Breaking solubility of metal-organic cages via polymer carrier for concentrated type II porous liquid to extract n-alkanes

Abstract

Type II porous liquids that exhibit host-guest properties derived from molecular cages are of potential utility in liquid-liquid separations; however, those with metal-organic cages (MOCs) as pore hosts are extremely rare due to the limited solubility of MOCs in cavity-excluded solvents. Here, we report the use of polyvinylpyrrolidone (PVP) to deliver polyoxovanadate-organic hybrid cages (HD) in polyethylene glycol (PEG) for a concentrated type II porous liquid (HDPVP/PEG). Structural characterizations and modeling studies collectively confirm that the PVP-PEG compatibility and the HD-PVP interaction enable the high HD concentration in PEG. The minimal loading of PVP coupled with the steric hindrance of PVP and PEG ensure the permanent porosity and room-temperature fluidity. HDPVP/PEG exhibits high uptake and selectivity toward C5–C7 n-alkanes over their branched isomers due to the host-guest interactions between HD and n-alkanes. The design strategy of HDPVP/PEG was successfully extended to other typical MOCs and commonly-used cavity-excluded solvents.