Method for copolymerization preparation of graphitic phase carbon nitride with structural defects and application

Abstract

The application belongs to the technical field of wastewater treatment, and particularly relates to a method for preparing graphite phase carbon nitride with structural defects by copolymerization and application. 4 The g-C3N4 with structural defects (CND) is formed by high-temperature calcination of bromine malondialdehyde and carbon nitride precursors, and has simple preparation process and low cost; the CND can effectively degrade dyes and common water pollutants such as bisphenol A by activating persulfate at room temperature. The detection mechanism is to oxidize organic pollutants by direct electron transfer. Meanwhile, the g-C3N4 with structural defects is a non-metallic catalyst, and does not cause secondary pollution when used for activating persulfate to degrade organic pollutants in water, is convenient to separate from water and recycle, and has wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment. Specifically, it relates to a preparation method of a catalyst of polymeric carbon nitride with structural defects and application thereof in activating persulfate to degrade pollutants in water. BACKGROUND

[0002] Traditional wastewater treatment technologies such as physical adsorption, flocculation, and biochemical methods are difficult to remove water-borne organic pollutants. In recent years, researchers have proposed using advanced oxidation technology to treat water-borne pollutants. The essence is to generate hydroxyl radicals (·OH) and other active species with strong oxidation ability through various pathways to completely oxidize water-borne organic pollutants into CO2, H2O, and other non-toxic small molecules, or to convert pollutants into intermediate products with good biochemical properties. In recent years, it has been found that sulfate radicals (·SO4 - ) have more excellent degradation effect and application range than hydroxyl radicals (·OH). In addition, ·SO4 - has good stability, high solubility, various activation methods, and wide application range. Moreover, it has a long lifespan, which is conducive to sufficient contact with pollutants and greatly improves the effect of degrading pollutants. Therefore, activating persulfate to generate sulfate radicals (·SO4 - ) to degrade water-borne organic pollutants has become a research hotspot and is expected to become an advanced oxidation technology with good application prospects.

[0003] So far, most of the reported catalysts for activating persulfate contain transition metals. These catalysts often have the problem of secondary pollution caused by metal leaching in practical applications, which is difficult to meet the actual demand. Graphitic carbon nitride is a recently discovered polymer semiconductor catalyst. This non-metallic catalyst has the advantages of being non-toxic and stable, and is applied in various fields. However, pure g-C3N4 has poor ability to activate persulfate. Therefore, it is a worthwhile direction to explore to modify it into a high-efficiency non-metallic persulfate activator. SUMMARY

[0004] In view of the above problems, the present application provides a graphitic carbon nitride catalyst material with structural defects, a preparation method thereof, and application thereof. The material has simple synthesis technology and is easy to operate. It shows good catalytic activity in activating persulfate to degrade wastewater and has good application prospects.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] A structural defect g-C3N4 catalytic material is prepared by copolymerization of bromine malondialdehyde and a precursor of g-C3N4; a preparation method thereof is to calcine the precursor of carbon nitride and bromine malondialdehyde together to form the new copolymerization catalytic material; and the method specifically comprises the following steps:

[0007] 1) mixing the precursor of carbon nitride and bromine malondialdehyde and sufficiently grinding to obtain a solid mixture in different proportions;

[0008] 2) calcining the obtained solid mixture in a muffle furnace to obtain a brown-black solid powder, i.e. the structural defect g-C3N4.

[0009] The precursor of carbon nitride is urea.

[0010] The grinding experiment is 5-15 min.

[0011] The calcination is performed in air, the calcination temperature is 550 DEG C, and the calcination time is 1-5 h.

[0012] The mass ratio of bromine malondialdehyde to the precursor of carbon nitride is 1:30-100.

[0013] Further, the amount of added bromine malondialdehyde is 0 mg, 100 mg, 200 mg, 300 mg of bromine malondialdehyde per 10 g of the precursor of carbon nitride.

[0014] The structural defect g-C3N4 catalytic material can efficiently activate persulfate to effectively degrade organic pollutants in water. Specifically, the method comprises the following steps: adding the structural defect g-C3N4 as a catalyst in wastewater containing organic pollutants, adding the oxidant persulfate after the catalyst is completely dispersed and adsorbed with the substrate, and continuously stirring, the catalyst produces active substances by activating persulfate to degrade organic matter in water.

[0015] The organic pollutants include bisphenol A, p-chlorophenol, orange II, tetracycline hydrochloride, the pH value of the wastewater is 3-9, and the concentration is 1-100 mg / L. The oxidant persulfate is peroxymonosulfate.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] (1) The g-C3N4 with structural defects as a catalytic material is synthesized by one-step thermal polymerization. Bromomalonaldehyde is a small molecule organic matter. Because it contains a conjugated structure and an aldehyde group, it is conducive to copolymerization with urea to prepare carbon nitride. Meanwhile, the incorporation of element oxygen with strong electron-withdrawing ability can change the electronic distribution of the system and make the pi conjugated electron delocalization. And because of the change of electronic structure, the intermolecular charge transfer ability is enhanced. Therefore, the carbon nitride with structural defects prepared by copolymerization of urea and bromomalonaldehyde can activate persulfate to degrade pollutants. The detection results show that the activity of the catalyst is obviously higher than that of pure g-C3N4.

[0018] (2) The method of the present application is simple, the raw material price is low, the reaction condition is mild, the production cost is low, it is green and environmental protection, and it is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 XRD spectrum of the catalyst prepared in Examples 1-4.

[0020] Figure 2 Fourier infrared spectrum of the catalyst prepared in Examples 1-4.

[0021] Figure 3 Behavior of the catalyst prepared in Examples 1-4 in activating persulfate to degrade bisphenol A.

[0022] Figure 4 Cycle experiment of the catalyst prepared in Example 4 in activating persulfate to degrade bisphenol A.

[0023] Figure 5 Behavior of the catalyst prepared in Example 4 in activating persulfate to degrade different pollutants.

[0024] Figure 6 Performance comparison of the catalyst prepared in Example 4 and metal oxide cobalt tetroxide (Co3O4) in degrading bisphenol A per gram of catalyst. DETAILED DESCRIPTION

[0025] In order to make the content described in the present application more convenient to understand, the technical solutions described in the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0026] Example 1:

[0027] 10g of urea was placed in a crucible and calcined in a muffle furnace at 550℃ for 2h to obtain pure g-C3N4.

[0028] Example 2:

[0029] 10 g urea and 100 mg bromo malondialdehyde were put in a mortar, then ground for 10 min. The ground mixture was transferred to a crucible and calcined at 550 °C for 2 h in a muffle furnace to obtain CND-100.

[0030] Example 3:

[0031] 10 g urea and 200 mg bromo malondialdehyde were put in a mortar, then ground for 10 min. The ground mixture was transferred to a crucible and calcined at 550 °C for 2 h in a muffle furnace to obtain CND-200.

[0032] Example 4:

[0033] 10 g urea and 300 mg bromo malondialdehyde were put in a mortar, then ground for 10 min. The ground mixture was transferred to a crucible and calcined at 550 °C for 2 h in a muffle furnace to obtain CND-300.

[0034] Application Example Activated persulfate degradation of pollutants activity test

[0035] g-C3N4, CND-100, CND-200, CND-300, respectively, were used as catalysts to activate the following degradation reactions. 50 mg of catalyst was added to a 200 mL reactor, and 150 mL of 20 mg / L organic pollutant solution was added. The pollutants were bisphenol A (BPA), p-chlorophenol (4-CP), orange II (OA), and tetracycline hydrochloride (TCH). Then the system was purged with condensed water to keep it at a constant temperature of 25 °C. First, stir for 30 minutes to allow the catalyst to adsorb bisphenol A to equilibrium. Then add 40 mg / L of potassium hydrogen persulfate (KHSO5) to start the reaction. The reaction time was 15 minutes, and 0.5 mL was taken every 3 minutes, and 0.5 mL of methanol was used to quench the unreacted potassium hydrogen persulfate. Then test the high performance liquid chromatogram of the sample, and according to the peak area of the organic matter, the concentration change in the degradation process is obtained.

[0036] Note: Figures 1-5 Description of the drawings

[0037] Figure 1 The XRD spectrum of the catalyst prepared in Examples 1-4 is shown in the figure. As can be seen from the figure, there are characteristic diffraction peaks centered at 2θ = 27.4° and 2θ = 13.1°, corresponding to the (002) crystal plane and (100) crystal plane of carbon nitride. Compared with g-C3N4, the intensity of these two diffraction peaks of CND is significantly weakened, and the diffraction peak at 2θ = 13.1° disappears. This indicates that the structure of CND is more disordered. Figure 2is the Fourier infrared spectrum of the catalyst prepared in Examples 1-4. As can be seen from the figure, the overall molecular structure of carbon nitride is not destroyed after the introduction of bromine malondialdehyde. Figure 3 is the activity graph of the catalyst prepared in Examples 1-4 in activating persulfate to degrade bisphenol A. As can be seen from the figure, the activity of CND is obviously higher than that of g-C3N4. With the increase of the amount of bromine malondialdehyde, the more structural defects of carbon nitride after copolymerization, the more conducive to the adsorption and activation of persulfate, so the catalytic performance of CND-300 sample is the best. Figure 4 is the activity graph of the cycle experiment of CND-300 sample in Example 4. As can be seen from the figure, the catalyst still has high activity after five cycles. Figure 5 is the activity graph of CND-300 sample in Example 4 in degrading different organic pollutants. As can be seen from the figure, the catalyst has universality in wastewater treatment technology. Figure 6 is the performance comparison of CND-300 sample prepared in Example 4 and metal oxide cobalt tetroxide (Co3O4) in degrading bisphenol A per gram of catalyst. As can be seen from the figure, the performance of CND-300 in activating persulfate to degrade bisphenol A is 5 times that of Co3O4, and CND-300 is a non-metal catalyst, which does not have the problem of secondary pollution caused by metal leaching in the reaction process.

[0038] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A method for copolymerizing graphitic carbon nitride with structural defects, characterized in that: Graphitic carbon nitride with structural defects was synthesized by thermal polymerization after mixing malondialdehyde with carbon nitride precursors. The mass ratio of malondialdehyde to carbon nitride precursor is 1:30 to 100; Thermal polymerization refers to heating the temperature to 550°C in air at a rate of 5°C / min, and then holding it at that temperature for 1 to 5 hours. The precursor of the carbon nitride used is urea.

2. Graphite-phase carbon nitride with structural defects obtained by the method according to claim 1.

3. The application of graphitic carbon nitride with structural defects as described in claim 2 as a catalyst in the catalytic activation of persulfate to degrade pollutants in water.

4. The application according to claim 3, characterized in that, Includes the following steps: In wastewater containing organic pollutants, graphitic carbon nitride with structural defects is added as a catalyst. 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 the persulfate to produce active substances.

5. The application according to claim 4, characterized in that: The organic pollutants include bisphenol A, p-chlorophenol, orange yellow II, and tetracycline hydrochloride. The pH of the wastewater is 3-9, and the concentration is 1-100 mg / L.

6. The application according to claim 4, characterized in that: The oxidizing agent persulfate is permonosulfate.

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