Flexible Bipyridinium Constructed Porous Frameworks with Superior Broad-Spectrum Adsorption toward Organic Pollutants

A flexible bipyridinium ligand has been introduced into a series of isomorphous metal-organic frameworks to yield porous materials with subtriangular 1D channel and cagelike pore space. The introduction of bipyridinium molecules into the porous frameworks leads to the formation of 1D channel with positively charged surface, which shows high affinities to polar molecules such as methanol, ethanol, and water vapor. Additionally, the bipyridinium molecules possess conjugated pyridyl rings connected by carbon-carbon single bonds, which can rotate freely to keep twisted or large-conjugated planar configuration by controlling coordination condition during the self-assembly process. The cagelike pore space formed by these flexible bipyridinium molecules contains arene-arene stacked pyridyl rings and thus renders abundant π-π interaction sites for efficient adsorption of benzene and toluene molecules, and is also large enough to accommodate cyclohexane molecules. These metal-organic frameworks show efficient adsorption for benzene, toluene, and cyclohexane molecules through high utilization efficiency of unique pore space, and display rarely broad-spectrum adsorptivity to various organic pollutants with hydrophilic/hydrophobic, conjugated/nonconjugated characteristics.