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 degrees, which suggests selective separation capacity for oil and high permeation flux up to 4018 L.m- 2 & BULL;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 degrees 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 & BULL;h-1. Thus, OD-SiO2 @sand shows promising applicability in the field of oil recovery and oil quality improvement.

Automated summary

In this study, a smart quartz sand with controllable wettability was designed for efficient oil-water separation and water in oil emulsion separation. The quartz sand exhibited superhydrophobicity and hydrophilicity, maintaining separation performance under different pH conditions. It also demonstrated efficient demulsification and separation capacity, showing promising applicability in the field of oil recovery and oil quality improvement.