In the US, the oil industry produces over 15 billion barrels of wastewater contaminated with crude oil microdroplets annually. Current technologies are unable to remove these microdroplets at different pH conditions. Herein, an innovative surface engineered sponge (SEnS) was designed by combining surface chemistry, surface charge, roughness, and surface energy. Under all pH conditions, the SEnS rapidly adsorbed oil microdroplets with 95-99% removal efficiency predominantly by Lifshitz-van der Waals forces. Furthermore, at the best pH value, 92% of the oil was adsorbed within 10 min due to synergistic Lifshitz-van der Waals and acid-base (electrostatic attractive interactions and hydrogen bond) forces. The adsorbed crude oil was recovered at ambient conditions while the cleaned SEnS was reused up to five times for crude oil adsorption. Due to the process efficacy, sponge reuse, and oil recovery, this adsorptive-recovery method using SEnS demonstrates great potential for the industrial recovery of oil from wastewater.Recently, surface engineered sponges (SEnS) have emerged as promising adsorbents for oil microdroplets. 7-9 Due to their low cost, ease of fabrication, and high uptake capacity, sponges have great potential as industrial-scale sorbents. 10 To date, most sponge surfaces have been tailored to adsorb surfactant-stabilized pure hydrocarbon emulsions, which exhibit monotonous wetting at different pH values. 7,8 In contrast, crude oil is a complex mixture of ionic, polar, and non-polar components. 11,12 As a result, depending on pH, these complex chemical mixtures can exhibit large variability in physicochemical properties 13,14 leading to a broad range of contact angles at a solid surface. 9 Furthermore, the fundamental mechanisms governing variation in crude oil wetting behaviour with pH, which are important for material design, are not well understood.This work develops new sponges that are robust to the variable pH-responsive wetting behaviour of crude oil. Desirable sponge surface properties for microdroplets adsorption over broad pH conditions were hypothesized. To complement crude oil composition variability, the sponge surface is predicted to need organic, acid and base sites for effective oil adsorption (Figure 1a).Along with tailored surface chemistry, 15-17 the surface charge, [17][18][19] and roughness 20-22 may also invoke favorable wetting behavior 23-26 at the sponge surface (Figure 1b), enabling adsorption of oil droplets over a broad pH range. Based on these properties, the crude oil adsorption process efficacy can be predicted and validated experimentally.Herein, the aforementioned approach was applied to develop SEnS for adsorptive recovery of crude oil microdroplets for variable pH conditions. The SEnS consists of an acid-base polyester Affiliations
