Underoil superhydrophilic surfaces: water adsorption in metal-organic frameworks

Highly hydrophilic surfaces in oil are usually difficult to prepare due to the high surface tension of water. In nature, sarcocarps such as Chinese yam can reserve water to keep itself fresh. Inspired by the unique wetting properties of sarcocarps, metal-organic frameworks (MOFs) that can capture moisture from the atmosphere spontaneously have been proposed as building blocks for construction of underoil superhydrophilic surfaces. Herein, a mussel-inspired preparation method was adopted to coat HKUST-1 tightly on stainless-steel meshes. The MOF-based surfaces showed remarkable self-cleaning properties to crude oil under water, and could realize high-efficiency, on-demand separation of oil-in-water and water-in-oil emulsions via selective water filtration and adsorption, respectively. Water adsorption in MOFs could be extended to other extreme wettability and interfacial issues.