CN113275002B - A kind of C/MoO2 porous photocatalyst and preparation method and application thereof - Google Patents

Abstract

The invention relates to the field of photocatalysis, and relates to a C/ _MoO2 porous photocatalyst and a preparation method and application thereof. In the photocatalyst, C is coated on the surface of MoO ₂ ; the photocatalyst has a hollow structure, the particle size is less than 2000 nm, and the pore size of the composite catalyst is less than 20 nm; when preparing the photocatalyst, NTA and MoCl ₅ are first used The precursors were prepared in a high-temperature reaction kettle, and the C/MoO ₂ porous photocatalyst was prepared by the sintering method. The catalyst provided by the invention has both good adsorption performance and excellent photocatalytic performance, has a high specific area, has a high density of catalytic active centers, the porous and hollow structure increases the specific surface area, can effectively improve the light absorption rate, and delay the electron-hole recombination. In the application, the requirements of the synthetic ammonia reaction can be reduced; the synthesis method provided by the invention has the characteristics of mild conditions, simple and easy-to-obtain synthesis conditions, and high purity, and is suitable for large-scale production applications.

Description

A kind of C/MoO2 porous photocatalyst and preparation method and application thereof

technical field

The invention relates to the field of photocatalysis, in particular to a C/MoO ₂ porous photocatalyst and a preparation method and application thereof.

Background technique

In recent years, the problems of environmental pollution and energy shortage have become increasingly serious, and people have concentrated on research and development of various new energy technologies and equipment. Photocatalysis technology is widely regarded as an important way to solve environmental pollution and energy crisis due to its environmental friendliness and high chemical energy. With the development of industry and agriculture, ammonia has become an important chemical substance for fertilizer and chemical synthesis in agriculture and industry. At present, the synthesis of ammonia in industry is completed by the traditional Haber-Bosch process, which has harsh reaction conditions and high energy consumption, that is, under the conditions of 15-25MPa pressure and 673-873K temperature, the energy consumption accounts for 1% of the global energy. above. At present, the synthesis of ammonia in industry is completed by the traditional Haber-Bosch process, which has harsh reaction conditions and high energy consumption, that is, under the conditions of 15-25MPa pressure and 673-873K temperature, the energy consumption accounts for 1% of the global energy. above. Mo has become one of the most researched elements in the field of photocatalytic nitrogen fixation. However, in Mo-containing catalysts, the photogenerated electron-hole pairs are very easy to recombine quickly, which seriously affects its photocatalytic performance and becomes its main defect as a photocatalyst. Precious metal catalysts can well avoid these shortcomings. However, the expensive price , uncontrollable content, and destructive conjugation systems limit their applications. Therefore, it is necessary to find suitable photocatalysts to improve their photocatalytic performance.

Publication No. CN106976910A, discloses a porous carbon-supported molybdenum oxide nanoparticle composite material and a preparation method thereof. The preparation method includes the following steps: (1) using porous carbon to adsorb molybdate to obtain a precursor; (2) heat-treating the precursor in a hydrogen-argon atmosphere to obtain the porous carbon-supported molybdenum oxide nanometers Granular composites. Compared with other methods, the method has the advantages of low cost, simple process, clear product, and the obtained molybdenum oxide nanoparticles have uniform particle size and high height. Dispersion, no agglomeration, suitable for large-scale production; the porous carbon-supported molybdenum oxide nanoparticle composite material of the present invention has huge potential application value in industrial catalysis, electrochemistry or other scientific fields.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a C/MoO ₂ porous photocatalyst. The invention has both good adsorption performance and excellent photocatalytic performance, has high specific area and high density of catalytic active centers, and the porous and hollow structure increases the specific surface area. The absorption rate slows down the electron-hole recombination rate.

One aspect of the present invention provides a C/MoO ₂ porous photocatalyst, the photocatalyst comprises a hollow sphere structure with a porous surface composed of MoO ₂ , the surface of the MoO ₂ particles is wrapped with C, the catalyst particle size is less than 2000nm, and the The pore size of the composite catalyst is less than 20 nm.

_The surface porous hollow sphere structure of the present invention, the porous and hollow structures increase the specific surface area, so that the outer surface layer of the catalyst is equivalent to a porous film, which can slow down the recombination of electron holes. Changing the band structure can reduce the recombination rate of electron holes.

Preferably, the particle size of the photocatalyst is 1000-2000 nm; the pore size of the composite catalyst is 5-15 nm. When the particle size is small, the value of aperture/particle size is too small, the number of refraction and reflection of light becomes smaller, and the utilization rate of light is reduced. It is not conducive to prolong the recombination of electron holes; when the particle size is too large, a shell structure is formed, and the stability is not good. Therefore, the preferred particle size of the present invention is 1000-2000 nm.

Secondly, the present invention also provides the preparation method of the photocatalyst as described in any one of the above, the preparation process comprises the following steps:

(1) Disperse the MoCl ₅ powder in a solvent, stir at room temperature until dissolved, add NTA, and stir to obtain a homogeneous solution, and the molar ratio of the raw material NTA to MoCl ₅ is 3:1 to 1:3;

(2) adding the solution of step (1) into the autoclave, then placing the autoclave in an oven, and reacting at 155～185°C for 5～7h to obtain a reaction product;

(3) the reaction product obtained in step (2) is separated, cleaned and dried to obtain a precursor;

(4) Under the protection of gas, the precursor is calcined at 450-550° C. for 2-3 hours, and cooled to room temperature to obtain a carbon/molybdenum dioxide nanosphere photocatalyst.

The key of the present invention is to control the reaction temperature and time. In the reaction of step (2), NAT has good coordination performance and can provide four coordination bonds to form metal chelates. If the temperature is too high at this time or the reaction If the time is too long, the chelate will decompose, and if the temperature is too low, the yield of the precursor during the reaction time will be too low. Therefore, the preferred step (2) in this scheme needs to react at 155-185°C for 5-7 hours. In the calcination reaction of step (4), the complex decomposes, gas molecules are generated, and there is no material supplement, so that the pore-like morphology is formed. In addition, due to the high temperature of the precursor, the hollow sphere structure and morphology of the catalyst will collapse. If the reaction time is too low, the product will agglomerate; if the reaction time is too long, the pore size of the catalyst particles will be too small; if the reaction time is too short, the hollow sphere structure of the catalyst cannot be formed well, and it is difficult to achieve the expected effect. Therefore, in this experiment, the preferred step (4) is: Calcined at 450～550℃ for 2～3h.

Preferably, the solvent described in the step (1) is one or more of water, isopropanol, ethylene glycol and ethanol; the stirring adopts a magnetic stirring method and is subjected to ultrasonic treatment.

In order to obtain a uniform solution, the present invention selects magnetic stirring and ultrasonic treatment in the process of stirring and homogenizing the solution.

Preferably, the reaction temperature in the step (2) is 160-180°C; the reaction time is 6-6.5h.

In the present invention, it is preferable to strictly control the temperature at 160-180° C., and react for 6-6.5 hours to prepare the precursor, and the obtained product has good uniformity and yield.

Preferably, the cleaning in the step (3) is at least a water wash and an alcohol wash; the separation in the step (3) adopts centrifugation; the rotational speed of the centrifugation is 3500-4500r/min, and the centrifugation time is 5-10min; drying is adopted for drying; the temperature of the drying treatment is 55-65° C., and the drying time is 12-24h.

The purpose of an alcohol wash is for faster drying and to carry away moisture in the process of alcohol release.

Preferably, the protective gas is argon gas; the calcination equipment is a muffle furnace, the calcination temperature is 460-480°C, and the calcination time is 2.4-2.6h.

The present invention can be carried out in a muffle furnace. Argon gas is passed for a period of time before the calcination reaction to ensure that the air in the muffle furnace is emptied.

Furthermore, the catalyst of the present invention can be used for ammonia synthesis reaction, that is, the present invention provides a photocatalyst for ammonia synthesis, the working temperature range of the catalyst includes 25-40°C, and the working pressure range includes 1-2MPa.

Using the catalyst of the invention can synthesize ammonia gas in a lower temperature range and pressure range, and the invention slows down the rate of electron holes, promotes the ammonia synthesis reaction, and reduces the conditions of the ammonia synthesis reaction.

Compared with the prior art, the beneficial effects of the present invention are:

1. The catalyst provided by the present invention has both good adsorption performance and excellent photocatalytic performance, has a high specific area, has a high density of catalytic active centers, and the porous and hollow structure increases the specific surface area, which can effectively improve the light absorption rate and delay electron emptying. hole compound;

2. The catalyst provided by the present invention can reduce the requirement of synthetic ammonia reaction;

3. The synthesis method provided by the present invention has the characteristics of mild conditions, simple and easy-to-obtain synthesis conditions, and high purity, and is suitable for large-scale production applications.

Description of drawings

Fig. 1 is the XRD picture of catalyst provided by the invention;

Fig. 2 is the SEM picture of catalyst provided by the invention;

Figure 3 is a TEM picture of the catalyst provided by the present invention.

Detailed ways

The present invention will be further described below in conjunction with the embodiments. The devices, materials and methods involved in the present invention, unless otherwise specified, are all known devices, materials and methods in the art.

General Example

A preparation method of C/MoO ₂ porous photocatalyst:

( ₁ ) Disperse 0.2g MoCl powder in a mixed solution of 10ml deionized water and 20ml isopropanol, stir magnetically and ultrasonically treat to a homogeneous solution, add 0.14g NTA, stir magnetically and then undergo ultrasonic treatment to obtain a homogeneous solution;

(2) adding the solution obtained in step (1) into an autoclave, then placing the autoclave in an oven, and reacting at 155-185° C. for 5-7 hours to obtain a reaction product;

(3) The reaction product obtained in the separation step (2) was centrifuged for 5 minutes at a rotating speed of 4000 r/min, and the separated product was washed with water three times and washed with alcohol three times, and then dried at 60 °C for 12 hours to obtain the precursor;

(4) The precursor was placed in a muffle furnace, calcined at 450-550° C. for 2-3 hours under the protection of argon, and cooled to room temperature to obtain a carbon/molybdenum dioxide nanosphere photocatalyst.

Example 1

A preparation method of C/MoO ₂ porous photocatalyst:

( ₁ ) Disperse 0.2g MoCl powder in a mixed solution of 10ml deionized water and 20ml isopropanol, stir magnetically and ultrasonically treat to a homogeneous solution, add 0.14g NTA, stir magnetically and then undergo ultrasonic treatment to obtain a homogeneous solution;

(2) adding the solution obtained in step (1) into the autoclave, then placing the autoclave in an oven, and reacting at 155°C for 5 hours to obtain a reaction product;

(3) The reaction product obtained in the separation step (2) was centrifuged for 5 minutes at a rotating speed of 4000 r/min, and the separated product was washed with water three times and washed with alcohol three times, and then dried at 60 °C for 12 hours to obtain the precursor;

(4) The precursor was placed in a muffle furnace, calcined at 450 °C for 2 h under the protection of argon, and cooled to room temperature to obtain a carbon/molybdenum dioxide nanosphere photocatalyst.

Example 2

Compared with Example 1, the difference of this example is that the reaction temperature of step (2) is 170°C, and the other conditions are the same as those of Example 1.

Example 3

Compared with Example 1, the difference of this example is that the reaction temperature of step (2) is 185° C., and other conditions are the same as those of Example 1.

Example 4

Compared with Example 1, the difference of this example is that the reaction temperature of step (4) is 500° C., and other conditions are the same as those of Example 1.

Example 5

Compared with Example 1, the difference of this example is that the reaction temperature of step (4) is 550° C., and other conditions are the same as those of Example 1.

Example 6

Compared with Example 1, the difference of this example is that the reaction time of step (2) is 6h, and the remaining conditions are the same as those of Example 1.

Example 7

Compared with Example 1, the difference of this example is that the reaction time of step (2) is 7h, and the remaining conditions are the same as those of Example 1.

Example 8

Compared with Example 1, the difference of this example is that the reaction time of step (4) is 2.5h, and other conditions are the same as those of Example 1.

Example 9

Compared with Example 1, the difference of this example is that the reaction time of step (4) is 3h, and the remaining conditions are the same as those of Example 1.

Comparative Example 1

Compared with Example 1, the difference of this comparative example is that the reaction temperature of step (2) is 130° C., and other conditions are the same as those of Example 1.

Comparative Example 2

Compared with Example 1, the difference of this comparative example is that the reaction temperature of step (2) is 210° C., and other conditions are the same as those of Example 1.

Comparative Example 3

Compared with Example 1, the difference of this comparative example is that the reaction time of step (2) is 3h, and the remaining conditions are the same as those of Example 1.

Comparative Example 4

Compared with Example 1, the difference of this comparative example is that the reaction time of step (2) is 10h, and the remaining conditions are the same as those of Example 1.

Comparative Example 5

Compared with Example 1, the difference of this comparative example is that the reaction temperature of step (4) is 300° C., and other conditions are the same as those of Example 1.

Comparative Example 6

Compared with Example 1, the difference of this comparative example is that the reaction temperature of step (4) is 500° C., and other conditions are the same as those of Example 1.

Comparative Example 7

Compared with Example 1, the difference of this comparative example is that the reaction time of step (4) is 1h, and the remaining conditions are the same as those of Example 1.

Comparative Example 8

Compared with Example 1, the difference of this comparative example is that the reaction time of step (4) is 5h, and the remaining conditions are the same as those of Example 1.

Comparative Example 9

Compared with Example 1, the difference of this comparative example is that this comparative example is MoO ₂ powder, and other conditions are the same as those of Example 1.

The samples obtained in Examples 1-9 and Comparative Examples 1-9 were detected by the following methods:

1. The prepared samples were observed by SEM to measure particle size, pore size, etc.;

2. Catalytic performance test: Mix 40 mg of the prepared photocatalyst with 60 mL of deionized water, stir evenly, and use ion chromatography to check whether there is ammonium pollution before the reaction. If the environment is free from ammonium pollution, 40 mg of the sample and 60 mL of The quartz container of deionized water was put into the high-pressure reaction kettle. The system was first ventilated with argon gas for half an hour to ensure no pollution, and an external exhaust pipe was used to remove excess nitrogen in the reaction kettle in time. h One sample was taken to detect the concentration of ammonium ions, five times in total, and the temperature was kept between 25-40°C during the reaction.

The specific results are shown in Table 1.

Table 1 Test results

Comparing Examples 1-3 and 1-2, it can be seen that during the preparation of the precursor, the temperature has a great influence on the final performance of the catalyst. In terms of the diameter and pore size of the catalyst particles, the experimental values are not much different. However, the influence of temperature lies in the yield of the precursor, so under the condition of too high or low temperature, too low yield is the main factor affecting the test results.

Comparing Example 1 with Example 4-5 and Comparative Example 3-4, it can be seen that in the process of preparing the precursor, the reaction time has a great influence on the final performance of the catalyst. The values are not much different. The influence of the reaction time lies in the yield of the precursor. Therefore, under the reaction time that is too long or too short, the yield is too low, which is the main factor affecting the test results.

Comparing Example 1 with Examples 6-7 and Comparative Examples 5-6, it can be seen that during the calcination reaction, the temperature has a greater impact on the final performance of the catalyst, and the temperature can affect the particle size, pore size and pore size distribution, And temperature also has an effect on determining whether the reaction is complete, particle size, pore size and distribution, and whether the reaction is complete will affect the catalyst performance. Under the condition of low temperature, the small pore size of the particle is large, the reaction is not complete, and the test result is poor, such as Comparative Example 5; under the condition of high temperature, the particle size is small in size, and the number of micropores on the surface is small, resulting in poor test results. , as in Comparative Example 6.

Comparing Example 1 with Examples 8-9 and Comparative Examples 7-8, it can be seen that during the calcination reaction, the reaction time has a greater impact on the final performance of the catalyst, and the reaction time will affect the particle size, pore size and pore size. Particle size, pore size and distribution, and reaction completeness all affect catalyst performance. Under the condition of short reaction time, the small pore size of the particles is large, the reaction is not complete, and the test results are poor, such as Comparative Example 7; under the condition of long reaction time, the large particle size of the particles is small, and the number of surface micropores is small, which leads to the test results. poor, as in Comparative Example 8.

Comparing Examples 1-9 and Comparative Example 9, it can be seen that the existence of C promotes the synthesis of NH ₃ , which may be caused by the existence of C changing the energy band structure of the material.

The above are only preferred embodiments of the present invention and do not limit the present invention. Any simple modifications, changes and equivalent structural transformations made to the above embodiments according to the technical essence of the present invention still belong to the technology of the present invention. The scope of protection of the program.

Claims (8)

1. a preparation method of C/MoO ₂ porous photocatalyst, it is characterized in that: described photocatalyst comprises by MoO ₂ the hollow sphere structure that constitutes porous surface, and MoO ₂ particle surface has C wrapping, catalyst particle diameter is less than 2000 nm, and the pore size of the composite catalyst is less than 20 nm; The preparation method of the C/MoO ₂ porous photocatalyst comprises the following steps: (1) Disperse the MoCl ₅ powder in a solvent, stir at room temperature until dissolved, add NTA, and stir to obtain a homogeneous solution. The molar ratio of raw material NTA to MoCl ₅ is 3:1 to 1:3; (2) adding the solution obtained in step (1) into the autoclave, placing the autoclave in an oven, and reacting at 155-185 °C for 5-7 hours to obtain a reaction product; (3) separating the reaction product obtained in step (2), cleaning and drying to obtain a precursor; (4) Under the protection of gas, the precursor is calcined at 450-550° C. for 2-3 hours, and cooled to room temperature to obtain a carbon/molybdenum dioxide nanosphere photocatalyst. 2 . The preparation method of the C/MoO ₂ porous photocatalyst according to claim 1 , wherein the particle size of the photocatalyst is 1000-1500 nm. 3 . 3 . The preparation method of the C/MoO ₂ porous photocatalyst according to claim 1 , wherein the pore size of the composite catalyst is 5-15 nm. 4 . 4 . The preparation method of C/MoO ₂ porous photocatalyst according to claim 1 , wherein the solvent in the step (1) is one or more of water, isopropanol, ethylene glycol and ethanol. 5 . Species; the stirring adopts magnetic stirring and ultrasonic treatment. 5 . The preparation method of the C/MoO ₂ porous photocatalyst according to claim 1 , wherein the reaction temperature in the step (2) is 160-180° C.; and the reaction time is 6-6.5 h. 6 . 6 . The preparation method of C/MoO ₂ porous photocatalyst according to claim 1 , wherein the cleaning in the step (3) is at least one water washing and one alcohol washing; the separation in the step (3) is at least one time. 7 . Centrifugal treatment is adopted; the rotating speed of the centrifugal treatment is 3500-4500 r/min, and the centrifugation time is 5-10 min; drying is adopted for drying; the temperature of the drying treatment is 55-65 ℃, and the drying time is 12 -24h. 7. The preparation method of C/MoO ₂ porous photocatalyst according to claim 1, wherein the protective gas is argon; the calcination equipment is a muffle furnace, the calcination temperature is 460-480 °C, and the calcination time is 460-480 °C. for 2.4-2.6 h. 8. application of the photocatalyst prepared by the preparation method according to one of claims 1 to 7 for synthesizing ammonia in ammonia synthesis, wherein the catalyst working temperature range is 25-40 °C, and the working pressure The range is 1-2 MPa.

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