CN113673086B - Analysis method of reaction mechanism of photocatalytic hydrogen peroxide production - Google Patents

Abstract

The invention discloses an analysis method of a reaction mechanism for producing hydrogen peroxide by photocatalysis, which comprises the following steps: and simulating a reaction path contained in the corresponding model of the photocatalyst to be researched according to the active species generated by the photocatalyst to be researched in the photocatalytic hydrogen peroxide production process, the conversion process of each active species and the electron and hole distribution result of the corresponding model of the photocatalyst to be researched, and analyzing the reaction mechanism of hydrogen peroxide production. The analysis method provided by the invention adopts the experimental result determined by an experimental means, so that the accuracy of the result can be ensured, meanwhile, the specific process of chemical reaction can be more intuitively and specifically analyzed by theoretical calculation on molecular and even atomic scales, and further, the accuracy is further improved under the mutual verification of the experimental result and theoretical calculation analysis, so that the reaction mechanism of the photocatalytic hydrogen peroxide production can be efficiently analyzed on the premise of high accuracy, and the method has the advantages of strong universality, high efficiency, low cost, accuracy and the like, and has high use value and good application prospect.

Description

An analytical method for the reaction mechanism of photocatalytic production of hydrogen peroxide

Technical field

The invention belongs to the field of photocatalysis and relates to a method for analyzing the reaction mechanism of photocatalytic production of hydrogen peroxide. Specifically, it relates to a method for analyzing the reaction mechanism of photocatalytic production of hydrogen peroxide by combining experiments and theoretical calculations.

Background technique

Thanks to its low cost, low energy consumption, and sustainability, photocatalytic technology has received widespread attention in the direction of producing hydrogen peroxide. However, most researchers currently do not pay enough attention to the reaction mechanism of photocatalytic production of hydrogen peroxide, and the proposed mechanism is also very simple, that is, photogenerated holes oxidize alcohol to produce aldehydes and hydrogen ions, while photogenerated electrons promote the one-step two-electron or two-step conversion of oxygen. One-step single-electron reduction generates hydrogen peroxide. These mechanisms do not take into account that the reactive oxygen species generated in the photoreaction system and also have oxidizing ability may also directly oxidize alcohol to directly generate hydrogen peroxide. Therefore, the photocatalytic production of hydrogen peroxide is analyzed. The mechanism helps to discover the limiting and promoting factors in the hydrogen peroxide generation process, which is extremely important for further improving the production of hydrogen peroxide. Therefore, based on the limitations of currently proposed mechanisms and the importance of revealing the complete reaction mechanism, it is necessary to develop accurate and efficient mechanism analysis methods.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a method for analyzing the reaction mechanism of photocatalytic hydrogen peroxide production with strong universality, high efficiency, low cost and accuracy.

In order to solve the above technical problems, the present invention adopts the following technical solutions:

An analytical method for the reaction mechanism of photocatalytic production of hydrogen peroxide, including the following steps:

S1. Construct a model of the photocatalyst to be studied;

S2. Analyze the electron and hole distribution of the corresponding model of the photocatalyst to be studied;

S3. According to the active species produced by the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide and the conversion process of each active species, as well as the electron and hole distribution results of the corresponding model of the photocatalyst to be studied analyzed in step S2, simulate the process to be studied. Study the reaction paths included in the photocatalyst corresponding model, and analyze the reaction mechanism of the photocatalyst to be studied to produce hydrogen peroxide.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved. In step S1, when the photocatalyst to be studied is an improved photocatalyst, constructing a model of the photocatalyst to be studied includes the following steps:

S1-1. Analyze the atoms of the photocatalyst to be studied based on the X-ray photoelectron spectroscopy characterization results, elemental analysis characterization results and Fourier transform infrared spectroscopy characterization results of the photocatalyst to be studied and the original photocatalyst corresponding to the photocatalyst to be studied. Changes and changes in each functional group;

S1-2. Based on the atomic changes and changes in each functional group of the photocatalyst to be studied, build a model of the photocatalyst to be studied based on the model of the original photocatalyst.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved. In step S1, when the photocatalyst to be studied is a newly synthesized photocatalyst, constructing a model of the photocatalyst to be studied includes the following steps:

S1-1. Based on the X-ray photoelectron spectroscopy characterization results, elemental analysis characterization results and Fourier transform infrared spectroscopy characterization results of the photocatalyst to be studied, analyze the atomic conditions and various functional groups of the photocatalyst to be studied;

S1-2. Construct a model of the photocatalyst to be studied based on the atoms and functional groups of the photocatalyst to be studied.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved by using computer software to construct a model of the photocatalyst to be studied; the computer software is VESTA.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved. In step S2, computer software is used to perform theoretical calculations on the model of the photocatalyst to be studied in step S1, and the electrons and holes of the corresponding model of the photocatalyst to be studied are analyzed. The hole distribution was obtained to obtain the electron-hole isosurface diagram of the corresponding model of the photocatalyst to be studied; the computer software was Gaussian 16C01, the functional used was M06-2X, and the basis set was 6-311G**.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved. In step S3, computer software is used to simulate the reaction paths included in the corresponding model of the photocatalyst to be studied. According to the energy barrier of the rate-limiting step corresponding to each reaction path As a result, the reaction mechanism of hydrogen peroxide produced by the photocatalyst to be studied was determined; the computer software was CP2K, the module used was Quickstep, and the methods used were DIMER and CI-NEB.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved, and the reaction path corresponding to the lowest value of the energy barrier of the rate-limiting step is used as the reaction mechanism of the photocatalyst to produce hydrogen peroxide to be studied.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved. In step S3, the active species produced by the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide and the conversion process of each active species are determined by The sacrificial agent experimental results and free radical capture experimental results of the photocatalyst were studied and analyzed, including the following steps:

(1) Examine the effects of different sacrificial agents on the amount of hydrogen peroxide produced by photocatalysis of the photocatalyst to be studied, and analyze the activity of the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide based on the production results of hydrogen peroxide under different sacrificial agent conditions. Species;

(2) Select the corresponding capture agent according to the type of active species produced by the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide obtained in step (1);

(3) Examine the impact of the corresponding capture agent on the transformation relationship between the active species analyzed in step (1). Based on the transformation relationship between the active species, analyze the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide. Transformation process of active species.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved. The sacrificial agent used in the sacrificial agent experiment of the photocatalyst to be studied is p-benzoquinone or tryptophan; the reaction of the sacrificial agent experiment The concentration of the sacrificial agent in the system is controlled between 0.1M and 10M; the capture agent used during the sacrificial agent experiment of the photocatalyst to be studied is TEMP or DMPO; the concentration of the capture agent in the reaction system of the free radical capture experiment is controlled at 0.1M～10M.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved. When the photocatalyst to be studied is an improved photocatalyst, it includes an element-doped photocatalyst, a supported photocatalyst or a defective photocatalyst; The element-doped photocatalyst includes one of various element-doped carbon nitride, boron nitride and covalent organic framework materials; the supported photocatalyst includes single-atom supported carbon nitride, nitride One of boron and covalent organic framework materials; the defective photocatalyst is one of nitrogen-deficient carbon nitride, boron nitride, and covalent organic framework materials.

The above-mentioned analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide is further improved. When the photocatalyst to be studied is nitrogen-deficient carbon nitride, the active species produced in the photocatalytic production of hydrogen peroxide is free superoxide anion. radicals and singlet oxygen; the conversion process of the active species is to first convert superoxide anion radicals into singlet oxygen, and then convert singlet oxygen into hydrogen peroxide;

When the photocatalyst to be studied is nitrogen-deficient carbon nitride, the simulated reaction paths of the nitrogen-deficient carbon nitride are as follows:

Article 1: The methylene hydrogen on isopropyl alcohol is first transferred to a nitrogen atom near the nitrogen defect, and oxygen receives an electron and is reduced to a superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred to The superoxide anion radical becomes an OOH species. Finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide;

Article 2: The methylene hydrogen on isopropyl alcohol is first transferred to a nitrogen atom near the cyano group, and oxygen receives a photo-generated electron and is reduced to a superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred It becomes OOH species on the superoxide anion radical, and finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide;

Article 3: The methylene hydrogen on isopropyl alcohol is first transferred to a carbon atom in the nitrogen defect, and oxygen receives a photo-generated electron and is reduced to superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred to The superoxide anion radical becomes an OOH species. Finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide;

Article 4: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into superoxide anion radical. The methylene hydrogen and hydroxyl hydrogen of isopropyl alcohol are directly transferred to the superoxide anion radical to form peroxide. hydrogen;

Article 5: The oxygen adsorbed on the surface of the nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into a superoxide anion radical, which is then oxidized to singlet oxygen by the hole. The methylene hydrogen and hydroxyl hydrogen of isopropyl alcohol are directly transferred. to singlet oxygen to form hydrogen peroxide;

Article 6: The oxygen adsorbed on the surface of the nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into a superoxide anion radical, which is then oxidized to singlet oxygen by the hole. The methylene hydrogen of isopropyl alcohol is first transferred to the adjacent H ₃ O ⁺ is formed on a water molecule. This H ₃ O ⁺ transfers a hydrogen to another water molecule to form H ₃ O ⁺ . At the same time, it returns to a water molecule. The generated H ₃ O ⁺ transfers a hydrogen to singlet oxygen, and at the same time, the hydroxyl hydrogen of isopropanol is also transferred to singlet oxygen to form hydrogen peroxide;

Article 7: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride obtains a photo-generated electron and is converted into superoxide anion radical. The superoxide anion radical on the surface desorbs into the solution to form free superoxide anion radical, isopropyl The methylene hydrogen and hydroxyl hydrogen of the alcohol are directly transferred to the free superoxide anion radical to form hydrogen peroxide;

Article 8: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into superoxide anion radical, which is then oxidized to singlet oxygen by holes. Subsequently, the singlet oxygen on the surface is desorbed into the solution to form free radicals. The singlet oxygen, methylene hydrogen and hydroxyl hydrogen of isopropyl alcohol are directly transferred to the free singlet oxygen to form hydrogen peroxide;

Among them, the energy barriers of the rate-limiting steps corresponding to the first to eighth reaction paths are 0.82eV, 2.37eV, 1.75eV, 0.79eV, 0.80eV, 0.66eV, 0.77eV, 0.71eV;

Comparing the energy barriers of the rate-limiting steps of each reaction path, the sixth reaction path corresponding to the lowest value of the energy barrier of the rate-limiting step is used as the reaction mechanism for the photocatalytic production of hydrogen peroxide by nitrogen-deficient carbon nitride.

Compared with the prior art, the advantages of the present invention are:

The invention provides an analysis method for the reaction mechanism of photocatalytic production of hydrogen peroxide, based on the active species produced by the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide and the conversion process of each active species, and the corresponding model of the photocatalyst to be studied The electron and hole distribution results are used to simulate the reaction path included in the corresponding model of the photocatalyst to be studied, and the reaction mechanism of the photocatalyst to be studied to produce hydrogen peroxide is analyzed. In the present invention, experimental means are used to determine the experimental results, which can ensure the accuracy of the results. At the same time, theoretical calculations can more intuitively and specifically analyze the specific process of the chemical reaction at the molecular or even atomic scale, and then combine the experimental results with the theoretical calculation analysis. Through mutual verification, the accuracy is further improved, so that the reaction mechanism of photocatalytic hydrogen peroxide production can be efficiently analyzed with high accuracy. In addition, both experimental methods and theoretical calculations can obtain results in a short time, and the analysis efficiency is very high, which is very conducive to guiding the actual preparation of photocatalysts based on the final results, including the improvement of photocatalysts. Furthermore, the analytical cost of the present method is very low compared to the use of restrictive and expensive in situ characterization experiments. The analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide of the present invention has the advantages of strong universality, high efficiency, low cost, accuracy, etc., and can be widely used to analyze and determine the reaction mechanism of photocatalytic production of hydrogen peroxide by the photocatalyst to be studied. It has high use value and good application prospects.

Description of the drawings

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention.

Figure 1 is a comparison diagram of the N/C atomic ratio of carbon nitride and nitrogen-deficient carbon nitride in Example 1 of the present invention.

Figure 2 is a Fourier transform infrared spectrum of carbon nitride and nitrogen-deficient carbon nitride in Example 1 of the present invention.

Figure 3 is a high-resolution photoelectron spectrum of carbon nitride and nitrogen-deficient carbon nitride in Example 1 of the present invention.

Figure 4 is an electron hole isosurface diagram of the carbon nitride model of nitrogen defects in Example 1 of the present invention.

Figure 5 is a comparison chart of the photocatalytic production of hydrogen peroxide from nitrogen-deficient carbon nitride in Example 1 of the present invention under different conditions.

Figure 6 is an electron paramagnetic resonance image of nitrogen-deficient carbon nitride under different conditions in Example 1 of the present invention.

FIG. 7 is a reaction path diagram included in the carbon nitride corresponding model for nitrogen defects in Embodiment 1 of the present invention.

Figure 8 is a rate-limiting step barrier diagram of each reaction path included in the nitrogen-deficient carbon nitride model in Embodiment 1 of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments of the specification, but the protection scope of the present invention will not be limited thereby.

The raw materials and instruments used in the following examples are all commercially available; the light source system is a PLS-SXE 300C xenon lamp, purchased from Beijing Pofilai Technology Co., Ltd. The software used is Gaussian 16C01, CP2K, VESTA.

Example 1

An analysis method for the reaction mechanism of photocatalytic production of hydrogen peroxide, specifically: analyzing the reaction mechanism of nitrogen-deficient carbon nitride in photocatalytic production of hydrogen peroxide, including the following steps:

S1. Construct a model of nitrogen-deficient carbon nitride:

S1-1. Carry out X-ray photoelectron spectroscopy, elemental analysis and Fourier transform infrared spectroscopy characterization of carbon nitride (original photocatalyst) and nitrogen-deficient carbon nitride (photocatalyst to be studied). According to carbon nitride (original photocatalyst) and nitrogen-deficient carbon nitride (photocatalyst to be studied) characterization results of The changes in each functional group are as follows:

Conduct organic element analysis and X-ray photoelectron spectroscopy analysis on carbon nitride and nitrogen-deficient carbon nitride. At the same time, the N/C atomic ratio of carbon nitride and nitrogen-deficient carbon nitride is determined by organic element analysis and photoelectron spectroscopy. The results are shown in Figure 1. Figure 1 is a comparison diagram of the N/C atomic ratio of carbon nitride and nitrogen-deficient carbon nitride in Example 1 of the present invention. As can be seen from Figure 1, compared with carbon nitride, the N/C atomic ratio of nitrogen-deficient carbon nitride is reduced, which shows that the N element content in nitrogen-deficient carbon nitride is reduced, which is determined by photoelectron spectroscopy. The N/C atom ratio decreases more significantly, further indicating that the N element on the surface is mainly reduced.

Fourier transform infrared spectroscopy was performed on carbon nitride and nitrogen-deficient carbon nitride, and the results are shown in Figure 2. Figure 2 is a Fourier transform infrared spectrum of carbon nitride and nitrogen-deficient carbon nitride in Example 1 of the present invention. As can be seen from Figure 2, compared with carbon nitride, nitrogen-deficient carbon nitride generates cyano groups (C≡N) and reduces amino groups (N-H).

High-resolution X-ray photoelectron spectroscopy was performed on carbon nitride and nitrogen-deficient carbon nitride, and the results are shown in Figure 3. Figure 3 is a high-resolution photoelectron spectrum of carbon nitride and nitrogen-deficient carbon nitride in Example 1 of the present invention. It can be seen from Figure 3 that in the preparation method of nitrogen-deficient carbon nitride, the addition of NaOH leads to the generation of cyano groups, the reduction of amino groups, and the number of dicoordinated N atoms (N _2C ) is also reduced. Since the generation of cyano groups and the reduction of amino groups will not lead to the reduction of N element, this shows that N defects are mainly caused by the reduction of N _2C .

S1-2. According to the atomic changes and changes in each functional group of the nitrogen-deficient carbon nitride in step S1-1, based on the carbon nitride model, use computer software (VESTA, version 3.5.7) to construct nitrogen The model of defective carbon nitride is specifically as follows: According to the changes of nitrogen atoms and functional groups of nitrogen-deficient carbon nitride, the model of carbon nitride is adjusted in the computer software. The specific steps are to add cyano groups groups, reduce amino groups, add nitrogen defects, and construct a model of carbon nitride with nitrogen defects.

S2. Use computer software (Gaussian 16C01, the functional used is M06-2X, the basis set is 6-311G**) to perform theoretical calculations on the model of nitrogen-deficient carbon nitride in step S1, and analyze the nitrogen-deficient carbon nitride. Corresponding to the electron and hole distribution of the model, the electron hole isosurface diagram of the nitrogen-deficient carbon nitride corresponding model is obtained. The results are shown in Figure 4.

Figure 4 is an electron hole isosurface diagram of the carbon nitride model of nitrogen defects in Example 1 of the present invention. It can be seen from Figure 6 that D ₀ →D ₂ is brightly excited and the corresponding holes and electrons are respectively distributed at the nitrogen defect site and the 1,4 sites (NV1,4) of melon near the nitrogen defect, D ₀ →D ₃ It is also a bright excitation and the corresponding holes and electrons are respectively distributed on the N atoms near the nitrogen defect and at the nitrogen defect site, while D ₀ →D ₁ and D ₀ →D ₄ are dark excitations.

S3. According to the active species produced by nitrogen-deficient carbon nitride in the photocatalytic production of hydrogen peroxide and the conversion process of each active species, as well as the electron and hole distribution of the corresponding model of nitrogen-deficient carbon nitride analyzed in step S2 As a result, the reaction path included in the corresponding model of simulated nitrogen-deficient carbon nitride was analyzed, and the reaction mechanism of hydrogen peroxide produced from nitrogen-deficient carbon nitride was analyzed, as follows:

S3-1. Examine the effect of nitrogen-deficient carbon nitride on hydrogen peroxide production under different conditions, and analyze the active species produced by nitrogen-deficient carbon nitride in the photocatalytic production of hydrogen peroxide and the conversion process of each active species.

Control group: Mix nitrogen-deficient carbon nitride, isopropyl alcohol and water in a light-proof environment, and the resulting mixed solution undergoes a photocatalytic reaction under visible light (simulating sunlight light source) for 1 hour to prepare hydrogen peroxide. After the reaction, , detect the production of hydrogen peroxide; the concentration of nitrogen-deficient carbon nitride in the resulting mixed liquid is 1.0g/L, and the volume ratio of isopropyl alcohol and water is 1/9.

Sacrificial experimental group: Before the photocatalytic reaction, different sacrificial agents (p-benzoquinone, p-benzoquinone) were added to the mixed solution. Other reaction conditions were the same as those in the control group. After the reaction, the conditions of different sacrificial agents were measured. of hydrogen peroxide production. In the sacrificial experimental group, the concentration of the sacrificial agent in the mixed solution was all 0.14M.

Based on the hydrogen peroxide production of the control group (without sacrificial agent), by comparing the corresponding hydrogen peroxide production data under different sacrificial agents, the active species produced by nitrogen-deficient carbon nitride in the photocatalytic production of hydrogen peroxide were analyzed and determined. The results are shown in Figure 5. Figure 5 is a comparison chart of the photocatalytic production of hydrogen peroxide from nitrogen-deficient carbon nitride in Example 1 of the present invention under different conditions. As can be seen from Figure 5, under normal conditions, nitrogen-deficient carbon nitride can produce nearly 500 μM hydrogen peroxide through photocatalysis in one hour. After adding the sacrificial agent of superoxide anion radical, p-benzoquinone, the production of hydrogen peroxide is zero. After adding the sacrificial agent of singlet oxygen, tryptophan, the production of hydrogen peroxide is greatly reduced. It can be speculated that superoxide anion radicals and singlet oxygen may be intermediate products in the photocatalytic reaction.

Based on the results of the sacrificial agent experiment, TEMP was used as the capture agent to continue the free radical capture experiment.

Free radical capture experimental group: Before performing the photocatalytic reaction, add p-benzoquinone or p-benzoquinone/TEMP to the mixed solution respectively. In the free radical capture experimental group, the concentrations of p-benzoquinone and TEMP in the controlled mixed solution are both 0.14M, other reaction conditions were the same as the control group. During the reaction process, the signal intensity of different active species produced by nitrogen-deficient carbon nitride in the photocatalytic production of hydrogen peroxide is detected, specifically:

Electron paramagnetic resonance experiments were conducted on nitrogen-deficient carbon nitride under different capture agent conditions, and the results are shown in Figure 6. Figure 6 is an electron paramagnetic resonance image of nitrogen-deficient carbon nitride under different conditions in Example 1 of the present invention. It can be seen from Figure 6a and 6b that nitrogen-deficient carbon nitride exhibits obvious superoxide anion radical and singlet oxygen signals respectively under light illumination, which proves that superoxide anion radical and singlet oxygen do exist in the photocatalytic reaction. middle. In order to further verify the relationship between superoxide anion radicals and singlet oxygen, electron paramagnetic resonance signal detection of singlet oxygen was performed after using p-benzoquinone to capture superoxide anion radicals. The results in Figure 6c show that the signal from singlet oxygen disappears completely and only the signal resulting from the interaction of p -quinone and TEMP is detected, since the signal observed in the p -quinone/TEMP system is similar to that of the nitrogen-deficient carbon nitride/p Benzoquinone/TEMP is the same. Therefore, part of the superoxide anion radicals may not be directly converted to hydrogen peroxide, but first converted to singlet oxygen.

Based on the above results, it can be seen that the active species generated by nitrogen-deficient carbon nitride in the photocatalytic production of hydrogen peroxide are superoxide anion radicals and singlet oxygen, and the conversion process of the active species is first converted from superoxide anion radicals into Singlet oxygen is then converted into hydrogen peroxide.

S3-2. Use computer software (CP2K, version 7.1, the module used is Quickstep, and the methods used are DIMER and CI-NEB) to analyze the photocatalytic production of hydrogen peroxide from the nitrogen-deficient carbon nitride in step S3-1. The active species and conversion process, the electron hole isosurface diagram of the nitrogen-deficient carbon nitride corresponding model analyzed in step S2 are used to perform transition state theoretical calculations, and the reaction paths included in the nitrogen-deficient carbon nitride corresponding model are simulated, The results are shown in Figure 7. At the same time, the energy barrier results of the rate-limiting steps corresponding to each reaction path are obtained. As shown in Figure 8, according to the energy barrier results of the rate-limiting steps corresponding to each reaction path, the photocatalyst to be studied is determined to produce peroxidation. Hydrogen reaction mechanism.

FIG. 7 is a reaction path diagram included in the carbon nitride corresponding model for nitrogen defects in Embodiment 1 of the present invention. It can be seen from Figure 7 that the simulated reaction paths of nitrogen-deficient carbon nitride are as follows:

Article 1: The methylene hydrogen on isopropyl alcohol is first transferred to a nitrogen atom near the nitrogen defect, and oxygen receives an electron and is reduced to a superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred to The superoxide anion radical becomes an OOH species. Finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide;

Article 2: The methylene hydrogen on isopropyl alcohol is first transferred to a nitrogen atom near the cyano group, and oxygen receives a photo-generated electron and is reduced to a superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred It becomes OOH species on the superoxide anion radical, and finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide;

Article 3: The methylene hydrogen on isopropyl alcohol is first transferred to a carbon atom in the nitrogen defect, and oxygen receives a photo-generated electron and is reduced to superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred to The superoxide anion radical becomes an OOH species. Finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide;

Article 4: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into superoxide anion radical. The methylene hydrogen and hydroxyl hydrogen of isopropyl alcohol are directly transferred to the superoxide anion radical to form peroxide. hydrogen;

Article 5: The oxygen adsorbed on the surface of the nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into a superoxide anion radical, which is then oxidized to singlet oxygen by the hole. The methylene hydrogen and hydroxyl hydrogen of isopropyl alcohol are directly transferred. to singlet oxygen to form hydrogen peroxide;

Article 6: The oxygen adsorbed on the surface of the nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into a superoxide anion radical, which is then oxidized to singlet oxygen by the hole. The methylene hydrogen of isopropyl alcohol is first transferred to the adjacent H ₃ O ⁺ is formed on a water molecule. This H ₃ O ⁺ transfers a hydrogen to another water molecule to form H ₃ O ⁺ . At the same time, it returns to a water molecule. The generated H ₃ O ⁺ transfers a hydrogen to singlet oxygen, and at the same time, the hydroxyl hydrogen of isopropanol is also transferred to singlet oxygen to form hydrogen peroxide;

Article 7: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride obtains a photo-generated electron and is converted into superoxide anion radical. The superoxide anion radical on the surface desorbs into the solution to form free superoxide anion radical, isopropyl The methylene hydrogen and hydroxyl hydrogen of the alcohol are directly transferred to the free superoxide anion radical to form hydrogen peroxide;

Article 8: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into superoxide anion radical, which is then oxidized to singlet oxygen by holes. Subsequently, the singlet oxygen on the surface is desorbed into the solution to form free radicals. Of singlet oxygen, the methylene hydrogen and hydroxyl hydrogen of isopropanol are directly transferred to free singlet oxygen to form hydrogen peroxide.

Figure 8 is a rate-limiting step barrier diagram of each reaction path included in the nitrogen-deficient carbon nitride model in Embodiment 1 of the present invention. It can be seen from Figure 8 that the energy barriers of the rate-limiting steps corresponding to the first to eighth reaction paths are 0.82eV, 2.37eV, 1.75eV, 0.79eV, 0.80eV, 0.66eV, 0.77eV, and 0.71eV.

It can be seen from Figure 7 and Figure 8 that by comparing the energy barriers of the rate-limiting step of each reaction path, the results show that the sixth reaction path corresponding to the lowest value of the energy barrier of the rate-limiting step is used as the photocatalytic production of nitrogen-deficient carbon nitride. The reaction mechanism of hydrogen peroxide, that is, the path using superoxide anion radicals or singlet oxygen as the driving force for oxidation is more favorable than the path using holes as the driving force for oxidation. Among them, reaction path six is the most favorable, which shows that the surface The synergistic effect of singlet oxygen and water bridge plays a major role in the generation of hydrogen peroxide.

In this embodiment, the method for preparing carbon nitride includes the following steps:

(1) Calculate 15 grams of melamine in a muffle furnace at 550°C for 4 hours at a rate of 10°C min ^-1 to obtain a carbon nitride sample.

In this embodiment, the method for preparing nitrogen-deficient carbon nitride includes the following steps:

(1) Dissolve 15 grams of melamine in a NaOH aqueous solution containing 30 ml of water and 1.5 grams of NaOH and stir evenly.

(2) Evaporate the water in the mixed solution obtained in step (1) to dryness.

(3) The resulting solid mixture obtained in step (2) was calcined in a muffle furnace at 550°C for 4 hours at a rate of 10°C min ^-1 .

(4) Wash the sample obtained in step (3) with ethanol and water several times and then dry it to obtain a nitrogen-deficient carbon nitride sample.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited only to the above embodiments. All technical solutions falling under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, improvements and modifications may be made without departing from the principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims (9)

1. An analytical method for the reaction mechanism of photocatalytic production of hydrogen peroxide, which is characterized by comprising the following steps: S1. Construct a model of the photocatalyst to be studied; S2. Analyze the electron and hole distribution of the corresponding model of the photocatalyst to be studied; S3. According to the active species produced by the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide and the conversion process of each active species, as well as the electron and hole distribution results of the corresponding model of the photocatalyst to be studied analyzed in step S2, simulate the process to be studied. Study the reaction paths included in the photocatalyst corresponding model, and analyze the reaction mechanism of the photocatalyst to be studied to produce hydrogen peroxide; In step S1, when the photocatalyst to be studied is an improved photocatalyst, constructing a model of the photocatalyst to be studied includes the following steps: S1-1. Analyze the atoms of the photocatalyst to be studied based on the X-ray photoelectron spectroscopy characterization results, elemental analysis characterization results and Fourier transform infrared spectroscopy characterization results of the photocatalyst to be studied and the original photocatalyst corresponding to the photocatalyst to be studied. Changes and changes in each functional group; S1-2. Based on the atomic changes and changes in each functional group of the photocatalyst to be studied, build a model of the photocatalyst to be studied based on the model of the original photocatalyst; Or, in step S1, when the photocatalyst to be studied is a newly synthesized photocatalyst, constructing a model of the photocatalyst to be studied includes the following steps: S1-1. Based on the X-ray photoelectron spectroscopy characterization results, elemental analysis characterization results and Fourier transform infrared spectroscopy characterization results of the photocatalyst to be studied, analyze the atomic conditions and various functional groups of the photocatalyst to be studied; S1-2. Construct a model of the photocatalyst to be studied based on the atoms and functional groups of the photocatalyst to be studied. 2. The analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide according to claim 1, characterized in that computer software is used to construct a model of the photocatalyst to be studied; the computer software is VESTA. 3. The analysis method of photocatalytic production of hydrogen peroxide reaction mechanism according to claim 2, characterized in that, in step S2, computer software is used to theoretically calculate the model of the photocatalyst to be studied in step S1, and analyze the photocatalyst to be studied. The electron and hole distribution of the corresponding model of the catalyst was obtained to obtain the electron hole isosurface diagram of the corresponding model of the photocatalyst to be studied; the computer software was Gaussian 16 C01, the functional used was M06-2X, and the basis set was 6- 311G**. 4. The analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide according to claim 3, characterized in that, in step S3, computer software is used to simulate the reaction path included in the corresponding model of the photocatalyst to be studied, and according to the corresponding reaction path The energy barrier results of the rate-limiting step determine the reaction mechanism of the photocatalyst to be studied to produce hydrogen peroxide; the computer software is CP2K, the module used is Quickstep, and the methods used are DIMER and CI-NEB. 5. The analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide according to claim 4, characterized in that the reaction path corresponding to the lowest value of the energy barrier of the rate-limiting step is used as the reaction mechanism of the photocatalyst to be studied to produce hydrogen peroxide. . 6. The analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide according to claim 4, characterized in that, in step S3, the active species and each activity produced by the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide The conversion process of species is obtained by analyzing the sacrificial agent experimental results and free radical capture experimental results of the photocatalyst to be studied, and includes the following steps: (1) Examine the effects of different sacrificial agents on the photocatalytic production of hydrogen peroxide by the photocatalyst to be studied, and analyze the activity of the photocatalyst under study in the photocatalytic production of hydrogen peroxide based on the production results of hydrogen peroxide under different sacrificial agent conditions. Species; (2) Select the corresponding capture agent according to the type of active species produced by the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide obtained in step (1); (3) Examine the impact of the corresponding capture agent on the transformation relationship between the active species analyzed in step (1). Based on the transformation relationship between the active species, analyze the photocatalyst to be studied in the photocatalytic production of hydrogen peroxide. Transformation process of active species. 7. The analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide according to claim 6, characterized in that the sacrificial agent used in the sacrificial agent experiment process of the photocatalyst to be studied is p-benzoquinone or tryptophan; The concentration of the sacrificial agent in the reaction system of the sacrificial agent experiment is controlled between 0.1M and 10M; the capture agent used in the sacrificial agent experiment of the photocatalyst to be studied is TEMP or DMPO; the reaction system of the free radical capture experiment The concentration of medium capture agent is controlled at 0.1M ~ 10M. 8. The analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide according to any one of claims 1 to 7, characterized in that when the photocatalyst to be studied is an improved photocatalyst, it includes an element-doped photocatalyst. Catalyst, supported photocatalyst or defective photocatalyst; the element-doped photocatalyst includes one of various element-doped carbon nitride, boron nitride and covalent organic framework materials; the supported photocatalyst The photocatalyst includes one of single atom-supported carbon nitride, boron nitride and covalent organic framework materials; the defective photocatalyst is one of nitrogen-deficient carbon nitride, boron nitride and covalent organic framework materials. one of them. 9. The analysis method of the reaction mechanism of photocatalytic production of hydrogen peroxide according to claim 8, characterized in that when the photocatalyst to be studied is nitrogen-deficient carbon nitride, the photocatalytic production of hydrogen peroxide is The active species are superoxide anion radicals and singlet oxygen; the conversion process of the active species is to first convert superoxide anion radicals into singlet oxygen, and then convert singlet oxygen into hydrogen peroxide; When the photocatalyst to be studied is nitrogen-deficient carbon nitride, the simulated reaction paths of the nitrogen-deficient carbon nitride are as follows: Article 1: The methylene hydrogen on isopropyl alcohol is first transferred to a nitrogen atom near the nitrogen defect, and oxygen receives an electron and is reduced to a superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred to The superoxide anion radical becomes an OOH species. Finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide; Article 2: The methylene hydrogen on isopropyl alcohol is first transferred to a nitrogen atom near the cyano group, and oxygen receives a photo-generated electron and is reduced to a superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred It becomes OOH species on the superoxide anion radical, and finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide; Article 3: The methylene hydrogen on isopropyl alcohol is first transferred to a carbon atom in the nitrogen defect, and oxygen receives a photo-generated electron and is reduced to superoxide anion radical, and then the hydroxyl hydrogen on isopropyl alcohol is spontaneously transferred to The superoxide anion radical becomes an OOH species. Finally, OOH combines with the hydrogen on the nitrogen atom to form hydrogen peroxide; Article 4: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into superoxide anion radical. The methylene hydrogen and hydroxyl hydrogen of isopropyl alcohol are directly transferred to the superoxide anion radical to form peroxide. hydrogen; Article 5: The oxygen adsorbed on the surface of the nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into a superoxide anion radical, which is then oxidized to singlet oxygen by the hole. The methylene hydrogen and hydroxyl hydrogen of isopropyl alcohol are directly transferred. to singlet oxygen to form hydrogen peroxide; Article 6: The oxygen adsorbed on the surface of the nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into a superoxide anion radical, which is then oxidized to singlet oxygen by the hole. The methylene hydrogen of isopropyl alcohol is first transferred to the adjacent H ₃ O ⁺ is formed on a water molecule. This H ₃ O ⁺ transfers a hydrogen to another water molecule to form H ₃ O ⁺ . At the same time, it returns to a water molecule. The generated H ₃ O ⁺ transfers a hydrogen to singlet oxygen, and at the same time, the hydroxyl hydrogen of isopropanol is also transferred to singlet oxygen to form hydrogen peroxide; Article 7: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride obtains a photo-generated electron and is converted into superoxide anion radical. The superoxide anion radical on the surface desorbs into the solution to form free superoxide anion radical, isopropyl The methylene hydrogen and hydroxyl hydrogen of the alcohol are directly transferred to the free superoxide anion radical to form hydrogen peroxide; Article 8: Oxygen adsorbed on the surface of nitrogen-deficient carbon nitride receives a photo-generated electron and is converted into superoxide anion radical, which is then oxidized to singlet oxygen by holes. Subsequently, the singlet oxygen on the surface is desorbed into the solution to form free radicals. The singlet oxygen, methylene hydrogen and hydroxyl hydrogen of isopropyl alcohol are directly transferred to the free singlet oxygen to form hydrogen peroxide; Among them, the energy barriers of the rate-limiting steps corresponding to the first to eighth reaction paths are 0.82eV, 2.37eV, 1.75eV, 0.79eV, 0.80eV, 0.66eV, 0.77eV, 0.71eV; Comparing the energy barriers of the rate-limiting steps of each reaction path, the sixth reaction path corresponding to the lowest value of the energy barrier of the rate-limiting step is used as the reaction mechanism for the photocatalytic production of hydrogen peroxide by nitrogen-deficient carbon nitride.