Water treatment composition and application

Abstract

The invention belongs to the technical field of water treatment, and discloses a water treatment composition and application. A water treatment composition includes modified graphite phase carbon nitride having high crystallinity and low defect density, and monochloramine. According to the method, the conventional thought of purely pursuing high specific surface area is abandoned, and the modified graphite phase carbon nitride with high crystallinity and low defect density is prepared by creatively controlling the low flow rate of inert gas in the pyrolysis process. The highly ordered crystal structure and the pure chemical skeleton bring a breakthrough in intrinsic photoelectric properties, and experiments prove that the contribution of the improvement of the crystallinity to the properties is far greater than the improvement of the pure specific surface area. Due to the structural stability brought by high crystallinity, the modified graphite phase carbon nitride can keep high catalytic activity in recycling. Meanwhile, the water treatment composition shows efficient degradation capacity on various types of typical organic pollutants, shows good broad-spectrum applicability, and has a wide practical application prospect.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and more specifically to water treatment compositions and their applications. Background Technology

[0002] With the acceleration of industrialization, the treatment of recalcitrant organic pollutants (such as dyes, antibiotics, and endocrine disruptors) in water bodies has become a major environmental challenge. Advanced oxidation technologies (AORs) have attracted much attention due to their ability to generate highly reactive oxidizing species. Among them, AOR processes based on monochloramine (NH₂Cl) activation show potential for the selective degradation of specific pollutants due to their ability to generate highly selective and long-lived reactive nitrogen species. However, the oxidation capacity of NH₂Cl itself is limited, and its activation efficiency is highly dependent on the development of efficient catalysts.

[0003] Graphitic carbon nitride (g-C3N4), as a non-metallic, visible-light-responsive semiconductor catalyst, has been widely studied due to its good chemical stability and low cost. To improve its catalytic performance, current technologies primarily focus on modification. Common modification strategies include morphology control, elemental doping, and the construction of heterojunctions.

[0004] However, the inventors found that the existing technology still has the following limitations: (1) Single modification target: its improvement mainly focuses on physical morphology (specific surface area and porosity), while insufficient attention is paid to the crystallinity and chemical defect density of the crystal structure that determine the intrinsic photoelectric properties of g-C3N4. High specific surface area is often accompanied by more grain boundaries and surface defects, which may become recombination centers of photogenerated electron-hole pairs, thus inhibiting the effective separation and transport of charges. (2) Unclear synergistic mechanism: when g-C3N4 with this kind of physical modification is used for NH2Cl activation, the synergistic catalytic mechanism between the two is unclear, the performance improvement is limited, and the problem of single NH2Cl activation path and low efficiency has not been solved. (3) Questionable long-term effect: materials with many structural defects have poor stability in long-term photocatalysis and are prone to photocorrosion or deactivation.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The present invention aims to solve at least any of the above-mentioned technical problems, and provides a water treatment composition and its application.

[0007] To achieve the above objectives, the first technical solution adopted by the present invention is as follows: A water treatment composition comprising: modified graphitic carbon nitride having high crystallinity and low defect density, and monochloramine.

[0008] Preferably, the high crystallinity is manifested in that the full width at half maximum (FWHM) of the diffraction peaks corresponding to the (002) crystal plane in the X-ray diffraction pattern is less than 1.0°; The low defect density is characterized by an EPR signal intensity of no more than 0.08 au, and in X-ray photoelectron spectroscopy, the area ratio of the NC=N bond peak in the C1s spectrum is no less than 60%, and the area ratio of the peak corresponding to the edge amino group in the N1s spectrum is less than 10%.

[0009] Preferably, the concentrations of each component are: 0.3-0.8 g / L of modified graphitic carbon nitride and 5-20 mgCl2 / L of monochloramine.

[0010] Preferably, the preparation method of modified graphitic carbon nitride includes: mixing melamine with ammonium chloride and then pyrolyzing it under an inert atmosphere, wherein the volumetric flow rate of the inert gas is <5 L / h throughout the pyrolysis process.

[0011] Preferably, the weight ratio of melamine to ammonium chloride is 1:(0.1-1.0).

[0012] Preferably, the pyrolysis is performed by heating to 520-580°C at a heating rate of 2-5°C / min, and then pyrolyzing at this temperature for 3.4-4.5 hours. After the reaction is completed, the temperature is cooled to room temperature.

[0013] Preferably, it also includes selenite, the concentration of which, by mass of Se, is 0.1-5 mg / L.

[0014] Preferably, the selenite is selected from at least one of sodium selenite, potassium selenite, or ammonium selenite.

[0015] The second technical solution adopted in this invention is: Application of any of the above-described water treatment compositions in the photocatalytic degradation of organic pollutants in water.

[0016] Preferably, the organic pollutant includes at least one of dye compounds, antibiotic compounds, endocrine disruptors, or pesticide residues.

[0017] Preferably, the specific method of the application includes: adding the water treatment composition to the water body to be treated, and reacting it for 10-60 minutes under visible light irradiation with a wavelength of 420-430 nm and a light intensity of 400-1000 W / m².

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention abandons the conventional approach of simply pursuing high specific surface area. It innovatively utilizes a key process—controlling the low flow rate (<5 L / h) of inert gas during pyrolysis—to prepare modified graphitic carbon nitride with high crystallinity and low defect density. This highly ordered crystal structure and pure chemical framework lead to a breakthrough in intrinsic photoelectric properties. Experiments have demonstrated that increased crystallinity contributes far more to performance than simply increasing specific surface area. Thanks to the structural stability derived from high crystallinity, the modified graphitic carbon nitride of this invention maintains high catalytic activity during recycling. Furthermore, this water treatment composition exhibits highly efficient degradation capabilities against various types of typical organic pollutants (including cationic dyes, antibiotics, phenolic endocrine disruptors, etc.), demonstrating excellent broad applicability and promising prospects for practical applications. Attached Figure Description

[0019] Figure 1 SEM image of the modified graphitic carbon nitride prepared in Example 1; Figure 2 SEM image of unmodified graphitic carbon nitride in Comparative Example 6; Figure 3 XRD images of Example 1 and Comparative Example 6; Figure 4 FTIR images of Example 1 and Comparative Example 6; Figure 5 XPS full spectra of Example 1 and Comparative Example 6; Figure 6 The high-resolution XPS spectrum of C1s in Example 1; Figure 7 The high-resolution XPS spectrum of C1s in Comparative Example 6; Figure 8 The N1s high-resolution XPS spectrum of Example 1; Figure 9 The image shows the N1s high-resolution XPS spectrum of Comparative Example 6. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The first embodiment of the present invention provides a water treatment composition comprising: modified graphitic carbon nitride having high crystallinity and low defect density, and monochloramine.

[0022] One of the core components of the water treatment composition of this invention is modified graphitic carbon nitride with high crystallinity and low defect density. This structure limits and focuses on the intrinsic electronic structure quality of the material, which is the fundamental reason for its excellent photocatalytic performance. The loose nanosheet structure of the material is a natural manifestation and functional extension of this high-quality intrinsic structure in its external morphology. Together, they constitute a highly efficient and synergistic catalytic system.

[0023] High crystallinity refers to a high degree of long-range order in the atomic arrangement of a material and a complete crystal lattice. For the modified graphitic carbon nitride of this invention, the full width at half maximum (FWHM) of the X-ray diffraction peak corresponding to the (002) crystal plane is less than 1.0°, which is a direct quantitative indicator. High crystallinity means that photogenerated electrons and holes encounter less grain boundary scattering and defect trapping when transported within the material, thus exhibiting extremely high mobility and extremely low bulk recombination rate.

[0024] Low defect density refers to a material with a pure chemical framework and a very low number of non-ideal bonds (such as C-C bonds) and structural termination points (such as edge amino groups -NH2). Through XPS quantization, the modified graphitic carbon nitride of this invention requires the NC=N bond peak area to be no less than 60%, while the peak area corresponding to edge amino groups in the N1s spectrum is less than 10%. Low defect density ensures a longer lifetime for photogenerated carriers, and the material's band structure is more conducive to light absorption and charge separation. This is the chemical basis for achieving high quantum efficiency and stability.

[0025] To obtain the modified graphitic carbon nitride with the specific structure described above, the pyrolysis atmosphere during its preparation process needs to be controlled. Specifically, the preparation method of modified graphitic carbon nitride includes: mixing melamine with ammonium chloride and then pyrolyzing it under an inert atmosphere. Throughout the pyrolysis process, the volumetric flow rate of the inert gas needs to be controlled to be <5 L / h.

[0026] This preparation method uses melamine as a precursor and ammonium chloride as a dynamic gas template agent, and the two are mixed at a weight ratio of 1:(0.1-1.0), preferably 1:0.2. This ratio range can provide moderate and continuous gas release. The key to this preparation method is that the volumetric flow rate of the inert gas must be controlled at <5 L / h throughout the pyrolysis process.

[0027] As is known to those skilled in the art, pyrolysis of melamine as a precursor at 550-600°C for 2-4 hours under an inert atmosphere is the conventional process for preparing graphitic carbon nitride. However, based on the aforementioned conventional pyrolysis parameters, this invention has discovered through extensive experiments that strictly controlling the volumetric flow rate of the inert gas to below 5 L / h, preferably 2-4 L / h, throughout the entire pyrolysis process is key to obtaining modified graphitic carbon nitride with high crystallinity and low defect density.

[0028] In existing technologies, higher flow rates, such as 20-100 L / h, are typically used to quickly remove byproducts. However, this invention creates a quasi-static or high-concentration template atmosphere reaction environment through a low flow rate. Specifically, (1) Maintaining a high-concentration gas template: A low flow rate can slow down the discharge rate of NH3 and HCl (decomposition products of ammonium chloride), extending their residence time in the reaction zone. These gases can act as annealing and repair agents, effectively repairing structural defects generated during the condensation process of the precursor, promoting more orderly stacking of triazine ring units, thereby improving crystallinity. (2) Controlling reaction kinetics: Preventing ammonium chloride from decomposing rapidly due to excessive flow rate, which would lead to premature depletion of the gas template. A stable and continuous template atmosphere is conducive to the formation of a complete and uniform lamellar structure and inhibits the generation of impurities such as amorphous carbon, thereby reducing defect density. (3) Suppressing side reactions: A strictly inert environment can effectively prevent the oxidation of the carbon skeleton at high temperatures, reduce amorphous impurity carbon, and improve crystal purity. Through the aforementioned low-nitrogen gas flow rate process, while achieving high crystallinity and low defect density, the material naturally grows into loose two-dimensional nanosheets with a thickness of approximately 30-50 nm. This morphology is not an independently pursued goal, but rather an inevitable result of high-quality crystal growth in a confined two-dimensional direction and good exfoliation due to the gentle gas template effect. Therefore, the loose nanosheet structure can be regarded as a reliable morphological marker and accompanying characteristic of high-quality intrinsic structure. The core high crystallinity and low defect density solve the efficiency problem of charge generation and transport, ensuring that a sufficient number of highly active charge carriers can reach the material surface. The accompanying loose nanosheet structure solves the efficiency problem of reactant contact and mass transfer; its large specific surface area and open channels greatly promote the adsorption, diffusion, and contact probability of reactants (monochloramine, pollutants) with surface charges.

[0029] Existing technologies may also achieve a certain loose morphology, but their core is to sacrifice crystallinity and introduce defects in exchange for a high specific surface area. This invention, through process innovation, simultaneously obtains a beneficial loose nanosheet morphology while significantly improving crystallinity and greatly reducing defect density, achieving a unity of quality and quantity, thereby resulting in a leapfrog improvement in performance.

[0030] Another core component of the water treatment composition of this invention is monochloramine (NH2Cl). It is a key reactant in a highly efficient synergistic catalytic reaction with the aforementioned modified graphitic carbon nitride with a specific structure. The synergistic catalytic mechanism is as follows: Under visible light excitation, the highly crystalline, low-defect modified graphitic carbon nitride efficiently generates and separates photogenerated electrons and holes. These charge carriers rapidly migrate to the surface due to the excellent conductivity within the material. Simultaneously, the accompanying loose nanosheet structure provides abundant surface sites and open mass transfer channels, ensuring that monochloramine molecules can be fully adsorbed and approach these active sites. Subsequently, efficient dual-pathway activation occurs: a non-radical-dominated direct electron transfer pathway—photogenerated holes or electrons migrating to the surface directly undergo interfacial electron transfer with adsorbed NH2Cl, initiating N-Cl bond breaking and generating highly reactive nitrogen species (RNS); and a radical-involved indirect activation pathway—part of the electrons react with dissolved oxygen to generate superoxide radicals that activate monochloramine.

[0031] In some preferred embodiments, to achieve optimal treatment efficiency and economic benefits, the concentrations of each component in the water treatment composition are as follows: modified graphitic carbon nitride 0.3-0.8 g / L, and monochloramine 5-20 mg / L (based on Cl mass). This concentration range of modified graphitic carbon nitride ensures a sufficient density of catalytically active centers in the water body, while avoiding light-shielding effects and unnecessary cost increases due to excessively high concentrations. The monochloramine concentration range is matched to the catalyst dosage, providing sufficient activatable precursors to ensure complete reaction while effectively controlling byproduct formation and treatment costs.

[0032] In some preferred embodiments, the water treatment composition may be further incorporating selenite (such as sodium selenite, potassium selenite, ammonium selenite, etc.) to construct a more powerful ternary catalytic system and improve the water treatment effect.

[0033] The introduction of selenite (taking SeO3²⁻ as an example) adds a fourth-level synergistic effect on the basis of the original binary synergy: (1) SeO3²⁻ is an excellent electron acceptor, which can quickly capture photogenerated electrons migrating from the conduction band of modified graphitic carbon nitride, suppress the recombination of electron-hole pairs, and use more charge carriers for subsequent reactions, thereby improving quantum efficiency. (2) The intermediate-valence selenium active species (such as SeO2•⁻) generated by reduction can directly participate in the activation process of NH2Cl, promote the breaking of N-Cl bonds, and enrich the generation pathway and diversity of active nitrogen species (RNS). (3) Its adsorption will change the charge distribution and hydrophilicity / hydrophobicity of the catalyst surface, which may be more conducive to the enrichment and directional adsorption of NH2Cl molecules near the active site. (4) Selenium redox cycle (SeO3²⁻) 2- / Se 0 / SeO3 2- It can sustainably participate in the electron transport chain, effectively extending the long-term activity of the catalytic system.

[0034] The preferred concentration of selenite, calculated by mass of selenium (Se), is 0.1-5 mg / L. Significant performance improvements can be observed within this trace range; excessive addition not only diminishes the effectiveness but may also raise additional environmental concerns.

[0035] The second embodiment of the present invention provides the application of any of the water treatment compositions described herein in the photocatalytic degradation of organic pollutants in water.

[0036] The water treatment composition of this invention is specifically designed for the photocatalytic deep degradation of various stubborn organic pollutants in water. Based on the highly oxidizing reactive nitrogen species (RNS) it generates, this system exhibits excellent degradation capabilities for a variety of organic pollutants with different structures, including but not limited to: dye compounds (such as Rhodamine B, methylene blue), antibiotic compounds (such as tetracycline, sulfamethoxazole), endocrine disruptors (such as bisphenol A), and pesticide residues (such as atrazine). Its broad-spectrum nature stems from the high reactivity of RNS with electron-rich groups (such as aromatic rings, amino groups, and double bonds) in organic matter.

[0037] As a specific example, the application method is as follows: Add the calculated amount of modified graphitic carbon nitride powder to the water to be treated, and disperse it thoroughly by stirring or sonication. Subsequently, add a predetermined concentration of monochloramine solution and selenite solution (if used) sequentially or simultaneously, and mix thoroughly.

[0038] The photocatalytic reaction conditions are as follows: Light source: A visible light source with a dominant emission wavelength in the range of 420-430 nm (such as a specific wavelength LED lamp or a filtered xenon lamp). This wavelength band matches well with the semiconductor absorption edge of modified graphitic carbon nitride. Light intensity: Maintained at 400-1000 W / m². Appropriate light intensity is a prerequisite for ensuring sufficient photon flux to drive the photocatalytic reaction. Reaction time: Typically, 10-60 minutes is sufficient to achieve excellent removal efficiency (>90%) for most target pollutants. The specific time can be adjusted according to the complexity of the water quality and treatment standards.

[0039] After the reaction, the catalyst can be easily recovered using conventional solid-liquid separation methods such as sedimentation, filtration, and centrifugation, taking advantage of the solid properties of the modified graphitic carbon nitride. Due to its excellent stability resulting from its high crystallinity, the catalyst can be recycled multiple times without significant activity decay after simple cleaning and drying.

[0040] The following examples illustrate the water treatment composition, its application, and its effects in detail.

[0041] Examples 1-5: Preparation of Modified Graphite Phase Carbon Nitride Melamine and ammonium chloride were mixed and then pyrolyzed under an inert atmosphere. After the reaction was completed, the mixture was cooled to room temperature. Throughout the pyrolysis process, the volumetric flow rate of the inert gas needed to be controlled to be <5 L / h. The mass ratio of melamine to ammonium chloride and the pyrolysis conditions for each embodiment are shown in Table 1.

[0042] Comparative Examples 1-9 Referring to the preparation methods of Examples 1-5, the amounts of melamine and ammonium chloride were changed to be outside the range specified in this invention. The raw materials and pyrolysis conditions of each comparative example are shown in Table 1.

[0043] Table 1 .

[0044] The modified graphitic carbon nitride obtained in the above examples and comparative examples was characterized in terms of structure and tested in terms of optical and electrochemical properties. The specific methods are as follows: BET: The specific surface area of ​​the sample was determined using the nitrogen adsorption-desorption method (BET method). The specific surface area and mesopore size distribution of the samples were determined using an ASAP 2460 fully automated specific surface area and porosity analyzer from Micron Instruments, Inc. Before testing, the dried powder samples were placed in sample tubes and pretreated under dynamic vacuum in a stepwise degassing process: first, physically adsorbed impurities were removed at 100°C, followed by treatment at 800°C for 8 hours to obtain a clean and stable sample surface. The pretreated sample tubes were accurately weighed and transferred to the analysis station. Analysis was performed in a liquid nitrogen (77K) isothermal bath, with high-purity nitrogen (N2) as the adsorbate. The specific surface area of ​​the samples was calculated using the Brunauer-Emmett-Teller (BET) method. For data processing, data points within the relative pressure (P / P0) range of 0.05–0.30 were selected for linear fitting of the nitrogen adsorption isotherm to ensure a correlation coefficient (R²) greater than 0.999. The pore size distribution of the mesopores was calculated based on the Barrett-Joyner-Halenda (BJH) model from the desorption branch of the adsorption isotherm, and the most probable pore size and cumulative pore volume were reported.

[0045] XRD: The crystal structure of the sample is characterized using X-ray diffraction. Before testing, the catalyst powder to be tested was thoroughly ground in an agate mortar until it reached a fine powder state without any graininess, in order to eliminate the influence of preferred orientation. Then, the ground powder was spread evenly in the center of the groove in the glass sample holder and gently pressed flat with a glass slide to ensure the sample surface was flat and flush with the sample holder plane. The crystal structure of the sample was characterized using an Empyrea X-ray diffractometer from Malvern Panaco, UK. The test conditions were as follows: a CuKα radiation source (Kα1=1.54060 Å, Kα2=1.54443 Å), a tube voltage of 40 kV, a tube current of 40 mA, and a continuous scanning mode using a goniometer with a fixed divergence slit. The scanning range 2θ was 5 °–85 °, the scanning rate was 5 ° / min, and the sampling step size was 0.0263 °.

[0046] XPS: X-ray photoelectron spectroscopy is used to determine and analyze the elemental composition and chemical bonding state of the sample surface. The surface elemental composition and valence state analysis of the samples were performed using a K-Alpha X-ray photoelectron spectrometer from Thermo Fisher Scientific. Before testing, the dried powder sample was uniformly adhered to a double-sided conductive carbon tape and placed in an ultra-high vacuum analysis chamber, maintaining a basic vacuum of 10... -9 The excitation source was monochromatic AlKα radiation with a beam diameter of 400 μm. To eliminate the charging effect on the sample surface, a dual-beam neutralization gun was used for charge compensation during the test. The pass energy for the full spectrum scan was set at 1360 eV with a step size of 1.0 eV; the pass energy for the high-resolution fine spectrum was set at 20 eV with a step size of 0.1 eV. The binding energies of all elements were calibrated for charge using the C1s peak (284.8 eV) of the exogenous contaminant carbon as a reference.

[0047] EPR: The peak-to-peak intensity values ​​of the EPR signal are recorded using an electron paramagnetic resonance spectrometer. Before testing, the solid catalyst to be tested was thoroughly dried in a vacuum drying oven to remove the influence of physically adsorbed water on dielectric loss. After removal, it was gently ground into a uniform fine powder in an agate mortar. 10 mg of powder was weighed and placed into a clean quartz EPR NMR tube. The tube wall was gently tapped to allow the powder to settle to the bottom, ensuring a uniform height. The EPR spectra of the solid samples were recorded at room temperature using a Bruker EMX plus X-band electron paramagnetic resonance spectrometer. The test conditions were as follows: microwave frequency of 9.84 GHz, microwave power of 2.00 mW, magnetic field scan centered at 3503.1 G, scan width of 100 G, and signal modulation using a modulation frequency of 100 kHz and a modulation amplitude of 1.0 G. To improve the signal-to-noise ratio, the spectrum of each sample was the cumulative result of four scans, with a single scan time of 15 s and a time constant of 20.48 ms.

[0048] FT-IR: Fourier transform infrared (FT-IR) spectroscopy was used to identify functional groups and confirm the material structure. A Nicolet NEXUS 670 Fourier transform infrared spectrometer (USA) was used, and infrared spectra were acquired using the potassium bromide pellet method, with a scanning range of 400 to 4000 cm⁻¹. -1 .

[0049] Figure 1 This is a SEM image of the modified graphitic carbon nitride prepared in Example 1. Figure 2 The image shows the SEM image of unmodified graphitic carbon nitride in Comparative Example 6. Figure 1 and Figure 2 It can be seen that Comparative Example 6 exhibits a more obvious blocky structure and macroscopic structural defects, while Example 1 shows an obvious nanosheet structure on its surface. The nanosheet thickness is about 30-50 nm, and the surface smoothness is improved, showing an obvious two-dimensional planar structure, which also indicates a large specific surface area.

[0050] Figure 3 The XRD images of Example 1 and Comparative Example 6 are from... Figure 3 It can be seen that the diffraction peaks of the sample in Example 1 are higher and sharper, indicating that the sample has better crystallinity, higher degree of graphitization, and more regular layered structure; the diffraction peaks of the sample in Comparative Example 6 are relatively wider and have lower intensity, indicating that the sample has poorer crystallinity, lower degree of graphitization, more defects in the layered structure, or higher degree of disorder.

[0051] Figure 4 The images shown are FTIR images from Example 1 and Comparative Example 6. The spectrum can be divided into three main regions: 3000 to 3400 cm⁻¹. -1 The broad spectral band is attributed to the stretching vibrations of NH and OH; 1200 to 1600 cm⁻¹ -1 The region is caused by typical CN heterocyclic stretching vibrations, representing an aromatic carbonitride framework; 810 cm- 1 The peaks correspond to the characteristic peaks of the triazine ring and are a significant fingerprint of graphitic carbon nitride. A comparison shows that the spectrum of Example 1 exhibits a dominant CN heterocyclic band (1200 to 1600 cm⁻¹). -1 Additional subtle peaks appeared between the two phases. These new signals indicate a more ordered and perfect graphitic carbon nitride framework, suggesting that ammonium chloride-assisted synthesis promoted a higher degree of polymerization, allowing previously masked weak vibrational modes to be detected.

[0052] Figure 5 The XPS full spectra of Example 1 and Comparative Example 6 show that Example 1 has a higher surface oxygen content (47.18%), while Comparative Example 6 has a higher nitrogen content (5.40%). Figure 6, 7 The C1s high-resolution spectra of the two samples are shown below. In Example 1, the proportion of NC=N bonds (61.3%) was significantly higher than that of Comparative Example 6 (50.8%), while the proportion of C-NH2 (12.5%) was lower than that of Comparative Example 6 (20.4%). Figure 8 , 9 The N1s high-resolution spectrum shows that the proportion of NH bonds in Comparative Example 6 (12.5%) is significantly higher than that in Example 1 (7.6%). These results indicate that although the total nitrogen content of Example 1 is lower, its g-C3N4 skeleton is more regular and has fewer surface defects; while the nitrogen in Comparative Example 6 mainly exists in the form of edge amino groups.

[0053] The data results are shown in Table 2.

[0054] Table 2 .

[0055] Examples 6-16 Water Treatment Compositions The water treatment compositions in Examples 6-10 include modified graphitic carbon nitride and monochloramine at different concentrations, and the water treatment compositions in Examples 11-16 also include selenite at different concentrations. The specific components and concentrations are shown in Table 3.

[0056] Comparative Examples 10-17 By changing the composition and amount of modified graphitic carbon nitride or monochloramine, and comparing it with Examples 6-16, the raw materials and amounts are shown in Table 3.

[0057] Table 3 .

[0058] Example 17 Application of water treatment composition Take 50 mL of simulated wastewater (target pollutant concentrations: Rhodamine B: 20 ​​mg / L; Tetracycline: 15 mg / L; Bisphenol A: 10 mg / L; Sulfamethoxazole: 12 mg / L), adjust the pH to 7.2, and add the water treatment compositions of Examples 6-16 and Comparative Examples 10-17 respectively. After stirring in the dark for 10 minutes, irradiate the mixture under visible light (light intensity 700 W / m²) for reaction. The visible light wavelength for Examples 6-16 and Comparative Examples 10-17 is 420 nm, and the visible light wavelength for Examples 11-16 is 425 nm. The reaction temperature is 25 ± 2°C. Samples are taken at 0, 10, 20, 30, 40, and 60 min, filtered, and the concentration of the target pollutants is measured. The degradation efficiency for each target pollutant is calculated using the formula: Degradation efficiency (%) = (Initial pollutant concentration - Pollutant concentration at sampling time) / Initial pollutant concentration. The results are shown in Tables 4-7.

[0059] Table 4. Rhodamine B degradation efficiency (%) Table 5 Tetracycline Degradation Efficiency (%) Table 6. Bisphenol A degradation efficiency (%) Table 7. Degradation efficiency of sulfamethoxazole (%) .

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A water treatment composition, characterized in that, include: Modified graphitic carbon nitride with high crystallinity and low defect density, and monochloramine.

2. The water treatment composition according to claim 1, characterized in that, The high crystallinity is manifested in the fact that the full width at half maximum (FWHM) of the diffraction peaks corresponding to the (002) crystal plane in the X-ray diffraction pattern is less than 1.0°; The low defect density is characterized by an EPR signal intensity of no more than 0.08 au, and in X-ray photoelectron spectroscopy, the area ratio of the NC=N bond peak in the C1s spectrum is no less than 60%, and the area ratio of the peak corresponding to the edge amino group in the N1s spectrum is less than 10%.

3. The water treatment composition according to claim 1, characterized in that, The concentrations of each component are: modified graphitic carbon nitride 0.3-0.8 g / L, monochloramine 5-20 mgCl2 / L.

4. The water treatment composition according to claim 1, characterized in that, The preparation method of modified graphitic carbon nitride includes: mixing melamine with ammonium chloride and then pyrolyzing it under an inert atmosphere. During the entire pyrolysis process, the volumetric flow rate of the inert gas is <5 L / h.

5. The water treatment composition according to claim 4, characterized in that, The weight ratio of melamine to ammonium chloride is 1:(0.1-1.0).

6. The water treatment composition according to claim 4, characterized in that, The pyrolysis involves heating to 520-580℃ at a rate of 2-5℃ / min and pyrolyzing at this temperature for 3.5-4.5 hours. After the reaction is complete, the temperature is cooled to room temperature.

7. The water treatment composition according to any one of claims 1-6, characterized in that, It also includes selenite, with a concentration of 0.1-5 mg / L based on the mass of Se.

8. The water treatment composition according to claim 7, characterized in that, The selenite is selected from at least one of sodium selenite, potassium selenite, or ammonium selenite.

9. The use of the water treatment composition according to any one of claims 1-8 in the photocatalytic degradation of organic pollutants in water.

10. The application as described in claim 9, characterized in that, The organic pollutants include at least one of dye compounds, antibiotic compounds, endocrine disruptors, or pesticide residues.

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