(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. Nanosized SnO2,on the other hand, is an important sensing material for ethanol detection  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. Here, the adsorption properties of H2O on the surface of SnO2, TiO2 and of Sn1-xTixO2 have been investigated using density functional theory (DFT) within the Gaussian and Plane Wave (GPW) formalism. The solid solutions Sn1-xTixO2 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.
 Righettoni, M.; Tricoli, A.; Pratsinis, S.E. Anal. Chem. 2010, 82, 3581.  Tricoli, A; Graf, M; Mayer, F.; Kuehne, S.; Hierlemann, A.; Pratsinis, S.E. Adv. Mater. 2008, 20, 3005.  Tricoli, A.; Righettoni, M.; Pratsinis, S. E. Nanotechnology 2009, 20, 315502.
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