Calcium ferrite and carbon nitride composite photocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of photocatalysis, and provides a calcium ferrite and carbon nitride composite photocatalyst and a preparation method and application thereof.The preparation method comprises the steps that melamine is calcined, and carbon nitride is obtained; mixing the calcium nitrate tetrahydrate solution and the iron nitrate nonahydrate solution, and performing hydrothermal reaction to obtain calcium ferrite; carbon nitride, calcium ferrite and water are mixed and subjected to a hydrothermal reaction, and the calcium ferrite and carbon nitride composite photocatalyst is obtained. The band edge positions of the carbon nitride and the calcium ferrite are matched, and after the carbon nitride and the calcium ferrite are compounded, the soft lamellar structure of the carbon nitride can construct a heterojunction with the calcium ferrite to promote the separation of photon-generated carriers and make the catalytic reaction more efficient, so that the composite material can more effectively degrade tetracycline in the organic polluted water body.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and particularly relates to a calcium ferrite-carbon nitride 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 the imbalance of the normal human flora, cause allergies and even poisoning, seriously endanger human health, and cause irreversible environmental pollution. Therefore, exploring an efficient remediation technology for tetracycline-polluted 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.

[0003] Methods such as adsorption, electrochemistry, and photocatalysis have all achieved good results in eliminating tetracycline pollution. Among them, photocatalysis adds a photocatalyst to water, and the photocatalyst generates oxidizing free radicals under light irradiation, which can oxidize and decompose tetracycline in water into CO2, H2O, and inorganic salts. Compared with other technologies, this technology is an emerging technology with high efficiency, environmental friendliness, and broad application prospects.

[0004] Calcium ferrite (CaFe2O4) is a narrow-bandgap (bandgap width about 2 eV) p-type semiconductor with a conduction band edge of -0.1 eV and a valence band edge of +1.9 eV, which can achieve the oxidation of tetracycline. At the same time, its unique structure of multi-metal orbital hybridization gives it long-term stability to light response, and Ca and Fe are rich in reserves and the preparation cost is low. However, the photocatalytic activity of CaFe2O4 is affected by the separation and migration of carriers, and the light conversion efficiency is much lower than the theoretical value. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide a calcium ferrite-carbon nitride composite photocatalyst, a preparation method thereof, and an application thereof.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of a calcium ferrite-carbon nitride composite photocatalyst, comprising the following steps:

[0008] (1) Calcining melamine to obtain carbon nitride;

[0009] (2) Mixing a calcium nitrate tetrahydrate solution and an iron nitrate nonahydrate solution and then performing a hydrothermal reaction to obtain calcium ferrite;

[0010] (3) Mix carbon nitride, calcium ferrite and water, and carry out hydrothermal reaction to obtain the calcium ferrite-carbon nitride composite photocatalyst.

[0011] Preferably, in step (1), the heating rate of calcination is 3-7 °C / min, the target temperature is 400-600 °C, and the calcination time after reaching the target temperature is 2-6 h;

[0012] After the calcination in step (1) is completed, secondary calcination is carried out, and the conditions of secondary calcination are the same as those of the calcination.

[0013] Preferably, in step (2), the mass ratio of calcium nitrate tetrahydrate to water in the calcium nitrate tetrahydrate solution is 1-1.2:30-50;

[0014] The mass ratio of ferric nitrate nonahydrate to water in the ferric nitrate nonahydrate solution is 4-4.1:30-50;

[0015] The mass ratio of calcium nitrate tetrahydrate to ferric nitrate nonahydrate is 1-1.2:4-4.1.

[0016] Preferably, in step (2), the pH of the mixed system is 10-12.

[0017] Preferably, in step (2), the temperature of the hydrothermal reaction is 170-190 °C and the time is 8-12 h.

[0018] Preferably, in step (3), the mass ratio of carbon nitride, calcium ferrite and water is 0.5-1.5:1-1.5:70-90.

[0019] Preferably, in step (3), the temperature of the hydrothermal reaction is 170-190 °C and the time is 3-6 h.

[0020] The present invention also provides a calcium ferrite-carbon nitride composite photocatalyst prepared by the preparation method of the calcium ferrite-carbon nitride composite photocatalyst.

[0021] The present invention also provides the application of the calcium ferrite-carbon nitride composite photocatalyst in the degradation of tetracycline.

[0022] The present invention provides a preparation method of a calcium ferrite-carbon nitride composite photocatalyst, which comprises the following steps: (1) calcining melamine to obtain carbon nitride; (2) mixing a calcium nitrate tetrahydrate solution and an iron(III) nitrate nonahydrate solution and then carrying out a hydrothermal reaction to obtain calcium ferrite; (3) mixing carbon nitride, calcium ferrite and water and carrying out a hydrothermal reaction to obtain the calcium ferrite-carbon nitride composite photocatalyst. The band edge positions of carbon nitride (C3N4) and calcium ferrite (CaFe2O4) match, and C3N4 is cheap, easily available, environmentally friendly and safe. After C3N4 and CaFe2O4 are compounded, the soft sheet structure of C3N4 can form a heterojunction with CaFe2O4, promoting the separation of photo-generated carriers and making the catalytic reaction more efficient, so that the composite material can more effectively degrade tetracycline in organic polluted water bodies.

[0023] The preparation method provided by the present invention is simple, low-cost, non-toxic and harmless; the prepared catalyst has strong photocatalytic activity, stable structure, green and efficient, and has good photocatalytic performance for tetracycline under light irradiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the SEM image and elemental analysis diagram of calcium ferrite and calcium ferrite-carbon nitride composite photocatalyst in Example 1;

[0025] Figure 2 It is the degradation curve diagram of carbon nitride, calcium ferrite and calcium ferrite-carbon nitride composite photocatalyst for a tetracycline solution with a concentration of 14 mg / L in Example 1;

[0026] Figure 3 It is the degradation curve diagram of the calcium ferrite-carbon nitride composite photocatalyst for tetracycline solutions with different concentrations in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The present invention provides a preparation method of a calcium ferrite-carbon nitride composite photocatalyst, which comprises the following steps:

[0028] (1) Calcining melamine to obtain carbon nitride;

[0029] (2) Mixing a calcium nitrate tetrahydrate solution and an iron(III) nitrate nonahydrate solution and then carrying out a hydrothermal reaction to obtain calcium ferrite;

[0030] (3) Mixing carbon nitride, calcium ferrite and water and carrying out a hydrothermal reaction to obtain the calcium ferrite-carbon nitride composite photocatalyst.

[0031] In the present invention, the heating rate of the calcination in step (1) 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.

[0032] In the present invention, after the calcination in step (1) is completed, it is naturally cooled to room temperature and then ground, and then secondary calcination is carried out.

[0033] In the present invention, after the calcination in step (1) is completed, secondary calcination is carried out, and the conditions of the secondary calcination are the same as those of the calcination.

[0034] In the present invention, after the secondary calcination is completed, it is naturally cooled to room temperature and then ground to obtain carbon nitride.

[0035] In the present invention, the mass ratio of calcium nitrate tetrahydrate to water in the calcium nitrate tetrahydrate solution in step (2) is preferably 1 - 1.2:30 - 50, more preferably 1.05 - 1.15:35 - 45, and still more preferably 1.08 - 1.12:38 - 42.

[0036] In the present invention, the mass ratio of ferric nitrate nonahydrate to water in the ferric nitrate nonahydrate solution is preferably 4 - 4.1:30 - 50, more preferably 4.02 - 4.08:35 - 45, and still more preferably 4.04 - 4.06:38 - 42.

[0037] In the present invention, the mass ratio of calcium nitrate tetrahydrate to ferric nitrate nonahydrate is preferably 1 - 1.2:4 - 4.1, more preferably 1.05 - 1.15:4.02 - 4.08, and still more preferably 1.08 - 1.12:4.04 - 4.06.

[0038] In the present invention, the calcium nitrate tetrahydrate solution and the ferric nitrate nonahydrate solution are mixed into a homogeneous system.

[0039] In the present invention, the pH of the mixed system in step (2) is preferably 10 - 12, more preferably 10.5 - 11.5, and still more preferably 10.8 - 11.2.

[0040] 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 8 - 12 h, more preferably 9 - 11 h, and still more preferably 9.5 - 10.5 h.

[0041] In the present invention, after the hydrothermal reaction in step (2) 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. It is dried to constant weight to obtain calcium ferrite.

[0042] In the present invention, in step (3), the mass ratio of the carbon nitride, calcium ferrite, and water is preferably 0.5 - 1.5:1 - 1.5:70 - 90, more preferably 0.6 - 1.4:1.1 - 1.4:75 - 85, and still more preferably 0.8 - 1.2:1.2 - 1.3:78 - 82.

[0043] In the present invention, in step (3), the mixing method is ultrasonic, and the ultrasonic time is preferably 20 - 30 min, more preferably 22 - 28 min, and still more preferably 24 - 26 min.

[0044] In the present invention, in step (3), the temperature of the hydrothermal reaction 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.

[0045] In the present invention, after the hydrothermal reaction in step (3) is completed, it is naturally cooled to room temperature, then washed until neutral and dried to obtain a calcium ferrite-carbon nitride composite photocatalyst.

[0046] The present invention also provides a calcium ferrite-carbon nitride composite photocatalyst prepared by the preparation method of the calcium ferrite-carbon nitride composite photocatalyst.

[0047] The present invention also provides the application of the calcium ferrite-carbon nitride composite photocatalyst in the degradation of tetracycline.

[0048] The technical solutions provided by the present invention are described in detail below with reference to the examples, but they should not be construed as limiting the protection scope of the present invention.

[0049] Example 1

[0050] Put melamine in a ceramic crucible, heat it to 450°C at a rate of 5°C / min, and calcine it at 450°C for 2 h; then naturally cool it to room temperature and grind it. Heat it to 450°C at a rate of 5°C / min and perform secondary calcination at 450°C for 2 h, and cool it to room temperature and grind it to obtain carbon nitride.

[0051] Dissolve 1.18 g of calcium nitrate tetrahydrate in 40 g of water to obtain a calcium nitrate tetrahydrate solution; dissolve 4.04 g of ferric nitrate nonahydrate in 40 g of water to obtain a ferric nitrate nonahydrate solution; mix the calcium nitrate tetrahydrate solution and the ferric nitrate nonahydrate solution evenly, and adjust the pH to 11; then carry out hydrothermal reaction at 180 °C for 10 h, and after completion, naturally cool to room temperature and wash until neutral, and dry the solid at 60 °C to constant weight to obtain calcium ferrite.

[0052] Take 1 g of carbon nitride, 1.2 g of calcium ferrite and 80 g of water and mix them, and ultrasonicate for 20 min; then carry out hydrothermal reaction at 180 °C for 4 h, naturally cool to room temperature, wash until neutral and dry to obtain a calcium ferrite-carbon nitride composite photocatalyst.

[0053] Carry out SEM observation and elemental analysis on the calcium ferrite and the calcium ferrite-carbon nitride composite photocatalyst in Example 1, and the obtained SEM images and elemental analysis diagrams are as Figure 1 shown. Figure 1 In (a) is the SEM image of calcium ferrite, Figure 1 in (b) is the SEM image of the calcium ferrite-carbon nitride composite photocatalyst, Figure 1 in (c) is the elemental analysis diagram of calcium ferrite, Figure 1 in (d) is the elemental analysis diagram of the calcium ferrite-carbon nitride composite photocatalyst. It can be seen from (a) and (b) that the prepared calcium ferrite presents a cube or cuboid shape with a smooth surface; while the calcium ferrite-carbon nitride composite photocatalyst after being coated with C3N4 presents a 3D structure stacked by cubes. This may be due to the formation of a heterojunction after the C3N4 composite and the change of the crystal formation process of the calcium ferrite-carbon nitride composite photocatalyst. It can be seen from (c) and (d) that the elemental analysis results of the calcium ferrite-carbon nitride composite photocatalyst are similar to those of calcium ferrite. The calcium ferrite-carbon nitride composite photocatalyst contains a large number of absorption peaks of Ca, Fe, N, and C, and the peaks of C and N are significantly higher than those of calcium ferrite, indicating that carbon nitride and calcium ferrite are successfully composite.

[0054] Prepare 200 mL of a tetracycline solution with a concentration of 14 mg / L, add 0.05 g of the carbon nitride, calcium ferrite and calcium ferrite-carbon nitride composite photocatalyst in Example 1 respectively, add a magnetic rotor, place it on a magnetic stirrer in a reaction box for dark treatment for 30 minutes, take samples every 15 minutes during the dark treatment process, and then react under light irradiation for 60 minutes. In the first 40 minutes of the light reaction, take samples every 10 minutes, and in the last 40 - 80 minutes of the light reaction, take samples every 20 minutes; the volume taken each time is 4 mL, and after filtering through a filter membrane, it is filled into a brown injection vial; after sampling is completed, detect the content of tetracycline in the sample, and the results are as Figure 2 shown. It can be seen from the figure that compared with before the composite, the calcium ferrite-carbon nitride catalyst has a significant improvement in the removal effect of tetracycline.

[0055] Prepare a 200 mL tetracycline solution with a concentration of 6 mg / L, add the calcium ferrite carbon nitride composite photocatalyst in Example 1, add a magnetic rotor, place it 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 the reaction is carried out under light irradiation for 60 minutes. In the first 40 minutes of the light reaction, samples are taken every 10 minutes, and in the last 40 - 80 minutes of the light reaction, samples are taken every 20 minutes; the volume of each sample taken is 4 mL, and after filtration through a filter membrane, it is filled into a brown injection vial; after sampling is completed, the content of tetracycline in the sample is detected; the degradation effect of the calcium ferrite carbon nitride composite photocatalyst in Example 1 on tetracycline solutions with different concentrations is as Figure 3 shown. It can be seen from the figure that the prepared calcium ferrite carbon nitride composite photocatalyst has a good removal effect on low-concentration tetracycline in water.

[0056] As can be seen from the above examples, the calcium ferrite carbon nitride composite photocatalyst provided by the present invention. The band edge positions of carbon nitride and calcium ferrite are matched. After combining C3N4 with CaFe2O4, the soft lamellar structure of C3N4 can form a heterojunction with CaFe2O4, promoting the separation of photo-generated carriers and making the catalytic reaction more efficient, so that the composite material can more effectively degrade tetracycline in organic polluted water bodies.

[0057] 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 calcium ferrite-carbon nitride composite photocatalyst, characterized in that, It includes the following steps: (1) Calcine melamine to obtain carbon nitride; (2) Mix a calcium nitrate tetrahydrate solution and an iron(III) nitrate nonahydrate solution and then carry out a hydrothermal reaction to obtain calcium ferrite; (3) Mix carbon nitride, calcium ferrite and water and carry out a hydrothermal reaction to obtain the calcium ferrite-carbon nitride composite photocatalyst.

2. The preparation method of the calcium ferrite-carbon nitride composite photocatalyst according to claim 1, characterized in that, In step (1), the heating rate of the calcination is 3 - 7 °C / min, the target temperature is 400 - 600 °C, and the calcination time after reaching the target temperature is 2 - 6 h; In step (1), after the calcination is completed, secondary calcination is carried out, and the conditions of the secondary calcination are the same as those of the calcination.

3. The preparation method of the calcium ferrite-carbon nitride composite photocatalyst according to claim 2, wherein, In step (2), the mass ratio of calcium nitrate tetrahydrate to water in the calcium nitrate tetrahydrate solution is 1 - 1.2:30 - 50; The mass ratio of iron(III) nitrate nonahydrate to water in the iron(III) nitrate nonahydrate solution is 4 - 4.1:30 - 50; The mass ratio of calcium nitrate tetrahydrate to iron(III) nitrate nonahydrate is 1 - 1.2:4 - 4.

1.

4. The preparation method of the calcium ferrite-carbon nitride composite photocatalyst according to claim 3, characterized in that, In step (2), the pH of the mixed system is 10 - 12.

5. The preparation method of the calcium ferrite-carbon nitride composite photocatalyst according to claim 4, wherein, In step (2), the temperature of the hydrothermal reaction is 170 - 190 °C and the time is 8 - 12 h.

6. The preparation method of the calcium ferrite-carbon nitride composite photocatalyst according to claim 5, characterized in that, In step (3), the mass ratio of carbon nitride, calcium ferrite and water is 0.5 - 1.5:1 - 1.5:70 - 90.

7. The preparation method of the calcium ferrite-carbon nitride composite photocatalyst according to claim 6, characterized in that, In step (3), the temperature of the hydrothermal reaction is 170 - 190 °C and the time is 3 - 6 h.

8. The calcium ferrite-carbon nitride composite photocatalyst prepared by the preparation method of the calcium ferrite-carbon nitride composite photocatalyst according to any one of claims 1 - 7.

9. The application of the calcium ferrite-carbon nitride composite photocatalyst according to claim 8 in the degradation of tetracycline.

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