Nanopore engineering in graphene oxide membranes: A critical review of KOH activation, pre-oxidation, and desalination performance

Chemical nanoporation of graphene oxide (GO) membranes via KOH activation and pre-oxidation is the most scalable route to in-plane nanopore formation in two-dimensional carbon materials. However, no chemically nanopored GO membrane has simultaneously achieved the triple performance threshold we propose for nanofiltration-competitive desalination: NaCl rejection ' 80% at brackish-water concentrations (≥2 g/L), water permeance ' 5 LMH/bar at ≥ 10 bar, and stability ' 100 h in cross-flow. This review diagnoses why this gap persists after a decade of effort and provides a roadmap for closing it. Five interconnected limitations are identified: (1) neglect of pre-oxidation degree, the C/O ratio, as the variable governing pore nucleation; (2) uncritical transfer of the KOH activation mechanism from bulk activated carbon to two-dimensional GO without verification; (3) isotropic lateral etching that consistently yields 2–10 nm pores rather than sub-nanometer dimensions required for NaCl exclusion; (4) absence of deliberately engineered pore-edge chemistry, the dominant determinant of ion selectivity; and (5) recurring characterization gaps in which dry-state measurements can systematically overstate performance. We examine each limitation mechanistically, benchmark all reported data against commercial nanofiltration standards, and develop nine recommendations to redirect the field toward genuine desalination-relevant progress.