A carbon-deficient g-C3N4 catalytic material and its preparation method

Abstract

This invention relates to the field of catalytic materials technology, specifically to a carbon-deficient g-C3N4 catalytic material and its preparation method. The preparation method provided by this invention only requires grinding, heat preservation reaction, acid washing and etching, and filtration, drying and collection. The operation is simple, and the prepared material has good stability, which can better ensure its application performance. The catalytic material provided by this application has carbon defects and is yellowish-brown in color. Its band gap is smaller than that of CN, which enhances the absorption of visible light. At the same time, the introduction of carbon vacancies generates new charge transfer channels and non-radiative pathways, which hinder the recombination of photo-excited electron-hole pairs. This makes the separation efficiency of photogenerated electron-hole pairs on its surface higher and the recombination rate lower, thus achieving better catalytic effects.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, and in particular to a carbon-deficient g-C3N4 catalytic material and its preparation method. Background Technology

[0002] Due to its excellent optical and electrical properties, g-C3N4 has attracted widespread attention and application in photocatalysis, energy storage, solar cells, electrocatalysis, light-emitting displays, biomedicine, and environmental remediation. However, the traditional g-C3N4 suffers from the tendency for photogenerated carriers to recombine and a limited number of catalytically active sites, significantly hindering its practical application in many fields. Introducing carbon defects into the g-C3N4 unit structure can efficiently modulate the electronic band structure of the photocatalyst, suppress the recombination of photogenerated carriers, and construct surface active sites, thereby improving its catalytic performance in photocatalytic reactions.

[0003] Currently, although some preparation processes and methods for introducing carbon defects exist, they suffer from drawbacks such as cumbersome steps, long processes, and limited visible light absorption. Based on this research, this application provides a simple carbon-deficient g-C3N4 catalytic material and its preparation method to better solve the aforementioned technical problems. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a carbon-deficient g-C3N4 catalytic material and its preparation method. The preparation steps are simple, significantly improving the separation efficiency of electron-hole pairs and providing more surface active sites, thus better meeting application requirements.

[0005] The technical solution adopted in this invention is:

[0006] A method for preparing a carbon-deficient g-C3N4 catalytic material includes the following preparation steps:

[0007] Mix urea powder, hexachlorotriphosphazene powder and ferric nitrate nonahydrate evenly and then grind thoroughly.

[0008] Then wrap it with aluminum foil, place it in a tube furnace, use argon as a protective gas, and keep it at 530-580℃ for 3-5 hours.

[0009] After natural cooling, the resulting product was dispersed in hydrofluoric acid and then stirred, acid-washed, and etched.

[0010] Finally, the product was filtered, collected, dried, and thoroughly ground in an agate mortar to obtain a yellowish-brown product, CCNx.

[0011] Furthermore, the mass ratio of the urea powder, hexachlorotriphosphazene powder, and ferric nitrate nonahydrate is 5:0.3:0.8-1.2.

[0012] Further, after the urea powder, hexachlorotriphosphazene powder and ferric nitrate nonahydrate are mixed evenly and ground thoroughly, the mixture is placed in a covered porcelain boat, wrapped with a layer of aluminum foil, and then placed in a tube furnace.

[0013] Furthermore, the heating rate in the tube furnace is 3-5℃ / min.

[0014] Furthermore, the argon flow rate was 15 mL / min.

[0015] Furthermore, the obtained product needs to be placed in 40% hydrofluoric acid by mass for stirring, acid washing, and etching.

[0016] Furthermore, the volume of the hydrofluoric acid is 8-10 mL, and the stirring and acid washing time is 22-26 h.

[0017] Based on the same inventive concept, this application also provides a carbon-deficient g-C3N4 catalytic material prepared by the above-described preparation method.

[0018] Furthermore, the material has a carbon defect structure and is yellowish-brown in color.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. The preparation method of carbon defective g-C3N4 catalytic material provided by the present invention has a simple process flow. The preparation process only requires grinding, heat preservation reaction, acid washing and etching, and filtration, drying and collection. The operation is simple, the prepared material has good stability, and can better ensure its application performance.

[0021] 2. The carbon-deficient g-C3N4 catalytic material provided in this application has carbon defects and is yellowish-brown in color. Its band gap is smaller than that of CN, which greatly enhances the absorption of visible light by the catalytic material. At the same time, the introduction of carbon vacancies creates new channels for charge transfer, resulting in non-radiative pathways that hinder the recombination of photoexcited electron-hole pairs. This makes the separation efficiency of photogenerated electron-hole pairs on its surface higher and the recombination rate lower, thus achieving better catalytic effects. Attached Figure Description

[0022] Figure 1 These are photographs of CN and CCNx samples prepared in the embodiments of this application;

[0023] Figure 2 The XRD patterns of the CN and CCNx samples prepared in the embodiments of this application are shown below.

[0024] Figure 3 The UV-Vis absorption spectra of the CN and CCNx samples prepared in the embodiments of this application are shown below.

[0025] Figure 4The PL spectra of the CN and CCNx samples prepared in the embodiments of this application are shown below.

[0026] Figure 5 The time-resolved fluorescence emission decay spectra of CN and CCNx prepared in the embodiments of this application are shown.

[0027] Explanation of reference numerals in the attached figures:

[0028] CN~a;

[0029] CCN0.8~b;

[0030] CCN1.0~c;

[0031] CCN1.2~d. Detailed Implementation

[0032] To facilitate understanding of the present invention, it will be described more fully below through embodiments, and preferred embodiments of the present invention are given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Any other implementation schemes obtained by modifying or equivalently substituting the technical solutions of the present invention without inventive step are all within the protection scope of the present invention.

[0033] 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. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0034] The numerical values ​​disclosed in the embodiments of this invention are approximate values, not definitive values. Where error or experimental conditions permit, all values ​​within the error range may be included, and the specific numerical values ​​disclosed in the embodiments of this invention are not limited to those specified.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] The following are specific embodiments of this application.

[0037] Example 1

[0038] The preparation method of the carbon-deficient g-C3N4 catalytic material provided in this embodiment includes the following steps:

[0039] Weigh out 5g of urea powder, 0.3g of hexachlorotriphosphazene powder, and 0.8g of ferric nitrate nonahydrate, mix them thoroughly, and grind them completely. Place the mixture in a covered porcelain boat and wrap it with a layer of aluminum foil. Place it in a tube furnace, use argon as a protective gas (flow rate 15mL / min), and heat it to 550℃ at a rate of 3℃ / min. Hold it at this temperature for 4 hours. After natural cooling, disperse the obtained product in 10mL of 40% hydrofluoric acid, stir, and acid-etch for 24 hours. Finally, collect the sample by filtration, dry it, and grind it thoroughly in an agate mortar to collect the yellowish-brown product CCN0.8.

[0040] Example 2

[0041] The difference between this embodiment and Example 1 is that the mass of ferric nitrate nonahydrate added is 1g, and the final product collected is a yellowish-brown product CCN1.0.

[0042] Example 3

[0043] The difference between this embodiment and Example 1 is that the mass of ferric nitrate nonahydrate added is 1.2g, and the final product collected is a yellowish-brown product CCN1.2.

[0044] In contrast, g-C3N4(CN) material was also prepared.

[0045] Preparation of raw CN: Weigh 5g of urea powder, grind it thoroughly, put it into a covered porcelain boat, wrap it with a layer of aluminum foil, place it in a tube furnace, use argon as a protective gas (flow rate 15mL / min), heat it to 550℃ at a heating rate of 3℃ / min, hold it at that temperature for 4h, and after natural cooling, grind it to obtain the light yellow product CN.

[0046] For convenience, the original CN sample is labeled as sample a, the CCN0.8 sample in Example 1 is labeled as sample b, the CCN1.0 sample in Example 2 is labeled as sample c, and the CCN1.2 sample in Example 3 is labeled as sample d.

[0047] See Figure 1 The image shows photographs of CN and CCNx samples. As can be seen from the sample photographs, the CCNx sample prepared in the embodiments of this application has a significantly different color compared to the original CN. It can be inferred that its microstructure has also undergone substantial changes. Therefore, CN and CCNx samples are materials with inherently different properties.

[0048] Specifically, see Figure 2 The figure shows the XRD characterization of CN and CCNx samples.

[0049] Depend on Figure 2It can be seen that the diffraction peaks of CN and CCNx appear in roughly the same positions, indicating that the basic structure of g-C3N4 is still preserved. Furthermore, Figure 2 shows that the (002) crystal plane diffraction peak of CN appears at 27.3° (corresponding to a crystal plane spacing of 0.329 nm), while with the increase of ferric nitrate nonahydrate content, the diffraction peaks of CCNx (x = 0.8, 1.0, 1.2) appear at 27.0°, 26.6°, and 26.6° respectively, and their intensity decreases significantly. The shift of the diffraction peaks to lower angles indicates that the interlayer spacing is gradually increasing (corresponding to crystal plane spacings of 0.332 nm, 0.337 nm, and 0.337 nm respectively). This is mainly because the presence of carbon vacancies weakens the van der Waals forces and conjugation effects between layers, thus causing the crystal plane spacing to increase. Compared to the (100) crystal plane of CN at 12.9°, the (100) crystal plane diffraction peak of CCNx disappears, which means that the heptaazine unit structure within the CCNx sample layer is destroyed.

[0050] The CN and CCNx (x = 0.8, 1.0, 1.2) samples were tested using a UV-Vis spectrophotometer. The test results are shown in [reference needed]. Figure 3 As shown in the figure, both CN and CCNx exhibit typical semiconductor absorption spectra. CN has a relatively weaker absorption range compared to CCNx, with its main absorption region in the ultraviolet region and moderate absorption of visible light. The absorption edge of CN is located at 435 nm, while the absorption edges of CCNx are 442 nm, 459 nm, and 471 nm, respectively. From CN to CCNx, the corresponding absorption edges shift to varying degrees, and the absorption edge of CCNx for visible light is larger than that of CN. The band gaps are calculated using the Kubelka–Munk equation: the band gap of CN is 2.85 eV, while the band gaps of CCNx are 2.81 eV, 2.70 eV, and 2.63 eV, respectively (Table 1 below). The band gaps corresponding to CCNx are all smaller than those of CN, significantly enhancing the absorption of visible light by the catalytic material.

[0051] See Table 1 below for details, which shows the absorption edge and band gap width of CN and CCNx.

[0052] Table 1 Absorption edge and band gap width of CN and CCNx

[0053] sample Absorption edge (nm) Band gap width (eV) CN 435 2.85 CCN0.8 442 2.81 CCN1.0 459 2.70 CCN1.2 471 2.63

[0054] Besides light absorption, the transfer and separation of photoexcited charges are crucial to photocatalytic reactions. Therefore, room temperature PL emission spectroscopy was used to characterize the recombination rate and lifetime of photoexcited carriers.

[0055] See Figure 4The figure shows the photoluminescence (PL) spectra of CN and CCNx (x = 0.8, 1.0, 1.2) at room temperature under 360 nm excitation. All four samples exhibit a PL peak at approximately 435 nm. The CCNx sample shows a lower PL signal intensity than the CN sample, indicating that its surface has higher efficiency in separating photogenerated electron-hole pairs and a lower recombination rate. The decrease in fluorescence intensity is because the introduction of carbon vacancies promotes efficient separation of photogenerated carriers, thereby suppressing the recombination behavior of photogenerated electron-hole pairs.

[0056] The charge transfer kinetics decay of CN and CCNx were analyzed using TRPL spectroscopy. (See [link to relevant documentation]). Figure 5 As shown, the luminescence decay curves were analyzed using a double exponential fitting method. Compared with CN, the carrier lifetimes of the CCNx samples were shortened. The relevant kinetic data and average fluorescence lifetimes are shown in Table 2 below.

[0057] Table 2 Kinetic parameters for sample excitation decay analysis

[0058] sample <![CDATA[τ1(ns)]]> <![CDATA[τ2(ns)]]> A1 A2 <![CDATA[T avg (ns)]]> CN 1.9650 7.0108 711.3048 299.5930 4.9947 CCN0.8 0.4161 4.0000 1153.6001 33.8072 1.2038 CCN1.0 0.4250 5.2793 1339.4532 15.8298 1.0464 CCN1.2 0.4455 8.1470 1332.7708 12.1452 1.5456

[0059] As shown in Table 2 above, the fluorescence lifetimes of CN and CCNx (x = 0.8, 1.0, 1.2) are 4.9947 ns, 1.2038 ns, 1.0464 ns, and 1.5456 ns, respectively. It can be seen that the fluorescence lifetime of CCNx is reduced by 3.7909 ns, 3.9483 ns, and 3.4491 ns compared to CN. This can be attributed to the introduction of carbon vacancies, which creates new charge transfer channels and a non-radiative pathway, thus hindering the recombination of photoexcited electron-hole pairs.

[0060] In summary, the carbon-deficient g-C3N4 catalytic material provided in this application has carbon defects and is yellowish-brown in color. Its band gap is smaller than that of CN, which greatly enhances the absorption of visible light by the catalytic material. At the same time, the introduction of carbon vacancies creates new charge transfer channels and non-radiative pathways, which hinder the recombination of photoexcited electron-hole pairs. This results in higher separation efficiency and lower recombination rate of photogenerated electron-hole pairs on its surface, thus achieving better catalytic effects.

[0061] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a carbon-defect type g-C3N4 catalytic material, characterized in that, The preparation method comprises the following steps: The urea powder, hexachlorotriphosphazene powder and iron nitrate nonahydrate are mixed uniformly and then ground thoroughly; Then the mixture is wrapped with aluminum foil paper and placed in a tube furnace, with argon as the protective gas, at 530-580℃ for 3-5 h; After natural cooling, the obtained product is dispersed in hydrofluoric acid and stirred for acid washing and etching; Finally, the product is collected by filtration, dried and ground thoroughly in an agate mortar to obtain a yellow-brown carbon-defect g-C3N4 product CCNx; The mass ratio of the urea powder, hexachlorotriphosphazene powder and iron nitrate nonahydrate is 5:0.3:0.8-1.

2.

2. The method for preparing carbon-defect g-C3N4 catalytic material according to claim 1, characterized in that, The mixture of the urea powder, hexachlorotriphosphazene powder and iron nitrate nonahydrate is ground thoroughly and then loaded into a porcelain boat with a cover, wrapped with an aluminum foil paper and placed in a tube furnace.

3. The method for preparing the carbon-deficient g-C3N4 catalytic material according to claim 1, characterized in that, The heating rate in the tube furnace is 3-5℃ / min. 4.The method for preparing carbon-defect g-C3N4 catalytic material according to claim 1, characterized in that, The flow rate of argon is 15 mL / min. 5.The method for preparing carbon-defect g-C3N4 catalytic material according to claim 1, characterized in that, The obtained product needs to be placed in hydrofluoric acid with a mass fraction of 40% and stirred for acid washing and etching.

6. The method of claim 5, wherein the carbon-deficient g-C3N4 catalytic material is prepared by the steps of: (a) mixing a carbon source and a nitrogen source to form a mixture; (b) heating the mixture to form a carbon-deficient g-C3N4 catalytic material. The volume of the hydrofluoric acid is 8-10 mL, and the stirring time for acid washing is 22-26 h.

7. A carbon-defect g-C3N4 catalytic material prepared by the preparation method of any one of claims 1-6.

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