Highly crystalline inverse opal transition metal oxides via a combined assembly of soft and hard chemistries

A combined assembly of soft ansd hard chemistries is employed to generate highly crystalline three-dimensionality ordered macroporous (3DOM) niobia (Nb2O5) and titania (TiO2) structures by colloidal crystal templating. Polysterene spheres with sp(2) hybridized carbon are used in a reverse-template infiltration technique based on the aqueous liquid phase deposition of the metal oxide in the interstitial spaces of a colloidal assembly. Heating under inert atmospheres as high as 900 degrees C converts the polymer into study carbon that acts as a scaffold and keeps the macropores open while the oxides crystalize. Using X-ray diffraction it is demonstrate that for both oxides this approach leads to highly crystalline materials while heat treatments to lower temperatures commonly used for polymer colloidal templating, in particular for niobia, results in only weakly crystallized materials. Furthermore it is demonstrated that heat treatment directly to higher temperatures without generating the carbon scaffold leads to collapse of the macrostructure. The approach should in principle be applicable to othe 3DOM materials that require heat treatments to higher termperatures.