A halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst, its preparation method and application

Abstract

This invention relates to the fields of environmental nanomaterials and photocatalytic wastewater treatment technology, and particularly to a halide-intercalated spinel-graphite phase carbon nitride heterojunction catalyst, its preparation method, and its application. The invention involves mixing melamine, a halogen source, and water, followed by a first calcination to obtain halide-intercalated carbon nitride. Then, a metal salt, water, halide-intercalated carbon nitride, and citric acid are mixed, and the pH is adjusted to acidity to form a gel-like mixture. Finally, the gel-like mixture is subjected to a second calcination to obtain the halide-intercalated spinel-graphite phase carbon nitride heterojunction catalyst. The metal active component is chemically bonded into the carbon nitride framework, significantly improving its lifespan. The built-in electric field induced by halogen intercalation accelerates photogenerated charge separation, increases the density of surface active sites, and significantly improves catalytic efficiency. This catalyst exhibits high mass transfer efficiency, is recyclable, and maintains high degradation capacity over a wide pH range and in wastewater containing interfering ions.

Description

Technical Field

[0001] This invention relates to the fields of environmental nanomaterials and photocatalytic wastewater treatment technology, and particularly to a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst, its preparation method, and its application. Background Technology

[0002] With the continuous improvement of industrialization, water pollution and shortage have received increasing attention. Among these, organic pollutants are highly toxic and difficult to degrade, seriously threatening human health and ecological security. Traditional physical, chemical, or biological treatment technologies have many limitations in terms of treatment efficiency, cost control, and stability. Photocatalysis, as a green and sustainable advanced oxidation process, has received widespread attention in recent years. Graphitic carbon nitride (g–C3N4), as a stable, non-toxic, low-cost, and easily prepared layered material, has great potential in photocatalytic pollutant degradation. However, due to its inherent characteristics, the rapid recombination of photogenerated electrons and holes and the relatively slow charge migration rate limit its photocatalytic activity. To address these issues, researchers have employed many different modification methods, including defect engineering, surface modification, chemical element doping, and the construction of heterojunctions.

[0003] Ion intercalation has proven to be an effective method. It can not only modulate the electronic structure of g-C3N4, creating more favorable channels for electron migration between its layers, thus significantly improving the material's photogenerated charge transport efficiency and separation capability, but also avoid the sp-axis effects of heteroatoms such as K, Na, Co, and S on g-C3N4 in doping methods. 2 The disruption of the π-conjugated system improves catalyst stability. Studies have shown that intercalated ions can transform g–C3N4 sheets stacked by van der Waals forces into covalently bonded sheets, ultimately enhancing their photocatalytic degradation performance. However, the intercalation process expands the interlayer spacing of g–C3N4, which, while beneficial for mass transport and exposing more active sites, may also weaken the van der Waals forces between layers. This can lead to structural instability during repeated photocatalytic cycles, and even the collapse or exfoliation of the layered structure. This reduces the material's mechanical strength and long-term stability. Furthermore, during the photocatalytic reaction, intercalated ions may partially dissolve or leach into the reaction solution, causing secondary pollution.

[0004] On the other hand, spinel ferrites (MFe2O4, M = Ni, Co, Cu, Zn, etc.) are a class of structurally stable and diverse metal oxide semiconductor materials. Due to their excellent thermal stability, magnetic responsiveness, and tunable band structure, they are widely used in photocatalysis. When combined with g-C3N4 to form a heterojunction, it not only expands the light absorption range but also creates effective band matching between the two semiconductors, thereby promoting efficient separation of photogenerated electrons and holes and suppressing carrier recombination. Studies have shown that constructing ZnFe2O4 / g-C3N4 heterojunctions to form S-type charge migration pathways effectively improves the redox capacity and stability of the system, exhibiting superior catalytic activity. However, precisely controlling the size, morphology, dispersion uniformity, and loading of ZnFe2O4 nanoparticles on the g-C3N4 substrate remains a challenge. Agglomeration or uneven loading reduces the effective interfacial area and charge transfer efficiency.

[0005] Therefore, how to obtain a high-performance composite catalyst with high photocatalytic activity, strong structural stability, low ion leaching resistance, and easy recycling through the synergistic construction of halide ion intercalation and spinel heterostructure has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst, its preparation method and application, in order to solve the problems existing in the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst, comprising the following steps:

[0009] (1) Melamine, halogen source and water are mixed and calcined for the first time to obtain halide-intercalated carbon nitride.

[0010] (2) After mixing metal salt, water, halide ion intercalated carbon nitride and citric acid, the pH is adjusted to acidic to form a gel-like mixture.

[0011] (3) The gel-like mixture was subjected to a second calcination to obtain a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst.

[0012] Optionally, the halogen source includes ammonium chloride, ammonium bromide, or ammonium iodide.

[0013] Optionally, the molar ratio of melamine to halogen source is 1:5 to 35; the molar ratio of melamine to water is 0.022 to 0.041 mol: 80 to 100 mL.

[0014] Optionally, the heating rate of the first calcination is 2℃ / min, the temperature is 480~550℃, and the holding time is 3~5h.

[0015] Optionally, the metal cation in the metal salt is iron ion and M ion, wherein the M ion includes nickel ion, cobalt ion, copper ion, manganese ion or zinc ion; the acid radical anion in the metal salt is sulfate ion, chloride ion or nitrate ion; and the molar ratio of iron ion to M ion is 1.3 to 2.7:1.

[0016] Optionally, in step (2), the ratio of the metal salt to water is 0.8-1.8 mmol: 10 mL; the molar ratio of citric acid to metal salt is 1-2:1; and the ratio of the metal salt to halide ion intercalated carbon nitride is 0.8-1.8 mmol: 0.5 g.

[0017] Optionally, the pH in step (2) is adjusted to 2.5 to 3.5, and the temperature at which the gel-like mixture is formed is 80 to 95°C.

[0018] Optionally, the heating rate of the second calcination is 5-8℃ / min, the temperature is 370-450℃, and the holding time is 2-3h.

[0019] The present invention also provides a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst prepared by the above preparation method.

[0020] This invention also provides the application of the above-mentioned halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst in photocatalytic degradation of organic matter.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention employs an in-situ sol-gel conversion method, using halogen-intercalated g-C3N4 nanosheets as the substrate material. During the sol-gel process, metal salts are introduced, and calcination allows the metal ions to synergistically interact with the halogens between the g-C3N4 layers, forming a metal-composite S-type heterojunction in situ (halogen ion-intercalated spinel-graphite phase carbon nitride heterojunction catalyst). During the heterostructure construction process, metal ferrites are chemically bonded into the g-C3N4 interface, ultimately yielding a composite material with a heterojunction structure. This effectively improves the charge transfer efficiency and mechanical stability of the heterojunction interface, avoids the use of toxic solvents or complex interface modifications, eliminates the need for additional organic waste treatment, and simplifies the synthesis process. The metal composition can be precisely controlled through macroscopic adjustment, facilitating large-scale production.

[0023] A stable interface is formed between the metal ferrite and the halide-ion intercalated graphitic carbon nitride (H)-g-C3N4 substrate through strong interactions, solving the problems of easy agglomeration of metal particles and rapid charge recombination in traditional heterojunctions, and significantly improving the service life. The mesoporous structure of the heterojunction allows for control over pore size and hollow layer thickness, enabling precise control over the visible light absorption range and carrier separation efficiency, and significantly reducing the recombination rate of photogenerated electron-hole pairs.

[0024] The built-in electric field induced by halogen intercalation accelerates photogenerated charge separation, increasing the density of surface active sites. Halogen-intercalated metal composite S-type heterojunction materials exhibit excellent catalytic performance, demonstrating high efficiency in degrading organic pollutants in visible light / PMS systems with low metal leaching and maintaining high catalytic activity even after recycling. Their self-supporting layered structure combines high specific surface area and strong adsorption capacity, enabling simultaneous high-efficiency adsorption and catalytic degradation of organic pollutants. They maintain high degradation efficiency across a wide pH range and in wastewater containing interfering ions, making them highly applicable to industrial applications. Attached Figure Description

[0025] Figure 1 The XRD pattern of the catalyst intercalation substrate prepared in Example 1;

[0026] Figure 2 The image shows the FT-IR spectrum of the catalyst intercalation substrate prepared in Example 2. Detailed Implementation

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0030] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0031] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0032] All raw materials used in this invention can be obtained commercially or prepared using existing technologies.

[0033] This invention provides a method for preparing a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst, comprising the following steps:

[0034] (1) Melamine, halogen source and water are mixed and calcined for the first time to obtain halide-intercalated carbon nitride.

[0035] (2) After mixing metal salt, water, halide ion intercalated carbon nitride and citric acid, the pH is adjusted to acidic to form a gel-like mixture.

[0036] (3) The gel-like mixture was subjected to a second calcination to obtain a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst.

[0037] This invention utilizes in-situ intercalation of melamine and a halogen source to form a halide-ion-intercalated graphitic carbon nitride (H)-g-C3N4 substrate. A nano-metal oxide composite halide-ion-intercalated graphitic carbon nitride (H)-g-C3N4 heterojunction is then constructed using the sol-gel method. This utilizes an S-type charge transfer mechanism to enhance the separation efficiency of photogenerated carriers, while leveraging the visible light response of g-C3N4 and the strong redox properties of metal oxides. This addresses the problems of excessively rapid carrier recombination and poor cycle stability in traditional catalysts. By introducing a transition metal as a metal source and employing the halogen intercalation process to increase the specific surface area, construct interlayer pathways and porous structures, the carrier separation rate and charge transfer rate are controlled, enhancing the adsorption and degradation capacity for organic pollutants. Furthermore, embedding the metal into the layered heterojunction structure solves the problems of difficult recovery and low regeneration efficiency in traditional catalysts. The mesoporous structure of the heterojunction increases the contact efficiency between the catalyst and pollutants in water, while facilitating separation during practical use, improving recovery efficiency, and avoiding secondary pollution.

[0038] Step (1) involves dissolving melamine and a halogen source in deionized water, stirring magnetically, drying, and then performing a first calcination to obtain halogen-intercalated carbon nitride.

[0039] In this invention, the halogen source includes ammonium chloride, ammonium bromide or ammonium iodide, preferably ammonium chloride or ammonium bromide, and more preferably ammonium chloride.

[0040] In this invention, the molar ratio of melamine to halogen source is 1:5 to 35, preferably 1:10 to 30, more preferably 1:15 to 25, and even more preferably 1:20 to 22; the molar ratio of melamine to water is 0.022 to 0.041 mol: 80 to 100 mL, for example, 0.0317 mol: 90 mL, 0.0301 mol: 90 mL, 0.0333: 90 mL, 0.0285 mol: 90 mL, 0.03568 mol: 90 mL, 0.0325 mol: 90 mL, or 0.0381 mol: 90 mL, etc.

[0041] In this invention, the magnetic stirring time is 24 hours; the drying temperature is 85-100°C, preferably 90-95°C, and the drying time is 10-12 hours, preferably 10-11 hours.

[0042] In this invention, the heating rate of the first calcination is 2℃ / min, the temperature is 480~550℃, preferably 490~540℃, more preferably 500~530℃, even more preferably 510~520℃, and the holding time is 3~5h, preferably 3~4h.

[0043] Step (2) involves dissolving the metal salt in deionized water, then adding halide ion-intercalated carbon nitride, dispersing it evenly, adding citric acid, dissolving it, then adding sodium hydroxide solution to adjust the pH to acidic, and then heating it to a gel state to form a gel-like mixture.

[0044] In this invention, the metal cations in the metal salt are iron ions and M ions, wherein the M ions include nickel ions, cobalt ions, copper ions, manganese ions, or zinc ions; the acid radical anions in the metal salt are sulfate ions, chloride ions, or nitrate ions; the molar ratio of iron ions to M ions is 1.3 to 2.7:1, preferably 1.5 to 2.5:1, more preferably 1.8 to 2.4:1, and even more preferably 2 to 2.2:1.

[0045] In this invention, in step (2), the ratio of the metal salt to water is 0.8-1.8 mmol:10 mL, preferably 0.9-1.6 mmol:10 mL, more preferably 1-1.5 mmol:10 mL, and even more preferably 1.2-1.3 mmol:10 mL;

[0046] The molar ratio of citric acid to metal salt is 1 to 2:1, preferably 1.1 to 1.8:1, more preferably 1.3 to 1.6:1, and even more preferably 1.4 to 1.5:1;

[0047] The ratio of the metal salt to the halide ion intercalated carbon nitride is 0.8–1.8 mmol:0.5 g, preferably 0.9–1.6 mmol:0.5 g, more preferably 1–1.5 mmol:0.5 g, and even more preferably 1.2–1.3 mmol:0.5 g.

[0048] In this invention, the pH is adjusted to 2.5-3.5, preferably 3, using sodium hydroxide with a concentration of 10 mol / L. The temperature for forming the gel-like mixture is 80-95°C, preferably 82-92°C, more preferably 85-90°C, and even more preferably 87-88°C.

[0049] This invention employs an in-situ sol-gel conversion synthesis route to prepare halide ion intercalated graphitic carbon nitride (H)-g-C3N4 nanocomposite materials with a layered heterojunction structure. This avoids the complex interface modification steps in traditional heterojunction preparation and can effectively improve the charge transfer efficiency and structural stability of the heterojunction interface.

[0050] Step (3) involves first drying the gel-like mixture, then performing a second calcination, and finally cooling, washing, and drying to obtain a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst.

[0051] In this invention, the drying temperature of the gel-like mixture is 120°C, and the drying time is 15 to 35 hours, preferably 16 to 30 hours, and more preferably 20 to 24 hours.

[0052] In this invention, the heating rate of the second calcination is 5-8℃ / min, preferably 5-6℃ / min, the temperature is 370-450℃, preferably 390-440℃, more preferably 400-430℃, even more preferably 410-420℃, and the holding time is 2-3h, preferably 2h.

[0053] In the synthesis process, this invention significantly reduces heat treatment time through calcination. Simultaneously, the introduction of transition metal salts into the precursor solution synergistically improves the mixing uniformity of the metal components and the g-C3N4 substrate, promoting the formation of a highly dispersed composite structure where halide ions are intercalated between the graphitic carbon nitride (H)-g-C3N4 layers. This invention regulates the interlayer charge distribution of g-C3N4 through in-situ halogen intercalation, anchoring the active metal components to the heterojunction framework via chemical bonding. This avoids the metal particle agglomeration and interfacial charge recombination problems caused by traditional loading methods, improving the photogenerated carrier separation efficiency and maintaining stable catalytic activity after multiple cycles.

[0054] The present invention also provides a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst prepared by the above preparation method.

[0055] This invention also provides the application of the above-mentioned halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst in photocatalytic degradation of organic matter.

[0056] In this invention, the organic compound is preferably an organic compound having an aromatic ring.

[0057] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0058] Example 1

[0059] ZnFe2O4 / (Cl)-g-C3N4 heterojunction catalyst

[0060] (1) Preparation of Cl intercalated g-C3N4 substrate

[0061] (1-1) Take a dry and clean beaker, add 0.0317 mol melamine and 0.9508 mol ammonium chloride, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90℃ for 12 hours to obtain the precursor.

[0062] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. The temperature was held for calcination for 4 hours and then cooled to obtain Cl-intercalated g-C3N4 (Cl-g-C3N4).

[0063] (2) Preparation of heterojunction

[0064] (2-1) Weigh 0.38 mmol zinc nitrate hexahydrate and 0.78 mmol ferric nitrate nonahydrate, add 10 mL of deionized water to dissolve, then add 0.5 g Cl-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0065] (2-2) Add 1.254 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15h.

[0066] (3) Calcination and forming

[0067] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain the ZnFe2O4 / (Cl)-g-C3N4 composite catalyst.

[0068] ZnFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalysts have important applications in wastewater treatment. They can improve charge transfer rates and reduce metal ion loss. The ZnFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. Finally, the degradation rate of bisphenol A reached 97.7%. The ZnFe2O4 / (Cl)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 95.0% bisphenol A degradation rate even after 5 cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 97.0 ± 0.5%. - NO3 - H2PO4 - HCO3 - Even with coexisting ions, the degradation rate still reaches 90.3±1.2%.

[0069] Figure 1 This is the XRD pattern of the composite catalyst, from Figure 1 The peaks at 2θ = 30.1°, 35.2°, 52.5°, 56.8° and 62.5° correspond to the spinel phase crystal planes (220), (311), (422), (511) and (440) of zinc ferrite, indicating the successful preparation of zinc ferrite. In addition, the weak peak at 2θ = 27.5° corresponds to the (001) crystal plane of g-C3N4, indicating the successful preparation of the composite catalyst.

[0070] Example 2

[0071] MnFe2O4 / (Cl)-g-C3N4 heterojunction catalyst

[0072] (1) Preparation of Cl intercalated g-C3N4 substrate

[0073] (1-1) Take a dry and clean beaker, add 0.0301 mol melamine and 0.9039 mol ammonium chloride, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90℃ for 12 hours to obtain the precursor.

[0074] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. The temperature was held for calcination for 4 hours and then cooled to obtain Cl-intercalated g-C3N4 (Cl-g-C3N4).

[0075] (2) Preparation of heterojunction

[0076] (2-1) Weigh 0.9 mmol of ferric nitrate nonahydrate and 0.5 mmol of manganese nitrate tetrahydrate, add 10 mL of deionized water to dissolve, then add 0.5 g of Cl-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0077] (2-2) Add 1.482 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15h.

[0078] (3) Calcination and forming

[0079] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain the MnFe2O4 / (Cl)-g-C3N4 composite catalyst.

[0080] MnFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalysts have important applications in wastewater treatment. They can improve charge transfer rates and reduce metal ion loss. The MnFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. The final result showed a bisphenol A degradation rate of 96.3%. The MnFe2O4 / (Cl)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 94.8% bisphenol A degradation rate even after five cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 96.0 ± 0.6%. - NO3- H2PO4 - HCO3 - Even with coexisting ions, the degradation rate still reaches 90.0 ± 1.0%.

[0081] Figure 2 This is the FT-IR spectrum of the catalyst intercalation substrate, from... Figure 2 It can be determined that the height is 1200-1650cm. -1 The strong absorption peaks between them correspond to the stretching vibrations of the CN and C=N bonds, specifically at 807 cm⁻¹. -1 and 1244cm -1 The vibrational peaks correspond to the stretching vibrations of its triazine ring and CN bond, and show a slight shift compared to g-C3N4, indicating a change in the CN coordination environment, which can be attributed to the successful introduction of the Cl intercalation structure.

[0082] Example 3

[0083] CuFe2O4 / (Cl)-g-C3N4 heterojunction catalyst

[0084] (1) Preparation of Cl intercalated g-C3N4 substrate

[0085] (1-1) Take a dry and clean beaker, add 0.0333 mol melamine and 0.9207 mol ammonium chloride, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90 °C for 12 hours to obtain the precursor.

[0086] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. The temperature was held for calcination for 4 hours and then cooled to obtain Cl-intercalated g-C3N4 (Cl-g-C3N4).

[0087] (2) Preparation of heterojunction

[0088] (2-1) Weigh 1.1 mmol of ferric nitrate nonahydrate and 0.5103 mmol of copper nitrate trihydrate, add 10 mL of deionized water to dissolve, then add 0.5 g of Cl-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0089] (2-2) Add 1.71 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15h.

[0090] (3) Calcination and forming

[0091] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain CuFe2O4 / (Cl)-g-C3N4 composite catalyst.

[0092] The CuFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalyst has important applications in wastewater treatment. It can improve charge transfer rates and reduce metal ion loss. The CuFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. Finally, the degradation rate of bisphenol A reached 95.8%. The CuFe2O4 / (Cl)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 94.2% bisphenol A degradation rate even after five cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 95.0 ± 0.8%. - NO3 - H2PO4 - HCO3 - Even with coexisting ions, the degradation rate still reaches 90.0 ± 0.6%.

[0093] Example 4

[0094] NiFe2O4 / (Cl)-g-C3N4 heterojunction catalyst

[0095] (1) Preparation of Cl intercalated g-C3N4 substrate

[0096] (1-1) Take a dry and clean beaker, add 0.0285 mol melamine and 0.5734 mol ammonium chloride, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90 °C for 12 hours to obtain the precursor.

[0097] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. The temperature was held for calcination for 4 hours and then cooled to obtain Cl-intercalated g-C3N4 (Cl-g-C3N4).

[0098] (2) Preparation of heterojunction

[0099] (2-1) Weigh 0.8 mmol of ferric nitrate nonahydrate and 0.5 mmol of nickel nitrate hexahydrate, add 10 mL of deionized water to dissolve, then add 0.5 g of Cl-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0100] (2-2) Add 1.368 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15h.

[0101] (3) Calcination and forming

[0102] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain the NiFe2O4 / (Cl)-g-C3N4 composite catalyst.

[0103] NiFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalysts have important applications in wastewater treatment. They can improve charge transfer rates and reduce metal ion loss. The NiFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. Finally, the degradation rate of bisphenol A reached 96.5%. The NiFe2O4 / (Cl)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 94.5% bisphenol A degradation rate even after five cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 96.0 ± 0.7%. - NO3 - H2PO4 - HCO3 - Even with coexisting ions, the degradation rate still reaches 90.0 ± 1.3%.

[0104] Example 5

[0105] CoFe2O4 / (Cl)-g-C3N4 heterojunction catalyst

[0106] (1) Preparation of Cl intercalated g-C3N4 substrate

[0107] (1-1) Take a dry and clean beaker, add 0.03568 mol melamine and 0.8211 mol ammonium chloride, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90℃ for 12 hours to obtain the precursor.

[0108] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. The temperature was held for calcination for 4 hours and then cooled to obtain Cl-intercalated g-C3N4 (Cl-g-C3N4).

[0109] (2) Preparation of heterojunction

[0110] (2-1) Weigh 0.665 mmol of ferric nitrate nonahydrate and 0.3168 mmol of cobalt nitrate hexahydrate, add 10 mL of deionized water to dissolve, then add 0.5 g of Cl-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0111] (2-2) Add 1.596 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15 h.

[0112] (3) Calcination and forming

[0113] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain the CoFe2O4 / (Cl)-g-C3N4 composite catalyst.

[0114] CoFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalysts have important applications in wastewater treatment. They can improve charge transfer rates and reduce metal ion loss. The CoFe₂O₄ / (Cl)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. Finally, the degradation rate of bisphenol A reached 97.0%. The CoFe2O4 / (Cl)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 94.6% bisphenol A degradation rate even after five cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 96.0 ± 0.9%. - NO3 - H2PO4 - HCO3- Even with the presence of coexisting ions, the degradation rate still reaches 90.0 ± 0.8%.

[0115] Example 6

[0116] ZnFe2O4 / (Br)-g-C3N4 heterojunction catalyst

[0117] (1) Preparation of Br-intercalated g-C3N4 substrate

[0118] (1-1) Take a dry and clean beaker, add 0.0325 mol melamine and 0.5346 mol ammonium bromide, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90 °C for 12 hours to obtain the precursor.

[0119] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. The temperature was held for calcination for 4 hours and then cooled to obtain Br-intercalated g-C3N4 (Br-g-C3N4).

[0120] (2) Preparation of heterojunction

[0121] (2-1) Weigh 0.3815 mmol zinc nitrate hexahydrate and 0.7343 mmol ferric nitrate nonahydrate, add 10 mL of deionized water to dissolve, then add 0.5 g Br-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0122] (2-2) Add 2.052 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15h.

[0123] (3) Calcination and forming

[0124] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain the ZnFe2O4 / (Br)-g-C3N4 composite catalyst.

[0125] ZnFe₂O₄ / (Br)-g-C₃N₄ heterojunction catalysts have important applications in wastewater treatment. They can improve charge transfer rates and reduce metal ion loss. The ZnFe₂O₄ / (Br)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. Finally, the degradation rate of bisphenol A reached 97.5%. The ZnFe2O4 / (Br)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 94.7% bisphenol A degradation rate even after five cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 97.0 ± 0.6%. - NO3 - H2PO4 - HCO3 - Even with coexisting ions, the degradation rate still reaches 90.0±1.1%.

[0126] Example 7

[0127] ZnFe2O4 / (I)-g-C3N4 heterojunction catalyst

[0128] (1) Preparation of I-intercalated g-C3N4 substrate

[0129] (1-1) Take a dry and clean beaker, add 0.0381 mol melamine and 0.4234 mol ammonium iodide, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90 °C for 12 hours to obtain the precursor.

[0130] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. It was then held at the temperature for 4 hours and cooled to obtain I intercalated g-C3N4 (Ig-C3N4).

[0131] (2) Preparation of heterojunction

[0132] (2-1) Prepare metal salt solution according to the molar ratio of [Fe]:[Zn] = 2.4:1: Weigh 0.4419 mmol zinc nitrate hexahydrate and 1.0608 mmol ferric nitrate nonahydrate, add 10 mL of deionized water to dissolve, then add 0.5 g Ig-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0133] (2-2) Add 2.28 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15h.

[0134] (3) Calcination and forming

[0135] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain the ZnFe2O4 / (I)-g-C3N4 composite catalyst.

[0136] ZnFe₂O₄ / (I)-g-C₃N₄ heterojunction catalysts have important applications in wastewater treatment. They can improve charge transfer rates and reduce metal ion loss. The ZnFe₂O₄ / (I)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. The final result showed a bisphenol A degradation rate of 96.2%. The ZnFe2O4 / (I)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 93.8% bisphenol A degradation rate even after 5 cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 96.0 ± 0.2%. - NO3 - H2PO4 - HCO3 - Even with coexisting ions, the degradation rate still reaches 90.0±1.2%.

[0137] Example 8

[0138] CuFe2O4 / (Br)-g-C3N4 heterojunction catalyst

[0139] (1) Preparation of Br-intercalated g-C3N4 substrate

[0140] (1-1) Take a dry and clean beaker, add 0.0357 mol melamine and 0.5768 mol ammonium bromide, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90 °C for 12 hours to obtain the precursor.

[0141] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. The temperature was held for calcination for 4 hours and then cooled to obtain Br-intercalated g-C3N4 (Br-g-C3N4).

[0142] (2) Preparation of heterojunction

[0143] (2-1) Weigh 0.8034 mmol of ferric nitrate nonahydrate and 0.3153 mmol of copper nitrate trihydrate, add 10 mL of deionized water to dissolve, then add 0.5 g of Br-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0144] (2-2) Add 2.166 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15 h.

[0145] (3) Calcination and forming

[0146] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain CuFe2O4 / (Br)-g-C3N4 composite catalyst.

[0147] CuFe₂O₄ / (Br)-g-C₃N₄ heterojunction catalysts have important applications in wastewater treatment. They can improve charge transfer rates and reduce metal ion loss. The CuFe₂O₄ / (Br)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. The final result showed a bisphenol A degradation rate of 95.2%. The CuFe2O4 / (Br)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 93.5% bisphenol A degradation rate even after five cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 95.0 ± 0.2%. - NO3 - H2PO4 - HCO3 - Even with coexisting ions, the degradation rate still reaches 90.0 ± 0.4%.

[0148] Example 9

[0149] CuFe2O4 / (I)-g-C3N4 heterojunction catalyst

[0150] (1) Preparation of I-intercalated g-C3N4 substrate

[0151] (1-1) Take a dry and clean beaker, add 0.0397 mol melamine and 0.4142 mol ammonium iodide, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90℃ for 12 hours to obtain the precursor.

[0152] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. It was then held at the temperature for 4 hours and cooled to obtain I intercalated g-C3N4 (Ig-C3N4).

[0153] (2) Preparation of heterojunction

[0154] (2-1) Weigh 0.8031 mmol of ferric nitrate nonahydrate and 0.5857 mmol of copper nitrate trihydrate, add 10 mL of deionized water to dissolve, then add 0.5 g of Br-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0155] (2-2) Add 1.938 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15h.

[0156] (3) Calcination and forming

[0157] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain CuFe2O4 / (I)-g-C3N4 composite catalyst.

[0158] CuFe₂O₄ / (I)-g-C₃N₄ heterojunction catalysts have important applications in wastewater treatment. They can improve charge transfer rates and reduce metal ion loss. The CuFe₂O₄ / (I)-g-C₃N₄ heterojunction catalyst prepared in this example can be used to catalyze the degradation of a 0.1 mmol / L bisphenol A solution. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 mg of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. The final result showed a bisphenol A degradation rate of 95.4%. The CuFe2O4 / (I)-g-C3N4 heterojunction catalyst exhibits extremely low metal leaching and maintains a 93.2% bisphenol A degradation rate even after 5 cycles. Within the initial pH range of 3.5–9.0, the bisphenol A degradation rate remains stable at 95.0 ± 0.3%. - NO3 - H2PO4 - HCO3 - Even with the presence of coexisting ions, the degradation rate still reaches 90.0 ± 0.3%.

[0159] Comparative Example 1

[0160] Take a dry and clean beaker, add 0.0317 mol melamine and 0.9508 mol ammonium chloride, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90℃ for 12 hours to obtain the precursor.

[0161] The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. It was then held at that temperature for 4 hours and cooled to obtain Cl-intercalated g-C3N4 (Cl-g-C3N4).

[0162] The Cl-g-C3N4 prepared in this example can be used to catalyze the degradation of a bisphenol A solution with an initial concentration of 0.1 mmol / L. Add 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 g of Cl-g-C3N4, and 100 mL of freshly prepared 1.0 mmol / L PMS solution to a dry, clean beaker. Shake the mixture at 200 rpm for 30 min. The visible light source is a 300-watt xenon lamp equipped with a 400 nm cutoff filter. Finally, the degradation rate of bisphenol A was found to be 43%, which is low.

[0163] Similar to Example 1, the only difference is that a heterojunction system was not constructed. The composite catalyst prepared in this comparative example has fewer active catalytic sites.

[0164] Comparative Example 2

[0165] Preparation of ZnFe2O4 / g-C3N4 heterojunction

[0166] (1) Preparation of g-C3N4 substrate

[0167] Take a dry and clean ceramic crucible with a lid, add 0.0397 mol of melamine, transfer it to a muffle furnace, heat it to 550℃ at a rate of 5℃ / min, hold it at that temperature for 4 hours, and after cooling, obtain g-C3N4.

[0168] (2) Preparation of heterojunction

[0169] (2-1) Weigh 0.38 mmol zinc nitrate hexahydrate and 0.78 mmol ferric nitrate nonahydrate, add 10 mL of deionized water to dissolve, then add 0.5 g g-C3N4 and sonicate for 30 minutes until uniformly dispersed.

[0170] (2-2) Add 1.938 mmol of hydrated citric acid to the mixture, stir to dissolve, then add 10M NaOH solution dropwise to adjust the pH to 3.0, transfer to an 80℃ oil bath and stir until gel-like, then dry at 120℃ for 15h.

[0171] (3) Calcination and forming

[0172] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain the ZnFe2O4 / g-C3N4 composite catalyst.

[0173] The ZnFe2O4 / g-C3N4 heterojunction catalyst prepared in this example can be used to catalyze the degradation of a bisphenol A solution with an initial concentration of 0.1 mmol / L. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 g of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. The final result showed a bisphenol A degradation rate of 75.6%.

[0174] Similar to Example 1, the only difference is that no halogen source was introduced in step (1). The composite catalyst prepared in this comparative example lacks an intercalation structure, thereby reducing the electron migration rate and degradation performance.

[0175] Comparative Example 3

[0176] Preparation of direct composite catalysts without citric acid bridging agent

[0177] (1) Preparation of Cl intercalated g-C3N4 substrate

[0178] (1-1) Take a dry and clean beaker, add 0.0317 mol melamine and 0.9508 mol ammonium chloride, pour in 90 mL deionized water until completely dissolved, stir magnetically for 24 hours, and then dry at 90℃ for 12 hours to obtain the precursor.

[0179] (1-2) The precursor was transferred to a muffle furnace and heated to 520°C at a rate of 2°C / min. The temperature was held for calcination for 4 hours and then cooled to obtain Cl-intercalated g-C3N4 (Cl-g-C3N4).

[0180] (2) Preparation of heterojunction

[0181] (2-1) Weigh 0.38 mmol zinc nitrate hexahydrate and 0.78 mmol ferric nitrate nonahydrate, add 10 mL of deionized water to dissolve, then add 0.5 g Cl-g-C3N4, and sonicate for 30 minutes until uniformly dispersed.

[0182] (2-2) Adjust the pH of the mixture to 3.0, transfer it to an 80℃ oil bath and stir until it becomes gel-like, then dry it at 120℃ for 15 hours.

[0183] (3) Calcination and forming

[0184] (3-1) The dried solid was ground and placed in a muffle furnace, heated to 400℃ at a rate of 5℃ / min, calcined for 2 hours, cooled, washed and dried to obtain the ZnFe2O4 / (Cl)-g-C3N4 composite catalyst.

[0185] The ZnFe2O4 / (Cl)-g-C3N4 catalyst prepared in this example can be used to catalyze the degradation of a bisphenol A solution with an initial concentration of 0.1 mmol / L. 100 mL of 0.1 mmol / L bisphenol A solution, 0.03 g of catalyst, and 100 mL of freshly prepared 1.0 mmol / L PMS solution were added to a dry, clean beaker. The mixture was shaken at 200 rpm for 30 min under a 300 W xenon lamp equipped with a 400 nm cutoff filter. The final result showed a bisphenol A degradation rate of 55.7%, which is low.

[0186] Similar to Example 1, the only difference is that no chelating agent was introduced in step (2-2). The composite catalyst prepared in this comparative example has a loose heterojunction structure and low catalytic activity.

[0187] In summary, the halide-intercalated spinel-graphite carbon nitride heterojunction catalyst of this invention exhibits excellent catalytic performance, controllable metal loading, and a simple and easy preparation method, possessing ideal macroscopic structure and catalytic performance. The strong interaction between the metal compound and the substrate allows for the simultaneous utilization of the advantages of both the metal compound and the g-C3N4 substrate in practical wastewater treatment systems, improving mass and heat transfer efficiency and contact efficiency, thereby enhancing catalytic efficiency. Furthermore, it ensures the catalyst is firmly bonded to the support, and its interlayer structure simultaneously enhances the adsorption capacity of organic pollutants and the photocatalytic reaction efficiency. The strong interaction between the metal oxide and the halide-intercalated graphite carbon nitride (H)-g-C3N4 not only improves mass and heat transfer efficiency but also reduces metal ion leaching loss, extends catalyst lifespan, and lowers regeneration and recycling costs.

[0188] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst, characterized in that, Includes the following steps: (1) Melamine, halogen source and water are mixed and calcined for the first time to obtain halogen ion intercalated carbon nitride; (2) After mixing metal salt, water, halide ion intercalated carbon nitride and citric acid, the pH is adjusted to acidic to form a gel-like mixture; (3) The gel-like mixture was subjected to a second calcination to obtain a halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst; The metal cations in the metal salt are iron ions and M ions, wherein the M ions include nickel ions, cobalt ions, copper ions, manganese ions, or zinc ions.

2. The preparation method according to claim 1, characterized in that, The halogen source includes ammonium chloride, ammonium bromide, or ammonium iodide.

3. The preparation method according to claim 1, characterized in that, The molar ratio of melamine to halogen source is 1:5~35; the ratio of melamine to water is 0.022~0.041 mol:80~100 mL.

4. The preparation method according to claim 1, characterized in that, The heating rate of the first calcination is 2 °C / min, the temperature is 480~550 °C, and the holding time is 3~5 h.

5. The preparation method according to claim 1, characterized in that, The anion in the metal salt is sulfate, chloride, or nitrate; the molar ratio of iron ions to M ions is 1.3 to 2.7:

1.

6. The preparation method according to claim 1, characterized in that, In step (2), the ratio of the metal salt to water is 0.8~1.8 mmol:10 mL; the molar ratio of citric acid to metal salt is 1~2:1; and the ratio of the metal salt to halide ion intercalated carbon nitride is 0.8~1.8 mmol:0.5 g.

7. The preparation method according to claim 1, characterized in that, In step (2), the pH is adjusted to 2.5~3.5, and the temperature at which the gel-like mixture is formed is 80~95 ℃.

8. The preparation method according to claim 1, characterized in that, The heating rate for the second calcination is 5~8 ℃ / min, the temperature is 370~450 ℃, and the holding time is 2~3 h.

9. The halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the halide ion intercalated spinel-graphite phase carbon nitride heterojunction catalyst according to claim 9 in photocatalytic degradation of organic matter.

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