Photocatalytic Activities Of Titanium Oxide Doped By Metal And Non Metal:Environmental Applications

Semiconductor photocatalysis has been intensively studied in recent decades for a wide variety of application such as water and air treatment. The majority of photocatalysts are, however, wide band-gap semiconductors which are active only under UV irradiation.Titanium dioxide TiO2 (titania) is such a photocatalyst. However, it is cheap, non-toxic and one of the most efficient semiconductor photocatalysts for extensive environmental applications because of its strong oxidizing power, high photochemical corrosive resistance and low cost. Due to these inherent properties, TiO2 is the most suitable candidate for degradation and complete mineralization of toxic organic pollutants in water. But it is necessary to decrease its band gap by using different ways of doping.In order to effectively utilize visible light or solar radiation, this thesis investigates visible-light driven photocatalysts including metal (Nd doped TiO2), nonmetal (N-doped TiO2), or N-doped TiO2/MWCNTS nanocomposites. We found nitrogen or neodymium doped TiO2 nanoparticles had photocatalytic activities for Rh-B and benzene degradation under visible-light irradiation. In addition, visible-light photocatalytic activities of TiO2 are enhanced by N doping with the presence of carbon nanotubes as a support. It is shown that these nanocomposites can have enhanced photocatalytic activity via effective charge separation of photogenerated electrons and holes in TiO2 under visible-light irradiation. These systems can degrade a variety of organic pollutants. The main works are focus on:1) A new way to dope TiO2 nanoparticles by using ethylene-diaminetetraacetic acid (EDTA).2) Titanium dioxide (TiO2) doped with neodymium (Nd), one rare earth element for the photocatalytic degradation of Rhodamine-B under visible light.3) A comparative study between the N doping TiO2 without and with the presence of carbon nanotubes as support.In addition, all the samples were synthesized by sol-gel method. The prepared samples were characterized by scanning electronic microscopy, X-ray diffractometer, Raman spectroscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and Brunauer-Emmet-Teller measurement. The performance of the resulting N-doped TiO2, Nd-doped TiO2 and N-doped TiO2/MWCNTs for water purification was evaluated by the degradation of Rhodamine B (RhB) and benzene in comparison with P25 or pure TiO2. The conclusion we can make is as follow:Through simple sol-gel process, nitrogen and neodymium as Nd3+ can be incorporated into crystal lattice of TiO2, leading to its response to visible light. The mechanism study shows that hydroxide radicals produced by Nd doped TiO2 under visible light are one of reactive species for Rh-B degradation and photogenerated electrons are mainly responsible for the formation of the reactive species.With the presence of EDTA during preparation, the surface area of the prepared samples become larger, pore size smaller and pore size distribution narrower. The N-doped TiO2 nanoparticles have high enough activity for benzene degradation. They may be useful for real water purification by using solar light.Moreover, nitrogen through EDTA with the presence of MWCNTs as a support shows good activity.All these nanocomposite systems prepared in this thesis have abilities to degrade the Rhodamine-B solution (which has a risk of ser ious damage to eyes, an evidence of a carcinogenic effect, harmful in contact with skin, toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment) and toxic benzene.