Daniel Ferry

Multilevel modular mesocrystalline organization in red coral

Abstract Biominerals can achieve complex shapes as aggregates of crystalline building blocks. In the red coral skeleton, we observe that these building blocks are arranged into eight hierarchical levels of similarly (but not identically) oriented modules. The modules in each hierarchical level assemble into larger units that comprise the next higher level of the hierarchy, and consist themselves of smaller, oriented modules. EBSD and TEM studies show that the degree of crystallographic misorientation between the building blocks decreases with decreasing module size. We observe this organization down to a few nanometers. Thus, the transition from imperfect crystallographic order at millimeter scale to nearly perfect single crystalline domains at nanometer scale is progressive. The concept of “mesocrystal” involves the three-dimensional crystallographic organization of nanoparticles into a highly ordered mesostructure. We add to this concept the notion of “multilevel modularity.” This modularity has potential implications for the origin of complex biomineral shapes in nature. A multilevel modular organization with small intermodular misorientations combines a simple construction scheme, ruled by crystallographic laws, with the possibility of complex shapes. If the observations we have made on red coral extend to other biominerals, long-range crystallographic order and interfaces at all scales may be key to how some biominerals achieve complex shapes adapted to the environment in which they grow.

Automated Determination of Aggregate Primary Particle Size Distribution by TEM Image Analysis: Application to Soot

In many applications, nanoparticles appear to be in an aggregated form. Thus, a complete description of their morphology involves an analysis of their size at different scales, from the aggregate size to the primary particle size. In this study, we present an automated method for the determination of the primary particle size distribution. It is based on an image-processing algorithm operating Euclidian distance mapping leading to a function that contains information about aggregates morphology. This algorithm is first applied to virtual aggregates with point contact between spheres, generated by diffusion limited cluster aggregation code. It shows that obtained functions can be used to retrieve the parameters of the primary particle diameter size distribution. However, it also demonstrates that overlapping or necking effects between primary spheres can have an impact on the shape of the function. The analysis is also performed on real soot images generated by ethylene diffusion flame and civil aviation engine that are different from a physicochemical point of view. This leads to the definition of a calibrated morphological function that can be used for the determination of the parameters of the primary diameter distributions of real soot particles. Finally, the same method is applied to TEM images of soot generated by a commercial soot generator miniCAST. Three operating conditions were investigated showing that generators can be used to produce soot particles with morphologies similar to those produced by jet engines. Copyright 2014 American Association for Aerosol Research

Oligothiophene Self-Assembly on the Surface of ZnO Nanorods: Toward Coaxial p–n Hybrid Heterojunctions

We describe herein the design, synthesis and detailed structural characterization of hybrid 1D nanostructures. They are prepared by supramolecular self-assembly of oligothiophene molecules on the surface of zinc oxide nanorods in solution at room temperature. Electronic absorption spectroscopy and X-ray diffraction show that both organic and inorganic components in the coaxial p-n heterojunctions are crystalline. Especially, it is demonstrated that the organic compounds form a self-assembled monolayer at the surface of the nanorods, which is not the case when zinc oxide quantum dots are instead used. As a result of their hybrid nature, the 1D nanostructures lead to ambipolar semiconducting nanostructured materials as active layers in field-effect transistors.

Assessing Optical Properties and Refractive Index of Combustion Aerosol Particles Through Combined Experimental and Modeling Studies

The variability of optical properties of combustion particles generated from a propane diffusion flame under varying fuel-to-air (C/O) ratios was studied with a three-wavelength nephelometer, a particle soot absorption photometer, and an integrating sphere photometer. Information on particle size distribution, morphology, and elemental carbon to total carbon (EC/TC) ratios were obtained from scanning mobility particle sizer measurements, transmission electron microscopy analyses, and thermal-optical analyses. Particles generated under a low C/O ratio (0.22) showed high elemental carbon fraction (EC/TC = 0.77) and low brown carbon to equivalent black carbon (BrC/EBC) ratio (0.01), and were aggregates composed of small primary particles. Rayleigh–Debye–Gans theory reproduced experimental single-scattering albedo, ω, absorption, and scattering Ångström exponents within 56, 3, and 18%, respectively. In contrast, particles produced under a high C/O ratio (0.60) showed low elemental carbon fraction (EC/TC = 0.09) and high BrC/EBC ratio >100, and were smaller and spherical in shape. Their optical properties were better modeled with Mie theory. By minimizing the difference between calculated and measured ω and Ångström exponents, refractive indices of OC at three visible wavelengths were deduced. Contrary to the widely accepted assumption that refractive index of BC is wavelength independent, BC-rich particles exhibited absorption Ångström exponent >1.0 which implies some degree of wavelength dependence. Copyright 2015 American Association for Aerosol Research

Co-grafting of porphyrins and fullerenes on ZnO nanorods: Towards supramolecular donor-acceptor assembly

This work presents the synthesis and physico-chemical characterization of a novel artificial photosynthetic design, using anisotropic semiconducting nanorods as scaffolds to assemble organic donor-acceptor complexes on their surface. These hierarchical hybrid D-A assemblies were obtained by the co-grafting of porphyrins and fullerenes on the ZnO nanorods. Polarity of the solvent and porphyrin to fullerene ratios were investigated to be markedly influencing the donor-acceptor interaction under the co-grafted conditions on ZnO nanorods. Fourier transform infrared spectroscopy, cyclic voltammetry, electronic absorption and fluorescence spectroscopic techniques were used to characterize the formation and investigate the optoelectronic properties of porphyrin-fullerene complexes on the surface of ZnO. To the best of our knowledge, this is the first example of highly interacting porphyrin-fullerene complexes on ZnO nanorods, which may allow generating efficient nanosystems for artificial photosynthesis and harvesting of solar energy.

Cobalt thiocyanate reagent revisited for cocaine identification on TLC

In this present work, the capability and structure determination of a cobalt thiocyanate complex—stabilized by glycerol—which detects cocaine (acid and base) in samples without interfering with cutting substances are studied by a TLC method.

N‐Substituted Azacalixphyrins: Synthesis, Properties, and Self‐Assembly

Pre- and postintroduction of substituents with respect to the macrocyclization step leads to previously unknown N-substituted azacalixphyrins. The stepwise synthetic approach has been studied in detail to highlight the key role of the N-substituents of the precursors and/or intermediates in terms of reactivity. Based on a combined experimental and theoretical investigation, the relationship between the properties of the macrocycles and their degree of substitution is rationalized. Depending on the nature of the N-substituents, the formation of supramolecular ribbon-like structures could also be observed, as demonstrated by combined TEM, SEM, AFM, and FTIR experiments.

First in-flight synchrotron X-ray absorption and photoemission study of carbon soot nanoparticles

Many studies have been conducted on the environmental impacts of combustion generated aerosols. Due to their complex composition and morphology, their chemical reactivity is not well understood and new developments of analysis methods are needed. We report the first demonstration of in-flight X-ray based characterizations of freshly emitted soot particles, which is of paramount importance for understanding the role of one of the main anthropogenic particulate contributors to global climate change. Soot particles, produced by a burner for several air-to-fuel ratios, were injected through an aerodynamic lens, focusing them to a region where they interacted with synchrotron radiation. X-ray photoelectron spectroscopy and carbon K-edge near-edge X-ray absorption spectroscopy were performed and compared to those obtained for supported samples. A good agreement is found between these samples, although slight oxidation is observed for supported samples. Our experiments demonstrate that NEXAFS characterization of supported samples provides relevant information on soot composition, with limited effects of contamination or ageing under ambient storage conditions. The highly surface sensitive XPS experiments of airborne soot indicate that the oxidation is different at the surface as compared to the bulk probed by NEXAFS. We also report changes in soot’s work function obtained at different combustion conditions.

Clogging of Industrial High Efficiency Particulate Air (HEPA) Filters in Case of Fire: From Analytical to Large-Scale Experiments

The Institute of Radioprotection and Nuclear Safety (IRSN in French) is conducting research on the impact of a fire on the behaviour of containment devices such as high efficiency particulate air (HEPA) pleated filters for radioactive materials. This work aims to study the clogging of HEPA filters in case of fire involving realistic materials (polymers making up gloves boxes, waste treatment solvent, hydraulic oil, solid material mixtures making up a trash bin, electrical cables, and cabinets) used in nuclear facilities, from the medium to large scale. The clogging kinetics of industrial pleated HEPA filters is monitored by measuring the pressure drop of the filters and the filtered air temperature at a given filtration velocity (from 0.23 to 2.1 cm/s). Upstream HEPA filters, combustion aerosols are characterized in terms of size distribution, mass concentration, composition, and particle morphology using, respectively, a DMS500 (CambustionLTD), glass fiber filter sampling, and transmission electron microscope analysis of particles deposited on TEM grids. Particles emitted denote well-known fractal morphology, are composed of carbonaceous primary particles with diameters ranging from 31 nm to 48 nm and showing an high clogging efficiency. An empirical relationship has been successfully applied to the obtained results for a larger range of fuels, filtration velocities and fire conditions. Finally, experiments have been performed on a large-scale facility, using full-scale fire scenarios (electrical cabinet, constant, and variable filtration velocity) and a reasonable agreement was observed with our empirical relationship. At this scale, particles appear to be compact, with a complex composition and diameters close to 220 nm with a lower clogging efficiency. Copyright 2014 American Association for Aerosol Research

Physicochemical properties of aerosol released in the case of a fire involving materials used in the nuclear industry

For industrial concerns, and more especially for nuclear applications, the characterization of soot is essential for predicting the behaviour of containment barriers in fire conditions. This study deals with the characterization (emission factor, composition, size, morphology, microstructure) of particles produced during thermal degradation of materials found in nuclear facilities (electrical cables, polymers, oil and solvents). Small-scale experiments have been conducted for oxygen concentrations [O2] ranging from 15% to 21% in order to imitate the oxygen depletion encountered during a confined fire. Particles denote distinct shapes, from aggregates composed of monomers with diameters ranging from 31.2 nm to 52.8 nm, to compact nanoparticles with diameters ranging from 15 nm to 400 nm, and their composition strongly depends on fuel type. Despite the organic to total carbon ratio (OC/TC), their properties are poorly influenced by the decrease in [O2]. Finally, two empirical correlations are proposed for predicting the OC/TC ratio and the monomer diameter, respectively, as a function of the fuels carbon to hydrogen ratio and the emission factor.