Heterogeneity of Adsorption Sites and Adsorption Kinetics of n-Hexane on Metal–Organic Framework MIL-101(Cr)

The heterogeneity of adsorption sites and adsorption kinetics of n-hexane on a chromium terephthalate-based metal–organic framework MIL-101(Cr) were studied by gravimetric method and temperature-programmed desorption (TPD) experiments. The MIL-101 crystals were synthesized by microwave irradiation method. The adsorption isotherms and kinetic curves of n-hexane on the MIL-101 were measured. Desorption activation energies of n-hexane from the MIL-101 were estimated by TPD experiments. The results showed that equilibrium amount of n-hexane adsorbed on the MIL-101 was up to 5.62 mmol·g− 1 at 298 K and 1.6 × 104 Pa, much higher than that of some activated carbons, zeolites and so on. The isotherms of n-hexane on the MIL-101 could be well fitted with Langmuir–Freundlich model. TPD spectra exhibit two types of adsorption sites on the MIL-101 with desorption activation energies of 39.41 and 86.69 kJ·mol− 1. It reflects the surface energy heterogeneity on the MIL-101 frameworks for n-hexane adsorption. The diffusion coefficients of n-hexane are in the range of (1.35–2.35) × 10− 10 cm2·s− 1 with adsorption activation energy of 16.33 kJ·mol− 1.

The heterogeneity of adsorption sites and adsorption kinetics of n-hexane on a chromium terephtalate-based metal–organic framework MIL-101(Cr) were studied by the gravimetric method and temperature programmed desorption (TPD) experiments. Left: the isotherms and kinetic curves of n-hexane on the MIL-101 at different temperatures. Middle: schematic view of MIL-101 without and with the adsorption of n-hexane vapor. Right: TPD profiles of n-hexane on the MIL-101, exhibiting two types of adsorption sites on the MIL-101 and reflecting the surface energy heterogeneity for n-hexane adsorption.Figure optionsDownload as PowerPoint slide