Adsorption equilibrium and kinetics of p-xylene on chromium-based metal organic framework MIL-101

The adsorption and diffusion properties of p-xylene on the chromium-terphthalate-based crystals (MIL-101) and the surface energy of MIL-101 were investigated by using gravimetric and inverse gas chromatography (IGC) techniques. The nanocrystal MIL-101 (∼100 nm) was synthesized by using microwave irradiation method. Adsorption isotherms and kinetic curves of p-xylene on the MIL-101 were measured at temperatures of (288, 298, 308 and 318) K and vapor pressures up to 6 mbar, respectively. Results show that the amount adsorbed of p-xylene on the synthesized MIL-101 was up to 10.9 mmol/g at 288 K and 6 mbar. The isosteric adsorption heat of p-xylene on the MIL-101 was in the range of 24.8–44.3 kJ/mol, which decreased with an increase in amount adsorbed of p-xylene on the MIL-101. The diffusion coefficients of p-xylene within the MIL-101 were in the range of 2.80–10.1 × 10−10 cm2/s at 288–318 K with activation energy of 30.9 kJ/mol. Three polar probes (acetone, toluene and p-xylene) were used to characterize the surface property of the MIL-101 by using IGC technique. IGC measurement results showed that the specific component (ΔGas) of the free energy of adsorption for polar probe molecules on the MIL-101 followed the order: p-xylene > toluene > acetone.

► The amount adsorbed of p-xylene on the synthesized MIL-101 was up to 10.9 mmol/g (288 K and 6 mbar).
► Isosteric heats of p-xylene adsorption were 24.8–44.3 kJ/mol over the p-xylene uptake range of 4–8 mmol/g.
► P-xylene diffusivities within MIL-101 were of 2.80–10.1 × 10–10 cm2/s in 288–318 K with activation energy of 30.9 kJ/mol.
► The order of polar probes (−ΔGas) in MIL-101 were given as p-xylene > toluene > acetone.