Thin Films of Thermally Stable Ordered Mesoporous Rh2O3 (I) for Visible-Light Photocatalysis and Humidity Sensing

The preparation of highly ordered mesoporous thin films of rhodium sesquioxide (Rh2O3) on silicon and quartz glass substrates by dip-coating via solution-based block copolymer self-assembly is reported. Hydrated rhodium chloride is shown to be an effective precursor for sol-gel processing of Rh2O3. Heating in air to 600 degrees C crystallizes single-phase Rh2O3 (I) while fully preserving the cubic symmetry 3D pore-solid architecture, whereas at 750 degrees C only the in-plane pore order is retained. Interestingly, there is no crystalline-crystalline transformation upon heating to 1000 degrees C, despite distinct microstructure coarsening. The thermal stability of the sol-gel-derived material in terms of mesostructure retention can be significantly enhanced by atomic layer deposition surface treatment, making the block copolymer-templated thin films interesting for demanding applications. Furthermore, the results of preliminary humidity sensing and photochemical activity measurements indicate that the nanocrystalline Rh2O3 (I) shows promising properties as a sensor material and a visible-light photocatalyst.