Combined hydrothermal and mechanochemical control of structural modifications of zirconium dioxide for catalytic applications†

The influence of hydrothermal treatment (HTT) and subsequent mechanochemical treatment (MChT, milling) on the porous and crystalline structure of precipitated zirconium dioxide was studied. It has been established that HTT at 300 °C promotes the transformation of amorphous ZrO₂ into a pure monoclinic phase, as well as the formation of a uniform mesoporous structure which has higher thermal stability. Soft dry milling (300 rpm, 0.5–1 h) of hydrothermally modified monoclinic ZrO₂ causes the introduction of defects into its structure without a noticeable change in the phase composition. The presence of defects is confirmed directly using UV-vis spectra and indirectly by the manifestation of photocatalytic activity of milled samples under visible irradiation. Importantly, it is found that after calcination of milled samples at 500 °C a high fraction of defects remains preserved which opens up the potential of using zirconium dioxide modified in this way as a catalyst or catalytic support with added specific properties offered by defects.