Combination of an electrodeless quartz crystal microbalance and spectrometric methods and application in monitoring adsorption kinetics of iodine on metal-organic frameworks films

In this work, the combination of an electrodeless quartz crystal microbalance (EL-QCM) and spectrometric techniques was designed to investigate the adsorption kinetics of iodine onto two metal-organic frameworks film, MIL-101 and ZIF-67. The concentrations of I 2 adsorbed on film and in vapor phase were monitored simultaneously in real time by the frequency of EL-QCM and the absorbance, respectively. It was shown that ZIF-67 film has a high adsorption capacity of 4.41   g/g to I 2 , which is much higher than that of MIL-101 (0.58   g/g). The 2-methylimidazole unit in ZIF-67 plays an important role for I 2 adsorption with a capacity of 3.15   g/g. For adsorption on MIL-101, the amount of I 2 adsorbed at equilibrium obeys the Henry’s law. The amounts of I 2 adsorbed on ZIF-67 film increases with increasing concentration of I 2 vapor in accelerating slope due to the condensation of I 2 vapor. The diffusion coefficients of I 2 in MIL-101 and ZIF-67 films were estimated to be 6.1   ×   10 −16 and 3.7   ×   10 −16   m 2 /min, respectively. By using the concentration-time curves, adsorption kinetic parameters were estimated based on a simplified model including reversible and irreversible adsorption states. This method offers the advantage to record simultaneously the changes in both of the amount adsorbed and the vapor concentration of a corrosive adsorbate with UV-vis absorbance.