Spill-SOS: Self-Pumping Siphon-Capillary Oil Recovery.

Oil spills remain worldwide challenge and need emergency "spill-SOS" actions once happen. Conventional methods suffer from complex process and high cost. Here, we demonstrate a solar-heating siphon-capillary oil skimmer (S-SOS) that harvests solar energy, gravitational potential energy and solid surface energy to enable efficient oil spill recovery in a self-pumping manner. The S-SOS is assembled by an inverted U-shape porous architecture combining solar-heating, siphon and capillary effects, and works without any external power and manual interventions. Importantly, solid surface energy is used by capillary adsorption to enable the self-starting behaviour, gravitational potential energy is utilized by siphon transport to drive the oil flow, and solar energy is harvested by solar-thermal conversion to facilitate the transport speed. In the proof-of-concept work, an all-carbon hierarchical architecture (VG/GF) is fabricated by growing vertically-oriented graphene nanosheets (VGs) on a monolith of graphite felt (GF) via a plasma-enhanced method to serve as the U-shape architecture. Consequently, an oil-recovery rate of 35.2 L m-2 h-1 is obtained at ambient condition. When exposed to a normal solar irradiation, the oil-recovery rate dramatically increases to 123.3 L m-2 h-1. Meanwhile, the solar-thermal energy efficiency is calculated to be 75.3%. Moreover, the S-SOS system presents excellent stability without obvious performance-degradation over 60 hours. The outstanding performance is ascribed to the enhanced siphon action, capillary action, photonic absorption and interfacial heating in the plasma-made graphene nanostructures. Multiple merits make the current S-SOS design and the VG/GF nanostructures promising for efficient oil recovery and transport of energy stored in chemical bonds.