Femtosecond laser engineered eggshell membrane for durable oil/water separation under harsh conditions

Abstract

Membranes with super-wettability have been widely used to treat oily wastewater, but the construction of most of these membranes involves the use of corrosive and even toxic chemicals, and they often exhibit poor chemical durability. Therefore, green and durable super-wetting membranes are urgently required for remediating oily wastewater under harsh conditions. In this study, we report an eggshell membrane (ESM) with super-wettability as a green and durable candidate for efficient oil/water separation under harsh conditions. Specifically, naturally hydrophilic chicken ESMs are directly roughened and drilled using a femtosecond laser, without using any chemicals. Laser-engineered ESMs (LEESMs) possess superhydrophilicity in air and superoleophobicity under water, which renders them capable of separating immiscible oil/water mixtures after they are pre-wetted using water. Results show that the pre-wetted LEESM can cyclically treat various oil/water mixtures with a separation efficiency of >98.6% and water flux of >10000 L·m-2·h-1. Because of the inherent chemical resistance of ESM itself, the LEESMs show excellent durability towards highly corrosive aqueous solutions such as HCl (1 M), NaOH (1 M), and saturated NaCl solution (26.5 wt %). The LEESM retained its underwater superoleophobicity after being immersed in these corrosive solutions for 12 h; therefore, it could be used to separate mixtures of toluene and corrosive solutions efficiently for more than 10 cycles, demonstrating remarkable durability and recyclability in terms of oil/water separation under harsh conditions. Moreover, when the LEESM is pre-wetted or contaminated by oils, it can be easily cleaned by immersing in water, thereby restoring its underwater superoleophobicity and oil/water separation capacity, which prevents it from being fouled during long-term usage. Therefore, this green, anti-corrosive, and self-cleaning LEESM offers insights into the design and fabrication of advanced membranes for practical oily wastewater remediation, as well as the developing and utilization of bio-wastes.