Nitrogen-doped TiO₂ Modified With NH₄F For Efficient Photocatalytic Degradation Of Formaldehyde Under Blue Light-emitting Diodes

In this thesis, the preparation and modification of N-TiO2 semiconductor photocatalyst as well as its photocatalytic performance for degradation of formaldehyde were searched. The reseach works is composed of three parts:The first part, a nitrogen-doped TiO2 (N-TiO2) photocatalyst consisted of nanoparticles was prepared by the calcination of the hydrolysis product of Ti(SO4)2 with aqueous ammonia. The prepared samples were characterized by XRD, UV-vis diffuse reflectance spectra (DRS), transmission electron microscope (TEM), thermogravimetric and differential thermal analysis (TG-DTA) and BET. Its photocatalytic activity was evaluated by degradation of formaldehyde under visible irradiation using blue light LED as light source. The catalyst is consisted of anatase phase. Nitrogen-doping leads to extend optical absorption to the visible-light region. The photocatalyst prepared at lower drying temperature has smaller particle size and larger specific surface area than that prepared at higher drying temperature. The drying temperature has significant influence on its photoctalytic activity and the photocatalyst dried at lower temperature has higher photocatalyitic activity than that dried at higher temperature.In the second part, the nitrogen-doped TiO2 (N-TiO2) photocatalyst prepared by the above method (part 1) was treated with NH4F (F-N-TiO2) by an impregnation-calcination method. The photocatalyst (F-N-TiO2) was characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR), UV-vis diffusive reflectance spectroscopy (DRS), BET and X-ray photoelectron spectroscopy (XPS). With blue light-emitting diode (LED) as light source, its photocatalytic activity for degradation of formaldehyde was investigated. NH4F treatment increases markedly photocatalytic activity of N-TiO2. The NH4F treatment not only increases its visible absorption but also decreases the oxygen vacancies of F-N-TiO2 and the specific surface area. Increase of the absorption can be attributed to further nitrogen doping due to oxygen vacancies derived from previous nitrogen doping, while fluorine doping can decrease the defects. The photocatalytic activity of F-N-TiO2 depends on the visible absorption, the specific surface area and the defects. The preparation conditions, such as calcination temperature and initial molar ratio of NH4F to N-TiO2, have a great influence on the photocatalytic activity.In the third part, the efects of reaction conditions on photocatalytic performance for degradation of formaldehyde, such as the temperature, humidity and light intensity are investigated.