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Current methods to remove oil microdroplets from wastewater are ineffective at the variable pH conditions commonly found in wastewater. This study presents a surface-engineered sponge that synergistically combines surface chemistry, charge and roughness, providing a solution to this problem.

In the United States, the oil industry produces over 15 billion barrels of wastewater contaminated with crude oil microdroplets annually. Current methods are ineffective for the removal of these microdroplets at the variable pH conditions commonly found in wastewater. Here, an innovative surface-engineered sponge (SEnS) that synergistically combines surface chemistry, charge and roughness, provides a solution to this problem. Over broad pH conditions, the SEnS rapidly adsorbed oil microdroplets with 95-99% removal efficiency, predominantly facilitated by Lifshitz-van der Waals forces. At the optimum pH, 92% of the oil was adsorbed within 10 min. The oil was subsequently recovered by solvent extraction under ambient conditions, and the cleaned SEnS was reused for oil microdroplets adsorption ten times. The combined efficacy and reusability can enable large-scale removal and recovery of crude oil microdroplets from wastewater.