Tan Xuecai

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

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.

Surface thermodynamic properties of different-sized nano octahedral cadmium molybdate

A series of nano octahedral CdMoO 4 with different sizes were prepared by reverse-microemulsion method at room temperature, and the constitute, structure and morphology were characterized. Based on the essential difference between thermodynamic properties of nano CdMoO 4 and bulk CdMoO 4 , the equations for acquiring surface thermodynamic properties of nano CdMoO 4 were derived via combining the basic theory of chemical thermodynamics with thermokinetics theory. According to the derived equations, surface thermodynamic functions such as specific surface Gibbs free energy, specific surface enthalpy and specific surface entropy of the prepared nano octahedral CdMoO 4 at 298.15 K were successfully gained by in situ microcalorimetry. Briefly, this work presented an effective and general method to obtain thermodynamic functions of nano materials.

Thermodynamic functions of tetrapod-shaped ZnO nanostructures

Tetrapod-shaped ZnO nanostructures with uniform size and morphology were prepared by a simple and mild microemulsion-mediated hydrothermal route. The characterization results revealed that each tetrapod-shaped nanostructure consisted of four nanoneedles which were about 250 nm in length. Based on the known thermodynamic functions of bulk ZnO, thermodynamic functions of nano ZnO with bulk ZnO were associated through designing a thermochemical cycle according to thermodynamic potential function method. And combined with thermokinetic theory, transition state theory and microcalorimetry, standard molar enthalpy of formation, standard molar Gibbs free energy of formation and standard molar entropy at 298.15 K for the as-achieved tetrapod-shaped ZnO nanostructures were gained as (-329.37 ± 0.43) kJ mol -1 , (-318.51 ± 0.03) kJ mol -1 and (20.36 ± 1.05) J mol -1 K -1 , respectively.