Properties and Reactivity of Nanoconfined Aqueous Systems Are Modulated by the Confining Material

The reactivity of water, along with underlying intermolecular interactions, is profoundly altered under nanoconfinement. The properties of the confining material dictate the spatial dependence of reactivity, determining whether chemical processes are stabilized at the interface or within subsurface layers. Under confinement, water reorganizes into distinct coordination environments where hydronium maintains tri-coordination across regions, while hydroxide and other ions exhibit geometry- and environment-dependent solvation patterns. These confinement-enforced structural motifs modulate charge delocalization and proton-transfer pathways, thereby reshaping the thermodynamics and kinetics of aqueous reactions. Mechanical flexibility of the confining framework further tunes the free-energy landscape by reducing the entropic penalty associated with restricted molecular motion, enabling a broader configurational space compared to rigid pores. Together, these findings reveal how layer-specific solvation, interfacial polarization, and framework flexibility collectively govern the reactivity of confined water, offering molecular-level insights for designing adaptive nanoscale interfaces relevant to catalysis, energy storage, and separations.