Minimal cross-sensitivity to humidity during ethanol detection by SnO2-TiO2 solid solutions

A nanocomposite material is presented that optimally combines the excellent gas sensitivity of SnO2 and the selectivity of TiO2. Nanostructured, rutile titanium-tin oxide solid solutions up to 81.5% Ti, as determined by x-ray diffraction, are made by scalable spray combustion (flame spray pyrolysis) of organometallic precursor solutions, directly deposited and in situ annealed onto sensing electrodes in one step. Above that content, segregation of anatase TiO2 takes place. It was discovered that at low titanium contents (less than 5 Ti%), these materials exhibit higher sensitivity to ethanol vapor than pure SnO2 and, in particular, limited cross-sensitivity to relative humidity, a long standing challenge for metal oxide gas sensors. These solid solutions are aggregated nanoparticles with an enhanced presence of Ti on their surface as indicated by Raman and IR-spectroscopy. The presence of such low Ti-content in the SnO2 lattice drastically reduces the band gap of these solid solutions, as determined by UV-vis absorption, almost to that of pure TiO2. Furthermore, titania reduces the number of rooted and terminal OH species (that are correlated to the cross-sensitivity of tin oxide to water) on the particle surface as determined by IR-spectroscopy. The present material represents a new class of sensors where detection of gases and organic vapors can be accomplished without pre-treatment of the gas mixture, avoiding other semiconducting components that require more heating power and that add bulkiness to a sensing device. This is attractive in developing miniaturized sensors especially for microelectronics and medical diagnostics.