Carbon nitride nanoflower photocatalyst assembled by nanosheets, and preparation method and application thereof

Abstract

This invention discloses a carbon nitride nanoflower photocatalyst assembled from nanosheets, its preparation method, and its applications, belonging to the field of photocatalytic materials technology. The method first obtains a supramolecular intermediate via a hydrothermal method, and then calcines it in a muffle furnace to obtain carbon nitride nanoflowers assembled from nanosheets. The carbon nitride nanoflowers assembled from nanosheets possess abundant edge active sites and shorter electron transfer paths. Simultaneously, their unique electronic structure facilitates extended absorption of visible light, solving the problems of existing photocatalysts such as few exposed active sites, slow carrier separation rates, and low visible light utilization, thereby improving their photocatalytic activity. The photocatalyst prepared by this invention can efficiently and stably generate H2O2 in pure water under visible light conditions.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, specifically to a carbon nitride nanoflower photocatalyst assembled from nanosheets, its preparation method, and its application. Background Technology

[0002] Hydrogen peroxide (H2O2) is a promising energy carrier and an environmentally friendly oxidant widely used in industrial and medical fields such as organic synthesis, drinking water treatment, and wastewater treatment. With increasing environmental protection requirements, the demand for H2O2 is expected to increase significantly. The traditional anthraquinone (AQ) process for producing H2O2 is cumbersome and causes organic pollution. Photocatalytic production of H2O2, using O2 and H2O as raw materials, solar energy as the energy source, and semiconductors as the photocatalyst, is a green chemical process with advantages such as mild reaction conditions, simple and controllable operation, and no secondary pollution. In recent years, photocatalytic production of H2O2 has attracted widespread attention.

[0003] Carbon nitride is an N-type semiconductor photocatalyst based on a non-metallic polymer. Its synthesis process is simple, and the raw materials are inexpensive and readily available. Carbon nitride has a band gap of approximately 2.7 eV, corresponding to a light absorption cutoff wavelength of 460 nm, making it a potential photocatalyst capable of absorbing visible light. Its bottom potential (CB) is -1.3 V vs. NHE, lower than the reduction potential of O2, and its top potential (VB) is 1.4 V vs. NHE, lower than the oxidation potential of H2O2, thus effectively preventing the oxidative decomposition of H2O2. However, problems such as a limited number of exposed active sites, slow carrier separation rate, and low visible light utilization severely limit the performance of carbon nitride in the photocatalytic production of H2O2. Summary of the Invention

[0004] The purpose of this invention is to provide a carbon nitride nanoflower photocatalyst assembled from nanosheets, its preparation method, and its application. This catalyst has abundant edge active sites, a wider light absorption range, and a shorter photogenerated electron transfer path, thereby reducing the recombination efficiency of photogenerated carriers and improving its photocatalytic activity, thus solving the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a carbon nitride nanoflower photocatalyst assembled from nanosheets, wherein the carbon nitride nanoflower photocatalyst assembled from nanosheets is first obtained by hydrothermal method to obtain supramolecular intermediate, and then calcined in muffle furnace.

[0006] Furthermore, a carbon nitride nanoflower photocatalyst assembled from nanosheets includes the following preparation steps:

[0007] (1) Melamine and benzomelamine were placed in deionized water and magnetically stirred at room temperature to disperse them, resulting in a mixed dispersion.

[0008] (2) The mixed dispersion was transferred to a hydrothermal reactor for reaction; the resulting reaction product was allowed to stand, then centrifuged, washed, and dried to obtain a supramolecular intermediate;

[0009] (3) Add supramolecular intermediates to the crucible, then place it in a muffle furnace and heat it to a certain temperature at a certain heating rate, and then keep it at that temperature for a certain time to obtain carbon nitride nanoflower photocatalyst assembled from nanosheets.

[0010] Furthermore, in step (1), the mass ratio of melamine, benzomelamine, and deionized water is 1:1:30 to 3:3:60, and the stirring time is 30 to 90 minutes.

[0011] Furthermore, the reaction temperature in step (2) is 140–220°C, and the reaction time is 8–16 h.

[0012] Furthermore, in step (3), the mass of the supramolecular intermediate is 0.5–2 g, the calcination temperature is 350–500 °C, the heating rate is 1–4 °C / min, and the calcination temperature is maintained for 2–5 h.

[0013] Furthermore, the feature is that the carbon nitride nanoflower photocatalyst assembled from nanosheets is used to photocatalyze the production of H2O2 in pure water under visible light conditions.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0015] The raw materials are simple and readily available, the operation is straightforward, and the reproducibility and controllability are excellent. The reaction uses only two reagents: melamine and benzomelamine, and only water as a solvent, making it environmentally friendly. Melamine and benzomelamine combine to form crystal nuclei for epitaxial growth. Melamine and benzomelamine form a conjugated planar structure, which serves as the framework. After heat treatment, nanosheets are formed. The presence of benzene rings at the edge of the benzomelamine with benzene ring substituents and their steric hindrance effect lead to the assembly of nanosheets into a flower-like structure with the center as the core. Compared to ordinary carbon nitride, the carbon nitride nanoflowers assembled from nanosheets weaken electron layer interactions and interlayer van der Waals forces, resulting in a wider light absorption range, more edge active sites, and shorter electron transfer paths. Photogenerated carriers transfer before recombination, effectively promoting the generation of photocatalytic substances and thus improving photocatalytic performance. Under visible light conditions, H₂O₂ can be generated efficiently and stably in pure water. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0017] Figure 1 SEM image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this invention;

[0018] Figure 2 The XRD pattern of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this invention;

[0019] Figure 3 The infrared spectrum of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this invention;

[0020] Figure 4 The solid-state ultraviolet diffuse reflectance image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this invention;

[0021] Figure 5 The steady-state fluorescence image is shown for the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this invention.

[0022] Figure 6 Photocurrent diagram of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this invention;

[0023] Figure 7 The graph shows the performance of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this invention in producing H2O2 under pure water conditions. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] (1) Place 1g of melamine and 3g of benzomelamine in a beaker containing 60mL of deionized water and disperse them by magnetic stirring at room temperature for 60min to obtain a mixed dispersion.

[0027] (2) Transfer the mixed dispersion to a 100mL hydrothermal reactor, place it in a constant temperature oven at 200℃ for 12h, wait for the reactor to cool naturally to room temperature, centrifuge at 9000r / min for 3min, wash 3 times with deionized water, place it in a constant temperature oven at 60℃ for 12h to obtain supramolecular intermediate.

[0028] (3) Weigh 1g of supramolecular intermediate and place it in a crucible. The crucible should be covered and placed in a muffle furnace for heating. The heating parameters are as follows: set the temperature to rise from room temperature to 450℃ at a uniform rate within 215min and maintain it at 450℃ for 4h. Then cool it naturally. The dark yellow solid obtained is carbon nitride nanoflower assembled from nanosheets. Carefully grind it to obtain the photocatalyst.

[0029] Figure 1 This is a scanning electron microscope (SEM) image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this embodiment. As can be seen from the image, the prepared sample consists of a nanoflower structure assembled from nanosheets.

[0030] Figure 2 The image shows the X-ray diffraction pattern of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this embodiment. Ordinary carbon nitride exhibits two characteristic diffraction peaks at approximately 13° and 27°, while the carbon nitride nanoflowers show almost no diffraction peak at 13.1°, indicating that the carbon nitride nanoflowers have a smaller interlayer distance.

[0031] Figure 3 The image shows the infrared spectrum of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this embodiment. The carbon nitride nanoflowers have similar infrared vibration peaks to ordinary carbon nitride, which indicates that the framework structure of the carbon nitride nanoflowers is consistent with that of ordinary carbon nitride.

[0032] Figure 4 This is a solid-state UV diffuse reflectance image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this embodiment. Compared to ordinary carbon nitride, the light absorption of the carbon nitride nanoflowers shows a significant redshift, and its absorption intensity is also significantly enhanced. Better light absorption is beneficial for improving photocatalytic performance.

[0033] Figure 5 This is the steady-state fluorescence image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this embodiment. The fluorescence intensity of the carbon nitride nanoflowers is significantly weaker, indicating a decrease in the recombination efficiency of photogenerated carriers. Simultaneously, the redshift of the fluorescence peak position, consistent with the solid-state UV diffuse reflectance pattern, demonstrates a reduction in the bandgap value of the carbon nitride nanoflowers.

[0034] Figure 6 The image shows the photocurrent of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this embodiment. The carbon nitride nanoflowers exhibit a stronger photocurrent intensity than ordinary carbon nitride and remain stable after five light switching cycles, indicating that they have better separation efficiency of photogenerated carriers, which is beneficial for improving photocatalytic activity.

[0035] Figure 7The activity diagram of the photocatalytic production of H2O2 by the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this embodiment includes the following steps: 20 mg of carbon nitride nanoflower photocatalyst was weighed into a 50 mL photoreaction flask, 20 mL of deionized water was added, and the mixture was magnetically stirred for 30 min in the dark to allow the reaction system to reach adsorption equilibrium. After the dark reaction was completed, the light source (300 W xenon lamp λ>420 nm) was turned on, and 1 mL of sample was taken every 10 min. After centrifugation, the concentration of H2O2 was tested using the DPD method. The results show that the fragmented carbon nitride photocatalyst exhibits a higher H2O2 production rate, while ordinary carbon nitride produces almost no H2O2.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A carbon nitride nanoflower photocatalyst assembled from nanosheets, characterized in that, The preparation steps include the following: (1) Melamine and benzomelamine are placed in deionized water and magnetically stirred at room temperature to disperse them, so as to obtain a mixed dispersion; the mass ratio of melamine, benzomelamine and deionized water is 1:1:30~3:3:

60. (2) The mixed dispersion is transferred to a hydrothermal reactor for reaction; the resulting reaction product is allowed to stand, then centrifuged, washed, and dried to obtain a supramolecular intermediate; the reaction temperature is 140~220℃; the reaction time is 8~16h; (3) Add supramolecular intermediates to the crucible, then place it in a muffle furnace and heat it to a certain temperature at a certain heating rate, and then keep it at that temperature for a certain time to obtain carbon nitride nanoflower photocatalyst assembled from nanosheets.

2. The carbon nitride nanoflower photocatalyst assembled from nanosheets according to claim 1, characterized in that, The stirring time in step (1) is 30~90 min.

3. The carbon nitride nanoflower photocatalyst assembled from nanosheets according to claim 1, characterized in that, The mass of the supramolecular intermediate in step (3) is 0.5~2g, the calcination temperature is 350~500℃, the heating rate is 1~4℃ / min, and the calcination temperature is maintained for 2~5h.

4. The use of the carbon nitride nanoflower photocatalyst assembled from nanosheets according to any one of claims 1 to 3, characterized in that, It is used for photocatalytic production of H2O2 in pure water under visible light conditions.

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