Preparation method of embedded p-n heterojunction photocatalyst

Abstract

The invention discloses a preparation method and application of an embedded p-n heterojunction PEA2PbBr4-CeO2 photocatalyst, and belongs to the field of environment friendliness and energy sustainable development. The preparation method comprises the following steps: firstly, preparing CeO2 nanoparticles by a hydrothermal method, then adding a precursor solution containing PEABr and PbBr2 into a CeO2 nanoparticle dispersion liquid, and obtaining the embedded p-n heterojunction PEA2PbBr4-CeO2 photocatalyst by a simple anti-solvent method. The photocatalyst is simple in preparation method, low in cost, high in safety and strong in reproducibility, has a large and tight contact area due to a unique embedded structure, and can provide more active sites and electron transfer paths, so that the photocatalyst shows excellent photocatalytic performance in a reaction of selectively oxidizing toluene and derivatives thereof.

Description

Technical Field

[0001] The present invention relates to a catalyst preparation technology and its application field, and specifically to the preparation of an embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst and its application in the selective photocatalytic oxidation of toluene and its derivatives to generate high value-added products. Background Art

[0002] Selective oxidation of toluene to produce benzaldehyde is an important route for the synthesis of high value-added chemicals. 3 The high dissociation energy of the )-H bond makes the activation of toluene very challenging, which usually requires harsh reaction conditions such as corrosive oxidants or high reaction temperatures. 3 )-H bond is a green synthetic strategy with great potential for synthesizing high value-added products under mild conditions. Therefore, it is necessary to develop a photocatalyst with high light energy utilization and effective separation of electron-hole pairs.

[0003] In recent years, metal halide perovskites have become a research hotspot for photocatalytic oxidation of toluene due to their high absorption coefficient, adjustable energy bands, and good physical and chemical properties. However, severe charge recombination limits their photocatalytic efficiency. Composite catalysts connected by different phase interfaces usually exhibit special functions that single-component catalysts cannot achieve. Based on such considerations, heterojunctions have often been constructed in recent years to help separate photogenerated electrons and holes. Among them, Type-II heterojunctions have become a relatively ideal heterojunction due to their good photocatalytic activity. Type-II heterojunctions can be divided into pp, nn, and pn heterojunctions according to the relationship between the energy band structures. In these structures, the huge difference in the Fermi level between p-type and n-type semiconductors causes significant charge redistribution, thereby forming a strong built-in electric field, which is a strong driving force for charge separation and directional electron transfer, which makes the pn heterojunction exhibit the most superior photocatalytic performance. At the same time, based on the advantages of heterojunctions, the design of material nanostructures is also a key to the synthesis of efficient photocatalysts. Therefore, combining the construction of heterojunctions with the design of material nanostructures provides a new reference for the design and development of efficient photocatalysts. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst, which combines the construction of the heterojunction with the design of the material nanostructure, and adopts an in-situ growth strategy to enable the PEA2PbBr4 perovskite to grow rapidly and wrap CeO2 nanoparticles as nucleation sites, thereby forming an embedded structure with a large and close contact interface, which can provide more active sites and abundant charge transfer channels, and can thus be used to achieve efficient photocatalytic oxidation of toluene and its derivatives.

[0005] To achieve the above object, the present invention adopts the following technical solution: An embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst, the preparation method of which comprises the following steps: (1) Ce (NO3)3•6H2O and PVP were added to deionized water and stirred to dissolve, and then sodium hydroxide solution was added dropwise thereto. After stirring evenly, the mixture was transferred to a hydrothermal reactor for reaction. After the reaction, the mixture was washed by centrifugation with ethanol and deionized water several times, and then dried in a vacuum oven at 60 °C for 12 h to obtain CeO2 powder. (2) PEABr and PbBr2 are dissolved in N,N-dimethylformamide (DMF) to form a precursor solution, and then the CeO2 powder obtained in step 1) is ultrasonically dispersed in toluene, and the prepared precursor solution is added thereto under vigorous stirring conditions. After continuing to stir and mix for 3 hours, the precipitate is collected by centrifugation and dried at 60°C overnight to obtain the PEA2PbBr4-CeO2 photocatalyst.

[0006] Furthermore, the mass ratio of Ce (NO3)3•6H2O, PVP and sodium hydroxide used in step (1) is 6.5:3:6.

[0007] Furthermore, the reaction temperature in step (1) is 180°C and the reaction time is 24 h.

[0008] Furthermore, the mass ratio of PEABr and PbBr2 used in step (2) is 1.3:1.

[0009] Furthermore, the volume ratio of toluene and DMF used in step (2) is 20:1.

[0010] Furthermore, the rotation speed of the vigorous stirring in step (2) is 500 rpm~1000 rpm; the rotation speed of the centrifugation is 6000 rpm.

[0011] Furthermore, in the obtained PEA2PbBr4-CeO2 photocatalyst, the mass proportion of CeO2 is 2.5%-10%, preferably 5%.

[0012] The obtained PEA2PbBr4-CeO2 photocatalyst can be used for the photocatalytic selective oxidation of toluene and its derivatives such as p-bromotoluene, p-chlorotoluene, p-fluorotoluene, o-xylene, p-xylene, and m-xylene.

[0013] The present invention has the following significant advantages: 1. The PEA2PbBr4-CeO2 photocatalyst prepared by the present invention utilizes the strong built-in electric field and high carrier separation ability of the pn heterojunction, which is beneficial to improving the photocatalytic activity of the reaction.

[0014] 2. The PEA2PbBr4-CeO2 photocatalyst prepared by the present invention is a PEA2PbBr4 layered structure in which CeO2 nanoparticles are embedded. This unique embedded structure can form a large and close contact interface, thereby providing more active sites and abundant charge transfer channels.

[0015] 3. In the preparation process of the present invention, the photocatalytic oxidation performance of the photocatalyst can be regulated by changing the introduction ratio of CeO2 in the PEA2PbBr4-CeO2 photocatalyst.

[0016] 4. The PEA2PbBr4-5%CeO2 photocatalyst prepared by the present invention has the highest conversion rate of toluene, which is 10050 μmol g -1 h -1 , is blank PEA2PbBr4 (1160 μmol g -1 h -1 ), while maintaining a high selectivity of 86% and satisfactory long-term stability, and its production process is environmentally friendly.

[0017] 5. The PEA2PbBr4-CeO2 photocatalyst prepared by the present invention can be used for the selective oxidation of toluene and its derivatives using sunlight as driving energy and oxygen as oxidant, which is beneficial to the sustainable development of the environment and energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 XRD patterns of PEA2PbBr4, CeO2 and PEA2PbBr4-CeO2 heterojunction composites with different ratios.

[0019] Figure 2 SEM images of PEA2PbBr4 (a), CeO2 (b) and PEA2PbBr4-CeO2 heterojunction composites with different ratios (cf).

[0020] Figure 3 This is the MS diagram of electrochemical test of PEA2PbBr4 and CeO2.

[0021] Figure 4 TEM image and element distribution diagram of the prepared PEA2PbBr4-5%CeO2 heterojunction composite material.

[0022] Figure 5 This is a comparison chart of the activity of PEA2PbBr4, CeO2 and PEA2PbBr4-CeO2 heterojunction composites with different ratios for selective oxidation of toluene.

[0023] Figure 6This is the GC-MS spectrum of substances in the reaction liquid after selective oxidation of toluene using PEA2PbBr4-5%CeO2 heterojunction composite material.

[0024] Figure 7 This is a comparison chart of the activity of selective oxidation of toluene and its derivatives using PEA2PbBr4-5%CeO2 photocatalyst.

[0025] Figure 8 Long-term activity diagram of PEA2PbBr4-5%CeO2 photocatalyst for selective oxidation reaction for 8h. DETAILED DESCRIPTION

[0026] An embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst, the preparation method of which comprises the following steps: (1) Ce (NO3)3•6H2O and PVP were added to deionized water and stirred to dissolve, and then sodium hydroxide solution was added dropwise thereto. After stirring evenly, the mixture was transferred to a hydrothermal reactor and reacted at 180°C for 24 h. After the reaction, the mixture was centrifuged and washed several times with ethanol and deionized water, and then dried in a vacuum oven at 60°C for 12 h to obtain CeO2 powder. The mass ratio of Ce (NO3)3•6H2O, PVP and sodium hydroxide used was 6.5:3:6. (2) PEABr and PbBr2 were dissolved in DMF at a mass ratio of 1.3:1 to form a precursor solution, and then the CeO2 powder obtained in step 1) was ultrasonically dispersed in toluene, and the prepared precursor solution was added thereto under vigorous stirring conditions at 500 rpm~1000 rpm. After continuing to stir and mix for 3 h, the precipitate was collected by centrifugation at 6000 rpm and dried overnight at 60 °C to obtain a PEA2PbBr4-CeO2 photocatalyst, in which the mass proportion of CeO2 was 2.5%-10%; the volume ratio of toluene and DMF used was 20:1.

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific examples. Unless otherwise specified, the reagents, materials, and instruments used in the following examples can be obtained through commercial means, and the operating environment is a conventional environment; the specific operating methods and testing methods involved are conventional methods in the art.

[0028] Comparative Example 1 Preparation of PEA2PbBr4 perovskite: Weigh 24.2 mg PEABr and 18.3 mg PbB2, dissolve in 1 mL DMF to form a precursor solution, then add the precursor solution dropwise into 20 mL toluene, continue stirring for 30 min, centrifuge at 6000 rpm for 2 min, put the collected solid into a vacuum oven, and dry it at 60 °C overnight to obtain PEA2PbBr4 perovskite.

[0029] Comparative Example 2 Preparation of CeO2 nanoparticles: Weigh 0.65 g Ce (NO3)3•6H2O and 0.3 g PVP, add to 30 mL deionized water and stir for 60 min, then add 30 mL of aqueous solution containing 0.6 g sodium hydroxide, stir evenly and transfer the mixed solution to a hydrothermal reactor and react at 180 °C for 24 h; after the reaction, centrifuge and wash with ethanol and deionized water several times in sequence, then dry in a vacuum oven at 60 °C for 12 h, and collect the obtained CeO2 powder. Example

[0030] Take 1.9 mg of CeO2 prepared in Comparative Example 2 and ultrasonically disperse it in 20 mL of toluene. At the same time, dissolve 24.2 mg of PEABr and 18.3 mg of PbBr2 in 1 mL of DMF to form a precursor solution. Then, under vigorous stirring at 500 rmp~1000 rpm, add the precursor solution dropwise to the toluene solution of CeO2, continue stirring and mixing for 3 hours, centrifuge at 6000 rmp for 2 minutes, put the collected solid into a vacuum oven, and dry it at 60 ° C overnight to obtain a PEA2PbBr4-5%CeO2 heterojunction composite material.

[0031] At the same time, by changing the amount of CeO2 added, PEA2PbBr4-CeO2 heterojunction composite materials with CeO2 mass proportions of 2.5%, 7.5%, and 10% were obtained and characterized.

[0032] Characterization analysis: Figure 1 Figure 2 shows the XRD patterns of PEA2PbBr4, CeO2 and PEA2PbBr4-CeO2 heterojunction composite materials with different ratios. It can be seen from the figure that all materials have good crystal structures, and the crystallinity of perovskite PEA2PbBr4 is stronger than that of CeO2. Therefore, in the PEA2PbBr4-CeO2 heterojunction composite material, although the addition ratio of CeO2 increases, the XRD diffraction peaks of the composite material are consistent with those of perovskite PEA2PbBr4.

[0033] Figure 2The SEM images of PEA2PbBr4, CeO2 and PEA2PbBr4-CeO2 heterojunction composites with different ratios are shown in Figure 1. It can be clearly seen that with the increase of CeO2 content, the number of particles embedded in the PEA2PbBr4-CeO2 composite material increases significantly.

[0034] Figure 3 The electrochemical test MS graph of PEA2PbBr4 and CeO2 shows that the MS slope of PEA2PbBr4 is negative, indicating that it is a P-type semiconductor, and the MS slope of CeO2 is positive, indicating that it is an N-type semiconductor. Therefore, the prepared PEA2PbBr4-CeO2 is a pn heterojunction.

[0035] Figure 4 The TEM image and element distribution diagram of the prepared PEA2PbBr4-5%CeO2 heterojunction composite material. The characteristic lattice fringes representing PEA2PbBr4 and CeO2 can be clearly seen in the figure. In addition, Pb, Br, Ce, and O elements are evenly distributed on the nanosheet structure, which all indicate that there is good interface contact between PEA2PbBr4 and CeO2.

[0036] Application Example 1 Photocatalytic Selective Oxidation of Toluene Take 2 mL of acetonitrile, 1 mL of toluene and 10 mg of catalyst and put them in a 25 mL quartz reaction bottle. After stirring evenly, illuminate under visible light for 2 h, and then centrifuge to obtain the supernatant. Detect it by gas chromatography, and qualitatively and quantitatively analyze the products by retention time and peak area, and compare the production rates of the products.

[0037] Figure 5 The activity comparison of PEA2PbBr4, CeO2 and PEA2PbBr4-CeO2 heterojunction composite materials with different ratios for selective oxidation of toluene is shown in the figure. It can be seen that compared with PEA2PbBr4 and CeO2, PEA2PbBr4-CeO2 heterojunction composite materials have better activity for selective oxidation of toluene, among which PEA2PbBr4-5%CeO2 has the best effect, and its generation rate can reach 10050μmol g -1 h -1 .

[0038] Figure 6 This is the GC-MS spectrum of the products obtained by selective oxidation of toluene using PEA2PbBr4-5%CeO2 heterojunction composite materials. As can be seen from the figure, alcohols and aldehydes with high added value are generated, and no other products are produced.

[0039] Application Example 2 Photocatalytic Selective Oxidation of a Series of Toluene Derivatives Take 2 mL of acetonitrile, 1 mL of toluene derivative and 10 mg of PEA2PbBr4-5%CeO2 photocatalyst and put them in a 25 mL quartz reaction bottle. After stirring evenly, illuminate under visible light for 2 h, and then centrifuge to obtain the supernatant. Detect it by gas chromatography, and qualitatively and quantitatively analyze the product by retention time and peak area to obtain the product generation rate.

[0040] Figure 7 This is a comparison chart of the activity of selective oxidation of toluene derivatives using PEA2PbBr4-5%CeO2 photocatalyst. As can be seen from the figure, PEA2PbBr4-5%CeO2 has good catalytic oxidation activity for toluene derivatives with different structures.

[0041] Figure 8 This is a long-term activity diagram of the selective oxidation reaction of PEA2PbBr4-5%CeO2 photocatalyst for 8 hours. It can be seen from the figure that PEA2PbBr4-5%CeO2 can still maintain stable performance under long-term reaction.

[0042] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing an embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst, characterized in that: The following steps are involved: (1) Ce (NO3)3•6H2O and PVP were added to deionized water and stirred to dissolve, and then sodium hydroxide solution was added dropwise thereto. After stirring evenly, the mixture was transferred to a hydrothermal reactor for reaction. After the reaction, the mixture was centrifuged and washed several times with ethanol and deionized water, and then dried to obtain CeO2 powder. (2) PEABr and PbBr2 are dissolved in DMF to form a precursor solution, and then the CeO2 powder obtained in step 1) is ultrasonically dispersed in toluene, and the prepared precursor solution is added thereto under vigorous stirring conditions. After continuing to stir and mix for 3 hours, the precipitate is collected by centrifugation and dried at 60°C overnight to obtain the PEA2PbBr4-CeO2 photocatalyst.

2. The method for preparing the embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst according to claim 1, characterized in that: The mass ratio of Ce (NO3)3•6H2O, PVP and sodium hydroxide used in step (1) is 6.5:3:

6.

3. The method for preparing the embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst according to claim 1, characterized in that: The reaction temperature in step (1) is 180°C and the reaction time is 24 h.

4. The method for preparing the embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst according to claim 1, characterized in that: The mass ratio of PEABr and PbBr2 used in step (2) is 1.3:

1.

5. The method for preparing the embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst according to claim 1, characterized in that: The volume ratio of toluene and DMF used in step (2) is 20:

1.

6. The method for preparing the embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst according to claim 1, characterized in that: The rotation speed of the vigorous stirring in step (2) is 500 rpm~1000 rpm; the rotation speed of the centrifugation is 6000 rpm.

7. The method for preparing the embedded pn heterojunction PEA2PbBr4-CeO2 photocatalyst according to claim 1, characterized in that: In the obtained PEA2PbBr4-CeO2 photocatalyst, the mass proportion of CeO2 is 2.5%-10%.

8. Use of the PEA2PbBr4-CeO2 photocatalyst prepared by the method as claimed in claim 1 in the photocatalytic selective oxidation of toluene and its derivatives.

9. The use according to claim 8, characterized in that: The derivatives include p-bromotoluene, p-chlorotoluene, p-fluorotoluene, o-xylene, p-xylene and m-xylene.

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