Semiconducting metal oxides (e.g. SnO
2, WO
3 or TiO
2) are used in a wide variety of applications such as transparent conductors or isolators, photo catalysis and solar cells. In particular, metal-oxide nanoparticles are highly performing materials in the field of solid state gas sensors. Recently, it was shown that WO
3 can be used for selective detection of acetone already in particle per billion concentrations.[1] Nanosized SnO
2,on the other hand, is an important sensing material for ethanol detection [2] and represents an interesting alternative to WO
3. The major shortcoming of SnO
2, however, is its poor reliability in the presence of variable relative humidity. Doping of SnO
2 with other metal oxides is a promising way to overcome this shortcoming. It has in fact been shown that the selectivity of SnO
2 nanoparticles towards ethanol in the presence of water vapor is drastically increased already at low Ti-doping content.[3] Here, the adsorption properties of H
2O on the surface of SnO
2, TiO
2 and of Sn
1-xTi
xO
2 have been investigated using density functional theory (DFT) within the Gaussian and Plane Wave (GPW) formalism. The solid solutions Sn
1-xTi
xO
2 have been investigated for x values of 1.7% and 3.3%. Calculations have been coupled to temperature programmed desorption (TPD) experiments in order to identify surface species. This combined theoretical and experimental investigation indicates that the presence of titanium surface sites weakly bind surface water which is therefore promptly desorbed at the working temperature of the sensor (300°C). This study thus provides a basis for an improved mechanistic understanding of metal oxide based solid state gas sensors.
[1] Righettoni, M.; Tricoli, A.; Pratsinis, S.E. Anal. Chem. 2010, 82, 3581. [2] Tricoli, A; Graf, M; Mayer, F.; Kuehne, S.; Hierlemann, A.; Pratsinis, S.E. Adv. Mater. 2008, 20, 3005. [3] Tricoli, A.; Righettoni, M.; Pratsinis, S. E. Nanotechnology 2009, 20, 315502.
