Breathing Demulsification: A Three-Dimensional (3D) Free-Standing Superhydrophilic Sponge

A novel three-dimensional (3D) free-standing superhydrophilic sponge for industrial wastewater treatment was formed by combining chitosan and linear polyacrylamide (PAM). When the chitosan–PAM sponge is immersed into an oil-in-water emulsion, the milky white emulsion containing surfactant turns clear and clarified. Demulsification efficiency, capacity, and recyclability of this positively charged chitosan–PAM sponge to oil-in-water emulsions stabilized by different types of surfactants including anionic, nonionic, and cationic surfactants, has been investigated for further practical evaluation. A “breathing demulsification” mechanism is presented to explain this attractive demulsified process. The effective contact area between emulsion and sponge is increased by the microcomposite and nanocomposite hierarchical structure of the chitosan–PAM free-standing sponge. Then, interfacial interactions, size effect, and strain act as the driving force for the demulsification of the emulsified droplets at the surface of the sponge.