Directional polymerization terminated fragmented carbon nitride photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a directional polymerization terminated fragmented carbon nitride photocatalyst as well as a preparation method and application thereof, and relates to the technical field of photocatalytic materials. According to the invention, generation and polymerization of a heptazine repetitive unit are inhibited by utilizing a special position of a benzene ring and a steric hindrance effect, so that the purpose of polymerization termination is achieved. Firstly, an intermediate is obtained through a hydrothermal method, then fragmented carbon nitride is obtained through calcination of a tubular furnace under the argon condition, the energy band structure of the carbon nitride is improved by means of the characteristics of the fragmented structure, and meanwhile the fragmented carbon nitride has rich edge active sites and a shorter photo-induced electron transfer path; the problems that an existing photocatalyst is low in visible light utilization rate, few in exposed active sites, prone to carrier compounding and the like are solved. The whole preparation process has no special requirements on equipment, is simple to operate, easy to control, good in repeatability, green and environment-friendly, and is beneficial to industrial large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalytic materials, and in particular to a directional polymerization-terminated fragmented carbon nitride photocatalyst and a preparation method and application thereof. Background Art

[0002] Hydrogen peroxide (H2O2) is an environmentally friendly oxidant with a wide range of applications in wastewater treatment, disinfection, sterilization, bleaching and chemical synthesis. Currently, more than 95% of H2O2 is produced by the anthraquinone method. However, this process involves multiple steps, high energy consumption and serious pollution. At the same time, the transportation of high-concentration H2O2 poses a safety hazard. Photocatalytic technology can produce O2 in situ through the photocatalytic O2 reduction process, which is a promising green and sustainable method for producing H2O2.

[0003] Carbon nitride is the first polymer semiconductor material studied so far. It has a band gap suitable for visible light response (~2.7eV), is easy to prepare, has excellent chemical stability in strong acid and alkali media, and has special electronic structure. It is widely used in the field of photocatalytic production of H2O2. Studies have shown that O2 can be adsorbed on the heptazine unit, which is conducive to the formation of 1,4-endoperoxide intermediates, thereby improving the selectivity of H2O2 generation. In addition, the valence band potential of carbon nitride (1.4V) is low enough to effectively prevent the oxidative decomposition of H2O2. However, as a polymer with a high degree of polymerization, carbon nitride has limited available reactive sites and a long time required for electrons to migrate to the surface, which limits its performance in photocatalytic production of H2O2. Summary of the invention

[0004] The purpose of the present invention is to provide a fragmented carbon nitride photocatalyst with directional polymerization termination, as well as a preparation method and application. The method selects benzoguanamine with a benzene ring substituent as a raw material. Due to the presence of the edge position benzene ring and the steric hindrance effect of the existence thereof, the generation and polymerization of a large number of heptazine repeating units are inhibited, thereby achieving the purpose of polymerization termination; the method first obtains an intermediate by a hydrothermal method, and then calcines it in a tubular furnace under argon conditions to obtain fragmented carbon nitride; the fragmented carbon nitride 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.

[0005] The present invention provides the following technical solution: a method for preparing a fragmented carbon nitride photocatalyst with directional polymerization termination, comprising the following steps:

[0006] (1) firstly placing benzoguanamine in deionized water and dispersing it by magnetic stirring at room temperature to obtain a mixed dispersion;

[0007] (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 an intermediate;

[0008] (3) Add the intermediate into the crucible, then put it into a tubular furnace, heat it to a certain temperature at a certain heating rate under protective gas conditions, and then keep it warm for a certain period of time to obtain a fragmented carbon nitride photocatalyst with directional polymerization termination.

[0009] Furthermore, the mass ratio of benzoguanamine to deionized water in step (1) is 2:30 to 4:60, and the stirring time is 30 to 90 minutes.

[0010] Furthermore, the reaction temperature of step (2) is 140°C-220°C, and the reaction time is 8h-16h.

[0011] Furthermore, in the step (3), the mass of the intermediate is 0.5-1 g, the calcination temperature is 450° C.-550° C., the heating rate is 1-4° C. / min, the calcination temperature is maintained for 2-5 h, and the gas is argon.

[0012] Furthermore, the directional polymerization terminated fragmented carbon nitride photocatalyst is used for photocatalytic H2O2 production in pure water.

[0013] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0014] The raw materials are easy to obtain, the operation is simple, the repeatability is good, and the controllability is strong. In the reaction, only one drug, benzoguanamine, is used, and only water is used as a solvent, which is green and environmentally friendly. Compared with ordinary carbon nitride, fragmented carbon nitride has more edge active sites, shorter electron transfer paths, and a wider light absorption range, thereby improving the photocatalytic performance; under visible light conditions, H2O2 can be efficiently and stably generated in pure water. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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:

[0016] Figure 1 The schematic diagram of the synthesis of the fragmented carbon nitride terminated by directional polymerization prepared by the present invention;

[0017] Figure 2 TEM image of the fragmented carbon nitride terminated by directional polymerization prepared by the present invention;

[0018] Figure 3 The XRD pattern of the fragmented carbon nitride terminated by directional polymerization prepared by the present invention;

[0019] Figure 4 The infrared spectrum of the fragmented carbon nitride terminated by directional polymerization prepared by the present invention;

[0020] Figure 5 The solid ultraviolet diffuse reflectance image of the fragmented carbon nitride terminated by directional polymerization prepared by the present invention;

[0021] Figure 6 The steady-state fluorescence image of the fragmented carbon nitride terminated by directional polymerization prepared by the present invention;

[0022] Figure 7 The photocurrent diagram of the fragmented carbon nitride with directional polymerization termination prepared by the present invention;

[0023] Figure 8 This is a performance diagram of the directional polymerization terminated fragmented carbon nitride 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) 4 g of benzoguanamine was 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 obtained mixed dispersion was transferred to a 100 mL hydrothermal reactor, placed in a constant temperature oven at 200° C. for reaction for 12 h, and the reactor was naturally cooled to room temperature, centrifuged at 8000-10000 r / min for 3 min, washed with deionized water for 3 times, and placed in a constant temperature oven at 60° C. for drying for 12 h to obtain an intermediate;

[0028] (3) Weigh 0.6 g of the intermediate and place it in a crucible with a lid. Place the crucible on an ark and place it in the central temperature control zone of a tube furnace for calcination under an argon atmosphere. The heating parameters are as follows: set the temperature to rise uniformly from room temperature to 500°C within 240 min and maintain at 500°C for 4 h. Then cool naturally. The dark yellow solid obtained is the fragmented carbon nitride, which can be obtained by grinding carefully to obtain the photocatalyst.

[0029] Figure 1The synthesis principle diagram of the fragmented carbon nitride with directional polymerization termination prepared by the present invention. Due to the presence of the benzene ring at the edge position and its steric hindrance effect, the generation and polymerization of a large number of heptazine repeating units are inhibited, thereby achieving the purpose of polymerization termination.

[0030] Figure 2 The transmission electron microscope images of the fragmented carbon nitride photocatalyst with directional polymerization termination prepared in this example are shown in Figures a and b. It can be seen that the prepared sample is a fragmented carbon nitride structure.

[0031] Figure 3 This is the X-ray diffraction pattern of the fragmented carbon nitride photocatalyst with directional polymerization termination prepared in this example. Ordinary carbon nitride has two characteristic diffraction peaks of carbon nitride at about 13.1° and 27.3°, while the diffraction peak of fragmented carbon nitride at 13.1° is almost not observed, which indicates that the fragmented carbon nitride has a smaller interlayer distance.

[0032] Figure 4 This is the infrared spectrum of the directional polymerization terminated fragmented carbon nitride photocatalyst prepared in this example. The fragmented carbon nitride and ordinary carbon nitride have similar infrared vibration peaks, which indicates that the skeleton structure of the fragmented carbon nitride is consistent with that of ordinary carbon nitride.

[0033] Figure 5 This is a solid ultraviolet diffuse reflectance image of the fragmented carbon nitride photocatalyst with directional polymerization termination prepared in this embodiment. Compared with ordinary carbon nitride, the light absorption of fragmented carbon nitride 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.

[0034] Figure 6 This is the steady-state fluorescence image of the fragmented carbon nitride photocatalyst with directional polymerization termination prepared in this example. The fluorescence intensity of the fragmented carbon nitride is significantly weaker, indicating that the photogenerated carrier recombination efficiency of the fragmented carbon nitride is lower than that of ordinary carbon nitride. 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 fragmented carbon nitride.

[0035] Figure 7 This is the photocurrent diagram of the fragmented carbon nitride photocatalyst with directional polymerization termination prepared in this example. The fragmented carbon nitride exhibits a stronger photocurrent intensity than ordinary carbon nitride, and remains stable after six light switching cycles, indicating that it has a better separation efficiency of photogenerated carriers, which is beneficial to improving the photocatalytic activity.

[0036] Figure 8The activity diagram of the photocatalytic production of H2O2 by the fragmented carbon nitride photocatalyst terminated by directional polymerization prepared in this embodiment specifically includes the following steps: weigh 20 mg of fragmented carbon nitride photocatalyst in a 50 mL photoreaction bottle, add 20 mL of deionized water, and stir magnetically for 30 minutes 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 1 mL of sample every 10 minutes, 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.

[0037] 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 method for preparing a fragmented carbon nitride photocatalyst with directional polymerization termination, characterized in that: The steps include: (1) firstly placing benzoguanamine in deionized water and dispersing it by 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 an intermediate; (3) Add the intermediate into the crucible, then put it into a tubular furnace, heat it to a certain temperature at a certain heating rate under protective gas conditions, and then keep it warm for a certain period of time to obtain a fragmented carbon nitride photocatalyst with directional polymerization termination.

2. The method for preparing a directional polymerization terminated fragmented carbon nitride photocatalyst according to claim 1, characterized in that: The mass ratio of benzoguanamine to deionized water in step (1) is 2:30 to 4:60, and the stirring time is 30 to 90 minutes.

3. The method for preparing a directional polymerization terminated fragmented carbon nitride photocatalyst according to claim 1, characterized in that: The reaction temperature of step (2) is 140°C-220°C, and the reaction time is 8h-16h.

4. The method for preparing a directional polymerization terminated fragmented carbon nitride photocatalyst according to claim 1, characterized in that: The mass of the intermediate in step (3) is 0.5-1 g, the calcination temperature is 450° C.-550° C., the heating rate is 1-4° C. / min, the calcination temperature is maintained for 2-5 h, and the gas is argon.

5. Use of a directional polymerization terminated fragmented carbon nitride photocatalyst prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The directional polymerization-terminated fragmented carbon nitride photocatalyst is used for photocatalytic H2O2 production in pure water.

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