ANTIMONY(V) OXIDE GRAFTED ONTO A SILICA-GEL SURFACE - ACIDIC PROPERTIES AND THERMAL-STABILITY

Antimony(v) oxide grafted onto a silica gel surface was obtained in highly dispersed form, with antimony density of 0.65 atoms nm-2. The material presents Bronsted and Lewis acid properties different from pyrochlore, Sb2O5. These sites disappear upon thermal treatment at 500-degrees-C owing to reaction ot antimony oxide with the silica surface.88213193319

FTIR study of hydrogen and carbon monoxide adsorption on Pt/TiO2, Pt/ZrO2, and Pt/Al2O3

The Pt/TiO2, Pt/ZrO2, and Pt/Al2O3 catalysts submitted to low-temperature reduction (LTR, 200 degrees C) and high-temperature reduction (HTR, 500 degrees C) and exposed to hydrogen and carbon monoxide at room temperature were studied by infrared spectroscopy. There is a strong loss of transmission in the entire infrared spectra on Pt/TiO2 after its exposure to hydrogen, which is related to the reducibility of the support. A typical SMSI behavior (strong metal-support interaction), such as the decrease in carbon monoxide adsorption capacity, was detected on Pt/TiO2 and Pt/ZrO2 after exposure to hydrogen, even for the catalysts submitted to LTR treatment. Also a carbonyl band shift to lower wavenumber was observed on LTR-treated Pt/TiO2, Pt/ZrO2, and Pt/Al2O3 after exposure to hydrogen. We interpreted this SMSI behavior as an electronic rather than morphological effect, which was induced by the presence of hydrogen spillover.15238140814

Cobalt(II) hematoporphyrin IX and protoporphyrin IX complexes immobilized on highly dispersed titanium(IV) oxide on a cellulose microfiber surface: electrochemical properties and dissolved oxygen reduction study

Hematoporphyrin IX (8,13-bis(1-hydroxvethyl)-3,7.12.17-tetramethyl-21H-23H-porphine-2,18-dipropionic acid) and protoporphyrin IX (8,13-divinyl-3,7.12.17-tetramethyl-21H-23H-porphine-2. 18-dipropionic acid) were efficiently immobilized on a cellulose.,titanium (IV) oxide composite fiber surface by the reaction of the porphyrin COOH groups with TO,. presumably by forming the -COO-Ti chemical bond. Furthermore, Co(II) was incorporated into the porphyrin ring. with this reaction being followed by UV-vis spectra in the solid state and confirmed by, the change of the absorption bands due to a local symmetry change from D-2h to D-4h upon metallation of the porphyrin ring. Electrochemical studies by using cyclic voltammetry and chronoamperometry techniques, showed that the immobilized complexes catalyzed O-2 reduction at - 0.18 V for hematoporphyrin and - 0.20 V for protoporphyrin in 1 mol l(-1) KCl solution at pH 6. The cathodic current peak intensities plotted against O-2 concentrations in the range from 0.5 to 13 mg l(-1), showed a linear correlation, Rotating disk experiments were carried out in order to estimate the number of electrons involved on the process. It was observed that for both modified electrodes. dissolved O-2 was reduced to H2O2, in a two-electron process. (C) 2002 Elsevier Science B.V. All rights reserved.52341671646

Hybrid aniline/silica xerogel cation adsorption and thermodynamics of interaction

Aniline groups chemically immobilized on silica through the sol-gel process were employed to extract divalent nickel and manganese from aqueous solutions at room temperature. The maximum adsorption capacity of the xerogel was studied from adsorption isotherms using a batch technique. The isotherms obtained were adjusted following the Langmuir equation. The xerogel adsorbent appears to have better affinity for nickel than manganese. From calorimetric titration, thermodynamic data on cation/nitrogen basic atom interaction in the solid/liquid interface were determined. The enthalpic values, -0.46 +/- 0.02 and -0.29 +/- 0.02 kJ mol(-1) for nickel and manganese, respectively, are in agreement with the low availability of the basic nitrogen atom on the aniline group and also the possible steric hindrance of the phenyl group bonded to nitrogen. However, thermodynamics indicated the existence of favorable conditions for such cation-nitrogen interactions. (C) 2004 Elsevier Inc. All rights reserved.275238639

A sol-gel synthesis for thermally stable aniline/silica material

Aniline/silica sol-gel material was obtained. The aniline was immobilized on the silica surface using chloropropyltrimethoxysilane as bridge reagent. The base activator NaH was used to produce a fast SN2 reaction between the base and the alkylorganosilane. The resulting modified silica was characterized by elemental analysis and infrared spectroscopy using an oven cell. The organic coverage on the surface was proportional to the organic precursor concentration. The aniline/silica materials are thermally stable up to 300degreesC, in high vacuum.23212913

STRUCTURE AND ELECTROCHEMICAL PROPERTY OF THE COBALT(II) HEXACYANOFERRATE COMPLEX IMMOBILIZED ON SN(IV) OXIDE-COATED ON SILICA-GEL SURFACE

The complex cobalt hexacyanoferrate was immobilized onto a silica gel surface, chemically modified with tin(IV) oxide. The formal potential of the attached electroactive species was dependent on the supporting electrolyte used: NaNO3 = 0.39 V, KNO3 = 0.50 V and NH4NO3 = 0.53 V. A Nernstian behavior was observed for KNO3 and NH4NO3 and a quasi-Nernstian one for NaNO3 when they were used as the supporting electrolyte. The LiNO3 did not generate a reversible current peak since the hydrated ionic radius is larger than the zeolite-type cavity of the surface mixed valence complex.391333

The gelation temperature effects in the anilinepropylsilica xerogel properties

The sol-gel method was employed to obtain the hybrid nanometric anilinepropylsilica material, using different temperatures of gelation. The resulting powder materials were studied by FTIR, thermogravimetric analysis (TGA), SAXS and scanning electron microscopy (SEM) techniques. The organic phase incorporated in the material was very thermally stable and the gelation temperature produces morphological effects in the resulting anilinepropylsilica material. (C) 2002 Elsevier Science B.V, All rights reserved.55637838

The influence of Na+ on the anilinepropylsilica xerogel synthesis by using the fluoride nucleophilic catalyst

Anilinepropylsilica xerogel was obtained by using an appropriate organosilane and tetraethyl orthosilicate as precursor reagents. The gelation was carried out using HIF and NaF as catalysts. The presence of Na+ (when NaF was used) resulted in a decrease in the final organic content of the materials. This effect was interpreted as an inhibition of the organosilane polycondensation possibly due to the Na+ interaction with the SiO- groups of the hydrolyzed organosilane. The presence of Na+ also results in morphological changes in the xerogels.281217317

FeSbO4 phase formed at the surface of antimony(v) oxide grafted on silica gel

The FeSbO4 phase on antimony(v) oxide grafted onto a silica gel surface was obtained by two different ways: (i) by immersing the material, Sb/SiO2, in an aqueous solution of iron(nr) followed by heat treatment at 423 K or (ii) by immersing the material in a solution of Fe(CO)(5) in CCl4 followed by further hydrolysis and heat treatment: for treatment at 423 K, the separated phase Fe2O3 is observed while a new phase, FeSbO4, is formed upon heating the sample at 1073 K. In both cases an excess of antimony(v), in relation to iron(III), was found on the surface. This fact was interpreted as a result of antimony(v) migration from the internal to the external surface of the matrix when method (i) was used, and as due to a migration of iron(III) in the opposite direction, when the material was obtained by method (ii).9291569157