Showing papers in "Journal of Physical Chemistry B in 1997"
TL;DR: In this paper, a synthesis of highly luminescent (CdSe)ZnS composite quantum dots with CdSe cores ranging in diameter from 23 to 55 A was reported.
Abstract: We report a synthesis of highly luminescent (CdSe)ZnS composite quantum dots with CdSe cores ranging in diameter from 23 to 55 A. The narrow photoluminescence (fwhm ≤ 40 nm) from these composite dots spans most of the visible spectrum from blue through red with quantum yields of 30−50% at room temperature. We characterize these materials using a range of optical and structural techniques. Optical absorption and photoluminescence spectroscopies probe the effect of ZnS passivation on the electronic structure of the dots. We use a combination of wavelength dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, small and wide angle X-ray scattering, and transmission electron microscopy to analyze the composite dots and determine their chemical composition, average size, size distribution, shape, and internal structure. Using a simple effective mass theory, we model the energy shift for the first excited state for (CdSe)ZnS and (CdSe)CdS dots with varying shell thickness. Finally, we characterize the...
4,293 citations
TL;DR: In this paper, the authors present the full implementation of the integral equation formalism (IEF) formulated to treat solvent effects, which exploits a common approach for dielectrics of very different nature: standard isotropic liquids, intrinsically anisotropic media like liquid crystals, and ionic solutions.
Abstract: We present the full implementation of the integral equation formalism (IEF) we have recently formulated to treat solvent effects. The method exploits a single common approach for dielectrics of very different nature: standard isotropic liquids, intrinsically anisotropic media like liquid crystals, and ionic solutions. We report here an analysis of its both formal and technical details as well as some numerical applications addressed to state the achieved generalization to all kinds of molecular solutes and to show the equally reliable performances in treating such different environmental systems. In particular, we report, for isotropic liquids, data of solvation free energies and static (hyper)polarizabilities of various molecular solutes in water, for anisotropic dielectrics, a study of an SN2 reaction, and finally, for ionic solution, a study of some structural aspects of ion pairing.
1,834 citations
TL;DR: In this paper, the authors showed that the dependence of λmax for longitudinal resonance on the mean aspect ratio shows a deviation from the classical electrostatic model prediction at mean aspect ratios around 4 ± 1.
Abstract: Aqueous solutions containing a high yield of suspended gold nanorods have been successfully synthesized via an electrochemical method. The control of preparing gold nanorods with different aspect ratios can be attained. Their absorption spectral features show a dominant surface plasma band corresponding to the longitudinal resonance, SPl, and its λmax shifts markedly to the red as the aspect ratio is increased. Meanwhile, the dependence of λmax for longitudinal resonance on the mean aspect ratio shows a deviation from the classical electrostatic model prediction at mean aspect ratios around 4 ± 1, where it limits the validity of the classical electrostatic approximation.
1,537 citations
TL;DR: The optical absorption spectra of a series of nanocrystal gold molecules, passivated by a compact monolayer of n-alkylthiol(ate)shave have been measured across the electronic range (1.1−4.0 eV) in dilute solution at ordinary temperature as mentioned in this paper.
Abstract: The optical absorption spectra of a series of nanocrystal gold moleculeslarger, crystalline Au clusters that are passivated by a compact monolayer of n-alkylthiol(ate)shave been measured across the electronic range (1.1−4.0 eV) in dilute solution at ordinary temperature. Each of the ∼20 samples, ranging in effective core diameter from 1.4 to 3.2 nm (∼70 to ∼800 Au atoms), has been purified by fractional crystallization and has undergone a separate compositional and structural characterization by mass spectrometry and X-ray diffraction. With decreasing core mass (crystallite size) the spectra uniformly show a systematic evolution, specifically (i) a broadening of the so-called surface-plasmon band until it is essentially unidentifiable for crystallites of less than 2.0 nm effective diameter, (ii) the emergence of a distinct onset for strong absorption near the energy (∼1.7 eV) of the interbandgap (5d → 6sp), and (iii) the appearance in the smallest crystallites of a weak steplike structure above this onset...
1,297 citations
TL;DR: In this article, the properties of Li+ ion insertion in nanoporous TiO2 (anatase) electrodes were studied by voltammetry and linear and cyclic potential scans were recorded as a function of electrolyte con...
Abstract: Electrochemical properties of Li+ ion insertion in nanoporous TiO2 (anatase) electrodes were studied by voltammetry. Linear and cyclic potential scans were recorded as a function of electrolyte con ...
1,172 citations
TL;DR: In this article, a charge recombination between dye-sensitized nanocrystalline TiO2 electrodes and the I3/I-couple in nonaqueous solution is described.
Abstract: Charge recombination between dye-sensitized nanocrystalline TiO2 electrodes and the I3-/I- couple in nonaqueous solution is described. The sensitizer was [RuL2(NCS)2] (L = 2,2‘-bipyridyl-4,4‘-dicarboxylic acid). An apparent inequality between the dark current and the recombination current is ascribed to a voltage shift caused by a potential drop at the SnO2/TiO2 interface, ohmic losses in the SnO2 and TiO2, and an overpotential for the redox reaction at the Pt counter electrode. Treating the dye-coated TiO2 electrodes with pyridine derivatives (4-tert-butylpyridine, 2-vinylpyridine, or poly(2-vinylpyridine)) improves significantly both the open-circuit photovoltage Voc (from 0.57 to 0.73 V) and the cell conversion efficiency (from 5.8 to 7.5%) at a radiant power of 100 mW/cm2 (AM 1.5) with respect to the untreated electrode. An analytical expression relating Voc to the interfacial recombination kinetics is derived, and its limitations are discussed. Analysis of Voc vs radiant power data with this expressi...
906 citations
TL;DR: In this paper, a theoretical model of IMVS for dye-sensitized nanocrystalline semiconductor electrodes is developed, and analytical expressions for the frequency dependence of the photovoltage response at open circuit are derived.
Abstract: The charge-recombination kinetics and band edge movement in dye-sensitized nanocrystalline TiO2 solar cells are investigated by intensity modulated photovoltage spectroscopy (IMVS). A theoretical model of IMVS for dye-sensitized nanocrystalline semiconductor electrodes is developed, and analytical expressions for the frequency dependence of the photovoltage response at open circuit are derived. The model considers charge trapping/detrapping and electron transfer from the conduction band and surface states of the semiconductor to redox species at the solid/solution interface. IMVS is shown to be valuable in elucidating the contributions of band edge shift and recombination kinetics to changes of the open-circuit photovoltage (Voc) resulting from surface modifications of the semiconductor. IMVS measurements indicate that surface treatment of [RuL2(NCS)2] (L = 2,2‘-bipyridyl-4,4‘-dicarboxylic acid)-sensitized TiO2 electrodes with 4-tert-butylpyridine or ammonia leads to a significant band edge shift concomit...
841 citations
TL;DR: In this article, an exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction.
Abstract: Titanium(IV) oxide (TiO2) powders of various amorphous−anatase compositions were prepared by heat treatment (573−1073 K) of amorphous TiO2 in air and characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and BET surface area measurements. An exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction of amorphous phase. The fraction of anatase crystallites (f(anatase)) was calculated as the remainder after the amorphous phase and contaminated water or organic residue. The XRD data showed that the size of anatase crystallites was slightly decreased but almost constant along with the increase in f(anatase), being consistent with the small change in the BET surface area. These results suggest that each amorphous particle transforms into an anatase crystallite of similar size without sintering or crystal growth. The particles of mixture of amorphous and anatase were ...
782 citations
TL;DR: This article presents a general mechanism for protein folding and function and demonstrates the mechanism by designing model proteins capable of performing many of the energy conversions that sustain life and by designing diverse biomolecular machines and materials with promising applications for society.
Abstract: This article, on protein-based polymers comprised of repeating peptide sequences, reviews studies from the author's laboratory covering a period of more than two decades; it presents a general mechanism for protein folding and function and demonstrates the mechanism by designing model proteins capable of performing many of the energy conversions that sustain life and by designing diverse biomolecular machines and materials with promising applications for society. All polymers with the correct balance of apolar and polar moieties, including water soluble proteins and protein-based polymers, increase order by a hydrophobic folding and assembly transition as the temperature is raised above a critical onset temperature, designated as Tt. Instead of varying the temperature, however, innumerable variables lower the value of Tt from above to below the operating temperature to drive folding and function. Thus, this inverse temperature transition provides a fundamental mechanism whereby proteins fold and function ...
779 citations
TL;DR: In this paper, a new sensitizing dye−semiconductor system comprised of perylene derivatives on SnO2 has been characterized and shown to yield a short circuit photocurrent density of 3.26 mA/cm2, a photovoltage of −0.45 V, and overall cell efficiency of 0.89% at one sun light intensity.
Abstract: A new sensitizing dye−semiconductor system comprised of perylene derivatives on SnO2 has been characterized. The tetracarboxylic acid form (“PTCA”) of the commercially available dye perylene-3,4,9,10-tetracarboxylic dianhydride and the novel compound perylene-3,4-dicarboxylic acid-9,10-(5-phenanthroline)carboximide (“PPDCA”) adsorb strongly to the surface of colloidal films of SnO2 and inject electrons into the semiconductor film upon absorption of light. A film of PPDCA on SnO2 yields a short circuit photocurrent density of 3.26 mA/cm2, a photovoltage of −0.45 V, and an overall cell efficiency of 0.89% at one sun light intensity. Estimates of the oxidation potential of adsorbed PPDCA indicate that it may also be useful in a water-splitting configuration. The results presented here indicate that the perylene−SnO2 system is a promising dye−semiconductor combination and warrants further study.
762 citations
TL;DR: In this article, a comprehensive study was conducted on mesoporous MCM-41 and it was shown that three types of silanol groups, i.e., single, (SiO)3Si−OH, hydrogen-bonded, and geminal silanols, can be observed.
Abstract: A comprehensive study was conducted on mesoporous MCM-41. Spectroscopic examinations demonstrated that three types of silanol groups, i.e., single, (SiO)3Si−OH, hydrogen-bonded, (SiO)3Si−OH-OH−Si(SiO)3, and geminal, (SiO)2Si(OH)2, can be observed. The number of silanol groups/nm2, αOH, as determined by NMR, varies between 2.5 and 3.0 depending on the template-removal methods. All these silanol groups were found to be the active sites for adsorption of pyridine with desorption energies of 91.4 and 52.2 kJ mol-1, respectively. However, only free silanol groups (involving single and geminal silanols) are highly accessible to the silylating agent, chlorotrimethylsilane. Silylation can modify both the physical and chemical properties of MCM-41.
TL;DR: In this article, the photovoltaic cells were shown to convert sunlight to electrical power at an efficiency of 0.56% under full sun at the peak of the visible absorption band of the anthocyanin dye.
Abstract: colloidal TiO2 powder, is shown to convert sunlight to electrical power at an efficiency of 0.56% under full sun. Fluorescence quenching is observed for the excited state of the TiO2-adsorbed anthocyanin dye, cyanin, and the photocurrent spectrum correlates well with the optical absorption of the cyanin-sensitized TiO 2 nanocrystalline film. The incident photon-to-current efficiency of 19% at the peak of the visible absorption band of the dye, the open-circuit voltages of 0.5-0.4 V, and short-circuit photocurrents of 1.5-2.2 mA/cm 2 are remarkable for such a simple system and suggest efficient charge carrier injection. The ultrafast excitedstate dynamics of cyanin in solution are compared with those of surface-adsorbed cyanin on TiO2 and ZrO2 colloids, as well as complexed with Al(III) ions. A transient absorption signal with a risetime of <100 fs for cyanin-sensitized TiO2 nanoparticles is assigned to electrons injected from the dye to TiO 2. This signal is fit to a double-exponential decay with time constants of 0.52 and 67 ps. The 0.52 ps component is due to trapping of conduction band electrons or to fast direct recombination with the dye cation, while the 67 ps decay is attributed to trap state mediated indirect recombination. In contrast, stimulated emission with a 2.6 ps decay time is observed for cyanin in solution, cyanin on ZrO2, and cyanin complexed with Al(III) ions. When compared to the photon-to-current efficiency measured for the solar cell, the efficiency estimated from the injection and recombination rate constants suggests that electron recapture by the redox mediator and light screening mechanisms may limit the efficiency of the cell.
TL;DR: In this paper, the frequency-dependent photocurrent response of dye-sensitized TiO2 cells to modulated illumination was analyzed and analytical expressions were derived that describe generation, collection, and recombination of electrons in a thin layer nanocrystalline solar cell under conditions of steady illumination and with a superimposed small amplitude modulation.
Abstract: The frequency-dependent photocurrent response of dye-sensitized TiO2 cells to modulated illumination is analyzed. Analytical expressions are derived that describe generation, collection, and recombination of electrons in a thin layer nanocrystalline solar cell under conditions of steady illumination and with a superimposed small amplitude modulation. The analysis considers illumination from the contact side and from the counter electrode side, and characteristic differences in the intensity-modulated photocurrent response are predicted for the two cases. The attenuation of the ac photocurrent by the RC time constant of the cell is also considered. The theoretical analysis shows that intensity modulated photocurrent spectroscopy (IMPS) can provide new insight into the dynamics of electron transport and collection in the dye-sensitized solar cell. Experimental IMPS data measured for high-efficiency dye-sensitized cells are fitted to the theoretical model using Bode plots in order to derive values of the lif...
TL;DR: In this article, five massive gold-cluster molecules have been isolated in high yield and have undergone separate structural characterization, and their electronic structure has been deduced by optical absorption spectroscopy.
Abstract: Five massive gold-cluster molecules have been isolated in high yield and have undergone separate structural characterization, and their electronic structure has been deduced by optical absorption spectroscopy. These new molecules are distinguished by a crystalline (or quasicrystalline) core of densely packed Au atoms, ranging in size from ∼1.1 nm (∼40 atoms) to ∼1.9 nm (∼200 atoms), surrounded by a compact monolayer of various thio (RS) adsorbates. They are obtained as the thermally and environmentally stable products of the reductive decomposition of nonmetallic (−AuS(R)−) polymer in solution, are separated according to size by fractional crystallization or column chromatography, as monitored by high-mass spectrometry, and are characterized structurally by methods including X-ray diffraction (small and large angle), high-resolution electron microscopy, and scanning tunneling microscopy. The optical absorption spectra of dilute solutions of these molecules show size-dependent steplike structure with an on...
TL;DR: In this paper, the authors describe macroscopic electrolytic reduction of CO at a Cu electrode in various electrolyte solutions in order to reveal the unique properties of Cu electrodes in comparison with Fe and Ni electrodes.
Abstract: CO2 is electrochemically reduced to CH4, C2H4, and alcohols in aqueous electrolytes at Cu electrode with high current density. CO2 is initially reduced to adsorbed CO and further to hydrocarbons and alcohols. This paper describes macroscopic electrolytic reduction of CO at a Cu electrode in various electrolyte solutions in order to reveal the unique properties of Cu electrode in comparison with Fe and Ni electrodes. The reaction products from the Cu electrode are CH4, C2H4, C2H5OH, n-C3H7OH, CH3CHO, and C2H5CHO. Neither C2H6 nor CH3OH is produced. CH4 is favorably produced in aqueous KHCO3 of high concentrations (e.g. 0.3 mol dm-3), whereas C2H4 and C2H5OH are produced in dilute KHCO3 solutions (0.03 mol dm-3). Such product selectivity is derived from the electrogenerated OH- in the cathodic reaction, as is the case in the CO2 reduction. The partial current densities of CH4, C2H4, and C2H5OH are correlated with the electrode potential. Tafel relationships hold for C2H4 and C2H5OH irrespective of pH. The p...
TL;DR: In this article, the characterization of mixed oxides of TiO2/SiO2 and TiO 2/Al2O3 prepared by sol−gel methods is described.
Abstract: The characterization of mixed oxides of TiO2/SiO2 and TiO2/Al2O3 prepared by sol−gel methods is described. Application of the TiO2/Al2O3 material for the photocatalytic decomposition of salicylic acid gave improved activity relative to TiO2-only materials. The photocatalytic activity of TiO2/SiO2, TiO2/Al2O3, and TiO2 toward the photocatalytic decomposition of phenol demonstrated the enhancement of local TiO2 sites on TiO2/SiO2 materials relative to the other materials. The characterization of the catalysts indicates that the TiO2/SiO2 materials consist of matrix-isolated TiO2 quantum particles, while the TiO2/Al2O3 materials do not.
TL;DR: Raman spectra of clathrate hydrate guest molecules are presented for three known structures (I (sI), II (sII), and H (sH)) in the following systems:
Abstract: Raman spectra of clathrate hydrate guest molecules are presented for three known structures (I (sI), II (sII), and H (sH)) in the following systems: CH4 (sI), CO2 (sI), C3H8 (sII), CH4 + CO2 (sI), CD4 + C3H8 (sII), CH4 + N2 (sI), CH4 + THF-d8 (sII), and CH4 + C7D14 (sH). Relative occupancy of CH4 in the large and small cavities of sI were determined by deconvoluting the ν1 symmetric bands, resulting in hydration numbers of 6.04 ± 0.03. The frequency of the ν1 bands for CH4 in structures I, II, and H differ statistically, so that Raman spectroscopy is a potential tool to identify hydrate crystal structure. Hydrate guest compositions were also measured for two vapor compositions of the CH4 + CO2 system, and they compared favorably with predictions. The large cavities were measured to be almost fully occupied by CH4 and CO2, whereas only a small fraction of the small cavities are occupied by CH4. No CO2 was found in the small cavities. Hydration numbers from 7.27 to 7.45 were calculated for the mixed hydrate.
TL;DR: In this paper, a flexible three-centered water model (F3C) is proposed for simulation of biological macromolecules in solution, and the model is further tested by comparing calculated energetic, structural, and dynamic properties of liquid water, at several temperatures and pressures, with experiment.
Abstract: The objective of this work is to obtain a water model for simulations of biological macromolecules in solution. A pragmatic approach is taken in which we use the same type of force field for the water as used for the solute and derive the water potential as an integral part of the ENCAD macromolecular potential.1,2 Here we describe a flexible three-centered water model (F3C), which has already been used for many large-scale biological simulations, and compare it with other water models. The model is further tested by comparing calculated energetic, structural, and dynamic properties of liquid water, at several temperatures and pressures, with experiment. The F3C model is extremely simple and fits experimental data well for different temperatures, pressures, system sizes, and integration time steps. Because the F3C model works well with short-range truncation, it is well-suited to high-speed computation of long molecular dynamics trajectories of macromolecules in solution.
TL;DR: In this paper, a combination of a Voigt-type equivalent circuit analog and the Frumkin and Melik-Gaykazyan (FMG) model was used to model the Li ion migration through the surface films covering the graphite particles.
Abstract: Slow scan rate cyclic voltammetry (CV) and highly resolved (with respect to potential) electrochemical impedance spectroscopy (EIS) have been applied for lithiated graphite electrodes of different thicknesses The impedance spectra have been successfully modeled for the whole range of intercalation potentials, using a combination of a Voigt-type equivalent circuit analog and the Frumkin and Melik-Gaykazyan (FMG) model The Voigt-type analog, which is a series combination of R||C circuits, models the Li ion migration through the surface films covering the graphite particles The FMG model combines a finite-length Warburg element, which reflects solid state Li diffusion in the graphite particles in series with capacitance that reflects the bulk capacity of the graphite particles (doped with intercalated lithium) The highly anisotropic nature of the graphite particles predetermines different extensive properties, including their charge transfer resistance and the parameters of the finite-length Warburg The
TL;DR: The phase behavior of organically passivated 20−75 A diameter Ag and Au nanocrystals was investigated by examining surface−area isotherms of Langmuir monolayers and transmission electron micrographs of LB films as discussed by the authors.
Abstract: The phase behavior of organically passivated 20−75 A diameter Ag and Au nanocrystals is investigated by examining surface−area isotherms of Langmuir monolayers and transmission electron micrographs of Langmuir−Blodgett (LB) films. The effects of temperature, organic passivant chain length, and nanocrystal size and composition are studied. Three distinct types of phase behavior are observed and may be classified in terms of the extra (conical) volume (Ve) available to the alkyl capping group as it extends from a nearly spherical metal core. For Ve > 350 A3, the phase diagram is dominated by extended, low-dimensional structures that, at high pressures, compress into a two-dimensional foamlike phase. This behavior is rationalized as originating from the interpenetration of the ligand shells of adjacent particles. For Ve Ve > 150 A3, the particles condense to form closest packed structures, which, for suffici...
TL;DR: In this article, the potentiostatic electrochemical template synthesis of nanowires (Ni, Co, Cu, Au, and polyporrole) in polycarbonate track-etched membranes with nominal pore diameters dN between 10 and 200 nm is described.
Abstract: The potentiostatic electrochemical template synthesis of nanowires (Ni, Co, Cu, Au, and polyporrole) in polycarbonate track-etched membranes with nominal pore diameters dN between 10 and 200 nm is ...
TL;DR: In this article, the photochemical properties of nanostructured ZnO thin-film electrodes have been investigated in the UV and visible regions, and it has been shown that they may give high efficiencies in UV region, approaching unity for the Al-doped films.
Abstract: Photoelectrochemical properties of nanostructured ZnO thin film electrodes have been investigated in the UV and visible regions. For films consisting of 15 nm large undoped crystallites a maximum monochromatic current conversion efficiency of 58% was obtained in the visible using a ruthenium-based dye as a sensitizer. The overall solar energy conversion efficiency for this film was 2%. In comparison, sensitized films consisting of 150 nm large Al-doped crystallites yield a monochromatic current conversion efficiency of 31% and an overall solar energy conversion efficiency of 0.5%. The study also shows that nanostructured ZnO may give high efficiencies in the UV region, approaching unity for the Al-doped films.
TL;DR: In this paper, the pore size of MCM-41 materials was estimated based on geometrical considerations of the ratio of pore volume to pore wall volume for an infinite hexagonal array of cylindrical pores.
Abstract: Nitrogen adsorption measurements were performed over a wide range of relative pressures (10-6−0.995) for a series of siliceous MCM-41 samples obtained using alkyltrimethylammonium surfactants with different chain length. Both high- and low-pressure adsorption data were analyzed. The pore size was shown to increase in a regular way with the chain length of the surfactant used. Moreover, a very good correlation between the pore size and the interplanar spacing of the MCM-41 samples was observed. Methods used to calculate the pore diameter were critically compared, and a new procedure to estimate the pore size of MCM-41 materials was proposed. This new procedure is based on geometrical considerations of the ratio of the pore volume to the pore wall volume for an infinite hexagonal array of cylindrical pores. Adsorption measurements showed that the amount adsorbed in the low-pressure region increases with a decrease in the pore size of the samples probably because of the enhancement of the gas−surface interac...
TL;DR: In this paper, the authors developed and implemented a statistical mechanical integral equation theory to describe the hydration structure of complex molecules, which is an extension of the reference interaction site model (RISM) in three dimensions, yields the average density from the solvent interactions sites at all points around a molecular solute of arbitrary shape.
Abstract: We developed and implemented a statistical mechanical integral equation theory to describe the hydration structure of complex molecules. The theory, which is an extension of the reference interaction site model (RISM) in three dimensions, yields the average density from the solvent interactions sites at all points r around a molecular solute of arbitrary shape. Both solute−solvent electrostatic and van der Waals interactions are fully included, and solvent packing is taken into account. The approach is illustrated by calculating the average oxygen and hydrogen density of liquid water around two molecular solutes: water and N-methylacetamide. Molecular dynamics simulations are performed to test the results obtained from the integral equation. It is observed that important microscopic structural features of the average water density due to hydrogen bonding are reproduced by the integral equation. The integral equation has a simple formal structure and is easy to implement numerically. It offers a powerful ...
TL;DR: In this paper, the mechanism of photocatalytic oxidation of the model compounds dichloroacetate, DCA-, and thiocyanate, SCN-, have been investigated employing time-resolved laser flash photolysis.
Abstract: Details of the mechanism of the photocatalytic oxidation of the model compounds dichloroacetate, DCA-, and thiocyanate, SCN-, have been investigated employing time-resolved laser flash photolysis. Nanosized colloidal titanium dioxide (TiO2, anatase) particles with a mean diameter of 24 A were used as photocatalysts in optically transparent aqueous suspensions. Detailed spectroscopic investigations of the processes occurring upon band gap irradiation in these colloidal aqueous TiO2 suspensions in the absence of any hole scavengers showed that while electrons are trapped instantaneously, i.e., within the duration of the laser flash (20 ns), at least two different types of traps have to be considered for the remaining holes. Deeply trapped holes, h+tr, are rather long-lived and unreactive, i.e., they are transferred neither to DCA- nor to SCN- ions. Shallowly trapped holes, h+tr*, on the other hand, are in a thermally activated equilibrium with free holes which exhibit a very high oxidation potential. The ov...
TL;DR: In this paper, the solid state diffusion of lithium into graphite during electrochemical intercalation processes was investigated using potentiostatic intermittent titration (PITT) and impedance spectroscopy (EIS).
Abstract: The solid state diffusion of lithium into graphite during electrochemical intercalation processes was investigated using potentiostatic intermittent titration (PITT) and impedance spectroscopy (EIS...
TL;DR: In this article, the authors present a theory of dielectric relaxation of biological water, which is described in terms of a dynamic equilibrium between the free and bound water molecules, and then determined by the equilibrium constant between the two species and the rate of conversion from bound to free state and vice versa.
Abstract: Dielectric relaxation and NMR spectrum of water in biological systems such as proteins, DNA, and reverse micelles can often be described by two widely different time constants, one of which is in the picosecond while the other is in the nanosecond regime. Although it is widely believed that the bimodal relaxation arises from water at the hydration shell, a quantitative understanding of this important phenomenon is lacking. In this article we present a theory of dielectric relaxation of biological water. The time dependent relaxation of biological water is described in terms of a dynamic equilibrium between the free and bound water molecules. It is assumed that only the free water molecules undergo orientational motion; the bound water contribution enters only through the rotation of the biomolecule, which is also considered. The dielectric relaxation is then determined by the equilibrium constant between the two species and the rate of conversion from bound to free state and vice versa. However, the diele...
TL;DR: Titanium oxide species anchored within the Y-zeolite cavities by an ion exchange method exhibit a high and unique photocatalytic reactivity for the reduction of CO2 with H2O at 328 K with a high se
Abstract: Titanium oxide species anchored within the Y-zeolite cavities by an ion-exchange method exhibit a high and unique photocatalytic reactivity for the reduction of CO2 with H2O at 328 K with a high se
TL;DR: In situ hybridization with complementary oligomer strands, performed at the surface of modified electrodes, is clearly reflected by negative shifts of about 100 mV in the flat-band potential of the semiconductor.
Abstract: Homo-oligomer DNA strands were immobilized onto silicon/silicon dioxide electrodes using 3-aminopropyltriethoxysilane. These modified substrates were used as working electrodes in a three-electrode electrochemical cell. In-phase and out-of-phase impedances were measured in the range −1 to +1 V with respect to an Ag/AgCl reference electrode, with a superimposed 10 mV ac signal at frequencies of 20 and 100 kHz. Ex situ hybridization with complementary oligomer strands, performed at the surface of modified electrodes, is clearly reflected by negative shifts of about 100 mV in the flat-band potential of the semiconductor. Consecutive hybridization−denaturation steps show that the shifts are reproducible and the process is reversible. The in situ hybridization of complementary strands has also been observed with impedance measurements at Si/SiO2 substrates and with the use of a field effect device. The direct detection of hybridization with a field effect device was performed under constant drain current mode,...