Monitoring the thermally induced transition from sp3-hybridized into sp2-hybridized carbons

The preparation of carbons for technical applications is typically based on a treatment of a precursor, which is transformed into the carbon phase with the desired structural properties. During such treatment the material passes through several different structural stages, for example, starting from precursor molecules via an amorphous phase into crystalline-like phases. While the structure of non-graphitic and graphitic carbon has been well studied, the transformation stages from molecular to amorphous and non-graphitic carbon are still not fully understood. Disordered carbon often contains a mixture of sp3-, sp2-and sp1-hybridized bonds, whose analysis is difficult to interpret. We systematically address this issue by studying the transformation of purely sp3-hybridized carbons, that is, nanodiamond and adamantane, into sp2-hybridized non-graphitic and graphitic carbon. The precursor materials are thermally treated at different temperatures and the transformation stages are monitored. We employ Raman spectroscopy, WAXS and TEM to characterize the structural changes. We correlate the intensities and positions of the Raman bands with the lateral crystallite size La estimated by WAXS analysis. The behavior of the D and G Raman bands characteristic for sp2-type material formed by transforming the sp3-hybridized precursors into non-graphitic and graphitic carbon agrees well with that observed using sp2-structured precursors

Healthy living on a healthy planet - Summary

Unsere Lebensweise macht krank und zerstört die natürlichen Lebensgrundlagen. In der Vision „Gesund leben auf einer gesunden Erde“ werden menschliche Lebensbereiche – Ernähren, Bewegen, Wohnen – gesund und umweltverträglich gestaltet sowie planetare Risiken – Klimawandel, Biodiversitätsverlust, Verschmutzung – bewältigt. Gesundheitssysteme nutzen ihre transformativen Potenziale, Bildung und Wissenschaft befördern gesellschaftliche Veränderungen. Die Vision ist nur mit internationaler Kooperation realisierbar und erfordert eine globale Dringlichkeitsgovernance.Our lifestyle is making us ill and is destroying the natural life-support systems. In the vision of ‘healthy living on a healthy planet’, human spheres of life – what we eat, how we move, where we live – are designed to be both healthy and environmentally compatible, and planetary risks – climate change, biodiversity loss, pollution – have been overcome. Health systems harness their transformative potential; education and science promote societal change. The vision can only be realized with international cooperation and requires what the WBGU terms global urgency governance

Materials come around and go around: adapting to nature’s circularity

The present multiple crises, such as climate change, war, and the recent pandemic, highlight the need for a stable and secure resource supply chain to overcome resource scarcity and shortages in manufacturing as well as in goods for everyday needs. Today’s linear production chains and waste management systems contribute to disruptions in resource availability as well as to greenhouse gas emissions. The concept of a holistic circular economy, inspired by natural processes, could help to mitigate these challenges. With a primary goal of maintaining resources, as much as possible, in “closed loops,” the following three challenges should be addressed: (1) Dissipation of resources, (2) Irreversibility of some processes, and (3) Logistical, technological, and information. These challenges can be addressed, in part, by implementing computational technology and cascading mechanical and chemical recycling processes in waste and resource management. This article emphasizes the interconnection between resource scarcity and pollution and climate change, and proposes a holistic circular economy as an important contribution to addressing this challenge. This holistic circular economy can be inspired, in part, by nature’s self-healing, self-transformation, and self-disintegration capabilities. Another crucial part is a comprehensive understanding of the limited resources of the planet and the impact on the planet of using up these resources and, thereby, leading to a shift toward sustainable material use and waste management. The transition to a circular economy requires changes at many levels, encompassing materials research, technical engineering, industrial implementation, and societal adaptation. In both product and process development, regardless of the technological readiness level, life-cycle analyses must be performed that consider the impact on the planet. With the help of a “product passport,” a suitable legal framework can be created and implemented. Radical changes in the way we carry out research into technologically relevant materials can pave the way to a holistic circular economy

Raman Spectroscopic Study of the Optical Phonons of Mg2Si1−x Snx Solid Solutions

Mg2Si1−x Snx solid solutions are prepared in the composition range from x  = 0 to 1 by mechanical alloying using high‐energy ball milling followed by direct‐current sintering at 600–800 °C. X‐ray diffraction analysis confirms that the samples obtained are uniform solid solutions. Raman spectroscopy shows two first‐order phonon Raman bands and a distribution of Raman signals due to second‐order phonon Raman scattering. The first‐order Raman bands are assigned to the nondegenerate Raman‐forbidden F1u (LO) mode and the triply degenerate Raman‐allowed F2g mode. Both modes exhibit a linear shift of the phonon frequency with a composition showing a clear one‐mode behavior for this solid solution. The findings are discussed in the context of existing theories for the occurrence of the one‐mode or two‐mode behavior of phonons in solid solutions

Comparing Raman mapping and electron microscopy for characterizing compositional gradients in thermoelectric materials

We demonstrate that Raman mapping provides a cheap, fast, and non-invasive way of mapping compositional fluctuations occurring in state-of-the-art thermoelectric materials. Exemplarily, we discuss Raman results obtained on an Mg2Si–Mg2Sn diffusion couple and compare resulting compositional mappings with those obtained on the same sample using electron microscopy in conjunction with energy-dispersive X-ray emission and back-scattered electrons as probes. We obtained the same level of quantitative information by the three approaches. The lateral resolution achieved in the Raman mappings can be as good as 1.4 µm and typical recording times per data point are of the order of 50 s

Catalytic recycling of medical plastic wastes over La0.6Ca0.4Co1–Fe O3− pre-catalysts for co-production of H2 and high-value added carbon nanomaterials

In this work, waste medical masks collected from daily life usage were pyrolyzed and catalytically decomposed with perovskite-type La0.6Ca0.4Co1–xFexO3−δ pre-catalysts for co-production of carbon nanomaterials and H2. The influences of catalysis reaction temperature and Co/Fe ratio in the investigated pre-catalysts on the yields and selectivity of the gaseous products and carbon deposition were systematically studied. The physicochemical characteristics of the produced carbon nanomaterials were comprehensively characterized by the state-of-the-art techniques. La0.6Ca0.4Co0.2Fe0.8O3–δ possessed the highest hydrogen and carbon nanomaterials yields at 850 °C among all the investigated pre-catalysts. Especially, this pre-catalyst showed an excellent performance during the 10 cycles of successive deconstruction of plastic wastes with the highest hydrogen yield of 34.33 mmol / gplastic at the 7th cycle. More importantly, carbon nanotubes generated had higher graphitic characteristics and fewer defects. The presented results demonstrated that the developed perovskite-type pre-catalyst is a promising candidate for the production of hydrogen and carbon nanotube composites for energy storge applications from medical waste plastics