Preparation method and application of PVP-doped induced high-crystalline carbon nitride

Abstract

This invention provides a method for preparing PVP-doped induced highly crystalline carbon nitride. Urea is calcined at 450–650°C for 2–6 hours to obtain carbon nitride. The carbon nitride and PVP are then fully dispersed and dried in ethanol, followed by calcination at 300–500°C for 1–5 hours to obtain highly crystalline carbon nitride. Calcination selectively breaks the hydrogen bonds of carbon nitride without introducing additional elements, resulting in highly crystalline carbon nitride that can be used as a highly efficient photo-Fenton material for treating complex organic wastewater. This provides methodological support for subsequent large-scale production. PVP-doped induced highly crystalline carbon nitride can selectively remove strongly hydrophilic pollutants from complex wastewater and exhibits good anti-interference performance against both anionic and aqueous matrices.

Description

Technical Field

[0001] This invention belongs to the field of optical Fenton technology, specifically relating to a method for preparing and applying PVP-doped highly crystalline carbon nitride. Background Technology

[0002] With industrial development, wastewater discharge has increased year by year. This wastewater contains various highly toxic and inhibitory organic pollutants, posing significant safety hazards to human health and ecosystems. Persulfate photo-Fenton technology based on non-metallic semiconductor materials, with its strong oxidizing power and wide pH applicability, has been widely applied in organic wastewater treatment. Among these, carbon nitride-based persulfate photo-Fenton technology has attracted considerable attention due to the ability of the Lewis acid nitrogen sites of carbon nitride to adsorb and extend the O / O bonds of persulfate, thereby rapidly improving its activation efficiency. There are two main activation mechanisms for persulfate: free radical activation and non-free radical activation. Non-free radical activation exhibits strong resistance to water matrix interference and has significant advantages in the selective removal of organic pollutants from wastewater. However, non-free radical activation of persulfate is often accompanied by free radical activation, which produces highly oxidizing SO4. ·- The presence of ·OH groups makes persulfate-based photo-Fenton systems highly susceptible to becoming radical-dominated oxidation systems. Therefore, there is an urgent need to develop methods for the targeted construction of non-radical oxidation systems that selectively remove organic pollutants.

[0003] Surface-mediated electron transport is considered an efficient non-radical reaction. Studies have shown that increasing the proportion of surface-mediated electron transport pathways improves pollutant removal efficiency. Previous research has indicated a close relationship between persulfate adsorption and surface-mediated electron transport, with crystallinity closely related to adsorption energy. Therefore, improving the crystallinity of carbon nitride is beneficial for developing selective photo-Fenton systems dominated by surface-mediated electron transport. However, carbon nitride prepared by traditional methods such as thermal polymerization, solid-phase chemical methods, electrochemical deposition, and solvothermal methods generally suffers from low crystallinity.

[0004] In recent years, some researchers have used high-temperature calcination methods involving the blending of NaCl, LiCl / KCl, or NaNO3 / KNO3 molten salts with carbon / nitrogen precursors (urea, melamine, thiourea, dicyandiamine) to improve the crystallinity of carbon nitride (Appl. Catal. B: Environ. 2024, 342, 123340, CN116920906A, CN113318765B, CN110124719A, CN115254164A, CN116605850A, CN116920906A). However, this method is cumbersome and causes secondary pollution. Other researchers have used non-metallic doping such as boron (B) and phosphorus (P) to selectively disrupt the hydrogen bonds formed by NH / NH2 within the carbon nitride framework, thereby improving the crystallinity of carbon nitride (ACS. Appl. Mater. Interf. 2019, 11, 17341-17349). However, the addition of non-metallic materials can easily disrupt the original monomeric structure of carbon nitride, thereby altering its properties.

[0005] Polyvinylpyrrolidone (PVP) contains abundant carbon-based functional groups. In-situ doping with PVP during the preparation of carbon nitride can achieve a simple and environmentally friendly preparation of highly crystalline carbon nitride without introducing additional elements to disrupt its structure. Currently, although there are studies utilizing PVP to dope carbon nitride, these studies primarily utilize the dispersion characteristics of PVP to regulate the morphology of chromium oxide supported on carbon nitride using melamine as a precursor, thereby improving the denitrification performance of the catalyst (CN111229278A).

[0006] Currently, methods for preparing highly crystalline carbon nitride suffer from problems such as cumbersome operation, secondary pollution, and structural damage. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing highly crystalline carbon nitride induced by PVP doping. This method is simple to operate and environmentally friendly without introducing additional elements to destroy the carbon nitride structure. It constructs a persulfate photo-Fenton system dominated by surface-mediated electron transport, which can efficiently and selectively remove organic pollutants from complex wastewater.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing PVP-doped highly crystalline carbon nitride involves calcining urea at 450–650°C for 2–6 hours to obtain carbon nitride, and then dispersing and drying the carbon nitride and PVP in ethanol, followed by calcination at 300–500°C for 1–5 hours to obtain highly crystalline carbon nitride.

[0010] As a more preferred technical solution of the present invention, the mass ratio of PVP to carbon nitride is 0.005:100-0.05:100.

[0011] As a more preferred technical solution of the present invention, the mass ratio of PVP to carbon nitride is 0.03:100.

[0012] As a preferred technical solution of the present invention, the high-temperature calcination temperature of urea is 550°C and the time is 4 hours.

[0013] As a preferred technical solution of the present invention, the high-temperature calcination temperature of carbon nitride and PVP is 400°C and the time is 3 hours.

[0014] Another object of this invention is to provide the application of the aforementioned highly crystalline carbon nitride in photo-selective Fenton removal of organic pollutants in water. The organic pollutants are one or more of tetracycline hydrochloride, 4-chlorophenol, bisphenol A, atrazine, sulfamethoxazole, and carbamazepine.

[0015] Another objective of this invention is to provide the application of the aforementioned highly crystalline carbon nitride in photo-Fenton removal of tetracycline hydrochloride from water, wherein the dosage of the highly crystalline carbon nitride is 0.1–0.4 g / L.

[0016] Another objective of this invention is to provide the application of the aforementioned highly crystalline carbon nitride in the removal of organic pollutants from water using a photo-based Fenton cycle, wherein the dosage of the highly crystalline carbon nitride is 0.1–0.4 g / L.

[0017] Another objective of this invention is to provide the application of the aforementioned highly crystalline carbon nitride in the removal of tetracycline hydrochloride from water using a photo-based Fenton cycle, wherein the dosage of the highly crystalline carbon nitride is 0.1–0.4 g / L.

[0018] The beneficial effects are as follows:

[0019] The preparation method provided by this invention is simple to operate, environmentally friendly, and highly reproducible. It utilizes PVP to regulate carbon-hydrogen bonds in nitride to enhance crystallinity. The raw materials are only carbon-containing PVP and urea, meaning that calcination selectively breaks carbon-hydrogen bonds in nitride without introducing additional elements, thus preparing highly crystalline carbon nitride. This method is suitable for mass production and provides methodological support for the subsequent large-scale preparation of photo-Fenton materials for the efficient treatment of complex organic wastewater. The induced highly crystalline carbon nitride prepared can selectively remove strongly hydrophilic pollutants from complex wastewater, including anions (SO42-). 2- NO 3- and Cl - Both the water matrix (such as tap water and secondary effluent) and the water matrix (such as tap water and secondary effluent) have good anti-interference performance. Attached Figure Description

[0020] Figure 1 The morphology of 3PVP / CN in Example 3 and CN in Comparative Example 1 is characterized, where a is a transmission electron microscope image and b is a high-power transmission electron microscope (HRTEM) image.

[0021] Figure 2 The X-ray diffraction (XRD) patterns of PVP / CN in Examples 1-4 and CN in Comparative Example 1 are shown.

[0022] Figure 3 Fourier transform infrared (FT-IR) spectra of PVP / CN in Examples 1-4 and CN in Comparative Example 1;

[0023] Figure 4 X-ray photoelectron spectroscopy (XPS) of PVP / CN in Examples 1-4 and CN in Comparative Example 1;

[0024] Figure 5 The electron spin resonance (EPR) spectra of PVP / CN in Examples 1-4 and CN in Comparative Example 1 are shown.

[0025] Figure 6 The UV-Vis diffuse reflectance spectra (UV-visDRS) of PVP / CN in Examples 1-4 and CN in Comparative Example 1 are shown.

[0026] Figure 7 The efficiency of CN-based Fenton photochemical ion removal of tetracycline hydrochloride in comparative examples 1-5;

[0027] Figure 8 The efficiency of PVP / CN-based Fenton removal of tetracycline hydrochloride in Examples 3, 5, 6, 7 and 8;

[0028] Figure 9 The efficiency of PVP / CN in Examples 1-4 and CN photo-Fenton in Comparative Example 1 in removing tetracycline hydrochloride;

[0029] Figure 10 The total organic carbon (TOC) removal efficiency of PVP / CN in Examples 1-4 and CN photo-Fenton in Comparative Example 1 is compared with that of tetracycline hydrochloride.

[0030] Figure 11 Identification of major active species of tetracycline hydrochloride removed from different systems, 3PVP / CN in Example 3 and CN in Comparative Example 1;

[0031] Figure 12 The efficiency of photo-based Fenton removal of tetracycline hydrochloride under different 3PVP / CN dosage conditions in Example 3;

[0032] Figure 13 Example 3 shows the efficiency of 3PVP / CN photo-Fenton photoremoval of tetracycline hydrochloride at different concentrations.

[0033] Figure 14 Example 3 shows the photo-Fenton removal efficiency of tetracycline hydrochloride using 3PVP / CN under different anion conditions;

[0034] Figure 15 The efficiency of photo-Fenton removal of tetracycline hydrochloride by 3PVP / CN under different actual water matrix conditions in Example 3;

[0035] Figure 16 The efficiency of 3PVP / CN in Example 3 and CN photo-Fenton in Comparative Example 1 in removing different organic pollutants;

[0036] Figure 17 The efficiency of 3PVP / CN cyclic light-based Fenton-like light in removing tetracycline hydrochloride in Example 3;

[0037] Figure 18 XRD patterns and FT-IR patterns before and after 3PVP / CN removal in Example 3. Detailed Implementation

[0038] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0040] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0041] Comparative Example 1

[0042] 1.35g of urea was placed in a covered crucible and then placed in a tube furnace. The temperature was increased at a rate of 2.5℃ / min, and the calcination was carried out at 550℃ for 4 hours. After cooling in a muffle furnace, carbon nitride, denoted as CN, was obtained.

[0043] Comparative Example 2

[0044] 1.35g of urea was placed in a covered crucible and then placed in a tube furnace. The temperature was increased at a rate of 2.5℃ / min, and the calcination was carried out at 550℃ for 2 hours. After cooling in a muffle furnace, carbon nitride was obtained, denoted as CN-2h.

[0045] Comparative Example 3

[0046] 1.35g of urea was placed in a covered crucible and then placed in a tube furnace. The temperature was increased at a rate of 2.5℃ / min, and the calcination was carried out at 550℃ for 6 hours. After cooling in a muffle furnace, carbon nitride was obtained, denoted as CN-6h.

[0047] Comparative Example 4

[0048] 1.35g of urea was placed in a covered crucible and then placed in a tube furnace. The temperature was increased at a rate of 2.5℃ / min, and the calcination was carried out at 450℃ for 4 hours. After cooling in a muffle furnace, carbon nitride was obtained, denoted as CN-450℃.

[0049] Comparative Example 5

[0050] 1.35g of urea was placed in a covered crucible and then placed in a tube furnace. The temperature was increased at a rate of 2.5℃ / min, and the calcination was carried out at 650℃ for 4 hours. After cooling in the muffle furnace, carbon nitride was obtained, denoted as CN-650℃.

[0051] Example 1

[0052] 0.068 mg of PVP (the mass ratio of PVP to CN in Comparative Example 1 was 0.005%) and 1.35 g of CN were dispersed in 50.0 mL of ethylene glycol. After stirring for 24 h, the mixture was dried at 60 °C for 12 h, then placed in a covered crucible and calcined at 400 °C for 3 h at a rate of 3.0 °C / min. After cooling in a muffle furnace, carbon nitride with different degrees of crystallinity was obtained, denoted as 0.5 PVP / CN.

[0053] Example 2

[0054] 0.136 mg of PVP (the mass ratio of PVP to CN in Comparative Example 1 was 0.01%) and 1.35 g of CN were dispersed in 50.0 mL of ethylene glycol. After stirring for 24 h, the mixture was dried at 60 °C for 12 h, then placed in a covered crucible and calcined at 400 °C for 3 h at a rate of 3.0 °C / min. After cooling in a muffle furnace, carbon nitride with different degrees of crystallinity was obtained, denoted as 1 PVP / CN.

[0055] Example 3

[0056] 0.408 mg of PVP (the mass ratio of PVP to CN in Comparative Example 1 was 0.03%) and 1.35 g of CN were dispersed in 50.0 mL of ethylene glycol. After stirring for 24 h, the mixture was dried at 60 °C for 12 h, then placed in a covered crucible and calcined at 400 °C for 3 h at a rate of 3.0 °C / min. After cooling in a muffle furnace, carbon nitride with different degrees of crystallinity was obtained, denoted as 3PVP / CN.

[0057] Example 4

[0058] 0.680 mg of PVP (PVP to CN of Comparative Example 1, mass ratio of 0.05%) and 1.35 g of CN were dispersed in 50.0 mL of ethylene glycol. After stirring for 24 hours, the mixture was dried at 60 °C for 12 hours, then placed in a covered crucible and calcined at 400 °C for 3 hours at a rate of 3.0 °C / min. After cooling in a muffle furnace, carbon nitride with different degrees of crystallinity was obtained, denoted as 5PVP / CN.

[0059] Example 5

[0060] 0.680 mg of PVP (the mass ratio of PVP to CN in Comparative Example 1 was 0.03%) and 1.35 g of CN were dispersed in 50.0 mL of ethylene glycol. After stirring for 24 hours, the mixture was dried at 60 °C for 12 hours, then placed in a covered crucible and calcined at 300 °C for 3 hours at a rate of 3.0 °C / min. After cooling in a muffle furnace, carbon nitride with different degrees of crystallinity was obtained, denoted as 3PVP / CN-300 °C.

[0061] Example 6

[0062] 0.680 mg PVP (PVP to CN of Comparative Example 1, mass ratio of 0.03%) and 1.35 g CN were dispersed in 50.0 mL of ethylene glycol. After stirring for 24 hours, the mixture was dried at 60 °C for 12 hours, then placed in a covered crucible and calcined at 500 °C for 3 hours at a rate of 3.0 °C / min. After cooling in a muffle furnace, carbon nitride with different degrees of crystallinity was obtained, denoted as 3PVP / CN-500 °C.

[0063] Example 7

[0064] 0.408 mg PVP (the mass ratio of PVP to CN in Comparative Example 1 was 0.03%) and 1.35 g CN were dispersed in 50.0 mL of ethylene glycol. After stirring for 24 h, the mixture was dried at 60 °C for 12 h, then placed in a covered crucible and calcined at 400 °C for 1 h at a rate of 3.0 °C / min. After cooling in a muffle furnace, carbon nitride with different degrees of crystallinity was obtained, denoted as 3PVP / CN⁻¹h.

[0065] Example 8

[0066] 0.408 mg PVP (the mass ratio of PVP to CN in Comparative Example 1 was 0.03%) and 1.35 g CN were dispersed in 50.0 mL of ethylene glycol. After stirring for 24 h, the mixture was dried at 60 °C for 12 h, then placed in a covered crucible and calcined at 400 °C for 5 h at a rate of 3.0 °C / min. After cooling in a muffle furnace, carbon nitride with different degrees of crystallinity was obtained, denoted as 3PVP / CN-5h.

[0067] like Figure 1 As shown, in the morphological characterization of 3PVP / CN in Example 3 and CN in Comparative Example 1, a and b are transmission electron microscopy (TEM) and high-magnification transmission electron microscopy (HRTEM) images of 3PVP / CN in Example 3 and CN in Comparative Example 1, respectively. The morphology of 3PVP / CN in Example 3 did not change significantly compared to CN in Comparative Example 1; both are micron-scale ultrathin nanosheet structures. No lattice spacing was observed in the HRTEM image of CN in Comparative Example 1, but a crystal spacing (0.32 nm) corresponding to the carbon nitride (002) crystal plane was present in the HRTEM image of 3PVP / CN in Example 3. These results indicate that PVP doping successfully induced an increase in the crystallinity of CN.

[0068] XRD comparison of PVP / CN in Examples 1 to 4 and CN in Comparative Example 1: Figure 2 As shown, the diffraction peaks at 13.0° and 27.5° correspond to the (100) and (002) crystal planes of PVP / CN in Examples 1 to 4 and CN in Comparative Example 1, respectively. With increasing PVP doping concentration, the intensity of the two diffraction peaks initially increases and then decreases. The crystallinity of Examples 1 to 4 and Comparative Example 1 are 0.64, 0.65, 0.72, 0.79, and 0.68, respectively, indicating that PVP can improve the crystallinity of CN, but the doping ratio has an impact on crystallinity.

[0069] FT-IR comparisons of Examples 1 to 4 and Comparative Example 1 Figure 3 As shown, the PVP / CN of Examples 1 to 4 and the CN of Comparative Example 1 all exhibit three infrared absorption peaks. The peak is located at 809 cm⁻¹. -1 The peak value is caused by the bending vibration of the s-triazine unit. It is located at 1211-1647 cm⁻¹. -1 The broad peaks originate from the C=N and CN heterocyclic framework. They are located at 3047-3400 cm⁻¹. -1 The peaks correspond to -NH2 and =NH bonds. As the PVP doping concentration increases from 0 to 0.05%, the infrared peaks of -NH2 and =NH shift from 3414 cm⁻¹ to 3270 cm⁻¹. -1 This indicates that the hydrogen bonds formed by -NH2 and =NH in carbon nitride are broken.

[0070] XPS comparison of PVP / CN in Examples 1 to 4 and CN in Comparative Example 1 Figure 4As shown in the figure. Figures a and b represent the C1s XPS and N1s XPS of Examples 1 to 4 and Comparative Example 1, respectively. Peaks with binding energies of 288.1 and 284.5 eV correspond to NC=N and CC / C=C, respectively. Peaks with binding energies of 401.0, 399.7, and 398.4 eV correspond to CNH / NC...N, N-(C)3, and CN=C, respectively. The peak area ratio (0.57) of CN in Example 43 (PVP / CN) is higher than that of CN in Example 1, indicating that carbon was successfully incorporated into the CN monomer.

[0071] Electron spin resonance (EPR) comparisons of Examples 1 to 4 and Comparative Example 1: Figure 5 As shown, an EPR signal with a g value of 2.003 was observed, and the EPR signal increased with increasing PVP doping concentration. This was attributed to the fact that after PVP doping disrupted hydrogen bonds, the electron density of the carbon and nitrogen sites in CN was reconfigured, resulting in a large accumulation of unpaired electrons at the nitrogen sites.

[0072] The UV-Vis diffuse reflectance spectra (UV-vis DRS) of PVP / CN in Examples 1 to 4 and CN in Comparative Example 1 are compared. Figure 6 As shown, the absorption band edge of Example 1 CN is located at 410.6 nm. As the PVP doping concentration increases from 0.005% to 0.5%, the absorption band edge of PVP / CN shifts from 421.8 nm to 426.1 nm. Compared to Example 1 and Comparative Example 1, the light absorption efficiency of PVP / CN in Examples 2-4 is significantly improved in the visible light region, with Example 3 PVP / CN exhibiting the strongest absorption of visible light. The above structures demonstrate that PVP doping, by disrupting hydrogen bonds, enhances the light absorption efficiency.

[0073] Application Example 1

[0074] Applications of PVP / CN in Examples 1-8 and CN photo-Fenton in Comparative Examples 1-5 for the removal of tetracycline hydrochloride

[0075] First, 0.01 g of the catalysts prepared in Examples 1-8 and Comparative Examples 1-5 were placed in 20 mL of tetracycline hydrochloride aqueous solution (TCH, 0.04 mM). Then, PMS and visible light were introduced to activate the reaction. Visible light was provided by a 300.0 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) with a filter for wavelengths less than 420 nm. The light intensity was 122.9 mW / cm². 2 (Lighting area = 3.34cm) 2 During the reaction, 2.0 mL of sample was collected every 10 minutes and filtered through a 0.22 μm filter membrane, followed by the addition of excess sodium thiosulfate (1 mM Na2S2O3). The concentration of tetracycline hydrochloride was determined using an Agilent 1260 high-performance liquid chromatography (HPLC) system.

[0076] Application Example 2

[0077] Application of 3PVP / CN photo-based Fenton selective removal of different organic pollutants

[0078] First, 0.01 g of the 3PVP / CN catalyst from Example 3 was placed in 20 mL of an aqueous solution containing tetracycline hydrochloride (TC H, 0.04 mM), 4-chlorophenol (4-CP, 0.04 mM), bisphenol A (BPA, 0.04 mM), atrazine (ATZ, 0.04 mM), sulfamethoxazole (SMX, 0.04 mM), and carbamazepine (CBZ, 0.04 mM). Then, PMS and visible light were introduced to activate the reaction. Visible light was provided by a 300.0 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) with a filter for wavelengths less than 420 nm. The light intensity was 122.9 mW / cm². 2 (Lighting area = 3.34cm) 2 During the reaction, 2.0 mL of sample was collected every 10 minutes and filtered through a 0.22 μm filter membrane, followed by the addition of 1 mM Na₂S₂O₃. The concentrations of different organic pollutants were determined using an Agilent 1260 high-performance liquid chromatograph.

[0079] Application Example 3

[0080] Application of 3PVP / CN circulating light-based Fenton removal of TCH

[0081] First, 0.01 g of the 3PVP / CN catalyst from Example 3 was placed in 20 mM of TCH aqueous solution (TCH, 0.04 mM). Then, PMS and visible light were introduced to activate the reaction. Visible light was provided by a 300.0 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) with a filter for wavelengths less than 420 nm. The light intensity was 122.9 mW / cm². 2 (Lighting area = 3.34cm) 2 During the reaction, 2.0 mL of sample was collected every 10 minutes and filtered through a 0.22 μm filter membrane, followed by the addition of 1 mM Na₂S₂O₃. After reacting for 1 hour, the sample was centrifuged and dried for the next removal cycle. This procedure was repeated four times, and the TCH concentration for each cycle was determined using an Agilent 1260 high-performance liquid chromatograph.

[0082] The efficiency of CN-type Fenton in removing TCH in Comparative Examples 1-5 is as follows: Figure 7As shown, the efficiency of CN photo-Fenton in removing TCH in Comparative Example 1 reached 72.4%. Compared with CN in Comparative Example 1, the efficiency of CN-2h (59.3%) in Comparative Example 2, CN-6h (66.4%) in Comparative Example 3, and CN-450℃ (70.4%) and CN-650℃ in Comparative Example 3 decreased to 60.1%.

[0083] The efficiency of TCH removal by PVP / CN optical Fenton in Examples 3, 5, 6, 7 and 8 is as follows: Figure 8 As shown. The TCH removal efficiency of 3PVP / CN in Example 3 was 90.0%, which was higher than that of 3PVP / CN at 300℃ (78.5%) in Example 5, 3PVP / CN at 500℃ (80.5%) in Example 6, 3PVP / CN at 1h (82.1%) in Example 7 and 3PVP / CN at 5h (84.2%) in Example 8.

[0084] The efficiency of TCH removal in PVP / CN of Examples 1-4 and CN of Comparative Example 1 is as follows: Figure 9 As shown. After 1 hour of photo-Fenton reaction, the TCH removal efficiency of CN in Comparative Example 1 was 72.4%. Compared with the removal efficiency of CN in Comparative Example 1, the TCH removal efficiency of PVP / CN in Examples 1 to 4 was improved. However, with the increase of PVP doping amount, the removal efficiency showed a trend of first increasing and then decreasing. This result indicates that carbon nitride prepared by the method of the present invention is helpful for the removal of tetracycline hydrochloride, but excessive PVP doping blocks active sites, and the removal efficiency decreases.

[0085] The TOC efficiencies of PVP / CN in Examples 1-4 and CN optical Fenton removal in Comparative Example 1 are as follows: Figure 10 As shown, the TOC removal efficiency of CN-based optical Fenton in Comparative Example 1 was 32.3%. Compared to CN in Comparative Example 1, the TOC removal efficiency of 0.5 PVP / CN in Example 1 was significantly improved to 58.6%, indicating that PVP doping accelerated the conversion of large TCH molecules into smaller molecules by CN. With increasing PVP doping concentration, the TOC removal efficiency showed a trend of first increasing and then decreasing, with the highest TOC removal rate observed in 3 PVP / CN in Example 3, consistent with the TCH removal trend.

[0086] The identification results of the main active species for TCH removal in different systems, 3PVP / CN in Example 3 and CN in Comparative Example 1, are as follows: Figure 11 As shown. In the CN / PMS system of Comparative Example 1, ·OH, 1 O2 and SO4 - The contribution rates were 51.1%, 27.4%, and 21.5%, respectively, indicating that ·OH is the main active species. In Comparative Example 1, CN, in the photo-Fenton system, besides ·OH, 1O2 and SO4 - This also produced h + , O2 - and e - In Example 3, the 3PVP / CN matrix in the Fenton-like system showed a surface-mediated electron transport path contribution rate of 73.5%, significantly higher than that of ·OH (7.4%). 1 O2 (15.4%) and SO4 - The contribution rate was 3.7%. In the optical Fenton system, the 3PVP / CN of Example 3 showed a surface-mediated electron transport contribution rate of up to 63.3%, which is the main reaction pathway.

[0087] The efficiency of photo-Fenton removal of TCH under different dosage conditions of 3PVP / CN in Example 3 is as follows: Figure 12 As shown, when the dosage of 3PVP / CN in Example 3 was 0.1 g / L, the TCH removal efficiency was 76.8%. As the dosage increased from 0.1 g / L to 0.4 g / L, the TCH removal efficiency first increased to 90.0% and then decreased to 82.6%. Appropriately increasing the catalyst can enhance the active sites and accelerate the removal of pollutants, but excessive catalyst will compete for the adsorption of organic pollutants, leading to a decrease in TCH removal efficiency.

[0088] Example 3: 3PVP / CN photo-Fenton removal efficiency of TCH at different concentrations. Figure 13 As shown, in Example 3, the 3PVP / CN achieved a degradation rate of 90.0% for 0.02, 0.03, and even 0.04 mM TCH in a photo-Fenton system within 1 hour. When the TCH concentration was increased to 0.05 mM, the degradation efficiency of 3PVP / CN in the photo-Fenton system also reached 81.3% after 1 hour.

[0089] Example 3: The photo-Fenton removal efficiency of TCH by 3PVP / CN under different anionic and humic acid conditions is as follows: Figure 14 As shown. Example 3's 3PVP / CN in SO4 2- NO3 - and Cl - The removal efficiencies of TCH in the presence of anions and humic acid reached 88.2%, 85.7%, and 85.4%, respectively. Compared with the conditions without anions and humic acid, the removal efficiency of TCH did not change significantly.

[0090] The photo-Fenton removal efficiency of TCH by 3PVP / CN in Example 3 and CN in Comparative Example 1 under different actual water matrix conditions is as follows: Figure 15As shown. Compared to the TCH removal efficiency (38.65%) in deionized water matrix, the TCH removal efficiency of CN in Comparative Example 1 was reduced to 32.6% and 31.8% in tap water and secondary effluent, respectively. The 3PVP / CN in Example 3 achieved TCH removal efficiencies of 90.0%, 88.4%, and 87.6% in deionized water, tap water, and secondary effluent, respectively, indicating that the photo-Fenton system based on 3PVP / CN in Example 3 has anti-interference performance.

[0091] The removal efficiencies of 3PVP / CN in Example 3 and CN photo-Fenton in Comparative Example 1 for different organic pollutants are as follows: Figure 16 As shown. In Comparative Example 1, the CN removed 6.51%, 0.73%, 5.05%, 9.67%, and 4.16% of 4-CP, BPA, ATZ, SMX, and CBZ in the optical Fenton system, respectively. Compared to the CN in Comparative Example 1, the 3PVP / CN in Example 3 showed improved overall efficiency and strong selectivity in removing 4-CP (27.55%), BPA (43.77%), ATZ (15.0%), SMX (96.35%), and CBZ (16.20%) in the optical Fenton system.

[0092] Example 3 shows the efficiency of 3PVP / CN cyclic optical Fenton-like TCH removal as follows: Figure 17 As shown, after four cycles, the TCH degradation efficiency of the 3PVP / CN in Example 3 decreased by only 2.9%, indicating that the 3PVP / CN in Example 3 has good cyclic degradation performance.

[0093] The XRD and FT-IR spectra of the 3PVP / CN reaction before and after Example 3 are as follows: Figure 18 As shown, the XRD and FT-IR spectra of 3PVP / CN before and after the reaction in Example 3 remained essentially unchanged, indicating that 3PVP / CN in Example 3 has a stable phase structure and functional group structure.

[0094] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing PVP-doped induced highly crystalline carbon nitride, characterized in that: urea is calcined at 450~650℃ for 2~6h to obtain carbon nitride; carbon nitride and PVP are fully dispersed in ethylene glycol; after drying, they are calcined at 300~500℃ for 1~5h to obtain highly crystalline carbon nitride; wherein the mass ratio of PVP to carbon nitride is 0.03:

100.

2. The method for preparing PVP-doped induced highly crystalline carbon nitride according to claim 1, wherein the urea is calcined at a temperature of 550°C for 4 hours.

3. The method for preparing PVP-doped induced highly crystalline carbon nitride according to claim 1, wherein the carbon nitride and PVP are calcined at a temperature of 400°C for 3 hours.

4. The application of PVP-doped induced highly crystalline carbon nitride prepared by the method of claim 1 in the photo-Fenton selective removal of organic pollutants in water.

5. The application of PVP-doped induced highly crystalline carbon nitride prepared by the method of claim 1 in the removal of organic pollutants from water using a photo-based Fenton cycle.

6. The application according to claim 4 or 5, characterized in that: The organic pollutants include one or more of tetracycline hydrochloride, 4-chlorophenol, bisphenol A, atrazine, sulfamethoxazole, and carbamazepine.

7. The application according to claim 6, characterized in that: The dosage of the highly crystalline carbon nitride is 0.1~0.4 g / L.

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