Rodrigo A. Iglesias

Adsorption of phenosafranin at the water ∣ 1,2 DCE interface: a voltammetric approach☆

Abstract In the present paper the interfacial behavior of a cationic dye, phenosafranin (PhS+), is voltammetrically analyzed. A sharp and narrow peak during the negative sweep was observed. The dependence of this peak on concentration, sweep rate and switch potential was a clear indication of an adsorption–desorption process similar to those observed on solid electrodes. It was determined that the adsorbed species results from the ion pairing between dicarbollylcobaltate (DCC−) and PhS+ at the interface as the process is observed only when the interface is polarized at the potential transfer of DCC−. The process fitted with a Frumkin isotherm and indicated a strong attractive interaction (g=−2.3) between the adsorbed species. This interaction was also analyzed spectrophotometrically.

Charge Extraction From TiO2 Nanotubes Sensitized With CdS Quantum Dots by SILAR Method

Quantum dot (QD) solar cells based on different materials have received a noticeable interest during the past ten years; however, their efficiency and stability are still the main drawback of this technology, which leads to a lack of performance of these devices. There are several electron loss (and efficiency) processes involved after photon absorption, but perhaps the main issue is with the electron recombination after excitation of the surface. In this paper, we have studied the dependence of short-circuit photocurrent of TiO2 nanotubes with varying amounts of CdS QDs deposited by the successive ionic layer adsorption and reaction method. We have found that there is an optimum coverage of CdS in order to achieve the maximum photocurrent value. This behavior is explained and characterized in terms of prevailing recombination processes at higher CdS coverage, where quantum confinement becomes less important. By using the charge extraction method, we could determine the time dependence of electrode charge and indicates that the back reaction of electrons with the redox electrolyte present in solution is of the first order in electron density and that it originates from the electrons present in the TiO2 conduction band.

Exploring weak intermolecular interactions in thiocyanate-bonded Zn(II) and Cd(II) complexes with methylimidazole: crystal structures, Hirshfeld surface analysis and luminescence properties

Four new thiocyanate-Zn(II) and -Cd(II) complexes with 1-methylimidazole (1-MeIm) and 2-methylimidazole (2-MeIm), namely, Zn(1-MeIm)2(SCN)2 (1), Zn(2-MeIm)2(SCN)2 (2), Cd(1-MeIm)4(SCN)2 (3) and polymeric [Cd(2-MeIm)2(SCN)2]n (4), have been synthesized and characterized by IR, Raman and UV-Vis spectroscopy. The thermal behavior for all complexes was evaluated by thermo-gravimetric analysis and differential thermal analysis. The crystal structures of complexes 1–4 were solved by single-crystal X-ray diffraction methods. A study of intermolecular interactions in the solid state compounds revealed that molecules are linked by weak N–H⋯S and C–H⋯S hydrogen bonds and also by C–H⋯π interaction in the case of structures 2–4, which are responsible for the formation and stability of the molecular assemblies. Hirshfeld surfaces and 2D-fingerprint plots allowed us to visualize the intermolecular contacts and their relative contributions to the total surface for each compound. A comparative analysis against similar halogen-bonded complexes was carried out to investigate the tendency of inter-molecular interactions to form contacts in crystals by using the enrichment ratio descriptor. The emission spectra of the free imidazole derivatives and their Zn(II) and Cd(II) complexes were recorded in acetonitrile solutions. The emissions observed in the spectra of complexes were ascribed to the intra-ligand transitions and ligand-to-metal charge transfer and we have observed an interesting correlation between the fluorescence intensities and C–H⋯π interactions.