Preparation method and application of a center-hollow hydrangea-shaped porous carbon nitride microsphere

Abstract

This invention discloses a method for preparing and applying centrally open-cell, hydrangea-shaped porous carbon nitride microspheres. The preparation process includes: preparing a supramolecular precursor using melamine and cyanuric chloride, and then calcining the precursor at high temperature in a tube furnace to obtain carbon nitride microspheres. This invention rapidly and easily prepares centrally open-cell, hydrangea-shaped porous carbon nitride microspheres with novel morphology and highly efficient visible light activity. The resulting photocatalyst surpasses that of simple hollow carbon nitride microspheres, improving visible light utilization, reducing photogenerated electron-hole recombination rate, and enabling efficient removal of organic pollutants and inactivation of pathogenic bacteria in water under visible light irradiation.

Description

Technical Field

[0001] This invention belongs to the field of new carbon nitride materials, and relates to the preparation method and application of a centrally open-pore hydrangea-shaped porous carbon nitride microsphere (g-C3N4), especially its application as an environmental photocatalyst material. Background Technology

[0002] Because emerging pollutants have a significant impact on environmental ecosystems, their control is of great concern. Rubber antioxidants N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its derivative 6PPD-quinone (6PPD-Q) are a newly emerging class of pollutants that pose a significant threat to the ecological environment [J Hazard Mater, 2023, 454:131459]. However, few reports have documented effective control measures for these pollutants. With the rapid development of the automotive and rubber-related industries, pollution derived from these industrial additives represents a significant public health hazard. Furthermore, environmental water bodies contain various antibiotic residues such as doxycycline and harmful pathogens. These pollutants remain in aquatic systems for extended periods, continuously harming organisms in the food chain. Therefore, it is urgent to develop a rapid and effective method for removing trace amounts of highly toxic pollutants and microbial contamination from water. Numerous methods have been explored to address the problem of organic pollutants in water, such as adsorption, photocatalysis, biodegradation, and advanced oxidation methods. Among these methods, photocatalysis has attracted widespread attention from scientists due to its green, efficient, economical, and environmentally friendly characteristics. Utilizing photocatalysts to degrade organic pollutants, inactivate harmful bacteria, and catalyze the generation of clean energy has become one of the most popular research directions in recent decades [Chem.Eng.J, 2021, 405:12806]. However, these photocatalysts suffer from two key drawbacks: unstable performance in practical applications and excessively high usage costs due to complex preparation processes.

[0003] Graphitic carbon nitride (g-C3N4) and its derivatives possess advantages such as controllable morphology and environmental friendliness, thus exhibiting great development potential. However, g-C3N4 has a small specific surface area and poor photocatalytic activity due to its narrow visible light absorption range, limiting its practical application. In contrast, porous carbon nitride with a larger specific surface area, shorter carrier transport distance, and higher charge separation efficiency has greater research value. However, how to efficiently and easily prepare porous carbon nitride remains a current research hotspot and challenge. In current research reports, hollow or layered spherical photocatalysts of g-C3N4 are mostly prepared using hard template or soft template methods. Hard template methods mostly utilize SiO2 microspheres as templates [Mater Sci Eng B, 2015, 202: 1-7], which involves long preparation cycles, cumbersome steps, and the corrosive agents (HF or NH4HF2) required for template removal are harmful to the environment, posing an uncontrollable risk during application. Soft templates suffer from poor stability, and the instability of the template during preparation leads to uncontrollable final product morphology [Appl. Catal. B, 2015, 165: 503-510]. Therefore, although the preparation of the above-mentioned carbon nitride hollow microspheres is difficult and involves hazardous chemicals such as hydrofluoric acid during use, the obtained samples lack pores in the middle, have low catalytic activity, and poor structural stability. They are prone to structural collapse during use, leading to a decrease in activity, making it difficult to meet practical requirements. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of low photocatalytic efficiency and difficult preparation of existing porous carbon nitride microspheres, and to provide a green and simple method for preparing hydrangea-shaped porous carbon nitride microspheres with a central opening, and its application in environmental pollution control, especially in the photocatalytic degradation of new pollutants. This method utilizes melamine and cyanuric chloride dissolved in dimethyl sulfoxide. Melamine and cyanuric chloride can form hydrogen bonds; one melamine molecule can form three hydrogen bonds with cyanuric chloride, exhibiting strong structural orientation. Based on this principle, supramolecular assembly is expected to occur in the solvent, forming micron- or nano-scale oriented structures. These structures are retained in the formed carbon nitride during subsequent calcination under nitrogen protection. During calcination, partial mass loss causes collapse, generating centrally open pores. This structure facilitates multiple reflections of incident light within the pores, improving visible light utilization. The preparation process is simple, rapid, and easy to operate. The resulting photocatalyst has a regular morphology and good visible light photocatalytic efficiency, showing significant effects on the degradation of organic pollutants in water and the inactivation of Staphylococcus aureus. The technical solution of this invention is as follows:

[0005] This invention provides a method for preparing hydrangea-shaped porous carbon nitride microspheres with a central opening, comprising the following steps:

[0006] 1) Weigh out different masses of melamine and cyanuric chloride, and dissolve them in dimethyl sulfoxide at a mass ratio of 1:0.5-1 respectively; sonicate them at 20-25℃ for 30 minutes, then mix the two solutions, centrifuge, wash and dry the mixture to obtain the precursor of hydrangea-shaped carbon nitride microspheres;

[0007] 2) Take the hydrangea-shaped carbon nitride microsphere precursor obtained in step 1 and place it in a tube furnace. Keep it at 480-520℃ for 2-4 hours under nitrogen atmosphere protection. Then cool it naturally to room temperature and grind it into powder to prepare hydrangea-shaped porous carbon nitride microspheres with central opening.

[0008] In some specific embodiments, in step (1), when both melamine and cyanuric chloride are 0.5g, the dimethyl sulfoxide used for dissolution can be 10-15ml, and the ultrasonic temperature can be room temperature. Specifically, the drying conditions can be drying at 60℃ for 12h.

[0009] Preferably, in step 1, the mass ratio of melamine to cyanuric chloride is 1:1.

[0010] Preferably, in step 1, the washing specifically involves rinsing with deionized water 3 to 5 times and rinsing with anhydrous ethanol 3 to 5 times.

[0011] Preferably, in step 2, the heating rate of the tubular furnace is 2.5℃ / min, and the holding time is 4h.

[0012] Preferably, the nitrogen gas pressure in step 2 is 0.1 MPa and the flow rate is 50 ml / min.

[0013] Another aspect of the present invention provides a photocatalytic application of the aforementioned centrally perforated, hydrangea-shaped porous carbon nitride microspheres. This photocatalytic application refers to the catalytic degradation of organic matter or the catalytic inactivation of pathogenic bacteria under visible light. More specifically, the organic matter is 6PPD-Q and doxycycline; the pathogenic bacteria is Staphylococcus aureus.

[0014] Compared with the prior art, the beneficial effects of the present invention are: the preparation method of the present invention is simple, requires no template agent, is economical and convenient, and the prepared photocatalyst has a regular central open-pore spherical morphology and excellent visible light photocatalytic performance, and can efficiently degrade organic pollutants and inactivate Staphylococcus aureus under visible light irradiation.

[0015] This invention successfully obtained centrally open-pore, hydrangea-shaped porous carbon nitride microspheres through self-assembly without the need for additional template agents. The porous structure with central openings effectively improves the photocatalytic performance of the semiconductor material. The increased specific surface area provides abundant active sites for redox reactions. The central openings promote light reflection and refraction within the material, thereby enhancing light absorption and utilization. The thin-film structure of the microspheres shortens the transport distance of longitudinal charge carriers to the reaction interface. Therefore, this material exhibits high visible light photocatalytic activity, which is of great significance for the effective treatment of pollutants in water. Attached Figure Description

[0016] Figure 1 Here is a scanning electron microscope image of the ordinary carbon nitride microspheres prepared in Comparative Example 1;

[0017] Figure 2 This is a scanning electron microscope image of the hydrangea-shaped porous carbon nitride microspheres with a central opening prepared in Example 1.

[0018] Figure 3 Transmission electron microscopy image of the hydrangea-shaped porous carbon nitride microspheres with a central opening prepared in Example 1;

[0019] Figure 4 The XRD patterns are of the hydrangea-shaped porous carbon nitride microspheres with central openings prepared in Example 1 and the ordinary carbon nitride microspheres prepared in Comparative Example 1.

[0020] Figure 5 The graph shows the photocatalytic degradation performance of 6PPD-Q by the centrally open hydrangea-shaped porous carbon nitride microspheres prepared in Example 1 and the ordinary carbon nitride microspheres prepared in Comparative Example 1 under visible light irradiation.

[0021] Figure 6 The graph shows the photocatalytic degradation performance of doxycycline under visible light irradiation of the hydrangea-shaped porous carbon nitride microspheres with central openings prepared in Example 1 and the ordinary carbon nitride microspheres prepared in Comparative Example 1.

[0022] Figure 7 The graph shows the photocatalytic inactivation performance of the centrally pored, hydrangea-shaped porous carbon nitride microspheres prepared in Example 1 and the ordinary carbon nitride microspheres prepared in Comparative Example 1 under visible light irradiation. Detailed Implementation

[0023] The following examples will illustrate the implementation of this application in detail, so that the process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0024] Unless otherwise specified, all raw materials and equipment used in this application are commonly used in the field and are derived from commercially available products. Unless otherwise specified, all methods used in this application are conventional methods in the field.

[0025] There are many other feasible technical solutions in this application, which will not be listed here. All technical solutions claimed in the claims of this application are feasible.

[0026] The terms "comprising" or "including" are intended to indicate that a composition (e.g., a medium) and a method include the listed elements, but do not exclude other elements. When used to define compositions and methods, "consisting substantially of" means excluding other elements that are of any significance to the combination for the stated purpose. Therefore, a composition consisting substantially of the elements defined herein does not exclude other materials or steps that do not materially affect the essential and novel features of the claimed application. "Constitutes" means excluding trace elements and substantial method steps that are other components. Embodiments defined by each of these transitional terms are within the scope of this application.

[0027] Example 1:

[0028] 1) Melamine and cyanuric chloride were dissolved in dimethyl sulfoxide respectively; the mixture was sonicated at 20-25℃ for 30 minutes, then the two solutions were mixed, the mixture was rinsed 3 times with deionized water and 3 times with anhydrous ethanol, and dried at 60℃ for 12 hours to obtain the precursor of hydrangea-shaped carbon nitride microspheres.

[0029] 2) The carbon nitride precursor prepared in step 1 was placed in an alumina crucible and heated in a tube furnace at 500°C for 4 hours under a nitrogen atmosphere at a heating rate of 2.5°C / min. The nitrogen pressure was 0.1 MPa and the flow rate was 50 ml / min. After calcination, the sample was naturally cooled to room temperature, and then ground into powder to prepare hydrangea-shaped porous carbon nitride microspheres with a central opening.

[0030] Example 2: Unlike Example 1, the amount of dimethyl sulfoxide used for dissolution in step 1 is 15 ml. Everything else is the same as in Example 1.

[0031] Example 3: Unlike Example 1, the heating rate of the tubular furnace in step 2 is 2℃ / min. Everything else is the same as in Example 1.

[0032] Example 4: Unlike Example 1, the holding time in the tubular furnace in step 2 is 2 hours. Everything else is the same as in Example 1. The porous carbon nitride microspheres prepared in Examples 2 and 3 have similar morphologies to those in Example 1.

[0033] Comparative Example 1:

[0034] Reference [Small, 2016, 12(26): 3543-3549] describes a method involving mixing 0.75g of cyanuric chloride and 75ml of acetonitrile, stirring until a transparent solution is obtained; then, the solution is placed in a 100ml polytetrafluoroethylene liner, sealed, and placed in a stainless steel autoclave. The autoclave is then heated to 200℃ for 20h in a high-temperature drying oven and cooled to room temperature. Finally, the product obtained from the above reaction is centrifuged and washed multiple times with ethanol and deionized water, and dried in an oven at 70℃ for 12h to obtain carbon nitride microspheres. The ordinary carbon nitride microspheres prepared by this method exhibit severe aggregation, have a smooth surface, and few active sites.

[0035] Comparative Example 2:

[0036] Chinese patent CN110465318A (A carbon quantum dot-supported hollow porous carbon nitride sphere composite photocatalyst and its preparation method and application) describes a method involving mixing ethanol, ammonia, and ultrapure water, adding tetraethoxysilane, and stirring at a constant rate to prepare solution A. A mixture B of tetraethoxysilane and n-octadecyltrimethoxysilane is then added dropwise to solution A, allowed to stand at room temperature, and the resulting solid is calcined at 500–550°C to obtain a silica sphere template. The silica sphere template, carbon quantum dot solution, and ammonia nitrile are mixed and stirred at 60–70°C, and the resulting mixture is calcined at 500–550°C in a nitrogen atmosphere to obtain powder C. NH4HF2 solution is added to powder C to remove the template, followed by washing with water and drying to obtain hollow porous carbon nitride microspheres. This method is complex, and NH4HF2 solution is a hazardous chemical, posing safety hazards during use.

[0037] The present invention uses the following examples to verify that the centrally pore-shaped porous carbon nitride microsphere photocatalyst has improved visible light efficiency:

[0038] The scanning electron microscope image of the ordinary carbon nitride microspheres obtained in Comparative Example 1 is shown below. Figure 1 As shown in the figure, a regular spherical structure can be seen with a smooth surface and no petal-like structure.

[0039] Scanning electron microscope (SEM) image of the centrally open-pore, hydrangea-shaped porous carbon nitride microsphere visible light photocatalyst prepared in Example 1 is shown below. Figure 1 As shown in the figure, the microspheres have a diameter ranging from 1 to 3 μm. The petal-like structures on the microspheres are clearly visible, forming a unique hydrangea-like porous structure with a central opening.

[0040] Transmission electron microscopy (TEM) image of the centrally pored, hydrangea-shaped porous carbon nitride microspheres prepared in Example 1 is shown below. Figure 2 As shown, from Figure 2 The presence of obvious pores indicates the existence of a central opening, and the overall shape is regular, indicating a spherical structure.

[0041] The XRD patterns of the centrally pored, hydrangea-shaped porous carbon nitride microspheres and ordinary carbon nitride microspheres prepared in Example 1 are shown below. Figure 4 As shown, the XRD patterns of the two are similar. The first peak is located at 13.3°, corresponding to the (100) crystal plane of the in-plane structure of the 3S-triazine unit. This may be due to the larger planar size of the hydrangea-shaped porous carbon nitride microspheres with central openings compared to ordinary carbon nitride microspheres. The sharp peaks observed at 27.5° are due to the in-plane stacking of the (002) crystal plane of the conjugated aromatic system, indicating high crystallinity and regular crystal plane growth.

[0042] To verify the activity of the centrally pored, hydrangea-shaped porous carbon nitride microspheres obtained in Example 1 as a photocatalytic material, the following tests were conducted.

[0043] Test Example 1: Visible Photocatalytic Activity

[0044] Take 20 mg of the hydrangea-shaped porous carbon nitride microspheres with a central opening obtained in Example 1 and place them in a 150 ml beaker. Then add 100 ml of 6PPD-Q solution with a concentration of 10 ppm. Place the beaker under a 300 W xenon lamp with constant magnetic stirring. Cover the xenon lamp with a 420 nm filter to filter out ultraviolet light. Take 5 ml of the mixture every 10 min, dilute it and measure the absorbance change of 6PPD-Q by high performance liquid chromatography. After the measurement, pour it back and continue the reaction.

[0045] Test Example 2: Visible light photocatalytic degradation activity of antibiotics

[0046] Take 20 mg of the hydrangea-shaped porous carbon nitride microspheres with a central opening obtained in Example 1 and place them in a 150 ml beaker. Then add 100 ml of doxycycline solution with a concentration of 20 mg / L. Place the beaker under a 300 W xenon lamp with constant magnetic stirring. Cover the xenon lamp with a 420 nm filter to filter out ultraviolet light. Take 5 ml of the reaction solution every 10 min and measure the change in absorbance of doxycycline using an ultraviolet spectrophotometer. After the measurement is completed, pour the solution back in and continue the reaction.

[0047] Test Example 3: Visible Light Sterilization Catalytic Activity

[0048] Prepare a Staphylococcus aureus suspension by diluting the suspension with phosphate-buffered saline (PBS, 0.01 M, pH 7.4) to obtain approximately 10 μL of Staphylococcus aureus per milliliter. 7Cell counting was performed at colony-forming units (CFU / ml). A 300W xenon lamp with a 420nm cutoff filter was used as the light source, and the temperature of the reaction system was controlled at 20°C using a super-constant temperature water bath. 20 ml of Staphylococcus aureus suspension and 10 mg of catalyst powder were placed in a 50 ml beaker. The mixture was kept in the dark for 30 minutes to achieve uniform dispersion. Under 60-minute illumination, 500 μl of the reaction solution was collected every 30 minutes and diluted with PBS. 100 μl of the test suspension was spread onto freshly prepared LB agar plates and incubated at 37°C for 24 hours. Colony counts were then performed to determine surviving colonies.

[0049] The visible light catalytic degradation of 6PPD-Q solution and doxycycline over time by the centrally open-pore, hydrangea-shaped porous carbon nitride microspheres prepared in this embodiment are shown below. Figure 5 , Figure 6 As shown, the photocatalytic inactivation effect of Staphylococcus aureus over time is as follows: Figure 7 As shown in the figure, the hydrangea-shaped porous carbon nitride microspheres with central openings exhibit excellent visible light photocatalytic performance. The hydrangea-shaped porous structure is more conducive to the migration and effective separation of photogenerated electrons and holes, and the larger specific surface area provides more catalytic active sites.

[0050] The visible light catalytic degradation effect of the hydrangea-shaped porous carbon nitride microspheres with central openings prepared in Example 1 on the degradation of Staphylococcus aureus solution over time is as follows: Figure 6 As shown in the figure, the hydrangea-shaped porous carbon nitride microspheres with a central opening have good visible light photocatalytic performance and can completely inactivate 7 log cfu / ml of Staphylococcus aureus within 90 minutes.

[0051] The contents not described in detail in this application specification are common knowledge to those skilled in the art.

[0052] As used throughout the specification and claims, the term "comprising" is an open-ended term and should therefore be interpreted as "comprising but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error.

[0053] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0054] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be protected within the scope of the appended claims.

Claims

1. The application of a centrally pore-shaped, hydrangea-like porous carbon nitride microsphere in the catalytic degradation of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone 6PPD-Q under visible light, characterized in that, The method for preparing the hydrangea-shaped porous carbon nitride microspheres with a central opening includes the following steps: 1) Melamine and cyanuric chloride were dissolved separately in dimethyl sulfoxide at a mass ratio of 1:1; the solutions were sonicated at 20-25 °C for 30 minutes; after the solutions were clear, the two solutions were mixed; the mixture was then centrifuged, washed, and dried to obtain carbon nitride microsphere precursors. 2) Take the carbon nitride microsphere precursor obtained in step 1) and place it in a tube furnace. Keep it at 480~520 ℃ for 2~4 h under nitrogen atmosphere protection. Then cool it naturally to room temperature and grind it into powder to prepare hydrangea-shaped porous carbon nitride microspheres with central opening.

2. The application according to claim 1, characterized in that, In step 1), the washing specifically involves rinsing with deionized water 3 to 5 times and rinsing with anhydrous ethanol 3 to 5 times.

3. The application according to claim 1, characterized in that, In step 2), the heating rate of the tubular furnace is 2.0~2.5 ℃ / min, and the holding time is 4 h.

4. The application according to claim 1, characterized in that, The nitrogen gas pressure in step 2) is 0.08~0.12 MPa, and the flow rate is 40~60 ml / min.

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