A V2C MXene photocatalyst composite material, its preparation method and application

Abstract

The present invention belongs to the technical field of photocatalytic materials, and provides a V2CMXene photocatalyst composite material, a preparation method thereof and an application. V2CMXene has a unique accordion-like nanosheet structure and excellent cocatalyst potential; under light illumination, g-C3N4 absorbs a part of visible light to obtain sufficient energy (E≤hv), and can generate some photo-generated carriers. Doping V2CMXene can promote the transfer of the generated photo-generated carriers and inhibit the rapid recombination between electron-hole pairs (e ‑ -h + ). Therefore, the photo-generated carriers on the conduction band (CB) of g-C3N4 can rapidly transfer to the surface of V2CMXene. Then, these transferred photo-generated electrons further react with organic molecules to generate ·OH and CO2. The data of the examples show that the obtained photocatalyst composite material has a catalytic rate of up to 99.3% for methyl orange dye within 120 min.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and particularly relates to a V2C MXene photocatalyst composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Among synthetic dyes, anionic azo dyes are widely used. Methyl orange (MO) is a typical anionic azo dye, which is highly toxic and carcinogenic to humans. Directly discharging it into water will cause water pollution. At present, many treatment methods for dye wastewater have been explored, such as adsorption method, precipitation method, filtration method, coagulation method, and so on. These methods can remove most pollutants, but there are still some substances that cannot be completely removed, and complex precipitate substances are produced, etc.

[0003] Photocatalysts are currently effective technologies for solving wastewater pollution. Photocatalysts absorb light energy to generate photoinduced carriers, and then generate active groups to react with dye wastewater to produce CO2 and H2O. They are environmentally friendly, sustainable, environmentally friendly, and efficient, and most photocatalysts have excellent cycle stability. Photocatalysts are also divided into metal-based photocatalysts and semiconductor-based photocatalysts. Metal-based photocatalysts will dissolve harmful metal ions during the photocatalytic process and have certain biological toxicity, so researchers have focused on semiconductor photocatalysts.

[0004] Semiconductor photocatalysts have great potential in solving water pollution problems. Among them, g-C3N4 is widely used in the degradation of organic pollutants by semiconductor photocatalysts due to its non-toxicity, non-metallicity, unique electronic band structure, and excellent performance. However, its slow charge migration rate and high carrier recombination rate limit its photocatalytic application. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a V2C MXene photocatalyst composite material, a preparation method thereof, and an application thereof. The V2C MXene photocatalyst composite material of the present invention has a fast charge migration rate and a low carrier recombination rate.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a V2C MXene photocatalyst composite material, including g-C3N4 with a lamellar structure and V2C MXene with a lamellar structure, and the V2C MXene is dispersed on the surface of the lamellae of the g-C3N4.

[0008] The present invention also provides a preparation method of the V2C MXene photocatalyst composite material described in the above technical solution, including the following steps:

[0009] Mix V2AlC and HF solution, carry out an etching reaction to obtain a V2C dispersion;

[0010] Mix the V2C dispersion and tetramethylammonium hydroxide, carry out an intercalation reaction to obtain V2C MXene;

[0011] Mix the V2C MXene, g-C3N4 and water, carry out a composite reaction to obtain the V2C MXene photocatalyst composite material.

[0012] Preferably, the temperature for mixing V2AlC and HF solution is room temperature, the time is 24 - 30 h, and the mixing of V2AlC and HF solution is carried out under stirring; the temperature of the etching reaction is 40 - 55 °C, the time is 24 - 48 h, and the etching reaction is carried out under stirring.

[0013] Preferably, the temperature of the intercalation reaction is 45 - 55 °C, the time is 24 - 48 h, and the intercalation reaction is carried out under stirring.

[0014] Preferably, the concentration of the HF solution is ≥49 wt%, the tetramethylammonium hydroxide is used in the form of a tetramethylammonium hydroxide solution, and the mass fraction of the tetramethylammonium hydroxide solution is 5% - 25%; the dosage ratio of V2AlC, HF solution and tetramethylammonium hydroxide solution is 1 g : 20 mL : 20 mL.

[0015] Preferably, the preparation method of g-C3N4 includes the following steps: subject urea to a high-temperature reaction to obtain g-C3N4; the temperature of the high-temperature reaction is 545 - 555 °C, the time is 3 h; the heating rate to the temperature of the high-temperature reaction is 2.5 °C / min.

[0016] Preferably, the mass ratio of g-C3N4 to V2C MXene is 10 : 1.

[0017] Preferably, the time of the composite reaction is 2 - 4 h, and the composite reaction is carried out under stirring.

[0018] Preferably, after the composite reaction, freeze-drying is further included.

[0019] The present invention also provides the application of the V2C MXene photocatalyst composite material described in the above technical solution or the V2C MXene photocatalyst composite material obtained by the preparation method described in the above technical solution in the photocatalytic degradation of organic dyes.

[0020] The present invention provides a V2C MXene photocatalyst composite material, which includes g-C3N4 with a lamellar structure and V2C MXene with a lamellar structure, and the V2C MXene is dispersed on the surface of the lamellae of the g-C3N4.

[0021] In the present invention, V2C MXene has a unique accordion-like nanosheet structure and excellent cocatalyst potential; under light illumination, after g-C3N4 absorbs a part of visible light and obtains sufficient energy (E≤hv), it can generate some photoinduced carriers, and the doped V2C MXene can promote the transfer of the generated photoinduced carriers and inhibit the rapid recombination between electron-hole pairs (e - -h + ). Therefore, the photoinduced carriers on the conduction band (CB) of g-C3N4 can rapidly transfer to the surface of V2C MXene. Then, these transferred photoinduced electrons further react with organic molecules to generate ·OH and CO2. That is to say, the obtained V2C MXene photocatalyst composite material has more photoinduced carriers, faster charge mobility, and lower electron-hole pair recombination rate. The data of the examples show that the obtained V2C MXene photocatalyst composite material has a catalytic rate of up to 99.3% for methyl orange dye within 120 min; it belongs to a very efficient photocatalyst among two-dimensional semiconductor-based photocatalysts and has excellent photocatalytic performance.

[0022] The present invention also provides a preparation method of the V2C MXene photocatalyst composite material described in the above technical solution, including the following steps: mixing V2AlC and an HF solution, carrying out an etching reaction to obtain a V2C dispersion; mixing the V2C dispersion and tetramethylammonium hydroxide, carrying out an intercalation reaction to obtain V2C MXene; mixing the V2C MXene, g-C3N4, and water, carrying out a composite reaction to obtain the V2C MXene photocatalyst composite material. The preparation method of the present invention can prepare V2C with a lamellar structure and can composite g-C3N4 and V2C together, so that V2C is dispersed on the surface of the lamellae of the g-C3N4.

[0023] Further, after the composite reaction, freeze-drying is carried out, and the obtained V2C MXene photocatalyst composite material maintains its original properties and activities, and the XRD data shows that the crystal form of the product is also good.

[0024] Further, the preparation method of the present invention does not use high-pressure and high-temperature reactions, has low cost, is simple to operate, and has a simple process.

[0025] The present invention also provides an application of the V2C MXene photocatalyst composite material described in the above technical solution or the V2C MXene photocatalyst composite material obtained by the preparation method described in the above technical solution in photocatalytic degradation of organic dyes. The obtained V2C MXene photocatalyst composite material has a catalytic rate of up to 99.3% for methyl orange dye within 120 min; it belongs to a very efficient photocatalyst among two-dimensional semiconductor-based photocatalysts and has excellent photocatalytic performance. Description of the Drawings

[0026] Figure 1 It is a schematic diagram of the morphology of the V2C MXene photocatalyst composite material provided by the present invention;

[0027] Figure 2 It is the XRD spectrum of the g-C3N4@V2C MXene photocatalyst composite material obtained in Example 1;

[0028] Figure 3 It is the morphology and element distribution of the g-C3N4@V2C MXene photocatalyst composite material obtained in Example 1;

[0029] Figure 4 It is the SEM image of the V2C MXene obtained in Step 2 of Example 4;

[0030] Figure 5 It is the SEM image of the V2C MXene obtained in Step 2 of Example 4;

[0031] Figure 6 It is the SEM images of the g-C3N4@V2C MXene photocatalyst composite material obtained in Example 4 at different magnifications;

[0032] Figure 7 It is the TEM spectrum of the g-C3N4@V2C MXene photocatalyst composite material obtained in Example 4;

[0033] Figure 8 It is the XPS spectrum of the g-C3N4@V2C MXene photocatalyst composite material obtained in Example 4;

[0034] Figure 9 It is the photoluminescence spectrum of the g-C3N4@V2C MXene photocatalyst composite material obtained in Example 2;

[0035] Figure 10 It is the effect diagram of the g-C3N4@V2C MXene photocatalyst composite material obtained in Example 4 for degrading methyl orange;

[0036] Figure 11Photocatalytic degradation comparison diagram of the g-C3N4@V2C MXene photocatalyst composites obtained in Example 4, Comparative Example 1 and Comparative Example 2. Detailed implementation mode

[0037] The present invention provides a V2C MXene photocatalyst composite, which includes g-C3N4 with a lamellar structure and V2C MXene with a lamellar structure, and the V2C MXene is dispersed on the surface of the lamellae of the g-C3N4.

[0038] The schematic diagram of the morphology of the V2C MXene photocatalyst composite provided by the present invention is as Figure 1 shown. The following combines Figure 1 to describe the morphology of the V2C MXene photocatalyst composite provided by the present invention.

[0039] The V2C MXene photocatalyst composite provided by the present invention is a two-dimensional material, which is composed of flat and regularly shaped 2D / 2D structure nanosheets. The specific structure is that the smaller lamellar structure of V2C is uniformly dispersed on the surface of the larger lamellae of g-C3N4. In the V2C MXene photocatalyst composite of the present invention, g-C3N4 and V2C are in very close contact. Such a D / 2D nanosheet structure helps the close contact between g-C3N4 and V2C, and improves the photocatalytic rate.

[0040] The present invention also provides a preparation method of the V2C MXene photocatalyst composite described in the above technical solution, including the following steps:

[0041] Mix V2AlC and HF solution, carry out an etching reaction to obtain a V2C dispersion;

[0042] Mix the V2C dispersion and tetramethylammonium hydroxide, carry out an intercalation reaction to obtain V2C MXene;

[0043] Mix the V2C MXene, g-C3N4 and water, carry out a composite reaction to obtain the V2C MXene photocatalyst composite.

[0044] In the present invention, unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0045] The present invention mixes V2AlC and HF solution, and carries out an etching reaction to obtain a V2C dispersion.

[0046] In the present invention, the particle size of the V2AlC is preferably 200 mesh. In the present invention, the concentration of the HF solution is preferably ≥49 wt%, and more preferably 49 wt%. In the present invention, the dosage ratio of the V2AlC and the HF solution is preferably 1 g:20 mL.

[0047] In the present invention, the temperature for mixing V2AlC and HF solution is preferably room temperature, and the time is preferably 24 - 30 h. The mixing of V2AlC and HF solution is preferably carried out under stirring conditions. In the present invention, the temperature of the etching reaction is preferably 40 - 55 °C, and the time is preferably 24 - 48 h. The etching reaction is preferably carried out under stirring conditions.

[0048] In the present invention, by adding HF solution, the aluminum layer of V2AlC can be etched away, turning V2AlC into V2C.

[0049] After obtaining the V2C dispersion, the present invention mixes the V2C dispersion and tetramethylammonium hydroxide to carry out an intercalation reaction to obtain V2C MXene.

[0050] In the present invention, tetramethylammonium hydroxide is preferably used in the form of a tetramethylammonium hydroxide solution, and the mass fraction of the tetramethylammonium hydroxide solution is preferably 5% - 25%. In the present invention, the dosage ratio of V2AlC to the tetramethylammonium hydroxide solution is 1 g : 20 mL.

[0051] In the present invention, the temperature of the intercalation reaction is preferably 45 - 55 °C, and the time is preferably 24 - 48 h. The intercalation reaction is preferably carried out under stirring conditions.

[0052] After the intercalation reaction, the present invention preferably performs ethanol washing, water washing, and freeze-drying in sequence. In the present invention, the methods of ethanol washing and water washing are preferably centrifugal washing; the rotation speed of centrifugation is preferably 6000 - 8000 rpm. The present invention does not specifically limit the dosage and number of times of ethanol washing and water washing, as long as the pH value of the obtained washing liquid is 6 - 7. The present invention does not specifically limit the conditions of freeze-drying, as long as it can be dried.

[0053] In the present invention, a large number of functional groups on the surface of V2C make the V2C sheets negatively charged. To achieve charge balance, H + will enter the interlayer. If treated with tetramethylammonium hydroxide (TMAOH, an alkaline solution), the cations in TMAOH will replace H + inserted into the interlayer, expanding the interlayer spacing of V2C.

[0054] After obtaining V2C MXene, the present invention mixes the V2C MXene, g-C3N4, and water to carry out a composite reaction to obtain the V2C MXene photocatalyst composite material.

[0055] In the present invention, the preparation method of g-C3N4 preferably includes the following steps:

[0056] The urea is subjected to a high-temperature reaction to obtain the g-C3N4. In the present invention, the temperature of the high-temperature reaction is preferably 545 - 555 °C, more preferably 550 °C, and the time is preferably 3 h; the rate of heating to the temperature of the high-temperature reaction is preferably 2.5 °C / min. In the present invention, the high-temperature reaction is preferably carried out in a muffle furnace.

[0057] In the present invention, the water is preferably deionized water.

[0058] In the present invention, the mixing of V2C MXene, g-C3N4 and water is preferably as follows: g-C3N4 is ultrasonically dispersed in water to obtain a g-C3N4 dispersion; V2C MXene is added to the g-C3N4 dispersion and ultrasonic treatment is carried out. In the present invention, the time of ultrasonic dispersion is preferably 10 min. In the present invention, the concentration of the g-C3N4 dispersion is preferably 1 - 10 mg / mL, more preferably 2 - 8 mg / mL. In the present invention, the time of ultrasonic treatment is preferably 30 min.

[0059] In the present invention, the mass ratio of g-C3N4 to V2C MXene is preferably 10:1.

[0060] In the present invention, the time of the composite reaction is preferably 2 - 4 h, more preferably 3 h; the composite reaction is preferably carried out under stirring conditions.

[0061] After the composite reaction, the present invention preferably further includes freeze-drying. The present invention does not specifically limit the conditions of the freeze-drying, as long as it can be dried. In the present invention, the freeze-drying is preferably carried out in a freeze-dryer.

[0062] The present invention also provides the application of the V2C MXene photocatalyst composite material described in the above technical solution or the V2C MXene photocatalyst composite material obtained by the preparation method described in the above technical solution in the photocatalytic degradation of organic dyes. In the present invention, when the V2C MXene photocatalyst composite material is applied to degrade organic dyes, the dosage of the V2C MXene photocatalyst composite material is preferably 0.8 - 1 mg / mL. In the present invention, the application of the V2C MXene photocatalyst composite material to degrade organic dyes is preferably carried out under illumination conditions. In the present invention, the organic dyes preferably include methyl orange.

[0063] The following examples are used to describe in detail the V2C MXene photocatalyst composite material provided by the present invention, its preparation method and application, but they should not be construed as limiting the protection scope of the present invention.

[0064] Example 1

[0065] Step 1: Add 50 g of urea powder into an alumina crucible, heat it to 550 °C in a muffle furnace at a heating rate of 2.5 °C / min and hold for 3 h. The obtained yellow solid is ground into powder and denoted as g-C3N4.

[0066] Step 2: Mix 2 g of V2AlC with 40 mL of 49 wt% HF, stir at room temperature for 24 h, then stir the solution at 50 °C for 24 h, and then add 40 mL of 25 wt% TMAOH solution and continue to stir for 24 h. The stirred suspension is centrifuged multiple times with ethanol and deionized water at 8000 rpm until the pH reaches 7, and dried in a freeze dryer for 24 h to obtain V2C MXene.

[0067] Step 3: Add 400 mg of g-C3N4 into 50 mL of deionized water and sonicate for 10 min, then add 40 mg of V2C MXene into g-C3N4 and sonicate together for 30 min. Finally, stir magnetically for 3 h to obtain a uniformly dispersed mixed solution, which is dried in a freeze dryer for 24 h to obtain the g-C3N4@V2C MXene photocatalyst composite.

[0068] Example 2

[0069] Step 1: Add 20 g of urea powder into an alumina crucible, heat it to 550 °C in a muffle furnace at a heating rate of 2.5 °C / min and hold for 3 h. The obtained yellow solid is ground into powder and denoted as g-C3N4.

[0070] Step 2: Mix 1 g of V2AlC with 20 mL of 49 wt% HF, stir at room temperature for 24 h, then stir the solution at 40 °C for 24 h, and then add 20 mL of 25 wt% TMAOH solution and continue to stir for 24 h. The stirred suspension is centrifuged multiple times with ethanol and deionized water at 6000 rpm until the pH reaches 7, and dried in a freeze dryer for 24 h to obtain V2C MXene.

[0071] Step 3: Add 400 mg of g-C3N4 into 50 mL of deionized water and sonicate for 10 min, then add 40 mg of V2C MXene into g-C3N4 and sonicate together for 30 min. Finally, stir magnetically for 3 h to obtain a uniformly dispersed mixed solution, which is dried in a freeze dryer for 24 h to obtain the g-C3N4@V2C MXene photocatalyst composite.

[0072] Example 3

[0073] Step 1: Add 20 g of urea powder into an alumina crucible and heat it in a muffle furnace at a heating rate of 2.5 °C / min to 550 °C and hold for 3 h. The obtained yellow solid is ground into powder and denoted as g-C3N4.

[0074] Step 2: Mix 1 g of V2AlC with 20 mL of 49 wt% HF, stir at room temperature for 24 h, then stir the solution at 50 °C for 24 h, and then add 20 mL of 25 wt% TMAOH solution and continue to stir for 24 h. The stirred suspension is centrifuged multiple times with ethanol and deionized water at 7000 rpm until the pH reaches 6, and dried in a freeze dryer for 24 h to obtain V2C MXene.

[0075] Step 3: Add 100 mg of g-C3N4 into 50 mL of deionized water and ultrasonicate for 10 min, then add 10 mg of V2C MXene into g-C3N4 and ultrasonicate together for 30 min, and finally stir magnetically for 3 h to obtain a uniformly dispersed mixed solution, which is dried in a freeze dryer for 48 h to obtain the g-C3N4@V2C MXene photocatalyst composite.

[0076] Example 4

[0077] Step 1: Add 20 g of urea powder into an alumina crucible and heat it in a muffle furnace at a heating rate of 2.5 °C / min to 550 °C and hold for 3 h. The obtained yellow solid is ground into powder and denoted as g-C3N4.

[0078] Step 2: Mix 1 g of V2AlC with 20 mL of 49 wt% HF, stir at room temperature for 24 h, then stir the solution at 50 °C for 24 h, and then add 20 mL of 5 wt% TMAOH solution and continue to stir for 24 h. The stirred suspension is centrifuged multiple times with ethanol and deionized water at 7000 rpm until the pH reaches 6, and dried in a freeze dryer for 24 h to obtain V2C MXene.

[0079] Step 3: Add 100 mg of g-C3N4 into 50 mL of deionized water and ultrasonicate for 10 min, then add 10 mg of V2C MXene into g-C3N4 and ultrasonicate together for 30 min, and finally stir magnetically for 3 h to obtain a uniformly dispersed mixed solution, which is dried in a freeze dryer for 48 h to obtain the g-C3N4@V2C MXene photocatalyst composite.

[0080] It can be seen that adding TMAOH solutions with different concentrations can also obtain V2C MXene with good morphology.

[0081] Comparative Example 1

[0082] Step 1: Add 50 g of urea powder into an alumina crucible, heat it in a muffle furnace at a heating rate of 5 °C / min to 550 °C and hold for 3 h. The obtained yellow solid is ground into powder and denoted as g-C3N4.

[0083] Step 2: Mix 2 g of V2AlC with 40 mL of 49 wt% HF, stir at room temperature for 24 h, then stir the solution at 50 °C for 24 h, and then add 40 mL of 25 wt% TMAOH solution and continue to stir for 24 h. The stirred suspension is centrifuged multiple times with ethanol and deionized water at 8000 rpm until the pH reaches 7, and dried in a freeze dryer for 24 h to obtain V2C MXene.

[0084] Step 3: Add 200 mg of g-C3N4 into 50 mL of deionized water and ultrasonicate for 10 min, then add 20 mg of V2C MXene into g-C3N4 and ultrasonicate together for 30 min. Finally, stir magnetically for 3 h to obtain a uniformly dispersed mixed solution, which is dried in a freeze dryer for 24 h to obtain the g-C3N4@V2C MXene photocatalyst composite material.

[0085] Comparative Example 2

[0086] Step 1: Add 50 g of urea powder into an alumina crucible, heat it in a muffle furnace at a heating rate of 5 °C / min to 550 °C and hold for 2 h, then hold at 500 °C for 2 h. The obtained yellow solid is ground into powder and denoted as g-C3N4.

[0087] Step 2: Mix 2 g of V2AlC with 40 mL of 49 wt% HF, stir at room temperature for 24 h, then stir the solution at 50 °C for 24 h, and then add 40 mL of 25 wt% TMAOH solution and continue to stir for 24 h. The stirred suspension is centrifuged multiple times with ethanol and deionized water at 8000 rpm until the pH reaches 7, and dried in a freeze dryer for 24 h to obtain V2C MXene.

[0088] Step 3: Add 200 mg of g-C3N4 into 50 mL of deionized water and ultrasonicate for 10 min, then add 20 mg of V2C MXene into g-C3N4 and ultrasonicate together for 30 min. Finally, stir magnetically for 3 h to obtain a uniformly dispersed mixed solution, which is dried in a freeze dryer for 24 h to obtain the g-C3N4@V2C MXene photocatalyst composite material.

[0089] Comparative Example 3

[0090] Step 1: Add 50 g of urea powder into an alumina crucible, heat it in a muffle furnace at a heating rate of 2.5 °C / min to 550 °C and hold for 2 h, then hold at 500 °C for 2 h. The obtained yellow solid is ground into powder and denoted as g-C3N4.

[0091] Step 2: Mix 2 g of V2AlC with 40 mL of 49 wt% HF, stir at room temperature for 24 h, and then stir the solution at 50 °C for 24 h. The stirred suspension is centrifuged multiple times with ethanol and deionized water at 8000 rpm until the pH reaches 7, and dried in a freeze-drying oven for 24 h to obtain V2C MXene.

[0092] Step 3: Add 200 mg of g-C3N4 into 50 mL of deionized water and ultrasonicate for 10 min, then add 20 mg of V2C MXene into g-C3N4 and ultrasonicate together for 30 min. Finally, stir magnetically for 3 h to obtain a uniformly dispersed mixed solution, which is dried in a freeze-drying oven for 24 h to obtain the g-C3N4@V2C MXene photocatalyst composite.

[0093] Figure 2 XRD pattern of the g-C3N4@V2C MXene photocatalyst composite obtained in Example 1. It can be seen from Figure 2 that the obtained g-C3N4@V2C MXene photocatalyst composite has a good crystal form. Both g-C3N4 and the g-C3N4@V2C MXene photocatalyst composite have two strong peaks at 13.1° (100) and 27.3° (002), and the (010) crystal plane of V2C exists in the XRD of g-C3N4@V2C MXenes.

[0094] Figure 3 Morphology and element distribution of the g-C3N4@V2C MXene photocatalyst composite obtained in Example 1. It can be seen from Figure 3 that the layered structure of g-C3N4@V2C MXene has no obvious change, indicating that the introduction of V2C MXene does not affect the basic structure of g-C3N4. The element distributions of C, N, and V in the g-C3N4@V2C MXene composite are very uniform.

[0095] Figure 4 SEM image of V2C MXene obtained in Step 2 of Example 4. It can be seen from Figure 4 that the Al layer of V2AlC is basically etched away, and the accordion-like morphology of V2C is more obvious.

[0096] Figure 5 SEM image of V2C MXene obtained in Step 2 of Example 4. It can be seen from Figure 4It can be seen that the accordion morphology of V2C is very obvious.

[0097] Figure 6 SEM images of the g-C3N4@V2C MXene photocatalyst composite obtained in Example 4 at different magnifications. Figure 6 It can be seen that the morphologies of the g-C3N4@V2C MXene photocatalyst composite at different magnifications are consistent. It is a 2D material composed of flat lamellar nanosheets. There is an obvious wrinkled agglomerated lamellar structure in the composite, which is a typical morphology of g-C3N4. Under the action of intense ultrasonic and stirring, the large accordion sheet structure of V2C becomes smaller sheet structures and is uniformly distributed on the surface of g-C3N4 or between the lamellae of g-C3N4. The contact between g-C3N4 and V2C in the figure is very close, and the closely contacted 2D / 2D nanosheet structure helps to improve the photocatalytic rate.

[0098] Figure 7 TEM spectrum of the g-C3N4@V2C MXene photocatalyst composite obtained in Example 4. Figure 7 The crystal plane spacings of the two different materials can be clearly observed. Moreover, it can be observed that V2C nanosheets are attached to the edges of g-C3N4, and the crystal plane spacing (d = 0.15 nm), corresponding to the (011) crystal plane of V2C.

[0099] Figure 8 XPS spectrum of the g-C3N4@V2C MXene photocatalyst composite obtained in Example 4. Figure 8 It can be seen that C1s, N1s, V2p, and O1s exist in the g-C3N4@V2C MXene composite. For the C1s peak, there are two peaks located at 288.3 eV and 284.8 eV respectively. For the N1s peak, there are two peaks located at 401.3 eV and 398.8 eV. For the V2p peak, there is one peak located at 516.3 eV. For the O1s peak, there is one peak located at 532.5 eV.

[0100] Figure 9 Photoluminescence spectrum of the g-C3N4@V2C MXene photocatalyst composite obtained in Example 2. Figure 9 It can be seen that under the same 350 nm excitation light, there is a broad emission peak located at 470 nm. However, the peak intensity of the g-C3N4@V2C MXene photocatalyst is lower, indicating that the recombination rate of electron-hole pairs becomes lower and there are more photo-generated carriers, which helps to improve the photocatalytic efficiency.

[0101] Under visible light, the g-C3N4@V2C MXene photocatalyst composite prepared in Example 4 and the g-C3N4 prepared in Step 1 of Example 3 were respectively placed in a methyl orange solution with a concentration of 10 mg / L. The dosages of both the g-C3N4@V2C MXene photocatalyst composite and g-C3N4 were 1 mg / mL. The change in the concentration of the target dye was detected using a UV-visible spectrophotometer (UV-vis). The results are as Figure 10 shown. From Figure 10 it can be seen that the catalytic efficiency was as high as 99.3% after 120 min, while the catalytic efficiency of g-C3N4 after 120 min was only 60.4%.

[0102] Figure 11 It is the photocatalytic degradation efficiency diagram of the g-C3N4@V2C MXene photocatalyst composites obtained in Example 4, Comparative Example 1, and Comparative Example 2. From Figure 11 it can be seen that g-C3N4 at different firing temperatures will affect the final degradation performance of the composite material. The composite material obtained by combining g-C3N4 and V2C with a heating rate of 2.5 °C / min, a heating time of 3 h, and a heating holding temperature of 550 °C has the best photocatalytic degradation performance, which is 99.3%. Followed by g-C3N4 with a heating rate of 5 °C / min, a heating time of 3 h, and a heating holding temperature of 550 °C. Finally, it is g-C3N4 with a heating rate of 5 °C / min, a heating time of 2 h, and a heating holding temperature of 550 °C, and a heating time of 2 h, and a heating holding temperature of 550 °C.

[0103] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A V2C MXene photocatalyst composite material, characterized in that, It includes g-C3N4 with a lamellar structure and V2CMXene with a lamellar structure, and the V2CMXene is dispersed on the surface of the lamellae of the g-C3N4; The preparation method of the V2CMXene photocatalyst composite material includes the following steps: Mix V2AlC and an HF solution and carry out an etching reaction to obtain a V2C dispersion; Mix the V2C dispersion and tetramethylammonium hydroxide and carry out an intercalation reaction to obtain V2CMXene; Mix the V2CMXene, g-C3N4 and water and carry out a composite reaction to obtain the V2CMXene photocatalyst composite material.

2. The preparation method of the V2CMXene photocatalyst composite material according to claim 1, characterized in that, It includes the following steps: Mix V2AlC and an HF solution and carry out an etching reaction to obtain a V2C dispersion; Mix the V2C dispersion and tetramethylammonium hydroxide and carry out an intercalation reaction to obtain V2CMXene; Mix the V2CMXene, g-C3N4 and water and carry out a composite reaction to obtain the V2CMXene photocatalyst composite material.

3. The preparation method according to claim 2, characterized in that, The temperature for mixing the V2AlC and the HF solution is room temperature, and the time is 24 - 30 h. The mixing of the V2AlC and the HF solution is carried out under stirring; the temperature of the etching reaction is 40 - 55 °C, and the time is 24 - 48 h. The etching reaction is carried out under stirring.

4. The preparation method according to claim 2, characterized in that, The temperature of the intercalation reaction is 45 - 55 °C, and the time is 24 - 48 h. The intercalation reaction is carried out under stirring.

5. The preparation method according to claim 2, characterized in that, The concentration of the HF solution is ≥49 wt%, the tetramethylammonium hydroxide is used in the form of a tetramethylammonium hydroxide solution, and the mass fraction of the tetramethylammonium hydroxide solution is 5% - 25%; the dosage ratio of the V2AlC, the HF solution and the tetramethylammonium hydroxide solution is 1 g : 20 mL : 20 mL.

6. The preparation method according to claim 2, wherein The preparation method of the g-C3N4 includes the following steps: Carry out a high-temperature reaction on urea to obtain the g-C3N4; the temperature of the high-temperature reaction is 545 - 555 °C, and the time is 3 h; the heating rate to the temperature of the high-temperature reaction is 2.5 °C / min.

7. The preparation method according to claim 2 or 6, characterized in that, The mass ratio of the g-C3N4 to the V2CMXene is 10:

1.

8. The preparation method according to claim 2, characterized in that, The time of the composite reaction is 2 - 4 h, and the composite reaction is carried out under stirring.

9. The preparation method according to claim 2, characterized in that, After the composite reaction, it also includes carrying out freeze-drying.

10. The application of the V2CMXene photocatalyst composite material described in claim 1 or the V2CMXene photocatalyst composite material obtained by the preparation method described in any one of claims 2 - 9 in the photocatalytic degradation of organic dyes.

Images