Atomic Force Microscopy and X-ray Photoelectron Spectroscopy Study of NO2 Reactions on CaCO3 (101̅4) Surfaces in Humid Environments.

A.c. (a.c.) mode at. force microscopy (AFM) combined with phase imaging and XPS were used to study the effect of nitrogen dioxide (NO2) adsorption on calcium carbonate (CaCO3) (101̅4) surfaces at 296 K in the presence of relative humidity (RH). At 70% RH, CaCO3 (101̅4) surfaces undergo rapid formation of a metastable amorphous calcium carbonate layer, which in turn serves as a substrate for recrystn. of a nonhydrated calcite phase, presumably vaterite. The adsorption of nitrogen dioxide changes the surface properties of CaCO3 (101̅4) and the mechanism for formation of new phases. In particular, the 1st calcite nucleation layer serves as a source of material for further island growth; when it is depleted, there is no change in total vol. of nitrocalcite, Ca(NO3)2, particles formed whereas the total no. of particles decreases. These particles are mobile and coalesce. Phase imaging combined with force curve measurements reveals areas of inhomogeneous energy dissipation during the process of water adsorption in relative humidity expts., as well as during nitrocalcite particle formation. Potential origins of the different energy dissipation modes within the sample are discussed. Finally, XPS anal. confirms that NO2 adsorbs on CaCO3 (101̅4) as nitrate (NO3-) regardless of environmental conditions or the pretreatment of the calcite surface at different relative humidity. [on SciFinder(R)]