Reduced Graphene Oxide Lamellar Membranes for Selective Ion Rejection in Nanofiltration: Role of Interlayer Spacing and Surface Functionalization

This study investigates reduced graphene oxide lamellar membrane performance for selective ion rejection in nanofiltration within the context of membrane science and water treatment engineering, an area of growing scientific importance given its implications for drinking water desalination, produced water treatment, and selective ion recovery. Using pressure-driven dead-end filtration cell measurements with inductively coupled plasma mass spectrometry for permeate ion quantification, we examine size exclusion and Donnan exclusion through nanometer-scale lamellar channels rejecting hydrated ions in 18 rGO membrane variants across three interlayer spacing categories drawn from laboratory pressure filtration setup at 1-10 bar transmembrane pressure. Results indicate that amine-spacer rGO membranes with 9.8-angstrom interlayer spacing achieve 96.4% Mg2+ rejection and 94.1% Ca2+ rejection while maintaining water flux of 18.4 L/m2/h/bar, outperforming commercial NF membranes (p < 0.001), with 96.4% Mg2+ ion rejection as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to membrane science and water treatment engineering and carry actionable implications for the design of programs and policies targeting drinking water desalination, produced water treatment, and selective ion recovery.