CN108435212B - Molybdenum disulfide-based nano material for efficient photocatalytic water decomposition and hydrogen production and preparation method thereof - Google Patents

Abstract

The invention relates to a molybdenum disulfide-based nanomaterial for high-efficiency photocatalytic decomposition of water to produce hydrogen and a preparation method. The structure is that molybdenum trioxide is a core and molybdenum disulfide is a shell. The non-metallic semiconductor molybdenum trioxide is added, and its plasmon effect can be used to broaden the absorption range of visible light. In addition, the energy level structure of molybdenum trioxide can also be adjusted by doping hydrogen ions to better match the energy of molybdenum disulfide. The order matching promotes the separation of photogenerated excitons, and more importantly, the interface between molybdenum disulfide and molybdenum trioxide can be effectively regulated to promote electron transfer. At the same time, the preparation process is simple and the cost is low. It can further promote the wide application of photocatalytic water splitting for hydrogen production.

Description

Molybdenum disulfide-based nanomaterials and preparation methods for efficient photocatalytic water splitting for hydrogen production

technical field

The invention belongs to the field of catalysis, and relates to a molybdenum disulfide-based high-efficiency photocatalytic water-decomposition nanomaterial for hydrogen production and a preparation method.

Background technique

Photocatalytic hydrogen production technology can well cope with the current energy crisis and environmental pollution problems, and is a technology with great development potential. At present, molybdenum disulfide and its composites have been widely studied in the field of photocatalytic hydrogen production. During photocatalysis, the semiconductor absorbs light to generate excitons, which are subsequently separated at the interface. Light absorption and interface engineering are two key factors for whether a material exhibits high photocatalytic performance. The photocatalytic performance can be improved by forming heterojunctions with P-type semiconductors and N-type semiconductors and introducing metal nanoplasmons to form composite nanomaterials, but light absorption and interface engineering are generally relatively independent and difficult to improve simultaneously. For example, noble metal nanoparticles/molybdenum disulfide composites, loaded noble metal nanomaterials can enhance the visible light absorption of the material through the plasmon resonance effect, (Qi K, Yu S, Wang Q, et al. Decoration of the inert basal plane of defect-rich MoS2 with Pd atoms forachieving Pt-similar HER activity[J].Journal of Materials Chemistry A, 2016; 4(11):4025-4031.) However, photo-generated carrier recombination is still serious, and the cost of containing noble metals in composite materials is high. Therefore, the research on noble metal nanoparticles/molybdenum disulfide composites is limited. (Meng X.Atomic-scale surfacemodifications and novel electrode designs for high-performance sodium-ionbatteries via atomic layer deposition[J].Journal of Materials Chemistry A,2017,5(21).); Research on inexpensive and sustainable nanoscale Materials are considered to be one of the most effective strategies for improving nanomaterials. The addition of non-metallic plasmons can simultaneously achieve broadband light absorption and improve interfacial contact, which is a promising photocatalytic material.

SUMMARY OF THE INVENTION

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a molybdenum disulfide-based nanomaterial for high-efficiency photocatalytic decomposition of water to produce hydrogen and a preparation method. It is composed of molybdenum dioxide and molybdenum trioxide to form a core-shell structure, in which molybdenum trioxide is the core and molybdenum disulfide is the shell. The better energy level matching of molybdenum dioxide and molybdenum trioxide can promote the separation of photogenerated carriers, and the interface between the two is optimized to promote electron transfer, thereby realizing efficient photocatalytic water splitting for hydrogen production.

Technical solutions

A molybdenum disulfide-based nanomaterial for high-efficiency photocatalytic decomposition of water to produce hydrogen is characterized in that the structure is that molybdenum trioxide is a core and molybdenum disulfide is a shell.

A method for preparing a nanomaterial for the high-efficiency photocatalytic decomposition of water to produce hydrogen based on the molybdenum disulfide base, characterized in that the steps are as follows:

Step 1. Preparation of molybdenum trioxide nanomaterials: dissolve 7wt% of polyvinyl alcohol in dimethylformamide and stir at 55-70°C, then add mass 1-2g of ammonium molybdate to obtain a uniform precursor solution; Spinning technology, the material prepared by using the precursor solution is calcined in the air at 280-340 ° C for 1-3 hours to obtain molybdenum trioxide nanomaterials; the electrospinning uses a syringe with a needle tip diameter of 0.5 mm and a volume of 20 ml, The electric field voltage is 16-18KV, and the flow rate is controlled at 0.7-1.0ml/h;

Step 2. Preparation of hydrogen ion-doped molybdenum trioxide nanomaterials: The molybdenum trioxide nanomaterials are placed in a quartz tube, and calcined at 200-400° C. for 0-4h in a hydrogen atmosphere, the hydrogen flow rate is controlled at 8-10ppm, and the heating rate is 5-10℃/min, after natural cooling, hydrogen ion-doped molybdenum trioxide nanomaterials are obtained;

Step 3, preparation of molybdenum disulfide/molybdenum trioxide nanomaterials: take the amount and concentration of the substance as 2.0-3.0 mmol sodium molybdate and 4.0-5.0 mmol cysteine, dissolve in deionized water and mix to obtain solution A; take 0.5- 1.0 g of hydrogen ion-doped molybdenum trioxide nanomaterials were dissolved in deionized water to obtain solution B, and solution B was added dropwise to solution A for 20-40 min, followed by sonication at 180-200 ° C for 9-16 h. Hydrothermal reaction; centrifugal cleaning at 4500-6000 rpm after the reaction, followed by drying at 60-80° C. to obtain molybdenum disulfide/molybdenum trioxide core-shell nanomaterials.

Characterization: Take 50 mg of molybdenum disulfide/molybdenum trioxide nanomaterials and disperse them in 50 ml of deionized water. The photocatalytic production of hydrogen was tested with a photocatalytic device. The test conditions for photocatalytic hydrogen production are as follows: the light source is a xenon lamp with a power of 150W, the intensity of the xenon lamp light source is controlled by a current, and the current is 15A. Sampling and testing were carried out every 30 minutes, and a total of 8 samples were taken.

beneficial effect

The invention proposes a molybdenum disulfide-based nanomaterial for high-efficiency photocatalytic decomposing of water to produce hydrogen and a preparation method. The structure is that molybdenum trioxide is a core and molybdenum disulfide is a shell. The non-metallic semiconductor molybdenum trioxide is added, and its plasmon effect can be used to broaden the absorption range of visible light. In addition, the energy level structure of molybdenum trioxide can also be adjusted by doping hydrogen ions to better match the energy of molybdenum disulfide. The order matching promotes the separation of photogenerated excitons, and more importantly, the interface between molybdenum disulfide and molybdenum trioxide can be effectively regulated to promote electron transfer. At the same time, the preparation process is simple and the cost is low. It can further promote the wide application of photocatalytic water splitting for hydrogen production.

Compared with the noble metal/molybdenum disulfide composite material hydrogen production catalyst, the molybdenum disulfide/molybdenum trioxide composite nanomaterial provided by the present invention can not only widen the absorption range of visible light, reduce the photo-generated carrier recombination efficiency, but also have the advantages of The energy level structure can also be regulated by doping hydrogen ions to better match the energy level of molybdenum disulfide to promote the separation of photogenerated excitons. More importantly, the interface between molybdenum disulfide and molybdenum trioxide can be effectively regulated to promote electron transfer. . At the same time, the preparation process is simple and the cost is reduced. It can further promote the wide application of the photocatalytic splitting of water for hydrogen production.

Description of drawings

Figure 1 is a scanning electron microscope image of molybdenum disulfide/molybdenum trioxide nanomaterials. where 200nm is the size scale

Figure 2 is a transmission electron microscope image of molybdenum disulfide/molybdenum trioxide nanomaterials. where 100nm is the size scale

Figure 3 is the hydrogen production test chart of molybdenum disulfide/molybdenum trioxide nanomaterials

Detailed ways

The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

Example 1:

Polyvinyl alcohol (7 wt %) was dissolved in dimethylformamide and stirred at 60° C. overnight, after which 1.5 g of ammonium molybdate was added to obtain a uniform electrospinning solution. A syringe with a needle tip diameter of 0.5mm and a volume of 20ml was used, the electric field voltage was set to 16KV, and the flow rate was controlled at 0.7ml/h for electrospinning. Dissolve 2.0 mmol sodium molybdate and 4.0 mmol cysteine in deionized water to obtain solution A, take 0.5 g of molybdenum oxide nanomaterials and dissolve them in deionized water to obtain solution B, add solution B dropwise to solution A and ultrasonically 20min, and then a hydrothermal reaction was carried out at 180°C for 12h. After the reaction, centrifugal washing at 4500 rpm was performed, followed by drying at 65° C. to obtain the molybdenum disulfide/molybdenum trioxide nanocomposite material.

Characterization: Take 50 mg of molybdenum disulfide/molybdenum trioxide nanomaterials and disperse them in 50 ml of deionized water. The photocatalytic production of hydrogen was tested with a photocatalytic device. The test conditions for photocatalytic hydrogen production are as follows: the light source is a xenon lamp with a power of 150W, the intensity of the xenon lamp light source is controlled by a current, and the current is 15A. Sampling was carried out every 30 minutes. A total of 8 samples were taken, after 4 cycles. The results show that the maximum hydrogen production of this material is 1772.3 μmol/g.

Embodiment 2:

Polyvinyl alcohol (7 wt %) was dissolved in dimethylformamide and stirred at 55° C. overnight, after which 2 g of ammonium molybdate was added to obtain a uniform electrospinning solution. A syringe with a needle tip diameter of 0.5mm and a volume of 20ml was used, the electric field voltage was set to 17KV, and the flow rate was controlled at 0.8ml/h for electrospinning preparation, and then calcined at 300°C for 2h in air to obtain molybdenum trioxide nanomaterials. Dissolve 2.5 mmol sodium molybdate and 4.0 mmol cysteine in deionized water to obtain solution A, take 0.6 g of molybdenum oxide nanomaterials and dissolve them in deionized water to obtain solution B, add solution B dropwise to solution A and ultrasonically 25min, and then a hydrothermal reaction was carried out at 190°C for 9h. After the reaction is completed, centrifugal washing at 5000 rpm is carried out, followed by drying at 60° C. to obtain the molybdenum disulfide/molybdenum trioxide nanocomposite material.

Characterization: Take 50 mg of molybdenum disulfide/molybdenum trioxide nanomaterials and disperse them in 50 ml of deionized water. The photocatalytic production of hydrogen was tested with a photocatalytic device. The test conditions for photocatalytic hydrogen production are as follows: the light source is a xenon lamp with a power of 150W, the intensity of the xenon lamp light source is controlled by a current, and the current is 15A. Sampling was carried out every 30 minutes. A total of 8 samples were taken, after 4 cycles. The results show that the maximum hydrogen production of this material is 2368.3 μmol/g.

Embodiment three:

Polyvinyl alcohol (7 wt %) was dissolved in dimethylformamide and stirred at 65° C. for one night, and then 1 g of ammonium molybdate was added to obtain a uniform electrospinning solution. A syringe with a needle tip diameter of 0.5mm and a volume of 20ml was used, the electric field voltage was set to 17KV, and the flow rate was controlled at 0.9ml/h for electrospinning. Dissolve 3.0 mmol sodium molybdate and 4.5 mmol cysteine in deionized water to obtain solution A, take 0.8 g of molybdenum oxide nanomaterials and dissolve in deionized water to obtain solution B, add solution B dropwise to solution A and ultrasonically 30 min, and then a hydrothermal reaction was carried out at 200 °C for 16 h. After the reaction, centrifugal washing at 5,500 rpm was performed, followed by drying at 70° C. to obtain the molybdenum disulfide/molybdenum trioxide nanocomposite material.

Characterization: Take 50 mg of molybdenum disulfide/molybdenum trioxide nanomaterials and disperse them in 50 ml of deionized water. The photocatalytic production of hydrogen was tested with a photocatalytic device. The test conditions for photocatalytic hydrogen production are as follows: the light source is a xenon lamp with a power of 150W, the intensity of the xenon lamp light source is controlled by a current, and the current is 15A. Sampling was carried out every 30 minutes. A total of 8 samples were taken, after 4 cycles. The results show that the maximum hydrogen production of this material is 3365.6 μmol/g.

Embodiment 4:

Polyvinyl alcohol (7 wt %) was dissolved in dimethylformamide and stirred at 70° C. overnight, after which 1.5 g of ammonium molybdate was added to obtain a uniform electrospinning solution. A syringe with a needle tip diameter of 0.5mm and a volume of 20ml was used, the electric field voltage was set to 18KV, and the flow rate was controlled at 1.0ml/h for electrospinning preparation, and then calcined at 340°C for 2.5h in air to obtain molybdenum trioxide nanomaterials. Dissolve 3.0 mmol sodium molybdate and 5.0 mmol cysteine in deionized water to obtain solution A, take 1.0 g of molybdenum oxide nanomaterials and dissolve them in deionized water to obtain solution B, add solution B dropwise to solution A and ultrasonically 40min, and then a hydrothermal reaction was carried out at 200°C for 14h. After the reaction, centrifugal washing at 6000 rpm was performed, followed by drying at 80° C. to obtain the molybdenum disulfide/molybdenum trioxide nanocomposite material.

Characterization: Take 50 mg of molybdenum disulfide/molybdenum trioxide nanomaterials and disperse them in 50 ml of deionized water. The photocatalytic production of hydrogen was tested with a photocatalytic device. The test conditions for photocatalytic hydrogen production are as follows: the light source is a xenon lamp with a power of 150W, the intensity of the xenon lamp light source is controlled by a current, and the current is 15A. Sampling was carried out every 30 minutes. A total of 8 samples were taken, after 4 cycles. The results show that the maximum hydrogen production of this material is 2150.3 μmol/g.

Claims (1)

1. A method for preparing molybdenum disulfide-based nano material for hydrogen production by photocatalytic decomposition of water is characterized by comprising the following steps: the structure of the molybdenum disulfide-based nano material for hydrogen production by photocatalytic water decomposition is that molybdenum trioxide is used as a core, and molybdenum disulfide is used as a shell; the method comprises the following specific steps:

step 1, preparing a molybdenum trioxide nano material: dissolving 7 wt% of polyvinyl alcohol in dimethylformamide, stirring at 55-70 ℃, and then adding 1-2g of ammonium molybdate to obtain a uniform precursor solution; calcining the material prepared by using the precursor solution in air at 280-340 ℃ for 1-3h by adopting an electrostatic spinning technology to obtain a molybdenum trioxide nano material; the needle point diameter adopted in the electrostatic spinning is 0.5mm, the volume is 20ml of the injector, the electric field voltage is 16-18KV, and the flow rate is controlled to be 0.7-1.0 ml/h;

step 2, preparing the hydrogen ion doped molybdenum trioxide nano material: placing the molybdenum trioxide nano material in a quartz tube, calcining for 0-4h at the temperature of 200-;

step 3, preparing the molybdenum disulfide/molybdenum trioxide nano material: dissolving 2.0-3.0mmol of sodium molybdate and 4.0-5.0mmol of cysteine in deionized water, and mixing to obtain a solution A; dissolving 0.5-1.0g of hydrogen ion-doped molybdenum trioxide nano material in deionized water to obtain a solution B, dropwise adding the solution B into the solution A, performing ultrasonic treatment for 20-40min, and performing hydrothermal reaction at 180-200 ℃ for 9-16 h; and after the reaction is finished, performing centrifugal cleaning at 4500-6000 rpm, and drying at 60-80 ℃ to obtain the molybdenum disulfide/molybdenum trioxide core-shell nano material.

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