Biochar composite photocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of photocatalysis, and provides a biochar composite photocatalyst and a preparation method and application thereof.The preparation method comprises the steps that a calcium nitrate tetrahydrate solution and an iron nitrate nonahydrate solution are mixed and then subjected to a hydrothermal reaction, and calcium ferrite is obtained; the preparation method comprises the following steps: mixing carbon nitride, calcium ferrite and water, and carrying out hydrothermal reaction to obtain calcium ferrite carbon nitride; performing pyrolysis on the rice hull powder to obtain biochar; the preparation method comprises the following steps: mixing calcium ferrite, carbon nitride, biochar and water, and carrying out hydrothermal reaction to obtain the biochar composite photocatalyst. The preparation method is simple, low in cost, non-toxic and harmless; the raw materials of the biochar-loaded calcium ferrite and carbon nitride composite photocatalyst are from agricultural and forestry wastes, so that a way is provided for recycling the wastes in agriculture and forestry; according to the biochar-loaded calcium ferrite and carbon nitride composite photocatalyst, the photocatalytic activity of CaFe2O4 is effectively improved, and efficient degradation of tetracycline is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysis, and particularly to a biochar composite photocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Tetracycline has become one of the most widely used antibiotics due to its broad-spectrum antibacterial and growth-promoting properties. However, the absorption rate of tetracycline is relatively low, and 70% - 90% of it is excreted with feces and urine and enters the environment with wastewater, becoming one of the antibiotics with the highest detection frequency in surface water. Long-term exposure to an environment containing tetracycline and tetracycline resistance genes can lead to imbalance of the normal human flora, trigger allergies and even poisoning, seriously endanger human health, and cause irreversible environmental pollution. Therefore, exploring an efficient repair technology for tetracycline-contaminated water bodies, accelerating its degradation in the environment, and reducing the threat to the aquatic ecosystem and water environment safety is an urgent problem to be solved in the current field of water pollution control. Summary of the Invention

[0003] The purpose of the present invention is to provide a biochar composite photocatalyst, a preparation method thereof, and an application thereof to solve the problem of difficult degradation of tetracycline.

[0004] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a preparation method of a biochar composite photocatalyst, comprising the following steps:

[0006] (1) Mix a calcium nitrate tetrahydrate solution and an iron(III) nitrate nonahydrate solution, and then carry out a hydrothermal reaction to obtain calcium ferrite.

[0007] (2) Mix carbon nitride, calcium ferrite, and water, and carry out a hydrothermal reaction to obtain calcium ferrite carbon nitride.

[0008] (3) Pyrolyze rice husk powder to obtain biochar.

[0009] (4) Mix calcium ferrite carbon nitride, biochar, and water, and carry out a hydrothermal reaction to obtain the biochar composite photocatalyst.

[0010] Preferably, in step (1), the mass ratio of calcium nitrate tetrahydrate to water in the calcium nitrate tetrahydrate solution is 0.5 - 2:20 - 60;

[0011] The mass ratio of iron(III) nitrate nonahydrate to water in the iron(III) nitrate nonahydrate solution is 2 - 6:20 - 60;

[0012] The mass ratio of calcium nitrate tetrahydrate to iron(III) nitrate nonahydrate is 0.5 - 2:2 - 6;

[0013] The pH of the mixed system in step (1) is 10 - 12.

[0014] Preferably, in step (1), the temperature of the hydrothermal reaction is 170-190 °C and the time is 8-12 h.

[0015] Preferably, in step (2), the mass ratio of the carbon nitride, calcium ferrite and water is 0.5-1.5:1-3:50-100.

[0016] Preferably, in step (2), the temperature of the hydrothermal reaction is 170-190 °C and the time is 3-6 h.

[0017] Preferably, in step (3), the mesh number of the rice husk powder is 80-120 meshes;

[0018] In step (3), the heating rate of the pyrolysis is 3-7 °C / min, the target temperature is 400-600 °C, and the pyrolysis time after reaching the target temperature is 5-8 h.

[0019] Preferably, in step (4), the mass ratio of the calcium ferrite carbon nitride, biochar and water is 1-3:0.05-2:50-100.

[0020] Preferably, in step (4), the temperature of the hydrothermal reaction is 170-190 °C and the time is 3-6 h.

[0021] The present invention also provides a biochar composite photocatalyst prepared by the preparation method of the biochar composite photocatalyst.

[0022] The present invention also provides the application of the biochar composite photocatalyst in the degradation of tetracycline.

[0023] The present invention provides a preparation method of a biochar composite photocatalyst, comprising the following steps: (1) mixing a calcium nitrate tetrahydrate solution and an iron nitrate nonahydrate solution and then carrying out a hydrothermal reaction to obtain calcium ferrite; (2) mixing carbon nitride, calcium ferrite and water and carrying out a hydrothermal reaction to obtain calcium ferrite carbon nitride; (3) pyrolyzing rice husk powder to obtain biochar; (4) mixing calcium ferrite carbon nitride, biochar and water and carrying out a hydrothermal reaction to obtain the biochar composite photocatalyst.

[0024] In the present invention, the band gap of calcium ferrite (CaFe2O4) is about 2 eV, which has the potential for photocatalytic degradation of tetracycline. However, its carriers are prone to recombination, resulting in low photocatalytic efficiency. The band edge position of carbon nitride (C3N4) matches that of CaFe2O4, enabling the formation of a heterojunction. Moreover, the delocalized π-conjugated system formed by the sp2 hybridization of C and N in C3N4 is very suitable for the transfer of photo-generated electrons. After forming a heterojunction with CaFe2O4, C3N4 can effectively improve the degradation ability of tetracycline. The porous structure and large specific surface area of carbon materials can effectively enhance the adsorption capacity of the photocatalyst for tetracycline. At the same time, the good conductivity of carbon materials can also promote electron transfer, improving the photocatalytic effect from multiple aspects. The present invention uses biochar materials, which have a wide range of raw material sources, simple preparation processes, and low costs. They can not only enhance the photocatalytic effect but also solve the environmental hazards brought by organic waste.

[0025] The preparation method of the present invention is simple, low in cost, non-toxic and harmless; the raw materials of the biochar-supported calcium ferrite carbon nitride composite photocatalyst come from agricultural and forestry waste, providing a way for the resource utilization of agricultural and forestry waste; the biochar-supported calcium ferrite carbon nitride composite photocatalyst effectively improves the photocatalytic activity of CaFe2O4 and realizes the efficient degradation of tetracycline. Description of the Drawings

[0026] Figure 1 XRD patterns of each material in Example 1;

[0027] Figure 2 Treatment effect diagrams of each material on tetracycline in Example 1;

[0028] Figure 3 Treatment effect diagrams of the biochar composite photocatalysts prepared in Examples 1 to 4 on tetracycline. Detailed Embodiments

[0029] The present invention provides a preparation method of a biochar composite photocatalyst, which comprises the following steps:

[0030] (1) Mix a calcium nitrate tetrahydrate solution and an iron nitrate nonahydrate solution and carry out a hydrothermal reaction to obtain calcium ferrite;

[0031] (2) Mix carbon nitride, calcium ferrite and water and carry out a hydrothermal reaction to obtain calcium ferrite carbon nitride;

[0032] (3) Pyrolyze rice husk powder to obtain biochar;

[0033] (4) Mix calcium ferrite carbon nitride, biochar and water and carry out a hydrothermal reaction to obtain the biochar composite photocatalyst.

[0034] In the present invention, the mass ratio of calcium nitrate tetrahydrate to water in the calcium nitrate tetrahydrate solution in step (1) is preferably 0.5 - 2:20 - 60, more preferably 0.6 - 1.8:30 - 50, and still more preferably 0.8 - 1.4:35 - 45.

[0035] In the present invention, the mass ratio of ferric nitrate nonahydrate to water in the ferric nitrate nonahydrate solution is preferably 2 - 6:20 - 60, more preferably 3 - 5:30 - 50, and still more preferably 3.5 - 4.5:35 - 45.

[0036] In the present invention, the mass ratio of calcium nitrate tetrahydrate to ferric nitrate nonahydrate is preferably 0.5 - 2:2 - 6, more preferably 0.6 - 1.8:3 - 5, and still more preferably 0.8 - 1.4:3.5 - 4.5.

[0037] In the present invention, the calcium nitrate tetrahydrate solution and the ferric nitrate nonahydrate solution are mixed into a homogeneous system.

[0038] In the present invention, the pH of the mixed system in step (1) is preferably 10 - 12, more preferably 10.5 - 11.5, and still more preferably 10.8 - 11.2.

[0039] In the present invention, the temperature of the hydrothermal reaction in step (1) is preferably 170 - 190°C, more preferably 175 - 185°C, and still more preferably 178 - 182°C; the time is preferably 8 - 12 h, more preferably 9 - 11 h, and still more preferably 9.5 - 10.5 h.

[0040] In the present invention, after the hydrothermal reaction in step (1) is completed, it is naturally cooled to room temperature, washed until neutral, and then dried; the drying temperature is preferably 50 - 70°C, more preferably 55 - 65°C, and still more preferably 58 - 62°C, and dried to constant weight to obtain calcium ferrite.

[0041] In the present invention, a method for preparing carbon nitride is also provided, which includes the following steps:

[0042] Melamine is sequentially calcined, ground, secondarily calcined, and secondarily ground to obtain carbon nitride.

[0043] In the present invention, the heating rate of the calcination is preferably 3 - 7°C / min, more preferably 3.5 - 6.5°C / min, and still more preferably 4 - 5°C / min; the target temperature is preferably 400 - 600°C, more preferably 450 - 550°C, and still more preferably 480 - 520°C; the calcination time after reaching the target temperature is preferably 2 - 6 h, more preferably 3 - 5 h, and still more preferably 3.5 - 4.5 h.

[0044] In the present invention, after the calcination is completed, it is naturally cooled to room temperature and ground, and then secondarily calcined.

[0045] In the present invention, the conditions for the secondary calcination are the same as those for the calcination.

[0046] In the present invention, after the secondary calcination, it is naturally cooled to room temperature and then ground to obtain carbon nitride.

[0047] In the present invention, the mass ratio of the carbon nitride, calcium ferrite and water described in step (2) is preferably 0.5 - 1.5:1 - 3:50 - 100, more preferably 0.6 - 1.4:1.5 - 2.5:60 - 90, and still more preferably 0.8 - 1.2:1.8 - 2.3:70 - 80.

[0048] In the present invention, the mixing method in step (2) is ultrasonic, and the ultrasonic time is preferably 15 - 30 min, more preferably 20 - 25 min, and still more preferably 22 - 23 min.

[0049] In the present invention, the temperature of the hydrothermal reaction in step (2) is preferably 170 - 190 °C, more preferably 175 - 185 °C, and still more preferably 178 - 182 °C; the time is preferably 3 - 6 h, more preferably 3.5 - 5.5 h, and still more preferably 4 - 5 h.

[0050] In the present invention, after the hydrothermal reaction in step (2) ends, it is naturally cooled to room temperature, then washed to neutral and dried; the drying temperature is preferably 50 - 70 °C, more preferably 55 - 65 °C, and still more preferably 58 - 62 °C, and dried to constant weight to obtain calcium ferrite carbon nitride.

[0051] In the present invention, the rice husks are washed, the washing reagent is water, and the number of washing times is 5 - 9 times; after washing, it is dried, and the drying temperature is preferably 50 - 70 °C, more preferably 55 - 65 °C, and still more preferably 58 - 62 °C; after drying, it is crushed to obtain rice husk powder.

[0052] In the present invention, the mesh number of the rice husk powder described in step (3) is preferably 80 - 120 mesh, more preferably 85 - 115 mesh, and still more preferably 90 - 110 mesh.

[0053] In the present invention, the heating rate of the pyrolysis in step (3) is preferably 3 - 7 °C / min, more preferably 3.5 - 6.5 °C / min, and still more preferably 4 - 5 °C / min; the target temperature is preferably 400 - 600 °C, more preferably 450 - 550 °C, and still more preferably 480 - 520 °C; the pyrolysis time after reaching the target temperature is preferably 5 - 8 h, more preferably 6 - 7 h, and still more preferably 6.4 - 6.6 h.

[0054] In the present invention, after the pyrolysis in step (3) is completed, it is naturally cooled to room temperature, washed, and dried to obtain biochar. The drying temperature is preferably 50 - 70 °C, more preferably 55 - 65 °C, and even more preferably 58 - 62 °C.

[0055] In the present invention, the mass ratio of calcium ferrite carbon nitride, biochar, and water in step (4) is preferably 1 - 3:0.05 - 2:50 - 100, more preferably 1.5 - 2.5:0.1 - 1.5:60 - 90, and even more preferably 1.8 - 2.2:0.5 - 1:70 - 80.

[0056] In the present invention, the mixing method in step (4) is ultrasonic. The ultrasonic time is preferably 15 - 30 min, more preferably 20 - 25 min, and even more preferably 22 - 23 min.

[0057] In the present invention, the temperature of the hydrothermal reaction in step (4) is preferably 170 - 190 °C, more preferably 175 - 185 °C, and even more preferably 178 - 182 °C; the time is preferably 3 - 6 h, more preferably 3.5 - 5.5 h, and even more preferably 4 - 5 h.

[0058] In the present invention, after the hydrothermal reaction in step (4) is completed, it is naturally cooled to room temperature, then washed and dried; the drying temperature is preferably 50 - 70 °C, more preferably 55 - 65 °C, and even more preferably 58 - 62 °C. It is dried to a constant weight to obtain the biochar composite photocatalyst.

[0059] The present invention also provides a biochar composite photocatalyst prepared by the preparation method of the biochar composite photocatalyst.

[0060] The present invention also provides the application of the biochar composite photocatalyst in the degradation of tetracycline.

[0061] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0062] Example 1

[0063] 10 g of melamine is placed in a ceramic crucible, heated to 450 °C (heating rate 5 °C / min), calcined in a muffle furnace for 2 h, ground after being naturally cooled to room temperature, re - placed in the muffle furnace for secondary calcination under the same conditions, and ground after cooling to room temperature to obtain C3N4.

[0064] Dissolve 1.18 g of calcium nitrate tetrahydrate and 4.04 g of iron(III) nitrate nonahydrate separately in 40 g of ultrapure water, mix them into a homogeneous solution, adjust the pH of the solution to 11, then transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner, and carry out a hydrothermal reaction at 180 °C for 10 h. After the sample is cooled to room temperature, wash it until neutral, put it in an oven at 60 °C to dry, and then grind the sample to obtain CaFe2O4.

[0065] Disperse 1 g of the prepared pale-yellow C3N4 powder and 1.2 g of the prepared brick-red CaFe2O4 powder in 80 g of ultrapure water, ultrasonically treat for 20 min, transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner, carry out a hydrothermal reaction at 180 °C for 4 h. After the sample is cooled to room temperature, wash it until neutral, dry it at 60 °C, and then grind the sample to obtain calcium ferrate carbon nitride.

[0066] Wash 150 g of rice husks 4 times with tap water, then wash 3 times with deionized water, dry in the air, put them in an oven at 60 °C to dry, and then crush them with a crusher and pass through a 100-mesh sieve. Put 5 g of the rice husk powder into a tubular furnace, heat it to 500 °C at a rate of 4 °C / min, and then pyrolyze for 7 h. After the sample is cooled to room temperature, take it out, wash it, and put it in an oven at 60 °C to dry to obtain biochar.

[0067] Disperse 1 g of the prepared calcium ferrate carbon nitride and 0.25 g of the prepared biochar in 80 g of ultrapure water, ultrasonically treat for 20 min, transfer it to a stainless-steel autoclave with a polytetrafluoroethylene liner, carry out a hydrothermal reaction at 180 °C for 4 h. After the sample is cooled to room temperature, wash it, dry it at 60 °C, and then grind the sample to obtain a biochar-supported calcium ferrate carbon nitride composite photocatalyst with a mass ratio of 25%.

[0068] Carry out XRD observations on the carbon nitride, calcium ferrate, calcium ferrate carbon nitride, biochar, and biochar-supported calcium ferrate carbon nitride in Example 1. The results are as Figure 1 shown. It can be seen that the (100) and (002) crystal planes in the graphite structure of carbon nitride appear at 13.3° and 27.5° respectively; the characteristic peaks of calcium ferrate appear at 24.03°, 33.5°, 35.5°, 40.7°, 49.3°, 53.8°, 62.3° and 63.9° respectively, corresponding to the (220), (320), (121), (310), (331), (151), (620) and (022) crystal planes of CaFe2O4; the characteristic peak at 26.6° of biochar corresponds to the (003) crystal plane of graphite-phase carbon; obvious diffraction peaks of carbon nitride and calcium ferrate can be seen in calcium ferrate carbon nitride; while the biochar-supported calcium ferrate carbon nitride composite photocatalyst shows the characteristic peaks of carbon nitride, calcium ferrate and biochar at the same time, but the diffraction peaks of biochar and carbon nitride are weak, indicating that the biochar-supported calcium ferrate carbon nitride photocatalyst is successfully compounded.

[0069] Example 2

[0070] The difference between Example 2 and Example 1 is that the dosage of biochar is changed to 0.15 g, and a biochar-supported calcium ferrite carbon nitride composite photocatalyst with a mass ratio of 15% is prepared.

[0071] Example 3

[0072] The difference between Example 3 and Example 1 is that the dosage of biochar is changed to 0.5 g, and a biochar-supported calcium ferrite carbon nitride composite photocatalyst with a mass ratio of 50% is prepared.

[0073] Example 4

[0074] The difference between Example 4 and Example 1 is that the dosage of biochar is changed to 0.1 g, and a biochar-supported calcium ferrite carbon nitride composite photocatalyst with a mass ratio of 10% is prepared.

[0075] Performance Test

[0076] Prepare a tetracycline solution with a mass concentration of 14 mg / L. Take 200 mL of the tetracycline solution respectively, add 0.05 g of the prepared photocatalyst into the tetracycline solution, add a magnetic rotor, and take an initial sample.

[0077] Place the above tetracycline solution on a magnetic stirrer in the reaction box for dark treatment for 30 minutes. During the dark treatment, samples are taken every 15 minutes, and then reacted under light irradiation for 60 minutes. During the first 40 minutes of the light reaction, samples are taken every 10 minutes, and during the last 40 - 80 minutes of the light reaction, samples are taken every 20 minutes; the volume taken each time is 4 mL, and after filtration through a filter membrane, it is filled into a brown injection vial.

[0078] After sampling, detect the content of tetracycline in the sample.

[0079] Test the various materials in Example 1 according to the above method, and the treatment effect is as Figure 2 shown. It can be seen from the figure that after loading with biochar, the degradation effect of the photocatalyst on tetracycline is greatly improved.

[0080] Test the biochar-supported calcium ferrite carbon nitride composite photocatalysts prepared in Examples 1 - 4 according to the above method, and the treatment effect is as Figure 3 shown. It can be seen from the figure that the biochar-supported calcium ferrite carbon nitride composite photocatalyst with a mass ratio of 25% has the best effect on removing tetracycline.

[0081] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a biochar composite photocatalyst, characterized in that, It includes the following steps: (1) Mix a calcium nitrate tetrahydrate solution and an iron(III) nitrate nonahydrate solution, and then carry out a hydrothermal reaction to obtain calcium ferrite; (2) Mix carbon nitride, calcium ferrite and water, and carry out a hydrothermal reaction to obtain calcium ferrite carbon nitride; (3) Pyrolyze rice husk powder to obtain biochar; (4) Mix calcium ferrite carbon nitride, biochar and water, and carry out a hydrothermal reaction to obtain the biochar composite photocatalyst.

2. The preparation method of the biochar composite photocatalyst according to claim 1, characterized in that, In step (1), the mass ratio of calcium nitrate tetrahydrate to water in the calcium nitrate tetrahydrate solution is 0.5 - 2:20 - 60; In the iron(III) nitrate nonahydrate solution, the mass ratio of iron(III) nitrate nonahydrate to water is 2 - 6:20 - 60; The mass ratio of calcium nitrate tetrahydrate to iron(III) nitrate nonahydrate is 0.5 - 2:2 - 6; In step (1), the pH of the mixed system is 10 - 12.

3. The preparation method of the biochar composite photocatalyst according to claim 2, wherein, In step (1), the temperature of the hydrothermal reaction is 170 - 190 °C, and the time is 8 - 12 h.

4. The preparation method of the biochar composite photocatalyst according to claim 3, wherein, In step (2), the mass ratio of carbon nitride, calcium ferrite and water is 0.5 - 1.5:1 - 3:50 - 100.

5. The preparation method of the biochar composite photocatalyst according to claim 4, wherein, In step (2), the temperature of the hydrothermal reaction is 170 - 190 °C, and the time is 3 - 6 h.

6. The preparation method of the biochar composite photocatalyst according to claim 5, wherein, In step (3), the mesh number of the rice husk powder is 80 - 120 mesh; In step (3), the heating rate of the pyrolysis is 3 - 7 °C / min, the target temperature is 400 - 600 °C, and the pyrolysis time after reaching the target temperature is 5 - 8 h.

7. The preparation method of the biochar composite photocatalyst according to claim 6, characterized in that, In step (4), the mass ratio of calcium ferrite carbon nitride, biochar and water is 1 - 3:0.05 - 2:50 - 100.

8. The preparation method of the biochar composite photocatalyst according to claim 7, wherein, In step (4), the temperature of the hydrothermal reaction is 170 - 190 °C, and the time is 3 - 6 h.

9. The biochar composite photocatalyst prepared by the preparation method of the biochar composite photocatalyst according to any one of claims 1 - 8.

10. The application of the biochar composite photocatalyst according to claim 9 in the degradation of tetracycline.

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