Size- and Geometry-Dependent pH-Responsive Nanochannel Membranes Functionalized with Glycine and Pentylamine

Artificial membranes are widely used to mimic the selective transport behavior of biological ion channels and pumps, particularly their stimulus-responsive regulation capabilities. Herein, solid-state nanochannels are chemically functionalized with glycine (Gly) and pentylamine to precisely tune interfacial chemistry and surface charge states. Owing to distinct pore sizes and geometric confinement, cylindrical and conical nanochannels exhibit markedly different pH-responsive ion transport mechanisms. In cylindrical nanochannels with relatively large diameters, ion transport is dominated by bulk ionic conduction, and the pH dependence mainly arises from the different mobilities of H⁺ and OH^- ions. In contrast, conical nanochannels with narrow tips display surface-charge-governed transport, where pH and salt concentration jointly modulate electric double layer overlap and ion current rectification. Under acidic conditions, the functionalized nanochannels show suppressed ionic conduction associated with a hydrophobic interfacial state, while alkaline environments induce enhanced conduction due to increased surface charge density and wettability. These results establish a geometry-dependent pH-gating mechanism, providing a rational design strategy for responsive ion-transport membranes in sensing and separation applications.