Hard Photonic Glasses and Corundum Nanostructured Films from Aluminothermic Reduction of Helicoidal Mesoporous Silicas

We have investigated the aluminothermic reduction of photonic chiral nematic mesoporous silica films templated by cellulose nanocrystals. The mechanical hardness and ordered structure of aluminothermally reduced materials are found to be dependent on the surface contact between aluminum and silica reactants. By heating the silica films in a close contact with aluminum, the silica films undergo a surface aluminothermic reduction to generate photonic mesoporous glasses with enhanced mechanical hardness. The aluminothermic reduction of the silica is significantly enhanced when the reactants are in direct contact, transforming the helicoidal mesoporous silica films into colorful, stiff alumina/silicon replicas. Iridescent mesoporous films of corundum and corundum/silicon nanostructures are obtained from the alumina/silicon composites by selective etching of impurities. Our findings demonstrate that the aluminothermic reduction of silica is a simple process to improve the mechanical strength of chiroptical mesoporous glasses and is also a new one-step hard templating of hierarchically mesoporous corundum-based nanomaterials.