Thermochemistry of nanodiamond terminated by oxygen containing functional groups

The standard enthalpies of formation at 25 °C of nanodiamonds terminated by oxygen containing functional groups have been investigated by high-temperature oxidation calorimetry. Depending on the amount of oxygen containing functional groups, the nanodiamonds (plus oxygen and hydrogen as represented in the surface functional groups) can be up to 52 kJ mol-1 more stable in enthalpy than graphite, which means that less heat is evolved during oxidation of nanodiamonds terminated by oxygen containing functional groups, since their surface carbon is already partially oxidized. The stability of the nanodiamonds terminated by oxygen containing functional groups increases (enthalpy of formation becomes more negative) with increasing surface area within the studied range, reflecting the dominant effect of higher content of surface functional groups over the destabilizing effect of higher surface-to-volume ratio typical for nanoparticles.