(155d) Tuning d-Spacing of Graphene-Oxide Via Covalent Crosslinking with Triaminotriptycene for Improved Water Stability and Molecular Sieving

Membrane-based water treatment technologies are important for water purification and desalination due to their high efficiency and low energy consumption. Conventional polymer membranes, however, suffer from inherent material limitations, such as a permeability-selectivity trade-off and chemical stability in harsh operating conditions. Graphene-based membranes have been widely studied for water treatment due to their excellent chemical stability and ultra-fast water permeation. Graphene-oxide (GO) sheets can be easily assembled into lamella membranes by scalable techniques. Water permeation is controlled by a slip-flow process of water molecules through the graphitic region, as in carbon nanotubes, between neighboring interlayer sheets. Rejection is controlled by the size sieving of guest molecules through interlayer and inter-edge spacing, as well as the interaction of functional groups on GO sheets with guest molecules. When hydrated, GO sheets are easily intercalated due to the abundant hydrophilic functional groups, which enlarges the interlayer spacing from ~ 3.5 Ã… to the range of 9-12 Ã… and affects the long-term stability of GO films.

Herein, we introduce covalently crosslinked GO membranes with triaminotriptycene molecules for water treatment. The graphene oxide was prepared by modified Hummer’s method. Amine-crosslinked triptycene/GO composite films were prepared through filtration using vacuum-assisted self-assembly and post-treatment steps. The chemical modification of GO sheets by amine crosslinking was demonstrated by X-ray photoelectron spectroscopy and ATR-IR. The interlayer spacing of modified GO films in the dry and hydrated states with respect to different spacer loading was observed by powder X-ray diffraction. The interlayer spacing of dry GO film was varied from 8.0 to 16 Å with various amounts of spacer loading. The swelling of GO sheets was suppressed due to the crosslink as observed by XRD. The water permeability and ion/molecular rejection were investigated by dead-end testing, and the stability of modified films at different temperatures and pH ranges was studied. This study demonstrates an opportunity to tune spacing of GO sheets for water-based separations.