<i>In situ</i> growth of octa-phenyl polyhedral oligomeric silsesquioxane nanocages over fluorinated graphene nanosheets: super-wetting coatings for oil and organic sorption

Superhydrophobic surfaces offer significant advantages through their hierarchical micro/nanostructures, which create optimal surface roughness and low surface energy, making the development of robust surfaces essential for enhancing their physical and chemical stability. Here, we introduce <i>in situ</i> growth of octa-phenyl polyhedral oligomeric silsesquioxane (O-Ph-POSS) nanocages over multi-layered fluorinated graphene (FG) nanosheets through hydrolysis/condensation of phenyl triethoxysilane in an alkaline medium to produce a robust POSS-FG superhydrophobic hybrid. The efficient <i>in situ</i> growth of O-Ph-POSS nanocages over FG nanosheets was confirmed by FT-IR spectroscopy, PXRD, SEM, TEM, TG analysis, ²⁹Si NMR spectroscopy, N₂ adsorption-desorption isotherms and XP spectroscopy. The as-synthesized O-Ph-POSS over FG becomes superhydrophobic with a water contact angle (WCA) of 152 ± 2° and a surface free energy (SFE) of 5.6 mJ m^-2. As a result of the superhydrophobic property and robust nature of the POSS nanocage, O-Ph-POSS over FG nanosheets revealed the absorption capability for oils/organic solvents ranging from 200 to 500 wt% and were applied to coat onto the polyurethane (PU) sponge to effectively separate various oils and organic solvents from water mixtures, achieving separation efficiencies between 90% and 99%. Importantly, O-Ph-POSS-FG@Sponge still retained a separation efficiency of over 95% even after 25 separation cycles for hexane spill in water. The sponge efficiently separates toluene and chloroform using a vacuum pump, achieving flux rates of up to 20 880 and 12 184 L m^-2 h^-1, respectively. Weather resistance tests of O-Ph-POSS-FG@Sponge, prepared at intervals of 1 week and 1 year, showed that aged samples retained similar WCA values to freshly prepared sponges, confirming their long-term durability and performance. Mechanical stability assessments indicated that O-Ph-POSS-FG@Sponge maintained superhydrophobic properties, with WCA values of 151 ± 2° for tape peeling and emery paper treatments and 150 ± 2° for knife cutting, highlighting its excellent stability under physical deformation. Additionally, leveraging the exceptional resistance of O-Ph-POSS, the superhydrophobic O-Ph-POSS-FG@Sponge exhibited excellent stability and durability, even under supercooled and hot conditions during oil/water separation. Optical microscopy analysis of O/W and W/O emulsions, both stabilized by a surfactant, revealed complete droplet separation, further confirming the O-Ph-POSS-FG@Sponge's effectiveness for emulsion separation applications. The present work provides a straightforward method for the large-scale production of robust, superhydrophobic materials suitable for cleaning up oil spills on water surfaces.