Preparation And Performance Research Of Electrospun PAN/TiO₂ Oriented Fiber Membrane For Organic Wastewater Treatment

In recent years,with the rapid development of the printing and dyeing industry,the discharge of organic wastewater has caused more and more serious environmental pollution problems.How to safely and effectively remove pollutants in wastewater has become the research direction of many scholars.Electrospinning technology and photocatalysis technology are widely used in the field of wastewater treatment,but there are also some shortcomings at this stage,such as the low reusability of electrospun fiber membrane and the low recyclability of the photocatalyst.To solve the above problems,electrospinning technology and photocatalytic technology are used to prepare a composite fiber membrane that can adsorb and degrade pollutants using polyacrylonitrile（PAN）and nano titanium dioxide（TiO₂）.The PAN fiber acts as a carrier of TiO₂ to improve the recyclability of the photocatalyst.In addition,the photocatalytic reaction can degrade the pollutants on the surface of the fiber membrane and regenerate the adsorbent in situ to improve the reusability of the fiber membrane.At the same time,the oriented fiber membrane is used to support the photocatalyst to improve the mechanical properties of the composite fiber membrane in a specific direction without reducing the photocatalyst utilization rate and the specific surface area of the electrospun fiber membrane.A new method is proposed to characterize the orientation degree of fiber membrane.This method can solve the problem that the traditional method has a large error in calculating the orientation degree of thick fiber film.In addition,different substances are used to simulate the organic wastewater discharged in the actual industrial production,and the influence of different liquid environments on the wastewater treatment performance of composite fiber membrane is explored.It can provide a reference for the practical application of composite fiber membrane in the field of wastewater treatment.The research content is as follows:（1）The effects of different experimental conditions on the microscopic appearance and orientation of the fiber membrane during the electrospinning process are explored through experiments.The results show that the solution concentration,drum speed,and spinning voltage have a greater impact on the microscopic appearance and fiber diameter of the fiber membrane,while the nozzle diameter has a small effect.The rotation speed of the drum has a great influence on the degree of orientation of the fiber film.Increasing the rotation speed of the drum can increase the degree of orientation of the fiber film.（2）The PAN/TiO₂ oriented fiber membrane prepared by electrospinning technology is a hydrophobic fiber membrane with an average contact angle of 122.4°,a specific surface area of 21.6421 m²/g,and an average pore size of 131.422（?）.The UV light source with 365 nm wavelength was selected for the subsequent photocatalytic reaction because the critical wavelength of excitation photocatalytic effect calculated by the Tauc plot method was 388.7nm.The infrared absorption spectrum shows that PAN material has good stability,and the photocatalytic reaction will not cause obvious changes to its functional groups.（3）The PAN/TiO₂ oriented fiber membrane has good adsorption and catalytic degradation capabilities for pollutants in wastewater.The adsorption capacity of the composite fiber membrane for organic dyes is about 2.652 mg/g in the adsorption equilibrium,and the reaction rate constant during the catalytic degradation process is about 0.005 min^-1.In addition,the composite fiber membrane does not appear the phenomenon of secondary pollution caused by a large number of photocatalysts falling off in the process of use,and it still has a strong ability to remove pollutants after several cycles of use,which indicates that the composite fiber membrane can effectively solve the problems of low reusability of electrospun fiber membrane and low recyclability of the photocatalyst.（4）The experimental results show that different liquid environments have a greater impact on the adsorption and catalytic efficiency of the composite fiber membrane.The decolorization rate of methylene blue solution in the liquid environment of pH=11 is 69.0%,while the decolorization rate of methylene blue solution in the liquid environment of pH=3 is only 53.3%,which shows that the composite fiber membrane is more suitable for treating alkaline wastewater.The adsorption and catalytic efficiency of PAN/TiO₂ oriented fiber membrane will decrease with the increase of the salt ion concentration in the liquid environment.When the concentration of sodium chloride in the methylene blue solution rises from 0 mol/L to 0.9 mol/L,the decolorization rate of methylene blue solution decreases from68.5%to 32.3%.Compared with the concentration of salt ions,the type of salt ions has a smaller impact on the adsorption performance of PAN/TiO₂ oriented fiber membranes,but has a greater impact on the catalytic performance of PAN/TiO₂ oriented fiber membranes.In addition,the catalytic activity of the composite fiber membrane will be inhibited in the liquid containing alcohol because the alcohol molecules will consume the active substances in the photocatalytic process.