Method for preparing molybdenum nitride by combining chemical vapor deposition method with gas-solid-solid growth mechanism

Abstract

The invention belongs to the technical field of molybdenum nitride preparation, and particularly relates to a method for preparing molybdenum nitride by combining a chemical vapor deposition method with a gas-solid-solid growth mechanism. According to the invention, (NH4) 6Mo7O24 is used as a precursor, and a chemical vapor deposition method is combined with a gas-solid-solid growth mechanism to controllably construct the two-dimensional molybdenum nitride material. The characterization proves that the porous gamma-Mo2N material with a regular surface and a two-dimensional plane structure is successfully prepared on the surface of the Al2O3 (0001) substrate. By optimizing growth conditions, controllable synthesis of material morphology and structure is realized. Raman spectrum analysis shows that the surface of the prepared gamma-Mo2N is rich in active sites, and the gamma-Mo2N can obviously interact with adsorbed oxygen-containing small molecules, so that the gamma-Mo2N is proved to have excellent surface reaction activity. The research provides a new strategy for preparation of a transition metal nitride (TMNx) model structure, and reveals a key role of a VSS mechanism in nitride film growth.

Description

Technical Field

[0001] The present invention belongs to the technical field of molybdenum nitride preparation, and specifically relates to a method for preparing molybdenum nitride by utilizing a chemical vapor deposition method combined with a gas-solid-solid growth mechanism. Background Art

[0002] Transition metal carbides and nitrides (TMCx, TMNx) are emerging members of the two-dimensional material family, based on ceramic materials with ternary layered structures. A unique feature of this class of materials is that the outer electrons of carbon (C) or nitrogen (N) transfer to the metal's d orbital, resulting in an outer electron orbital configuration similar to that of the precious metal platinum (Pt). This important discovery has prompted in-depth research on other early transition metal carbides and nitrides. With their excellent physicochemical properties, TMCx and TMNx have shown broad application prospects in catalysis, including hydrocarbon isomerization, hydrogenation, and electrochemical hydrogen evolution reactions. Studies have shown that factors such as crystal structure, site occupancy, metal-to-carbon-nitrogen ratio, surface termination, and defects can significantly affect the reactivity of TMCx and TMNx catalysts.

[0003] Transition metal molybdenum nitrides (TMNs) are compounds formed by the insertion of nitrogen atoms into the interstitial spaces of the Mo lattice. MoNs possess properties of covalent solids, ionic crystals, and transition metals, exhibiting high hardness, high melting point, corrosion resistance, and excellent electrical and thermal conductivity. They demonstrate excellent catalytic activity in reactions such as ammonia synthesis, hydrodenitrogenation, and hydrodesulfurization, with some properties approaching or exceeding those of traditional precious metal catalysts, earning them the nickname "quasi-platinum catalysts." Compared to traditional oxide supports, TMCx and TMNx offer multiple advantages as catalyst supports. First, they can form strong interactions with the supported metal, significantly manipulating the geometric and electronic structure of the metal species. Second, these support materials exhibit unique electronic effects and interfacial synergies, providing new avenues for improving catalytic performance. Due to the diversity and complexity of the variables involved in actual catalytic systems, identifying the active structures of these catalytic reactions is challenging. Therefore, to simplify the complexity of the research objectives, the use of model catalysts with well-defined surfaces combined with in situ surface science analysis can effectively aid in the identification of active sites and reaction intermediates. Therefore, the controllable preparation of ultra-thin epitaxial TMCx and TMNx with regular morphology is of great significance for basic research and practical applications. Summary of the Invention

[0004] The purpose of the present invention is to address the existing problems and provide a method for preparing molybdenum nitride by utilizing chemical vapor deposition combined with a gas-solid-solid growth mechanism.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism comprises the following steps:

[0007] S1. Pretreatment of growth substrate:

[0008] The Al2O3 (0001) substrate was cleaned with anhydrous ethanol and deionized water in a cycle, and the surface moisture was drained. Then, the substrate surface was purged with a high-purity N2 gas flow and then treated with an oxygen plasma cleaner for 30 minutes.

[0009] S2. Preparation of precursor solution and spin coating on substrate surface:

[0010] Weigh (NH4)6Mo7O 24 4H2O was dissolved in deionized water and then shaken in an ultrasonic cleaner to make (NH4)6Mo7O 24 The precursor (NH4)6Mo7O is fully dissolved 24 solution, and then the pretreated Al2O3(0001) substrate was subjected to the precursor (NH4)6Mo7O 24 The solution is spin-coated, and after the spin coating is completed, (NH4)6Mo7O 24 / Al2O3(0001) was placed under an infrared heating lamp for drying;

[0011] S3. Synthesis of two-dimensional porous molybdenum nitride:

[0012] Spin-coated (NH4)6Mo7O 24 / Al2O3(0001) was placed in the center of the reaction zone of a tubular furnace. Before heating, Ar gas was introduced to exhaust the air in the quartz tube. Then, NH3 was introduced to heat the substrate to 550°C at a heating rate of 8-12°C / min. After the reaction was completed, NH3 was turned off and the substrate was allowed to cool naturally in an Ar atmosphere.

[0013] After this stage is over, NH3 is reintroduced, and the heating rate is set to 1-3°C / min. After heating to 300°C, the heating rate is set to 1°C / min again, and heated to 700°C, and kept warm for 1.5-2.5h. After the reaction is completed, cool to room temperature in an NH3 atmosphere, turn off NH3, and take out.

[0014] Furthermore, the cyclic cleaning described in step S1 includes 2 to 3 cycles, and the specific operation of each cycle is: first immerse the Al2O3 (0001) substrate in anhydrous ethanol, ultrasonically treat it for 10 to 15 minutes, pour out the ethanol, and rinse it with deionized water 3 to 5 times.

[0015] Furthermore, the purity of the high-purity N2 gas flow in step S1 is ≥99.999%.

[0016] Furthermore, the technical parameters of the oxygen plasma treatment in step S1 are: the gas is pure oxygen with a purity of ≥99.99%; the gas pressure is 60-100 Pa, and the power is 60-100 W.

[0017] Furthermore, the (NH4)6Mo7O 24 The mass volume ratio of 4H2O to deionized water is 3g:20mL.

[0018] Furthermore, the parameters used in the spin coating process described in step S2 are: a rotation speed of 2000 to 4000 rpm, a time of 25 to 35 s, and a volume of the precursor solution of 0.15 to 0.25 mL.

[0019] Furthermore, the drying temperature in step S2 is 90-100°C.

[0020] Furthermore, the flow rate of the Ar gas in step S3 is 100 sccm, and the time is 30 minutes.

[0021] Furthermore, the flow rate of NH3 when introducing in step S3 is 10 sccm and the time is 60 minutes.

[0022] Furthermore, the flow rate of NH3 when it is introduced again in step S3 is 50 sccm, and the time is 30 minutes.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The present invention first is (NH4)6Mo7O 24 It decomposes into MoO3, and then the H formed by the dissociation of NH3 at high temperature can remove the O in MoO3, and then the N in NH3 reacts with Mo to form Mo2N. The present invention first adopts rapid heating in ammonia because the degree of nitridation is low in this process, which can cause excess MoO3 to begin sublimation at a temperature below its melting point, thus effectively limiting the thickness of the precursor. In addition, the wettability of the substrate Al2O3 (0001) surface and the interaction between it and MoO3 promote its two-dimensional layered growth. The reason for the subsequent slow segmented nitridation is that the nitridation process of molybdenum involves multiple steps and may generate multiple intermediate phases (such as MoO3→MoO2→Mo3N2→Mo2N). If the heating or nitridation rate is too fast, it may lead to incomplete nitridation, residual MoO2 or low-valent nitrides (such as Mo3N2), affecting the purity of the final product. The segmented heating can gradually drive out oxygen and promote uniform nitridation, ensuring the acquisition of a single γ-Mo2N.

[0025] 2. The present invention uses (NH4)6Mo7O 24Using γ-Mo2N as a precursor, a two-dimensional molybdenum nitride material was controllably constructed by chemical vapor deposition combined with a gas-solid-solid growth mechanism. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and other characterizations confirmed that a porous γ-Mo2N material with a regular surface and a two-dimensional planar structure was successfully prepared on the surface of an Al2O3 (0001) substrate. By optimizing the growth conditions, the controllable synthesis of the material morphology and structure was achieved. Raman spectroscopy analysis showed that the prepared γ-Mo2N surface is rich in active sites and can significantly interact with adsorbed oxygen-containing small molecules (such as H2O, O2, etc.), confirming its excellent surface reactivity. This study provides a new strategy for the preparation of model structures of transition metal nitrides (TMNx) and reveals the key role of the VSS mechanism in the growth of nitride films. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The hydrophilic effect diagram before and after plasma treatment;

[0027] Figure 2 It is the overall growth flow chart;

[0028] Figure 3 SEM images and EDS-mapping images of molybdenum nitride prepared by traditional methods;

[0029] Figure 4 The SEM image and EDS-mapping image of molybdenum nitride prepared by the method of the present invention;

[0030] Figure 5 TEM image and selected area electron diffraction pattern of molybdenum nitride prepared by the method of the present invention;

[0031] Figure 6 are the lattice fringes and lattice spacing of regions A and B;

[0032] Figure 7 The XRD pattern of molybdenum nitride prepared by the method of the present invention;

[0033] Figure 8 The XPS spectrum of molybdenum nitride prepared by the method of the present invention;

[0034] Figure 9 This is the Raman spectrum of molybdenum nitride prepared by the method of the present invention. DETAILED DESCRIPTION

[0035] In the following description, specific details such as specific system structures and technologies are provided for the purpose of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may also be implemented in other embodiments without these specific details.

[0036] Unless otherwise specified, the raw materials used in the present invention are all derived from conventional products purchased on the market. Ammonium molybdate and anhydrous ethanol of the present invention were purchased from Tianjin Komeo Chemical Reagent Co., Ltd., all of which were analytically pure and without purification process before use. Al2O3 (0001) was purchased from Hefei Kejing Material Technology Co., Ltd. and was hydrophilized before use. Scanning electron microscopy was completed on a field emission scanning electron microscope (JSM-7800), transmission electron microscopy test model was JEM-2100, and X-ray photoelectron spectroscopy test model was Specs PHOIBOS-100. X-ray diffraction test model was Rigaku Smartlab.

[0037] Example 1

[0038] A method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism comprises the following steps:

[0039] S1. Pretreatment of growth substrate:

[0040] The Al2O3 (0001) substrate was cleaned with anhydrous ethanol and deionized water in a cycle, and the surface moisture was drained. Then, the substrate surface was purged with a high-purity N2 gas flow (purity ≥ 99.999%), and then treated with an oxygen plasma cleaner for 30 minutes.

[0041] The cyclic cleaning process includes two cycles, and the specific operation of each cycle is as follows: first, immerse the Al2O3 (0001) substrate in anhydrous ethanol, ultrasonically treat for 10 minutes, pour out the ethanol, and rinse with deionized water three times;

[0042] The technical parameters of the oxygen plasma treatment are: the gas is pure oxygen with a purity of ≥99.99%; the gas pressure is 60 Pa, and the power is 60 W;

[0043] S2. Preparation of precursor solution and spin coating on substrate surface:

[0044] Weigh 3g (NH4)6Mo7O 24 ·4H2O was dissolved in 20mL of deionized water, and then shaken in an ultrasonic cleaner to make (NH4)6Mo7O 24 The precursor (NH4)6Mo7O is fully dissolved 24 solution, and then the pretreated Al2O3(0001) substrate was subjected to the precursor (NH4)6Mo7O 24 The solution is spin-coated, and after the spin coating is completed, (NH4)6Mo7O 24 / Al2O3(0001) was placed under an infrared heating lamp and dried at 90℃;

[0045] The parameters used in the spin coating process are: rotation speed of 2000 rpm, time of 25 s, and volume of precursor solution of 0.15 mL;

[0046] S3. Synthesis of two-dimensional porous molybdenum nitride:

[0047] Spin-coated (NH4)6Mo7O 24 / Al2O3(0001) was placed in the center of the reaction zone of a tubular furnace. Before heating, Ar gas (100 sccm, 30 min) was introduced to exhaust the air in the quartz tube. Then, NH3 (10 sccm, 60 min) was introduced to heat the substrate to 550°C at a heating rate of 8°C / min. After the reaction was completed, NH3 was turned off and the substrate was allowed to cool naturally in the Ar atmosphere.

[0048] After this stage is over, NH3 is reintroduced (50sccm for 30min), the heating rate is set to 1℃ / min, and after heating to 300℃, the heating rate is set to 1℃ / min again, and it is heated to 700℃ and kept warm for 1.5h. After the reaction is completed, the temperature is cooled to room temperature in an NH3 atmosphere, NH3 is turned off, and the product can be taken out.

[0049] Example 2

[0050] A method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism comprises the following steps:

[0051] S1. Pretreatment of growth substrate:

[0052] The Al2O3 (0001) substrate was cleaned with anhydrous ethanol and deionized water in a cycle, and the surface moisture was drained. Then, the substrate surface was purged with a high-purity N2 gas flow (purity ≥ 99.999%) and then treated with an oxygen plasma cleaner for 30 minutes.

[0053] The cyclic cleaning process includes two cycles, and the specific operation of each cycle is as follows: first, immerse the Al2O3 (0001) substrate in anhydrous ethanol, ultrasonically treat for 12 minutes, pour out the ethanol, and rinse with deionized water four times;

[0054] The technical parameters of the oxygen plasma treatment are as follows: the gas is pure oxygen with a purity of ≥99.99%; the gas pressure is 80 Pa, and the power is 80 W;

[0055] S2. Preparation of precursor solution and spin coating on substrate surface:

[0056] Weigh 3g (NH4)6Mo7O 24 ·4H2O was dissolved in 20mL of deionized water, and then shaken in an ultrasonic cleaner to make (NH4)6Mo7O 24The precursor (NH4)6Mo7O is fully dissolved 24 solution, and then the pretreated Al2O3(0001) substrate was subjected to the precursor (NH4)6Mo7O 24 The solution is spin-coated, and after the spin coating is completed, (NH4)6Mo7O 24 / Al2O3(0001) was placed under an infrared heating lamp and dried at a temperature of 95°C;

[0057] The parameters used in the spin coating process are: rotation speed of 3000 rpm, time of 30 s, and volume of precursor solution of 0.2 mL;

[0058] S3. Synthesis of two-dimensional porous molybdenum nitride:

[0059] Spin-coated (NH4)6Mo7O 24 / Al2O3(0001) was placed in the center of the reaction zone of a tubular furnace. Before heating, Ar gas (100 sccm, 30 min) was introduced to exhaust the air in the quartz tube. Then, NH3 (10 sccm, 60 min) was introduced to heat the substrate to 550°C at a heating rate of 10°C / min. After the reaction was completed, NH3 was turned off and the substrate was allowed to cool naturally in the Ar atmosphere.

[0060] After this stage is over, NH3 is reintroduced (50sccm for 30min), the heating rate is set to 2℃ / min, and after heating to 300℃, the heating rate is set to 1℃ / min, and it is heated to 700℃ and kept warm for 2h. After the reaction is completed, the temperature is cooled to room temperature in an NH3 atmosphere, NH3 is turned off, and the mixture can be taken out.

[0061] Example 3

[0062] A method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism comprises the following steps:

[0063] S1. Pretreatment of growth substrate:

[0064] The Al2O3 (0001) substrate was cleaned with anhydrous ethanol and deionized water in a cycle, and the surface moisture was drained. Then, the substrate surface was purged with a high-purity N2 gas flow (purity ≥ 99.999%), and then treated with an oxygen plasma cleaner for 30 minutes.

[0065] The cyclic cleaning process includes three cycles, and the specific operation of each cycle is as follows: first, immerse the Al2O3 (0001) substrate in anhydrous ethanol, ultrasonically treat for 15 minutes, pour out the ethanol, and rinse with deionized water five times;

[0066] The technical parameters of the oxygen plasma treatment are: the gas is pure oxygen with a purity of ≥99.99%; the gas pressure is 100 Pa, and the power is 100 W;

[0067] S2. Preparation of precursor solution and spin coating on substrate surface:

[0068] Weigh 3g (NH4)6Mo7O 24 ·4H2O was dissolved in 20mL of deionized water, and then shaken in an ultrasonic cleaner to make (NH4)6Mo7O 24 The precursor (NH4)6Mo7O is fully dissolved 24 solution, and then the pretreated Al2O3(0001) substrate was subjected to the precursor (NH4)6Mo7O 24 The solution is spin-coated, and after the spin coating is completed, (NH4)6Mo7O 24 / Al2O3(0001) was placed under an infrared heating lamp and dried at a temperature of 100°C;

[0069] The parameters used in the spin coating process are: rotation speed of 4000 rpm, time of 35 s, and volume of precursor solution of 0.25 mL;

[0070] S3. Synthesis of two-dimensional porous molybdenum nitride:

[0071] Spin-coated (NH4)6Mo7O 24 / Al2O3(0001) was placed in the center of the reaction zone of a tubular furnace. Before heating, Ar gas (100 sccm, 30 min) was introduced to exhaust the air in the quartz tube. Then, NH3 (10 sccm, 60 min) was introduced to heat the substrate to 550°C at a heating rate of 12°C / min. After the reaction was completed, NH3 was turned off and the substrate was allowed to cool naturally in the Ar atmosphere.

[0072] After this stage is over, NH3 is reintroduced (50sccm for 30min), the heating rate is set to 3℃ / min, and after heating to 300℃, the heating rate is set to 1℃ / min, and it is heated to 700℃ and kept warm for 2.5h. After the reaction is completed, the temperature is cooled to room temperature in an NH3 atmosphere, NH3 is turned off, and the sample can be taken out.

[0073] Comparative Example 1

[0074] On the basis of Example 2, the oxygen plasma cleaning machine treatment is not performed, and the remaining steps are the same as the technical solution of Example 2.

[0075] like Figure 1 As shown in (b), the surface treated with oxygen plasma cleaning is more hydrophilic and the precursor solution can spread on the surface. On the contrary, the untreated surface is less hydrophilic ( Figure 1(a) The precursor solution is in the form of droplets on the sapphire surface and fails to spread.

[0076] Comparative Example 2

[0077] The traditional synthesis method of molybdenum nitride, the typical chemical vapor deposition (CVD) growth of Mo2N is mainly through thermal decomposition of (NH4)6Mo7O 24 The precursor is nitrided in an ammonia atmosphere. The specific growth steps involve calcining powdered ammonium molybdate at 500°C for 4 hours in a muffle furnace, followed by temperature-programmed nitriding in NH3. The nitriding process involves increasing the temperature at 5°C / min to 300°C, then increasing the temperature at 1°C / min to 700°C, and holding for 2 hours.

[0078] The molybdenum nitride prepared in Example 2 and Comparative Example 1 was characterized, and the test methods and results are as follows.

[0079] 1. Morphology and composition characterization of two-dimensional molybdenum nitride

[0080] Figure 3 The microstructure of molybdenum nitride (Comparative Example 2) prepared by the traditional method is shown. Figure 3 As shown in (a, b), the scanning electron microscopy (SEM) characterization results show that the Mo2N material prepared by the traditional method does not form a regular two-dimensional morphology, but exhibits typical fractal growth characteristics. Figure 3 As shown in Figures (c, d), X-ray energy dispersive spectroscopy (EDS-mapping) analysis reveals that despite the material's fractal morphology, the Mo and N elements maintain a uniform spatial distribution within the nanosheet structure, confirming the uniformity of the nitridation process. The formation of this fractal structure is likely related to the random distribution of nucleation sites and anisotropic growth dynamics during vapor deposition, demonstrating the limitations of conventional CVD processes in controlling two-dimensional morphology.

[0081] Figure 4 The microstructure and element distribution characteristics of molybdenum nitride prepared by the vapor-solid-solid (VSS) growth mechanism combined with the segmented amination strategy in Example 2 are shown. Figure 4 As shown in (a), a two-dimensional sheet structure with regular geometric morphology was successfully grown on the surface of the Al2O3 (0001) substrate, which mainly showed rectangular and long strip morphologies, indicating that the VSS mechanism has a significant regulatory effect on the anisotropy of crystal growth. It is worth noting that due to the inevitable uneven thickness during the precursor spin coating process, a small amount of agglomerated structure still exists in local areas. Further morphological statistics ( Figure 4 (b)) shows that the average lateral size of the obtained MoN nanosheets is 2-3 μm, but the size of some structures can exceed 20 μm. Different from the traditional dense structure, the high magnification SEM image ( Figure 4(c) clearly shows that molybdenum nitride presents a unique loose porous morphology. This open three-dimensional pore structure may be derived from the staged regulation of reaction kinetics during the stepwise amination process. In order to verify the chemical uniformity of the material, a typical layer structure was selected for EDS-mapping analysis ( Figure 4 (d-f)). The results show that the Mo and N elements maintain a highly uniform spatial distribution within the porous framework, confirming the advantage of the VSS mechanism in maintaining the stoichiometric ratio. This synergistic effect of the porous structure and uniform element distribution may provide unique structural advantages for Mo2N applications in catalysis or energy storage.

[0082] 2. Structural Characterization of Two-Dimensional Molybdenum Nitride

[0083] In order to deeply analyze the microstructural characteristics of molybdenum nitride on the surface of Al2O3 (0001) substrate, high-resolution transmission electron microscopy (HRTEM) was used for systematic characterization. Figure 5 As shown in (a), the HRTEM image clearly shows that the two-dimensional layered structure is composed of a large number of randomly oriented nano-grains stacked together, with uniform grain size distribution and clearly visible grain boundaries. Lattice fringe analysis shows that there are obvious orientation differences between adjacent grains, forming a typical polycrystalline interface structure, confirming that the prepared molybdenum nitride is a polycrystalline two-dimensional material. Further selected area electron diffraction (SAED) analysis ( Figure 5 (b) The diffraction pattern exhibits a characteristic pattern consisting of multiple sets of concentric diffraction rings. This diffraction feature arises from the contributions of a large number of randomly oriented nanocrystals within the material. Each diffraction ring corresponds to Bragg diffraction from a different crystal plane. This result corroborates the polycrystalline structure observed by HRTEM.

[0084] In order to further clarify the crystallographic characteristics of the material, Figure 5 The A and B regions marked in (a) were subjected to high-resolution lattice analysis. The HRTEM test results show that ( Figure 6 (a)), region A shows clear lattice fringes of 0.24 nm, which is completely consistent with the (111) crystal plane spacing of γ-Mo2N. In region B ( Figure 6 A lattice spacing of 0.20 nm is observed in (b), corresponding to the (200) plane of γ-Mo2N. Notably, the two adjacent regions exhibit different crystal plane orientations and lack a defined orientation relationship with the substrate, confirming the non-epitaxial growth of the polycrystalline structure. This polycrystalline nature corroborates the aforementioned SAED analysis results, further revealing the unique nucleation and growth behavior of γ-Mo2N under the VSS growth mechanism.

[0085] 3. In order to characterize the crystal structure and phase composition of the molybdenum nitride catalyst, a systematic phase analysis was carried out using X-ray diffraction (XRD) technology. Figure 7 As shown, the XRD diffraction pattern of the sample shows a series of characteristic diffraction peaks, the positions and relative intensities of which are completely consistent with the standard diffraction card of γ-Mo2N (PDF#25-1366). Specifically, the characteristic diffraction peaks observed at 2θ=37.4°, 43.5°, 63.1° and 75.7° correspond to the diffraction of the (111), (200), (220) and (311) crystal planes of the γ-Mo2N cubic crystal system, respectively. The sharp morphology and high intensity of the diffraction peaks indicate that the prepared molybdenum nitride sample has excellent crystallinity. In addition, the other diffraction peaks appearing in the XRD pattern are all attributed to the signals of the Al2O3 (0001) matrix, and no diffraction peaks of any impurities are detected, which fully confirms that the sample has a high phase purity and does not contain other impurity phases. This result is consistent with the observation results of transmission electron microscopy (TEM), further verifying that the prepared γ-Mo2N sample has a single phase composition and good crystal quality. XRD analysis results show that the synthesis method adopted in this study can successfully prepare high-purity and well-crystalline γ-Mo2N catalyst materials, which lays an important structural foundation for its subsequent catalytic performance research.

[0086] 4. Chemical Characterization of 2D MoN

[0087] In order to further explore the chemical state and stoichiometric ratio of molybdenum nitride, X-ray photoelectron spectroscopy (XPS) was used to systematically characterize the molybdenum nitride samples. Figure 8 (a) shows the full XPS spectrum of the sample, in which the characteristic signal peaks of Mo 3d, Mo 3p, O 1s and Al 2p can be clearly observed, indicating that the sample is mainly composed of Mo, N, O and substrate Al2O3 (0001). Figure 8 (b) is the high-resolution XPS spectrum of Mo 3d, which can be analyzed into four characteristic peaks after peak fitting. Among them, the double peaks at binding energy of 228.5eV and 231.6eV correspond to Mo3d5 / 2 and Mo 3d respectively. 3 / 2 , belonging to the low-price state Mo δ +(0<δ<2), indicating that Mo forms a bond with N (Mo-N). The double peaks at 232.1eV and 235.2eV correspond to Mo 6 +(Mo 3d 5 / 2 and Mo 3d 3 / 2 ), indicating that there is a certain degree of oxidation (Mo-O) on the sample surface. This oxidation may be due to the thin layer of MoO formed on the surface of the sample after it is exposed to air. x , but Mo-N is still the main component.

[0088] Due to Mo 3p 3 / 2The binding energy ranges of N1s (~394.6eV) and N1s (~397.8eV) overlap, and peak fitting is used to further analyze this region. The results show that the peaks at binding energies of 394.6eV and 412.6eV correspond to Mo 3p 3 / 2 and Mo3p 1 / 2 , which is also attributed to the Moδ+-N bond, further confirming the existence of the Mo-N bond. The peaks at the binding energies of 397.3 eV and 416.0 eV correspond to the Mo 6 +-O bonds are consistent with the analysis results of the Mo 3d spectrum. The characteristic peak at a binding energy of 397.8 eV is attributed to N1s, indicating that the nitrogen element exists in a chemically bonded form (Mo-N). Quantitative analysis of the Mo 3d and N1s peak areas indicates that the atomic ratio of Mo to N is approximately 2:1. Combined with the XRD and TEM results (the cubic phase structure and clear lattice fringes of γ-Mo2N), it is confirmed that the prepared sample is a molybdenum nitride material with a stoichiometric ratio close to Mo2N. In summary, XPS analysis not only reveals the dominant role of Mo-N bonds on the sample surface, but also confirms the presence of a small surface oxide layer. Combined with the XRD and TEM data, it can be determined that the catalyst has the crystal structure of γ-Mo2N and is of high purity.

[0089] Figure 8 Middle: (a) Full spectrum of molybdenum nitride, (b) Mo 3d, (c) Mo 3p, and (d) O 1s.

[0090] By analyzing the spectra of Mo 3d, Mo 3p and O1s, the results show the existence of Mo-O bonding, which indicates that the surface of Mo2N is highly active in the air and is easy to react with small oxygen molecules, and the surface is easily oxidized to form a surface oxide layer. In order to further confirm the formation of the surface oxide layer, the Mo2N surface was characterized by Raman. Figure 9 As shown, the Raman results show that the -1 There is a strong characteristic peak signal, which belongs to MoO3. It is worth noting that Mo2N has no characteristic Raman signal peak. This is because Mo2N is a nitride with metallic or metal-like properties, with a large number of free electrons between its conduction band and valence band. In Raman measurements, these free electrons strongly absorb the incident laser and produce a plasmon resonance effect, which leads to severe quenching of the Raman signal.

[0091] In summary, the present invention uses (NH4)6Mo7O 24As a precursor, porous γ-Mo2N with a regular surface and two-dimensional planar structure was successfully prepared on an Al2O3(0001) substrate via chemical vapor deposition combined with a VSS growth mechanism. This study provides an effective strategy for the preparation of TMNx model structures and lays a foundation for the subsequent research and application of nitride thin film materials.

[0092] The present invention is not limited to the above-mentioned specific implementation methods. Various changes made by ordinary technicians in this field based on the above-mentioned concept without creative work are all within the scope of protection of the present invention.

Claims

1. A method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism, characterized in that: The steps include: S1. Pretreatment of growth substrate: The Al2O3 (0001) substrate was cleaned with anhydrous ethanol and deionized water in a cycle, and the surface moisture was drained. Then, the substrate surface was purged with a high-purity N2 gas flow and then treated with an oxygen plasma cleaner for 30 minutes. S2. Preparation of precursor solution and spin coating on substrate surface: Weigh (NH4)6Mo7O 24 4H2O was dissolved in deionized water and then shaken in an ultrasonic cleaner to make (NH4)6Mo7O 24 The precursor (NH4)6Mo7O is fully dissolved 24 solution, and then the pretreated Al2O3(0001) substrate was subjected to the precursor (NH4)6Mo7O 24 The solution is spin-coated, and after the spin coating is completed, (NH4)6Mo7O 24 / Al2O3(0001) was placed under an infrared heating lamp for drying; S3. Synthesis of two-dimensional porous molybdenum nitride: Spin-coated (NH4)6Mo7O 24 / Al2O3(0001) was placed in the center of the reaction zone of a tubular furnace. Before heating, Ar gas was introduced to exhaust the air in the quartz tube. Then, NH3 was introduced to heat the substrate to 550°C at a heating rate of 8-12°C / min. After the reaction was completed, NH3 was turned off and the substrate was allowed to cool naturally in an Ar atmosphere. After this stage is over, NH3 is reintroduced, and the heating rate is set to 1-3°C / min. After heating to 300°C, the heating rate is set to 1°C / min again, and heated to 700°C, and kept warm for 1.5-2.5h. After the reaction is completed, cool to room temperature in an NH3 atmosphere, turn off NH3, and take out.

2. The method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: The cyclic cleaning described in step S1 includes 2 to 3 cycles, and the specific operation of each cycle is: first immerse the Al2O3 (0001) substrate in anhydrous ethanol, ultrasonically treat it for 10 to 15 minutes, pour out the ethanol, and rinse it with deionized water 3 to 5 times.

3. The method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: The purity of the high-purity N2 gas flow in step S1 is ≥99.999%.

4. The method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: The technical parameters of the oxygen plasma treatment in step S1 are: the gas is pure oxygen with a purity of ≥99.99%; the gas pressure is 60-100 Pa, and the power is 60-100 W.

5. The method for preparing molybdenum nitride by chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: (NH4)6Mo7O described in step S2 24 The mass volume ratio of 4H2O to deionized water is 3g:20mL.

6. The method for preparing molybdenum nitride by utilizing chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: The parameters used in the spin coating process described in step S2 are: a rotation speed of 2000-4000 rpm, a time of 25-35 s, and a volume of the precursor solution of 0.15-0.25 mL.

7. The method for preparing molybdenum nitride by utilizing chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: The drying temperature in step S2 is 90-100°C.

8. The method for preparing molybdenum nitride by utilizing chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: The Ar gas in step S3 has an introduction rate of 100 sccm and a time of 30 minutes.

9. The method for preparing molybdenum nitride by utilizing chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: The flow rate of NH3 when introducing in step S3 is 10 sccm and the time is 60 minutes.

10. The method for preparing molybdenum nitride by utilizing chemical vapor deposition combined with a gas-solid-solid growth mechanism according to claim 1, characterized in that: The flow rate of NH3 when it is introduced again in step S3 is 50 sccm, and the time is 30 minutes.

Images