(373h) Investigation of H2O Adsorption On Rutile (110) Surfaces of TiO2, SnO2 and Their Solid Solutions by First-Principles Calculations

Semiconducting metal oxides (e.g. SnO₂, WO₃ or TiO₂) 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 WO₃ can be used for selective detection of acetone already in particle per billion concentrations.[1] Nanosized SnO₂,on the other hand, is an important sensing material for ethanol detection [2] and represents an interesting alternative to WO₃. The major shortcoming of SnO₂, however, is its poor reliability in the presence of variable relative humidity. Doping of SnO₂ with other metal oxides is a promising way to overcome this shortcoming. It has in fact been shown that the selectivity of SnO₂ nanoparticles towards ethanol in the presence of water vapor is drastically increased already at low Ti-doping content.[3] Here, the adsorption properties of H₂O on the surface of SnO₂, TiO₂ and of Sn_1-xTi_xO₂ have been investigated using density functional theory (DFT) within the Gaussian and Plane Wave (GPW) formalism. The solid solutions Sn_1-xTi_xO₂ 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.