Method for degrading RhB through photocatalytic activation of PMS driven by synthetic P-doped tubular carbon nitride

Abstract

The invention relates to the technical field of water pollution, in particular to a method for degrading RhB through photocatalytic activation of PMS driven by synthesized P-doped tubular carbon nitride. The preparation method comprises the following steps: S1, preparing P-doped tubular carbon nitride; s2, applying the P-doped tubular carbon nitride obtained in the step S1 to photocatalytic activation of PMS; and S3, the photocatalytic activated PMS is used for degrading RhB. According to the method for degrading RhB by synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS, phosphoric acid and melamine are used as raw materials, and the P-doped carbon nitride (5P-TCN) with a tubular structure is prepared through a precursor self-assembly method; and the PMS-photocatalysis effect of the photocatalyst on a typical organic pollutant rhodamine B (RhB) under the action of visible light is evaluated through batch experiments.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution, and particularly to a method for degrading RhB by photocatalytic activation of PMS driven by synthesized P-doped tubular carbon nitride. Background Art

[0002] With the continuous development of industrialization, the sewage discharge has been increasing year by year, and the water pollution problem has become one of the obstacles affecting the sustainable development of mankind. Rhodamine B (RhB) is a typical industrial dye molecule, which is widely used in manufacturing industries such as textiles, pigments, and cosmetics. It has certain toxicity and carcinogenicity, and may cause various diseases such as human respiratory infections or skin and gastrointestinal irritation infections. Moreover, it has high water solubility and stability and is difficult to be removed by biodegradation. Therefore, seeking an efficient and green feasible method to remove RhB in sewage is of great significance to our lives. Compared with traditional sewage treatment methods such as adsorption, membrane filtration, and centrifugal separation, advanced processes such as photocatalysis, persulfate activation, and electrochemical oxidation have higher efficiency in degrading organic pollutants. Among many sewage treatment technologies, photocatalysis, as an advanced oxidation technology (AOP), is a sustainable solar energy collection and environmentally friendly photooxidation technology, which has the advantages of low cost, simple operation, and environmental friendliness, and is an important strategy to alleviate the energy crisis and the increasingly serious environmental problems. However, there are still some limitations in large-scale photocatalytic applications. First, problems such as weak light absorption ability, narrow light response range, and wide bandgap limit the application of photocatalytic material reagents. Second, currently mainly used metal-based photocatalysts must consider the elution of heavy metals during actual application, which will cause secondary pollution to the environment. Therefore, the preparation of efficient and environmentally friendly photocatalytic materials to remove organic dyes has become a key issue in global sewage treatment.

[0003] Graphitic carbon nitride (g-C 3 N 4 ) is a stable and non-secondary-polluting carbon-based non-metallic organic semiconductor with a bandgap of about 2.7 eV. Due to its suitable bandgap, stable physical and chemical properties, and high visible light utilization rate, it has been proven to be a promising photocatalyst and is widely used in fields such as solar energy conversion and sewage purification. However, the bulk g-C 3 N 4 obtained by simple calcination has defects such as narrow visible light absorption range, few surface active sites, and fast recombination of photogenerated carriers, which limit its practical application. Therefore, in order to improve the photocatalytic performance of g-C 3 N 4 , people have actively explored various strategies to improve the above defects, such as constructing heterojunctions, element doping, morphology regulation, and defect engineering. Among these strategies, element doping and morphology regulation are considered to be effective ways to improve the photocatalytic performance of g-C 3 N 4A very direct and effective method for photocatalytic performance. For example, doping g-C with non-metallic elements C, O, S, P 3 N 4 has been proven to be able to improve photocatalytic performance. The morphological regulation of photocatalysts is generally achieved by improving their particle size, pore size, or by adjusting the bulk to sheet-like or porous shapes, increasing the active sites of the catalyst, regulating its optoelectronic properties, reducing the recombination rate of carriers, etc. to improve the catalytic performance. Recent studies have shown that the synthesis and modification of g-C 3 N 4 by supramolecular precursor self-assembly has become a mature method for morphological regulation. However, most molecular self-assembly methods have certain limitations. Organic solvents or templating agents are usually required during the synthesis process, which is not environmentally friendly and requires additional post-treatment steps. Therefore, it is particularly important to find a simple and green self-assembly method for the morphological regulation of g-C 3 N 4 .

[0004] Although the modification of the catalyst can improve the photocatalytic performance of g-C 3 N 4 to a certain extent, the inherent band structure and light absorption range of g-C 3 N 4 limit its ability to efficiently degrade organic pollutants through photocatalysis. The photocatalytic coupling process has been proven to be an effective way to solve the above problems, such as the mature photo-Fenton process, photoelectrocatalytic process, enzyme-photo coupling catalysis, etc. In addition, the advanced oxidation technology based on peroxymonosulfate (PMS) to assist photocatalysis has increasingly been proven to be an ideal choice for improving catalytic performance, and light can continuously induce the activation of PMS. However, most of the current catalysts for efficiently activating PMS are mainly metals, and the problems of increased color in sewage and the dissolution of toxic metal ions cannot be avoided, which limits their practical applications. However, in the non-metallic catalyst g-C 3 N 4 , the electron-rich N sites contain two coordinated triazine groups and three coordinated nitrogen atoms. These sites act as electron donors and can promote the cleavage of the O-O bond in the PMS molecule under the action of light. Secondly, during the photocatalytic process, g-C 3 N 4 generates electron-hole pairs under light excitation. PMS captures the electrons in the conduction band to generate sulfate radicals, inhibiting the recombination of electron-hole pairs.

[0005] Therefore, the use of PMS to assist photocatalysis is considered to be a very effective method for improving the degradation of organic pollutants in sewage. It not only has excellent oxidation ability but also improves energy utilization efficiency, with great economic and environmental advantages. Summary of the Invention

[0006] Based on this, it is necessary to provide a method for degrading RhB by synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS to solve the technical problems proposed in the above background technology.

[0007] To solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The method for degrading RhB by synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS is as follows:

[0009] S1: Prepare P-doped tubular carbon nitride;

[0010] S2: Apply the P-doped tubular carbon nitride obtained in step S1 to photocatalytically activate PMS;

[0011] S3: Use the photocatalytically activated PMS to degrade RhB.

[0012] As a preferred embodiment of the method for degrading RhB by synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS provided by the present invention, in step S1, the preparation of P-doped tubular carbon nitride is as follows:

[0013] S11: Dissolve 2 g of melamine in 50 mL of deionized water, ultrasonicate for 5 min, and add 5 mL of phosphoric acid to the melamine solution;

[0014] S12: Stir the product obtained in S11 in a water bath at 80 °C for 30 min. After complete mixing, transfer it to a 100 mL autoclave with a polytetrafluoroethylene liner and place it in a constant temperature drying oven to heat at 180 °C for 10 h; after cooling to room temperature, the product is washed three times with ultrapure water and ethanol, centrifuged, and dried in a vacuum drying oven at 60 °C for 6 h to obtain a self-assembled complex of melamine and phosphoric acid, which is 5PMHP;

[0015] S13: Place the complex obtained in S12 in a 10 mL covered corundum boat, and heat it to 500 °C at a rate of 2.5 °C / min in a tubular furnace, keep it at this temperature for 4 h, and then cool it to room temperature.

[0016] As a preferred embodiment of the method for degrading RhB by synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS provided by the present invention, in step S2, the application of the P-doped tubular carbon nitride obtained in step S1 to photocatalytically activate PMS is as follows:

[0017] S21: Add a certain amount of photocatalytic material to the sewage containing different pollutants, ultrasonicate the catalyst suspension for 5 min to make the sample evenly dispersed;

[0018] S22: Continuously stir for 30 min under dark conditions to achieve adsorption-desorption equilibrium;

[0019] S23: Use a xenon lamp and a cut-off filter as the light source, keep a distance of 10 cm between the light source and the reactor, and carry out photocatalysis at all reaction temperatures maintained at 25 °C.

[0020] As a preferred embodiment of the method for degrading RhB by synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS provided by the present invention, in step S23, after turning on the xenon lamp, a certain amount of PMS is added, 2 mL of the catalyst suspension is extracted every 3 min, and the photocatalyst is removed through a 0.22-μm filter head.

[0021] As a preferred embodiment of the method for degrading RhB by synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS provided by the present invention, in step S3, the photocatalytic activation of PMS is used to degrade RhB, and the steps are as follows:

[0022] Degrade RhB with different volumes of PMS.

[0023] As a preferred embodiment of the method for degrading RhB by synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS provided by the present invention, in the PMS-assisted photocatalytic system, ·SO 4 - , h + , ·O 2 - , 1 O 2 and ·OH all participate in the degradation of RhB, and ·O 2 - plays a major role, while 1 O 2 , ·OH, h + and ·SO 4 - play a minor role;

[0024] With the addition of PMS, the free radicals show higher EPR signals, generate more ROSs, and improve the efficiency of photocatalytic degradation of RhB.

[0025] It can be undoubtedly seen that through the above technical solutions of the present application, the technical problems to be solved by the present application can surely be solved.

[0026] At the same time, through the above technical solutions, the present invention has at least the following beneficial effects:

[0027] The method for synthesizing P-doped tubular carbon nitride to drive the photocatalytic activation of PMS for the degradation of RhB provided by the present invention uses phosphoric acid and melamine as raw materials to prepare P-doped carbon nitride with a tubular structure (5P-TCN) through a precursor self-assembly method, and evaluates its PMS-photocatalytic effect on the typical organic pollutant rhodamine B (RhB) under visible light through batch experiments;

[0028] With the synergistic effect of PMS, the degradation effect of 5P-TCN on RhB is significantly improved, and the degradation rate constant is 111.8 times that of the original. It provides a green approach for the development of low-cost photocatalysts, and further proves its excellent efficiency in the photocatalytic synergistic activation of PMS for the degradation of RhB in combination with PMS;

[0029] Compared with the original g-C 3 N 4 The P-TCN synthesized by calcining the self-assembled precursor without using templates and organic solvents has a significantly accelerated photocatalytic degradation rate of RhB under the synergistic effect of PMS. More notably, this catalyst does not contain metals, has great economic advantages and no secondary environmental pollution, does not require the removal of the template agent after synthesis, is simple to operate, and has the potential for scale-up; The method of directly preparing P-doped tubular carbon nitride using phosphoric acid and rapidly photocatalytically degrading organic pollutants in sewage under the synergistic effect of PMS may provide some insights for finding efficient and environmentally friendly methods for degrading organic pollutants and has broad industrial prospects. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is the schematic diagram of the preparation principle of the photocatalyst of the present invention;

[0032] Figure 2 It is the schematic diagram of the microscopic structure of the catalyst of the present invention;

[0033] Figure 3 It is the analysis schematic diagram of BCN, HCN and xP-TCN of the present invention;

[0034] Figure 4 It is the XPS schematic diagram of BCN and 5P-TCN of the present invention;

[0035] Figure 5 It is the schematic diagram of the photocatalytic efficiency of different catalysts of the present invention;

[0036] Figure 6 Schematic diagram of influencing factors for photocatalytic degradation of RhB by 5P-TCN of the present invention assisted by PMS;

[0037] Figure 7 Schematic diagram of BCN, HCN and 5P-TCN of the present invention;

[0038] Figure 8 Schematic diagram of different reactive oxygen species (ROSs) in the present invention in the reaction of PMS and photocatalysis synergy;

[0039] Figure 9 Schematic diagram of possible degradation pathways of RhB in the 5P-TCN / vis / PMS system of the present invention;

[0040] Figure 10 Schematic diagram of possible degradation mechanism of RhB in the 5P-TCN / vis / PMS system of the present invention;

[0041] Figure 11 Schematic diagram of the generation of 5P-TCN of the present invention;

[0042] Figure 12 Element distribution map of 5PHMP of the present invention;

[0043] Figure 13 Schematic diagram of element content of 5P-TCN of the present invention;

[0044] Figure 14 Schematic diagram of adsorption curve of 5P-TCN of the present invention to RhB;

[0045] Figure 15 Schematic diagram of degradation of different RhB solutions at natural pH of the present invention;

[0046] Figure 16 Schematic diagram of degradation kinetic curve in the radical quenching experiment of the present invention. Detailed implementation manners

[0047] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0049] It should be noted that, without conflict, the embodiments in the present invention and the features and technical solutions in the embodiments can be combined with each other.

[0050] It should be noted that similar reference numerals and letters indicate similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0051] Example 1

[0052] Refer to Figures 1 - 16 , a method for synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS for the degradation of RhB.

[0053] 1. Experimental section

[0054] 1.1 Chemicals

[0055] Melamine, phosphoric acid (H 3 PO 4 ), RhB, methylene blue (MB), malachite green (MG), methyl orange (MO), methanol (MeOH), tert-butanol (TBA), p-benzoquinone (P-BQ), furfuryl alcohol (FFA), disodium ethylenediaminetetraacetate (EDTA-2Na), PMS (KHSO 5 ·0.5KHSO 4 ·0.5K 2 SO 4 ), NaCl, NaHCO 3 , Na 2 SO 4 , NaNO 3 , Na 2 HPO 4 . All commercially purchased chemicals are of analytical grade and do not require additional purification steps. The pH of the reaction system was adjusted with 1 mM NaOH and HCl, and the required solutions were prepared with deionized water to eliminate ion interference in the water.

[0056] 1.2 Synthesis process

[0057] P-doped tubular carbon nitride was prepared by a hydrothermal self-assembly method, as Figure 1As shown. Briefly, 2 g of melamine was dissolved in 50 mL of deionized water and sonicated for 5 min. A certain amount (3 mL, 4 mL, 5 mL, 6 mL) of phosphoric acid was added to the melamine solution. The resulting product was stirred in a water bath at 80 °C for 30 min. After complete mixing, it was transferred to a 100 mL high-pressure reactor with a polytetrafluoroethylene liner and placed in a constant-temperature drying oven and heated at 180 °C for 10 h. After waiting to cool to room temperature, the product was washed three times with ultrapure water and ethanol, centrifuged, and dried in a vacuum drying oven at 60 °C for 6 h to obtain a self-assembled complex of melamine and phosphoric acid, named 5PMHP (hydrothermal product of phosphoric acid and melamine, x = 3, 4, 5, 6). Finally, the complex was placed in a 10 mL covered corundum boat and heated in a tube furnace (under N 2 atmosphere) at a heating rate of 2.5 °C / min to 500 °C, held at this temperature for 4 h, and then cooled to room temperature. According to the different amounts of phosphoric acid added, the resulting products were named xP-TCN (x = 3, 4, 5, 6). This preparation method does not require the use of organic solvents and templating agents, so it is safer and more environmentally friendly.

[0058] The bulk carbon nitride obtained by directly calcining melamine in a tube furnace under the same conditions was denoted as BCN. The carbon nitride obtained by hydrothermally treating melamine without adding phosphoric acid and then calcining it in a tube furnace under the same conditions was denoted as HCN.

[0059] 1.3 Degradation performance test of the photocatalytic oxidation system for organic pollutants

[0060] The photocatalytic oxidation (PO) system consists of a photocatalyst and visible light. A certain amount of photocatalytic material was added to the sewage containing different pollutants. The catalyst suspension was sonicated for 5 min to make the sample evenly dispersed, and then continuously stirred for 30 min under dark conditions to achieve adsorption-desorption equilibrium. Subsequently, a 350 W xenon lamp and a 420 nm cut-off filter were used as the light source, and the distance between the light source and the reactor was maintained at 10 cm. All reaction temperatures were maintained at 25 °C for photocatalytic experiments. After turning on the xenon lamp, a certain amount of PMS was added. Every 3 min, 2 mL of the catalyst suspension was extracted, and the photocatalyst was removed through a 0.22 μm filter head. The absorbance of the solution at the maximum wavelength was measured with a UV-visible spectrophotometer.

[0061] 2. Results and discussion

[0062] 2.1 Structure and chemical composition of the catalyst

[0063] SEM images show the microstructures and morphologies of BCN, HCN, 5PMHP, and 5P-TCN. Example two and Figure 11 Analysis shows the growth mechanisms of 5PMHP and 5P-TCN.

[0064] ReferenceFigure 2 , where the SEM images of (a) BCN, (b) HCN, (c) 5PMHP, and (d) 5P-TCN; (e) TEM images of BCN, (f) HCN, (g) 5PMHP, and (h) 5P-TCN; (i) elemental distribution map of 5P-TCN Figure 2 a shows the structure of BCN, which consists of massive particles and a smooth surface, being typical morphological features of bulk carbon nitride. Figure 2 b shows the structure of HCN. Compared with BCN, the massive particles become smaller but there are no obvious other changes. Figure 2 c is the self-assembled intermediate 5PMHP Figure 2 d is the structure of 5P-TCN. The surface still retains a layered stacking structure, greatly expanding the surface area, adsorption sites, and active centers of carbon nitride. The formation of hollow carbon nitride is due to the rapid crystallization of the supramolecular precursor, resulting in uneven density of the hexagonal prism-shaped polymer. The higher the density on the surface and the lower the density in the internal region, causing the pyrolysis or etching of the precursor to start from the center of the hexagonal prism and gradually extend outward, forming a tubular structure.

[0065] Scanning of BCN, HCN, 5PMHP, and 5P-TCN by TEM also proves their internal structures. BCN ( Figure 2 e) and HCN ( Figure 2 f) show a typical massive dense morphology, but the massive volume of HCN becomes smaller. 5PMHP has a dense solid hexagonal prism structure ( Figure 2 g), and after calcination, it shows a tubular structure with a very transparent surface ( Figure 2 h), further confirming the tubular structure of 5P-TCN. The surface is very thin, which is beneficial for shortening the charge. At the same time, energy spectrum analysis and elemental mapping method are used to detect and study the elemental distribution and composition of the materials. It can be seen from Figure 12 that the P element adheres to the surface of the precursor 5PMHP. After further calcination, the P element reacts with 5PMHP to form 5P-TCN. The elemental mapping diagram ( Figure 2 i) shows that C, N, O, and P elements are evenly distributed in 5P-TCN. C and N are the main elements of the material, while the O element mainly comes from externally absorbed O 2 and CO 2 , and the content of P is 0.43%. The elemental content is shown in Figure 13 . The results show that P is successfully doped into carbon nitride, and a P-doped tubular carbon nitride composite material is successfully prepared.

[0066] Reference Figure 3 , where (a) XRD spectrum, (b) FT-IR spectrum, (c) N of BCN and 5P-TCN 2Adsorption - desorption isotherms, and (d) pore size distribution curves of each sample. The crystal structure of the materials was analyzed by XRD ( Figure 3 a), pure carbon nitride has two obvious characteristic peaks, which are the (100) characteristic plane at 12.9° and the (002) characteristic plane at 27.4°, corresponding to the triazine ring structural unit and the interlayer stacking of the aromatic system on the carbon nitride plane respectively. HCN also has these two peaks, indicating that the crystal structure has not changed after the hydrothermal reaction. After introducing P, the (100) peak gradually disappears. It is speculated that P affects the growth process of the carbon nitride plane, reducing the plane size. This may be due to the breaking of hydrogen bonds during the hydrothermal process, resulting in a wider spacing of the tri - s - triazine rings within the plane. In addition, as the P content increases, the (002) peak gradually weakens and shifts towards a larger diffraction angle, indicating that P is successfully introduced, promoting the polymerization of the supramolecular precursor and the reconstruction of the lattice by reducing the stacking spacing of the carbon nitride monolayer, affecting the interlayer structure of g - C 3 N 4 . In summary, P doping has no obvious change on the crystal structure of g - C 3 N 4 , and no other crystal impurities are generated. The structure of the synthesized samples was characterized by infrared spectroscopy ( Figure 3 b), the FTIR spectra of all samples show several typical absorption bands corresponding to the characteristic structure of g - C 3 N 4 . The broadband in the range of 3000 - 3500 cm -1 is usually related to the stretching vibration modes of the residual amino group (N - H) and the absorbed water (O - H) in g - C 3 N 4 . The peaks observed at 1623 and 1555 cm -1 correspond to the stretching vibration of the C = N bond within the heptazine unit, while the peaks at 1408, 1320 and 1236 cm -1 correspond to the inherent C - N stretching vibration of the heptazine unit. The peaks at 1456 and 1203 cm -1 correspond to the C - N stretching of the C - NHx group, and the peaks at 887 and 808 cm -1 are caused by the vibration of the triazine ring and the tri - s - triazine ring, which also confirms that the addition of P does not change the basic chemical structure of g - C 3 N 4 , but only affects the crystal structure, resulting in the disappearance of the (100) peak in the XRD results. The results show that P doping has no effect on the chemical structure of g - C 3 N 4 .

[0067] The pore size, specific surface area and pore size distribution of the catalyst were analyzed by N 2 adsorption - desorption isotherms and the BJH method respectively.

[0068] Using N 2 The pore size, specific surface area, and pore size distribution of the catalyst were analyzed by adsorption - desorption isotherms and the BJH method, respectively. Table 1 shows the corresponding S BET , pore volume, and pore size distribution of BCN and 5P - TCN catalysts. From Figure 3 c, it can be seen that both the BCN and 5P - TCN isotherms exhibit type - IV adsorption curves and H3 - type hysteresis loops, indicating that the materials have mesoporous characteristics. In addition, from the pore size distribution of BCN and 5P - TCN catalysts ( Figure 3 d), it can be seen that the tubular structure greatly increases the pore volume of carbon nitride between pore sizes of approximately 2 - 20 nm, making 5P - TCN have a larger specific surface area (31.092 m 2 .g -1 ), which is 5.25 times that of BCN (5.918 m 2 .g -1 ). The larger specific surface area can provide more active reaction sites, which will help improve the catalytic degradation performance of 5P - TCN towards pollutants.

[0069] Table S1 Pore size distribution of BCN and 5P - TCN

[0070]

[0071] Reference Figure 4 , where (a) total spectrum, (b) high - resolution C1s spectrum, (c) high - resolution N1s spectrum, and (d) high - resolution P2p spectrum of 5P - TCN,

[0072] XPS analysis was further used to explore the molecular structure and atomic valence states of BCN and 5P - TCN. The XPS survey spectrum ( Figure 4 a) shows that the BCN material contains C, N, and O elements, and 5P - TCN contains C, N, O, and P elements, which is consistent with the EDS results. Note that due to the low detection limit of the instrument and the P element content being less than 1%, the peak is not obvious. Figure 4 b is the high - resolution C1s spectrum of the two samples. By fitting, four peaks can be obtained, with binding energies of approximately 284.8 eV, 286.5 eV, 288.1 eV, and 293.5 eV, corresponding to graphitic carbon (C - C / C═C), surface uncompensated amino groups (C - NHx), tris - s - triazine unit sp 2 carbon (N - C═N), and π - electron delocalization, respectively. Figure 4c is the high-resolution N1s spectra of the two samples. Four peaks can be obtained by fitting. The peaks with three binding energies of approximately 398.6 eV, 400.0 eV, and 401.0 eV correspond to the bridging nitrogen atoms (C-N=C), tertiary nitrogen atoms (N-C 3 ) and amino nitrogen atoms (C-Nx) of the tri-s-triazine unit, respectively. The peak at a binding energy of 404.2 eV is attributed to π-excitation. The high-resolution spectrum of 5P-TCN at 133.4 eV ( Figure 4 d) corresponds to the P-N coordination bond, indicating that P may replace C to form a P-N bond on the triazine ring. In addition, the weakening of the N-C=N peak intensity (peak area) in the C1s of 5P-TCN also confirms this point.

[0073] 2.2 Photocatalytic oxidation system for the degradation of RhB

[0074] Reference Figure 5 , where (a) the degradation effect of different catalysts on RhB, (b) the corresponding first-order kinetic model, (c) the k constant. (d) The degradation effect of RhB under different systems, (e) the corresponding first-order kinetic model (f) the k constant,

[0075] To evaluate the photocatalytic efficiency of different catalysts, the degradation performance of different catalysts on RhB was studied under simulated visible light (greater than 420 nm) irradiation (unless otherwise specified, it was under the original pH condition, and the original pH was approximately 4.3). Figure 5 a shows the degradation performance of different catalysts (400 mg / L) on RhB (10 mg / L). Within 15 min, the degradation rate of RhB by BCN under visible light was only 3.9%. To study the synergistic effect of PMS activation and photocatalysis on improving the degradation rate of RhB, PMS (400 mg / L) was introduced into the reaction system. The addition of PMS significantly increased the degradation rate of RhB by BCN, reaching a degradation rate of 61.9% within 15 min. Combining with the pseudo-first-order kinetic model of the degradation of RhB by BCN ( Figure 5 b) and the obtained degradation kinetic constant k was 0.0641 min -1 ( Figure 5c) is 25.6 times that without PMS. The degradation rate of RhB by HCN obtained only by calcination after hydrothermal treatment shows only a slightly insignificant improvement compared to BCN because HCN only slightly shrinks in volume without other changes. In sharp contrast, the formation of the tubular structure greatly improves the degradation rate of RhB in this system. In addition, different amounts of P element introduction make the degradation rate of the catalyst for RhB show a trend of first increasing and then decreasing. Among them, the degradation performance of 5P-TCN reaches the best, and the degradation rate of RhB within 15 min reaches 98.1%, and the degradation rate is 4.4 times that of BCN. This indicates that the change in degradation performance due to element doping is not the more the better. When the doping element concentration is too high: on the one hand, it will cause the destruction of the tri-s-triazine structure in g-C 3 N 4 ; on the other hand, the dopant will turn the generated isolated energy levels into recombination centers of photogenerated electron-hole pairs, reducing the yield of photogenerated carriers. In short, the degradation rate constant (k) of the 5P-TCN / vis / PMS system for RhB is 111.8 times that of the BCN photocatalytic system, which indicates that a certain amount of P-doped tubular carbon nitride can effectively improve the photocatalytic performance.

[0076] To further explore the catalytic performance of different systems, the effects of different catalytic systems on the degradation performance of RhB were studied. As Figure 5 shown in Fig. d, it can be clearly seen that in the dark, only light, only PMS, only 5P-TCN, and PMS / vis systems, the RhB solution can hardly be degraded within 15 min. In the 5P-TCN / PMS system and the 5P-TCN / vis system, the degradation rates of RhB within 15 min are only 19.5% and 88.8% respectively. Combining with the pseudo-first-order kinetic model ( Figure 5 Fig. e) and the obtained degradation kinetic constant k values are only 0.0129 min -1 and 0.1424 min -1 ( Figure 5 Fig. f). However, the degradation performance in the 5P-TCN / vis / PMS system is significantly better than all other systems, and the degradation rate reaches 98.1% within 15 min. More importantly, the degradation rate constant (k) reaches 0.2796 min -1 , which are 21.7 times and 2.0 times the degradation of RhB by 5P-TCN under only PMS and only light conditions respectively. This indicates that there is a synergistic effect between photocatalysis and PMS. Due to the differences in experimental systems and conditions, direct numerical comparison with other studies is not possible. However, the degradation performance of the prepared 5P-TCN / vis / PMS system is at the forefront among non-metallic carbon nitride-based photocatalytic materials and even better than many metal-based photocatalysts (Table S2).

[0077] Table S2 Research on the degradation of RhB by g-C 3 N 4 -based catalysts

[0078]

[0079] Reference Figure 6 , (a) Catalyst concentration, (b) RhB concentration, (c) PMS concentration, (d) Original pH, (e) Coexisting ions (if not otherwise specified, C RhB = 10 mg / L, C cat = 400 mg / L, C PMS = 400 mg / L, pH was not adjusted and was approximately 4.4), (f) Actual water samples. (g) Universality test. (h) Three-cycle experiment, and (i) XRD patterns of pristine and recycled 5P-TCN.

[0080] Taking the 5P-TCN / vis / PMS system as an example, the effects of catalyst dosage, pollutant concentration, and PMS dosage on the degradation performance of RhB were investigated. At different amounts, the adsorption of RhB by the catalyst 5P-TCN was negligible. As shown in Figure 13 and Figure 14 , during the 30-min dark adsorption process of thoroughly stirring a 400-mg / L 5P-TCN and 10-mg / L RhB solution, the adsorption amount of the catalyst to RhB was only 6.6% and the adsorption-desorption equilibrium could be reached within 30 min. As shown in Figure 6 a and Figure 15 a, when the initial concentration of the RhB solution was 10 mg / L and the PMS dosage was 400 mg / L at natural pH, as the catalyst increased from 200 mg / L to 500 mg / L, the degradation rate of RhB could reach about 98%, but the degradation rate constant (k) showed a trend of first increasing and then decreasing, reaching the maximum value when the catalyst dosage was 400 mg / L. Research shows that a higher catalyst dosage can improve the reaction efficiency because more reactive sites increase and more free radicals are generated. However, using an excessive amount of catalyst will instead reduce the catalytic effect, which is due to the excessive catalyst reducing the transparency of the solution, hindering light penetration, and reducing light utilization.

[0081] In actual sewage, the initial concentration of pollutants may vary. Therefore, it is of great significance to study the effect of concentration on the degradation rate. As shown in Figure 6 b and Figure 15b. The degradation performance of RhB at different initial concentrations (5, 10, 15, and 20 mg / L) was investigated under natural pH with a catalyst dosage of 400 mg / L and a PMS dosage of 400 mg / L. As the concentration increased, the degradation rate of RhB gradually decreased. When the initial concentration of RhB was 20 mg / L, the degradation rate was only 89.2% within 15 min.

[0082] It can be concluded that high concentrations of RhB are not conducive to photocatalytic elimination. This is because the increase in the amount of pollutants causes a decrease in the transmittance of visible light. More importantly, due to the competitive consumption of oxidizing species, a higher RhB concentration requires more time to achieve the same degradation rate. However, in actual wastewater, the pollutant concentration does not reach such a high level, and the degradation rate is still very high at low concentrations, indicating the practical applicability of this system.

[0083] Subsequently, the relationship between the dosage of PMS (100, 200, 400, and 800 mg / L) and the degradation performance of RhB was investigated (as shown in Figure 6 c and Figure 15 c). As the dosage of PMS increased, RhB could be almost completely degraded within 15 min, but the degradation rate first increased and then decreased. This is because the dosage of PMS is related to the amount of ·SO 4 - during the degradation process of RhB. The more PMS, the more free radicals are generated. Therefore, it is expected to generate more free radicals at higher PMS concentrations. However, when the dosage of the catalyst is fixed, the number of photo-generated carriers may not be sufficient to activate all PMS. In addition, excessive PMS will cause ·SO 4 - to quench and generate ·SO 5 - with lower oxidation ability.

[0084] Considering the presence of various inorganic salts and other impurities in actual wastewater, the effects of pH, various co-existing ions (HPO 4 2- , HCO 3 - , SO 4 2- , NO 3 - , Cl - , 5 mM) and different water sources on the degradation performance were investigated under the conditions of a catalyst dosage of 400 mg / L, a PMS dosage of 400 mg / L, and an RhB concentration of 10 mg / L. The pH value plays a key role in water treatment. Therefore, the RhB solution was adjusted to a wide pH range from strongly acidic to strongly alkaline environments ( Figure 6 d and Figure 15 d) to explore the effect of the pH value on this system.

[0085] The stronger the acidity of the solution, the better the degradation effect on RhB. When the pH value increases from 3 to 9, the degradation rate of RhB can remain above 92% within 15 min, indicating that the 5P-TCN / vis / PMS system has strong pH tolerance in a wide pH range. However, under strong alkaline conditions (pH = 11), it is not conducive to the degradation of RhB, and the degradation rate of RhB drops sharply to 42.7% within 15 min, and the k value drops to 0.0352 min -1 . This is probably because under alkaline conditions, ·SO 4 - / ·OH reacts with OH - to generate ·OH, and the lower oxidation potential and shorter lifetime of ·OH weaken the degradation of RhB in this system. The coexisting ion experiments ( Figure 6 e and Figure 15 e) also confirmed the above conclusion.

[0086] In the presence of HPO 4 2- and HCO 3 - anions, the degradation rates of RhB are 42.7% and 60.9% respectively. While in the presence of NO 3 - , Cl - , there is a slight promoting effect on the degradation of RhB. The stronger the acidity of the coexisting ions, the larger the k value, which further confirms the influence of pH on the degradation of RhB in this system. In addition, when Cl - coexists, there is an extremely high degradation rate (k = 0.3076 min -1 ) to degrade RhB, which is due to the reaction of Cl - with HSO 5 - to generate Cl 2 and HClO (Equation 1-7), promoting the degradation of RhB. The above results show that the 5P-TCN / vis / PMS system has good pH adaptability and can effectively degrade RhB in a wide pH range.

[0087] Cl - +HSO 5 - →SO 4 2- +HClO (1)

[0088] ·SO 4 - +Cl - →SO 4 2- +·Cl (2)

[0089] ·Cl + Cl - →·Cl 2 - (3)

[0090] ·Cl 2 - +·Cl 2 - →Cl 2 +2Cl - (4)

[0091] ·SO 4 - +HCO 3 - →·HCO 3 - +SO 4 2- (5)

[0092] ·OH + HCO 3 - →CO 3 2- +H 2 O (6)

[0093] ·OH + HPO 4 2- →·HPO 4 - +OH - (7)

[0094] To further evaluate the practicality of the 5P-TCN / vis / PMS system in actual water bodies, tap water and lake water were used to prepare RhB solutions to simulate wastewater ( Figure 6 f and Figure 15 f). There was a certain degree of inhibition in the degradation of RhB in the system, and the k values were 0.1148 and 0.1313 min -1 . This is because the components in these actual waters are complex, including soluble natural organic matter, various ions, and other impurities. Generally speaking, however, the 5P-TCN / vis / PMS system has strong adaptability to both lake water and tap water, and the removal rate remains above 80%.

[0095] A universality test was carried out on the catalyst ( Figure 6 g). Three organic dyes, MB, MG, and MO, were degraded in the same system, and more than 92% could be degraded within 15 min. Therefore, it shows that the catalytic effect of the 5P-TCN / vis / PMS system has universality and has the potential for practical application. To evaluate the recyclability and stability of 5P-TCN, a recycling test was carried out. From Figure 6It can be seen that after three cycles, the degradation rate hardly decreased, and more than 98% of RhB could still be degraded within 15 min, showing very strong stability and promising for the recycling of materials.

[0096] The specific experimental method of the cycle is shown in Example 2. In addition, the crystal phases of 5P-TCN before and after repeated reactions were analyzed by XRD (as Figure 6 i), and the characteristic peaks of the catalyst were well preserved, further proving its good stability and the prospect of large-scale application.

[0097] 2.3 Photocatalytic mechanism research

[0098] Reference Figure 7 , where (a) UV-vis DRS diagram, (b) Tauc diagram, (c) VB-XPS spectrum diagram, (d) schematic diagram of band gap structure, (e) PL spectrum diagram.

[0099] The optical absorption characteristics and band structure of the catalyst were revealed by UV-Vis diffuse reflection analysis. As Figure 7 a, compared with the original g-C 3 N 4 , both HCN and 5P-TCN have significant red shifts, with a wider light absorption range, which is more conducive to light absorption. Using the UV-vis DRS data, the corresponding values of the band gap energy were converted with αhν = A(hν - Eg)exp(n / 2) (Eg is the band gap energy, An is the proportionality constant, h is Planck's constant, α is the absorption coefficient, ν is the vibration frequency, n = 4). From Figure 7 the Tauc diagram in b, the Eg values of BCN, HCN, and 5P-TCN were estimated to be 2.81, 2.71, and 2.70 eV, respectively. The band edge potential was analyzed by valence band XPS. As Figure 6 shown in c, the valence band (VB) values of each catalyst were calculated by E VB-NHE = φ + E VB-XPS - 4.44 (E VB-NHE represents the potential of the normal hydrogen electrode in the neutral state, and φ is the work function of the device, with a value of 4.2). The E VB-XPS of BCN, TCN, and 5P-TCN were 2.13, 2.03, and 1.98 eV, respectively. Therefore, the E VB-NHE of BCN, TCN, and 5P-TCN were 2.81, 2.71, and 2.70 eV, respectively.

[0100] According to the Eg and EVB-NHE obtained above, E CB-NHE = E VB-NHE - Eg (E CB-NHEThe potential of the normal hydrogen electrode in the neutral state was used to determine the conduction band (CB) value, and the ECB-NHE values of BCN, HCN, and 5P-TCN were -0.68, -0.68, and -0.72 eV, respectively.

[0101] In summary, the schematic diagrams of the energy band structures of BCN, HCN, and 5P-TCN are as shown in Figure 7 Figure d. It can be seen that the hydrothermally treated carbon nitride mainly reduces the bandgap energy, while the doping of P element and the morphology further shift the VB value upward, making it easier for O 2 to be converted into ·O 2 - . Although the reduction of the bandgap energy can promote the excitation of photoelectrons, it may also hinder the dissociation of excitons.

[0102] To further evaluate the separation and transfer efficiency of photogenerated charges, the steady-state PL spectra of BCN, HCN, and 5P-TCN were measured ( Figure 7 Figure e). The strongest fluorescence intensity of BCN indicates that the recombination rate of photogenerated electrons and holes is relatively high. The fluorescence intensity of hydrothermally treated HCN does not decrease significantly, probably because the hydrothermal treatment does not cause other changes except for a slight reduction in the volume of carbon nitride. The fluorescence intensity of 5P-TCN decreases significantly, indicating that the formation of P-doped tubular carbon nitride improves the charge transfer rate, thereby inhibiting the recombination of photogenerated electrons and holes.

[0103] Reference Figure 8 , (a) The effect of different quenchers on the degradation of RhB. (b) ESR spectra of the 5P-TCN / vis and 5P-TCN / vis / PMS systems (capturing ·O 2 - )). (c) EIS diagrams and (d) photocurrent response curves of BCN and 5P-TCN were investigated to examine the contributions of different reactive oxygen species (ROSs) during the reaction of PMS and photocatalysis in synergy. Radical quenching experiments were carried out in different systems.

[0104] ·O 2 - , ·OH, 1 O 2 , ·SO 4 - / ·OH, and h + were quenched with p-BQ (1 mM), TBA (1 mM), FFA (1 mM), MeOH (1 mM), and EDTA-2Na (1 mM), respectively. The RhB degradation curves and k values were obtained as shown in Figure 8 Figure a and Figure 16 Figure b. The addition of all quenchers led to a decrease in the RhB degradation efficiency to varying degrees. Among them, the addition of p-BQ significantly inhibited the degradation of RhB, indicating that ·O2 - is the main active substance for RhB degradation. The contributions of other free radicals to the photocatalytic degradation efficiency of RhB are in the order of ·OH > 1 O 2 > ·SO 4 - / ·OH > h + . It is not difficult to see from the energy band structure that in the 5P-TCN / vis / PMS system, the direct oxidation of OH - to ·OH is thermodynamically very favorable. The EPR analysis further confirmed the formation of the main active substances ·OH, 1 O 2 , ·SO 4 - / ·OH, ·O 2 - in the 5P-TCN / vis / PMS system (such as Figure 8 b-d). No signals of ·OH, 1 O 2 , ·SO 4 - / ·OH, ·O 2 - were observed in the dark. Typical signals of ·OH, 1 O 2 , ·SO 4 - / ·OH, ·O 2 - were detected in the 5P-TCN / vis system, indicating that the generation of ROSs is related to the excitation of carriers in photoinduced 5P-TCN, which is consistent with the previous discussion. Under illumination, after adding PMS, the signal intensities of ·OH, 1 O 2 , ·SO 4 - / ·OH, ·O 2 - were significantly higher than those in the 5P-TCN / vis system, demonstrating that the synergistic activation of PMS in photocatalysis enhanced the generation of ROSs, thereby improving the degradation performance of RhB. To further compare the differences in the electrochemical properties of the catalysts and the changes in photocurrent responses under different systems, a series of control experiments were carried out using an electrochemical workstation.

[0105] Among them, the Nyquist plot of electrochemical impedance spectroscopy (EIS) reveals the charge transfer ability of the catalyst and the electrode ion diffusion process ( Figure 8 e). The curve slope of 5P-TCN is smaller than that of BCN, indicating that the electron transfer resistance is smaller, which can more effectively promote the separation and migration of electrons and reduce the recombination of electron-hole pairs. In addition, Figure 8f shows the comparison of photocurrent responses of the samples. The photocurrent response intensity of 5P-TCN is significantly higher than that of BCN, further confirming the promoting effect of 5P-TCN on the photocatalytic degradation of RhB. In summary, the substitution of N atoms on carbon nitride by P atoms and the morphological changes have enhanced the light absorption of carbon nitride, making the separation of electrons and holes more effective, thereby accelerating charge transfer and improving the photocatalytic efficiency.

[0106] Reference Figure 9 , detected and analyzed by LC-MS, showing the formation of some intermediates during the catalytic degradation of RhB in the 5P-TCN / vis / PMS system, as shown in Table S1. Combining the reported studies and the results of LC-MS analysis, the possible degradation pathway of RhB in the 5P-TCN / vis / PMS system was proposed ( Figure 9 ). Generally, RhB molecules in the 5P-TCN / vis / PMS system will adsorb on the catalyst surface and then undergo a series of degradation reactions, including N-deethylation, deamination, dealkylation, decarboxylation, cleavage of chromophores, ring cracking, and mineralization. Initially, the methyl group in the RhB (m / z = 443) molecule is attacked by ROSs and falls off, resulting in deethylation, gradually removing the ethyl groups on the molecule to form intermediates (m / z = 429, 415, 387, 359, 331). Then, the compound (m / z = 331) undergoes deamination to generate compounds (m / z = 318, 316), and decarboxylation reaction to generate compounds (m / z = 274) and compounds (m / z = 278, 222, 182) induced by decarboxylation reaction. Subsequently, ring-opening reactions occur to form some low-molecular-weight organic acids or amides (m / z = 166, 160, 150, 138, 122, 102, 94, 74). Finally, the low-molecular-weight organic acids or amides are further mineralized and ultimately decomposed into CO 2 、H 2 O and some small molecules such as alcohols and amines.

[0107] First, under visible light excitation, the photo-generated carriers on the surface of 5P-TCN are separated into electrons (e - ) and holes (h + ) and move to the catalyst surface to undergo a series of reactions (Equation 8). O 2 reacts with electrons to generate ·O 2 - (Equation 9), and h + can directly oxidize and degrade RhB or oxidize OH - into ·OH (Equations 10 and 11). With the addition of PMS, HSO 5 - captures photo-generated e- and is reduced to ·SO 4 -(Formula 12), ·SO 4 - reacts with H 2 O or OH - to generate ·OH (Formulas 12, 13, and 14). HSO 5 - captures h + to generate SO 5 - (Formula 15). For 1 the formation of O 2 it can be generated by oxidizing ·O 2 - and ·SO 5 - (Formulas 16 and 17).

[0108] 5P-TCN + hv → h + + e - (8)

[0109] O 2 + e - → ·O 2 - (9)

[0110] h + + RhB → H 2 O + CO 2 + other products (10)

[0111] OH - + h + → ·OH (11)

[0112] HSO 5 - + e - → SO 4 - + OH - (12)

[0113] ·SO 4 - + H 2 O → SO 4 2- + ·OH + H + (13)

[0114] ·SO 4 - + OH - → SO4 2- + ·OH (14)

[0115] HSO 5 - + h+ →SO 5 - +H + (15)

[0116] h + +·O 2 - → 1 O 2 (16)

[0117] 2·SO 5 - →2·SO 4 - + 1 O 2 (17)

[0118] According to the above experimental data, in the PMS-assisted photocatalytic system, ·SO 4 - 、h + 、·O 2 - 、 1 O 2 and ·OH all participated in the degradation of RhB, and ·O 2 - played a major role, while 1 O 2 、·OH、h + and ·SO 4 - played a minor role. With the addition of PMS, the free radicals showed higher EPR signals, indicating the generation of more ROSs, thus improving the efficiency of photocatalytic degradation of RhB.

[0119] 3. Conclusion

[0120] Refer to Figure 10 , to solve the disadvantages of traditional photocatalysts such as metal ion dissolution, narrow light absorption range, and poor stability in water treatment, the present invention prepared a P-doped tubular carbon nitride (P-TCN) photocatalyst by the precursor self-assembly method. The carefully adjusted 5P-TCN has a larger specific surface area (31.092 m 2 ·g -1) and a wider light response range (460 nm), making the kinetic constant k value of the 5P-TCN / vis / PMS system for degrading RhB 111.8 times that of BCN / vis. The electron circulation system composed of photo-generated electrons and holes provided by the excited 5P-TCN enhances the generation of ROSs under the synergistic action of PMS, enabling 5P-TCN to effectively drive the metal-free PMS-photocatalytic reaction within a wide pH range, with a degradation rate of RhB reaching over 98% within 15 min, solving the problem of poor degradation of aromatic proteins, tryptophan, and other proteins by the photocatalytic oxidation system. The present invention provides a very promising metal-free catalyst, solving many problems existing in traditional photocatalytic oxidation processes and PMS oxidation processes in wastewater treatment, and having important theoretical research and practical application significance in environmental wastewater treatment.

[0121] Example 2

[0122] It is disclosed on the basis of the above Example 1.

[0123] Catalyst growth mechanism

[0124] When H 3 PO 4 After adding the melamine suspension, it will be partially hydrolyzed into cyanuric acid. Melamine and cyanuric acid are bonded by supramolecular self-assembly and vertically stacked through p-p interactions to gradually grow into a solid hexagonal prism hydrothermal intermediate 5PMHP with a diameter of about 3 μm. P attaches to the surface of the intermediate ( Figure 12 ), and through the calcination process and reaction with melamine, it enters the g-C 3 N 4 skeleton to generate P-doped hollow tubular-structured carbon nitride.

[0125] Cyclic experiment method

[0126] In the cyclic test, 20 mg of the catalyst was added to 50 mL of RhB (10 mg / L) solution. The catalyst suspension was ultrasonically treated for 5 min to uniformly disperse the sample, and then continuously stirred in the dark for 30 min to reach the adsorption-desorption equilibrium. Subsequently, a photocatalytic experiment was carried out under visible light of a 350 W xenon lamp with a 420 nm cut-off filter. During the whole experiment, about 2.0 mL of the catalyst suspension was extracted every 3 minutes with a syringe, and the photocatalytic material was removed through a 0.22 μm filter head.

[0127] The visible light irradiation time of RhB was 15 min, and then the absorbance was measured at a wavelength of 554 nm by a UV-2600 type ultraviolet spectrophotometer. Finally, the remaining photocatalytic suspension in the photoreactor was obtained by filtration, washed several times with ethanol and ultrapure water, and dried at 60 °C for 2 hours.

[0128] To obtain the catalyst required for the first cycle experiment, the experiment was conducted multiple times, and the obtained catalyst powder was used as the catalyst for the first cycle experiment. The procedure for the first cycle experiment was the same as before. The catalyst powder obtained from the first recycling experiment was used as the catalyst for the second recycling experiment. The procedure for the second cycle experiment was the same as the previous one. The catalyst powder obtained from the second recycling experiment was used as the catalyst for the third recycling experiment. The procedure for the third cycle experiment was the same as the previous one.

[0129] Table S3 Possible intermediates for RhB degradation in the 5P-TCN\vis\PMS system

[0130]

[0131]

[0132]

[0133] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for synthesizing P-doped tubular carbon nitride to drive photocatalytic activation of PMS to degrade RhB, characterized in that: Here are the steps: S1: Preparation of P-doped tubular carbon nitride; S2: applying the P-doped tubular carbon nitride obtained in step S1 to photocatalytically activate PMS; S3: Photocatalytically activated PMS is used to degrade RhB.

2. The method for degrading RhB by synthesizing P-doped tubular carbon nitride driven by photocatalytic activation of PMS according to claim 1, characterized in that: In step S1, P-doped tubular carbon nitride is prepared in the following steps: S11: 2 g of melamine was dissolved in 50 mL of deionized water, ultrasonicated for 5 min, and 5 mL of phosphoric acid was added to the melamine solution; S12: The product obtained in S11 was stirred in a water bath at 80°C for 30 min. After complete mixing, it was transferred to a 100 mL high-pressure reactor with a polytetrafluoroethylene liner and placed in a constant temperature drying oven and heated at 180°C for 10 h. After cooling to room temperature, the product was washed three times with ultrapure water and ethanol, centrifuged and dried in a vacuum drying oven at 60°C for 6 h to obtain a self-assembled complex of melamine and phosphoric acid, which is 5PMHP. S13: The complex obtained in S12 was placed in a 10 mL covered corundum boat, heated to 500°C at 2.5°C / min in a tube furnace, kept at this temperature for 4 h, and then cooled to room temperature.

3. The method for degrading RhB by synthesizing P-doped tubular carbon nitride driven by photocatalytic activation of PMS according to claim 1, characterized in that: In step S2, the P-doped tubular carbon nitride obtained in step S1 is applied to photocatalytic activation of PMS, and the steps are as follows: S21: A certain amount of photocatalytic material was added to sewage containing different pollutants, and the catalyst suspension was ultrasonically treated for 5 min to make the sample evenly dispersed; S22: Stir continuously for 30 min in dark conditions to reach adsorption-desorption equilibrium; S23: A xenon lamp and a cutoff filter were used as the light source, and a distance of 10 cm was maintained between the light source and the reactor. All reaction temperatures were maintained at 25°C for photocatalysis.

4. The method for degrading RhB by synthesizing P-doped tubular carbon nitride driven by photocatalytic activation of PMS according to claim 3, characterized in that: In step S23, after turning on the xenon lamp, a certain amount of PMS was added, 2 mL of the catalyst suspension was extracted every 3 minutes, and the photocatalyst was removed through a 0.22 μm filter head.

5. The method for degrading RhB by synthesizing P-doped tubular carbon nitride driven by photocatalytic activation of PMS according to claim 1, characterized in that: In step S3, photocatalytically activated PMS is used to degrade RhB, and the steps are as follows: RhB was degraded by PMS with different capacities.

6. The method for degrading RhB by synthesizing P-doped tubular carbon nitride driven by photocatalytic activation of PMS according to any one of claims 1 to 5, characterized in that: In the PMS-assisted photocatalytic system, SO4 - 、h + 、O2 - , 1 Both O2 and ·OH participate in the degradation of RhB. - Plays a major role, and 1 O2, OH, h + and SO4 - Play a minor role; With the addition of PMS, the free radicals exhibited higher EPR signals and generated more ROSs, which improved the efficiency of photocatalytic degradation of RhB.

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