SYNTHESIS, GROWTH AND PHYSICO-CHEMICAL PROPERTIES OF TITANIUM DIOXIDE NANOTUBES FOR PHOTOCATALYTIC WATER PURIFICATION

Abstract

Titanium dioxide (TiO2) photocatalysis is a promising method for decomposition of organic contaminants in water and belong to new a class of water purification methods called advanced oxidation processes (AOPs). AOPs encompass direct photolysis, Fenton processes;Ozonation; TiO2 heterogeneous catalysis; and TiO2 photo-catalysis. This work explores synthesis of Titanium dioxide nanotubes (TNTs) using electrochemical anodisation on Ti substrate as a simple method to make novel TiO2 photocatalysts with high surface area and tunable physicochemical properties for enhanced photocatalysis. By systematically exploring process parameters for the synthesis of TNTs by anodisation such as voltage, electrolyte composition and preparation, electrode separation distance, water content, anodisation time, Ti foil annealing as well as templating through second step anodisation; high quality TNTs were synthesized. The TNTs were grown in a third generation electrolyte comprising a mixture of ammonium fluoride and ethylene glycol with little amounts of water. Smooth TNTs were grown at water contents below 7vol % with high water contentsabove 10 vol% introducing ripples and transformation into spongy structure. A combination of proper electrolyte preparation procedures, proper control of process control variables, electrolyte composition, pre-heat treatment of Ti foils and post heat treatment of TNTs yielded high order and self-organization TNTs in single step anodisation.Template assisted growth in second step anodization yielded superior order and hexagonally ordered quality TNTs whose absorption spectra was shifted to the visible region about 600nm due to photonic effect and which exhibited promising photocatalytic activities upon post annealing of the as-prepared TNTs. Pre-heat treatment of Ti foils in Nitrogen atmosphere below 440oC encouraged TNT growth with increasing TNT length, yielding close- packing and self-organization of TNTs. Metal doping of TNTs was adopted to further enhance the photocatalytic activity. In this research, a novel, low cost technique was developed and adopted to deposit transition metal nanoparticles on the surface of TNTs. This work provides new insight into synthesis of well-structured and ordered TNTs with promising photocatalytic properties, and ways to improve their photocatalytic activity by means of structuring to bring about photonic effect and sequential metallic doping to enhance the photocatalytic activity of the photocatalysts.