CN116099565A - Red supermolecule graphite phase carbon nitride photocatalyst capable of improving visible light utilization rate and preparation method thereof - Google Patents

Abstract

The invention relates to a red supermolecule graphite phase carbon nitride photocatalyst for improving visible light utilization rate and a preparation method thereof. Mixing ethanol and deionized water with cyanuric acid, and stirring. Then, P-MA was added to the cyanuric acid solution, and nitric acid was added. Then placing the mixture into an oil bath pot, stirring the mixture at the temperature of 80 ℃, and then placing the mixture into a vacuum drying oven for drying to obtain a yellow precursor with high viscosity. And finally, placing the precursor into a crucible, placing the crucible into a muffle furnace for calcination to enable the precursor to undergo phase change, and cooling the precursor to room temperature. Thus obtaining ACCN with ultra-high light absorption capacity. Compared with the method for forming supermolecule self-assembly by using melamine and cyanuric acid, the photocatalyst prepared by the method has stronger light absorption capacity to visible light and higher hydrogen evolution performance, and the used raw materials are low in cost, easy to obtain, environment-friendly and capable of being prepared on a large scale.

Description

Red supramolecular graphite phase carbon nitride photocatalyst and preparation method for improving visible light utilization

technical field

The invention belongs to the field of photocatalytic functional materials, and relates to a red supramolecular graphite phase carbon nitride photocatalyst for improving the utilization rate of visible light and a preparation method thereof.

Background technique

The excessive use of non-renewable energy such as fossil fuels will make the future energy crisis more and more serious. Human beings urgently need clean and pollution-free renewable energy. Since Japanese scientist Fujishima Akira discovered in 1967 that water molecules on the surface of titanium dioxide electrodes undergo oxidation reactions to generate oxygen under ultraviolet light, human research on photocatalytic technology has been in full swing. gC ₃ N ₄ is easy to prepare and environmentally friendly The advantages of no pollution, rich reserves of constituent elements, and good stability are favored by researchers. However, its low photocatalytic efficiency still limits its further practical application. The main reasons are the following three points: First, due to the high surface energy of gC ₃ N ₄ nanomaterials, according to the principle that the lower the energy, the more stable, the polymerization When gC ₃ N ₄ is formed, agglomeration will occur spontaneously to reduce the surface energy, and thus the active sites of the photocatalyst cannot be fully exposed; second, the general photocatalyst can only absorb and utilize 3-5% of the solar spectrum Ultraviolet light (less than 400nm), but the abundant visible light (400-700nm) of content (42-43%) has not been fully utilized; Third, due to the strong Coulomb force between photogenerated electrons and photogenerated holes, photogenerated loads The flow electrons are easy to recombine, and only a small part of the photogenerated electrons participate in the hydrogen evolution reaction. Therefore, researchers try to overcome the above three difficulties by various means. The ACCN obtained by the invention has a large specific surface area of 65.173m ² /g, and promotes the electron excitation of the lone pair of electrons on the nitrogen atom at n→π ^* , so that the visible light absorption rate of 400nm-650nm is significantly improved. Therefore, the ACCN prepared in this invention has important significance and reference on the issue of improving the utilization rate of visible light.

Literature 1 "Tahereh Mahvelati-Shamsabadi, Hossein Fattahimoghaddam, et al.Synthesis of hexagonal rosettes of gC ₃ N ₄ with boosted charge transfer for the enhanced visible-light photocatalytic hydrogen evolution and hydrogenperoxide production[J].Journal of Collo id and Interface Science, 2021, 597,345-360." discloses a method of utilizing melamine and cyanuric acid complexes to synthesize graphite phase carbon nitride, mixing melamine and cyanuric acid (total 5g) in 100ml of deionized water for 6h in equimolar ratio , and then the solution was placed in a centrifuge at a speed of 4000 rpm to centrifuge three times to obtain a white precipitate, dried overnight at a temperature of 70° C., and finally calcined to obtain graphite phase carbon nitride. Although this method prolongs the lifetime of photogenerated carriers and improves the active sites for photocatalytic reactions. However, the utilization rate of abundant visible light is low, which limits the improvement of photocatalytic activity.

Document 2 "Shuo Zhao, Yiwei Zhang, et al. Facile one-step synthesis of hollowmesoporous gC ₃ N ₄ spheres with ultrathin nanosheets for photoredox watersplitting [J]. Carbon, 2018, 126, 247-256." discloses a method using melamine and The hydrogen-bonded supramolecular self-assembly of cyanuric acid and the structure- _directed properties of ionic liquids have led to the development of a synthetic high-specific-surface-area, high-porosity hollow mesoporous _gC3N4 sphere. Although the gC ₃ N ₄ prepared by this method exposed more active sites, the separation rate of photogenerated carriers was improved, and the rate of photocatalytic hydrogen evolution was also improved. However, the stability of the material prepared by this method is very poor. After four cycles of 16 hours, the performance drops to 73%. Moreover, the material has a high absorption of ultraviolet light, but absorbs abundant visible light. rare.

In the published methods of supramolecular self-assembly using cyanuric acid and melamine, more attention is paid to photocatalysts through the modification of photocatalyst materials to obtain large specific surface areas and reduce the recombination rate of photogenerated carriers. problems, but there are still challenges in broadening the absorption of visible light. This invention uses nitric acid to protonate the precursor, so that nitrate ions and cyanuric acid can coordinate the polymerization of the precursor melamine, so that the structure of the heptazine ring unit Distortion occurs, and the order degree of the regular melem ring is destroyed to a certain extent, so that the lone pair of electrons on the nitrogen atom in the melem ring can also undergo n→π ^* excitation, so that more photogenerated loads can be generated. The flow particles participate in the hydrogen evolution reaction, and the obtained ACCN can absorb the wavelength of about 400nm to 650nm, which greatly improves the light utilization rate of the sample in the visible light region, and has a specific surface area of 65m ² /g, providing a large number of active sites for the catalytic reaction , which is of great significance in the academic research of photocatalytic hydrogen evolution.

Contents of the invention

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a red supramolecular graphite phase carbon nitride photocatalyst and its preparation method to improve the utilization rate of visible light, so as to make up for the insufficient utilization rate of gC ₃ N ₄ to visible light in the existing method . The method treats melamine with nitric acid to obtain protonated melamine, and the protonated melamine and cyanuric acid form a new supramolecular self-assembled complex, which can be obtained by adding nitric acid in the process of forming the complex and drying it in a vacuum oven. The viscous yellow-brown precursor undergoes phase transition after high-temperature calcination, and ACCN with ultra-high light-absorbing ability can be obtained.

Technical solutions

A method for preparing a red supramolecular graphite phase carbon nitride photocatalyst that improves the utilization rate of visible light, characterized in that the steps are as follows:

Step 1: Weigh melamine with a weight of 1-2g, put it into 25-75ml of concentrated nitric acid, and stir evenly;

Step 2: filter the melamine treated with nitric acid in step 1 and wash it with deionized water several times to obtain a solid product, add the solid product to the cyanuric acid solution, and perform ultrasonic treatment;

Described cyanuric acid solution is the mixed solution of the deionized water of 20～60ml, the dehydrated alcohol of 20～60ml and 1～3g cyanuric acid;

Step 3: Stir the above mixed solution in an oil bath at a temperature of 70-90° C. for 4-12 hours and then dry to obtain a yellow-brown precursor;

Step 4: Grind the yellow-brown precursor and put it into a crucible, place it in a muffle furnace to raise the temperature to 530-550°C at a rate of 2-5°C/min, keep it warm for 2-4 hours, and cool it down to room temperature. The light red powder is ACCN.

The above ratio is the measurement for preparing one portion.

The concentration of the concentrated nitric acid is 68%.

Stirring evenly in the step 1 is to use a magnetic stirrer to stir for 1-3 hours.

The filtration of described step 2 adopts filter paper.

The step 2 was washed three times with deionized water.

The step 2 is added into the cyanuric acid solution and then ultrasonically treated for 30-60 minutes.

The mixed solution of cyanuric acid was stirred for at least 30 minutes when mixed.

The step 3 is to dry in a vacuum oven at 75-90°C.

A red supramolecular graphite phase carbon nitride photocatalyst prepared by the method is characterized in that: the red supramolecular graphite phase carbon nitride ACCN catalyst has a large specific surface area of 65.173m ² /g, and promotes nitrogen atoms The lone pair of electrons is excited by n→π ^* electrons, which significantly increases the visible light absorption rate at 400nm-650nm by 2.18 times compared with that of CCN prepared by traditional methods.

Beneficial effect

The present invention proposes a red supramolecular graphite phase carbon nitride photocatalyst for improving the utilization rate of visible light and a preparation method thereof, which is a red supramolecular graphite phase carbon nitride (gC ₃ N ₄ ) photocatalyst and a method for improving the utilization rate of visible light. The preparation method is to obtain the red graphite phase carbon nitride (ACCN) with enhanced light absorption ability through a simple two-step method. First, melamine was added into concentrated nitric acid for protonation treatment for one hour, then the nitric acid was filtered out through filter paper, and then washed with deionized water three times to obtain protonated melamine (P-MA). Secondly, take ethanol and deionized water respectively and place them in a beaker, add cyanuric acid into the beaker and stir for half an hour. Then add P-MA into the prepared cyanuric acid solution, and then drop an appropriate amount of nitric acid with a rubber dropper. Because the P-MA agglomeration phenomenon is very serious, in order to form the supramolecular self-assembly of melamine and cyanuric acid more effectively, the cyanuric acid solution added with P-MA is treated with ultrasonic waves at first, then placed in an oil bath Stir at a temperature of 80° C., and then dry in a vacuum oven to obtain a viscous yellow precursor. Finally, the precursor is placed in a crucible, put into a muffle furnace for calcination to undergo a phase transition, and then cooled to room temperature. ACCN with ultra-high light-absorbing ability can be obtained. Compared with the disclosed method of using melamine and cyanuric acid to form supramolecular self-assembly through the modification of the precursor, the photocatalyst prepared by the method has stronger light absorption ability for visible light and has higher hydrogen evolution performance , the raw materials used are cheap and easy to obtain, environmentally friendly, and can be prepared on a large scale.

The beneficial effects of the present invention are: the reagents nitric acid, melamine and cyanuric acid used in the method are relatively cheap, and the complexes are formed by using the intermolecular force between each other, and the introduction of an appropriate amount of nitrate ions can synergize the cyanuric acid molecules Affect the polymerization of the precursor melamine, twist the structural unit of the heptazine ring, make the lone pair of electrons on the nitrogen atom in gC ₃ N ₄ be excited by visible light, and the electrons transition from the n energy level to π ^* , greatly improving the gC ₃ The utilization rate of N ₄ to visible light, the material obtained by this method not only shortens the distance between gC ₃ N ₄ molecular layers but also has a relatively large specific surface area, and the shortened layer spacing is conducive to electrons along the π-π conjugated direction conduction, which facilitates electron transport. The large specific surface area can provide a large number of active sites for the photocatalytic hydrogen evolution reaction. The ACCN obtained by the method does not contain toxic metal elements, has low production cost, and can realize large-scale production.

Description of drawings

Fig. 1 is a transmission electron microscope (TEM) picture of the ACCN powder photocatalyst prepared in Example 3 of the present invention.

Curve 1 and curve 2 in Fig. 2 are respectively the gC ₃ N ₄ prepared by the traditional method and the X-ray diffraction (XRD) spectrum of the ACCN photocatalyst prepared by the present invention prepared by Example 3 of the present invention

Curve 3 and curve 4 in Fig. 3 are respectively the ultraviolet-visible absorption spectrum (UV-vis) of ACCN prepared by supramolecular self-assembly method and gC ₃ N ₄ prepared by traditional method in Example 3 of the present invention

Curve 5 and Curve 6 in Fig. 4 are graphs comparing the hydrogen evolution performance of ACCN prepared in Example 3 of the present invention and gC ₃ N ₄ prepared by traditional methods.

Fig. 5 is a comparative diagram of effective light utilization of ACCN prepared in Example 3 of the present invention and CCN prepared by a traditional method.

Figure 6: is a scanning electron microscope (SEM) picture of the ACCN powder photocatalyst prepared in Example 3 of the present invention.

Detailed ways

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

Embodiment one:

Step 1: Weigh 1 g of melamine and put it into 75 ml of concentrated nitric acid with a concentration of 68%, and stir for 3 hours with a magnetic stirrer.

Step 2: Measure 60ml of deionized water and 20ml of absolute ethanol into a 100ml beaker, add 3g of cyanuric acid and stir for 30min.

Step 3: Filter the nitric acid-treated melamine in step 1 with filter paper and wash it three times with deionized water, then add the cleaned solid product into the cyanuric acid solution in step 2, and ultrasonicate for 60 minutes.

Step 4: Stir the above mixed solution in an oil bath at a temperature of 70° C. for 12 hours, and put it into a vacuum drying oven to dry at 80° C.

Step 5. Grind the yellowish-brown precursor obtained after drying in step 4, put it into a crucible, place it in a muffle furnace to raise the temperature to 530°C at a rate of 5°C/min, keep it warm for 2 hours, and cool to room temperature to obtain The light red powder is ACCN.

Embodiment two:

Step 1. Weigh 1.5 g of melamine and put it into 25 ml of concentrated nitric acid with a concentration of 68%, and stir for 2 h with a magnetic stirrer.

Step 2: Measure 20ml of deionized water and 60ml of absolute ethanol into a 100ml beaker, add 1g of cyanuric acid and stir for 30min.

Step 3: filter the melamine treated with nitric acid in step 1 with filter paper and wash it three times with deionized water, then add the cleaned solid product into the cyanuric acid solution in step 2, and ultrasonicate for 40 minutes.

Step 4: Stir the above mixed solution in an oil bath at a temperature of 90° C. for 4 hours, and put it into a vacuum drying oven to dry at 80° C.

Step 5. Grind the yellow-brown precursor obtained after drying in step 4, put it into a crucible, place it in a muffle furnace to raise the temperature to 540°C at a rate of 2°C/min, keep it warm for 3 hours, and cool to room temperature to obtain The light red powder is ACCN.

Embodiment three:

Step 1. Weigh 2 g of melamine and put it into 50 ml of concentrated nitric acid with a concentration of 68%, and stir for 1 h with a magnetic stirrer.

Step 2: Measure 40ml of deionized water and 40ml of absolute ethanol into a 100ml beaker, add 2g of cyanuric acid and stir for 30min.

Step 3: filter the nitric acid-treated melamine in step 1 with filter paper and wash it three times with deionized water, then add the cleaned solid product into the cyanuric acid solution in step 2, and ultrasonicate for 30 minutes.

Step 4: Stir the above mixed solution in an oil bath at a temperature of 80° C. for 5 hours, and put it into a vacuum drying oven to dry at 80° C.

Step 5. Grind the yellow-brown precursor obtained after drying in step 4, put it into a crucible, place it in a muffle furnace to raise the temperature to 550°C at a rate of 2°C/min, keep it warm for 4 hours, and cool to room temperature to obtain The light red powder is ACCN.

Figure 1 is a transmission electron microscope (TEM) picture of the ACCN photocatalyst prepared in Example 3 of the present invention. In previous reports, the agglomeration of melamine without any modification is very serious, and this morphology is not conducive to the transmission of electrons and active sites. It is difficult to expose the points. From the figure, we can see that the synthesized ACCN has no obvious agglomeration phenomenon, and this thin ACCN is conducive to the migration of photo-generated carriers from the center of the sample to the surface, thus avoiding the photo-generated carriers. Recombination occurs inside the sample.

Curve 1 and Curve 2 in Fig. 2 are the XRD patterns of gC ₃ N ₄ prepared by the traditional method in Example 3 of the present invention and ACCN prepared in this invention. Comparing curve 1 and curve 2, it can be seen that the (002) crystal plane of ACCN moves at a high angle, which means that the distance between graphite phase carbon nitride layers is reduced, which is conducive to the stacking direction of electrons along the π-π conjugated plane At the same time, it was also found that the crystallinity of ACCN decreased, mainly because the nitrate ion distorted the heptazine ring unit, which greatly reduced the long-range order of the sample.

Curve 3 and curve 4 in Fig. 3 are the ultraviolet-visible light absorption collection spectrum (UV-vis) of the ACCN that the example ₃ of the present invention makes and the gC that adopts traditional method to prepare N ₄ (UV-vis), can observe from curve 4 that sample is more than 450nm Visible light is not well absorbed, and the red graphite phase carbon nitride we prepared this time can absorb visible light from 400nm to 650nm, thereby greatly promoting photocatalytic performance.

Curve 5 and curve 6 in Fig. 4 are the photocatalytic hydrogen evolution performance of the ACCN prepared by Example 3 of the present invention and gC ₃ N ₄ prepared by the traditional method are compared, it can be seen that the red graphite phase carbon nitride has improved photocatalytic The hydrogen evolution rate, the total hydrogen production in 4 hours is 4 times that of gC ₃ N ₄ synthesized by traditional methods. The reason is attributed to the excellent light absorption ability of ACCN for visible light, large specific surface area and good carrier separation ability.

Fig. 5 is a comparative diagram of effective light utilization of ACCN prepared in Example 3 of the present invention and CCN prepared by a traditional method. The area of the shaded part in the figure represents the effective visible light of ACCN and CCN, and these photons can directly excite the semiconductor photocatalyst to generate photogenerated carriers and then participate in the photocatalytic reaction. Compared with CCN prepared by traditional methods, the effective absorbance of ACCN prepared in Example 3 of this project was significantly increased by 2.18 times, which is very beneficial to improve the photocatalytic efficiency.

Fig. 6 is a scanning electron microscope (SEM) picture of the ACCN powder photocatalyst prepared in Example 3 of the present invention. It can be seen that the flaky carbon nitride can provide more active sites for the photocatalytic reaction, which is beneficial to the photocatalytic reaction.

Claims (9)

1. a preparation method of a red supramolecular graphite phase carbon nitride photocatalyst that improves visible light utilization rate, is characterized in that the steps are as follows: Step 1: Weigh melamine with a weight of 1-2g, put it into 25-75ml of concentrated nitric acid, and stir evenly; Step 2: filter the melamine treated with nitric acid in step 1 and wash it with deionized water several times to obtain a solid product, add the solid product to the cyanuric acid solution, and perform ultrasonic treatment; Described cyanuric acid solution is the mixed solution of the deionized water of 20～60ml, the dehydrated alcohol of 20～60ml and 1～3g cyanuric acid; Step 3: Stir the above mixed solution in an oil bath at a temperature of 70-90° C. for 4-12 hours and then dry to obtain a yellow-brown precursor; Step 4: Grind the yellow-brown precursor and put it into a crucible, place it in a muffle furnace and raise the temperature to 530-550°C at a rate of 2-5°C/min, keep it warm for 2-4 hours, and cool to room temperature. The light red powder is ACCN. The above ratio is the measurement for preparing one portion. 2. The preparation method of the red supramolecular graphite phase carbon nitride photocatalyst for improving the utilization rate of visible light according to claim 1, characterized in that: the concentration of the concentrated nitric acid is 68%. 3 . The preparation method of the red supramolecular graphite phase carbon nitride photocatalyst for improving the utilization rate of visible light according to claim 1 , characterized in that: in the step 1, stir evenly with a magnetic stirrer for 1-3 hours. 4. The preparation method of the red supramolecular graphite phase carbon nitride photocatalyst that improves the utilization rate of visible light according to claim 1, characterized in that: filter paper is used for filtering in the step 2. 5. The preparation method of the red supramolecular graphite phase carbon nitride photocatalyst for improving the utilization rate of visible light according to claim 1, characterized in that: the step 2 is washed three times with deionized water. 6. The preparation method of the red supramolecular graphite phase carbon nitride photocatalyst for improving the utilization rate of visible light according to claim 1, characterized in that: the step 2 is added into the cyanuric acid solution and then ultrasonically treated for 30-60 minutes. 7. The preparation method of the red supramolecular graphite phase carbon nitride photocatalyst that improves the utilization rate of visible light according to claim 1, characterized in that: the mixed solution of cyanuric acid is stirred for at least 30 min when mixed. 8. The preparation method of the red supramolecular graphite phase carbon nitride photocatalyst for improving the utilization rate of visible light according to claim 1, characterized in that: the step 3 is to put it into a vacuum drying oven and dry it at 75-90°C. 9. A red supramolecular graphite phase carbon nitride photocatalyst prepared by the method according to any one of claims 1 to 8, characterized in that: the red supramolecular graphite phase carbon nitride ACCN catalyst has a mass of 65.173m ² /g It has a large specific surface area and promotes the electron excitation of the lone pair of electrons on the nitrogen atom at n→π ^* , so that the visible light absorption rate at 400nm-650nm is significantly increased by 2.18 times compared with the CCN prepared by the traditional method.

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