Preparation method and application of anthraquinone-loaded phosphorus-doped graphitic carbon nitride / biochar photocatalytic composite material

Abstract

The invention discloses a method for preparing a phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material loaded with anthraquinone and its application. The present invention aims to solve the problem of poor catalytic performance and stability of existing g-C3N4 photocatalytic materials. Preparation method: 1. Prepare biochar; 2. Add melamine to ultrapure water, then add diammonium hydrogen phosphate, and obtain P@g-C3N4 material after heating reaction; 3. Evaporate the suspension of P@g-C3N4 material and biochar, and obtain P-doped g-C3N4-BC material after calcination treatment; 4. Stir and mix the P@g-C3N4-BC dispersion and anthraquinone solution, and collect the solid-phase reactant. The present invention reduces the probability of electron-hole recombination by doping with phosphorus element, and improves the effective separation of electrons and holes. In addition, the introduction of P element in g-C3N4 makes the carbon nitride surface in an electron-rich state, increases the conduction band position, enhances the photoelectron reducibility, and significantly improves the photocatalytic performance.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalytic water pollution control, and in particular relates to a preparation method and application of a composite photocatalytic material. Background Art

[0002] Photocatalytic oxidation is a novel water treatment technology that has attracted attention due to its green and clean characteristics. In recent years, carbon-based nanostructures have been widely used in the field of photocatalysis. The environmentally friendly g-C3N4 is an emerging non-metallic photocatalyst with a suitable band gap, chemical stability, non-toxicity, and low cost. However, g-C3N4 suffers from low electronic conductivity, low quantum yield, weak light absorption, and easy recombination of photogenerated holes and electrons, which limits its catalytic performance and stability. Element doping is one of the effective means to improve the electronic structure and surface morphology of g-C3N4 materials.

[0003] In the field of photocatalysis, carbon materials with large specific surface areas are often used as supports for g-C3N4. On the one hand, carbon materials provide a large surface area and anchoring sites for photoactive species; on the other hand, carbon materials can reduce charge recombination, which can enhance the photocatalytic activity of g-C3N4. Among various carbon materials, biochar has a large specific surface area, a rich and developed pore structure, good biochemical thermal stability, and abundant surface functional groups, making it widely used in fields such as environmental remediation. It can also be used as a co-catalyst to positively influence the photocatalytic removal of pollutants.

[0004] In addition, anthraquinone (AQ), as a type of carbonyl compound, has been applied in the field of photocatalysis due to its advantages of low cost, simple composition, and unique redox activity: AQ can accept photogenerated electrons (e - ), thereby greatly improving the separation and transfer of photogenerated carriers on the photocatalyst. In addition, AQ and its derivatives (AQs) are also well-known for their photosensitivity properties. Therefore, this organic photocatalyst can play an effective role in the degradation of PPCPs. AQ can be connected to g-C3N4 through non-covalent π-π stacking or covalent linkage. Combining photoactive molecules with carbon-based materials is an effective strategy to prevent the dissolution of organic molecules and improve the optical absorption properties of composites. Covalent functionalization can anchor more photoactive molecules on graphene and prevent the desorption and decomposition of the anchored active molecules during the photocatalytic process. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of poor catalytic performance and stability of existing g-C3N4 photocatalytic materials, and to provide a preparation method for loading anthraquinone onto P-doped g-C3N4-BC composite materials, and apply it to the photocatalytic degradation process of azo dyes.

[0006] The preparation method of the anthraquinone-loaded phosphorus-doped graphite carbon nitride (P@g-C3N4) / biochar photocatalytic composite material of the present invention is achieved by the following steps:

[0007] 1. In a tubular furnace, dried sludge is pyrolyzed at 500-600°C under a nitrogen atmosphere, ground, washed, and dried to obtain biochar;

[0008] Second, melamine was added to ultrapure water, followed by (NH4)2HPO4. After ultrasonic oscillation, the mixture was placed in a water bath to evaporate the water. After drying and grinding, the mixture was placed in a muffle furnace and kept at 500-600°C for 3-4 hours. After cooling, the mixture was crushed into powder to obtain P@g-C3N4 material.

[0009] 3. Add P@g-C3N4 material and biochar to deionized water, ultrasonically disperse to obtain a suspension, place it in a water bath to evaporate the water, dry and grind it, place it in a muffle furnace, and calcine it at a temperature of 550-600°C to obtain P-doped g-C3N4-BC material (P@g-C3N4-BC) after grinding;

[0010] 4. The P-doped g-C3N4-BC material was dispersed in deionized water and ultrasonically treated to obtain a P@g-C3N4-BC dispersion. Anthraquinone was dissolved in 1-methyl-2-pyrrolidone to obtain an anthraquinone solution. The P@g-C3N4-BC dispersion and the anthraquinone solution were stirred and mixed for 10 to 15 hours. The suspension was filtered to collect the solid-phase reactant, which was washed and dried to obtain an anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material.

[0011] The mass ratio of the P-doped g-C3N4-BC material and anthraquinone in step four is (1 to 1.5): (1 to 1.5).

[0012] The application of the anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material of the present invention is to add the anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material to wastewater containing dyes, and perform photocatalytic reaction by xenon lamp irradiation to degrade the dyes.

[0013] The present invention can reduce the probability of electron-hole recombination by doping with phosphorus (P) elements, thereby improving the effective separation of electrons and holes, which is conducive to the progress of photocatalytic reactions. In addition, the introduction of P elements into g-C3N4 puts the carbon nitride surface in an electron-rich state, increases the conduction band position, enhances the photoelectron reducibility, and significantly improves the photocatalytic performance. Anthraquinone AQ is connected to g-C3N4 through non-covalent π-π stacking, electrostatic attraction or hydrogen bonding, which can anchor more photoactive molecules on biochar and prevent the desorption and decomposition of the anchored active molecules during the photocatalytic process.

[0014] The present invention relates to a method for preparing an anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material, and uses Reactive Red 2 (RR2) as a target pollutant to explore the degradation efficiency of the anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material on Reactive Red 2. The present invention has the following beneficial effects:

[0015] 1. Biochar is prepared from dewatered sludge from sewage treatment plants. The raw materials are widely available and biochar is easy to prepare, which reduces costs and achieves sludge reduction and resource utilization.

[0016] 2. Doping of P element in g-C3N4 can inhibit the occurrence of electron-hole recombination phenomenon, effectively improve the band structure of carbon nitride, and improve the photocatalytic efficiency.

[0017] 3. The large specific surface area of ​​biochar can serve as a carrier to anchor g-C3N4. On the other hand, carbon materials can reduce charge recombination, thereby improving the photocatalytic activity of g-C3N4 materials and efficiently removing reactive red 2.

[0018] 4. Anthraquinone, as a photosensitizer, can undergo photochemical reactions under ultraviolet or visible light irradiation, involving the excitation and transfer of electrons, thereby inducing the generation of reactive oxygen species and promoting the progress of photocatalytic reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning electron microscope image of the anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material P@g-C3N4-BC-AQ prepared in Example;

[0020] Figure 2 A test chart showing the effect of catalyst addition on photocatalytic efficiency in the examples;

[0021] Figure 3 A test chart showing the effect of the mass ratio of biochar to melamine on the photocatalytic efficiency of the composite material in the examples;

[0022] Figure 4 This is a test diagram showing the effect of the initial concentration of Reactive Red 2 on the photocatalytic efficiency in the examples;

[0023] Figure 5 This is a performance test diagram of the catalytic degradation of Reactive Red 2 in Example 1 and Comparative Examples 2-5. DETAILED DESCRIPTION

[0024] Specific embodiment 1: The preparation method of the anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material in this embodiment is implemented according to the following steps:

[0025] 1. In a tubular furnace, dried sludge is pyrolyzed at 500-600°C under a nitrogen atmosphere, ground, washed, and dried to obtain biochar;

[0026] Second, melamine was added to ultrapure water, followed by (NH4)2HPO4. After ultrasonic oscillation, the mixture was placed in a water bath to evaporate the water. After drying and grinding, the mixture was placed in a muffle furnace and kept at 500-600°C for 3-4 hours. After cooling, the mixture was crushed into powder to obtain P@g-C3N4 material.

[0027] 3. Add P@g-C3N4 material and biochar to deionized water, ultrasonically disperse to obtain a suspension, place it in a water bath to evaporate the water, dry and grind it, place it in a muffle furnace, and calcine it at a temperature of 550-600°C to obtain P-doped g-C3N4-BC material (P@g-C3N4-BC) after grinding;

[0028] 4. The P-doped g-C3N4-BC material was dispersed in deionized water and ultrasonically treated to obtain a P@g-C3N4-BC dispersion. Anthraquinone was dissolved in 1-methyl-2-pyrrolidone to obtain an anthraquinone solution. The P@g-C3N4-BC dispersion and the anthraquinone solution were stirred and mixed for 10 to 15 hours. The suspension was filtered to collect the solid-phase reactant, which was washed and dried to obtain an anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material.

[0029] The mass ratio of the P-doped g-C3N4-BC material and anthraquinone in step four is (1 to 1.5): (1 to 1.5).

[0030] The anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material prepared in this embodiment can effectively utilize light energy and improve the absorption capacity of visible light, thereby stimulating the generation of more active species and improving the degradation capacity of pollutants.

[0031] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that in step 1, the temperature is raised to 500-600° C. at a heating rate of 10° C. / min, and the pyrolysis treatment is performed for 1.5-2.5 hours.

[0032] Specific embodiment three: The difference between this embodiment and specific embodiment one or two is that the particle size of the biochar after grinding in step one is 200-300 meshes.

[0033] Specific embodiment 4: The difference between this embodiment and any one of specific embodiments 1 to 3 is that in step 2, the mass ratio of melamine to (NH4)2HPO4 is 1:0.5-3.

[0034] Specific embodiment 5: This embodiment differs from any one of specific embodiments 1 to 4 in that in step 2, the temperature is raised to 550° C. at a heating rate of 5° C. / min and kept at this temperature for 3 h.

[0035] Specific embodiment six: The difference between this embodiment and any one of specific embodiments one to five is that in step three, the mass ratio of P@g-C3N4 material to biochar is 4 to 30:1.

[0036] In this embodiment, the mass ratio of P@g-C3N4 material and biochar is optimized to 10-15:1, and the mass ratio is further optimized to 10:1.

[0037] Specific embodiment seven: This embodiment differs from any one of specific embodiments one to six in that in step three, the calcination treatment is performed at a temperature of 550° C. for 3 hours.

[0038] Specific embodiment eight: The difference between this embodiment and any one of specific embodiments one to seven is that in step four, the P-doped g-C3N4-BC material is dispersed in deionized water, and the ultrasonic treatment time is 120 to 180 minutes.

[0039] Specific embodiment 9: This embodiment differs from any one of specific embodiments 1 to 7 in that in step 4, the solid phase reactant is washed with 1-methyl-2-pyrrolidone, ethanol and deionized water in sequence.

[0040] Example 1: The preparation method of the anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material of this embodiment is carried out according to the following steps:

[0041] First, the mud cake obtained from the sludge dewatering workshop of the sewage treatment plant was cut into small pieces of 3-5 cm, placed in an oven at 105°C for drying, and then placed in a high-temperature tube furnace. The dried mud blocks were pyrolyzed at 500°C for 2 hours under a nitrogen atmosphere at a heating rate of 10°C / min. The granules were ground into particles of 200-300 mesh, washed, and dried to obtain biochar.

[0042] Second, melamine was added to ultrapure water, followed by 0.2 g of (NH4)2HPO4. After ultrasonic oscillation for 0.5 h, the mixture was placed in a water bath to evaporate the water. The mixture was dried at 70 ° C, ground, and placed in a muffle furnace. The temperature was controlled to rise at a rate of 5 ° C / min and kept at 550 ° C for 3 h. After cooling, the mixture was crushed into powder to obtain P@g-C3N4 material.

[0043] 3. P@g-C3N4 material and biochar were added to deionized water and ultrasonically dispersed to obtain a suspension. The suspension was stirred on a magnetic stirrer for 15 h, evaporated in a water bath, dried at 70 ° C, ground, placed in a muffle furnace, and calcined at 550 ° C for 3 h. After grinding, P-doped g-C3N4-BC material (P@g-C3N4-BC) was obtained.

[0044] 4. Disperse 500 mg of P-doped g-C3N4-BC material in 100 ml of deionized water and ultrasonically treat to obtain P@g-C3N4-BC dispersion. Dissolve 500 mg of anthraquinone in 100 ml of 1-methyl-2-pyrrolidone to obtain anthraquinone solution. The P@g-C3N4-BC dispersion and anthraquinone solution are stirred and mixed at room temperature for 12 h. The suspension is filtered to collect the solid phase reactant, which is washed with 1-methyl-2-pyrrolidone, ethanol and deionized water in turn to remove unreacted AQ. After drying at 60 °C, the anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material (P@g-C3N4-BC-AQ) is obtained.

[0045] Comparative Example 2: In this example, melamine is placed in a muffle furnace, heated to 550°C at a heating rate of 5°C / min, kept warm for 3 hours, taken out after cooling to 50°C, crushed into powder for standby use, and g-C3N4 is obtained.

[0046] Comparative Example 3: In this example, biochar is mixed with deionized water, ultrasonically treated to form an evenly dispersed suspension, fully mixed with melamine under magnetic stirring, and then filtered. The mixture is dried at 70°C and then ground. The light gray material is placed in an alumina crucible and heated in a muffle furnace to obtain a yellow-green product g-C3N4-BC.

[0047] Comparative Example 4: This example uses the P@g-C3N4 material obtained in step 2 of Example 1.

[0048] Comparative Example 5: This example uses the P-doped g-C3N4-BC material obtained in step 3 of Example 1, namely P@g-C3N4-BC.

[0049] Application example: Application of P@g-C3N4-BC-AQ in the photocatalytic degradation of Reactive Red 2. Reactive Red 2 was used as the target pollutant with an initial concentration of 20 mg / L, and the photocatalytic degradation experiment was carried out in a beaker. Before the start of the reaction, the simulated dye wastewater containing Reactive Red 2 was mixed with a specific amount of catalyst and stirred for 30 minutes in the dark to achieve adsorption equilibrium. A 300W xenon lamp was used as the light source with an AM 1.5G filter, and wavelengths from 320 to 780nm were allowed to pass. The average incident light intensity on the surface of the reaction solution was determined to be 60mW·cm -2. First, the suspension was stirred for 30 minutes by dark adsorption to reach adsorption-desorption equilibrium, and then the photocatalytic degradation experiment was carried out with continuous stirring. The reaction operating conditions for treating dye wastewater were as follows: the amount of composite material used as catalyst was 20 mg, the initial concentration of Reactive Red 2 was 20 mg / L, the reaction solution volume was 100 mL, the initial pH was set to 7, and the pH of the solution was adjusted with H2SO4 (1 mol / L) and NaOH (1 mol / L).

[0050] The dosage of P@g-C3N4-BC-AQ was changed to study the effect of the dosage of the catalyst on the photocatalytic degradation efficiency of Reactive Red 2. The dosages were 5, 10, 15, 20 and 25 mg respectively. Figure 2 The effect of P@g-C3N4-BC-AQ dosage on the photocatalytic degradation efficiency of Reactive Red 2 is shown. When the dosage of P@g-C3N4-BC-AQ increases from 5 mg to 20 mg, the degradation efficiency of Reactive Red 2 gradually increases. Increasing the dosage of photocatalyst can increase the active sites, thereby increasing the yield of reaction species, and the photocatalytic efficiency gradually increases. When the catalyst dosage is further increased to 25 mg, the removal rate of Reactive Red 2 decreases. This may be because the aggregation of the photocatalyst increases the turbidity of the solution, resulting in the influence of light penetration, affecting the absorption of light by the photocatalyst, and failing to further improve the photocatalytic activity. Therefore, the optimal dosage of P@g-C3N4-BC-AQ is 20 mg, which is used in subsequent experimental studies.

[0051] Table 1 Degradation effect data of Reactive Red 2 under different P@g-C3N4-BC-AQ dosage conditions

[0052] <![CDATA[Dosage of P@g-C3N4-BC-AQ (mg)]]> 5 10 15 20 25 RR2 removal rate (%) 48.8 71.1 80.0 87.7 74.4

[0053] Figure 3 The effect of the mass ratio of biochar to P@g-C3N4 on the photocatalytic degradation efficiency of Reactive Red 2 by P@g-C3N4-BC-AQ during the preparation process of Example 1 is described. The mass ratios of biochar to P@g-C3N4 are 0, 2.5%, 5%, 10% and 20%, respectively. The mass ratio of biochar to P@g-C3N4 is 10%, which means that the mass ratio of biochar to P@g-C3N4 is 0.1:1. The experimental results are shown in Figure 1. Figure 4As shown. When the mass ratio increases from 0 to 10%, the degradation efficiency of Reactive Red 2 continues to improve. Thereafter, when the mass ratio increases to 20%, the degradation efficiency of Reactive Red 2 does not increase further. This is because the number of fixed sites of P@g-C3N4 on a unit mass of BC is limited. The increase in BC mass will not further increase the fixed amount of P@g-C3N4 on the surface, and the amount of AQ connected to P@g-C3N4 will not change significantly. The number of active species in the reaction system is relatively stable. Therefore, the photocatalytic efficiency will not be further improved. Therefore, the mass ratio of biochar to P@g-C3N4 was set to 10% for subsequent experiments.

[0054] Table 2 Degradation effect data of Reactive Red 2 under different mass ratios of biochar to P@g-C3N4

[0055] <![CDATA[Mass ratio of biochar to P@g-C3N4]]> 0 2.5％ 5％ 10％ 20％ RR2 removal rate (%) 71.1 75 81.3 87.7 87.2

[0056] The initial concentration of Reactive Red 2 was changed to study the effect of the concentration of Reactive Red 2 on the photocatalytic degradation efficiency. The initial concentration was set at 10, 20, 30, and 40 mg / L. The results are shown in Figure 2. Figure 4 As shown in the figure, the increase in Reactive Red 2 concentration inhibited the removal efficiency of Reactive Red 2. Specifically, when the initial concentration of Reactive Red 2 was 10 mg / L, the degradation efficiency was the highest, reaching 96%, while when the Reactive Red 2 concentration was 40 mg / L, the removal efficiency decreased to 48%. This may be because high concentrations of Reactive Red 2 produced more intermediates during the photocatalytic process, blocking the active sites of P@g-C3N4-BC-AQ. In addition, these intermediates can compete with Reactive Red 2 and consume the active species ROS, which in turn leads to a decrease in the removal rate of Reactive Red 2.

[0057] Table 3 Degradation effect data of Reactive Red 2 under different initial concentrations of Reactive Red 2

[0058] Reactive Red 2 initial concentration (mg / L) 10 20 30 40 RR2 removal rate (%) 96 87.7 60.5 47.8

[0059] Through the above experiments, the optimal conditions for material preparation and photocatalytic reaction were obtained. When the mass ratio of melamine to P@g-C3N4 was 10% and the catalyst dosage was 20mg, the best reaction effect was obtained. Under these conditions, the catalysts prepared in Cases 1 to 4 were tested and compared for their photocatalytic degradation effects on Reactive Red 2. The specific experimental results are as follows: Figure 5 As shown, the results show that the P@g-C3N4-BC-AQ composite material prepared by the present invention has a high efficiency in photocatalytic degradation of Reactive Red 2 and can effectively degrade low concentration azo dyes.

[0060] Table 4 Degradation effect data of Reactive Red 2 in implementation cases and comparative cases

[0061]

Claims

1. A method for preparing anthraquinone-loaded phosphorus-doped graphite carbon nitride / biochar photocatalytic composite material, characterized in that The preparation method is achieved by the following steps:

1. In a tubular furnace, dried sludge is pyrolyzed at 500-600°C under a nitrogen atmosphere, ground, washed, and dried to produce biochar. Second, melamine was added to ultrapure water, followed by (NH4)2HPO4. After ultrasonic oscillation, the mixture was placed in a water bath to evaporate the water. After drying and grinding, the mixture was placed in a muffle furnace and kept at 500-600°C for 3-4 hours. After cooling, the mixture was crushed into powder to obtain P@g-C3N4 material.

3. Add P@g-C3N4 material and biochar to deionized water, ultrasonically disperse to obtain a suspension, place it in a water bath to evaporate the water, dry and grind it, place it in a muffle furnace, and calcine it at a temperature of 550-600°C to obtain P-doped g-C3N4-BC material after grinding; Fourth, the P-doped g-C3N4-BC material was dispersed in deionized water and ultrasonically treated to obtain a P@g-C3N4-BC dispersion. Anthraquinone was dissolved in 1-methyl-2-pyrrolidone to obtain an anthraquinone solution. The P@g-C3N4-BC dispersion and the anthraquinone solution were stirred and mixed for 10-15 hours. The suspension was filtered to collect the solid-phase reactant, which was washed and dried to obtain an anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material. The mass ratio of the P-doped g-C3N4-BC material and anthraquinone in step 4 is (1~1.5): (1~1.5).

2. The method for preparing the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material according to claim 1, characterized in that In step 1, the temperature is raised to 500-600°C at a heating rate of 10°C / min and the pyrolysis treatment is performed for 1.5-2.5 hours.

3. The method for preparing the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material according to claim 1, characterized in that The particle size of the biochar after grinding in step 1 is 200~300 mesh.

4. The method for preparing the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material according to claim 1, characterized in that In step 2, the mass ratio of melamine to (NH4)2HPO4 is 1:0.5~3.

5. The method for preparing the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material according to claim 1, characterized in that In step 2, the temperature was raised to 550°C at a heating rate of 5°C / min and kept at this temperature for 3 h.

6. The method for preparing the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material according to claim 1, characterized in that In step three, the mass ratio of P@g-C3N4 material and biochar is 4~30:

1.

7. The method for preparing the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material according to claim 1, characterized in that In step 3, the calcination treatment is carried out at a temperature of 550° C. for 3 h.

8. The method for preparing the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material according to claim 1, characterized in that In step 4, the P-doped g-C3N4-BC material is dispersed in deionized water, and the ultrasonic treatment time is 120~180 minutes.

9. The method for preparing the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material according to claim 1, characterized in that In step 4, the solid phase reactant is washed with 1-methyl-2-pyrrolidone, ethanol and deionized water in sequence.

10. Use of the anthraquinone-loaded phosphorus-doped graphite-phase carbon nitride / biochar photocatalytic composite material prepared by the preparation method according to claim 1, characterized in that The anthraquinone-loaded P@g-C3N4 / biochar photocatalytic composite material was added to wastewater containing dyes, and a photocatalytic reaction was carried out under xenon lamp irradiation to degrade the dyes.

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