Boron is a contaminant of considerable interest for seawater desalination. Current state-of-the-art reverse osmosis membranes are inefficient at excluding boric acid, largely because of its small size and electrically neutral state at ambient conditions. Boron selective resins, often made from macroporous polymers bearing boron chelating functional groups, are a promising technology for boron removal from water owing to their low cost and excellent selectivity. However, current commercial resins suffer from low capacities, slow boron uptake kinetics, and poor stability/reusability. Porous aromatic frameworks (PAFs), a relatively new class of porous polymers with exceptionally high surface areas (up to 5600 m<sup>2</sup>/g), remarkable chemical stability, and chemical structures that are amenable to diverse functionalization, have the potential to overcome these drawbacks. In this study, novel boron-selective PAFs were synthesized by post-synthetically appending N-methyl-D-glucamine, an effective boron chelating moiety, to the pore walls of the high surface area parent frameworks. Relative to a state-of-the-art commercial resin, Amberlite IRA743, the boron-selective PAFs demonstrated up to 70% higher adsorption capacities and markedly faster adsorption rates, owing to greater functional group loading and higher porosities, respectively, relative to the resin. The boron adsorption rate constants of both frameworks, determined via a pseudo-second order rate model, represent the highest values reported in the open literature—in most cases orders of magnitude higher than those of other boron-selective adsorbents. The PAFs were readily regenerated by a mild acid/base treatment and maintained their boron uptake capacities for at least 10 cycles. These results highlight the numerous advantages of porous aromatic frameworks over traditional porous polymers in water treatment applications.

Functionalized porous aromatic frameworks for rapid boron removal from aqueous solutions

2019 Fall National Meeting

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