UV Irradiation and Near Infrared Characterization of Laboratory Mars Soil Analog Samples

The search for molecular biosignatures at the surface of Mars is complicated by an intense irradiation in the mid- and near-ultraviolet (UV) spectral range for several reasons: (i) many astrobiologically relevant molecules are electronically excited by efficient absorption of UV radiation and rapidly undergo photochemical reactions; (ii) even though the penetration depth of UV radiation is limited, aeolian erosion continually exposes fresh material to radiation; and (iii) UV irradiation generates strong oxidants such as perchlorates that can penetrate deep into soils and cause subsurface oxidative degradation of organics. As a consequence, it is crucial to investigate the effects of UV radiation on organic molecules embedded in mineral matrices mimicking the martian soil, in order to validate hypotheses about the nature of the organic compounds detected so far at the surface of Mars by the NASA Mars Science Laboratory’s (MSL) Curiosity rover, as well as organics that will be possibly found by the next rover missions Mars 2020 (NASA) and ExoMars 2022 (ESA-Roscosmos). In addition, studying the alteration of possible molecular biosignatures in the martian environment will help to redefine the molecular targets for life detection missions and devise suitable detection methods. Here we report the results of mid- and near-UV irradiation experiments of Mars soil analog samples obtained adsorbing relevant organic molecules on a clay mineral that is quite common on Mars, i.e. montmorillonite, doped with 1 wt% of magnesium perchlorate. Specifically, we chose to investigate the photostability of a plausible precursor of the chlorohydrocarbons detected on Mars by the Curiosity rover, namely phthalic acid, along with the biomarkers of extant life L-phenylalanine and L-glutamic acid, which are proteomic amino acids, and adenosine 5’-monophosphate, which is a nucleic acid component. We monitored the degradation of these molecules adsorbed on montmorillonite through in situ spectroscopic analysis, investigating the reflectance properties of the samples in the Near InfraRed (NIR) spectral region. Such spectroscopic characterization of molecular alteration products provides support for two upcoming robotic missions to Mars that will employ NIR spectroscopy to look for molecular biosignatures, through the instruments SuperCam on board Mars 2020, ISEM, Ma_Miss and MicrOmega on board ExoMars 2022

Process sequence of soil aggregate formation disentangled through multi-isotope labelling

Microaggregates (250 µm) that resisted 60 J mL−1 ultrasonic dispersion. Afterwards, we assessed the C, N, Fe, and Si stable isotope composition in each size fraction. After four weeks we found a rapid build-up of stable macroaggregates comprising almost 50 % of soil mass in the treatment with plants and respective soil rooting, but only 5 % when plants were absent. The formation of these stable macroaggregates proceeded with time. Soil organic carbon (SOC) contents were elevated by 15 % in the large macroaggregates induced by plant growth. However, the recovery of EPS-derived 13C was below 20 % after 4 weeks, indicating rapid turnover in treatments both with and without plants. The remaining EPS-derived C was mainly found in macroaggregates when plants were present and in the occluded small microaggregates (<20 µm) when plants were absent. The excess of bacterial 15N closely followed the pattern of EPS-derived 13C (R2 = 0.72). In contrast to the organic gluing agents, the goethite-57Fe and montmorillonite-29Si were relatively equally distributed across all size fractions. Overall, microaggregates were formed within weeks. Roots enforced this process by stabilizing microaggregates within stable macroaggregates. As time proceeded the labelled organic components decomposed, while the labelled secondary oxides and clay minerals increasingly contributed to aggregate stabilization and turnover at the scale of months and beyond. Consequently, the well-known hierarchical organization of aggregation follows a clear chronological sequence of stabilization and turnover processes

Synthèse et caractérisation de phyllosilicates 2:1 de type saponite et d'organophyllosilicates 2:1

Ce travail est consacré à la synthèse de phyllosilicates 2:1 de type saponite en milieu fluoré par voie hydrothermale et d'organophyllosilicates 2:1 par voie douce. Les différents paramètres gérant l'intégration de l'aluminium dans les couches tétraédriques du feuillet font l'objet d'une étude détaillée. En milieu basique, la saponite est obtenue dans une large gamme de taux de substitution tétraédrique. En milieu acide, ce taux est relativement faible. Un mécanisme de formation du feuillet est proposé. Un hydroxyde double lamellaire en milieu basique et un acide polysilicique en milieu acide sont à l'origine de la formation d'un phyllosilicate. Des matériaux hybrides lamellaires de divers types sont également synthétisés : un organo-aluminosilicate lamellaire différent d'un phyllosilicate, un organo-magnésoaluminosilicate apparenté à un phyllosilicate 2:1. Un mécanisme de formation du feuillet est aussi proposé. Ces matériaux se sont révélés intéressants dans la rétention de cations de métaux lourds.The present work deals with the hydrothermal synthesis of 2:1 phyllosilicate with a saponite type-like structure in fluoride medium and the soft and direct synthesis of 2:1 organophyllosilicates. The effects of the different parameters controlling the presence of aluminum in the tetrahedral sheet were studied. Saponite was only obtained for a low substitution rate of aluminum in fluoride and acidic medium, whereas high substitution rate in basic medium has been provided a saponite-like structure. A proposition of a formation mechanism is given. In basic medium, the 2:1 phyllosilicate structure is induced by the hydrotalcite formation and in acidic medium by the polysilicic acid formation.Different kind of hybrid lamellar materials were also prepared : a lamellar organoaluminosilicate having no phyllosilicate structure, a lamellar organomagnesoaluminosilicate having, as inorganic parent, a 2:1 phyllosilicate structure. A formation mechanism was proposed. These materials are very interesting in the chelating of heavy metal cations.MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF

Aerosol-assisted self-assembly of hybrid Layered Double Hydroxide particles into spherical architectures

66-4 FIELD Section Title:Surface Chemistry and Colloids 78 Laboratoire des Materiaux Inorganiques, Clermont Universite, Universite Blaise Pascal, Clermont-Ferrand, Fr. FIELD URL: written in EnglishAcetate intercalated NiAl-Layered Double Hydroxide nanoparticles were prepd. by polyol process and further used as building blocks to form hybrid LDH spheres by a spray drying technique. The spherical aggregated LDH particles display a polydispersed size with a diam. ranging from 47 nm to 2 μm. The anal. of the thermal behavior evidenced that the spherical form was maintained upon calcination up to 1100°, giving rise to derived mixed oxide (NiO + NiAl2O4) nanospheres. The spherical morphol. of the LDH materials was also retained during anion exchange process. The replacement of the intercalated acetate anion by of a voluminous anion such as dodecylsulfate induces an increase of the nanosphere mean diam. of 65%. The different materials were characterized using x-ray diffraction, FTIR spectroscopy, scanning and transmission electron microscopies, dynamic light scattering, thermal anal. and nitrogen sorption. [on SciFinder(R)

Nanosized microporous crystals: emerging applications

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Organoclays used as colloidal and rheological additives in oil-based drilling fluids: An overview

International audienceThe objective of this paper is to give an overview of the synthesis, properties of different organoclays, including organo-montmorillonite, organo-sepiolite and organo-palygorskite, and their use as rheological additives in oil-based drilling fluids. The researches performed until the present moment are described and summarized. A significant amount of work had been done in this area, including the rheological behavior at normal and high temperature, the structure changes of organoclays in oil-based system, thermal stability and the rheological mechanisms. The role of layered and fibrous organoclays in oil-based drilling fluids in the enhancement of the rheological properties and thermal stability is deeply reviewed

Rapid and complete prediction of Madder natural dyes’ color and properties through computational method

Experimental chemists traditionally hold experimentation in high regard, but computational chemistry has the potential to revolutionize this perspective. Our work exemplifies this shift, employing computational methods such as Density Functional Theory (DFT), Time-Dependent Density Functional Theory (TD-DFT), and Quantum Mechanic/Molecular Mechanic (QM/MM) to delve into the realm of photodegradation of color. Focused on Madder dye, a natural and historical pigment renowned for its diverse color properties, we tackle challenges that traditional experimentation struggled to address. The historical difficulty in deciphering the spectroscopic properties of Madder\u27s colorants due to extraction challenges, impurities, and high costs is overcome through computational spectroscopy techniques. By marrying computational insights with experimental data, we predict UV-Vis, color, and NMR spectra, considering factors like pH, solvent effects, and conformers. The study underscores the impact of solute-solvent interactions on reproducing experimental measurements, laying the foundation for a comprehensive database to understand color properties in cultural heritage. These initial findings pave the way for future exploration of complex systems like Madder lake. This transformative shift empowers researchers and scientists to conquer crucial challenges in comprehending the properties of ancient colors for cultural heritage preservation, advancing the development of durable bio-sourced colors, and discovering new color applications

Rapid and direct synthesis of spherical organotalc

Organotalcs, in which organic moieties are covalently bonded to Si atoms belonging to the tetrahedral sheets, are usually prepared by a sol-gel process starting from ethanolic solution of Mg nitrate, organo-alcoxysilanes, and aqueous sodium hydroxide solution. In this case, gypsum-like particles are obtained. In this work, evaporation-induced self-assembly within aerosols was used for the first time in order to prepare organotalc spheres. These hybrid lamellar materials can be used as environmental barriers, as polymer fillers, and as catalytic supports. Using octyltriethoxysilane as a source of Si, spherical particles with sizes ranging from 20 nm to 1 μm are obtained. X-ray diffraction and transmission electron microscopy images show that the d value equals 2.8 nm meaning that, in this case, organic moities are either alternatively distributed or identically tilted in the interlayer space. Compared to the classical synthesis at room temperature or in autoclaves, and besides being a continuous process, the reaction time is reduced to several minutes instead of hours. Homogeneous forms are obtained by aerosol whereas irregular shapes are obtained in the classical synthesis

Hydrothermalisme expérimental en conditions martiennes : La matière organique structure l’assemblage minéral

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