Membrane science emerging as a convergent scientific field with molecular origins and understanding, and global impact.

Membrane separations science concerns the selective transport of chemical species across molecularly designed barriers that are effectively two-dimensional. This interdisciplinary field has become the focus of many scientific communities in recent years, including researchers in supramolecular chemistry, materials science, environmental science, polymer science (chemistry and physics), colloid and interface science, nanofluidics, structural biology, and biophysics. The great attraction of membrane science is the connection and visibility of the broad impacts of the final application, which is even apparent while working at the smallest scales. The “big picture” challenges that membrane science seeks to address include water purification, wastewater treatment, desalination, carbon dioxide capture, food and dairy processing, removal of pathogens (including viruses), hydrocarbon processing, and resource recovery from wastes, among a wide variety of applications. These topics span many urgent societally relevant themes of clean water and air, public health, climate change, waste minimization, and energy production. The assembled special issue of PNAS illustrates the convergence emerging in the field across scales (from molecular self-assembly to industrial scale separations), disciplines (from biophysics to industrial scale hydrocarbon separations), materials (from membrane proteins to graphene), and approaches (molecular analysis to economic analysis). The issue also highlights emerging areas of interest, including biomimetics, ion–ion separations, membrane process residuals (brine) treatment, hydrocarbon separations using membranes, and technologies for wastewater resource recovery. The papers are organized by applications, and within each application area by scale and approach. In general, this special issue is roughly divided into three main sections: biologically inspired ideas and applications to separation processes in aqueous liquids, gas and hydrocarbon separations, and improving current membranes and membrane processes. The first section of this special issue is on biologically inspired ideas for designing more selective and energy-efficient membranes. A unique feature of biological membranes is the exceptional ion selectivity seen in membrane proteins … [↵][1]1To whom correspondence may be addressed. Email: manish.kumar{at}utexas.edu or hastone{at}Princeton.edu. [1]: #xref-corresp-1-1