Showing papers by "Prashant V. Kamat published in 1998"
TL;DR: In this article, the 40−60 nm clusters were observed to break up into smaller clusters (5−20 nm) with 355 nm laser-pulse excitation and the choice of excitation wavelength provided the size selectivity in the fragmentation of the clusters.
Abstract: Silver colloids of particle diameter 40−60 nm have been synthesized using a chemical reduction method in aqueous medium. These nanoclusters are photoactive and exhibit transient bleaching in the 400−500 nm region followed by a strong absorption in the visible−near-infrared region when subjected to 355 nm laser-pulse excitation. The transient bleaching of the surface plasmon absorption band is a monophotonic process, while the absorption growth in the red region is a biphotonic process arising from the photoejection of electrons. The 40−60 nm clusters were observed to break up into smaller clusters (5−20 nm) with 355 nm laser-pulse excitation. The choice of excitation wavelength provides the size selectivity in the fragmentation of the clusters. For example, when the excitation wavelength was switched to 532 nm, only larger (or irregularly shaped) particles were found to break up.
578 citations
TL;DR: In this paper, the degradation of a reactive black dye in oxygen saturated aqueous solution has been investigated using a high frequency ultrasonic generator, which results in 65% mineralization as measured by the decrease in the total organic content.
148 citations
TL;DR: In this article, a composite thin film electrode comprised of SnO2/Bi2S3 nanocrystallites has been prepared by sequential deposition of the nanoclusters onto an optically transparent electrode and its photoelectrochemical behavior has been studied.
Abstract: Quantized semiconductor nanoclusters of Bi2S3 are prepared in acetonitrile by reacting BiI3 with H2S or Na2S. Both preparation methods yield stable colloids with particle diameters of ≤5 nm. Excitation with a 355-nm laser pulse results in transient bleaching in the 400−500-nm region. This process is followed by the formation of S-surf with a difference absorption maximum around 540 nm. This we attribute to the chemical changes associated with the hole-trapping process. A composite thin film electrode comprised of SnO2/Bi2S3 nanocrystallites has been prepared by sequential deposition of SnO2 and Bi2S3 films onto an optically transparent electrode, and its photoelectrochemical behavior has been studied. The thin film is photoactive in the visible and near-IR and exhibits an incident photon to photocurrent efficiency (IPCE) of ∼15% at 400 nm.
139 citations
TL;DR: In this article, the potential of a coupled electrode in bringing about an efficient charge separation in nanocrystalline DSPE cells has been highlighted, and the importance of the proper placement of the energy levels of individual semiconductor components in the coupled system for vectorial el...
Abstract: In an effort to suppress charge recombination in nanoporous dye sensitized photoelectrochemical (DSPE) solar cells, nanocrystalline coupled semiconductor electrodes of the type OTE/SnO2/TiO2 have been prepared, and their photosensitization with a ruthenium polypyridyl complex, Ru(II), has been carried out (OTE is an optically transparent electrode). Improved photoresponse, i.e., higher incident photon to current conversion efficiency (IPCE), higher photovoltage, lower back-electron-transfer rate, kr, and similar front- and back-face action spectra in the coupled OTE/SnO2/TiO2/Ru(II) system compared to those for simple OTE/SnO2/Ru(II) and OTE/TiO2/Ru(II) ones emphasize the potential of a coupled electrode in bringing about an efficient charge separation in nanocrystalline DSPE cells. A negligible photocurrent in a reverse composite OTE/TiO2/SnO2/Ru(II) system underscores the importance of the proper placement of the energy levels of individual semiconductor components in the coupled system for vectorial el...
128 citations
TL;DR: In this paper, a thin film of SiO2 and SnO2 cast on an optically transparent electrode was modified with ruthenium(II) polypyridyl complex, Ru(bpy)2 (bpy-COOH)2+, Ru(II).
Abstract: Nanostructured thin films of SiO2 and SnO2 cast on an optically transparent electrode were modified with ruthenium(II) polypyridyl complex, Ru(bpy)2(bpy-COOH)2+, Ru(II). Kinetic and mechanistic details of interaction between iodide ions and excited Ru(II), as well as regeneration of the sensitizer by iodide ions, were elucidated using emission spectroscopy and laser flash photolysis. The reaction between excited Ru(II) and I- in SiO2 films which occurred with a rate constant of 1.0 × 108 M-1 s-1 produced low yields of electron-transfer products. In the case of SnO2 films modified with Ru(II), the charge injection was the dominant process with the production of oxidized sensitizer, Ru(III). The reaction between Ru(III) and I- controls the regeneration of sensitizer in a photochemical solar cells. The oxidation of I- by Ru(III) in SnO2 films as confirmed from the production of I2•- occurred with a rate constant of 1.2 × 1010 M-1 s-1.
105 citations
TL;DR: In this article, two new pyrrolidinofullerenes, 1 and 2, have been synthesized and their photophysical properties have been investigated, and their singlet and triplet excited states have been examined with picosecond and nanosecond laser flash photolysis.
Abstract: Two new pyrrolidinofullerenes, 1 and 2, have been synthesized, and their photophysical properties have been investigated. The pyrrolidinofullerene 1 has three phenyl groups attached to the 1, 2, and 5 positions of the pyrrolidine ring. The pyrrolidinofullerene 2, on the other hand, has a flexible attachment with an N-methylaniline end group and is the prototype of a fullerene-aniline dyad. Singlet and triplet excited-state properties of these two functionalized fullerene derivatives have been examined with picosecond and nanosecond laser flash photolysis. The singlet and triplet excited states of these fullerenes exhibit characteristic absorption bands in the vis-IR region of the spectrum. The functionalization of C 60 with pyrrolidine groups shift the excited-state absorption maxima to the blue. Three different quenchers, O 2 , TEMPO, and ferrocene, are employed to investigate the reactivity of triplet excited states. The bimolecular quenching rate constants determined for these quenchers were in the range of 5.3 × 10 8 to 7.7 × 10 9 M -1 s -1 . The excited-state interactions of these functionalized fullerenes are compared to that of C 60 .
82 citations
TL;DR: In this paper, the spectral characterization of the oxidized form of Ru(II) cis-di(isothiocyanato)bis(4,4‘-dicarboxy-2,2'bipyridyl), (commonly known as N3-dye) in aqueous solution is made by reacting the title compound with pulse radiolytically generated radicals N3• and Br2-•.
Abstract: The spectral characterization of the oxidized form of (ruthenium(II) cis-di(isothiocyanato)bis(4,4‘-dicarboxy-2,2‘-bipyridyl), (commonly known as N3-dye) in aqueous solution is made by reacting the title compound with pulse radiolytically generated radicals N3• and Br2-•. The one-electron oxidized form of Ru(II)-dye initially formed in both these oxidation reactions shows absorption maxima at 320 and 740 nm. Following radiolysis, the one-electron oxidized form of Ru(II)-dye undergoes further transformations to yield a stable product that exhibits a characteristic absorption maximum at 440 nm. Our preliminary results provide the spectral evidence for the formation of two different species that follow the oxidation of Ru(II)-dye.
48 citations
TL;DR: In this paper, radiolysis of aqueous solutions of TNT was examined to provide fundamental information concerning the reactions of TNT with radical species in water, and the bimolecular rate constant for the reaction between TNT and - OH was determined to be 4.3 x 10 8 mol -1 s −1 s -1.
Abstract: Radiolysis of aqueous solutions of TNT was examined to provide fundamental information concerning the reactions of TNT with radical species in water. γ-Radiation was used in conjunction with radical scavengers to compare yields for radiation-induced TNT transformation under oxidizing and reducing conditions and in the presence and absence of oxygen. Pulse radiolytic techniques were employed to determine rate constants and absorption spectra for the reactions of TNT with the hydroxyl radical and the aqueous electron. TNT was rapidly transformed under both reducing (1% tert-butyl alcohol, N 2 sparged) and oxidizing (N 2 O sparged) conditions although rates under reducing conditions were greater. The initial yield for transformation of a 350 μmol L -1 TNT solution under reducing conditions was 0.14 μmol/J as opposed to 0.10 μmol/J measured in oxidizing conditions. The reactions of TNT with reduced oxygen species were found to be highly inefficient in aqueous solution. Although TNT is transformed by both oxidizing and reducing radicals, TNT degradation yields in the absence of a radical scavenger were low, indicating that under these conditions there were significant secondary reactions in which the species resulting from reactions between TNT and the primary radicals further reacted to reform the parent compound. The bimolecular rate constant for the reaction between TNT and - OH was determined to be 4.3 x 10 8 mol -1 s -1 . Byproduct analyses from γ-radiolysis suggest that hydroxyl radical abstraction of a methyl hydrogen to form the trinitrotoluyl radical is an initial oxidative reaction. The bimolecular rate constant for the reaction between TNT and e aq - was measured as 3.5 x 10 10 mol -1 s -1 . These results provide quantitative and qualitative insight into the reactions between TNT and the various aqueous radicals produced in many remediation processes.
18 citations
TL;DR: In this paper, the oxidation of dimethyl methylphosphonate (DMMP) was examined under ultrasonic conditions (640 kHz) in oxygen saturated aqueous solutions, and the initial rates of oxidation were determined as a function of initial DMMP concentration.
Abstract: The oxidation of dimethyl methylphosphonate (DMMP) was examined under ultrasonic conditions (640 kHz) in oxygen saturated aqueous solutions. Acetic acid, formic acid, methylphosphonic acid, phosphate, and oxalic acid have been identified as the major products produced during the sonolytic irradiation of DMMP. The initial rates of oxidation were determined as a function of initial DMMP concentration. The kinetic behavior of the system is consistent with the Langmuir-Hinshelwood model implying oxidative processes occur at or near the gas-liquid interface during cavitation. Mechanistic implications and conclusions are discussed based on the product distributions and kinetic parameters.
8 citations
TL;DR: Basic understanding of these radical reaction intermediates and the kinetic parameters of various radical reactions can be useful in designing strategies for the destruction of other harmful organophosphorus compounds.
Abstract: Abstract The radiolytic reactions of the diethyl benzylphosphonate (DEBP) have been investigated upon reaction with pulse radiolytically generated e-aq, hydroxyl, azide and Cl2 -• radicals. Oxidation with hydroxyl radical yields a transient intermediate with absorption maximum at 320 nm and kinetic parameters, consistent with hydroxyl radical addition to the aromatic ring. Benzyl radical, if formed, appears to be a minor reaction product as a result of hydroxyl radical reactions. The bimolecular rate constant for hydroxyl radical is 7± 1 × 1O9 M-1 s-1, in neutral and alkaline solutions. DEBP does not appear to react with N3• and Cl2-•. The bimolecular rate constant for reduction of DEBP by hydrated electrons is 8±2 × 1O7 M-1s-1. Hydroxyl radical appears to be the predominant species responsible for the degradation of DEBP in the radiolytic treatment. Basic understanding of these radical reaction intermediates and the kinetic parameters of various radical reactions can be useful in designing strategies for the destruction of other harmful organophosphorus compounds.