Production of nanostructured TiO2 for photocatalysis application

In recent years heterogeneous photocatalysis has attracted a great interest because of its potential to remove aqueous and air pollutants through complete mineralization. Even though the technologies for the synthesis of photocatalysts for industrial production already exist, there are a number of technological problems concerned with the industrial-scale using of TiO2. First of all, TiO2 (anatase) can be excited only with UV light which is quite expensive and requires special protective measures to use it. Then, the missing of recovery of the TiO2 nanoparticles from the treated wastewater leads both to the treatment cost and the presence of TiO2 powder dispersion inside the purified solution stream. The objective of this research work was focused to face both the above mentioned two disadvantages. In order to recover the used nanoparticles it was developed a technology for the production of composite core/shell/shell Fe3O4/SiO2/TiO2 nanoparticles by wet chemical synthesis. These nanoparticles were recovered by using an electromagnetic trap and successfully re-used. Moreover, in order to accomplish the photocatalysis by using visible the doping of TiO2 was studied and a process procedure was developed and successfully applied, with regard to a sol-gel material adopted for coating. The core/shell/shell nanoparticles operation process was realized in three steps: 1) Fe3O4 magnetic nanoparticles precipitation by Spinning Disc Reactor, 2) Fe3O4/SiO2 core/shell nanoparticles synthesis by using of the Stöber method, 3) TiO2 external layer production by sol-gel method. Synthesis of the nitrogen-doped titanium dioxide was carried out by using 2- ethylmethylamine as dopant and its subsequent immobilization on the glass spheres was obtained by applying a deep-coating technique. The activity of the developed photocatalysts was checked by degradation of the methylene blue, phenol and 2-chlorophenol in aqueous solutions, olive mill wastewater and ethylene in gas phase. Composite core/shell/shell photocatalyst demonstrated high catalytic activity (more than 90% in case of MB and 2-CP degradation, 50% of OMWW degradation) and very reproducible results. 57% of OMWW degradation under the visible light and more than 60% of phenol degradation was achieved as a result of photocatalysis assisted by nitrogen doped titanium dioxide immobilized on the glass beads. Nitrogen doped titanium dioxide demonstrated a slight photocatalytic activity under the visible light irradiation in gas phase. Different models such as pseudo-first order, second order, Langmuir-Hinshelwood and Hugul were adopted to describe the kinetics of the photo-chemical reactions.