Graphene oxide nanosheets for drinking water purification by tandem adsorption and microfiltration

Graphene nanosheets have outstanding adsorption efficiency toward organic molecules but the potential as sorbent for water purification is strongly limited by the tedious recovery of the nanosheets after the treatment, which can cause secondary contaminations. Here, we demonstrate that graphene oxide (GO) and reduced GO (rGO) nanosheets aggregation in tap water, enabling their separation by dead-end microfiltration (MF) on commercial polymeric hollow fiber modules. No evidence of GO/rGO contamination was found in microfiltered water and chemical potability of treated water was confirmed by standard protocols. Moreover, GO/rGO can be recovered (by inverting the filtration modality from IN-OUT to OUT-IN), washed and reused, this allowing the regeneration and reuse of both graphene nanosheets and the filtration module. The procedure (called here GO + MF) was optimized on tap water spiked with ofloxacin (OFLOX) or methylene blue (MB), as reference. The optimized procedure was then applied both with GO and rGO to the removal of a mixture of perfluoroalkyl substances (PFASs) from tap water at mu g/L levels, the highest concentration found in water resources abstracted for water consumption. We demonstrate that rGO + MF procedure allows to remove 138 mu g/g of total PFASs in only 30 min, i.e. an efficiency 3-5 times higher than granular activated carbon (43 mu g/g) used in real potabilization plants for PFASs removal.