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 oilwater 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 (similar to >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. TheUV-vis spectroscopy showed packing density (Gamma = similar to 4.35 x 10(-7) mol.cm(-2)) of the 4-ABA in TiO2@4-ABA/SA approach which caused to high rate of switching in wettability (similar to 5 s per cycle). Transition between superhydrophobic (CA = similar to 152.39 degrees) and hydrophilic (CA = similar to 26.11 degrees) 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.