Rhodium as efficient additive for boosting acetone sensing by TiO2 nanocrystals. Beyond the classical view of noble metal additives

Anatase TiO nanocrystals were prepared by solvothermal synthesis and modified by in- situ generated Rh nanoparticles, with a starting nominal Rh:Ti atomic concentration of 0.01 and 0.05. After heat-treatment at 400 °C the TiO host was still in the anatase crystallographic phase, embedding Rh nanoparticles homogeneously distributed and whose surface had been oxidized to RhO, as established by X-ray diffraction, Transmission Electron Microscopy and X-ray Photoelectron spectroscopy. Moreover, Rh seemed also homogeneously distributed in elemental form or as RhO nanoclusters. The acetone sensing properties of the resulting materials were enhanced by Rh addition, featuring a response increase of one order of magnitude at the best operating temperature of 300 °C. Moreover, Rh addition enlarged the detection range down to 10 ppm whereas pure TiO was not able of giving an appreciable response already at a concentration as high as 50 ppm. From the sensing data, the enhancement of the sensor response was attributed to the finely dispersed Rh species and not to the oxidized Rh nanocrystals.