Phosphorus-nickel co-doped carbon nitride composite material for photocatalytic-Fenton degradation of pollutants as well as preparation method and application of phosphorus-nickel co-doped carbon nitride composite material

Abstract

The invention provides a phosphorus-nickel co-doped carbon nitride composite material for photocatalytic-Fenton degradation of pollutants and a preparation method and application thereof, and the preparation method comprises the following steps: in a muffle furnace, heating urea and ammonium dihydrogen phosphate to convert into phosphorus-doped carbon nitride; the preparation method comprises the following steps: dissolving phosphorus-doped carbon nitride in absolute ethyl alcohol, adding an anhydrous nickel chloride aqueous solution, carrying out ultrasonic treatment, drying, placing in a muffle furnace, and carrying out high-temperature heating conversion to obtain the phosphorus-nickel co-doped carbon nitride composite material. According to the metal monatomic catalyst synthesized by adopting a specific preparation method, the yield of photo-generated hydrogen peroxide is selectively improved while separation and transfer of photo-generated carriers are synergistically promoted by two sites; and the iron circulation can be well promoted, so that the photocatalytic-Fenton pollutant degradation effect which is comparable with that of precious metal doping is realized.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, and in particular to a phosphorus-nickel co-doped carbon nitride composite material for photocatalytic-Fenton degradation of pollutants, its preparation method and uses. Background Technology

[0002] Due to the widespread use of organic pollutants in personal care products, pesticides, dyes, and industrial chemicals, large quantities of organic pollutants enter the aquatic environment with industrial wastewater, posing a serious threat to natural ecosystems and human life. Organic pollutants in wastewater are persistent, difficult to degrade, and toxic, making their degradation a pressing issue in environmental research. The Fenton reaction, through the redox interaction between Fe(II) and hydrogen peroxide, effectively generates highly reactive free radicals (ROS), thereby effectively attacking and degrading target organic pollutants. However, due to the lack of effective degradation pathways and low selectivity of active sites in single photocatalytic and Fenton reactions, the efficiency of completely mineralizing pollutants through selective oxidation is extremely low. Therefore, constructing a photocatalytic-Fenton system to generate hydrogen peroxide in situ and then combining it with the Fenton reaction is an effective means of efficiently degrading pollutants.

[0003] In recent years, carbon nitride, as a novel polymer semiconductor material, has become a hot research topic in the field of photocatalysis due to its advantages such as good visible light response, narrow band gap (2.70 eV), chemical stability, low cost and ease of production, non-toxicity, high thermal stability, and resistance to acids and alkalis. However, due to the N... 2p and C 2pDue to orbital hybridization, carbon nitride exhibits severe photogenerated carrier recombination. In addition, low light absorption efficiency and low conductivity significantly limit its photocatalytic activity, resulting in less than ideal applications in photocatalysis. Non-metallic doping is considered an effective way to improve the photogenerated electron-hole migration conversion rate of carbon nitride, not only regulating its electron mobility but also narrowing the band gap of semiconductor materials to improve conductivity. Huang et al. successfully prepared P / O co-doped carbon nitride catalysts that enhanced visible light photocatalytic activity, increased the specific surface area of ​​the material, and narrowed the band gap. Metallic doping introduces impurity energy levels into the band gap by connecting with the carbon nitride framework, thereby enhancing visible light absorption and increasing photocatalytic activity by narrowing the band gap. Among commonly used transition metals, nickel is considered one of the most promising metals; incorporating nickel into carbon-based materials can effectively improve the performance and corrosion resistance of photocatalytic materials. Compared with traditional catalysts, single-atom catalysts possess high selectivity and metal atom stability. In recent years, researchers have discovered that unsaturated coordinating atoms on the surface of carbon nitride can serve as active sites for catalysis. The pyridine nitrogen and six times the pore diameter of carbon nitride provide favorable conditions for capturing single metal atoms. Furthermore, the presence of empty d orbitals in transition metals such as Fe, Co, and Ni allows some transition metals to coordinate with pyridine nitrogen. Cao et al. reported a novel photocatalytic system in which single-atom Co was inserted into the cavity of carbon nitride, increasing the active sites on the material surface and exhibiting high photocatalytic performance in the H2 production system. Li and Bi et al. reported that doping single-atom Pt into carbon nitride to create surface defects improved the photocatalytic H2 production performance, increasing the H2 production rate by 50 times compared to pure carbon nitride. Zhang and Lan et al. pointed out that a single-atom Pt / CN catalyst synthesized in a 2:1 ratio could simultaneously produce H2 and O2 without the addition of a sacrificial agent. Vile and Albani et al. used density functional theory (DFT) to calculate the adsorption energy on the catalyst, demonstrating that the Pd / CN catalyst exhibited higher activity and selectivity compared to the undoped catalyst.

[0004] In treating organic pollutants, both single photocatalytic reactions and single Fenton reactions are ineffective. From a degradation pathway perspective, they lack a route that can effectively promote the complete mineralization of organic pollutants. Regarding the selectivity of active sites, they struggle to precisely target pollutants. Related studies show that in common organic pollutant treatment scenarios, the efficiency of complete mineralization through selective oxidation of these two single reactions is extremely low, typically only reaching 10%-20%, resulting in a large amount of residual organic pollutants and continued environmental harm. Furthermore, existing carbon nitride materials have inherent limitations. Severe recombination of photogenerated carriers prevents the electron-hole pairs generated during photocatalysis from fully participating in the reaction, leading to significant carrier recombination waste and reduced photocatalytic efficiency. Their low light absorption efficiency and insufficient utilization of visible light (absorbing only about 30% of visible light energy) result in low efficiency in converting light energy into chemical energy. Low conductivity also hinders electron transport, making the catalytic reaction difficult to carry out efficiently. These combined problems result in poor practical application of photocatalytic degradation of pollutants, with the degradation rate and extent of organic pollutants falling far short of actual needs.

[0005] Research on using phosphorus and nickel dual doping to improve the photocatalytic degradation performance of materials faces numerous challenges. Uniform doping with two elements is difficult; during material preparation, phosphorus and nickel are not evenly distributed within the matrix, leading to inhomogeneous material properties. The competition between the two active sites is significant; the active sites formed by phosphorus and nickel cannot work synergistically in the catalytic reaction, but instead compete with each other, reducing the overall catalytic efficiency. In actual photocatalytic degradation experiments of organic pollutants, the degradation efficiency of phosphorus-nickel dual-doped materials is not significantly improved compared to single-element doped materials. In some cases, the degradation efficiency is only 50%-70% of that of single-element doped materials, failing to effectively overcome the catalytic efficiency bottleneck and greatly limiting its application in the degradation of organic pollutants. Therefore, how to improve the photocatalytic activity of dual-element doped carbon nitride has become an urgent problem to be solved. Summary of the Invention

[0006] This invention aims to solve the problems in the prior art by precisely controlling the phosphorus / nickel doping ratio through elemental doping technology and developing precise loading technologies such as atomic layer deposition. It balances the regulatory effects of dual elements on band structure and carrier migration, breaks through the "doping antagonism" bottleneck, improves the photocatalytic activity of dual-element doped carbon nitride, and achieves efficient operation of the closed-loop pathway of "photocatalytic hydrogen peroxide production - Fenton reaction degradation of pollutants". This promotes the industrial application of low-cost and high-efficiency photocatalytic materials, solves the problem of organic pollutant degradation, and provides a more effective technical means for the treatment of organic pollutants in the aquatic environment.

[0007] One of the objectives of this invention is to provide a method for preparing a phosphorus-nickel co-doped carbon nitride composite material for photocatalytic-Fenton degradation of pollutants.

[0008] The second objective of this invention is to provide a phosphorus-nickel co-doped carbon nitride composite material prepared by the above method.

[0009] A third objective of this invention is to provide the use of the above-mentioned phosphorus-nickel co-doped carbon nitride composite material in photocatalytic hydrogen peroxide production and Fenton reaction degradation of pollutants.

[0010] To achieve the above objectives, the following technical solution is adopted:

[0011] In a first aspect, the present invention provides a method for preparing a phosphorus-nickel co-doped carbon nitride composite material for photocatalytic-Fenton degradation of pollutants, comprising the following steps:

[0012] (1) In a muffle furnace, urea and ammonium dihydrogen phosphate are heated to convert into phosphorus-doped carbon nitride;

[0013] (2) Dissolve phosphorus-doped carbon nitride in anhydrous ethanol, add anhydrous nickel chloride aqueous solution, sonicate, dry, place in muffle furnace, and heat at high temperature to convert into phosphorus-nickel co-doped carbon nitride composite material.

[0014] The following is a detailed explanation of each step.

[0015] Step (1)

[0016] Preparation of phosphorus-doped carbon nitride by high-temperature thermal polymerization: The raw materials urea and ammonium dihydrogen phosphate are transferred to a crucible, mixed evenly, and heated in a muffle furnace to convert them into phosphorus-doped carbon nitride.

[0017] In some embodiments, in step (1), the mass ratio of ammonium dihydrogen phosphate to urea is 1:10 to 1:100; preferably, the amount of urea used is 10-20g and the amount of ammonium dihydrogen phosphate used is 0.5g; preferably, the crucible size is 30-60mL, more preferably 50mL.

[0018] In some embodiments, in step (1), the muffle furnace heating program is set as follows: heating rate of 1-5°C / min, heating to 500-600°C, and continuing for 2-6 hours. Preferably, the muffle furnace heating program is set as follows: heating rate of 5°C / min, heating to 550°C, and continuing for 4 hours.

[0019] This step involves the high-temperature thermal polymerization of urea and ammonium dihydrogen phosphate. At high temperature, the ammonium dihydrogen phosphate decomposes to produce PO4. 3-Reacting with nitrogen-containing intermediates from urea pyrolysis, P atoms utilize their empty 3d orbitals to form PN covalent bonds with lone pairs of electrons from N atoms, achieving P doping. The decomposition of urea and ammonium dihydrogen phosphate releases gases such as NH3 and CO2, leaving pores that form a porous structure. Gas disturbances and the stress during polymerization cause the lamellar carbon nitride to curl and entangle, and combined with the charge effect of P doping, forms a porous spiral structure.

[0020] Step (2)

[0021] Nickel-phosphorus co-doped carbon nitride was prepared using atomic-level dispersion and interface engineering techniques.

[0022] In some embodiments, in step (2), the mass of nickel chloride in the added aqueous nickel chloride solution accounts for 1-15% of the mass of phosphorus-doped carbon nitride.

[0023] Preferably, the concentration of the nickel chloride aqueous solution is 2.0 g / L, the amount added is 7.5 mL, and the mass of phosphorus-doped carbon nitride is 100 mg.

[0024] In some embodiments, in step (2), the heating atmosphere of the muffle furnace is an inert gas atmosphere, such as any one or a combination of nitrogen, argon, and helium;

[0025] Preferably, the inert gas atmosphere is a nitrogen environment.

[0026] In some embodiments, in step (2), the muffle furnace heating program is set as follows: heating rate 1-5°C / min, heating to 400-500°C, and lasting for 2-6 hours;

[0027] Preferably, the muffle furnace heating program is set as follows: heating rate 2℃ / min, heating to 450℃, and continuing for 2 hours.

[0028] In some embodiments, step (2) specifically includes: weighing 100.0 mg of phosphorus-doped carbon nitride into a crucible, adding 20 ml of anhydrous ethanol to dissolve it, then adding 7.5 mL of a 2.0 g / L nickel chloride aqueous solution, sonicating the mixed solution for 1 h, drying it in an oven for 8 h, filling the crucible with nitrogen and then covering it, placing it in a muffle furnace, heating it at a rate of 2 °C / min, heating it to 450 °C, and continuing for 2 hours, and converting it into phosphorus-nickel co-doped carbon nitride through high-temperature heating.

[0029] This step introduces nickel into phosphorus-doped carbon nitride, which rapidly polymerizes at high temperatures to form a rigid structure that fixes the coordinated nickel ions. Phosphorus doping introduces more defect sites, strengthens the interaction between nickel and the framework, and promotes single-atom dispersion.

[0030] This invention presents a phosphorus-nickel co-doped carbon nitride material prepared by a specific method. By precisely controlling the phosphorus / nickel doping ratio and employing a "phosphorus-controlled band structure and nickel-optimized active site" approach, the synergistic effect of the two elements on band structure and carrier migration is balanced, overcoming the "doping antagonism" bottleneck and significantly improving the photocatalytic activity of the two-element doped carbon nitride. Specifically, phosphorus doping alters the band structure of carbon nitride, broadening the light absorption range to the visible light region and optimizing the conduction / valence band positions, providing more favorable potential conditions for hydrogen peroxide generation. Nickel single atoms are loaded onto carbon nitride through atomic-level uniform distribution and interface control technology, forming a strong metal-support interaction. This accelerates the transfer of photogenerated electrons from carbon nitride to nickel sites, reducing recombination. Furthermore, the unsaturated coordination environment of the single atoms serves as a highly efficient catalytic center, promoting O2 adsorption and hydrogen peroxide generation. The two elements form a synergistic mechanism of "electronic structure regulation - charge separation - active site construction," resulting in a 6-fold increase in hydrogen peroxide production during photocatalysis compared to pure carbon nitride. This material exhibits unique advantages in the photocatalysis-Fenton system: phosphorus doping promotes the migration of photogenerated electrons to generate hydrogen peroxide in situ, while nickel single atoms efficiently activate the hydrogen peroxide to produce ·OH radicals, forming a closed-loop pathway of "photocatalytic hydrogen peroxide production-Fenton reaction degradation of pollutants." Furthermore, the Fenton reaction generates more ·OH radicals, achieving efficient degradation of pollutants. This technological approach is of great significance for promoting the industrial application of low-cost, high-efficiency photocatalytic materials and solving the problem of organic pollutant degradation.

[0031] Secondly, the present invention provides a phosphorus-nickel co-doped carbon nitride composite material prepared by the above preparation method.

[0032] The phosphorus-nickel co-doped carbon nitride composite material includes phosphorus-doped carbon nitride and nickel metal single atoms loaded on the surface of the phosphorus-doped carbon nitride, forming a porous spiral phosphorus-nickel co-doped carbon nitride composite material.

[0033] Thirdly, the present invention provides the use of the above-mentioned phosphorus-nickel co-doped carbon nitride composite material in photocatalytic hydrogen peroxide production and Fenton reaction degradation of pollutants.

[0034] The material of this invention has excellent photocatalytic ability to produce oxidizing free radicals, which can increase the production of hydrogen peroxide. It will achieve good results in the photocatalytic degradation of 2,4-dichlorophenol, photocatalytic degradation of rhodamine B, photocatalytic degradation of bisphenol A, and photocatalytic production of hydrogen peroxide.

[0035] Beneficial effects:

[0036] Current research on carbon nitride degradation of organic pollutants mainly employs single-element doping or multi-element doping methods to improve catalytic performance. However, these methods suffer from problems such as uneven doping, poor synergistic effects, and limited improvement in catalytic efficiency. The phosphorus-nickel co-doped carbon nitride composite material prepared in this invention can achieve 99.2% mineralization of organic pollutants within 20 minutes. After six cycles, the degradation efficiency remains above 85%, demonstrating excellent and stable degradation effects in both simulated sunlight and actual industrial wastewater treatment scenarios.

[0037] Experiments show that the hydrogen peroxide yield of this invention is 6 times higher than that of pure carbon nitride, generating 687.71 μmol / L within 60 minutes. -1 h -1 H2O2 exhibits hydrogen peroxide production performance exceeding that of most element-doped composite materials. Furthermore, by combining it with the Fenton reaction, it can completely degrade 20 mg / L of 2,4-dichlorophenol within 20 minutes, with no significant performance change after 6 cycles.

[0038] This material exhibits good pollutant degradation efficiency and hydrogen peroxide generation capacity under both acidic, alkaline, and neutral conditions. The system can completely degrade most typical pollutants within 60 minutes. Attached Figure Description

[0039] Figure 1 This is a transmission electron microscope (TEM) image of the phosphorus-doped carbon nitride prepared in Example 1.

[0040] Figure 2 Transmission electron microscopy (TEM) image of the nickel-phosphorus co-doped carbon nitride prepared in Example 1.

[0041] Figure 3 The image shows the FT-IR spectrum of the nickel-phosphorus co-doped carbon nitride prepared in Example 1.

[0042] Figure 4 The image shows the XRD pattern of the nickel-phosphorus co-doped carbon nitride prepared in Example 1.

[0043] Figure 5 The diagram shows the effect of different doping ratios of phosphorus-nickel co-doped carbon nitride on pollutant degradation.

[0044] Figure 6 The graph shows the degradation effect of different catalyst systems.

[0045] Figure 7 Graphs showing the effects of different catalytic systems on pollutant degradation.

[0046] Figure 8 The diagram shows the effect of homogeneous and heterogeneous Fenton reactions on pollutant degradation.

[0047] Figure 9 The graph shows the results of the cyclic experiment.

[0048] Figure 10 The graph shows the effect of phosphorus-nickel co-doped carbon nitride on pollutant degradation under different pH conditions.

[0049] Figure 11 The graph shows the yield of hydrogen peroxide produced by different catalysts.

[0050] Figure 12 The graph shows the performance of phosphorus-nickel co-doped carbon nitride in degrading different pollutants.

[0051] Figure 13 This is a TEM image of a material where nickel single atoms have not yet formed. Detailed Implementation

[0052] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0054] Reagents:

[0055] Urea was purchased from Tianjin Guangfu Technology Development Co., Ltd.

[0056] Potassium phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium hydroxide, and anhydrous ethanol were all purchased from Tianjin Kemei Chemical Reagent Co., Ltd.

[0057] Anhydrous nickel(II) chloride was purchased from THICA (Shanghai) Chemical Industry Development Co., Ltd.

[0058] 2,4-Dichlorophenol was purchased from Shanghai Aladdin Reagent Co., Ltd.

[0059] Ferric chloride was purchased from Tianjin Jindong Tianzheng Fine Chemical Reagent Factory.

[0060] Methanol and acetonitrile were purchased from Thermo Fisher Scientific China's official website;

[0061] N,N-diethyl-p-phenylenediamine and peroxidase were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0062] Phosphoric acid was purchased from Tianjin Damao Chemical Reagent Factory.

[0063] instrument:

[0064] The instruments used in this experiment were: a 300W xenon lamp (PLS-SXE300, Beijing Bofei Technology Co., Ltd.), a high-angle annular dark-field special aberration corrected transmission electron microscope (HAADF-STEM, JEM-2100F), an X-ray diffractometer (XRD, Bruker, D8 Advance, Germany), a Fourier transform infrared spectrometer (FT-IR, LUMOS, Bruker), a Hitachi U-2900 UV-Vis spectrophotometer, and an Agilent 1260 high-performance liquid chromatograph.

[0065] Example 1

[0066] A method for preparing a phosphorus-nickel co-doped carbon nitride composite material includes the following steps:

[0067] (1) Transfer 10g of urea and 0.5g of ammonium dihydrogen phosphate to a 50mL crucible, and then heat it to 550℃ in a muffle furnace at a heating rate of 5℃ / min. After holding at 550℃ for 4 hours, allow it to cool naturally to room temperature to obtain phosphorus-doped carbon nitride. The obtained product is denoted as α-0.5P-CN (transmission electron microscopy image as shown). Figure 1 (As shown). Figure 1 Medium-phosphorus-doped carbon nitride exhibits a layered stacked structure. α- represents the phosphorus added before the formation of carbon nitride.

[0068] (2) Weigh 100.0 mg α-0.5P-CN and dissolve it in 20 ml of anhydrous ethanol. Then add 7.5 ml of nickel chloride aqueous solution (concentration 2.0 g / L). Sonicate the mixed solution for 1 h, dry it in an oven for 8 h, fill the crucible with nitrogen, cover it, and place it in a muffle furnace. Heat the crucible to 450 °C at a rate of 2 °C / min and continue for 2 h to convert it into nickel-phosphorus co-doped carbon nitride. The obtained product is denoted as a-0.5P-β-7.5Ni-CN, where β- represents the addition after the formation of carbon nitride (transmission electron microscopy image as shown). Figure 2 As shown, the FT-IR plot is as follows Figure 3 As shown, the XRD pattern is as follows Figure 4 (As shown). Figure 2 Compared to Chinese materials Figure 1 It exhibits a porous, spiral-shaped stacked structure, which increases the specific surface area and enhances the adsorption capacity. Figure 3 The FT-IR images show that after the introduction of Ni and P elements, the main structure of the phosphorus-nickel co-doped carbon nitride still exhibits a similar typical heptaazine ring structure, proving that the sample preparation process did not destroy the main structure of CN. Figure 4 The XRD pattern shows that the phosphorus-nickel co-doped carbon nitride still has the two XRD diffraction peaks characteristic of the original CN, indicating that the introduction of P and Ni sources has not changed the basic crystal phase of the CN material.

[0069] Example 2

[0070] A method for preparing a carbon nitride composite material with altered phosphorus-nickel doping ratio includes the following steps:

[0071] (1) 10g of urea and different masses (0.5g, 0.6g, 0.7g) of ammonium dihydrogen phosphate were transferred to a 50mL crucible and then heated to 550℃ in a muffle furnace at a heating rate of 5℃ / min. After holding at 550℃ for 4 hours, the mixture was naturally cooled to room temperature to obtain phosphorus-doped carbon nitride with different doping ratios.

[0072] (2) 100.0 mg of phosphorus-doped carbon nitride with different doping ratios was dissolved in 20 mL of anhydrous ethanol. Then, different volumes (5 mL, 7.5 mL, 10 mL) of nickel chloride aqueous solution (concentration 2.0 g / L) were added. The mixed solution was ultrasonically treated for 1 h, dried in an oven for 8 h, and the crucible was filled with nitrogen, covered, and placed in a muffle furnace. The temperature was increased to 450 °C at a rate of 2 °C / min and maintained for 2 hours, converting it into phosphorus-nickel co-doped carbon nitride with different doping ratios. The effect on pollutant degradation is as follows: Figure 5 Experiments show that materials with different doping ratios have significantly lower efficiency in degrading pollutants than α-0.5P-β-7.5Ni-CN, highlighting the importance of precisely controlling the doping ratio.

[0073] Comparative Example 1

[0074] A method for preparing a phosphorus-doped carbon nitride composite material includes the following steps:

[0075] 10g of urea and 0.5g of ammonium dihydrogen phosphate were transferred to a 50mL crucible and then heated to 550℃ in a muffle furnace at a heating rate of 5℃ / min. After holding at 550℃ for 4 hours, the mixture was naturally cooled to room temperature to obtain phosphorus-doped carbon nitride. The obtained product was denoted as α-0.5P-CN.

[0076] Comparative Example 2

[0077] A method for preparing a nickel-doped carbon nitride composite material includes the following steps:

[0078] (1) Transfer 10g of urea to a 50mL crucible, and then heat it to 550℃ in a muffle furnace at a heating rate of 5℃ / min. After holding at 550℃ for 4 hours, cool it naturally to room temperature to obtain carbon nitride. The obtained product is denoted as CN.

[0079] (2) Weigh 100.0 mg CN and dissolve it in 20 ml of anhydrous ethanol. Then add 7.5 ml of nickel chloride aqueous solution (concentration 2.0 g / L). Sonicate the mixed solution for 1 h, dry it in an oven for 8 h, fill the crucible with nitrogen and cover it. Place it in a muffle furnace and heat it to 450 °C at a heating rate of 2 °C / min for 2 h to convert it into nickel-doped carbon nitride. The obtained product is denoted as β-7.5Ni-CN.

[0080] Comparative Example 3

[0081] Preparation of Ni-Pg-C3N4 by Zhu et al.:

[0082] Carbon nitride and sodium hypophosphite were ground and mixed evenly in proportion. The mixture was heated to the calcination temperature in an argon atmosphere and held for a period of time. After natural cooling, it was washed with deionized water and finally vacuum dried to obtain carbon phosphide. The obtained carbon phosphide and nickel chloride were added to a triethanolamine solution, ultrasonically dispersed, irradiated with a xenon lamp for a period of time, and finally separated and vacuum dried to obtain a nickel-carbon phosphide photocatalyst.

[0083] The difference from the example is that this patent uses melamine high-temperature copolymerization to obtain ordinary carbon nitride, which is then mixed with sodium hypophosphite and calcined for phosphating, and finally modified with in-situ photodeposition of metallic nickel.

[0084] Phosphorus doping effect:

[0085] In this invention, urea and ammonium dihydrogen phosphate are used as raw materials for high-temperature thermal polymerization, during which the phosphorus source (ammonium dihydrogen phosphate) and the nitrogen source (urea) participate in the reaction simultaneously. From the initial stage of the reaction, phosphorus atoms form PN covalent bonds with nitrogen-containing intermediates generated by the pyrolysis of the nitrogen source, directly embedding into the forming carbon nitride framework, achieving uniform doping at the atomic level. This in-situ doping method can precisely control the phosphorus doping ratio, ensuring a tight bond between phosphorus atoms and the carbon nitride framework, resulting in significant optimization of the material's band structure. For example, it can effectively broaden the light absorption range to the visible light region and precisely adjust the conduction band / valence band potential, laying a good foundation for subsequent synergistic effects with nickel single atoms.

[0086] Zhu's patent involves first synthesizing pure carbon nitride, followed by phosphating to introduce phosphorus. In this process, phosphorus atoms primarily exist in the carbon nitride material as surface modifications or defect fillers, making it difficult for them to penetrate deep into the carbon nitride framework. This leads to uneven phosphorus doping and weak bonding between phosphorus atoms and the framework. Furthermore, because phosphorus is introduced later, it is difficult to precisely control the doping ratio, and the secondary processing may damage the original structure of the previously formed carbon nitride, making it difficult for phosphorus to form an effective "phosphorus-nickel" synergistic mechanism with any subsequently introduced elements such as nickel.

[0087] Formation of porous spiral structure:

[0088] In this invention, during the high-temperature thermal polymerization process, urea and ammonium dihydrogen phosphate decompose simultaneously, releasing gases such as NH3, CO2, and H2O. As these gases escape simultaneously from the polymerization system, they create uniformly distributed pores within the material. Simultaneously, the disturbances caused by the gas escape and the stress generated during polymerization induce the coiling and entanglement of the carbon nitride sheet structure. Furthermore, phosphorus doping influences the local charge distribution, further stabilizing this coiling and entanglement, ultimately leading to a stable porous helical structure with a large specific surface area. This structure not only provides more favorable sites for the subsequent anchoring of nickel single atoms but also facilitates the adsorption and mass transfer processes of the reactants.

[0089] Zhu's patent states that the carbon nitride structure generated in the early stages is relatively dense. Although some pores may be created during subsequent phosphating through etching and other processes, it is difficult to form a uniform and ideal porous structure. Furthermore, the already formed lamellar structure is quite rigid, making it difficult to induce spiral curling during secondary phosphating. The material ultimately tends to exhibit a blocky or disordered stacked morphology. Such a structure has a small specific surface area and insufficient exposure of active sites, significantly affecting the efficiency of photocatalytic reactions such as the Fenton reaction.

[0090] Nickel single-atom formation mechanism:

[0091] In the process of preparing phosphorus-doped carbon nitride by high-temperature thermal polymerization, the carbon nitride framework is formed simultaneously. The abundant N atoms and O atoms from the phosphate groups form strong coordination bonds with nickel ions. Simultaneously, the rigid structure formed by the rapid polymerization of carbon nitride at high temperatures fixes the coordinated nickel ions in specific positions, restricting their migration and aggregation. Furthermore, the structural defects introduced by phosphorus doping provide more stable sites for nickel single atoms. These multiple effects promote the uniform dispersion and firm anchoring of nickel in single-atom form on the carbon nitride surface.

[0092] Zhu's patented method involves first preparing carbon nitride, then loading a nickel source onto the carbon nitride through stirring and ultrasonic dispersion, followed by phosphating. In this process, nickel ions primarily adhere to the carbon nitride surface through physical adsorption or weak interactions, lacking the strong coordination anchoring and rigid structural fixation found in direct preparation methods. In subsequent processing, nickel ions are prone to migration and aggregation, making it difficult to form a stable single-atom dispersion; they instead exist more as nanoparticles or small clusters.

[0093] Effect of nickel single atom action:

[0094] The nickel single atom of this invention has an unsaturated coordination environment, which serves as a highly efficient catalytic center. It can promote O2 adsorption and hydrogen peroxide generation, while accelerating the transfer of photogenerated electrons from carbon nitride to nickel sites, reducing recombination. Together with phosphorus doping, it forms a mechanism of "electronic structure regulation-charge separation-active site construction", which greatly improves photocatalytic activity and increases hydrogen peroxide production by 6 times compared to pure carbon nitride.

[0095] Zhu's patented method: Because nickel exists mostly in a non-single-atom form, the number of active sites and catalytic efficiency are limited. Furthermore, the interaction between nickel and carbon nitride is weak, resulting in low photogenerated electron transfer efficiency and difficulty in forming an effective synergistic effect with phosphorus. This leads to a weak ability to generate active species through photocatalysis and overall poor catalytic performance.

[0096] Comparative Example 4

[0097] The difference between this comparative example and Example 1 is that the calcination temperature in step (2) is increased from 450°C to 700°C. Excessive temperature will destroy the Ni-N coordination bonds of the CN skeleton, causing nickel single atoms to migrate and agglomerate into nanoparticles.

[0098] Comparative Example 5

[0099] A method for preparing a phosphorus-nickel co-doped carbon nitride composite material includes the following steps:

[0100] (1) Transfer 10g of urea to a 50mL crucible, and then heat it to 550℃ in a muffle furnace at a heating rate of 5℃ / min. After holding at 550℃ for 4 hours, allow it to cool naturally to room temperature to obtain carbon nitride.

[0101] (2) Weigh 100.0 mg CN and dissolve it in 20 ml of anhydrous ethanol. Then add 0.5 g ammonium dihydrogen phosphate and 7.5 ml of nickel chloride aqueous solution (concentration of 2.0 g / L). Sonicate the mixed solution for 1 h, dry it in an oven for 8 h, fill the crucible with nitrogen and cover it, place it in a muffle furnace, and heat it to 450 °C at a heating rate of 2 °C / min for 2 hours to convert it into nickel-phosphorus co-doped carbon nitride.

[0102] Specific material structure diagram is as follows: Figure 13 As shown, the bright spots are clustered together and not evenly dispersed on the catalyst surface.

[0103] Experiment 1: Catalyst Photocatalytic-Fenton Degradation of Pollutants Test

[0104] Experimental samples: Examples 1-3, carbon nitride.

[0105] Experimental procedure:

[0106] Using 2,4-dichlorophenol as the target pollutant, we verified the ability of the photocatalyst to degrade the pollutant.

[0107] (1) Preparation of pollutant solution

[0108] Place 0.02 g of 2,4-dichlorophenol on an analytical balance, transfer it to a 1 L volumetric flask, add an appropriate amount of ultrapure water, shake thoroughly to dissolve, and then dilute to the mark with ultrapure water to obtain a 20 mg / L 2,4-dichlorophenol solution.

[0109] (2) Photocatalytic-Fenton degradation reaction

[0110] Take 40 mL of the contaminant solution and place it in a 100 mL beaker for later use. Weigh 10 mg of the pre-activated photocatalyst, grind it, and transfer it to the beaker. Add 30 mg of Fe(III). After sonicating and aerating in the dark for 30 min, transfer the mixture to a quartz reactor. Place the quartz reactor on a thermostatic magnetic stirrer, adjust the temperature to 25 °C, and set the stirring speed to 200 rpm. Stir in the dark for 30 min to allow 2,4-dichlorophenol to reach adsorption-desorption equilibrium on the photocatalyst surface. Then, turn on a 300 W xenon lamp equipped with a filter (to filter out light with wavelengths less than 420 nm) as a visible light source and start timing. At 0, 5, 10, 15, and 20 min, take out 2 mL of the reaction solution and add 2 mL of NaOH solution to remove Fe(III). Filter the solution through a 0.22 μm diameter filter to obtain a clear solution for testing.

[0111] (3) Detection and Result Calculation

[0112] The clarified solution was analyzed using high-performance liquid chromatography (HPLC). The HPLC system was configured with a C18 column, a mobile phase of methanol-0.1% phosphoric acid water mixture (80:20 v / v), a flow rate of 1.0 mL / min, a column temperature of 30 °C, an injection volume of 50 μL, and a detection wavelength of 280 nm. The concentration of 2,4-dichlorophenol in the sample was calculated by comparing with a standard curve. Furthermore, due to the change in the initial concentration of the pollutant, the degradation performance of the photocatalyst at different concentrations could be compared to further explore its applicability.

[0113] Experimental results: such as Figure 6 As shown.

[0114] from Figure 5 It can be seen that once the α-0.5P-β-7.5Ni-CN composite material is added, the degradation of 20 mg / L 2,4-dichlorophenol can be completed within 20 minutes under xenon lamp irradiation, while the monomer g-C3N4 and single-element doped carbon nitride only degrade about 40%. This was demonstrated in light control experiments without photocatalyst irradiation, dark control experiments without added materials, photocatalytic degradation experiments without Fe(III), and homogeneous Fenton reactions. Figure 7, Figure 8 The pollutants were hardly degraded within 20 minutes, indicating that the degradation activity mainly came from the catalyst being in a heterogeneous photocatalytic-Fenton system.

[0115] Experiment 2 Cyclic Experiment

[0116] Experimental sample: Example 1.

[0117] Experimental procedure: After one degradation experiment, the α-0.5P-β-7.5Ni-CN composite material was collected by centrifugation and thoroughly washed with ethanol and distilled water. The collected photocatalyst was dried at 60℃ and then the cycle was repeated for a total of 6 times.

[0118] Experimental results: such as Figure 9 As shown.

[0119] from Figure 9 It can be seen that after 6 cycles, the degradation effect did not change significantly, indicating that α-0.5P-β-7.5Ni-CN has good stability and reusability.

[0120] Experiment 3 pH Degradation Experiment

[0121] Experimental sample: Example 1.

[0122] Experimental procedure: The pollutant solution was adjusted to different pH values ​​using potassium hydroxide and perchloric acid to conduct degradation experiments.

[0123] Experimental results: such as Figure 10 As shown.

[0124] from Figure 10 It can be seen that regardless of whether the pollutant solution is adjusted to acid, alkaline or neutral, the catalyst can completely degrade the pollutants within 30 minutes, indicating the good applicability of α-0.5P-β-7.5Ni-CN.

[0125] Experiment 4: Photocatalytic Generation of Hydrogen Peroxide

[0126] Experimental samples: Examples 1-3, carbon nitride.

[0127] Experimental Procedure: The concentration of H₂O₂ in the photocatalytic system was determined using the POD-DPD method. Quantitative amounts of the reaction solution were collected at regular time intervals. 0.4 mL of potassium phosphate buffer solution, 3 mL of deionized water, 0.05 mL of N,N-diethyl-1,4-phenylene diamine, and peroxidase were added to the sample, and the mixture was shaken for 90 seconds. The reaction product exhibited strong absorbance at 551 nm, and quantitative analysis was performed using a Hitachi U-2900 UV-Vis spectrophotometer.

[0128] Experimental results: such as Figure 11 As shown.

[0129] from Figure 11 It can be seen that the α-0.5P-β-7.5Ni-CN composite material generates significantly more hydrogen peroxide than the monomer g-C3N4 and single-element doped carbon nitride, producing 687.71 μmol / L of hydrogen peroxide within 60 min. -1 h -1 H2O2 produces hydrogen peroxide better than most element-doped composite materials.

[0130] Experiment 5: Catalyst Degradation of Typical Pollutants

[0131] Experimental sample: Example 1.

[0132] Experimental procedure: 2,4-Dichlorophenol, bisphenol A, rhodamine B, and sulfadiazine were used as target pollutants, all at a concentration of 10 mg / L, to verify the photocatalyst's ability to degrade multiple pollutants.

[0133] Experimental results: such as Figure 12 As shown.

[0134] from Figure 12 It can be seen that the α-0.5P-β-7.5Ni-CN composite material completely degrades 2,4-dichlorophenol, bisphenol A, rhodamine B, and sulfadiazine within the ranges of 12, 25, 15, and 90 min, respectively, verifying the universality of this catalyst in dealing with different pollutants.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a phosphorus-nickel co-doped carbon nitride composite material for photocatalytic-Fenton degradation of pollutants, characterized in that, Includes the following steps: (1) In a muffle furnace, urea and ammonium dihydrogen phosphate are heated to convert into phosphorus-doped carbon nitride; (2) Dissolve phosphorus-doped carbon nitride in anhydrous ethanol, add anhydrous nickel chloride aqueous solution, sonicate, dry, place in muffle furnace, and heat at high temperature to convert into phosphorus-nickel co-doped carbon nitride composite material.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of ammonium dihydrogen phosphate to urea is 1:10 to 1:

100.

3. The preparation method according to claim 1, characterized in that, In step (1), the muffle furnace heating program is set as follows: heating rate 1-5℃ / min, heating to 500-600℃, and lasting for 2-6 hours.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass of nickel chloride in the added nickel chloride aqueous solution accounts for 1-15% of the mass of phosphorus-doped carbon nitride.

5. The preparation method according to claim 1, characterized in that, In step (2), the heating atmosphere of the muffle furnace is an inert gas atmosphere.

6. The preparation method according to claim 1, characterized in that, In step (2), the muffle furnace heating program is set as follows: heating rate 1-5℃ / min, heating to 400-500℃, and lasting for 2-6 hours.

7. The preparation method according to claim 1, characterized in that, Step (2) specifically includes: weighing 100.0 mg of phosphorus-doped carbon nitride into a crucible, adding 20 ml of anhydrous ethanol to dissolve it, then adding 7.5 mL of a 2.0 g / L nickel chloride aqueous solution, sonicating the mixed solution for 1 h, drying it in an oven for 8 h, filling the crucible with nitrogen and then covering it, placing it in a muffle furnace, heating it at a rate of 2 °C / min, heating it to 450 °C, and continuing for 2 hours, converting it into phosphorus-nickel co-doped carbon nitride through high-temperature heating.

8. A phosphorus-nickel co-doped carbon nitride composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The phosphorus-nickel co-doped carbon nitride composite material according to claim 8, characterized in that, The phosphorus-nickel co-doped carbon nitride composite material includes phosphorus-doped carbon nitride and nickel metal single atoms loaded on the surface of the phosphorus-doped carbon nitride, forming a porous spiral phosphorus-nickel co-doped carbon nitride composite material.

10. Use of the phosphorus-nickel co-doped carbon nitride composite material of claim 8 or 9 in photocatalytic hydrogen peroxide production and Fenton reaction degradation of pollutants.

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