Excess enthalpy and luminescence studies of SnO2 nanoparticles

The extra reactivity of nano materials is attributed to the excess surface energy stored in the sample. The excess enthalpy of SnO2 nano-particles were measured as a function of particle size using a calvet calorimeter. SnO2 with particle size 11, 27, 47 nm and bulk samples (1 microm) were dropped from room temperature to 987, 936 and 885 K and their H(T)-H298 values were determined. The excess enthalpies for SnO2 samples with particle sizes 11, 27 and 47 nm compared to the bulk sample calculated from the difference between H(T)-H298 values of the nano and the bulk samples were found to be 15.06, 3.05, 2.21 kJ x mol(-1) respectively. Luminescence experiments reveal that the surface trap electron density decreases with increase of particle size. The excess enthalpy is related to the surface trap intensity.