Preparation And Properties Of Titania-based Composite Fibers

The population,industry,and economy of China are among the top in the world,which determines our huge demand for water resources.However,with the rapid growth of population and economy,the discharge of organic wastewater is also increasing.Waste water is often discharged by textile mills,food processing factories,printing and dyeing plants,etc.The components of the waste water are complex.If they are not treated effectively,they will cause adverse effects on animals and the natural environment.Therefore,the accurate and efficient treatment of water quality issues has become a top priority in China.Traditional sewage treatment methods,such as biological and physical methods,require high reaction conditions,long treatment cycles,and are prone to secondary pollution.In this case,photocatalytic method,which can directly apply natural light to treat pollutants and be environmentally-friendly and efficient has emerged.TiO₂ semiconductor material has a suitable energy band structure,at the same time,it has low cost and would cause no threat to environment,and thus can be widely used as photocatalysts.However,it can only absorb ultraviolet light?5%of the the sunlight?due to its relatively wide band gap.The absorption and utilization of light is limited,and the generated electrons and holes are easily recombined,resulting in poor performance of the catalysts prepared only by TiO₂.Therefore,we try to improve its photocatalytic efficiency by means of surface modification,non-metal semiconductor compounding and noble metal modification.In this paper,a series of semiconductor catalysts based on TiO₂ were successfully prepared using sol-gel method combined with electrospinning technology using anhydrous ethanol,dimethylformamide,glacial acetic acid,urea,tetra-n-butyl titanate,silver nitrate and other raw materials.TG-DSC,FT-IR,XRD,SEM,BET and UV-vis were used to characterize them and study the relationship between the morphology and microstructure of titania-based composite semiconductor nanofibers and their photocatalytic properties.The conclusions obtained are as follows:1.The TiO₂ nanofibers with wrinkled morphology were prepared by electrospinning.By adding different mass percentages of tetrabutyl titanate?TNBT?to the precursor,fibers with different specific surface areas and porosity were produced.Fibers were made up of a myriad of nanoparticles.When the content of TNBT in the precursor was low,the aggregation of nanoparticles was relatively loose,and the wrinkled surface and internal porous structure of the fiber were formed.This morphology allowed the sample to have a higher specific surface area,promoting the diffusion and transfer of photogenerated carriers.However,when the content of TNBT was further increased,the particles constituting the sample were connected more closely,the surface of the fiber was relatively smooth,the internal particles of the fiber were difficult to contact with external substances,and the carriers were difficult to diffuse and migrate.The experiment showed that when the content of TNBT was 20%,the TPNs-20sample had the best morphology and structural characteristics,which was most conducive to the degradation of the Methyl Orange?MO?solution.2.TiO₂/g-C₃N₄ composite nanofibers were prepared by electrospinning.We applied urea as a raw material for the preparation of g-C₃N₄.Its narrow band gap extended the light absorption range of the catalyst to the visible light region,so that the catalyst can better utilize solar energy without changing the structure.In addition,due to the indefinite-domain conjugated?structure of g-C₃N₄,the probability of recombination of electron-hole pairs was greatly reduced,resulting in the increase of free radicals in the dye.Composite TiO₂ and g-C₃N₄ can enlarge their specific surface area and establish a heterojunction between the interfaces of the two semiconductors,which can accelerate the transfer of electrons and holes.In addition,after urea was added,many pores generated inside and on the surface of TiO₂ nanofibers due to volatilization of urea.The pores inside and on the surface of the fiber as well as its wrinkled morphorlogy allowed the catalyst to have a larger specific surface area,which accelerated the dispersion and transfer of carriers.When urea was added in an amount of 0.6 mg,the porosity and specific surface area of the fiber were maximized,so the TU0.6 sample had the best catalytic performance.3.Ag-TiO₂ composite nanofibers were prepared by electrospinning.The microstructure and photocatalytic properties of the composite fibers were mainly affected by the loading amount of Ag.On the one hand,Ag nanoparticles would produce surface plasmon resonance due to light irradiation,forming a strong electric field on their surface,forcing the electrons in TiO₂ to migrate and increase the appearance of electron-hole pairs;On the other hand,the Fermi level of Ag was lower than that of TiO₂,which made electrons excited by light migrate to the surface of Ag according to the principle of the lowest energy,enabling effective separation of electrons and holes.Therefore,the prepared Ag-TiO₂ composite nanofibers had better photocatalytic properties.It was found that when the content of Ag to be loaded is less than 1%,the internal synergy of the catalyst was weak because the content of Ag was too low,and when it exceeded 1%,Ag would agglomerate on the surface of the fiber and influenced the crystallization and growth of TiO₂ and it would slow down the generation and migration of photogenerated carriers,which was not conducive to catalysis.Therefore,when the content of Ag accounts for 1%of TiO₂ in the fiber,the AT1 sample had the best photocatalytic performance.