Surface Chemistry of α-FeOOH Nanorods and Microrods with Gas-Phase Nitric Acid and Water Vapor: Insights into the Role of Particle Size, Surface Structure, and Surface Hydroxyl Groups in the Adsorption and Reactivity of α-FeOOH with Atmospheric Gases.

Heterogeneous interactions of H2O and HNO3 on goethite, α-FeOOH, a component of mineral dust aerosol, are studied with simultaneous QCM measurements and ATR-FTIR spectroscopy. Lab. synthesized α-FeOOH of varying sizes (microrods and nanorods) when exposed to gas phase H2O and HNO3 results in the uptake of these gases. This combined approach of QCM measurements and ATR-FTIR spectroscopy allows for both quantification of the amt. of uptake and spectroscopic data that provides information on speciation of adsorbed products. In the case of H2O, both microrods and nanorods take up H2O and that the total amts. of H2O, when normalized to surface area, are similar. However, for HNO3 uptake, the satn. coverage of total and irreversibly bound HNO3 on microrods is higher than that on nanorods, a size effect which is attributed to surface structural changes that occur as a function of particle size. Also, a study of the behavior of HNO3 reacted with α-FeOOH in aq. media was carried out such as to better understand the effects of atm. processing upon dispersal within the hydrosphere. [on SciFinder(R)]