A solid-state perspective is offered for a discussion of silverbased ternary and quaternary oxide... more A solid-state perspective is offered for a discussion of silverbased ternary and quaternary oxide semiconductors for applications related to solar fuels photogeneration and environmental remediation. The rather unique d10 electron configuration in these compounds is shown to impart interesting effects on their optoelectronic properties, and in turn, the photocatalytic activity of these compounds. This Minireview focuses on the structural aspects, electronic band structures, synthetic advances, and finally photoelectrochemical and photocatalytic applications of 32 compounds within the two oxide families, of the generic formula: Ag x B y O z or Ag x B y C n O z , where B and C are metals or non-metals other than silver.
Abstract Applications of dynamic dielectric analysis (DDA) in studies on the thermal decompositio... more Abstract Applications of dynamic dielectric analysis (DDA) in studies on the thermal decomposition and phase transformations of solid materials are discussed. Three illustrative examples are presented for (a) a system undergoing a chemical reaction or thermal alteration on application of heat, (b) a system undergoing a crystallographic transformation and (c) detection of moisture in naturally occurring materials. The advantages derived by applying a combination of DDA and a conventional thermal analysis technique such as DTA to studies on thermal processes are demonstrated. It is shown that the information obtained from techniques such as DTA or TG is limited in scope unless used in conjunction with a method which sheds light on the mechanistic aspects of the physical or chemical process of interest.
Preparation and Characterization of the Sulfamates of Estra-3,17ζ-diols. Rapid Conversion of 16α-... more Preparation and Characterization of the Sulfamates of Estra-3,17ζ-diols. Rapid Conversion of 16α-Fluoroestradiol into 16α-Fluoroestradiol-3,17β-disulfamate.
Abstract The temperature-dependent electrical, mechanical, and thermal behavior of Green River oi... more Abstract The temperature-dependent electrical, mechanical, and thermal behavior of Green River oil shales of varying oil yields in the range ∼20–400 1 ton −1 have been studied by a variety of complementary techniques including thermosonimetry, a.c. electrical conductivity measurements, dielectric spectroscopy in the microwave frequency domain, and differential scanning calorimetry. A close correlation exists in the data obtained by the above techniques although there are significant differences in the sensitivity of the selected measurement probes to various processes taking place in the material. At least four distinct chemical or physical processes are identified in the temperature range from ambient to ∼500°C for Green River oil shales. Possible origin(s) for these processes and the effects that they manifest in the thermophysical behavior of these materials are discussed in the light of data obtained by the various techniques.
… Journal of Pharmacy and Pharmaceutical Sciences, 2010
The present aim of the work was undertaken with one objective to develop gastroresistant drug del... more The present aim of the work was undertaken with one objective to develop gastroresistant drug delivery system for pantoprazole. Pantoprazole is an acid labile drug, which can be degraded in the stomach. Therefore, the drug should be targeted to intestine; to bypass the stomach the gastroresistant double walled microspheric drug delivery system was adopted. The formulations were developed consisting of double wall. The primary wall composed of mucoadhesive polymer sod. CMC and a release controlling polymer sod. alginate. The second wall coating the primary microspheres was composed of eudragit S‐100.The effect of polymer concentration on the particle size, shape drug entrapment efficiency, mucoadhesive property, release study of core microspheres were evaluated. Key word: Gastroresistant, Enteric coated, w/o emulsification/solvent evaporation, Pantoprazole, Acid labile, Microspheres.
... AmsterdamPrinted in The Netherlands TORNIAL ANALYSES OF OIHO BITUMINOUS COALS RJ ROSENVOLD, J... more ... AmsterdamPrinted in The Netherlands TORNIAL ANALYSES OF OIHO BITUMINOUS COALS RJ ROSENVOLD, JB DUBOW "and K. RAJESHWAR *' Department of Electrical Engineering, Colorado State Unieersitv. Fort Collins. ... New York. 1965. pp. 56. 86. 10 K. Rajeshwar. ...
The thermogravlmetnc (TG) assay method prevrously proposed [l] to measure potential oil yields of... more The thermogravlmetnc (TG) assay method prevrously proposed [l] to measure potential oil yields of 011 shale samples has been extended to include samples from the Logan Wash, Rock Springs and Vernal deposits in the trr-state area. The key result emerging from this study IS that the correlation previously shown between Fischer assay and percent wetght loss at 500°C remains vahd regardless of the parttcular deposnional area m a given formatron.
In recent years, it has become increasingly apparent that the information gleaned from convention... more In recent years, it has become increasingly apparent that the information gleaned from conventional thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetry (TG) can be considerably magnified in scope by combining them with mechanistic probes which are responsive to changes taking place in the sample on a molecular level. This is particularly true in the case of naturally occurring complex materials such as coals, oil shales and tar sands. The utility of simultaneous parameter measurements was illustrated for such materials by combining dielectric measurements with differential thermal analysis (DTA) [l-3]. On the basis of this approach, it was proposed that an ideal combination would be that coupling “primary” thermal analysis techniques such as DSC (or DTA) and TG with mechanistic probes such as thermoelectrometry and thermoacoustimetry [ 41. In this communication, we present yet another piece of experimental evidence in favor of the above concept. It is shown that a combined use of the two techniques of DSC and thermoacoustimetry results in a powerful analytical tool which is responsive to changes both in the thermal as well as in the mechanical properties of the test sample as a function of temperature. More significantly, the extreme sensitivity of the thermoacoustimetric probe and the loss of valuable mechanistic information-that would have resulted from a DSC examination alone are highlighted by the present results. The proof-of-concept measurements are illustrated on a sample of Utah tar sand bitumen, although, in principle, the conclusions apply equally well to all materials. Thermoacoustimetry was carried out according to the technique and procedures outlined in a previous paper [5]. Differential scanning calorimetry was performed on a DuPont 990 Thermal Analysis System *:* equipped with the DSC accessory module. Both sets of measurements were carried out under identical conditions of heating rate, sample preparation, ambient atmosphere, etc. to eliminate artifacts in the correlation of thermoacoustimetric and DSC data. The sample of Utah tar sand bitumen (P.R. Springs, Main Canyon) was obtained from the Laramie Energy Technology Center.
TiO2 suspensions in water were used to inactivate Escherichia coli and Hansenula polymorpha. Two ... more TiO2 suspensions in water were used to inactivate Escherichia coli and Hansenula polymorpha. Two types of batch reactors employing static and recireulating solutions were used in this study. Sonolysis using a 20 kHz ultrasonic unit was found to enhance the microorganism inactivation in aII instances, although the enhancement was more modest for the batch recirculation reactor. These data are interpreted within the framework of four possible mechanisms. The mechanism based on sonolytic creation of,OH appears to provide the most satisfactory explanation of the data trends. The present data also implicate .OH as the dominant bactericidal agent in irradiated TiO2 suspensions.
The photocatalytic reaction pathways undergone by Pb(II) ions in UV-irradiated TiO2 suspensions a... more The photocatalytic reaction pathways undergone by Pb(II) ions in UV-irradiated TiO2 suspensions are described. It is shown that these species can participate in both electron-mediated (reductive) as well as hole-mediated (oxidative) photoreaction pathways depending on platinization of the TiO2 surface, the ambient atmosphere (whether O2 or N2), and the presence of co-added organic substrates such as aliphatic alcohols. Even the counterions for Pb(II), namely nitrate, can play an important role in the reductive reaction pathway.
Using hexavalent chromium [Cr(VI)] and methylene blue (MB) as model substrates, we discuss three ... more Using hexavalent chromium [Cr(VI)] and methylene blue (MB) as model substrates, we discuss three aspects of TiO2-based heterogeneous photocatalysis. We show first that a given TiO2 sample may not be simultaneously optimal for photocatalytically driving the reduction of Cr(VI) and the oxidation of MB. We further show that a TiO2 sample that strongly adsorbs either of these substrates in the dark is not optimal as a photocatalyst. The other two aspects concern circumventing the rather poor surface catalytic properties and visible light photoresponse of TiO2, respectively. Strategies revolving around the visible light photoexcitation of the substrate itself and metal-modification of the TiO2 surface, are described as possible solutions.
An automated technique has been developed which enables a rapid determination of the dielectric p... more An automated technique has been developed which enables a rapid determination of the dielectric properties of a material over a wide range of temperatures and frequencies. The speed of data acquisition and the range of temperature and frequencies that can be investigated in a single experiment using this technique, exceed the capabilities of techniques currently employed for dielectric analysis. Frequencies for dielectric measurements can be pre-selected in increments over the range 50 Hz-l MHz. Temperature range for these measurements extends from 25°C to 800°C. The present technique, which features extensive automation in data acquisition and processing, is illustrated by measurements on minerals and shales. The dynamic nature of the above technique also facilitates effective coupling with conventional thermal analysis techniques.
Mixtures of aluminum chloride (AlCl3) with triethylammonium chloride (Et3NHCl), 1,6-ethyl lutidin... more Mixtures of aluminum chloride (AlCl3) with triethylammonium chloride (Et3NHCl), 1,6-ethyl lutidinium bromide (EtluBr), tert-butyl pyridinium bromide (BPBr), and dialkyl imidazolium chloride (R2ImCl), in certain molar ratios yielded ionic liquids at room temperature which were studied with respect to their applicability as electrolytes in photoelectrochemical (PEC) cells. Background voltammograms were obtained for these electrolytes on carbon and n-GaAs electrodes. The anodic stability limit was found to be enhanced on n-GaAs relative to carbon in all cases. The cathodic decomposition potential of the electrolyte showed a smaller positive shift on n-GaAs with the exception of the 3:1 AlCl3-BPBr electrolyte. The difference in electrolyte stability behavior on carbon and n-GaAs is interpreted in terms of carrier density effects. Cyclic voltammograms were compared on carbon in the various electrolytes for a model redox system comprising the ferrocene/ferricenium couple. The separation o...
and CHARLES W. HICKCOX Magnetic, M6ssbauer effect, and thermal properties have been evaluated for... more and CHARLES W. HICKCOX Magnetic, M6ssbauer effect, and thermal properties have been evaluated for specimens of the mineral ankerite and are contrasted with slimilar measur,?,ents m•ned for Lhe mi. Lnera! siderite to dete__rm_ ine if ankerite (and ferroan dolomite), like siderite, may be important in paleomagnetism as a producer of secondary, spurious remanent moments as the result of oxidation in air. Our data indicate that ankerite and siderite both have comparable thermal stabilities and that ankerite does break down to form iron oxides at temperatures as low as 250øC during thermal demagnetization. We conclude from our data that any iron carbonate, siderite, ankerite, or ferroan dolomite, may readily oxidize in air to maghemite or hematite thus producing a spurious remanent moment (RM) that can dominate the magnetic properties of the specimen. Thermal demagnetization of ankerite or siderite at lower temperatures (below 250øC) does not appear to produce such a spurious RM. As might be expected, the quantity of secondary iron oxides produced by oxidation is limited by the iron content in the carbonate crystal lattice. Oxidized siderite produces significantly greater amounts of iron oxides than equivalent percentages of ankerite, which in tum produces more iron oxides than equal amounts of ferroan dolomite in a given sample.
A solid-state perspective is offered for a discussion of silverbased ternary and quaternary oxide... more A solid-state perspective is offered for a discussion of silverbased ternary and quaternary oxide semiconductors for applications related to solar fuels photogeneration and environmental remediation. The rather unique d10 electron configuration in these compounds is shown to impart interesting effects on their optoelectronic properties, and in turn, the photocatalytic activity of these compounds. This Minireview focuses on the structural aspects, electronic band structures, synthetic advances, and finally photoelectrochemical and photocatalytic applications of 32 compounds within the two oxide families, of the generic formula: Ag x B y O z or Ag x B y C n O z , where B and C are metals or non-metals other than silver.
Abstract Applications of dynamic dielectric analysis (DDA) in studies on the thermal decompositio... more Abstract Applications of dynamic dielectric analysis (DDA) in studies on the thermal decomposition and phase transformations of solid materials are discussed. Three illustrative examples are presented for (a) a system undergoing a chemical reaction or thermal alteration on application of heat, (b) a system undergoing a crystallographic transformation and (c) detection of moisture in naturally occurring materials. The advantages derived by applying a combination of DDA and a conventional thermal analysis technique such as DTA to studies on thermal processes are demonstrated. It is shown that the information obtained from techniques such as DTA or TG is limited in scope unless used in conjunction with a method which sheds light on the mechanistic aspects of the physical or chemical process of interest.
Preparation and Characterization of the Sulfamates of Estra-3,17ζ-diols. Rapid Conversion of 16α-... more Preparation and Characterization of the Sulfamates of Estra-3,17ζ-diols. Rapid Conversion of 16α-Fluoroestradiol into 16α-Fluoroestradiol-3,17β-disulfamate.
Abstract The temperature-dependent electrical, mechanical, and thermal behavior of Green River oi... more Abstract The temperature-dependent electrical, mechanical, and thermal behavior of Green River oil shales of varying oil yields in the range ∼20–400 1 ton −1 have been studied by a variety of complementary techniques including thermosonimetry, a.c. electrical conductivity measurements, dielectric spectroscopy in the microwave frequency domain, and differential scanning calorimetry. A close correlation exists in the data obtained by the above techniques although there are significant differences in the sensitivity of the selected measurement probes to various processes taking place in the material. At least four distinct chemical or physical processes are identified in the temperature range from ambient to ∼500°C for Green River oil shales. Possible origin(s) for these processes and the effects that they manifest in the thermophysical behavior of these materials are discussed in the light of data obtained by the various techniques.
… Journal of Pharmacy and Pharmaceutical Sciences, 2010
The present aim of the work was undertaken with one objective to develop gastroresistant drug del... more The present aim of the work was undertaken with one objective to develop gastroresistant drug delivery system for pantoprazole. Pantoprazole is an acid labile drug, which can be degraded in the stomach. Therefore, the drug should be targeted to intestine; to bypass the stomach the gastroresistant double walled microspheric drug delivery system was adopted. The formulations were developed consisting of double wall. The primary wall composed of mucoadhesive polymer sod. CMC and a release controlling polymer sod. alginate. The second wall coating the primary microspheres was composed of eudragit S‐100.The effect of polymer concentration on the particle size, shape drug entrapment efficiency, mucoadhesive property, release study of core microspheres were evaluated. Key word: Gastroresistant, Enteric coated, w/o emulsification/solvent evaporation, Pantoprazole, Acid labile, Microspheres.
... AmsterdamPrinted in The Netherlands TORNIAL ANALYSES OF OIHO BITUMINOUS COALS RJ ROSENVOLD, J... more ... AmsterdamPrinted in The Netherlands TORNIAL ANALYSES OF OIHO BITUMINOUS COALS RJ ROSENVOLD, JB DUBOW "and K. RAJESHWAR *' Department of Electrical Engineering, Colorado State Unieersitv. Fort Collins. ... New York. 1965. pp. 56. 86. 10 K. Rajeshwar. ...
The thermogravlmetnc (TG) assay method prevrously proposed [l] to measure potential oil yields of... more The thermogravlmetnc (TG) assay method prevrously proposed [l] to measure potential oil yields of 011 shale samples has been extended to include samples from the Logan Wash, Rock Springs and Vernal deposits in the trr-state area. The key result emerging from this study IS that the correlation previously shown between Fischer assay and percent wetght loss at 500°C remains vahd regardless of the parttcular deposnional area m a given formatron.
In recent years, it has become increasingly apparent that the information gleaned from convention... more In recent years, it has become increasingly apparent that the information gleaned from conventional thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetry (TG) can be considerably magnified in scope by combining them with mechanistic probes which are responsive to changes taking place in the sample on a molecular level. This is particularly true in the case of naturally occurring complex materials such as coals, oil shales and tar sands. The utility of simultaneous parameter measurements was illustrated for such materials by combining dielectric measurements with differential thermal analysis (DTA) [l-3]. On the basis of this approach, it was proposed that an ideal combination would be that coupling “primary” thermal analysis techniques such as DSC (or DTA) and TG with mechanistic probes such as thermoelectrometry and thermoacoustimetry [ 41. In this communication, we present yet another piece of experimental evidence in favor of the above concept. It is shown that a combined use of the two techniques of DSC and thermoacoustimetry results in a powerful analytical tool which is responsive to changes both in the thermal as well as in the mechanical properties of the test sample as a function of temperature. More significantly, the extreme sensitivity of the thermoacoustimetric probe and the loss of valuable mechanistic information-that would have resulted from a DSC examination alone are highlighted by the present results. The proof-of-concept measurements are illustrated on a sample of Utah tar sand bitumen, although, in principle, the conclusions apply equally well to all materials. Thermoacoustimetry was carried out according to the technique and procedures outlined in a previous paper [5]. Differential scanning calorimetry was performed on a DuPont 990 Thermal Analysis System *:* equipped with the DSC accessory module. Both sets of measurements were carried out under identical conditions of heating rate, sample preparation, ambient atmosphere, etc. to eliminate artifacts in the correlation of thermoacoustimetric and DSC data. The sample of Utah tar sand bitumen (P.R. Springs, Main Canyon) was obtained from the Laramie Energy Technology Center.
TiO2 suspensions in water were used to inactivate Escherichia coli and Hansenula polymorpha. Two ... more TiO2 suspensions in water were used to inactivate Escherichia coli and Hansenula polymorpha. Two types of batch reactors employing static and recireulating solutions were used in this study. Sonolysis using a 20 kHz ultrasonic unit was found to enhance the microorganism inactivation in aII instances, although the enhancement was more modest for the batch recirculation reactor. These data are interpreted within the framework of four possible mechanisms. The mechanism based on sonolytic creation of,OH appears to provide the most satisfactory explanation of the data trends. The present data also implicate .OH as the dominant bactericidal agent in irradiated TiO2 suspensions.
The photocatalytic reaction pathways undergone by Pb(II) ions in UV-irradiated TiO2 suspensions a... more The photocatalytic reaction pathways undergone by Pb(II) ions in UV-irradiated TiO2 suspensions are described. It is shown that these species can participate in both electron-mediated (reductive) as well as hole-mediated (oxidative) photoreaction pathways depending on platinization of the TiO2 surface, the ambient atmosphere (whether O2 or N2), and the presence of co-added organic substrates such as aliphatic alcohols. Even the counterions for Pb(II), namely nitrate, can play an important role in the reductive reaction pathway.
Using hexavalent chromium [Cr(VI)] and methylene blue (MB) as model substrates, we discuss three ... more Using hexavalent chromium [Cr(VI)] and methylene blue (MB) as model substrates, we discuss three aspects of TiO2-based heterogeneous photocatalysis. We show first that a given TiO2 sample may not be simultaneously optimal for photocatalytically driving the reduction of Cr(VI) and the oxidation of MB. We further show that a TiO2 sample that strongly adsorbs either of these substrates in the dark is not optimal as a photocatalyst. The other two aspects concern circumventing the rather poor surface catalytic properties and visible light photoresponse of TiO2, respectively. Strategies revolving around the visible light photoexcitation of the substrate itself and metal-modification of the TiO2 surface, are described as possible solutions.
An automated technique has been developed which enables a rapid determination of the dielectric p... more An automated technique has been developed which enables a rapid determination of the dielectric properties of a material over a wide range of temperatures and frequencies. The speed of data acquisition and the range of temperature and frequencies that can be investigated in a single experiment using this technique, exceed the capabilities of techniques currently employed for dielectric analysis. Frequencies for dielectric measurements can be pre-selected in increments over the range 50 Hz-l MHz. Temperature range for these measurements extends from 25°C to 800°C. The present technique, which features extensive automation in data acquisition and processing, is illustrated by measurements on minerals and shales. The dynamic nature of the above technique also facilitates effective coupling with conventional thermal analysis techniques.
Mixtures of aluminum chloride (AlCl3) with triethylammonium chloride (Et3NHCl), 1,6-ethyl lutidin... more Mixtures of aluminum chloride (AlCl3) with triethylammonium chloride (Et3NHCl), 1,6-ethyl lutidinium bromide (EtluBr), tert-butyl pyridinium bromide (BPBr), and dialkyl imidazolium chloride (R2ImCl), in certain molar ratios yielded ionic liquids at room temperature which were studied with respect to their applicability as electrolytes in photoelectrochemical (PEC) cells. Background voltammograms were obtained for these electrolytes on carbon and n-GaAs electrodes. The anodic stability limit was found to be enhanced on n-GaAs relative to carbon in all cases. The cathodic decomposition potential of the electrolyte showed a smaller positive shift on n-GaAs with the exception of the 3:1 AlCl3-BPBr electrolyte. The difference in electrolyte stability behavior on carbon and n-GaAs is interpreted in terms of carrier density effects. Cyclic voltammograms were compared on carbon in the various electrolytes for a model redox system comprising the ferrocene/ferricenium couple. The separation o...
and CHARLES W. HICKCOX Magnetic, M6ssbauer effect, and thermal properties have been evaluated for... more and CHARLES W. HICKCOX Magnetic, M6ssbauer effect, and thermal properties have been evaluated for specimens of the mineral ankerite and are contrasted with slimilar measur,?,ents m•ned for Lhe mi. Lnera! siderite to dete__rm_ ine if ankerite (and ferroan dolomite), like siderite, may be important in paleomagnetism as a producer of secondary, spurious remanent moments as the result of oxidation in air. Our data indicate that ankerite and siderite both have comparable thermal stabilities and that ankerite does break down to form iron oxides at temperatures as low as 250øC during thermal demagnetization. We conclude from our data that any iron carbonate, siderite, ankerite, or ferroan dolomite, may readily oxidize in air to maghemite or hematite thus producing a spurious remanent moment (RM) that can dominate the magnetic properties of the specimen. Thermal demagnetization of ankerite or siderite at lower temperatures (below 250øC) does not appear to produce such a spurious RM. As might be expected, the quantity of secondary iron oxides produced by oxidation is limited by the iron content in the carbonate crystal lattice. Oxidized siderite produces significantly greater amounts of iron oxides than equivalent percentages of ankerite, which in tum produces more iron oxides than equal amounts of ferroan dolomite in a given sample.
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Papers by K. Rajeshwar