Chemistry in nanopores: Fine tuning chemical interactions for CO2 capture, water treatment and catalysis

Abstract

Nanopores (< 100 nm) in porous polymers offer confined spaces with vast contact surfaces and tunable functionalities. We have developed a family of nanoporous covalent organic polymers (COPs 1-200) through scalable, catalyst free conditions that feature a wide range of functional groups available for chemical interactions. In particular, azo (N=N) groups were shown to selectively separate CO2 from N2 by the discovery of an N2-phobic mechanism (1). By varying chain length of a covalently tethered amine within a nanopore, we optimized CO2 binding energy, leading to new CO2 sorbent designs (2). Charged organic molecules are captured by a size and charge dependent separation using fluorinated porous networks (3). This unique interaction of fluorine with charged species enables considerable promise in water treatment technologies. Nanopores with heterocyclic pore wall chemistries (e.g. benzoxazoles) enable catalytic, oxidative, metal-free coupling of amines. Another, highly charged COP system converts epoxides and CO2 into cyclic carbonates with unprecedented selectivity and conversion at near ambient conditions. When the nanopores are loaded with nanoparticles, the porous host and the reactive nanocrystal display a symbiotic action. A poisoned Pd nanoparticle in a sulfur COP catalyzes acetylene reduction into ethylene with exceptional yields (4). Caged cobalt oxide within an amide porous polymer is found to be as active as a Pd in CO oxidation (5). Finally, nanoscale iron particles remain highly reactive if concealed within the confined spaces of porous polymers (6).