TiO2 core-shell and core-dual-shell nanoparticles with tunable heterojunctions and visible to near-infrared extinctions

The popular use of titanium dioxide (TiO2) among metal oxides in a variety of optoelectronic applications can be attributed to its low cost and strong extinction in the UV region. However, TiO2 suffers from an inability to utilize a major part of the solar spectrum, and from rapid electron-hole recombination of photo-generated charge carriers. These challenges can be resolved by incorporating gold-silver nanoshells (GS-NS) with localized surface plasmon resonances (LSPR) into TiO2 nanostructures, with the overall goal of understanding near-field LSPR activation as well as electron-transfer and charge-trapping characteristics in core-shell and core-dual-shell systems. A method for the synthesis of core-shell nanoparticles consisting of a hollow gold-silver nanoshell core with a TiO2 shell (GS-NS@TiO2) is presented. Synthesis of core-dual-shell nanoparticles with either a semiconducting or insulating interlayer between the GS-NS core and TiO2 shell (GS-NS@SnO2@TiO2 and GS-NS@SiO2@TiO2) is also presented. In addition to a strong tunable surface plasmon resonance in the visible to near-IR region that allows better utilization of the solar spectrum by the TiO2 shell, incorporation of a GS-NS core leads to significant suppression of electron-hole recombination processes in TiO2, further demonstrating the advantages of the plasmonic core and metal oxide shell architecture. The near-field LSPR properties and charge transfer characteristics were further modified by the incorporation of SnO2 or SiO2 interlayers, with the SnO2 interlayer providing the most effective suppression of charge recombination. Reliable methods to fabricate composite TiO2-based nanoparticles with finely tunable optical and electrical properties are reported.