The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Brian G Frederick - One of the best experts on this subject based on the ideXlab platform.
-
frequencies and thermal stability of isolated surfaceHydroxyls on pyrogenic tio 2 nanoparticles
Journal of Physical Chemistry C, 2019Co-Authors: Akbar Mahdavishakib, Juan M Arceramos, Rachel N Austin, Thomas J Schwartz, Lars C Grabow, Brian G FrederickAbstract:The surface reactivity of TiO22 is often governed by Hydroxyl groups. Fourier transform infrared (FTIR) spectroscopy is the most commonly used method to study surface Hydroxyls. However, interpretation of the observed bands of powder samples is not straightforward. In this work, we propose a facet-specific assignment of the surface Hydroxyls of pyrogenic TiO2 (commonly known as P25 and P90) by comparison between experimentally observed FTIR bands of P90, rutile, and anatase with calculated vibrational frequencies for well-defined surface facets using density functional theory (DFT). Titania was calcined for extended periods in extremely dry O2 to remove carbonates and water for diffuse reflectance infrared spectroscopy (DRIFTS) measurements of the most thermally stable Hydroxyls remaining in the 300 – 400 °C range. Reactions of the deHydroxylated surfaces with H2(D2) provided further insight into Hydroxyl formation. Theoretical assignments of Hydroxyls were based on the calculated thermal stability of hyd...
Kangle Lv - One of the best experts on this subject based on the ideXlab platform.
-
photocatalytic selective oxidation of phenol to produce dihydroxybenzenes in a tio2 uv system Hydroxyl radical versus hole
Applied Catalysis B-environmental, 2016Co-Authors: Mei Li, Kangle Lv, Xiaofeng Wu, Qin Li, Wingkei Ho, Hengpeng Ye, Dongyun DuAbstract:Abstract Photocatalytic oxidation plays an important role in organic synthesis. This research systematically studied the effect of reactive oxidation species (ROSs) such as surface-bounded Hydroxyl radicals ( OHb), free Hydroxyl radicals ( OHf), and hole (h+) on the photocatalytic selective oxidation of phenol in the TiO2/UV system and its corresponding important chemical intermediates, dihydroxybenzenes. Experimental results showed that (1) the oxidation of phenol by Hydroxyl radicals, whether in free ( OHf) or bounded states ( OHb), led mainly to the ortho- (catechol) and para-oriented hydroxy derivatives (hydroquinone), whereas the meta-oriented hydroxy derivative (resorcinol) became the main product when holes were used as the active species; (2) in naked TiO2 suspensions, where OHb was the main ROSs, the selectivity of the catechol detected in the solution was much lower than that on the surface of the fluorinated TiO2 system (TiO2-F), where OHf served as the main ROSs. This finding can be attributed to the very strong catechol adsorption on the surface of naked TiO2. However, this adsorption was severely inhibited in the presence of fluorine because of the competitive adsorption between catechol and fluoride ions over TiO2 photocatalyst; and (3) the hole oxidation of phenol provided a slower oxidation rate but a higher yield of dihydroxybenzenes compared with Hydroxyl radical-mediated oxidation.
Birger Lindberg Moller - One of the best experts on this subject based on the ideXlab platform.
-
the in vitro substrate regiospecificity of recombinant ugt85b1 the cyanohydrin glucosyltransferase from sorghum bicolor
Phytochemistry, 2003Co-Authors: Karina Sinding Hansen, Carl Erik Olsen, David B Tattersall, Patrik R Jones, Charlotte Kristensen, Birger Lindberg MollerAbstract:Abstract The in vitro substrate specificity of UDP-glucose: p -hydroxymandelonitrile- O -glucosyltransferase from Sorghum bicolor (UGT85B1) was examined using a range of potential acceptor molecules, including cyanohydrins, terpenoids, phenolics, hexanol derivatives and plant hormones. Qualitative enzyme activity assays employing 20 different putative substrates were performed and 15 proved to be glucosylated using recombinant UGT85B1 isolated from Escherichia coli . K m and k cat values were determined for nine of these substrates including mandelonitrile, geraniol, nerol and β-citronellol, 2-hydroxy-3-methoxybenzyl alcohol, 1-hexanol, cis -3-hexen-1-ol, 3-methyl-3-buten-1-ol and 3-methyl-2-buten-1-ol. UGT85B1 has a rather broad substrate specificity in vitro but shows regiospecificity, demanding the presence of a sterically unhindered Hydroxyl group e.g. as part of a cyanohydrin function, as a primary alcohol or as a phenolic Hydroxyl group and being influenced by the stereochemistry and/or interactive chemistry of the substituents on the Hydroxyl-bearing carbon atom.
Dongyun Du - One of the best experts on this subject based on the ideXlab platform.
-
photocatalytic selective oxidation of phenol to produce dihydroxybenzenes in a tio2 uv system Hydroxyl radical versus hole
Applied Catalysis B-environmental, 2016Co-Authors: Mei Li, Kangle Lv, Xiaofeng Wu, Qin Li, Wingkei Ho, Hengpeng Ye, Dongyun DuAbstract:Abstract Photocatalytic oxidation plays an important role in organic synthesis. This research systematically studied the effect of reactive oxidation species (ROSs) such as surface-bounded Hydroxyl radicals ( OHb), free Hydroxyl radicals ( OHf), and hole (h+) on the photocatalytic selective oxidation of phenol in the TiO2/UV system and its corresponding important chemical intermediates, dihydroxybenzenes. Experimental results showed that (1) the oxidation of phenol by Hydroxyl radicals, whether in free ( OHf) or bounded states ( OHb), led mainly to the ortho- (catechol) and para-oriented hydroxy derivatives (hydroquinone), whereas the meta-oriented hydroxy derivative (resorcinol) became the main product when holes were used as the active species; (2) in naked TiO2 suspensions, where OHb was the main ROSs, the selectivity of the catechol detected in the solution was much lower than that on the surface of the fluorinated TiO2 system (TiO2-F), where OHf served as the main ROSs. This finding can be attributed to the very strong catechol adsorption on the surface of naked TiO2. However, this adsorption was severely inhibited in the presence of fluorine because of the competitive adsorption between catechol and fluoride ions over TiO2 photocatalyst; and (3) the hole oxidation of phenol provided a slower oxidation rate but a higher yield of dihydroxybenzenes compared with Hydroxyl radical-mediated oxidation.
Akbar Mahdavishakib - One of the best experts on this subject based on the ideXlab platform.
-
frequencies and thermal stability of isolated surfaceHydroxyls on pyrogenic tio 2 nanoparticles
Journal of Physical Chemistry C, 2019Co-Authors: Akbar Mahdavishakib, Juan M Arceramos, Rachel N Austin, Thomas J Schwartz, Lars C Grabow, Brian G FrederickAbstract:The surface reactivity of TiO22 is often governed by Hydroxyl groups. Fourier transform infrared (FTIR) spectroscopy is the most commonly used method to study surface Hydroxyls. However, interpretation of the observed bands of powder samples is not straightforward. In this work, we propose a facet-specific assignment of the surface Hydroxyls of pyrogenic TiO2 (commonly known as P25 and P90) by comparison between experimentally observed FTIR bands of P90, rutile, and anatase with calculated vibrational frequencies for well-defined surface facets using density functional theory (DFT). Titania was calcined for extended periods in extremely dry O2 to remove carbonates and water for diffuse reflectance infrared spectroscopy (DRIFTS) measurements of the most thermally stable Hydroxyls remaining in the 300 – 400 °C range. Reactions of the deHydroxylated surfaces with H2(D2) provided further insight into Hydroxyl formation. Theoretical assignments of Hydroxyls were based on the calculated thermal stability of hyd...
