Fabrication of superhydrophobic filter paper and foam for oil–water separation based on silica nanoparticles from sodium silicate

We demonstrate the synthesis of hydrophobic silica nanoparticles from sodium silicate and their application in separation of the oil–water mixture. For this, hydrophobic silica nanoparticles of size 35 ± 8 nm were initially synthesized by sol–gel method using sodium silicate and trimethylchlorosilane, and further deposited on commercially available filter paper and polyurethane foam by dip coating technique. The coating cycles were optimized for filter paper to ensure that fibers of the filter paper have been completely covered with hydrophobic silica nanoparticles to provide an ideal porous superhydrophobic/superoleophilic framework for gravity based separation of oil–water mixtures. It was confirmed by water contact angle of ~155° and sliding angle <5°. Whereas the superhydrophobic polyurethane foam was utilized for collection of oil from oil–water mixtures via absorption. The capability of these materials to separate oil from water was tested against the mixtures of water with n-hexane, gasoline, diesel, kerosene oil and engine oil. Moreover, the produced particles can also be used for fabrication of semi-transparent superhydrophobic surfaces.