Freeze casting, also known as ice templating, is a particularly versatile technique that has been applied extensively for the fabrication of well‐controlled biomimetic porous materials based on ceramics, metals, polymers, biomacromolecules, and carbon nanomaterials, endowing them with novel properties and broadening their applicability. The principles of different directional freeze‐casting processes are described and the relationships between processing and structure are examined. Recent progress in freeze‐casting assisted assembly of low dimensional building blocks, including graphene and carbon nanotubes, into tailored micro‐ and macrostructures is then summarized. Emerging trends relating to novel materials as building blocks and novel freeze‐cast geometries—beads, fibers, films, complex macrostructures, and nacre‐mimetic composites—are presented. Thereafter, the means by which aligned porous structures and nacre mimetic materials obtainable through recently developed freeze‐casting techniques and low‐dimensional building blocks can facilitate material functionality across multiple fields of application, including energy storage and conversion, environmental remediation, thermal management, and smart materials, are discussed.

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Amorphous polymer-derived silicon oxycarbide (SiOC) is an attractive candidate for Li-ion battery anodes, as an alternative to graphite, which is limited to a theoretical capacity of 372 mAh/g. However, SiOC tends to exhibit poor transport properties and cycling performance as the result of sparsely distributed carbon clusters and inefficient active sites. To overcome these limitations, we designed and fabricated a layered graphene/SiOC heterostructure by solvent assisted infiltration of a polymeric precursor into a modified 3D graphene aerogel skeleton. The use of a high-melting-point solvent facilitated the precursor's freeze-drying, which following pyrolysis yielded SiOC as a layer supported on the surface of nitrogen doped reduced graphene oxide aerogels. The fabrication method employed here modifies the composition and microstructure of the SiOC phase. Among the studied materials, highest levels of performance were obtained for a sample of moderate SiOC content, in which the graphene network constituted 19.8wt% of the system. In these materials a stable reversible charge capacity of 751 mAh/g was achieved at low charge rates. At high charge rates of 1480 mA/g the capacity retention was ~95% (352 mAh/g) after 1000 consecutive cycles. At all rates, Colombic efficiencies >99% were maintained following the first cycle. Performance across all indicators was majorly improved in the graphene aerogel/SiOC nanocomposites, compared with unsupported SiOC. Performance was attributed to mechanisms across multiple lengthscales. The presence of oxygen rich SiO4−xCx tetrahedra units and a continuous free-carbon network within the SiOC provide sites for reversible lithiation, while high ionic and electronic transport is provided by the layered graphene/SiOC heterostructure.

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.

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We have developed a new sol–gel route to synthesise Al2O3–SiO2 composite aerogels with different alumina/silica (Al/Si) molar ratios using an inexpensive inorganic salt.