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.
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The data used in the current manuscript are available from C.B.P. upon reasonable request.
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We thank S. Shah and R. Pini for providing access to the X-ray microCT instrument and image analysis, and J. P. M. Trusler for the tensiometer at the Chemical Engineering Department, Imperial College London. We also thank L. Fiddes for confocal and AFM imaging, A. Stammitti Scarpone for crude oil interfacial tension measurement, A. Kondor and J. Acs for surface energy measurements and T. Luxbacher of Anton–Paar for zeta potential measurements. We also thank Y. Lu for artistic contribution to Fig. 1a,b. P.C. appreciates a Bert Wasmund Graduate Fellowship in Sustainable Energy Research, Queen Elizabeth II/Herbert A. Staneland Graduate Scholarship in Science and Technology, William Dubar Memorial Scholarship in Mechanical Engineering, and Ontario Graduate Scholarship. The research work was supported by the Natural Sciences and Engineering Research Council of Canada (grant no. NSERC DG 154279-2010), Consortium of Cellular and Microcellular Plastics and Natural Resources Canada Oil Spill Response Program (grant no. OSRS2-011), Department of Fisheries and Oceans (grant no. MECTS-3955465), Natural Sciences and Engineering Research Council of Canada Discovery Grant, Engineering and Physical Sciences Research Council, UK, and National Natural Science Foundation of China (grant no. 51902287).
Based on the datasets used in the manuscript, a patent application has been filed (British Provisional Patent Application no. GB 1905680.3).
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Supplementary Figs. 1–8, Discussion, Tables 1 and 2 and refs. 1 and 2.
The three-dimensional view of the SEnS, obtained using in-situ micro-CT, shows the adsorbed oil droplets spread on the pore surface and remain trapped inside. The images are not to scale.
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Cherukupally, P., Sun, W., Wong, A.P.Y. et al. Surface-engineered sponges for recovery of crude oil microdroplets from wastewater. Nat Sustain (2019). https://doi.org/10.1038/s41893-019-0446-4
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