Charged functional group effects on a metal-organic framework for selective organic dye adsorptions

A quaternary N-alkyl ammonium salt-containing zinc-based metal-organic framework (MOF) was synthesized and tested for selective organic dye adsorption experiments. Through covalent post-synthetic modification (PSM), the tertiary amine-containing MOF was converted into a quaternary N-alkyl ammonium salt-containing MOF under solid-state methylation conditions. The positively charged MOF was found to exclusively adsorb the negatively charged organic dye, while the positively charged organic dyes were not adsorbed. This separation experiment revealed that functional group control is an important and critical factor for molecule separations using porous materials.