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. Graphical Preparation process of halogen-free magnetic superhydrophobic flame-retardant H-Fe 3 O 4 /PU sponge.