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Joseph T. Hupp - One of the best experts on this subject based on the ideXlab platform.
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Electrochemical Quartz Crystal Microbalance Studies of Electron Addition at Nanocrystalline Tin Oxide/Water and Zinc Oxide/Water Interfaces: Evidence for Band-Edge-Determining Proton Uptake
The Journal of Physical Chemistry B, 1997Co-Authors: Buford I. Lemon, Joseph T. HuppAbstract:Electrochemical quartz crystal microbalance (EQCM) measurements provide compelling evidence for charge-Compensating Cation uptake by nanocrystalline SnO2 and ZnO electrodes during electron addition. Comparative light water/heavy water measurements establish that the adsorbed or intercalated ions are protons or deuterons. Additional studies as a function of pH implicate water, rather than hydronium ions, as the proton source. The new results, when combined with previous results for titanium dioxide in nonaqueous electrolytes, suggest that charge-Compensating Cation intercalation is a general mode of reactivity for metal oxide semiconductors. Finally, the new observations raise significant fundamental questions concerning (1) chemical control of band energetics, (2) possible band-edge-unpinning phenomena, and (3) relationships between band edge energies and driving forces for isolated electron transfer reactions.
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Photochemical quartz crystal microbalance study of the nanocrystalline titanium dioxide semiconductor electrode/water interface: Simultaneous photoaccumulation of electrons and protons
The Journal of Physical Chemistry, 1996Co-Authors: Buford I. Lemon, Joseph T. HuppAbstract:Photochemical quartz crystal microbalance (PQCM) studies of nanocrystalline titanium dioxide films show evidence of charge-Compensating Cation intercalation during photolytically induced accumulation layer formation. The manifestation and magnitude of mass uptake (intercalation) are dependent, respectively, on the illumination and intensity of illumination provided. Isotope experiments performed in H2O and D2O unambiguously identify the Cations as protons and deuterons. The experiments extend earlier experiments with dark TiO2 (and other metal oxide semiconductors) that have implicated Cation intercalation as the primary process involved in charge compensation under accumulation conditions.
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Energetics of Semiconductor Electrode/Solution Interfaces: EQCM Evidence for Charge-Compensating Cation Adsorption and Intercalation during Accumulation Layer Formation in the Titanium Dioxide/Acetonitrile System
The Journal of Physical Chemistry, 1995Co-Authors: L. Andrew Lyon, Joseph T. HuppAbstract:Abstract : Combined reflectance, electrochemical quartz crystal microbalance and conventional voltammetric measurements on high area titanium dioxide electrodes in dry, electrolyte-containing solutions of acetonitrile show that electron accumulation layer formation is coupled directly to irreversible intercalation (e.g. Li+ or Na+) or to quasi-reversible adsorption (tetraethylammonium ion) of charge Compensating Cations. Difficulty in achieving intercalation with these ions appears to account for the extreme negative shift of the flatband potential in acetonitrile, in comparison to aqueous solutions. More generally, the charge compensation based adsorption/intercalation phenomenon appears to play a key role in defining the conduction band edge energetics of titanium dioxide and presumably other metal. jg
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energetics of semiconductor electrode solution interfaces eqcm evidence for charge Compensating Cation adsorption and intercalation during accumulation layer formation in the titanium dioxide acetonitrile system
The Journal of Physical Chemistry, 1995Co-Authors: Andrew L Lyon, Joseph T. HuppAbstract:Abstract : Combined reflectance, electrochemical quartz crystal microbalance and conventional voltammetric measurements on high area titanium dioxide electrodes in dry, electrolyte-containing solutions of acetonitrile show that electron accumulation layer formation is coupled directly to irreversible intercalation (e.g. Li+ or Na+) or to quasi-reversible adsorption (tetraethylammonium ion) of charge Compensating Cations. Difficulty in achieving intercalation with these ions appears to account for the extreme negative shift of the flatband potential in acetonitrile, in comparison to aqueous solutions. More generally, the charge compensation based adsorption/intercalation phenomenon appears to play a key role in defining the conduction band edge energetics of titanium dioxide and presumably other metal. jg
Oliver Schäf - One of the best experts on this subject based on the ideXlab platform.
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Zeolites are effective ROS-scavengers in vitro.
Biochemical and biophysical research communications, 2011Co-Authors: Perrine Pellegrino, Bernard Mallet, Stephane Delliaux, Yves Jammes, Régis Guieu, Oliver SchäfAbstract:We report on the use of zeolites to limit the effects of reactive oxygen species (ROS) on human albumin under in vitro conditions. Zeolites of different structure type, channel size, channel polarity, and charge-Compensating Cation were screened for the elimination of ROS, notably HO(·), resulting from the Fenton reaction. A test based on ischemia-modified albumin (IMA) was used as a marker to monitor the activity of HO(·) after co-exposure of human serum to these zeolites. Two commercial zeolites, faujasite (FAU 13×, channel opening 0.74×0.74 nm with Na(+) as charge-Compensating Cation) and ferrierite (FER, channel opening 0.54×0.42 nm with H(+) as charge-Compensating Cation), were found to reduce IMA formation by more than 65% due to removal of HO(·) relative to reference values. It was established that partial ion exchange of the zeolites' respective charge-Compensating Cation vs. Fe(3+) implicated in the Fenton reaction plays a major role in HO(·) deactivation process. Moreover, our results show that no saturation of the respective zeolite active sites occurred. This is possible only when ROS are actively converted to water molecules within the zeolite void system, which generates H(+) ion transport. Because zeolites cannot be administered in blood, their use in medicine should be limited to extra corporeal circuits. Zeolites could be of use during cardiopulmonary bypass or hemodialysis procedures.
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Adsorption of small uremic toxin molecules on MFI type zeolites from aqueous solution
Adsorption-journal of The International Adsorption Society, 2008Co-Authors: David Bergé-lefranc, Oliver Schäf, C. Vagner, Pascal Boulet, H. Pizzala, Jean-louis Paillaud, Bogdan Kuchta, Renaud DenoyelAbstract:Adsorption properties of zeolites were investigated for the removal of p-cresol from aqueous solutions at 37 °C within the context of studying alternative methods to dialysis for removing uremic toxin from blood. MFI-framework type zeolites with different degrees of hydrophobicity and charge Compensating Cations were prepared: one pure silica MFI and four alumino-silicate MFIs (Si/Al = 30), with H+, Na+, K+ and Mg2+ as charge Compensating Cations. Adsorption isotherms and microcalorimetric measurements show a high affinity of p-cresol for all MFI type zeolites. The best capacity is obtained for the pure silica MFI, whereas the alumino-silicate samples show a higher affinity in the low concentration range. In the case of pure silica sample, the microscopic adsorption mechanism including the role of confined water is elucidated with the help of NMR, X-ray analysis (including Rietveld refinement) and Monte Carlo simulations. For all samples the high affinity is preserved in physiological serum solution, even in the presence of other toxin molecules such as urea. It is also shown that the Compensating Cation state of the samples is imposed by the physiological medium.
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Adsorption of small uremic toxin molecules onto zeolites: a first step towards an alternative kidney
From Zeolites to Porous MOF Materials - The 40th Anniversary of International Zeolite Conference Proceedings of the 15th International Zeolite Confere, 2007Co-Authors: David Bergé-lefranc, Oliver Schäf, C. Vagner, Pascal Boulet, H. Pizzala, Jean-louis Paillaud, Renaud DenoyelAbstract:Abstract The model-like adsorption properties of MFI-type zeolites with different degrees of hydrophobicity and charge Compensating Cations were investigated for the removal of p-cresol from different aqueous solutions at 37°C. Pure silica MFI and alumino-silicate MFI (Si/Al = 30.4), with H + , Na + , K + and Mg 2+ as charge Compensating Cations were used for the study. Adsorption isotherms and microcalorimetric measurements show a strong affinity of p-cresol towards all MFI type zeolites. This strong affinity is still present in physiological serum solution containing urea molecules. The effect of the nature of the charge Compensating Cation and present water molecules on p-cresol affinity is discussed together with spectroscopic results and Monte-Carlo simulations of the adsorption process.
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Sensor Response of Stilbite Single Crystals Under “in Situ” Conditions
MRS Proceedings, 2002Co-Authors: Oliver Schäf, H. Ghobarkar, Philippe KnauthAbstract:The isothermal conductivity of natural stilbite single crystals depends on water content, polar organic molecule concentration and charge Compensating Cation species. The observed interaction processes are almost completely adsorptive at temperatures below 110°C; catalytic oxidation of the organic molecules is taking place at much higher temperatures, where zeolitic water is almost completely desorbed. A schematic model describing the observed conductivity modifiCations is developed.
Charles H. F. Peden - One of the best experts on this subject based on the ideXlab platform.
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Non-thermal plasma-assisted NOx reduction over alkali and alkaline earth ion exchanged Y, FAU zeolites
'Elsevier BV', 2015Co-Authors: Kwak Jahun, Charles H. F. PedenAbstract:The catalytic activities of a series of alkali and alkaline earth Cation exchanged Y, FAU zeolites were investigated in the non-thermal plasma-assisted NOx reduction reaction using a simulated diesel engine exhaust gas mixture. The catalytic activity of the Y, FAU zeolite showed significant variations with both the nature of the charge Compensating Cation, and the method of catalyst preparation. Our results show that conventional multiple solution ion exchange is insufficient to prepare the most active catalyst for the given Cationic form. The highest NOx conversion level was achieved over a Ba-Y, FAU which was prepared by a multiple ion exchange method, in which each solution ion exchange step was followed by a high temperature calcination. A systematic change in the catalytic activity was observed as a function of the charge density around the charge Compensating Cation. For both catalyst series (alkali and alkaline earth ion exchanged Y, FAU), the specific activity decreased with increasing electrostatic field around the charge Compensating Cation. The large difference in the NOx reduction activity at a given e/r ratio. however, may suggest different reaction mechanisms for the two sets of catalysts. Indeed, there is a noticeable difference in the product distribution (selectivity) for the alkali and alkaline earth series of catalysts. Our results also reveal that extreme care must be taken when catalytic activities are compared for seemingly similar materials. We found that two base zeolite materials with identical Si/Al ratios, obtained from the same manufacturer but from different synthesis batches show significantly different catalytic behavior. (C) 2003 Published by Elsevier B.Vclose283
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Non-thermal plasma-assisted NOx reduction over alkali and alkaline earth ion exchanged Y, FAU zeolites
Catalysis Today, 2004Co-Authors: Ja Hun Kwak, János Szanyi, Charles H. F. PedenAbstract:Abstract The catalytic activities of a series of alkali and alkaline earth Cation exchanged Y, FAU zeolites were investigated in the non-thermal plasma-assisted NO x reduction reaction using a simulated diesel engine exhaust gas mixture. The catalytic activity of the Y, FAU zeolite showed significant variations with both the nature of the charge Compensating Cation, and the method of catalyst preparation. Our results show that conventional multiple solution ion exchange is insufficient to prepare the most active catalyst for the given Cationic form. The highest NO x conversion level was achieved over a Ba-Y, FAU which was prepared by a multiple ion exchange method, in which each solution ion exchange step was followed by a high temperature calcination. A systematic change in the catalytic activity was observed as a function of the charge density around the charge Compensating Cation. For both catalyst series (alkali and alkaline earth ion exchanged Y, FAU), the specific activity decreased with increasing electrostatic field around the charge Compensating Cation. The large difference in the NO x reduction activity at a given e / r ratio, however, may suggest different reaction mechanisms for the two sets of catalysts. Indeed, there is a noticeable difference in the product distribution (selectivity) for the alkali and alkaline earth series of catalysts. Our results also reveal that extreme care must be taken when catalytic activities are compared for seemingly similar materials. We found that two base zeolite materials with identical Si/Al ratios, obtained from the same manufacturer but from different synthesis batches show significantly different catalytic behavior.
Marc Frère - One of the best experts on this subject based on the ideXlab platform.
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Characterisation of palladium supported on exchanged BEA and FAU zeolites for VOCs catalytic oxidation
Studies in Surface Science and Catalysis, 2007Co-Authors: Haingomalala Lucette Tidahy, S. Siffert, Jean-françois Lamonier, E. A. Zhilinskaya, Antoine Aboukaïs, X. Canet, G. Deweireld, Marc Frère, J.-m. GireaudonAbstract:0.5wt% palladium supported on exchanged BEA and FAU zeolites have been characterised for volatile organic compounds (VOCs) catalytic oxidation. BEA and FAU zeolites have been exchanged with different Cations to study the influence of alkali metal Cations (Na + , Cs + ) and H + in Pd based catalysts on propene total oxidation. Oxidation of propene depends significantly on the type of zeolites and on the Compensating Cation of the zeolite. According to sample, the catalytic activity is explained by the surface areas of the catalysts, the adsorption energies for VOC, the influence of the electronegativity of the Compensating Cation on the Pd particles, the Pd dispersion and the PdO reducibility.
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Influence of the exchanged Cation in Pd/BEA and Pd/FAU zeolites for catalytic oxidation of VOCs
Applied Catalysis B: Environmental, 2007Co-Authors: Haingomalala Lucette Tidahy, S. Siffert, Jean-françois Lamonier, E. A. Zhilinskaya, Antoine Aboukaïs, X. Canet, R. Cousin, G. De Weireld, Marc FrèreAbstract:sous presse0.5wt% palladium supported on exchanged BEA and FAU zeolites were prepared, characterized and tested in the total oxidation of volatile organic compounds (VOCs). The BEA and FAU zeolites were exchanged with different Cations to study the influence of alkali metal Cations (Na+, Cs+) and H+ in Pd based catalysts on propene and toluene total oxidation. The exchange with different Cations (Na+, Cs+) and H+ led to a decrease of the surface area and the micropore volume. All Pd/BEA and Pd/FAU zeolites were found to be powerful catalysts for the total oxidation of VOCs. They were active at low temperature and totally selective for CO2 and H2O. However, their activity depends significantly on the type of zeolite and on the nature of the charge-Compensating Cation. The activity order for propene and toluene oxidation on FAU catalysts, Pd/CsFAU > Pd/NaFAU > Pd/HFAU, is the reverse than the activity order on BEA catalysts: Pd/HBEA > Pd/NaBEA > Pd/CsBEA. The catalytic activities can be rationalized in terms of the influence of the electronegativity of the charge-Compensating Cation on the Pd particles, the Pd dispersion, the PdO reducibility and the adsorption energies for VOCs
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Adsorption of Alkanes and Aromatic Compounds on Various Faujasites in the Henry Domain. 1. Compensating Cation Effect on Zeolites Y
Journal of Chemical & Engineering Data, 2007Co-Authors: X. Canet, F. Gilles, And Guy De Weireld, Marc FrèreAbstract:Volatile organic compounds (VOCs) released in the atmosphere are responsible for important climate changes on earth, and some may have short- and long-term adverse health effects. The recovery of these VOCs can be a solution to reduce pollution. At low pressure, Henry constants are needed to develop recovery processes. Representative molecules were chosen to determine adsorption data. Nine alkanes (linear, cyclic, and branched molecules with carbon numbers between five and eight) and four aromatic and chlorinated compounds on a series of faujasite zeolites (HY, LiY, NaY, KY, RbY, and CsY) with the same Si/Al ratio were studied in the Henry domain at temperatures ranging from (448.15 to 673.15) K using the well-known pulse chromatography technique. The zeolites were characterized to determine the main structural properties such as cell parameters, chemical composition, porous volume, specific surface area, and water adsorption capacity. The Henry constant increases with rising Cation size and probe molecul...
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Influence of the exchanged Cation in Pd/BEA and Pd/FAU zeolites for catalytic oxidation of VOCs
Applied Catalysis B-environmental, 2006Co-Authors: Haingomalala Lucette Tidahy, S. Siffert, Jean-françois Lamonier, E. A. Zhilinskaya, Antoine Aboukaïs, X. Canet, R. Cousin, G. De Weireld, Marc FrèreAbstract:Abstract 0.5 wt% palladium supported on exchanged BEA and FAU zeolites were prepared, characterized and tested in the total oxidation of volatile organic compounds (VOCs). The BEA and FAU zeolites were exchanged with different Cations to study the influence of alkali metal Cations (Na + , Cs + ) and H + in Pd-based catalysts on propene and toluene total oxidation. The exchange with different Cations (Na + , Cs + ) and H + led to a decrease of the surface area and the micropore volume. All Pd/BEA and Pd/FAU zeolites were found to be powerful catalysts for the total oxidation of VOCs. They were active at low temperature and totally selective for CO 2 and H 2 O. However, their activity depends significantly on the type of zeolite and on the nature of the charge-Compensating Cation. The activity order for propene and toluene oxidation on FAU catalysts, Pd/CsFAU > Pd/NaFAU > Pd/HFAU, is the reverse of the activity order on BEA catalysts: Pd/HBEA > Pd/NaBEA > Pd/CsBEA. The catalytic activities can be rationalized in terms of the influence of the electronegativity of the charge-Compensating Cation on the Pd particles, the Pd dispersion, the PdO reducibility and the adsorption energies for VOCs.
Renaud Denoyel - One of the best experts on this subject based on the ideXlab platform.
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Adsorption of small uremic toxin molecules on MFI type zeolites from aqueous solution
Adsorption-journal of The International Adsorption Society, 2008Co-Authors: David Bergé-lefranc, Oliver Schäf, C. Vagner, Pascal Boulet, H. Pizzala, Jean-louis Paillaud, Bogdan Kuchta, Renaud DenoyelAbstract:Adsorption properties of zeolites were investigated for the removal of p-cresol from aqueous solutions at 37 °C within the context of studying alternative methods to dialysis for removing uremic toxin from blood. MFI-framework type zeolites with different degrees of hydrophobicity and charge Compensating Cations were prepared: one pure silica MFI and four alumino-silicate MFIs (Si/Al = 30), with H+, Na+, K+ and Mg2+ as charge Compensating Cations. Adsorption isotherms and microcalorimetric measurements show a high affinity of p-cresol for all MFI type zeolites. The best capacity is obtained for the pure silica MFI, whereas the alumino-silicate samples show a higher affinity in the low concentration range. In the case of pure silica sample, the microscopic adsorption mechanism including the role of confined water is elucidated with the help of NMR, X-ray analysis (including Rietveld refinement) and Monte Carlo simulations. For all samples the high affinity is preserved in physiological serum solution, even in the presence of other toxin molecules such as urea. It is also shown that the Compensating Cation state of the samples is imposed by the physiological medium.
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Adsorption of small uremic toxin molecules onto zeolites: a first step towards an alternative kidney
From Zeolites to Porous MOF Materials - The 40th Anniversary of International Zeolite Conference Proceedings of the 15th International Zeolite Confere, 2007Co-Authors: David Bergé-lefranc, Oliver Schäf, C. Vagner, Pascal Boulet, H. Pizzala, Jean-louis Paillaud, Renaud DenoyelAbstract:Abstract The model-like adsorption properties of MFI-type zeolites with different degrees of hydrophobicity and charge Compensating Cations were investigated for the removal of p-cresol from different aqueous solutions at 37°C. Pure silica MFI and alumino-silicate MFI (Si/Al = 30.4), with H + , Na + , K + and Mg 2+ as charge Compensating Cations were used for the study. Adsorption isotherms and microcalorimetric measurements show a strong affinity of p-cresol towards all MFI type zeolites. This strong affinity is still present in physiological serum solution containing urea molecules. The effect of the nature of the charge Compensating Cation and present water molecules on p-cresol affinity is discussed together with spectroscopic results and Monte-Carlo simulations of the adsorption process.