A method for preparing boron-doped g-C3N4

Abstract

A method for preparing boron-doped g-C3N4 includes the following steps: adding K2B4O7·4H2O or KBH4 as a boron source to g-C3N4, grinding and mixing thoroughly, calcining under an argon atmosphere, cooling to room temperature, washing, and drying to obtain boron-doped g-C3N4. The boron-doped g-C3N4 prepared by this invention exhibits higher activity and selectivity in the photocatalytic oxidation of cinnamaldehyde to benzaldehyde, making the reaction process more efficient, green, and easy to control. By selecting a suitable boron precursor, the goal of efficient and selective solar-driven organic synthesis is achieved. This not only provides a new route for the selective oxidation of cinnamaldehyde to benzaldehyde but also provides new catalysts and process options for other organic synthesis reactions.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic material synthesis technology, specifically relating to the preparation and application of boron-doped graphitic carbon nitride g-C3N4. Background Technology

[0002] Benzaldehyde, a fragrance consumed second only to vanillin in annual consumption, is also an important pharmaceutical raw material, primarily obtained through synthesis from petrochemical raw materials or extraction from natural sources. Synthesizing natural benzaldehyde from cinnamon oil is one of the three main methods for obtaining natural benzaldehyde besides extraction from natural sources. Cinnamaldehyde (3-phenyl-2-propenal), the main component of cinnamon oil, is a typical α,β-unsaturated aldehyde. The reaction to prepare benzaldehyde from cinnamaldehyde is essentially a process of selectively oxidizing the carbon-carbon double bond in its structure to an aldehyde group. The selective oxidation of inexpensive and readily available alkenes is one of the main methods for obtaining high-value-added aldehydes and ketone carbonyl compounds. Utilizing light energy instead of traditional thermal or chemical energy to overcome the activation energy required for the reaction allows the reaction to be completed under milder and greener conditions.

[0003] Graphitic carbon nitride (g-C3N4), as a non-metallic semiconductor photocatalyst free of heavy metals, has been proven to have visible light response, and its conduction band (CB) is sufficient to photoreduc O2 to oxygen species with moderate oxidizing power rather than hydroxyl radicals. However, due to severe recombination of photogenerated carriers, a low valence band position, and unsatisfactory light absorption, g-C3N4 exhibits poor photocatalytic activity. To improve this, non-metallic doping can maintain g-C3N4 as a non-metallic semiconductor photocatalyst, which can avoid heavy metal problems at the source in the preparation of flavorings and other food-related products and additives; it also has the advantages of low cost and wide availability of raw materials, and its high electronegativity can also modulate the electron cloud in g-C3N4 to generate special active sites. Boron is a non-metallic element, but it exhibits some metallic properties in its crystalline state. In its crystal structure, it can usually form stable chemical bonds. Boron doping of g-C3N4 can improve its photocatalytic activity, showing high conversion rate and selectivity in the photocatalytic oxidation of cinnamaldehyde to benzaldehyde. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method for preparing and applying boron-doped graphitic carbon nitride g-C3N4.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing boron-doped g-C3N4 includes the following steps:

[0007] K₂B₄O₇·₄H₂O or KBH₄ was added to g-C₃N₄ as a boron source. After thorough grinding and mixing, the mixture was calcined under an inert atmosphere, cooled to room temperature, washed, and dried to obtain boron-doped g-C₃N₄.

[0008] The K2B4O7·4H2O and g-C3N4 are mixed in a mass ratio of 1 to 5:5;

[0009] The KBH4 and g-C3N4 are mixed at a mass ratio of 1 to 5:5;

[0010] The boron-doped g-C3N4 product obtained using K2B4O7·4H2O as the boron source is designated BCN, and its structural formula is as follows:

[0011]

[0012] The boron-doped g-C3N4 product obtained using KBH4 as the boron source is designated KBCN, and its structural formula is as follows:

[0013]

[0014] The calcination temperature is 350–600℃, and the calcination time is 30–120 min.

[0015] The drying process involves vacuum drying at 50–70°C for 5–8 hours.

[0016] A method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde with oxygen includes the following steps:

[0017] (1) In the reactor, add photocatalyst g-C3N4, BCN or KBCN to cinnamaldehyde, or dissolve cinnamaldehyde in a solvent.

[0018] (2) Introduce oxygen into the reactor, turn on the light source to irradiate the reaction system, and carry out the reaction under vigorous stirring;

[0019] (3) Filter out the catalyst, extract the reaction product and separate benzaldehyde.

[0020] The amount of photocatalyst g-C3N4, BCN, or KBCN added is 1-30% of the mass of cinnamaldehyde.

[0021] The solvent is acetonitrile, alcohol, ether, water, or petroleum ether.

[0022] The light source is a xenon lamp with a light power density of 200–500 mW / cm². 2

[0023] During the reaction, the temperature of the reaction system is maintained at room temperature by circulating cooling water.

[0024] Photocatalysts g-C3N4, BCN, or KBCN are used in the photocatalytic oxidation of cinnamaldehyde to prepare benzaldehyde.

[0025] A boron-doped g-C3N4 photocatalyst, BCN, has the following structural formula:

[0026]

[0027] A boron-doped g-C3N4 photocatalyst KBCN has the following structural formula:

[0028]

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The boron-doped g-C3N4 prepared in this invention exhibits higher activity and selectivity in the photocatalytic oxidation of cinnamaldehyde to benzaldehyde, making the reaction process more efficient, green, and easier to control. By selecting a suitable boron precursor, the goal of efficient and selective solar-driven organic synthesis is achieved. This not only provides a new route for the selective oxidation of cinnamaldehyde to benzaldehyde but also offers new catalysts and process options for other organic synthesis reactions. Attached Figure Description

[0031] Figure 1 X-ray diffraction patterns of g-C3N4, BCN, and KBCN.

[0032] Figure 2 This is a SEM image of g-C3N4.

[0033] Figure 3 This is a SEM image of BCN.

[0034] Figure 4 This is a SEM image from KBCN.

[0035] Figure 5 This is an energy-dispersive X-ray spectrometer (EDS) image from BCN.

[0036] Figure 6 This is an energy-dispersive X-ray spectrometer (EDS) image from KBCN.

[0037] Figure 7 These are the results of X-ray photoelectron spectroscopy (XPS) measurements. Here, intensity represents the intensity, and binding energy represents the binding energy.

[0038] Figure 8 The photocatalytic oxidation performance of cinnamaldehyde by g-C3N4, BCN, and KBCN is given. Here, Conversion represents the conversion rate, and Selectivity represents the selectivity. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through embodiments.

[0040] Example 1

[0041] I. Preparation of photocatalysts g-C3N4, BCN and KBCN

[0042] 10g of urea was placed in a ceramic crucible and then placed in a muffle furnace and calcined in air at 550℃ for 4h with a heating rate of 5℃ / min to obtain g-C3N4.

[0043] 0.30 g of g-C3N4 and 0.17 g of K2B4O7·4H2O were thoroughly ground and mixed at room temperature, then placed into a covered ceramic boat. The boat was placed in a tube furnace and calcined at 450 °C for 90 min under an argon atmosphere, with a programmed temperature increase of 2.3 °C / min. After the sample cooled to room temperature, it was washed three times with water and three times with alcohol, and then vacuum dried at 60 °C to obtain the boron-doped g-C3N4 product, designated BCN.

[0044] 0.30 g of g-C3N4 and 0.12 g of KBH4 were thoroughly ground and mixed at room temperature, then placed into a covered ceramic boat. The boat was placed in a tube furnace and calcined at 450 °C for 30 min under an argon atmosphere, with a programmed temperature increase of 2.3 °C / min. After the sample cooled to room temperature, it was washed three times with water and three times with alcohol, and then vacuum dried at 60 °C to obtain the boron-doped g-C3N4 product, designated KBCN.

[0045] II. X-ray diffraction analysis of photocatalysts g-C3N4, BCN, and KBCN

[0046] The crystal structure of the photocatalysts was analyzed using X-ray diffraction (SmartLab 3KW, Rigaku Corporation, Japan) with an operating voltage of 40 kV and an operating current of 30 mA. X-ray diffraction (XRD) patterns of the photocatalysts g-C3N4, BCN, and KBCN were obtained, as shown below. Figure 1 As shown, two characteristic peaks appear at 13.4° and 27.3°, consistent with the signal of the standard card (PDF Card No. 87-1525) of g-C3N4.

[0047] III. Scanning Electron Microscopy (SEM) Analysis of Photocatalysts g-C3N4, BCN, and KBCN

[0048] Scanning electron microscope images of g-C3N4, BCN, and KBCN are shown below. Figure 2 , Figure 3 and Figure 4As shown, they all exhibit a thick and dense layered stacked structure; however, Figure 4 The surface of KBCN is rougher, and this is more obvious when magnified, with more pores and larger pore sizes.

[0049] IV. Energy Dispersive Spectroscopy (EDS) Analysis of Photocatalysts BCN and KBCN

[0050] like Figure 5 As shown, the energy dispersive image of BCN shows that B was successfully doped into the g-C3N4 structure and is uniformly distributed.

[0051] like Figure 6 As shown, the energy dispersive spectroscopy image of KBCN shows that B was successfully doped into the g-C3N4 structure and is uniformly distributed.

[0052] V. Chemical composition of photocatalysts g-C3N4, BCN, and KBCN was determined using X-ray photoelectron spectroscopy (XPS) (K-Alpha, Thermo Scientific, USA), with a reference C1s binding energy of 284.8 eV.

[0053] Figure 7 (a) shows the C1s spectra of g-C3N4, BCN, and KBCN, where the three peaks at 288.2, 286.3, and 284.8 eV are assigned to N–C=N and C–NH, respectively. x And C–C.

[0054] Figure 7 In (b), the three peaks in the N1s spectrum, at 401.3, 400.4, and 398.7 eV, are assigned to C–N–H, N–(C)3, and C–N=C, respectively. Meanwhile, the C1s and N1s signals of the doped BCN and KBCN both shift slightly towards higher binding energies, indicating that boron successfully enters the g-C3N4 structure, altering the original chemical environment surrounding the C and N atoms.

[0055] Figure 7 The B1s binding energy values ​​in (c) indicate that the sites where boron atoms enter g-C3N4 are not entirely consistent when doped with two different boron sources, K2B4O7·4H2O and KBH4. However, the binding energies of the B1s peaks of BCN and KBCN are both between 193.0 eV for boron oxides and hydroxides and 190.0 eV for hexagonal boron nitride, which is the binding energy when B and N atoms are bonded. This indicates that the doped boron atoms are introduced and replace C atoms in the π-conjugated network of g-C3N4. The B1s binding energy of BCN is 192.2 eV, which is the binding energy of boron atoms using three sp... 2 The hybrid orbitals are respectively associated with the sp orbitals of the three nitrogen atoms. 2Hybridized orbitals form σ bonds, while the empty p orbitals of boron form π bonds with the lone pair electrons in the unhybridized p orbitals of one of the nitrogen atoms. Therefore, in the >B=N< configuration, boron carries a positive charge due to its lower electronegativity than nitrogen, while the nitrogen atom carries a negative charge. The B1s binding energy of KBCN is 191.4 eV, which is produced by both types of boron atoms; that is, boron doped in KBCN exists in two types, the same as in BCN, and also in another type bonded to only two nitrogen atoms. In this case, the three sp... 2 Only two of the hybrid orbitals form σ bonds with nitrogen atoms, so there is a single electron in its outer shell.

[0056] Based on the above measurement results and analysis, the structural formula of the boron-doped g-C3N4 product BCN obtained using K2B4O7·4H2O as the boron source is as follows:

[0057]

[0058] Based on the above measurement results and analysis, the structural formula of the boron-doped g-C3N4 product KBCN obtained using KBH4 as the boron source is as follows:

[0059]

[0060] VI. Activity Testing of Photocatalysts g-C3N4, BCN, and KBCN for the Photocatalytic Oxidation of Cinnamaldehyde to Benzaldehyde

[0061] (1) Photocatalytic oxidation of cinnamaldehyde to prepare benzaldehyde

[0062] Inside the reactor, a mixture of 30 mg photocatalyst, 1 mmol (132.159 mg by mass) of cinnamaldehyde, and 10 mL of acetonitrile was added. The reactor was evacuated to a vacuum, and high-purity oxygen gas was introduced to reach ambient pressure. The mixture was then vigorously stirred in the dark for 30 minutes using a magnetic stirrer. A 300 W xenon lamp was then turned on as the light source from above. Furthermore, during the photocatalytic oxidation of cinnamaldehyde, the solution temperature was maintained at 25°C using circulating cooling water. After 14 hours, the reaction product was collected, and the catalyst was filtered off.

[0063] (2) Product composition analysis after photocatalytic reaction

[0064] (2.1) Analytical Methods

[0065] Using o-dichlorobenzene as an internal standard, the cinnamaldehyde content after the reaction was analyzed by gas chromatography (GC-2018, Shimadzu, Japan) using the internal standard method (CN 116496153A) after being diluted to volume with anhydrous ethanol.

[0066] (2.2) Test reagents

[0067] Potassium borohydride (AR grade) was purchased from Nanning Lantian Experimental Equipment Co., Ltd.

[0068] Urea (AR grade), cinnamaldehyde (AR grade), and o-dichlorobenzene (GR grade) were purchased from Aladdin Biochemical Reagent Research Co., Ltd.

[0069] Potassium tetraborate tetrahydrate (AR grade) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0070] Anhydrous ethanol (AR grade) and acetonitrile (AR grade) were purchased from Xilong Technology Co., Ltd.

[0071] Ultra-high purity argon (99.999%), ultra-high purity nitrogen (99.999%), ultra-high purity air, and oxygen (99.9%) were purchased from Guangxi Ruida Chemical Technology Co., Ltd.

[0072] (2.3) GC-2018 analysis conditions

[0073] The gas chromatography column was an AE.SE-54 capillary column with a diameter of 30m × 0.32mm × 0.25μm. The column temperature was 160℃, the vaporization chamber temperature was 260℃, and the flame ionization detector (FID) temperature was 260℃.

[0074] (2.4) GC-MS analysis results of the product composition after photocatalytic reaction

[0075] Table 1. GC-MS analysis results of cinnamaldehyde after KBCN catalysis.

[0076]

[0077] (2.5) Results of selectivity and conversion rate tests of photocatalysts g-C3N4, BCN and KBCN

[0078] like Figure 8 As shown, compared with g-C3N4, the KBCN sample achieved a cinnamaldehyde conversion rate of 73.8% and a benzaldehyde selectivity of 74.1% after 14 hours of photoreaction. This indicates that the strong reducing power of KBH4 alters the structure of g-C3N4 while incorporating boron. Boron-doped g-C3N4 experiments were conducted using K2B4O7·4H2O, a boron source with the same alkali metal element but no reducing power. After photoreaction under the same conditions, the BCN sample achieved a conversion rate of 65.2% and a selectivity of 61.3%, with a weaker increase in activity compared to g-C3N4 doped with KBH4 as the boron source.

[0079] Example 2

[0080] A method for preparing boron-doped g-C3N4 includes the following steps: K2B4O7·4H2O is added to g-C3N4 as a boron source, and after thorough grinding and mixing, the mixture is calcined under an inert atmosphere. After cooling to room temperature, it is washed and dried to obtain boron-doped g-C3N4, designated BCN. The K2B4O7·4H2O and g-C3N4 are mixed at a mass ratio of 1:5. The calcination temperature is 350℃, and the calcination time is 30 min. The drying is performed under vacuum at 50℃ for 5 h.

[0081] Example 3

[0082] A method for preparing boron-doped g-C3N4 includes the following steps: K2B4O7·4H2O is added to g-C3N4 as a boron source, and after thorough grinding and mixing, the mixture is calcined under an inert atmosphere. After cooling to room temperature, it is washed and dried to obtain boron-doped g-C3N4, designated BCN. The K2B4O7·4H2O and g-C3N4 are mixed at a mass ratio of 5:5. The calcination temperature is 600℃, and the calcination time is 120 min. The drying is performed under vacuum at 70℃ for 8 h.

[0083] Example 4

[0084] A method for preparing boron-doped g-C3N4 includes the following steps: K2B4O7·4H2O is added to g-C3N4 as a boron source, and after thorough grinding and mixing, the mixture is calcined under an inert atmosphere. After cooling to room temperature, it is washed and dried to obtain boron-doped g-C3N4, designated BCN. The K2B4O7·4H2O and g-C3N4 are mixed at a mass ratio of 5:5. The calcination temperature is 400℃, and the calcination time is 90 min. The drying is performed under vacuum at 60℃ for 6.5 h.

[0085] Example 5

[0086] A method for preparing boron-doped g-C3N4 includes the following steps: K2B4O7·4H2O is added to g-C3N4 as a boron source, and after thorough grinding and mixing, the mixture is calcined under an inert atmosphere. After cooling to room temperature, it is washed and dried to obtain boron-doped g-C3N4, designated BCN. The K2B4O7·4H2O and g-C3N4 are mixed at a mass ratio of 1:5, 2:5, 3:5, 4:5, or 5:5. The calcination temperature is 350, 400, 450, 500, 550, or 600℃, and the calcination time is 30, 40, 50, 60, 70, 80, 90, 100, 110, or 120 min. The drying is performed under vacuum at 50, 55, 60, 65, or 70℃ for 5, 6, 7, or 8 h.

[0087] Example 6

[0088] A method for preparing boron-doped g-C3N4 includes the following steps: KBH4 is added to g-C3N4 as a boron source, and after thorough grinding and mixing, the mixture is calcined under an inert atmosphere. After cooling to room temperature, it is washed and dried to obtain boron-doped g-C3N4, designated KBCN. The KBH4 and g-C3N4 are mixed at a mass ratio of 1:5, 2:5, 3:5, 4:5, or 5:5. The calcination temperature is 350, 400, 450, 500, 550, or 600℃, and the calcination time is 30, 40, 50, 60, 70, 80, 90, 100, 110, or 120 min. The drying is performed under vacuum at 50, 55, 60, 65, or 70℃ for 5, 6, 7, or 8 h.

[0089] Example 7

[0090] A method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde with oxygen includes the following steps:

[0091] (1) In the reactor, cinnamaldehyde is dissolved in a solvent and then photocatalyst g-C3N4 is added;

[0092] (2) Introduce oxygen into the reactor, turn on the light source to irradiate the reaction system, and carry out the reaction under vigorous stirring;

[0093] (3) Filter out the catalyst, extract the reaction product and separate benzaldehyde.

[0094] The amount of photocatalyst g-C3N4 added is 1%, 3%, 6%, 9%, 12%, 15%, 18%, 21%, 24%, 27%, or 30% of the mass of cinnamaldehyde.

[0095] The solvent is acetonitrile, alcohol, ether, water, or petroleum ether. The concentration of cinnamaldehyde in the solvent is not limited to the reaction; in this example, it is 500-1000 mg / L.

[0096] During the reaction, the temperature of the reaction system is maintained at room temperature by circulating cooling water.

[0097] Example 8

[0098] A method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde with oxygen includes the following steps:

[0099] (1) In the reactor, cinnamaldehyde is dissolved in a solvent and then the photocatalyst BCN is added;

[0100] (2) Introduce oxygen into the reactor, turn on the light source to irradiate the reaction system, and carry out the reaction under vigorous stirring;

[0101] (3) Filter out the catalyst, extract the reaction product and separate benzaldehyde.

[0102] The amount of photocatalyst BCN added is 1%, 3%, 6%, 9%, 12%, 15%, 18%, 21%, 24%, 27%, or 30% of the mass of cinnamaldehyde.

[0103] The solvent is acetonitrile, alcohol, ether, water, or petroleum ether. The concentration of cinnamaldehyde in the solvent is not limited to the reaction; in this example, it is 500-1000 mg / L.

[0104] During the reaction, the temperature of the reaction system is maintained at room temperature by circulating cooling water.

[0105] Example 9

[0106] A method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde with oxygen includes the following steps:

[0107] (1) In the reactor, cinnamaldehyde is dissolved in a solvent and then the photocatalyst KBCN is added;

[0108] (2) Introduce oxygen into the reactor, turn on the light source to irradiate the reaction system, and carry out the reaction under vigorous stirring;

[0109] (3) Filter out the catalyst, extract the reaction product and separate benzaldehyde.

[0110] The amount of photocatalyst KBCN added is 1%, 5%, 10%, 15%, 20%, 25%, or 30% of the mass of cinnamaldehyde.

[0111] The solvent is acetonitrile, alcohol, ether, water, or petroleum ether. Regardless of the concentration of cinnamaldehyde in the solvent, a photocatalytic reaction can occur; in this example, the concentration is 500-1000 mg / L.

[0112] During the reaction, the temperature of the reaction system is maintained at room temperature by circulating cooling water.

[0113] Example 10

[0114] A method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde with oxygen includes the following steps:

[0115] (1) In the reactor, the photocatalyst BCN was added to cinnamaldehyde;

[0116] (2) Introduce oxygen into the reactor, turn on the light source to irradiate the reaction system, and carry out the reaction under vigorous stirring;

[0117] (3) Filter out the catalyst, extract the reaction product and separate benzaldehyde.

[0118] The amount of photocatalyst BCN added is 1%, 3%, 6%, 9%, 12%, 15%, 18%, 21%, 24%, 27%, or 30% of the mass of cinnamaldehyde.

[0119] During the reaction, the temperature of the reaction system is maintained at room temperature by circulating cooling water.

[0120] Example 11

[0121] A method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde with oxygen includes the following steps:

[0122] (1) Add the photocatalyst KBCN to cinnamaldehyde in the reactor;

[0123] (2) Introduce oxygen into the reactor, turn on the light source to irradiate the reaction system, and carry out the reaction under vigorous stirring;

[0124] (3) Filter out the catalyst, extract the reaction product and separate benzaldehyde.

[0125] The amount of photocatalyst KBCN added is 1%, 5%, 10%, 15%, 20%, 25%, or 30% of the mass of cinnamaldehyde.

[0126] During the reaction, the temperature of the reaction system is maintained at room temperature by circulating cooling water.

Claims

1. A method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde with oxygen, characterized in that, Includes the following steps: (1) In the reactor, add photocatalyst g-C3N4, BCN or KBCN to cinnamaldehyde, or dissolve cinnamaldehyde in a solvent; The structural formula of the photocatalyst BCN is as follows: ； The structural formula of the photocatalyst KBCN is as follows: ； (2) Introduce oxygen into the reactor, turn on the light source to irradiate the reaction system, and carry out the reaction under vigorous stirring; (3) Filter out the catalyst, extract the reaction product and separate benzaldehyde.

2. The method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde according to claim 1, characterized in that, The amount of photocatalyst g-C3N4, BCN or KBCN added is 1 to 30% of the mass of cinnamaldehyde.

3. The method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde according to claim 1, characterized in that, The solvent is acetonitrile, alcohol, ether, water, or petroleum ether.

4. The method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde according to claim 1, characterized in that, During the reaction, the temperature of the reaction system is maintained at room temperature by circulating cooling water.

5. The method for preparing benzaldehyde by photocatalytic oxidation of cinnamaldehyde according to claim 1, characterized in that, The preparation method of the photocatalysts BCN and KBCN includes the following steps: K₂B₄O₇·₄H₂O or KBH₄ was added to g-C₃N₄ as a boron source. After thorough grinding and mixing, the mixture was calcined under an inert atmosphere, cooled to room temperature, washed, and dried to obtain boron-doped g-C₃N₄. The K2B4O7·4H2O and g-C3N4 are mixed in a mass ratio of 1~5:5; The KBH4 and g-C3N4 are mixed at a mass ratio of 1 to 5:

5.

6. The preparation method according to claim 5, characterized in that, The calcination temperature is 350~600 ℃, and the calcination time is 30~120 min.

7. The preparation method according to claim 5, characterized in that, The drying process involves vacuum drying at 50-70°C for 5-8 hours.

8. Application of photocatalysts g-C3N4, BCN, or KBCN in the photocatalytic oxidation of cinnamaldehyde to benzaldehyde. The structural formula of the photocatalyst BCN is as follows: ； The structural formula of the photocatalyst KBCN is as follows: 。

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