Aqueous Molecular Sieving and Strong Gas Adsorption in Highly Porous MOFs with a Facile Synthesis

Aqueous molecular sieving is demonstrated in a new series
of isostructural metal organic frameworks based on the perylene tetracarboxylate
(PTC) ligand. The frameworks can be formed in water at room temperature
with Mg, Ni, and other first row transition metal ions and adopt a
highly porous topology that results in predicted surface areas of
over 2000 m2 g–1 and periodic channels
of around 6 Å in diameter. Unusually, the M-PTC MOFs are highly
resistant to moisture and can be readily synthesized on multigram
scales. The frameworks have been shown to exhibit molecular sieving
in the absorption from mixtures of organic molecules at low aqueous
concentrations, with an application demonstrated on a dangerous water-borne
herbicide, Paraquat. Ni-PTC also exhibits a structural flexibility
that leads to strong and selective gas adsorption characteristics,
with an IAST selectivity of 300 for carbon dioxide being adsorbed
over nitrogen. Binding enthalpies for hydrogen and carbon dioxide
are also very strong in comparison to other MOFs, at 10.75 and 52.50
kJ/mol respectively.