CHEMIJA. 2012. Vol. 23. No. 3. P. 187–193 © Lietuvos mokslų akademija, 2012 Photocatalytic and adsorptive properties of titanium dioxide prepared by thermal decomposition of metatitanic acid Silvija Mockūnaitė, Simona Ostachavičiūtė, Eugenijus Valatka* Department of Physical Chemistry, Kaunas University of Technology, Radvilėnų 19, LT-50254 Kaunas, Lithuania * Corresponding author. E-mail: eugenijus.valatka@ktu.lt Several types of titania-based photocatalysts were prepared by the thermal decomposition of metatitanic acid. Te obtained photocatalysts were characterized by X-ray difraction, Fourier transform infrared spectroscopy and thermal analysis. Te photoreduction of po- tassium dichromate was used as a model reaction in order to evaluate the photocatalytic activity of the prepared catalysts. Te infuence of methanol on the rate of photoreduction was also investigated. It was determined that the most active catalyst is obtained during annealing of metatitanic acid at 400 °C and contains 69.3% of rutile and 30.7% of anatase. Cr(VI) adsorption is best described by the Langmuir adsorption isotherm. Titania catalyst modifed with copper, cobalt, zinc or tungsten additives has larger adsorption capacity for Cr(VI), but smaller photoreduction rate as compared to pure TiO 2 . Key words: photocatalysis, adsorption, titanium dioxide, thermal decomposition, metati- tanic acid INTRODUCTION TiO 2 -based heterogeneous photocatalysis continues to be a very actively developing feld of fundamental and applied re- search [1–4]. It has been established that the nanostructured TiO 2 can be used as an efcient photocatalyst for the oxidation of various organic compounds, the removal of some metal ions, the photosplitting of water, the manufacture of dye-sensitized solar cells. Te main disadvantage of TiO 2 is its ability to act as a photocatalyst only under UV irradiation. For this reason, there is a need for new TiO 2 -based materials which could be sensitive to visible light. One of the possible ways to extend the spectral response of TiO 2 is its modifcation with narrow band- gap semiconductors, such as Cu 2 O, Fe 2 O 3 , CdSe. Under UV irradiation, the photoelectrons and holes are generated in TiO 2 particles. Tese charge carriers are cha- racterized by very strong redox properties and are able to oxidize and reduce many organic and inorganic substances on the surface of photocatalyst. Recently, an increased atten- tion has been paid to the simultaneous oxidation of organic pollutants and the reduction of toxic metal ions, such as Cr(VI) [5–7]. For example, it has been shown in numerous papers that highly toxic, mutagenic and carcinogenic Cr(VI) ions can be photocatalytically reduced to less harmful Cr(III) ions [8–28]. Te contamination of wastewater by Cr(VI) ions usually originates from industrial processes such as paint production, leather tanning or electroplating. Te preferred treatment is the reduction of Cr(VI) to Cr(III) upon the ad- dition of sodium thiosulfate, ferrous sulfate, sulfur dioxide gas or sodium bisulfate / metabisulfte. Aferwards, Cr(III) ions can be precipitated as Cr(OH) 3 . However, these methods require extensive use of chemicals and heterogeneous photo- catalytic reduction may be used as an alternative. Te aim of the current work was to obtain new TiO 2 - based photocatalysts and to study their adsorbtion capacity and photocatalytic activity. Te photoactivity of the prepared