Efficient demulsification of ultralow-concentration crude oil-in-water emulsion by three-dimensional superhydrophilic channels

Efficient extraction of crude oil, the major energy resource of current concern and high demand worldwide, is of paramount importance in both energy and environmental fields. However, it remains a great challenge to separate the crude oil-in-water emulsions with an ultralow oil content of <200 ppm. Here, the three-dimensional and superwetting channels are developed by coating titanium foams with anodic TiO2 nanotube arrays. The channels render superhydrophilic and underwater superoleophobic feature, which enables rapid formation of water channels that expel the oil droplets. A high separation efficiency of similar to 96.8% and low total organic carbon content of similar to 6 ppm are thus achieved for the ultralow-concentration crude oil-in-water emulsions. The pressure and time dependence of the separation process is systematically studied with a critical pressure of 12.25 kPa. Such a high performance is close to the theoretical limit imposed by the ultralow concentration, and shows obvious advances over either organic membranes or inorganic frameworks.