A Stable Porphyrin Functionalized Graphite Electrode Used at the Oxygen Evolution Reaction Potential

Many researches have been devoted to rechargeable power generators that can store (but also release) energy. This availability is ensured through (e. g.) the oxygen evolution reaction (OER). However, (i) large values of the overpotentials and (ii) a progressive detriment of the anode (graphite) electrode limit the ultimate device. In view of enhancing the electrode performances, graphite was protected by following different strategies, which oblige to follow precise preparation protocols. Here, we prove that a thin layer of free-base porphyrin molecules is able to protect the underneath graphite electrode from detriment even if many (about 100) electrochemical cycles are performed.     

Driving Organic Nanocrystals Dissolution Through Electrochemistry

We have recently discussed how organic nanocrystal dissolution appears in different morphologies and the role of the solution pH in the crystal detriment process. We also highlighted the role of the local molecular chemistry in porphyrin nanocrystals having comparable structures: in water-based acid solutions, protonation of free-base porphyrin molecules is the driving force for crystal dissolution, whereas metal (Zn^II) porphyrin nanocrystals remain unperturbed. However, all porphyrin types, having an electron rich π-structure, can be electrochemically oxidized. In this scenario, a key question is: does electrochemistry represent a viable strategy to drive the dissolution of both free-base and metal porphyrin nanocrystals? In this work, by exploiting electrochemical atomic force microscopy (EC-AFM), we monitor in situ and in real time the dissolution of both free-base and metal porphyrin nanocrystals, as soon as molecules reach the oxidation potential, showing different regimes according to the applied EC potential.     

The water-silicas interfacial interaction energies

The water-silicas interfacial interaction energies were calculated for samples of quartz, silicas and silicas outgassed at high temperatures using own and published data of the spreading pressure of water, its surface tension, its contact angle and using formulas obtained by the combination of the Young equation with a general equation of pair interaction. The values obtained for 18 different samples were in the range 7.80-6.92 kJ mol⁻¹. Lower values of energies are for samples that contain relatively less amounts of water at P/P₀ = 0.25 and are characterized also by relatively low values of surface pressures.     

Growth-related properties and postgrowth phenomena in organic molecular thin films

The problem of monitoring the structural and morphological evolutions of thin films of organic molecular materials during their growth by organic molecular beam epitaxy and in the postgrowth stage is addressed here by a combination of in situ optical reflectance anisotropy measurements, ex situ optical and morphological investigations, and theoretical simulation of the material optical response. For alpha-quaterthiophene, a representative material in the class of organic molecular semiconductors, the results show that molecules crystallize in the first stage of growth in metastable structures, even when deposition is carried out at room temperature. In the postdeposition stage, the film structure evolves within a few days to the known equilibrium structure of the low temperature polymorph. When deposition is carried out at low substrate temperatures, an evolution of the film morphology is also demonstrated.     

The direction of the dipole moments of furan,thiophen, and pyrrole: A controversial question

The report that the dipole moment in the five-membered heterocyclic rings, furan, thiophene, and pyrrole has the positive pole on the heteroatom is contradicted with arguments based on reactivity data, theoretical calculations and moment values of substituted derivatives. In actuality, the dipole moment in furan and thiophene is directed from the ring (positive pole) to the heteroatom (negative pole).     

ARDESIA: A fast silicon drift detector X-ray spectrometer for synchrotron applications

ARDESIA, a four-channel X-ray spectrometer based on silicon drift detectors (SDDs), is presented. It has been developed for synchrotron applications targeting especially X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) with good energy resolution at high count rates (a few Mcps per second). The main target applications are XRF and XAFS techniques. The system features a 2 × 2 monolithic array of 5-mm-pitch SDDs cooled with a double Peltier scheme and coupled to a four-channel CUBE charge preamplifier. Different digital pulse processors allowing operation in Mcps per second count rates are employed. The results of preliminary characterization measurements performed at both the LNF DAΦNE-Light DXR1 beamline and the ESRF LISA BM-08 are reported, in particular, XRF measurements on low atomic number elements (down to the Carbon K-line, 270 eV) and extended X-ray absorption fine structure of trace materials in pyrite.     

Dynamic Multi-level Overlay Graphs for Shortest Paths

Multi-level overlay graphs represent a speed-up technique for shortest paths computation which is based on a hierarchical decomposition of a weighted directed graph G. They have been shown to be experimentally efficient, especially when applied to timetable information. However, no theoretical result on the cost of constructing, maintaining and querying multi-level overlay graphs in a dynamic environment is known. In this paper, we show theoretical properties of multi-level overlay graphs that lead us to the definition of a new data structure for the computation and the maintenance of an overlay graph of G while weight decrease or weight increase operations are performed on G. Our solution is theoretically faster than the recomputation from scratch and allows queries that can be performed more efficiently than running Dijkstra’s shortest paths algorithm on G. This work was partially supported by the Future and Emerging Technologies Unit of EC (IST priority – 6th FP), under contract no. FP6-021235-2 (project ARRIVAL).     

Partial specific adsorption of organic molecules in binary mixtures of adsorbents: 2,2'-bipyridine on kaolinite and hematite and 1,10-phenanthroline on montmorillonite and hydroxy-Al montmorillonite

The adsorption of 2,2'-bipyridyl in binary mixtures of sodium kaolinite and hematite at pH 6.6 and of 1,10-phenanthroline in binary mixtures of sodium montmorillonite and hydroxy-Al montmorillonite at pH 7.5 was studied as a function of the equilibrium concentration and composition of the mixture. A model is presented for determining the partial specific adsorption of two adsorbents by each component of the mixture, based on the graphic method for determining partial quantities. The partial specific adsorption values obtained for binary mixtures of Na-kaolinite with hematite and Na-montmorillonite with hydroxy-Al montmorillonite are strongly influenced by the concentration of adsorbates and adsorbents in the mixtures.     

The surface energy of kaolinite

The surface energy of kaolinite was determined from the water adsorption isotherm, the water/kaolinite contact angle, and the surface tension of water, using a formula obtained by combining the Young equation with the general equation of pair interaction. This formula could be represented by a polynomial function whose roots gave one real value of 252.57±2.75 mJ m^–2 for the surface energy of kaolinite. An important feature of the procedure for obtaining this energy is the use of the Young equation to determine the range in which the value of the surface energy lies.