Size effects on reaction kinetics and surface thermodynamic properties of nano-octahedral cadmium molybdate

Abstract

Nano-octahedral cadmium molybdate (CdMoO4) samples of various particle sizes were prepared using an inverse-phase microemulsion method at room temperature. The thermodynamics of the reactions of the samples with hydrochloric acid were studied using in situ microcalorimetry. A combination of thermodynamic theory, transition-state theory, and thermochemical cycles was used to obtain the kinetic parameters and surface thermodynamic functions of the nano-octahedral CdMoO4 particles. The dependences of the reaction kinetics and surface thermodynamic properties on particle size and temperature were discussed, and the reasons for the dependences were explored. The results showed that the rate constant, specific Gibbs free energy, specific surface enthalpy, and specific surface entropy increased with decreasing particle size, whereas the activation energy decreased with decreasing particle size. The rate constant, activation Gibbs free energy, specific surface enthalpy, and specific surface entropy increased with increasing temperature; however, the opposite trend was observed for the specific Gibbs free energy. The surface thermal capacity decreased with increasing temperature in the critical size ranged from 30 to 200 nm; this is clearly different from the thermal capacity behavior of traditional heat-storage materials.