Investigation of a family of structurally-related guanidinium ionic liquids through XPS and thermal analysisPublished: 01 March 2019 by Elsevier BV in Journal of Molecular Liquids
A family of structurally-related guanidinium bistriflimide ionic liquids has been prepared and characterized. TGA analyses showed a high thermal stability for all the proposed ionic liquids while DSC and XPS analyses divided them into distinct subsets depending on whether one or more constraining cycles were present. The results obtained highlighted the influence of the cation structure on some of the physico-chemical properties and thus the possibility to tune them by selecting proper substituents. The solvatochromic parameters of a selected guanidinium IL have also been studied.
Intrinsic defects in CsPbBr3 microcrystalline films have been studied using thermally stimulated current (TSC) technique in a wide temperature range (100–400 K). Below room temperature, TSC emission is composed by a set of several energy levels, in the range 0.11–0.27 eV, suggesting a quasi-continuum distribution of states with almost constant density. Above room temperature, up to 400 K, the temperature range of interest for solar cells, both dark current and photocurrent, are mainly dominated by energy levels in the range 0.40–0.45 eV. Even if measured trap densities are high, in the range 1013–1016 cm−3, the very small capture cross-sections, about 10−26 m2, agree with the high defect tolerance characterizing this material.
Improved functional performances of traditional artistic pottery by sol-gel nanoparticles depositionPublished: 20 November 2018 by IOP Publishing in Materials Research Express
This work is focused on the realization of a new manufacturing process based on the introduction of TiO2 nanostructured coatings on the surface of red earthenware pottery for domestic use. The aim of the study is to improve the technical properties of the product made from lime and iron-rich clays used to produce traditional artistic Tuscan pottery (Italy). The identified strategy involves the application of nanoparticles onto the surface of ceramic substrates via a sol-gel based process; the initial porosity of the earthenware promotes the insertion of inert nanoparticles in the outermost part of the ceramic material by simple immersion of bisqueware in the colloidal solutions of nanoparticles. Morphological investigation of the functionalized surfaces has been carried out by scanning electron microscope and atomic force microscopy, while the effectiveness of the treatment was checked by evaluating the water absorption capacity in compliance with the standard method AS-1012.21-1999. The obtained results show a reduction of surface porosity, which turns into a reduced water uptake respect to the traditional pottery, maintaining, at the same time, identical aesthetical characteristics.
Palladium surfaces, pretreated with a solution of 2,2’-bipyridine (bpy) as ligand molecule, were SERS-activated by means of laser-ablated Ag colloidal nanoparticles. XPS and Raman measurements, along with DFT simulations, evidenced the species formed on the metal surface as bpy-Pd(OH)2, which appears quite similar, from both structural and spectroscopic points of view, to the bpy-PdCl2coordination compound, whose catalytic activity is well known. Based on these observations, the use of Pd substrates coated with bpy is proposed for reactions of heterogeneous catalysis, instead of using bpy-PdCl2 as homogeneous catalyst. Moreover, palladium nanoparticles could be prepared by laser ablation in aqueous solution of bpy, exhibiting both colloidal stability and catalytic activity.
Stereoselective Double Reduction of 3-Methyl-2-cyclohexenone, by Use of Palladium and Platinum Nanoparticles, in Tandem ...Published: 19 October 2018 by MDPI in Nanomaterials
The combination of metal nanoparticles (Pd or Pt NPs) with NAD-dependent thermostable alcohol dehydrogenase (TADH) resulted in the one-flask catalytic double reduction of 3-methyl-2-cyclohexenone to 3-(1S,3S)-methylcyclohexanol. In this article, some assumptions about the interactions between a chemocatalyst and a biocatalyst have been proposed. It was demonstrated that the size of the NPs was the critical parameter for the mutual inhibition: the bigger the NPs, the more harmful for the enzyme they were, even if the NPs themselves were only moderately inactivated. Conversely, the smaller the NPs, the more minimal the TADH denaturation, although they were dramatically inhibited. Resuming, the chemocatalysts were very sensitive to deactivation, which was not related to the amount of enzyme used, while the inhibition of the biocatalyst can be strongly reduced by minimizing the NPs/TADH ratio used to catalyze the reaction. Among some methods to avoid direct binding of NPs with TADH, we found that using large Pd NPs and protecting their surfaces with a silica shell, the overall yield of 3-(1S,3S)-methylcyclohexanol was maximized (36%).
Low-Temperature Continuous-Flow Dehydration of Xylose Over Water-Tolerant Niobia-Titania Heterogeneous CatalystsPublished: 24 September 2018 by Wiley in ChemSusChem
The sustainable conversion of vegetable biomass‐derived feeds to useful chemicals requires innovative routes matching environmental and economical criteria. The approach herein pursued is the synthesis of water‐tolerant, unconventional solid acid monolithic catalysts based on a mixed niobia‐titania skeleton building up a hierarchical open‐cell network of meso and macropores, and tailored for use under continuous flow conditions. The materials were characterized by spectroscopic, microscopy and diffraction techniques showing a reproducible, isotropic structure and an increasing Lewis / Brønsted acid sites ratio with increasing Nb content. The catalytic dehydration reaction of xylose to furfural was investigated as representative application. The efficiency of the catalyst showed to be dramatically affected by the niobia content in the titania lattice. The presence of as low as 2% wt niobium resulted in ther highest furfural yield at 140 °C reaction temperature under continuous flow conditions, using H2O / Υ‐valerolactone as safe monophasic solvent system. The interception of a transient 2,5‐anhydroxylose species suggested the dehydration process to occur via a cyclic intermediates mechanism. The catalytic activity and the formation of the anhydro intermediate were related to the LAS/BAS ratio and indicated a significant contribution of xylose‐xylulose isomerization. No significant catalyst deactivation was observed over 4 days usage.
Investigations on the Electrochemical Atomic Layer Growth of Bi2Se3 and the Surface Limited Deposition of Bismuth at the...Published: 14 August 2018 by MDPI in Materials
The Electrochemical Atomic Layer Deposition (E-ALD) technique is used for the deposition of ultrathin films of bismuth (Bi) compounds. Exploiting the E-ALD, it was possible to obtain highly controlled nanostructured depositions as needed, for the application of these materials for novel electronics (topological insulators), thermoelectrics and opto-electronics applications. Electrochemical studies have been conducted to determine the Underpotential Deposition (UPD) of Bi on selenium (Se) to obtain the Bi2Se3 compound on the Ag (111) electrode. Verifying the composition with X-ray Photoelectron Spectroscopy (XPS) showed that, after the first monolayer, the deposition of Se stopped. Thicker deposits were synthesized exploiting a time-controlled deposition of massive Se. We then investigated the optimal conditions to deposit a single monolayer of metallic Bi directly on the Ag.
On the Contrasting Effect Exerted by a Thin Layer of CdS against the Passivation of Silver Electrodes Coated with ThiolsPublished: 31 July 2018 by MDPI in Surfaces
The passivation of metal electrodes covered by self-assembled monolayers of long-chain thiols is well known. The disappearance of the voltammetric peak of redox species in solution is a classical test for the formation of full layers of thiols. Similar studies on semiconductors are still very limited. We used silver surfaces covered by an ultrathin layer of CdS as substrate for self-assembling of n-hexadecanethiol (C16SH), and we compared the experimental results with those obtained by using the bare silver surface as substrate. The strong insulating effect of C16SH deposited on Ag(III) is shown by the inhibition of the voltammetric peak of Ru(NH3)63+/2+. On the contrary, the voltammogram obtained on CdS-covered Ag(III) is very similar to that obtained on the bare Ag(III) electrode, thus suggesting that the presence of CdS exerts a contrasting effect on the passivation of the silver electrode. A crucial point of our work is to demonstrate the effective formation of C16SH monolayers on Ag(III) covered by CdS. The formation of full layers of C16SH was strongly suggested by the inhibition of the stripping peak of Cd from the CdS deposit covered by C16SH. The presence of C16SH was confirmed by electrochemical quartz crystal microbalance (EQCM) measurements as well as by Auger electron spectroscopy (AES) analysis.
Electroplating processes are widely employed in industrial environments for a large variety of metallic coatings, ranging from technological to decorative applications. Even if the galvanic electrodeposition is certainly a mature technology, new concepts, novel applications, environmental legislation and the new material requirements for next-generation devices make the scientific research in this field still very active. This review focuses mostly at the decorative and wearable applications, and aims to create a bridge between the past knowledge and the future direction that this process, i.e., electrodeposition, is taking. Both the theoretical fundamentals as well as some of the most widespread practical applications—limited to metallic and alloy coatings—are explored. As an integral part of the industrial process, we take a look at the main techniques thought which the quality control of deposits and surfaces is carried out. Finally, global industrial performance and research directions towards sustainable solutions are highlighted.
<strong>Investigations on the Electrochemical Atomic Layer Growth of Bi<sub>2</sub>Se<sub>3</sub> and the Surface Limite...Published: 21 May 2018 by MDPI AG in Proceedings of The 3rd International Electronic Conference on Materials Sciences
<p><span>The Electrochemical Atomic Layer Deposition (E-ALD) technique is used for the deposition of ultrathin film of bismuth (Bi) compounds. Exploiting the E-ALD it was possible to obtain high controlled nanostructured depositions as needed for the application of these materials for novel electronics (topological insulators) and opto-electronics applications. Electrochemical studies have been conducted to determine the Underpotential Deposition (UPD) of Bi on selenium (Se) to obtain the Bi<sub>2</sub>Se<sub>3</sub> compound on the Ag (111) electrode. Verifying the composition with the X-ray Photoelectron Spectroscopy (XPS) emerged that, after the first monolayer, the deposition of Se is stopped. Thicker deposits were synthesized exploiting a time-controlled deposition of massive Se. Then we move to discover the optimal conditions to deposit a single monolayer of metallic Bi directly on Ag.</span></p> <p><span> </span></p>
In recent times, halide perovskites have attracted the attention of the scientific community because of their semiconducting properties, low cost, and easy synthesis methods; characteristics that make them suitable for application as solar cells and in other fields of electronics. However, these materials are subject to significant chemical and structural degradation and performance decrease over time. This degradation remains a critical factor that prevents their widespread use. In the present paper, we investigated the stability of different bromine-based perovskites: hybrid, MAPbBr3 (MA:NH3CH3+) and inorganic, CsPbBr3 and RbPbBr3. The samples were prepared via single-step solution synthesis as thin films on Au/Pd coated glass substrates and the ageing process was carried out in air within a climatic chamber maintained at 50 °C and 75%RH humidity. The structural and chemical evolution of the perovskites was evaluated as a function of the exposure time by means of AFM, and AR-XPS, while their optoelectronic properties were monitored by indirect bandgap measurement. We observed that the inorganic perovskites resulted more stable than mixed organic–inorganic perovskites. Nevertheless, degradation remains present and further studies are necessary if these materials are to be used for practical applications.
Type I and type II residual stress in iron meteorites determined by neutron diffraction measurementsPublished: 01 April 2018 by Elsevier BV in Planetary and Space Science
In this work we present a preliminary investigation by means of neutron diffraction experiment to determine the residual stress state in three different iron meteorites (Chinga, Sikhote Alin and Nantan). Because of the very peculiar microstructural characteristic of this class of samples all the systematic effects related to the measuring procedure such as crystallite size and composition were taken into account and a clear differentiation in the statistical distribution of residual stress in coarse and fine grained meteorites was highlighted. Moreover, the residual stress state was statistically analysed in three orthogonal directions finding evidence of the existence of both type I and type II residual stress components. Finally, the application of von Mises approach allowed to determine the distribution of type II stress.
Different Conditions of Formation Experienced by Iron Meteorites as Suggested by Neutron Diffraction InvestigationPublished: 12 January 2018 by MDPI in Minerals
In this communication, we report the results of a preliminary neutron diffraction investigation of iron meteorites. These planetary materials are mainly constituted by metallic iron with variable nickel contents, and, owing to their peculiar genesis, are considered to offer the best constrains on the early stages of planetary accretion. Nine different iron meteorites, representative of different chemical and structural groups, thought to have been formed in very different pressure and temperature conditions, were investigated, evidencing variances in crystallites size, texturing, and residual strain. The variability of these parameters and their relationship, were discussed in respect to possible diverse range of petrological conditions, mainly pressure and cooling rate, experienced by these materials during the crystallization stage and/or as consequence of post accretion events.
Metal Nanoparticles Supported on Perfluorinated Superacid Polymers: A Family of Bifunctional Catalysts for the Selective...Published: 09 October 2017 by Wiley in ChemCatChem
We describe the rational design of a new versatile family of bifunctional catalytic materials based on the combination of supported metal nanoparticles (Pd, Rh, Ru) and the superacid, perfluorinated Aquivion® PFSA polymer. The heterogeneous catalysts were tested in the multi-step valorisation of representative plant derivatives to high-added-value chemicals. Particularly, the conversion of (+)-citronellal to (-)-menthol and levulinic acid to γ-valerolactone was achieved in one pot and in one stage in the water phase and shows full selectivity at a high conversion level under mild reaction conditions. The results are discussed in terms of the catalyst micro-structure.
Aluminizing via Ionic Liquid Electrodeposition and Pack Cementation: A Comparative Study with Inconel 738 and a CoNiCrAl...Published: 19 June 2017 by MDPI in Coatings
A novel aluminizing process based upon room temperature Al-electrodeposition from Ionic Liquids followed by diffusion heat treatment was applied on bare- and CoNiCrAlY-coated Inconel 738 (IN738). The aluminized samples were tested by isothermal oxidation at 1000 °C in air. The microstructural and chemical evolution of the samples were determined as function of oxidation time and compared with the currently applied coatings obtained via pack cementation. The newly proposed method is suitable for the CoNiCrAlY coating, but not for the bare IN738. In the latter, the formed Al-enriched layer is much thinner and the anticorrosion properties resulted in being reduced. This is probably due to the presence of precipitates, which slow down the aluminum inward diffusion impairing the formation of a well-developed interdiffusion zone (IDZ). Traces of the electrolyte, embedded during the Al-electrodeposition process, can be seen as the origin of these precipitates.
A new synthetic approach for the production of carbon nanomaterials (CNM) decorated with organophosphorus moieties is presented. Three different triphenylphosphine oxide (TPPO) derivatives were used to decorate oxidized multiwalled carbon nanotubes (ox-MWCNTs) and graphene platelets (GPs). The TPPOs chosen bear functional groups able to react with the CNMs by Tour reaction (an amino group), nitrene cycloaddition (an azido group) or CuAAC reaction (one terminal C–C triple bond). All the adducts were characterized by FTIR, Raman spectroscopy, TEM, XPS, elemental analysis and ICP-AES. The cycloaddition of nitrene provided the higher loading on ox-MWCNTs and GPs as well, while the Tour approach gave best results with nanotubes (CNTs). Finally, we investigated the possibility to reduce the TPPO functionalized CNMs to the corresponding phosphine derivatives and applied one of the materials produced as heterogeneous organocatalyst in a Staudinger ligation reaction.
Magneto-Plasmonic Colloidal Nanoparticles Obtained by Laser Ablation of Nickel and Silver Targets in WaterPublished: 03 February 2017 by American Chemical Society (ACS) in The Journal of Physical Chemistry C
Ionic liquids can remove proteins and the cellulosic cell wall from pollen grains assuring grain integrity and allowing direct functionalization of the sporopollenin. We report a green, facile chemical approach to isolate sporopollenin capsules from pollen grains based on the use of ionic liquids (ILs). Depending on the IL structure, it is possible to remove proteins and the cellulose-rich cell wall (intine) assuring grain integrity and simultaneously obtaining a direct functionalization of the sporopollenin.
Carbon supported Rh nanoparticles for the production of hydrogen and chemicals by the electroreforming of biomass-derive...Published: 01 January 2017 by Royal Society of Chemistry (RSC) in RSC Advances
An electrolyzer assembled with a Rh/C nanostructured anode electrode, promotes the partial oxidation of alcohols and high-purity hydrogen evolution in alkaline media at low energy input.
Aziridine-Functionalized Multiwalled Carbon Nanotubes: Robust and Versatile Catalysts for the Oxygen Reduction Reaction ...Published: 31 October 2016 by American Chemical Society (ACS) in ACS Applied Materials & Interfaces
Since their discovery, ionic liquids (ILs) have attracted a wide interest for their potential use as a medium for many chemical processes, in particular electrochemistry. As electrochemical media they allow the electrodeposition of elements that are impossible to reduce in aqueous media. We have investigated the electrodeposition of aluminium from 1-butyl-3-methyl-imidazolium chloride ((Bmim)Cl)/AlCl3 (40/60 mol %) as concerns the effect of deposition parameters on the quality of the deposits. Thick (20 μm) aluminium coatings were electrodeposited on brass substrates at different temperatures and mixing conditions (mechanical stirring and sonication). These coatings were investigated by means of scanning electron microscope, roughness measurements, and X-ray diffraction to assess the morphology and the phase composition. Finally, electrochemical corrosion tests were carried out with the intent to correlate the deposition parameters to the anti-corrosion properties.
Surface study of metal-containing ionic liquids by means of photoemission and absorption spectroscopiesPublished: 01 June 2016 by Elsevier BV in Surface Science
Highlights•Surface structures of metal-containing imidazolium-based ionic liquids were studied.•Surface composition was evaluated using AR-XPS.•Shifts of the N 1 s peak of bistriflamide as function of the metal indicate different coordination strengths.•Even in the case of very weak bonding (Ag) the presence of metal ions leads to surface rearrangements respect to the pure ILs. AbstractThe vacuum/liquid interface of different ionic liquids obtained by dissolving bistriflimide salts of Ag, Al, Cu, Ni and Zn in 1-butyl-3-methylimidazolium bistriflimide ([bmim][Tf2N]) was investigated under vacuum using AR-XPS and NEXAFS. The XPS spectra show chemical shifts of the nitrogen of the bistriflimide anion as a function of the metal type, indicating different strength of the coordination bonds. In silver bearing ILs, silver ions were found to be only weakly coordinated. On the contrary, Ni, Cu, Zn and especially Al exhibit large chemical shifts attributable to strong interaction with the bistriflimide ions. The outermost surface was enriched with or depleted of metal ions as a function of the nature of the metals. Nickel and zinc tend to slightly concentrate at the surface while copper, silver and especially aluminum are depleted at the surface. We also observed that the aliphatic alkyl chains of the cations tend to protrude outside the surface in all systems studied. However, the presence of metals generally increases the amount of bistriflimide at the vacuum/liquid interface. Graphical abstract
<p>Since their discovery, ionic liquids (IL) have attracted a wide interest for their potential use as medium for many chemical processes, which vary from extraction, to catalysis, to organic synthesis. Their use as electrochemical media allowed the electrodeposition of metal that are impossible to reduce in aqueous media.<br />In particular, the first generation ILs (the so called chloroaluminated ILs) have made possible the deposition of Aluminium from his chloride salt. Despite the discovery of this process in the nineties, nowadays aluminium electrodeposition from chloroaluminate ILs still maintains a number of open issues regarding both fundamental and technological aspects.<br />The present communication aims to shed some light about the aluminium electrodeposition process as concerns the effect of deposition parameters. Thick Al-coatings (20 μm) were electrodeposited on brass substrate at different temperature, potential and stirring conditions. The so obtained coatings were investigated by means of optical and electronic microscope (Figure 1), rugosimetry and X-ray diffraction to asses their morphology and phase composition. Finally, with the intent to correlate the coating structures with their corrosion properties, electrochemical corrosion tests (Open Circuit Potential, Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy) were performed.</p>
In this communication, we demonstrate the use of neutron tomography for the structural characterization of iron meteorites. These materials prevalently consist of metallic iron with variable nickel content. Their study and classification is traditionally based on chemical and structural analysis. The latter requires cutting, polishing and chemical etching of large slabs of the sample in order to determine the average width of the largest kamacite lamellae. Although this approach is useful to infer the genetical history of these meteorites, it is not applicable to small or precious samples. On the base of different attenuation coefficient of cold neutrons for nickel and iron, neutron tomography allows the reconstruction of the Ni-rich (taenite) and Ni-poor (kamacite) metallic phases. Therefore, the measure of the average width of the largest kamacite lamellae could be determined in a non-destructive way. Furthermore, the size, shape, and spatial correlation between kamacite and taenite crystals were obtained more efficiently and accurately than via metallographic investigation.
Arrangements of enantiopure and racemic ionic liquids at the liquid/air interface: the role of chirality on self-assembl...Published: 01 January 2016 by Royal Society of Chemistry (RSC) in RSC Advances
Chiral ionic liquids (CILs) have been obtained in high yield using commercial propylene oxide or natural alcohols (citronellol and nopol) as building blocks. The self-assembly ability at the interface IL/air for some couples of enantiopure and racemic CILs was explored by angle resolved XPS.
Fabrication and characterization of Ag/Pd colloidal nanoparticles as stable platforms for SERS and catalytic application...Published: 01 November 2015 by Elsevier BV in Materials Chemistry and Physics
Highlights•Stable Ag/Pd colloids were prepared by laser ablation and galvanic replacement.•Ag/Pd nanoparticles were characterized byTEM microscopy, UV–vis and XPS spectroscopy.•Ag/Pd colloids showed SERS efficiency and catalytic activity to reduce nitroarenes. AbstractWe prepared stable Ag/Pd colloids to be used as both SERS-active and catalytic platforms by combining pulsed laser ablation of Ag in pure water and galvanic replacement with a successive addition of Pd(II) nitrate. Beyond UV–vis absorption and microscopic characterization, we also performed XPS tests that, by utilizing different Ar sputtering times, permitted to evaluate the Pd/Ag ratio in the nanoparticles and to confirm the results of the TEM analysis concerning their structure; Raman measurements performed in Ag/Pd colloidal suspensions allowed evaluating their SERS activity. We assessed both the Pd/Ag ratio and the timing that are required to obtain stable bimetallic colloids. The influence of the Ag colloid ageing on its reactivity with Pd(II) ions has been explained by the effects induced by the adsorbed charged species on the surface of the silver particles. This process is described by the observed temporal evolution of the ζ-potential of the Ag colloid. Lastly, we demonstrated the double functionality of our Ag/Pd nanostructures by SERS monitoring the Pd-induced catalytic reduction of the nitro group of 2-amino, 5-nitropyridine with subsequent formation of 2,5-diaminopyridine. These Ag/Pd colloidal particles allowed observing reactions induced by nanosized palladium by SERS measurements, without interference of residual reducing agents or by-products, as instead could occur for metal colloids obtained by chemical routes.
Surface-enhanced Raman scattering of ‘push–pull’ molecules: disperse orange 3 adsorbed on Au and Ag nanoparticlesPublished: 23 October 2015 by IOP Publishing in Journal of Optics
Disperse orange 3 is a typical push–pull chromophore, formed by a p-disubstituted azobenzene with an electron donor aminogroup and an electron-withdrawing nitrogroup at the ends of the molecule. This promotes a large electron mobility over all the π-conjugated system of the molecule and allows a different adsorption on metal depending on the surface properties of the substrate. The SERS spectra indicates that the molecule is adsorbed on gold nanoparticles (NPs) via nitrogroup, whereas the azogroup is involved in the interaction with the silver NPs.
Petrologic and Minerochemical Trends of Acapulcoites, Winonaites and Lodranites: New Evidence from Image Analysis and EM...Published: 02 July 2015 by MDPI in Geosciences
A comprehensive classification of primitive achondrites is difficult due to the high compositional and textural variability and the low number of samples available. Besides oxygen isotopic analysis, other minerochemical and textural parameters may provide a useful tool to solve taxonomic and genetic problems related to these achondrites. The results of a detailed modal, textural and minerochemical analysis of a set of primitive achondrites are presented and compared with literature data. All the samples show an extremely variable modal composition among both silicate and opaque phases. A general trend of troilite depletion vs. silicate fraction enrichment has been observed, with differences among coarse-grained and fine-grained meteorites. In regard to the mineral chemistry, olivine shows marked differences between the acapulcoite-lodranite and winonaite groups, while a compositional equilibrium between matrix and chondrules for both groups, probably due to the scarce influence of metamorphic grade on this phase, was observed. The analysis of Cr and Mn in clinopyroxene revealed two separate clusters for the acapulcoite/lodranite and winonaite groups, while the analysis of the reduction state highlighted three separate clusters. An estimate of equilibrium temperatures for the acapulcoite-lodranite and winonaite groups is provided. Finally, proposals regarding the genetic processes of these groups are discussed.
Azole derivatives are common inhibitors of copper corrosion due to the chemical adsorption occurring on the metal surface that gives rise to a protective film. In particular, 1,2,4-triazole performs comparable to benzotriazole, which is much more widely used, but is by no means an environmentally friendly agent. In this study, we have analyzed the adsorption of 1,2,4-triazole on copper by taking advantage of the surface-enhanced Raman scattering (SERS) effect, which highlights the vibrational features of organic ligand monolayers adhering to rough surfaces of some metals such as gold, silver and copper. To ensure the necessary SERS activation, a roughening procedure was implemented on the copper substrates, resulting in nanoscale surface structures, as evidenced by microscopic investigation. To obtain sufficient information on the molecule–metal interaction and the formation of an anticorrosive thin film, the SERS spectra were interpreted with the aid of theoretical calculations based on the density functional theory (DFT) approach.
Since the second half of the 20th century, various devices have been developed in order to reduce the emissions of harmful substances at the exhaust pipe of combustion engines. In the automotive field, the most diffuse and best known device of this kind is the “three way” catalytic converter for engines using the Otto cycle designed to abate the emissions of carbon monoxide, nitrogen oxides and unburnt hydrocarbons. These catalytic converters can function only by means of precious metals (mainly platinum, rhodium and palladium) which exist in a limited supply in economically exploitable ores. The recent increase in prices of all mineral commodities is already making these converters significantly expensive and it is not impossible that the progressive depletion of precious metals will make them too expensive for the market of private cars. The present paper examines how this potential scarcity could affect the technology of road transportation worldwide. We argue that the supply of precious metals for automotive converters is not at risk in the short term, but that in the future it will not be possible to continue using this technology as a result of increasing prices generated by progressive depletion. Mitigation methods such as reducing the amounts of precious metals in catalysts, or recycling them can help but cannot be considered as a definitive solution. We argue that precious metal scarcity is a critical factor that may determine the future development of road transportation in the world. As the problem is basically unsolvable in the long run, we must explore new technologies for road transportation and we conclude that it is likely that the clean engine of the future will be electric and powered by batteries.
X-ray micro-computer aided tomography (μ-CT), together with optical microscopy and imaging, have been applied to the study of six moldavite samples. These techniques enabled a complete characterization to be made of the textural features of both Muong Nong-type and common splashform moldavites. A detailed study of the size and distribution of pores or bubbles confirmed the marked variability in pore size among the samples, as well as within each sample, and indicated in the Muong Nong-type moldavites the presence of at least two deformation stages which occurred before and after pore formation.
Tailoring Carbon Nanotube N-Dopants while Designing Metal-Free Electrocatalysts for the Oxygen Reduction Reaction in Alk...Published: 19 August 2013 by American Chemical Society (ACS) in ACS Catalysis
We exploited alternated electrodeposition of Cu, Sn and S to obtain CuxSnySz thin films. These materials are kesterite‐type chalcogenides that have attracted a relevant interest from worldwide researchers as low cost and high conversion efficiency solar cell devices. Films were grown on silver substrate, controlling the growth of the electrodeposited structures at the nanometric level. The obtained films were characterized by diffuse reflectance spectroscopy, voltammetric stripping and atomic force microscopy. Experimental bandgap energies resulted linearly modulated by changes of chemical composition and thickness. On the basis of these results, we candidate electrodeposition as a room temperature method to obtain thin films for solar cell technology with low energy investment and negligible environmental impact. Copyright © 2013 John Wiley & Sons, Ltd.
We have prepared, for the first time, stable and uncapped Ag/Cu-based bifunctional nanoparticles (NPs) (BFNPs) in water, by combining ps laser ablation in liquid environment and galvanic replacement. The particles were obtained in a single step by 1,064 nm irradiation of a Cu target in water solutions of AgNO3 or AgNO2. Under proper salt concentration and irradiation conditions, the laser beam activates formation of deep orange colloids, which are positively charged and stable for weeks. High resolution transmission electron microscopy (HRTEM) analysis showed a predominance of composite crystalline nanostructures with size in the 1–15 nm range and consisting of fcc Ag and fcc Cu (or its oxides). While CuO tenorite crystalline phase was detected by HRTEM, X-ray photoelectron spectroscopy analysis permitted to observe also the Cu(I) oxidation state of Cu, being the Cu(I)/Cu(II) ratio different in the samples obtained in AgNO3 or AgNO2 baths. Functionalization with organic ligands and subsequent Raman tests demonstrated the SERS activity of the BFNPs and the existence of different complexing surface sites.
SERS investigation of possible extraterrestrial life traces: Experimental adsorption of adenine on a Martian meteoritePublished: 03 May 2012 by Wiley in Meteoritics & Planetary Science
– The identification of adenine by surface enhanced Raman scattering (SERS) on different mineral phases of a Martian meteorite Dar al Gani (DaG) 670 has been adopted as a test to verify the capability of this technique to detect trace amounts of organic or biological substances deposited over, or contained in, extraterrestrial materials. Raman spectra of different phases of meteorite (olivine, pyroxene, and ilmenite), representative of Martian basaltic rocks, have been measured by three laser sources with wavelengths at 785, 632.8, and 514.5 nm, coupled to a confocal micro‐Raman apparatus. Adenine deposited on the Martian meteorite cannot be observed in the normal Raman spectra; when, instead, meteorite is treated with silver colloidal nanoparticles, the SERS bands of adenine are strongly enhanced, allowing an easy and simple identification of this nucleobase at subpicogram level.
Coordination Environment of Highly Concentrated Solutions of Cu II in Ionic Liquids through a Multidisciplinary ApproachPublished: 06 February 2012 by Wiley in ChemPhysChem
The coordination environment around CuII in highly concentrated solutions of copper(II) salts (CuCl2 and Cu(Tf2N)2) in two pure ionic liquids bearing the same anion, namely, 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) and 1‐butyl‐3‐methylimidazolium chloride ([bmim]Cl), is investigated by X‐ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, EPR spectroscopy and DFT calculations. Moreover, the electrochemical behavior of these mixtures is studied. Whereas reversible reduction of CuII to copper metal can be observed in the 1:1 [bmim][Tf2N]:Cu(Tf2N)2 solution, 2:1 and 1:1 [bmim]Cl:CuCl2 mixtures showed one‐electron reduction of CuII to CuI with formation of a permanent deposit of CuCl. XPS, UV/Vis and EPR spectra as well as DFT calculations suggest the formation in [bmim]Cl of dynamic coordination complexes arising from the interaction between CuCl2 and [bmim]+Cl− . The two long‐lived situations are probably trigonal and deformed tetrahedral copper(II) chloride coordination complexes ([CuCl3]− and [CuCl4]2−, respectively).
The adsorption of adenine on silver and gold surfaces has been investigated combining density functional theory calculations with surface-enhanced Raman scattering and angle-resolved X-ray photoelectron spectroscopy measurements, obtaining useful insight into the orientation and interaction of the nucleobase with the metal surfaces.
Physico-chemical properties of Pd nanoparticles produced by Pulsed Laser Ablation in different organic solventsPublished: 01 January 2012 by Elsevier BV in Applied Surface Science
Palladium nanoparticles are arousing an increasing interest because of their strong activity in heterogeneous catalysis in a wide range of reactions. Driven by the interest of producing Pd nanoparticles to be deposited for catalysis over hydrophobic supports, we investigated their synthesis via Pulsed Laser Ablation in Liquid in several organic solvents, as acetone, ethanol, 2-propanol, toluene, n-hexane. The colloids were produced by using a Nd:YAG ns laser and without the addition of surfactant agents. The morphology, composition, stability and oxidation state of the obtained nanoparticles were investigated by TEM-EDS analysis, UV–vis spectroscopy, X-ray Photoelectron Spectroscopy and micro-Raman spectroscopy. The results evidence that the nature of the solvent influences both the yield and the physico-chemical properties of the produced nanoparticles. While in acetone and alcohols spheroidal, non aggregated and stable particles are obtained, in case of toluene and n-hexane few unstable particles surrounded by a gel-like material are produced. Raman/XPS measurements suggest the presence of amorphous or graphitic carbon onto crystalline Pd nanoparticles, which could have hindered their growth and determined the observed smaller sizes if compared to nanoparticles produced in water. The stability of Pd colloids obtained in acetone and alcohols was attributed to adsorbed anions like enolates or alcoholates; non polar solvents like toluene and n-hexane, unable to give rise to adsorbed anionic species, cannot provide any stabilization to the palladium nanoparticles. XPS analyses also evidenced a partial oxidation of particles surface, with a ratio Pd2+:Pd0 of 1:2.5 and 1:4 in acetone and ethanol, respectively. Highlights► Colloids were prepared in acetone, ethanol, 2-propanol, toluene and n-hexane. ► Instrumental parameters and role of solvent were investigated. ► Colloids were characterized by UV–vis, TEM-EDS, XPS and micro-Raman. ► Acetone and alcohols gave spheroidal, stable and crystalline Pd NP. ► Unstable colloids, carbon-rich material, were obtained in toluene and n-hexane.
Interfaces and surfaces are the regions where important events happen: catalysis, molecular recognition, charge transfer, polymerization, and many other critical processes take place at the boundary between one medium and another. In this article we discuss the interface (liquid/air) properties of ionic liquids (ILs) containing dissolved metal ions with the aim to show the possibility to use metal salts to transform ILs and their surfaces into engineered liquid supports to apply in material sciences, separation procedures or to use as optical devices.
Surface-Enhanced Raman Scattering Investigation of Nucleobases Adsorbed on Samples of Martian Analogue MaterialPublished: 01 October 2011 by Informa UK Limited in Spectroscopy Letters
The identification of two nucleobases (adenine and hypoxanthine) by Surface-Enhanced Raman Scattering (SERS) on different mineral substrates was adopted as a test case to verify the capability of this analytical technique to detect trace amounts of organic or biological substances deposited over, or contained in, Martian regolith. Raman spectra were collected on polished samples of calcite, dolomite, magnesite, siderite, anhydrite, and gypsum, onto which traces of nucleobases were added. While spectroscopic features of the two nucleobases could not be observed in normal Raman spectrum, the addition of silver nanoparticles allowed easy identification of the vibrational bands characteristic of the two nucleobases.
In this paper we report the results of a deep investigation of gold title in jewellery alloys by means of potentiometric titration. After reviewing the suitable reactions for such purpose we focused on the most profitable one, which involves the use of hexadecylpyridinium chloride (CPC). This cation gives rise to selective and quantitative precipitation of AuCl4−. We completely revised a method previously proposed by W.S. Selig in the 80’s, by improving the sampling preparation and by optimizing the titration steps. Then, the new proposed method was tested on a large number of different alloys, commonly used for goldsmithery purposes. The obtained gold titles were compared with the data achieved by fire assay, giving rise to a very good agreement. At the light of these results, the present method can be rightfully considered a cheaper and “greener” alternative to the traditional one.
This paper is dedicated to the study of electrodeposited aluminium layers as anticorrosion protective coatings on metallic substrates. The aim of this approach is to propose a non-toxic alternative to the traditional nickel–chromium coating, for anticorrosive and decorative purposes. Aluminium was electrodeposited on carbon steel substrates from chloroaluminate based ionic liquids with and without the addition of 1,10-phenantroline. In the first case, the Al deposits are dense but dull, while in the latter homogeneous and bright coatings suitable for decorative purposes were achieved.The corrosion properties of carbon steel coated with bright and dull Al coating were evaluated by means of electrochemical techniques (open circuit potential and potentiodynamic polarization curves) and free corrosion tests, carried out in a salt-spray cabinet on Al and Ni–Cr plated car wheel bolts. According to these tests, we found the Al coating provides nearly the same corrosion resistance as the Ni–Cr, with the advantage to being totally free of harmful metals.
Oxidative post-treatments for enhanced corrosion resistance of aluminium electrodeposited from ionic liquidsPublished: 01 January 2010 by Elsevier BV in Corrosion Science