Reliable access to critical minerals like lithium and cobalt is crucial to the nation’s economy. These materials are often found as dissolved ions in aqueous streams such as geothermal brines, water produced from oil drilling, leachates from mining, and industrial wastewater. Extracting these ions is difficult because they are mixed with similar, more abundant ions. Membranes can recover ions effectively, but they struggle to separate the desired ions from the undesired ones. This CAREER project will show how controlling the arrangement of chemical groups inside the pores of a membrane can improve ion separation. It will study how ions move through membrane pores, and how the specific patterns of chemical groups can favor one ion over another. The results will provide rules for designing better materials for ion separation. They will also help improve the domestic supply of critical minerals. Educational activities will integrate research into courses, provide hands-on training, and engage high school students and local communities. Ion–ion separation remains challenging because conventional membranes rely on size exclusion and electrostatic interactions, which are insufficient to distinguish ions with similar physicochemical properties. This CAREER project will establish a mechanistic framework for ion-selective transport. The central hypothesis is that selective ion transport arises from the precise spatial arrangement of ion-interacting functional groups under confinement. This modulates the free energy landscape for ion migration and enables efficient, reversible hopping between binding sites. This hypothesis will be tested by (1) developing well-defined experimental model systems using nanoporous graphene and metal–organic frameworks to independently control pore size, degree of confinement, and the spatial distribution of chemical groups within the pores; (2) quantifying how ion sorption thermodynamics and kinetics depends on the degree of confinement, func