Membrane filtering material, preparation method therefor, and use thereof in treatment of aerosol

Abstract

Disclosed in the present invention are a membrane filtering material, a preparation method therefor, and the use thereof in the treatment of an aerosol. The preparation method comprises the following

Description

[0002] The present application relates to the technical field of aerosol treatment, in particular to a membrane filter material, a preparation method therefor, and a use thereof in treatment of aerosol. BACKGROUND

[0003] An aerosol is a multi-phase system including a gas and solid and liquid particles suspended in the gas. A hazardous aerosol containing a hazardous substance may travel a long distance due to the wind system, which not only poses a significant threat to the human living environments, but may also impact the global climate change. A radioactive aerosol refers to an aerosol containing radionuclides, which is highly hazardous and would lead to serious internal irradiation hazards upon inhalation by humans or animals and further endanger ecosystems if left untreated and discharged into the atmosphere. In some specific working conditions, the filter material for treating the radioactive aerosol needs to exhibit the characteristic of high-temperature resistance. For example, in a scenario such as the failure of the seal of the cover gas in the lead-based fast reactor in the nuclear energy system, where the argon gas carrying the plutonium aerosol is rapidly discharged into the containment chamber on the top of the reactor in a short period while releasing a large amount of heat, the conventional filter materials often fail to effectively purify the gas in such temperature environment and may even be melted to completely lose the ability to purify. CN204294017U discloses a nuclear island air filter for treating the radioactive aerosol, which includes a filter element fixed to a box body by an adhesive and is not suitable for operation in a high-temperature environment due to the melting of the adhesive at the high temperature. CN106128538A discloses a method and a device for removing 210Po from a lead-based fast reactor or ADS subcritical system, wherein the device is mainly composed of a ceramic filtration membrane, glass fibers, and a filtration cloth, which has a high cost of filtration due to the presence of the rare earth component in the filtration membrane. CN106757528B discloses an ultralow-density fluffy silica fiber and a preparation method thereof, the obtained silica fiber has the advantages of high-temperature resistance and high filter fineness, and the method adopts the electrospinning technique which is simple in operation and low in cost, however, the silica fiber generally has a weak affinity with nuclides. SUMMARY

[0004] In view of above, there is a need to develop a preparation method for a membrane filter material that exhibits a high-temperature resistance, a high filtration efficiency, and a low cost and can be used to treat the aerosol, especially the radioactive aerosol containing polonium or other nuclides, at a high temperature to purify the air in the nuclear power plant or used to filter other hazardous aerosols to purify the atmosphere.

[0005] An objective of the present application is to provide a membrane filter material with a high-temperature resistance, a high filter fineness, and a high polonium affinity and a preparation method therefor. The objective can be achieved by the following technical solutions.

[0006] In a first aspect of the present application, a preparation method for a membrane filter material is provided, including steps of

[0007] mixing polyvinyl alcohol with water to prepare a PVA aqueous solution;

[0008] mixing water, tetraethyl orthosilicate, and phosphoric acid and hydrolyzing the tetraethyl orthosilicate to prepare a Si hydrolyzed liquid;

[0009] mixing the Si hydrolyzed liquid with an iron salt to prepare a Si / Fe hydrolyzed liquid;

[0010] mixing the PVA aqueous solution with the Si / Fe hydrolyzed liquid and aging to prepare a spinning precursor liquid;

[0011] subjecting the spinning precursor liquid to electrospinning to prepare a precursor nanofiber membrane; and

[0012] drying the precursor nanofiber membrane and calcining the precursor nanofiber membrane under a reducing atmosphere to prepare a Fe / Fe2O3 / SiO2 hybrid nanofiber membrane.

[0013] In some embodiments of the present application, in the preparation method for the membrane filter material, the PVA aqueous solution contains the polyvinyl alcohol in an amount of 5wt% to 20wt%.

[0014] In some embodiments of the present application, in the preparation method for the membrane filter material, in the step of mixing the water, the tetraethyl orthosilicate, and the phosphoric acid, a molar ratio of the water to the tetraethyl orthosilicate to the phosphoric acid is (5 to 20):1:(0.005 to 0.015), and / or a time of the hydrolyzing is 4 h to 18 h.

[0015] In some embodiments of the present application, in the preparation method for the membrane filter material, in the step of mixing the Si hydrolyzed liquid with the iron salt, a molar ratio of Si to Fe is (2 to 16):1, and / or the iron salt is iron nitrate, iron chloride, or a combination thereof.

[0016] In some embodiments of the present application, in the preparation method for the membrane filter material, in the step of mixing the PVA aqueous solution with the Si / Fe hydrolyzed liquid and aging, a mass ratio of the PVA aqueous solution to the Si / Fe hydrolyzed liquid is 1 :(0.5 to 2.5), the aging is performed by standing, and a time of the aging is 4 h to 24 h.

[0017] In some embodiments of the present application, in the preparation method for the membrane filter material, a molar ratio of Si to Fe is (2 to 8): 1, and / or a mass ratio of the PVA aqueous solution to the Si / Fe hydrolyzed liquid is 1:(0.5 to 1.5).

[0018] In some embodiments of the present application, in the preparation method for the membrane filter material, the aging is performed at a room temperature of 20°C to 30°C for a time of 6 h to 24 h.

[0019] In some embodiments of the present application, in the preparation method for the membrane filter material, the aging is performed in a water bath at a temperature of 40°C to 70°C for a time of 4 h to 20 h.

[0020] In some embodiments of the present application, in the preparation method for the membrane filter material, the electrospinning is performed with the following parameters: a receiving distance of 5 cm to 25 cm, and / or a pushing and injection speed of 0.8 mL / h to 3 mL / h, and / or a voltage is 6 kV to 15 kV.

[0021] In some embodiments of the present application, in the preparation method for the membrane filter material, in the step of drying the precursor nanofiber membrane and calcining the precursor nanofiber membrane under the reducing atmosphere, the drying is performed at a temperature of 60°C to 100°C for a time of 4 h to 8 h, and / or the reducing atmosphere is a mixed atmosphere of an inert gas and hydrogen gas.

[0022] In some embodiments of the present application, in the preparation method for the membrane filter material, the calcining is performed at a temperature of 350°C to 800°C for a time of 1 h to 8 h.

[0023] In some embodiments of the present application, in the preparation method for the membrane filter material, the concentration of the hydrogen gas in the mixed atmosphere is 5%, the inert gas is selected from nitrogen gas or argon gas, and the calcining is performed at a temperature of 450°C to 700°C for a time of 2 h to 8 h.

[0024] In a second aspect of the present application, a membrane filter material is provided, which is prepared by the preparation method provided in the first second aspect of the present application.

[0025] In a third aspect of the present application, a use of the membrane filter material provided in the second aspect of the present application in treatment of an aerosol is provided. The aerosol is selected from a polonium aerosol, an iodine aerosol, or a lead-bismuth aerosol.

[0026] In some embodiments of the present application, the membrane filter material is used to treat the aerosol at 25°C to 450°C.

[0027] In the preparation method for the membrane filter material provided in the present application, the sol-gel electrospinning is adopted in combination with the heat treatment, the sol-gel precursor liquid is formed from the polyvinyl alcohol, the tetraethyl orthosilicate, and the iron salt, the calcining under the reducing atmosphere is performed to remove organics and reduce Fe2O3 on the surface of the hybrid fiber to Fe. The resulting Fe / Fe2O3 / SiO2 hybrid nanofiber membrane has excellent comprehensive performance of high-temperature resistance and high polonium affinity. The filtration with a high efficiency of above 98% and even above 99% can be achieved within the high temperature range of 300°C to 400°C

[0028] The inventors have found that the doping with elemental Fe improves the filtration effect of SiO2 nanofiber on the polonium aerosol, but leads to decreased spinnability of the spinning precursor liquid and increased brittleness of the fiber. In some preferred embodiments of the present application, the problems of spinnability deterioration of the spinning precursor liquid and increase in fiber brittleness can be improved by adjusting process conditions such as the type of iron salt, the Si / Fe ratio, the spinning parameters, and the calcining temperature.

[0029] The electrospinning is low in cost and controllable in spinning process, and uses a device which is simple to operate. Utilizing the electrospinning device to prepare the membrane filter material not only meets the filtration requirement but also reduces the filtration cost. In addition, the fiber prepared by electrospinning exhibits the characteristics of large specific surface area, small pore size, and high porosity, leading to excellent filter fineness and low pressure drop, even for aerogels with particle sizes below the submicron level.

[0030] The Fe / Fe2O3 / SiO2 hybrid nanofiber membrane provided in the present application is a flexible inorganic nanofiber membrane that has characteristics of high-temperature resistance, high filter fineness, and high polonium affinity.

[0031] The Fe / Fe2O3 / SiO2 hybrid nanofiber membrane provided in the present application can be used to filter the polonium aerosol in high-temperature environments to rapidly reduce the polonium concentration in a short time. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application and to more completely understand the present application and its beneficial effects, the accompanying drawings to be used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some of the embodiments of the present application, and other accompanying drawings may be obtained from these drawings without creative work by those skilled in the art. It should also be noted that FIG. 1 is drawn in a simplified form and is used only for convenience and clarity to aid in the illustration of the present application. The various dimensions of components shown in FIG. 1 are arbitrarily illustrated and may be accurate or may not be drawn to the actual scale. For example, the dimensions of the components are suitably exaggerated in some places in the accompanying drawings for clarity of illustration. Unless otherwise noted, the individual components in the drawings are not drawn to scale. The size of each of the components in the present application is not limited in the present application.

[0033] The same reference numerals in the following description indicate the same component.

[0034] FIG. 1 is a schematic diagram of an electrospinning device for preparing a Fe / Fe2O3 / SiO2 hybrid nanofiber membrane in Example 1.

[0035] FIG. 2 is a SEM image of the Fe / Fe2O3 / SiO2 hybrid nanofiber membrane prepared in Example 1.

[0036] FIG. 3 is a SEM image of the Fe / Fe2O3 / SiO2 hybrid nanofiber membrane prepared in Example 1 after filtration which contains elements Pb, Bi, and Te.

[0037] FIG. 4 is a XRD image of the Fe / Fe2O3 / SiO2 hybrid nanofiber membrane prepared in Example 1 after and before filtration.

[0038] FIG. 5 is a graph comparing the filter efficiencies at different filtration temperatures of the Fe / Fe2O3 / SiO2 hybrid nanofiber membrane prepared in Example 1.

[0039] Reference numerals:

[0040] 1 -springe pump, 2-spining precursor liquid, 3-streched polymer, 4-barrel receiver, 5-high- voltage power supply. DETAILED DESCRIPTION

[0041] The present application will be further described in conjunction with accompanying drawings, embodiments, and examples. It should be understood that the embodiments are merely for illustrating the present application, and are not intended to limit the scope of the present application. In addition, it should be understood that various modifications and improvements can be made to the present application by a person skilled in the art after reading the contents taught by the present application, and all those equivalent forms shall fall within the protection scope defined by the appended claims of the present application.

[0042] Unless otherwise defined, all the technical and scientific terms used herein have the same meanings as the meanings commonly understood by a person skilled in the art to which the present application pertains. The terms used in the specification of the present application are merely for describing the embodiments and examples, and are not intended to limit the present application.

[0043] Terms

[0044] Unless otherwise stated or contradicted, the terms or phrases used herein have the following meanings:

[0045] As used herein, the terms “and / or”, “or / and”, “as well as / or” when used in a list of two or more associated items, mean that any one of the items can be selected, and any or all combinations of the items can be selected. The any or all combinations include the combination of any two of the associated listed items, the combination of any more of the associated listed items, or the combination of all associated listed items. It is to be noted that when connecting at least three items with a combination of at least two conjunctions selected from “and / or”, “or / and”, and “as well as / or”, it is to be understood that, in the present application, the technical solution undoubtedly includes all technical solutions that are connected by “logical AND” and also undoubtedly includes all technical solutions that are connected by “logical OR”. For example, “A and / or B” includes A, B, and A+B. For another example, “A, and / or, B, and / or, C, and / or, D” includes any one of A, B, C, and D (i.e., technical solutions connected by “logical OR”), and any and all combinations of A, B, C, D, such as the combination of any two or three of A, B, C, and D and the combination of A, B, C, and D (i.e., technical solutions connected by “logical AND”).

[0046] In the present application, terms such as “preferred”, “preferably”, and “better” are only used to describe an embodiment or example with better effect, and should not be construed as constituting a limitation on the protection scope of the present application.

[0047] In the present application, the terms “first”, “second”, “third”, etc., in “first aspect”, “second aspect”, “third aspect”, etc., are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or quantity, or as implicitly specifying the importance or quantity of the technical features indicated. Moreover, “first”, “second”, “third”, and the like only serve the purpose of non-exhaustive enumeration, and should not be construed as constituting a closed-ended limitation of quantity.

[0048] In the present application, among the technical features described in an open-ended manner, a closed technical solution comprising the enumerated features is included, and an open-ended technical solution comprising the enumerated features is also included.

[0049] The present application relates to numerical intervals (i.e., ranges of values), wherein, unless otherwise specifically stated, the selectable numerical values are considered to be distributed continuously within the numerical intervals and include the two numerical endpoints (i.e., the minimum value and the maximum value) of the range of numerical values, as well as each of the numerical values between these two numerical endpoints. Unless otherwise specified, when the numerical range is directed only to integers within that numerical range, the two endpoint integers of that numerical range are included, as well as each integer between the two endpoints. In addition, when multiple ranges are provided to describe the feature or characteristic, the ranges may be combined. In other words, unless otherwise indicated, the ranges disclosed herein should be construed as including any and all sub-ranges subsumed therein.

[0050] In the present application, unless otherwise specifically defined, the temperature parameters allow for both constant temperature treatment and treatment within a certain temperature range. It should be understood that the constant temperature treatment allows for fluctuations within the precision range of the instrument.

[0051] Unless otherwise specified, the calcining temperature as used herein refers to a temperature set in the calcining device.

[0052] In the present application, “room temperature” refers to the condition without temperature control, generally is 4°C to 35°C, preferably 4°C to 30°C, more preferably, for example, 20±5°C, 20°C to 30°C, and the like. The “room temperature” in the present application is, for example, 15°C, 16°C, 18°C, 20°C, 25°C, 26°C, 28°C, 30°C, 32°C, 35°C, etc.

[0053] In the present application, unless otherwise specified, the percentage contents refer to volume percentages for gas-gas mixtures, mass percentages (wt%) for solid-solid mixtures, volume percentages %(v / v) for liquid-liquid mixtures, and mass percentages (wt%) or weight / volume percentages (w / v) for solid-liquid mixtures.

[0054] In the present application, %(w / w) and wt% both refer to weight percentages.

[0055] PVA refers to polyvinyl alcohol. TEOS refers to tetraethyl orthosilicate.

[0056] The present application provides a preparation method for a membrane filter material, including steps of

[0057] SI00, mixing polyvinyl alcohol with water to prepare a PVA aqueous solution;

[0058] S200, mixing water, tetraethyl orthosilicate, and phosphoric acid and hydrolyzing the tetraethyl orthosilicate to prepare a Si hydrolyzed liquid;

[0059] S300, mixing the Si hydrolyzed liquid with an iron salt to prepare a Si / Fe hydrolyzed liquid;

[0060] S400, mixing the PVA aqueous solution with the Si / Fe hydrolyzed liquid and aging to prepare a spinning precursor liquid;

[0061] S500, subjecting the spinning precursor liquid to electrospinning to prepare a precursor nanofiber membrane; and

[0062] S600, drying the precursor nanofiber membrane and calcining the precursor nanofiber membrane under a reducing atmosphere to prepare a Fe / Fe2O3 / SiO2 hybrid nanofiber membrane.

[0063] In the preparation method provided in the present application, the sol-gel electrospinning is adopted in combination with the heat treatment, the sol-gel precursor liquid is formed from the polyvinyl alcohol, the tetraethyl orthosilicate, and the iron salt, the calcining under the reducing atmosphere is performed to remove organics and reduce Fe2O3 on the surface of the hybrid fiber to Fe. The resulting Fe / Fe2O3 / SiO2 hybrid nanofiber membrane has excellent comprehensive performance of high-temperature resistance, high filter fineness, and high polonium affinity.

[0064] SI00: Preparation of PVA aqueous solution

[0065] In some embodiments of the present application, the polyvinyl alcohol is mixed with water by stirring. The stirring time is 2 h to 12 h, preferably, 4 h to 8 h.

[0066] In some specific embodiments of the present application, the stirring time is 6 h.

[0067] The PVA aqueous solution, as a precursor fluid, needs to have a suitable viscosity.

[0068] In some embodiments of the present application, the PVA aqueous solution contains the polyvinyl alcohol (PVA) in an amount of 5wt% to 20wt%.

[0069] In some preferred embodiments of the present application, the amount of the polyvinyl alcohol in the PVA aqueous solution is 5wt% to 18wt%, 5wt% to 16wt%, 5wt% to 12wt%, 5wt% to 10wt%, 7wt% to 12wt%, 7wt% to 15wt%, 7wt% to 18t%, 10wt% to 20wt%, 15wt% to 20wt%, or 18wt% to 20wt%.

[0070] In some specific embodiments of the present application, the amount of the polyvinyl alcohol in the PVA aqueous solution is 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, llwt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, or20wt%.

[0071] S200: Preparation of Si hydrolyzed liquid

[0072] In some embodiments of the present application, the molar ratio of water to tetraethyl orthosilicate to phosphoric acid is (5 to 20):1:(0.005 to 0.015).

[0073] In some preferred embodiments of the application, the molar ratio of water to tetraethyl orthosilicate to phosphoric acid is (10 to 20):1:(0.01 to 0.015).

[0074] In some specific embodiments of the present application, the molar ratio of water to tetraethyl orthosilicate to phosphoric acid is 15:1:0.01.

[0075] After the water, tetraethyl orthosilicate, and phosphoric acid are mixed, the tetraethyl orthosilicate is hydrolyzed by the phosphoric acid to form the Si hydrolyzed liquid. The hydrolyzing is performed under condition including but not limited to stirring. The hydrolyzing time should be sufficient to ensure thorough hydrolyzation.

[0076] In some embodiments of the present application, the hydrolyzing time is 4 h to 18 h, preferably 8 h to 12 h.

[0077] S300: Preparation of Si / Fe hydrolyzed liquid

[0078] Metals have a higher affinity with polonium than oxides. The inventors have found that the doping with elemental Fe improves the filtration effect of Si O2 nanofiber on the polonium aerosol, but leads to decreased spinnability of the spinning precursor solution and increased brittleness of the fiber. The enthalpy of adsorption of polonium onto metallic iron was predicted to be -346 kJ / mol by a semi-empirical model, which was higher than that of SiCh at -125 kJ / mol, indicating that the doping with Fe could improve the capture and filtration effect of the SiCh fiber on volatile polonium.

[0079] The doping with Fe element is preferably achieved by introducing iron nitrate or iron chloride.

[0080] The amount of the iron salt, if excessive, would lead to poor spinnability of the spinning liquid, making it difficult to spin or resulting in increased brittleness and fragility of the spun fiber, and if insufficient, would compromise the adsorption enhancement effect of elements such as Po. By controlling the molar ratio of Si to Fe within an appropriate range (e.g., (2 to 8): 1), a better spinning performance can be achieved, and the flexibility and filtration effect of the spun fiber can be optimized.

[0081] In some embodiments of the present application, the molar ratio of Si to Fe is (2 to 16): 1.

[0082] In some preferred embodiments of the present application, the molar ratio of Si to Fe is (2 to 8):1.

[0083] In some specific embodiments of the present application, the molar ratio of Si to Fe is 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, or 2:1.

[0084] S400: Preparation of spinning precursor liquid

[0085] In step 400, the PVA aqueous solution and the Si / Fe hydrolyzed liquid are mixed by a method including but not limited to stirring. The stirring time should be adequate to ensure uniform mixing and can be adjusted according to the actual situation.

[0086] In some embodiments of the present application, the mass ratio of the PVA aqueous solution to the Si / Fe hydrolyzed liquid is 1:(0.5 to 2.5), preferably 1:(1 to 2).

[0087] In some specific embodiments of the present application, the mass ratio of the PVA aqueous solution to the Si / Fe hydrolyzed liquid is 2:1, 1.5:1, 1:1, 1:1.5, 1:2, or 1:2.5.

[0088] In step S400, through aging, the spinnability of the spinning liquid is enhanced while the flexibility of the spun fiber is enhanced. In some embodiments of the present application, the aging method is standing at room temperature, and the aging time is 6 h to 24 h, preferably 10 h to 24 h, and more preferably 12 h to 18 h.

[0089] In some embodiments of the present application, the aging method is aging in a water bath, the aging temperature is 40°C to 70°C, and the aging time is 4 h to 20 h, preferably 6 h to 16 h, and more preferably 6 h to 10 h.

[0090] In some specific embodiments of the present application, the aging method is standing at room temperature, and the aging time is 16 h.

[0091] S500: Preparation of precursor nanofiber membrane

[0092] The electrospinning is low in cost and controllable in spinning process, and uses device that is simple to operate. Utilizing the electrospinning device to prepare the membrane filter material not only meets the filtration requirement but also reduces the filtration cost. In addition, the fiber prepared by electrospinning exhibits the characteristics of large specific surface area, small pore size, and high porosity, leading to excellent filter fineness and low pressure drop, even for aerogels with particle sizes below the submicron level.

[0093] In some embodiments of the present application, the precursor nanofiber membrane is prepared by injecting the spinning precursor liquid prepared in step S400 into a syringe having a nozzle and fixed to an electrospinning device mechanism, and adjusting the spinning voltage, the receiving distance, and the pushing and injection speed.

[0094] Parameters such as the spinning voltage, the receiving distance, and the pushing distance all have an effect on the diameter and the mechanical properties of the spun film.

[0095] In some embodiments of the present application, the spinning voltage is 6 kV to 15 kV, preferably 8 kV to 12 kV.

[0096] In some embodiments of the present application, the receiving distance is 5 cm to 25 cm, preferably 10 cm to 20 cm.

[0097] In some embodiments of the present application, the pushing and injection speed is 0.8 mL / h to 3 mL / h, preferably 1 mL / h to 2 mL / h.

[0098] The spinning voltage, the receiving distance, and the pushing and injection speed also need to be considered as a whole, and the parameters need to be coordinated to achieve optimal material properties.

[0099] In some embodiments of the present application, the spinning voltage is 6 kV to 15 kV, the receiving distance is 5 cm to 25 cm, and the pushing and injection speed is 0.8 mL / h to 3 mL / h.

[0100] In some embodiments of the present application, the spinning voltage is 8 kV to 12 kV, the receiving distance is 10 cm to 20 cm, and the pushing and injection speed is 1 mL / h to 2 mL / h.

[0101] In some specific embodiments of the present application, the spinning voltage is 10 kV, the receiving distance is 15 cm, and the pushing and injection speed is 1 mL / h.

[0102] S600: Preparation of Fe / Fe2O3 / SiO2 hybrid nanofiber membrane

[0103] In step S600, the precursor nanofiber membrane prepared in S500 needs to be dried before the calcining to remove the residual solvent and the volatile component therein. The higher the drying temperature, the shorter the drying time required. The drying method includes, but is not limited to, oven-drying.

[0104] In some embodiments of the present application, the drying temperature is 60°C to 100°C, the drying time is 1 h to 8 h, and the drying method is oven-drying.

[0105] In some embodiments of the present application, the drying temperature is 60°C to 80°C, the drying time is 4 h to 8 h, and the drying method is oven-drying.

[0106] In some embodiments of the present application, the drying temperature is 80°C to 100°C, the drying time is 1 h to 4 h, and the drying method is oven-drying.

[0107] In step S600, the purpose of calcining is, on the one hand, to remove organics on the precursor nanofiber membrane, and, on the other hand, to reduce Fe3+ on the surface of the fiber to Fe, to further improve the adsorption capacity of the fiber for the polonium element, and thus the calcining needs to be carried out under the reducing atmosphere. The reducing atmosphere is an inert gas in combination with the hydrogen gas. The inert gas can be the nitrogen gas, the argon gas, or other common inert gas. The combination of the inert gas with the hydrogen gas is in the form of, for example, H2 / Ar, H2 / N2, 5%H2 / Ar, or 3%H2 / N2. The concentration of the hydrogen gas in 3% to 5% is sufficient for the reduction. The higher the concentration of the hydrogen gas, the higher the efficiency of the reduction, but for safety considerations, the concentration of the hydrogen gas should not be too high.

[0108] In some embodiments of the present application, the reducing atmosphere is selected from H2 / Ar or H2 / N2, more preferably H2 / AE

[0109] In some embodiments of the present application, the reducing atmosphere is 5% H2 / AE

[0110] In some embodiment of the present application, the calcining temperature is 350°C to 800°C, the calcining time is 1 h to 8 h. Further, the calcining temperature is 450°C to 800°C and the calcining time is 2 h to 4 h. More preferably, the calcining temperature is 450°C to 700°C and the calcining time is 2 h to 4 h.

[0111] In some embodiments of the present application, the calcining temperature is 550°C, the calcining time is 2 h, and the reducing atmosphere is 5% H2 / AE

[0112] In some embodiments of the present application, the calcining temperature is 500°C, the calcining time is 2 h, and the reducing atmosphere is 5% H2 / AE

[0113] In a second aspect of the present application, a membrane filter material is provided, which is prepared by the preparation method described in the first aspect. The membrane filter material is the Fe / Fe2O3 / SiO2 hybrid nanofiber membrane, which is a flexible inorganic nanofiber membrane with high-temperature resistance, high filter fineness, and high polonium affinity.

[0114] By testing the high-temperature filtration effect of the filtration membrane in the present application, it is found that the filtration membrane has a good filtration effect even in the temperature range of 300°C to 450°C, with the filtration efficiency of 97% above, even 99% above at 400°C. The install location of the membrane filter material is not specifically limited, as long as it is in line with the design principle of the filtration device and can realize the purpose of filtration. The number of membrane filter materials is also not specifically limited and may be 1, 2, or more. When the number of the membrane filter material is more than one, the distribution of the membrane filter materials is not specifically limited. The membrane filter materials may be arranged adjacent to each other, or installed separately in different modules. It is to be understood that the number and the distribution of the membrane filter materials should be appropriate to enable the filtration purpose to be realized.

[0115] FIG. 1 is a schematic diagram of an electrospinning device of an embodiment of the present application, including a syringe pump 1, a barrel receiver 3, and a high-voltage power supply 5. The spinning precursor liquid 2 is injected into the syringe pump 1 so as to be pushed. Under the action of the electric field, the droplet at the needle tip will be changed from a sphere to a cone (i.e., a Taylor cone). After the spinning is initiated, the liquid first enters the cone-jet zone, and the diameter of the jet becomes smaller and smaller until it bends under the actions of both the surface charge repulsion and the strong electric field. Subsequently, the jet enters the whipping instability zone, the jet accelerates while oscillating like a whip, where the diameter of the jet decreases dramatically, and the solvent volatilizes. Finally, the jet solidifies to form a fiber with an ultrafine diameter, i.e., the stretched polymer 3 (the shape in Figure 1 is only an example and should not be construed as constituting a limitation on the protection scope of the present application).

[0116] In a third aspect of the present application, a use of the membrane filter material described in the second aspect in treatment of an aerosol is provided. The membrane filter material provided in the present application, specifically Fe / Fe2O3 / SiO2 hybrid nanofiber membrane, can be used to filter the aerosol, in particular the polonium aerosol, at high temperature and rapidly reduce the radioactivity concentration of nuclides in a short period of time.

[0117] In some embodiments of the present application, the membrane filter material is used to treat the polonium aerosol, and the effective filtration for the polonium aerosol is mainly based on the small pore size characteristic of the filtration membrane itself and the adsorption and binding enhancement effect of Fe on the surface of the filtration membrane on polonium.

[0118] In some embodiments of the present application, the membrane filter material is used to treat the iodine aerosol or the lead-bismuth aerosol, and the effective filtration for the above-mentioned aerosol of the filtration membrane is mainly based on the small pore size characteristic of the filtration membrane itself.

[0119] In some embodiments of the present application, the membrane filter material is suitable for treating the aerosol at 25°C to 450°C.

[0120] Some specific examples are shown below.

[0121] In the following specific examples, for experimental parameters which are not specified, reference is preferentially made to the teaching provided in this application document, or to experimental manuals in the art or other experimental methods known in the art, or to experimental conditions recommended by the manufacturers.

[0122] In the following specific examples, the raw materials and reagents involved are commercially available, or can be readily obtained or prepared by a person skilled in the art.

[0123] Raw Material:

[0124] Deionized water was made from a laboratory water purification system with water purifier model of Center-EDI 90V.

[0125] Tetraethyl orthosilicate (TEOS) was analytically pure and from Sinopharm Chemical Reagent Co. Ltd.

[0126] Phosphoric acid (H2PO4) was analytically pure and from Xilong Chemical Co. Ltd.

[0127] Ferric nitrate nonahydrate (Fe(NO3)3 9H2O), ferric trichloride hexahydrate (FeCh 6H2O), and nitric acid (HNO3) were analytically pure and from Guangdong Guanghua Technology Co. Ltd.

[0128] Polyvinyl alcohol (PVA) was from Sinopharm Chemical Reagent Co. Ltd.

[0129] Example 1

[0130] A flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane was prepared by following operating steps:

[0131] (1.1) PVA was dissolved in deionized water and stirred until clarified and transparent, with a stirring temperature of 80°C and a stirring time of 6 h, to obtain a 10 wt% PVA aqueous solution as a precursor liquid. Deionized water, tetraethyl orthosilicate (TEOS), and phosphoric acid were mixed in a molar ratio of H2O:TEOS:H3PO4 of 10:1:0.01 and stirred uniformly to obtain a Si hydrolyzed liquid. The obtained Si hydrolyzed liquid was mixed uniformly with ferric nitrate nonahydrate (Fe(NO3)3 9H2O) by stirring in a molar ratio of Si to Fe of 4:1 to obtain a Si / Fe hydrolyzed liquid. Then the 10 wt% PVA solution prepared as described above was mixed with the Si / Fe hydrolyzed liquid obtained as described above in a mass ratio of 1:1, and aging for a time of 16 h to obtain a spinning precursor liquid.

[0132] (1.2) The spinning precursor liquid prepared in (1.1) was injected into a syringe equipped with a nozzle and fixed to the electrospinning device mechanism as shown in FIG. 1, and electrospinning was then carried out to obtain a precursor nanofiber membrane, with the following electrospinning parameters: a receiving distance of 17 cm, a pushing and injection speed of 1 mL / h, and a voltage of 9 kV.

[0133] (1.3) The precursor nanofiber membrane obtained in (1.2) was placed into an oven and dried at a drying temperature of 80°C for a drying time of 6 h, and then placed into a tube furnace with 5% H2 / Ar atmosphere introduced and calcined at a calcining temperature of 550°C for a time of 2 h to obtain a flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane.

[0134] Example 2

[0135] A flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane was prepared, differing from Example 1 in that the molar ratio of Si to Fe in the preparation of Si / Fe hydrolyzed liquid in step (1.1) was 2:1, while the remaining steps were the same as in Example 1.

[0136] Example 3

[0137] A flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane was prepared, differing from Example 1 in that the molar ratio of Si to Fe in the preparation of Si / Fe hydrolyzed liquid in step (1.1) was 8:1, while the remaining steps were the same as in Example 1.

[0138] Example 4

[0139] A flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane was prepared, differing from Example 1 in that ferric trichloride hexahydrate (FeCEAFEO) instead of ferric nitrate nonahydrate (Fe(NO3)3 9H2O) was used in the preparation of Si / Fe hydrolyzed liquid in step (1.1), the mass ratio of the PVA solution to the Si / Fe hydrolyzed liquid in the preparation of the spinning precursor liquid was 1.5:1, the drying temperature was 90 °C, and the calcining temperature was 500 °C in the preparation of the flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane, while the remaining steps were the same as in Example 1.

[0140] Comparative Example 1

[0141] A nanofiber membrane was prepared, differing from Example 1 in that no Fe was introduced (Fe was introduced in form of Fe(NO3)3 9H2O in Example 1), while the remaining steps were the same as in Example 1. Specifically, in step (1.1), PVA was dissolved in deionized water and stirred until clarified and transparent, with a stirring temperature of 80°C and a stirring time of 6 h, to obtain a 10 wt% PVA aqueous solution as a precursor liquid; deionized water, tetraethyl orthosilicate (TEOS), and phosphoric acid were mixed in a molar ratio of H2O:TEOS:H3PO4 of 10:1:0.01 and stirred uniformly to obtain a Si hydrolyzed liquid; then the 10 wt% PVA solution prepared as described above was mixed with the Si hydrolyzed liquid obtained as described above in a mass ratio of 1:1, and aging for a time of 16 h to obtain a spinning precursor liquid.

[0142] Comparative Example 2

[0143] A flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane was prepared by a method substantially the same as in Example 1, except for that the molar ratio of Si to Fe in the preparation of Si / Fe hydrolyzed liquid in step (1.1) was 1:1, while the remaining parameters were the same as in Example 1.

[0144] Comparative Example 3

[0145] A flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane was prepared by a method substantially the same as in Example 1, except for that the calcining temperature in the step (1.3) was 900°C, while the remaining parameters were the same as in Example 1.

[0146] Example 5 Performance test of nanofiber membrane

[0147] 5.1 Temperature resistance test

[0148] The nanofiber membranes prepared in Examples 1 to 4 and Comparative examples 1 to 3 were tested for the temperature resistance by the following method: the nanofiber membranes were calcined for no less than 6 h at 700 °C under an Ar atmosphere, and the material performances were subsequently observed. The results showed that there were no significant differences in the flexibility and the surface morphology among the materials, indicating that the test samples exhibited resistance to the temperature up to 700°C.

[0149] 5.2. Filter fineness test

[0150] The nanofiber membranes prepared in Examples 1 to 4 and Comparative examples 1 to 3 were tested for the filter fineness by the following method: the pore size ranges of the nanofiber membranes were tested using a specific surface area and pore size analyzer (BET) to obtain the filter fineness of the filtration membrane for the aerosol.

[0151] 5.3. Filtration efficiency test

[0152] The nanofiber membranes prepared in Examples 1 to 4 and Comparative examples 1 to 3 were tested for the filtration efficiency.

[0153] Te and Po (radionuclides) are elements of the same family with similar chemical properties, and their volatilization forms are consistent after heating, so the filtration efficiency of the nanofiber membrane for the radionuclide Po can be referred to the filtration efficiency for the element Te. The volatilization forms of Te and Po can also be found in the results of the XRD test decribed below.

[0154] The method for testing the filtration efficiency for the element Te was as follows: 5% of Te was doped into lead-bismuth eutectic (LBE) alloy to prepare a Te-doped lead-bismuth alloy, which was heated to produce a Te aerosol. The Te aerosol was filtered with the nanofiber membrane. The filtered Te aerosol was further filtered with a high-efficiency filtration membrane to capture the element Te that had not been filtered by the nanofiber membrane. The filtration membrane was dissolved in nitric acid, and the amount of Te captured (the mass of Te) was accurately determined using an ICP (ICAP7000, Thermo Fisher) instrument.

[0155] The filtration efficiency for elemental Te was calculated with the following equation:

[0156] q = x 100%

[0157] wherein q is the filtration efficiency, mi is the mass of the nuclide Te in the tail gas before the filtration with the electrospun filtration membrane, m2 is the mass of the nuclide Te in the tail gas after the filtration with the electrospun filtration membrane.

[0158] The filtration efficiencies at different temperatures of the flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane prepared in Example 1 were shown in FIG. 5, where the horizontal axis denotes the filtration temperature of the electrospun filtration membrane and the vertical axis denotes the filtration efficiency of the fiber filtration membrane. The prepared flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane has excellent filtration performance within the high temperature range of 300 °C ~ 450 °C, with filtration and removal efficiency of more than 97%, specifically with the filtration efficiency for the element Te at a temperature at or below 400 °C being more than 99%. It should be understood that the effective filtration of the filtration membrane for the aerosol is mainly based on the small pore size of the filtration membrane itself, as well as the adsorption and binding enhancement effect of Fe on the surface of the membrane on the nuclides. Due to the small pore size of the membrane itself, good filtration effects can also be achieved for other aerosols such as iodine 20 and lead-bismuth aerosols.

[0159] 5.4 Surface morphology test

[0160] The flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane in Example 1 was subjected to the SEM test both before and after filtration, with instrument model SU5000, Hitachi. The scanning results are shown in FIGS. 2 and 3. FIG. 2 is the SEM image of the flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane before filtration. As can be seen from FIG. 2, the fibers before filtration have smooth surfaces and uniform sizes with an average diameter of 366 nm. FIG. 3 is the SEM image of a flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane after filtration which contains Pb, Bi, and Te. As can be seen from FIG. 3, the aerosol in the high-temperature filtration environment was efficiently captured and adhered to the fiber filtration membrane.

[0161] 5.5 XRD test

[0162] The flexible Fe / Fe2O3 / SiO2 hybrid nanofiber membrane in Example 1 was subjected to the XRD test both before and after filtration, with instrument model Rigaku D / MAX 2500V, scanning angle of 5° to 80°, scanning speed of 5° / min, and a step size of 0.02. The diffraction result is shown in FIG.4. In FIG.4, S denotes amorphous material (Fe / Fe2O3 / SiO2 hybrid nanofiber membrane), B denotes amorphous Bi, T denotes amorphous PbTe, the horizontal axis denotes 29, the vertical axis denotes the diffraction angle, and the peak at 21° corresponds to the amorphous material (Fe / Fe2O3 / SiO2 hybrid nanofiber membrane). As can be seen from FIG. 4, the flexible Fe / Fe2O3 / SiO2 hybrid fiber before the capturing test shows an amorphous broad peak of 21° in FIG. 4, and the flexible flexible Fe / Fe2O3 / SiO2 hybrid fiber deposited with the elements Pb, Bi, and Te after capturing test shows PbTe and Bi diffraction peaks in addition to the amorphous broad peak of 21°, which suggests that during the volatilization of PbBiTe and the filtration process, the element Te is volatilized as PbTe vapor, and this result is consistent with the volatilization of Po as PbPo vapor on the surface of the lead-bismuth pool in the lead-based reactor.

[0163] 5.6 Analysis of test results

[0164] The above-described temperature resistance, filter fineness, filtration efficiency, and performance parameters are detailed in Table 1. Table 1 Performance parameters of Fe / Fe2O3 / SiO2 hybrid nanofiber membranes of Examples 1 to 4 and Comparative examples 1 to 3 Temperature resistance (°C) Filter fineness Oa(nm) Filtration efficiency pb(%) Performance characteristic Example 1 700 11.9 99.21 Fiber flexibility is good. Example 2 700 10.5 99.47 Fiber flexibility is average. Example 3 700 13.2 98.45 Fiber flexibility is average. Example 4 700 12.3 99.24 Fiber flexibility is good. Comparative example 1 700 15.5 91.54 Fiber flexibility is good. Comparative example 2 / / / The spinnability is poor, the fibers cannot form film, and the viscosity is difficult to control. Comparative example 3 / / / The fibers have increased brittleness due to the too high calcining temperature, with fiber breakage. average pore diameter, b filtration temperature of 400 °C

[0165] From Table 1, according to the performance test results of the Fe / Fe2O3 / SiO2 hybrid nanofiber membranes prepared in Examples 1 to 4, the Fe / Fe2O3 / SiO2 hybrid nanofiber membrane provided in the present application has good temperature resistance even at temperature up to 700°C, good filter fineness with a pore diameter less than 15 nm, and good filtration efficiency of more than 98% in all examples, even more than 99% in some examples.

[0166] The filter fineness of Comparative Example 1 (15.5 nm) is slightly lower than that of Examples 1 to 4 (10.5 nm to 13.2 nm), and the filtration efficiency of Comparative Example 1 (93.54%) was significantly lower than that of Examples 1 to 4 (98.45 to 99.61%), which suggests that the introduction of Fe improves the filter fineness and the filtration efficiency of SiO2 nanofiber membrane for LBE-Te. This is because Fe has high affinity with Po, enhancing the adsorption of the fiber membrane for Po. According to the test results of the filter fineness and the filtration efficiency of Examples 1 to 3, within a certain range, the greater the Fe content in the fiber membrane, the higher the filter fineness and the filtration efficiency. However, the Fe content if too high would compromise the spinnability. The too high Fe content in Comparative example 2 led to the difficulty in controlling 22 the viscosity of the solution and to the poor spinnability, so that it was difficult to spin fibers or the fibers spun had very poor performance. The calcining temperature in Comparative example 3 was too high, and the Fe and Fe2Os grains in the hybrid nanofibers would grow and bond, which increased the brittleness of the fibers, leading to fiber breakage and then fiber membrane fragmentation.

[0167] In Comparative example 1, the filtration membrane can achieve a filtration efficiency of more than 90% for the aerosol through only the pore diameter structure of the filtration membrane itself without the adsorption enhancement effect of element Fe, indicating that the filtration membrane will have a better filtration effect on most aerosols, including, but not limited to, polonium aerosols, iodine aerosols, and lead-bismuth aerosols.

[0168] The technical features of the above-mentioned embodiments and examples can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the embodiments and examples are described. However, as long as there is no contradiction in the combination of these technical features, the combinations should be considered as in the scope of the present application.

[0169] The above-described embodiments are only several implementations of the present application, and the descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present application. It should be understood by those of ordinary skill in the art that various modifications and improvements can be made without departing from the concept of the present application, and all fall within the protection scope of the present application. It should also be understood that after reading the above teachings of the presentation application, a person skilled in the art may make various changes or modifications to the presentation application, and the equivalent forms obtained will also fall within the scope of protection of the present application. It should also be understood that the technical solutions obtained by the person skilled in the art through logical analysis, reasoning, or limited experimentation based on the technical solutions provided in the present application are within the scope of protection of the claims appended to the present application. Therefore, the patent protection of the present application shall be defined by the appended claims, and the specification and accompanying drawings can be used to interpret the contents of the claims. 08 05 25

Claims

1. A preparation method for a membrane filter material, comprising steps of:mixing polyvinyl alcohol with water to prepare a PVA aqueous solution;mixing water, tetraethyl orthosilicate, and phosphoric acid and hydrolyzing the tetraethyl orthosilicate to prepare a Si hydrolyzed liquid;mixing the Si hydrolyzed liquid with an iron salt to prepare a Si / Fe hydrolyzed liquid;mixing the PVA aqueous solution with the Si / Fe hydrolyzed liquid and aging to prepare a spinning precursor liquid;subjecting the spinning precursor liquid to electrospinning to prepare a precursor nanofiber membrane; anddrying the precursor nanofiber membrane and calcining the precursor nanofiber membrane under a reducing atmosphere to prepare a Fe / Fe2O3 / SiO2 hybrid nanofiber membrane.

2. The preparation method for the membrane filter material according to claim 1, wherein the PVA aqueous solution contains the polyvinyl alcohol in an amount of 5wt% to 20wt%.

3. The preparation method for the membrane filter material according to claim 1, wherein in the step of mixing the water, the tetraethyl orthosilicate, and the phosphoric acid, a molar ratio of the water to the tetraethyl orthosilicate to the phosphoric acid is (5 to 20):1:(0.005 to 0.015), and / or a time of the hydrolyzing is 4 h to 18 h.

4. The preparation method for the membrane filter material according to claim 1, wherein in the step of mixing the Si hydrolyzed liquid with the iron salt, a molar ratio of Si to Fe is (2 to 16):1, and / or the iron salt is iron nitrate, iron chloride, or a combination thereof.

5. The preparation method for the membrane filter material according to claim 1, wherein in the step of mixing the PVA aqueous solution with the Si / Fe hydrolyzed liquid and aging, a mass ratio of the PVA aqueous solution to the Si / Fe hydrolyzed liquid is 1:(0.5 to 2.5), the aging is performed by standing, and a time of the aging is 4 h to 24 h.

6. The preparation method for the membrane filter material according to claim 2, wherein a molar ratio of Si to Fe is (2 to 8): 1, and / or a mass ratio of the PVA aqueous solution to the Si / Fe hydrolyzed liquid is 1:(0.5 to 1.5).

7. The preparation method for the membrane filter material according to claim 2, wherein the aging is performed at a room temperature of 20°C to 30°C for a time of 608 05 25h to 24 h.

8. The preparation method for the membrane filter material according to claim 2, wherein the aging is performed in a water bath at a temperature of 40°C to 70°C for a time of 4 h to 20 h.

9. The preparation method for the membrane filter material according to any one of claims 1 to 8, wherein the electrospinning is performed with the following parameters: a receiving distance of 5 cm to 25 cm, a pushing and injection speed of 0.8 mL / h to 3 mL / h, and a voltage is 6 kV to 15 kV.

10. The preparation method for the membrane filter material according to any one of claims 1 to 9, wherein in the step of drying the precursor nanofiber membrane and calcining the precursor nanofiber membrane under a reducing atmosphere, the drying is performed at a temperature of 60°C to 100°C for a time of 4 h to 8 h, and / or the reducing atmosphere is a mixed atmosphere of an inert gas and hydrogen gas.

11. The preparation method for the membrane filter material according to claim 10, wherein the calcining is performed at a temperature of 350°C to 800°C for a time of 1 h to 8 h.

12. The preparation method for the membrane filter material according to claim 10, wherein the inert gas is selected from nitrogen gas or argon gas, and the calcining is performed at a temperature of 450°C to 700°C for a time of 2 h to 8 h.

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