Melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material as well as in-situ construction method and photocatalytic application thereof

Abstract

The invention discloses a melam-cyanuric acid supramolecule / BiOCl heterojunction composite material as well as an in-situ construction method and photocatalytic application thereof. A low-temperature molten salt pyrolysis process is adopted, bismuth salt, urea, sodium chloride and potassium chloride are directly mixed, and the melam-cyanuric acid supramolecule (MC) and bismuth oxychloride composite material (MC / BiOCl) is prepared through in-situ one-step pyrolysis. According to the invention, BiOCl and MC are compounded in situ to construct an organic-inorganic hybrid heterojunction system, so that the problem of high photogenerated electron-hole pair recombination rate of BiOCl under simulated sunlight irradiation is effectively solved. MC / BiOCl has the advantages of high stability, high photocatalytic rate and the like under simulated sunlight, and can be applied to degradation of organic pollutants such as rhodamine B, tetracycline and petroleum hydrocarbons. The preparation method of the composite material is simple, the synthetic material and the solvent are green and environment-friendly, actual production requirements are met, and the composite material has a great application prospect.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic nanocomposite material preparation technology, specifically relating to a method for in-situ construction of melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials using urea polycondensation reaction in a low-temperature molten salt medium. Background Technology

[0002] Currently, commonly used methods for treating industrial wastewater containing organic pollutants include physical methods such as adsorption, membrane filtration, and reverse osmosis. These methods can only pretreat the wastewater and cannot truly remove organic pollutants. Chemical oxidation methods, while capable of completely oxidizing and degrading dyes, can easily cause secondary pollution due to the large quantities of chemical oxidants added. Biological aerobic and anaerobic oxidation methods are less expensive and less polluting, but have lower degradation efficiency and higher costs. Photocatalysis technology, due to its low cost, high efficiency, and environmental friendliness, has been widely used in the degradation of organic pollutant wastewater, heavy metal ion wastewater, and photocatalytic water splitting for hydrogen production.

[0003] Bismuth oxychloride (BiOCl), a typical layered semiconductor photocatalyst, has a tetragonal crystal structure [Bi2O2]. 2+ and Cl - Intercalation structures have attracted widespread attention due to their unique electronic structure and optical properties. However, their wide bandgap leads to low utilization efficiency of visible light, and the easy recombination of photogenerated electron-hole pairs limits their practical applications. To improve the photocatalytic performance of BiOCl, researchers often combine BiOCl with other semiconductors (biochar, Bi2O3, iron oxides, etc.) to construct heterojunctions to enhance the photogenerated carrier (electron-hole) ratio. - and h + The separation of ) thus prolongs e - and h +This extends their lifespan and increases their reactivity. For example, Qu et al. (Dual-modified β-Bi2O3 / BiOCl photocatalysts for efficient tetracycline hydrochloride degradation in wastewater: Role of heterojunctions and oxygen vacancies, Journal of Water Process Engineering, 71 (2025):107386) prepared β-Bi2O3 / BiOCl using a solvothermal method and used it for photocatalytic degradation of tetracycline hydrochloride. Chen et al. (Photodegradation of carbamazepine with BiOCl / Fe3O4 catalyst under simulated solar light irradiation, Journal of Colloid and Interface Science, 502(2017): 89–99) prepared BiOCl / Fe3O4 catalyst by adding bismuth nitrate pentahydrate to a suspension of Fe3O4 containing surfactants sodium dodecyl sulfonate and sodium chloride using a precipitation method. BiOCl / Fe3O4 can effectively degrade carbamazepine under simulated sunlight irradiation. Niu et al. (Kitchen-waste-derived biochar modified nanocomposites with improved photocatalytic performances for degrading organic contaminants, Environmental Research 214(2022): 114068–114078) used an ultrasonic-solvothermal method with bismuth nitrate pentahydrate, sodium chloride, and biochar as raw materials. Hou et al. (BiOCl / cattail carbon composites with hierarchical structure for enhanced photocatalytic activity, Solar Energy 211(2020): 1263–1269) used a coprecipitation method with bismuth nitrate pentahydrate, potassium chloride, ethylene glycol, thiourea, biochar, and acetic acid solution as raw materials. Both teams prepared biochar-doped BiOCl. Furthermore, both teams' biochar-doped BiOCl could degrade tetracycline under 500 W Xe lamp visible light (λ>420 nm) irradiation.CN115501893A discloses a method for preparing a g-C3N5-BiOCl heterojunction photocatalyst. The method involves dropping a sodium carbonate solution into a mixed dispersion of g-C3N5 nanosheets, bismuth nitrate pentahydrate, and potassium chloride, followed by a solvothermal reaction in an ethylene glycol medium to prepare the g-C3N5-BiOCl heterojunction photocatalyst. Ji et al. (Enhancing the performance of pollution degradation through secondary self-assembled composite supramolecular heterojunction photocatalyst BiOCl / PDI under visible light irradiation, Chemosphere 253 (2020): 126751–126763) employed a three-step method: hydrothermal calcination to prepare BiOCl, acidification self-assembly of perylene diimide precursors to prepare the supramolecular material perylene diimide (PDI), and finally, a constant-temperature water bath heating method using triethylamine and nitric acid to regulate electrostatics to prepare BiOCl / PDI. BiOCl / PDI was degraded by visible light at wavelengths greater than 420 nm, with each degradation method involving 5 mg / L. -1 Phenol, methyl orange, Rh B and 10 mg L -1 Rh B, the results showed that BiOCl / PDI only affected Rh B (10 mg L). -1 It exhibits a significant degradation effect (degradation rate of 78.9%). CN117797877A first prepares Bi / BiOCl and Ce-UiO-66-H respectively via a solvothermal method, and then sonicates Bi / BiOCl and Ce-UiO-66-H in DMF for 2 hours to form a heterojunction composite Ce-MOF / Bi / BiOCl photocatalyst, which has the performance of highly efficient photocatalytic degradation of tetracycline.

[0004] As can be seen from the above, existing literature and patents prepare BiOCl-based heterojunctions or their doped structures through two-step or multi-step precipitation methods, thermal methods, etc. These methods have drawbacks such as lengthy and complex preparation steps, weak interactions between heteromaterials, and expensive organic reagents required for some preparation methods, thus limiting their large-scale practical application. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies, such as the complex preparation process of BiOCl-based heterojunctions and the weak interaction between heteromaterials. It provides a simple, low-cost, and environmentally friendly low-temperature molten salt method for one-step preparation of urea-derived carbon and nitrogen species—melamine-cyanuric acid supramolecular (MC)—and BiOCl heterojunction (MC / BiOCl) composite materials, and to apply this to the field of photocatalysis to improve photocatalytic efficiency. The molten salt method, as a mature (mixed) crystal growth method, has advantages such as low synthesis temperature, good crystal morphology, and high phase purity.

[0006] The in-situ construction method of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material provided by the present invention is as follows: urea, bismuth salt, sodium chloride, and potassium chloride are thoroughly ground and mixed. The resulting mixture is placed in a crucible, the crucible lid is closed, and the crucible is wrapped with 1-2 layers of aluminum foil. The mixture is then heat-treated at 220-280 °C for 2-6 hours in air or an inert atmosphere. After natural cooling to room temperature, the mixture is washed with deionized water and dried to obtain the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material.

[0007] In the above-mentioned in-situ construction method of the bismuth salt-cyanuric acid supramolecular / BiOCl heterojunction composite material, the mass ratio of bismuth salt to urea is 1:0.5 to 1:5, the mass ratio of sodium chloride to potassium chloride is 1:1 to 1:5, and the ratio of the total molar amount of chlorine in sodium chloride and potassium chloride to the molar amount of bismuth in bismuth salt is 3:1 to 15:1.

[0008] Furthermore, in the above-mentioned in-situ construction method of the bismuth salt-cyanuric acid supramolecular / BiOCl heterojunction composite material, the preferred mass ratio of the bismuth salt to urea is 1:1 to 1:3, the mass ratio of sodium chloride to potassium chloride is 1:1 to 1:3, and the ratio of the total molar amount of chlorine in the sodium chloride and potassium chloride to the molar amount of bismuth in the bismuth salt is 5:1 to 13:1.

[0009] Furthermore, it is preferred that the above-mentioned bismuth salt is at least one of bismuth nitrate, bismuth chloride, or bismuth sulfate.

[0010] Furthermore, in the above-mentioned in-situ construction method of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material, it is preferable to heat-treat at 250 °C for 4 hours in air or an inert atmosphere.

[0011] The in-situ construction method of this invention yields a melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material, wherein BiOCl exists in a nanosheet structure, and the self-assembled nanosheets of BiOCl are uniformly composited with the melamine-cyanuric acid supramolecular network structure, with strong interaction between the two.

[0012] This invention also provides the application of the above-mentioned melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material in the photocatalytic degradation of organic pollutants. The organic pollutant is any one of rhodamine B, tetracycline antibiotics, petroleum hydrocarbon pollutants, etc.

[0013] The reaction mechanism of this invention is as follows: bismuth salt serves as the bismuth source, and NaCl-KCl molten salt serves as the medium and chlorine source, promoting the reaction of Bi at high temperature. 3+ O 2- Cl - Ion rearrangement. In a stable environment free from gas interference, the reaction proceeds slowly and orderly, resulting in a more thermodynamically stable and structurally complex n-type semiconductor, Bi. 12 O 17 Cl2 grows preferentially. Its regular layered structure is manifested in the strong and sharp diffraction peaks at 12.0°, 24.2°, and 36.6°. After the addition of urea, on the one hand, urea acts as a pore-opening agent: the decomposition of urea produces a large amount of NH3 and CO2 gas, which disrupts the formation of Bi. 12 O 17 The stable chlorine environment and ion concentration required by Cl2 force the reaction to shift towards the formation of the simpler BiOCl. On the other hand, urea undergoes a condensation reaction at 220–280 °C, generating a series of condensation products such as melamine, melamine, and cyanuric acid. These products are precursors to graphitic carbon nitride (g-C3N4), which, at this temperature, have not yet fully polymerized to g-C3N4, but instead form melamine-cyanuric acid supramolecular structures. In the aforementioned environment, the formation of BiOCl and the formation of the melamine-cyanuric acid complex occur simultaneously and in the same location. They are not formed separately and then mixed, but rather they come into close contact and recombine in situ during the reaction, thus forming a melamine-cyanuric acid supramolecular / BiOCl heterostructure.

[0014] The beneficial effects of this invention are as follows:

[0015] 1. This invention completes the urea polycondensation and BiOCl crystallization processes in one step in a sodium chloride-potassium chloride low-temperature molten salt, enabling BiOCl to form a tight molecular / nanoscale interface with melamine-cyanuric acid supramolecular in-situ composite. This greatly promotes the effective separation of photogenerated electron-hole pairs, endowing the composite material with significantly enhanced photocatalytic activity. Under simulated sunlight, it can photocatalytically degrade various types of organic pollutants (such as Rhodamine B, tetracycline, and petroleum hydrocarbons). It has the advantages of high stability and high photocatalytic rate, effectively solving the problems of poor visible light response of BiOCl and high recombination rate of melamine-cyanuric acid supramolecular photogenerated electron-hole pairs.

[0016] 2. This invention uses urea as a precursor to synthesize melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials in a one-step process in low-temperature molten salt, simplifying the process and reducing energy consumption. Furthermore, the molten salt medium is recyclable, and all synthetic materials and solvents are green and non-toxic, offering advantages such as low cost, environmental friendliness, and high energy efficiency. It fully meets actual production needs and demonstrates great application potential. In addition, the in-situ construction method of melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials provided by this invention is also applicable to the preparation of composite materials of melamine-cyanuric acid supramolecular materials with other metal semiconductors (such as FeOCl, Fe2O3, AgCl, etc.) or melamine-cyanuric acid supramolecular / BiOCl heterojunction-based composite materials doped with semiconductor elements (such as Fe, Ag, copper, tungsten, etc.).

[0017] 3. This invention successfully utilizes urea as a "reaction switch" to separate a single-phase catalyst (Bi) from a reactive state. 12 O 17 The evolution from Cl2 to heterojunction composite materials (melamine-cyanuric acid / BiOCl). Moreover, the melamine-cyanuric acid / BiOCl heterojunction catalyst exhibits a photocatalytic degradation rate far exceeding that of single components due to its highly efficient charge separation capability. Attached Figure Description

[0018] Figure 1 This is the energy spectrum of the melamine-cyanuric acid supramolecular (MC) prepared in Comparative Example 1.

[0019] Figure 2 This is the XRD pattern of the melamine-cyanuric acid supramolecular (MC) prepared in Comparative Example 1.

[0020] Figure 3 The infrared spectra are those of melamine (a), cyanuric acid (b), and the melamine-cyanuric acid supramolecular (c) prepared in Comparative Example 1.

[0021] Figure 4 This is a SEM image of the melamine-cyanuric acid supramolecular prepared in Comparative Example 1.

[0022] Figure 5 The images show the XRD patterns of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials prepared in Examples 1-3.

[0023] Figure 6 These are SEM images of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials prepared in Examples 1-3.

[0024] Figure 7 These are the photocatalytic degradation effects of Rhodamine B by the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials prepared in Examples 1-3.

[0025] Figure 8 This is a photocatalytic degradation effect of tetracycline by the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material (MC / BiOCl-4h) prepared in Example 2.

[0026] Figure 9 The photocatalytic degradation of 3 by the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material (MC / BiOCl-4h) prepared in Example 2. # Color changes of the oil-water system at different times (a: 0 h; b: 1 h; c: 3 h) and UV-Vis spectrum (d) (reaction conditions: pH=10, T=25℃).

[0027] Figure 10 This is the XRD pattern of the sample prepared in Comparative Example 2.

[0028] Figure 11 This is the energy spectrum of the sample prepared in Comparative Example 2.

[0029] Figure 12 The melamine-cyanuric acid supramolecular (MC) prepared in Comparative Example 1 and the Bi prepared in Comparative Example 2 12 O 17 Comparison of the photocatalytic degradation effect of Cl2 and the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material (MC / BiOCl-4 h) prepared in Example 2 on Rh B.

[0030] Figure 13 The effect of different inhibitors on the photocatalytic degradation efficiency of RhB by the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material (MC / BiOCl-4 h) prepared in Example 2.

[0031] Figure 14 The UV-Vis diffuse reflectance spectra and Tauc insets are of the melamine-cyanuric acid supramolecular prepared in Comparative Example 1, the purchased BiOCl, and the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material (MC / BiOCl-4 h) prepared in Example 2.

[0032] Figure 15 This is the pathway of photogenerated charge separation in the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material prepared in Example 2. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] Comparative Example 1

[0035] Weigh 1.8 g of urea, 1.0 g of sodium chloride, and 1.25 g of potassium chloride into an agate mortar and grind them thoroughly until homogeneous. Transfer the homogeneous powder to a 45 mL covered ceramic crucible, cover it, and wrap it with two layers of aluminum foil. Place the foil-wrapped crucible in a muffle furnace and heat it to 250 °C at a heating rate of 5 °C / min under air atmosphere, and maintain the temperature at this temperature for 4 hours. After the reaction is complete, allow it to cool naturally to room temperature. Remove the sample, wash it with deionized water, and filter it to obtain a white solid. Dry the white solid in an 80 °C oven for 6 hours to obtain melamine-cyanuric acid supramolecular (MC).

[0036] Depend on Figure 1 It is known that MC contains three elements: C, N, and O; small amounts of other elements, Na and K, are introduced by external molten salt; Al and Si are introduced by the ceramic crucible; and Au is introduced by gold sputtering during electron microscopy imaging. Table 1 shows the mass percentage of C, N, H, and estimated O as determined by the elemental analyzer. It can be seen that the data measured by the elemental analyzer are basically consistent with the results of the energy dispersive spectroscopy (EDS) determination. This is similar to cyanuric acid (C3N3O3H3) and melamine (C6N... 11 The theoretical chemical formula for the formation of supramolecular molecules (C9N) by reacting H9 in a 1:1 molar ratio is (C9N). 14 O3H 12 Compared to C9N, 14 O8H 21 (Experimental) compared to C9N 14 O3H 12 (Theoretically) there are 5 extra O and 9 extra H, which is very close to the composition of 4 water molecules and 1 -OH. This indicates that the present invention has successfully synthesized MC hydrate; at the same time, the terminal groups (-OH) of MC adsorbed on the crystal surface or defect sites contribute additional OH.

[0037] Table 1. Content of each element in MC and the estimated experimental formula.

[0038]

[0039] from Figure 2 Characteristic diffraction peaks attributable to melamine molecules (e.g., 2θ = 10.8°, 24.6°) and weak characteristic diffraction peaks attributable to cyanuric acid (e.g., 2θ = 21.24°, 22.35°, 29.62°, 32.26°, 33.74°) can be observed. Simultaneously, sharp, strong diffraction peaks at 2θ = 13.87° and 27.80°, which do not belong to either melamine or cyanuric acid, indicate a long-range ordered layered supramolecular structure formed by the hydrogen bonding assembly of cyanuric acid and melamine molecules. The XRD pattern of MC is a superposition of the characteristic peaks of the two components (melamine and cyanuric acid) and the new structure generated by their hydrogen bonding assembly.

[0040] Depend on Figure 3 It can be seen that MC and its three molecules, melamine and cyanuric acid, are all located at approximately 3289, 3103, 1573, 1472, 1392, 1185, 943–982, and 688–723 cm⁻¹. -1 Typical fingerprint peaks of melamine, cyanuric acid, and their supramolecular components appeared at [locations missing]. These peaks mainly originated from the NH stretching vibration (3289–3103 cm⁻¹). -1 ), skeletal vibrations of aromatic rings (triazine rings) (1573–943 cm⁻¹) -1 ) and out-of-plane bending vibrations of NH (943–982 cm) -1 Out-of-plane bending vibration of the triazine ring (688–723 cm) -1 However, compared with melamine and cyanuric acid, MC exhibits more pronounced NH stretching vibrations, triazine ring skeletal vibrations, and NH out-of-plane bending vibrations (943–982 cm⁻¹). -1 The triazine ring showed significant sharpening and splitting of its out-of-plane bending vibration. Additionally, the NH stretching vibrations at 3465 cm⁻¹ belonged to the free NH₂ of melamine and to the imino group (-NH₃-) of cyanurate, respectively. -1 3397 cm -1 The peak disappears at 3568 cm⁻¹; meanwhile, MC is at 3568 cm� -1 A weak absorption peak was observed, indicating that the NH2 group on the cyanuric acid is no longer in a free state, but is deeply involved in the formation of hydrogen bonds (C=O…HN). Cyanuric acid showed a peak at approximately 1789 cm⁻¹. -1 The peak attributable to the C=O stretching vibration undergoes a significant redshift after forming the MC, at 1694 cm⁻¹. -1 The presence of a strong double peak nearby indicates that this is not an isolated hydrogen bond, but rather the formation of an extended, highly ordered two-dimensional hydrogen bond network. The MC value is at 780 cm⁻¹. -1 A new absorption peak appears at 886 cm⁻¹. -1 The bimodal distribution indicates that melamine and cyanuric acid molecules are locked in specific relative positions and orientations through a strong hydrogen bond network, resulting in the characteristic vibrations of the triazine ring (780 and 886 cm⁻¹). -1 The MC becomes more defined and sharper. In short, the MC is between 780 and 886cm. -1 The absorption peak further corroborates the formation of the MC structure.

[0041] Depend on Figure 4 It is evident that MC is composed of loose, irregular sheet-like structures, with faint traces of stacked layered structures visible at the edges.

[0042] Example 1

[0043] Weigh 1.8 g of urea, 0.5 g of sodium chloride, 0.65 g of potassium chloride, and 1.0 g of bismuth nitrate pentahydrate into an agate mortar and grind them thoroughly until homogeneous. Transfer the homogeneous powder to a 45 mL covered ceramic crucible, cover it, and wrap it with two layers of aluminum foil. Place the foil-wrapped crucible in a muffle furnace and heat it to 250 °C at a heating rate of 5 °C / min under air atmosphere, and maintain the temperature at this temperature for 2 hours. After the reaction is complete, allow it to cool naturally to room temperature. Remove the sample, wash it with deionized water, and filter it to obtain a white solid. Dry the white solid in an 80 °C forced-air drying oven for 10 hours to obtain the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material, denoted as MC / BiOCl-2 h.

[0044] Example 2

[0045] In this embodiment, a crucible wrapped with aluminum foil was placed in a muffle furnace and heated to 250 °C at a heating rate of 5 °C / min under an air atmosphere, and held at this temperature for 4 hours. Other steps were the same as in Example 1, resulting in a melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material, denoted as MC / BiOCl-4 h.

[0046] Example 3

[0047] In this embodiment, a crucible wrapped with aluminum foil was placed in a muffle furnace and heated to 250 °C at a heating rate of 5 °C / min under an air atmosphere, and held at this temperature for 6 hours. Other steps were the same as in Example 1, resulting in a melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material, denoted as MC / BiOCl-6 h.

[0048] Depend on Figure 5 It can be seen that the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials prepared in Examples 1 to 3 all exhibited BiOCl (standard card PDF) at 2θ values ​​of 11.88° (110), 23.96° (220), 32.56° (400), 33.42° (112), 41° (312), and 46.74° (440). # Characteristic diffraction peaks corresponding to the crystal planes (97-002-9143) were observed. Simultaneously, a characteristic diffraction peak corresponding to MC appeared at 2θ = 27.8°. This indicates the successful preparation of the MC / BiOCl heterojunction composite material.

[0049] Depend on Figure 6 As can be seen from Example 1, in the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material, BiOCl grows on the MC surface as plate-like or plate-like aggregates, and the MC matrix is ​​dense. Figure 6As can be seen from b, in the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material prepared in Example 2, BiOCl self-assembles into spherical flower-like growths on the lamellar MC surface. Figure 6 As can be seen from c, in the honey-cyanuric acid supramolecular / BiOCl heterojunction composite material prepared in Example 3, some sheet-like BiOCl particles grow on the MC surface, and some sheet-like BiOCl particles are free outside the MC.

[0050] Application Example 1

[0051] Photocatalytic degradation of Rhodamine B organic pollutants

[0052] The photocatalytic performance of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials prepared in Examples 1-3 was evaluated using Rhodamine B dye (RhB) as the target pollutant. Specifically, 40 mg of the composite material was dispersed in 120 mL of RhB solution (concentration 35 mg / L). After adsorption in the dark for 40 minutes to reach equilibrium, the material was irradiated with a xenon lamp of 200 W or higher to induce a photocatalytic reaction. Samples were taken periodically, and the absorbance of the sample solution was measured at different reaction times after centrifugation. The concentration of residual RhB at different reaction times was calculated based on the standard curve equation of the RhB solution (Y = 0.03146X + 0.2731 (R² = 0.999)).

[0053] Depend on Figure 7 It can be seen that the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite materials prepared in Examples 1-3 almost turned colorless after interacting with Rh B solution for 30 minutes. Figure 7 interpolate Figure 1 Comparison of reaction rate constants fitted by the kinetic model revealed that: MC / BiOCl-4 h (k=0.227) > MC / BiOCl-2 h (k=0.168) > MC / BiOCl-6 h (k=0.122), indicating that MC / BiOCl-4 h has the best photocatalytic effect.

[0054] Application Example 2

[0055] Photocatalytic degradation of tetracycline pollutants

[0056] The photocatalytic performance of MC / BiOCl-4 h prepared in Example 1 was evaluated using tetracycline antibiotic dyes as the target pollutant. Specifically, 40 mg of MC / BiOCl-4 h was dispersed in 120 mL of a tetracycline-simulated pollutant solution (concentration 10 mg / L). After adsorption in the dark for 40 minutes to reach equilibrium, a 200 W xenon lamp was used for photocatalytic reaction. Samples were taken periodically, and the solution concentration was determined after centrifugation. Figure 8It can be seen that when the tetracycline solution was irradiated with a 300 W xenon lamp for 45 minutes, the degradation rate of tetracycline by MC / BiOCl-4 h reached 90%. Figure 8 The results show that the MC / BiOCl-4 h of the present invention can also efficiently degrade tetracycline organic pollutants.

[0057] Application Example 3

[0058] Photocatalytic degradation of petroleum hydrocarbon pollutants

[0059] Disperse 0.100 g MC / BiOCl-4 h in a sleeve cup containing 120 mL of deionized water (pH = 8.6), and accurately pipette 0.4 mL of the solution. # Oil (3) # The oil components (contents are shown in Table 1) are added to the sleeve cup and magnetically stirred to form 3 # Oil-water mixture. After adsorption in the dark for 40 minutes to reach equilibrium, irradiate with a 200 W xenon lamp for 3 minutes. # The oil-water mixture underwent a photocatalytic reaction. Samples were taken periodically and centrifuged; the upper layer (3 μL) was collected. # Oil-water mixture. The upper layer (3) was determined by potassium dichromate titration. # Chemical oxygen demand (COD) of oil-water mixtures. Two parallel experiments were conducted simultaneously, one under light and one in the dark, and the COD was calculated for different reaction times. # COD removal rate in oil-water mixture.

[0060] Table 1 3 # Content of major components in oil (unit: mg / L)

[0061]

[0062] Table 2. Photocatalytic degradation of MC / BiOCl-4 h 3 # Oil data

[0063]

[0064] Depend on Figure 9 It can be seen that in the dark state 3 # The oil-water mixture presented as a turbid, heterogeneous system. After 1 hour of degradation, the lower aqueous phase became significantly clearer, while the upper oil phase showed a significant increase in volume. This is likely due to the increase in hydrophobic intermediates during the degradation process. After 3 hours of degradation, the water showed no significant turbidity, and the oil layer completely disappeared, indicating that the system contained 3... # The oil was largely decomposed, which is consistent with the COD removal rate results (Table 2). Similarly, the changes in the UV-Vis spectrum curves show that as the degradation time increases, the absorption peak of the benzene ring at 220 nm gradually weakens and eventually disappears. Therefore, 3 #The oil was basically decomposed by MC / BiOCl-4 h under 300 W xenon lamp irradiation, forming small-molecule inorganic substances such as carbon dioxide and water.

[0065] Comparative Example 2

[0066] Without adding urea, the other steps are the same as in Example 2.

[0067] Figure 10 The XRD pattern of the sample prepared for Comparative Example 2 is shown. It can be seen that this XRD pattern shows the presence of values ​​corresponding to Bi at 2θ values ​​of 12.0° (001), 24.2° (002), and 36.6° (003). 12 O 17 The characteristic diffraction peaks of the corresponding crystal plane of Cl2 (JCPDS 37-0702) and the relative intensity characteristics also conform to Bi. 12 O 17 The typical XRD characteristics of Cl2 (no impurities, peak shape matching) indicate that Bi was successfully prepared in Comparative Example 2. 12 O 17 Cl2 photocatalytic materials.

[0068] Figure 11 The image shows the energy dispersive spectroscopy (EDS) spectrum of the sample prepared for Comparative Example 2. It can be seen that the sample prepared for Comparative Example 2 mainly contains three elements: O, Cl, and Bi. In addition, a small amount of Na was introduced by external molten salt; Al and Si were introduced by the ceramic crucible; and Au was introduced by gold sputtering during electron microscopy imaging. The chemical formula for the combination of O, Cl, and Bi is Bi₂O₃Cl₂→Bi. 12 O 18 Cl2, with Bi 12 O 17 The elemental composition of Cl2 is basically the same. (It may originate from the nitrogen (N) and excess oxygen produced during the thermal decomposition of the precursor bismuth pentahydrate.) It may also be present in Bi... 12 O 17 During the growth of Cl2 crystals, they are either encapsulated in the interlayer or adsorbed on the surface. Figure 10 and Figure 11 It was found that the sample prepared in Comparative Example 2 was a Bi co-modified with N and O. 12 O 17 Cl2.

[0069] Figure 12 The MC / BiOCl-4h, MC, and Bi prepared in Example 2, Comparative Example 1, and Comparative Example 2 are examples of this study. 12 O 17 A comparison of the effect of Cl2 on RhB adsorption in the dark state and the photocatalytic degradation activity of RhB. From Figure 12 The dark-state adsorption data show that MC has no significant adsorption effect on RhB; MC / BiOCl-4h and Bi 12 O17 The adsorption removal rates of Cl2 on Rh B in the dark state after 30 min were 29% and 11%, respectively. Adsorption is a prerequisite for the photocatalytic degradation of organic pollutants. Figure 12 The changes in RhB solution concentration and the photocatalytic reaction rate constant during the photocatalytic process show that the MC prepared in Comparative Example 1 did not have a significant photocatalytic degradation effect on RhB; the Bi prepared in Comparative Example 2... 12 O 17 Cl2 exhibits photodegradation of RhB solution, but its rate constant for photocatalytic degradation of RhB (0.0558 min) is low. -1 The rate constant of the photocatalytic degradation of RhB by MC / BiOCl-4 prepared in Example 2 (0.230 min) was significantly lower than that of the rate constant of the photocatalytic degradation of RhB by MC / BiOCl-4 prepared in Example 2 (0.230 min). -1 ).

[0070] To further investigate the mechanism of efficient photocatalytic degradation of RhB by MC / BiOCl-4h, free radical inhibitors—isopropanol (hydroxyl radical ·OH) and histidine (singlet oxygen)—were added to the MC / BiOCl-4h photocatalytic degradation RhB system prepared in Example 2 of Application Example 1. 1 O2), p-benzoquinone (superoxide radical·O2) - ), EDTA-2Na (photogenerated holes h) + ).like Figure 13 As shown, compared with the removal rate without inhibitors (30 minutes, 100%), the addition of histidine and p-benzoquinone reduced the RhB degradation rate to 20.5% and 62.5%, respectively. Isopropanol and EDTA-2Na had no significant effect on the RhB degradation rate. Therefore, under air and light conditions, the main reactive species for the rapid degradation of RhB by MC / BiOCl-4 h is singlet oxygen (…). 1 O2) and superoxide radicals (·O2) - ).

[0071] Depend on Figure 14The UV-Vis diffuse reflectance spectra and Tauc insets of the methyl cyanuric acid supramolecular (MC), BiOCl, and MC / BiOCl-4h show that BiOCl exhibits strong absorption in the UV region (200–400 nm), consistent with its characteristics as a typical UV-responsive semiconductor. MC shows strong absorption in the UV region (200–248 nm), with an absorption intensity higher than BiOCl. Both MC and BiOCl show weak absorption in the visible region (>400 nm), with MC slightly stronger than BiOCl. The MC / BiOCl-4h heterojunction shows significantly higher absorption intensity in the UV region (200–400 nm) than BiOCl, and its absorption intensity in the visible region (400–800 nm) reaches 0.1, significantly higher than both MC and BiOCl, indicating that the formation of the heterojunction between MC and BiOCl enhances the visible light capture capability. Figure 14 The inset shows that the band gaps of BiOCl and MC are 3.10 and 3.44, respectively. This indicates that MC can absorb ultraviolet photons with energies higher than 3.44 eV (corresponding to 360 nm). BiOCl can absorb ultraviolet-violet light with energies higher than 3.10 eV (corresponding to 400 nm). When BiOCl and MC are combined, this system can absorb all light extending from 3.44 eV downwards, thus broadening the spectral range that the composite can utilize to some extent.

[0072] On the other hand, MC / BiOCl-4h and BiOCl both have a band gap of 3.10, but their photocatalytic performance is significantly improved. This indicates that the photocatalytic activity here is not determined by the band gap width, but by the heterojunction formed in situ by MC and BiOCl, which effectively promotes the spatial separation of photogenerated electron-hole pairs between the two materials. Specifically, when BiOCl and MC tightly bind to form a complex, a tight interfacial contact is established between them. Due to the difference in their band structures (the energy levels at the bottom of the conduction band and the top of the valence band), a built-in electric field is formed at the interface, driving the directional migration of photogenerated carriers. Figure 15 The path of charge separation is clearly shown.

[0073]

[0074] (1)

[0075] (2)

[0076] like Figure 15 As shown, under the drive of the built-in electric field of the heterojunction, photogenerated electrons (e... - () will migrate from the conduction band of MC to the conduction band of BiOCl; photogenerated holes (h +Photogenerated electrons migrate from the valence band of BiOCl to the MC valence band. This results in electron enrichment on the BiOCl surface and, similarly, hole enrichment on the MC supramolecular surface. This process achieves spatial separation of photogenerated electrons and holes, significantly reducing their recombination probability and allowing more charge carriers to migrate to the catalyst surface to participate in redox reactions, thereby significantly improving photocatalytic efficiency. Photogenerated electrons (e) in the BiOCl conduction band migrate from the valence band of BiOCl to the MC valence band. - ) reacts with adsorbed O2 to produce superoxide radicals (·O2) - Photogenerated holes in the MC valence band react with adsorbed O2 to form singlet oxygen (). 1 O2). Organic pollutant molecules are first adsorbed onto the surface of the MC / BiOCl-4h heterojunction through adsorption, hydrogen bonding, or π-π stacking, while a large number of superoxide radicals (·O2) are absorbed. - ) and singlet oxygen ( 1 O2 is concentrated here, achieving integrated "adsorption-degradation" and greatly improving degradation efficiency.

Claims

1. A method for in-situ construction of a melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material, characterized in that: Urea, bismuth salt, sodium chloride, and potassium chloride are thoroughly ground and mixed. The resulting mixture is placed in a crucible, the crucible lid is closed, and the crucible is wrapped with 1-2 layers of aluminum foil. The mixture is then heat-treated at 220-280 °C for 2-6 hours in air or an inert atmosphere. After natural cooling to room temperature, the mixture is washed with deionized water and dried to obtain the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material.

2. The in-situ construction method of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material according to claim 1, characterized in that: The mass ratio of bismuth salt to urea is 1:0.5 to 1:5, the mass ratio of sodium chloride to potassium chloride is 1:1 to 1:5, and the ratio of the total molar amount of chlorine in sodium chloride and potassium chloride to the molar amount of bismuth in bismuth salt is 3:1 to 15:

1.

3. The in-situ construction method of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material according to claim 1, characterized in that: The mass ratio of bismuth salt to urea is 1:1 to 1:3, the mass ratio of sodium chloride to potassium chloride is 1:1 to 1:3, and the ratio of the total molar amount of chlorine in sodium chloride and potassium chloride to the molar amount of bismuth in bismuth salt is 5:1 to 13:

1.

4. The in-situ construction method of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material according to claim 1, characterized in that: The bismuth salt is at least one of bismuth nitrate, bismuth chloride, or bismuth sulfate.

5. The in-situ construction method of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material according to claim 1, characterized in that: Heat treatment at 250 °C for 4 hours in air or an inert atmosphere.

6. The melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material obtained by the in-situ construction method according to any one of claims 1 to 5, wherein BiOCl exists in the composite material in a nanosheet structure and is composited with the melamine-cyanuric acid supramolecular network.

7. The application of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material according to claim 6 in the photocatalytic degradation of organic pollutants.

8. The application of the melamine-cyanuric acid supramolecular / BiOCl heterojunction composite material according to claim 7 in the photocatalytic degradation of organic pollutants, characterized in that: The organic pollutant is any one of rhodamine B, tetracycline antibiotics, or petroleum hydrocarbon pollutants.

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