The presence of persistent hydroxide (-OH) groups in nano-crystals of ZrO2 is expected to affect its chemical reactivity, and to increase hydrophilicity of the crystal nano-surfaces. On the other hand, the -OH groups may dump - through the quenching - luminescence of fluorochromes added to the zirconium dioxide. Therefore probing of -OH groups in preparations of ZrO2 is of technological interest.
The strong infrared absorption around 3400 cm-1, corresponding to stretching vibrations of -OH bonds, make FT-IR spectroscopy a very sensitive tool for detection of hydroxyl groups. Yet, focusing on this spectral region is very risky, as a spontaneous absorption of atmospheric water vapor by a hydroscopic powder after heating is likely to give rise to artifacts. That is why the synthetic procedure was modified by a partial isotopic substitution of hydrogen with deuteron. Namely, during the chemical synthesis and precipitation of the ZrO2 roughly 40-50 % of water was replaced with heavy water (D2O). As a consequence, a portion of -OH groups was substituted with -OD groups on the ZrO2 surface being simultaneously trapped within the nano-structure. The -OD stretching vibrations are seen as a separate infrared band at 2600-2400 cm-1. The band is not overlapped by other infrared peaks in ZrO2 and its intensity can be conveniently (without the danger of artifact generated upon handling the sample in the air) treated as a yardstick of the number of hydroxide groups present in the ZrO2.
Nanocrystallie zirconia powders were produced using a microwave driven hydrothermal process under pressure up to 5.5 MPa. For FT-IR spectra, KBr-based pellets containing 1 wt.% of ZrO2 were prepared. All the FTIR spectra were collected in a transmission mode on a Nicolet NEXUS FT-IR spectrometer equipped with a liquid nitrogen-cooled MTC detector.