Abstract: Thoracic (PM10), fine thoracic (PM2.5) and sub-micrometer (PM1) airborne particulate matter was sampled during day and night. In total, about 100 indoor and outdoor samples were collected for each fraction at ten different office environments. Energy-dispersive X-ray fluorescence spectrometry and ion chromatography were applied for the quantification of some major and minor elements and ions in the collected aerosols. During daytime, mass concentrations were in the ranges: 1129, 8.124, and 6.618 μg m−3, with averages of 20 ± 1, 15.0 ± 0.9, and 11.0 ± 0.8 μg m−3, respectively. At night, mass concentrations were found to be significantly lower for all fractions. Indoor PM1 concentrations exceeded the corresponding outdoor levels during office hours and were thought to be elevated by office printers. Particles with diameters between 1 and 2.5 μm and 2.5 and 10 μm were mainly associated with soil dust elements and were clearly subjected to distinct periods of settling/resuspension. Indoor NO3 − levels were found to follow specific microclimatic conditions at the office environments, while daytime levels of sub-micrometer Cl− were possibly elevated by the use of Cl-containing cleaning products. Indoor carbon black concentrations were sometimes as high as 22 μg m−3 and were strongly correlated with outdoor traffic conditions.

Abstract: Some volatile organic compounds (VOCs), generated and accumulated in exhibition cases, are capable of inducing degradation in historical artifacts. In this context, it is of special importance to distinguish between VOCs emitted by the construction materials and/or the historical objects, with the ultimate goal of proposing an appropriate mitigation strategy. To pursue this goal, a comprehensive analysis based on solid phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) has been optimized. The sampling setup used in this study does not require any modification of the exhibition design, and the testing remained nearly invisible and unobtrusive to museum visitors. This methodology has been applied to an issue encountered at the National Museum of the American Indian (Smithsonian Institution), where an unpleasant smell was detected in airtight exhibition cases already on display containing sensitive historical objects. The analysis of the volatiles emitted by construction materials allowed for identification of characteristic markers emitted by each material, and the ability to identify their overall contribution in the exhibition case. Via this method, SPME-GC-MS confirmed via the detection of some specific markers that the unpleasant smell was released by one of the construction materials and had accumulated in the exhibition case. In addition, due to the measurements taken in different positions around the exhibition cases, results were useful to point out the range of efficiency of the sorbent material placed in some of the exhibition cases as a first attempt of mitigation technique. (C) 2020 Elsevier Masson SAS. All rights reserved.

Abstract: Introducing defects in TiO2-based photocatalytic materials is a promising strategy for improving light-driven CO2 reduction. However, defects such as oxygen vacancies are generally unstable. As a solution and to further enhance the photocatalytic activity, metal doping has been applied. This mini review aims to summarize recent progress in this particular field. Herein, we have classified metal-doped architectures into three different categories: single metal doping, alloy- and co-doping, and doping of morphologically nanoengineered TiO2−x substrates. The direct relationship between specific metals and product selectivity remains complex, as selectivity can vary significantly among seemingly similar materials. However, numerous methods do show promise in fine-tuning selectivity towards either CO or CH4. In terms of photocatalytic turnover, remarkable yields have been reported in isolated reports, but insufficient experimental data and divergent reaction conditions hamper a true comparison. This puts an emphasis on the need for standardized activity testing.

Abstract: This paper discusses the possibility of retrieving the electron distribution (with highlighted valence electron distribution information) of materials from recorded HREM images. This process can be achieved by solving two inverse problems: reconstruction of the exit wave and reconstruction of the electron distribution from exit waves. The first inverse problem can be solved using a focal series reconstruction method. We show that the second inverse problem can be solved by combining a series of exit waves recorded at different thickness conditions. This process is designed based on an improved understanding of the dynamical scattering process. It also explains the fundamental difficulty of obtaining the valence electron distribution information and the basis of our solution.

Abstract: A hybrid model, called the hybrid plasma equipment model (HPEM), was used to study an inductively coupled plasma in gas mixtures of H2 or NH3 with CH4 or C2H2 used for the synthesis of carbon nanotubes or carbon nanofibres (CNTs/CNFs). The plasma properties are discussed for different gas mixtures at low and moderate pressures, and the growth precursors for CNTs/CNFs are analysed. It is found that C2H2, C2H4 and C2H6 are the predominant molecules in CH4 containing plasmas besides the feedstock gas, and serve as carbon sources for CNT/CNF formation. On the other hand, long-chain hydrocarbons are observed in C2H2-containing plasmas. Furthermore, the background gases CH4 and C2H2 show a different decomposition rate with H2 or NH3 addition at moderate pressures.

Abstract: Statistical parameter estimation theory is proposed as a method to quantify electron microscopy images. It aims at obtaining precise and accurate values for the unknown structure parameters including, for example, atomic column positions and types. In this theory, observations are purely considered as data planes, from which structure parameters have to be determined using a parametric model describing the images. The method enables us to measure positions of atomic columns with a precision of the order of a few picometers even though the resolution of the electron microscope is one or two orders of magnitude larger. Moreover, small differences in averaged atomic number, which cannot be distinguished visually, can be quantified using high-angle annular dark field scanning transmission electron microscopy images. Finally, it is shown how to optimize the experimental design so as to attain the highest precision. As an example, the optimization of the probe size for nanoparticle radius measurements is considered. It is also shown how to quantitatively balance signal-to-noise ratio and resolution by adjusting the probe size.

Abstract: We have realized a reversible structure transformation of one-dimensional 1D K4CdCl6-type Sr3CoMO6 with the Co2+/M4+ cation ordering into the two-dimensional 2D double layered Ruddlesden-Popper structure Sr3CoMO7-delta with a random distribution of Co and M (with M = Ru, Ir) upon increasing the partial oxygen pressure. The combined soft and hard X-ray absorption spectroscopy studies show that under transformation, Co and M cations were oxidized to Co3+ and M5+. During oxidation, high-spin Co2+ in Sr3CoMO6 first transforms into high-spin Co3+ in oxygen-deficient Sr3CoMO7-delta, and then further transforms into low-spin Co3+ in fully oxidized Sr3CoMO7 upon further increasing the partial pressure of oxygen. The 1D Sr3CoMO6 compound is magnetically ordered at low temperatures with the magnetic moments lying along the c-axis. Their alignment is parallel for Sr3CoRuO6 and antiparallel for Sr3CoIrO6. The 2D compounds reveal a spin-glass-like behavior related to the random distribution of magnetic cations in the structure.

Abstract: As electron energy-loss spectroscopy (EELS) and x-ray absorption spectroscopy (XAS) probe the same transitions from coreshell states to unoccupied states above the Fermi energy, it should always be possible to apply the two techniques to the same physical phenomena, such as magnetic dichroism, and obtain the same information. Indeed, the similarity in the expression of the electron and x-ray cross-sections had been already exploited to prove the equivalence of x-ray magnetic linear dichroism and anisotropy in EELS, by noting that the polarization vector of a photon plays the same role as the momentum transfer in electron scattering. Recently, the same was proven true for x-ray magnetic circular dichroism (XMCD) by establishing a new TEM technique called EMCD (electron energy-loss magnetic chiral dichroism) (Schattschneider P et al 2006 Nature 441 4868), which makes use of special electron scattering conditions to force the absorption of a circularly polarized virtual photon. The intrinsic advantage of EMCD over XMCD is the high spatial resolution of electron microscopes, which are readily available. Among the particular obstacles in EMCD that do not exist for synchrotron radiation, is the notoriously low signal and the very particular scattering conditions necessary to observe a chiral dichroic signal. In spite of that, impressive progress has been made in recent years. The signal strength could be considerably increased, and some innovations such as using a convergent beam have been introduced. EMCD has evolved into several techniques, which make full use of the versatility of the TEM and energy filtering, spectroscopy or STEM conditions (Rubino S 2007 Magnetic circular dichroism in the transmission electron microscope PhD Thesis Vienna University of Technology, Vienna, Austria).