A modified Ti3C2MXene composite g-C3N4 photocatalytic material, its preparation method and application

Abstract

This invention belongs to the field of semiconductor photocatalysis technology, specifically relating to a modified Ti3C2 MXene / g-C3N4 composite photocatalytic material, its preparation method, and its applications. The preparation method innovatively modifies the surface of Ti3C2 MXene with caffeic acid to form a caffeic acid-carbon-coated Ti3C2 MXene coating, which is then further composited with g-C3N4. A binary or ternary molten salt system is used to construct the fluid reaction environment, while molten salt ions are used to etch and morphology-control the composite g-C3N4, aiming to improve the photogenerated charge separation efficiency and thus optimize the photocatalytic hydrogen production performance of the semiconductor material.

Description

Technical Field

[0001] This invention relates to the field of semiconductor photocatalysis technology, specifically to a modified Ti3C2MXene composite g-C3N4 photocatalytic material, its preparation method, and its application. Background Technology

[0002] Semiconductor photocatalysis, as an artificial energy conversion technology that simulates natural photosynthesis, has shown broad application prospects in sustainable energy production and environmental pollution control in recent years. Among many photocatalytic materials, graphitic carbon nitride (g-C3N4) has become a research hotspot due to its suitable band structure, excellent stability, and environmentally friendly properties. However, g-C3N4 prepared by the traditional thermal polycondensation method has significant shortcomings: poor mass transfer during the solid-state reaction leads to excessive interlayer packing, incomplete condensation reaction results in low crystallinity, small specific surface area, and severe carrier recombination, all of which limit its catalytic performance.

[0003] As a novel two-dimensional nanomaterial, Ti3C2MXene, with its unique layered structure and excellent physicochemical properties, has shown broad application prospects in multiple research fields. This material is composed of transition metal carbonitride compounds, and its unique atomic arrangement endows it with excellent chemical stability and outstanding electrical conductivity. Notably, this layered structure is rich in redox active sites, and coupled with its unique photoelectric conversion capability, it can effectively promote the separation and transport of photogenerated charge carriers when combined with semiconductors, significantly improving interfacial charge transfer efficiency. In the field of photocatalysis, researchers have explored various strategies for combining Ti3C2MXene with g-C3N4-based materials, including heterojunction construction and elemental doping modifications. Due to its rich surface metal active sites, this material is very suitable for constructing Schottky heterojunctions. Furthermore, its tunable surface functional groups (-OH, -O, and -F) combined with its unique layered characteristics provide an ideal platform for loading g-C3N4, thereby further enhancing the hydrogen production performance of the composite catalyst. However, two-dimensional MXene is easily oxidized in air and water, affecting its conductivity and stability. Therefore, inhibiting the oxidation of MXene has become a key research focus and challenge. Summary of the Invention

[0004] The purpose of this invention is to address the problems of poor conductivity and slow carrier migration rate of existing g-C3N4 materials, and to provide a modified Ti3C2MXene composite g-C3N4 photocatalytic material, its preparation method, and its applications. To address these issues, this invention innovatively modifies the surface of Ti3C2MXene with caffeic acid to form a caffeic acid-carbon-coated Ti3C2MXene coating, which is then further composited with g-C3N4. A binary or ternary molten salt system is used to construct the fluid reaction environment, and molten salt ions are used to etch and morphology-control the composite g-C3N4, aiming to improve the photogenerated charge separation efficiency, thereby optimizing the photocatalytic hydrogen production performance of the semiconductor material.

[0005] This invention provides a method for preparing a modified Ti3C2MXene / g-C3N4 composite photocatalytic material, comprising the following steps: (1) Disperse Ti3C2MXene nanosheets in deionized water to prepare a dispersion with a concentration of 0.1-2 mg / mL. Add caffeic acid and mix. Under a protective atmosphere, add Tris-HCl solution with a concentration of 0.01-0.2 mol / L dropwise, stirring the reaction and controlling the dropwise addition time to 0.1-2 h. After the dropwise addition is completed, sonicate and stir for 10-60 min to obtain a caffeic acid@MXene mixture; wherein the mass of the caffeic acid is 5-80 wt% of the mass of Ti3C2MXene nanosheets. (2) Add g-C3N4 powder to the caffeic acid@MXene mixture obtained in step (1) at a mass-to-liquid ratio of 1:10-1:200 g / mL, continue ultrasonic stirring for 30-60 min, centrifuge, wash, and vacuum dry to obtain the composite precursor; (3) The composite precursor obtained in step (2) is mixed with binary molten salt or ternary molten salt at a mass ratio of 1:4-1:6, ground evenly, and heated to 450-600℃ at a heating rate of 5~10℃ / min under a protective atmosphere for 2-6 h. After natural cooling, it is soaked in hot water at 80~100℃, filtered, washed, and dried to obtain the modified Ti3C2MXene / g-C3N4 composite photocatalytic material.

[0006] Further, in step (1), the concentration of the dispersed Ti3C2MXene nanosheets is 0.1-0.5 mg / mL.

[0007] Further, in step (1), the mass of the acidic coffee is 20-50 wt% of the mass of the Ti3C2MXene nanosheets.

[0008] Further, in step (1), the concentration of the Tris-HCl solution is 0.05-0.15 mol / L and the dropping time is 0.5-1.5 h.

[0009] Further, in step (1), the pH of the Tris-HCl solution is 8.5, and the total amount added is 0.05-0.5 times the volume of the mixed solution.

[0010] Further, in step (2), the mass-to-liquid ratio of the g-C3N4 powder to the caffeic acid@MXene mixture is 1:100-1:200 g / mL.

[0011] Furthermore, in step (2), the washing process involves alternating between deionized water and anhydrous ethanol for 3-5 times.

[0012] Furthermore, in step (3), the binary molten salt is KCl-LiCl, and the mass ratio of KCl to LiCl is 2.75:2.25.

[0013] Furthermore, in step (3), the ternary molten salt is KCl-NaCl-LiCl, and the mass ratio of KCl:NaCl:LiCl is 44:51:5.

[0014] Furthermore, in step (3), the washing process involves alternating between deionized water and anhydrous ethanol for 3-5 times.

[0015] Furthermore, in step (3), the drying temperature is 60-90℃.

[0016] A second aspect of the present invention provides a modified Ti3C2MXene / g-C3N4 composite photocatalytic material prepared by the preparation method described in the present invention.

[0017] Furthermore, the composite photocatalytic material comprises a one-dimensional needle-like hierarchical structure, wherein the needle-like hierarchical structure is formed by g-C3N4 forming a heterojunction structure on the surface of caffeic acid carbon-coated Ti3C2MXene.

[0018] Furthermore, the needle-like units of the needle-like hierarchical structure have a diameter distribution of 1-50 nm and a length distribution of 0.1-1 μm.

[0019] Furthermore, the specific surface area of ​​the needle-like hierarchical structure is 70-150 m². 2 / g.

[0020] A third aspect of this invention provides the application of the modified Ti3C2MXene / g-C3N4 composite photocatalyst material described herein in the fields of sustainable energy production and environmental pollution control. The modified Ti3C2MXene / g-C3N4 composite photocatalyst material achieves a maximum hydrogen production rate of 19.36 mmol / h. -1 g -1 .

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: 1. In this invention, the hydrogen production rate at CMC / 5-ms is optimal, reaching 19.36 mmol / h. -1 g -1 The CMC / O-ms of Ti3C2MXene / g-C3N4 treated with molten salt without added caffeic acid (7.68 mmol h) was significantly higher than that of Ti3C2MXene / g-C3N4. -1 g -1 The concentration was increased by 2.52 times, and it was even higher than the original g-C3N4 (0.38 mmol h). -1 g -1 It has 50.95 times the catalytic activity.

[0022] 2. This invention systematically studies the effects of different types and contents of polyphenols in the molten salt system on the stability and conductivity of MXene and MXene composite g-C3N4; explores the modification rules of polyphenols on MXene and MXene composite g-C3N4 and the photocatalytic hydrogen production enhancement mechanism. Finally, through high-temperature molten salt (ms) treatment, a carbonized caffeic acid@Ti3C2MXene / g-C3N4 composite material with a needle-like hierarchical structure was obtained.

[0023] 3. In this invention, the needle-like structure of the modified Ti3C2MXene / g-C3N4 composite photocatalytic material not only significantly increases the specific surface area of ​​the material but also enhances its light absorption capacity; furthermore, this needle-like structure can form a local electric field to promote charge separation. In addition, the metal-like properties of caffeic acid@Ti3C2MXene and g-C3N4 form a heterojunction, further promoting the separation and transport of photogenerated carriers. This unique one-dimensional needle-like structure and the formation of the heterojunction effectively enhance the carrier separation efficiency and photocatalytic hydrogen production activity. Attached Figure Description

[0024] Figure 1 The diagram shown is a flowchart of the preparation process of the composite photocatalytic material in a preferred embodiment of the present invention. Figure 2 The XRD patterns of CMC / 5-ms and CMC / 0-ms prepared in Example 1 are shown. Figure 3 The image shown is a TEM image of CMC at 5-ms prepared in Example 1; Figure 4 The fluorescence spectra of the CMC / 0-ms and CTMC / 5-ms samples prepared in Example 1 are shown. Figure 5 The photocatalytic hydrogen production performance of the sample prepared in this invention with CMC / x-ms; Figure 6The stability of the CMC / 5-ms photocatalytic hydrogen production cycle of the sample prepared for this invention was tested. Figure 7 The image shown is a SEM image of MCS-13-ms prepared in Comparative Example 1. Figure 8 The image shown is a SEM image of DCS-1 prepared in Comparative Example 2. Figure 9 The image shown is a CN-ms SEM image of g-C3N4 prepared in Comparative Example 3 after molten salt etching. Detailed Implementation

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] According to a first aspect of the present invention, a method for preparing a modified Ti3C2MXene / g-C3N4 composite photocatalytic material is provided, comprising the following steps: (1) Disperse Ti3C2MXene nanosheets in deionized water to prepare a dispersion with a concentration of 0.1-2 mg / mL. Add caffeic acid and mix. Under a protective atmosphere, add Tris-HCl solution with a concentration of 0.01-0.2 mol / L dropwise, stirring the reaction and controlling the dropwise addition time to 0.1-2 h. After the dropwise addition is completed, sonicate and stir for 10-60 min to obtain a caffeic acid@MXene mixture; wherein the mass of the caffeic acid is 5-80 wt% of the mass of Ti3C2MXene nanosheets. (2) Add g-C3N4 powder to the caffeic acid@MXene mixture obtained in step (1) at a mass-to-liquid ratio of 1:10-1:200 g / mL, continue ultrasonic stirring for 30-60 min, centrifuge, wash, and vacuum dry to obtain the composite precursor; (3) The composite precursor obtained in step (2) is mixed with binary molten salt or ternary molten salt at a mass ratio of 1:4-1:6, ground evenly, and heated to 450-600℃ at a heating rate of 5~10℃ / min under a protective atmosphere for 2-6 h. After natural cooling, it is soaked in hot water at 80~100℃, filtered, washed, and dried to obtain the modified Ti3C2MXene / g-C3N4 composite photocatalytic material.

[0027] In this invention, in step (1), the protective atmosphere is a gas that does not affect the effect of this invention, and generally is not limited to nitrogen or argon.

[0028] In this invention, the stirring speed in step (1) can be selected from a wide range. The following example illustrates a stirring speed of 100-500 r / min.

[0029] In this invention, the conditions for the ultrasound in step (1) can be selected from a wide range. As illustrated below, the power of the ultrasound is 300-500 W and the frequency is 30-50 kHz.

[0030] In some embodiments, in step (1), the concentration of the dispersed Ti3C2MXene nanosheets is 0.1-0.5 mg / mL.

[0031] In some embodiments, in step (1), the mass of the acidic coffee is 20-50 wt% of the mass of the Ti3C2MXene nanosheets.

[0032] In some embodiments, in step (1), the concentration of the Tris-HCl solution is 0.05-0.15 mol / L and the dropping time is 0.5-1.5 h.

[0033] In some embodiments, in step (1), the pH of the Tris-HCl solution is 8.5 and the total amount added is 0.05-0.5 times the volume of the mixed solution.

[0034] In this invention, the stirring speed in step (2) can be selected from a wide range. The following example illustrates a stirring speed of 100-500 r / min.

[0035] In this invention, the centrifugation conditions in step (2) can be selected within a wide range. The following example illustrates a centrifugation speed of 3000-5000 r / min and a centrifugation time of 3-30 min.

[0036] In this invention, the conditions for vacuum drying in step (2) can be selected from a wide range. The following example illustrates that the vacuum drying conditions are 60-90°C for 4-12 hours.

[0037] In some embodiments, in step (2), the mass-to-liquid ratio of the g-C3N4 powder to the caffeic acid@MXene mixture is 1:100-1:200 g / mL.

[0038] In some embodiments, in step (2), the washing process involves alternating between deionized water and anhydrous ethanol for 3-5 times.

[0039] In this invention, in step (3), the protective atmosphere is a gas that does not affect the invention effect, and generally is not limited to nitrogen or argon.

[0040] In some embodiments, in step (3), the binary molten salt is KCl-LiCl, and the mass ratio of KCl to LiCl is 2.75:2.25.

[0041] In some embodiments, in step (3), the ternary molten salt is KCl-NaCl-LiCl, and the mass ratio of KCl:NaCl:LiCl is 44:51:5.

[0042] In some embodiments, in step (3), the washing process involves alternating between deionized water and anhydrous ethanol for 3-5 times.

[0043] In this invention, the drying conditions in step (3) can be selected from a wide range. The following example illustrates that the drying conditions are 60-90°C for 2-6 hours.

[0044] A second aspect of the present invention provides a modified Ti3C2MXene / g-C3N4 composite photocatalytic material prepared by the preparation method described in the present invention.

[0045] In this invention, caffeic acid is polymerized in situ on the surface of Ti3C2MXene to form a caffeic acid@MXene coating, thereby modifying the Ti3C2MXene surface. The caffeic acid@MXene is organically combined with the amino groups on the surface of g-C3N4 through hydrogen bonding via reduced phenolic hydroxyl groups. Simultaneously, a fluid environment created by molten salt is used to etch and regulate the morphology of g-C3N4 into a needle-like hierarchical structure. Molten salt ion etching of layered g-C3N4 forms a nanorod-like structure, while the modified two-dimensional MXene serves as a support carrier, guiding the directional growth of g-C3N4 nanorods. Due to the diffusion and convection of the high-temperature molten salt fluid, a needle-like structure with pointed ends is ultimately formed.

[0046] In some embodiments, the composite photocatalytic material comprises a one-dimensional needle-like hierarchical structure, wherein the needle-like hierarchical structure is a heterojunction structure formed by g-C3N4 on the surface of caffeic acid carbon-coated Ti3C2MXene.

[0047] In some embodiments, the needle-like units of the needle-like hierarchical structure have a diameter distribution of 1-50 nm and a length distribution of 0.1-1 μm.

[0048] In some embodiments, the specific surface area of ​​the needle-like hierarchical structure is 70-150 m². 2 / g.

[0049] A third aspect of this invention provides the application of the modified Ti3C2MXene / g-C3N4 composite photocatalyst material described herein in the fields of sustainable energy production and environmental pollution control. The modified Ti3C2MXene / g-C3N4 composite photocatalyst material achieves a maximum hydrogen production rate of 19.36 mmol / h.-1 g -1 .

[0050] In this invention, the photocatalytic hydrogen production activity of the composite photocatalytic material is increased by more than 5000% compared with that of pure g-C3N4.

[0051] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Unless otherwise specified, the raw materials used in the following examples are all publicly available in the prior art, such as those that can be directly purchased or prepared according to publicly available preparation methods. Melamine, tannic acid, dopamine, caffeic acid, potassium chloride, lithium chloride, etc., in the examples were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; triethanolamine and chloroplatinic acid, etc., were all purchased from Sinopharm Chemical Reagent Co., Ltd.

[0053] Preparation of g-C3N4 A certain amount of melamine (MA) was placed in a crucible, covered, and placed in a muffle furnace (under nitrogen atmosphere). The temperature was increased to 550 °C at a rate of 10 °C per minute, and the mixture was thermally polycondensed for 2 hours. After natural cooling to room temperature, a light yellow blocky product was obtained. The product was then ground into powder to obtain g-C3N4.

[0054] Example 1 The specific preparation process for CMC / x-ms is as follows: Figure 1 As shown: 1. Preparation of caffeic acid@MXene mixture: Take 13 mg Ti3C2MXene powder, disperse it in 70 mL deionized water, add x mg of caffeic acid (CA) (x = 1, 3, 5, 10), place it in a 200 mL sealed container, and purge the container with nitrogen gas to remove all air. Stir for 1 h, and simultaneously add 10 mL of a solution with pH 8.5 and a concentration of 0.1 mol / L dropwise. -1 Add the Tris-HCl solution to the above mixed suspension and control the addition time to 60 min; purge with nitrogen again and sonicate the mixture continuously in a sealed container (power 300 W, frequency 40 kHz) for 30 min; to obtain caffeic acid@MXene.

[0055] 2. Preparation of composite photocatalytic materials: 0.45 g g-C3N4 powder was added to the above caffeic acid@MXene mixture, and the mixture was ultrasonicated and stirred for 1 h. After centrifugation, washing, and vacuum drying (60℃, 12 h), the results were recorded as CMC (1, 3, 5, 10 mg). 3. Morphology Control: CMC powder was mixed with 2.75 times its mass of KCl and 2.25 times its mass of LiCl, and rapidly ground until homogeneous. The mixture was then transferred to a crucible and heated to 500 °C for 4 h in a tube furnace under a nitrogen atmosphere at a heating rate of 10 °C / min. After the tube furnace temperature cooled to room temperature, the sample was soaked in hot water at 80–100 °C for 6 h, filtered, washed, and dried at 80 °C. The resulting sample was named CMC / x-ms, where x = (1, 3, 5, 10 mg), CM represents caffeic acid-coated Ti3C2MXene, C represents g-C3N4, and ms indicates that the catalyst was treated with molten salt (KCl-LiCl).

[0056] Example 2 1. Preparation of tannic acid@MXene mixture: Take 13 mg Ti3C2MXene powder, disperse it in 70 mL deionized water, add x mg of tannic acid (TA) (1, 3, 5, 10), place it in a 200 mL sealed container, and purge the container with nitrogen gas to remove all air. Stir for 1 h, and simultaneously add 10 mL of 0.1 mol / L tannic acid solution with pH 8.5 dropwise. -1 Add the Tris-HCl solution to the above mixed suspension and control the addition time to 60 min; purge with nitrogen again and sonicate the mixture continuously in a sealed container (power 300 W, frequency 40 kHz) for 30 min; to obtain tannic acid@MXene.

[0057] 2. Preparation of composite photocatalytic materials: 0.45 g g-C3N4 powder was added to the above tannic acid@MXene mixture, and the mixture was sonicated and stirred for 1 h. After centrifugation, washing, and vacuum drying (60℃, 12 h), the results were recorded as TMC (1, 3, 5, 10 mg). 3. Morphology control: TMC powder was mixed with 2.75 times its mass of KCl and 2.25 times its mass of LiCl, and rapidly ground until homogeneous. The mixture was then transferred to a crucible and held at 500 °C for 4 h in a tube furnace under a nitrogen atmosphere. After the tube furnace temperature cooled to room temperature, the mixture was soaked in hot water at 80-100 °C for 6 h, filtered, washed, and dried at 80 °C. The resulting sample was named TMC / x-ms, where x = (1, 3, 5, 10 mg), TM represents tannic acid-coated Ti3C2MXene, C represents g-C3N4, and ms indicates that the catalyst was treated with molten salt (KCl-LiCl).

[0058] Example 3 1. Preparation of polydopamine@MXene mixture: Take 13 mg Ti3C2MXene powder, disperse it in 70 mL deionized water, add x mg of dopamine (DA) (x = 1, 3, 5, 10), place it in a 200 mL sealed container, and purge the container with nitrogen gas to remove all air. Stir for 1 h, and simultaneously add 10 mL of a solution with pH 8.5 and a concentration of 0.1 mol / L dropwise. -1 Add the Tris-HCl solution to the above mixed suspension and control the addition time to 30 min; purge with nitrogen again and sonicate the mixture continuously in a sealed container (power 300 W, frequency 40 kHz) for 30 min; to obtain polydopamine@MXene.

[0059] 2. Preparation of composite photocatalytic materials: 0.45 g g-C3N4 powder was added to the above polydopamine@MXene mixture, and the mixture was ultrasonicated and stirred for 1 h. After centrifugation, washing, and vacuum drying (60℃, 12 h), the mixture was labeled as DMC (1, 3, 5, 10 mg). 3. Morphology control: DMC powder was mixed with 2.75 times its mass of KCl and 2.25 times its mass of LiCl, and rapidly ground until homogeneous. The mixture was then transferred to a crucible and held at 500℃ for 4 h in a tube furnace under a nitrogen atmosphere. After the tube furnace temperature cooled to room temperature, the mixture was soaked in hot water at 80~100℃ for 6 h, filtered, washed, and dried at 80℃. The resulting sample was named DMC / x-ms, where x = (1, 3, 5, 10 mg), DM represents polydopamine-coated Ti3C2MXene, C represents g-C3N4, and ms indicates that the catalyst was treated with molten salt (KCl-LiCl).

[0060] Photocatalytic water splitting hydrogen production performance test The photocatalytic hydrogen production performance of this invention was tested in accordance with GB / T 26915-2011 "Test Method for Water Splitting Performance of Photocatalytic Materials". A 300W xenon lamp equipped with an AM1.5G filter was used as a simulated solar light source, and the light power density at the reactor's light-receiving window was calibrated to 100 mW / cm². 2 The reaction was carried out in a closed quartz photoreactor with a circulating water-cooled jacket, and the reaction temperature was controlled at (25±1)℃ by a low-temperature constant temperature circulating water bath.

[0061] Accurately weigh 50 mg of the photocatalyst to be tested and add it to a reactor containing 100 mL of 10 vol% triethanolamine aqueous solution. Sonicate for 5 min to ensure uniform dispersion of the catalyst. After sealing, connect to a vacuum reaction system. Vacuum the system and then purge it with high-purity argon three times to completely remove dissolved oxygen and air. After confirming that the system is airtight, turn on magnetic stirring and let it stand in the dark for 30 min. After verifying that there is no background hydrogen production, start the photocatalytic reaction. Use a gas chromatograph with a 5A molecular sieve column equipped with a thermal conductivity detector (TCD) and high-purity argon as the carrier gas to quantitatively detect hydrogen in the system at 30-minute intervals. The amount of hydrogen generated is calibrated by the external standard method, and the hydrogen production rate per unit time and per unit mass of catalyst is calculated.

[0062] The hydrogen production performance of pure g-C3N4 is 0.38 mmol / h. -1 g -1 .

[0063] The test results of the materials described in Examples 1-3 are shown in Tables 1-3: Table 1 Table 2 Table 3 analyze 1. In this invention, the hydrogen production rate at CMC / 5-ms is optimal, reaching 19.36 mmol / h. -1 g -1 The CMC / 0-ms of Ti3C2MXene / g-C3N4 treated with molten salt without added caffeic acid was 7.68 mmol / L. -1 g -1 The increase was 2.52 times, which is higher than the CN-ms (2.64 mmol h) of g-C3N4 treated with molten salt. -1 g -1 It is 7.33 times that of the original g-C3N4 (0.38 mmol h). -1 g -1 It has 50.95 times the catalytic activity.

[0064] 2. In the experiment using tannic acid, the hydrogen production rate of TMC / 5-ms was optimal, reaching 14.75 mmol / h. -1 g -1 Compared to Ti3C2MXene / g-C3N4 without added tannins, the TMC / O-ms (7.68 mmol h) -1 g -1The improvement was nearly 2 times, which is higher than the CN-ms (2.64 mmol h) of g-C3N4 treated with molten salt. -1 g -1 It is 5.58 times that of the original g-C3N4 (0.38 mmol h). -1 g -1 It has 38.8 times the catalytic activity.

[0065] 3. In the experiment using dopamine, the hydrogen production rate of DMC / 3-ms was optimal, reaching 11.52 mmol / h. -1 g -1 Compared to Ti3C2MXene / g-C3N4 without dopamine, DMC / O-ms (7.68 mmol h) -1 g -1 This represents a 1.5-fold increase, and is 4.36 times that of molten salt-treated g-C3N4 (2.64 mmol h⁻¹ g⁻¹); it is also significantly higher than that of the original g-C3N4 (0.38 mmol h⁻¹ g⁻¹). -1 g -1 It has 30.3 times the catalytic activity.

[0066] Comparative Example 1 (The uncoated Ti3C2MXene / g-C3N4 after molten salt etching is designated as MCS-x-ms) x mg of Ti3C2MXene (x = 0, 8, 13, 18, 23) was ultrasonically dispersed for 2 h, then 0.45 g of C3N4 was added and stirred for 4 h. After washing with deionized water, the mixture was dried in an oven at 60 ℃. KCl and LiCl (KCl mass = 2.75 times the mixed powder mass, LiCl mass = 2.25 times the mixed powder mass) were added to the Ti3C2MXene and g-C3N4 mixture and rapidly and uniformly ground. The uniformly ground powder was transferred to a 25 ml ceramic crucible and kept at 550 ℃ under N2 protection for 2 h. After the tube furnace temperature cooled to room temperature, the mixture was soaked in deionized water for 6 h, filtered, washed, and dried at 80 ℃. The samples were named MCS-x-ms (x = 0, 8, 13, 18, 23), where M represents Ti3C2MXene, C represents g-C3N4, x represents the mass of Ti3C2MXene, and ms represents molten salt (KCl-LiCl).

[0067] Effect: Appearance is as follows Figure 7 The image shows a mushroom-like structure.

[0068] Among them, MCS-13-ms (i.e., the comparative samples CMC / 0-ms, TMC / 0-ms, and DMC / 0-ms in Examples 1, 2, and 3 above) showed the best hydrogen production performance, reaching 7.68 mmol h⁻¹.-1 g -1 .

[0069] Comparative Example 2 (The dopamine-coated g-C3N4, after being etched by molten salt, is designated as DCS-x) 0.2 g of g-C3N4 powder was weighed and dispersed with different masses (0.5, 1, 2, 4 mg) of dopamine hydrochloride (DA) in 70 mL of ultrapure water. The dispersion was ultrasonically assisted for 10 min to obtain a homogeneous suspension. Subsequently, 10 mL of 0.1 M Tris-HCl buffer solution (pH 8.5) was slowly injected using a microsyringe. Total reaction times of 15, 30, 60, 90, and 120 min were achieved by adjusting the injection rate, with continuous mechanical stirring throughout the process. After the reaction was complete, the product was collected by vacuum filtration and washed with ultrapure water until the filtrate was neutral. Finally, it was dried in a vacuum oven at 60 °C for 12 h. The dried product (0.2 g) was rapidly ground uniformly with KCl (mass ratio 1:2.75) and LiCl (mass ratio 1:2.25) in an agate mortar and transferred to a 25 mL ceramic crucible. The temperature was increased to 550℃ (N2 atmosphere) in a tube furnace at a heating rate of 10 ℃ / min, and calcined at this temperature for 2 h. After the temperature in the tube furnace cooled to room temperature, the sample was soaked in deionized water for 6 h, filtered and washed, and dried at 80℃. The obtained sample was named DCS-x (x=0, 0.5, 1, 2, 4, corresponding to the number of milligrams of DA added).

[0070] Effect: Appearance is as follows Figure 8 The three-dimensional flower cluster structure shown.

[0071] Among them, the DCS-1 with DA addition of 1 mg and Tris-HCl buffer solution (pH 8.5) added over a dropping time of 30 min showed the best hydrogen production performance, reaching 8.14 mmol / h. -1 g -1 .

[0072] Comparative Example 3 (Comparison sample between the two treatment methods: g-C3N4 randomly etched with molten salt) Add 2.75 times the mass of KCl and 2.25 times the mass of LiCl to g-C3N4 powder and grind rapidly and uniformly. Transfer the uniformly ground powder to a 25 ml ceramic crucible and heat at 450-550 ℃ under N2 protection for 1-4 h. After the tube furnace temperature drops to room temperature, soak in deionized water for 6 h, filter and wash, and dry at 80 ℃. The sample is named CN-ms, where ms represents molten salt (KCl-LiCl).

[0073] Effect: Appearance is Figure 9The stacked rod-shaped structure shown.

[0074] The optimal hydrogen production performance was observed at 550℃ under N2 protection for 2 hours, reaching 2.64 mmol / h. -1 g -1 .

[0075] Results and Discussion Figure 2 Characteristic peaks of CMC / 5-ms and CMC / 0-ms can be observed. The two peaks at 13.01° and 27.01° belong to the (100) in-plane peak and the (002) π-π interlayer stacking peak, respectively, proving that after molten salt treatment, both CMC / 5-ms and CMC / 0-ms maintain the basic structural unit of g-C3N4.

[0076] Figure 3 As can be seen, under molten salt etching, CMC / 5-ms exhibits a needle-like hierarchical structure, indicating that the presence of polyphenol-coated Ti3C2MXene nanosheets guides the formation of needle-like structures in g-C3N4 nanorods during molten salt treatment, with g-C3N4 nanoneedles growing on polyphenol-coated Ti3C2MXene nanosheets. The one-dimensional needle-like structure significantly increases the contact area between g-C3N4 and MXene, providing a directional transport path for electron-hole pairs, which is beneficial for interfacial charge transfer. The needle tips and edges typically possess higher chemical activity, which is beneficial for catalytic or adsorption reactions. Furthermore, the grown needles can act as "spacers," preventing the MXene nanosheets from re-stacking during drying or forming, thus maintaining their high specific surface area.

[0077] like Figure 4 As shown in the fluorescence spectrum, the fluorescence intensity of CMC / 5-ms modified with Ti3C2MXene was significantly lower than that of unmodified CMC / 0-ms. This fully confirms that the addition of caffeic acid@Ti3C2MXene can effectively promote charge separation.

[0078] like Figure 5 As shown, compared to the catalyst without caffeic acid@Ti3C2MXene, the hydrogen evolution performance of CMC / 5-ms is significantly improved, with the best sample exhibiting a hydrogen evolution activity of 19.36 mmol / h. -1 g -1 The activity was 2.52 times that of CMC / 0-ms and 50.95 times that of the catalyst g-C3N4 obtained by one-step thermal polymerization. However, when the amount of caffeic acid added was x=10, the hydrogen production activity began to decrease, possibly because the amount of caffeic acid@MXene added was too large, which covered the reactive sites of the catalyst.

[0079] Figure 6The photocatalytic hydrogen production cycle stability of CMC / 5-ms modified with caffeic acid@Ti3C2MXene was tested. After 4 cycles, the photocatalytic hydrogen production performance of CMC / 5-ms did not decrease significantly, which confirmed its good catalytic stability.

[0080] The embodiments of this application have been described above with reference to the accompanying drawings. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the core ideas of this application. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a modified Ti3C2 MXene / g-C3N4 composite photocatalytic material, characterized in that, Includes the following steps: (1) Disperse Ti3C2 MXene nanosheets in deionized water to prepare a dispersion with a concentration of 0.1-2 mg / mL. Add caffeic acid and mix. Under a protective atmosphere, add Tris-HCl solution with a concentration of 0.01-0.2 mol / L dropwise, stirring the reaction and controlling the dropwise addition time to 0.1-2 h. After the dropwise addition is completed, sonicate and stir for 10-60 min to obtain a caffeic acid@MXene mixture; wherein the mass of the caffeic acid is 5-80 wt% of the mass of Ti3C2 MXene nanosheets. (2) Add g-C3N4 powder to the caffeic acid@MXene mixture obtained in step (1) at a mass-to-liquid ratio of 1:10-1:200 g / mL, continue ultrasonic stirring for 30-90 min, centrifuge, wash, and vacuum dry to obtain the composite precursor; (3) The composite precursor obtained in step (2) is mixed with binary molten salt or ternary molten salt at a mass ratio of 1:4-1:6, ground evenly, and heated to 450-600℃ at a heating rate of 5~10℃ / min under a protective atmosphere for 2-6 h. After natural cooling, it is soaked in hot water at 80~100℃, filtered, washed, and dried to obtain the modified Ti3C2 MXene / g-C3N4 composite photocatalytic material.

2. The preparation method according to claim 1, characterized in that, In step (1), The concentration of the dispersed Ti3C2 MXene nanosheets is 0.1-0.5 mg / mL; and / or The mass of the acidic coffee is 20-50 wt% of the mass of Ti3C2 MXene nanosheets.

3. The preparation method according to claim 1, characterized in that, In step (1), The concentration of the Tris-HCl solution is 0.05-0.15 mol / L, and the dropping time is 0.5-1.5 h; and / or The pH of the Tris-HCl solution is 8.5, and the total amount added is 0.05-0.5 times the volume of the mixed solution.

4. The preparation method according to claim 1, characterized in that, In step (2), The mass-to-liquid ratio of the g-C3N4 powder to the caffeic acid@MXene mixture is 1:100-1:200 g / mL; and / or The washing process involves alternating between deionized water and anhydrous ethanol for 3-5 washes.

5. The preparation method according to claim 1, characterized in that, In step (3), The binary molten salt is KCl-LiCl, with a KCl to LiCl mass ratio of 2.75:2.25; and / or The ternary molten salt is KCl-NaCl-LiCl, with a mass ratio of KCl:NaCl:LiCl of 44:51:

5.

6. The preparation method according to claim 1, characterized in that, In step (3), The washing process involves alternating between deionized water and anhydrous ethanol for 3-5 cycles; and / or The drying temperature is 60-90℃.

7. A modified Ti3C2MXene / g-C3N4 composite photocatalytic material, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. The composite photocatalytic material according to claim 7, characterized in that, The composite photocatalytic material comprises a one-dimensional needle-like hierarchical structure, wherein the needle-like hierarchical structure is formed by g-C3N4 on the surface of Ti3C2 MXene coated with caffeic acid carbon to form a heterojunction structure.

9. The composite photocatalytic material according to claim 8, characterized in that, The needle-like hierarchical structure has needle-like units with a diameter distribution of 1-50 nm and a length distribution of 0.1-1 μm; and / or The specific surface area of ​​the needle-like hierarchical structure is 70-150 m². 2 / g.

10. The application of the modified Ti3C2MXene / g-C3N4 composite photocatalyst material according to any one of claims 7-9 in the fields of sustainable energy production and environmental pollution control, characterized in that, The modified Ti3C2MXene / g-C3N4 composite photocatalyst material achieved a maximum hydrogen production rate of 19.36 mmol / h. -1 g -1 .

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