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Carbon nanostructures in form of 3D carbon foams are mainly popular in materials community because of their ultralow densities, variable morphologies, and remarkable properties, etc. One of these foams is Aerographite, which exhibits a tetrapodal interconnected morphology. Similar to other synthetic carbon structures, the lattice defects are formed during the synthesis of Aerographite, which can be healed by a post-thermal treatment. Aerographite shows a property dependency on wall thickness (number of graphitic layers), which affects both, the electrical and mechanical properties. In this study, the wall thickness is tailored by varying of the total reaction time during the replication process. The influence of the thermal treatment of Aerographite on its mechanical performance in an Aerographite-epoxy nanocomposite, by determining the fracture toughness (K1C) in three-point bending tests (SEN-3PB), is investigated. An increase of the fracture toughness with increasing wall thickness is observed for untreated Aerographite. The graphitization of Aerographite leads to a reduction of the mechanical properties, by increasing the crystalline width. Consequently, the measured fracture toughness is dependent on the graphitization, the calculated crystalline width and the wall thickness of tubes in the hollow Aerographite tetrapodal network. Finally, based on these relations, a phenomenological mechanical failure model is developed and briefly discussed.

The coating of porous scaffolds with nanoparticles is crucial in many applications, for example to generate scaffolds for catalysis or to make scaffolds bioactive. A standard and well-established method for coating surfaces with charged nanoparticles is electrophoresis, but when used on porous scaffolds, this method often leads to a blockage of the pores so that only the outermost layers of the scaffolds are coated. In this study, the electrophoretic coating process is monitored in situ and the kinetics of nanoparticle deposition are investigated. This concept can be extended to design a periodic electrophoretic deposition (PEPD) strategy, thus avoiding the typical blockage of surface pores. In the present work we demonstrate successful and homogeneous electrophoretic deposition of hydroxyapatite nanoparticles (HAn, diameter ≤200 nm) on a fibrous graphitic 3D structure (ultralightweight aerographite) using the PEPD strategy. The microfilaments of the resulting scaffold are covered with HAn both internally and on the surface. Furthermore, protein adsorption assays and cell proliferation assays were carried out and revealed that the HAn-decorated aerographite scaffolds are biocompatible. The HAn decoration of the scaffolds also significantly increases the alkaline phosphatase activity of osteoblast cells, showing that the scaffolds are able to promote their osteoblastic activity.

Carbon foams are characterised by their high specific surface areas (SSAs) in combination with ultra-low densities. Due to these unique properties, carbon foams are particularly suitable for applications such as catalysts, where high surface area is essential. Metals or metal oxides are added to the carbon structure to increase the catalytically effectiveness. In this study, we present a new and efficient manufacturing method, with the potential for a large-scale production resulting in a 3D hierarchical carbon foam with incorporated catalytically metal or metal oxides. The manufacturing starts with the preparation of a ceramic zinc oxide (ZnO) precursor powder containing catalytically active materials (Me/MexOy), uniaxial pressing and sintering yielding to templates. The replication of the template morphology into a hollow carbon structure in the chemical vapour deposition (CVD) process, in which the catalytic materials remain in the carbon foam. Furthermore, the morphology of these structures and the grain size distribution are investigated using scanning electron (SEM) and transmission electron microscopy (TEM). The final amount of catalytically particles is analysed by thermal gravimetric analysis (TGA). Finally, the SSA of the synthesised carbon-based catalysts is measured by Brunauer-Emmett-Teller (BET) method.

Funder: Deutsche Forschungsgemeinschaft (German Research Foundation); doi: https://doi.org/10.13039/501100001659, Laser diodes are efficient light sources. However, state-of-the-art laser diode-based lighting systems rely on light-converting inorganic phosphor materials, which strongly limit the efficiency and lifetime, as well as achievable light output due to energy losses, saturation, thermal degradation, and low irradiance levels. Here, we demonstrate a macroscopically expanded, three-dimensional diffuser composed of interconnected hollow hexagonal boron nitride microtubes with nanoscopic wall-thickness, acting as an artificial solid fog, capable of withstanding ~10 times the irradiance level of remote phosphors. In contrast to phosphors, no light conversion is required as the diffuser relies solely on strong broadband (full visible range) lossless multiple light scattering events, enabled by a highly porous (>99.99%) non-absorbing nanoarchitecture, resulting in efficiencies of ~98%. This can unleash the potential of lasers for high-brightness lighting applications, such as automotive headlights, projection technology or lighting for large spaces.

Aerographite is a 3D interconnected carbon foam with a hollow tetrapodal morphology. The properties of Aerographite, especially the electrical conductivity, are strongly dependent on the wall thickness, the degree of graphitization and the ambient temperature. The tailored-carbon-structures like wall thickness (number of layer) and state of graphitization determine the electrical properties of the carbon foam. The wall thickness of Aerographite can be controlled by a stepwise reduction of solid arms of sacrificial template with respect to synthesis time, in which wall thicknesses between 3 and 22 nm can be easily achieved. The decreasing of the wall thickness leads to a reduced electrical conductivity of untreated Aerographite. Contrary, the conductivity of annealed Aerographite increased with reducing of the wall thicknesses. The morphology of Aerographite has been analyzed via scanning electron (SEM), transmission electron (TEM) microscopy and Raman spectroscopy. Furthermore, the dependency of the electrical conductivity on the temperature is measured and based on this the band gap energy is calculated. As a result, Aerographite shows a metallic conductive behaviour which can be changed semiconducting nature by further high temperature treatment.

In the present work, we report on development of three-dimensional flexible architectures consisting of an extremely porous three-dimensional Aerographite (AG) backbone decorated by InP micro/nanocrystallites grown by a single step hydride vapor phase epitaxy process. The systematic investigation of the hybrid materials by scanning electron microscopy demonstrates a rather uniform spatial distribution of InP crystallites without agglomeration on the surface of Aerographite microtubular structures. X-ray diffraction, transmission electron microscopy and Raman scattering analysis demonstrate that InP crystallites grown on bare Aerographite are of zincblende structure, while a preliminary functionalization of the Aerographite backbone with Au nanodots promotes the formation of crystalline In2O3 nanowires as well as gold-indium oxide core-shell nanostructures. The electromechanical properties of the hybrid AG-InP composite material are shown to be better than those of previously reported bare AG and AG-GaN networks. Robustness, elastic behavior and excellent translation of the mechanical deformation to variations in electrical conductivity highlight the prospects of AG-InP applications in tactile/strain sensors and other device structures related to flexible electronics.

In this work, individual hollow and mesoporous graphitic microtubes were integrated into electronic devices using a FIB/SEM system and were investigated as gas and vapor sensors by applying different bias voltages (in the range of 10 mV–1 V). By increasing the bias voltage, a slight current enhancement is observed, which is mainly attributed to the self-heating effect. A different behavior of ammonia NH3 vapor sensing by increasing the applied bias voltage for hollow and mesoporous microtubes with diameters down to 300 nm is reported. In the case of the hollow microtube, an increase in the response was observed, while a reverse effect has been noticed for the mesoporous microtube. It might be explained on the basis of the higher specific surface area (SSA) of the mesoporous microtube compared to the hollow one. Thus, at room temperature when the surface chemical reaction rate (k) prevails on the gas diffusion rate (DK) the structures with a larger SSA possess a higher response. By increasing the bias voltage, i.e., the overall temperature of the structure, DK becomes a limiting step in the gas response. Therefore, at higher bias voltages the larger pores will facilitate an enhanced gas diffusion, i.e., a higher gas response. The present study demonstrates the importance of the material porosity towards gas sensing applications.