Metal-cation-modified graphene oxide membranes for water permeation

The stability of graphene oxide (G-O) membranes in water can be enhanced via the simple addition of metal-cations to the planar laminate structure, however, the relationship between valency and hydration radius and the properties and performance of the membrane structure is unclear. This study examines the impacts of adsorbed monovalent (K+ and Na+), divalent (Cu2+ and Mn2+) and trivalent (Al3+, Fe3+ and La3+) cations on permeation for G-O membranes in water vapor permeation and pervaporation. Metal-cations with high electronegativity and a small hydration radius possess greater binding strength that constrains the G-O laminate channels (d-spacing). Both water permeation methods show a positive trend between permeation and interlayer spacing for metal-cations with the same valency. Amongst the different valence states, steric exclusion from cations is dominant for minimal water layers (water vapor permeation), while the ability for cations to attract and hold water molecules inside its outer shell has a greater effect on swollen channels (pervaporation). These findings help pave the road towards G-O based applications in next generation water filtration methods for desalination and wastewater treatment.