Ultrathin Films and Hollow Shells with Pillared Architectures Fabricated via Layer-by-Layer Self-Assembly of Titania Nanosheets and Aluminum Keggin Ions

Abstract

Inorganic multilayer films and hollow shells with pillared architectures have been fabricated layer-by-layer on spherical poly(methyl methacrylate) (PMMA) templates as well as flat substrates through the electrostatic self-assembly technique. Positively charged polyoxocations of aluminum Keggin ions were employed both as inorganic binder and as pillaring agent in electrostatic self-assembly with exfoliated unilamellar crystallites of Ti0.91O2, yielding new types of ultrathin films and core−shell composites. Ultraviolet−visible absorption spectra revealed progressive enhancement of absorbance with increasing deposition cycles, indicating the regular growth of multilayer assemblies of titania nanosheets and aluminum polyoxocations. Evolution of a Bragg peak with a periodicity of ca. 1.5 nm and its enhancement also supported the formation of nanostructured multilayer films and shells, accommodating aluminum polyoxocations in the nanosheet gallery. Depth X-ray photoelectron spectra confirmed their inorganic nature. Calcination at 400 °C produced ultrathin films and hollow shells with alumina pillars between the titania sheets. N2 adsorption results revealed a high specific surface area of 260 m2 g-1 and nanoporous feature for the pillared hollow spheres.