Implanting polyethylene glycol into MIL-101(Cr) as hydrophobic barrier for enhancing toluene adsorption under highly humid environment

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 Å) 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).