Interaction of indoor air pollutants with titanium dioxide catalyst coatings studied by chemical ionization mass spectrometry.

摘要

Preventing the build-up of indoor pollutants represents an emerging goal in environmental chemistry. Heterogeneous catalysis provides an attractive method of remediating indoor air pollution, but optimization through rational catalyst design requires a detailed understanding of the catalytic surface and surface-pollutant interactions. In this work, a chemical ionization mass spectrometry (CIMS) system was built to study the interaction of acetone, a common indoor air pollutant, with Degussa P25 TiO2, an inexpensive catalyst widely used to degrade volatile organic compounds into carbon dioxide and water. While employing acetone partial pressures commonly found indoors, experiments were carried out in the presence and absence of UV light to isolate thermal reactivity from photochemical pathways, and deconvolute non-reactive and reactive thermal binding processes.; Equilibrium and dynamic experiments carried out at room temperature were used to determine the uptake coefficient and the adsorption free energy for acetone on Degussa P25. Equilibrium binding constants, reported for temperatures between 300 and 400 K, provide adsorption enthalpies and entropies. A discussion of the applicability of adsorption models based on statistical thermodynamics is included.; We have also studied the adsorption and photochemistry of acetone and several possible oxidation and condensation products that may be formed during the adsorption and/or the photocatalytic degradation of acetone on titanium dioxide catalysts. We report non-reactive uptake coefficients for acetone, formic acid, acetic acid, mesityl oxide and diacetone alcohol, as well as results from photochemical studies. We quantify, on a per-molecule basis, the room-temperature photocatalytic conversion of the species under investigation to CO2 and related oxidation products. The data presented here suggests that catalytic surfaces that enhance formate and acetate production from acetone precursors are likely to facilitate the photocatalytic remediation of acetone in indoor environments at room temperature.; This work provides new physical parameters for the interaction of an actual indoor air pollutant with a well-known catalyst. Taken together, the results of this work may be used to guide rational catalyst design, leading to next-generation materials that maximize desired pollutant-catalyst interactions. As such, it contributes to current efforts to improve the quality of indoor air through heterogeneous catalysis remediation strategies.