Hard Templating Pathways for the Synthesis of Nanostructured Porous Co3O4

Abstract

The present study is concerned with the nanocasting preparation of Co 3 O 4 nanostructures employing two-dimensional (2D) hexagonal SBA-15 and three-dimensional (3D) cubic KIT-6 as hard templates. The influence of framework connectivity of the parent silica and loading of the cobalt source are studied in detail. Structures can be tailored as isolated or randomly organized Co 3 O 4 nanowires or as highly ordered mesoporous Co 3 O 4 networks retaining the symmetry of the silica parent using 2D hexagonal parent materials. Applying cubic KIT-6 silica with suitable wall thickness and degree of framework interconnectivity as a template, we can vary the pore size of mesostructured Co 3 O 4 from 3 nm up to values as high as 10 nm. To verify the influence of surface properties and texture, we employed different mesoporous silicas that were conventionally calcined at 550 °C and equivalent silica materials microwave treated in the presence of a concentrated H 2 O 2 /HNO 3 mixture. The parent silica materials and the resulting Co 3 O 4 were characterized in detail at different steps during the templating route by nitrogen physisorption measurements and powder X-ray diffraction. Transmission electron microscopy and scanning electron microscopy investigations were performed to visualize the structure and morphology of the nanocast materials, and thermogravimetry−differential thermal analyses (TG−DTA) were done to follow the formation of Co 3 O 4 . With our method, preparation of nanocast Co 3 O 4 is highly reproducible, regardless of template shapes and sizes, which makes the pathway much more versatile for a great variety of templates.