Syntheses of Metal-Organic Frameworks and Aluminophosphates under Microwave Heating: Quantitative Analysis of Accelerations

Several porous materials such as metal-organic frameworks (MOFs) and aluminophosphates have been synthesized with microwave and conventional electric heating in various temperatures and times to investigate the quantitative acceleration in the synthesis of porous materials by microwaves. From the analysis of the acceleration under microwave heating with the Eyring equation, it can be understood that, irrespective of the type of porous materials, the acceleration by microwaves is mainly due to decreased activation free energy (Delta G(double dagger)) even though the activation energy (E-a) and activation enthalpy (Delta H-double dagger) are increased. The decreased activation free energy is mainly due to the high activation entropy (Delta S-double dagger) of microwave synthesis compared with the entropy of conventional electric synthesis. Accelerated synthesis with microwaves may be explained with changes of relative energies of intermediates for high activation entropy.