Development of Functional Flax Fibers Through Self-Assembled Nanoparticles for Oil-Water Separation

Abstract

Oil-water separation has attracted extensive attention since frequent oil leakage incidents and oily-wastewater discharge caused serious disaster to the environment. Traditional separation technologies have difficulties in dealing with rapid and widespread oil spills and may cause secondary pollution. The use of oil barriers with special wettability is a promising alternative for separating oil from water. Natural materials, such as biomass have advantages of biological degradability, resource abundance, and low cost. In this study, environmentally friendly, reusable, and low-cost functionalized flax fibers were fabricated to separate oil from water. Flax fibers were modified by plasma-induced poly (acrylic acid) (PAA) polymerization followed by nano-TiO2 self-assembly to obtain a hydrophilic surface. In order to identify the significant preparation parameters and reveal their complicated interactions, a two-level factorial design was employed. Plasma treatment power, plasma treatment gas flow rate, PAA concentration, and nano-TiO2 concentration were found to be able to improve the hydrophilicity significantly. The modified fiber was characterized by synchrotron-based Fourier transform infrared spectroscopy (FTIR) and X-ray fluorescence (XRF). The chemical images of hydroxyl, carboxyl, and TiO2 nanoparticles (TiO2 NPs) on flax fiber surface were measured and analyzed. The TiO2 NPs were found randomly fixed on flax fiber surface. The modified flax fiber was verified to have good capability of separating oil from water. The hydrophilicity of modified flax fiber was significantly improved, with water contact angle decreasing from 97.4° to 25.9° and almost doubled maximum oil holding pressure. The modified flax fiber showed stable performance of immiscible light oil-water mixture separation in harsh conditions, such as alkaline (pH = 12) and saline (2%) conditions. These excellent performances remained stable after multiple cycles. Therefore, the modified flax fiber has potential to be used as an oil barrier for immiscible oil-water separation. Furthermore, a photo-induced HDTMS-ZnO coated flax fiber was developed for on-demand oil-water separation. The HDTMS-ZnO coated flax fiber had properties of transferable hydrophobic/underwater oleophilic in the dark and hydrophilic/underwater oleophobic under UV irradiation. A full experimental design was applied to explore the impact between hexadecyltrimethoxysilane (HDTMS) and ZnO nanoparticles (ZnO NPs) concentrations on the modified fiber performance. The optimal combination was found to be 0.1vol% HDTMS and 1.0 wt% ZnO NPs. The modified fiber samples before and after UV treatment were characterized by scanning electron microscope (SEM) and synchrotron-based FTIR and XRF. The hydrophobic functional groups and ZnO NPs distribution were investigated on flax fiber surface. It was interesting to find that the concentration of alkyl groups decreased with the increase of ZnO NPs concentration under UV irradiation, which contributed to reversible wettability. Hence, the developed flax fiber with this switchable behaviour has promising application including the separation of immiscible oil-water mixture and oil-in-water emulsion scenarios.