Preparation of Halogen‐Free Magnetic Superhydrophobic Flame‐Retardant PU‐Based Sponge for Oil–Water Separation

In this work, in order to achieve the halogen‐free magnetic superhydrophobic flame‐retardant PU‐based sponge for oil–water separation, the pure PU sponge was first coated with the flame‐retardant alternate cationic poly(ethylene imine) (PEI) and anionic phytic acid (PA) layers using a self‐assembly method, and then was further covered by the hydrophobic hexadecyltrimethoxysilane (HDTMS)‐modified magnetic Fe 3 O 4 nanoparticles using the hydrophobic Sylgard 184 siloxane adhesive to form a series of H‐Fe 3 O 4 /PU sponges. The structure of the resulting H‐Fe 3 O 4 /PU sponges was studied by scanning electron microscope, energy‐dispersive x‐ray mapping, Fourier transform infrared spectroscope, wide‐angle x‐ray diffraction, x‐ray photoelectron spectroscope, Raman spectroscope, and thermogravimetry analysis, confirming the existence of PEI, PA, HDTMS, Fe 3 O 4 nanoparticles, and Sylgard 184 siloxane adhesive on the PU sponge surface. The H‐Fe 3 O 4 /PU sponge obtained through seven layers of self‐assembly not only was superhydrophobic with the water contact angle of 153 o and magnetic with the magnetization strength of 7.9 emu/g at 50,000 Oe but also has the flame‐retardancy characteristic. In addition, it was found that the oil–water separation could be realized by direct adsorption and gravity filtration using the H‐Fe 3 O 4 /PU sponge, and the reusing of the H‐Fe 3 O 4 /PU sponge for oil adsorption was stable due to its good mechanical property.