| With the acceleration of the industrialization process,environmental pollution has become increasingly serious and pose a serious threat to human health,especially in developing countries.In which,different sizes of particulate matter(PM)are the main air pollutants.PM is rich in a large number of toxic and harmful components,and has a long residence time in the atmosphere,which has a great impact on the quality of the atmospheric environment.Studies have shown that the smaller the particles are,the greater the harm to human health,for the PM with smaller diameter can enter the deeper area of the respiratory tract.The particles under 10?m diameter are usually deposited in the upper respiratory tract,but when it below 2 ?m can penetrate deep into the alveoli.After the fine particles enter the alveoli of the human body,it directly affects the ventilation function of the lungs,making the body easy to be in anoxic state.A large number of epidemiological studies have shown that long-term exposure to fine particulate matter can seriously affect the human immune system and nervous system,increasing the risk of acute respiratory diseases,cardiovascular and cerebrovascular diseases.Therefore,the public usually needs to take measures for outdoor personal protection during the haze day,mainly focusing on the use of air filters.There are two types of commonly utilized air filters,one is a porous membrane filter,made by creating pores on a solid substrate usually with a very small pore size to filter the larger size of the PM.However,this type of filter has a low porosity(30%),contributing to a high filtration efficiency but the gas permeability is poor.Another is nanofiber air filter under a combination effect of thick physical barrier and adhesion to remove PM.In order to achieve high efficiency,the nanofiber membranes are usually very thick generally with a poor gas permeability.In addition,studies have found that when the surface of the nanofiber is modified to match the surface properties of the PM,the capture ability of single nanofiber can be significantly increased.Therefore,in order to meet the requirements of high-efficiency and low-resistance PM filters,we have developed new nanofiber filter membranes with high filtration efficiency,low airflow resistance and excellent mechanical properties based on the existing research results.The nanofiber membrane prepared via electrospinning method always has a series of advantages such as large specific surface area,high porosity and simple preparation process.Therefore,a uniform nanofiber filter is prepared by the method of electrospinning to carry out the following studies:(1)Reduced graphene oxidation(rGO)functionalized polyacrylonitrile(PAN)nanofiber membrane with high-efficiency and low-resistance was prepared through inserting rGO nanosheets on/in the surface of PAN nanofibers by one-step electrospinning.The results showed that the comprehensive filtration performance of composite nanofiber membrane under high air flow has been significantly improved.And,nanofiber membrane containing 2.5 wt.%rGO nanosheets showed the best PM removal efficiency(99.9%),and quality factor(0.094 Pa-1).In addition,the tensile strength(0.48?1.25 MPa)of PAN nanofiber membrane modified by rGO nanosheets are much higher than the tensile strength(0.19 MPa)of the pure PAN nanofiber membrane,indicating that the mechanical properties of the pure PAN nanofiber membrane can be significantly improved through compositing with rGO nanosheets.(2)Next,we prepared carbon-based TiO2 nanofiber heterojunction membrane inspired by the photoelectric effect of semiconductor nanomaterials to improve the inherent defects of polymer nanofiber membrane(poor thennal stability,almost no adsorption effect on 0.3 ?m PM)through a combination of electrospinning and heat treatment,and get a successfully enhanced PM capture efficiency comparing with pure carbon nanofiber membrane from 40.71%to 99.92%.The pressure drop of the composite keep below 70 Pa and the quality factor is as high as 0.11 Pa-1.At the same time,the flexibility of the composite carbon nanofiber membrane is crucially improved due to the small size effect of the TiO2 nanoparticles.Moreover,it was proved via designing the light experiment that the prepared carbon-based TiO2 nanofiber membrane has excellent PM removal efficiency under ultraviolet light irradiation,especially for PM0.3.According to the energy band bending theory of the semiconductor composite and combining with UPS test and FDTD simulation,it indicated that the heterojunction of semiconductor TiO2 and carbon can form a built-in electric field under the action of the Schottky barrier.And it clearly explained that the excellent single nanofiber filtration performance of the composite membranes mainly depends on the electrostatic adsorption effect,which establish a foundation for the future research experiments. |
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