An N v CN composite photocatalyst, preparation method and application thereof in hydrogen production by water photolysis

Abstract

The application belongs to the technical field of photocatalytic material preparation, and particularly relates to a kind of N v CN composite photocatalyst, preparation method and its application in the aspect of water splitting for hydrogen production. The application introduces N-(4-cyanophenyl)-glycine as a precursor to synthesize N v CN photocatalyst. The nitrogen vacancy introduced by N-(4-cyanophenyl)-glycine can form a local state, accelerate charge transfer and enhance light absorption capacity, thereby obtaining maximum photocatalytic activity under visible light and maintaining long-term stability, thus effectively improving photocatalytic performance. The test shows that the hydrogen production efficiency of pure CN is 327.5 μmol h ‑ 1 g ‑1 , and the hydrogen production efficiency of N v CN composite photocatalyst is increased to 1632.0 μmol h ‑1 g ‑1 . This use of N-(4-cyanophenyl)-glycine realizes the adjustment of CN electronic configuration, promotes its photocatalytic properties for producing H2.

Description

TECHNICAL FIELD

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

[0002] The information disclosed in this Background section is for the purpose of increasing the understanding of the background of the application without admitting that such information forms any part of prior art.

[0003] Solar energy is widely regarded as a green and sustainable resource because it can solve energy shortage and environmental restoration problems. At present, people have explored various strategies for utilizing solar energy, and photocatalytic water splitting for hydrogen production is considered as one of the most promising technologies due to its green, sustainable and environmentally friendly characteristics.

[0004] In recent years, photocatalytic degradation method has attracted widespread attention due to its green and efficient characteristics, and semiconductor materials applied in the field of photocatalysis have gradually become an emerging field. Graphitic nitride g-C3N4, one of the most concerned semiconductor materials, has become a new material in this field due to its excellent catalytic performance and suitable band gap. Polymeric graphitic carbon nitride (g-C3N4, referred to as CN) has become a widely studied photocatalyst in the field of water splitting for hydrogen production due to its suitable electronic properties, stability and visible light absorption capacity. However, its photocatalytic efficiency is often limited by low charge carrier separation and migration efficiency, insufficient light absorption and other shortcomings.

[0005] In the field of photocatalytic hydrogen evolution, the existing technology usually uses original CN as a photocatalyst for photocatalytic decomposition of water for hydrogen production. However, the traditional CN is limited in photocatalytic performance due to poor charge carrier separation and transport performance, few active sites for hydrogen evolution reaction and weak light absorption capacity. Although various methods for improving CN preparation have been proposed, including element doping, structure modification and heterojunction formation, these strategies are usually difficult to achieve the desired balance between improving photocatalytic performance and maintaining excellent stability. It is a challenging problem to induce these vacancies and accelerate their effect on photocatalytic hydrogen production by means of N vacancy engineering to improve the photocatalytic activity of original CN. SUMMARY

[0006] To solve the above problems, the application provides a N v CN composite photocatalyst, a preparation method thereof and application thereof in water splitting for hydrogen production. The application provides a more controllable and effective strategy for constructing and distributing N vacancies in CN to address the above challenges, specifically by introducing N-(4-cyanophenyl)-glycine as a precursor to synthesize Nv The nitrogen vacancy induced by N-(4-cyanophenyl)-glycine can form a local state, accelerate charge transfer and enhance light absorption capacity, thereby obtaining maximum photocatalytic activity under visible light and maintaining long-term stability, so as to effectively improve the photocatalytic performance. At the same time, by optimizing the vacancy structure and distribution, the application realizes the acceleration of photocatalytic hydrogen production without losing the stability of photocatalysis, and provides a feasible solution for upgrading the photocatalytic hydrogen production technology.

[0007] The reaction process involved in the application involves the following regulation mechanism:

[0008] The method for regulating the photocatalytic water splitting process on the N vacancy of CN by one-step synthesis method includes pyrolysis of urea and N-(4-cyanophenyl) glycine. N-(4-cyanophenyl)-glycine contains a -C≡N group and a glycine skeleton. 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) interacts with the CN network, and at the same time, pyrolysis causes some C-N bonds in CN to become weak and decompose, thereby causing the formation of nitrogen vacancies (N v ) in CN. In this way, the application uses N-(4-cyanophenyl)-glycine to regulate the electronic configuration of CN, promoting its photocatalytic properties for producing H2.

[0009] Specifically, the technical solutions of the application are as follows:

[0010] In a first aspect of the application, an N v CN composite photocatalyst is provided, 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 a second aspect of the application, a preparation method of the above-mentioned N v CN composite photocatalyst is provided, which specifically includes the following steps: mixing urea and N-(4-cyanophenyl)-glycine, dispersing them in a mixed solvent, and pyrolyzing the obtained solid after water bath evaporation of the solvent to obtain the N v CN composite photocatalyst.

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

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

[0014] Preferably, the temperature of the water bath evaporation of the solvent is 75-85℃, and preferably 80℃.

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

[0016] In a third aspect, the application provides an N v Application of the CN composite photocatalyst in photocatalytic water splitting for hydrogen production.

[0017] In a fourth aspect, the application provides an N v A method for photocatalytic water splitting for hydrogen production by using the CN composite photocatalyst, comprising the following steps: dispersing the N v CN composite photocatalyst in an aqueous solution containing an electron donor, and mixing the solution to perform a reaction under visible light irradiation, thereby releasing hydrogen.

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

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

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

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

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

[0023] The application focuses on precisely constructing and distributing N vacancies to accelerate photocatalytic hydrogen production without losing photocatalytic stability. Specifically, by utilizing the advantages of N-(4-cyanophenyl) glycine-derived vacancies, the photocatalytic activity is promoted by enhancing the separation and transport of carriers. The catalyst effectively improves the performance of water splitting for hydrogen production, and the hydrogen production efficiency of pure CN is 327.5 μmol h -1 g-1 and N v The water-splitting hydrogen production efficiency of the CN composite photocatalyst is increased to 1632.0 μmol h -1 g -1 .

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

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

[0026] The drawings accompanying the specification of the present application form a part thereof and serve to further understand the present application, the illustrative embodiments thereof and the description thereof. The drawings do not limit the present application in any way.

[0027] Figure 1 N v X-ray diffraction patterns (XRD) of the CN composite photocatalyst prepared in Examples 1-4 of the present application and the CN photocatalyst prepared in Comparative Example 1;

[0028] Figure 2 N v Fourier transform infrared spectra (FTIR) of the CN composite photocatalyst prepared in Examples 1-4 of the present application and the CN photocatalyst prepared in Comparative Example 1;

[0029] Figure 3 N v Ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) of the CN composite photocatalyst prepared in Examples 1-4 of the present application and the CN photocatalyst prepared in Comparative Example 1;

[0030] Figure 4 N v Photoluminescence spectra (PL) of the CN composite photocatalyst prepared in Examples 1-4 of the present application and the CN photocatalyst prepared in Comparative Example 1;

[0031] Figure 5 N v Stability and recyclability test of the CN-3 composite photocatalyst prepared in Example 3 of the present application;

[0032] Figure 6 N v Comparison chart of the photocatalytic hydrogen production rate of the CN composite photocatalyst prepared in Examples 1-4 of the present application and the CN photocatalyst prepared in Comparative Example 1. DETAILED DESCRIPTION

[0033] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0034] The application will be described in further detail below with reference to specific embodiments. It should be noted that the specific embodiments described are illustrative in nature and are not intended to limit the application.

[0035] Example 1 This embodiment provides a kind of N v CN composite photocatalyst and preparation method thereof, including steps as follows:

[0036] (1) 10 g urea and 1 mg N-(4-cyanophenyl)-glycine are dissolved in 5 mL deionized water and 25 mL anhydrous ethanol mixed solvent, and continuous stirring is carried out until complete dispersion.

[0037] (2) the solution is transferred to water bath system, and the solvent is evaporated at constant temperature stirring of 80 DEG C.

[0038] (3) the dried solid is placed in a covered crucible, and heated to 550 DEG C at a heating rate of 5 DEG C / min in air for 2 hours, and N v CN-1 composite photocatalyst is obtained after natural cooling.

[0039] Example 2 This embodiment provides a kind of N v CN composite photocatalyst and preparation method thereof, including steps as follows:

[0040] (1) 10 g urea and 3 mg N-(4-cyanophenyl)-glycine are dissolved in 5 mL deionized water and 25 mL anhydrous ethanol mixed solvent, and continuous stirring is carried out until complete dispersion.

[0041] (2) the solution is transferred to water bath system, and the solvent is evaporated at constant temperature stirring of 80 DEG C.

[0042] (3) the dried solid is placed in a covered crucible, and heated to 550 DEG C at a heating rate of 5 DEG C / min in air for 2 hours, and N v CN-3 composite photocatalyst is obtained after natural cooling.

[0043] Example 3 This embodiment provides a kind of N v CN composite photocatalyst and preparation method thereof, including steps as follows:

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

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

[0046] (3) The dried solid was placed in a covered crucible and heat-treated in air at a heating rate of 5℃ / min to 550℃ for 2 hours. After natural cooling, N was obtained. 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 10g of urea and 7mg of N-(4-cyanophenyl)-glycine in a mixed solvent of 5mL of deionized water and 25mL of anhydrous ethanol, and stir continuously until completely dispersed.

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

[0050] (3) The dried solid was placed in a covered crucible and heat-treated in air at a heating rate of 5℃ / min to 550℃ for 2 hours. After natural cooling, N was obtained. 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 10g of urea in a mixed solvent of 5mL deionized water and 25mL anhydrous ethanol, and stir continuously until completely dispersed.

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

[0054] (3) The dried solid was placed in a covered crucible and heated to 550°C in air at a heating rate of 5°C / min for 2 hours. After natural cooling, CN photocatalyst was obtained.

[0055] Experimental Example 1 This experimental example involves structural determination of the photocatalysts prepared in Examples 1-4 and Comparative Example 1.

[0056] like Figure 1 As shown, CN and N vThe XRD patterns of CN-X (X = 1, 3, 5 or 7) photocatalysts show two characteristic peaks around 13.2° and 27.5°, which are attributed to the (100) plane and (002) plane, respectively, related to the repeated heptazine units and the layered assembly of the heptazine-like skeleton. In the N v The intensity of these two peaks in the CN-X samples is slightly lower compared to the pristine CN, which proves that N vacancies have been incorporated into the CN skeleton.

[0057] As shown in Fig. 1, CN and N Figure 2 CN-X samples show similar characteristic peaks. Specifically, the peak at 806 cm v -1 The peaks in the range of 1150-700 cm -1 -1 The peaks in the range of 3200-3600 cm

[0058] The N-(4-cyanophenyl) glycine contains a -C≡N group and a glycine backbone. However, no -C≡N peak was found when analyzing the -C≡N CN samples, indicating that the high-temperature calcination led to the decomposition of the -C≡N group.

[0059] As shown in Fig. 1, CN and N Figure 3 CN-X samples show similar characteristic peaks. Specifically, the peak at 806 cm v The UV-Vis diffuse reflectance spectra of CN-X photocatalysts show that N v CN-X photocatalysts have a significantly better light absorption ability than CN, confirming that the introduction of N vacancies effectively improves the visible light absorption ability of CN, which is beneficial to generate more photoexcited electron-hole pairs.

[0060] As shown in Fig. 1, CN and N Figure 4 CN-X samples show similar characteristic peaks. Specifically, the peak at 806 cm v The photoluminescence (PL) results of CN-X samples were used to evaluate the transport and separation efficiency of photoexcited charge carriers. It can be noted that the PL peak intensity of N v CN-X samples is significantly lower than that of CN, confirming that the overall PL emission intensity is significantly reduced. This result indicates that the introduction of N vacancies in CN effectively reduces the recombination of photoexcited charge carriers.

[0061] Based on the above characterization, it is not difficult to analyze that the photocatalyst prepared in Example 3 has the best performance. Therefore, the inventors tested the stability and recyclability of the photocatalyst prepared in Example 3 and performed XPS tests:

[0062] As shown in Fig. 1, CN and N Figure 5 ​​As shown, it can be clearly seen that the optimal photocatalyst maintains excellent hydrogen evolution stability in the continuous 5 reaction cycles, and the results show that the designed photocatalyst has extremely high efficiency, stability and recyclability.

[0063] As shown in Table 1, through element content and atomic ratio analysis, compared with CN (1.34), the N / C ratio of CN-3 (1.47) is significantly reduced, which proves the efficient generation of N vacancies. v v As shown in Table 1, through element content and atomic ratio analysis, compared with CN (1.34), the N / C ratio of CN-3 (1.47) is significantly reduced, which proves the efficient generation of N vacancies.

[0064] Table 1

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

[0066] Experimental Example 1 :

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

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

[0069] In a typical experiment, 0.05 g of photocatalyst was dispersed in 100 mL of aqueous solution containing 10% (volume fraction) triethanolamine (TEOA). Subsequently, 1% (mass fraction) platinum (Pt) was loaded as a co-catalyst on the surface of the photocatalyst by the method of photodeposition of H2PtCl6·6H2O. Before irradiation using a 300 W band-pass filter (λ≥420 nm) xenon lamp as a 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℃ by circulating cooling water. The generated hydrogen was detected by a gas chromatograph (GC 1120, Shanghai Sunway Hengping Scientific Instrument Co., Ltd.) equipped with a thermal conductivity detector and a 5A molecular sieve column, with nitrogen as the carrier gas.

[0070] Experimental results analysis:

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

[0072] As shown in Table 1, through element content and atomic ratio analysis, compared with CN (1.34), the N / C ratio of CN-3 (1.47) is significantly reduced, which proves the efficient generation of N vacancies. Figure 6 As shown in Table 1, through element content and atomic ratio analysis, compared with CN (1.34), the N / C ratio of CN-3 (1.47) is significantly reduced, which proves the efficient generation of N vacancies.​-1 g -1 , 1632.0 μmol h -1 g -1 , 1038.2 μmol h -1 g -1 , 880.9 μmol h -1 g -1 The hydrogen production efficiency of pure CN prepared in Comparative Example 1 was 327.5 μmol h -1 g -1 ; it can be noted that the optimal N v CN-3 photocatalyst achieved 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 descriptions are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An N2O reagent for photocatalytic water splitting to produce hydrogen. v CN composite photocatalyst, characterized in that... It comprises a polymerized graphitic carbon nitride matrix, wherein nitrogen vacancies induced by N-(4-cyanophenyl)-glycine are introduced into the matrix framework; urea and N-(4-cyanophenyl)-glycine are mixed and dispersed in a mixed solvent, and the solid obtained after evaporating the solvent in a water bath is subjected to a pyrolysis reaction to obtain N v CN composite photocatalyst; the mass ratio of urea to N-(4-cyanophenyl)-glycine is 10 g:(1~7) mg.

2. The N according to claim 1 v The method for preparing CN composite photocatalyst is characterized by, Specifically, urea and N-(4-cyanophenyl)-glycine are mixed and dispersed in a mixed solvent. After evaporating the solvent in a water bath, the resulting solid undergoes a pyrolysis reaction to obtain N... v CN composite photocatalyst; the mass ratio of urea to N-(4-cyanophenyl)-glycine is 10 g:(1~7) mg.

3. The N as described in claim 2 v The method for preparing CN composite photocatalyst is characterized by, The mixed solvent is a mixture of anhydrous ethanol and deionized water, and the volume ratio of anhydrous ethanol to deionized water is 5~5.5:

1.

4. The N as described in claim 2 v The method for preparing CN composite photocatalyst is characterized by, The temperature for evaporating the solvent in the water bath is 75~85℃.

5. The N as described in claim 4 v The method for preparing CN composite photocatalyst is characterized by, The temperature at which the solvent is evaporated in the water bath is 80°C.

6. The N as described in claim 2 v The method for preparing CN composite photocatalyst is characterized by, The pyrolysis reaction is carried out by heating to 550-560℃ at a heating rate of 4-5.5℃ / min and holding for 1.5-2.5 h.

7. The N as described in claim 6 v The method for preparing CN composite photocatalyst is characterized by, The pyrolysis reaction was carried out by heating to 550°C at a rate of 5°C / min and holding for 2 hours.

8. The N according to claim 1 v Application of CN composite photocatalyst in photocatalytic water splitting for hydrogen production.

9. The N according to claim 1 v The method for hydrogen production by photocatalytic water splitting using CN composite photocatalyst is characterized by... Includes the following steps: taking the N as described in claim 1 v CN composite photocatalyst is dispersed in an aqueous solution containing electron donors. The mixture reacts under visible light irradiation to release hydrogen.

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

11. The method as described in claim 9, characterized in that, It also includes loading metal Pt as a co-catalyst on the surface of a composite photocatalyst in a mixed solution by photodeposition. The loading of the metal Pt is 0.8~1 wt.%; the visible light irradiation is performed using a xenon lamp with a 300 W bandpass filter, and the wavelength λ of the filter is ≥420 nm.

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