阅读说明：本技术 臭氧分解催化剂及其制备方法与应用 (Ozone decomposition catalyst and preparation method and application thereof ) 是由 张彭义 曹冉冉 高乐乐 于 2019-11-27 设计创作，主要内容包括：本发明涉及一种臭氧分解催化剂的制备方法,其特征在于,包括：a)将高锰酸盐与无机铵盐的混合水溶液与醇类还原剂充分反应得到第一反应液；b)将所述第一反应液固液分离,固体组分与无机铵盐水溶液混匀静置老化得到第二反应液；c)将所述第二反应液固液分离,将固体组分干燥。本发明所提供的制备方法温和且成本低,制备条件不需要高温高压,可以大规模生产,且催化剂中不需要贵金属作为活性组分。在室温且潮湿的条件下,本发明的催化剂高效稳定地分解空气中的臭氧,性能非常优越。(The invention relates to a preparation method of an ozone decomposition catalyst, which is characterized by comprising the following steps: a) fully reacting a mixed aqueous solution of permanganate and inorganic ammonium salt with an alcohol reducing agent to obtain a first reaction solution; b) carrying out solid-liquid separation on the first reaction liquid, uniformly mixing a solid component with an inorganic ammonium salt aqueous solution, standing and aging to obtain a second reaction liquid; c) and carrying out solid-liquid separation on the second reaction liquid, and drying a solid component. The preparation method provided by the invention is mild and low in cost, the preparation conditions do not need high temperature and high pressure, the large-scale production can be realized, and noble metals are not needed in the catalyst as active components. Under the conditions of room temperature and humidity, the catalyst of the invention can efficiently and stably decompose ozone in air, and has excellent performance.)

1. A method for preparing an ozonolysis catalyst, comprising:

a) fully reacting a mixed aqueous solution of permanganate and inorganic ammonium salt with an alcohol reducing agent to obtain a first reaction solution;

b) carrying out solid-liquid separation on the first reaction liquid, uniformly mixing a solid component with an inorganic ammonium salt aqueous solution, standing and aging to obtain a second reaction liquid;

c) and carrying out solid-liquid separation on the second reaction liquid, and drying a solid component.

2. The method for preparing an ozonolysis catalyst according to claim 1, wherein the molar ratio of the alcohol reducing agent to the permanganate in step a) is 0.25 to 6.5; the molar ratio of ammonium ions to manganese atoms in the first reaction liquid is 0.25-8;

in the step b), the molar ratio of newly added ammonium ions to manganese atoms in the first reaction liquid is 0-8;

optionally, the mixed aqueous solution in the step a) is obtained by mixing a permanganate aqueous solution and an inorganic ammonium salt aqueous solution, wherein the concentration of the permanganate aqueous solution is 5 g/L-150 g/L, and the concentration of the inorganic ammonium salt aqueous solution is 5 g/L-250 g/L;

in the step b), the concentration of the inorganic ammonium salt aqueous solution is 0 g/L-250 g/L.

3. The method for producing an ozonolysis catalyst according to claim 1, wherein the reaction is carried out at 10 ℃ to 90 ℃ with stirring for 0.5 to 24 hours.

4. The method for preparing an ozonolysis catalyst according to claim 1, wherein the aging by standing is carried out at 10 ℃ to 90 ℃ for not less than 3 hours.

5. The method for preparing an ozonolysis catalyst according to claim 1, wherein the drying is oven-drying at a temperature of 80 ℃ to 120 ℃.

6. The method of producing an ozonolysis catalyst according to any one of claims 1 to 5, wherein the permanganate is selected from a salt of lithium, sodium, potassium, ammonium, calcium, barium, zinc, magnesium, mercury, cadmium, rubidium, or a mixture of any two or more thereof;

and/or, in step a) and step b), the inorganic ammonium salt is independently selected from one or more of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium bromide, ammonium iodide, ammonium bisulfate, ammonium carbonate and ammonium bicarbonate;

and/or the alcohol reducing agent is selected from one or more of methanol, ethanol and glycol.

7. The ozonolysis catalyst prepared as described above.

8. A catalyst composition comprising the ozone decomposition catalyst of claim 7 and a binder.

9. An atmosphere contacting surface coated with the catalyst composition of claim 8.

10. An apparatus having the atmosphere contacting surface of claim 9.

Technical Field

The invention relates to a chemical catalytic decomposition technology, belongs to the technical field of pollutant decomposition in ambient air, and particularly relates to an ozone decomposition catalyst and a preparation method and application thereof.

Background

Near-surface ozone pollution is becoming more severe, ozone being a strong oxide that can have serious adverse effects on human Health, and studies have shown that long term exposure to low concentrations of ozone can increase the mortality of the public due to respiratory diseases (Environmental Health Perspectives,2017,125:8CID: 087021). The environmental air quality standard (GB3095-2012) updated in 2012 of China stipulates that the maximum daily 8-hour average ozone concentration limit value is 100 mu g/m³(Primary standard) and 160. mu.g/m³(secondary standard), 1 hour average ozone concentration limit of 160. mu.g/m³(Primary standard) and 200. mu.g/m³(secondary standard). In addition, in the special requirements of air purifiers with antibacterial, degerming and purifying functions for household and similar electric appliances (GB21551.3-2010) in China, the harmful substances generated by the air purifiers are also specified as follows: the ozone concentration (5 cm at the air outlet) is not higher than 100 μ g/m³Therefore, it is very important to control the concentration of ozone. As is well known, methods for removing ozone include a thermal decomposition method, an activated carbon adsorption method, a chemical liquid absorption method, and the like, but generally have problems of high energy consumption, secondary pollution, and the like. At present, room temperature catalytic decomposition is the most potential and promising ozone decomposition method, and the key point of the technology lies in the preparation of high-performance and low-cost catalyst. Among all the explored catalysts, the noble metal has excellent catalytic ozonolysis performance, but the noble metal is expensive and cannot realize large-scale production and application. Among transition metal oxides, manganese dioxide has the characteristics of abundant resources, low price and relatively excellent performance, and has become the key point of many researches. However, in the process of ozone decomposition, the activity of manganese oxide is greatly reduced due to the competitive adsorption of water molecules and ozone molecules (Catalysis Communications 59(2015) 156-160). In practical application, a large amount of water molecules always exist in the air, so that the development of a catalyst with high performance in a humid environment has great challenges and application prospects. In recent years, a study (Applied Catalysis B: Environmental 201(2017) 503-510) has been reported on the reaction of cryptomelane-type manganese dioxide for catalytically decomposing ozone: in the test of 6 hours, the test period,at 30 ℃, the ozone concentration at the inlet is about 40ppm, the relative humidity is 45 percent and the space velocity is 600L-g^-1·h^-1Under the condition, the synthesized Ce doped alpha-MnO₂Exhibits excellent ozonolysis performance. But the hydrothermal synthesis mode adopted by the method is difficult to realize mass production.

Therefore, in order to effectively reduce the pollution of ozone in the ambient air and further reduce the harm of ozone to human bodies, the manganese dioxide catalyst which is simple in preparation process, low in cost, suitable for batch production, resistant to inactivation at room temperature, high in efficiency and long in service life has important practical value for economically and effectively removing the ozone pollution in the ambient air.

Disclosure of Invention

In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

the invention relates to a preparation method of an ozone decomposition catalyst, which comprises the following steps:

a) fully reacting a mixed aqueous solution of permanganate and inorganic ammonium salt with an alcohol reducing agent to obtain a first reaction solution;

b) carrying out solid-liquid separation on the first reaction liquid, uniformly mixing a solid component with an inorganic ammonium salt aqueous solution, standing and aging to obtain a second reaction liquid;

c) and carrying out solid-liquid separation on the second reaction liquid, and drying a solid component.

According to one aspect of the invention, the invention also relates to the ozonolysis catalyst prepared by the method and the application thereof.

Compared with the prior art, the invention has the beneficial effects that:

(1) the preparation method is mild and low in cost, the preparation conditions do not need high temperature and high pressure, large-scale production can be realized, and noble metals are not needed in the catalyst as active components.

(2) Under the conditions of room temperature and humidity, the catalyst of the invention can efficiently and stably decompose ozone in air, and has excellent performance.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is an X-ray diffraction pattern of the manganese dioxide catalyst of example 1;

in FIG. 2, (a), (b), (c), (d), (e) are scanning electron micrographs at different magnifications of the catalyst sample of example 1; (f) is a transmission electron micrograph of a catalyst sample;

FIG. 3 is a Fourier transform infrared spectrum of the manganese dioxide catalyst of example 2;

FIG. 4 is a nitrogen desorption curve and a pore size distribution plot at 77K for the manganese dioxide catalyst of example 3;

FIG. 5 is a graph of the conversion of the manganese dioxide catalyst of example 3 to catalyze ozonolysis at various humidities;

FIG. 6 life curve of manganese dioxide catalyst prepared in example 4 catalyzing ozonolysis at 50% relative humidity.

Detailed Description

Reference will now be made in detail to embodiments of the invention, one or more examples of which are described below. Each example is provided by way of explanation, not limitation, of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment.

It is therefore intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present invention are disclosed in or are apparent from the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention.

The invention relates to a preparation method of an ozone decomposition catalyst, which comprises the following steps:

a) fully reacting a mixed aqueous solution of permanganate and inorganic ammonium salt with an alcohol reducing agent to obtain a first reaction solution;

b) carrying out solid-liquid separation on the first reaction liquid, uniformly mixing a solid component with an inorganic ammonium salt aqueous solution, standing and aging to obtain a second reaction liquid;

c) and carrying out solid-liquid separation on the second reaction liquid, and drying a solid component.

In some embodiments, in step b), the solid component is washed and then mixed with an aqueous solution of an inorganic ammonium salt.

In some embodiments, the molar ratio of the alcoholic reducing agent to the permanganate in step a) is 0.25 to 6.5, and optionally 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5, 5.5 or 6; the molar ratio of ammonium ions to manganese atoms in the first reaction liquid is 0.25-8, and 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7 or 7.5 can also be selected;

in the step b), the molar ratio of the newly added ammonium ions to the manganese atoms in the first reaction solution is 0-8, and 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7 or 7.5 can be selected;

in some embodiments, the mixed aqueous solution in step a) is obtained by mixing an aqueous permanganate solution with a concentration of 5g/L to 150g/L (alternatively, 20g/L, 30g/L, 40g/L, 50g/L, 60g/L, 70g/L, 80g/L, or 90g/L, 100g/L, 110g/L, 120g/L, 130g/L, or 140g/L) and an aqueous inorganic ammonium salt solution with a concentration of 5g/L to 250g/L (alternatively, 10g/L, 20g/L, 30g/L, 40g/L, 50g/L, 60g/L, 70g/L, 80g/L, 90 g/L), 100g/L, 110g/L, 120g/L, 130g/L, 140g/L, 150g/L, 160g/L, 170g/L, 180g/L, 190g/L, 200g/L, 210g/L, 220g/L, 230g/L, or 240 g/L);

in step b), the concentration of the inorganic ammonium salt aqueous solution is 0g/L to 250g/L, or 0.1g/L, 0.5g/L, 1g/L, 2g/L, 3g/L, 4g/L, 5g/L, 10g/L, 20g/L, 30g/L, 40g/L, 50g/L, 70g/L, 90g/L, 110g/L, 130g/L, 150g/L, 170g/L, 190g/L, 210g/L or 230 g/L.

In some embodiments, the reaction is performed at 10 ℃ to 90 ℃, and optionally at 20 ℃, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃ or 80 ℃ with stirring;

in some embodiments, the reaction is stirred for a period of time of 0.5 to 24 hours, such as 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, or 22 hours.

In some embodiments, the static aging is performed at 10 ℃ to 90 ℃, such as 20 ℃, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃ or 80 ℃.

In some embodiments, the time of standing is 3 hours or more, for example 12h, 24h, 48h, 60h, 72h, 120h, or 140 h.

In some embodiments, the drying is drying, and the drying temperature is 80 ℃ to 120 ℃, or 90 ℃, 100 ℃ and 110 ℃.

In some embodiments, the permanganate salt is selected from a salt of lithium, sodium, potassium, ammonium, calcium, barium, zinc, magnesium, mercury, cadmium, rubidium or a mixture of any two or more thereof.

In some embodiments, in step a) and step b), the inorganic ammonium salt is independently selected from one or more of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium bromide, ammonium iodide, ammonium bisulfate, ammonium carbonate, and ammonium bicarbonate.

In some embodiments, the alcoholic reducing agent is selected from one or more of methanol, ethanol, and ethylene glycol.

In some embodiments, no noble metal is added to the process.

In some embodiments, the noble metal is selected from the group consisting of platinum group metals, silver, and gold.

In some embodiments, the platinum group metal is selected from platinum, palladium, and rhodium.

In some embodiments, no additional pH modifier is added to the system of the reaction.

According to one aspect of the invention, the invention also relates to an ozonolysis catalyst prepared according to the method described above.

According to one aspect of the invention, the invention also relates to a catalyst composition comprising an ozone decomposition catalyst as described above and a binder.

In some embodiments, the binder is an inorganic binder, preferably a silicate-based, alumina-based or ammonium zirconium carbonate-based inorganic binder.

In some embodiments, the binder is polyethylene, polypropylene, polyolefin copolymers, polyisoprene, polybutadiene copolymers, chlorinated rubber, nitrile rubber, polychloroprene, ethylene propylene diene monomer rubber, polystyrene, polyacrylates, polymethacrylates, polyacrylonitrile, polyvinyl esters, polyvinyl halides, polyamides, acrylic polymers, vinyl acrylic polymers, ethylene vinyl acetate copolymers, styrene-acrylic polymers, polyvinyl alcohol, thermoplastic polyesters, thermosetting polyesters, polyphenylene oxide, polyphenylene sulfide, fluorinated polymers, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyvinyl fluoride, chloro/fluoro copolymers, ethylene, chlorotrifluoroethylene copolymers, polyamides, phenolic resins, epoxy resins, polyurethanes, silicone polymers, or mixtures of any two or more thereof.

According to one aspect of the invention, the invention also relates to an atmosphere contacting surface coated with a catalyst composition as described above.

In some embodiments, the atmosphere contacting surface comprises a heat exchanger, a fan blade, a fan grill, or a conduit for transporting a fluid.

In some embodiments, the heat exchanger comprises a radiator, an intake air cooler, an air conditioning condenser, an oil cooler, a power steering oil cooler, or a transmission oil cooler.

According to one aspect of the invention, the invention also relates to a device having an atmosphere contacting surface as described above.

In some embodiments, the device is a vehicle device, such as a building air conditioning system or a mobile billboard.

In some embodiments, the device is a power tool, such as a lawn mower, cutter, lawnmower, circular saw, chain saw, or leaf blower/harvester.

In some embodiments, the device is a ventilation device (e.g., an air conditioner), an air humidification device, or an air purification device.

In some embodiments, the device is a uv disinfection device.

Embodiments of the present invention will be described in detail with reference to examples.

Example 1

10g of potassium permanganate is weighed and dissolved in 500mL of deionized water, and the potassium permanganate solution is dissolved by ultrasonic and stirring to form a uniform solution. And (3) weighing 20g of ammonium chloride, adding the ammonium chloride into the potassium permanganate solution, and dissolving by ultrasonic and stirring to completely and uniformly mix the ammonium chloride. 10mL of methanol was then added and the resulting solution was placed in a water bath at 60 ℃ with constant stirring for 1 h. And then filtering the obtained solid, washing with deionized water, putting the solid into 250mL of 1mol/L ammonium sulfate solution, stirring to uniformly mix the solid and the ammonium sulfate solution, placing the obtained suspension in a water bath at 60 ℃, standing and aging for 24 hours, filtering the obtained solid, washing with deionized water, and drying in an oven at 105 ℃ to obtain the manganese dioxide catalyst.

FIG. 1 is an X-ray diffraction pattern of the manganese dioxide catalyst of example 1, wherein the diffraction peaks at 12.3 °, 25.2 °, 37.6 ° and 65.6 ° correspond to the {001}, {002}, { -111}, and {020} crystal planes of birnessite-type manganese dioxide according to XRD standard card (JCPDS 80-1098), respectively, thereby showing that the synthesized catalyst is classified into birnessite-type manganese dioxide having a layered structure.

Fig. 2 is a scanning electron microscope and a transmission electron microscope photograph of the manganese dioxide catalyst in example 1, wherein the magnifications of (a), (b), (c), (d), and (e) are 5 thousand times, 1 ten thousand times, 2 ten thousand times, 5 ten thousand times, and 10 ten thousand times, respectively, and we see that a sample is mainly composed of ultrathin nanosheets having a transverse diameter of about 500nm and a thickness of about 10nm, and the nanosheets are self-assembled into a shape similar to a tremella, and have a plurality of macropores or even micron-sized pores, so that the shape of the sample looks fluffy, which is very favorable for mass transfer of gas molecules, thereby being favorable for the catalytic reaction, and the material also contains some nanoparticles and is dotted among the ultrathin nanosheets. (f) The nano-sheet is a transmission electron microscope photo of a sample, can be seen to be consistent with the photo of a scanning electron microscope, and consists of an ultrathin nano-sheet and a part of nano-particles, wherein the nano-sheet is very thin and is almost transparent under the transmission electron microscope.

Example 2

6g of sodium permanganate is weighed and dissolved in 120mL of deionized water, and the solution is dissolved by ultrasonic and stirring to form a uniform solution. 6g of ammonium bisulfate is weighed and added into the potassium permanganate solution, and the mixture is dissolved by ultrasonic and stirring to be completely and uniformly mixed. 7mL of methanol was then added and the resulting solution was placed in a water bath at 70 ℃ with constant stirring for 6 h. And then filtering the obtained solid, washing with deionized water, putting the solid into 100mL of 0.3mol/L ammonium bicarbonate solution, stirring to completely and uniformly mix the solid and the ammonium bicarbonate solution, placing the obtained suspension in a water bath at 50 ℃, standing and aging for 120h, filtering the obtained solid, washing with deionized water, and drying in an oven at 95 ℃ to obtain the manganese dioxide catalyst.

FIG. 3 is a Fourier transform infrared spectrum of the manganese dioxide catalyst of example 2 at 1400cm^-1And 3124cm^-1The peak of (A) belongs to NH₄ ⁺(J.Phys.chem.A 2005,109,1337-1342) which shows that much NH is present on the surface of the manganese dioxide catalyst₄ ⁺And the manganese dioxide catalyst is combined with oxygen atoms on the surface through hydrogen bonds, and the surface adsorbed ammonium ions increase the acidity of the surface of the manganese dioxide catalyst, so that the adsorption of ozone molecules is increased.

Measuring the content of elements in the manganese dioxide catalyst by using an inductively coupled plasma emission spectrometer to obtain an N/Mn element molar ratio of 0.24, and obtaining NH of the N element by X-ray photoelectron spectroscopy₄ ⁺Are present at the surface or between layers, these results are consistent with those of Fourier transform infrared spectroscopy, indicating a large numberAmmonium ions exist on the surface or between layers of the manganese dioxide catalyst, and the activity of catalyzing ozonolysis is promoted.

Example 3

10g of ammonium permanganate is weighed and dissolved in 200mL of deionized water, and the solution is dissolved by ultrasonic and stirring to form a uniform solution. 5g of ammonium sulfate is weighed and added into the sodium permanganate solution, and the mixture is dissolved by ultrasonic and stirring to be completely and uniformly mixed. 5mL of ethylene glycol was then added and the resulting solution was placed in a water bath at 80 ℃ with continued stirring for 2 h. And then filtering the obtained solid, washing with deionized water, putting the solid into 200mL of 0.6mol/L ammonium chloride solution, stirring to completely and uniformly mix the solid and the ammonium chloride solution, placing the obtained suspension in a water bath at 65 ℃, standing and aging for 60 hours, filtering the obtained solid, washing with deionized water, and drying in an oven at 80 ℃ to obtain the manganese dioxide catalyst.

FIG. 4 is a nitrogen adsorption/desorption curve at 77K for the manganese dioxide catalyst of example 3, which has a specific surface area of 220m calculated according to the BET method²(ii) in terms of/g. The inset in fig. 4 is the pore size distribution plot of the manganese dioxide catalyst of example 3, and we see that the manganese dioxide catalyst of the present invention has a hierarchical porous structure with pore centers at 7nm, 12nm, 16nm, and 29nm, respectively, and a pore volume of 0.84cc/g calculated according to NL-DFT method, indicating that the catalyst of the present invention has a large specific surface area and a hierarchical porous structure, which facilitates the rapid transport of water molecules and ozone molecules, and the larger pores make water molecules less prone to condense on the surface of the catalyst, enabling the manganese dioxide catalyst to maintain a high catalytic ozone decomposing activity stably and permanently in a humid environment.

FIG. 5 shows the performance of the manganese dioxide catalyst of example 3 in catalyzing the degradation of ozone under different humidity conditions, wherein the experimental conditions are set such that the initial concentration of ozone is 100ppm and the gas flow rate is 1L/min at 25 ℃, the gas flow continuously passes through 0.1g of the catalyst prepared in example 3 with 40-60 mesh, and the relative humidity is adjusted to 50%, 70%, and 90%, and the ozone conversion rate of the manganese dioxide catalyst obtained by the present invention is stabilized at 100%, 86%, and 69% after 8 hours. Therefore, the manganese dioxide ozone decomposition catalyst obtained by the preparation method has excellent performance under general humidity, can completely decompose ozone by 100 percent, and has excellent catalytic ozone decomposition performance under high humidity, which shows that the manganese dioxide catalyst has wider applicable humidity range.

Example 4

8g of potassium permanganate is weighed and dissolved in 150mL of deionized water, and the potassium permanganate solution is dissolved by ultrasonic and stirring to form a uniform solution. 6g of ammonium bromide is weighed and added into the ammonium permanganate solution, and the mixture is dissolved by ultrasonic and stirring to be completely and uniformly mixed. 10mL of ethanol was then added and the resulting solution was placed in a water bath at 30 ℃ with constant stirring for 8 h. And then filtering the obtained solid, washing with deionized water, putting the solid into 400mL of 2mol/L ammonium nitrate solution, stirring to completely and uniformly mix the solid and the ammonium nitrate solution, placing the obtained suspension in a water bath at 75 ℃ for standing and aging for 50h, filtering the obtained solid, washing with deionized water, and drying in an oven at 90 ℃ to obtain the manganese dioxide catalyst.

Taking the material prepared in example 4 as an example, the stability and life of the performance of manganese dioxide catalyst in catalyzing and decomposing ozone were examined. Under the conditions that the initial concentration of ozone was set at 100ppm at 25 c, the relative humidity was 50% and the gas flow rate was 1L/min, and the above gas flow was continuously passed through 0.1g of the manganese dioxide catalyst prepared in example 4 of 40 to 60 mesh, the conversion rate of ozone was almost maintained at 100% after 36 hours and the conversion rate of ozone was still 86% after 120 hours of reaction, as shown in fig. 6. Indicating that the catalyst has very high stability and life.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.