Carbon nitride nanoflower photocatalyst assembled by nanosheets as well as preparation method and application of carbon nitride nanoflower photocatalyst

Abstract

The invention discloses a carbon nitride nanoflower photocatalyst assembled by nanosheets as well as a preparation method and application thereof, and relates to the technical field of photocatalytic materials. The method comprises the following steps: firstly, obtaining a supramolecular intermediate through a hydrothermal method, and calcining the supramolecular intermediate through a muffle furnace to obtain carbon nitride nanoflowers assembled by nanosheets; the nanosheet-assembled carbon nitride nanoflower has abundant edge active sites and a shorter electron transfer path, and meanwhile, the unique electronic structure of the nanosheet-assembled carbon nitride nanoflower is beneficial to expansion of absorption of visible light, so that the problems of few exposed active sites, low carrier separation rate, low visible light utilization rate and the like of an existing photocatalyst are solved; therefore, the photocatalytic activity is improved. The photocatalyst prepared by the invention can efficiently and stably generate H2O2 in pure water under the condition of visible light.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalytic materials, and in particular to a carbon nitride nanoflower photocatalyst assembled from nanosheets, a preparation method and an application thereof. Background Art

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

[0003] Carbon nitride is an N-type semiconductor photocatalyst of high molecular non-metallic polymer. Its synthesis process is simple and the raw materials are cheap and easy to obtain. The band gap of carbon nitride is about 2.7eV, and the corresponding light absorption cutoff wavelength is 460nm. It is a potential photocatalyst that can absorb visible light. Its CB bottom potential is -1.3Vvs.NHE, which is lower than the reduction potential of O2, and its VB top potential is 1.4Vvs.NHE, which is lower than the oxidation potential of H2O2, so it can effectively prevent the oxidative decomposition of H2O2. However, the problems of few exposed active sites, slow carrier separation rate and low visible light utilization rate have seriously limited the performance of carbon nitride in photocatalytic production of H2O2. Summary of the invention

[0004] The purpose of the present invention is to provide a carbon nitride nanoflower photocatalyst assembled from nanosheets, a preparation method and an application thereof, wherein the 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, so as to solve the problems existing in the prior art.

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

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

[0007] (1) dispersing melamine and benzoguanamine in deionized water under magnetic stirring at room temperature to obtain a mixed dispersion;

[0008] (2) transferring the mixed dispersion to a hydrothermal reactor for reaction; allowing the obtained reaction product to stand, centrifugally separating, washing, and drying to obtain a supramolecular intermediate;

[0009] (3) The supramolecular intermediate is added into the crucible, and then the crucible is placed in a muffle furnace and heated to a certain temperature at a certain heating rate, and then kept warm for a certain period of time, thereby obtaining a carbon nitride nanoflower photocatalyst assembled from nanosheets.

[0010] Furthermore, in step (1), the mass ratio of melamine, benzoguanamine 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 hours.

[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, it is characterized in that the carbon nitride nanoflower photocatalyst assembled from nanosheets is used to photocatalytically produce 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 easy to obtain, the operation is simple, the repeatability is good, and the controllability is strong. In the reaction, only two drugs, melamine and benzoguanamine, are used, and only water is used as a solvent, which is green and environmentally friendly. Melamine and benzoguanamine combine to form a crystal nucleus and grow epitaxially, and melamine and benzoguanamine form a conjugated planar structure. With this as the skeleton, it is formed into a nanosheet after heat treatment. At the same time, under the influence of the presence of the edge benzene ring of benzoguanamine with a benzene ring substituent and its steric hindrance effect, the center is used as the core, and the nanosheets are assembled to form a flower-like structure. Compared with ordinary carbon nitride, the carbon nitride nanoflowers assembled by nanosheets weaken the interaction between the electron layers and the interlayer van der Waals force, so that it has a wider light absorption range, more edge active sites and a shorter electron transfer path. The photogenerated carriers are transferred before the recombination, which effectively promotes the generation of photocatalytic substances, thereby improving the photocatalytic performance. Under visible light conditions, H2O2 can be efficiently and stably generated in pure water. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 This is a SEM image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared by the present invention;

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

[0019] Figure 3 This is an infrared spectrum of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared by the present invention;

[0020] Figure 4 This is a solid ultraviolet diffuse reflectance image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared by the present invention;

[0021] Figure 5 This is a steady-state fluorescence image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared by the present invention;

[0022] Figure 6 The photocurrent diagram of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared by the present invention;

[0023] Figure 7 This is a performance diagram of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared by the present invention in producing H2O2 under pure water conditions. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] Example 1

[0026] (1) 1 g of melamine and 3 g of benzoguanamine were placed in a beaker containing 60 mL of deionized water, and dispersed by magnetic stirring at room temperature for 60 min to obtain a mixed dispersion;

[0027] (2) The mixed dispersion was transferred to a 100 mL hydrothermal reactor, placed in a constant temperature oven at 200 °C for 12 h, and the reactor was naturally cooled to room temperature, centrifuged at 9000 r / min for 3 min, washed with deionized water three times, and placed in a constant temperature oven at 60 °C for 12 h to obtain a supramolecular intermediate;

[0028] (3) Weigh 1 g of the supramolecular intermediate and place it in a crucible with a lid, and heat it in a muffle furnace; the heating parameters are as follows: set the temperature to rise uniformly from room temperature to 450°C within 215 minutes, and maintain it at 450°C for 4 hours; then cool it naturally, and the dark yellow solid obtained is the carbon nitride nanoflowers assembled by nanosheets, which can be ground carefully to obtain the photocatalyst.

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

[0030] Figure 2 This is the X-ray diffraction pattern of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this example. Ordinary carbon nitride has two characteristic diffraction peaks of carbon nitride at about 13° and 27°, while the diffraction peak of carbon nitride nanoflower at 13.1° is almost not observed, which indicates that carbon nitride nanoflower has a smaller interlayer distance.

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

[0032] Figure 4 This is a solid ultraviolet diffuse reflectance image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this embodiment. Compared with ordinary carbon nitride, the light absorption of carbon nitride nanoflowers has undergone a significant red shift, and its absorption intensity has also been significantly enhanced. Better light absorption capacity is conducive to the improvement of photocatalytic performance.

[0033] Figure 5 This is the steady-state fluorescence image of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this example. The fluorescence intensity of the carbon nitride nanoflower is significantly weaker, indicating that the photogenerated carrier recombination efficiency of the carbon nitride nanoflower is reduced. At the same time, the red shift of the fluorescence peak position is consistent with the solid ultraviolet diffuse reflectance image, proving the reduction of the band gap value of the carbon nitride nanoflower.

[0034] Figure 6 This is the photocurrent diagram of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared in this example. The carbon nitride nanoflower exhibits a stronger photocurrent intensity than ordinary carbon nitride, and remains stable after five light switching cycles, indicating that it has a better separation efficiency of photogenerated carriers, which is beneficial to improving the photocatalytic activity.

[0035] Figure 7The activity diagram of the photocatalytic production of H2O2 by the carbon nitride nanoflower photocatalyst assembled by nanosheets prepared in this embodiment specifically includes the following steps: weigh 20mg of carbon nitride nanoflower photocatalyst in a 50mL photoreaction bottle, add 20mL of deionized water, and stir magnetically for 30min under dark conditions to allow the reaction system to reach adsorption equilibrium. After the dark reaction is completed, turn on the light source (300W xenon lamp λ>420nm), extract 1mL of sample every 10min, and test the concentration of H2O2 by DPD method after centrifugation. 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 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 the spirit or essential features of the invention. 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, and it is intended that all variations within the meaning and scope of the equivalent elements of the claims be included in the invention. Any marking in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A carbon nitride nanoflower photocatalyst assembled from nanosheets, It is characterized in that The method comprises the following preparation steps: (1) dispersing melamine and benzoguanamine in deionized water under magnetic stirring at room temperature to obtain a mixed dispersion; (2) transferring the mixed dispersion to a hydrothermal reactor for reaction; allowing the obtained reaction product to stand, centrifugally separating, washing, and drying to obtain a supramolecular intermediate; (3) The supramolecular intermediate is added into the crucible, and then the crucible is placed in a muffle furnace and heated to a certain temperature at a certain heating rate, and then kept warm for a certain period of time, thereby obtaining a carbon nitride nanoflower photocatalyst assembled from nanosheets.

2. A method for preparing a carbon nitride nanoflower photocatalyst assembled from nanosheets according to claim 1, It is characterized in that In step (1), the mass ratio of melamine, benzoguanamine and deionized water is 1:1:30 to 3:3:60, and the stirring time is 30 to 90 minutes.

3. A method for preparing a carbon nitride nanoflower photocatalyst assembled from nanosheets according to claim 1, It is characterized in that The reaction temperature in step (2) is 140-220° C., and the reaction time is 8-16 hours.

4. A method for preparing a carbon nitride nanoflower photocatalyst assembled from nanosheets according to claim 1, It is characterized in that The mass of the supramolecular intermediate in step (3) 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.

5. Use of the carbon nitride nanoflower photocatalyst assembled from nanosheets prepared by the method according to any one of claims 1 to 4, It is characterized in that The carbon nitride nanoflower photocatalyst assembled from nanosheets is used to photocatalyze H 2 O 2 Production.

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