Mariangela Longhi | Università degli Studi di Milano - State University of Milan (Italy) (original) (raw)
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Papers by Mariangela Longhi
Journal of Physical Chemistry B, 2003
ABSTRACT O2 evolution from a mixed Mg−LiCoO2 oxide is investigated in base solutions of alkali me... more ABSTRACT O2 evolution from a mixed Mg−LiCoO2 oxide is investigated in base solutions of alkali metal cations (0.1−2 M LiOH, KOH, or CsOH) without added supporting electrolytes. Tafel slopes range 30−50 mV/decade, scarcely related to the used alkali. However, Tafel lines are displaced to more positive potentials in passing from CsOH to KOH and LiOH at the same concentration, and moreover, reaction orders with respect to OH- decrease from 3 to 1 along the same alkali sequence with fractional rather than integer values. The reaction mechanism is examined on the assumption that Temkin-type adsorption conditions apply to the many reacting intermediates possibly involved. Analytical equations representing Tafel slope and reaction order in Temkin conditions are derived and reported for many frequently adopted O2 evolution pathways, most of them for the first time. From these equations, the experimental behavior is reconciled with a constant mechanism (Kobussen's path) in which the rate-determining step varies depending on the alkali cation, shifting forward in the sequence of elementary steps from early positions in CsOH and KOH to the last one in which molecular O2 is released in LiOH. Cation interactions with reacting surface sites apparently intervene to modify the reaction activation free energy profile, stronger for Li+ than K+ and Cs+. Structural relations with Li+ (and Mg2+) sites in the oxide lattice may be involved. However, the interaction sequence, Li+ > K+ > Cs+, is similar to that observed at the interface of many structurally and chemically unrelated oxides suspended in water and is attributed to entropic contributions from interactions of water molecules bonded in the hydration ion cosphere and at the oxide−solution interface.
Journal of Physical Chemistry C, 2013
Positronium (Ps) has been the subject of several experimental and theoretical investigations due ... more Positronium (Ps) has been the subject of several experimental and theoretical investigations due to its many scientific applications. In this work high positronium yield was found in engineered porous silica. The studied materials were pellets of swollen MCM-41 and of commercial Davicat 1700, obtained by different compression pressures, with mesopores characterized by different structural and chemical features. The measurements were performed with a variable energy positron beam at room temperature. An estimation of the Ps mean diffusion length was obtained by measuring capped samples. A selected swollen MCM-41 sample (0.39 g/cm 3 ) was measured also at cryogenic temperature (8 K). In this material both the Ps yield and the Ps diffusion length are found to be independent of temperature. The pore surface of the swollen MCM-41 samples is very interesting in comparison to commercial silica as it possesses hydrophobic patches to avoid ice formation at low temperature. Positron lifetime measurements show a high Ps survival time inside the mesoporous materials (∼110 ns), which promotes a high Ps mobility during cooling inside the pores favoring diffusion lengths up to 1 μm for swollen MCM-41 materials. Besides, it was possible to estimate the total Ps yield coming up outside the sample at high implantation energies and the time between the implantation of positrons and the Ps release.
![Research paper thumbnail of Charge-Transfer Patterns for [Ru(NH3)6]3+/2+ at SAM Modified Gold Electrodes: Impact of the Permeability of a Redox Probe](https://attachments.academia-assets.com/48117271/thumbnails/1.jpg)
](The Open Physical Chemistry Journal, 2008
Electrochemical performance of a [Ru(NH 3 ) 6 ] 3+/2+ redox couple at gold electrodes modified by... more Electrochemical performance of a [Ru(NH 3 ) 6 ] 3+/2+ redox couple at gold electrodes modified by alkanethiol self assembled monolayer (SAM) films of the type [-SH -(CH 2 ) n -CH 3 ] with different number of methylene units (n = 2 to 10) in the presence and absence of glucose additives has been studied using fast scan cyclic and steady-state voltammetry. Specific scatter of measured rate constants caused by enhanced sensitivity of this probe to minor defects of SAMs has been observed in a general agreement with the published data for thicker SAMs (n = 9 to 18). In addition, we have disclosed the anomalous viscosity-imposed drop of the heterogeneous rate constant for the case of Au electrodes modified by thinner n-alkanethiol SAMs (n = 2, 4). Taking into the account the fact of [Ru(NH 3 ) 6 ] 3+/2+ couple's capability to penetrate into the SAM interior, we ascribe the obtained results to the manifestation of the solvent-friction mechanism under the condition where the redox species presumably together with a few of solvating water molecules reside in a SAM's peripheral interior marked by much higher local viscosity (slower dielectric relaxation) compared to the electrolyte solution.
Journal of Electroanalytical Chemistry, 2005
PNA oligomers are promising candidates as DNA probes on account of their very high DNA binding po... more PNA oligomers are promising candidates as DNA probes on account of their very high DNA binding power, but they generally require an appropriate electrochemically or spectroscopically active marker. This paper describes the systematic electrochemical characterization of two newly synthesized PNA monomers, derivatised with one or three active ferrocene groups, and of their precursors. Our monomers show high electrochemical activity in
Journal of Electroanalytical Chemistry, 2003
The silver surface screening effects by specifically adsorbed halide anions in the electrocatalyt... more The silver surface screening effects by specifically adsorbed halide anions in the electrocatalytic reduction of a model organic bromide (acetobromoglucose) have been studied by cyclic voltammetry on controlled mono- and polycrystalline silver surfaces in acetonitrile+0.1 M tetraethylammonium perchlorate medium as a function of the concentration cX of added TEAX (X=Cl, Br, or I, TEA, tetraethylammonium). The reduction peak potentials, Ep,
Electrochemistry Communications, 2002
ABSTRACT A technique is described to obtain supported oxide powder electrodes. Preformed powders ... more ABSTRACT A technique is described to obtain supported oxide powder electrodes. Preformed powders are first embedded into a gold substrate, as reported by Totir et al. [D.A. Totir, B.D. Cahan, D.A. Scherson, Electrochim. Acta 45 (1999) 161], and then made to adhere in place by heating at T∼260–300 °C in flowing oxygen. This latter step is of the greatest importance to obtain reliable electrodes for use in aqueous electrolytes. Electrode stability and reproducibility are examined on voltammetric and O2 evolution results using Co3O4 as a sensitive test oxide material. Many independent Au–Co3O4 electrodes compare favourably with one another and with graphite-supported electrodes from an unrelated, room temperature binding technique. Substrate and oxide-substrate junction effects are minimised.
Chemistry of Materials, 2006
ABSTRACT The paper describes a single-step procedure by which linear terminal diamines are direct... more ABSTRACT The paper describes a single-step procedure by which linear terminal diamines are directly anchored onto activated carbon in sizable amounts (5%). Evidence for the formation of real amide bonds is provided by using a range of spectroscopic and “in situ” electrochemical determinations (X-ray photoelectron spectroscopy, Brunauer−Emmett−Teller, Fourier transform infrared, Boehm titrations, and potentiometric acid−base titrations). Results on the reaction stoichiometry are also given, showing that diamines and surface carboxyls react in a close to 1:1 molar ratio. Terminal −NH2 groups not engaged in amide bonds are free to react further and, in the present conditions, show well-defined proton adsorption behavior.
Journal of Electroanalytical Chemistry, 1999
The electrochemical behaviour of Co 3 O 4 from exhaustive cobalt nitrate decomposition (T =260 -8... more The electrochemical behaviour of Co 3 O 4 from exhaustive cobalt nitrate decomposition (T =260 -850°C) is investigated on graphite-supported electrodes, mainly relying on quasi-reversible results. Two well defined 1 − e − redox systems are observed related to Co 2 + /Co 3 + and Co 3 + /Co 4 + reactions of non-equivalent oxide surface sites. Oxide stoichiometry is directly estimated by voltammetry in 'wet' conditions and depends on preparation temperature as in ex situ solid state data. Adsorption of surface intermediates involved in charge transfer is examined. Langmuir and Temkin-type adsorption isotherms are obeyed for the Co 2 + /Co 3 + and Co 3 + /Co 4 + redox systems, respectively. Unusually negative (attractive) lateral interaction parameters are calculated for the latter system. Separation of oxide and graphite currents is achieved to permit real electrode surface area determination.
Journal of Physical Chemistry B, 2003
ABSTRACT O2 evolution from a mixed Mg−LiCoO2 oxide is investigated in base solutions of alkali me... more ABSTRACT O2 evolution from a mixed Mg−LiCoO2 oxide is investigated in base solutions of alkali metal cations (0.1−2 M LiOH, KOH, or CsOH) without added supporting electrolytes. Tafel slopes range 30−50 mV/decade, scarcely related to the used alkali. However, Tafel lines are displaced to more positive potentials in passing from CsOH to KOH and LiOH at the same concentration, and moreover, reaction orders with respect to OH- decrease from 3 to 1 along the same alkali sequence with fractional rather than integer values. The reaction mechanism is examined on the assumption that Temkin-type adsorption conditions apply to the many reacting intermediates possibly involved. Analytical equations representing Tafel slope and reaction order in Temkin conditions are derived and reported for many frequently adopted O2 evolution pathways, most of them for the first time. From these equations, the experimental behavior is reconciled with a constant mechanism (Kobussen's path) in which the rate-determining step varies depending on the alkali cation, shifting forward in the sequence of elementary steps from early positions in CsOH and KOH to the last one in which molecular O2 is released in LiOH. Cation interactions with reacting surface sites apparently intervene to modify the reaction activation free energy profile, stronger for Li+ than K+ and Cs+. Structural relations with Li+ (and Mg2+) sites in the oxide lattice may be involved. However, the interaction sequence, Li+ > K+ > Cs+, is similar to that observed at the interface of many structurally and chemically unrelated oxides suspended in water and is attributed to entropic contributions from interactions of water molecules bonded in the hydration ion cosphere and at the oxide−solution interface.
Journal of Physical Chemistry C, 2013
Positronium (Ps) has been the subject of several experimental and theoretical investigations due ... more Positronium (Ps) has been the subject of several experimental and theoretical investigations due to its many scientific applications. In this work high positronium yield was found in engineered porous silica. The studied materials were pellets of swollen MCM-41 and of commercial Davicat 1700, obtained by different compression pressures, with mesopores characterized by different structural and chemical features. The measurements were performed with a variable energy positron beam at room temperature. An estimation of the Ps mean diffusion length was obtained by measuring capped samples. A selected swollen MCM-41 sample (0.39 g/cm 3 ) was measured also at cryogenic temperature (8 K). In this material both the Ps yield and the Ps diffusion length are found to be independent of temperature. The pore surface of the swollen MCM-41 samples is very interesting in comparison to commercial silica as it possesses hydrophobic patches to avoid ice formation at low temperature. Positron lifetime measurements show a high Ps survival time inside the mesoporous materials (∼110 ns), which promotes a high Ps mobility during cooling inside the pores favoring diffusion lengths up to 1 μm for swollen MCM-41 materials. Besides, it was possible to estimate the total Ps yield coming up outside the sample at high implantation energies and the time between the implantation of positrons and the Ps release.
The Open Physical Chemistry Journal, 2008
Electrochemical performance of a [Ru(NH 3 ) 6 ] 3+/2+ redox couple at gold electrodes modified by... more Electrochemical performance of a [Ru(NH 3 ) 6 ] 3+/2+ redox couple at gold electrodes modified by alkanethiol self assembled monolayer (SAM) films of the type [-SH -(CH 2 ) n -CH 3 ] with different number of methylene units (n = 2 to 10) in the presence and absence of glucose additives has been studied using fast scan cyclic and steady-state voltammetry. Specific scatter of measured rate constants caused by enhanced sensitivity of this probe to minor defects of SAMs has been observed in a general agreement with the published data for thicker SAMs (n = 9 to 18). In addition, we have disclosed the anomalous viscosity-imposed drop of the heterogeneous rate constant for the case of Au electrodes modified by thinner n-alkanethiol SAMs (n = 2, 4). Taking into the account the fact of [Ru(NH 3 ) 6 ] 3+/2+ couple's capability to penetrate into the SAM interior, we ascribe the obtained results to the manifestation of the solvent-friction mechanism under the condition where the redox species presumably together with a few of solvating water molecules reside in a SAM's peripheral interior marked by much higher local viscosity (slower dielectric relaxation) compared to the electrolyte solution.
Journal of Electroanalytical Chemistry, 2005
PNA oligomers are promising candidates as DNA probes on account of their very high DNA binding po... more PNA oligomers are promising candidates as DNA probes on account of their very high DNA binding power, but they generally require an appropriate electrochemically or spectroscopically active marker. This paper describes the systematic electrochemical characterization of two newly synthesized PNA monomers, derivatised with one or three active ferrocene groups, and of their precursors. Our monomers show high electrochemical activity in
Journal of Electroanalytical Chemistry, 2003
The silver surface screening effects by specifically adsorbed halide anions in the electrocatalyt... more The silver surface screening effects by specifically adsorbed halide anions in the electrocatalytic reduction of a model organic bromide (acetobromoglucose) have been studied by cyclic voltammetry on controlled mono- and polycrystalline silver surfaces in acetonitrile+0.1 M tetraethylammonium perchlorate medium as a function of the concentration cX of added TEAX (X=Cl, Br, or I, TEA, tetraethylammonium). The reduction peak potentials, Ep,
Electrochemistry Communications, 2002
ABSTRACT A technique is described to obtain supported oxide powder electrodes. Preformed powders ... more ABSTRACT A technique is described to obtain supported oxide powder electrodes. Preformed powders are first embedded into a gold substrate, as reported by Totir et al. [D.A. Totir, B.D. Cahan, D.A. Scherson, Electrochim. Acta 45 (1999) 161], and then made to adhere in place by heating at T∼260–300 °C in flowing oxygen. This latter step is of the greatest importance to obtain reliable electrodes for use in aqueous electrolytes. Electrode stability and reproducibility are examined on voltammetric and O2 evolution results using Co3O4 as a sensitive test oxide material. Many independent Au–Co3O4 electrodes compare favourably with one another and with graphite-supported electrodes from an unrelated, room temperature binding technique. Substrate and oxide-substrate junction effects are minimised.
Chemistry of Materials, 2006
ABSTRACT The paper describes a single-step procedure by which linear terminal diamines are direct... more ABSTRACT The paper describes a single-step procedure by which linear terminal diamines are directly anchored onto activated carbon in sizable amounts (5%). Evidence for the formation of real amide bonds is provided by using a range of spectroscopic and “in situ” electrochemical determinations (X-ray photoelectron spectroscopy, Brunauer−Emmett−Teller, Fourier transform infrared, Boehm titrations, and potentiometric acid−base titrations). Results on the reaction stoichiometry are also given, showing that diamines and surface carboxyls react in a close to 1:1 molar ratio. Terminal −NH2 groups not engaged in amide bonds are free to react further and, in the present conditions, show well-defined proton adsorption behavior.
Journal of Electroanalytical Chemistry, 1999
The electrochemical behaviour of Co 3 O 4 from exhaustive cobalt nitrate decomposition (T =260 -8... more The electrochemical behaviour of Co 3 O 4 from exhaustive cobalt nitrate decomposition (T =260 -850°C) is investigated on graphite-supported electrodes, mainly relying on quasi-reversible results. Two well defined 1 − e − redox systems are observed related to Co 2 + /Co 3 + and Co 3 + /Co 4 + reactions of non-equivalent oxide surface sites. Oxide stoichiometry is directly estimated by voltammetry in 'wet' conditions and depends on preparation temperature as in ex situ solid state data. Adsorption of surface intermediates involved in charge transfer is examined. Langmuir and Temkin-type adsorption isotherms are obeyed for the Co 2 + /Co 3 + and Co 3 + /Co 4 + redox systems, respectively. Unusually negative (attractive) lateral interaction parameters are calculated for the latter system. Separation of oxide and graphite currents is achieved to permit real electrode surface area determination.