Designing superoleophobic and flame retardant coatings from fly ash based on layer-by-layer approach

The superoleophobic, superhydrophilic, and flame-retardant coatings were obtained through layer-by-layer (LBL) technology using fly ash (FA) as the core. Chitosan (CS), phytic acid (PA), and fluorosurfactant (FS50) were assembled onto FA by LBL assembly using the principle of electrostatic adsorption. The CS and PA were recycled assembled on FA core for 10 layers, which was further deposited with FS50 molecules as the final layer (marked as FA@CS-PA10@FS50). Multifunctional coatings consisted of the FA@CS-PA10@FS50 powders and polymer binders were formed and could be used on a variety of substrates of various shape and size. The obtained coatings presented superoleophobicity, superhydrophilicity, and flame retardance. The contact angles (CAs) of coated substrates were all greater than 150 degrees towards various oils (rapeseed oil, diesel, hexadecane, and dodecane), while achieved water CAs as low as 0 degrees. The as-fabricated coatings could efficiently separate different oil/water mixtures and lotions while avoiding pollution of the separated materials. The coatings also achieved superior flame retardance, and the fire was self-extinguished within 13 s. Moreover, it also obtained excellent mechanical durability.