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-SiO2@sand) with controllable wettability was designed as a filter media for efficient oil-water mixtures and water in oil emulsions separation. The OD-SiO2@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-SiO2@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-SiO2@sand exhibits superhydrophobicity and hydrophilicity in neutral and acidic solutions resulting from the reversible protonation of grafted DTP, which was revealed by 1H NMR and molecular dynamics simulations. OD-SiO2@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-SiO2@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-SiO2@sand shows promising applicability in the field of oil recovery and oil quality improvement.