DFT Study on the Enhancement of Isobaric Specific Heat of GaN and InN Nanosheets for Use as Nanofluids in Solar Energy Plants.

In this work, GaN and InN nanosheets with dodecylamine (DDA) as surfactant have been studied as nanofluids to be used in solar plants. The interactions between the sheets and the surfactants have been performed using density functional theory. The most favorable interaction site on the surface corresponds to the metallic atom of the sheet with the N atom of the surfactant. In this interaction, the pair of electrons of N from the surfactant with the metal atom of the sheet play a stabilizing role, which is corroborated by electron localization function (ELF), quantum theory of atoms in molecules (QTAIM), and density of states (DOS) analysis. The isobaric specific heat values for the most favorable interaction were obtained in the presence of water, ethylene glycol, and diphenyl oxide as solvents for the first time. The highest value corresponds to systems with diphenyl oxide, being the values obtained of 0.644 J/gK and 0.363 J/gK for GaN-DDA and InN-DDA systems, respectively. These results open the possibilities of using GaN-DDA and InN-DDA systems in solar energy applications.

Enantioselective synthesis of 4-amino-3,4-dihydrocoumarins and their non-cyclic hydroxyester precursors: Biological evaluation for the treatment of glioblastoma multiforme.

The stereoselective addition of ethyl acetate enolate to the C═N bond of N-tert-butylsulfinylimines has been investigated in depth. A significant effect of the LHMDS amount and the N-sulfinylimine nature on the stereoselectivity of the process was observed. Conditions were found where sulfinylimines of differently substituted salicylaldehydes derivatives, ethyl acetate, and LHMDS afforded the corresponding addition products as a single diastereomer in good yields. The developed protocol was successfully applied to the first stereoselective synthesis of differently substituted 4-amino-3,4-dihydrocoumarin derivatives. Computational models confirmed the prominent role of the ortho aryl substituent in the stereoselectivity of the process. A significant and selective cytotoxic activity against Glioblastoma Multiforme (GBM) cancer line has been determined for the noncyclic hydroxy ester derivative.

Chitosan biofilms: Insights for the selective electromembrane extraction of fluoroquinolones from biological samples.

A selective electromembrane extraction procedure for the extraction of Enrofloxacin, Marbofloxacin and Flumequine, usually employed as antibiotic in veterinarian use, is proposed by using a chitosan biofilm, composed by 60% (w/w) chitosan and 40% (w/w) Aliquat®336, as active biopolymeric support. The interaction mechanism occurring between the target drugs and the biopolymer has been deeply studied using the Quantum Theory of Atoms in Molecules. The obtained results show the interaction between the extracted fluoroquinolones and the biomembrane is stabilized by two hydrogen bonds formed between both the carboxyl and keto groups of the drugs with both the amine and hydroxyl groups of glucosamine in the biopolymer. The energetic results agree with the high extraction efficiency obtained for Marbofloxacin, Enrofloxacin and Flumequine in terms of enrichment factors (83, 82 and 58, respectively) in presence of other fluoroquinolones. Under optimum conditions, the proposed electromembrane extraction method exhibits wide linear ranges of 4.2-200 µg L-1, 5.6-200 µg L-1 and 5.1-200 µg L-1, respectively; low limits of detection close to 1.3 µg L-1 and appropriate repeatability (relative standard deviation values 4-7%).

The Role of the Interactions at the Tungsten Disulphide Surface in the Stability and Enhanced Thermal Properties of Nanofluids with Application in Solar Thermal Energy.

Transition metal dichalcogenides (TMCs) exhibit unique properties that make them of interest for catalysis, sensing or energy storage applications. However, few studies have been performed into nanofluids based on TMCs for heat transfer applications. In this study, nanofluids based on 2D-WS2 are prepared by liquid phase exfoliation to analyze their potential usage in concentrating solar power plants. Periodic-Density Functional Theory (DFT) calculations were performed to rationalize the success of the exfoliation process. The hydrogen bond interaction between the hydroxyl group from PEG, which acts as a surfactant, and the S atoms of the WS2 surface stabilizes the nanosheets in the fluid. Electron localization function (ELF) analysis is indicative of the stability of the S-H interaction from WS2 with the molecules of surfactant due to the tendency to interact through weak intermolecular forces of van der Waals solids. Moreover, improvements in thermal properties were also found. Isobaric specific heat increased by up to 10% and thermal conductivity improved by up to 37.3%. The high stability of the nanofluids and the thermal improvements were associated with the high surface area of WS2 nanosheets. These results suggest that these nanofluids could be a promising heat transfer fluid in concentrating solar power plants.

Novel WS2-Based Nanofluids for Concentrating Solar Power: Performance Characterization and Molecular-Level Insights.

Nano-colloidal suspensions of nanomaterials in a fluid, nanofluids, are appealing because of their interesting properties related to heat transfer processes. While nanomaterials based on transition metal chalcogenides (TMCs) have been widely studied in catalysis, sensing, and energy storage applications, there are few studies of nanofluids based on TMCs for heat transfer applications. In this study, the preparation and analysis of nanofluids based on 2D-WS2 in a typical heat transfer fluid (HTF) used in concentrating solar power (CSP) plants are reported. Nanofluids prepared using an exfoliation process exhibited well-defined nanosheets and were highly stable. The nanofluids were characterized in terms of properties related to their application in CSP. The presence of WS2 nanosheets did not modify significantly the surface tension, the viscosity, or the isobaric specific heat, but the thermal conductivity was improved by up to 30%. The Ur factor, which characterizes the thermal efficiency of the fluid in the solar collector, shows an enhancement of up to 22% in the nanofluid, demonstrating great promise for CSP applications. The Reynolds number and friction factor of the fluid were not significantly modified by the addition of the nanomaterial to the HTF, which is also positive for practical applications in CSP plants. Ab initio molecular dynamics simulations of the nanoparticle/fluid interface showed an irreversible dissociative adsorption of diphenyl oxide molecules on the WS2 edge, with very low kinetic barrier. The resulting "decoration" of the WS2 edge dramatically affects the nature of the interface interactions and is therefore expected to affect significantly the rheological and transport properties of the nanofluids.

Steric Tuning of Sulfinamide/Sulfoxides as Chiral Ligands with C1, Pseudo-meso, and Pseudo-C2 Symmetries: Application in Rhodium(I)-Mediated Arylation.

A new family of sulfinamide/sulfoxide derivatives was synthesized as chiral bidentate ligands by stereoselective additions of methylsulfinyl carbanions to N-tert-butylsulfinylimines. The new ligands, with C1, pseudo-meso, and pseudo-C2 symmetries, were successfully assayed in Rh-catalyzed additions of arylboronic acids to activated ketones. The sterically dissymmetric C1 ligand (RS,SC,RS)-N-[1-(phenylsulfinyl)-3-methylbut-2-yl] tert-butylsulfinamide turned out to be the optimal one, allowing the 1,4-additions of diverse arylboronic acids, on different α,ß-unsaturated cyclic ketones with high chemical yields and enantioselectivities up to >99% ee.

Revealing at the molecular level the role of the surfactant in the enhancement of the thermal properties of the gold nanofluid system used for concentrating solar power.

A molecular dynamics study based on gold nanofluids performed with and without the presence of tetraoctylammonium halide as a surfactant in a base fluid is presented. The base fluid consisting of a mixture of biphenyl and diphenyl oxide is used in concentrating solar power (CSP) plants. The radial distribution functions (RDFs) and spatial distribution functions (SDFs) were analysed with the temperature. Theoretical results indicate that the surfactant acts as a kind of net around the nanoparticle that plays an active role in enhancing the thermal properties of the gold nanofluid system. A greater lability of the base fluid-surfactant interactions than the base fluid-gold nanoparticle interactions is observed. At lower temperatures, there is an inner layer around the gold nanoparticle with two surfactant molecules close to the metal. At a higher temperature a ratio of gold nanoparticles : diphenyl oxide molecules of 1 : 4 is maintained in the inner layer for the systems with and without the presence of a surfactant. At the highest temperatures, the presence of the surfactant in a second shell impedes the approximation of the fifth diphenyl oxide molecule. Thus, the surfactant affects the macroscopic properties of the gold nanofluid system at the molecular level.

The Role of Surfactants in the Stability of NiO Nanofluids: An Experimental and DFT Study.

This study shows an analysis of the stability of nanofluids based on a eutectic mixture of diphenyl oxide and biphenyl, which is used as a heat transfer fluid (HTF) in concentrating solar energy, and NiO nanoparticles. Two surfactants are used to analyse the stability of the nanofluids: benzalkonium chloride (BAC) and 1-octadecanethiol (ODT). From an experimental perspective, the stability is analysed by means of UV/Vis spectroscopy, particle size measurements through the dynamic light-scattering technique, and ζ-potential measurements. The results show that the stability of the nanofluids improves with the use of BAC. DFT calculations are performed to understand the role played by the surfactants. The interaction of the surfactants with both the fluid and the NiO (100) surface is studied. Quantum theory of atoms in molecules (QTAIM) analysis shows that hydrogen bridge interactions favour the stability of the fluid-surfactant mixture. The more stabilising NiO-surfactant interaction involves the Ni-H interaction of the -SH and -CH3 groups of ODT and BAC. Also, nanofluids with BAC are favoured over those with ODT, which is in agreement with experimental results. The structural and electronic effects of incorporating the surfactant onto the NiO (100) surface are shown by using electron localisation function analysis, the non-covalent interaction index and projected density of states.

A Study of Overheating of Thermostatically Controlled TiO2 Thin Films by Using Raman Spectroscopy.

In this study a classic Raman spectroscopy method is applied and the intensity ratio of Stokes and anti-Stokes peaks is used to measure the temperature of thermostatically controlled TiO2 thin films. In addition, three mathematical formulae are used and analyzed to estimate the temperature of the TiO2 thin films. Overheating of the samples above the thermostatically controlled temperature was observed while recording the Raman spectra, with a temperature increase of up to 30 K being detected. DFT-periodic calculations showed that the anatase (101) surface had a smaller band gap than bulk anatase. Thus, it can absorb the laser radiation with a wavelength of 532 nm that is used in the experimental setup. Part of the absorbed photon energy transfers into phonon energy, heating up the anatase phase, thus leading to the heating of the samples. Moreover, overheating of the samples indicates that the experimental method used in this study can lead to deviations in their real absolute temperature values.

Revealing the role of Pb(2+) in the stability of organic-inorganic hybrid perovskite CH3NH3Pb1-xCdxI3: an experimental and theoretical study.

This paper presents the synthesis of organic-inorganic hybrid perovskite CH3NH3Pb1-xCdxI3. The effect of incorporating Cd(2+) or Pb(2+) on the stability of the perovskite structure was analysed from a theoretical and experimental viewpoint. The XRD results showed that the tetragonal perovskite structure was formed for x values of up to 0.5, which seems to indicate that the presence of a considerable amount of Pb(2+) is necessary to stabilise the structure. In turn, UV-Vis spectroscopy showed how the presence of Cd(2+) led to a reduction in the optical band gap of the perovskite structure of up to 9% for CH3NH3Pb0.5Cd0.5I3 with regard to the MAPbI3 structure. Moreover, periodic-DFT calculations were performed to understand the effect of the increased concentration of Cd on the structural and electronic properties of MAPbI3 perovskites. The analysis of both the ELF and the non-covalent interaction (NCI) index show the important role played by the Pb(2+) ions in stabilizing this kind of hybrid perovskite structures. Finally, the DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy. The theoretical band gap values decreased as the concentration of Cd increased.

New insights into organic-inorganic hybrid perovskite CH3NH3PbI3 nanoparticles. An experimental and theoretical study of doping in Pb²âº sites with Sn²âº, Sr²âº, Cd²âº and Ca²âº.

This paper presents the synthesis of the organic-inorganic hybrid perovskite, CH3NH3PbI3, doped in the Pb(2+) position with Sn(2+), Sr(2+), Cd(2+) and Ca(2+). The incorporation of the dopants into the crystalline structure was analysed, observing how the characteristics of the dopant affected properties such as the crystalline phase, emission and optical properties. XRD showed how doping with Sn(2+), Sr(2+) and Cd(2+) did not modify the normal tetragonal phase. When doping with Ca(2+), the cubic phase was obtained. Moreover, DR-UV-Vis spectroscopy showed how the band gap decreased with the dopants, the values following the trend Sr(2+) < Cd(2+) < Ca(2+) < CH3NH3PbI3 ≈ Sn(2+). The biggest decrease was generated by Sr(2+), which reduced the CH3NH3PbI3 value by 4.5%. In turn, cathodoluminescence (CL) measurements confirmed the band gap obtained. Periodic-DFT calculations were performed to understand the experimental structures. The DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy, with the values calculated following the trend Sn(2+) ≈ Pb(2+) > Cd(2+) > Sr(2+) for the tetragonal structure and Pb(2+) > Ca(2+) for the cubic phase. The electron localization function (ELF) analysis showed similar electron localizations for undoped and Sn(2+)-doped tetragonal structures, which were different from those doped with Sr(2+) and Cd(2+). Furthermore, when Cd(2+) was incorporated, the Cd-I interaction was strengthened. For Ca(2+) doping, the Ca-I interaction had a greater ionic nature than Cd-I. Finally, an analysis based on the non-covalent interaction (NCI) index is presented to determine the weak-type interactions of the CH3NH3 groups with the dopant and I atoms. To our knowledge, this kind of analysis with these hybrid systems has not been performed previously.

Tm-doped TiO2 and Tm2Ti2O7 pyrochlore nanoparticles: enhancing the photocatalytic activity of rutile with a pyrochlore phase.

Tm-doped TiO2 nanoparticles were synthesized using a water-controlled hydrolysis reaction. Analysis was performed in order to determine the influence of the dopant concentration and annealing temperature on the phase, crystallinity, and electronic and optical properties of the resulting material. Various characterization techniques were utilized such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and UV-vis spectroscopy. For the samples annealed at 773 and 973 K, anatase phase TiO2 was obtained, predominantly internally doped with Tm(3+). ICP-AES showed that a doping concentration of up to 5.8 atom % was obtained without reducing the crystallinity of the samples. The presence of Tm(3+) was confirmed by X-ray photoelectron spectroscopy and UV-vis spectroscopy: the incorporation of Tm(3+) was confirmed by the generation of new absorption bands that could be assigned to Tm(3+) transitions. Furthermore, when the samples were annealed at 1173 K, a pyrochlore phase (Tm2Ti2O7) mixed with TiO2 was obtained with a predominant rutile phase. The photodegradation of methylene blue showed that this pyrochlore phase enhanced the photocatalytic activity of the rutile phase.

Introducing "UCA-FUKUI" software: reactivity-index calculations.

A new software (UCA-FUKUI) has been developed to facilitate the theoretical study of chemical reactivity. This program can calculate global parameters like hardness, softness, philicities, and Fukui condensed functions, and also local parameters from the condensed functions. To facilitate access to the program we have developed a very easy-to-use interface. We have tested the performance of the software by calculating the global and local reactivity indexes of a group of representative molecules. Finite difference and frontier molecular orbital methods were compared and their correlation tested. Finally, we have extended the analysis to a set of ligands of importance in coordination chemistry, and the results are compared with the exact calculation. As a general trend, our study shows the existence of a high correlation between global parameters, but a weaker correlation between local parameters.

Thermo-selective Tm(x)Ti(1-x)O(2-x/2) nanoparticles: from Tm-doped anatase TiO2 to a rutile/pyrochlore Tm2Ti2O7 mixture. An experimental and theoretical study with a photocatalytic application.

This is an experimental and theoretical study of thulium doped TiO2 nanoparticles. From an experimental perspective, a method was used to synthesize thulium-doped TiO2 nanoparticles in which Tm(3+) replaces Ti(4+) in the lattice, which to our knowledge has neither been reported nor studied theoretically so far. Different proportions of anatase and rutile phases were obtained at different annealing temperatures, and XRD and Raman spectroscopy also revealed the presence of a pyrochlore phase (Tm2Ti2O7) at 1173 K. Thus, the structure of the Tm-doped nanoparticles was thermally-controlled. Furthermore, XPS showed the presence of Tm(3+) in the samples synthesized, which produces oxygen vacancies to maintain the local neutrality in the lattice. The presence of Tm(3+) in the samples led to changes in the UV-Vis absorption spectra, so they showed photoluminescence properties and new states in the band gap, which produce a new lower energy electronic transition than the main TiO2 one. Periodic DFT calculations were performed to understand the experimentally produced structures. The production of oxygen vacancies was analysed and the changes generated in the structure were fully detailed. The DOS and PDOS analyses confirmed the experimental results obtained using UV-Vis spectroscopy, and showed that the new electronic states in the band gap are due to interactions of the f state of Tm and the p state of O. Likewise, the charge study and the ELF analysis indicate that when Tm is introduced into the TiO2 structure, the Ti-O bond around the oxygen vacancy is strengthened. Finally, an example of a photocatalytic application was developed to show the high efficiency of the samples due to the heterojunction in the interfaces of the phases in the samples, which improved the charge separation and the good charge carrier mobility due to the presence of the pyrochlore phase, as was also shown theoretically.

Electronic and structural properties of highly aluminum ion doped TiO(2) nanoparticles: a combined experimental and theoretical study.

This study presents the experimental and theoretical study of highly internally Al-doped TiO2 nanoparticles. Two synthesis methods were used and detailed characterization was performed. There were differences in the doping and the crystallinity, but the nanoparticles synthesized with the different methods share common features. Anatase to rutile transformation occurred at higher temperatures with Al doping. X-ray photoelectron spectroscopy showed the generation of oxygen vacancies, which is an interesting feature in photocatalysis. In turn, the band-gap energy and the valence band did not change appreciably. Periodic density functional calculations were performed to model the experimentally doped structures, the formation of the oxygen vacancies, and the band gap. Calculation of the density of states confirmed the experimental band-gap energies. The theoretical results confirmed the presence of Ti(4+) and Al(3+) . The charge density study and electron localization function analysis indicated that the inclusion of Al in the anatase structure resulted in a strengthening of the TiO bonds around the vacancy.

Experimental and theoretical study of the electronic properties of Cu-doped anatase TiO2.

A good correlation was obtained between the electronic properties of Cu-doped anatase TiO2 by virtue of both physical chemistry characterization and theoretical calculations. Pure and Cu-doped TiO2 were synthesized. The composition, structural and electronic properties, and the band gap energy were obtained using several techniques. The method of synthesis used produces Cu-doped anatase TiO2, and XRD, XPS and Raman spectroscopy indicate that Cu atoms are incorporated in the structure by substitution of Ti atoms, generating a distortion of the structure and oxygen vacancies. In turn, the band gap energy of the synthesized samples decrease drastically with the Cu doping. Moreover, periodic density functional theory (DFT-periodic) calculations were carried out both to model the experimentally observed doped structures and to understand theoretically the experimental structures obtained, the formation of oxygen vacancies and the values of the band gap energy. From the analysis of density of states (DOS), projected density of states (PDOS) and the electron localization function (ELF) a decrease in the band gap is predicted upon increasing the Cu doping. Thus, the inclusion of Cu in the anatase structure implies a covalent character in the Cu-O interaction, which involves the appearance of new states in the valence band maximum with a narrowing in the band gap.

New insights on the 7-azaindole photophysics: the overlooked role of its non phototautomerizable hydrogen bonded complexes.

In this paper we explore the formation and the photophysical properties of the scarcely studied open hydrogen bonded aggregates of 7-Azaindole, 7AI. Thus, we have analyzed the influence that the increase of the 7AI concentration and the decrease of the temperature have on the 7AI photophysics. To help the interpretation of the results, the 7AI-Pyridine system has been used as the model for the analysis of the photophysical properties attributable to the open N(pyrrolic) - H · · · N(pyridinic) hydrogen bonded aggregates. Also, the hydrogen bond interactions have been studied by means of the atom in molecule approach from the Bader theory. Experimental and theoretical results support that the formation of open hydrogen bonded aggregates, (-7AI-)n with n ≥ 2 can efficiently compete with that of the profusely studied centro-symmetric cyclic dimer (7AI)2. Moreover, these aggregates suffer a proton-driven electron transfer process that strongly quenches their room temperature fluorescence and, therefore, masks their presence in the 7AI solutions. Therefore, because most of the studies on the 7AI photophysics have been interpreted without considering the existence of such aggregates and, more important, ignoring its quenching process, many conclusions obtained from these studies should be carefully revised.

The near-mid-IR HOMO-LUMO gap in amide linked porphyrin-rhodamine dyads.

Novel amide linked porphyrin-rhodamine dyads yield utmost intense red-shifted electronic transitions beyond the near-infrared region.

Electrophilic reactivity of tetrabromorhodamine 123 is bromine induced: convergent interpretation through complementary molecular descriptors.

Nucleophilic addition of water and of methanol to 3,6-diamino-2,4,5,7-tetrabromo-9-[2-(methoxycarbonyl) phenyl]-9H-xanthen-9-ylium, 4BrR123, yields respectively 2-(3,6-diamino-2,4,5,7-tetrabromo-9-hydroxy-9H-xanthen-9-yl)xanthyl benzoate, HO4BrR123 and 2-(3,6-diamino-2,4,5,7-tetrabromo-9-methoxy-9H-xanthen-9-yl)xanthyl benzoate, MeO4BrR123. The novel experimental results are addressed theoretically. The linear free energy relationship, LFER, second-order perturbation theory analysis of the natural bond orbital, NBO, and quantum theory of atoms in molecules, QTAIM, lead to the same conclusion: the electron-withdrawing effect of bonded Br atoms in 4BrR123 extremely enhances the molecular electrophilicity, as compared to 3,6-diamino-9-[2-(methoxycarbonyl) phenyl]-9H-xanthen-9-ylium, R123. The reactivity of these diaminoxanthylium cations is discussed in the context of local and global softness in extended conjugated systems.

Reorganization of self-assembled dipeptide porphyrin J-aggregates in water-ethanol mixtures.

The self-assembly of a neutral meso-methoxyphenylporphyrin functionalized with a dipeptide glycilglycine substituent (MGG) in water and in water-ethanol mixtures was studied by absorption and fluorescence spectroscopy. In water, hydrophobic interactions and the noncovalent intermolecular hydrogen bonding between the terminal carboxylate group of one porphyrin and the hydrogen atoms of the pyrrolic nitrogens of another porphyrin originate nonspecific disorganized H- and J-aggregates. The addition of ethanol (0.1-25% v/v) to the water creates small clusters within which porphyrin J-aggregates reorganize as revealed by a narrow intense band detected by the Rayleigh light scattering (RLS) at 443 nm. Similar phenomenology is detected in SDS premicellar aggregates. Computational DFT calculations of a model dimer formation stabilized via intermolecular hydrogen bonding estimate an energy gain of -22 kJ mol(-1) and a center-to-center and interplane distances between porphyrin moieties of 16.8 and 3.7 Å, respectively. The kinetics of the J-aggregate formation could be fitted with a time-dependent model, and an activation energy of 96 kJ mol(-1) was estimated. The aggregate's morphology of MGG was followed by transmission electron microscopy (TEM) which showed rod-type structures of 5-8 µm evolving to spherical particles with increased ethanol content. Similar images and sizes were obtained in analogous samples using fluorescence lifetime imaging microscopy (FLIM) and dynamic light scattering (DLS). The formation of excitonically coupled supramolecular MGG structures of brickwork or staircase types is proposed in these water-ethanol mixtures.