Impact ionization of high-velocity cosmic dust particles has been used as a basic principle for dust detectors in space for many decades. It has provided optimum means to gain insight into the dust environment in the solar system. The Ulysses Dust Detector System provided for the first time impact ionization-based detection of interstellar dust (ISD) in the solar system and discovered surprisingly heavy ISD particles with sizes up to a few microns. Studies based on astronomical observations of the local interstellar medium, on the other hand, sug-gested a much smaller upper limit of around 0.25 mu m (silica) or 1 mu m (graphite) for the size distribution of ISD particles. Therefore, it has been suggested that low-density fluffy dust particles may mimic the impact signals of heavier compact particles. In this work, we discuss a series of impact experiments that have been performed at the Heidelberg dust accelerator facility with the Cosmic Dust Analyzer flight spare unit, to compare the high-velocity impact ionization properties of compact and hollow silicate particles, and carbon aerogel particles with each other and with literature data. The experiments indicate differences in the collected total amount of impact charges and how quickly the charges are collected, between impacts from compact particles and their non-compact coun-terparts. The results of this first study suggest that fluffy particles generate less ions upon impact than their compact counterparts, opposite to the suggested explanation for the heavy ISD particles. Data from the performed impact experiments indicate that a secondary process (e.g. secondary impacts from ejecta or more target material ionization) could be the main cause for the observed differences. These results imply that the previously detected heavy ISD particles may be real. We identify the key problems with the performed dust experiments and advise that future impact ionization instruments should additionally be calibrated with improved low-density fluffy dust particles that better represent the properties of cosmic dust particles.

Gallic acid and urea are used to produce C2NO materials with moderately defined micropores via direct condensation and ring closure. These materials show a unique heterocycle containing carbonaceous structure and feature an unusually high content of heteroatoms (nitrogen and oxygen) lining the insides of pores while having high specific surface areas. The multifunctional carbon materials demonstrate good performance for selective CO2 capture resulting from adjustable porosity and polarizability. In view of the simplicity of the salt flux synthetic method and the advantage of the available sustainable starting synthons, the C2NO framework has potential for use in diverse practical applications.

Microporous carbons of high nitrogen-content and diverse nitrogen-doping sites were studied for CO2 electro-chemical reduction. The unique feature of these carbon materials is the presence of chemically heterogeneous nitrogen species of various reactivity. The systematic surface chemistry study reveals that some nitrogen moiety, even though it has no direct catalytic role in the CO formation during CO2 reduction process, protects the active pyridinic nitrogen from oxidation. In that protection mechanism, these species, instead of pyridines, are oxidized. Therefore, that nitrogen is believed to be responsible for the exceptional stability of the carbon catalysts found in this study. Besides CO and CH4, methanol, formic acid and C-3 hydrocarbons (acetone and propanol) were also detected as reduction products. C-3 hydrocarbons are the first reported products among the metal-free catalysts for CO2 reduction. The results suggest that the C-3 products could be formed when more than one nitrogen sites are located close to each other in the pore space. Furthermore, the differences in the porosity suggest that the microporous structure of the carbons favors the hydrocarbons formation. Eventually, the carbons described herein offer a unique combination of chemical and physical properties, which give further insights into the electrochemical reduction of CO2 on functional carbon materials.

Guest editors Lei Jiang, Markus Antonietti and Nina Fechler introduce this Journal of Materials Chemistry A themed issue on green materials and surfaces.

A high-throughput composite catalyst is prepared from porous carbon with an unconventional nanocube morphology decorated with nickel nanoparticles. Owing to the advantageous properties of the designed carbon support, the composite combines a high surface area and a hierarchical pore structure with high functionality. Furthermore, the regularly shaped nanocubes allow for a good packing of a fixed-bed flow reactor, in which the internal transport pores cannot be blocked and stay open for efficient column performance. The composite is employed as a catalyst in the hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF), showing good catalytic performance and overcoming the conventional problem of column blocking.

Functional porous carbon nanospheres synthesized from cheap and sustainable precursors exhibited excellent properties as electrodes for supercapacitors.

Herein, porous photoactive nanocomposites are prepared by a simple one-pot synthesis approach using a salt and aqueous media. Within this reactive hypersaline route, the salt not only serves in the structuring of the composite but also becomes an integral active part of it. Here, the addition of sodium thiocyanate to a titania precursor guides, on the one hand, the formation of needle-shaped nanoparticles and, on the other hand, forms yellow compound isoperthiocyanic acid, which is homogeneously incorporated into the porous nanocomposite. Compared to a pure titania reference, this material reveals a 7-fold-increased photodegradation rate of Rhodamine B as a model compound. This reveals the reactive hypersaline route to be a promising and facile synthesis route toward photoactive porous materials.

Nano-sized nitrogen-doped carbon spheres are synthesized from two cheap, readily available and sustainable precursors: tannic acid and urea. In combination with a polymer structuring agent, nitrogen content, sphere size and the surface (up to 400 m(2)g(-1)) can be conveniently tuned by the precursor ratio, temperature and structuring agent content. Because the chosen precursors allow simple oven synthesis and avoid harsh conditions, this carbon nanosphere platform offers a more sustainable alternative to classical soots, for example, as printing pigments or conduction soots. The carbon spheres are demonstrated to be a promising as conductive carbon additive in anode materials for lithium ion batteries.

Via utilizing a phenomenon that is usually observed in the food industry, a scalable, safe, and cheap synthesis method for processable and functional porous carbons has been presented. Using simple sugars in combination with urea, low melting liquids can be formed that are also stable at room temperature without recrystallization. Due to low vapor pressure, these melts can be easily stored and handled for further use as carbon precursors. The resulting carbon materials possess high nitrogen content and are obtained in high yield. The liquid precursor state also allows the addition of further substances, and highly porous carbon monoliths can be formed by the introduction of a salt/fiber mixture. Herein, cellulose was found to serve as an efficient additive, which resulted in processable viscoelastic doughs without the alteration of the final carbon properties. This method is of special importance with regard to industrial processes as compared to standard carbonization, and it becomes possible to handle intermediates in a green body fashion. Eventually, compared to pre-baked bread rolls, storable intermediates can be processed which inherently contain already all the final carbon properties. The carbon cookies were stable against oxidation and were shown to be highly suitable as a sorption material, which was demonstrated via dye-removal from an aqueous solution.

Future electronics applications such as wearable electronics depend on the successful construction of energy-storage devices with superior flexibility and high electrochemical performance. However, these prerequisites are challenging to combine: External forces often cause performance degradation, whereas the trade-off between the required nanostructures for strength and electrochemical performance only results in diminished energy storage. Herein, a flexible supercapacitor based on tannic acid (TA) and carbon nanotubes (CNTs) with a unique nanostructure is presented. TA was self-assembled on the surface of the CNTs by metal-phenolic coordination bonds, which provides the hybrid film with both high strength and high pseudocapacitance. Besides 17-fold increased mechanical strength of the final composite, the hybrid film simultaneously exhibits excellent flexibility and volumetric capacitance.

A hierarchically porous carbon monolith (97% porosity) was generated through the carbonization of an emulsion-templated monolith formed from a chain extended, urea-based, deep-eutectic polymer. The highly interconnected micrometer-scale porous structure had a high specific surface area (812 m2g−1, largely microporous) and exhibited promising results for aqueous solution sorption applications.

Nitrogen-doped carbon monoliths can be prepared from liquid, deep eutectic mixtures of urea and hexaketocyclohexane octahydrate, which are structured by chitosan as a natural in-situ scaffold and support. The as-formed polymer monolith can then be transformed into the respective nitrogen-doped carbon monolith with a high surface area, high mesoporosity and high nitrogen-content. The surface functionality as well as the access to the internal pore structure were demonstrated by carbon dioxide and dye sorption experiments. The applied synthetic procedure is simple, does not require additional activation steps and uses cheap and naturally abundant compounds avoiding typical and hazardous formaldehyde resins. Eventually, this offers a safe and sustainable alternative to current carbon monolith synthesis.

A novel dual-imprinting method is suggested to provide a straightforward strategy to synthesize highly pyridinic N-enriched hierarchically nanostructured carbon for energy applications.

The synthesis of carbon nanoarchitectures from pre-organized precursor complexes with appropriate bonding patterns, here squaric acid and urea, is described. It is shown that depending on the precursor ratio, different crystal morphologies are formed, which can be transformed into nitrogen-containing carbons with either lamellar or hollow tube-like morphology. It is noted that despite the very different architecture, the composition of the final carbons is always close to a ‘C2N’ stoichiometry. Copyright © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Graphical Abstract The polymerization of phenol–formaldehyde resin under hypersaline conditions, for example, in the presence of ZnCl2, generates a black monolith. In their Communication on page 14623 ff., N. Fechler, M. Antonietti, S. H. Yu et al. further show that a foam-like carbon aerogel with good mechanical robustness can be directly obtained from the monolith without any special drying processes. ZnCl2 plays a key role in this process, serving as dehydration agent, foaming agent, and porogen.