A pH-responsive superwetting nanostructured copper mesh film for separating both water-in-oil and oil-in-water emulsions

Recently, superwetting separating materials for emulsified oil/water mixtures have become a new research focus due to their special advantages such as high efficiency and high flux. So far, although lots of superhydrophobic/superoleophilic and superhydrophilic/underwater superoleophobic films have been prepared for the separation of water-in-oil and oil-in-water emulsions, respectively, smart films that can switch between the above two wetting states and be suitable for the separation of both the two types of emulsions are still rare. Herein, we advance a simple strategy by creating a nanostructure and attaching responsive molecules onto the copper mesh substrate, and report a novel pH-responsive nanostructured copper mesh film. Results indicate that the nanostructure can not only effectively adjust the substrate pore size from the microscale to the nanoscale to meet the requirements for emulsion separation, but can also enhance the surface wettabilities. Combined with the responsive molecules, the film wettability can be switched reversibly between the superhydrophobic/superoleophilic and the superhydrophilic/underwater superoleophobic states. As a result, both water-in-oil and oil-in-water emulsions can be separated on the film with high efficiency and high flux due to the synergy effect between the nanoscale pore structure and the switchable wettability. Given the as-prepared film has such a smart ability, it is believed to be potentially useful in many practical applications, such as sewage treatment and oil recovery.