Oxidation-controlled nanoporous graphene laminate membranes via intercalation chemistry for desalination

Abstract

Graphene oxide (GO) laminate membranes exhibit remarkable molecular separation performance. However, swelling in water expands the interlayer spacing, limiting salt retention in desalination. On the other hand, narrow interlayer spacing is a barrier that does not allow water transport. This study introduces oxidation-controlled nanoporous graphene (OCNG) laminate membranes, developed using graphite intercalation compound chemistry, resulting in abundant nanopores (1-4.5 nm). In addition, the oxidation degree of graphene was controlled by intercalant to avoid expansion of interlayer spacing larger than the size of the hydrated ions. Because the nanopore provides an additional transport channel for water and compact interlayer structure filters the hydrated ions by physical sieving, in forward osmosis desalination, OCNG membranes exhibit exceptional selectivity, removing >98-99 % of typical seawater ions over a broad salinity range (0.1-1 M), and maintain high performance despite acidic conditions, high chlorine exposure, and prolonged operation (30 days). Furthermore, the OCNG membranes proved their versatility in real seawater desalination with abundant impurities and metal-ion enrichment from acidic leaching solution of spent Li-ion batteries, showing a promising diversity in their application. These findings highlight the potential of graphene membranes in various ion separation areas performed in harsh chemical environments.