Potassium and multiple types of iodine co-doped carbon nitride and preparation method and application thereof

Abstract

The invention discloses a potassium and multiple types of iodine co-doped carbon nitride and a preparation method and application thereof. The preparation method specifically comprises the following steps: dissolving potassium iodide in water to obtain a potassium iodide solution, then photo-oxidizing the potassium iodide solution to obtain a photo-oxidized potassium iodide solution; adding melamine to the photo-oxidized potassium iodide solution, stirring and evaporating at 80-100°C, and then putting it into a muffle furnace, heating it to 500-600°C at a heating rate of 2-5°C / min, and then keeping it warm and calcining it for 2-4 hours, cooling it to room temperature, and then washing and drying it with water to obtain potassium and multiple types of iodine co-doped carbon nitride. The potassium and multiple types of iodine co-doped carbon nitride of the present invention can effectively improve the photocatalytic performance of carbon nitride and improve the photocatalytic production rate of hydrogen peroxide.

Description

Technical Field

[0001] The invention belongs to the field of material technology and relates to a graphite phase carbon nitride photocatalyst, and in particular to a potassium and multiple types of iodine co-doped carbon nitride and a preparation method and application thereof. Background Art

[0002] As an important multifunctional chemical resource, hydrogen peroxide is widely used in papermaking, chemical synthesis, environmental protection, medical disinfection and other fields. Currently, most of the world's hydrogen peroxide is produced by the anthraquinone process, but this process is complicated, cumbersome to operate, and there is a risk of leakage of organic raw materials.

[0003] Photocatalytic technology uses solar energy to synthesize hydrogen peroxide from the earth's abundant water and oxygen resources. Compared with the anthraquinone process, this synthesis method uses sunlight as the only energy supply, has mild reaction conditions, simple and controllable operation, and no secondary pollution. It is considered to be an attractive path to sustainable green development. However, existing photocatalytic materials still have various problems.

[0004] As an environmentally friendly, physically and chemically stable, cheap and easy-to-prepare catalyst, graphite carbon nitride is widely used in visible light water splitting to produce hydrogen and organic wastewater degradation. However, graphite carbon nitride also faces problems such as fast carrier recombination and insufficient solar energy absorption. Heteroatom doping is considered to be an effective way to mitigate these defects.

[0005] The common method currently is to improve the light absorption performance of graphite phase carbon nitride, optimize the electronic structure, promote the transfer of photogenerated carriers, and improve the photocatalytic performance of the catalyst by introducing heteroatoms such as iodine and potassium. For example, Chinese Patent 202011118096.3 improves its photocatalytic efficiency by co-doping iodine and potassium. On the one hand, the band gap of carbon nitride is reduced by doping with inorganic iodine elements, and on the other hand, the separation efficiency of photogenerated electrons and holes is improved by doping with metal element potassium, and the photocatalytic efficiency of carbon nitride is improved by the synergistic effect of the two. However, the current heteroatom doping still has some limitations in practical applications. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a potassium and multiple types of iodine co-doped carbon nitride and a preparation method and application thereof. The potassium and multiple types of iodine co-doped carbon nitride of the present invention can effectively improve the photocatalytic performance of carbon nitride and increase the photocatalytic production rate of hydrogen peroxide.

[0007] The technical solution of the present invention is achieved in this way:

[0008] A method for preparing potassium and multiple types of iodine co-doped carbon nitride, specifically comprising the following steps:

[0009] (1) dissolving potassium iodide in water to obtain a potassium iodide solution, and then subjecting the potassium iodide solution to photo-oxidation treatment to obtain a photo-oxidized potassium iodide solution;

[0010] (2) Add melamine to the photo-oxidized potassium iodide solution, evaporate to dryness with stirring at 80-100 °C, place in a muffle furnace, and heat to 500-600 °C at a heating rate of 2-5 °C / min, then keep warm and calcine for 2-4 h. After cooling to room temperature, wash with water and dry, potassium and various types of iodine co-doped carbon nitride is obtained.

[0011] Furthermore, the mass ratio of potassium iodide to melamine is 1~4:1.

[0012] Furthermore, the mass ratio of potassium iodide to melamine is 3:1.

[0013] Furthermore, the specific steps of the photo-oxidation treatment in step (1) are: placing the potassium iodide solution under xenon lamp illumination conditions, and the illumination time is ≤2.5 h.

[0014] Furthermore, the photo-oxidation treatment time is 1.5~2 h.

[0015] The potassium and multiple types of iodine co-doped carbon nitride prepared by the above-mentioned method for preparing potassium and multiple types of iodine co-doped carbon nitride is used as a photocatalyst to produce hydrogen peroxide or degrade organic pollutants.

[0016] Furthermore, potassium and various types of iodine co-doped carbon nitride were used as photocatalysts to produce hydrogen peroxide. The specific steps were as follows: the photocatalyst was dissolved in a mixed solution of water and organic alcohol and ultrasonically treated for 0 to 5 min, then reacted in the dark for 5 to 10 min, and then placed under visible light conditions.

[0017] Furthermore, the organic alcohol accounts for 10-50% of the total volume of the mixed solution of water and the organic alcohol; the mass volume ratio of the photocatalyst to the mixed solution is 1 mg: 1-5 mL.

[0018] Furthermore, the organic alcohol is one of methanol, ethanol, isopropanol or tert-butanol.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention treats potassium iodide by photo-oxidation and then mixes it with melamine and calcines it, thereby adding potassium and various iodine substances (iodine anions I - and iodine trianion I3 -), the incorporation of potassium and iodine can improve the light absorption performance of carbon nitride, optimize the electronic structure, and enhance the photocatalytic performance of carbon nitride; at the same time, the embedded multi-type iodine substances can form a redox system, and the I - and I3 - The redox cycles further accelerate the migration and separation of photogenerated carriers, further improving the photocatalytic performance of carbon nitride.

[0021] 2. The preparation process of the present invention is simple, easy to operate, and is conducive to industrial production. The prepared potassium and various types of iodine co-doped carbon nitride can efficiently degrade organic pollutants and remove total organic carbon. It exhibits an excellent photoproduction rate (34.27 mmol / gh) in the process of visible light catalytic production of hydrogen peroxide, which is far higher than the photoproduction rate (0.4~15mmol / gh) of similar catalysts (carbon nitride-based heteroatom-doped catalysts, carbon nitride crystalline catalysts, carbon nitride defective catalysts, etc.). It also maintains a relatively high hydrogen peroxide photoproduction rate in liquid waste liquid, showing great practical application potential.

[0022] 3. The present invention controls the heating rate to 2-5°C / min, which is beneficial for the carbon nitride precursor to have sufficient time to cross-link during the polymerization process to obtain carbon nitride with higher crystallinity and better catalytic performance; and by controlling the mass ratio of potassium iodide and melamine, the embedding amount of iodine and potassium in carbon nitride is optimized to avoid a low embedding amount, which makes it impossible for potassium and iodine to fully play the role of accelerating carrier migration and separation, and to avoid an excessively high embedding amount that affects the photocatalytic performance of carbon nitride itself and reduces the catalytic efficiency of carbon nitride. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 - Scanning electron microscope pictures and transmission electron microscope pictures of the carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0024] Figure 2 - X-ray diffraction spectra of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0025] Figure 3 -X-ray photoelectron spectra of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0026] Figure 4 -I 3d X-ray photoelectron energy fine spectra of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0027] Figure 5 - Photoelectric properties of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0028] Figure 6-The photocatalytic production rate of hydrogen peroxide by the carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0029] Figure 7 -The photocatalytic production rate of hydrogen peroxide by the carbon nitride prepared in Examples 1 to 4.

[0030] Figure 8 -The recycling performance of the carbon nitride prepared in Example 1 in producing hydrogen peroxide under visible light catalysis.

[0031] Fig. 9 - The efficiency of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 in in-situ degradation of organic matter under visible light catalysis.

[0032] Fig.10 -The rate of visible light photocatalytic production of hydrogen peroxide by the carbon nitride prepared in Example 1 in liquid wastewater. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0034] Example 1: Potassium and various iodine co-doped carbon nitride (CN-KI-2h)

[0035] First, weigh 6 g of potassium iodide and 2 g of melamine for later use. Add 100 mL of deionized water to a clean 250 mL beaker, dissolve the weighed potassium iodide in it, and then place the potassium iodide solution under a xenon lamp light source for photooxidation for 2 hours. Then add the weighed melamine, transfer it to an oil bath, stir and evaporate to dryness at 100 °C, and collect the product. The obtained product is ground and placed in a covered crucible, and the temperature is raised to 550 °C in a muffle furnace at a heating rate of 2.5 °C / min, calcined at this temperature for 4 hours, and collected and ground after naturally cooling to room temperature. Finally, the ground product is added to 200 mL of deionized water, stirred at room temperature for 8 hours, centrifuged, and dried at 60 °C to obtain potassium and multiple types of iodine co-doped carbon nitride, named CN-KI-2h.

[0036] Comparative Example 1: Carbon Nitride (CN)

[0037] Add 100 mL of deionized water to a clean 250 mL beaker, dissolve 2 g of melamine in it, transfer to an oil bath, stir and evaporate to dryness at 100 °C and collect the product. Grind the obtained product and place it in a covered crucible, heat it to 550 °C in a muffle furnace at a heating rate of 2.5 °C / min, calcine at this temperature for 4 hours, collect and grind the product after cooling naturally to room temperature. Finally, add 200 mL of deionized water, stir at room temperature for 8 hours, centrifuge and dry at 60 °C to obtain the bulk carbon nitride material, named CN.

[0038] Comparative Example 2: Potassium and iodine co-doped carbon nitride (CN-KI-0h)

[0039] First weigh 6 g of potassium iodide and 2 g of melamine for later use, add 100 mL of deionized water to a clean 250 mL beaker, dissolve the weighed potassium iodide in it, and then stir the potassium iodide solution in the dark for 2 hours. Then add the weighed melamine, transfer it to an oil bath, stir and evaporate to dryness at 100 °C, and collect the product. The obtained product is ground and placed in a covered crucible, and the temperature is raised to 550 °C in a muffle furnace at a heating rate of 2.5 °C / min, calcined at this temperature for 4 hours, and collected and ground after naturally cooling to room temperature. Finally, the ground product is added to 200 mL of deionized water, stirred at room temperature for 8 hours, centrifuged, and dried at 60 °C to obtain a carbon nitride material co-doped with potassium and iodine, named CN-KI-0h.

[0040] Example 2: Co-doping of Carbon Nitride with Potassium and Iodine in Different Ratios (CN-KI-2:2)

[0041] First, weigh 2 g of potassium iodide and 2 g of melamine for later use. Add 100 mL of deionized water to a clean 250 mL beaker, dissolve the weighed potassium iodide in it, and then place the potassium iodide solution under a xenon lamp light source for photooxidation for 2 hours. Then add the weighed melamine, transfer it to an oil bath, stir and evaporate to dryness at 100 °C, and collect the product. The obtained product is ground and placed in a covered crucible, and the temperature is raised to 550 °C in a muffle furnace at a heating rate of 2.5 °C / min, calcined at this temperature for 4 hours, and collected and ground after naturally cooling to room temperature. Finally, the ground product is added to 200 mL of deionized water, stirred at room temperature for 8 hours, centrifuged, and dried at 60 °C to obtain potassium and multiple types of iodine co-doped carbon nitride, named CN-KI-2:2.

[0042] Example 3: Co-doping of Carbon Nitride with Potassium and Iodine in Different Ratios (CN-KI-2:4)

[0043] First, weigh 4 g of potassium iodide and 2 g of melamine for later use. Add 100 mL of deionized water to a clean 250 mL beaker, dissolve the weighed potassium iodide in it, and then place the potassium iodide solution under a xenon lamp light source for photooxidation for 2 hours. Then add the weighed melamine, transfer it to an oil bath, stir and evaporate to dryness at 100 °C, and collect the product. The obtained product is ground and placed in a covered crucible, and the temperature is raised to 550 °C in a muffle furnace at a heating rate of 2.5 °C / min, calcined at this temperature for 4 hours, and collected and ground after naturally cooling to room temperature. Finally, the ground product is added to 200 mL of deionized water, stirred at room temperature for 8 hours, centrifuged, and dried at 60 °C to obtain potassium and multiple types of iodine co-doped carbon nitride, named CN-KI-2:4.

[0044] Example 4: Co-doping of Carbon Nitride with Potassium and Iodine in Different Ratios (CN-KI-2:8)

[0045] First weigh 8 g of potassium iodide and 2 g of melamine for later use, add 100 mL of deionized water to a clean 250 mL beaker, dissolve the weighed potassium iodide in it, and then place the potassium iodide solution under a xenon lamp light source for photooxidation for 2 hours. Then add the weighed melamine, transfer it to an oil bath, stir and evaporate to dryness at 100 ° C, and collect the product. The obtained product is ground and placed in a covered crucible, and the temperature is raised to 550 ° C in a muffle furnace at a heating rate of 2.5 ° C / min, calcined at this temperature for 4 hours, and collected and ground after naturally cooling to room temperature. Finally, the ground product is added to 200 mL of deionized water, stirred at room temperature for 8 hours, centrifuged, and dried at 60 ° C to obtain potassium and multiple types of iodine co-doped carbon nitride, named CN-KI-2:8.

[0046] 1. The scanning electron microscope photographs and transmission electron microscope photographs, X-ray diffraction spectra, X-ray photoelectron energy spectra and I 3d X-ray photoelectron energy fine spectra of the carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown respectively. Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown:

[0047] Figure 1 a, b, and c are scanning electron microscope photos of carbon nitride obtained in Example 1, Comparative Example 1, and Comparative Example 2, respectively. Figure 1 d, e, and f are transmission electron microscope photos of carbon nitride obtained in Example 1, Comparative Example 1, and Comparative Example 2, respectively. Figure 1It can be seen that the carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 all present a block shape, and the surface distribution is irregular granular. There is no obvious difference in the morphology of Example 1, Comparative Example 1 and Comparative Example 2 in the scanning electron microscope photographs and the transmission electron microscope photographs, indicating that the present invention will not affect the morphology of carbon nitride.

[0048] Depend on Figure 2 It can be seen from the X-ray photoelectron spectroscopy results that Example 1, Comparative Example 1 and Comparative Example 2 all have obvious diffraction peaks near 27.6°, which indicates that all three have formed a typical carbon nitride structure. Compared with Comparative Example 1, the diffraction peaks near 27.6° in Example 1 and Comparative Example 2 are slightly offset and weakened, which is caused by the embedding of iodine and potassium.

[0049] Depend on Figure 3 It can be seen that the carbon nitrides prepared in Example 1, Comparative Example 1 and Comparative Example 2 all contain carbon and nitrogen elements, and the carbon nitrides in Example 1 and Comparative Example 2 also contain potassium and iodine elements. Figure 4 It can be seen that the carbon nitride in Example 1 contains I - and I3 - Two iodine substances, the carbon nitride in Comparative Example 2 contains I - An iodine substance.

[0050] 2. The carbon nitrides prepared in Example 1, Comparative Example 1 and Comparative Example 2 were fixed on conductive glass respectively, and the photocurrent response and electrochemical impedance of the three carbon nitrides were measured by a three-electrode system. The results are as follows: Figure 5 As shown in the figure, it can be seen that the photocurrent response value of the carbon nitride in Example 1 is the strongest and the resistance value is the smallest, and the photocurrent response value and resistance value of the carbon nitride in Comparative Example 2 are in the middle. Compared with Comparative Example 1, it is shown that the doping of potassium and iodine elements can improve the catalytic performance of carbon nitride. Compared with Comparative Example 2, Example 1 shows that the incorporation of multiple types of iodine substances can further enhance the catalytic performance of carbon nitride.

[0051] 3. Weigh 5 mg of CN-KI-2h, CN-KI-0h, CN, CN-KI-2:2, CN-KI-2:4 and CN-KI-2:8 respectively, place them in a double-layer glass beaker containing 9 mL of deionized water and 1 mL of isopropanol mixed solution, first ultrasonicate for 5 min to fully disperse them, then react in the dark for 10 min to reach adsorption and desorption equilibrium, and then carry out visible light catalytic reaction. The light source is a 300 W xenon lamp (wavelength greater than 420 nm) equipped with a UV cutoff filter. The sampling time is 0, 10, 20, and 30 min. After sampling, the catalyst is separated by centrifugation, 1 mL of supernatant is taken, 0.5 mL of 3 mol / L sulfuric acid solution and 0.5 mL of 0.5 mol / L potassium titanium oxalate solution are added thereto and the volume is fixed. After 10 min of full color development, the ultraviolet absorption intensity of pertitanic acid at 400 nm is measured by a UV-visible spectrophotometer to determine the concentration of hydrogen peroxide.

[0052] The results are as follows Figure 6 As shown in the figure, under visible light irradiation, the concentration of hydrogen peroxide in CN-KI-2h, CN-KI-0h and CN gradually increases with the extension of reaction time. After normalization of yield, CN-KI-2h has a higher hydrogen peroxide photoproduction rate of 34.27 mmol / gQh compared with CN-KI-0h and CN, which is 107 times that of CN and 1.5 times that of CN-KI-0h. The improvement of catalytic performance of CN-KI-0h compared with CN is attributed to the improvement of light absorption performance of the catalyst by heteroatom doping and the optimization of its electronic structure; while the improvement of catalytic performance of CN-KI-2h compared with CN-KI-0h is mainly attributed to the formation of redox mediators by various types of iodine substances, which further accelerates the separation and migration of photogenerated carriers through redox cycles during the photocatalytic reaction.

[0053] The efficiency of photocatalytic production of hydrogen peroxide by carbon nitride prepared at different calcination ratios is shown in Figure 2. Figure 7 As shown in the figure, with the increase of potassium iodide, the hydrogen peroxide production first increases and then decreases. This is because more potassium and iodine substances are embedded in carbon nitride, which improves the photocatalytic performance, but excessive potassium and iodine embedding will affect the photocatalytic performance of carbon nitride itself, resulting in a decrease in catalytic activity. Therefore, CN-KI-2h shows the best hydrogen peroxide production efficiency.

[0054] The carbon nitride of Example 1 for photoproduction of hydrogen peroxide was then centrifuged, washed and dried, and the stability test was repeated under the conditions described above. Figure 8 As shown, the hydrogen peroxide photoproduction rate remained above 7.5 mM in the five cycle experiments, and the hydrogen peroxide photoproduction rate was 30 mmol / gQh in the fifth cycle experiment, showing high stability and reusability.

[0055] 4. Weigh 5 mg of CN-KI-2h, CN-KI-0h and CN respectively, place them in a double-layer glass beaker containing 10 mL of 5 mg / L sulfamethoxazole solution, first ultrasonicate for 5 min to fully disperse them, then react in the dark for 30 min to reach adsorption and desorption equilibrium, and then carry out photocatalytic reaction. The light source is a 300 W xenon lamp (wavelength greater than 420 nm) equipped with a UV cutoff filter. The sampling time is 0, 5, 10, 15, and 20 min. After sampling, the catalyst is separated by centrifugation, and the concentration of pollutants in the sample is analyzed by liquid chromatography.

[0056] The results are as follows Fig. 9 As shown in the figure, CN-KI-2h, CN-KI-0h and CN all had a certain degradation effect on sulfamethoxazole under visible light conditions, and the degradation rate of CN-KI-2 h was the fastest. Sulfamethoxazole could be completely removed after 10 min of reaction, and the corresponding total organic carbon removal rate was as high as 51%.

[0057] 5. Weigh 5 mg CN-KI-2h and place it in a double-layer glass beaker containing 10 mL of liquid waste liquid. First, ultrasonicate it for 5 minutes to fully disperse it, then react it in the dark for 10 minutes to reach adsorption and desorption equilibrium, and then carry out photocatalytic reaction. The light source is a 300 W xenon lamp (wavelength greater than 420 nm) equipped with a UV cutoff filter. The sampling time is 0, 10, 20, and 30 min. After sampling, the catalyst is separated by centrifugation, and 1 mL of supernatant is taken. 0.5 mL of 3 mol / L sulfuric acid solution and 0.5 mL of 0.5 mol / L potassium titanium oxalate solution are added to it and the volume is fixed. After 10 minutes of full color development, the ultraviolet absorption intensity of pertitanic acid at 400 nm is measured by a UV-visible spectrophotometer to determine the concentration of hydrogen peroxide.

[0058] The results are as follows Fig.10 As shown in the figure, the concentration of hydrogen peroxide gradually increased with the extension of reaction time. After 30 min of reaction, the concentration of hydrogen peroxide was 4.1 mM and there was an upward trend, indicating that CN-KI-2h still maintained a high visible light production rate of hydrogen peroxide in liquid waste liquid, showing great practical application potential.

[0059] Finally, it should be noted that the above embodiments of the present invention are only examples for illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes and modifications can be made based on the above description. It is impossible to list all implementation methods here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing carbon nitride co-doped with potassium and multiple types of iodine, characterized in that: The specific steps include: (1) dissolving potassium iodide in water to obtain a potassium iodide solution, and then subjecting the potassium iodide solution to photo-oxidation treatment to obtain a photo-oxidized potassium iodide solution; (2) Add melamine to the photo-oxidized potassium iodide solution, stir and evaporate to dryness at 80-100°C, then place in a muffle furnace and heat to 500-600°C at a heating rate of 2-5°C / min, then keep warm and calcine for 2-4 h, cool to room temperature, wash with water and dry to obtain potassium and iodine anions I - and iodine trianion I3 - Multiple types of iodine co-doped carbon nitride; The mass ratio of potassium iodide to melamine is 1~4:

1.

2. The method for preparing carbon nitride co-doped with potassium and multiple types of iodine according to claim 1, characterized in that: The mass ratio of potassium iodide to melamine is 3:

1.

3. The method for preparing carbon nitride co-doped with potassium and multiple types of iodine according to claim 1, characterized in that: The specific steps of the photo-oxidation treatment in step (1) are as follows: placing the potassium iodide solution under xenon lamp illumination conditions, and the illumination time is ≤2.5h.

4. The method for preparing carbon nitride co-doped with potassium and multiple types of iodine according to claim 3, characterized in that: The photo-oxidation treatment time is 1.5~2 h.

5. A potassium and multiple types of iodine co-doped carbon nitride, characterized in that: The carbon nitride is prepared by the method for preparing carbon nitride co-doped with potassium and multiple types of iodine as described in any one of claims 1 to 4.

6. Use of the potassium and multiple types of iodine co-doped carbon nitride as claimed in claim 5 as a photocatalyst for producing hydrogen peroxide or degrading organic pollutants.

7. The use of potassium and multiple types of iodine co-doped carbon nitride according to claim 6, characterized in that: Potassium and various types of iodine co-doped carbon nitride are used as photocatalysts to produce hydrogen peroxide. The specific steps are as follows: the photocatalyst is dissolved in a mixed solution of water and organic alcohol and ultrasonically treated for 0 to 5 min, then reacted in the dark for 5 to 10 min, and then placed under visible light conditions.

8. The use of potassium and multiple types of iodine co-doped carbon nitride according to claim 7, characterized in that: The organic alcohol accounts for 10-50% of the total volume of the mixed solution of water and the organic alcohol; the mass volume ratio of the photocatalyst to the mixed solution is 1 mg: 1-5 mL.

9. The use of potassium and multiple types of iodine co-doped carbon nitride according to claim 8, characterized in that: The organic alcohol is one of methanol, ethanol, isopropanol or tert-butanol.

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