The Impact of Silanol Defects on the Properties of Zeolite-Based Microporous Water

Microporous particles with hydrophobic internal surfaces and hydrophilic external surfaces can dramatically enhance the gas-carrying capacity and gas transfer kinetics of aqueous solutions. Pure-silica zeolites are particularly well suited to forming aqueous dispersions with dry and gas-filled micropores─termed “microporous water”─but the zeolite particles typically do not retain their full solid-state gas sorption capacity in the solution phase. Moreover, covalent surface functionalization through silanization reactions can lead to significant additional reductions in gas-carrying capacity. Here, we show that internal silanol defects are directly responsible for the lower O₂-carrying capacities and that removal of these defects through an ammonium fluoride treatment restores the gas-carrying capacity of microporous water to 100% of its theoretical value. This further allows covalent surface functionalization to be carried out while preserving the internal porosity─and aqueous phase gas-carrying capacity─of the zeolite. In addition, we investigate how internal silanol defects impact the thermodynamics of noncovalent polymer intrusion into the zeolite particles in aqueous dispersions. Collectively, these results provide new insights into how silanol defects influence the bulk properties of zeolite-based microporous water.