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In this work, we synthesized and characterized mesoporous thin films of SiO2and NiTiO3structured by a surfactant called Brij58. These films were fabricated by the method of dip coating and the best conditions for well-structured thin films were investigated as a function of surfactant concentration and different types of substrates. These films have been characterized by X-ray reflectivity which was calculated using the matrix formalism. We demonstrated that the silicon substrate had a great effect on the structure and porosity of the fabricated films for both SiO2and NiTiO3. Furthermore, we found that mesoporosity has been increased as a function of the surfactant concentration in the solution. This experimental procedure allows also to produce NiTiO3powders which have been characterized by X-ray diffraction. The XRD coupled to the crystallographic software “Maud”shows that the samples are constituted by 98, 2% NiTiO3powders. [ABSTRACT FROM AUTHOR]

In the low-frequency regime, ≈1 THz, glasses show an anomalous excess in their vibrational density of states called the boson peak (BP). The origin of BP has been a subject of debate since its first discovery a few decades ago. Although BP has been the focus of numerous studies, no conclusive answers have been found about its origins, which remained elusive to date. Here, we present results based on molecular dynamics of several binary and ternary silicate glasses with different network intermediates and modifier oxides. The vibrational density of states and the BP are reported for all the studied glasses. Their correlation with the elastic constant C 44 , structural, and dynamical properties are extensively discussed in terms of Voronoi atomic volume and the vibrational mean square displacement of Q 4 species specifically. We also question the classical classification of alkali oxides as modifiers, and we suggest that Li 2 O plays the role of pseudo-intermediate oxide in lithium silicate glasses. This claim is supported by the effect of Li on various vibrational modes, and this effect differs from the other alkali metals. Furthermore, we demonstrate a correlation between the BP intensities and both the Voronoi volume of the Q 4 and Q 3 units and vibrational mean square displacements.

We conducted an extensive investigation using density functional theory (DFT) calculations and ReaxFF molecular dynamics (MD) simulations to elucidate the mechanisms of desulfurization and denitrogenation on Cu(100) surfaces. This study encompassed both pristine surfaces and those modified with Pt or Rh transition metals. Our primary objective was to gain a deep understanding of the adsorption behavior of thiophene (C 4 H 4 S) and pyridine (C 5 H 5 N) molecules on stepped Cu(100) surfaces, which serve as models for sulfur and nitrogen compounds. We systematically explored the interplay among water, adsorption efficiency, and surface regeneration capabilities. Using DFT, we thoroughly examined various aspects, including interaction energies, charge transfers, changes in electron density, and alterations in work function upon molecule adsorption. Notably, we observed a decrease in the interaction energy of thiophene, whereas that of pyridine increased when adsorbed on Pt/Rh-doped surfaces compared to pristine ones. Thiophene adsorption reduced the work function, potentially enhancing detectability, without causing inhibitory effects on any surface. Stepped Cu(100) surfaces demonstrated a strong affinity for thiophene, exhibiting an energy difference of approximately 86 kJ mol -1 . However, this trend reversed on doped surfaces, where pyridine displayed stronger adsorption than thiophene, resulting in energy differences of around 123 kJ mol -1 and 62 kJ mol -1 on Pt-Cu and Rh-Cu surfaces, respectively. Moreover, our investigation highlighted the regeneration capacity of these surfaces, indicating that all surfaces can be considered promising candidates for desulfurization, while only Cu and Pt-Cu surfaces were found to be suitable for denitrogenation. Furthermore, results from MD simulations in combination with potential of mean force (PMF) simulations at 300 K, aligned with DFT calculations, confirmed the adsorption configurations of pyridine and thiophene. This analysis demonstrated the competitive advantage of thiophene over pyridine in adsorption and highlighted the inhibitory effect of water on pyridine adsorption on the Cu(100) surface.

The paper elucidates the main driving mechanisms at play during the early stage of the Ti/CuO thermite reaction using reactive forcefields in the frame of molecular dynamics calculations. Results show that TiO preferentially forms in immediate contact to pure Ti at temperatures as low as 200 K rather than TiO 2 . Increasing the temperature to 700 K, the 2 nm TiO 2 in contact to Ti is found to be homogeneously depleted from half of its oxygen atoms. Also, the first signs of CuO decomposition are observed at 600 K, in correlation with the impoverishment in oxygen atom reaching the titanium oxide layer immediately in contact to CuO. Further quantification of the oxygen and titanium mass transport at temperatures above 700 K suggests that mostly oxygen atoms migrate from and across the titanium oxide interfacial layer to further react with the metallic titanium fuel reservoir. This scenario is opposed to the one of the Al/CuO system, for which the mass transport is dominated by the Al fuel diffusion across alumina. Further comparison of both thermites sheds light on the enhanced reactivity of the Ti-based thermite, for which CuO decomposition is promoted at lower temperature, and offers a novel understanding of thermite initiation at large.

This theoretical work aims to understand the influence of nanopores at CuO-Al nanothermite interfaces on the initial stage of thermite reaction. ReaxFF molecular dynamics simulations were run to investigate the chemical and structural evolution of the reacting interface between the fuel, Al, and oxidizer, CuO, between 400 and 900 K and considering interfaces with and without a pore. Results show that the initial alumina layer becomes enriched with Al and grows primarily into the Al metal at higher temperatures. The modification of alumina is driven by simultaneous Al and O migration between metallic Al and the native amorphous Al 2 O 3 layer. However, the presence of a pore significantly affects the growth kinetics and the composition of this alumina layer at temperatures exceeding 600 K, which impacts the initiation properties of the nanothermite. In the system without a pore, where Al is in direct contact with CuO, a ternary aluminate layer, a mixture of Al, O, and Cu, is formed at 800 K, which slows Al and O diffusion, thus compromising the nanothermite reactivity in fully dense Al/CuO composites. Conversely, the presence of a pore between Al and CuO promotes Al enrichment of the alumina layer above 600 K. At that temperature, any free oxygen molecules in the pore become attached to the reactive alumina surface resulting in a rapid oxygen pressure drop in the pore. This is expected to accelerate the reduction of the adjacent CuO as observed in experiments with Al/CuO composites with porosity at the CuO-Al interfaces.

We study reactivity and leaching at the calcium sodium borosilicate (CNBS)-water interface by means of a Car-Parrinello ab initio molecular dynamics simulation over a simulation time of 100 ps. With an emphasis on the comparison between the behaviors of Ca 2+ and Na + cations at the CNBS glass-water interface, different mechanism events during the trajectory are revealed, discussed, and correlated with other density functional theory calculations. We show that Na + ions can be released in solution, while Ca 2+ cannot leave the surface of CNBS glass. This release is correlated with the vacancy energy of Ca 2+ and Na + cations. Here, we found that the CNBS structure with the Na + cation vacancy is energetically more favorable than the structure with the Ca 2+ cation vacancy. The calcium adsorption site has been shown to have a greater affinity for water than can be found in the case of the sodium site, demonstrating that affinity may not be considered a major factor controlling the release of cations from the glass to the solution.

Graphene oxide (GO) represents a complex family of materials related to graphene: easy to produce in large quantities, easy to process, and convenient to use as a basis for further functionalization, with the potential for wide-ranging applications such as in nanocomposites, electronic inks, biosensors and more. Despite their importance, the key structural traits of GO, and the impact of these traits on properties, are still poorly understood due to the inherently berthollide character of GO which complicates the establishment of clear structure/property relationships. Widely accepted structural models of GO frequently neglect the presence of extended topological defects, structural changes to the graphene basal plane that are not removed by reduction methods. Here, a combination of experimental approaches and molecular simulations demonstrate that extended topological defects are a common feature across GO and that the presence of these defects strongly influences the properties of GO. We show that these extended topological defects are produced following even controlled 'gentle' functionalization by atomic oxygen and are comparable to those obtained by a conventional modified Hummers' method. The presence of the extended topological defects is shown to play an important role in the retention of oxygen functional groups after reduction. As an exemplar of their effect on the physical properties, we show that the GO sheets display a dramatic decrease in strength and stiffness relative to graphene and, due to the presence of extended structural defects, no improvement is seen in the mechanical properties after reduction. These findings indicate the importance of extended topological defects to the structure and properties of functionalized graphene, which merits their inclusion as a key trait in simple structural models of GO.

In this study, density functional theory (DFT) calculations have been performed to investigate the adsorption mechanisms of toluene and water onto various cationic forms of Y zeolite (LiY, NaY, KY, CsY, CuY and AgY). Our computational investigation revealed that toluene is mainly adsorbed via π-interactions on alkalis exchanged Y zeolites, where the adsorbed toluene moiety interacts with a single cation for all cases with the exception of CsY, where two cations can simultaneously contribute to the adsorption of the toluene, hence leading to the highest interaction observed among the series. Furthermore, we find that the interaction energies of toluene increase while moving down in the alkaline series where interaction energies are 87.8, 105.5, 97.8, and 114.4 kJ/mol for LiY, NaY, KY and CsY, respectively. For zeolites based on transition metals (CuY and AgY), our calculations reveal a different adsorption mode where only one cation interacts with toluene through two carbon atoms of the aromatic ring with interaction energies of 147.0 and 131.5 kJ/mol for CuY and AgY, respectively. More importantly, we show that water presents no inhibitory effect on the adsorption of toluene, where interaction energies of this latter were 10 kJ/mol (LiY) to 47 kJ/mol (CsY) higher than those of water. Our results point out that LiY would be less efficient for the toluene/water separation while CuY, AgY and CsY would be the ideal candidates for this application.

Brillouin light scattering (BLS) spectroscopy and molecular dynamic (MD) simulations allowed the identification of a relationship between the elastic properties and the structure of K-containing glasses of formula (K 2 O) x -(SiO 2 ) 1- x , having different K 2 O concentrations. Excellent agreement was observed between experimental data and simulations. The peculiar elastic properties observed for these potassium silicate glasses have been extensively discussed in terms of structural and energetic features of the materials. Elastic properties were shown to be strongly dependent on the asymmetry of potential energy in the K-BO interactions and the K-NBO interactions. A low K 2 O content (below 10-15% K 2 O) appeared to be in favor of K + -BO interactions and high asymmetry of potential energy, whereas a high K 2 O content (from 10 to 15% K 2 O) was in favor of K + -NBO interactions with lower asymmetry. Our results suggest a possible explanation to the observed anomalous dependence of elastic properties of potassium silicate glasses with K 2 O amount.

This paper investigates the parameters that influence the selective adsorption of phenol, toxic molecule, from a semi-model biofuel mixture containing alkanes and different proportions of aromatic compounds. The adsorption capacity, selectivity and regeneration ability of different adsorbents, i.e. zeolites, silica-based solids, alumina and activated carbon, were related to their textural properties and the nature, strength or location of their acidic sites. This work demonstrates that phenol differently adsorbs in the micropores and mesopores. In the micropores of faujasites, phenol is condensed into the supercages. Otherwise, in the mesopores of the zeolite, phenol interacts with the silanol groups. On purely siliceous adsorbents, a ratio of one phenol adsorbed on one silanol group could be established. As for selectivity, the strong acidic sites of the faujasites are necessary to favor phenol adsorption compared to toluene. By contrast, the amount of strong Brønsted and Lewis acid sites limits regeneration. Hence, a compromise has to be found and the best performances were obtained using a slightly dealuminated zeolitic adsorbent presenting both micro and mesopores., (Copyright © 2019. Published by Elsevier B.V.)

The intrinsic Brønsted acid strength in solid acids relates to the energy required to separate a proton from a conjugate base, for example a negatively charged zeolite framework. The reliable characterization of zeolites' intrinsic acidity is fundamental to the understanding of acid catalysis and setting in relation solid Brønsted acids with their activity and selectivity. Here, we report an infrared spectroscopic study with partial isotopic deuterium exchange of a series of 15 different acidic aluminosilicate materials, including ZSM-5 zeolites with very few defects. Varying Temperature Infrared spectroscopy (VTIR) permitted estimating activation energies for proton diffusion. Two different proton transfer mechanisms have been distinguished for two different temperature ranges. Si-rich zeolites appeared to be promising proton-transfer materials ( E act. < 40 kJ mol -1 ) at temperatures above 150 °C (423 K). Further, a linear bathochromic shift of the Si-(OD)-Al stretching vibration as a function of temperature was observed. It can be assumed that this red-shift is related to the intrinsic O-(H/D) bond strength. This observation allowed the extrapolation and estimation of precise v(O-D)@0 K values, which could be attributed to distinct crystallographic locations through Density Functional Theory (DFT) calculations. The developed method was used to reliably determine the likelihood of the position of a proton in ZSM-5 zeolites under catalytically relevant conditions ( T > 423 K), which has so far never been achieved by any other technique.

Molecular dynamics (MD) simulations and Brillouin light scattering (BLS) spectroscopy experiments have been carried to study the structure of sodium silicate glasses (SiO 2 ) (100-X) (Na 2 O) X , where X ranges from 0 to 45 at room temperature. The MD-obtained glass structures have been subjected to energy minimization at zero temperature to extract the elastic constants also obtained by BLS spectroscopy. The structures obtained are in good agreement with the structural experimental data realized by different techniques. The simulations show that the values of the elastic constants as a function of X (i.e., Na 2 O mol %) agree well with those measured by BLS spectroscopy. The variations of elastic constants C 11 and C 44 as a function of Na 2 O mol % are discussed and correlated to structural results and potential energies of oxygen atoms.