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Surface Hydroxyl Groups (surface + hydroxyl_groups)
Selected AbstractsPoorly crystalline mineral phases protect organic matter in acid subsoil horizonsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2005M. Kleber Summary Soil minerals are known to influence the biological stability of soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations. The subsoil horizons represent six soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (14C) content after oxidation in all 12 soils. The amount of stable organic C did not depend on clay content or the content of dithionite,citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R2 = 0.78). Our results suggest that in acid soils, organic matter is preferentially protected by interaction with poorly crystalline minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid soils. The results imply a finite stabilization capacity of soil minerals for organic matter, limited by the area density of reactive surface sites. [source] The effect of water on particle size, porosity and the rate of drug release from implanted titania reservoirsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2010Tessy Lopez Abstract The implantation of controlled drug release devices represents a new strategy in the treatment of neurodegenerative disorders. Sol,gel titania implants filled with valproic acid, have been used for this purpose to treat induced epilepsy in rats. The kinetics of the drug release depend on: (a) porosity, (b) chemical interactions between valproic acid and surface hydroxyl groups of titania, (c) particle size, and (d) particle size agglomerates. The concentration of water used in the hydrolysis reaction is an important variable in the degree of porosity, hydroxylation, and structural defects of the nanostructured titanium oxide reservoir. The titanium n -butoxide/water ratio was systematically varied during the sol,gel synthesis, while maintaining the amount of valproic acid constant. Characterization studies were performed using DTA-TGA, FTIR, Raman, TEM, SEM, BET, and in vitro release kinetic measurements. The particle agglomerate size and porosity were found to depend on the amount of water used in the sol,gel reaction. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Structure, texture and surface acidity studies of a series of mixed zinc,aluminum (60,90 molar % Al) phosphate catalystsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2001Karim Mtalsi Abstract A series of mixed zinc,aluminum phosphate (ZnAlP) catalysts containing 40,90 aluminum molar % were synthesized by a coprecipitation method and characterized by nitrogen adsorption,desorption, X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption (TPD) of ammonia. The presence of aluminum greatly affected the surface properties of Zn3(PO4)2 by delaying the crystallization process of Zn3(PO4)2. All amorphous samples were shown to be mesoporous and they contained two types of aluminum surface hydroxyl groups and one type of phosphorus hydroxyl group, as shown by DRIFT spectra. The specific surface area and the acidity of ZnAlP increased on increasing the aluminum content. On the other hand, a great difference in the texture and the concentration of surface acid sites was found by changing the precipitating agent and calcination temperature. Thus these factors also play an important role in the final properties of these catalysts. © 2001 Society of Chemical Industry [source] Support-dependent activity of noble metal substituted oxide catalysts for the water gas shift reactionAICHE JOURNAL, Issue 10 2010Parag A. Deshpande Abstract The water gas shift reaction was carried out over noble metal ion substituted nanocrystalline oxide catalysts with different supports. Spectroscopic studies of the catalysts before and after the reaction showed different surface phenomena occurring over the catalysts. Reaction mechanisms were proposed based upon the surface processes and intermediates formed. The dual site mechanism utilizing the oxide ion vacancies for water dissociation and metal ions for CO adsorption was proposed to describe the kinetics of the reaction over the reducible oxides like CeO2. A mechanism based on the interaction of adsorbed CO and the hydroxyl group was proposed for the reaction over ZrO2. A hybrid mechanism based on oxide ion vacancies and surface hydroxyl groups was proposed for the reaction over TiO2. The deactivation of the catalysts was also found to be support dependent. Kinetic models for both activation and deactivation were proposed. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Enhanced Ability of Nanostructured Titania Film to Assist Photodegradation of Rhodamine B in Water Through Natural AgingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007Jin-Ming Wu Gradually but significantly improved abilities of titania films with various nanofeatures and crystal structures to assist photodegradation of trace rhodamine B in water were observed when the films were subjected to natural aging. The so-called natural aging behavior can be attributed to the gradual increase in the surface hydroxyl groups that are beneficial to the photocatalytic reaction. [source] | |||||||||||||