NOPR Collection:

Absorption and fluorescence spectra of tetrakis(sulphonatophenyl) porphyrin in Triton X-100 micelles: Analysis in terms of four-orbital model parameter

1989-09-01T00:00:00Z

Title: Absorption and fluorescence spectra of tetrakis(sulphonatophenyl) porphyrin in Triton X-100 micelles: Analysis in terms of four-orbital model parameter Authors: Basu, Sekhar; Paul, Tapan K; Roy, Sarmila Abstract: Effects of Triton X-100 micelles on the absorption and emission properties of tetrakis(sulphonatophenyl)porphyrin (TPPS) have been studied. An analysis of the absorption spectra in terms of four-orbital model of porphyrin excited state reveals that there is no ground state complex formation. The TPPS molecule is strongly hydrophilic so there is very little possibility of its solubilization within neutral Triton X-100 micelles. Enhancement of fluorescence intensity with increase in surfactant concentration is caused by the surface adsorption of the TPPS molecule at the hydrophilic mantle of the micelle, i.e. the Stern layer, where it is exposed to water, and van der Waals interaction is the main binding force. The inhibition of the radiation less decay by micellar aggregates, rationalized in terms of rigidization of the TPPS by the local environment of the micelle, is further confirmed from fluorescence polarization spectroscopy. Page(s): 729-734

Electrocatalytic activities of some codeposited binary noble metal surfaces over carbon substrates for anodic oxidation of methanol - in alkaline medium: Part I-Platinum-noble codeposits

1989-09-01T00:00:00Z

Title: Electrocatalytic activities of some codeposited binary noble metal surfaces over carbon substrates for anodic oxidation of methanol - in alkaline medium: Part I-Platinum-noble codeposits Authors: Guha, Prabir K; Bhattacharya, Abhijit; Kundu, Kiron K Abstract: Electrocatalytic activities of binary noble metal codeposits Pt-Pd, Pt-Rh, Pt-Ru, Pt-Ir and Pt-Au of different compositions over carbon substrate have been studied for the anodic oxidation of methanol in alkaline medium. Galvanostatic steady state and slow sweep cyclic voltammetric methods in conjunction with chronopotentiometric estimation of roughness factor (R_f) and examination of the geometric properties of the electrodes from scanning electron micrographs (SEM) are employed. Catalytic activities of these binary deposits are better than the Pt-deposited electrode. The electrocatalytic activities reach a maximum at a particular composition depending on the cometal, the order being: Rh > Ru >Pd > Ir > Au. The peak current density (i_p) and roughness factor (R_f) values also exhibit similar type of variations with maxima lying at the composition of maximal activities. The observed enhancement of catalytic activities of C/Pt electrodes with addition of cometals can be explained with the help of well known 'bi-functional theory' of alloy electrocatalysts. A careful analysis of the results, in particular the SEM's, reveal that while the extrinsic geometric properties are very much responsible for the observed activities, intrinsic electronic properties of the codeposits are equally important. Page(s): 735-744

Topological investigations of molecular species that characterize binary mixtures of N,N-dimethylformamide and formamide with aniline and o-toluidine

1989-09-01T00:00:00Z

Title: Topological investigations of molecular species that characterize binary mixtures of N,N-dimethylformamide and formamide with aniline and o-toluidine Authors: Singh, Prem P; Yadav, Satyamanyu Abstract: The results of topological investigations of the volumetric and enthalpic effects in binary mixtures of formamide or N,N-dimethylformamide (A) with aniline and o-toluidine (B) indicate that the state of association of (A) and (B) in an (A-B) mixture is determined by the molecular entity of (A) in the mixture, and that all these mixtures are characterised by specific interactions between the components (A) and (B) resulting in the formation of molecular complexes. The energetics of the solution process characteristics of these (A-B) mixtures have also beep investigated. Page(s): 745-751

Photo electrochemical studies on thin film Pb3O4 photoelectrodes

1989-09-01T00:00:00Z

Title: Photo electrochemical studies on thin film Pb3O4 photoelectrodes Authors: Kumar, Sudhir; Sharon, Maheshwar; Jawalekar, S R Abstract: Photoelectrochemical properties of thin film of Pb₃O₄ prepared by thermal annealing of electrodeposited thin film of PbO₂ have been studied. Energy levels of band diagram of Pb₃O₄ are experimentally found to be 4.26 eV and 6.40 eV for conduction and valence bands respectively. It is observed that Fe(CN)₆^-3/Fe(CN)₆ ^-4 electrolyte gives the maximum photo-current with this material. Effect of thickness of thin film of Pb₃O₄ on the photoconversion efficiency has been calculated. A maximum efficiency of 0.21 % with a fill factor 0.4 has been observed with 0.6 micron thick film. Prolonged illumination of the electrode results in decrease of photo-current suggesting the unstability of film over a long period. Page(s): 752-756