Simultaneous Electrodeposition of MnO2 and Mn(OH)(2) for Supercapacitor Studies

Among the various Mn compounds, both MnO2 and Mn(OH)2 are electrochemically active in supercapacitor studies. MnO2 and Mn(OH)2 are simultaneously deposited, through a one-pot method, on the anode and cathode, respectively, of a galvanostatic electrolysis cell consisting of aqueous Mn(NO3)2 electrolyte. MnO2 and Mn(OH)2 coated stainless steel (SS) electrodes are found to exhibit a capacitive behavior with a high specific capacitance. MnO2/SS and Mn(OH)2/SS electrodes are used as the negative and positive electrodes, respectively, in assembling nonsymmetrical capacitors and testing. The results indicate that both Mn-based electrodes prepared simultaneously in a single electrolysis possess interesting electrochemical properties for supercapacitor application.

The effect of composition, electron irradiation and quenching on ionic conductivity in a new solid polymer electrolyte: (PEG) (x) NH4I

We have prepared, characterized and investigated a new PEG-2000 based solid polymer electrolyte (PEG) x NH4I. Ionic conductivity measurements have been made as a function of salt concentration as well as temperature in the range 265–330 K. Selected compositions of the electrolyte were exposed to a beam of 8 MeV electrons to an accumulated dose of 10 kGy to study the effect on ionic conductivity. The electrolyte samples were also quenched at liquid nitrogen temperature and conductivity measurements were made. The ionic conductivity at room temperature exhibits a characteristic double peak for the composition x = 20 and 70. Both electron beam irradiation and quenching at low temperature have resulted in an increase in conductivity by 1–2 orders of magnitude. The enhancement of conductivity upon irradiation and quenching is interpreted as due to an increase in amorphous region and decrease in crystallinity of the electrolyte. DSC and proton NMR measurements also support this conclusion.

Mössbauer studies of the corrosion products of iron formed in aqueous ammonium nitrate solution

The products of corrosion reaction of electrolytic iron in 45% ammonium nitrate solution formed under various conditions of time, temperature and pH have been analysed mainly by Mössbauer spectroscopy, in combination with X-ray diffraction, infrared absorption and electron microscopy techniques. γ-Fe00H is found to be the major product of hydrolytic precipitation at pH > 5.6 while only α-FeOOH is formed at pH < 3.0. In the pH range 3.0 < pH < 5.0, α-Fe00H and ferrihydrite are both formed. However, once the nuclei of α-Fe00H are formed under low pH conditions, their growth is favoured even in the otherwise unfavourable slightly acidic medium, resulting in a hydrous α-Fe00H which has two distinct hyperfine fields at the 57Fe nucleus. Magnetite is always formed in the vicinity of the metal and its rate of formation on the surface increases with temperature. α-Fe203 is the major product of hydrolytic precipitation at temperatures >80C. The possible mechanisms for the formation of each of the corrosion products are discussed.

Enhanced ionic conduction in dispersed solid electrolyte systems CaF2---Al2O3 and CaF2---CeO2

Dispersions of Al2O3 as well as CeO2 in CaF2 are found to enhance the conductivity of CaF2. Both these systems are biphasic and the electrical conduction in them is purely ionic in nature. At 650 K the increase in the ionic conductivity of the dispersed solid electrolyte system CaF2---Al2O3 is by about two orders of magnitude in relation to the conductivity of the host electrolyte CaF2, whereas for the CaF2---CeO2 system it is about three orders of magnitude. Some aspects of the increase in the ionic conductivities of CaF2---Al2O3 and CaF2---CeO2 electrolytes can be explained by a recent theoretical model. It is proposed that a substantial enhancement in the vacancy concentration of CaF2, brought about by the attraction of F− ions to the surface of Al2O3 (or CeO2), is responsible for the low temperature increase in the ionic conductivity of CaF2.

Photodimerization of coumarin in aqueous and micellar media

The photochemical and photophysical processes of many organic compounds are a function of the environment in which they are present. In this connection we have chosen to investigate the environmental perturbations on the photodimerization of coumarin,l and the results of our study in aqueous and micellar media are presented in this paper. Coumarin has historically been the subject of intense photochemical and spectroscopic interest, mainly as a consequence of its importance in biological systems. Coumarin has been chosen for our investigation as its fascinating photochemical behavior has been fairly well explored,2 and therefore the environmental influence, which is the subject of our concern, would be easily understandable.

Determination of the thermodynamic properties of xMgO + (1 x)MnO (s, sln) from a solid-electrolyte galvanic cell in the temperature range 1163 to 1318 K

The thermodynamic activities of MgO in the NaCl-type solid solutions which can exist in xMgO + (1 x)MnO have been determined in the temperature range 1163 to 1318 K from a solid-state galvanic cell incorporating MgF2 as the solid electrolyte. The activities of MnO have been calculated by a graphical Gibbs-Duhem integration method. The activities of both the components exhibit positive deviations from ideality over the entire composition range. The excess molar enthalpies are found to be positive. Further, xMgO + (1 - x)MnO does not conform to regular-solution behaviour. The origin of the excess thermodynamic properties is discussed in relation to the cationic size disparity and the crystal-field effects.

Solubility of ibuprofen in aqueous ethanol at low ethanol contents

The solubility of ibuprofen was measured in water (W) - ethanol (E) mixtures from 0 to 50% w/w ethanol at 10, 25 and 40 °C by the dissolution method using UV spectrophotometry to determine the ibuprofen concentrations. The UV calibration for ibuprofen in different water - ethanol mixtures showed Beer - Lambert linearity, however the slopes differed, which indicated the structure of the drug is influenced by the solvent system i.e. the water - ethanol ratio. The ibuprofen solubility in water (zero ethanol) is low (~ 50 ppm) but increases near exponentially with increasing ethanol content. At 40 °C, there is phase separation between 34% and 63% w/w E/(E+W). The solubility data will be used to select precipitation crystallizer conditions to directly produce free flowing ibuprofen particles (<5 m) for developing a dry powder inhaler (DPI) formulation for lung delivery.

Nanostructured Peptide Fibrils Formed at the Organic-Aqueous Interface and Their Use as Templates To Prepare Inorganic Nanostructures

Formation of fibril-type nanostructures of the Alzheimer's beta-amyloid diphenylalanine (L-Phe-L-Phe, FF) at the organic-aqueous interface and the factors affecting their structures have been investigated. Such nanostructures are also formed by bovine serum albumin and bovine pancreas insulin. The concentration of the precursor taken in the aqueous layer plays an important role in determining the morphology of the nanostructures, The addition of curcumin to the organic layer changes the structure of the self-assembled one-dimensional aggregates of diphenylalanine. By coating the diphenylalanine dipeptide fibrils with appropriate precursors followed by calcination in air, it has been possible to obtain one-dimensional nanostructures of inorganic materials.

Surface-enhanced Raman scattering of molecules adsorbed on nanocrystalline Au and Ag films formed at the organic-aqueous interface

Surface-enhanced Raman scattering (SERS) of pyridine adsorbed on ultrathin nanocrystalline Au and Ag films generated at the liquid-liquid interface has been investigated. The shifts and intensification of bands formed with these films comprising metal nanoparticles are comparable to those found with other types of Au and Ag substrates. SERS of rhodamine 6G adsorbed on Ag films has also been studied. The results demonstrate that nanocrystalline metal films prepared by the simple method involving the organic-aqueous interface can be used effectively for SERS investigations.

The formation of a p-n junction in a polymer electrolyte top-gated bilayer graphene transistor

We show simultaneous p- and n-type carrier injection in a bilayer graphene channel by varying the longitudinal bias across the channel and the top-gate voltage. The top gate is applied electrochemically using solid polymer electrolyte and the gate capacitance is measured to be 1.5 microF cm(-2), a value about 125 times higher than the conventional SiO(2) back-gate capacitance. Unlike the single-layer graphene, the drain-source current does not saturate on varying the drain-source bias voltage. The energy gap opened between the valence and conduction bands using top- and back-gate geometry is estimated.

Fluorescent alamethicin fragments A study of membrane activity and aqueous phase aggregation

The linear polypeptide antibiotic alamethicin is known to form channels in artificial lipid membranes. Synthetic 13- and 17-residue alamethicin fragments, labelled with a fluorescent dansyl group at the N-terminus, have been shown to translocate divalent cations across phospholipid membranes and to uncouple oxidative phosphorylation in rat liver mitochondria, in a manner analogous to the parent peptides. From studies of the aqueous phase aggregation behavior of the peptides, as well as their interaction with rat liver mitochondria, it is concluded that the interaction of the peptides with membranes is a complex process, probably involving both aqueous and membrane phase aggregation.

Dendritic structures produced on solidification of multicomponent aqueous solutions

Dendrite structures of ice produced on undirectional solidification of ternary and quaternary aqueous solutions have been studied. Upon freezing, solutions containing more than one solute produce plate-shaped dendrites of ice. The spacing between dendrites increase linearly with the distance from the chill surface and the square root of local solidification time (or square root of inverse freezing rate) for any fixed composition. For fixed freezing conditions, the dendrite spacings from multicomponent aqueous solutions were a function of the concentrations and diffusion coefficients of the individual solutes. The dendrite spacing produced by freezing of a solution was changed by the addition of a solute different from those already present. If the main diffusion coefficient of the added solute is higher than that of solutes already present, the dendrite spacing is increased and vice versa. The dendrite spacing in multi-component systems increases with the total solute concentration if the constituent solutes are present in equal amounts. The dendrite spacing obtained on freezing of these dilute multicomponent solutions can be expressed by regression equations of the type Image Full-size image (2K) where L is the dendrite spacing in microns, C1, C2 and C3 are concentrations of individual solutes, Θf is the total freezing time and A1 −A8 are constants. A Yates analysis of the dendrite spacings in a factorial design of quaternary solutions indicates that there are strong interactions between individual solutes in regard to their effect on the dendrite spacings. A mass transport analysis has been used to calculate the interdendritic supersaturation ΔC of the individual solutes, the supercooling in the interdendritic liquid ΔT, and the transverse growth velocity of the dendrites, VT. In ternary solutions if two solutes are present in equal amount the supersaturation of the solute with higher main diffusion coefficient is lower, and vice versa. If a solute with higher main diffusion coefficient is added to a binary solution, the interface growth velocity, the interdendritic supersaturation of the base solute and the interdendritic supercooling increase with the quantity of solute added.