A CoP / SCN heterojunction photocatalyst and its preparation method and application

Abstract

The present invention discloses a CoP / SCN heterojunction photocatalyst and its preparation method and application. The present invention prepares carbon nitride quantum dots by a top-down acidification method, and successfully prepares a novel carbon nitride quantum dot assembly (SCN) by static self-assembly. On this basis, CoP is loaded on the carbon nitride quantum dot assembly by an impregnation-phosphating method to obtain CoP / SCN. The special defect structure of SCN not only provides more anchoring sites for Co atoms, but also gives it a better adsorption capacity and a special coordination environment, and provides unique support for CoP. Compared with the original carbon nitride quantum dot assembly, the band gap of CoP / SCN is effectively reduced by 1.07eV, thereby having better hydrogen production performance, and providing a new idea for the design and synthesis of an efficient carbon nitride hydrogen evolution photocatalyst. The CoP / SCN heterojunction photocatalyst has good photocatalytic properties and high stability.

Description

Technical Field

[0001] The present invention relates to a CoP / SCN heterojunction photocatalyst and a preparation method and application thereof, belonging to the technical field of energy materials. Background Art

[0002] Environmental pollution and energy shortages caused by the massive consumption of fossil fuels are becoming increasingly serious. Therefore, the pursuit of clean, efficient, and sustainable energy is a major focus in today's society. Photocatalysis is an energy conversion process that converts light energy into chemical energy, providing a clean and sustainable energy source. However, its practical application is hampered by the low efficiency of photocatalysts in converting light energy. Therefore, the development of photocatalysts with efficient energy conversion is crucial.

[0003] Carbon nitride is a cheap, readily available, stable and non-toxic organic semiconductor with high thermal and chemical stability. These unique properties lead to many promising applications, such as photocatalytic water splitting, oxygen evolution reaction and carbon dioxide reduction to hydrocarbon fuels. Among them, photocatalytic water splitting to produce hydrogen is an effective method to provide clean energy, but the bulk precursor carbon nitride (BCN) produced by thermal polymerization usually produces a relatively low surface area and has fewer exposed active sites, which limits the application of carbon nitride in the field of photocatalysis. In existing reports, constructing carbon nitride with molecular-level or ultra-thin structural features and functionalized composites are effective ways to overcome the above problems, greatly improving the performance of carbon nitride in photocatalytic water splitting. Summary of the Invention

[0004] Purpose of the invention: The first purpose of the present invention is to provide a CoP / SCN heterojunction photocatalyst, the second purpose of the present invention is to provide a method for preparing the CoP / SCN heterojunction photocatalyst, and the third purpose of the present invention is to provide the application of the CoP / SCN heterojunction photocatalyst in photocatalytic hydrogen evolution.

[0005] Technical solution: The preparation method of the CoP / SCN heterojunction photocatalyst of the present invention comprises the following steps:

[0006] (1) calcining melamine at high temperature, acidifying it, washing it by centrifugation until it is neutral, dissolving it with a solvent, adjusting the pH, hydrothermally treating it, and ultrasonicating it to obtain carbon nitride quantum dots;

[0007] (2) allowing the carbon nitride quantum dots to stand and freeze-dry to form spindle-shaped carbon nitride quantum dot assemblies (SCN);

[0008] (3) Using Co(NO3)2·6H2O ethanol solution, Co ions were anchored on the surface of the carbon nitride quantum dot assembly by static reflux method, dried, and phosphated with sodium hypophosphite as a phosphorus source to obtain a carbon nitride quantum dot assembly photocatalyst.

[0009] Furthermore, in step (1), the high-temperature calcination is carried out under nitrogen protection at a heating rate of 5°C / min, at 550-600°C for 2-4 hours, preferably at 600°C for 2 hours.

[0010] Furthermore, in step (1), the acid used in the acidification treatment is one or more of hydrochloric acid, nitric acid, and sulfuric acid. Nitric acid is preferred because nitric acid and carbon nitride have similar elemental compositions, strong oxidizing properties, and obvious effects.

[0011] Furthermore, in step (1), during the acidification treatment, ultrasonic treatment is first performed at room temperature for 0.5-1 h, and refluxed at 85-100°C for 12-24 h, preferably ultrasonic treatment is performed for 1 h, and refluxed at 85°C for 12 h, and the solid-liquid ratio of the carbon nitride to the acid is 0.2:100-0.5:100 g / mL, and preferably the solid-liquid ratio of the carbon nitride to the acid is 0.3:100 g / mL.

[0012] Furthermore, in step (1), the solvent is one or more of deionized water, methanol, and ethanol, preferably deionized water.

[0013] Furthermore, in step (1), the pH is 6-8, preferably pH 7,

[0014] Furthermore, in step (1), the temperature of the hydrothermal treatment is 180-200° C., preferably 200° C., and the time of the hydrothermal treatment is 12-24 h, preferably 12 h.

[0015] Furthermore, in step (1), the frequency of the ultrasound is 70-90 Hz, preferably 80 Hz, and the time of the ultrasound is 4-8 h, preferably 4 h.

[0016] Furthermore, in step (2), the standing time is more than 8 hours.

[0017] Furthermore, in step (2), the freeze-drying temperature is -40-50°C, and the freeze-drying time is 24-48 hours.

[0018] Furthermore, in step (3), the concentration of the Co(NO3)2·6H2O ethanol solution is 1-4 mg / mL, preferably 1 mg / mL.

[0019] Furthermore, in step (3), the solid-liquid ratio of the carbon nitride quantum dot assembly to the Co(NO3)2·6H2O ethanol solution during the standing reflux is 1:1-4:1 mg / mL, preferably 2:1 mg / mL.

[0020] Furthermore, in step (3), the temperature of the standing reflux is 80-90° C., preferably 80° C., and the time of the standing reflux is 8-12 h, preferably 8 h.

[0021] Furthermore, in step (3), the drying temperature is 60-80°C, preferably 60°C, and the drying time is more than 12 hours.

[0022] Furthermore, in step (3), the phosphating temperature is 300-350°C, preferably 320°C, the phosphating time is 1-3h, preferably 2h, the heating rate is 2°C / min, and the mass ratio of the Co ion to the sodium hypophosphite is 1:4.

[0023] The CoP / SCN heterojunction photocatalyst is obtained by the preparation method of the present invention.

[0024] Application of the CoP / SCN heterojunction photocatalyst of the present invention in photocatalytic hydrogen evolution.

[0025] The present invention prepares carbon nitride quantum dots by a top-down acidification method, and successfully prepares a new type of carbon nitride quantum dot assembly (SCN) by static self-assembly. On this basis, CoP (CoP / SCN) is loaded on the carbon nitride quantum dot assembly by an impregnation-phosphating method. The special defect structure of the carbon nitride quantum dot assembly not only provides more anchoring sites for Co atoms, giving it better adsorption capacity and a special coordination environment, but also provides unique support for CoP. Experimental facts also prove that compared with the original carbon nitride quantum dot assembly, the band gap of CoP / SCN is effectively reduced by 1.07eV, thereby having better hydrogen production performance. The present invention provides a new idea for the design and synthesis of efficient carbon nitride hydrogen evolution photocatalysts.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0027] (1) The carbon nitride quantum dot assembly photocatalyst prepared by the present invention has cheap raw materials and has good photocatalytic performance and high stability.

[0028] (2) The present invention provides a special method for regulating the assembly of carbon nitride quantum dots. During the process of forming quantum dots after carbonation, defect structures are easily formed, thereby forming intermediate valence states of C and N elements and increasing the pathway for electron transition. The carbon nitride after reassembly of quantum dots has more active sites, providing more anchoring sites for the doping of Co ions, thereby promoting the thermodynamic and kinetic processes in the catalytic process and enhancing its photocatalytic performance. This provides a new approach for the design and synthesis of efficient hydrogen evolution reaction photocatalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a scanning electron microscope image of the material SCN-1 prepared in Example 1;

[0030] Figure 2is a scanning electron microscope image of the material SCN-2 prepared in Example 2;

[0031] Figure 3 is a scanning electron microscope image of the material SCN-3 prepared in Example 3;

[0032] Figure 4 This is a high-magnification transmission electron micrograph of the material SCN-3 prepared in Example 3;

[0033] Figure 5 is a scanning electron microscope image of the material SCN-4 prepared in Example 4;

[0034] Figure 6 is a scanning electron microscope image of the material SCN-5 prepared in Example 5;

[0035] Figure 7 is a scanning electron microscope image of the PCN material prepared in Example 6;

[0036] Figure 8 is a scanning electron microscope image of the material prepared in Example 7;

[0037] Figure 9 This is a comparison chart of the hydrogen production rates of the materials prepared in Example 7. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0039] Example 1 Preparation of Carbon Nitride Quantum Dot Shuttle Assembly SCN

[0040] 10g of melamine was placed in a porcelain boat and calcined at 600°C for 2h (heating rate 5°C / min) under a nitrogen atmosphere. The carbon nitride precursor was then cooled naturally to obtain a carbon nitride precursor. 0.3g of the carbon nitride precursor was dissolved in 100ml of concentrated nitric acid, first ultrasonicated at room temperature for 1h, then placed in an oil bath and stirred at 85°C for 12h. After cooling naturally, the nitric acid was filtered out and the remaining solid was centrifuged and washed until neutral. Dissolved in 70ml of deionized water, the solution was transferred to a 100ml reactor, and a small amount of acetic acid was added to adjust the pH to 5. The reaction was hydrothermally reacted at 200°C for 12h. After cooling naturally, the solution after the hydrothermal reaction was transferred to a beaker and ultrasonicated for 4h, then allowed to stand for 8h. Finally, it was freeze-dried at -40-50°C for 24h to obtain the carbon nitride quantum dot spindle assembly SCN-1.

[0041] The SCN-1 assembly prepared in this example was analyzed by scanning electron microscopy. Figure 1 shown. Figure 1 is a scanning electron microscope image of SCN-1 prepared in Example 1. Figure 1It can be seen that the surface of the SCN-1 prepared in this embodiment is relatively rough, and the diameter is about 200 to 300 nm.

[0042] Example 2 Preparation of Carbon Nitride Quantum Dot Shuttle Assembly SCN

[0043] Place 10g of melamine in a porcelain boat and calcine it at 600℃ for 2h (heating rate 5℃ / min) under a nitrogen atmosphere, then cool naturally to obtain a carbon nitride precursor. Take 0.3g of carbon nitride precursor and dissolve it in 100ml concentrated nitric acid. First, ultrasonicate it at room temperature for 1h, then place it in an oil bath and stir and reflux at 85℃ for 12h. After cooling naturally, filter out the nitric acid and centrifuge the remaining solid until it is neutral. Dissolve it in 70ml of deionized water and transfer it to a 100ml reactor. Add a small amount of ammonia water to adjust the pH to 9. Hydrothermally react at 200℃ for 12h. After cooling naturally, transfer the solution after the hydrothermal reaction to a beaker and ultrasonicate it for 4h, then let it stand for 8h. Finally, freeze-dry it at -40--50℃ for 24h to obtain the assembly SCN-2.

[0044] The SCN-2 assembly prepared in this example was analyzed by scanning electron microscopy. Figure 2 shown. Figure 2 is a scanning electron microscope image of SCN-2 prepared in Example 2. Figure 2 It can be seen that the SCN-2 prepared in this example has a tendency to spindle-shaped polymerization.

[0045] Example 3 Preparation of Carbon Nitride Quantum Dot Shuttle Assembly SCN

[0046] 10g of melamine was placed in a porcelain boat and calcined at 600°C for 2h (heating rate 5°C / min) under a nitrogen atmosphere. The carbon nitride precursor was then cooled naturally to obtain a carbon nitride precursor. 0.3g of the carbon nitride precursor was dissolved in 100ml of concentrated nitric acid, first ultrasonicated at room temperature for 1h, then placed in an oil bath and stirred at 85°C for 12h. After cooling naturally, the nitric acid was filtered out and the remaining solid was centrifuged and washed until neutral. Dissolved in 70ml of deionized water and transferred to a 100ml reactor. The pH was not adjusted, at which point the pH was around 7. The solution was hydrothermally reacted at 200°C for 12h. After cooling naturally, the solution after the hydrothermal reaction was transferred to a beaker and ultrasonicated for 4h, then allowed to stand for 8h. Finally, it was freeze-dried at -40-50°C for 24h to obtain the assembly SCN-3.

[0047] The SCN-3 assembly prepared in this example was subjected to scanning electron microscopy and high-magnification transmission electron microscopy analysis. Figure 3-4 shown. Figure 3 This is a scanning electron microscope image of SCN-3 prepared in Example 3. Figure 4 This is a high-magnification transmission electron microscope image of SCN-3 prepared in Example 3. Figure 3 and Figure 4 It can be seen that the SCN-3 prepared in this example is a smooth spindle-shaped hollow assembly.

[0048] Example 4 Preparation of Carbon Nitride Quantum Dot Shuttle Assembly SCN

[0049] 10g of melamine was placed in a porcelain boat and calcined at 600°C for 2h (heating rate 5°C / min) under a nitrogen atmosphere. The carbon nitride precursor was then cooled naturally to obtain a carbon nitride precursor. 0.2g of the carbon nitride precursor was dissolved in 100ml of concentrated nitric acid, first ultrasonicated at room temperature for 1h, then placed in an oil bath and stirred at 85°C for 12h. After cooling naturally, the nitric acid was filtered out and the remaining solid was centrifuged and washed until neutral. Dissolved in 70ml of deionized water and transferred to a 100ml reactor. The pH was not adjusted, at which point the pH was around 7. The solution was hydrothermally reacted at 200°C for 12h. After cooling naturally, the solution after the hydrothermal reaction was transferred to a beaker and ultrasonicated for 4h, then allowed to stand for 8h. Finally, it was freeze-dried at -40-50°C for 24h to obtain the assembly SCN-4.

[0050] The SCN-4 assembly prepared in this example was analyzed by scanning electron microscopy. Figure 5 shown. Figure 5 is a scanning electron microscope image of SCN-4 prepared in Example 4. Figure 5 It can be seen that the SCN-4 prepared in this example is an irregular spherical aggregate.

[0051] Example 5 Preparation of Carbon Nitride Quantum Dot Shuttle Assembly SCN

[0052] 10g of melamine was placed in a porcelain boat and calcined at 600°C for 2h (heating rate 5°C / min) under a nitrogen atmosphere. The carbon nitride precursor was then cooled naturally to obtain a carbon nitride precursor. 0.5g of the carbon nitride precursor was dissolved in 100ml of concentrated nitric acid, first ultrasonically treated at room temperature for 1h, then placed in an oil bath and stirred at 85°C for 12h. After cooling naturally, the nitric acid was filtered out and the remaining solid was centrifuged and washed until neutral. It was dissolved in 70ml of deionized water and transferred to a 100ml reactor. The pH was not adjusted, at which point the pH was around 7. The solution was hydrothermally reacted at 200°C for 12h. After cooling naturally, the solution after the hydrothermal reaction was transferred to a beaker and ultrasonicated for 4h, then allowed to stand for 8h. Finally, it was freeze-dried at -40-50°C for 24h to obtain the assembly SCN-5.

[0053] The SCN-5 assembly prepared in this example was analyzed by scanning electron microscopy. Figure 6 shown. Figure 6 is a scanning electron microscope image of SCN-5 prepared in Example 5. Figure 6It can be seen that the SCN-5 prepared in this example is an irregular lamellar aggregate.

[0054] Example 6 Preparation of Carbon Nitride Quantum Dot Spindle Assembly Phosphated PCN

[0055] 10 mg of SCN-3 prepared in Example 3 was placed in a porcelain boat wrapped in aluminum foil. Then 0.6 g of sodium hypophosphite was weighed and phosphated at 320°C for 2 h in a slow argon flow with a heating rate of 2°C / min to obtain a PCN sample.

[0056] The PCN prepared in this example was analyzed by scanning electron microscopy. Figure 7 shown. Figure 7 This is a scanning electron microscope image of the PCN material prepared in Example 6. Figure 7 Scanning electron microscopy images show that the basic morphology of SCN-3 is well maintained and is not affected by phosphating.

[0057] Example 7 Preparation of CoP Photocatalyst Loaded in Carbon Nitride Quantum Dot Assembly

[0058] 10 mg of each of SCN-1, SCN-2, SCN-3, SCN-4, and SCN-5 prepared in Examples 1-5 was dissolved in 45 ml of ethanol solution, then mixed with 5 ml of a 1 mg / ml Co(NO3)2·6H2O ethanol solution, refluxed at 80°C for 8 h, and finally dried at 60°C for 12 h. The samples were then placed in a tube furnace and phosphated at 320°C for 2 h under an argon atmosphere using 0.6 g of sodium hypophosphite as the phosphorus source at a heating rate of 2°C / min to obtain the final samples CoP / SCN-1, CoP / SCN-2, CoP / SCN-3, CoP / SCN-4, and CoP / SCN-5.

[0059] The CoP / SCN-1, CoP / SCN-2, CoP / SCN-3, CoP / SCN-4 and CoP / SCN-5 prepared in this example were analyzed by scanning electron microscopy. Figure 8 shown. Figure 8 is a scanning electron microscope image of the material prepared in Example 7, wherein Figure 8 a is CoP / SCN-1, Figure 8 b is CoP / SCN-2, Figure 8 c is CoP / SCN-3, Figure 8 d is CoP / SCN-4, Figure 8 e is CoP / SCN-5. Figure 8It can be observed that the static reflow and phosphating processes destroyed the basic morphology of CoP / SCN-1 and SCN-5, and only CoP / SCN-2, CoP / SCN-3, and CoP / SCN-4 maintained the basic morphology, and CoP was evenly distributed on the surface of CoP / SCN-2, CoP / SCN-3, and CoP / SCN-4.

[0060] Example 8

[0061] An online photocatalytic hydrogen evolution system (Shimadzu GC 2014) was used, connected to an online gas chromatograph (SP7800, TCD, molecular sieve: 5A, Beijing Kerida Co., Ltd.), and argon gas at a temperature of 20°C was used as a carrier gas. First, 5 mg of the photocatalyst synthesized in Example 7 was added to a special quartz container equipped with a magnetic stirrer, and a solvent mixture consisting of 5 mL of triethanolamine and 45 mL of deionized water. During the reaction preparation process, the mixture was ultrasonically treated for 10 minutes to obtain a uniform suspension, which was kept under vacuum to remove CO2 and O2 dissolved in the water. A 300W xenon lamp (Oriel, USA) equipped with an AM1.5G spectrum filter was used as a light source. The generated gas was collected and analyzed every hour, and the photocatalytic hydrogen production rate of 5 mg of carbon nitride precursor (BCN) catalyst was tested in the same way.

[0062] The following formula is used to calculate the hydrogen production rate:

[0063]

[0064] Wherein, vH2 is the hydrogen generation rate (%), n(H2) is the amount of hydrogen (μmol), t is the reaction time (h), and m(catalyst) is the mass of the catalyst (mg).

[0065] The results are as follows Figure 9 shown. Figure 9 : is a comparison chart of the hydrogen production rates of CoP / SCN-1, CoP / SCN-2, CoP / SCN-3, CoP / SCN-4, CoP / SCN-5 and carbon nitride precursor (BCN) synthesized in Example 7 of the present invention, Figure 9 It can be seen that the hydrogen production rates of CoP / SCN-1, CoP / SCN-2, CoP / SCN-3, CoP / SCN-4, and CoP / SCN-5 are much greater than those of the precursor carbon nitride, and the hydrogen production performance of the CoP / SCN-3 catalyst is better than that of CoP / SCN-1, CoP / SCN-2, CoP / SCN-4, and CoP / SCN-5. This shows that the hollow spindle-shaped carbon nitride catalyst we constructed is helpful in improving the photocatalytic performance of carbon nitride.

Claims

1. A method for preparing a CoP / SCN heterojunction photocatalyst, characterized in that: The following steps are involved: (1) calcining melamine at high temperature, acidifying it, washing it by centrifugation until it is neutral, dissolving it with a solvent, adjusting the pH, hydrothermally treating it, and ultrasonicating it to obtain carbon nitride quantum dots; (2) allowing the carbon nitride quantum dots to stand and freeze-dry to form a spindle-shaped carbon nitride quantum dot assembly; (3) Using Co(NO3)2·6H2O ethanol solution, Co ions were anchored on the surface of the carbon nitride quantum dot assembly by static reflux method, dried, and phosphated with sodium hypophosphite as the phosphorus source to obtain CoP / SCN heterojunction photocatalyst.

2. The preparation method according to claim 1, characterized in that In step (1), the high-temperature calcination is carried out under nitrogen protection at a temperature of 500-600° C. for 2-4 hours at a heating rate of 5° C. / min.

3. The preparation method according to claim 1, characterized in that In step (1), the acid used in the acidification treatment is one or more of hydrochloric acid, nitric acid, and sulfuric acid. During the acidification treatment, ultrasonic treatment is first performed at room temperature for 0.5-1h, and then refluxed at 85-100°C for 12-24h. The solid-liquid ratio of the carbon nitride to the acid is 0.2:100-0.5:100 g / mL.

4. The preparation method according to claim 1, characterized in that In step (1), the solvent is one or more of deionized water, methanol, and ethanol, the pH is 6-8, the temperature of the hydrothermal treatment is 180-200° C., the time of the hydrothermal treatment is 12-24 h, the frequency of the ultrasound is 70-90 Hz, and the time of the ultrasound is 4-8 h.

5. The preparation method according to claim 1, characterized in that In step (2), the standing time is more than 8 hours, the freeze-drying temperature is -40-50°C, and the freeze-drying time is 24-48 hours.

6. The preparation method according to claim 1, characterized in that In step (3), the concentration of the Co(NO3)2·6H2O ethanol solution is 1-4 mg / mL, and the solid-liquid ratio of the carbon nitride quantum dot assembly to the Co(NO3)2·6H2O ethanol solution during the static reflux is 1:1-4:1 mg / mL.

7. The preparation method according to claim 1, characterized in that In step (3), the temperature of the standing reflux is 80-90° C., the time of the standing reflux is 8-12 h, the temperature of the drying is 60-80° C., and the time of the drying is more than 12 h.

8. The preparation method according to claim 1, characterized in that In step (3), the phosphating temperature is 300-350°C, the phosphating time is 1-3h, and the heating rate is 2°C / min.

9. The CoP / SCN heterojunction photocatalyst obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the CoP / SCN heterojunction photocatalyst according to claim 9 in photocatalytic hydrogen evolution.

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