pH-sensitive organic diimide materials-based superhydrophobic surface for oil-water separation applications

Abstract

pH-responsive superhydrophobic surfaces (SHSs) have recently represented reliable ability in oil-water separation applications. In this work, for the first time we could develop a switchable SHS based on (E)-4-(anthracen-9-yldiazenyl) benzoic acid (4-ABA) pH-responsive organic molecules and stearic acid (SA) using self-assembly method for oil-water separation applications. Molecular structure of 4-ABA obtains the smart pH sensitive SHS and makes it able to use in oil-water separation process. TiO2 decorated 4-ABA and SA composite (TiO2@4-ABA/SA)-based SHS could tune the surface charge in different pH (2.0–7.0) and subsequently could influence on wettability and contact angle (CA) of surface which makes the surface suitable to represent oil-water separation properties. Density functional theory (DFT) mechanic quantum calculation showed stable absorption of the 4-ABA molecules on TiO2 nanoparticles (∼ >1.3 eV) that rely on the reusability (>20 cycles) of the surface during oil-water separation. Morphology of switchable SHSs were considered by scanning electron microscopy (SEM) and wettability of the surface has been evaluated by CA. The UV–vis spectroscopy showed packing density (Γ = ∼4.35 × 10−7 mol.cm−2) of the 4-ABA in TiO2@4-ABA/SA approach which caused to high rate of switching in wettability (∼5 s per cycle). Transition between superhydrophobic (CA = ∼152.39°) and hydrophilic (CA = ∼26.11°) states is the main advantage of this surface obtained from the different charges of the surface in various pH. Therefore, the 4-ABA molecules-based pH-responsive SHS with ability in adjusting the surface wettability can be applied for oil-water separation applications. The mentioned versatile advantages open a new horizoffn for environmentally friendly applications of this approach which cannot achieved by conventional methods and materials.