Preparation of defect-state carbon nitride and application of photocatalytic activation of persulfate to degrade organic pollutants

Abstract

The application belongs to the technical field of wastewater treatment, and particularly relates to preparation of defect-state carbon nitride and application of photocatalytic activation of persulfate to degrade organic pollutants. The defect g-C3N4 (DCN) in the application is prepared by high-temperature thermal etching of formamide on synthesized g-C3N4, and has simple preparation process and low cost. When the DCN is used as a photocatalyst to activate persulfate under visible light irradiation, it can effectively degrade dyes and common pollutants such as phenol in water. Detection shows that the reaction mechanism is to generate sulfate radicals (•SO4 ‑ ) with extremely strong oxidation capacity to degrade organic pollutants. Meanwhile, when the DCN is used as a non-metallic catalyst to photocatalytically activate persulfate to degrade organic pollutants in water, there is no problem of secondary pollution, the DCN is easy to separate from water and recycle, and has wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology. Specifically, it relates to a method for preparing a catalyst containing defective polymeric carbon nitride and its application in the photocatalytic activation of persulfate degradation of pollutants in water. Background Technology

[0002] In my country, the water environment has suffered varying degrees of damage. The large-scale discharge of wastewater from various factories and untreated domestic sewage has seriously impacted economic and social development. Traditional wastewater treatment technologies, such as physical adsorption, flocculation, and biochemical methods, are insufficient to remove recalcitrant organic pollutants from water. In recent years, researchers have proposed using advanced oxidation technologies to treat pollutants in water. Essentially, this involves generating highly reactive species with strong oxidizing capabilities, such as hydroxyl radicals (•OH), through various reactions to completely oxidize various organic pollutants in the water into non-toxic small molecules such as CO2 and H2O, or to convert pollutants into intermediate products with good biochemical properties. Recent studies have found that sulfate radicals (•SO4)... - Because it has superior degradation effects and wider applicability compared to hydroxyl radicals (•OH), and also possesses advantages such as good stability, high solubility, diverse activation methods, and broad applicability, it produces •SO4. - Its longer lifespan allows for greater contact with pollutants, significantly improving the degradation efficiency. Therefore, photocatalytic activation of persulfate generates sulfate radicals (•SO4). - Degrading organic pollutants in wastewater has become a research hotspot and is expected to become an advanced oxidation technology with good application prospects.

[0003] To date, most reported photocatalysts for activating persulfate contain transition metals. These catalysts often suffer from secondary pollution due to metal leaching in practical applications, making them unsuitable for practical needs. Graphitic carbon nitride is a recently discovered polymer semiconductor catalyst. This non-metallic catalyst is used in various fields due to its non-toxicity and good stability. However, pure g-C3N4 has poor activation ability for persulfate; therefore, modifying it into a highly efficient non-metallic persulfate activator is a worthwhile direction to explore. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a defective graphitic carbon nitride catalytic material, its preparation method, and its applications. The material has a simple and easy-to-operate synthesis technique, exhibits good catalytic activity in the photocatalytic activation of persulfate degradation of wastewater, and has promising application prospects.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A defective g-C3N4 catalytic material is prepared by thermal etching of pure g-C3N4 with formamide at high temperature; the preparation method involves thermal polymerization of urea in air to obtain g-C3N4. The defective g-C3N4 is prepared by thermal etching of pure g-C3N4 with formamide under an argon atmosphere to form the novel photocatalytic material; specifically, it includes the following steps:

[0007] 1) A certain amount of carbon nitride precursor was calcined in a muffle furnace to obtain a pale yellow solid powder, which is pure g-C3N4 without etching.

[0008] 2) The pure g-C3N4 synthesized above was ultrasonically mixed with formamide in a certain proportion, and then the mixture was calcined in an inert atmosphere in a tube furnace. The resulting solid sample was g-C3N4 containing defects.

[0009] The carbon nitride precursor is urea.

[0010] The ultrasonic mixing time is 5-15 min.

[0011] The calcination process for synthesizing g-C3N4 was carried out in air at a temperature of 550 °C for 1–5 h.

[0012] The calcination process of the hot etching process is carried out under an argon atmosphere at a temperature of 500 ℃ for 1 to 5 hours.

[0013] The mass ratio of unetched pure g-C3N4 to formamide is 1:15-50.

[0014] The amount of formamide added is 0 mL, 3 mL, 5 mL, 7 mL, or 10 mL per 200 mg g-C3N4.

[0015] The defective g-C3N4 catalytic material can efficiently activate persulfate under visible light irradiation, thereby effectively degrading organic pollutants in water. Specifically, the process includes the following steps: adding defective g-C3N4 as a catalyst to wastewater containing organic pollutants; after the catalyst is completely dispersed and reaches adsorption equilibrium with the substrate, adding the oxidant persulfate and continuously stirring; the catalyst degrades organic matter in the water by activating the persulfate under visible light irradiation to produce active substances.

[0016] Furthermore, the visible light source is a xenon lamp with a light intensity of 100–600 mW / cm². -2 The oxidant persulfate is permonosulfate with a concentration of 10–1000 mg / L.

[0017] Furthermore, the organic pollutants include phenol, bisphenol A, ciprofloxacin, orange II, trimethoprim, and tetracycline hydrochloride; the wastewater has a pH of 3–9 and a concentration of 1–100 mg / L.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) This invention synthesizes defective g-C3N4 as a catalyst material via a simple solvothermal etching method. Formamide, as a small-molecule liquid solvent, enables the pure g-C3N4 to be uniformly dispersed at room temperature. Furthermore, due to its boiling point of 210℃, it vaporizes and decomposes during gradual heating, altering the structure of pure g-C3N4 under an inert atmosphere, thus creating defects. Therefore, the catalyst material exhibits defects in the carbon nitride structure through formamide etching. The generation of defects enhances its adsorption capacity for persulfate, increases the electron transfer rate, strengthens light absorption, and weakens the recombination of photogenerated carriers. Test results show that the photocatalytic activation activity of this catalyst for persulfate is significantly higher than that of blank g-C3N4.

[0020] (2) The method of the present invention is simple, the raw materials are inexpensive, the reaction conditions are mild, the production cost is low, and it is suitable for large-scale production. Attached Figure Description

[0021] Figure 1 The XRD patterns are of the catalysts prepared in Examples 2-6.

[0022] Figure 2 Fourier transform infrared spectra of the catalysts prepared in Examples 2-6.

[0023] Figure 3 The photocatalytic activation behavior of the catalysts prepared in Examples 2-6 for the degradation of phenol by persulfate.

[0024] Figure 4 The photocatalytic activation of the catalyst prepared in Example 5 for the degradation of phenol by persulfate was tested in a cyclic experiment.

[0025] Figure 5 The photocatalytic activation behavior of the catalyst prepared in Example 5 in the degradation of different pollutants by persulfate is shown.

[0026] Figure 6 This is a comparison of the degradation of phenol per gram of the catalyst prepared in Example 5 and the commonly used commercial photocatalyst titanium dioxide P25. Detailed Implementation

[0027] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0028] Example 1:

[0029] 10g of urea was ground into a fine powder and placed in a crucible. The crucible was then calcined at 550℃ for 2 hours in a muffle furnace to obtain pure g-C3N4.

[0030] Example 2:

[0031] The pure g-C3N4 obtained in Example 1 was thoroughly ground for 10 min and then transferred to a crucible. It was then calcined at 500°C for 2 h in a tube furnace under an argon atmosphere to obtain the comparative sample CN.

[0032] Example 3:

[0033] 200 mg of pure g-C3N4 obtained in Example 1 was thoroughly ground for 10 min and then ultrasonically mixed with 3 mL of formamide for 15 min. The resulting mixture was transferred to a crucible and calcined in a muffle furnace at 500 °C for 2 h under an argon atmosphere to obtain DCN3.

[0034] Example 4:

[0035] 200 mg of pure g-C3N4 obtained in Example 1 was thoroughly ground for 10 min and then ultrasonically mixed with 5 mL of formamide for 15 min. The resulting mixture was transferred to a crucible and calcined at 500 °C for 2 h in an argon atmosphere in a muffle furnace to obtain DCN5.

[0036] Example 5:

[0037] 200 mg of pure g-C3N4 obtained in Example 1 was thoroughly ground for 10 min and then ultrasonically mixed with 7 mL of formamide for 15 min. The resulting mixture was transferred to a crucible and calcined in a muffle furnace at 500 °C for 2 h under an argon atmosphere to obtain DCN7.

[0038] Example 6:

[0039] 200 mg of pure g-C3N4 obtained in Example 1 was thoroughly ground for 10 min and then ultrasonically mixed with 10 mL of formamide for 15 min. The resulting mixture was transferred to a crucible and calcined at 500 °C for 2 h in an argon atmosphere in a muffle furnace to obtain DCN10.

[0040] Application example: Photoactivated persulfate degradation pollutant activity test

[0041] CN, DCN3, DCN5, DCN7, and DCN10 were used as catalysts for activation and degradation reactions as follows. 50 mg of catalyst was added to a 200 mL reactor, followed by 150 mL of a 10 mg / L solution of organic pollutants. The pollutants included phenol (PE), bisphenol A (BPA), ciprofloxacin (CIP), oxytocin (OA), trimethoprim (TMP), and tetracycline hydrochloride (TCH). The system was then purged with cooling water to maintain a constant temperature of 25°C. The mixture was stirred for 30 minutes to allow the catalyst and pollutants to reach adsorption equilibrium. Then, 200 mg / L potassium persulfate (PMS) was added, and a xenon lamp was lit to initiate the reaction. The reaction time was 90 minutes, with 0.5 mL samples taken every 15 minutes. Unreacted PMS was quenched with 0.5 mL of methanol. The high-performance liquid chromatography (HPLC) chromatograms of the samples were then analyzed, and the concentration changes during degradation were determined based on the peak areas of the corresponding organic compounds.

[0042] Note: Figures 1-5 Description

[0043] Figure 1 The figures show the XRD patterns of the catalysts prepared in Examples 2-6. As can be seen from the figures, characteristic diffraction peaks centered at 2θ = 27.3° and 2θ = 13.1° exist, corresponding to the (002) and (100) crystal planes of carbon nitride. Compared to CN, the intensity of the diffraction peak at 2θ = 27.3° of DCN is significantly weakened, which is due to defects introduced after etching. Figure 2 These are Fourier transform infrared (FTIR) spectra of the catalysts prepared in Examples 2-6. As can be seen from the figures, the overall molecular structure of carbon nitride was not destroyed after formamide etching; however, a few methyl groups generated after formamide reduction were attached to the CN molecular structure. Figure 3 The figures show the photocatalytic activation activity of the catalysts in Examples 2-6 for the degradation of phenol by persulfate. As can be seen from the figures, the activity of DCN is significantly higher than that of CN. With increasing formamide content, the photocatalytic activity of the DCN sample gradually increases due to defect formation, with DCN7 exhibiting the best activity. This is because excessive formamide etching can cause a light-shielding effect in the sample. Figure 4 This is the activity graph of the DCN7 sample in Example 5 after a cycle experiment. As can be seen from the graph, the catalyst still has high activity after five cycles. Figure 5 This is an activity graph of the DCN7 sample in Example 5 for degrading different organic pollutants. As can be seen from the graph, the catalyst has universality in wastewater treatment technology. Figure 6 This is a comparison of the degradation of phenol by each gram of DCN7 prepared in Example 5 and the commonly used commercial photocatalyst titanium dioxide P25. As shown in the figure, the photocatalytic activation performance of DCN7 in degrading phenol by persulfate is 5 times that of titanium dioxide P25.

[0044] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing defective carbon nitride, characterized in that: It was prepared by thermal etching of pure g-C3N4 with formamide at high temperature; The mass ratio of unetched pure g-C3N4 to formamide is 1:15-50; High-temperature thermal etching refers to heating to 500°C in an argon atmosphere at a heating rate of 5°C / min, and then holding at that temperature for 1 to 5 hours.

2. The preparation method according to claim 1, characterized in that: Unetched pure g-C3N4 was prepared by heating urea to 550 °C in air at a heating rate of 5 °C / min, and then holding at that temperature for 1 h to 5 h.

3. Defective carbon nitride prepared by the preparation method according to claim 1 or 2.

4. The application of the defective carbon nitride as described in claim 3 as a photocatalyst in the activation of persulfate degradation of pollutants in water under visible light irradiation.

5. The application according to claim 4, characterized in that, Includes the following steps: Defective carbon nitride is added as a catalyst to wastewater containing organic pollutants. After the catalyst is completely dispersed and reaches adsorption equilibrium with the substrate, persulfate is added as an oxidant and the mixture is continuously stirred. The catalyst degrades organic matter in the water by activating persulfate under visible light irradiation to produce active substances.

6. The application according to claim 5, characterized in that: The visible light source is a xenon lamp with a light intensity of 100–600 mW·cm. -2 The oxidant persulfate is permonosulfate with a concentration of 10–1000 mg / L.

7. The application according to claim 5, characterized in that: The organic pollutants include phenol, bisphenol A, ciprofloxacin, orange II, trimethoprim, and tetracycline hydrochloride; the pH of the wastewater is 3-9, and the concentration is 1-100 mg / L.

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