LAUSR

Abstract Undoped ZrO2 with tetragonal and/or monoclinic structure was synthesized by the Pechini method. Samples were used for the adsorption of methylene blue (MB) in the dark and under ultraviolet irradiation. Despite the absence of dopants, tetragonal phase was predominant after calcination at 600 and 800 °C, while the monoclinic phase was obtained after calcination at 1000 °C. Different behaviours were observed for samples with different crystalline structures. For the monoclinic zirconia, 74% of the solution was decolourized after 16 h in the dark, and this value increased to 80% when the solution was irradiated with a UV lamp. For the tetragonal zirconia, the influence of irradiation was more important, and the decolourization of the solution increased from 40% in the dark to 100% under UVC irradiation. This result indicated that a meaningful change took place on the surface of the tetragonal zirconia during irradiation, but no meaningful photocatalytic activity was observed, and adsorption was responsible for the solution decolourization. In addition to environmental remediation, the adsorption of MB onto the t-ZrO2 led to the formation of a new product, a ZrO2/MB composite that may be used as a pigment, with very low MB solubility in water and blue colour, stable under UVA irradiation.