The Effect of the Polyaromatic Hydrocarbon in the Formation of Fullerenes

Tremendous advances in nanoscience have been made since the discovery of fullerenes. However, the short timescale of the growth process and high-energy conditions of synthesis result in severe constraints to investigation of the mechanism of fullerene formation. In this work, we attempted to reveal the formation process by analyzing the variation in the yield of fullerenes under different conditions. Experiments and theoretical analysis show that the formation of fullerenes could be affected by the addition of polycyclic aromatic compounds. It is proposed that the formation of C₆₀ during arc-discharge synthesis is fragment assembling, while the yield of C_2m (m=35, 38, 39) is strongly enhanced by building-block splicing. In addition, several features of the building blocks are put forward to predict the extent of their influence to the formation of larger fullerenes C_2n (n≥42). This work not only provides essential insight into the formation process of fullerenes, but more importantly also paves the way to improving the yield of larger fullerenes selectively.

Imaging nanocarbon materials: soot particles in flames are not structurally homogeneous

For the first time, nascent soot particles are probed by using helium-ion microscopy (HIM). HIM is a technique that is similar to scanning electron microscopy (SEM) but it can achieve higher contrast and improved surface sensitivity, especially for carbonaceous materials. The HIM microscope yields images with a high contrast, which allows for the unambiguous recognition of smaller nascent soot particles than those observed in previous transmission electron microscopy studies. The results indicate that HIM is ideal for rapid and reliable probing of the morphology of nascent soot, with surface details visible down to approximately 5 nm, and particles as small as 2 nm are detectable. The results also show that nascent soot is structurally and chemically inhomogeneous, and even the smallest particles can have shapes that deviate from a perfect sphere.

Distinction of gaseous soot precursor molecules and soot precursor particles through photoionization mass spectrometry

Samples were drawn from sooting premixed low-pressure ethylene oxygen flames and investigated through photoionization mass spectrometry using either KrF or ArF lasers as the radiation source. With the former, mass spectra were obtained as described in the literature and characterized through a series of signal groups, one for each C-number and extending to about m/z 1000, assigned as a PAH series. When the ArF laser was used the same series was observed with a somewhat higher sensitivity. In addition, a new series was observed overlaid on the PAH series and starting at about m/z 680. The new series exhibited abundant ions and it completely dominated the spectrum beyond m/z 1000. This series was identified as being the spectrum of soot precursor particles. Through measurement of the ionization order it was concluded that at least two photons are needed for ionization of PAHs whereas the particles need only one photon. Consequently, they can be measured with high sensitivity when an ArF laser is used as the radiation source. Furthermore, the discrimination of soot precursor molecules and soot precursor particles becomes possible through photoionization and this enables an improved understanding of the mass spectra. This should allow a particle growth mechanism to be deduced in the near future.

Atmospheric Aerosols: Composition, Transformation, Climate and Health Effects

Aerosols are of central importance for atmospheric chemistry and physics, the biosphere, climate, and public health. The airborne solid and liquid particles in the nanometer to micrometer size range influence the energy balance of the Earth, the hydrological cycle, atmospheric circulation, and the abundance of greenhouse and reactive trace gases. Moreover, they play important roles in the reproduction of biological organisms and can cause or enhance diseases. The primary parameters that determine the environmental and health effects of aerosol particles are their concentration, size, structure, and chemical composition. These parameters, however, are spatially and temporally highly variable. The quantification and identification of biological particles and carbonaceous components of fine particulate matter in the air (organic compounds and black or elemental carbon, respectively) represent demanding analytical challenges. This Review outlines the current state of knowledge, major open questions, and research perspectives on the properties and interactions of atmospheric aerosols and their effects on climate and human health.

End-cap stabilized oligoynes: model compounds for the linear sp carbon allotrope carbyne

Three series of differently 3,5-disubstituted alpha,omega-diphenylpolyynes Ar-(C[triple bond]C)n-Ar (n=2, 4, 6, 8, 10) were synthesized under optimized Cadiot-Chodkiewicz conditions, isolated and completely characterized. These compounds can be considered as model substances for the hypothetical one-dimensional carbon allotrope carbyne Cx. The longest sp-carbon chain contains 20 atoms and is therefore the longest, purely organic polyyne studied with NMR techniques. Extinction coefficients over 600,000 M(-1) cm(-1) represent the highest measured quantitative values for that compound class so far. Comparisons with previous investigations and electrochemical studies allow the assignment of absorption for both wavelength regions structuring the UV/Vis spectra. Based on the trends in the spectroscopic behaviour of those molecules with increasing chain length, electronic as well as the NMR properties of carbyne are predicted, in line with our previously reported results. The observed stability properties promise the synthesis of even longer polyynes.