Synthesis of copper nanoparticles within the interlayer space of titania nanosheet transparent films

Abstract

We report the first in situ synthesis of copper nanoparticles (CuNPs) within the interlayer space of inorganic layered semiconductors (titania nanosheet films) through the following steps. A sintered titania nanosheet (s-TNS) film was synthesised, forming a transparent, layered semiconductor film (∼2 μm thick). A considerable amount of copper ions (ca. 68% relative to the cation exchange capacity of TNSs) was intercalated in the s-TNSs using the methyl viologen-containing s-TNSs as the intermediate. The resultant copper-containing s-TNS (TNS/Cu²⁺) film was treated with an aqueous solution of NaBH₄, resulting in a colour change. Extinction spectra of NaBH₄-treated films exhibited a wide extinction band at λ_max (the extinction band maximum) = 683 nm. The spectral shapes and λ_max were similar to those for copper nanoparticles on TiO₂ surfaces. Transmission electron microscopy analysis demonstrated the wide distribution of electron dense particles on the titania sheet of NaBH₄-treated TNS/Cu²⁺. XRD analysis and absorption/extinction analysis with different amounts of TNSs suggest that CuNPs were formed within the interlayer space rather than the surface of TNSs through NaBH₄ treatment. Repeatable oxidation and reduction behaviour, i.e. colouration and decolouration cycles of the copper species within TNS films, was investigated.