A Bismuth Ferrite Nanocomposite Crystal / PET Composite Nanofiber Electret Air Filtration Material and Its Preparation Method

Abstract

The present invention discloses a bismuth ferrite nanocomposite crystal / PET composite nanofiber electret air filtration material and a preparation method thereof, a non-woven air filtration material with a long-term electret effect and a preparation method thereof. Bismuth ferrite nanocomposite crystals are synthesized in one step by regulating the reaction time through a hydrothermal reaction. The bismuth ferrite nanocomposite crystal / PET composite nanofiber electret filtration material prepared by blending bismuth ferrite nanocomposite crystals with PET, using an electrospinning method and an electret treatment process, has the characteristics of light weight, good permeability, large specific surface area, high porosity, etc. It has excellent air filtration performance and certain degradability, and is environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of air filtration, and particularly relates to a bismuth ferrite nanomixed crystal / PET composite nanofiber electret air filtration material and a preparation method thereof, and a non-woven air filtration material with a long-term electret effect and a preparation method thereof. Background Art

[0002] With the industrialization process, the economic development of mankind and the living standards of residents have made remarkable progress. However, the resulting environmental problems have become increasingly serious. The problem of air pollution has become a common concern of all mankind. The existence of substances such as dust, bacteria, viruses, and microorganisms in the air seriously affects the environmental quality and also has an adverse impact on people's physical health. In order to ensure the safety of people's lives and work, air filtration devices such as individual protective masks and air purifiers have been widely used in many fields. Non-woven materials are widely used in industries, medical care, hygiene and other fields due to their excellent filtration performance. In order to improve the filtration performance, the electret process is used for the post-treatment of non-woven filtration materials to make the filtration materials carry static charges. Compared with traditional filtration materials, in addition to relying on mechanical filtration mechanisms such as Brownian motion, inertial collision, gravitational sedimentation, and interception to achieve the filtration of particulate matter, electret filtration materials can also effectively capture smaller-sized particulate matter by means of electrostatic attraction and electrostatic induction, and thus have higher filtration effects.

[0003] Non-woven filtration materials are usually high-molecular fibers such as polypropylene (PP), polyethylene terephthalate (PET), and polytetrafluoroethylene (PTFE). Their own polarization intensity is very weak, and it is difficult to form long-term static charges on their own surfaces. Usually, inorganic materials such as tourmaline, silicon dioxide, and zirconium phosphate need to be added to the filtration materials, and composite filtration materials are made through processes such as spinning, and then electret filtration materials are obtained through electret process treatment. Since there are polar substances such as water molecules and charged particles in the air, a compensation effect will be generated on the surface charges of the electret filtration materials, resulting in a large loss of charges and a decrease in filtration performance. Zhang Jie et al. reported that after the PP melt-blown non-woven filtration materials containing nano-tourmaline were electret-treated, after 24 hours, the surface voltage decayed by about 50%. Therefore, how to slow down the loss of surface charges in the atmospheric environment to obtain a long-term electret effect is of great value for electret filtration materials. In addition, since filtration materials such as PP, PE, and PTFE are all non-biodegradable materials, the use of a large number of disposable masks and filter materials will further exacerbate the environmental pollution problem. Summary of the Invention

[0004] The purpose of the present invention is to provide a bismuth ferrite nanomixed crystal / PET composite nanofiber electret air filtration material, a non-woven air filtration material with a long-term electret effect.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material.

[0006] The object of the present invention is achieved by the following scheme: A bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material, wherein the electret air filtration material is composed of bismuth ferrite nanocomposite and PET nanofibers, and the mass ratio of bismuth ferrite nanocomposite to PET nanofibers is (2.0 - 9.0):100.0.

[0007] The bismuth ferrite nanocomposite is a mixture of BiFeO 3 and Bi 25 FeO 40 , and the mass ratio of BiFeO 3 to Bi 25 FeO 40 is 1.0:(0.5 - 2.0).

[0008] The present invention provides a method for preparing a bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material, and the steps are as follows:

[0009] (1) Add 3.0 - 5.0 parts by weight of Fe(NO 3 ) 3 .9H 2 O and 3.0 - 5.0 parts by weight of Bi(NO 3 ) 3 .5H 2 O to 55.0 - 65.0 parts by weight of deionized water. After stirring evenly, slowly add 25.0 - 40.0 parts by weight of 25 wt% KOH solution drop by drop under strong stirring. After continuing to stir for 30 - 60 min, transfer the obtained yellow mixed solution to a hydrothermal reaction kettle and react at 150 - 170 °C for 30 - 36 h. After the reaction is completed, naturally cool to room temperature, filter to obtain a solid substance, repeat washing 3 times with ethanol and deionized water, and place it in an oven at 60 - 80 °C for drying for 10 - 12 h to recover bismuth ferrite nanocomposite;

[0010] (2) Add the bismuth ferrite nanocomposite prepared in step (1) to a mixed solution of trifluoroformic acid and dichloromethane. After magnetic stirring, perform ultrasonic dispersion treatment for 30 - 60 min using ultrasonic waves to obtain a bismuth ferrite nanocomposite dispersion;

[0011] (3) Weigh a certain amount of PET masterbatch and add it to the bismuth ferrite nanocomposite dispersion prepared in step (2). Heat it in a water bath to 60 - 80 °C and stir vigorously for 12 - 24 h until the PET masterbatch is completely dissolved to obtain a mixed solution ①;

[0012] (4) Electrospin the mixed solution ① obtained in step (3). The working conditions of the electrospinning device are as follows: the voltage of the high-voltage generator is 10 - 40 kV; the distance from the nozzle to the receiving base fabric is 10 - 20 cm; the nozzle diameter is 0.1 - 3.0 mm; the flow rate of the spinning solution is 0.5 - 3.0 mL / h; the receiving time is 5 - 15 min, to obtain bismuth ferrite nanomixed crystal / PET composite nanofibers;

[0013] (5) Perform corona charging electret treatment on the bismuth ferrite nanomixed crystal / PET composite nanofibers obtained in step (4), with the voltage ranging from -10 kV to -20 kV, the distance between the upper and lower electrodes being 1 - 3 cm, and the charging time being 3 - 6 min, finally obtaining a bismuth ferrite nanomixed crystal / PET composite nanofiber electret air filtration material.

[0014] In step (1), the molar ratio of Fe(NO 3 ) 3 .9H 2 O and Bi(NO 3 ) 3 .5H 2 O is 1:1.

[0015] In step (2), the mass fraction of bismuth ferrite nanomixed crystals in the bismuth ferrite nanomixed crystal dispersion is 0.5 - 1.0 wt%.

[0016] In step (2), the mass ratio of trifluoroformic acid to dichloromethane is 1:9.

[0017] In step (3), the mass ratio of PET masterbatch to the bismuth ferrite nanomixed crystal dispersion is 1:(4 - 9).

[0018] In step (4), the diameter of the bismuth ferrite nanomixed crystal / PET composite nanofibers is 0.2 - 0.6 μm.

[0019] The perovskite structure BiFeO 3 in the trigonal crystal system has ferroelectricity and is prone to spontaneous polarization, which is beneficial for the formation of surface charges on the composite nanofibers during the electret treatment process and has long-term stability; the pyrochlore structure Bi 25 FeO 40 in the body-centered cubic crystal system, as a narrow-band semiconductor, has high visible light catalytic activity and helps the degradation of PET fibers under natural conditions. The bismuth ferrite nanomixed crystal / PET composite nanofiber electret filtration material prepared by blending bismuth ferrite nanomixed crystals with PET and using the electrospinning method and the electret treatment process has the characteristics of light weight, good permeability, large specific surface area, high porosity, etc. It has excellent air filtration performance and certain degradability, and is environmentally friendly.

[0020] Compared with the existing electret air filtration materials and their preparation methods, the present invention has the following advantages:

[0021] 1. The present invention synthesizes bismuth ferrite nanomixed crystals in one step by hydrothermal reaction through controlling the reaction time. Among them, BiFeO 3 has a perovskite structure of trigonal system, has ferroelectricity, is prone to spontaneous polarization, is conducive to the formation of surface charges on the composite nanofibers during the electret treatment process and has long-term stability; Bi 25 FeO 40 has a bismuthite structure of body-centered cubic system, is a narrow-band semiconductor, has high visible light catalytic activity, and helps the degradation of PET fibers under natural conditions.

[0022] 2. The present invention blends bismuth ferrite nanomixed crystals with PET, and prepares a bismuth ferrite nanomixed crystal / PET composite nanofiber electret filtration material through electrospinning method and electret treatment process. It has the characteristics of light weight, good permeability, large specific surface area, high porosity, etc. While having excellent air filtration performance, it also has certain degradability and is environmentally friendly. Specific Embodiments

[0023] The technical solutions of the present invention will be further described below according to specific embodiments. The protection scope of the present invention is not limited to the following embodiments. These examples are listed only for illustrative purposes and do not limit the present invention in any way.

[0024] Example 1

[0025] A bismuth ferrite nanomixed crystal / PET composite nanofiber electret air filtration material is prepared according to the following steps:

[0026] (1) Add 3.0 parts by weight of Fe(NO 3 ) 3 .9H 2 O and 3.6 parts by weight of Bi(NO 3 ) 3 .5H 2 O to 55.0 parts by weight of deionized water, so that Fe(NO 3 ) 3 .9H 2 O and Bi(NO 3 ) 3 .5H 2The molar ratio of O is 1:1. After stirring evenly, 38.4 parts by weight of 25 wt% KOH solution is added dropwise under strong stirring; after continuing to stir for 30 min, the obtained yellow mixed solution is transferred to a hydrothermal reaction kettle and reacted at 150 °C for 36 h; after the reaction is completed, it is naturally cooled to room temperature, the solid substance is filtered, washed 3 times repeatedly with ethanol and deionized water, placed in an oven at 60 °C and dried for 12 h to recover bismuth ferrite nanomixed crystals;

[0027] (2) Add 0.50 part by weight of the bismuth ferrite nanomixed crystals prepared in step (1) to a mixed solution of trifluoroformic acid and dichloromethane with a weight of 9.95 parts. After magnetic stirring, ultrasonic dispersion treatment is carried out for 30 min using ultrasonic waves to obtain a 0.5 wt% bismuth ferrite nanomixed crystal dispersion;

[0028] (3) Weigh 20.0 parts by weight of PET masterbatch and add it to 80.0 parts by weight of the 0.5 wt% bismuth ferrite nanomixed crystal dispersion prepared in step (2). Heat it in a water bath to 60 °C and stir vigorously for 24 h until the PET masterbatch is completely dissolved to obtain mixed solution ①;

[0029] (4) Electrospinning is carried out on the mixed solution ① obtained in step (3). The working conditions of the electrospinning device are: the voltage of the high-voltage generator is 10 kV; the distance from the nozzle to the receiving base fabric is 10 cm; the nozzle diameter is 0.5 mm; the spinning solution flow rate is 1.0 mL / h; the receiving time is 15 min to obtain bismuth ferrite nanomixed crystal / PET composite nanofibers;

[0030] (5) The bismuth ferrite nanomixed crystal / PET composite nanofibers obtained in step (4) are subjected to corona charging electret treatment with a voltage of -10 kV, the distance between the upper and lower electrodes is 1 cm, and the charging time is 6 min to finally obtain a bismuth ferrite nanomixed crystal / PET composite nanofiber electret air filtration material.

[0031] In step (1) of Example 1, the prepared bismuth ferrite nanomixed crystals are a mixture of BiFeO 3 and Bi 25 FeO 40 , and the mass ratio of BiFeO 3 to Bi 25 FeO 40 is 1.0:0.6; in step (4), the diameter of the prepared bismuth ferrite nanomixed crystal / PET composite nanofibers is 0.3 μm, and the mass ratio of bismuth ferrite nanomixed crystals to PET nanofibers is 2.0:100.0.

[0032] Example 2

[0033] A bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material is prepared according to the following steps:

[0034] (1) Add 5.0 parts by weight of Fe(NO 3 ) 3 .9H 2 O and 6.0 parts by weight of Bi(NO 3 ) 3 .5H 2 O to 65.0 parts by weight of deionized water, so that the molar ratio of Fe(NO 3 ) 3 .9H 2 O to Bi(NO 3 ) 3 .5H 2 O is 1:1. After stirring evenly, add 24.0 parts by weight of 25 wt% KOH solution drop by drop under strong stirring; continue stirring for 60 min, then transfer the obtained yellow mixed solution to a hydrothermal reaction kettle, react at 170 °C for 30 h, naturally cool to room temperature after the reaction, filter to obtain a solid substance, wash it repeatedly 3 times with ethanol and deionized water, and dry it in an oven at 80 °C for 10 h to recover bismuth ferrite nanocomposite;

[0035] (2) Add 1.00 part by weight of the bismuth ferrite nanocomposite prepared in step (1) to a mixed solution of 9.90 parts by weight of trifluoroformic acid and 89.10 parts by weight of dichloromethane. After magnetic stirring, perform ultrasonic dispersion treatment for 60 min using ultrasonic waves to obtain a 1.0 wt% bismuth ferrite nanocomposite dispersion;

[0036] (3) Weigh 10.0 parts by weight of PET masterbatch and add it to 90.0 parts by weight of the 1.0 wt% bismuth ferrite nanocomposite dispersion prepared in step (2). Heat it in a water bath to 80 °C and stir vigorously for 12 h until the PET masterbatch is completely dissolved to obtain a mixed solution ①;

[0037] (4) Electrospun the mixed solution ① obtained in step (3). The working conditions of the electrospinning device are: the voltage of the high-voltage generator is 40 kV; the distance from the nozzle to the receiving substrate is 20 cm; the nozzle diameter is 3.0 mm; the flow rate of the spinning solution is 3.0 mL / h; the receiving time is 5 min to obtain bismuth ferrite nanocomposite / PET composite nanofibers;

[0038] (5) Perform corona charging electret treatment on the bismuth ferrite nanocomposite / PET composite nanofibers obtained in step (4), with a voltage of -20 kV, an upper and lower electrode spacing of 3 cm, and a charging time of 3 min to finally obtain a bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material.

[0039] Among them, the bismuth ferrite nanomixed crystal prepared in step (1) is a mixture of BiFeO 3 and Bi 25 FeO 40 , and the mass ratio of BiFeO 3 to Bi 25 FeO 40 is 1.0:1.8; in step (4), the diameter of the prepared bismuth ferrite nanomixed crystal / PET composite nanofiber is 0.5 μm, and the mass ratio of the bismuth ferrite nanomixed crystal to the PET nanofiber is 9.0:100.0.

[0040] Example 3

[0041] A bismuth ferrite nanomixed crystal / PET composite nanofiber electret air filtration material is prepared according to the following steps:

[0042] (1) Add 4.0 parts by weight of Fe(NO 3 ) 3 .9H 2 O and 4.8 parts by weight of Bi(NO 3 ) 3 .5H 2 O to 60.0 parts by weight of deionized water, so that the molar ratio of Fe(NO 3 ) 3 .9H 2 O to Bi(NO 3 ) 3 .5H 2 O is 1:1. After stirring evenly, add 31.2 parts by weight of 25 wt% KOH solution drop by drop under strong stirring; continue stirring for 45 min, then transfer the obtained yellow mixed solution to a hydrothermal reaction kettle, react at 160 °C for 34 h, naturally cool to room temperature after the reaction, filter to obtain a solid substance, wash it repeatedly 3 times with ethanol and deionized water, and place it in an oven at 80 °C for 10 h to recover the bismuth ferrite nanomixed crystal;

[0043] (2) Add 0.75 part by weight of the bismuth ferrite nanomixed crystal prepared in step (1) to a mixed solution of 9.93 parts by weight of trifluoroformic acid and 89.33 parts by weight of dichloromethane. After magnetic stirring, perform ultrasonic dispersion treatment for 60 min with ultrasonic waves to obtain a 0.75 wt% bismuth ferrite nanomixed crystal dispersion;

[0044] (3) Weigh 15.0 parts by weight of PET masterbatch and add it to 85.0 parts by weight of the 1.0 wt% bismuth ferrite nanomixed crystal dispersion prepared in step (2). Heat it in a water bath to 70 °C and stir vigorously for 12 h until the PET masterbatch is completely dissolved to obtain mixed solution ①;

[0045] (4) Electrospin the mixed solution ① obtained in step (3). The working conditions of the electrospinning device are as follows: the voltage of the high-voltage generator is 20 kV; the distance from the nozzle to the receiving base fabric is 15 cm; the nozzle diameter is 2.0 mm; the flow rate of the spinning solution is 2.0 mL / h; the receiving time is 10 min, to obtain bismuth ferrite nanocrystalline / PET composite nanofibers;

[0046] (5) Perform corona charging electret treatment on the bismuth ferrite nanocrystalline / PET composite nanofibers obtained in step (4). The voltage is -15 kV, the distance between the upper and lower electrodes is 2 cm, and the charging time is 4.5 min, finally obtaining a bismuth ferrite nanocrystalline / PET composite nanofiber electret air filtration material.

[0047] Among them, in step (1), the prepared bismuth ferrite nanocrystalline is a mixture of BiFeO 3 and Bi 25 FeO 40 , and the mass ratio of BiFeO 3 to Bi 25 FeO 40 is 1.0:1.2; in step (4), the diameter of the prepared bismuth ferrite nanocrystalline / PET composite nanofibers is 0.4 μm, and the mass ratio of bismuth ferrite nanocrystalline to PET nanofibers is 4.25:100.0.

[0048] Comparative Example 1

[0049] In Comparative Example 1, the reaction time in the hydrothermal reaction kettle in step (1) was extended from 36 h in Example 1 to 40 h, the additive dosage was the same as that in Example 1, and other preparation conditions were the same. What was recovered was Bi 25 FeO 40 single-phase nanocrystals.

[0050] Bi 25 FeO 40 nanocrystalline / PET composite nanofiber electret air filtration material was prepared using the same additive dosage and process conditions as in Example 1. Among them, the diameter of the Bi 25 FeO 40 nanocrystalline / PET composite nanofibers prepared in step (4) was 0.35 μm.

[0051] Comparative Example 2

[0052] In Comparative Example 2, the reaction time in the hydrothermal reaction kettle in step (1) was reduced from 30 h in Example 2 to 26 h, the additive dosage was the same as that in Example 2, and other preparation conditions were the same. What was recovered was BiFeO 3 single-phase nanocrystals.

[0053] The BiFeO was prepared with the same additive amount of auxiliary agents and process conditions as in Example 2 3 nanocrystalline / PET composite nanofiber electret air filtration material. Among them, the diameter of the BiFeO 3 nanocrystalline / PET composite nanofiber prepared in step (4) is 0.45 μm.

[0054] Compared with Comparative Example 1, the surface charge formed after the corona charging electret treatment of the bismuth ferrite nanomixed crystal / PET composite nanofiber electret air filtration material prepared in Examples 1-3 of the present invention has long-term stability, and has higher air filtration efficiency and longer service life cycle. 3

[0055] Compared with Comparative Example 2, the Bi in the bismuth ferrite nanomixed crystal / PET composite nanofiber electret air filtration material of Examples 1-3 of the present invention 25 FeO 40 endows the filtration material with certain photocatalytic degradability after being discarded after use, and has little harm to the environment.

[0056] Those skilled in the art should note that the embodiments described in the present invention are merely exemplary, and various other substitutions, changes and improvements can be made within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments, but is only defined by the claims.​

Claims

1. A bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material, characterized in that, the electret air filtration material is composed of bismuth ferrite nanocomposite and PET nanofibers, and the mass ratio of bismuth ferrite nanocomposite to PET nanofibers is (2.0 - 9.0):100.0; The bismuth ferrite nanocomposite crystal is BiFeO 3 and Bi 25 FeO 40 mixture, and the mass ratio of BiFeO 3 to Bi 25 FeO 40 is 1.0:(0.5 - 2.0).

2. A preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to claim 1, characterized in that, the steps are as follows: (1) Add 3.0 - 5.0 parts by weight of Fe(NO 3 ) 3 .9H 2 O and 3.0 - 5.0 parts by weight of Bi(NO 3 ) 3 .5H 2 O to 55.0 - 65.0 parts by weight of deionized water. After stirring evenly, add 25.0 - 40.0 parts by weight of 25 wt% KOH solution dropwise under strong stirring; continue stirring for 30 - 60 min, then transfer the obtained yellow mixed solution to a hydrothermal reaction kettle and react at 150 - 170 °C for 30 - 36 h; after the reaction is completed, cool naturally to room temperature, filter to obtain a solid substance, wash it repeatedly with ethanol and deionized water 3 times, place it in an oven at 60 - 80 °C and dry for 10 - 12 h to recover bismuth ferrite nanomixed crystals; (2) Add the bismuth ferrite nanocomposite prepared in step (1) into a mixed solution of trifluoroformic acid and dichloromethane. After magnetic stirring, perform ultrasonic dispersion treatment with ultrasonic waves for 30 - 60 min to obtain a bismuth ferrite nanocomposite dispersion; (3) Weigh a certain amount of PET masterbatch and add it to the bismuth ferrite nanocomposite dispersion prepared in step (2). Heat it in a water bath at 60 - 80 °C and stir vigorously for 12 - 24 h until the PET masterbatch is completely dissolved to obtain a mixed solution ①; (4) Electrospun the mixed solution ① obtained in step (3). The working conditions of the electrospinning device are: the voltage of the high - voltage generator is 10 - 40 kV; the distance from the nozzle to the receiving substrate is 10 - 20 cm; the nozzle diameter is 0.1 - 3.0 mm; the flow rate of the spinning solution is 0.5 - 3.0 mL / h; the receiving time is 5 - 15 min to obtain bismuth ferrite nanocomposite / PET composite nanofibers; (5) Perform corona charging electret treatment on the bismuth ferrite nanocomposite / PET composite nanofibers obtained in step (4), with a voltage of - 10 kV to - 20 kV, the distance between the upper and lower electrodes is 1 - 3 cm, and the charging time is 3 - 6 min to finally obtain the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material.

3. The preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to claim 2, characterized in that, In the step (1), the molar ratio of Fe(NO 3 ) 3 .9H 2 O and Bi(NO 3 ) 3 .5H 2 O is 1:

1.

4. The preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to claim 2, characterized in that, in the step (2), the mass fraction of bismuth ferrite nanocomposite in the bismuth ferrite nanocomposite dispersion is 0.5 - 1.0 wt%.

5. The preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to claim 2, characterized in that, in the step (2), the mass ratio of trifluoroformic acid to dichloromethane is 1:

9.

6. The preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to claim 2, characterized in that, in the step (3), the mass ratio of PET masterbatch to the bismuth ferrite nanocomposite dispersion is 1:(4 - 9).

7. The preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to claim 2, characterized in that, in the step (4), the diameter of the bismuth ferrite nanocomposite / PET composite nanofibers is 0.2 - 0.6 μm.

8. The preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to any one of claims 2 to 7, characterized in that, it is prepared according to the following steps: (1) Add 3.0 parts by weight of Fe(NO 3 ) 3 .9H 2 O and 3.6 parts by weight of Bi(NO 3 ) 3 .5H 2 O to 55.0 parts by weight of deionized water, so that the molar ratio of Fe(NO 3 ) 3 .9H 2 O to Bi(NO 3 ) 3 .5H 2 O is 1:

1. After stirring evenly, dropwise add 38.4 parts by weight of 25 wt% KOH solution under strong stirring; continue stirring for 30 min, then transfer the obtained yellow mixed solution to a hydrothermal reaction kettle and react at 150 °C for 36 h; after the reaction is completed, naturally cool to room temperature, filter to obtain a solid substance, wash it repeatedly 3 times with ethanol and deionized water, and place it in an oven at 60 °C for drying for 12 h to recover bismuth ferrite nanomixed crystals. The prepared bismuth ferrite nanomixed crystals are a mixture of BiFeO 3 and Bi 25 FeO 40 , and the mass ratio of BiFeO 3 to Bi 25 FeO 40 is 1.0:0.6; (2) Add 0.50 parts by weight of the bismuth ferrite nanocomposite prepared in step (1) to a mixed solution of 9.95 parts by weight of trifluoroformic acid and dichloromethane. After magnetic stirring, perform ultrasonic dispersion treatment with ultrasonic waves for 30 min to obtain a 0.5 wt% bismuth ferrite nanocomposite dispersion; (3) Weigh 20.0 parts by weight of PET masterbatch and add it to 80.0 parts by weight of the 0.5 wt% bismuth ferrite nanocomposite dispersion prepared in step (2). Heat it in a water bath to 60 °C and stir vigorously for 24 h until the PET masterbatch is completely dissolved to obtain mixed solution ①; (4) Electrospun the mixed solution ① obtained in step (3). The working conditions of the electrospinning device are: the voltage of the high-voltage generator is 10 kV; the distance from the nozzle to the receiving substrate is 10 cm; the nozzle diameter is 0.5 mm; the spinning solution flow rate is 1.0 mL / h; the receiving time is 15 min to obtain bismuth ferrite nanocomposite / PET composite nanofibers. The diameter of the prepared bismuth ferrite nanocomposite / PET composite nanofibers is 0.3 μm, and the mass ratio of bismuth ferrite nanocomposite to PET nanofibers is 2.0:100.0; (5) Perform corona charging electret treatment on the bismuth ferrite nanocomposite / PET composite nanofibers obtained in step (4). The voltage is -10 kV, the distance between the upper and lower electrodes is 1 cm, and the charging time is 6 min to finally obtain the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material.

9. The preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to any one of claims 2 to 7, characterized in that, it is prepared according to the following steps: (1) Add 5.0 parts by weight of Fe(NO 3 ) 3 .9H 2 O and 6.0 parts by weight of Bi(NO 3 ) 3 .5H 2 O to 65.0 parts by weight of deionized water, so that the molar ratio of Fe(NO 3 ) 3 .9H 2 O to Bi(NO 3 ) 3 .5H 2 O is 1:

1. After stirring evenly, add 24.0 parts by weight of 25 wt% KOH solution dropwise under strong stirring; continue stirring for 60 min, then transfer the obtained yellow mixed solution to a hydrothermal reaction kettle and react at 170 °C for 30 h. After the reaction is completed, cool it naturally to room temperature, filter to obtain a solid substance, wash it repeatedly with ethanol and deionized water 3 times, and place it in an oven at 80 °C for drying for 10 h to recover bismuth ferrite nanomixed crystals. The prepared bismuth ferrite nanomixed crystals are a mixture of BiFeO 3 and Bi 25 FeO 40 . The mass ratio of BiFeO 3 to Bi 25 FeO 40 is 1.0:1.8; (2) Add 1.00 parts by weight of the bismuth ferrite nanocomposite prepared in step (1) to a mixed solution of 9.90 parts by weight of trifluoroformic acid and 89.10 parts by weight of dichloromethane. After magnetic stirring, perform ultrasonic dispersion treatment with ultrasonic waves for 60 min to obtain a 1.0 wt% bismuth ferrite nanocomposite dispersion; (3) Weigh 10.0 parts by weight of PET masterbatch and add it to 90.0 parts by weight of the 1.0 wt% bismuth ferrite nanocomposite dispersion prepared in step (2). Heat it in a water bath to 80 °C and stir vigorously for 12 h until the PET masterbatch is completely dissolved to obtain mixed solution ①; (4) Electrospun the mixed solution ① obtained in step (3). The working conditions of the electrospinning device are: the voltage of the high-voltage generator is 40 kV; the distance from the nozzle to the receiving substrate is 20 cm; the nozzle diameter is 3.0 mm; the spinning solution flow rate is 3.0 mL / h; the receiving time is 5 min to obtain bismuth ferrite nanocomposite / PET composite nanofibers. The diameter of the prepared bismuth ferrite nanocomposite / PET composite nanofibers is 0.5 μm, and the mass ratio of bismuth ferrite nanocomposite to PET nanofibers is 9.0:100.0; (5) The bismuth ferrite nanocomposite / PET composite nanofibers obtained in step (4) are subjected to corona charging electret treatment at a voltage of -20 kV, with the distance between the upper and lower electrodes being 3 cm and the charging time being 3 min, finally obtaining a bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material.

10. The preparation method of the bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material according to any one of claims 2 to 7, characterized in that, it is prepared according to the following steps: (1) Add 4.0 parts by weight of Fe(NO 3 ) 3 .9H 2 O and 4.8 parts by weight of Bi(NO 3 ) 3 .5H 2 O to 60.0 parts by weight of deionized water, so that the molar ratio of Fe(NO 3 ) 3 .9H 2 O to Bi(NO 3 ) 3 .5H 2 O is 1:

1. After stirring evenly, add 31.2 parts by weight of 25 wt% KOH solution dropwise under strong stirring; continue stirring for 45 min, then transfer the obtained yellow mixed solution to a hydrothermal reaction kettle, react at 160 °C for 34 h, naturally cool to room temperature after the reaction, filter to obtain a solid substance, wash it 3 times repeatedly with ethanol and deionized water, place it in an oven at 80 °C and dry for 10 h to recover bismuth ferrite nanomixed crystals. The prepared bismuth ferrite nanomixed crystals are a mixture of BiFeO 3 and Bi 25 FeO 40 . The mass ratio of BiFeO 3 to Bi 25 FeO 40 is 1.0:1.2; (2) 0.75 parts by weight of the bismuth ferrite nanocomposite prepared in step (1) is added to a mixed solution of 9.93 parts by weight of trifluoroformic acid and 89.33 parts by weight of dichloromethane. After magnetic stirring, ultrasonic dispersion treatment is carried out for 60 min using ultrasonic waves to obtain a 0.75 wt% bismuth ferrite nanocomposite dispersion liquid; (3) Weigh 15.0 parts by weight of PET masterbatch and add it to 85.0 parts by weight of the 1.0 wt% bismuth ferrite nanocomposite dispersion liquid prepared in step (2). Heat it in a water bath to 70 °C and stir vigorously for 12 h until the PET masterbatch is completely dissolved to obtain mixed solution ①; (4) The mixed solution ① obtained in step (3) is subjected to electrospinning. The working conditions of the electrospinning device are: the voltage of the high-voltage generator is 20 kV; the distance from the nozzle to the receiving substrate is 15 cm; the nozzle diameter is 2.0 mm; the spinning solution flow rate is 2.0 mL / h; the receiving time is 10 min, obtaining bismuth ferrite nanocomposite / PET composite nanofibers. The diameter of the prepared bismuth ferrite nanocomposite / PET composite nanofibers is 0.4 μm, and the mass ratio of the bismuth ferrite nanocomposite to the PET nanofibers is 4.25:100.0; (5) The bismuth ferrite nanocomposite / PET composite nanofibers obtained in step (4) are subjected to corona charging electret treatment at a voltage of -15 kV, with the distance between the upper and lower electrodes being 2 cm and the charging time being 4.5 min, finally obtaining a bismuth ferrite nanocomposite / PET composite nanofiber electret air filtration material.