Preparation And Photocatalytic Properties Of N,F Co-doped TiO_2-δ Supported By Carbon Nanofibers With Different Morphologies

Energy shortage and environmental pollution are two major problems for the moderrn world,and photocatalytic technology is one of the effective means to alleviate the above problems.TiO₂has attracted much attention due to its excellent photocatalytic activity,stability,environmental protection and other advantages.However,its band gap is too wide（about 3.2 e V）which can only responds to ultraviolet light.In addition,photo-generated electrons and holes are easily recombined and deactivated,and there are problems of agglomeration deactivation and difficulty in recycling caused by size effects.All this problems limit its application.Ion doping and supporting are effective methods to overcome the above problems.Carbon fiber is stable and easy to obtain.When it was used as a supporter of TiO₂,its large surface area can increase the active sites of the catalyst,and the carbon fibers of excellent conductivity can provide a channel for rapid transfer of photo-generated electrons,reducing the recombination of photo-generated carriers.In this thesis,polyacrylonitrile（PAN）was used as the carbon source,and tetrabutyl titanate was used as the titanium source,trifluoroacetic acid or ammonium fluoride were used as the fluorine source.Combining electro-spinning,solvothermal method and heat treatment,N,F co-doped TiO_2-δnano photocatalysts supported by carbon fibers with different mophologies were successfully prepared,which have high photocatalytic activity.（1）PAN nanofibers with diameters of about 200-300 nm were successfully prepared by optimizing the critical parameters of electrospinning.The mixed fibers were prepared by electrospinning with adding tetrabutyl titanate and trifluoroacetic acid to the precursor PAN solution.And then the N,F co-doped TiO_2-δnanofibers were obtained through heat treatment processing,which have good photo-degradation performance on various pollutants.（2）PAN nanofibers prepared by electrospinning were used as the precursor to prepare the bead-like carbon fibers supporting N,F co-doped TiO_2-δnano photocatalyst with solvothermal method and the following heat treatment,in which tetra-butyl titanate and ammonium fluoride were added during the solvothermal process.Under the same conditions,the degradation rates of Rhodamine B（Rh B）,methylene blue（MB）and Cr（VI）were 16,8.9 and 6 times of those of the commercial TiO₂,respectively.Ion doping and carbon fiber are the main reasons for the high activity of the obtained photocatalyst.PAN releases reducing gases during the heat treatment to reduce some TiO₂,which also contributes a lot in the enhancing the photocatalytic activity of the obtained catalyst.（3）Ammonium fluoride was added into the PAN solution to obtain PAN-NH₄F nanofibers by electrospinning.Using the above nanofibers as the precursor and tetrabutyl titanate as titanium source,F doped carbon nanotubes supporting N,F co-doped TiO_2-δwere successfully prepared by solvothermal method and the following heat treatment.The degradation rates of Rh B,MB and Cr（VI）were 25,14.8 and 8.5 times higher than that of the commercial TiO₂,respectively,under the same photocatalytic conditions.The performance of photocatalytic degradation on pollutants shows that the nanotube-like photocatalyst has superior photocatalytic activity.Because the nanotube has the higher surface area and F-doping improves the conductivity of carbon fiber.