ABSTRACT
Metal-organic frameworks (MOFs) are a rapidly growing class of materials that offer great promise in various applications. However, the synthesis remains challenging: for example, a range of crystal structures can often be accessed from the same building blocks, which complicates the phase selectivity. Likewise, the high sensitivity to slight changes in synthesis conditions may cause reproducibility issues. This is crucial, as it hampers the research and commercialization of affected MOFs. Here, it presents the first-ever interlaboratory study of the synthetic reproducibility of two Zr-porphyrin MOFs, PCN-222 and PCN-224, to investigate the scope of this problem. For PCN-222, only one sample out of ten was phase pure and of the correct symmetry, while for PCN-224, three are phase pure, although none of these show the spatial linker order characteristic of PCN-224. Instead, these samples resemble dPCN-224 (disordered PCN-224), which has recently been reported. The variability in thermal behavior, defect content, and surface area of the synthesised samples are also studied. The results have important ramifications for field of metal-organic frameworks and their crystallization, by highlighting the synthetic challenges associated with a multi-variable synthesis space and flat energy landscapes characteristic of MOFs.
ABSTRACT
Initially proposed by Lovric and Scholz to explain redox reactions in solid-phase voltammetry, the Scholz model's applications have expanded to redox reactions in various materials. As an extension of the Cottrell equation, the Scholz model enabled the quantification of electron hopping and ion diffusion with coefficients, De and Di, respectively. Research utilizing the Scholz model indicated that, in most cases, a huge bottleneck results from the ion diffusion which is slower than electron hopping by orders of magnitude. Therefore, electron and ion motion can be tuned and optimized to increase the charge transport and conductivity through systematic investigations guided by the Scholz model. The strategy may be extended to other solid-state materials in the future, e.g., battery anodes/cathodes. In this Perspective, the applications of the Scholz model in different materials will be discussed. Moreover, the limitations of the Scholz model will also be introduced, and viable solutions to those limitations discussed.
ABSTRACT
Living creatures are continuous sources of inspiration for designing synthetic materials. However, living creatures are typically different from synthetic materials because the former consist of living cells to support their growth and regeneration. Although natural systems can grow materials with sophisticated microstructures, how to harness living cells to grow materials with predesigned microstructures in engineering systems remains largely elusive. Here, an attempt to exploit living bacteria and 3D-printed materials to grow bionic mineralized composites with ordered microstructures is reported. The bionic composites exhibit outstanding specific strength and fracture toughness, which are comparable to natural composites, and exceptional energy absorption capability superior to both natural and artificial counterparts. This report opens the door for 3D-architectured hybrid synthetic-living materials with living ordered microstructures and exceptional properties.