pH-regulated superhydrophobic quartz sands for controllable oil-water separation

pH-regulated wettability transformation materials have gained increasing attention attributing to the capacity for sustainable oil-water separation. In this work, a smart quartz sand (OD-SiO 2 @sand) with controllable wettability was designed as a filter media for efficient oil-water mixtures and water in oil emulsions separation. The OD-SiO 2 @sand was synthesized by grafting nano-silica and modifying with two silane couplers, including N, N-Diethyl-3-(trimethoxysilyl)− 1-propanamine (DTP) and trimethoxy(octyl)silane (OTMS). OD-SiO 2 @sand featured superhydrophobicity with a water contact angle (WCA) of 151.6°, which suggests selective separation capacity for oil and high permeation flux up to 4018 L.m −2 ∙h −1 . Meanwhile, OD-SiO 2 @sand exhibits superhydrophobicity and hydrophilicity in neutral and acidic solutions resulting from the reversible protonation of grafted DTP, which was revealed by 1 H NMR and molecular dynamics simulations. OD-SiO 2 @sand posed controllable oil-water separation performance, which remains superhydrophobicity with a WCA of 150.4° after 10 cycles of filtration processes upon pH regulation. Furthermore, OD-SiO 2 @sand demonstrated efficient demulsification and separation capacity for various water in oil emulsions, achieving a purified oil size of less than 10 nm and a permeation flux up to 1850 L.m −2 ∙h −1 . Thus, OD-SiO 2 @sand shows promising applicability in the field of oil recovery and oil quality improvement.