In order to measure the oil–water separation efficiency, a sensitive method was used. When the modified cotton was brought into contact with a mixture of hexane (colored with oil red O) and 0.05 M AgNO3 aqueous solution, the oil was quickly absorbed by the modified cotton in a few seconds. Afterword, the absorbed oil was squeezed on the surface of 0.1 M NaCl aqueous solution. It is well known that Ag+ is very sensitive to Cl ions. Even if a tiny amount of AgNO3 was contact with the NaCl, a white precipitate was generated. As shown in Fig. 9a–c, the NaCl aqueous solution remained clear, indicating high oil–water separation efficiency. However, a white precipitate was formed when raw cotton was employed (Fig. 9d–f). In addition, the graphene coated cotton can also be used to quickly absorb chloroform, which was dyed with oil red O at the bottom of water (Fig. 10).
Mechanical squeezing procedure [4], burning processes [10], distillation [29] were usually employed for oil removal, all of which require long times for the separation of large amounts of oil pollutants from water surface. Thereby, fast oil removal is needed for the absorption of spill oil in water. In order to abbreviate the time needs for oil–water separation; a vacuum system was introduced (Fig. 11). We connected graphene coated cotton to a tube and placing it at the oil–water interface. Subsequently, we employed the vacuum system to remove the oil contaminant from water surface. Ultimately, the oil was collected in this way, with time increasing; water cannot permeate the filter. Hence, the graphene coated cotton can be used in large-scale removal of oils from water. Most interestingly, oil contaminant adsorbed by graphene coated cotton can be removed by soaking in the ethanol, after drying the recycling process was achieved. The facile fabrication method of graphene coated cotton indicating that they are promising candidates for oil-spill cleanup.