it in an agate mortar for 10-20 minutes, then weigh solid melamine and solid silver nitrite, grind them together with solid thiourea in an agate mortar for 10-20 minutes, mix them thoroughly, and obtain a precursor mixture. S2. Polish the edge of the ceramic crucible continuously with 400CW, 800CW and 1200CW sandpaper, then put the precursor mixture into the ceramic crucible, cover the top of the ceramic crucible with fluorine-doped tin oxide glass, and place the load on the top of the fluorine-doped tin oxide glass. S3. Place the ceramic crucible covered with fluorine-doped tin oxide glass into a muffle furnace for annealing and naturally cool to 20-25℃ to obtain a silver and sulfur co-doped graphite phase carbon nitride denitrification film.

2. The method for preparing a silver and sulfur co-doped graphite-phase carbon nitride denitrification film according to claim 1, characterized in that: In S1, the mass ratio of solid melamine to solid thiourea is 3:2, and the amount of solid silver nitrite is 1-7% of the sum of the masses of solid melamine and solid thiourea.

3. The method for preparing a silver-sulfur co-doped graphite-phase carbon nitride denitrification film according to claim 1, characterized in that, In S3, the annealing process specifically involves heating from 20-25℃ to 500-510℃ at a heating rate of 2-4℃ / minute, and then maintaining the temperature at 500-510℃ for 3 hours.

4. The silver-sulfur co-doped graphite phase carbon nitride denitration film prepared by the method described in any one of claims 1-3.

5. The application of the silver and sulfur co-doped graphite phase carbon nitride denitrification film as described in claim 4 in the removal of NO under light irradiation.

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