Distinguishing the (Almost) Indistinguishable

Zeolite and zeolite-like materials--crystalline solids containing a large number of uniformly sized pores with diameters of <2 nm--can discriminate between molecules that can enter the pore space and those that cannot on the basis of their size and shape. In his Perspective, Davis highlights the report by Lai et al., who have synthesized the first zeolite membrane that can separate para-xylene molecules from the only slightly larger ortho-xylene molecules, with high permeance of the para-xylene. The membrane was prepared using a clever integration of a number of synthetic steps and consists of a thin layer of zeolite ZSM-5 that is oriented to allow molecular transport through straight pores running perpendicular to the membrane surface.