Preparation And Photocatalytic Performance Of F-TiO₂ Photocatalyst

The environmental problems in today’s society is becoming increasingly serious. It is imminent to seek an economic and efficient environmental governance method. Titanium dioxide has become one of the most suitable semiconductor for environmental purification due to its characteristic, such as excellent photocatalysis, stability, low cost and non-toxic, etc. Nevertheless, TiO2 is limited by several undesirable characteristics, such as its wide band gap (3.2 eV) that can only be excited by ultraviolet light, which occupies only 7% of the entire solar spectrum. In addition, TiO2 exhibits rapid recombination of photo-induced electrons and holes (e-/h+), which significantly decreases quantum efficiency.This thesis focused on increasing the photocatalytic activity of TiO2 under simulated sunlight irradiation. F-TiO2、CF-TiO2 composites were synthesized via a simple sol-gel method by using NaF as the fluorine source followed by heat treatment at aerobic or anaerobic calcination, and their adsorption and photocatalytic ability have been evaluated. Optimum parameters of preparation factors such as the pH, inhibitor, reaction temperatures, calcination methods, calcination temperatures and calcination time were choosed by studing the adsorption and photocatalytic ability of composites made under different conditions. The morphology, crystal structure, optical absorption and surface property of samples were characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, N2 sorption, fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, and photoluminescence. The mechanisms for excellent photocatalytic ability of F-TiO2 and CF-TiO2 was discussed. Through a series of experimental study and analysis, the research results are as followed:The F-TiO2 was synthesized via a simple sol-gel method followed by calcination in an aerobic atmosphere, and the optimum preparation conditions are:pH=5, acetic acid,25℃ reaction temperature, n F/Ti=0.1,600℃ calcination temperature and 1h calcination time.The crystal phase of F-TiO2 in composites was still anatase, and the average size of F-TiO2 determined by the Scherrer equation is 16.89 nm. F-modification can generate more oxygen vacancies because of the replacement of surface -OH groups by the F species, which can inhibit the recombination of photoelectrons with holes by the captured photoelectrons, promote the generation of Ti3+ and narrow the band gap 2.75 eV, thereby enhancing the quantum efficiency of photocatalysis.The CF-TiO2 was synthesized via a simple sol-gel method followed by calcination in an anaerobic atmosphere, and the optimum preparation conditions are:n F/Ti=0.1 and 700℃ calcination temperature.CF-TiO2 shows an irregular cube structure.It consists of anatase (97.08%) and rutile (2.92%) phases, shows abundant micropore and mesoporous structures. The carbon atoms doped into the titania lattice and the oxygen vacancies level result in the narrowed band gap (2.50 eV) of the obtained composite. The fluorine species modified on the surface of titania inhibits the recombination of photo-induced e-/h+. The CF-TiO2 exhibited a superior photocatalytic activity.