Efficient separation of biphasic mixtures, especially oil/water mixtures, is critical to many applications, including wastewater treatment and chemical recovery. In search of smart materials for complex separations, such as on-demand operations, Kening Sun and co-workers, Harbin Institute of Technology, Heilongjiang, China, have developed a copper mesh film that can switch between different states of wettability in response to pH. The mesh is funtionalized with Cu(OH)₂ nanorods and then coated with thiols. With appropriate pore sizes, the resulting films turn from superhydrophobic to superhydrophilic when pH changes from 7 to 12. This allows water, but not oil, to go through.

The researchers have demonstrated the convenient pH-controlled separation of both immiscible and emulsive water/oil systems using this new type of mesh. In addition, when combined with other techniques, the switchable copper mesh may be used in microfluidic devices and controllable filtration, among others.

• pH-Controllable On-Demand Oil/Water Separation on the Switchable Superhydrophobic/Superhydrophilic and Underwater Low-Adhesive Superoleophobic Copper Mesh Film,
  Zhongjun Cheng, Jingwen Wang, Hua Lai, Ying Du, Rui Hou, Chong Li, Naiqing Zhang, Kening Sun,
  Langmuir 2015.
  DOI: 10.1021/la503676a