A polycationic covalent organic framework: a robust adsorbent for anionic dye pollutants

A polycationic two-dimensional (2D) covalent organic framework (PC-COF) has been prepared via the formation of imine bonds from the condensation of a rigid triangular triamine and a 4,4'-bipyridinium (BIPY)-derived dialdehyde. The new polycationic COF has a honeycomb structure with a pore diameter of about 5.8 nm. Powder X-ray diffraction (PXRD) and small-angle X-ray scattering (SAXS) experiments supported that the 2D layer structures stack into 3D porous frameworks and the adjacent BIPY dications stack in an eclipsed pattern, with chloride counterions being sandwiched in between the layers. PC-COF is highly stable in water, and functions as a robust adsorbent, as demonstrated by its high uptake capacity (>97%) towards a range of anionic organic dye pollutants from water even at a low concentration (3.2 x 10(-5) M). Moreover, the adsorbed guests could be released at high recovery rate, such as in the case of methyl orange.