A heterojunction photothermal catalyst and a preparation method thereof

Abstract

The application provides a kind of heterojunction photo-thermal catalyst and preparation method thereof, and the heterojunction photo-thermal catalyst includes cerium oxide rich in oxygen vacancy, elemental silver and manganese oxide, and the preparation method of the heterojunction photo-thermal catalyst includes the following steps: S1, preparing cerium oxide rich in oxygen vacancy, which can be cerium oxide or CeO x ; S2, preparing manganese oxide loaded silver particles, which can be manganese oxide loaded silver particles or Ag-MnO x ; S3, mixing cerium oxide rich in oxygen vacancy and manganese oxide loaded silver particles and ball milling to obtain CeOx / Ag-MnOx heterojunction photo-thermal catalyst. The heterojunction photo-thermal catalyst provided by the application has the effect of efficient photo-thermal synergistic catalytic degradation of volatile organic pollutants by combining the introduction of interface oxygen vacancy and mechanical ball milling.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photo-thermal catalysts, and particularly relates to a heterojunction photo-thermal catalyst and a preparation method thereof. BACKGROUND

[0002] Volatile gas pollutants (VOCs) are important air pollutants with wide sources and great harm. The photo-thermal synergistic catalytic oxidation technology has the advantages of traditional photocatalysis and thermal catalysis, and overcomes the low quantum efficiency of photocatalysis and the high energy consumption of thermal catalysis, and is a green and mild low-carbon pollution reduction technology. The key to photo-thermal catalytic degradation of volatile organic pollutants lies in the development of efficient photo-thermal catalysts. Patent application No. 201210029241.X discloses a preparation method of a CeO2-MnO2 composite catalyst with high photo-thermal synergistic catalytic purification of VOCs. The obtained CeO2-MnO2 composite catalyst can efficiently catalyze and degrade gaseous volatile organic pollutants such as benzene, toluene and acetone, greatly improving the catalytic purification efficiency of volatile organic gases. The scheme is only for CeO2-MnO2 composite catalyst, which needs high temperature to achieve good catalytic effect. Patent application No. 201710686051.8 discloses a preparation method and application of an Ag-loaded manganese oxide catalyst. The scheme can completely oxidize formaldehyde into harmless water and carbon dioxide under a light intensity lower than one sun. However, the scheme can only achieve good catalytic effect on formaldehyde which is easy to oxidize, but cannot achieve good catalytic effect on more difficult to handle benzene ring VOCs represented by toluene.

[0003] Compared with simple composite catalysts, constructing multi-component heterojunction composite materials is one of the effective ways to obtain high-efficiency photo-thermal synergistic catalysts. By forming a heterojunction, the band gap width of the photocatalyst can be adjusted, the redox ability can be changed, and the separation and transfer of photo-generated charges can be promoted. Although multi-component heterojunction composite materials have good catalytic effect, the photo-thermal catalytic performance of component heterojunction catalysts is not only related to the physical and chemical properties of the components, but also closely related to the combination mode of the components and the preparation method (Chemical Society Reviews 2014, 43, 5234; Applied Catalysis B: Environmental, 2021, 291, 120053). Therefore, it is not easy to design a heterojunction photo-thermal catalyst with good performance.

[0004] The existing heterojunction photo-thermal catalysts still have the technical problems of low solar energy utilization efficiency and low catalytic purification efficiency for more difficult to handle benzene ring VOCs than the thermal catalytic reaction system based on noble metal catalysts. SUMMARY

[0005] Therefore, the present application aims to provide a heterojunction photo-thermal catalyst with good photo-thermal catalytic effect and a preparation method thereof.

[0006] The present application provides a heterojunction photo-thermal catalyst, which comprises an oxide of cerium rich in oxygen vacancies, elemental silver and an oxide of manganese, and the ratio of the oxide of cerium, elemental silver and the oxide of manganese is 1-50:0.1-10:100 by weight percentage.

[0007] Preferably, the heterojunction photo-thermal catalyst is a type II catalyst.

[0008] The present application also provides a preparation method of a heterojunction photo-thermal catalyst, which comprises the following steps:

[0009] S1, preparing an oxide of cerium rich in oxygen vacancies, which can be cerium oxide or CeOx for example;

[0010] S2, preparing silver particles loaded with an oxide of manganese, which can be silver particles loaded with manganese oxide or Ag-MnOx for example;

[0011] S3, mixing the oxide of cerium rich in oxygen vacancies and the silver particles loaded with the oxide of manganese and ball milling to obtain a CeOx / Ag-MnOx heterojunction photo-thermal catalyst.

[0012] Preferably, in the step S1, the cerium dioxide is subjected to calcination treatment under a reducing atmosphere to obtain the oxide of cerium rich in oxygen vacancies; the calcination temperature is 300-700℃, more preferably 400-700℃; and the calcination time is 0.1-24h, more preferably 0.1-10h.

[0013] Preferably, in the step S2, after mixing the manganese salt precursor solution and the silver nitrate solution, the product is subjected to hydrothermal reaction and calcination; the calcination temperature is 300-700℃, the calcination time is 0.5-24h, the hydrothermal reaction temperature is 100-150℃, and the hydrothermal time is 1-30h, more preferably 10-30h, to obtain the silver particles loaded with the oxide of manganese.

[0014] Preferably, in the step S3, the mass ratio of the oxide of cerium rich in oxygen vacancies and the silver particles loaded with the oxide of manganese is (1-50):100, more preferably (1-20):100.

[0015] Preferably, in the step S3, the ball milling speed is 300-1000rpm, and the ball milling time is 0.1-60h, more preferably 10-40h.

[0016] Preferably, in the silver particles loaded with the oxide of manganese, the theoretical loading amount of Ag is 0.1-10%.

[0017] Preferably, the heterojunction photo-thermal catalyst is applied to photo-thermal catalytic purification of organic gas pollutants (such as VOCs) such as toluene, formaldehyde and other gas pollutants. The CeOx / Ag-MnOx heterojunction photo-thermal catalyst prepared by the present application, or the cerium oxide / silver / manganese oxide heterojunction photo-thermal catalyst

[0018] Advantages:

[0019] (1) The interface defect sites are introduced, the metal Ag particles are in-situ doped, and the mechanical ball milling process is combined, so that the designed heterojunction photo-thermal catalytic material has high light utilization.

[0020] By the combination of silver nanoparticles and manganese oxide and cerium oxide with excellent redox performance, the construction of oxygen defects and the mechanical strengthening of the heterojunction phase interface, excellent photo-thermal catalytic purification performance of VOCs pollutants such as toluene and formaldehyde is exhibited.

[0021] By combining the introduction of interface oxygen vacancies and mechanical ball milling method, volatile organic pollutants can be efficiently photo-thermal synergistically catalyzed and degraded, especially for degrading formaldehyde, toluene and other volatile organic pollutants, excellent performance is exhibited. Especially for the difficult-to-handle benzene ring VOCs, it has very high catalytic effect.

[0022] (2) It can completely catalyze and purify formaldehyde and other difficult-to-handle benzene ring VOCs such as toluene under visible light irradiation and mild reaction conditions. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be further described in detail below in combination with specific examples, so that those skilled in the art can better understand the present application and implement it. The examples are not intended to limit the present application.

[0024] Example 1

[0025] A cerium oxide / silver / manganese oxide heterojunction photo-thermal catalyst, the preparation steps are:

[0026] (1) Commercially available CeO2 was placed in a tube furnace and calcined at 500℃ for 0.5h under a hydrogen atmosphere to obtain CeOx. (2) 0.6 mmol KMnO4 was dissolved in deionized water to prepare solution A. Then, 0.9 mmol Mn(CH3COO)2·4H2O, a certain amount of silver nitrate, and a small amount of acetic acid solution were dissolved in 30 mL of deionized water to prepare solution B. Solution A was added dropwise to solution B, and after magnetic stirring for a certain period of time, the mixed solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene and hydrothermally reacted at 100℃ for 24h. After centrifugation, washing, and drying, the sample was calcined at 500℃ in air for 2h to obtain an Ag-MnOx sample with a theoretical Ag doping amount of 3wt.%. (3) At a mass ratio of CeOx to Ag-MnOx of 4:100, CeOx, Ag-MnOx and ball milling aid are mixed and placed in a ball milling jar. Then, ethanol and grinding balls are added as grinding aids. The mixture is wet-milled at 800 rpm for 20 h and dried to obtain CeOx / Ag-MnOx photothermal catalyst.

[0027] Comparative Example 1

[0028] A silver / manganese oxide heterojunction photothermal catalyst, which, compared to Example 1, does not contain cerium oxide.

[0029] The preparation steps are as follows: Solution A is prepared by dissolving 0.6 mmol KMnO4 in deionized water. Then, solution B is prepared by dissolving 0.9 mmol Mn(CH3COO)2·4H2O, a certain amount of silver nitrate, and a small amount of acetic acid in 30 mL of deionized water. Solution A is added dropwise to solution B, and after magnetic stirring for a certain period, the mixture is transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE) and subjected to hydrothermal reaction at 100 °C for 24 h. After centrifugation, washing, and drying, the sample is calcined in air at 500 °C for 2 h to obtain an Ag-MnOx sample with a theoretical Ag doping content of 3 wt.%.

[0030] Comparative Example 2

[0031] A cerium oxide / manganese oxide heterojunction photothermal catalyst, which does not contain silver compared to Example 1.

[0032] The preparation steps are as follows: (1) Commercial CeO2 is placed in a tube furnace and calcined at 500℃ for 0.5h under a hydrogen atmosphere to obtain CeOx. (2) 0.6mmol KMnO4 is dissolved in deionized water to prepare solution A, and then 0.9mmol Mn(CH3COO)2·4H2O and a small amount of acetic acid solution are dissolved in 30mL of deionized water to prepare solution B. Solution A is added dropwise to solution B, and after magnetic stirring for a certain period of time, the mixed solution is transferred to a stainless steel reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 100℃ for 24h. After centrifugation, washing and drying of the sample, it is calcined at 500℃ in air for 2h to obtain the MnOx sample. (3) At a mass ratio of CeOx to Ag-MnOx of 4:100, CeOx and MnOx and the ball milling aid were mixed and placed in a ball milling jar. Then, the grinding aid ethanol and grinding balls were added, and the mixture was wet-milled at 800 rpm for 20 h. After drying, CeOx / MnOx photothermal catalyst was obtained.

[0033] Comparative Example 3

[0034] A cerium oxide / silver / manganese oxide heterojunction photothermal catalyst, compared with Example 1, is prepared by a non-ball milling method.

[0035] The preparation steps are as follows: (1) Dissolve 0.6 mmol KMnO4 in deionized water to prepare solution A, and then dissolve 0.9 mmol Mn(CH3COO)2·4H2O, a certain amount of silver nitrate and a small amount of acetic acid solution in 30 mL of deionized water to prepare solution B. Add solution A dropwise to solution B, and after stirring magnetically for a certain period of time, transfer the mixed solution to a stainless steel reactor with a polytetrafluoroethylene liner, and perform hydrothermal reaction at 100℃ for 24 h. After centrifugation, washing and drying of the sample, calcine it in air at 500℃ for 2 h to obtain an Ag-MnOx sample with a theoretical Ag doping amount of 3 wt.%. (2) Disperse Ag-MnOx in deionized water, then add a certain amount of Ce(NO3)3·6H2O solution and stir to mix. Then add NaBH4, a reducing agent dissolved in deionized water, and stir vigorously for 30 minutes. After centrifugation, washing and drying, calcination at 500℃ for 2 hours yields a sample CeOx-R-Ag-MnO2 with a theoretical mass ratio of CeO2 to Ag-MnOx of 4:100.

[0036] Example 2

[0037] A cerium oxide / silver / manganese oxide heterojunction photothermal catalyst is prepared by the following steps: (1) Commercially available CeO2 is placed in a tube furnace and calcined at 400°C for 6 hours under a hydrogen atmosphere to obtain CeOx. (2) 0.6 mmol KMnO4 is dissolved in deionized water to prepare solution A, and then 0.9 mmol Mn(CH3COO)2·4H2O, a certain amount of silver nitrate and a small amount of acetic acid solution are dissolved in 30 mL of deionized water to prepare solution B. Solution A is added dropwise to solution B, and after magnetic stirring for a certain period of time, the mixed solution is transferred to a stainless steel reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 120°C for 12 hours. After centrifugation, washing and drying, the sample is calcined at 400°C in air for 6 hours to obtain an Ag-MnOx sample with a theoretical Ag doping amount of 1 wt.%. (3) At a mass ratio of CeOx to Ag-MnOx of 2:100, CeOx, Ag-MnOx and ball milling aid are mixed and placed in a ball milling jar. Then, ethanol and grinding balls are added as grinding aids. The mixture is wet-milled at 300 rpm for 48 h and dried to obtain CeOx / Ag-MnOx photothermal catalyst.

[0038] Example 3

[0039] A cerium oxide / silver / manganese oxide heterojunction photothermal catalyst is prepared by the following steps: (1) Commercial CeO2 is placed in a tube furnace and calcined at 700℃ for 0.2h under a hydrogen atmosphere to obtain CeOx. (2) 0.6 mmol KMnO4 is dissolved in deionized water to prepare solution A, and then 0.9 mmol Mn(CH3COO)2·4H2O, a certain amount of silver nitrate and a small amount of acetic acid solution are dissolved in 30 mL of deionized water to prepare solution B. Solution A is added dropwise to solution B, and after magnetic stirring for a certain time, the mixed solution is transferred to a stainless steel reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 150℃ for 6h. After centrifugation, washing and drying of the sample, it is calcined at 600℃ in air for 6h to obtain an Ag-MnOx sample with a theoretical Ag doping amount of 6wt.%. (3) At a mass ratio of CeOx to Ag-MnOx of 10:100, CeOx, Ag-MnOx and ball milling aid are mixed and placed in a ball milling jar. Then, ethanol and grinding balls are added as grinding aids. The mixture is wet-milled at 1000 rpm for 10 h and dried to obtain CeOx / Ag-MnOx photothermal catalyst.

[0040] Example 4

[0041] A cerium oxide / silver / manganese oxide heterojunction photothermal catalyst is prepared by the following steps: (1) Commercial CeO2 is placed in a tube furnace and calcined at 500°C for 2 hours under a hydrogen atmosphere to obtain CeOx. (2) 0.6 mmol KMnO4 is dissolved in deionized water to prepare solution A, and then 0.9 mmol Mn(CH3COO)2·4H2O, a certain amount of silver nitrate and a small amount of acetic acid solution are dissolved in 30 mL of deionized water to prepare solution B. Solution A is added dropwise to solution B, and after magnetic stirring for a certain period of time, the mixed solution is transferred to a stainless steel reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 100°C for 12 hours. After centrifugation, washing and drying, the sample is calcined at 500°C in air for 8 hours to obtain an Ag-MnOx sample with a theoretical Ag doping amount of 0.5 wt.%. (3) At a mass ratio of CeOx to Ag-MnOx of 2:100, CeOx, Ag-MnOx and ball milling aid are mixed and placed in a ball milling jar. Then, ethanol and grinding balls are added as grinding aids. The mixture is wet-milled at 800 rpm for 5 hours and dried to obtain CeOx / Ag-MnOx photothermal catalyst.

[0042] Effect Example

[0043] Approximately 0.2 g of each sample from Examples 1-4 and Comparative Examples 1-4 was applied to a 7.0 cm² plate. 2 The sample was placed on a quartz petri dish at the bottom of the reactor. Formaldehyde or toluene gas was injected into the reaction vessel by bubbling simulated air (O2:N2 = 1:3) at a controlled flow rate into the liquid formaldehyde or toluene, adjusting the initial concentration of formaldehyde or toluene to approximately 400–1000 ppm. The reaction was tested after adsorption-desorption equilibrium was reached and the temperature stabilized. A xenon lamp was used to simulate an optical density of 300 mW·cm⁻¹. 2 The catalytic reaction was carried out under sunlight irradiation, with an initial pressure of 0.5 MPa and a temperature of 90 °C. During the reaction, approximately 1 mL of the gas mixture was taken out at regular intervals using a gas sampling needle. The formaldehyde / toluene and carbon dioxide content in the gas was then analyzed using GC2030 and GC1690 gas chromatographs, respectively, and the formaldehyde / toluene elimination rate was calculated. The performance of photothermal synergistic purification of VOCs is listed in Table 1.

[0044] Table 1

[0045]

[0046] As shown in Table 1, the cerium oxide / silver / manganese oxide heterojunction photothermal catalysts prepared in Examples 1-4 using interfacial vacancies and ball milling exhibit excellent photothermal synergistic catalytic activity for purifying toluene or formaldehyde, with significantly better photothermal synergistic catalytic activity than other comparative examples. Example 4 demonstrates excellent catalytic activity for formaldehyde, achieving a 99% conversion rate in just 30 minutes. Examples 1-3 show that, under simulated sunlight, even difficult-to-treat toluene can achieve a 99% conversion rate within 50-70 minutes, demonstrating a very good photothermal synergistic catalytic effect.

[0047] In Comparative Example 1, the catalyst does not contain cerium oxides, and it cannot achieve a good catalytic effect for benzene ring VOCs, which are more difficult to treat, represented by toluene. It requires a very long reaction time (165 min) to achieve a conversion rate of 99%.

[0048] Comparative Example 2 does not contain silver, and the resulting catalyst has poor reactivity. It cannot achieve a good catalytic effect on the difficult-to-process toluene and requires a long time to obtain a 99% conversion rate.

[0049] Comparative Example 3 was prepared using a non-ball milling method, and the resulting catalyst also had poor reactivity. For toluene, which is difficult to process, it takes a long time to achieve a 99% conversion rate.

[0050] In summary, it can be seen that the heterojunction photothermal catalyst and its preparation method provided by the present invention, by combining the introduction of interfacial oxygen vacancies with mechanical ball milling, can efficiently catalyze the degradation of volatile organic pollutants through photothermal synergistic catalysis. It can completely catalyze the purification of typical VOCs such as formaldehyde and toluene, which are difficult to treat, under visible light irradiation and mild reaction conditions.

[0051] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. Use of a heterojunction photo-thermal catalyst for photo-thermal catalytic purification of toluene, characterized in that, The heterojunction photo-thermal catalyst comprises cerium oxide rich in oxygen vacancies, elemental silver and manganese oxide, and the ratio of the cerium oxide, the elemental silver and the manganese oxide is 1-50:0.1-10:100 by weight percentage; The preparation method of the heterojunction photo-thermal catalyst comprises: S1, calcining cerium dioxide under a reducing atmosphere to obtain cerium oxide rich in oxygen vacancies, the calcining temperature is 300-700 DEG C, and the calcining time is 0.1-24 h; S2, mixing a manganese salt precursor solution with a silver nitrate solution, then performing a hydrothermal reaction, and calcining the product for 0.5-24 h to obtain manganese oxide loaded silver particles; S3, mixing the silver particles loaded on the cerium oxide rich in oxygen vacancies and the manganese oxide by ball milling, the ball milling rotation speed is 300~1000 rpm, the ball milling time is 0.1~60 h; obtaining CeO x / Ag-MnO x heterojunction photo-thermal catalyst.

2. Use of the heterojunction photo-catalyst according to claim 1 for photo-catalytic purification of toluene, characterized in that, The heterojunction photo-thermal catalyst is a type II catalyst.

3. Use of the heterojunction photo-catalyst according to claim 1 for photo-catalytic purification of toluene, characterized in that, The hydrothermal reaction temperature is 100-150 DEG C, and the hydrothermal time is 1-30 h.

4. Use of the heterojunction photo-catalyst according to claim 1 for photo-catalytic purification of toluene, characterized in that, In the step S3, the mass ratio of the cerium oxide rich in oxygen vacancies and the manganese oxide loaded silver particles is (1-50):

100.

5. Use of the heterojunction photo-catalyst according to claim 1 for photo-catalytic purification of toluene, characterized in that, In the manganese oxide loaded silver particles, the theoretical loading amount of Ag is 0.1-10 wt%.

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