Nanocasting of carbon replicas of siliceous micro-or mesoporous materials has gained a lot of interest during the last years. Micro-and mesoporous carbons, respectively, are, depending on their pore size, interesting materials for a wide range of applications, including hydrogen storage, doublelayer capacitors, molecular separation, and catalysis. Recently, the synthesis of highly ordered micro-and mesoporous carbons possessing a narrow pore size distribution has been described. [1,2] Here, mesoscopically ordered silica is impregnated with a carbon precursor, which is subsequently carbonized under non-oxidizing conditions. Porous carbons are finally obtained through dissolution of the silica framework. In order to maintain the structural integrity of the thus prepared carbon matrix, the host matrix should have an interconnected porosity. Thus, suitable zeolites, [3] MCM-48, [2,4] SBA-1, [5] mesocellular foams, [6] SBA-15, [7] and HMS [8] (hexagonal mesoporous silica) materials, which all possess a three-dimensional (3D) interconnected porosity, have been found to be suitable template structures. To date, however, most of the carbon materials reported have been obtained as powders, with only a few exceptions. [9] This fact may limit the applicability of these materials when macroscopic morphologies, such as chromatographic columns or membrane reactors, are required. The present communication is, to the best of our knowledge, the first to describe the preparation of monolithic carbon possessing a hierarchical bimodal meso-and macroporosity. In a series of papers, Nakanishi et al. [10] have described a sol±gel synthesis route to monolithic silica possessing a bimodal, hierarchical meso-and macroporous structure. This type of monolith is now commercially available as a chromatographic column under the brand name Chromolith. The key to the synthesis is to balance the kinetics of phase separation versus gelation of the silica under acidic conditions; this can be achieved by the use of either homo-polymers or block co- COMMUNICATIONS

Colloidal lead-free perovskite nanocrystals have recently received extensive attention because of their facile synthesis, the outstanding size-tunable optoelectronic properties, and less or no toxicity in their commercial applications. Tin (Sn) has so far led to the most efficient lead-free solar cells, yet showing highly unstable characteristics in ambient conditions. Here, we propose the synthesis of all-inorganic mixture Sn-Ge perovskite nanocrystals, demonstrating the role of Ge 2+ in stabilizing Sn 2+ cation while enhancing the optical and photophysical properties. The partial replacement of Sn atoms by Ge atoms in the nanostructures effectively fills the high density of Sn vacancies, reducing the surface traps and leading to a longer excitonic lifetime and increased photoluminescence quantum yield. The resultant Sn-Ge nanocrystals-based devices show the highest efficiency of 4.9 %, enhanced by nearly 60 % compared to that of pure Sn nanocrystals-based devices.

In this paper, successful preparations of hierarchically porous cobalt oxide (Co3O4), tin oxide (SnO2), and manganese oxide (MnO2 or Mn2O3) monoliths by the nanocasting route are described. The starting SiO2 monoliths used as molds were prepared through a straightforward sol−gel process and contain macropores with adjustable size in the range of 0.5−30 μm as well as mesopores which can be altered between 3 and 30 nm. In the nanocasting process, the silica monoliths are impregnated with a metal salt solution, which is subsequently decomposed to a metal oxide by heat treatments to form a SiO2/MeO x composite. Finally, the silica part can be removed by leaching in either NaOH or hydrofluoric acid. The composite and replica structures have been characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, nitrogen physisorption, and transmission electron microscopy. The nanocast monoliths are positive replicas of the silica structure on the micrometer scale, meaning that the replicas have the same macroscopic morphology and macropore structure as the starting silica monoliths. In contrast, on the nanometer scale the replicated structure becomes an inverse (or a negative replica) of the silica mesopore structure. Furthermore, all prepared metal oxide monoliths are fully crystalline. When the hierarchical structure of the monoliths is combined with the unique chemical or physical properties of the used metal oxides, these novel materials have great potential in application areas such as catalysis, HPLC, and sensor materials.

Nanocast carbon monoliths exhibiting a three‐ or four‐modal porosity have been prepared by one‐step impregnation, using silica monoliths containing a bimodal porosity as the scaffold. Combined volume and surface templating, together with the controlled synthesis of the starting silica monoliths used as the scaffold, enables a flexible means of pore‐size control on several length scales simultaneously. The monoliths were characterized by nitrogen sorption, scanning electron microscopy, transmission electron microscopy, and mercury porosimetry. It is shown that the carbon monoliths represent a positive replica of the starting silica monoliths on the micrometer length scale, whereas the volume‐templated mesopores are a negative replica of the silica scaffold. In addition to the meso‐ and macropores, the carbon monoliths also exhibit microporosity. The different modes of porosity are arranged in a hierarchical structure‐within‐structure fashion, which is thought to be optimal for applications requiring a high surface area in combination with a low pressure drop over the material.