Measurement of adsorption isotherms in the gas phase on native titanium dioxide surfaces by quartz crystal microbalance technique

The surface of air exposed titanium dioxide is known to be significantly covered with hydrocarbons, which modify the properties of titanium based materials such as used for human implants. The n alcohols are among the most important organic contaminants in the ambient atmosphere with typical partial pressures of 5 x 10(-3) Pa [50 ppb (parts per 10(9))]. The authors measured adsorption isotherms of H2O and n alcohols up to butanol in the pressure range of 10(-6)-1000 Pa in a UHV chamber with a quartz crystal microbalance. The crystals were covered by physical vapor deposition titanium layers passivated in oxygen atmosphere. Significant adsorption was observed in the pressure range equivalent to atmospheric contamination. The data were fitted by sums of Brunauer, Emmett and Teller (BET) isotherms with a spectrum of adsorption energies ranging from the evaporation enthalpies of about 40 to 100 kJ/mol. Due to the high energy contributions, significant coverage of TiO2 by n alcohols is already possible at their typical partial pressures in air. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3294716]