Surface modification of melamine sponges for pH-responsive oil absorption and desorption

Inspired by the development of smart oil/water separation materials, a pH responsive melamine sponge has been obtained by grafting poly (4-vinylpyridine) on the skeleton surface through atom transfer radical polymerization. Through scanning electron microscopy and x-ray photoelectron spectroscopy, the successful grafting of poly (4-vinylprridine) onto the melamine sponge has been confirmed. When contacting with different pH water droplets in air, the as-prepared product shows excellent switchable wettability between super-hydrophilicity (0°) and highly hydrophobicity (135°). Meanwhile, this responsive sponge also exhibits super-hydrophilic/oleophobic property underwater at pH   =   1.0, and highly hydrophobic/super-oleophilic property in neutral solution at pH   =   7.0. Furthermore, the excellent responsiveness is remained after five cycle water contact angle tests between two different pH stages at pH 1.0 and 7.0. The modified melamine sponges could not only absorb the oil from the oily water at pH   =   7.0, but also quickly release the absorbed oil underwater at pH   =   1.0 without leaving any residues and hurting the environment nearly, showing a good potential in controlled oil/water separation and oil recovery.