Ultrathin porous carbon nitride nanosheet as well as preparation method and application thereof

Abstract

The invention 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: carrying out electrochemical auxiliary liquid-phase chemical stripping treatment on blocky g-C3N4 to obtain an ultrathin porous g-C3N4 nanosheet; and the electrolyte comprises a NaClO solution. According to the preparation method disclosed by the invention, blocky g-C3N4 is delaminated into the ultrathin porous g-C3N4 nanosheet by adopting a strategy of electrochemistry assisted liquid-phase chemical delamination and utilizing a synergistic effect of a Na < + > alkali metal embedded delamination layer and a ClO <-> chemical oxidation induced delamination layer in an electrolyte. The electrochemically-assisted chemical stripping treatment involved in the method is simple to operate, chemical reagents are low in cost, nontoxic and harmless, and the high-quality ultrathin porous g-C3N4 nanosheet material can be efficiently obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and in particular relates to an ultra-thin porous carbon nitride nanosheet and a preparation method and application thereof. Background Art

[0002] Heavy metal pollution is a widespread problem in both surface and groundwater in my country's aquatic environment. Hexavalent chromium (Cr(VI)), a typical heavy metal contaminant, poses a significant threat to human health and the ecological environment due to its high toxicity and strong mobility. Furthermore, the widespread presence of organic dye contaminants, such as rhodamine B (RhB), further exacerbates water pollution. Their persistence and bioaccumulation can damage aquatic ecosystems and pose potential risks to human health. Various water treatment technologies have been developed to remove Cr(VI) and RhB. Among them, the solar-driven photocatalytic reduction of Cr(VI) to the non-toxic trivalent chromium (Cr(III)) and the oxidative degradation of RhB to CO2 and H2O are considered to be economically feasible and promising strategies. Photocatalysts, as a key component of photocatalytic reactions, have attracted extensive research since the application of graphene-based carbon nitride (g-C3N4) in visible-light-driven photocatalytic water splitting to produce H2 and O2 in 2009. Their excellent physicochemical stability, low cost, and environmental friendliness have attracted extensive research attention. However, conventional bulk g-C3N4 is usually prepared by high-temperature calcination of nitrogen-containing carbon precursors, resulting in severe block stacking structure, low specific surface area, and high recombination rate of photogenerated electrons and holes, which severely limit its photocatalytic activity. Among various modification strategies based on g-C3N4 photocatalysts, the development of two-dimensional ultrathin porous g-C3N4 nanosheets with abundant edge reaction active sites and increased specific surface area has been proven to be the most promising approach.

[0003] At present, due to the weak van der Waals force between the layers of bulk g-C3N4 materials, it is possible to destroy the van der Waals force between the layers through chemical stripping technology, thereby obtaining ultra-thin porous g-C3N4 nanosheets. In the chemical stripping strategy of bulk g-C3N4 materials, alkali metal ions such as Li are intercalated. + , K + and Na + The ions can be embedded in the space between the two-dimensional structure layers of bulk g-C3N4 and react with the electronegative nitrogen-containing groups inside to form ion-dipole interactions, thereby effectively exfoliating the stacked bulk g-C3N4 materials. In addition, the bulk g-C3N4 materials can be oxidized and exfoliated by chemical reagents with high oxidizing properties, such as ClO -The synergistic effect of alkali metal ion-induced exfoliation and chemical oxidation etching is considered an effective strategy for preparing ultrathin porous g-C3N4 nanosheets. However, chemical exfoliation is incomplete, resulting in relatively thick g-C3N4 nanosheets. Summary of the Invention

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

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

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

[0007] The bulk g-C3N4 is subjected to electrochemically assisted liquid-phase chemical exfoliation to obtain ultrathin porous g-C3N4 nanosheets; the electrolyte includes a NaClO solution.

[0008] Preferably, the electrochemically assisted liquid phase chemical stripping treatment is to add bulk g-C3N4 into the electrolyte and mix them evenly, and then perform the stripping treatment using a three-electrode system.

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

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

[0011] The parameters of the pulse potential are set as follows: high potential +1.0~+1.5V, lasting 5~10s; low potential 0~+0.5V, lasting 1~5s, continuous operation; the duration of the stripping treatment 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 calcination time is 2-4 hours.

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

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

[0016] The present invention also provides an ultrathin porous g-C3N4 nanosheet prepared by the preparation method described in the above technical solution or the use of the ultrathin porous g-C3N4 nanosheet in the photocatalytic reduction of Cr(VI).

[0017] The present invention also provides an ultrathin porous g-C3N4 nanosheet prepared by the preparation method described in the above technical solution or the application of the ultrathin porous g-C3N4 nanosheet in the photocatalytic oxidation degradation of RhB.

[0018] The present invention provides a method for preparing ultrathin porous g-C3N4 nanosheets, comprising the following steps: subjecting bulk g-C3N4 to an electrochemically assisted liquid-phase chemical stripping treatment to obtain ultrathin porous g-C3N4 nanosheets; the electrolyte comprising one or more of a NaClO solution, a NaCl solution, an HClO solution, and an HCl solution. The present invention adopts an electrochemically assisted liquid-phase chemical stripping strategy, utilizing Na in the electrolyte solution to obtain an ultrathin porous g-C3N4 nanosheet. + Alkali metal intercalation and ClO - The synergistic effect of chemical oxidation-induced exfoliation can exfoliate bulk g-C3N4 into ultrathin porous g-C3N4 nanosheets. This method involves electrochemically assisted chemical exfoliation, which is simple to operate, can be processed at room temperature, uses low-cost, and non-toxic chemical reagents. It can efficiently produce high-quality, ultrathin porous g-C3N4 nanosheets and has potential for industrial applications in photocatalytic water environment treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 is a transmission electron microscope image of ultrathin porous NCOCN nanosheets;

[0021] Figure 2 Atomic force microscopy image (a) and corresponding thickness distribution image (b) of ultrathin porous NCOCN nanosheets;

[0022] Figure 3 Performance tests of bulk CN and ultrathin porous NCOCN nanosheets for photocatalytic reduction of Cr(VI) (a) and photocatalytic oxidation degradation of RhB (b) under visible light irradiation. DETAILED DESCRIPTION

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

[0024] The bulk g-C3N4 is subjected to electrochemically assisted liquid phase chemical exfoliation to obtain ultrathin porous g-C3N4 nanosheets; the electrolyte includes a NaClO solution.

[0025] As an embodiment of the present invention, the concentration of the NaClO solution may 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] As an embodiment of the present invention, the bulk g-C3N4 material can be obtained by calcining melamine (C3H6N6); the calcination temperature can be 500-550°C, specifically 500°C, 510°C, 520°C, 530°C, 540°C or 550°C, and the time can be 2-4h, specifically 2h, 3h or 4h; the heating rate of the temperature increased to the calcination temperature can be 2-5°C / min, specifically 2°C / min, 3°C / min, 4°C / min or 5°C / min. As an embodiment of the present invention, after the calcination, it also includes cooling to room temperature and then grinding to obtain bulk g-C3N4.

[0027] As an embodiment of the present invention, the electrochemically assisted liquid phase chemical stripping process is to add bulk g-C3N4 into an electrolyte and mix them uniformly, and then use a three-electrode system to perform the stripping process; the three-electrode system comprises a titanium mesh as a working electrode, a Pt sheet as a counter electrode, and an Ag / AgCl as a 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 +1. 5V, for 5 to 10 seconds, specifically 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds or 10 seconds; low potential 0 to +0.5V, specifically 0V, +0.1V, +0.2V, +0.3V, +0.4V or 0.5V, for 1 to 5 seconds, specifically 1 second, 2 seconds, 3 seconds, 4 seconds or 5 seconds, continuous operation; the duration of the stripping treatment can be 0.1 to 0.5h, specifically 0.1h, 0.2h, 0.3h, 0.4h or 0.5h. As an embodiment of the present invention, after the electrochemically assisted liquid phase chemical stripping treatment, the supernatant obtained by the electrochemically assisted liquid phase chemical stripping treatment is collected and centrifuged, and the precipitate obtained by centrifugation is washed with water and then dried; the number of water washings can be 3 times, and the water washing is preferably washed with water until neutral; the drying temperature can be 80°C and the time can be 10h.

[0028] The present invention also provides an ultrathin porous g-C3N4 nanosheet prepared by the preparation method described in the above technical solution or the use of the ultrathin porous g-C3N4 nanosheet described in the above technical solution in the photocatalytic reduction of Cr(VI).

[0029] The present invention also provides an ultrathin porous g-C3N4 nanosheet prepared by the preparation method described in the above technical solution or the use of the ultrathin porous g-C3N4 nanosheet described in the above technical solution in the photocatalytic oxidation degradation of RhB.

[0030] Compared with the existing technology, the ultrathin porous g-C3N4 nanosheet material prepared by the present invention is simple to operate, has low raw material cost and non-toxic chemical reagents, and has good peeling 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] In order to further illustrate the present invention, the scheme of the present invention is described in detail below with reference to the accompanying drawings and embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0032] Example 1

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

[0034] 12g of C3H6N6 powder was weighed and placed in a covered crucible. The crucible was then placed in a muffle furnace and heated to 550°C at a rate of 5°C / min and held for 4 hours. After the reaction temperature dropped to room temperature, the remaining solid product in the crucible was ground into a powder in a mortar, resulting in bulk g-C3N4, designated CN.

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

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

[0037] Figure 1 Transmission electron microscope image of NCOCN sample. Figure 1 It can be clearly observed that the sample has an obvious ultra-thin porous structure.

[0038] Figure 2 The atomic force microscope image of the NCOCN sample and the corresponding thickness distribution image are shown in Figure 2. Figure 2 It can be clearly observed that the sample has an ultrathin porous nanosheet structure, and the thickness of the nanosheet is 1.69 nm.

[0039] Comparative Example 1

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

[0041] 12g of C3H6N6 powder was weighed and placed in a covered crucible. The crucible was then placed in a muffle furnace and heated to 550°C at a rate of 5°C / min and held for 4 hours. After the reaction temperature dropped to room temperature, the remaining solid product in the crucible was ground into a powder in a mortar, resulting in bulk g-C3N4, designated CN.

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

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

[0044] After testing, the thickness of NCCN nanosheets is 3.48nm.

[0045] Comparative Example 2

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

[0047] 12g of C3H6N6 powder was weighed and placed in a covered crucible. The crucible was then placed in a muffle furnace and heated to 550°C at a rate of 5°C / min and held for 4 hours. After the reaction temperature dropped to room temperature, the remaining solid product in the crucible was ground into a powder in a mortar, resulting in bulk g-C3N4, designated CN.

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

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

[0050] After testing, the thickness of HCCN nanosheets is 3.25nm.

[0051] Comparative Example 3

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

[0053] 12g of C3H6N6 powder was weighed and placed in a covered crucible. The crucible was then placed in a muffle furnace and heated to 550°C at a rate of 5°C / min and held for 4 hours. After the reaction temperature dropped to room temperature, the remaining solid product in the crucible was ground into a powder in a mortar, resulting in bulk g-C3N4, designated CN.

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

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

[0056] After testing, the thickness of the HCOCN nanosheets was 2.63nm.

[0057] Application Example 1

[0058] The bulk CN and ultrathin porous NCOCN nanosheets prepared in Example 1 were used as photocatalysts to evaluate the performance of photocatalytic reduction of Cr(VI) under visible light irradiation. The test results are shown in Figure 3In (a), the experimental procedure is as follows: 50 mg of photocatalyst was added to 50 mL of a 40 ppm Cr(VI) solution in a quartz tube. Disodium ethylenediaminetetraacetic acid (EDTA) was used as a sacrificial agent, and four drops of concentrated nitric acid were added using a rubber-tipped pipette to adjust the pH of the solution. pH paper was used to determine the pH of the solution, which was adjusted to 2-3. To achieve adsorption and desorption equilibrium between the photocatalyst and the target pollutant, the reaction solution was placed in a photochemical reactor under dark conditions with continuous magnetic stirring for 40 minutes. The light source was then turned on for the photocatalytic reaction, with samples taken every 20 minutes. The photochemical reactor was equipped with a 500 W xenon lamp equipped with 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-visible spectrophotometer. An ethanolic solution of diphenylcarbazide (DPC) was used as a colorimetric reagent to avoid interference from Cr(III).

[0059] like Figure 3 As shown in (a), bulk CN has poor photocatalytic performance in the photocatalytic reduction of Cr(VI) to Cr(III), with a photocatalytic efficiency of approximately 20%. NCOCN nanosheets have a high photocatalytic reduction efficiency of Cr(VI) to Cr(III), approximately 90%. This performance improvement is 5% compared to the previously reported NaClO g-C3N4 sample (Diamond & Related Materials 88 (2018) 51-59) that achieved a photocatalytic reduction efficiency of approximately 85% for Cr(VI) to Cr(III) using chemical exfoliation under room temperature magnetic stirring conditions.

[0060] Comparative Application Example 1

[0061] The only difference from Application Example 1 is that the NCOCN nanosheets are replaced with NCCN, and the efficiency of the 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 the NCOCN nanosheets are replaced with HCCN, and the efficiency of the 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 the NCOCN nanosheets are replaced with HCOCN, and the efficiency of the 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 of photocatalytic oxidation degradation of RhB under visible light irradiation. The test results are shown in Figure 3 Middle (b). The photocatalytic activity of the prepared bulk CN and ultrathin porous NCOCN nanosheets was evaluated by photocatalytic oxidation degradation of RhB.

[0068] The experimental procedure is as follows: 50 mg of photocatalyst was added to 50 mL of a 40 ppm RhB solution in a quartz tube. To achieve adsorption and desorption equilibrium between the photocatalyst and the target pollutant, the reaction solution was placed in a photochemical reactor under dark conditions with continuous magnetic stirring for 40 minutes. The light source was then turned on for the photocatalytic reaction, with samples taken every 20 minutes. The photochemical reactor was equipped with a 500 W xenon lamp equipped with 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-visible spectrophotometer.

[0069] like Figure 3 As shown in (b), the performance of bulk CN in photocatalytic oxidation degradation of RhB is poor, with a photocatalytic efficiency of approximately 20%. In contrast, NCOCN nanosheets have a high efficiency of photocatalytic oxidation degradation of RhB, approximately 95%. This significantly improved photocatalytic activity is attributed to the unique ultrathin porous nanosheet structure (thickness 1.69 nm) obtained by the electrochemically 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 the NCOCN nanosheets are replaced with NCCN, and the efficiency of photocatalytic oxidation degradation of RhB by the NCCN nanosheets is 41%.

[0072] Comparative Application Example 5

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

[0074] Comparative Application Example 6

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

[0076] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing ultrathin porous g-C3N4 nanosheets, comprising the following steps: The bulk g-C3N4 is subjected to electrochemically assisted liquid-phase chemical exfoliation to obtain ultrathin porous g-C3N4 nanosheets; the electrolyte includes a NaClO solution.

2. The preparation method according to claim 1, wherein The electrochemically assisted liquid phase chemical stripping process is to add bulk g-C3N4 into the electrolyte and mix it evenly, and then use a three-electrode system to perform the stripping process.

3. The preparation method according to claim 1 or 2, wherein The concentration of the NaClO solution is 0.01-1M.

4. The preparation method according to claim 2, wherein The three-electrode system is composed of a titanium mesh as the working electrode, a Pt sheet as the counter electrode, and an Ag / AgCl as the reference electrode; The parameters of the pulse potential are set as follows: high potential +1.0~+1.5V, lasting 5~10s; low potential 0~+0.5V, lasting 1~5s, continuous operation; the duration of the stripping treatment is 0.1~0.5h.

5. The preparation method according to claim 1 or 2, wherein The blocky g-C3N4 is obtained by calcining melamine.

6. The preparation method according to claim 5, wherein The calcination temperature is 500-550° C., and the calcination time is 2-4 hours.

7. The ultrathin porous g-C3N4 nanosheet prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The thickness of the g-C3N4 nanosheet is 1.60-1.80 nm.

8. The ultrathin porous g-C3N4 nanosheet according to claim 7, characterized in that The porosity of the g-C3N4 nanosheets is 40-60%.

9. Use of the ultrathin porous g-C3N4 nanosheets prepared by the preparation method according to any one of claims 1 to 6 or the ultrathin porous g-C3N4 nanosheets according to claim 7 or 8 in the photocatalytic reduction of Cr(VI).

10. Use of the ultrathin porous g-C3N4 nanosheets prepared by the preparation method according to any one of claims 1 to 6 or the ultrathin porous g-C3N4 nanosheets according to claim 7 or 8 in the photocatalytic oxidation degradation of RhB.

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