Sulfonated carbon nitride nanosheet photocatalyst as well as preparation method and application thereof in photocatalytic hydrogen production

Abstract

The invention relates to the technical field of photocatalytic hydrogen production, and particularly discloses a sulfonated carbon nitride nanosheet photocatalyst which is prepared by the following steps: carrying out heat treatment on a nitrogen-containing precursor to obtain a carbon nitride precursor; uniformly mixing with a sulfuric acid solution, carrying out microwave treatment, and carrying out solid-liquid separation to obtain a sulfonated carbon nitride nanosheet photocatalyst; the sulfonated carbon nitride nanosheet photocatalyst prepared by the invention has a higher specific surface area, narrower band gap energy and a larger photoresponse range, has higher photocatalytic H2 production activity, and is wide in application prospect.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic hydrogen production technology, and in particular to a sulfonated carbon nitride nanosheet photocatalyst, its preparation method, and its application in photocatalytic hydrogen production. Background Technology

[0002] Hydrogen (H2) is a clean energy source with high energy density, is renewable and environmentally friendly. Photocatalysis, as a green energy conversion method, is based on catalysts and solar energy. Hydrogen is produced by using catalysts under sunlight. Therefore, this green energy conversion method has attracted widespread attention from all sectors.

[0003] However, traditional industrial hydrogen production not only causes severe environmental pollution but also exacerbates climate change and threatens energy security. In contrast, photocatalytic water splitting for hydrogen production is considered the optimal solution to address the growing energy demand and the resulting environmental problems.

[0004] Carbon nitride materials have become a research hotspot in photocatalytic materials in recent years due to their visible light response and ease of functionalization. As an analog of graphite and metal-free polymer n-type semiconductors, carbon nitride materials have a two-dimensional (2D) structure of triazine stacked by tertiary amines. Due to their unique electrical, optical, structural and physicochemical properties, carbon nitride materials have been recognized as a new type of multifunctional electronic, catalytic and energy materials.

[0005] However, the preparation of carbon nitride materials often has some problems. For example, graphitic carbon nitride materials are usually synthesized by high-temperature calcination of precursors such as melamine, and then modified by long-term calcination or hydrothermal methods. The carbon nitride materials obtained by this method have a low specific surface area, a wide band gap energy, and can only respond to light with λ≤460nm, which leads to low photocatalytic efficiency. Summary of the Invention

[0006] To address the technical problems existing in the background art, this invention proposes a method for preparing sulfonated carbon nitride nanosheet photocatalysts, comprising the following steps: S1. The nitrogen-containing precursor is heat-treated to obtain the carbon nitride precursor; S2. After mixing the carbon nitride precursor with sulfuric acid solution, microwave treatment was performed, and solid-liquid separation was performed to obtain sulfonated carbon nitride nanosheet photocatalyst.

[0007] Preferably, in step S1, the nitrogen-containing precursor is at least one of a triazine compound or a cyanamide compound; Preferably, the triazine compound is at least one of melamine or trithiocyanate; Preferably, the cyanamide compound is dicyandiamide.

[0008] Preferably, in step S1, the heat treatment temperature is 500-600℃, the heat treatment time is 2-5h, and the heating rate is 1-10℃ / min; Preferably, the heat treatment temperature is 550°C, the heat treatment time is 4 hours, and the heating rate is 5°C / min.

[0009] Preferably, in step S2, the carbon nitride nanosheet photocatalyst is further subjected to grinding into powder during calcination and collection, and the carbon nitride precursor is stirred evenly before being microwaved when mixed with the prepared sulfuric acid solution.

[0010] Preferably, in step S2, the concentration of the carbon nitride precursor in the sulfuric acid solution is 50 g / L.

[0011] Preferably, in step S2, the concentration of the sulfuric acid solution is 10-40 wt%; Preferably, the concentration of the sulfuric acid solution is 40 wt%.

[0012] Preferably, in step S2, during microwave processing, the microwave input power is 1560 W, the frequency is 300 MHz to 3 THz, and the microwave duration is 5-15 min. Preferably, the microwave frequency is 1000MHz and the microwave duration is 10min.

[0013] Preferably, in step S2, during microwave treatment, the heating rate is 12℃ / min and the temperature is 100-140℃; Preferably, the temperature is 120°C.

[0014] The present invention also proposes a sulfonated carbon nitride nanosheet photocatalyst, which is prepared by the above preparation method.

[0015] The absorption edge of the photocatalyst extends to approximately 600 nm.

[0016] The present invention also proposes an application of the above-mentioned sulfonated carbon nitride nanosheet photocatalyst in photocatalytic hydrogen production.

[0017] Beneficial effects of this invention: (1) In this invention, the carbon nitride precursor is treated by liquid-phase microwave method with sulfuric acid solutions of different concentrations as the reaction medium. The preparation method is simple and easy to operate, which greatly shortens the reaction time. Moreover, the obtained carbon nitride material has n-π* transition, which can improve the light absorption range. These states promote more photogenerated electrons to participate in the photocatalytic reaction, which significantly improves the photocatalytic activity. Furthermore, the photocatalytic H2 production activity of sulfonated carbon nitride nanosheet photocatalyst is about 3.5 times higher than that of unsulfonated nanosheets. (2) In this invention, the carbon nitride precursor is treated by calcining the original carbon nitride and then using a liquid-phase microwave method with sulfuric acid solutions of different concentrations as the reaction medium. This method transforms the carbon nitride precursor into an ultrathin two-dimensional structure through acid-assisted exfoliation, and at the same time, sulfonic acid groups (-SO3H) are introduced to modify the surface of the material. The carbon nitride photocatalytic material after microwave treatment has a higher specific surface area, a narrower band gap energy, and a larger photoresponse range, and also has a higher H2 generation rate. Attached Figure Description

[0018] Figure 1 These are high-resolution scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 of the present invention; wherein, Figure (a) is a high-resolution SEM image and Figure (b) is a high-resolution TEM image. Figure 2 The X-ray diffraction (XRD) patterns of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1 are shown. Figure 3 Fourier transform infrared (FT-IR) spectra of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1. Figure 4 Figure 1 shows the S2p and O1s X-ray photoelectron spectra of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 of the present invention; wherein, Figure (a) is the S2p X-ray photoelectron spectrum and Figure (b) is the O1s X-ray photoelectron spectrum. Figure 5 The UV-Vis spectra of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1 are shown. Figure 6 The specific surface area (BET) diagram and pore size adsorption diagram are shown for the sulfonated carbon nitride nanosheet photocatalyst in Example 1 and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1. Figure 7 Impedance diagrams (EIS) of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1. Figure 8 The steady-state fluorescence spectra (PL) of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1 are shown. Figure 9 The graph shows the H2 production under visible light for the sulfonated carbon nitride nanosheet photocatalyst in Example 1 of the present invention and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1. Figure 10 This is a graph showing the H2 production of sulfonated carbon nitride nanosheet photocatalyst under visible light for an extended period of time in an embodiment of the present invention. Figure 11 The images show the product diagrams of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1. Detailed Implementation

[0019] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0020] 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0021] The technical solution of the present invention will now be described more clearly and completely with reference to specific embodiments and comparative examples.

[0022] Example 1 This embodiment proposes a sulfonated carbon nitride nanosheet photocatalyst, the preparation method of which includes the following steps: (1) Weigh 10g of trithiocyanate and put it into a 50mL corundum crucible. Heat it in a muffle furnace under an air atmosphere to 550°C and keep it for 4 hours. The heating rate is 5°C / min. A yellow blocky product is obtained through thermal polymerization. After grinding for 30 minutes, carbon nitride precursor is obtained and denoted as CN. (2) Take deionized water into a 50mL beaker, add concentrated sulfuric acid, and slowly add it dropwise while stirring for 20 minutes to obtain a 40wt% sulfuric acid solution; (3) After grinding the carbon nitride precursor into powder, weigh 1g of carbon nitride precursor powder and add it to different 40wt% sulfuric acid solutions. Stir thoroughly until uniform and then transfer it into a polytetrafluoroethylene inner liner. Heat it to 120℃ at 12℃ / min in a liquid phase microwave chemical workstation and keep it at 120℃ for 10 minutes. (4) The reaction mixture in the polytetrafluoroethylene liner was transferred to a 50 mL centrifuge tube, washed alternately with ethanol and deionized water until neutral, and then dried at 70 °C to obtain a brown solid. The brown solid was ground for 30 minutes to obtain a sulfonated carbon nitride nanosheet photocatalyst, denoted as H2SO4-CN-4.

[0023] Example 2 This embodiment proposes a sulfonated carbon nitride nanosheet photocatalyst, which is prepared in the same way as in Example 1, except that "obtaining a 40wt% sulfuric acid solution" in step (2) is replaced with "obtaining a 30wt% sulfuric acid solution".

[0024] Example 3 This embodiment proposes a sulfonated carbon nitride nanosheet photocatalyst, which is prepared in the same way as in Example 1, except that "obtaining a 40wt% sulfuric acid solution" in step (2) is replaced with "obtaining a 20wt% sulfuric acid solution".

[0025] Example 4 This embodiment proposes a sulfonated carbon nitride nanosheet photocatalyst, which is prepared in the same way as in Example 1, except that "obtaining a 40 wt% sulfuric acid solution" in step (2) is replaced with "obtaining a 10 wt% sulfuric acid solution".

[0026] Example 5 This embodiment proposes a sulfonated carbon nitride nanosheet photocatalyst, which is prepared in the same way as in Example 1, except that “trithiocyanate” in step (2) is replaced with “melamine”.

[0027] Example 6 This embodiment proposes a sulfonated carbon nitride nanosheet photocatalyst, which is prepared in the same way as in Example 1, except that “trithiocyanate” in step (2) is replaced with “dicyandiamide”.

[0028] Example 7 This embodiment proposes a sulfonated carbon nitride nanosheet photocatalyst, which is prepared in the same way as in Example 1, except that in step (1), "heating to 550°C in a muffle furnace and holding for 4 hours at a heating rate of 5°C / min" is replaced with "heating to 500°C in a muffle furnace and holding for 4 hours at a heating rate of 1°C / min".

[0029] Example 8 This embodiment proposes a sulfonated carbon nitride nanosheet photocatalyst, which is prepared in the same way as in Example 1, except that in step (1), "heated to 550°C in a muffle furnace and held for 4 hours at a heating rate of 5°C / min" is replaced with "heated to 550°C in a muffle furnace and held for 3 hours at a heating rate of 10°C / min".

[0030] Comparative Example 1 This comparative example presents a common carbon nitride photocatalyst, which is prepared in the same way as in Example 1, except that steps (2)-(4) are deleted, and the common carbon nitride photocatalyst is finally obtained, denoted as CN.

[0031] Comparative Example 2 This comparative example presents a common carbon nitride photocatalyst, which is prepared in the same way as in Example 1, except that "obtaining a 40wt% sulfuric acid solution" in step (2) is replaced with "deionized water". The final product is an unsulfonated carbon nitride nanosheet photocatalyst, denoted as CN-0.

[0032] Comparative Example 3 This comparative example presents a common carbon nitride photocatalyst, which is prepared in the same way as in Example 1, except that in step (3), "heating to 120°C at 12°C / min in a liquid phase microwave chemistry workstation and holding at 120°C for 10 minutes" is replaced with "heating to 120°C at 12°C / min in an oil bath and holding at 120°C for 10 minutes". The resulting acidified carbon nitride photocatalyst heated by the oil bath is denoted as CN-4.

[0033] Comparative Example 4 This comparative example presents a common carbon nitride photocatalyst, which is prepared in the same way as in Example 1, except that "obtaining a 40 wt% sulfuric acid solution" in step (2) is replaced with "obtaining a 40 wt% hydrochloric acid solution", and finally a hydrochloric acid-modified carbon nitride nanosheet photocatalyst is obtained, denoted as HCl-CN-4.

[0034] Comparative Example 5 This comparative example presents a common carbon nitride photocatalyst, which is prepared in the same way as in Example 1, except that in step (2), “obtaining a 40 wt% sulfuric acid solution” is replaced with “obtaining a 40 wt% nitric acid solution”, and finally a hydrochloric acid-modified carbon nitride nanosheet photocatalyst is obtained, denoted as HNO3-CN-4.

[0035] Performance testing and results Figure 1 These are high-resolution scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of this invention. Reference Figure 1 It is known that the morphology of the sulfonated carbon nitride nanosheet photocatalyst of the present invention is a nanosheet structure.

[0036] Figure 2 These are the X-ray diffraction (XRD) patterns of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of the present invention and the ordinary carbon nitride photocatalyst described in Comparative Example 1. Figure 3 These are Fourier transform infrared (FT-IR) spectra of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of the present invention and the ordinary carbon nitride photocatalyst described in Comparative Example 1. Reference Figure 2 , 3 It is known that the sulfonated carbon nitride nanosheet photocatalyst of the present invention has better crystallinity and, on this basis, successfully introduces sulfonic acid groups.

[0037] Figure 4 These are the S2p and O1s spectra of the X-ray photoelectron spectroscopy of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of the present invention, wherein Figure (a) is the S2p spectrum of the X-ray photoelectron spectroscopy and Figure (b) is the O1s spectrum of the X-ray photoelectron spectroscopy. Reference Figure 4 It is evident that the sulfonated carbon nitride nanosheet photocatalyst of the present invention has successfully incorporated sulfonic acid groups.

[0038] Figure 5 These are the UV-Vis spectra of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of the present invention and the ordinary carbon nitride photocatalyst described in Comparative Example 1. Reference Figure 5 It is understood that the sulfonated carbon nitride nanosheet photocatalyst of the present invention improves the light absorption range.

[0039] Figure 6 This is a BET (Body Surface Area) diagram of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of the present invention and the ordinary carbon nitride photocatalyst described in Comparative Example 1. Reference Figure 6 It is known that the specific surface area of ​​the sulfonated carbon nitride nanosheet photocatalyst of the present invention is significantly increased after sulfonation.

[0040] Figure 7 These are impedance diagrams (EIS) of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of the present invention and the ordinary carbon nitride photocatalyst described in Comparative Example 1. Figure 8 These are the steady-state fluorescence spectra (PL) of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of the present invention and the ordinary carbon nitride photocatalyst described in Comparative Example 1. Reference Figure 7 , 8 It is known that the sulfonated carbon nitride nanosheet photocatalyst described in this invention has a higher charge carrier separation efficiency.

[0041] Figure 9 This is a graph showing the H2 production under visible light for the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of the present invention and the ordinary carbon nitride photocatalyst described in Comparative Example 1. Figure 10 This is a graph showing the H2 production of the sulfonated carbon nitride nanosheet photocatalyst described in Example 1 of this invention under visible light for an extended period of time; Reference Figure 9 , 10 It can be seen that the photocatalytic performance of the sulfonated carbon nitride nanosheet photocatalyst described in this invention is greatly improved and its stability is good.

[0042] Figure 11The images show the product diagrams of the sulfonated carbon nitride nanosheet photocatalyst in Example 1 and the unsulfonated carbon nitride nanosheet photocatalyst in Comparative Example 1.

[0043] Hydrogen production application test case (1) Take several 70 ml irradiation containers with quartz plates on top, weigh 0.02 g of the products from Examples 1-8 and Comparative Examples 1-5 respectively, place them in the above irradiation containers, add 20 mL of 10 wt% triethanolamine aqueous solution to each container, and add 106 μL of chloroplatinic acid hexahydrate containing 0.2 wt% Pt to the solution. (2) Seal the glass container obtained in step (1). Before the hydrogen production test by light irradiation, pump argon gas into the reactor 20 minutes in advance to remove excess air in the reaction system. (3) Place the glass container obtained in step (2) on the stirring table and irradiate it under a 300W xenon lamp. Every 1 hour, use the injection needle to extract 500µl of the gas generated in the reactor and inject the gas into the gas chromatograph to determine and calculate the amount of hydrogen produced by the sample under illumination.

[0044] The hydrogen production amounts of each embodiment and comparative example are shown in Table 1: Table 1. Hydrogen production rate data for each embodiment and comparative example.

[0045] As shown in Table 1, the embodiments of the present invention obtain sulfonated carbon nitride nanosheets by using raw materials such as melamine and sulfuric acid, and through simple operations such as stirring, calcination, and microwave treatment. The photocatalyst of sulfonated carbon nitride nanosheets has a 3.5-fold increase in photocatalytic H2 production activity compared to that of unsulfonated nanosheets, and also has a high specific surface area and an ultra-wide light response range, thereby improving the photocatalytic H2 production capacity. In addition, this preparation method greatly shortens the reaction time, has broad market prospects, and is suitable for industrial production.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a sulfonated carbon nitride nanosheet photocatalyst, characterized in that, Includes the following steps: S1. The nitrogen-containing precursor is heat-treated to obtain the carbon nitride precursor; S2. After mixing the carbon nitride precursor with sulfuric acid solution, microwave treatment was performed, and solid-liquid separation was performed to obtain sulfonated carbon nitride nanosheet photocatalyst.

2. The method for preparing the sulfonated carbon nitride nanosheet photocatalyst according to claim 1, characterized in that, In step S1, the nitrogen-containing precursor is at least one of a triazine compound or a cyanamide compound; Preferably, the triazine compound is at least one of melamine or trithiocyanate; Preferably, the cyanamide compound is dicyandiamide.

3. The method for preparing the sulfonated carbon nitride nanosheet photocatalyst according to claim 1 or 2, characterized in that, In step S1, the heat treatment temperature is 500-600℃, the heat treatment time is 2-5h, and the heating rate is 1-10℃ / min; Preferably, the heat treatment temperature is 550°C, the heat treatment time is 4 hours, and the heating rate is 5°C / min.

4. The method for preparing the sulfonated carbon nitride nanosheet photocatalyst according to any one of claims 1-3, characterized in that, In step S2, the concentration of the carbon nitride precursor in the sulfuric acid solution is 50 g / L.

5. The method for preparing the sulfonated carbon nitride nanosheet photocatalyst according to any one of claims 1-4, characterized in that, In step S2, the concentration of the sulfuric acid solution is 10-40 wt%. Preferably, the concentration of the sulfuric acid solution is 40 wt%.

6. The method for preparing the sulfonated carbon nitride nanosheet photocatalyst according to any one of claims 1-5, characterized in that, In step S2, during microwave processing, the microwave input power is 1560W, the frequency is 300MHz to 3THz, and the microwave time is 5-15min. Preferably, the microwave frequency is 1000MHz and the microwave duration is 10min.

7. The method for preparing the sulfonated carbon nitride nanosheet photocatalyst according to any one of claims 1-6, characterized in that, In step S2, during microwave treatment, the heating rate is 12℃ / min, and the temperature is 100-140℃. Preferably, the temperature is 120°C.

8. A sulfonated carbon nitride nanosheet photocatalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The application of the sulfonated carbon nitride nanosheet photocatalyst of claim 8 in photocatalytic hydrogen production.

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