Influence of the pH of the synthesis using sol-gel method on the structural and optical properties of TiO2

Abstract

The photocatalysis process using semiconductor materials, in particular TiO2, is one of the most attractive treatment for polluted waters decontamination because of its advantages over other oxidation processes [1-6]. In this study the effect on the physical properties of TiO2 due to the pH used during the manufacturing of the semiconductor is studied. Different samples were synthesized using ammonium hydroxide (NH4OH) and nitric acid (HNO3) as catalysts to provide basic and acid pH environments, respectively. Changes in composition, structure and morphology of the samples were studied and its dependence with the pH of the synthesis is discussed. Results indicate that the base catalysis favours the formation of anatase TiO2 crystalline phase with crystallite size ∼ 26nm obtained by Rietveld refinement; the spherical particles formed agglomerates of ∼100nm; the average pore size is in the range of mesopores and the surface area increases with the amount of NH4OH added in the process. On the other hand, with acid catalysis, a mixture of two crystalline phases, anatase and rutile, was obtained with crystallite sizes around 26 and 49nm, respectively. The grain size is several orders of magnitude higher than those obtained by basic catalysis. The photocatalytic activity was measured using methylene blue solutions to determine their degradation with radiation. Greater efficiency was observed in the photocatalysts synthesized with NH4OH.