Channeling carbon dioxide The separation of gas molecules with physisorbents can be challenging because there is often a tradeoff between capacity and selectivity. Zhou et al. report a template-free hydrothermal synthesis of the one-dimensional channel zeolite mordenite, in which some silicon was replaced by iron. Rather than forming a powder that requires further shaping, this mechanically stable material self-assembled into monoliths. Iron atoms bound in tetrahedral zeolite sites narrowed the channels and enabled the size-exclusion separation of carbon dioxide (CO ₂ ) over nitrogen (N ₂ ) and methane. High CO ₂ uptake and highly efficient CO ₂ –N ₂ separation was demonstrated for both dry and humid conditions. Science , aax5776, this issue p. 315