Gravity-separable emulsion membrane enabled by synergistic functionalization of silk cocoon, tannic acid, and LiCl

Abstract

Conventional treatment methods for oily wastewater in ship engine rooms often suffer from high energy consumption and poor efficiency in separating emulsified oils. Although the advent of superwetting materials has addressed these issues, their fabrication processes are typically complex and involve toxic reagents. In this study, we developed a simple, non-toxic, and cost-effective interfacial engineering approach to fabricate a high-performance oil–water separation membrane (CSTL). The membrane was constructed by in situ formation of a hydrogel coating on discarded silk cocoons via the reaction between silk fibroin (SF) and tannic acid (TA) in the presence of lithium chloride (LiCl). The resulting CSTL membrane exhibited excellent hydrophilicity, with a water contact angle (WCA) of 0° in air and an underwater oil contact angle (UOCA) of 145 ± 1°. Under gravity-driven conditions, the CSTL membrane achieved a high flux of 841 ± 5 L m⁻² h⁻¹ and a separation efficiency exceeding 99.7 % for oil-in-water emulsions. Moreover, the membrane retained its performance after 20 separation cycles and demonstrated good salt tolerance and antifouling capability. These advantages highlight the CSTL membrane as a promising green and efficient solution for the treatment of oily wastewater from marine sources.