Facile optimization of hierarchical topography and chemistry on magnetically active graphene oxide nanosheets.

Highly flexible and two-dimensional (2D) graphene oxide (GO) nanosheets have remained instrumental for developing different functional materials for practically relevant applications. In general, 2D GO is routinely assembled into different structures (i.e. layered, porous, etc.) for achieving desired properties. However, a facile approach for modifying GO nanosheets with (1) hierarchical topography and (2) desired chemistry is rare in the literature. In this report, adequate optimization of both hierarchical topography and low surface energy chemistry in a confined space (in the order of μm dimensions) of GO nanosheets is unprecedentedly carried out for achieving magnetically active and 2D 'confined-super-water-repellence'. A chemically reactive polymeric complex was covalently deposited on the GO-nanosheets through a facile 1,4-conjugate addition reaction for adopting a chemically reactive and hierarchically featured polymeric interface. Simultaneously, the deposition of iron oxide nanoparticles on the 2D-nanosheets rendered the entire material magnetically active. The post-covalent modification of these chemically/magnetically active and hierarchically featured GO-nanosheets with octadecylamine (ODA) yielded magnetically active and 2D 'confined-superhydrophobicity'. Further, this synthesized material was extended for addressing highly relevant and severe global challenges of 'oil-in-water' and 'water-in-oil' emulsion separation by either selective collection (with an efficiency of above 1000 wt%) of tiny oil-droplets from bulk water or forming magnetically active 'Pickering-type' aqueous droplets, respectively, under various practically relevant harsh conditions, including extremes of pH, salinity, surfactant contamination, etc. Further, appropriate functionalization of this chemically/magnetically active 2D nano-interface could be useful in developing functional interfaces for various applications related to energy, catalysis and healthcare.