MoO2 / Mo2N composite material as well as preparation method and application thereof

Abstract

The invention discloses a MoO2 / Mo2N composite material and a preparation method and application thereof.The MoO2 / Mo2N composite material is provided with a MoO2 and Mo2N mixed phase, the preparation method comprises the steps that a MoO3 precursor is placed in an open container, the open container is placed in an ammonia atmosphere to be subjected to calcination treatment, the MoO2 / Mo2N composite material is obtained, and the MoO2 / Mo2N composite material can be applied to photocatalytic CO2 reduction reaction. The method comprises the following steps: putting the composite material into a reactor with a quartz window, introducing a CO2 / H2O or CO2 / H2 mixed reactant, and reducing CO2 under an illumination condition. According to the invention, the problems of complex material synthesis process and high cost in the existing method are solved, and the synthesized MoO2 / Mo2N composite material is applied to photocatalytic CO2 reduction and has good reaction activity and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalyst materials, and specifically relates to a MoO2 / Mo2N composite material and a preparation method and application thereof. Background Art

[0002] Since the Industrial Revolution, traditional fossil energy has gradually penetrated and supported the development of modern society. However, the energy shortage and environmental pollution caused by the burning of a large amount of fossil energy are becoming increasingly prominent. On the one hand, it is necessary to vigorously develop green renewable energy such as wind power and solar energy, and on the other hand, it is necessary to capture, convert and reuse CO2 emitted in production and life. However, CO2 molecules are very stable in thermodynamics, and the bond energy of the C=O bond is as high as 750kJ / mol. The economic benefits of using traditional thermal catalysis to convert them are not ideal. Light-driven CO2 conversion is an effective way to use solar energy to convert greenhouse gases into fuels or high-value chemicals. This process can allow the reaction to proceed under milder conditions, which is of great significance for further transition to low-carbon energy.

[0003] The realization of light-driven CO2 conversion technology depends on the design and development of efficient photocatalysts. Traditional photocatalysts are mostly transition metal oxide semiconductors such as TiO2, Cu2O, and ZnO. The presence of oxygen vacancies in such catalysts helps the adsorption and activation of CO2. However, conventional transition metal oxides have very limited ability to absorb and utilize infrared light, which accounts for a large proportion of sunlight. Therefore, such catalysts usually need to be loaded with precious metal co-catalysts with plasmon effects such as Au, Pd, and Pt to improve the light utilization rate and catalytic activity of the catalyst. This leads to a complex catalyst synthesis process, which is difficult to mass produce, and has a high production cost and unsatisfactory economic benefits, thus limiting the development of the application of photocatalytic CO2 conversion technology.

[0004] The energy band structure of transition metal nitrides is similar to that of precious metals, with high electrical conductivity and narrow band gap, which is conducive to the efficient transmission of carriers and the absorption of light energy. Due to its potential to replace precious metal catalysts, it has received extensive attention in the field of light-driven CO2 conversion in recent years. The early synthesis methods of transition metal nitride photocatalysts mainly used metals and their oxides as precursors, nitrided or aminated at high temperatures, and then modified their surfaces by photodeposition, electrodeposition or impregnation after cooling, or loaded transition metal nitrides onto other carriers to improve the catalytic activity, such as Au / Cu3N (ACS Appl. Nano Mater. 2019, 2, 5009), Cr 0.5 Ti 0.5N / CdS (J. Mater. Chem. A 2020, 8, 15774), Mo2N / g-C3N4 (Appl. Catal. B-Environ. 2018, 238, 318-327), etc. This type of method has problems such as harsh synthesis conditions and complex synthesis pathways, which limits the further development of transition metal catalysts.

[0005] Therefore, there is an urgent need to develop a high-performance transition metal nitride catalyst that is simple, low-cost, and can be synthesized in large quantities. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a MoO2 / Mo2N composite material and a preparation method and application thereof. The present invention starts with the development of a new photocatalyst, explores a convenient, low-cost, batch-synthesized catalyst preparation strategy, and develops a new CO2 photocatalytic conversion system and technology with high efficiency, low cost, high selectivity and high stability, so as to promote the development of practical applications of photocatalytic CO2 conversion.

[0007] The technical solution of the present invention is:

[0008] The invention relates to a method for preparing a MoO2 / Mo2N composite material. A MoO3 precursor is placed in an open container, and the open container is placed in an ammonia atmosphere for calcination to obtain the MoO2 / Mo2N composite material.

[0009] The precursor can be any MoO3 with different properties. The present invention prefers nanomaterials. The MoO3 precursor is a material with a nanoscale internal structure or surface structure.

[0010] Preferably, the MoO3 precursor is MoO3 nanosheets and / or MoO3 nanowires.

[0011] Preferably, the MoO3 precursor is MoO3 nanosheets, and the preparation method of the MoO3 nanosheets is: dissolving metal Mo powder in a mixed solution of ethanol and H2O2, reacting at 150-200°C for 10-24h, and after washing and drying the product, a MoO3 precursor with a nanosheet morphology is obtained.

[0012] Preferably, the mass volume ratio of the metal Mo powder to the mixed solution of ethanol and H2O2 is 200-1000 mg / 30-150 mL.

[0013] Preferably, the calcination treatment conditions in an ammonia atmosphere are: firstly heating to 250-400°C at a heating rate of 5-10°C / min, and keeping warm for 10 minutes; then heating to 400-700°C at a heating rate of 1-10°C / min, and calcining for 1-8 hours.

[0014] Preferably, the ammonia flow rate is 10-100 mL / min.

[0015] Preferably, the open container is an alumina or quartz high temperature resistant container for containing the MoO3 precursor, and the mass of the precursor is 0.1-200g.

[0016] The invention also relates to a MoO2 / Mo2N composite material, which is prepared by the above preparation method. The MoO2 / Mo2N composite material has a mixed phase of MoO2 and Mo2N.

[0017] The present invention also relates to the application of the MoO2 / Mo2N composite material in photocatalytic CO2 reduction.

[0018] The present invention also relates to a photocatalytic CO2 reduction method, wherein the above-mentioned MoO2 / Mo2N composite material is placed in a reactor with a quartz window, wherein the quartz window is used to introduce light, and a CO2 / H2O or CO2 / H2 mixed reactant is introduced, and CO2 is reduced under light conditions, and the reduction products are CH4, CO, CH3OH, etc.

[0019] The beneficial effects of the present invention are:

[0020] (1) The present invention provides a method for preparing a MoO2 / Mo2N composite material. MoO3 is used as a precursor and a MoO2 / Mo2N composite material is obtained by an ammoniation method. The MoO2 / Mo2N composite material has a mesoporous structure (pore size 2-50nm), is mainly composed of Mo2N, and MoO2 nanoparticles are uniformly distributed in the Mo2N. The entire preparation process is simple, the conditions are controllable, and the cost is low. The mass synthesis of the material can be achieved, and the synthesized material has the characteristics of small particle size, large specific surface area, and good uniformity.

[0021] (2) The MoO2 / Mo2N composite material prepared by the present invention has a plasmon effect, has extremely strong light absorption ability, and exhibits precious metal-like properties; and in the material, the MoO2 phase has abundant oxygen vacancies, which is helpful for the activation of CO2, and Mo2N can also provide abundant active sites. When applied to mobile phase photocatalytic CO2 reduction, it has high activity and stability, fits the industrial production application scenario, and has the potential for practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0023] Figure 1 The X-ray powder diffraction pattern of the MoO2 / Mo2N composite material prepared in Example 1 of the present invention;

[0024] Figure 2This is a SEM morphology image of the MoO2 / Mo2N composite material prepared in Example 1 of the present invention;

[0025] Figure 3 The results of N2 physical adsorption and desorption tests of the MoO2 / Mo2N composite material prepared in Example 1 of the present invention, wherein the left figure is a N2 adsorption-desorption isotherm diagram, and the right figure is a pore size distribution diagram;

[0026] Figure 4 The graph is a test result of product generation rate and selectivity when the MoO2 / Mo2N composite material prepared in Example 1 of the present invention and the MoO3 precursor and the products obtained in various comparative examples are applied to photocatalytic CO2 reduction;

[0027] Figure 5 The X-ray powder diffraction pattern of the MoO2 / Mo2N composite material prepared in Example 2 of the present invention;

[0028] Figure 6 This is a SEM morphology image of the MoO2 / Mo2N composite material prepared in Example 2 of the present invention;

[0029] Figure 7 This is a graph showing the product generation rate and selectivity test results when the MoO2 / Mo2N composite material prepared in Example 2 of the present invention is applied to mobile phase photocatalytic CO2 reduction. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0031] Example 1

[0032] (1) MoO3 nanosheet precursor was synthesized by hydrothermal method: 1000 mg of metal Mo powder was dissolved in 150 mL of ethanol and H2O2 (the volume ratio of ethanol to H2O2 was 7:1) mixed solution, and the mixture was reacted at 180 °C for 16 h. After the product was washed and dried, a MoO3 precursor with nanosheet morphology was obtained.

[0033] (2) taking 3 g of the MoO3 nanosheet powder obtained in step (1) and placing it in a quartz boat, and then placing the quartz boat in a tube furnace;

[0034] (3) introducing ammonia gas at a flow rate of 50 mL / min into the above device, heating the tube furnace to 300°C at a heating rate of 5°C / min, and keeping the temperature for 10 min;

[0035] (4) Continue heating to 500°C at a heating rate of 1°C / min and keep at this temperature for 5 h;

[0036] (5) Cooling the above powder to room temperature to obtain a MoO2 / Mo2N composite material.

[0037] Figure 1 The XRD test results of the MoO2 / Mo2N composite material in Example 1 are shown. The precursor is MoO3 nanosheets, and after amination, a mixed phase of MoO2 and Mo2N is obtained. The XRD results show that the main body of the MoO2 / Mo2N composite material is cubic phase Mo2N, and the (-1 1 1) and (-2 1 2) peaks of MoO2 are observed at 26° and 42°, respectively, proving the existence of the MoO2 second phase.

[0038] Figure 2 It shows that the MoO2 / Mo2N composite material in Example 1 is in the shape of nanosheets.

[0039] Figure 3 It shows that the MoO2 / Mo2N composite material in Example 1 is a porous structure with a specific surface area of ​​up to 95.2 m2 / g and a pore size distribution of about 3 nm.

[0040] Example 2

[0041] (1) 10 g of MoO3 nanowire powder was placed in a quartz boat. The MoO3 nanowire was purchased from Suzhou Beike Nanotechnology Co., Ltd. and the purity was analytically pure. The quartz boat was then placed in a tube furnace.

[0042] (2) Ammonia gas at a flow rate of 100 mL / min was introduced into the above device, and the temperature of the tube furnace was increased to 400° C. at a heating rate of 5° C. / min and kept at this temperature for 10 min;

[0043] (3) Continue heating to 600°C at a heating rate of 1°C / min and keep at this temperature for 5 h;

[0044] (4) Cooling the above powder to room temperature to obtain a MoO2 / Mo2N composite material.

[0045] Figure 5 The XRD test results of the MoO2 / Mo2N composite material in Example 2 are shown. The precursor is MoO3 nanowires. After amination, characteristic peaks of Mo2N and MoO2 can be observed simultaneously in the XRD results, proving that the material is a mixed phase of MoO2 and Mo2N.

[0046] Figure 6 It shows that the MoO2 / Mo2N composite material in Example 2 is in the form of nanowires.

[0047] Comparative Example 1

[0048] The MoO2 powder purchased from Shanghai Aladdin Chemical Reagent Co., Ltd. is of analytical grade.

[0049] Comparative Example 2

[0050] The Mo2N powder purchased from Shanghai Aladdin Chemical Reagent Co., Ltd. was of analytical grade.

[0051] Comparative Example 3

[0052] The MoO2 powder and Mo2N powder purchased from Shanghai Aladdin Chemical Reagent Co., Ltd. were ground in mass ratios of 2:1, 1:1, and 1:2 to obtain uniformly mixed MoO2 / Mo2N powders, which were recorded as MoO2:Mo2N 2:1, MoO2:Mo2N 1:1, and MoO2:Mo2N 1:2.

[0053] Comparative Example 4

[0054] Using the same MoO3 nanosheet precursor as in Example 1, 3 g of MoO3 nanosheet powder was placed in a quartz boat, which was then placed in a tube furnace. Ammonia gas was introduced into the apparatus at a flow rate of 50 mL / min, and the temperature was increased to 500°C at a heating rate of 10°C / min and kept warm for 5 h, which was recorded as MoO2 / Mo2N one-step heating.

[0055] Application Example 1

[0056] The MoO2 / Mo2N composite material obtained in Example 1 and the precursor MoO3 nanosheets, the MoO2 powder in Comparative Example 1, the Mo2N powder in Comparative Example 2, the mixed powder ground and mixed in Comparative Example 3, and the product obtained by one-step heating in Comparative Example 4 were used as raw materials. 10 mg of each was loaded on a glass fiber, and then the glass fiber was placed in a quartz tube. Then, CO2 / H2 reaction gas (CO2:H2 volume ratio of 1:1) was filled into the reactor at a rate of 20 mL / min. At a light intensity of 1 W / cm 2 The product CO was obtained after 20 minutes of reaction under irradiation with spectral light.

[0057] Figure 4 It is shown that the MoO2 / Mo2N composite material in Example 1 has good photocatalytic CO2 reduction activity, the product is mainly CO, the generation rate is about 900mmol / g / h, and the product selectivity is >99%, which is much higher than the MoO3 precursor, Mo2N and MoO2, and the MoO2 / Mo2N mixed powder. Compared with the one-stage heating method, the two-stage heating method of the present invention is beneficial to maintaining the nano-morphology of the precursor and making the MoO2 component and the Mo2N component uniformly distributed.

[0058] Application Example 2

[0059] 10 mg of the MoO2 / Mo2N composite material powder obtained in Example 2 was loaded on a glass fiber, and the glass fiber was placed in a reactor with a quartz window. Then, a mixed reaction gas of CO2 / H2 (CO2:H2 volume ratio of 1:1) was introduced into the reactor at a rate of 20 mL / min. 2 The catalyst activity was evaluated under spectral light irradiation, and the product was detected every 1 hour.

[0060] Figure 7 It is shown that the MoO2 / Mo2N composite material in Example 2 has good photocatalytic CO2 reduction activity, high product selectivity, and extremely high stability, and can continue to react for 168 hours.

[0061] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A method for preparing a MoO2 / Mo2N composite material, characterized in that: The MoO3 precursor is placed in an open container, and the open container is calcined in an ammonia atmosphere to obtain a MoO2 / Mo2N composite material.

2. The preparation method according to claim 1, characterized in that: The MoO3 precursor is a material having a nanoscale internal structure or a surface structure.

3. The preparation method according to claim 2, characterized in that: The MoO3 precursor is MoO3 nanosheets and / or MoO3 nanowires.

4. The preparation method according to claim 2, characterized in that: The MoO3 precursor is MoO3 nanosheets. The preparation method of the MoO3 nanosheets is as follows: dissolving metal Mo powder in a mixed solution of ethanol and H2O2, reacting at 150-200°C for 10-24h, and washing and drying the product to obtain a MoO3 precursor with a nanosheet morphology.

5. The preparation method according to claim 1, characterized in that: The calcination treatment conditions in an ammonia atmosphere are: first, heat to 250-400°C at a heating rate of 5-10°C / min, and keep warm for 10 minutes; then heat to 400-700°C at a heating rate of 1-10°C / min, and calcine for 1-8 hours.

6. The preparation method according to claim 1, characterized in that: The ammonia flow rate is 10-100 mL / min.

7. The preparation method according to claim 1, characterized in that: The open container is an alumina or quartz high temperature resistant container.

8. A MoO2 / Mo2N composite material, characterized in that: The MoO2 / Mo2N composite material is prepared by the preparation method according to any one of claims 1 to 7 and has a mixed phase of MoO2 and Mo2N.

9. Use of the MoO2 / Mo2N composite material according to claim 8 in photocatalytic CO2 reduction.

10. A photocatalytic CO2 reduction method, characterized in that: The MoO2 / Mo2N composite material according to claim 8 is placed in a reactor with a quartz window, CO2 / H2O or CO2 / H2 mixed reactants are introduced, and CO2 is reduced under light conditions.

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