Polydopamine-based hybrid materials with tailored surface wettability for immiscible liquid separation

Abstract

Separation and purification of immiscible organic liquids which are commonly used in various industrial processes are highly necessary to ensure the harmless discharge to the environment. Among the methods, wettable materials have received considerable attention. Although many wetting materials have been developed to separate oil and water, the investigation of materials that are applicable for immiscible liquids separation is still seldom reported. Furthermore, simple and scalable fabrication is highly desired for practical application. In this thesis, I will introduce three novel wettable systems derived from surface modification of polydopamine (PDA). The strong adhesion and chemical versatility of PDA allow the coating on various materials with new properties. The coating also enables for designing novel materials with tailored wettability, which selectively allow the penetration of liquids. In the first project, I deposit PDA nanoparticles on the surface of cotton and kapok biomass fibers to fabricate dual-superlyophobic membranes. The interesting wetting behavior of the membranes allows selective penetration of water or oil, leading to the successful separation of oil and water. Understanding from the first project allows me to further develop super-wetting materials. In the second project, I employ PDA nanoparticles as the template to grow silicone micro-sheets (SMSs) derived from hydrolysis of octadecyltrichloro silane to fabricate various superlyophobic materials. It suggests that superlyophobic materials repel other high surface tension liquids such as formamide and diethylene glycol more effectively than superhydrophobic materials. The as-prepared materials are then applied to separate immiscible liquids by both absorption and membrane filtration. In the third project, the self-polymerization of dopamine reduces and functionalizes graphene oxide, forming GH-PDA porous particles with the assistance of ionic liquids. ZIF-8 nanocrystals are grown on to modulate pore sizes of porous graphene. The increasing amount of ZIF-8 results in the composite to convert from superamphiphobicity to omniphobicity, after fluoro-silane modification. The Ni foam coated with these tailored wettability graphene composite can effectively separate immiscible liquids.