Cotton fabrics modified with tannic acid/1-eicosanamine grafting layer for oil/water separation

The wettability of the surface of hydrophilic cotton fabrics was modified using a one-step protocol with tannic acid (TA) to provide its excess catechol groups to be grafted with 1-eicosanamine at pH 8.5 and room temperature with catalysts CuSO₄/H₂O₂. The modification over the synthesis conditions revised the contact angles of water and diiodomethane droplets from 132.68 ± 0.49° to 143.95 ± 0.80° and from 100.08°±1.42° to 82.96 ± 1.38°, respectively. The corresponding dispersive of the so-yielded cotton surface ranged from 8.6 to 16.0 mJ/m², and the polar components ranged from 0.08 to 2.7 mJ/m², much lower than polytetrafluoroethylene. The modified cotton fabrics are omniphobic and can repel water and commercial oil products. The absorption tests revealed that the modified cotton fabrics absorbed 1.10 g hexane/g cotton by contacting hexane (top)-water (bottom) layers and absorbed 1.26 g hexane/g cotton by contacting water first for 30 s, then hexane for another 30 s. The modified fabrics reveal good absorption reusability as hexane absorbent is even pre-saturated with water. This conclusion is also valid for commercial unleaded gasoline #95 and diesel. A parametric study revealed that the added catalysts and prolonged reaction time would enhance the hydrophobicity of the surface. These modified cotton fabrics can absorb oil from water and oil spills. Mechanisms corresponding to this observation are discussed.