Co-doping metal oxide nanotubes: superlinear photoresponse and multianalyte sensing

Abstract

Metal oxide nanotubes and standalone membranes have been extensively researched for potential applications ranging from electronics, optoelectronics, and photocatalysis, to filtration and gas sensing. Although the wide-bandgap of these nanotubes poses challenges for their utilization for photochemical conversion and charge transport, doped metal-oxide nanotubes provide an alternative to lower their bandgap and provide charge carriers for conduction and photochemistry. While many single-dopants have been successfully used, co-dopants can be used to manipulate the electronic density of states, photophysical and photochemical properties to obtain new and unexpected functionalities, sometimes even completely different from the individual dopants. Here the co-doped titanium dioxide (TiO2) nanotube membranes are described where the combined properties of the co-dopants differ from their monodoped counterparts. A detailed mechanistic model is provided to explain the new photophysical and photochemical properties of these co-doped metal oxide membranes, and novel functionalities resulting from such properties like superlinear photoresponse and enhanced gas sensing response. In addition, the potential applications of these functionalities are shown in photodetection and multianalyte sensing as portable devices.