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The removal of carbon dioxide (CO 2 ) from acetylene (C 2 H 2 ) is a critical industrial process for manufacturing high-purity C 2 H 2 . However, it remains challenging to address the tradeoff between adsorption capacity and selectivity, on account of their similar physical properties and molecular sizes. To overcome this difficulty, here we report a novel strategy involving the regulation of a hydrogen-bonding nanotrap on the pore surface to promote the separation of C 2 H 2 /CO 2 mixtures in three isostructural metal-organic frameworks (MOFs, named MIL-160, CAU-10H, and CAU-23, respectively). Among them, MIL-160, which has abundant hydrogen-bonding acceptors as nanotraps, can selectively capture acetylene molecules and demonstrates an ultrahigh C 2 H 2 storage capacity (191 cm 3 g -1 , or 213 cm 3 cm -3 ) but much less CO 2 uptake (90 cm 3 g -1 ) under ambient conditions. The C 2 H 2 adsorption amount of MIL-160 is remarkably higher than those for the other two isostructural MOFs (86 and 119 cm 3 g -1 for CAU-10H and CAU-23, respectively) under the same conditions. More importantly, both simulation and experimental breakthrough results show that MIL-160 sets a new benchmark for equimolar C 2 H 2 /CO 2 separation in terms of the separation potential (Δ q break H 2 H 2 productivity (6.8 mol/kg). In addition, in situ H 2 H 2 H 2 H 2 /CO 2 selectivity. This work provides a novel and powerful approach to address the tradeoff of this extremely challenging gas separation.

The defect concentration in the prototypical metal-organic framework UiO-66 can be well controlled during synthesis, leading to precisely tunable physicochemical properties for this structure. However, there has been a long-standing debate regarding the nature of the compensating species present at the defective sites. Here, we present unambiguous spectroscopic evidence that the missing-linker defect sites in an ambient environment are compensated with both carboxylate and water (bound through intermolecular hydrogen bonding), which is further supported by ab initio calculations. In contrast to the prevailing assumption that the monocarboxylate groups (COO - ) of the modulators form bidentate bonding with two Zr 4+ sites, COO - is found to coordinate to an open Zr 4+ site in an unidentate mode. The neighboring Zr 4+ site is terminated by a coordinating H 2 O molecule, which helps to stabilize the COO - group. This finding not only provides a new understanding of defect termination in UiO-66, but also sheds light on the origin of its catalytic activity.

We report the synthesis and characterization of a new class of 2D-covalent organic frameworks, called COFamides, whose layers are held together by amide hydrogen bonds. To accomplish this, we have designed monomers with a nonplanar structure that arises from steric crowding, forcing the amide side groups out of plane with the COF sheets orienting the hydrogen bonds between the layers. The presence of these hydrogen bonds provides significant structural stabilization as demonstrated by comparison to control structures that lack hydrogen bonding capability, resulting in lower surface area and crystallinity. We have characterized both azine and imine-linked versions of these COFs, named COFamide-1 and -2, respectively, for their surface areas, pore sizes, and crystallinity. In addition to these more conventional characterization methods, we also used variable temperature infrared spectroscopy methods and van der Waals density functional calculations to directly observe the presence of hydrogen bonding.