Two-Dimensional Titanium Dioxide-Surfactant Photoactive Supramolecular Networks: Synthesis, Properties, and Applications for the Conversion of Light Energy.

The desire to harness solar energy to address current global environmental problems led us to investigate two-dimensional (2D) core-shell hybrid photocatalysts in the form of a 2D-TiO2-surfactant, mainly composed of fatty acids. The bulk products, prepared by two slightly different methods, consist of stacked host-guest hybrid sheets held together by van der Waals forces between alkyl carboxylate moieties, favoring the synergistic conjugation of the photophysical properties of the core and the hydrophobicity of the self-assembled surfactant monolayer of the shell. X-ray diffraction and the vibrational characteristics of the products revealed the influence of synthesis strategies on two types of supramolecular aggregates that differ in the core chemical structure, guest conformers of alkyl surfactant tails and type, and the bilayer and monolayer of the structure of nanocomposites. The singular ability of the TiO2 core to anchor carboxylate leads to commensurate hybrids, in contrast to both layered clay and layered double-hydroxide-based ion exchangers which have been previously reported, making them potentially interesting for modeling the role of fatty acids and lipids in bio-systems. The optical properties and photocatalytic activity of the products, mainly in composites with smaller bandgap semiconductors, are qualitatively similar to those of nanostructured TiO2 but improve their photoresponse due to bandgap shifts and the extreme aspect-ratio characteristics of two-dimensional TiO2 confinement. These results could be seen as a proof-of-concept of the potential of these materials to create custom-designed 2D-TiO2-surfactant supramolecular photocatalysts.

The Synthesis of Sponge-like V2O5/CNT Hybrid Nanostructures Using Vertically Aligned CNTs as Templates.

The fabrication of sponge-like vanadium pentoxide (V2O5) nanostructures using vertically aligned carbon nanotubes (VACNTs) as a template is presented. The VACNTs were grown on silicon substrates by chemical vapor deposition using the Fe/Al bilayer catalyst approach. The V2O5 nanostructures were obtained from the thermal oxidation of metallic vanadium deposited on the VACNTs. Different oxidation temperatures and vanadium thicknesses were used to study the influence of these parameters on the stability of the carbon template and the formation of the V2O5 nanostructures. The morphology of the samples was analyzed by scanning electron microscopy, and the structural characterization was performed by Raman, energy-dispersive X-ray, and X-ray photoelectron spectroscopies. Due to the catalytic properties of V2O5 in the decomposition of carbonaceous materials, it was possible to obtain supported sponge-like structures based on V2O5/CNT composites, in which the CNTs exhibit an increase in their graphitization. The VACNTs can be removed or preserved by modulating the thermal oxidation process and the vanadium thickness.