Energy efficient, ultrahigh-flux separation of oily pollutants from water with superhydrophilic nanoscale metal-organic framework architectures.

The rising demand for clean water for a growing and increasingly urban global population is one of the most urgent issues of our time. Particularly, the increasing generation of wastewater by cities and industrial sources requires the development of novel platforms for separating contaminants such as oils. Here, we introduce the synthesis of a unique nanoscale architecture of pillar-like Co-CAT-1 metal-organic framework (MOF) crystallites on gold-coated woven stainless steel meshes with large, 50 µm apertures. These nanostructured mesh surfaces feature superhydrophilic and underwater superoleophobic wetting properties, allowing for gravity-driven, highly efficient oil-water separation featuring water fluxes of up to nearly one million L m-2 h-1. Water physisorption experiments reveal the hydrophilic nature of Co-CAT-1 with a total water uptake at room temperature of 470 cm3 g-1.  Furthermore, semiempirical molecular orbital calculations shed light on water affinity of the inner and outer pore surfaces. The MOF-based membranes enable high separation efficiencies for a number of liquids tested, including the notorious water pollutant, crude oil, affording chemical oxygen demand (COD) concentrations below 25 mg L-1 of the effluent. Our results demonstrate the great impact of suitable nanoscale surface architectures as a means of encoding on-surface extreme wetting properties, yielding energy-efficient water-selective large-aperture membranes. The extremely low resistance to flow and the resulting enormous flux capabilities hold great promise for water cleanup on a massive scale and for the design of practical, low-cost water purification devices that can be operated without external power source and without moving parts.