Heat capacity studies of surface water confined on cassiterite (SnO ₂) nanoparticles

Heat capacities have been measured on a series of 2, 6, 11, and 20 nm SnO ₂ nanoparticles with varying amounts of surface water as well as on a bulk parent material, in the temperature range from 2 to 300 K. By subtracting the heat capacity values for 2 nm SnO ₂ samples with different water contents, we calculated the heat capacity contribution of the anhydrous lattice and found that the lattice heat capacity of the nanoparticle is the same as that of the bulk material within experimental error. This is further confirmation that, for several systems, once one accounts properly for the heat capacity of adsorbed water there is no measurable excess lattice heat capacity related to particle size. Using this result, we have calculated the heat capacities of confined water on the surfaces of the various SnO ₂ nanoparticles and found the water behavior to be generally similar to that of bulk ice, although with some differences in detail. The heat capacity of confined water on these same SnO ₂ nanoparticles calculated from inelastic neutron scattering spectra and those determined calorimetrically agree within experimental error at temperatures below 200 K.