CN115779951A - Composite photocatalyst C-MoO 2 /C 3 N 4 And preparation method and application thereof - Google Patents

Abstract

The invention provides a composite photocatalyst C-MoO ₂ /C ₃ N ₄ and its preparation method and application, which belong to the technical field of nanomaterial synthesis and photocatalysis; Thermal reaction prepares carbon-doped C-MoO ₂ , and then self-assembles C ₃ N ₄ and C-MoO ₂ in a self-assembly solution to obtain a composite photocatalyst C-MoO ₂ /C ₃ N ₄ ; the composite photocatalyst The catalyst C‑MoO ₂ /C ₃ N ₄ is an S-type heterojunction, which can expand the absorption range of light, enhance the separation of photogenerated carriers, prolong the lifetime of carriers, and maintain a strong electron reduction ability and space The oxidation ability of holes has a good application in the field of photocatalytic hydrogen production from water.

Description

A kind of composite photocatalyst C-MoO2/C3N4 and its preparation method and application

technical field

The invention belongs to the technical field of nanomaterial synthesis and photocatalysis, and in particular relates to a composite photocatalyst C-MoO ₂ /C ₃ N ₄ and its preparation method and application.

Background technique

In recent years, hydrogen has been considered as an ideal, clean and sustainable candidate fuel to replace exhaustible fossil fuels. At present, the preparation of hydrogen mainly includes: thermochemical, photocatalytic, electrocatalytic and other technologies, using semiconductor Photocatalytic splitting of water to produce hydrogen, which converts solar energy into hydrogen energy, has attracted widespread attention.

At present, many semiconductors have been discovered and used for photocatalytic water splitting to produce hydrogen, mainly including sulfides, nitrides, oxides, hydroxides, and borides. Metal oxides and nitrides are widely used in these photocatalysts. C ₃ N ₄ has a good band gap and is a promising semiconductor photocatalyst, however, due to the rapid recombination of photogenerated electrons and holes and the lack of photocatalytic active sites, bare C ₃ N ₄ photocatalyzes H ₂ The activity of precipitation reaction is extremely low. These problems lead to the low yield of C ₃ N ₄ alone for photocatalytic splitting of water to produce hydrogen, which limits its practical application.

Molybdenum dioxide (MoO ₂ ) has high electrical conductivity and chemical stability similar to noble metals, making it a promising alternative for electron transfer, however, due to the relatively fast carrier recombination of MoO ₂ itself, pure MoO ₂ The performance as a photocatalyst is not high. Therefore, if MoO ₂ wants to improve the carrier separation efficiency, it can be recombined with another semiconductor to improve the photocatalytic performance of MoO ₂ . Although the existing combination of MoO ₂ and other semiconductors can improve the separation efficiency of carriers, it still has the problem of reduced redox potential, which limits the application of MoO ₂ composite catalysts. Therefore, it is necessary to provide a method capable of increasing the separation efficiency of carriers and simultaneously increasing the oxidation-reduction potential.

Contents of the invention

Aiming at some deficiencies in the prior art, the invention provides a composite photocatalyst C-MoO ₂ /C ₃ N ₄ and its preparation method and application. In the present invention, the C source is used to reduce the molybdenum source and prepare carbon-doped C-MoO ₂ through hydrothermal reaction, and then C ₃ N ₄ and C-MoO ₂ are self-assembled in the self-assembly solution to obtain a composite light Catalyst C-MoO ₂ /C ₃ N ₄ ; the composite photocatalyst C-MoO ₂ /C ₃ N ₄ is an S-type heterojunction, which can expand the absorption range of light, enhance the separation of photogenerated carriers, prolong the The lifespan of the flow electrons and the strong electron reduction ability and hole oxidation ability are maintained, so it has a good application in the field of photocatalytic hydrogen production from water.

The present invention firstly provides a composite photocatalyst _C - _{MoO 2} /C ₃ N ₄ , in which C is doped into MoO ₂ to obtain C-MoO _{2 particles ,} and then self-assembled C- _MoO2 particles supported on _C3N4 sheets.

The present invention also provides a preparation method for the composite photocatalyst C-MoO ₂ /C ₃ N ₄ , the method comprising:

Dissolving the carbon source and the molybdenum source in water and mixing them evenly, then performing a hydrothermal reaction, cooling, centrifuging, washing, and drying after the reaction, to obtain C-MoO ₂ ;

Disperse the C-MoO ₂ into n-hexane, then add C ₃ N ₄ and ultrasonically disperse until it is completely dispersed to obtain a mixed solution, stir the mixed solution until C-MoO ₂ is completely self-assembled on C ₃ N ₄ , centrifuge after the stirring and drying to obtain a composite photocatalyst C-MoO ₂ /C ₃ N ₄ .

Further, the carbon source includes starch, glucose or dicyandiamide, the molybdenum source includes ammonium molybdate or sodium molybdate, and the amount ratio of the carbon source to the molybdenum source is 1.4:10

Further, the condition of the hydrothermal reaction is to react at 180° C. for 6 hours.

Further, the mass ratio of C-MoO ₂ to C ₃ N ₄ is (1-11):100, and the ratio of C-MoO ₂ to n-hexane is 1-11g:20-50mL.

Further, the preparation method of C ₃ N ₄ is as follows: urea is calcined at 500-600° C., and cooled after the calcination to obtain C ₃ N ₄ .

Further, the calcination is to raise the temperature to 500-600° C. at a heating rate of 2-5° C./min, and then calcine for 2-4 hours.

Further, the stirring time is 5-12h.

The present invention also provides the use of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ in photocatalytic hydrogen production from water.

Compared with prior art, the beneficial effect of the present invention is:

The C-MoO ₂ /C ₃ N ₄ prepared in the present invention expands the absorption range of light, enhances the separation of photogenerated carriers, prolongs the life of carriers, and maintains strong electron reduction ability and hole separation. oxidation capacity. The experimental results show that the hydrogen evolution rate of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ is about 1.8 times that of pure C ₃ N ₄ .

In the present invention, C doped MoO ₂ is used to improve the carrier separation of MoO ₂ , thereby improving the photocatalytic performance of the composite catalyst. In the present invention, C ₃ N ₄ is flake-shaped, which has a large surface area, and C-MoO ₂ can be better supported on C ₃ N ₄ . The monolithic C-MoO ₂ /C ₃ N ₄ reduces the resistance of electron transport and thus has better photocatalytic performance. In addition, compared with the previous heterojunction, the S-type heterojunction has a better carrier separation effect due to the existence of a built-in electric field, and has a higher redox potential to make the reaction easier.

In the invention, a simple self-assembly method is adopted to synthesize a C-MoO ₂ /C ₃ N ₄ S type heterojunction composite photocatalyst, which has low cost, and is economical and environment-friendly.

Description of drawings

Fig. 1 is a synthesis process diagram of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ of the present invention.

Fig. 2 is a TEM image of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ of the present invention.

Fig. 3 is the performance diagram of the photocatalytic hydrogen production of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ and the comparison material of the present invention; Figure a is the performance diagram of C-MoO ₂ loaded with different masses on C ₃ N ₄ ; Panel b is the cycle performance graph of the best performing sample in panel a.

Fig. 4 is the XPS diagram of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ of the present invention and the comparative material, in which CMC is the abbreviation of C-MoO ₂ /C ₃ N ₄ .

Fig. 5 is a schematic diagram of the charge separation and transfer mechanism of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific examples, but the scope of protection of the present invention is not limited to the following specific embodiments, those skilled in the art can adopt other various specific embodiments to implement according to the content disclosed by the present invention Those of the present invention, or those that adopt the design structure and idea of the present invention and make simple changes or changes, all fall into the protection scope of the present invention. It should be noted that, in the case of no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Example 1:

Figure 1 is a schematic diagram of the synthesis of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ ; the figure directly reflects the synthesis process of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ , and first synthesized C-MoO ₂ and C ₃ N ₄ monomer, and then the composite C-MoO ₂ /C ₃ N ₄ is obtained by self-assembly method. The specific preparation process is as follows:

(1) Preparation of C-MoO ₂ :

Stir and dissolve 140mg of glucose in water, then add 1g of ammonium molybdate, and stir until completely dissolved. Put the mixed solution in a polytetrafluoroethylene reactor at 180°C for 6h, cool down after the reaction, centrifuge, wash, and dry in vacuum, and finally collect the C-MoO ₂ sample.

(2) Preparation of C ₃ N ₄ :

Put 5g of urea into a magnetic boat in a _N2 furnace at 550°C, 2.5°C/min, 4h, and finally cool to obtain _{a C3N4} sample.

(3) Preparation of C-MoO ₂ /C ₃ N ₄ :

Disperse 3mg of C-MoO ₂ completely in 20ml of n-hexane, then add 100mg of C ₃ N ₄ and sonicate until completely dispersed, then stir for 12h until C-MoO ₂ is completely self-assembled and poured onto C ₃ N ₄ . Centrifuge and dry in vacuum to obtain the composite sample C-MoO ₂ /C ₃ N ₄ .

Fig. 4 is the XPS diagram of composite photocatalyst C-MoO ₂ /C ₃ N ₄ , pure sample C ₃ N ₄ and C-MoO ₂ , it can be seen from the attached figure that the material has been successfully prepared. In addition, it can be seen from the figure that according to the shift of the peaks in the figure, it can be concluded that the electrons of C ₃ N ₄ will transfer to C-MoO ₂ to form a built-in electric field in the direction of C ₃ N ₄ points to C-MoO ₂ . When there is light, C-MoO ₂ and C ₃ N ₄ will generate photo-generated carriers, and due to the existence of the built-in electric field, the electrons at this time will flow from the conduction band of C-MoO ₂ to the valence band of C ₃ N ₄ , recombine with holes on the valence band of C ₃ N ₄ to form this S-type transfer path.

Example 2:

(1) Preparation of C-MoO ₂ :

Stir and dissolve 140mg of glucose in water, then add 1g of ammonium molybdate, and stir until completely dissolved. Put the mixed solution in a polytetrafluoroethylene reactor at 180°C for 6h, cool down after the reaction, centrifuge, wash, and dry in vacuum, and finally collect the C-MoO ₂ sample.

(2) Preparation of C ₃ N ₄ :

Put 5g of urea into a magnetic boat in a N2 furnace at 550°C, 2.5°C/min, 4h, and finally cool to obtain a C ₃ N ₄ sample.

(3) Preparation of C-MoO ₂ /C ₃ N ₄ :

Disperse 5mg of C-MoO ₂ completely into 20ml of n-hexane, then add 100mg of C ₃ N ₄ and sonicate until completely dispersed, then stir for 12h until C-MoO ₂ is completely self-assembled and poured onto C ₃ N ₄ . Centrifuge and dry in vacuum to obtain the composite sample C-MoO ₂ /C ₃ N ₄ .

Example 3:

(1) Preparation of C-MoO ₂ :

Stir and dissolve 140mg of glucose in water, then add 1g of ammonium molybdate, and stir until completely dissolved. Put the mixed solution in a polytetrafluoroethylene reactor at 180°C for 6h, cool down after the reaction, centrifuge, wash, and dry in vacuum, and finally collect the C-MoO ₂ sample.

(2) Preparation of C ₃ N ₄ :

Put 5g of urea into a magnetic boat in a N2 furnace at 550°C, 2.5°C/min, 4h, and finally cool to obtain a C ₃ N ₄ sample.

(3) Preparation of C-MoO ₂ /C ₃ N ₄ :

Disperse 7mg of C-MoO ₂ completely in 20ml of n-hexane, then add 100mg of C ₃ N ₄ and sonicate until completely dispersed, then stir for 12h until C-MoO ₂ is completely self-assembled and poured onto C ₃ N ₄ . Centrifuge and dry in vacuum to obtain the composite sample C-MoO ₂ /C ₃ N ₄ .

Example 4:

(1) Preparation of C-MoO ₂ :

Stir and dissolve 140mg of glucose in water, then add 1g of ammonium molybdate, and stir until completely dissolved. Put the mixed solution in a polytetrafluoroethylene reactor at 180°C for 6h, cool down after the reaction, centrifuge, wash, and dry in vacuum, and finally collect the C-MoO ₂ sample.

(2) Preparation of C ₃ N ₄ :

Put 5g of urea into a magnetic boat in a N2 furnace at 550°C, 2.5°C/min, 4h, and finally cool to obtain a C ₃ N ₄ sample.

(3) Preparation of C-MoO ₂ /C ₃ N ₄ :

Disperse 9 mg of C-MoO ₂ completely in 20 ml of n-hexane, then add 100 mg of C ₃ N ₄ and sonicate until completely dispersed, then stir for 12 h until C-MoO ₂ is completely self-assembled and poured onto C ₃ N ₄ . Centrifuge and dry in vacuum to obtain the composite sample C-MoO ₂ /C ₃ N ₄ .

Example 5:

(1) Preparation of C-MoO ₂ :

Stir and dissolve 140mg of glucose in water, then add 1g of ammonium molybdate, and stir until completely dissolved. Put the mixed solution in a polytetrafluoroethylene reactor at 180°C for 6h, cool down after the reaction, centrifuge, wash, and dry in vacuum, and finally collect the C-MoO ₂ sample.

(2) Preparation of C ₃ N ₄ :

Put 5g of urea into a magnetic boat in a N2 furnace at 550°C, 2.5°C/min, 4h, and finally cool to obtain a C ₃ N ₄ sample.

(3) Preparation of C-MoO ₂ /C ₃ N ₄ :

Disperse 11 mg of C-MoO ₂ completely into 20 ml of n-hexane, then add 100 mg of C ₃ N ₄ to ultrasonic to completely disperse, and then stir for 12 h until C-MoO ₂ is completely self-assembled and poured onto C ₃ N ₄ . Centrifuge and dry in vacuum to obtain the composite sample C-MoO ₂ /C ₃ N ₄ .

Embodiment 6:

(1) Preparation of _MoO2 :

144mg MoO ₃ , 48mg molybdenum powder. Add 40ml of water and stir for 2h to disperse. Put the mixed solution in a polytetrafluoroethylene reactor at 200°C for 15 hours, cool down after the reaction, centrifuge, wash, and dry in vacuum, and finally collect the MoO ₂ sample.

(2) Preparation of C ₃ N ₄ :

Put 5g of urea into a magnetic boat in a _N2 furnace at 550°C, 2.5°C/min, 4h, and finally cool to obtain _{a C3N4} sample.

(3) Preparation of C-MoO ₂ /C ₃ N ₄ :

Disperse 7mg of MoO ₂ completely in 20ml of n-hexane, then add 100mg of C ₃ N ₄ to ultrasonic to completely disperse, then stir for 12h until MoO ₂ is completely self-assembled and poured onto C ₃ N ₄ . Centrifuge and dry in vacuum to obtain composite MoO ₂ /C ₃ N ₄ .

The conditions for preparing hydrogen by photocatalytic water splitting in the present invention are as follows: the light source equipment used is a 300W xenon lamp, the reaction vessel is a 100mL flat-bottomed three-neck flask, and the sacrificial agent is a triethanolamine aqueous solution with a volume ratio of 10%. 10mg of the sample to be tested and 80mL of the corresponding type of sacrificial agent, 3% Pt as a group catalyst, ultrasonically stirred for 20min until the sample was uniformly dispersed in the aqueous solution. Next, connect the reactor with nitrogen gas for 10-20 minutes, remove excess air in the reactor, and pass nitrogen gas for 30-40 minutes when doing the cycle stability test. The gas chromatograph of Shimadzu type GC-8A with TCD detector was used to test the hydrogen production per unit time when the sample reacted, and the measurement results are shown in Figure 2.

It can be seen from Figure 2 that C-MoO ₂ is a particle of about 50nm, C ₃ N ₄ is a sheet structure, and the structure of the composite C-MoO ₂ /C ₃ N ₄ is that C-MoO ₂ is supported on C ₃ N ₄ On the surface, such a structure improves the transfer of carriers inside the material, and at the same time increases the active sites for reactions.

Fig. 3 is the performance diagram of the photocatalytic hydrogen production of the C-MoO ₂ /C ₃ N ₄ composite material of the present invention and the comparison material; Figure a is the performance diagram of C-MoO ₂ loaded with different masses on C ₃ N ₄ ; b is the cycle performance graph of the best performing sample in a. It can be seen from the figure that figure c shows the hydrogen production performance of pure MoO ₂ and C-doped MoO ₂ loaded on C ₃ N ₄ , and it can be seen from the figure that doping C can effectively improve the photogenerated current carrying capacity of MoO ₂ The separation of electrons can improve the performance of photocatalytic hydrogen production.

Figure 5 shows the catalytic mechanism of the composite photocatalyst in the photocatalytic cracking of water to produce hydrogen. C-MoO ₂ and C _{3 N 4} will generate photo-generated electrons after absorbing photons. Due to the existence of the built-in electric field, the The electrons will recombine with the holes on the C ₃ N ₄ valence band to improve the separation of photogenerated carriers, and the electrons on the C ₃ N ₄ conduction band will be captured by Pt to reduce H ⁺ to H ₂ ; while the C-MoO ₂ valence band The holes on are consumed by triethanolamine, forming a S-like electron transfer path.

The described embodiment is a preferred implementation of the present invention, but the present invention is not limited to the above-mentioned implementation, without departing from the essence of the present invention, any obvious improvement, replacement or modification that those skilled in the art can make Modifications all belong to the protection scope of the present invention.

Claims (9)

1. a kind of composite photocatalyst C-MoO ₂ /C ₃ N ₄ preparation method, it is characterized in that, described method comprises: Dissolving the carbon source and the molybdenum source in water and mixing them evenly, then performing a hydrothermal reaction, cooling, centrifuging, washing, and drying after the reaction, to obtain C-MoO ₂ ; Disperse the C-MoO ₂ into n-hexane, then add C ₃ N ₄ and ultrasonically disperse until it is completely dispersed to obtain a mixed solution, stir the mixed solution until C-MoO ₂ is completely self-assembled on C ₃ N ₄ , centrifuge after the stirring and drying to obtain a composite photocatalyst C-MoO ₂ /C ₃ N ₄ . 2. the preparation method of composite photocatalyst C-MoO ₂ /C ₃ N ₄ according to claim 1, is characterized in that, described carbon source comprises starch, glucose or dicyandiamide, and described molybdenum source comprises ammonium molybdate or sodium molybdate; the molar ratio of the carbon element to the molybdenum element is 1.4:10. 3. The preparation method of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ according to claim 1, characterized in that the condition of the hydrothermal reaction is to react at 180° C. for 6 hours. 4. the preparation method of composite photocatalyst C-MoO ₂ /C ₃ N ₄ according to claim 1, is characterized in that, the mass ratio of described C-MoO ₂ and C ₃ N ₄ is (1-11): 100, the amount ratio of C-MoO ₂ and n-hexane is 1-11g:20-50mL. 5. The preparation method of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ according to claim 1, characterized in that the preparation method of the C ₃ N ₄ is as follows: calcining urea at 500-600°C, Cool after calcination to obtain C ₃ N ₄ . 6. The preparation method of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ according to claim 5, characterized in that, the calcination is to raise the temperature to 500-600°C at a heating rate of 2-5°C/min, Then calcined for 2-4h. 7. The method for preparing the composite photocatalyst C-MoO ₂ /C ₃ N ₄ according to claim 1, characterized in that the stirring time is 5-12 hours. 8. The composite photocatalyst C-MoO ₂ /C ₃ N ₄ prepared by the method according to any one of claims 1 to 7, wherein C is doped into MoO ₂ in the composite photocatalyst C-MoO ₂ /C ₃ N ₄ C-MoO ₂ particles were obtained in the process, and then the C-MoO ₂ particles were self-assembled and supported on C ₃ N ₄ sheets. 9. The use of the composite photocatalyst C-MoO ₂ /C ₃ N ₄ described in claim 8 in photocatalytic hydrogen production from water.

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