A method for preparing a two-dimensional material few-layer

Abstract

The application belongs to the field of two-dimensional few-layer nanomaterial preparation and photocatalysis technology, and particularly relates to a preparation method of Bi2Ti2O7 / MXene two-dimensional composite few-layer material and application of the material in photocatalytic reduction of p-nitrophenol to p-aminophenol. The preparation method uses bismuth salt and titanium salt as raw materials, and polyhydric alcohol as a structure regulator. Bi2Ti2O7 two-dimensional few-layer material is prepared through hydrothermal reaction in an alkaline environment. Then, the surface of Bi2Ti2O7 is positively charged through surface protonation treatment, and the Bi2Ti2O7 is combined with MXene suspension through electrostatic interaction to construct two-dimensional composite few-layer material. The composite material has close interface contact and excellent photogenerated carrier separation efficiency, and exhibits significantly better catalytic activity than traditional morphology materials and simple mixed materials in the reaction of photocatalytic reduction of p-nitrophenol to p-aminophenol.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional nanomaterial preparation and photocatalysis technology, specifically relating to a method for preparing few layers of two-dimensional materials. Background Technology

[0002] p-Nitrophenol (4-NP) is a common industrial pollutant widely used in the production of pesticides, pharmaceuticals, dyes, and other chemicals. It is characterized by high toxicity, poor biodegradability, and strong carcinogenicity. The selective photocatalytic reduction of p-nitrophenol to p-aminophenol (4-AP) is an important strategy for environmental remediation and the synthesis of fine chemicals.

[0003] Bi₂Ti₂O₇, a bismuth-based semiconductor with a pyrochlore structure, possesses a suitable bandgap width (approximately 2.8 eV) and good visible light response characteristics, with a conduction band position of approximately -0.35 V (vs. NHE), and theoretically has the ability to reduce 4-NP. However, Bi₂Ti₂O₇ obtained by conventional preparation methods suffers from severe particle morphology defects. (1) Three-dimensional bulk particles: Bi2Ti2O7 prepared by solid-state sintering or conventional hydrothermal method is mostly irregular bulk particles (size 500 nm-1 μm), with a specific surface area of ​​less than 20 m² / g and insufficient exposure of active sites; (2) Disordered nanocrystal aggregates: Ordinary hydrothermal methods easily form disordered stacked agglomerates of nanocrystals. The particles are in close contact but lack an ordered pore structure, resulting in high mass transfer resistance. (3) Long carrier transport path: Photogenerated carriers in bulk materials need to diffuse over a long distance (>100 nm) to reach the surface, while the carrier diffusion length of Bi2Ti2O7 is only about 10-50 nm, resulting in a large amount of electron-hole recombination in the bulk. (4) Poor interfacial contact: When combined with a co-catalyst, simple mechanical mixing can only form point contact, resulting in low interfacial charge transfer efficiency and easy phase separation.

[0004] MXenes are a class of emerging two-dimensional transition metal carbides / nitrides with surfaces rich in functional groups such as -O, -OH, and -F. They typically carry a weak negative charge in water and exhibit high conductivity, good hydrophilicity, and mechanical flexibility. Constructing two-dimensional / two-dimensional heterojunctions by compositing Bi₂Ti₂O₇ with MXene can effectively promote the separation of photogenerated carriers. However, current technologies lack effective methods for preparing few-layer Bi₂Ti₂O₇, and the compositing with MXene often involves simple physical mixing, making it difficult to form tight interfacial contacts. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a few-layer two-dimensional material. By using a polyol-assisted hydrothermal synthesis and electrostatic interaction composite strategy, this method solves the technical problems caused by the morphology of traditional Bi2Ti2O7 particles, such as low specific surface area, severe carrier recombination, and poor interfacial contact. The invention also provides the application of the above material in the photocatalytic reduction of p-nitrophenol.

[0006] The first aspect of this invention provides a method for preparing a few layers of a two-dimensional material, comprising the following steps: (1) Dissolve bismuth salt in an acidic solution, add polyol structure modifier, stir to dissolve, add titanium salt, and continue stirring to form a homogeneous solution; (2) Add an alkaline solution to the solution obtained in step (1) to adjust the pH value to alkaline, stir and transfer to a hydrothermal reactor, react at 150-220℃ for 12-24 hours, cool, wash and dry to obtain Bi2Ti2O7 two-dimensional few-layer material; (3) The Bi2Ti2O7 two-dimensional few-layer material obtained in step (2) is subjected to surface protonation treatment to make its surface positively charged, and then dispersed in a solvent to obtain a Bi2Ti2O7 suspension; (4) Prepare a few-layer MXene suspension by ultrasonic exfoliation of MXene material; (5) Under stirring conditions, the positively charged Bi2Ti2O7 suspension obtained in step (3) is mixed with the MXene suspension obtained in step (4), and composited by electrostatic interaction. After post-treatment, a two-dimensional composite few-layer material of Bi2Ti2O7 / MXene is obtained.

[0007] Furthermore, the polyol structure modifier mentioned in step (1) is one or more of mannitol, sorbitol or pentaerythritol; the bismuth salt is Bi(NO3)3·5H2O; the titanium salt is tetrabutyl titanate, titanium tetrachloride or titanium oxysulfate; the molar ratio of Bi to Ti is 1:1; and the molar ratio of the structure modifier to Bi is (0.5-2):1.

[0008] The surface protonation treatment in step (3) involves dispersing Bi₂Ti₂O₇ in a 0.1-1 mol / L dilute acid solution and treating it for 1-4 hours until its Zeta potential reaches +25 mV to +40 mV. MXene, due to its rich surface with -O, -OH, and -F functional groups and thus carrying a weak negative charge (Zeta potential of approximately -10 mV to -20 mV), can electrostatically attract protonated Bi₂Ti₂O₇ without additional potential adjustment.

[0009] The mass ratio of Bi2Ti2O7 to MXene in step (5) is (5:1)-(1:2).

[0010] More preferably, the polyol structure modifier in step (1) is mannitol; the acidic solution is 2 mol / L dilute nitric acid; the stirring speed is 500 rpm and the stirring time is 2 hours.

[0011] In step (2), the pH value is adjusted to 10; the hydrothermal reaction temperature is 180℃ and the reaction time is 18 hours.

[0012] The preferred mass ratio of Bi2Ti2O7 to MXene in step (5) is 2:1; the post-treatment also includes heat treatment at 300°C for 2 hours under an argon atmosphere to enhance the interfacial bonding strength.

[0013] The second aspect of the present invention provides the application of a two-dimensional few-layer material in the photocatalytic reduction of p-nitrophenol to p-aminophenol. The Bi2Ti2O7 / MXene two-dimensional composite few-layer material prepared by the above method is used as a photocatalyst to catalytically reduce an aqueous solution of p-nitrophenol under visible light irradiation.

[0014] Mechanism explanation and beneficial effects This invention improves photocatalytic performance through a dual strategy of "morphology regulation + interfacial electrostatic interaction," and its mechanism and beneficial effects are as follows: (1) Polyol-assisted few-layer formation mechanism - solving the defects of specific surface area and active sites Polyols (such as mannitol) are rich in hydroxyl groups, which can react with Bi³ + and Ti 4+ The formation of coordination complexes alters crystal growth kinetics. During the hydrothermal process, polyols selectively adsorb onto specific crystal planes of Bi₂Ti₂O₇, suppressing the vertical stacking of layered structures and inducing the formation of few-layer nanosheets with a thickness of 3-5 nm (lateral dimensions of 200-500 nm). This two-dimensional few-layer morphology increases the specific surface area from <20 m² / g of traditional bulk materials to >80 m² / g, and increases the exposure of active sites by 3-4 times; simultaneously, it shortens the carrier transport path to the nanoscale (<5 nm), significantly suppressing electron-hole recombination.

[0015] (2) Electrostatic interaction interface recombination mechanism - solving interface poor contact defects MXene's surface is inherently weakly negatively charged (Zeta potential approximately -10 mV to -20 mV) due to its abundance of -O / -OH / -F functional groups, requiring no additional potential adjustment. Through protonation treatment, the hydroxyl groups on the Bi₂Ti₂O₇ surface become positively charged (Zeta potential +25 to +40 mV), generating electrostatic attraction with MXene. This drives a close surface-to-surface bonding between the two two-dimensional materials, rather than the point contact of traditional mechanical mixing, forming a large-area two-dimensional / two-dimensional heterojunction. This tight interface reduces charge transfer resistance by more than 50%, allowing photogenerated electrons to migrate from Bi₂Ti₂O₇ to MXene in a short time, and then transfer to reactant molecules via MXene's highly conductive network.

[0016] (3) Band matching and synergistic effect mechanism - enhancing photocatalytic activity and selectivity The Bi₂Ti₂O₇ conduction band position is approximately -0.35 V (vs. NHE), and the MXene Fermi level is approximately -0.5 V (vs. NHE), forming a Type-II heterojunction. The conduction band position of the composite material satisfies the thermodynamic requirements for the reduction of 4-NP to 4-AP (E0). 0 = -0.76V), but not enough to drive the hydrogen evolution reaction (E 0 = -0.41 V), therefore the 4-AP selectivity is >98%. The introduction of MXene also enhances the adsorption capacity for 4-NP, increasing the adsorption capacity by more than 2 times.

[0017] (4) Structural stability mechanism – ensuring recyclability The interfacial interactions formed by electrostatic forces effectively prevent the active components from detaching during the reaction process. The flexible nature of the two-dimensional few-layer structure allows it to maintain structural integrity during catalytic cycling, with an activity retention rate of >90% after 5 cycles.

[0018] Summary of beneficial effects: The Bi2Ti2O7 / MXene two-dimensional composite few-layer material prepared by this invention has a 3-fold increase in specific surface area, a 2-3-fold increase in carrier separation efficiency, a 50% increase in interfacial charge transfer efficiency, and a more than 2-fold increase in conversion rate and selectivity >98% in the photocatalytic reduction of p-nitrophenol, and also has good cycle stability. Attached Figure Description

[0019] Figure 1 This is a transmission electron microscope (TEM) image of the Bi2Ti2O7 / MXene two-dimensional composite few-layer material prepared in Example 1 of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be described in detail below through specific embodiments.

[0021] Example 1 (1) Preparation of Bi2Ti2O7 two-dimensional few-layer material: 1 mmol Bi(NO3)3·5H2O was dissolved in 20 mL of 2 mol / L dilute nitric acid, 1 mmol mannitol was added as a structure regulator, and the mixture was stirred at 500 rpm for 30 minutes. Then 1 mmol tetrabutyl titanate was added dropwise, and the mixture was stirred for 2 hours to form a homogeneous solution. 2 mol / L NaOH solution was added dropwise to adjust the pH to 10. After stirring for 1 hour, the mixture was transferred to a 50 mL hydrothermal reactor and reacted at 180℃ for 18 hours. After natural cooling, the mixture was centrifuged (8000 rpm, 5 minutes), washed three times each with deionized water and ethanol, and dried under vacuum at 60℃ for 12 hours to obtain Bi2Ti2O7 two-dimensional few-layer material.

[0022] (2) Surface protonation treatment: Bi2Ti2O7 was dispersed in 0.5 mol / L dilute hydrochloric acid, stirred at room temperature for 2 hours, centrifuged and washed until neutral, and redispersed in deionized water to prepare a 2 mg / mL suspension with a Zeta potential of +32 mV.

[0023] (3) Preparation of MXene suspension: Ti3C2T was prepared by HF etching method. x MXene was ultrasonically exfoliated at 400 W for 2 hours to prepare a suspension with a concentration of 1 mg / mL (due to the surface functional groups, the Zeta potential is approximately -15 mV, requiring no additional adjustment).

[0024] (4) Electrostatic composite: 50 mL of protonated Bi2Ti2O7 suspension was added dropwise to 100 mL of MXene suspension (mass ratio 2:1) under stirring at 500 rpm. The mixture was stirred at room temperature for 4 hours, allowed to stand for 2 hours, centrifuged (6000 rpm, 8 minutes), washed, vacuum dried at 60℃ for 12 hours, and heat-treated at 300℃ for 2 hours under argon atmosphere to obtain Bi2Ti2O7 / MXene two-dimensional composite few-layer material.

[0025] Transmission electron microscopy (TEM) characterization showed ( Figure 1 In Example 1, Bi₂Ti₂O₇ few-layer nanosheets were uniformly loaded onto the surface of MXene, forming a compact two-dimensional / two-dimensional heterostructure. The image shows that ultrathin Bi₂Ti₂O₇ nanosheets (light-colored transparent areas, approximately 3-5 nm thick) are uniformly distributed on the surface of MXene (dark-colored wrinkled areas), with a lateral dimension of approximately 200-500 nm. The edges exhibit obvious curled and wrinkled features, confirming a few-layer structure. MXene displays an accordion-like layered morphology, forming a large-area, close surface-to-surface contact with Bi₂Ti₂O₇.

[0026] Example 2 (1) Preparation of Bi2Ti2O7 two-dimensional few-layer material: 2 mmol Bi(NO3)3·5H2O was dissolved in 30 mL of 1 mol / L dilute nitric acid, 1 mmol sorbitol was added as a structure regulator, and after stirring and dissolving, 2 mmol titanium tetrachloride was added; 3 mol / L KOH solution was added dropwise to adjust the pH to 9, and the reaction was carried out at 160℃ for 20 hours to obtain Bi2Ti2O7 two-dimensional few-layer material.

[0027] (2) Surface protonation treatment: Dispersed in 0.1 mol / L dilute nitric acid, treated at room temperature for 4 hours, and a 1 mg / mL suspension was prepared with a Zeta potential of +28 mV.

[0028] (3) Preparation of MXene suspension: Nb2CT was prepared by LiF / HCl etching method. x MXene was prepared into a suspension after ultrasonic exfoliation (Zeta potential approximately -12 mV).

[0029] (4) Electrostatic composite: with a mass ratio of 3:1, Bi2Ti2O7 / Nb2CT was obtained by stirring at room temperature for 6 hours. x Two-dimensional composite few-layer materials.

[0030] Example 3 (1) Preparation of Bi2Ti2O7 two-dimensional few-layer material: 1 mmol Bi(NO3)3·5H2O was dissolved in 15 mL of 4 mol / L dilute nitric acid, and 1.5 mmol pentaerythritol was added as a structure regulator. After stirring and dissolving, 1 mmol titanium oxysulfate was added. Ammonia water was added dropwise to adjust the pH to 11. The reaction was carried out at 200℃ for 12 hours to obtain Bi2Ti2O7 two-dimensional few-layer material.

[0031] (2) Surface protonation treatment: Dispersed in 1 mol / L dilute sulfuric acid, treated at room temperature for 1 hour, and a 3 mg / mL suspension was prepared with a Zeta potential of +35 mV.

[0032] (3) Preparation of MXene suspension: Ti3C2T x Suspension (Zeta potential approximately -18 mV).

[0033] (4) Electrostatic composite: with a mass ratio of 1:1, stir at room temperature for 2 hours to obtain a two-dimensional composite few-layer material of Bi2Ti2O7 / MXene.

[0034] Comparative Example 1: Single Bi2Ti2O7 two-dimensional few-layer The two-dimensional few-layer material Bi2Ti2O7 prepared in step (1) of Example 1 was used directly as a control sample without protonation treatment and MXene composite.

[0035] Comparative Example 2: Bulk Bi2Ti2O7 and MXene were directly suspended and mixed (bulk direct mixing) (1) Preparation of bulk Bi2Ti2O7: 1 mmol Bi(NO3)3·5H2O and 1 mmol tetrabutyl titanate were dissolved in 40 mL of deionized water, stirred for 1 hour and then hydrothermally heated at 180℃ for 18 hours to obtain bulk Bi2Ti2O7 particles (size 500 nm-1 μm).

[0036] (2) Direct suspension mixing: The bulk Bi2Ti2O7 was directly mixed with the MXene suspension, stirred at 400 rpm for 4 hours at a mass ratio of 2:1, and then centrifuged and dried. Due to the inability to effectively protonate the bulk material and its large size, the contact with MXene was poor.

[0037] Comparative Example 3: Simple mixing of unprotonated Bi2Ti2O7 few-layer with MXene (unprotonated mixture) The two-dimensional few-layer Bi2Ti2O7 material prepared in step (1) of Example 1 was directly mixed with MXene suspension by simple mechanical stirring (400 rpm, 4 hours) without surface protonation treatment (Zeta potential approximately -5 mV, near neutral) at a mass ratio of 2:1. Due to the lack of electrostatic attraction, the two materials were difficult to form a close contact and were prone to phase separation.

[0038] Table 1. Pore structure parameters of the samples used in the examples and comparative examples. Table 1 above shows the pore structure parameters of the samples from the examples and comparative examples. As can be seen from Table 1, the specific surface area of ​​Example 1 (85.6 m² / g) is significantly higher than that of the bulk material in Comparative Example 2 (28.5 m² / g), an increase of approximately three times, demonstrating the effectiveness of polyol-assisted few-layer formation. The specific surface area of ​​Comparative Example 3 (42.8 m² / g) is significantly lower than that of Example 1, indicating that the two-dimensional nanosheets, without protonation, aggregate due to a lack of electrostatic attraction, resulting in a loss of specific surface area. The specific surface area of ​​the single few-layer material in Comparative Example 1 is 62.3 m² / g, lower than that of the composite material, indicating that the intercalation and exfoliation effect of MXene further inhibits stacking.

[0039] Application Examples and Photocatalytic Performance Testing Application Example 1: Photocatalytic Reduction of 4-NP by the Material in Example 1 The Bi₂Ti₂O₇ / MXene two-dimensional composite few-layer material prepared in Example 1 was used for the photocatalytic reduction of p-nitrophenol: 20 mg of catalyst was dispersed in 40 mL of a 20 mg / L 4-NP aqueous solution, and 40 mg of NaBH₄ was added as a reducing agent. The mixture was stirred in the dark for 30 minutes to reach adsorption-desorption equilibrium. A 300 W xenon lamp (equipped with a 420 nm cutoff filter) was used as the light source. Samples were taken every 10 minutes, and after centrifugation, the absorbance at 317 nm was measured to calculate the 4-NP conversion and 4-AP selectivity. The stability was assessed by 5 cycles.

[0040] Application Example 2: Photocatalytic Reduction of 4-NP by the Material in Example 2 Bi2Ti2O7 / Nb2CT prepared using Example 2 x The material was used as a catalyst, and the other conditions were the same as in Application Example 1.

[0041] Application Example 3: Photocatalytic Reduction of 4-NP by the Material in Example 3 The Bi2Ti2O7 / MXene material prepared in Example 3 was used as the catalyst, and the other conditions were the same as in Application Example 1.

[0042] Comparative application testing Comparative Application Example 1: Photocatalytic Reduction of 4-NP by the Material in Comparative Example 1 Comparative Example 1 used a single Bi2Ti2O7 two-dimensional few-layer material as the catalyst, and the other conditions were the same as in Application Example 1.

[0043] Comparative Application Example 2: Photocatalytic Reduction of 4-NP by the Material in Comparative Example 2 Comparative Example 2 used a bulk Bi2Ti2O7 and MXene direct suspension mixture as a catalyst, with other conditions the same as in Application Example 1.

[0044] Comparative Application Example 3: Photocatalytic Reduction of 4-NP by the Material in Comparative Example 3 The unprotonated simple mixed material of Comparative Example 3 was used as the catalyst, and the other conditions were the same as in Application Example 1.

[0045] Table 2 Comparison of photocatalytic reduction performance of different materials for p-nitrophenol Table 2 above shows a comparison of the photocatalytic reduction performance of p-nitrophenol using different materials. As can be seen from Table 2: (1) The conversion rate (98.6%) of Example 1 (electrostatic recombination) at 60 min was 1.7 times that of the single Bi2Ti2O7 few-layer material (58.3%). This demonstrates that the introduction of MXene significantly promotes carrier separation and electron transport, and that the tight interface formed by electrostatic recombination is superior to simple contact.

[0046] (2) The conversion rate of Example 1 at 60 min (98.6%) was significantly higher than that of the bulk direct-mixed material (42.6%), an improvement of 2.3 times. This demonstrates the key role of few-layer morphology in improving catalytic activity—bulk materials have a low specific surface area (28.5 m² / g), few active sites, and long carrier transport paths, resulting in poor performance.

[0047] (3) The conversion rate at 60 min in Example 1 (98.6%) was significantly higher than that of the unprotonated mixed material (51.2%), an increase of 1.9 times. This indicates that the electrostatic attraction generated by the protonation treatment is crucial for forming a tight interfacial contact. When unprotonated, both Bi2Ti2O7 and MXene are weakly negatively charged (or nearly neutral), repelling each other or lacking the ability to attract, resulting in severe stacking, poor interfacial contact, and low charge transfer efficiency.

[0048] (4) Cyclic stability: After 5 cycles, the activity retention rate of Example 1 was 94.5%, while that of Comparative Application Example 2 (direct mixing of bulk materials) was only 62.5%, and that of Comparative Application Example 3 (mixing without protonation) was only 71.8%, which proves that the strong interfacial bonding formed by electrostatic interaction effectively prevents the active components from falling off.

[0049] This invention addresses the shortcomings of traditional Bi₂Ti₂O₇ bulk particles, such as low specific surface area, easy carrier recombination, and poor interfacial contact. A polyol-assisted hydrothermal synthesis combined with electrostatic interaction was developed to successfully prepare a two-dimensional Bi₂Ti₂O₇ / MXene composite few-layer material. This material has a specific surface area of ​​85.6 m² / g, and achieves a conversion rate of 98.6% and a selectivity of 99.2% in the photocatalytic reduction of p-nitrophenol after 60 minutes, with a retention rate of 94.5% after 5 cycles. Its performance is significantly superior to single few-layer materials (1.7-fold improvement), bulk direct-mixed materials (2.3-fold improvement), and unprotonated mixed materials (1.9-fold improvement), demonstrating promising application prospects.

Claims

1. A method for preparing a few layers of a two-dimensional material, characterized in that, Includes the following steps: (1) Dissolve bismuth salt in an acidic solution, add polyol structure modifier, stir to dissolve, add titanium salt, and continue stirring to form a homogeneous solution; (2) Add an alkaline solution to the solution obtained in step (1) to adjust the pH value to alkaline, stir and transfer to a hydrothermal reactor, react at 150-220℃ for 12-24 hours, cool, wash and dry to obtain Bi2Ti2O7 two-dimensional few-layer material; (3) The Bi2Ti2O7 two-dimensional few-layer material obtained in step (2) is subjected to surface protonation treatment to make its surface positively charged, and then dispersed in a solvent to obtain a Bi2Ti2O7 suspension; (4) Prepare a few-layer MXene suspension by ultrasonic exfoliation of MXene material; (5) Under stirring conditions, the positively charged Bi2Ti2O7 suspension obtained in step (3) is mixed with the MXene suspension obtained in step (4), and composited by electrostatic interaction. After post-treatment, a two-dimensional composite few-layer material of Bi2Ti2O7 / MXene is obtained. The polyol structure modifier mentioned in step (1) is one or more of mannitol, sorbitol or pentaerythritol.

2. The preparation method according to claim 1, characterized in that, The bismuth salt mentioned in step (1) is Bi(NO3)3·5H2O, and the titanium salt is tetrabutyl titanate, titanium tetrachloride or titanium oxysulfate; the molar ratio of Bi to Ti is 1:1, and the molar ratio of the structure modifier to Bi is (0.5-2):

1.

3. The preparation method according to claim 2, characterized in that, The polyol structure modifier mentioned in step (1) is mannitol; the acidic solution is 1-4 mol / L dilute nitric acid; the stirring speed is 300-800 rpm and the stirring time is 0.5-3 hours.

4. The preparation method according to claim 1, characterized in that, In step (2), the pH value is adjusted to 8-11; the hydrothermal reaction temperature is 160-200℃, and the reaction time is 16-20 hours.

5. The preparation method according to claim 1, characterized in that, The surface protonation treatment in step (3) is as follows: Bi2Ti2O7 is dispersed in a 0.1-1 mol / L dilute acid solution and treated for 1-4 hours to make its Zeta potential reach +25 mV to +40 mV.

6. The preparation method according to claim 1, characterized in that, MXene in step (4) is Ti3C2T x , Nb2CT x or V2CT x ; the ultrasonic exfoliation power is 200-600 W, the time is 1-4 hours, and the concentration is 0.5-2 mg / mL.

7. The preparation method according to claim 1, characterized in that, The mass ratio of Bi2Ti2O7 to MXene in step (5) is (5:1)-(1:2); the post-treatment includes standing, centrifugation, washing and drying.

8. The preparation method according to any one of claims 1-7, characterized in that, It also includes heat treatment at 200-400℃ for 1-3 hours in an inert atmosphere to enhance the interfacial bonding strength.

9. The application of a two-dimensional few-layer material in the photocatalytic reduction of p-nitrophenol to p-aminophenol, characterized in that, The two-dimensional composite few-layer material of Bi2Ti2O7 / MXene prepared by any one of claims 1-8 was used as a photocatalyst to catalyze the reduction of p-nitrophenol aqueous solution under visible light irradiation.

10. The application according to claim 9, characterized in that, The photocatalytic reduction reaction conditions are as follows: catalyst dosage is 0.5-2 g / L, initial concentration of p-nitrophenol is 10-50 mg / L, pH value of reaction solution is 6-8, reducing agent is NaBH4, and visible light source is 300-500 W xenon lamp.

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