The aim of this work was to review and synthesize the existing knowledge on ultrafine particles in the air with a specific focus on those originating due to vehicles emissions. As the first step, the ...review considered instrumental approaches used for UF particle monitoring and the differences in the outcomes they provide. This was followed by a discussion on the emission levels of UF particles and their characteristics as a function of vehicle technology, fuel used and after-treatment devices applied. Specific focus was devoted to secondary particle formation in urban environments resulting from semi volatile precursors emitted by the vehicles. The review discussed temporal and spatial variation in UF particle concentrations, as well as particle chemical composition and relation with gaseous pollutants. Finally, the review attempted to quantify the differences between UF particle concentrations in different environments. These, as well as other aspects of UF characteristics and dynamics in the air, were discussed in the context of human exposure and epidemiological studies as well as in relation to management and control of the particles in vehicle-affected environments.
Applications of actinide chemistry, whether for energy or defense purposes, have left a legacy of potential waste hazards. The new expanded porphyrin ligand 1 forms stable complexes with both uranyl ...(UO22+) and neptunyl (NpO2+) ions and presents a potential new avenue for waste remediation.
The tetramethylammonium counterion was used to suppress formation of insoluble uranate salts, M2U2O7, and allow for a detailed structural and spectroscopic characterization of UO2(OH) n 2- n (n = 4, ...5) under highly alkaline aqueous solution conditions. Single crystals of Co(NH3)62UO2(OH)43·H2O were obtained by cooling a dilute solution of Co(NH3)6Cl3 and UO2(NO3)2·6H2O in 3.5 M (Me4N)OH to 5 °C. The asymmetric unit contains three distinct UO2(OH)4 2- ions, each displaying a pseudo-octahedral coordination geometry with trans oxo ligands. The three independent UO2(OH)4 2- ions in the unit cell give average UO and U−OH distances of 1.82(1) and 2.26(2) Å, respectively. EXAFS data on solid Co(NH3)62UO2(OH)43·H2O and aqueous UO2 2+ in 3.5 M (Me4N)OH solution were collected at the U LIII edge, and the resulting radial distribution function shows a single asymmetric peak. For the solid and solution, curve fitting reveals two near neighbors. For the crystalline solid, the first shell was fit with two O atoms at a distance of 1.81(1) Å, and the second shell was fit with 3.9(5) O atoms at a distance of 2.21(1) Å. For the solution sample, the first shell contains two O atoms with a UO distance of 1.79(1) Å, and the second O shell was fit with 5.2(5) O atoms at a U−O distance of 2.22(1) Å. The bond distances for both the solution and solid state samples correspond relatively well with the single-crystal diffraction data; however, the second-shell coordination number is larger in solution than in the solid state, indicating a greater number of OH ligands in solution than in the solid state. Both EXAFS and X-ray diffraction analyses reveal relatively long axial UO and short equatorial U−OH bonds. Raman spectra of single crystals of Co(NH3)62UO2(OH)43·H2O reveal a symmetrical OUO stretch at 796 cm-1, 74 cm-1 lower than that for the uranyl aquo ion. In solution, the symmetrical OUO stretch is at 786 cm-1, 10 cm-1 lower than observed in the solid state. 18O enrichment produces a shift to 752 cm-1 confirming the assignment in solution. Luminescence spectroscopy recorded as a function of hydroxide ion concentration reveals that an equilibrium exists between two species, assigned to UO2(OH)4 2- and UO2(OH)5 3-. The vibronic structure of the luminescence bands was used to determine a vibrational energy of 790 cm-1 for UO2(OH)5 3- to confirm its assignment. 17O NMR and 16O/18O Raman spectroscopies also reveal an unprecedented facile ligand exchange between UO and bulk solvent oxygen atoms. Line-broadening analysis of the 17O NMR data provide activation parameters of ΔH ⧧ = 9.8 ± 0.4 kcal/mol, ΔS ⧧ = −18 ± 6 cal/mol·K, and k ex 298K = 45 ± 15 s-1. Crystal data for Co(NH3)62UO2(OH)43·H2O: monoclinic space group C2/c, a = 17.4130(4) Å, b = 12.1794(3) Å, c = 15.3721(4) Å, β = 120.384(1)°, Z = 4, R1 = 0.0313, wR2 = 0.0734.
Hexavalent neptunium can be solubilized in 0.5–3.5 M aqueous MOH (M = Li+, Na+, NMe4 + = TMA+) solutions. Single crystals were obtained from cooling of a dilute solution of Co(NH3)6Cl3 and NpO2 2+ in ...3.5 M N(Me)4OH to 5 °C. A single-crystal X-ray diffraction study revealed the molecular formula of Co(NH3)62NpO2(OH)43·H2O, isostructural with the uranium analogue. The asymmetric unit contains three distinct NpO2(OH)4 2– ions, each with pseudooctahedral coordination geometry with trans-oxo ligands. The average NpO and Np–OH distances were determined to be 1.80(1) and 2.24(1) Å, respectively. EXAFS data and fits at the Np LIII-edge on solid Co(NH3)62NpO2(OH)43·H2O and aqueous solutions of NpO2 2+ in 2.5 and 3.5 M (TMA)OH revealed bond lengths nearly identical with those determined by X-ray diffraction but with an increase in the number of equatorial ligands with increasing (TMA)OH concentration. Raman spectra of single crystals of Co(NH3)62NpO2(OH)43·H2O reveal a ν1(ONpO) symmetric stretch at 741 cm–1. Raman spectra of NpO2 2+ recorded in a 0.6–2.2 M LiOH solution reveal a single ν1 frequency of 769 cm–1. Facile exchange of the neptunyl oxo ligands with the water solvent was also observed with Raman spectroscopy performed with 16O- and 18O-enriched water solvent. The combination of EXAFS and Raman data suggests that NpO2(OH)4 2– is the dominant solution species under the conditions of study and that a small amount of a second species, NpO2(OH)5 3–, may also be present at higher alkalinity. Crystal data for Co(NH3)62NpO2(OH)43·H2O: monoclinic, space group C2/c, a = 17.344(4) Å, b = 12.177(3) Å, c = 15.273 Å, β = 120.17(2)°, Z = 4, R1 = 0.0359, wR2 = 0.0729.
Experimental L(III) X-ray absorption near edge structure (XANES) spectra of the distorted octahedral neptunium oxo ions NpO(2)(OH)(4)(2-), NpO(4)(OH)(2)(3-), and NpO(6)(6-) are interpreted using ...relativistic full multiple scattering calculations of the X-ray absorption process. In this series of compounds, the neptunium cation exhibits two different oxidation states, VI and VII, with coordination spheres from di- to tetra oxo for the first two compounds. The comparison between calculated XANES spectra using the feff code and experimental ones shows that the main features in the spectra are determined by the local coordination around the actinide metal center. Furthermore, the projected density of electronic states (DOS) calculated from the XANES simulations using the feff code are compared to calculations using ADF code. They are both discussed in terms of molecular orbitals and qualitative evolution of bonding within this series of compounds.
Motor vehicles are major emitters of gaseous and particulate matter pollution in urban areas, and exposure to particulate matter pollution can have serious health effects, ranging from respiratory ...and cardiovascular disease to mortality. Motor vehicle tailpipe particle emissions span a broad size range from 0.003 to 10
μm, and are measured as different subsets of particle mass concentrations or particle number count. However, no comprehensive inventories currently exist in the international published literature covering this wide size range.
This paper presents the first published comprehensive inventory of motor vehicle tailpipe particle emissions covering the full size range of particles emitted. The inventory was developed for urban South-East Queensland by combining two techniques from distinctly different disciplines, from aerosol science and transport modelling. A comprehensive set of particle emission factors were combined with transport modelling, and tailpipe particle emissions were quantified for particle number (ultrafine particles), PM
1, PM
2.5 and PM
10 for light and heavy duty vehicles and buses. A second aim of the paper involved using the data derived in this inventory for scenario analyses, to model the particle emission implications of different proportions of passengers travelling in light duty vehicles and buses in the study region, and to derive an estimate of fleet particle emissions in 2026.
It was found that heavy duty vehicles (HDVs) in the study region were major emitters of particulate matter pollution, and although they contributed only around 6% of total regional vehicle kilometres travelled, they contributed more than 50% of the region's particle number (ultrafine particles) and PM
1 emissions. With the freight task in the region predicted to double over the next 20 years, this suggests that HDVs need to be a major focus of mitigation efforts. HDVs dominated particle number (ultrafine particles) and PM
1 emissions; and LDV PM
2.5 and PM
10 emissions. Buses contributed approximately 1–2% of regional particle emissions.
The compound SmN(SiMe3)23 has been investigated experimentally by X-ray crystallography and computationally by DFT methods. The structure is analogous to that of other ...trisbis(trimethylsilyl)amidolanthanides, featuring positional disorder of the metal atom above and below the plane defined by the three N donor atoms, resulting in a trigonal pyramidal configuration. One of the methyl groups of each amido ligand is placed above the apex of the pyramid at close distance to the metal center suggesting the presence of agostic interactions. The DFT calculations have been carried out on the real molecule and on a SiN(SiH3)(SiH2Me)3 model where the unique Me group was placed above the apex of the pyramid to probe the agostic interaction. In both cases, the optimized geometry reproduces very well the experimental structure and indicates the presence of β-Si−C agostic interactions. A comparison of the optimized geometries obtained in the presence/absence of the Sm d and the Si d orbitals serves to illustrate the relevance of these orbitals for (i) the establishment of the pyramidal configuration at Sm, (ii) the Sm−N bond length, and (iii) the Sm−(β-Si−C) bond length. The bonding analysis, which was carried out by both Mulliken and NBO methods, not only confirms the importance of the metal d orbitals for the Sm−N and Sm−(β-Si−C) chemical bonding but also illustrates the relevance of electrostatic terms in the agostic interaction. Sm−N and N−Si π bonding is present according to the bonding analysis but is not important for enforcing the planar configuration at N, nor the pyramidal configuration at Sm.
The coordination of f-block cations with Schiff base oligopyrrolic macrocycles is discussed. Analysis of the mesophase of a uranyl 2,5-diformylpyrrole-derived expanded porphyrin complex through ...temperature-dependent X-ray diffraction (XRD) methods has provided evidence for liquid-crystalline properties, and for molecular stacking into columns, arranged in a 2D hexagonal lattice. In separate studies, UV–vis spectral analysis has indicated the formation of three new f-block oligopyrrolic complexes. Addition of neptunyl (NpO
2
2+) or plutonyl (PuO
2
2+) chloride salts to the free base of a dipyrromethane-derived Schiff base macrocycle induces an immediate spectral change, namely the growth of a Q-like band at 630
nm. Such changes in the absorption spectra cause a dramatic color change from pale yellow to blue. It is postulated that oxidation of this macrocycle, stimulated by reduction of the metal center, leads to the observed spectral changes. An immediate visible and spectral change is also observed with the reaction of lutetium silylamide (LuN(Si(CH
3)
3)
2
3), with a different, tetrapyrrole-containing Schiff base macrocycle. In this case, the formation of a complex with 1:1 metal-to-ligand binding stoichiometry is further supported by MALDI-TOF mass spectrometry.
A new methodology for the preparation of alpha-diimines and beta-aminoenones has been devised and represents an alternative route to these and related nitrogenous ligands bearing highly ...electronegative substituents.
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