The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Atsushi Urakawa - One of the best experts on this subject based on the ideXlab platform.
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unravelling the role of oxygen vacancies in the mechanism of the reverse water gas shift reaction by operando drifts and ultraviolet Visible Spectroscopy
ACS Catalysis, 2018Co-Authors: L.f. Bobadilla, Jose Luis Santos, Svetlana Ivanova, José Antonio Odriozola, Atsushi UrakawaAbstract:The reaction mechanism of the reverse water–gas shift (RWGS) reaction was investigated using two commercial gold-based catalysts supported on Al2O3 and TiO2. The surface species formed during the reaction and reaction mechanisms were elucidated by transient and steady-state operando DRIFTS studies. It was revealed that RWGS reaction over Au/Al2O3 proceeds through the formation of formate intermediates that are reduced to CO. In the case of the Au/TiO2 catalyst, the reaction goes through a redox mechanism with the suggested formation of hydroxycarbonyl intermediates, which further decompose to CO and water. The Ti3+ species, the surface hydroxyls, and oxygen vacancies jointly participate. The absence of carbonyl species adsorbed on gold particles during the reaction for both catalysts indicates that the reaction pathway involving dissociative adsorption of CO2 on Au particles can be discarded. To complete the study, operando ultraviolet–Visible Spectroscopy was successfully applied to confirm the presence ...
Uma Maheshwara V Sarma - One of the best experts on this subject based on the ideXlab platform.
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decolorization and biodegradation of triphenylmethane dye brilliant green by aspergillus sp isolated from ladakh india
Process Biochemistry, 2012Co-Authors: Ganesh C Kumar, Poornima Mongolla, Joveeta Joseph, Uma Maheshwara V SarmaAbstract:Abstract Brilliant green, used extensively to color silk and wool in the commercial textile industry is a hazardous recalcitrant. Aspergillus sp. strain CB-TKL-1 isolated from a water sample from Tsumoriri Lake, Karzok, Ladakh, India, was found to completely decolorize this dye within 72 h when cultured under aerobic conditions at 25 °C. The extent of decolorization was monitored by the decrease in absorbance maxima of the dye by UV–Visible Spectroscopy. The decolorization was optimum at pH 5 and 35 °C when agitated at 200 rpm. Addition of glucose (2%) as a carbon source and sodium nitrate (0.2%) as a nitrogen source enhanced the decolorization ability of the culture. The culture exhibited maximum extent of decolorization of brilliant green with a C:N ratio of 2.5 after 72 h. Thirteen N -demethylated decolorized products of brilliant green were identified based on UV–Visible Spectroscopy, Fourier Transform Infrared (FT-IR) Spectroscopy and liquid chromatography–electrospray ionization mass spectrometry (LC–ESI-MS) analysis at the end of 72 h before mineralization. The difference of the relative absorption peaks in the decolorized sample indicated a linear release of N -demethylated compounds, indicating a stepwise N -demethylation in the decolorization process.
Darren J Lipomi - One of the best experts on this subject based on the ideXlab platform.
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measuring the glass transition temperature of conjugated polymer films with ultraviolet Visible Spectroscopy
Chemistry of Materials, 2017Co-Authors: Samuel E Root, Mohammad A Alkhadra, Daniel Rodriquez, Adam D Printz, Darren J LipomiAbstract:The glass transition temperature (Tg) of a conjugated polymer can be used to predict its morphological stability and mechanical properties. Despite the importance of this parameter in applications from organic solar cells to wearable electronics, it is not easy to measure. The Tg is often too weak to detect using conventional differential scanning calorimetry (DSC). Alternative methods—e.g., variable temperature ellipsometry—require specialized equipment. This paper describes a technique for measuring the Tg of thin films of semicrystalline conjugated polymers using only a hot plate and an ultraviolet–Visible (UV–vis) spectrometer. UV–vis Spectroscopy is used to measure changes in the absorption spectrum due to molecular-scale rearrangement of polymers when heated past Tg, corresponding to the onset of the formation of photophysical aggregates. A deviation metric, defined as the sum of the squared deviation in absorbance between as-cast and annealed films, is used to quantify shifts in the absorption spec...
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Measuring the Glass Transition Temperature of Conjugated Polymer Films with Ultraviolet–Visible Spectroscopy
2017Co-Authors: Samuel E Root, Mohammad A Alkhadra, Daniel Rodriquez, Adam D Printz, Darren J LipomiAbstract:The glass transition temperature (Tg) of a conjugated polymer can be used to predict its morphological stability and mechanical properties. Despite the importance of this parameter in applications from organic solar cells to wearable electronics, it is not easy to measure. The Tg is often too weak to detect using conventional differential scanning calorimetry (DSC). Alternative methodse.g., variable temperature ellipsometryrequire specialized equipment. This paper describes a technique for measuring the Tg of thin films of semicrystalline conjugated polymers using only a hot plate and an ultraviolet–Visible (UV–vis) spectrometer. UV–vis Spectroscopy is used to measure changes in the absorption spectrum due to molecular-scale rearrangement of polymers when heated past Tg, corresponding to the onset of the formation of photophysical aggregates. A deviation metric, defined as the sum of the squared deviation in absorbance between as-cast and annealed films, is used to quantify shifts in the absorption spectra. The glass transition is observed as a change in slope in a plot of the deviation metric versus temperature. To demonstrate the usefulness of this technique, a variety of semiconducting polymers are tested: P3BT, PBTTT-C14, F8BT, PDTSTPD, PTB7, PCDTBT, TQ1, and MEH-PPV. These polymers represent a range of solid-state morphologies, from highly ordered to predominantly amorphous. A successful measurement of Tg depends on the ability of the polymer to form photophysical aggregates. The results obtained using this method for P3BT, PBTTT-C14, F8BT, and PDTSTPD are in agreement with values of Tg that have been reported in the literature. Molecular dynamics simulations are used to show how the morphology evolves upon annealing: above the Tg, an initially kinetically trapped morphology undergoes structural rearrangement to assume a more thermodynamically preferred structure. The temperature at which onset of this rearrangement occurs in the simulation is concomitant with the spectroscopically determined value of Tg
L.f. Bobadilla - One of the best experts on this subject based on the ideXlab platform.
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unravelling the role of oxygen vacancies in the mechanism of the reverse water gas shift reaction by operando drifts and ultraviolet Visible Spectroscopy
ACS Catalysis, 2018Co-Authors: L.f. Bobadilla, Jose Luis Santos, Svetlana Ivanova, José Antonio Odriozola, Atsushi UrakawaAbstract:The reaction mechanism of the reverse water–gas shift (RWGS) reaction was investigated using two commercial gold-based catalysts supported on Al2O3 and TiO2. The surface species formed during the reaction and reaction mechanisms were elucidated by transient and steady-state operando DRIFTS studies. It was revealed that RWGS reaction over Au/Al2O3 proceeds through the formation of formate intermediates that are reduced to CO. In the case of the Au/TiO2 catalyst, the reaction goes through a redox mechanism with the suggested formation of hydroxycarbonyl intermediates, which further decompose to CO and water. The Ti3+ species, the surface hydroxyls, and oxygen vacancies jointly participate. The absence of carbonyl species adsorbed on gold particles during the reaction for both catalysts indicates that the reaction pathway involving dissociative adsorption of CO2 on Au particles can be discarded. To complete the study, operando ultraviolet–Visible Spectroscopy was successfully applied to confirm the presence ...
Alexis T Bell - One of the best experts on this subject based on the ideXlab platform.
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a study of oxygen vacancy formation and annihilation in submonolayer coverages of tio2 dispersed on mcm 48
Journal of Physical Chemistry C, 2010Co-Authors: Jennifer Strunk, William Collins Vining, Alexis T BellAbstract:The reduction and reoxidation of submonolayer coverages of TiO2 deposited onto MCM-48 were investigated. The deposited TiO2 was characterized by Raman and UV−Visible Spectroscopy. Raman spectra show that Ti atoms are bonded to the silica support by Ti−O−Si bonds and that crystalline TiO2 is not formed. The results of the Raman and UV−Visible Spectroscopy suggest that the dispersed TiO2 is present as two-dimensional oligomeric structures. Reduction in H2 at 923 K produces Ti3+ cations observable by EPR (g = 1.932), suggesting the formation of oxygen vacancies. The fraction of Ti that could be reduced increased with TiO2 surface concentration. This observation is attributed to the ease with which O atoms can be removed from the TiO2 overlayer as the size of the titania patches increases. The amount of oxygen removed during reduction was quantified by pulsed reoxidation. It was observed that the temperature required for complete reoxidation decreased with increasing surface coverage of the silica support by ...
