The Preparation Of TiO₂ Nanofiber And Photocatalysis Functions For The Degradation Of Formaldehyde

Recent years,people have been more and more concerned with the environment pollution such as waste water,air pollution and other outdoor pollutions,which has been a big problem.In fact,the indoor air pollution is much more serious than outdoors,and should be solved as soon as possible.Owning to the great potential in environment governance,semiconductor photocatalysis materials have attracted much attention of researchers.In the numerous semiconductor materials,TiO₂ possesses the characters of toxic,cheap,stable and excellent photocatalysis performance,and it has been studied deeply and widely.However,there are also many flaws in practical applications.TiO₂ nanoparticles tend to be agglomerated in the practical application,which leads to the decrease of its specific surface area and effective contact area with pollutants.Then,the life time of electron-hole pairs is a few nanoseconds,so it is extremely easy for them to combine,and this will greatly affect the photocatalystic activity and TiO₂ can only degrade the pollutants absorbed in the surface of the nanofiber.The energy gap of anatase TiO₂ is 3.2 e V,which causes that it only can be motivated by the UV light under 387 nm,and the energy it can absorb account for 5% of solar energy.In view of above questions,we set TiO₂ as our research object in the paper,and improve the performance of its practice applications and photocatalytic activity by compositing and loading the nanoparticles with the TiO₂.Main research contents and results include the following aspects:?1?PVP/TiO₂-SiO₂ precursor membranes were prepared by sol-gel method combined with electrospinning methods.After dried and heat treatment,TiO₂/SiO₂ nanofiber membranes with better flexibility were obtained.SEM images showed that the surface of the fiber was smooth and uniform,and the diameters were around 75-250 nm.The TEM images and XRD patterns showed that the fibers possessed excellent crystallinity and TiO₂ was mainly anatase phase in the fiber with the nanocrystals sizes in the range of 6-10 nm.SiO₂ was amorphous phase so that the nanofiber membrane had good mechanical properties and could be bent arbitrarily.TiO₂/SiO₂ nanofiber membranes had excellent filtration ability for PM2.5 and other suspended particulate matter in the air.Then,activated carbon fiber/TiO₂-SiO₂ membrane materials were obtained by physical bonding methods.In the photocatalytic degradation experiments,the degradation efficiency for formaldehyde could be more than 90% in two hours under UV light,which was better than TiO₂/SiO₂ nanofiber membranes.?2?Graphene quantum dots were synthesized by hydrothermal method.The sizes distribution were between 7 nm and 12 nm.Then the TiO₂/SiO₂ nanofiber membranes prepared in chapter 1 were immersed in the grapheme quantum dot solution,and we got the GQDs/TiO₂-SiO₂ composite fiber after drying and heat treatment.The composite membranes still maintain good crystallinity and mechanical properties.The edge of the absorption band of GQDs/TiO₂-SiO₂ composite fiber was extended to the visible region,so that the composite fiber could be used for photocatalytic degradation of pollutants under visible light,and had good photocatalytic activity.?3?The TiO₂/SiO₂ nanofiber membrane synthesized in chapter 1 was firstly introduced into the Ag NO3 solution and to be pre-reduced under UV irradiation.The membrane was then transferred to different concentrations of Ag NO3 solution for hydrothermal reaction to prepare Ag-loaded TiO₂/SiO₂ nanofibers.Ag nanoclusters were evenly distributed and stable on the fibers.The loading of Ag nanoparticles on the TiO₂/SiO₂ nanofibers lead to the rapidly transfer of photogenerated electrons,reducing the recombination of photo-generated electron-hole pairs,and also enhance the photocatalytic activity and broaden the light response range of TiO₂ obviously,so that it could has good absorption in the visible region.With the increase of the Ag content,the size of the loaded Ag nanoparticles gradually increased.It was not good for the photocatalytic acticity with too much Ag nanoparticles loaded in the fiber.The sample of 0.001-Ag-TiO₂/SiO₂ in the experiment was stable and possessed good morphology,and the photocatalytic degradation efficiency for formaldehyde was the best one under visible light.