Publications

Abstract Nano carbons, such as graphene and carbon nanotubes, show very interesting electrochemical properties and are becoming a focus of interest in many areas, including electrodeposition of carbon-metal composites for battery application. The aim of this study was to incorporate carbon materials (namely oxidized multi-walled carbon nanotubes (ox-MWCNT), pristine multi-walled carbon nanotubes (P-MWCNT), and reduced graphene oxide (rGO)) into a metallic tin matrix. Formation of the carbon-tin composite materials was achieved by electrodeposition from a choline chloride-based ionic solvent. The different structures and treatments of the carbon materials will create metallic composites with different characteristics. The electrochemical characterization of Sn and Sn composites was performed using chronoamperometry, potentiometry, electrochemical impedance, and cyclic voltammetry. The initial growth stages of Sn and Sn composites were characterized by a glassy-carbon (GC) electrode surface. Nucleation studies were carried out, and the effect of the carbon materials was characterized using the Scharifker and Hills (SH) and Scharifker and Mostany (SM) models. Through a non-linear fitting method, it was shown that the nucleation of Sn and Sn composites on a GC surface occurred through a 3D instantaneous process with growth controlled by diffusion. According to Raman and XRD analysis, carbon materials were successfully incorporated at the Sn matrix. AFM and SEM images showed that the carbon incorporation influences the coverage of the surface as well as the size and shape of the agglomerate. From the analysis of the corrosion tests, it is possible to say that Sn-composite films exhibit a comparable or slightly better corrosion performance as compared to pure Sn films.

Abstract Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate the reductive intramolecular cyclization of propargyl bromoethers derivatives, catalyzed by electrogenerated (1,4,8,11-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane) nickel(I), [Ni(tmc)](+), as the catalyst, in N,N,N-trimethyl-N-(2-hydroxyethyl) ammonium bis(trifluoromethylsulfonyl) imide, [N-1 1 1 2(OH)][NTf2] and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C(2)mim][NTf2] in the absence and in the presence of water. The results show that the reaction leads to the formation of the expected heterocyclic compounds, in moderate to good yields. These compounds are important intermediates in the synthesis of natural products with possible biological activities. (C) 2019 The Electrochemical Society.

Abstract Vanillin is a naturally occurring phenolic aldehyde that is world-wide known for its flavouring properties. This work reports an extensive experimental and computational study of its thermodynamic properties. The vapour pressures of crystalline and liquid phases of vanillin were measured in the following temperature ranges T = (321.0-350.7) K and (324.9-382.3) K respectively, using a static method based on diaphragm capacitance gauge. Additionally, the crystalline vapour pressures were also measured in the temperature interval T = (303.1-325.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization, at selected reference temperatures, were derived from the vapour pressure measurements. The enthalpies of vaporization and of sublimation, at T = 298.15 K, were also determined using Calvet microcalorimetry and the standard (p degrees = 10(5) Pa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, was calculated and compared with the values estimated by employing quantum chemical calculations. To analyse the thermodynamic stability of vanillin, the standard Gibbs energies of formation in crystalline and gaseous phases were calculated. The molar enthalpy of fusion determined using DSC is compared with indirect results determined using Calvet microcalorimetry and vapour pressure measurements. (C) 2018 Elsevier Ltd.

Abstract Er3+/Yb3+ codoped NaGdF4 upconversion phosphor is synthesized by thermal decomposition route. The phase confirmation of synthesized sample is further confirmed by x-ray diffraction analysis. Particle size and elemental composition of phosphor is analyzed by field emission scanning electron microscopy (FESEM) and energy dispersive x-ray (EDX), respectively. The upconversion emission is measured by exciting the sample with 976 nm diode laser source. The fluorescence intensity ratio (FIR) of two close levels H-2(11/2) and S-4(3/2) is taken into account to study thermometry ability of sample for the temperature range of 301-506 K at a constant laser power (17.60 W cm(-2)). The sensor sensitivity of phosphor is found to 5.107 x 10(-3) K-1 at 301 K.

Abstract This work presents an extended study of the thermal behavior of the alkyl and dialkylpyridinium derivatives of the bis(trifluoromethylsulfonyl)imide ionic liquid series, using high resolution power compensation differential scanning calorimetry (DSC) equipment. Temperatures, enthalpies, entropies, and the heat capacity change associated with the glass transition, as well as cold crystallization, solid-solid transitions, and melting, are used to evaluate their ability to form a glass and crystallize. The effects of the cation isomerization and the alkyl chain length increase were used to investigate the nature of the irregular thermal behavior of ionic liquids in general and to establish the link between their thermal properties and nanostructuration. The observed V-shape profile of the melting temperatures versus the alkyl side-chain length is interpreted as a consequence of the balance between the initial decrease of the magnitude of the electrostatic interaction and the regular increase of the dispersive van der Waals forces. The observed differentiation between the thermal behavior below and above the critical alkyl size, CAS, is analyzed and compared with the regular behavior of both the n-alkanes and the n-alkanols. Above the CAS, the entropy and enthalpy profiles present trends similar to those observed in the alkane and alcohol series, contrasting with those observed in the molten salts-like region. These results and evidence are a strong support to the interpretation of the effect of the ILs nanostructuration in the physical-chemical properties. We found a great similarity between the thermal behavior of the imidazolium and pyridinium cation core, highlighting the strong ability of ILs to form a nanostructured network with distinguishable polar and nonpolar domains in the liquid phase.

Abstract Twelve surface-active ionic liquids (SAILs) and surface-active derivatives, based on imidazolium, ammonium, and phosphonium cations and containing one, or more, long alkyl chains in the cation and/or the anion, were synthetized and characterized. The aggregation behavior of these SAILs in water, as well as their adsorption at solution/air interface, were studied by assessing surface tension and conductivity. The CMC values obtained (0.03-6.0 mM) show a high propensity of these compounds to self-aggregate in aqueous media. Their thermal properties were also characterized, namely the melting point and decomposition temperature by using DSC and TGA, respectively. Furthermore, the toxicity of these SAILs was evaluated using the marine bacteria Aliivibrio fischeri (Gram-negative). According to the EC50 values obtained (0.3-2.7 mg L-1), the surface-active compounds tested should be considered "toxic" or "highly toxic". Their ability to induce cell disruption of Escherichia coli cells (also Gram-negative), releasing the intracellular green fluorescent protein (GFP) produced, was investigated. The results clearly evidence the capability of these SAILs to act as cell disruption agents.

Abstract The Knudsen mass-loss effusion method was used to determine the sublimation vapour pressures, at different temperatures, of ortho and para aminophenols in the temperature intervals T = (321.1 to 343.3) K and T= (337.2 to 359.2) K, respectively. The vapour pressures of crystalline meta-aminophenol were measured using the referred to above technique, between (321.4 and 343.3) K, and a static method, based on capacitance diaphragm manometers, between (354.4 and 391.8) K. The latter technique was also used to measure the liquid vapour pressures of this isomer over the temperature range T = (370.0 to 423.3) K. The experimental results enabled the determination of the standard (p(0) = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the three compounds, and of vaporization of the meta isomer. The standard enthalpies of formation in the gaseous phase were calculated using quantum chemical calculations and also by combining literature results of enthalpies of formation in the crystalline phase with the sublimation enthalpies results determined in this work. Gas-phase absolute entropies and heat capacities of the three compounds studied were also calculated using theoretical methods. The standard Gibbs energies of formation in crystalline and gaseous phases were determined and used to evaluate the thermodynamic stability of the three isomers in standard conditions. DSC analysis enabled the determination of the temperature and molar enthalpies of fusion of the compounds studied. (C) 2018 Elsevier Ltd.

Abstract A storytelling approach has been seen as a powerful way to teach science and arouse interest and promote positive attitudes toward learning science in the early years. The purpose of our study was to determine how middle school students - Key Stage 3 (KS3) aged 12-14 in Portuguese schools - experienced learning chemistry through storytelling and how they, in turn, experienced creating stories using a storytelling approach with pre-school children. We aimed to perceive the appropriation of concepts of chemistry by the pre-school children through their drawings, the results collected during the pedagogical intervention and the recordings of the discussions between the pre-school children, the students and the pre-school teachers. The KS3 students were also given a self-assessment questionnaire as a way of assessing the pedagogical dynamics and the drive and motivation to learn chemistry. The study involved 53 children: 16 from KS3 and 37 from pre-school. The intervention took place during the KS3 students' chemistry classes and during the pre-schoolers' storytelling moment, a weekly 1 hour activity that took place at their kindergarten. We found that the use of a storytelling approach complemented with hands-on activities, as a strategy to teach acid-base content to KS3 students, contributed to their learning. Moreover, it was an important experience, which motivated them to write their stories and to prepare the activities for the pre-schoolers. We also found that the interaction of the older students with the pre-schoolers was profitable for both parts, since this type of activity promotes the acquisition of knowledge. During the storytelling moment and the hands-on activities with the pre-schoolers, we were able to witness that the younger students understood the concepts, enjoyed the interaction and felt captivated to learn science, through the questions they posed, the informal conversations and the drawings they made. This study showed us that the use of stories and hands-on activities is an effective strategy in motivating young people to learn chemistry.

Abstract Museums and exhibitions usually attempt to evaluate visitors' obtained knowledge through the use of traditional evaluation methods such as questionnaires. These are intrusive and may not provide correct results, especially due to the fact that visitors are usually not interested in being evaluated and may consider such questionnaires as intelligence tests. This paper proposes methods of design and creation of automatic evaluation techniques that make use of Virtual Reality (VR) in order to evaluate users' obtained knowledge after playing through a VR museum game experience. This Analysis System is non-intrusive (its methodology does not impact users' immersion and engagement), valid (can draw conclusions regarding users' obtained knowledge), and replicable (designed techniques can be used in a variety of experiences). Results indicate that the designed assessment techniques can be used to automatically evaluate the knowledge obtained by users throughout the experience, as well as some considerations to keep in mind when designing game experiences with these techniques.