BLEND MEMBRANES FOR DIRECT METHANOL AND PROTON EXCHANGE MEMBRANE FUEL CELLS

Sulphonated polystyrene ethylene butylene polystyrene(SPSEBS)prepared with 35%sulphonation was found to be highly elastic and enlarged up to 300%-400%of its initial length.It absorbed over 110%of water by weight.A major drawback of this membrane is its poor mechanical properties which are not adequate for use as polymer electrolytes in fuel cells.To overcome this,SPSEBS was blended with poly(vinylidene fluoride)(PVDF),a hydrophobic polymer.The blend membranes showed better mechanical properties than the base polymer.The effect of PVDF content on water uptake,ion exchange capacity and proton conductivity of the blend membranes was investigated.This paper presents the results of recent studies applied to develop an optimized in-house membrane electrode assembly(MEA)preparation technique combining catalyst ink spraying and assembly hot pressing.Easy steps were chosen in this preparation technique in order to simplify the method,aiming at cost reduction.The open circuit voltage for the cell with SPSEBS is 0.980 V which is higher compared to that of the cell with Nafion 117(0.790 V).From this study,it is concluded that a polymer electrolyte membrane suitable for proton exchange membrane fuel cell(PEMFC)and direct methanol fuel cell(DMFC)application can be obtained by blending SPSEBS and PVDF in appropriate proportions.The methanol permeability and selectivity showed a strong influence on DMFC performance.     

Synthesis and photocatalytic properties of a new heteropolyoxoniobate compound: K10[Nb2O2(H2O)2][SiNb12O40)·12H2O

The synthesis and photocatalytic properties of a heteropolyoxoniobate, K(10)[Nb(2)O(2)(H(2)O)(2)][SiNb(12)O(40)]·12H(2)O (1), are reported, revealing an important role of Zr(4+) additives in the crystallization. Compound 1 exhibits overall photocatalytic water splitting activity, and its photocatalytic activity is significantly higher than that of Na(10)[Nb(2)O(2)][SiNb(12)O(40)]·xH(2)O (2). Fluorescence lifetime measurements suggest that the enhanced photocatalytic activity of 1 likely results from a larger yield of longer-lived charge trapping states in 1 due to the coordination of one water molecule to the bridging Nb(5+), leading to highly unsymmetrical seven-coordinated Nb(5+) sites.     

Antibacterial,Antioxidant, Larvicidal and Anticancer Activities of Silver Nanoparticles Synthesized Using Extracts from Fruits of Lagerstroemia speciose and Flowers of Couroupita guianensis

The present study aimed to analyze the in vitro antibacterial, antioxidant, larvicidal and cytotoxicity properties of green synthesized silver nanoparticles (Ag NPs) using aqueous extracts from fruits of Lagerstroemia speciosa and flowers of Couropita guinensis. Synthesized Ag NPs were characterized using UV-DRS, FTIR, XRD, DLS, and High-Resolution SEM and TEM analyses. Absorption wavelength was observed at 386 nm by UV-DRS analysis and energy band gap was calculated as 3.24 eV. FTIR analysis showed the existence of various functional groups in the aqueous extract and in the NPs. DLS analysis showed the stability and particle size of the synthesized Ag NPs. SEM analysis revealed that Ag NPs are in a face centered cubic symmetry and spherical shape with a size of 23.9 nm. TEM analysis showed particle size as 29.90 nm. Ag NPs showed antibacterial activity against both Gram-positive and Gram-negative bacteria. DPPH scavenging trait of Ag NPs was ranging from 20.0 ± 0.2% to 62.4 ± 0.3% and observed significant larvicidal activity (LC50 at 0.742 ppm and LC90 at 6.061 ppm) against Culex quinquefasciatus. In vitro cytotoxicity activity of Ag NPs was also tested against human breast cancer (MCF-7) and fibroblast cells (L-929) and found that cells viabilities are ranging (500 to 25 µg/mL) from 52.5 ± 0.4 to 94.0 ± 0.7% and 53.6 ± 0.5 to 90.1 ± 0.8%, respectively. The synthesized Ag NPs have the potential to be used in the various biomedical applications.     

Formation and decay of N,N, N′, N′-tetraethyl-p-phenylenediamine radical cation in aqueous solution. A kinetic study by stopped-flow technique

A kinetic study has been carried out on the oxidation of N, N, N′, N′,-tetraethyl-p-phenylenediamine (TEPD) by metal ion like Ce⁴⁺, oxoanions viz., MnO₄^? and Cr₂O₇^2?; peroxides such as peroxomonosulphate (PMS), peroxodisulphate (PDS), and H₂O₂; and halogens namely Cl₂, Br₂, and I₂. The fast kinetics of the formation and decay of the radical cation TEPD^˙+ have been analyzed at 565 nm by the stopped-flow technique under pseudo-first-order conditions. From the kinetic data, it has been inferred that the reactions were found to be of first-order with respect to [TEPD] and [oxidant] but over all it has been of second-order. The observed second-order rate constants in both the formation and decay of TEPD^˙+ has been correlated with the oxidation potentials of the various oxidants employed in this study. The effect of pH on the oxidation has been investigated in the formation and decay of TEPD^˙+ as well as reduction studies have also been carried out using dithionite which has been found to regenerate the TEPD from the TEPD^˙+ and the corresponding rate constant has also been determined. Besides these, this article also explains how the TEPD, which forms TEPD^˙+ acts as a better electron relay than TMPD(N, N, N′, N′-tetramethyl-p-phenylenediamine) which forms TMPD^˙+, even though both of them undergo one-electron oxidation and are used in the chemical routes to solar energy conversions. The observed rate constants for electron transfer were correlated theoretically using Marcus theory. The observed and calculated rate constants have good correlation. © 1995 John Wiley & Sons, Inc.     

The photophysics of the 2,6 dialkoxy anthracenes: Evidence for excited state side-chain conformational relaxation

Three 2,6 dialkoxyanthracenes with varying ether sidechain lengths (methyl, n-propyl and n-hexyl) are synthesized and characterized. When compared to unsubstituted anthracene, the spectroscopic properties of the alkoxy-anthracenes are significantly different. The oscillator strength appears to be evenly distributed between the L_a and L_b states, rather than concentrated in the low-energy L_a state, and the transition dipole moments are rotated by ～30° in the molecular frame. More importantly, all three derivatives undergo an intramolecular conformational change in the excited state that gives rise to a reshaping of the fluorescence spectrum on the nanosecond timescale. This process has an activation energy of 8±1 kJ/mol. By ～150 K the fluorescence spectrum reflects only the high energy conformer, whose emission lineshape is similar to that of the unsubstituted anthracene. The temperature-dependent changes in the monomeric fluorescence spectra of these compounds will have to be taken into account in future studies of their solid-state spectroscopy.     

Dielectric studies of alkyl acrylates with primary alcohols using time domain reflectometry

Binary polar–polar liquid mixtures of alkyl acrylates (methyl acrylate, ethyl acrylate and butyl acrylate) with primary alcohols (propan-1-ol, butan-1-ol and hexan-1-ol) were subjected to dielectric studies at 303?K for different concentrations using time domain reflectometry (TDR) over the frequency range from 10?MHz to 10?GHz. Static permittivity (ε₀) dielectric constant at high frequency (ε_∞) and relaxation time (τ) were found through dielectric measurements for different concentrations of each system. The Bruggeman dielectric factor, Kirkwood correlation factor and the excess inverse relaxation time were determined and discussed to yield information on the molecular interactions of the systems. Deviations from the linearity of various models suggest molecular association through hydrogen bonding between the ?OH group of alcohols and C=O group of esters. The results also show a dependence of dielectric parameters on the alkyl chain length of both the alcohols and esters.     

Phosphonated mesoporous silica based composite membranes for high temperature proton exchange membrane fuel cells

Journal of Solid State Electrochemistry - Mesoporous Santa Barbara Amorphous (SBA-15) was synthesized, and it was grafted with phosphonate functionality using a simple two-step process involving...     

FTIR Study of Hydrogen Bonding Between Acrylic Esters and Alcohols

Hydrogen bonding between acrylic esters and alcohols has been studied in carbon tetrachloride by using the FTIR spectroscopic method. Utilizing the Nash method, the formation constant of the 1:1 complexes has been calculated. The formation constant and Gibbs energy change values vary with alcohol and ester chain length, which suggests that the proton donating ability of alcohols is in the order: 1-propanol < 1-butanol < 1-pentanol, and the accepting ability of acrylic esters is in the order: methyl methacrylate < ethyl methacrylate < butyl methacrylate.     

Kinetics and mechanism of oxidation of excited state Tris-(2,2′-bipyridyl)-ruthenium (II) complex by peroxomonosulfate,peroxodisulfate, and peroxodiphosphate

Excitation of Ru(bipy)₃²⁺ ion by visible radiation of wavelength λ = 436 nm in aqueous medium in presence of inorganic peroxides, peroxomonosulfate (PMS), peroxodisulfate (PDS), and peroxodiphosphate (PDP) was found to generate Ru(bipy)₃³⁺. The kinetics of this photochemical oxidation of Ru(bipy)₃²⁺ by each peroxide was followed spectrophotometrically and found to obey a total second-order, first-order each in [Ru(bipy)₃²⁺] and [peroxide]. In the absence of light, thermal reaction of PMS and PDS with Ru(bipy)₃²⁺ occurred but only when at 1.0 M [H⁺] and > 10^?2M [peroxide]. The reaction of PMS with the complex is found to be cyclic, ie., Ru(bipy)₃³⁺ formed oxidizes PMS itself and such a reaction was not observed in the case of PDS and PDP. The effects of pH, [peroxide], and [Ru(bipy)₃²⁺] on the visible light induced oxidation of Ru(bipy)₃²⁺ by these peroxides are investigated. The results are discussed with suitable reaction mechanisms.