Potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material as well as preparation and application thereof

Abstract

The invention discloses a potassium-doped carbon nitride and silver phosphate heterojunction photocatalytic material as well as preparation and application thereof. The material comprises nano-sheet potassium-doped carbon nitride and silver phosphate particles deposited on a potassium-doped carbon nitride sheet layer, and the potassium-doped carbon nitride and the silver phosphate particles form a heterojunction structure. The preparation method comprises the following steps: calcining a mixed solid of organic amine and a potassium source to obtain potassium-doped carbon nitride; dispersing potassium-doped carbon nitride in water to obtain a first suspension, adding an Ag < + > solution into the first suspension to obtain a second suspension, adding a phosphate solution into the second suspension, and reacting to obtain a first product; and centrifuging the first product to obtain a precipitate, washing and drying to obtain the K-C3N4 / Ag3PO4 heterojunction material. The photocatalytic oxidation desulfurization conversion rate of the material can reach 90% or above, and the material has excellent oxidative degradation capacity on sulfides such as DBT which are difficult to remove through traditional hydrodesulfurization and can meet the strict standard of deep desulfurization of fuel oil.

Description

Technical Field

[0001] This invention relates to a photocatalytic oxidation desulfurizer, and more particularly to a potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material, its preparation, and its application in fuel desulfurization. Background Technology

[0002] The environmental and industrial problems caused by sulfides such as sulfides, thiophene, and dibenzothiophene (DBT) in fuel oil are becoming increasingly prominent. The sulfur dioxide (SO2) released from the combustion of these sulfides can induce acid rain, corrode industrial equipment, poison platinum-based catalysts in automotive exhaust treatment systems, and harm the human respiratory and nervous systems. Fuel desulfurization technology can effectively remove sulfides from fuel oil.

[0003] Current mainstream fuel desulfurization technologies each have their limitations: Hydrodesulfurization (HDS) can remove simple sulfides, but deep desulfurization requires high temperature and pressure and expensive catalysts, resulting in high energy consumption and a tendency to reduce fuel octane number; it is also ineffective at removing thiophene sulfides. Adsorption desulfurization (ADS) can achieve deep desulfurization, but the adsorbent capacity and regeneration ability are limited. Physical extraction desulfurization (EDS) has solvents that are volatile and have high recovery costs. Biological desulfurization (BDS) has complex equipment and low catalyst efficiency. Chemical oxidation desulfurization (ODS) has problems with secondary pollution and high catalyst loss.

[0004] Photocatalytic oxidative desulfurization (PODS) has become a research hotspot due to its green and low-cost nature. Its core lies in the generation of active free radicals by photocatalysts under visible light to oxidize sulfides. However, existing photocatalytic systems still have shortcomings: pure graphitic carbon nitride (g-C3N4) has a wide band gap and narrow light absorption range, and a fast photogenerated electron-hole recombination rate; some composite modified photocatalysts suffer from poor interfacial contact, high electron transfer resistance, and dependence on non-green oxidants, failing to balance desulfurization efficiency, environmental friendliness, and industrial feasibility. Currently, there are no reports on photocatalytic materials prepared based on carbon nitride and metallic silver and their application in fuel desulfurization. Summary of the Invention

[0005] Objectives of this invention: The objective of this invention is to provide a potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material, addressing the problem of poor photocatalytic oxidation and desulfurization performance of existing photocatalytic materials. A second objective is to propose a method for preparing this potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material, solving the problem of how to prepare such a material. A third objective is to propose the application of this potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material in the photocatalytic degradation of sulfur-containing compounds in fuel oil, solving the problem of how to photocatalytically degrade sulfur-containing compounds in fuel oil.

[0006] Technical solution: The present invention discloses a potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material, comprising nanosheet-like potassium-doped carbon nitride and silver phosphate particles deposited on the potassium-doped carbon nitride sheets, wherein the potassium-doped carbon nitride and the silver phosphate particles form a heterojunction structure.

[0007] The second aspect of this invention discloses a method for preparing the above-mentioned potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material, comprising the following steps: (1) Calcining a mixture of organic amine and potassium source solid yields potassium-doped carbon nitride; (2) Disperse potassium-doped carbon nitride in water to obtain a first suspension, and then add Ag + The solution is added to the first suspension to obtain the second suspension. A phosphate solution is then added to the second suspension, and the reaction yields the first product. (3) Centrifuge the first product to collect the precipitate, wash and dry it to obtain K-C3N4 / Ag3PO4 heterojunction material.

[0008] Preferably, in step (1), the organic amine includes at least one of melamine, urea, and dicyandiamide, and the potassium source includes at least one of potassium chloride, potassium phosphate, potassium dihydrogen phosphate, potassium carbonate, potassium sulfate, and potassium nitrate.

[0009] Preferably, in step (1), the mass ratio of the organic amine to the potassium source is 5-20:2-10.

[0010] Preferably, in step (1), the calcination method is as follows: in an air atmosphere, the mixed solid of organic amine and potassium source is heated from room temperature to 500-600℃ at a rate of 1-10℃ / min and kept at the temperature for 1-10h to obtain the calcined product.

[0011] Preferably, in step (2), Ag + The solution is a 0.01-0.5M aqueous solution of silver nitrate, and the phosphate solution is a 0.01-0.5M aqueous solution of sodium phosphate. The mass ratio of potassium-doped carbon nitride to silver nitrate is 0.05-0.3:0.05-0.5.

[0012] Preferably, in step (2), Ag + The molar ratio with phosphate is 3-5:1.

[0013] Preferably, in step (2), Ag + The method for adding the solution to the first suspension is as follows: under stirring conditions at room temperature, add Ag... + The solution is slowly added dropwise to the first suspension, and the second suspension is obtained after stirring for 1-5 hours. The reaction conditions after adding phosphate solution are: stirring at room temperature for 1-10 hours.

[0014] Preferably, in step (1), the method for preparing the mixed solid of organic amine and potassium source is as follows: The organic amine and potassium source are dispersed in an alcohol solvent and stirred to obtain a mixture. The alcohol solvent in the mixture is removed, and the resulting dry solid is the mixed solid of organic amine and potassium source.

[0015] The third aspect of this invention discloses the application of the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material prepared by the above preparation method in the photocatalytic degradation of sulfur-containing compounds in fuel oil.

[0016] In some embodiments, the sulfur-containing compounds in the fuel oil include sulfides, thiophene, dibenzothiophene, and other thiophene derivatives.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) From the morphological level, potassium doping transforms the bulk structure of g-C3N4 into thinner two-dimensional nanosheets, significantly increasing the specific surface area and the number of active sites. At the same time, potassium-doped carbon nitride can serve as an excellent support, allowing Ag3PO4 nanoparticles to be uniformly loaded on its surface, effectively suppressing the aggregation problem of Ag3PO4. From the carrier transport level, PL spectroscopy characterization shows that the fluorescence intensity of K-C3N4 / Ag3PO4 is low, indicating that its photogenerated electron-hole recombination rate is significantly reduced and the carrier separation efficiency is significantly improved. Moreover, the interfacial electrostatic interaction of the heterojunction formed by potassium-doped carbon nitride and silver phosphate constructs an efficient Z-scheme carrier transport channel, reducing charge transfer resistance. The two work together to enhance the core driving force of the photocatalytic reaction.

[0018] (2) In photocatalytic oxidation desulfurization applications, the desulfurization conversion rate of K-C3N4 / Ag3PO4 is significantly higher than that of pure g-C3N4, K-C3N4 and Ag3PO4 monomer materials, reaching over 90%. The core reason is that the heterojunction structure broadens the visible light response range and promotes the transfer and separation of photogenerated carriers, exhibiting excellent oxidative degradation capabilities for sulfides that are difficult to remove by traditional hydrodesulfurization such as DBT, thus meeting the stringent standards for deep fuel desulfurization.

[0019] (3) The raw materials used in this invention are common analytical grade reagents such as melamine, potassium chloride, and silver nitrate, which are widely available and inexpensive. The preparation process does not require harsh conditions such as high temperature and high pressure. The muffle furnace calcination, ultrasonic dispersion, centrifugal washing and other processes are simple to operate and the energy consumption is much lower than that of traditional hydrodesulfurization technology. Moreover, the desulfurization process does not require the addition of harmful oxidants, which is in line with the development concept of green chemical industry. At the same time, the material structure has strong stability, which provides convenience for subsequent recycling and reuse and has high industrial application value. Attached Figure Description

[0020] Figure 1SEM images of samples from different catalytic materials; Figure 2 HRTEM and EDS images of different catalytic material samples; Figure 3 XRD patterns of samples from different catalytic materials; Figure 4 FTIR spectra of different catalytic material samples; Figure 5 Steady-state fluorescence spectra of different catalytic material samples; Figure 6 This is a comparison chart of the desulfurization performance of different catalytic material samples. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0022] Example 1: A method for preparing a potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material is as follows: (1) Weigh 12g of melamine and 6g of potassium chloride, put them into a 100mL glass beaker, add 50mL of anhydrous ethanol, place the beaker on a magnetic stirrer, and stir at 250r / min for 5h to ensure that the materials are mixed evenly. After stirring, transfer to a drying oven and dry overnight at 70℃ until the ethanol is completely evaporated to obtain a mixed solid.

[0023] The mixed solids were placed in a covered crucible, which was then placed in a muffle furnace. An air atmosphere and a heating program were set: the temperature was increased from room temperature to 550℃ at a rate of 3.5℃ / min, and held at this temperature for 4 hours to complete the thermal polymerization. After cooling, the product was ground and washed multiple times with deionized water to remove residual potassium chloride. It was then dried in a 65℃ drying oven to constant weight, yielding 3.5g of light yellow K-C3N4 powder, which was sealed for later use.

[0024] (2) Weigh 0.150g of K-C3N4 powder (particle size about 40μm), add 40mL of deionized water, and place it in a 300W ultrasonic instrument to disperse it ultrasonically for 30min to form a uniform K-C3N4 suspension.

[0025] Weigh 0.1825 g of silver nitrate and dissolve it in 10 mL of deionized water to obtain Ag. + Aqueous solution, Ag + The aqueous solution was slowly added dropwise to the K-C3N4 suspension, and stirred at 200 rpm for 3 hours at room temperature to ensure the Ag content was within acceptable limits. + After sufficient adsorption, a second suspension is obtained.

[0026] 0.1362 g of sodium phosphate dodecahydrate was weighed and dissolved in 10 mL of deionized water to obtain an aqueous solution of sodium phosphate. The aqueous solution of sodium phosphate was added dropwise to the second suspension and stirred at 200 r / min for 5 h. The precipitate was then collected by centrifugation at 5000 r / min. The precipitate was washed three times each with deionized water and ethanol, dried under vacuum at 60 °C for 12 h, and then ground into a fine powder to obtain the K-C3N4 / Ag3PO4 heterojunction material.

[0027] Example 2: A method for preparing a potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material is as follows: (1) Weigh 5g of melamine and 2g of potassium chloride, put them into a 100mL glass beaker, add 50mL of anhydrous ethanol, place the beaker on a magnetic stirrer, and stir at 250r / min for 5h to ensure that the materials are mixed evenly. After stirring, transfer to a drying oven and dry overnight at 70℃ until the ethanol is completely evaporated to obtain a mixed solid.

[0028] The mixed solids were loaded into a covered crucible, which was then placed in a muffle furnace. An air atmosphere and a heating program were set: the temperature was increased from room temperature to 500°C at a rate of 5°C / min, and held at this temperature for 10 hours to complete the thermal polymerization. After cooling, the product was ground and washed multiple times with deionized water to remove residual potassium chloride. It was then dried in a 65°C drying oven to constant weight, and the obtained K-C3N4 powder was sealed for later use.

[0029] (2) Weigh 0.2g of K-C3N4 powder (particle size about 40μm), add 40mL of deionized water, and place it in a 300W ultrasonic instrument to disperse it ultrasonically for 30min to form a uniform K-C3N4 suspension.

[0030] Weigh 0.21 mol of silver nitrate and dissolve it in 10 mL of deionized water to obtain Ag. + Aqueous solution, Ag + The aqueous solution was slowly added dropwise to the K-C3N4 suspension, and stirred at 200 rpm for 5 hours at room temperature to ensure the Ag content was within acceptable limits. + After sufficient adsorption, a second suspension is obtained.

[0031] 0.07 mol of sodium phosphate dodecahydrate was weighed and dissolved in 10 mL of deionized water to obtain an aqueous solution of sodium phosphate. The aqueous solution of sodium phosphate was added dropwise to the second suspension and stirred at 200 r / min for 8 h. The precipitate was then collected by centrifugation at 5000 r / min. The precipitate was washed three times each with deionized water and ethanol, dried under vacuum at 60 °C for 12 h, and then ground into a fine powder to obtain the K-C3N4 / Ag3PO4 heterojunction material.

[0032] Example 3: A method for preparing a potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material is as follows: (1) Weigh 20g of dicyandiamide and 10g of potassium phosphate, put them into a 100mL glass beaker, add 50mL of anhydrous ethanol, place the beaker on a magnetic stirrer, and stir at 350r / min for 3h to ensure that the materials are mixed evenly. After stirring, transfer to a drying oven and dry overnight at 70℃ until the ethanol has completely evaporated to obtain a mixed solid.

[0033] The mixed solids were placed in a covered crucible, which was then placed in a muffle furnace. An air atmosphere and a heating program were set: the temperature was increased from room temperature to 600°C at a rate of 10°C / min, and held for 1 hour to complete the thermal polymerization. After cooling, the product was ground and washed multiple times with deionized water to remove residual potassium chloride. It was then dried in a 60°C drying oven to constant weight, and the obtained K-C3N4 powder was sealed for later use.

[0034] (2) Weigh 0.05g of K-C3N4 powder (particle size about 40μm), add 40mL of deionized water, and place it in a 300W ultrasonic instrument to disperse it ultrasonically for 30min to form a uniform K-C3N4 suspension.

[0035] Weigh 0.04 mol of silver nitrate and dissolve it in 10 mL of deionized water to obtain Ag. + Aqueous solution, Ag + The aqueous solution was slowly added dropwise to the K-C3N4 suspension, and stirred at 500 r / min for 1 h at room temperature to obtain the second suspension.

[0036] 0.01 mol of sodium phosphate dodecahydrate was weighed and dissolved in 10 mL of deionized water to obtain an aqueous solution of sodium phosphate. The aqueous solution of sodium phosphate was added dropwise to the second suspension and stirred at 100 r / min for 10 h. The precipitate was then collected by centrifugation at 5000 r / min. The precipitate was washed three times each with deionized water and ethanol, dried under vacuum at 60 °C for 12 h, and then ground into a fine powder to obtain the K-C3N4 / Ag3PO4 heterojunction material.

[0037] Example 4: A method for preparing a potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material is as follows: (1) Weigh 15g of urea and 7g of potassium carbonate, put them into a 100mL glass beaker, add 50mL of anhydrous ethanol, place the beaker on a magnetic stirrer, and stir at 250r / min for 5h to ensure that the materials are mixed evenly. After stirring, transfer to a drying oven and dry overnight at 70℃ until the ethanol has completely evaporated to obtain a mixed solid.

[0038] The mixed solids were placed in a covered crucible, which was then placed in a muffle furnace. An air atmosphere and a heating program were set: the temperature was increased from room temperature to 600°C at a rate of 1°C / min, and held at this temperature for 1 hour to complete the thermal polymerization. After cooling, the product was ground and washed multiple times with deionized water to remove residual potassium chloride. It was then dried in a 65°C drying oven to constant weight, and the obtained K-C3N4 powder was sealed for later use.

[0039] (2) Weigh 0.1g of K-C3N4 powder (particle size about 40μm), add 40mL of deionized water, and place it in a 300W ultrasonic instrument to disperse it ultrasonically for 30min to form a uniform K-C3N4 suspension.

[0040] Weigh 0.18 mol of silver nitrate and dissolve it in 10 mL of deionized water to obtain Ag. + Aqueous solution, Ag + The aqueous solution was slowly added dropwise to the K-C3N4 suspension, and stirred at 200 rpm for 3 hours at room temperature to ensure the Ag content was within acceptable limits. + After sufficient adsorption, a second suspension is obtained.

[0041] 0.04 mol of sodium phosphate dodecahydrate was weighed and dissolved in 10 mL of deionized water to obtain an aqueous sodium phosphate solution. The aqueous sodium phosphate solution was added dropwise to the second suspension and stirred at 200 r / min for 5 h. The precipitate was then collected by centrifugation at 5000 r / min. The precipitate was washed three times each with deionized water and ethanol, dried under vacuum at 60 °C for 12 h, and then ground into a fine powder to obtain the K-C3N4 / Ag3PO4 heterojunction material.

[0042] Comparative Example 1: g-C3N4 was prepared as follows: Accurately weigh 12g of melamine, divide it into four equal portions, and place each portion into a lidded ceramic crucible. The crucibles are covered to reduce material volatilization during calcination. Place the crucibles in a muffle furnace, set the air atmosphere and heating program: 3.5℃ / min from room temperature to 550℃, hold for 4 hours to complete the thermal polymerization. After the furnace has naturally cooled to room temperature, remove the yellow solid product and grind it into a fine powder using an agate mortar and pestle. Approximately 5.5g of g-C3N4 sample was finally obtained and sealed in a sample vial for later use.

[0043] Comparative Example 2: Ag3PO4 was prepared as follows: The experiment was conducted on a light-protected workbench. First, 50 mL of 0.05 mol / L silver nitrate aqueous solution and an equal volume of 0.017 mol / L sodium phosphate dodecahydrate aqueous solution were prepared. The silver nitrate aqueous solution was added dropwise to the sodium phosphate aqueous solution at a rate of 1 drop / second, while maintaining a magnetic stirring speed of 250 r / min for 5 hours. After the reaction, the mixture was separated by centrifugation at 5000 r / min using a high-speed centrifuge. The solid product at the bottom was collected, washed three times with deionized water, and then three times with anhydrous ethanol to remove residual ions. Finally, it was dried in a vacuum oven at 60℃ for 12 hours, ground, and the Ag3PO4 sample was obtained and sealed for later use.

[0044] Comparative Example 3: Everything else is the same as in Example 1, except that: Replace the K-C3N4 powder in step (2) with the undoped g-C3N4 powder prepared in Comparative Example 1.

[0045] The K-C3N4 / Ag3PO4 sample prepared in Example 1 was subjected to HRTEM and EDS analysis, and the results are as follows: Figure 2 As shown. Figure 2 The two images in the upper middle section are HRTEM images, which clearly show the two-dimensional sheets of K-C3N4 and the lattice fringes of Ag3PO4 particles. There is a clear heterojunction interface between the two, and there are no obvious lattice defects at the interface, which proves that the heterojunction structure is well formed. Figure 2 The lower part of the figure shows the elemental distribution of EDS (corresponding to the elemental distribution of K, C, Ag, O, N, and P in the appendix): K is evenly distributed in the K-C3N4 region, Ag and P are concentrated in Ag3PO4 particles, C and N are characteristic elements of K-C3N4, and O covers the entire region. The distribution of each element is consistent with the material composition, confirming the successful synthesis of the K-C3N4 / Ag3PO4 composite material.

[0046] The K-C3N4, K-C3N4 / Ag3PO4 samples prepared in Example 1 and the catalytic material samples prepared in Comparative Examples 1-3 were examined by scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown, Figure 1 Figure (a) shows the g-C3N4 sample, (b) shows the K-C3N4 sample, (c) shows the Ag3PO4 sample, and (d) shows the Ag3PO4 / K-C3N4 sample. Figure 1 As shown, g-C3N4 exhibits a bulk, layered structure. In contrast, K-C3N4 displays a thinner two-dimensional nanosheet morphology, primarily due to the thermal etching of its bulk structure into numerous thin sheets after high-temperature molten salt treatment, resulting in a larger specific surface area and more reaction sites. Figure 1 As can be observed in Figure (c), the Ag3PO4 particles have an irregular spherical morphology, poor particle dispersibility, and are prone to aggregation. From... Figure 1 As shown in Figure (d), in the Ag3PO4 / K-C3N4 composite material, Ag3PO4 nanoparticles are uniformly deposited on the surface of K-C3N4, and no aggregation of Ag3PO4 nanoparticles was observed. This result indicates that K-C3N4 can serve as an effective support material, providing sufficient growth sites for Ag3PO4 nanoparticles and inhibiting their aggregation. The SEM, HRTEM, and EDS results of the heterojunction photocatalytic materials prepared in Examples 2-4 are similar to those in Example 1.

[0047] The above-mentioned g-C3N4, K-C3N4, Ag3PO4, and Ag3PO4 / K-C3N4 materials were subjected to XRD analysis, and the results are as follows: Figure 3 As shown. Figure 3 In the study, g-C3N4 exhibits distinct characteristic diffraction peaks at the 13.0° (100) and 27.4° (002) crystal planes, corresponding to its heptaazine unit structure and interlayer π-π stacking, respectively. The (100) crystal plane diffraction peak of K-C3N4 disappears, and the peak intensity of the (002) crystal plane is significantly reduced, indicating that potassium doping disrupts part of the graphite phase structure and increases the interlayer spacing. Ag3PO4 exhibits multiple characteristic peaks at angles such as 20.87°, 29.68°, and 33.30°, corresponding to crystal planes such as (110), (200), and (210), respectively, indicating high crystallinity. The g-C3N4 / Ag3PO4 spectrum shows that the g-C3N4 and Ag3PO4 composite material was successfully prepared. The simultaneous appearance of characteristic peaks of both K-C3N4 and Ag3PO4 in the K-C3N4 / Ag3PO4 spectrum, with no significant shift in peak shape, proves that the basic crystal structure of each component was not changed during the formation of the heterojunction. Infrared spectroscopy was performed on the above-mentioned g-C3N4, K-C3N4, Ag3PO4, and Ag3PO4 / K-C3N4 series material samples, and the results are as follows: Figure 4 As shown. By Figure 4 As can be seen, in the infrared spectrum of g-C3N4, firstly, at 809 cm⁻¹ -1 A sharp peak at 1200-1650 cm⁻¹ is attributed to the characteristic respiratory pattern of the tris-S-triazine unit. -1 The peak observed at 3100–3400 cm⁻¹ corresponds to the typical stretching mode of the CN and C=N heterocycles in g-C₃N₄. Furthermore, the peaks at 3100–3400 cm⁻¹ correspond to the typical stretching mode of the CN and C=N heterocycles in g-C₃N₄. -1 The peaks in the wavenumber range are attributed to NH stretching vibrations. The FT-IR spectra of these peaks measured with K-C3N4 and g-C3N4 are consistent with those measured with g-C3N4. Figure 1 Sample. The infrared spectrum of Ag3PO4 at 1020 cm⁻¹ -1 and 558cm -1 The two peaks at that point are considered to be PO4. 3- Characteristic peak, 1020 cm⁻¹ -1 The peak is considered to be due to the tensile vibration of the POP, and the 558 cm peak is considered to be due to -1 The peak at 3600-3300 cm⁻¹ is attributed to the O=PO bending vibration. Furthermore, in Ag₃PO₄ and a series of Ag₃PO₄ / d-C₃N₄ samples, the peak at 3600-3300 cm⁻¹ is also observed. -1The broadband at the point is considered to be the stretching vibration of hydrogen and oxygen in the water adsorbed on the material surface. The g-C3N4 / Ag3PO4 spectrum contains the characteristic absorption peaks of both g-C3N4 and Ag3PO4, confirming the successful preparation of the composite material. All characteristic peaks of K-C3N4 and Ag3PO4 were observed in the Ag3PO4 / K-C3N4 hybrid photocatalyst. This indicates that the coupling of Ag3PO4 and K-C3N4 is not a simple physical mixture of Ag3PO4 and K-C3N4, but rather an interfacial electrostatic interaction between Ag3PO4 and K-C3N4, which is also beneficial to the transport of charge carriers at the interface between Ag3PO4 and K-C3N4 in the designed Z-scheme catalyst.

[0048] To further analyze and understand the efficiency of photogenerated carrier separation in g-C3N4, K-C3N4, and Ag3PO4 / K-C3N4 series materials, the applicant measured the steady-state fluorescence (PL) spectra of the samples. The results are as follows: Figure 5 As shown. It is well known that a material with low photoluminescence intensity indicates low charge carrier recombination, suggesting that the material possesses high photocatalytic activity. From Figure 5 As can be seen, g-C3N4 exhibits the strongest fluorescence intensity, which is due to the low carrier separation efficiency in pure carbon nitride. Under 380 nm excitation, g-C3N4 displays a typical emission peak at 460 nm, a result corresponding to the UV-Vis spectrum. Compared to pure g-C3N4, the emission peak of K-C3N4 shows a redshift. Furthermore, Ag3PO4 / K-C3N4 exhibits the lowest photogenerated carrier separation efficiency, demonstrating that it has the highest photogenerated carrier separation efficiency among all composite materials.

[0049] The Ag3PO4 / K-C3N4 heterojunction material sample prepared in Example 1, and the g-C3N4, Ag3PO4, and Ag3PO4 / g-C3N4 samples prepared in Comparative Examples 1-3 were used as catalyst samples for photocatalytic oxidation desulfurization performance testing, as follows: Simulated fuel preparation: Weigh a certain mass of dibenzothiophene (DBT, a typical difficult-to-remove sulfide in fuel), add it to n-octane, stir to dissolve, and then make up to a final volume to prepare simulated fuel with a concentration of 200 ppm (calculated as sulfur element). Seal and store to prevent volatilization.

[0050] Photocatalytic reaction process: Measure 20 mL of the simulated fuel as described above and add it to a 100 mL photocatalytic reactor. Then weigh 0.05 g of Ag3PO4 / K-C3N4 heterojunction material or other catalyst sample and add it to the reactor. Seal the reactor with a quartz cap (quartz material ensures visible light transmission). Place the reactor on a magnetic stirrer and stir at 250 r / min for 1 hour under light-protected conditions to ensure sufficient contact between the material and the simulated fuel, reaching adsorption-desorption equilibrium and eliminating the interference of adsorption on desulfurization performance. After adsorption equilibrium is reached, turn on a 300W xenon lamp (maintaining a distance of 10 cm between the lamp source and the reactor to ensure uniform light intensity). Simultaneously, introduce air into the reactor through a gas flow meter, controlling the airflow rate at 50 mL / min (using oxygen in the air as the oxidant). Begin the photocatalytic oxidation desulfurization reaction. The total reaction time is 3 hours, and the change in sulfide concentration during the desulfurization reaction is monitored.

[0051] The formula for calculating the desulfurization rate η (%) is: η = (1-Ct / C0) × 100% Where C0 is the initial sulfur content of the fuel, and Ct is the sulfur content of the fuel after degradation.

[0052] Fuel desulfurization rate test results are as follows Figure 6 As shown, the photocatalytic oxidation desulfurization performance of different photocatalyst samples is illustrated. Compared with g-C3N4, K-C3N4, and Ag3PO4, Ag3PO4 / K-C3N4 exhibits the highest desulfurization conversion rate. The improved performance of the composite material is mainly due to the formation of an efficient heterojunction structure between Ag3PO4 and K-C3N4, which increases the visible light response range and promotes the transfer and separation of photogenerated carriers, thereby enhancing the desulfurization conversion capacity. The significantly lower desulfurization performance of Ag3PO4 / g-C3N4 compared to Ag3PO4 / K-C3N4 is primarily due to the failure of Ag3PO4 and g-C3N4 to form a good heterojunction structure, preventing them from synergistically enhancing the material's photocatalytic performance.

Claims

1. A potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material, characterized in that, It includes nanosheet-like potassium-doped carbon nitride and silver phosphate particles deposited on the potassium-doped carbon nitride sheets, wherein the potassium-doped carbon nitride and the silver phosphate particles form a heterojunction structure.

2. The method for preparing the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material according to claim 1, characterized in that, Includes the following steps: (1) Calcining a mixture of organic amine and potassium source solid yields potassium-doped carbon nitride; (2) Disperse potassium-doped carbon nitride in water to obtain a first suspension, and then add Ag + The solution is added to the first suspension to obtain the second suspension. A phosphate solution is then added to the second suspension, and the reaction yields the first product. (3) Centrifuge the first product to collect the precipitate, wash and dry it to obtain K-C3N4 / Ag3PO4 heterojunction material.

3. The method for preparing the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material according to claim 2, characterized in that, In step (1), the organic amine includes at least one of melamine, urea, and dicyandiamide, and the potassium source includes at least one of potassium chloride, potassium phosphate, potassium dihydrogen phosphate, potassium carbonate, potassium sulfate, and potassium nitrate.

4. The method for preparing the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material according to claim 2, characterized in that, In step (1), the mass ratio of the organic amine to the potassium source is 5-20:2-10.

5. The method for preparing the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material according to claim 2, characterized in that, In step (1), the calcination method is as follows: in an air atmosphere, the mixed solid of organic amine and potassium source is heated from room temperature to 500-600℃ at a rate of 1-10℃ / min and kept at the temperature for 1-10h to obtain the calcined product.

6. The method for preparing the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material according to claim 2, characterized in that, In step (2), Ag + The solution is a 0.01-0.5M aqueous solution of silver nitrate, and the phosphate solution is a 0.01-0.5M aqueous solution of sodium phosphate. The mass ratio of potassium-doped carbon nitride to silver nitrate is 0.05-0.3:0.05-0.

5.

7. The method for preparing the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material according to claim 2, characterized in that, In step (2), Ag + The molar ratio with phosphate is 3-5:

1.

8. The method for preparing the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material according to claim 2, characterized in that, In step (2), Ag + The method for adding the solution to the first suspension is as follows: under stirring conditions at room temperature, add Ag... + The solution is slowly added dropwise to the first suspension, and the second suspension is obtained after stirring for 1-5 hours. The reaction conditions after adding phosphate solution are: stirring at room temperature for 1-10 hours.

9. The method for preparing the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material according to claim 2, characterized in that, In step (1), the method for preparing the mixed solid of organic amine and potassium source is as follows: The organic amine and potassium source are dispersed in an alcohol solvent and stirred to obtain a mixture. The alcohol solvent in the mixture is removed, and the resulting dry solid is the mixed solid of organic amine and potassium source.

10. The application of the potassium-doped carbon nitride silver phosphate heterojunction photocatalytic material prepared by any one of claims 2-9 in the photocatalytic degradation of sulfur-containing compounds in fuel oil.

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