Highlights Metal–organic frameworks (MOFs) are used to directly initiate the gelation of graphene oxide (GO), producing MOF/rGO aerogels. The ultralight magnetic and dielectric aerogels show remarkable microwave absorption performance with ultralow filling contents. Abstract The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal–organic frameworks (MOFs) and graphene oxide (GO) building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications. Herein, we report a facile route for synthesizing MOF/reduced GO (rGO) aerogels based on the gelation of GO, which is directly initiated using MOF crystals. Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal–oxygen covalent or electrostatic interactions. The MOF/rGO-derived magnetic and dielectric aerogels Fe3O4@C/rGO and Ni-doped Fe3O4@C/rGO show notable microwave absorption (MA) performance, simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5 (− 58.1 dB and 6.48 GHz) and 2.8 mm (− 46.2 dB and 7.92 GHz) with ultralow filling contents of 0.7 and 0.6 wt%, respectively. The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation, which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering. This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.

Construction of nanofluidic devices with an ultimate ion selectivity analogue to biological ion channels has been of great interest for their versatile applications in energy harvesting and conversion, mineral extraction, and ion separation. Herein, we report a three-dimensional (3D) sub-1 nm nanofluidic device to achieve high monovalent metal ion selectivity and conductivity. The 3D nanofluidic channel is constructed by assembly of a carboxyl-functionalized metal–organic framework (MOF, UiO-66-COOH) crystals with subnanometer pores into an ethanediamine-functionalized polymer nanochannel via a nanoconfined interfacial growth method. The 3D UiO-66-COOH nanofluidic channel achieves an ultrahigh K+/Mg2+ selectivity up to 1554.9, and the corresponding K+ conductivity is one to three orders of magnitude higher than that in bulk. Drift-diffusion experiments of the nanofluidic channel further reveal an ultrahigh charge selectivity (K+/Cl–) up to 112.1, as verified by the high K/Cl content ratio in UiO-66-COOH. The high metal ion selectivity is attributed to the size-exclusion, charge selectivity, and ion binding of the negatively charged MOF channels. This work will inspire the design of diverse MOF-based nanofluidic devices for ultimate ion separation and energy conversion.

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Single-atom catalysts (SACs) have shown great potential in the electrochemical oxygen reduction reaction (ORR) toward hydrogen peroxide (H 2 O 2 ) production. However, current studies are mainly focused on 3d transition-metal SACs, and very little attention has been paid to 5d SACs. Here, a new kind of W SAC anchored on a porous O, N-doped carbon nanosheet (W 1 /NO-C) is designed and prepared via a simple coordination polymer-pyrolysis method. A unique local structure of W SAC, terdentate W 1 N 1 O 2 with the coordination of two O atoms and one N atom, is identified by the combination of aberrationcorrected scanning transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption fine structure spectroscopy. Remarkably, the as-prepared W 1 /NO-C catalyzes the ORR via a 2epathway with high onset potential, high H 2 O 2 selectivity in the wide potential range, and excellent operation durability in 0.1 m KOH solution, superior to most of state-of-the-art H 2 O 2 electrocatalysts ever reported. Theoretical calculations reveal that the C atoms adjacent to O in the W 1 N 1 O 2 -C moiety are the most active sites for the 2e -ORR to H 2 O 2 with the optimal binding energy of the HOO* intermediate. This work opens up a new opportunity for the development of high-performance W-based catalysts for electrochemical H 2 O 2 production.