Mössbauer-spectroscopic Characterization of the Local Surrounding of Tin Dopant Cations in the Bulk and on the Surface of YCrO3 Crystallites

2011 ◽  
Vol 66 (3) ◽  
pp. 239-244 ◽  
Author(s):  
Mikhail I. Afanasov ◽  
Alain Wattiaux ◽  
Christine Labrugère ◽  
Pavel B. Fabritchnyi ◽  
Claude Delmas
Keyword(s):  
Hyperfine Field ◽  
Isomer Shift ◽  
Coordination Number ◽  
Spin Polarization ◽  
Spectroscopic Characterization ◽  
Divalent State ◽  
Tetravalent State ◽  
Local Surrounding

119Sn Mössbauer spectra of tin-doped YCrO3, obtained by annealing in air of an YCr(119Sn4+)0.003(OH)6·xH2O precursor, provide evidence for the location of Sn4+ on the Cr3+ site in the bulk of crystallites. Below the Néel point of YCrO3 (TN = 141 K), Sn4+ ions are spinpolarized, the majority exhibiting a hyperfine field H of 80 kOe at 4.2 K. Analysis of the 119Sn spectra of another sample, obtained by impregnation of polycrystalline YCrO3 with a solution of 119SnCl4, shows that annealing in H2 results in the location of the dopant, in the divalent state, on the surface of the crystallites. The parameters of an in situ 119Sn spectrum at 295 K (isomer shift δ = 2.76 mm s−1 and quadrupole splitting EQ = 1.95 mm s−1) reveal the presence of Sn2+ ions on sites with a coordination number CN < 6. At 100 K these Sn2+ ions exhibit no spin polarization. Upon contact with air they are rapidly oxidized to the tetravalent state, as demonstrated by their modified isomer shift value δ = 0.06 mm s−1. For the large majority of both the residual “parent” Sn2+ ions and the “daughter” Sn4+ ones no spin polarization is observed down to 4.2 K. This means that surface-located tin dopant cations, regardless of their oxidation state, occupy the Y3+ sites with an equal number of Cr3+ neighbors having mutually opposite spin orientations.

Search for molecular biosignatures on Mars: laboratory simulations of UV irradiation of molecule-mineral complexes

2021 ◽  
Author(s):  
Teresa Fornaro ◽  
Giovanni Poggiali ◽  
Maria Angela Corazzi ◽  
Cristina Garcia ◽  
Giulia Dimitri ◽  
...  
Keyword(s):  
Amino Acids ◽  
Organic Compounds ◽  
Uv Irradiation ◽  
Organic Molecules ◽  
Spectroscopic Characterization ◽  
Sample Return ◽  
Laboratory Simulations ◽  
Prebiotic Molecules

&lt;div&gt;&amp;#160;&lt;/div&gt; &lt;p&gt;&lt;strong&gt;Abstract&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;We present laboratory activities of preparation, characterization, and UV irradiation processing of Mars soil analogues, which are key to support both in situ exploration and sample return missions devoted to detection of molecular biosignatures on Mars.&lt;/p&gt; &lt;p&gt;In detail we prepared analog mineral samples relevant to the landing sites of past, present and future Mars exploration missions, such as Gale Crater, Jezero Crater, and Oxia Planum. We doped these samples with a large variety of organic molecules (both biotic and prebiotic molecules) like amino acids, nucleotides, monosaccharides, aldehydes, lipids. We investigated molecular photostability under UV irradiation by monitoring in situ possible modifications of infrared spectroscopic features. These investigations provide pivotal information for ground analysis carried out by rovers on Mars.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Introduction&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;Laboratory simulations of Mars are key to support the scientific activity and technology development of life detection instruments on board present and upcoming rover missions such as Mars2020 Perseverance [1] and ExoMars2022 Rosalind Franklin [2]. Studies about the stability of organic molecules in a Martian-like environment allow us to explore the conditions for the preservation of molecular biosignatures and develop models for their degradation in the Martian geological record. A systematic study of the effects of UV radiation on a variety of molecule-mineral complexes mimicking Martian soil can be key for the selection of the most interesting samples to analyse in situ or/and collect for sample return. Testing the sensitivity of different techniques for detection of the diagnostic features of molecular biosignatures embedded into mineral matrices as a function of the molecular concentration helps the choice, design and operation of flight instruments, as well as the interpretation of data collected on the ground during mission operative periods.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Methods&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;Experimental analyses were conducted in the Astrobiology Laboratory at INAF-Astrophysical Observatory of Arcetri (Firenze, Italy). Laboratory activities pertain to: (i) synthesis of Mars soil analogues doped with organic compounds that are considered potential molecular biosignatures; (ii) UV-irradiation processing of the Mars soil analogues under Martian-like conditions; and (iii) spectroscopic characterization of the Mars soil analogues.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Results&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;Such studies have shown to be very informative in identifying mineral deposits most suitable for preservation of organic compounds, while highlighting the complementarity of different techniques for biomarkers detection, which is critical for ensuring the success of space missions devoted to the search for signs of life on Mars.&lt;/p&gt; &lt;p&gt;We will present a series of laboratory results on molecular degradation caused by UV on Mars and possible application to detection of organics by Martian rovers [3,4,5,6]. In detail, we investigated the photostability of several amino acids like glycine, alanine, methionine, valine, tryptophan, phenylalanine, glutamic acid, prebiotic molecules like urea, deoxyribose and glycolaldehyde, and biomarkers like nucleotides and phytane adsorbed on relevant Martian analogs. We monitored the degradation of these molecule-mineral complexes through in situ spectroscopic analysis, investigating the reflectance properties of the samples in the NIR/MIR 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.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Acknowledgements&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;This research was supported by the Italian Space Agency (ASI) grant agreement ExoMars n. 2017-48-H.0.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;[1] Farley K. A. et al. (2020) Space Sci. Rev. 216, 142.&lt;/p&gt; &lt;p&gt;[2] Vago, J. L. et al. (2017) Astrobiology 6, 309&amp;#8211;347.&lt;/p&gt; &lt;p&gt;[3] Fornaro T. et al. (2013) Icarus 226, 1068&amp;#8211;1085.&lt;/p&gt; &lt;p&gt;[4] Fornaro T. et al. (2018) Icarus 313, 38-60.&lt;/p&gt; &lt;p&gt;[5] Fornaro T. et al. (2020) Front. Astron. Space Sci. 7:539289.&lt;/p&gt; &lt;p&gt;[6] Poggiali G. et al. (2020) Front. Astron. Space Sci. 7:18.&lt;/p&gt;

Preparation and in-Situ Spectroscopic Characterization of Molecularly Dispersed Titanium Oxide on Silica

1998 ◽  
Vol 102 (29) ◽  
pp. 5653-5666 ◽  
Author(s):  
Xingtao Gao ◽  
Simon R. Bare ◽  
J. L. G. Fierro ◽  
Miguel A. Banares ◽  
Israel E. Wachs
Keyword(s):  
Titanium Oxide ◽  
Spectroscopic Characterization

In Situ Spectroscopic Characterization of Ni1–xZnx/ZnO Catalysts and Their Selectivity for Acetylene Semihydrogenation in Excess Ethylene

ACS Catalysis ◽  
2015 ◽  
Vol 5 (6) ◽  
pp. 3304-3315 ◽  
Author(s):  
Charles S. Spanjers ◽  
Richard S. Sim ◽  
Nicholas P. Sturgis ◽  
Bernd Kabius ◽  
Robert M. Rioux
Keyword(s):  
Spectroscopic Characterization

Mechanistic insights into pH-dependent hydrogen electrocatalysis by flipping interfacial water

2021 ◽  
Author(s):  
Qiang Sun ◽  
Nicholas Oliveira ◽  
Sergiy Tyukhtenko ◽  
Jason Guo ◽  
Nathalie Myrthil ◽  
...  
Keyword(s):  
Spectroscopic Characterization ◽  
Grand Challenge ◽  
Interfacial Water ◽  
Oxidation Reactions ◽  
Acid And Base ◽  
Ph Dependent ◽  
Exchange Membrane ◽  
Kinetics Of

A grand challenge in electrochemistry is to understand and promote electrochemical processes by exploring and exploiting the interface. Herein, we promoted the hydrogen evolution and oxidation reactions (HER/HOR) of platinum in base by employing N-methylimidazoles to reorientate interfacial water against the interfacial electric field as evidenced by in situ spectroscopic characterization of the interface. We accordingly established a unified mechanism by which the HER/HOR in acid and base proceeds via diffusion of proton and hydroxide, respectively, through interface via interfacial water by the Grotthuss mechanism. This mechanism accounts for the pH-dependent HER/HOR kinetics of platinum, a long-standing puzzle. Furthermore, we demonstrated 40% performance improvement of an anion exchange membrane electrolyzer by adding 1,2-dimethylimidazole into the alkaline solution fed into its Pt cathode.

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