Preparation method of foamy carbon-based manganese oxide photocatalyst for degrading volatile organic compounds

Abstract

The invention belongs to the technical field of material preparation and air pollution control, and particularly relates to preparation of a manganese oxide composite material photocatalyst with foamy carbon as a substrate material. According to the preparation method, a solution impregnation method is adopted, the surface of foamy carbon is pretreated and activated, an activated carbon skeleton can adsorb a material precursor more easily, and the MnxOy / FC composite material can be prepared through calcination. The MnxOy is anchored on the carbon skeleton, so that the loss of MnxOy nanoparticles in air flow is reduced, the secondary pollution possibly caused by the MnxOy nanoparticles in the catalytic reaction process is avoided, and the recycling of the material can be realized through the integral material design. Experiments prove that the degradation rate of the material to 600 ppm toluene under the irradiation of sunlight simulated by a 300 W xenon lamp reaches 95% within 30 min, the material has rapid degradation efficiency to toluene under the concentration of 100-2000 ppm, the reaction activity is basically kept unchanged in 20 cycle experiments, and the material has very strong stability. And the catalyst has good degradation performance on removal of gaseous pollutants such as formaldehyde, benzene and the like, and has universality. The preparation method is simple, the raw materials are low in price, the chemical properties of the materials are stable, no pollution is caused, the energy consumption in the preparation process is low, and the material shows excellent degradation performance on VOCs, can be applied to various waste gas emission or leakage environments and the like, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of novel catalyst preparation and air pollution control, and specifically relates to a preparation method and application process of a manganese oxide photocatalyst based on foamed carbon for degrading and removing volatile organic pollutants. Background Art

[0002] Air pollution caused by volatile organic compounds (VOCs) has become a huge threat to human health. It has attracted people's attention due to its high pathogenicity, strong diffusivity, high toxicity and wide sources. However, chemical industry, oil refining and even home decoration are continuously emitting VOCs into the environment. Therefore, it is very challenging to develop materials suitable for efficient removal of VOCs in various environments. Foamed carbon is a new type of carbon skeleton substrate material. Carbon materials have the advantages of large specific surface area, good conductivity and stable chemical properties. The good photothermal conversion performance of foamed carbon can effectively promote the reaction rate. Especially in photoinduced reactions, foamed carbon materials can convert sunlight into heat energy, increase the temperature of the reaction system, and thus accelerate the reaction process. Therefore, it can be used as a substrate material for photocatalysts. In the catalytic reaction process of traditional nanomaterials, the catalyst is corroded by reasons such as light energy, adsorption of pollutants and occupation of active sites, thus affecting its long-term performance. By synthesizing the catalyst on the surface of the foamed carbon skeleton, the metal center firmly anchored on the carbon carrier reduces the recombination of electrons and holes after charge transfer, enhances the reaction kinetics, and thus reduces the photocorrosion of the catalyst. The material designed and constructed in this patent is Mn x O y Mn deposited on the surface of carbon foam material x O y / FC composite materials, the preparation process is simple and easy to operate, x O y The loading amount of nanoparticles is adjustable and controllable, and experiments have shown that the material exhibits excellent conductivity and excellent catalytic VOCs removal effect. At the same time, due to the stability of the carbon material as a skeleton, the composite material has more stable properties and structure than traditional photocatalysts, and avoids the problem of powder catalysts being easily lost with the flow of air. Summary of the invention

[0003] The present invention aims to provide a method for preparing a novel carbon-based manganese oxide composite material, and the application direction of the material is the field of photodegradation of VOCs.

[0004] 1. The preparation scheme of the composite material is as follows: Step 1: Pretreatment of carbon foam Commercially available foam carbon was selected, and the foam carbon with a specification of 180×180×2 mm was cut into square foam carbon of 30×30×2 mm. The cut foam carbon was then soaked in acetone, ethanol, and water for ultrasonic washing for 30 min in sequence to remove impurities, and the washed foam carbon was dried for later use; Step 2: Mn x O y Preparation of / FC composites The foamed carbon obtained in step 1 was immersed in 30 mL of Mn(NO3)2 solution and stirred on a magnetic stirrer. The magnetic stirrer was taken out and the solution soaked with the foamed carbon was placed in a 60°C forced air drying oven for drying until the solvent in the solution was completely evaporated. Take out the foamed carbon and put it into a muffle furnace, heat it to 400℃ at a heating rate of 2℃ / min, and calcine it for 2 h. Then take it out. The obtained product is Mn x O y / FC composite materials; In step 2, the amount of solute in the Mn(NO3)2 solution is 2 mmol, 4 mmol, 6 mmol, 8 mmol, 10 mmol, and 15 mmol, respectively. In step 2, the speed of the magnetic stirrer is 100 r / min, and the stirring time is 8 h.

[0005] 2. Application of the catalyst material prepared in the present invention in the decomposition of VOCs: The prepared Mn x O y / FC composite materials were placed in a square reaction chamber for application experiments to remove VOCs. First, a bubbling machine was used to transfer a nitrogen / oxygen = 8 / 2 mixed gas into the reaction chamber to evacuate the air and seal it. Toluene was then injected into the reaction chamber with the bubbling machine and the concentration was controlled by the amount of toluene injected. A 300 W xenon lamp was used as the light source, and a gas infrared detector was used to detect the changes in the toluene gas concentration and the concentration of products such as CO2 in the reaction chamber. The removal effect and mineralization rate of the catalyst on toluene under light irradiation were determined.

[0006] The beneficial effects of the present invention are: (1) This invention prepared Mn for the first time x O y / FC composite material, which combines manganese oxide with foamed carbon material, has a simple preparation process, short time consumption, and excellent degradation effect. It is an excellent composite material for photocatalytic degradation of volatile organic compounds; (2) The present invention has a rapid response capability to low, medium and high concentrations of gaseous toluene, which can not only remove low concentrations of gaseous toluene in the atmosphere, but also provide a possibility for emergency treatment of gaseous toluene leakage; (3) The composite material prepared in the present invention is different from the traditional powder catalyst and is a monolithic catalyst, which avoids the problem of powder catalyst being difficult to place and recycle. Foamed carbon as a base material can provide a channel for electron transfer and active sites for photocatalytic reaction for manganese oxide, and can also serve as a skeleton structure of the supporting material to make the loaded oxide more stable.

[0007] Description of the drawings.

[0008] Figure 1 is the scanning electron microscope image of the material prepared in the embodiment, ac is the pretreated foam carbon material, de is Mn x O y / FC composite material. The scanning electron microscope image shows that the pretreated foam carbon has a three-dimensional skeleton structure and a smooth surface. x O y / FC composite materials are manganese oxides filled with small particles in the three-dimensional framework of foam carbon.

[0009] Figure 2 Mn in the embodiment x O y The X-ray scanning diffraction pattern of the / FC material corresponds to the diffraction peak position of MnO2, proving that the manganese oxide in the material mainly exists in the nature of MnO2.

[0010] Figure 3 The photocatalytic degradation of toluene by the materials prepared in the examples in a fixed cell reactor is compared. x O y The degradation rate of 600 ppm toluene was tested on the / FC composite material under 300 W xenon lamp irradiation, and the degradation effects of pure MnO2 and foamed carbon under the same conditions were compared. x O y / FC can completely degrade toluene in 20 min.

[0011] Figure 4 Mn in the embodiment x O y The cyclic properties of the photocatalytic degradation of toluene by / FC composite materials show that the degradation rate of the material has not decreased significantly after 20 cycles.

[0012] Figure 5 Mn in the embodiment x O y / FC composite materials degrade 800ppm formaldehyde, toluene and benzene respectively. Formaldehyde can be completely degraded in 15 minutes, toluene in 35 minutes and benzene in 50 minutes.

[0013] Figure 6 Mn xO y / FC composite materials have a high removal efficiency for toluene at different toluene concentrations. Experiments show that Mn x O y / FC composite materials can remove 100-2000 ppm of toluene within 30 min. DETAILED DESCRIPTION Example

[0015] This example uses a 3×3 cm square sheet of carbon foam. First, put it into a 100 mL beaker and use 50 mL acetone, 50 mL ethanol and 50 mL deionized water to ultrasonically wash for 20 min respectively. After taking it out, put it into a 60 ℃ constant temperature oven to dry. Mn x O y The preparation method of / FC composite material is as follows: 2 mmol, 4 mmol, 6 mmol, 8 mmol, 10 mmol, and 15 mmol of Mn(NO3)2·4H2O were added into a 100 mL beaker, 30 mL of deionized water was added, and the pretreated foamed carbon was put into the beaker after ultrasonic dissolution, magnetic stirring was performed for 8 h, and the foamed carbon was dried in a 60 ℃ constant temperature oven for 12 h. After the solvent was evaporated, the foamed carbon was put into a quartz porcelain boat, and calcined at 400 ℃ for 2 h in a muffle furnace to obtain Mn x O y / FC composite material. In this example, the prepared Mn x O y / FC composite materials were implanted in a square closed reactor with quartz glass above the reactor. A mixed gas of oxygen / nitrogen = 2 / 8 was used to purge the reaction chamber, and the air in the reaction chamber was emptied. Toluene was then injected and input into the reaction chamber along with the mixed gas. The toluene concentration was controlled by controlling the toluene injection amount. A 300 W xenon lamp was used as a light source to simulate sunlight, and a photospectral gas monitor was used to detect the toluene concentration in the reaction chamber and the concentration of products such as CO2. This process was repeated for all samples to detect their performance in removing toluene under light. The results show that: Mn x O y / FC can degrade 100-2000 ppm of toluene within 30 minutes, and the degradation rate of the material does not decrease significantly after 20 cycles, proving that the material has excellent reusability.

Claims

1. A method for preparing a foamed carbon-based manganese oxide photocatalyst for degrading volatile organic compounds, characterized in that: The following steps are involved: Step 1: Foam carbon pretreatment: Commercially available foam carbon was selected, placed in a beaker, and ultrasonically washed with acetone, ethanol and deionized water in sequence, and the foam carbon obtained after washing was dried and stored for later use.

2. Step 2, carbon-based manganese oxide, referred to as Mn x O y Preparation of / FC composites The pretreated carbon foam was placed in a manganese nitrate solution of a certain concentration and stirred on a magnetic stirrer at 100 r / min for 8 h. After the magnet was removed, the beaker was placed in a 60 °C oven for drying. After the solvent in the beaker was completely evaporated, the impregnated carbon foam was placed in a muffle furnace for calcination at a heating rate of 2 °C / min to 400 °C and maintained for 2 h. After cooling, Mn x O y / FC composite materials.

3. The Mn obtained by the method for preparing the foamed carbon-based manganese oxide photocatalyst according to claim 1 x O y / FC photocatalyst in the decomposition reaction of volatile organic compounds, characterized in that, The prepared MnxOy / FC composite material was implanted in a square closed reactor with quartz glass on top. An air bubbler was used to purge the reaction chamber to exhaust the air in the reaction chamber, and then toluene was injected and input into the reaction chamber with the mixed gas. The toluene concentration was controlled by controlling the toluene injection amount. Toluene was degraded under simulated sunlight, and the changes in toluene and product concentrations were detected to determine the photocatalytic degradation performance of the material on toluene.

4. The method for preparing the foamed carbon-based manganese oxide photocatalyst according to claim 1, characterized in that: In step 1, the amount of acetone, ethanol and water used for pretreatment ultrasonic washing (mL) and the area of ​​foam carbon (cm 2 ) ratio is 1:

1.

5. The method for preparing the foamed carbon-based manganese oxide photocatalyst according to claim 1, characterized in that: In step 2, the drying temperature is 55-80°C and the drying time is 12-24 hours.

6. The method for preparing the foamed carbon-based manganese oxide photocatalyst according to claim 1, characterized in that: In step 2, the calcination temperature of the foamed carbon is 300-600°C, the holding time is 1-4 h, and the heating rate and cooling rate are both 1-10°C / min.

7. The use of the carbon-based manganese oxide photocatalyst in the decomposition reaction of gaseous toluene according to claim 2, characterized in that: Toluene was degraded at ambient temperature using simulated sunlight as the light source.

8. Mn obtained by the method according to any one of claims 1 to 5 x O y / FC composite materials are used to degrade and remove volatile organic compounds in indoor, outdoor and industrial waste gases.

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