An ultrathin porous carbon nitride nanosheet and a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalysts, and particularly relates to an ultrathin porous carbon nitride nanosheet as well as a preparation method and application thereof. The preparation method comprises the following steps: performing electrochemical-assisted liquid-phase chemical exfoliation treatment on blocky g-C3N4 to obtain an ultrathin porous g-C3N4 nanosheet; and the electrolyte comprises a NaClO solution. By adopting the strategy of electrochemical-assisted liquid-phase chemical exfoliation, the Na + Alkali metal intercalation exfoliation and ClO ‑ The synergistic effect of chemical oxidation induced exfoliation is used to exfoliate the blocky g-C3N4 into the ultrathin porous g-C3N4 nanosheet. The method involves electrochemical-assisted chemical exfoliation treatment, which is simple in operation, low in chemical reagent cost, and non-toxic and harmless, and can efficiently obtain high-quality ultrathin porous g-C3N4 nanosheet material.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, specifically relating to an ultrathin porous carbon nitride nanosheet, its preparation method, and its application. Background Technology

[0002] Heavy metal pollution is a widespread problem in my country's surface water and groundwater environments. Hexavalent chromium (Cr(VI)), a typical heavy metal pollutant, poses a significant threat to human health and the ecological environment due to its high toxicity and strong mobility. Simultaneously, the widespread presence of organic dyes such as rhodamine B (RhB) further exacerbates water pollution; its persistence and bioaccumulation may damage aquatic ecosystems and pose potential harm to human health. Researchers have developed various water treatment technologies to remove Cr(VI) and RhB. Among these, solar-driven photocatalytic reactions, which can reduce Cr(VI) to non-toxic trivalent chromium (Cr(III)) and oxidize and degrade RhB into CO2 and H2O, are considered an economically feasible and promising strategy. Photocatalysts, as a key component of photocatalytic reactions, have attracted extensive research since 2009 when graphitic carbon nitride (g-C3N4) was used for visible light-driven photocatalytic water splitting to produce H2 and O2. Their advantages, including good physicochemical stability, low cost, and environmental friendliness, have led to their widespread study. However, conventional bulk g-C3N4 is typically produced by high-temperature calcination of nitrogen-containing carbon precursors, resulting in a severe bulky structure, low specific surface area, and high recombination rate of photogenerated electron-hole pairs, which significantly limits its photocatalytic activity. Among various modification strategies for g-C3N4-based photocatalysts, developing two-dimensional ultrathin porous g-C3N4 nanosheets with abundant edge reaction active sites and increased specific surface area has proven to be one of the most promising approaches.

[0003] Currently, due to the weak van der Waals forces between the layers of bulk g-C3N4 materials, these forces can be disrupted through chemical exfoliation techniques, thereby obtaining ultrathin porous g-C3N4 nanosheets. In the chemical exfoliation strategy for bulk g-C3N4 materials, alkali metal ion intercalation, such as Li... + K + and Na + These substances can be embedded in the spaces between layers of the bulk g-C3N4 two-dimensional structure and react with the electronegative nitrogen-containing groups inside to form ionic dipole interactions, thereby effectively exfoliating the layered bulk g-C3N4 material. Furthermore, the bulk g-C3N4 material can be oxidatively exfoliated using highly oxidizing chemical reagents, such as ClO. -Oxidative etching can be used to etch and peel off bulk g-C3N4 materials, thereby obtaining ultrathin porous g-C3N4 nanosheets. Therefore, the synergistic effect of alkali metal ion-induced peeling and chemical oxidative etching peeling is considered one of the effective strategies for preparing ultrathin porous g-C3N4 nanosheets. However, chemical peeling treatment often results in incomplete peeling of nanosheets, leading to a relatively large thickness of the g-C3N4 nanosheets. Summary of the Invention

[0004] The purpose of this invention is to provide an ultrathin porous carbon nitride nanosheet, its preparation method, and its application. The preparation method of the ultrathin porous carbon nitride nanosheet provided by this invention produces nanosheets with a smaller thickness.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing ultrathin porous g-C3N4 nanosheets, comprising the following steps:

[0007] Bulk g-C3N4 was subjected to electrochemical-assisted liquid-phase chemical exfoliation to obtain ultrathin porous g-C3N4 nanosheets; the electrolyte included NaClO solution.

[0008] Preferably, the electrochemical-assisted liquid-phase chemical stripping treatment involves adding blocky g-C3N4 to the electrolyte and mixing it thoroughly, then performing the stripping treatment using a three-electrode system.

[0009] Preferably, the concentration of the NaClO solution is 0.01–1 M.

[0010] Preferably, the three-electrode system uses a titanium mesh as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode;

[0011] The pulse potential parameters are set as follows: high potential +1.0~+1.5V, lasting 5~10s; low potential 0~+0.5V, lasting 1~5s, continuous operation; the peeling process duration is 0.1~0.5h.

[0012] Preferably, the blocky g-C3N4 is obtained by calcining melamine.

[0013] Preferably, the calcination temperature is 500–550°C and the time is 2–4 hours.

[0014] The present invention also provides ultrathin porous g-C3N4 nanosheets prepared by the preparation method described above, wherein the thickness of the g-C3N4 nanosheets is 1.60 to 1.80 nm.

[0015] Preferably, the porosity of the g-C3N4 nanosheets is 40-60%.

[0016] This invention also provides the application of ultrathin porous g-C3N4 nanosheets prepared by the preparation method described above, or the application of ultrathin porous g-C3N4 nanosheets prepared by the above technical solution in the photocatalytic reduction of Cr(VI).

[0017] This invention also provides the application of ultrathin porous g-C3N4 nanosheets prepared by the preparation method described above, or the ultrathin porous g-C3N4 nanosheets prepared by the above technical solution, in the photocatalytic oxidative degradation of RhB.

[0018] This invention provides a method for preparing ultrathin porous g-C3N4 nanosheets, comprising the following steps: subjecting bulk g-C3N4 to electrochemically assisted liquid-phase chemical exfoliation to obtain ultrathin porous g-C3N4 nanosheets; the electrolyte includes one or more of NaClO solution, NaCl solution, HClO solution, and HCl solution. This invention utilizes an electrochemically assisted liquid-phase chemical exfoliation strategy, taking advantage of the NaClO solution in the electrolyte solution... + Alkali metal intercalation and ClO - The synergistic effect of chemical oxidation-induced exfoliation can delaminate bulk g-C3N4 into ultrathin porous g-C3N4 nanosheets. This electrochemical-assisted chemical exfoliation method is simple to operate, can be performed at room temperature, uses low-cost, non-toxic chemical reagents, and can efficiently obtain high-quality ultrathin porous g-C3N4 nanosheet materials. These materials have potential for widespread application in photocatalytic water environment treatment and industrialization. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 These are transmission electron microscope images of ultrathin porous NCOCN nanosheets;

[0021] Figure 2 These are atomic force microscopy images (a) and corresponding thickness distribution images (b) of ultrathin porous NCOCN nanosheets;

[0022] Figure 3 The performance of photocatalytic reduction of Cr(VI) (a) and photocatalytic oxidative degradation of RhB (b) by bulk CN and ultrathin porous NCOCN nanosheets under visible light irradiation was tested. Detailed Implementation

[0023] This invention provides a method for preparing ultrathin porous g-C3N4 nanosheets, comprising the following steps:

[0024] Bulk g-C3N4 was subjected to electrochemical-assisted liquid-phase chemical exfoliation to obtain ultrathin porous g-C3N4 nanosheets; the electrolyte included NaClO solution.

[0025] In one embodiment of the present invention, the concentration of the NaClO solution can be 0.01 to 1 M, specifically 0.01 M, 0.02 M, 0.03 M, 0.04 M, 0.05 M, 0.06 M, 0.07 M, 0.08 M, 0.09 M or 1 M.

[0026] In one embodiment of the present invention, the blocky g-C3N4 material can be obtained by calcining melamine (C3H6N6); the calcination temperature can be 500-550℃, specifically 500℃, 510℃, 520℃, 530℃, 540℃, or 550℃, and the time can be 2-4 hours, specifically 2 hours, 3 hours, or 4 hours; the heating rate to the calcination temperature can be 2-5℃ / min, specifically 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min. In another embodiment of the present invention, after calcination, the material is further cooled to room temperature and then ground to obtain the blocky g-C3N4.

[0027] In one embodiment of the present invention, the electrochemical-assisted liquid-phase chemical stripping treatment involves adding blocky g-C3N4 to an electrolyte and mixing it thoroughly, followed by stripping using a three-electrode system. The three-electrode system uses a titanium mesh as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode. The pulse potential parameters are set to a high potential of +1.0 to +1.5V, specifically +1.0V, +1.1V, +1.2V, +1.3V, +1.4V, or +1V. The electrochemical-assisted liquid-phase chemical stripping treatment is performed at 5V for 5–10 seconds, specifically 5s, 6s, 7s, 8s, 9s, or 10s; at a low potential of 0–+0.5V, specifically 0V, +0.1V, +0.2V, +0.3V, +0.4V, or 0.5V, for 1–5 seconds, specifically 1s, 2s, 3s, 4s, or 5s, continuously; the stripping treatment duration is 0.1–0.5 hours, specifically 0.1 hours, 0.2 hours, 0.3 hours, 0.4 hours, or 0.5 hours. In one embodiment of the invention, after the electrochemical-assisted liquid-phase chemical stripping treatment, the supernatant obtained from the electrochemical-assisted liquid-phase chemical stripping treatment is collected and centrifuged. The precipitate obtained by centrifugation is washed with water and then dried; the number of water washes can be 3, preferably washing until neutral; the drying temperature can be 80°C, and the time can be 10 hours.

[0028] This invention also provides the application of ultrathin porous g-C3N4 nanosheets prepared by the preparation method described above, or the ultrathin porous g-C3N4 nanosheets described above in the photocatalytic reduction of Cr(VI).

[0029] This invention also provides the application of ultrathin porous g-C3N4 nanosheets prepared by the preparation method described above, or the ultrathin porous g-C3N4 nanosheets described above, in the photocatalytic oxidation degradation of RhB.

[0030] Compared with existing technologies, the ultrathin porous g-C3N4 nanosheet material prepared by this invention is simple to operate, has low raw material cost and non-toxic chemical reagents. At the same time, it has good exfoliation effect, high yield and is suitable for large-scale industrial continuous production, and has great application potential in the field of solving environmental water pollution control.

[0031] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0032] Example 1

[0033] (1) Preparation of bulk g-C3N4

[0034] Weigh 12g of C3H6N6 powder and pour it into a covered crucible. Place the crucible in a muffle furnace and set the heating program to heat to 550℃ at a heating rate of 5℃ / min and maintain for 4 hours. After the reaction temperature drops to room temperature, grind the remaining solid product in the crucible into powder in a mortar, which is blocky g-C3N4, and name it CN.

[0035] (2) Preparation of ultrathin porous g-C3N4 nanosheets

[0036] 1 g of blocky g-C3N4 was added to 200 mL of 1 M NaClO solution. Under ambient temperature and magnetic stirring, a traditional three-electrode system of an electrochemical workstation was used, with a titanium mesh as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode. The pulse potential was set to +1.0 V (10 s) / 0 V (5 s), and the total treatment time was 0.5 h. After the electrochemical-assisted liquid-phase chemical exfoliation reaction was completed, the supernatant was collected, and the precipitate was collected by high-speed centrifugation and washed three times with pure water. Finally, the precipitate was dried in a vacuum drying oven at 80 °C for 10 h to obtain ultrathin porous g-C3N4 nanosheets, which were named NCOCN.

[0037] Figure 1 Transmission electron microscope images of NCOCN samples, from Figure 1 It can be clearly observed that the sample has a distinct ultrathin porous structure.

[0038] Figure 2 Atomic force microscopy images and corresponding thickness distribution images of NCOCN samples, from Figure 2 It can be clearly observed that the sample has an ultrathin porous nanosheet structure with a nanosheet thickness of 1.69 nm.

[0039] Comparative Example 1

[0040] (1) Preparation of bulk g-C3N4

[0041] Weigh 12g of C3H6N6 powder and pour it into a covered crucible. Place the crucible in a muffle furnace and set the heating program to heat to 550℃ at a heating rate of 5℃ / min and maintain for 4 hours. After the reaction temperature drops to room temperature, grind the remaining solid product in the crucible into powder in a mortar, which is blocky g-C3N4, and name it CN.

[0042] (2) Preparation of g-C3N4 nanosheets

[0043] 1 g of blocky g-C3N4 was added to 200 mL of 1 M NaCl solution. Under ambient temperature and magnetic stirring, a traditional three-electrode system of an electrochemical workstation was used, with a titanium mesh as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode. The pulse potentials were set to +1.0 V (10 s) / 0 V (5 s), and the total treatment time was 0.5 h. After the electrochemical-assisted liquid-phase chemical exfoliation reaction was completed, the supernatant was collected, and the precipitate was collected by high-speed centrifugation and washed three times with pure water. Finally, the precipitate was dried in a vacuum drying oven at 80 °C for 10 h to obtain g-C3N4 nanosheets, which were named NCCN.

[0044] Tests showed that the thickness of NCCN's nanosheets is 3.48 nm.

[0045] Comparative Example 2

[0046] (1) Preparation of bulk g-C3N4

[0047] Weigh 12g of C3H6N6 powder and pour it into a covered crucible. Place the crucible in a muffle furnace and set the heating program to heat to 550℃ at a heating rate of 5℃ / min and maintain for 4 hours. After the reaction temperature drops to room temperature, grind the remaining solid product in the crucible into powder in a mortar, which is blocky g-C3N4, and name it CN.

[0048] (2) Preparation of g-C3N4 nanosheets

[0049] 1 g of blocky g-C3N4 was added to 200 mL of 1 M HCl solution. Using a traditional three-electrode system on an electrochemical workstation under magnetic stirring at room temperature, with a titanium mesh as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode, the pulse potential was set to +1.0 V (10 s) / 0 V (5 s), and the total treatment time was 0.5 h. After the electrochemical-assisted liquid-phase chemical exfoliation reaction was completed, the supernatant was collected, and the precipitate was collected by high-speed centrifugation and washed three times with pure water. Finally, the obtained precipitate was dried in a vacuum drying oven at 80 °C for 10 h to obtain g-C3N4 nanosheets, which were named HCCN.

[0050] Tests showed that the thickness of HCCN nanosheets is 3.25 nm.

[0051] Comparative Example 3

[0052] (1) Preparation of bulk g-C3N4

[0053] Weigh 12g of C3H6N6 powder and pour it into a covered crucible. Place the crucible in a muffle furnace and set the heating program to heat to 550℃ at a heating rate of 5℃ / min and maintain for 4 hours. After the reaction temperature drops to room temperature, grind the remaining solid product in the crucible into powder in a mortar, which is blocky g-C3N4, and name it CN.

[0054] (2) Preparation of g-C3N4 nanosheets

[0055] 1 g of blocky g-C3N4 was added to 200 mL of 1 M HClO solution. Under ambient temperature and magnetic stirring, a traditional three-electrode system of an electrochemical workstation was used, with a titanium mesh as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode. The pulse potential was set to +1.0 V (10 s) / 0 V (5 s), and the total treatment time was 0.5 h. After the electrochemical-assisted liquid-phase chemical exfoliation reaction was completed, the supernatant was collected, and the precipitate was collected by high-speed centrifugation and washed three times with pure water. Finally, the precipitate was dried in a vacuum drying oven at 80 °C for 10 h to obtain g-C3N4 nanosheets, which were named HCOCN.

[0056] Tests showed that the thickness of HCOCN nanosheets is 2.63 nm.

[0057] Application Example 1

[0058] The bulk CN and ultrathin porous NCOCN nanosheets prepared in Example 1 were used as photocatalysts for performance evaluation of photocatalytic reduction of Cr(VI) under visible light irradiation. The test results are shown in [Figure 1]. Figure 3In section (a), the specific experimental procedure is as follows: 50 mg of photocatalyst was added to a quartz tube containing 50 mL of 40 ppm Cr(VI) solution. Disodium ethylenediaminetetraacetate (EDTA) was used as a sacrificial agent. Four drops of concentrated nitric acid solution were added dropwise using a dropper to adjust the pH of the solution, and the pH was adjusted to 2–3 using pH paper. To achieve the adsorption and desorption equilibrium between the photocatalyst and the target pollutant, the reaction solution was first placed in a photochemical reactor under dark conditions and continuously stirred magnetically for 40 min. Then, the light source was turned on to carry out the photocatalytic reaction, and samples were taken every 20 min. The photochemical reactor was equipped with a 500 W xenon lamp and a filter with a wavelength greater than 420 nm. The absorbance of Cr(VI) in the solution was measured at a wavelength of 540 nm using a UV-Vis spectrophotometer. An ethanol solution of diphenylaminourea (DPC) was used as a colorimetric agent to avoid interference from Cr(III).

[0059] like Figure 3 As shown in (a), the photocatalytic reduction of Cr(VI) to Cr(III) by bulk CN exhibits poor photocatalytic performance, with a photocatalytic efficiency of approximately 20%. NCOCN nanosheets, on the other hand, demonstrate a high photocatalytic reduction efficiency of approximately 90% for Cr(VI) to Cr(III). This represents a 5% performance improvement compared to the previously reported efficiency of approximately 85% for the photocatalytic reduction of Cr(VI) to Cr(III) by NaClO g-C3N4 samples obtained under only room temperature magnetic stirring conditions using chemical exfoliation technology.

[0060] Comparative Application Example 1

[0061] The only difference from Application Example 1 is that NCOCN nanosheets are replaced with NCCN, and the efficiency of NCCN nanosheets in photocatalytic reduction of Cr(VI) to Cr(III) is 35%.

[0062] Comparative Application Example 2

[0063] The only difference from Application Example 1 is that NCOCN nanosheets are replaced with HCCN, and the efficiency of HCCN nanosheets in photocatalytic reduction of Cr(VI) to Cr(III) is 60%.

[0064] Comparative Application Example 3

[0065] The only difference from Application Example 1 is that NCOCN nanosheets are replaced with HCOCN, and the efficiency of HCOCN nanosheets in photocatalytic reduction of Cr(VI) to Cr(III) is 72%.

[0066] Application Example 2

[0067] The bulk CN and ultrathin porous NCOCN nanosheet photocatalysts prepared in Example 1 were used for performance evaluation testing of photocatalytic oxidation degradation of RhB under visible light irradiation. The test results are shown in […]. Figure 3 (b) Evaluation of the activity of the prepared bulk CN and ultrathin porous NCOCN nanosheet photocatalysts by their application in the photocatalytic oxidation degradation of RhB.

[0068] The specific experimental procedure is as follows: 50 mg of photocatalyst was added to a quartz tube containing 50 mL of 40 ppm RhB solution. To achieve adsorption and desorption equilibrium between the photocatalyst and the target pollutant, the reaction solution was first placed in a photochemical reactor under dark conditions and continuously magnetically stirred for 40 min. Then, the light source was turned on to carry out the photocatalytic reaction, and samples were taken every 20 min. The photochemical reactor was equipped with a 500 W xenon lamp and a filter with a wavelength greater than 420 nm. The absorbance of RhB in the solution was measured at a wavelength of 554 nm using a UV-Vis spectrophotometer.

[0069] like Figure 3 As shown in (b), the photocatalytic oxidation degradation of RhB by bulk CN is poor, with a photocatalytic efficiency of approximately 20%. In contrast, NCOCN nanosheets exhibit a high photocatalytic oxidation degradation efficiency of approximately 95% for RhB. This significantly enhanced photocatalytic activity stems from the unique ultrathin porous nanosheet structure (1.69 nm thick) obtained through an electrochemical-assisted liquid-phase chemical exfoliation strategy, which enhances the separation and transfer of photogenerated charge carriers.

[0070] Comparative Application Example 4

[0071] The only difference from Application Example 2 is that NCOCN nanosheets are replaced with NCCN, and the efficiency of NCCN nanosheets in photocatalytic oxidation degradation of RhB is 41%.

[0072] Comparative Application Example 5

[0073] The only difference from Application Example 2 is that NCOCN nanosheets are replaced with HCCN, and the efficiency of HCCN nanosheets in photocatalytic oxidation degradation of RhB is 65%.

[0074] Comparative Application Example 6

[0075] The only difference from Application Example 2 is that NCOCN nanosheets are replaced with HCOCN, and the efficiency of HCOCN nanosheets in photocatalytic oxidation degradation of Rh B is 76%.

[0076] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing ultrathin porous g-C3N4 nanosheets, comprising the following steps: Bulk g-C3N4 was subjected to electrochemical-assisted liquid-phase chemical exfoliation to obtain ultrathin porous g-C3N4 nanosheets; the electrolyte included NaClO solution. The electrochemical-assisted liquid-phase chemical stripping process involves adding blocky g-C3N4 to an electrolyte and mixing it thoroughly, then performing the stripping process using a three-electrode system. During the peeling process, the pulse potential parameters are set as follows: high potential +1.0~+1.5 V, lasting 5~10 s; low potential 0~+0.5 V, lasting 1~5 s, continuously running; the peeling process duration is 0.1~0.5 h. The thickness of the g-C3N4 nanosheets is 1.60~1.80 nm; The concentration of the NaClO solution is 0.01~1 M; The three-electrode system uses a titanium mesh as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode.

2. The preparation method according to claim 1, characterized in that, The blocky g-C3N4 was obtained by calcining melamine.

3. The preparation method according to claim 2, characterized in that, The calcination temperature is 500~550 ℃, and the time is 2~4 h.

4. The ultrathin porous g-C3N4 nanosheets prepared by the preparation method according to any one of claims 1 to 3 are characterized in that, The thickness of the g-C3N4 nanosheets is 1.60~1.80 nm.

5. The ultrathin porous g-C3N4 nanosheets as described in claim 4, characterized in that, The porosity of the g-C3N4 nanosheets is 40-60%.

6. The application of the ultrathin porous g-C3N4 nanosheets prepared by the preparation method according to any one of claims 1 to 3, or the ultrathin porous g-C3N4 nanosheets according to claim 4 or 5, in the photocatalytic reduction of Cr(VI).

7. The application of the ultrathin porous g-C3N4 nanosheets prepared by the preparation method according to any one of claims 1 to 3, or the ultrathin porous g-C3N4 nanosheets according to claim 4 or 5, in the photocatalytic oxidative degradation of Rh B.

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