Preparation method and application of a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions

Abstract

The present invention discloses a method for preparing a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions and its application. The present invention adopts a one-step two-stage chemical vapor deposition strategy to achieve a highly controllable synthesis of a molybdenum disulfide / molybdenum dioxide heterojunction. Compared with the traditional two-step chemical vapor deposition or mechanical stripping method, the present invention can achieve the preparation of wafer-level, high-quality molybdenum disulfide / molybdenum dioxide heterojunctions without introducing additional steps. By regulating the concentration of the metal source precursor, the molybdenum disulfide / molybdenum dioxide heterojunctions with different morphologies can be precisely controlled, thereby achieving the preparation of molybdenum disulfide / molybdenum dioxide heterojunctions with different dimensions, meeting the requirements of diversified application scenarios for heterojunction functionalization. In addition, the experimental results show that the prepared heterojunction exhibits excellent electrocatalytic performance in the field of electrocatalysis, providing an important experimental basis and theoretical foundation for the design of high-performance electrocatalysts.

Description

Technical Field

[0001] The present invention relates to the preparation of semiconductor or metal heterojunctions, and in particular to a preparation method and application of a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions. Background Art

[0002] In recent years, two-dimensional materials represented by transition metal sulfides (such as molybdenum disulfide, tungsten disulfide, etc.) have attracted much attention due to their ultra-thin thickness and unique electronic structure. In particular, there are no dangling bonds on the surface of this type of material, and the layers interact through van der Waals interactions. This feature allows different materials to construct multifunctional van der Waals heterostructures that surpass traditional materials without considering the limitations of lattice matching, and exhibit unique physical and chemical properties. Studies have shown that the zero-dimensional core-shell structure of molybdenum dioxide / molybdenum disulfide heterojunction can effectively increase the exposure of active sites and increase the Gibbs free energy of hydrogen adsorption, thereby significantly promoting the catalytic effect of hydrogen evolution reaction. In addition, the high-rectification Schottky diode constructed based on the two-dimensional / two-dimensional molybdenum dioxide / molybdenum diselenide heterojunction exhibits excellent photovoltaic effect, and its open circuit voltage and response speed can reach 0.26 eV and 5 ms, respectively. It is worth noting that as a non-layered metal oxide, molybdenum dioxide has a distorted octahedral structure of the monoclinic system. This low-symmetry structure makes it exhibit significant in-plane anisotropy in electrical and optical properties. In addition, molybdenum dioxide exhibits strong surface plasmon resonance, so it has broad application prospects in surface enhanced Raman. At the same time, its excellent chemical stability and metallic conductivity also make it a very promising capacitor electrode and catalyst material.

[0003] At present, the preparation method of traditional heterojunction mainly relies on physical stacking after mechanical peeling. However, this method is only suitable for preliminary research on conceptual devices, and it is difficult to achieve efficient preparation of large-area samples. In addition, although wet transfer technology is currently a common method for synthesizing large-area heterojunction samples, the key challenge faced by this method is that the residual compounds on the surface of the sample during the transfer process are difficult to completely remove, thereby affecting the performance of the heterojunction. On the other hand, when constructing a heterojunction using a two-step chemical vapor deposition method, impurities are often introduced during the material growth process, thereby destroying the properties of the intrinsic interface of the heterojunction. Therefore, the development of a simple, efficient method that can achieve large-area, high-quality heterojunction synthesis has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] In view of the technical problems such as limited sample size, residual surface compounds and interface contamination in the existing heterojunction preparation methods, the present invention provides a method for preparing a molybdenum disulfide / molybdenum dioxide heterojunction with a designable dimension and its application, and adopts a one-step two-stage chemical vapor deposition technology to realize the preparation of large-area, high-quality molybdenum disulfide / molybdenum dioxide heterojunctions. The method has the characteristics of simple operation and high efficiency. By accurately controlling the introduction time of the sulfur source precursor during the growth process, the molybdenum disulfide / molybdenum dioxide heterojunction can be highly controllably synthesized. In addition, the one-step two-stage chemical vapor deposition method adopted in the present invention avoids the introduction of additional steps and effectively maintains the original interface properties of the heterojunction. At the same time, by adjusting the concentration of the metal source precursor, the heterojunction sample can be expanded to different dimensions, covering two-dimensional / zero-dimensional, two-dimensional / one-dimensional and two-dimensional / two-dimensional, so as to meet the needs of diversified application scenarios.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions comprises the following steps:

[0007] S1. annealing pretreatment of the c-plane sapphire substrate used to grow the heterojunction;

[0008] S2. The metal molybdenum foil is oxidized in air to prepare molybdenum trioxide foil as a metal source precursor;

[0009] S3. Using a dual-temperature zone tubular furnace heating system, placing sulfur powder in a first heating zone, placing a molybdenum trioxide foil and an annealed sapphire substrate in a second heating zone, and vertically stacking the molybdenum trioxide foil on the surface of the sapphire substrate to form a face-to-face spatial confinement structure between the metal source and the substrate;

[0010] S4. Before heating, argon gas was introduced into the tube furnace to flush the reaction chamber until the heating began, and argon gas was continuously introduced as a carrier gas throughout the heating process;

[0011] S5. Set the heating program to raise the temperature of the first heating zone to 240-270 ° C and maintain for 3-8 minutes, and raise the temperature of the second heating zone to 770-790 ° C and maintain for 10-18 minutes;

[0012] S6. After the heating process in the first heating temperature zone is completed, the sulfur powder is moved out of the heating temperature zone using a magnetic suction device, while the heating process in the second heating temperature zone is maintained until completed, thereby preparing a large-area molybdenum disulfide / molybdenum dioxide heterojunction.

[0013] Furthermore, in S1, the annealing temperature is 1000-1100°C, the time is 210-300 minutes, the annealing gas atmosphere is an argon-oxygen mixed gas, the volume ratio of argon to oxygen is preferably 1:1, and the total flow rate is 150-200 sccm.

[0014] Further, in S2, the temperature of the oxidation treatment is 500-540°C, and the time is 10-18 minutes. More specifically, when synthesizing a two-dimensional / zero-dimensional molybdenum disulfide / molybdenum dioxide heterojunction, the oxidation treatment of the molybdenum foil is preferably heated at 500°C for 10-12 minutes; when synthesizing a two-dimensional / one-dimensional molybdenum disulfide / molybdenum dioxide heterojunction, the oxidation treatment of the molybdenum foil is preferably heated at 500°C for 14-18 minutes; when synthesizing a two-dimensional / two-dimensional molybdenum disulfide / molybdenum dioxide heterojunction, the oxidation treatment of the molybdenum foil is preferably heated at 520-540°C for 18 minutes.

[0015] Furthermore, in S3, the height of the space confinement constructed by the molybdenum trioxide foil and the sapphire substrate is 2-5 mm.

[0016] Furthermore, in S4, the flow rate of argon gas used for flushing is 250-500 sccm, the flushing time is 10-20 minutes, and when the heating starts, the flow rate of carrier gas argon gas is 100-150 sccm.

[0017] Further, in S5, the first heating temperature zone and the second heating temperature zone are heated and raised at the same time, and reach the set heating temperature in 20-25 minutes at the same time.

[0018] The molybdenum disulfide / molybdenum dioxide heterojunction prepared according to the above method can be used as a catalyst material in the field of electrocatalytic hydrogen evolution. Compared with molybdenum disulfide or molybdenum dioxide, the catalytic performance of the molybdenum disulfide / molybdenum dioxide heterojunction is more excellent.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Avoiding secondary contamination: In the traditional two-step chemical vapor deposition process of heterojunction synthesis, the sample is inevitably exposed to air or an environment containing pollutants, resulting in secondary contamination. The present invention adopts a one-step two-stage growth strategy, which does not require secondary growth, effectively avoids external contamination, ensures the integrity of the intrinsic interface properties of the heterojunction, and significantly improves the synthesis quality of heterojunction samples.

[0021] (2) Realization of large-area preparation: Compared with the heterojunction constructed by mechanical exfoliation, the present invention can realize the preparation of large-area (wafer-level) MoS2 / MoO2 heterojunction. The synthesis of wafer-level heterojunction can significantly reduce the application cost and is more in line with actual application needs.

[0022] (3) Highly controllable heterojunction synthesis: By regulating the oxidation conditions of the molybdenum foil, the present invention can highly controllably synthesize MoS2 / MoO2 heterojunctions of different dimensions to meet the needs of multifunctional applications.

[0023] (4) Convenient characterization capability: The heterojunction samples grown on the sapphire substrate of the present invention can be directly characterized by Raman spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, etc., to achieve the study of the sample morphology, structure and physical properties.

[0024] (5) Universality: The present invention has a certain degree of universality. By replacing the sulfur source with a selenium source, a molybdenum diselenide / molybdenum dioxide heterojunction can also be prepared.

[0025] (6) Excellent electrocatalytic performance: The MoS2 / MoO2 heterojunction prepared by the present invention exhibits excellent performance in the electrocatalytic hydrogen evolution reaction, and has higher catalytic efficiency and stability compared with MoS2 or MoO2 alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the growth principle of a one-step two-stage preparation of a molybdenum disulfide / molybdenum dioxide heterojunction corresponding to Example 1;

[0027] Figure 2 A digital photo image of a one-step two-stage preparation of a molybdenum disulfide / molybdenum dioxide heterojunction corresponding to Example 1;

[0028] Figure 3 Optical microscope characterization of the one-step two-stage preparation of the molybdenum disulfide / molybdenum dioxide heterojunction corresponding to Example 1;

[0029] Figure 4 Raman spectroscopy characterization of the one-step two-stage preparation of molybdenum disulfide / molybdenum dioxide heterojunction corresponding to Example 1;

[0030] Figure 5 X-ray diffraction characterization of the one-step two-stage preparation of the molybdenum disulfide / molybdenum dioxide heterojunction corresponding to Example 1;

[0031] Figure 6 The photoluminescence spectrum characterization of the one-step two-stage preparation of the molybdenum disulfide / molybdenum dioxide heterojunction corresponding to Example 1;

[0032] Figure 7 X-ray photoelectron spectroscopy characterization of the Mo 3d orbital of the MoS2 / MoO2 heterojunction prepared by the one-step two-stage method corresponding to Example 1;

[0033] Figure 8X-ray photoelectron spectroscopy characterization of the S 2p orbital of the molybdenum disulfide / molybdenum dioxide heterojunction prepared by the one-step two-stage method corresponding to Example 1;

[0034] Fig. 9 X-ray photoelectron spectroscopy characterization of the O 1s orbital of the MoS2 / MoO2 heterojunction prepared by the one-step two-stage method corresponding to Example 1;

[0035] Fig.10 A high-resolution transmission electron microscope image of a molybdenum disulfide / molybdenum dioxide heterojunction prepared by a one-step two-stage method corresponding to Example 1;

[0036] Fig.11 Selected area electron diffraction characterization of the one-step two-stage preparation of the molybdenum disulfide / molybdenum dioxide heterojunction corresponding to Example 1;

[0037] Fig.12 The optical microscope characterization of the morphology control of the MoS2 / MoO2 heterojunction based on different Mo foil oxidation conditions corresponding to Example 2;

[0038] Fig.13 The atomic force microscope characterization image of the two-dimensional / zero-dimensional MoS2 / MoO2 heterojunction prepared by the one-step two-stage method corresponding to Example 2;

[0039] Fig.14 The atomic force microscope characterization image of the two-dimensional / one-dimensional MoS2 / MoO2 heterojunction prepared by the one-step two-stage method corresponding to Example 2;

[0040] Fig.15 The atomic force microscope characterization image of the two-dimensional / two-dimensional MoS2 / MoO2 heterojunction prepared by the one-step two-stage method corresponding to Example 2;

[0041] Fig.16 The linear sweep voltammetric curves of molybdenum dioxide, molybdenum disulfide and molybdenum disulfide / molybdenum dioxide heterojunction in the electrocatalytic application described in Example 3;

[0042] Fig.17 is the Tafel slope of molybdenum dioxide, molybdenum disulfide and molybdenum disulfide / molybdenum dioxide heterojunction in the electrocatalytic application described in Example 3;

[0043] Fig.18 10 mA / cm2 for MoO2, MoS2, and MoS2 / MoO2 heterojunction in the electrocatalytic application described in Example 3 2 Histogram of overpotential and Tafel slope under ;

[0044] Fig.19 The Nyquist plots of molybdenum dioxide, molybdenum disulfide and molybdenum disulfide / molybdenum dioxide heterojunction in the electrocatalytic application described in Example 3;

[0045] Fig. 20 Cyclic voltammograms of molybdenum dioxide, molybdenum disulfide and molybdenum disulfide / molybdenum dioxide heterojunction in the electrocatalytic application described in Example 3;

[0046] Fig.21 The functional relationship between the capacitive current density and the scan rate of molybdenum dioxide, molybdenum disulfide and molybdenum disulfide / molybdenum dioxide heterojunction in the electrocatalytic application described in Example 3. DETAILED DESCRIPTION

[0047] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto. Example 1

[0048] MoS2 / MoO2 heterojunction was prepared based on a one-step two-stage chemical vapor deposition strategy using a dual-zone tube furnace. First, a c-plane sapphire substrate was selected as the growth substrate and placed in an argon-oxygen mixed gas atmosphere for high-temperature annealing: the gas flow rate was 200 sccm, the volume ratio of argon to oxygen was 1:1, and the c-plane sapphire substrate was annealed at 1000 °C for 240 minutes to eliminate surface impurities and optimize the growth interface. Secondly, the metal molybdenum foil was placed in air for oxidation treatment at 500 °C for 16 minutes to form molybdenum trioxide foil as a metal source precursor. 250 mg of sulfur powder was weighed, loaded into a quartz boat, and placed in the center of the first heating zone of the dual-zone tube furnace. Subsequently, the molybdenum trioxide foil was vertically stacked face to face on the surface of the pretreated c-plane sapphire substrate, and then the two were pushed into the center of the second heating zone. The confined height difference between the molybdenum trioxide foil and the c-plane sapphire substrate was 3 mm. Before starting the heating program, open the argon flushing valve and flush the reaction chamber at a flow rate of 250 sccm for 20 minutes to stabilize the growth environment in the reaction chamber and remove impurity gases. Subsequently, set the heating program. The first heating temperature zone and the second heating temperature zone are heated at the same time. The first heating temperature zone is heated to 235 ° C within 25 minutes and maintained at this temperature for 6 minutes. The second heating temperature zone is heated to 790 ° C within 25 minutes and maintained at this temperature for 10 minutes. When the first heating temperature zone is completed, the quartz boat containing sulfur powder is quickly pulled out by the magnetic suction device, while the growth conditions of the second heating temperature zone are kept unchanged, and the second stage of growth is continued. After the second heating temperature zone is completed, it is naturally cooled to room temperature, and then the c-plane sapphire substrate is taken out to complete the preparation of the molybdenum disulfide / molybdenum dioxide heterojunction. The schematic diagram of the one-step two-stage chemical vapor deposition growth principle described in the present invention is shown in the figure Figure 1 shown.

[0049] Figure 2The digital photo of the wafer-level MoS2 / MoO2 heterojunction prepared by growth is shown. The present invention comprehensively analyzes the micro-nanostructure of the heterojunction sample by various characterization methods. The results are as follows: Figures 2~11 The specific instructions are as follows:

[0050] Optical microscopy characterization: The optical microscopy characterization results show that the prepared MoS2 / MoO2 heterojunction exhibits two-dimensional / one-dimensional structural characteristics, indicating that this method can effectively achieve the directional growth of the heterojunction.

[0051] Raman spectroscopy characterization: Raman spectroscopy test results show that the coexistence of Raman characteristic peaks of molybdenum disulfide and molybdenum dioxide in the sample confirms the successful construction of the heterojunction, and the characteristic peak positions of each phase are consistent with the standard data, indicating that the material has good crystallinity.

[0052] X-ray diffraction (XRD) characterization: XRD test results show that the sample simultaneously exhibits diffraction peaks of the (002) crystal plane of MoS2 and diffraction peaks of the (100), (200) and (222) crystal planes of MoO2, further confirming the formation of the heterojunction and the integrity of its crystal structure.

[0053] Photoluminescence spectroscopy characterization: Compared with pure MoS2, the photoluminescence spectrum intensity of the heterojunction is significantly weakened, indicating that an obvious quenching effect occurs at the interface of the heterojunction. This phenomenon is closely related to the energy level structure and carrier transfer characteristics of the heterojunction.

[0054] X-ray photoelectron spectroscopy (XPS) characterization: XPS test results show that the binding energies of Mo 3d, S 2p and O 1S orbitals in the samples are highly consistent with the standard values, and the fitting curves are consistent with the experimental data, further confirming the chemical state and valence distribution of each element in the heterojunction.

[0055] Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) characterization: High-resolution TEM images show that the heterojunction sample has a periodic atomic arrangement structure, indicating that it has a high degree of crystallinity. SAED results clearly show two groups of diffraction spots of molybdenum disulfide and molybdenum dioxide, further confirming the clarity of the crystal structure of the heterojunction and its interface.

[0056] In summary, the results of the above-mentioned multiple characterization methods all consistently confirm that the present invention successfully prepared a wafer-level MoS2 / MoO2 heterojunction, and the heterojunction has good crystallinity and interface properties, providing a solid foundation for subsequent application research. Example 2

[0057] Under the premise of keeping the growth process described in Example 1 unchanged, the morphology of the heterojunction can be regulated by changing the oxidation conditions of the metal molybdenum foil, thereby preparing molybdenum disulfide / molybdenum dioxide heterojunctions of different dimensions. Fig.12 Optical microscope images of MoS2 / MoO2 heterojunctions synthesized under different oxidation conditions are shown, including oxidation of Mo foil at 500°C for 10 minutes, oxidation at 500°C for 16 minutes, and oxidation at 520°C for 18 minutes. The optical microscope characterization results show that with the increase of oxidation time or oxidation temperature, that is, the increase of the concentration of metal Mo source precursor, the morphology of MoO2 gradually changes from zero-dimensional nanoparticles to one-dimensional nanorods, and finally forms a two-dimensional nanosheet structure under high Mo source precursor concentration. Figures 13 to 15 Atomic force microscopy images of MoS2 / MoO2 heterojunctions with 2D / 0D, 2D / 1D, and 2D / 2D structures are shown respectively. Example 3

[0058] Under the premise of keeping the growth process and experimental conditions described in Example 1 unchanged, electrochemical tests and analyses were performed on the prepared two-dimensional / one-dimensional MoS2 / MoO2 heterojunction, MoS2 and MoO2. Fig.16 and Fig.17 Demonstrated at 10 mV s -1 Linear sweep voltammetry curve and Tafel slope at scan rate. The test results show that the MoS2 / MoO2 heterojunction exhibits a lower hydrogen evolution reaction overpotential and a smaller Tafel slope than MoS2 and MoO2 alone. Fig.18 As shown, at 10 mA cm -2 At the current density of 2.5 Å, the overpotential of the MoS2 / MoO2 heterojunction is 580 mV, and the Tafel slope is 256 mV dec. -1 . Fig.19 The corresponding electrochemical impedance test results show that the MoS2 / MoO2 heterojunction exhibits the lowest charge transfer resistance of 33.1 Ω. Fig. 20 As shown, the MoS2 / MoO2 heterojunction exhibits the largest double-layer capacitance. Fig.21 The electrochemical active area of ​​the MoS2 / MoO2 heterojunction is 246.01 μF / cm -2 , significantly higher than that of individual MoS2 and MoO2, and the heterojunction provides greater electrochemical activity. The above test results show that the MoS2 / MoO2 heterojunction has better performance in the field of electrochemical hydrogen evolution and shows good application prospects.

Claims

1. A method for preparing a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions, characterized in that: The steps include: S1. annealing pretreatment is performed on the c-plane sapphire substrate for growing the heterojunction, the annealing temperature is 1000-1100°C, the time is 210-300 minutes, the annealing gas atmosphere is an argon-oxygen mixed gas, the volume ratio of argon to oxygen is 1:1, and the flow rate is 150-200 sccm; S2. The metal molybdenum foil is oxidized in air at a temperature of 500-540 ° C for 10-18 minutes to prepare molybdenum trioxide foil as a metal source precursor; S3. Using a dual-temperature zone tubular furnace heating system, placing sulfur powder in the first heating zone, placing molybdenum trioxide foil and annealed sapphire substrate in the second heating zone, and vertically stacking the molybdenum trioxide foil on the surface of the sapphire substrate to construct a face-to-face spatial confinement structure of the metal source and the substrate; S4. Before heating, argon gas was introduced into the tube furnace to flush the reaction chamber until the heating began, and argon gas was continuously introduced as a carrier gas throughout the heating process; S5. Set the heating program to raise the temperature of the first heating zone to 240-270 ° C and maintain for 0-6 minutes, and raise the temperature of the second heating zone to 770-790 ° C and maintain for 10-18 minutes; S6. After the heating process in the first heating temperature zone is completed, the sulfur powder is moved out of the heating temperature zone using a magnetic suction device, while the heating process in the second heating temperature zone is maintained until completed, thereby preparing a large-area molybdenum disulfide / molybdenum dioxide heterojunction.

2. The method for preparing a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions according to claim 1, characterized in that: In S2, when synthesizing a two-dimensional / zero-dimensional MoS2 / MoO2 heterojunction, the oxidation treatment of the Mo foil is heating at 500°C for 10-12 minutes; When synthesizing a two-dimensional / one-dimensional MoS2 / MoO2 heterojunction, the oxidation treatment of the Mo foil is heating at 500°C for 14-18 minutes; when synthesizing a two-dimensional / two-dimensional MoS2 / MoO2 heterojunction, the oxidation treatment of the Mo foil is heating at 520-540°C for 18 minutes.

3. The method for preparing a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions according to claim 1, characterized in that: In S3, the spatial confinement height constructed by the molybdenum trioxide foil and the sapphire substrate is 2-5 mm.

4. The method for preparing a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions according to claim 1, characterized in that: In S4, the flow rate of argon gas used for flushing is 250-500 sccm, the flushing time is 10-20 minutes, and when the temperature starts to rise, the flow rate of carrier gas argon gas is 100-150 sccm.

5. The method for preparing a molybdenum disulfide / molybdenum dioxide heterojunction with designable dimensions according to claim 1, characterized in that: In S5, the first heating temperature zone and the second heating temperature zone are heated and raised at the same time, and reach the set heating temperature in 20-25 minutes.

6. Use of the molybdenum disulfide / molybdenum dioxide heterojunction obtained by the preparation method according to any one of claims 1 to 5 in electrocatalytic hydrogen evolution.

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