NvCN composite photocatalyst, preparation method and application of NvCN composite photocatalyst in hydrogen production through water photolysis

Abstract

The invention belongs to the technical field of photocatalytic material preparation, and particularly relates to an NvCN composite photocatalyst, a preparation method and application of the NvCN composite photocatalyst in hydrogen production through water photolysis. The N-(4-cyanophenyl)-glycine is introduced as a precursor to synthesize the NvCN photocatalyst containing nitrogen vacancies, the nitrogen vacancies introduced by the N-(4-cyanophenyl)-glycine can form a localized state, charge transfer is accelerated, and the light absorption capacity is enhanced, so that the maximum photocatalytic activity under visible light is obtained, the long-term stability is kept, and the preparation method is simple and easy to implement. The N-(4-cyanobenzoyl)-glycine has the advantages that the N-(4-cyanobenzoyl)-glycine can be used for effectively improving the photocatalytic performance, the hydrogen production efficiency of pure CN is 327.5 micromoles / h <-1 > g <-1 > through tests, the water photolysis hydrogen production efficiency of the NvCN composite photocatalyst is improved to 1632.0 micromoles / h <-1 > g <-1 >, the adjustment of CN electron configuration is realized by utilizing the N-(4-cyanobenzoyl)-glycine, and the photocatalytic characteristic of the N-(4-cyanobenzoyl)-glycine for producing H2 is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of photocatalytic materials, and particularly relates to an N v CN composite photocatalyst, a preparation method thereof, and an application thereof in photocatalytic water splitting for hydrogen production. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or an indication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] The rapid growth of global energy demand and the importance of solving environmental problems through sustainable energy production have become one of the most critical challenges. Solar energy is widely regarded as a green and sustainable resource because it can solve energy shortage and environmental remediation problems. Currently, various strategies for utilizing solar energy have been explored, and among them, photocatalytic water splitting for hydrogen production is regarded as one of the most promising technologies due to its green, sustainable, and environmentally friendly characteristics.

[0004] In recent years, the photocatalytic degradation method has attracted extensive attention due to its green and efficient characteristics, and semiconductor materials applied in the photocatalytic field have gradually become an emerging field. One of the most concerned semiconductor materials at present, graphitic carbon nitride g-C3N4, has become a new material in this field due to its excellent catalytic performance and suitable bandgap and other advantages. Polymerized graphitic carbon nitride (g-C3N4, abbreviated as CN) has become a photocatalyst widely studied in the field of water splitting for hydrogen production due to its suitable electronic properties, stability, and visible light absorption ability. However, its photocatalytic efficiency is often limited by disadvantages such as low charge carrier separation and migration efficiency and insufficient light absorption.

[0005] In the field of photocatalytic hydrogen evolution, the prior art usually uses raw CN as a photocatalyst for photocatalytic water splitting for hydrogen production. However, the photocatalytic performance of traditional CN is limited due to poor charge carrier separation and transport performance, a small number of active sites for the hydrogen evolution reaction, and weak light absorption ability. Although various improvements in the preparation method of CN have been proposed, including element doping, structure modification, and heterojunction formation, these strategies usually have difficulty achieving the required balance between improving photocatalytic performance and maintaining excellent stability. Improving the photocatalytic activity of raw CN by means of N vacancy engineering is a potential solution, but how to induce these vacancies and accelerate their role in photocatalytic hydrogen production remains a challenging problem. Summary of the Invention

[0006] To solve the above problems, the present invention provides an N vCN Composite Photocatalyst, Preparation Method Thereof and Application Therein for Hydrogen Production by Photocatalytic Water Splitting. The present invention addresses the above challenges by providing a more controllable and effective strategy for constructing and distributing N vacancies in CN, specifically by introducing N-(4-cyanophenyl)-glycine as a precursor to synthesize N v CN photocatalyst. The nitrogen vacancies introduced by N-(4-cyanophenyl)-glycine can form localized states, accelerate charge transfer and enhance light absorption ability, thereby obtaining the maximum photocatalytic activity under visible light and maintaining long-term stability, thus effectively improving the photocatalytic performance. At the same time, by optimizing the vacancy structure and distribution, the present invention realizes the acceleration of photocatalytic hydrogen production without loss of photocatalytic stability, providing a practical solution for upgrading the photocatalytic hydrogen production technology.

[0007] The regulation mechanism involved in the reaction process of the present invention:

[0008] The photocatalytic water splitting hydrogen production process is regulated on the N vacancies of CN by a one-step synthesis method, which includes pyrolyzing urea and N-(4-cyanophenyl)glycine. N-(4-cyanophenyl)-glycine contains -C≡N groups and a glycine backbone. High-temperature pyrolysis can decompose -C≡N, releasing nitrogen-containing species such as hydrogen cyanide (HCN) and some by-products (CO2 and H2O). The formed nitrogen-containing species (HCN) interact with the CN network, and at the same time pyrolysis causes some C-N bonds in CN to become weak and decompose, thereby resulting in the formation of nitrogen vacancies (N v ). In this way, the present invention realizes the regulation of the electronic configuration of CN by using N-(4-cyanobenzoyl)-glycine, promoting its photocatalytic characteristics for generating H2.

[0009] Specifically, the technical solution of the present invention is as follows:

[0010] In the first aspect of the present invention, there is provided an N v CN composite photocatalyst, which includes a polymeric graphite-phase carbon nitride matrix, and nitrogen vacancies induced by N-(4-cyanophenyl)-glycine are introduced into the skeleton of the matrix.

[0011] In the second aspect of the present invention, there is provided a preparation method of the above N v CN composite photocatalyst, specifically: mixing urea and N-(4-cyanophenyl)-glycine and dispersing them in a mixed solvent, and performing a pyrolysis reaction on the solid obtained after evaporating the solvent by water bath, thus obtaining the N v CN composite photocatalyst.

[0012] Preferably, the mass ratio of urea to N-(4-cyanophenyl)-glycine is 10 g : (1 - 7) mg.

[0013] Preferably, the mixed solvent is a mixed solution of absolute ethanol and deionized water, and the volume ratio of absolute ethanol to deionized water is 5-5.5:1.

[0014] Preferably, the temperature for evaporating the solvent in the water bath is 75-85°C, preferably 80°C.

[0015] Preferably, the pyrolysis reaction is heated to 550-560°C at a heating rate of 4-5.5°C / min, and the holding time is 1.5-2.5 h; more preferably, the pyrolysis reaction is heated to 550°C at a heating rate of 5°C / min, and the holding time is 2 h.

[0016] In the third aspect of the present invention, there is provided an application of the N v CN composite photocatalyst in photocatalytic water splitting for hydrogen production.

[0017] In the fourth aspect of the present invention, there is provided a method for photocatalytic water splitting for hydrogen production using an N v CN composite photocatalyst, comprising the following steps: dispersing the N v CN composite photocatalyst in an aqueous solution containing an electron donor, and reacting the mixed solution under visible light irradiation to achieve hydrogen release.

[0018] Preferably, the electron donor is selected from one or more of triethanolamine, methanol, ascorbic acid, lactic acid, and formic acid; the dosage ratio of the N v CN composite photocatalyst to the electron donor is 0.05 g:10 mL; the volume fraction of triethanolamine in the triethanolamine aqueous solution is 10 vol.%.

[0019] Preferably, the method further includes loading metal Pt as a co-catalyst on the surface of the composite photocatalyst by photodeposition in the mixed solution.

[0020] Preferably, the loading amount of the metal Pt is 0.8-1 wt.%; when using visible light irradiation, a 300 W xenon lamp with a band-pass filter is used, and the wavelength λ of the filter is ≥420 nm.

[0021] One or more embodiments of the present invention have at least the following beneficial effects:

[0022] (1) Traditional doping strategies may lead to uneven distribution of dopants or vacancies, thus making it difficult to predict the photocatalytic activity. In addition, most of these strategies will reduce the photocatalytic stability of CN, resulting in a decrease in efficiency during long-term use; moreover, traditional strategies have not fully explored the ability of N vacancies in CN to regulate photocatalytic performance under visible light.

[0023] The present invention focuses on precisely constructing and distributing N vacancies to accelerate photocatalytic hydrogen production without sacrificing photocatalytic stability. Specifically, it utilizes the advantages of organic molecule N-(4-cyanophenyl)glycine-derived vacancies to promote photocatalytic activity by enhancing the separation and transport of carriers. This catalyst effectively improves the performance of hydrogen production by photocatalytic water splitting. The hydrogen production efficiency of pure CN is 327.5 μmol h -1 g -1 , while that of the N v CN composite photocatalyst is increased to 1632.0 μmol h -1 g -1 .

[0024] (2) The present invention optimizes the calcination temperature and time of the precursor mixture to obtain the highest possible N vacancy density without destroying the CN structure and reducing its stability.

[0025] (3) The present invention regulates the photocatalytic water splitting hydrogen production process on the N vacancies of CN by a one-step synthesis method, which is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The attached drawings forming a part of this invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0027] Figure 1 XRD patterns of the N v CN composite photocatalysts prepared in Examples 1-4 of the present invention and the CN photocatalyst prepared in Comparative Example 1;

[0028] Figure 2 FTIR comparison diagrams of the N v CN composite photocatalysts prepared in Examples 1-4 of the present invention and the CN photocatalyst prepared in Comparative Example 1;

[0029] Figure 3 UV-vis DRS of the N v CN composite photocatalysts prepared in Examples 1-4 of the present invention and the CN photocatalyst prepared in Comparative Example 1;

[0030] Figure 4 PL of the N v CN composite photocatalysts prepared in Examples 1-4 of the present invention and the CN photocatalyst prepared in Comparative Example 1;

[0031] Figure 5 For the N prepared in Example 3 of the present invention vStability and Recyclability Tests of CN-3 Composite Photocatalyst

[0032] Figure 6 For the N prepared in Examples 1-4 of the present invention v Comparison chart of photocatalytic hydrogen production rates of CN composite photocatalyst prepared in Examples 1-4 of the present invention and CN photocatalyst prepared in Comparative Example 1 Detailed Description of the Invention

[0033] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0034] The present invention will be further described in detail below with reference to specific examples. It should be noted that the specific examples are explanations rather than limitations of the present invention.

[0035] Example 1 : This example provides a kind of N v CN composite photocatalyst and its preparation method, including the following steps:

[0036] (1) Dissolve 10 g of urea and 1 mg of N-(4-cyanophenyl)-glycine in a mixed solvent of 5 mL of deionized water and 25 mL of absolute ethanol, and continuously stir until completely dispersed.

[0037] (2) Transfer the solution to a water bath system and stir to evaporate the solvent at a constant temperature of 80 °C.

[0038] (3) Place the dried solid in a covered crucible, heat it to 550 °C in air at a heating rate of 5 °C / min for 2 hours, and naturally cool to obtain N v CN-1 composite photocatalyst.

[0039] Example 2 : This example provides a kind of N v CN composite photocatalyst and its preparation method, including the following steps:

[0040] (1) Dissolve 10 g of urea and 3 mg of N-(4-cyanophenyl)-glycine in a mixed solvent of 5 mL of deionized water and 25 mL of absolute ethanol, and continuously stir until completely dispersed.

[0041] (2) Transfer the solution to a water bath system and stir to evaporate the solvent at a constant temperature of 80 °C.

[0042] (3) Place the dried solid in a covered crucible, heat it to 550 °C in air at a heating rate of 5 °C / min for 2 hours, and naturally cool to obtain N v CN-3 composite photocatalyst.

[0043] Example 3 : This embodiment provides an N v CN composite photocatalyst and its preparation method, including the following steps:

[0044] (1) Dissolve 10 g of urea and 5 mg of N-(4-cyanophenyl)-glycine in a mixed solvent of 5 mL of deionized water and 25 mL of absolute ethanol, and continuously stir until completely dispersed.

[0045] (2) Transfer the solution to a water bath system and stir and evaporate the solvent at a constant temperature of 80 °C.

[0046] (3) Place the dried solid in a covered crucible, heat it to 550 °C in air at a heating rate of 5 °C / min for heat treatment for 2 hours, and naturally cool to obtain N v CN-5 composite photocatalyst.

[0047] Example 4 : This embodiment provides an NvCN composite photocatalyst and its preparation method, including the following steps:

[0048] (1) Dissolve 10 g of urea and 7 mg of N-(4-cyanophenyl)-glycine in a mixed solvent of 5 mL of deionized water and 25 mL of absolute ethanol, and continuously stir until completely dispersed.

[0049] (2) Transfer the solution to a water bath system and stir and evaporate the solvent at a constant temperature of 80 °C.

[0050] (3) Place the dried solid in a covered crucible, heat it to 550 °C in air at a heating rate of 5 °C / min for heat treatment for 2 hours, and naturally cool to obtain N v CN-7 composite photocatalyst.

[0051] Comparative Example 1 : This comparative example provides a CN photocatalyst and its preparation method, including the following steps:

[0052] (1) Dissolve 10 g of urea in a mixed solvent of 5 mL of deionized water and 25 mL of absolute ethanol, and continuously stir until completely dispersed.

[0053] (2) Transfer the solution to a water bath system and stir and evaporate the solvent at a constant temperature of 80 °C.

[0054] (3) Place the dried solid in a covered crucible, heat it to 550 °C in air at a heating rate of 5 °C / min for heat treatment for 2 hours, and naturally cool to obtain the CN photocatalyst.

[0055] Experimental Example 1 : This experimental example measures the structures of the photocatalysts prepared in Examples 1 to 4 and Comparative Example 1

[0056] As shown Figure 1 in, the XRD patterns of CN and N v CN-X (X = 1, 3, 5 or 7) photocatalysts show that two characteristic peaks are shown near 13.2° and 27.5°, which are attributed to the (100) plane and the (002) plane respectively, and they are related to the layered assembly of the repeating heptazine units and the heptazine-like backbone respectively. In N v CN-X samples, compared with the original CN, the intensities of these two peaks are slightly reduced, proving that N vacancies have been incorporated into the CN backbone.

[0057] As shown Figure 2 in, the FTIR spectra of CN and N v CN-X samples show that the two types of samples have similar characteristic peaks. Specifically, the peak at 806 cm -1 is related to the stretching vibration mode of the triazine unit, and the peaks in the range of 1150 - 700 cm -1 are related to the aromatic C-N heterocycle. In addition, the peaks in the range of 3200 - 3600 cm -1 are related to the uncondensed amino groups (-NH and O-H);

[0058] Among them, N-(4-cyanophenyl)glycine contains a -C≡N group and a glycine backbone. However, when analyzing the -C≡NNvCN sample, no -C≡N peak was found, indicating that the -C≡N group decomposed due to high-temperature calcination.

[0059] As shown Figure 3 in, the UV-visible diffuse reflectance spectra of CN and N v CN-X photocatalysts show that the light absorption ability of N v CN-X photocatalysts is significantly better than that of CN, confirming that the introduction of N vacancies effectively improves the visible light absorption ability of CN, which is beneficial to the generation of more photoexcited electron-hole pairs.

[0060] As shown Figure 4 in, the photoluminescence spectra (PL) results of CN and N v CN-X samples are used to evaluate the transport and separation efficiency of photoexcited charge carriers. It can be noted that compared with CN, the PL peak intensity of N v CN-X samples is significantly reduced, confirming that the overall PL emission intensity decreases significantly. This result indicates that the introduction of N vacancies in CN effectively reduces the recombination of photogenerated charge carriers.

[0061] From the above characterizations, it is not difficult to analyze that the photocatalyst prepared in Example 3 has the best performance. Based on this, the inventor carried out stability and recyclability tests and XPS tests on the photocatalyst prepared in Example 3:

[0062] As shownFigure 5 As shown, it can be clearly seen that the optimal photocatalyst maintained excellent hydrogen evolution stability in five consecutive reaction cycles, indicating that the designed photocatalyst has extremely high efficiency, stability, and recyclability.

[0063] As shown in Table 1, through the analysis of element content and atomic ratio, it can be seen that compared with CN (1.34), the N / C ratio of N v CN-3 (1.47) was significantly reduced, which proved the efficient generation of N v hydrogen.

[0064] Table 1

[0065] Sample C(％) N(％) O(％) N / C CN 38.0 55.8 6.2 1.47 <![CDATA[N v CN-3]]> 39.7 53.4 6.9 1.34

[0066] Test Example 1 :

[0067] In this test example, the photocatalytic hydrogen production rates of the N v CN composite photocatalysts prepared in Examples 1 to 4 and the CN photocatalyst prepared in Comparative Example 1 were measured and analyzed.

[0068] Photocatalytic H2 production measurement system: The photocatalytic water splitting hydrogen production experiment involved in this test example was carried out in a 500 mL Pyrex top-irradiation reaction vessel, which was connected to a closed gas circulation and evacuation system (Labsolar-6A, Beijing Perfectlight Technology Co., Ltd.).

[0069] In a typical experiment, 0.05 g of the photocatalyst was dispersed in 100 mL of an aqueous solution containing 10% (volume fraction) triethanolamine (TEOA). Subsequently, 1% (mass fraction) of platinum (Pt) was loaded on the surface of the photocatalyst as a co-catalyst by the method of photodeposition of H2PtCl6·6H2O. Before irradiating with a 300 W xenon lamp with a band-pass filter (λ≥420 nm) as the visible light source, the mixed solution was evacuated multiple times to remove air and other gases. During the reaction, the reaction solution was continuously stirred, and the reaction temperature was maintained at 6 °C by circulating cooling water. The hydrogen produced was detected by a gas chromatograph (GC 1120, Shanghai Shunyu Hengping Scientific Instrument Co., Ltd.) equipped with a thermal conductivity detector and a 5A molecular sieve column, using nitrogen as the carrier gas.

[0070] Analysis of experimental results:

[0071] The photocatalytic hydrogen evolution performance of the prepared photocatalysts under visible light (λ≥420 nm) was evaluated:

[0072] As Figure 6As shown, introducing N vacancies into CN significantly improves the photocatalytic hydrogen evolution rate. The hydrogen evolution rates corresponding to the photocatalysts prepared in Examples 1-4 are 1360.0 μmol h -1 g -1 , 1632.0 μmol h -1 g -1 , 1038.2 μmol h -1 g -1 , 880.9 μmol h -1 g -1 , respectively. The hydrogen production efficiency of the pure CN prepared in Comparative Example 1 is 327.5 μmol h -1 g -1 ; it can be noted that the optimal N v CN-3 photocatalyst achieves the highest hydrogen evolution rate, almost 5 times that of the original CN. This significantly improved activity is attributed to the introduction of N vacancies, which enhances the visible light absorption ability.

[0073] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A kind of N v CN composite photocatalyst, characterized in that It includes a polymeric graphitic carbon nitride matrix, and nitrogen vacancies induced by N-(4-cyanophenyl)-glycine are introduced into the framework of the matrix.

2. The preparation method of the N v CN composite photocatalyst according to claim 1, characterized in that Specifically: Urea and N-(4-cyanophenyl)-glycine are mixed and dispersed in a mixed solvent, and the solid obtained after evaporating the solvent by water bath is subjected to a pyrolysis reaction to obtain the N v CN composite photocatalyst.

3. The N as described in claim 2 v Preparation method of CN composite photocatalyst, characterized in that The mass ratio of the urea to N-(4-cyanophenyl)-glycine is 10 g : (1 - 7) mg.

4. The N as described in claim 2 v Preparation method of CN composite photocatalyst, characterized in that The mixed solvent is a mixture of absolute ethanol and deionized water, and the volume ratio of the absolute ethanol to the deionized water is 5 - 5.5 :

1.

5. The N as described in claim 2 v Preparation method of a CN composite photocatalyst, characterized in that The temperature for evaporating the solvent by water bath is 75 - 85 °C, preferably 80 °C.

6. The N as described in claim 2 v Preparation method of the CN composite photocatalyst, characterized in that The pyrolysis reaction is heated to 550 - 560 °C at a heating rate of 4 - 5.5 °C / min, and the heat preservation time is 1.5 - 2.5 h; Preferably, the pyrolysis reaction is heated to 550 °C at a heating rate of 5 °C / min, and the heat preservation time is 2 h.

7. Use of the N v CN composite photocatalyst in photocatalytic water splitting for hydrogen production.

8. A method for photocatalytic water splitting to produce hydrogen using the N v CN composite photocatalyst as claimed in claim 1, characterized in that comprising the following steps: dispersing the N v CN composite photocatalyst in an aqueous solution containing an electron donor, and reacting the mixture under visible light irradiation to achieve hydrogen release.

9. The method according to claim 8, wherein The electron donor is selected from one or more of triethanolamine, methanol, ascorbic acid, lactic acid, and formic acid; the v usage ratio of the N CN composite photocatalyst to the electron donor is 0.05 g: 10 mL; the volume percentage of triethanolamine in the triethanolamine aqueous solution is 10 vol.%.

10. The method according to claim 8, characterized in that, It also includes loading metal Pt as a co-catalyst on the surface of the composite photocatalyst by photodeposition method in the mixed solution; The loading amount of the metal Pt is 0.8 - 1 wt.%; when irradiated with visible light, a 300 W xenon lamp with a band-pass filter is used, and the wavelength λ of the filter is ≥420 nm.

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