Abstract
The fundamental mechanism behind oil/water separation materials is their surface wettability that allows either oil or water to pass through. The conventional materials for oil/water separation generally have extreme wettability, namely superhydrophilic for water separation and superhydrophobic for oil separation. Using easily accessible materials that are medium hydrophobic or even relatively hydrophilic for preparing highly efficient oil/water separators have rarely been reported. In this work, a new strategy by triggering phase transition of infused lubricant from liquid to solid state in porous structure is realized in fabricating slippery lubricant infused porous structure for oil/water separations. By infusing polyester fabric with coconut oil, after phase transition, excellent water repellency and oil permeability by an absorbing-permeating mechanism are achieved, despite the low water contact angle on the new material. Although the new phase transformable slippery lubricant infused porous structure, features much milder hydrophobicity than conventional oil/water separators, it can remove diverse types of oil from water with high efficiencies. The phase transformable slippery lubricant infused porous structure is able to maintain their water repellency after immersing in high concentration salt (10 wt% NaCl), acid (25 % HCl), alkaline (25 % NH3·H2O) solutions for 120 h, showing remarkably functional durability in harsh environment. The lubricant phase transition mechanism proposed in this study is universally applicable to porous substrates with various chemical compositions and pore structures, such as porous sponges or even daily life breads, for creating efficient oil/water separators, which can serve as a novel accessible design principle of phase transformable slippery lubricant infused porous structure for eco-friendly oil/water separators.
Highlights
The slippery lubricant infused porous structure (SLIPS) was known to possess low contact angle hysteresis that can enable water droplet sliding. (Wong et al, 2011) A successful oil/ water separation SLIPS material relies on the correct selection of substrate, infused lubricant and oil to be separated based on wettability, as detailed discussion on interfacial energy of wetting systems provided in supplementary Section S1
The phase transformable slippery lubricant infused porous structure (PTSLIPS) samples were found with exceptional capacity to effectively filter toxic oil species from water, despite of their medium hydrophobic nature, through a novel absorbing-permeating mechanism as discussed in supplementary S2
In the case that the lubricant in the pores was etched away by the chemicals and only remained on the walls of the pores, the samples might still maintain their oil/water potential by direct oil permeating similar to other reported superhydrophobic and superoleophilic materials. (Feng et al, 2004; Gao et al, 2013; Cao et al, 2013; Zhang and Seeger, 2011) All these results suggested that the PTSLIPS can serve as a resilient candidate for oil/ water separation in harsh chemical conditions
Summary
The leakage of oil and discharge of liquid industrial wastes result in release of tremendous toxic chemical compounds into environment and obviously threats to the global ecosystem. (Peterson et al, 2003; Schrope, 2011; Incardona et al, 2005; Joye, 2015) Conventional methods for the treatment of large-scale oil spill event, including in-situ burning, vacuum suction, and chemical dispersants-assisted degradation, are highly costly and relatively inefficient (Kleindienst et al, 2015; Fritt-Rasmussen et al, 2015, 2016). There are currently three main types of oil/water separation materials, the superhydrophobic and superoleophilic materials (Feng et al, 2004; Gao et al, 2013; Cao et al, 2013; Zhang and Seeger, 2011), the superhydrophilic and under-water superoleophobic materials (Xue et al, 2011; Wen et al, 2013; Zhang et al, 2013a), and the superhydrophilic and superoleophobic materials (Yang et al, 2012; Kota et al, 2012; Pan et al, 2018; Ponzio et al, 2016), being actively investigated These interface materials possess attractive oil/water separation properties originated from their varied affinities to oil and water, namely special surface wettability (Wang et al, 2015; Liu et al, 2014a). A feasible way to maintain lubricant stably in the SLIPS for oil/water separation is missing, which can broaden the applicability of SLIPS in oil/water separation
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