Implanting Polyethylene Glycol into MIL-101(Cr) as Hydrophobic Barrier for Enhancing Toluene Adsorption under Highly Humid Environment

Abstract Adsorption of volatile organic compounds (VOCs) under high humidity is crucial for metal-organic frameworks (MOFs) in practical applications. To enhance competitive adsorption of VOCs under humidity, polyethylene glycol (PEG) with hydrophobic short-chains was implanted as hydrophobic barrier into MIL-101(Cr). Characterization and simulation results showed that the terminal –OH groups of PEG chains were coordinated with the Cr sites in MIL-101(Cr) and formed a hydrophobic pore (11.2 A) of “cage-in-cage” geometry. PEG chains significantly hindered the diffusion of water into the MOFs while allowed toluene molecules. The new hydrophobic pores of PEG5@MIL-101 enhanced adsorption capacity and diffusivity for toluene by 30.8% (4.68 mmol/g at 1 mbar) and 31.5% (1.88×10-2), while decreased adsorption capacity and diffusivity for water by 53.7% and 26.8% compared to primary MOF. Breakthrough curve showed 3.3 times of toluene working capacity on PEG5@MIL-101 at 80% RH compared to pristine MIL-101(Cr).