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A way to obtain graphene-based materials on a large-scale level is by means of chemical methods for the oxidation of graphite to obtain graphene oxide (GO), in combination with thermal, laser, chemical and electrochemical reduction methods to produce reduced graphene oxide (rGO). Among these methods, thermal and laser-based reduction processes are attractive, due to their fast and low-cost characteristics. In this study, first a modified Hummer's method was applied to obtain graphite oxide (GrO)/graphene oxide. Subsequently, an electrical furnace, a fusion instrument, a tubular reactor, a heating plate, and a microwave oven were used for the thermal reduction, and UV and CO 2 lasers were used for the photothermal and/or photochemical reduction. The chemical and structural characterizations of the fabricated rGO samples were performed by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman spectroscopy measurements. The analysis and comparison of the results revealed that the strongest feature of the thermal reduction methods is the production of high specific surface area, fundamental for volumetric energy applications such as hydrogen storage, whereas in the case of the laser reduction methods, a highly localized reduction is achieved, ideal for microsupercapacitors in flexible electronics.

The management of Spent Nuclear Fuel (SNF) comprises different stages in which security is demonstrated. Nevertheless, fundamental research can lead to other design options that must be considered. Currently, one of the focuses is the dry interim storage option, as the shortest-term solution until final repositories are available. During this stage, one concern is the oxidation of the fuel. If UO 2 (SNF matrix) is exposed to air at high-enough temperature, formation of U 3 O 8 takes place. The larger volume of this phase could entail stresses on the SNF clad, which is the first barrier to prevent radioactive material release. It is known that this oxidation is a temperature-dependent reaction and ensuring an inert atmosphere discards any effect during SNF dry management. However, at what extent temperature and oxygen concentration would have an impact on the U 3 O 8 formation is not established, being the available experimental data very scarce. We follow this oxidation in representative ranges of temperature and oxygen concentration of dry storage facilities by using in-situ Raman spectroscopy. The results show that temperature is a more-affecting factor than the oxygen concentration at the studied conditions. Therefore, efforts to limit temperatures would yield more benefits in preserving fuel matrix integrity., (© 2023. The Author(s).)

The study of uranium oxides at different conditions is of paramount importance in the nuclear field, especially regarding characterization of the spent nuclear fuel behavior in dry storage scenarios. This paper reports results of XRD and Raman analysis on four powdered samples prepared in order to cover a specific stoichiometry range in UO 2+ x , i.e. x = 0.24, 0.26, 0.28 and 0.30. XRD results reveal a clear increase of the average tetragonal distortion with the increase in oxidation degree, with the main phase detected for all the samples being a weakly tetragonal phase identified as U 3 O 7- z ( c / a ≪ 1.032). U 4 O 9 has not been detected in any sample. The Raman study carried out consists of both qualitative and quantitative analysis. The former, where a profile analysis has been performed on the acquired spectra, shows that the most intense bands (centered at ∼455 and ∼635 cm -1 ) are actually a doublet each, in agreement with a previous experimental study. Moreover, this work shows, for the first time, that the band at ∼160 cm -1 is also a doublet, which makes its classical assignment no longer obvious. The most important and original results from this study are obtained by applying Quantitative Raman Spectroscopy (QRS). This analysis shows that the second contribution at ∼475 cm -1 to the known T 2g mode increases its relative intensity with the oxidation degree. This contribution may be related to the tetragonal distortion occurring in the cubic UO 2 lattice due to the addition of interstitial oxygen, based on its comparison with the obtained XRD outcomes. In addition, the so-called "defects band" (centered at around 600 cm -1 ) presents a remarkable kink, of around 20 cm -1 , in its Raman shift between UO 2.26 and UO 2.28 . Such behavior might be directly associated with the observed appearance of the stoichiometric U 3 O 7 phase ( c / a = 1.032) for UO 2.28 and UO 2.30 .

The Martian subsurface is more favorable for organic preservation than its surface because of the shielding effect of rocks from cosmic rays and UV radiation with increasing depth. Nevertheless, the natural radioactivity on Mars owing to U, Th, and K must be considered to study the possible extant and/or extinct life. Here, we demonstrate the importance of natural radiation on the amino acid glycine in two different chemical environments, GlyFeSO 4 5H 2 O and GlyMgSO 4 5H 2 O, which are coordination compounds considered relevant to Mars. The results show that after a 600 kGy dose of gamma radiation, glycine was more stable when it bonded to Mg in the GlyMgSO 4 5H 2 O coordination compound, it was less stable when it bonded to Fe in the GlyFeSO 4 5H 2 O compound. Studies on the effects of gamma radiation on preservation of organic molecules bound to minerals and other potential compounds on Mars are significantly important in the search for biosignatures., (© 2022. The Author(s).)

Identification of spectroscopic fingerprints that correspond to relevant molecules/minerals in a Mars-like environment is a crucial search in astrobiology. Therefore, we studied the stability of Gly·MgSO 4 ·5H 2 O under Mars-like surface conditions and compared it to the behavior of epsomite and glycine. Gly·MgSO 4 ·5H 2 O has been identified as a molecule of astrobiological interest since an amino acid and water molecules, which are essential for life, are part of its structure. Furthermore, this compound may form by the interaction of sulfate minerals with glycine-bearing aqueous solutions, and both could be present on Mars. The main analyses were performed by using in situ Raman spectroscopy, a ground-breaking technique for NASA and ESA Mars planetary missions. We have integrated a Raman spectrometer in a Planetary Atmosphere and Surfaces Chamber (PASC) and have identified the processing of molecules exposed to a simulated martian atmosphere, UV irradiation, and temperature. Our results show that pressure is critical to provoke amorphization of Gly·MgSO 4 ·5H 2 O, and the release of glycine from the compound; the stabilization effect at low temperature and stability of Gly·MgSO 4 ·5H 2 O is greater than to glycine and epsomite. The strategy employed here allows us to evaluate the effect of diverse simulated martian environmental conditions on molecular preservation by using Raman spectroscopy.

The ligand acetohydroxamic acid (AHA) suffers hydrolysis at acidic conditions. This reaction has been studied for a long time, due to its implications in different applications, by using indirect colorimetric methods. This work shows how Raman spectroscopy can be very useful as a direct technique for measuring the hydrolysis kinetics of AHA, faster, more versatile and easier compared with the indirect traditional UV-Vis method which needs a complex formation with Fe. Thereby, we present a detailed study of the qualitative and quantitative Raman spectra of 1 mol/L AHA and its hydrolysis products. These results enabled us to perform a complete kinetic study of this molecule at different pH ranging from 0.5 mol/L to 4 mol/L HNO 3 , i.e. not only at excess acidic conditions but also at limiting nitric acid conditions., (Copyright © 2019. Published by Elsevier B.V.)

The crystal structure, hydrogen bonding, mechanical properties and Raman spectrum of the lead uranyl silicate monohydrate mineral kasolite, Pb(UO 2 )(SiO 4 )·H 2 O, are investigated by means of first-principles solid-state methods based on density functional theory using plane waves and pseudopotentials. The computed unit cell parameters, bond lengths and angles and X-ray powder pattern of kasolite are found to be in very good agreement with their experimental counterparts. The calculated hydrogen atom positions and associated hydrogen bond structure in the unit cell of kasolite confirmed the hydrogen bond scheme previously determined from X-ray diffraction data. The kasolite crystal structure is formed from uranyl silicate layers having the uranophane sheet anion-topology. The lead ions and water molecules are located in the interlayer space. Water molecules belong to the coordination structure of lead interlayer ions and reinforce the structure by hydrogen bonding between the uranyl silicate sheets. The hydrogen bonding in kasolite is strong and dual, that is, the water molecules are distributed in pairs, held together by two symmetrically related hydrogen bonds, one being directed from the first water molecule to the second one and the other from the second water molecule to the first one. As a result of the full structure determination of kasolite, the determination of its mechanical properties and Raman spectrum becomes possible using theoretical methods. The mechanical properties and mechanical stability of the structure of kasolite are studied using the finite deformation technique. The bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson ratio and the ductility, hardness and anisotropy indices are reported. Kasolite is a hard and brittle mineral possessing a large bulk modulus of the order of B ∼ 71 GPa. The structure is mechanically stable and very isotropic. The large mechanical isotropy of the structure is unexpected since layered structures are commonly very anisotropic and results from the strong dual hydrogen bonding among the uranyl silicate sheets. The experimental Raman spectrum of kasolite is recorded from a natural mineral sample from the Jánská vein, Příbram base metal ore district, Czech Republic, and determined by using density functional perturbation theory. The agreement is excellent and, therefore, the theoretical calculations are employed to assign the experimental spectrum. Besides, the theoretical results are used to guide the resolution into single components of the bands from the experimental spectrum. A large number of kasolite Raman bands are reassigned. Three bands of the experimental spectrum located at the wavenumbers 1015, 977 and 813 cm -1 , are identified as combination bands., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The design of a safe spent nuclear fuel repository requires the knowledge of the stability of the secondary phases which precipitate when water reaches the fuel surface. Studtite is recognized as one of the secondary phases that play a key-role in the mobilization of the radionuclides contained in the spent fuel. Thereby, it has been identified as a product formed under oxidation conditions at the surface of the fuel, and recently found as a corrosion product in the Fukushima-Daiichi nuclear plant accident. Thermal stability is one of the properties that should be determined due to the high temperature of the fuel. In this work we report a detailed analysis of the structure and thermal stability of studtite. The structure has been studied both by experimental techniques (SEM, TGA, XRD and Raman spectroscopy) and theoretical DFT electronic structure and spectroscopic calculations. The comparison of the results allows us to perform for the first time the Raman bands assignment of the whole spectrum. The thermal stability of studtite has been analyzed by in situ Raman spectroscopy, with the aim of studying the effect of the heating rate and the presence of water. For this purpose, a new cell has been designed. The results show that studtite is stable under dry conditions only at temperatures below 30°C, in contrast with the higher temperatures published up to date (~130°C). Opposite behaviour has been found when studtite is in contact with water; under these conditions studtite is stable up to 90°C, what is consistent with the encounter of this phase after the Fukushima-Daiichi accident., (Copyright © 2016 Elsevier B.V. All rights reserved.)

This work presents a detailed study of hyperstoichiometric UO 2+x (0 < x < 0.25) oxides and an assessment of the structural evolution taking place as oxidation proceeds. For this purpose, different UO 2+x powder samples with controlled degree of non-stoichiometry have been identified by thermogravimetric analysis and characterized by X-ray diffraction (XRD) and Raman spectroscopy. XRD analysis reflects that the commonly assumed Vegard's law is not applicable over the whole hyperstoichiometry range, since a slight increase of the lattice constant is observed for 0.13 < x < 0.20. A quantitative Raman analysis of the UO 2+x spectra as a function of the oxidation degree is also shown. A new method to characterize any UO 2+x sample (for x < 0.20), based on the shift of the 630 cm -1 band observed in the Raman spectrum, is proposed here for the first time. Moreover, three structure transitions have been detected at x = 0.05, 0.11 and 0.20, giving rise to four distinct regions associated with consecutive structural rearrangements over the hyperstoichiometry range: x < 0.05, 0.05 < x < 0.11, 0.11 < x < 0.20 and 0.20 < x < 0.25.

Raman spectra of 1,2-ethylenediamine (EDA) in aqueous solutions are used to demonstrate that EDA molecules experience an anti-gauche conformational change resulting from the interactions with water. The observed Raman shift reveals a compressive (hydrophobic) effect of water on both methylene and amino groups of EDA. Raman spectra of EDA at high pressures are used as reference to quantify the intermolecular EDA-H 2 O interactions in terms of local pressures. These results are compared with macroscopic solvation pressures calculated from the cohesive energy parameter. We compare and discuss all our observations with available computational and experimental studies.

A rutherfordine mineral was studied by means of Raman spectroscopy combined with first principle calculations based on the density functional theory (DFT) method. The pseudopotential of a uranium atom was generated and its performance was evaluated for a series of uranium-containing minerals. The structure of rutherfordine was determined for two symmetries (Pmmn and Imm2) and the resulting lattice parameters, bond lengths, bond angles, and X-ray powder diffractogram were found to be in very good agreement with experimental values. The Raman spectrum was experimentally determined in the range 0-1700 cm(-1) and calculated using density functional perturbation theory. The non-scaled theoretical wavenumbers also agreed with the experimental values, and therefore a detailed interpretation of the theoretical spectra allowed us to assign the Raman bands found in the experimental spectrum.

Raman spectra of methanol-water mixtures were measured over the whole composition range at room conditions. The spectra are used to quantify the strength of intermolecular interactions in terms of local internal pressures. The conclusions derived from the spectroscopic analysis are discussed within the framework of the solvation pressure model using values of the cohesion energy density expected in the mixture. This work demonstrates that an appropriate analysis of Raman spectroscopy experiments can be used to quantify the local internal pressures due to intermolecular interactions in liquid mixtures, provided that high pressure results of the pure liquids are available.

We have carried out a systematic study of abiotic precipitation at different temperatures of several Mg and Ca carbonates (calcite, nesquehonite, hydrocalcite) present in carbonaceous chondrites. This study highlights the capability of Raman spectroscopy as a primary tool for performing full mineralogical analysis. The precipitation reaction and the structure of the resulting carbonates were monitored and identified with Raman spectroscopy. Raman spectroscopy enabled us to confirm that the precipitation reaction is very fast (minutes) when Ca(II) is present in the solution, whereas for Mg(II) such reactions developed at rather slow rates (weeks). We also observed that both the composition and the reaction mechanisms depended on temperature, which might help to clarify several issues in the fields of planetology and geology, because of the environmental implications of these carbonates on both terrestrial and extraterrestrial objects., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Several lines of evidence indicate the existence of salty liquid water below the icy surface of the satellite Europa. Depending on the chemical composition of the original interior brines, minerals that precipitate will be varied as will be the resulting physicochemical parameters of the evolving solutions such as pH and salinity. These parameters are determinants apropos to the study of the possible habitability of the satellite. In this work, experiments of fractional precipitation by cooling of several brines with different chemical composition (acid, alkaline, and neutral) were performed at 1 and 300 bar. The gradual decrease in temperature leads to mineral precipitation and changes in salinity and pH values. During the experiment, Raman spectroscopy was used to analyze quantitatively the variation of the salt concentration in the aqueous solutions. The obtained laboratory data indicate the manner in which cryomagma differentiation might occur on Europa. These endogenous processes of differentiation require planetary energy, which seems to have been plentiful during Europa's geological history. Ultimately, the dissipation of part of that energy is translated to a higher complexity of the cryopetrology in Europa's crust. From the results, we conclude that fractional differentiation processes of briny cryomagmas produce several types of igneous salty mineral suites on icy moons.

In this work, we study how structures develop on 2D dense binary colloidal monolayers as a function of the relative concentration of small/large particles. Translational and orientational distribution functions have been used to monitor the continuous phase transition through a detailed characterization of the global and local order. We have observed how a gradual enhancement in the number of particles of different sizes leads to a continuous vitrification process and how homogeneous binary glasses form in equimolar mixtures. Also, we have performed a simple calculation that relates the structures found to the pair dipolar potential, allowing the forecast of local structures in other arbitrary binary mixtures. Finally, we have corroborated the goodness of the binary systems as a glass-forming model by comparing the established scenario with the structural features found in partially aggregated monolayers.

The structure and the interaction potential of monolayers of charged polystyrene microparticles at fluid interfaces have been studied by optical microscopy. Microparticles of different sizes have been studied over a broad range of surface particle densities. The structural characterization is based on the analysis of images obtained by digital optical microscopy. From the experimental images, radial distribution functions, hexagonal bond order correlation functions, and temporal orientational correlation functions have been calculated for different monolayer states at both the air/water and oil/water interfaces. The interaction potential has been calculated from the structure factor using integral equations within the hypernetted chain closure relationship. For particles trapped at the oil-water interface, it was found that, upon increasing the surface coverage, a freezing transition occurs, that leads to the formation of a 2D crystalline structure. We have studied the freezing densities of particle monolayers at the oil/water interface and compared them with Monte Carlo simulation results reported by H. Löwen. In contrast, at the air-water interface, freezing is inhibited due to the formation of particle aggregates.

We address a systematic study of the three-phase contact angle, θ, of microparticles at flat fluid-liquid interfaces by using different experimental methods. We measured the dependence of θ not only on the particle chemical composition and size, but also on the solvent used to spread the microparticles onto the fluid interface. We found a non-expected and non-regular dependence of θ with size, chemical nature and spreading solvent used for the different particles studied. We propose that these dependences are due to porosity/roughness of the particles that allows the adsorption of the spreading solvent onto the solid particle surface. This conclusion is supported by the values of the line tensions estimated for the different systems.

The linear regime (LR) of viscoelastic behavior has been found to be limited to rather small values of strain, well below the strains found in many technological processes. A Fourier-transform method is described for analyzing the surface rheology data obtained in insoluble Langmuir polymer monolayers beyond the LR. In the concentrate regime, the monolayers show a transition from elastic to plastic behavior, which is characterized by high irreversibility. A simple 2-D rubber model is presented that describes the behavior of the monolayers in the non-linear region not too far from the end of the LR.

The dynamics of the liquid-air interface of aqueous solutions of a tensioactive triblock copolymer (Pluronic F-68) has been studied using surface quasielastic light scattering over a broad range of concentrations and temperatures. Ancillary surface tension and bulk rheometry data have been obtained for the same system. The results show that the classical theoretical spectrum for monolayers on a Newtonian fluid can be applied only for concentrations below 4.10(-2) mM. For concentrations above c = 14 mM a clear peak centered at zero frequency appears in the spectrum. This feature is incompatible with the classical theoretical spectrum. The SQELS spectra have been described in terms of the theory of Wang and Huang [Wang, C. H.; Huang, Q. R. J. Chem. Phys. 1997, 107, 5898] considering that the loss modulus of the concentrated solutions shows the existence of two relaxation modes even at low frequencies. The theory is able to explain the existence of a peak centered at zero frequency in the spectra, and the theoretical spectra point out the existence of an elastic peak together with the capillary one. There is a reasonable agreement between the relaxation times and the product Gtau obtained from the fits of the SQELS spectra to the theory of Wang and Huang and those obtained from bulk rheology.