Chemical ionization mass spectrometry as a tool for studying the surface interactions of the air pollutant acetone with Degussa P25 TiO₂

Indoor air pollution is an emerging problem in atmospheric chemistry. We have applied chemical ionization mass spectrometry (CIMS) to study the interaction of the indoor air pollutant acetone with Degussa P25 TiO₂, a possible remediation catalyst. Acetone partial pressures representative of those commonly found in both indoor and outdoor environments (10^-7 to 10^-4 Torr) are used. This partial pressure range is critical because the nonlinear relationship between gas phase concentration and surface coverage makes the extrapolation of high partial pressure data to environmentally relevant conditions challenging. Experiments carried out at 298 K allow for the deconvolution of non-reactive and reactive binding processes. Equilibrium and dynamic isotherm experiments yield a sticking coefficient of approximately 1 × 10^-4 that is independent of acetone partial pressures in the low partial pressure regime examined here. The room temperature equilibrium binding constant and the adsorption free energy are also reported. Additional experiments carried out between 300 and 400 K are used to determine enthalpies and entropies of adsorption and to discuss the applicability of different adsorption models.