Highly efficient fabrication of self-extinguished flame-retardant and underwater superoleophobic coatings through layer-by-layer method

In this paper, a layer-by-layer method was used to firstly prepare self-extinguished flame-retardant and multifunctional superwetting coatings, which were consisted of alternative charge adsorption of branched poly (ethylenimine) (BPEI), phytic acid (PA), and ammonium polyphosphate (APP) with only three bilayers. When the polyethylene terephthalate (PET) fabric was assembled with the coating, it obtained superior self-extinguished flame retardance after ignition for 5 s. The mesh deposited with the coatings showed instant superhydrophilicity and superior underwater superoleophobicity in various water/corrosive environments only if the top layer was PA. The coated mesh presented extremely stable and highly efficient oil-water separation capability with efficiency larger than 99%, which could quickly separate a series of immiscible mixtures of oil and water (also include corrosive liquids of strong acid/alkali/aqua regia, hot water, etc). Moreover, owing to its in-air superhydrophilicity and underwater superoleophobicity, and instant underoil superhydrophilicity, the coated mesh also could simultaneously efficiently separate various oil-in-water and water-in-oil emulsions. In addition, the coatings showed high absorption capabilities for various heavy metal ions due to the strong chelation ability of PA and BPEI molecules, which efficiently and successfully removed heavy metal ions from water.