Omar J. de Lima

Hybrid materials prepared by interlayer functionalization of kaolinite with pyridine-carboxylic acids

This paper presents the results of the functionalization of Brazilian São Simão kaolinite with pyridine-2-carboxylic and pyridine-2,6-dicarboxylic acids. The functionalization involved refluxing of the pyridine-carboxylic acid in the presence of kaolinite previously intercalated with dimethyl sulfoxide; both acids effectively displaced dimethyl sulfoxide from the clay interlayer. The resulting materials were characterized by X-ray diffraction, thermal analysis, infrared absorption spectroscopy, and C and N elemental analysis. The X-ray diffractograms revealed the incorporation of the acid molecules into the interlayer space of kaolinite. The thermogravimetric curves of the kaolinite samples functionalized with the pyridine-carboxylic acids indicated that the materials were thermally stable up to 300 degrees C. The displacements of the bands due to interlayer hydroxyls in the infrared absorption spectra also confirmed the functionalization of the kaolinite with the pyridine-carboxylic acids.

Porphyrins entrapped in an alumina matrix

Novel hybrid organic–inorganic catalysts constituted by iron(III) or manganese(III) 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin entrapped in an alumina amorphous matrix have been prepared. The hybrid materials were obtained by a non-hydrolytic sol–gel route, through the condensation of aluminium chloride with diisopropyl ether in the presence of metalloporphyrin. The presence of the metalloporphyrin entrapped in the alumina matrix is confirmed by ultraviolet–visible spectroscopy and electron spectroscopic imaging. The material was also analysed by infrared spectroscopy, selected area diffraction, scanning electron microscopy, thermogravimetric analysis and differential thermal analysis, and its surface area was determined. Comparison between the leaching of metalloporphyrin from non-hydrolytic materials and adsorbed metalloporphyrin on commercial neutral alumina confirms that in the non-hydrolytic materials the metalloporphyrin is entrapped and not just adsorbed on the alumina surface. The use of a conventional hydrolytic sol–gel process leads to the complete leaching of the metalloporphyrin from the matrix, underlining the importance of the non-hydrolytic alumina gel process in the matrix preparation. The prepared alumina matrix materials are amorphous, even after heat treatment up 270 °C. The new catalysts prepared were tested for their ability to catalyse the epoxidation of (Z)-cyclooctene using iodosylbenzene as oxygen donor, giving high yields in the epoxidation, similar to those obtained using the metalloporphyrin in solution or supported on a silica matrix.

Estudo das condições de estocagem do bagaço de cana-de-açúcar por análise térmica

An evaluation was made of the properties of sugarcane bagasse during the storage process for subsequent burning in a boiler. Samples of bagasse were collected over a period of 150 days from the Caete sugar mill (MG) at various points of the stockpile soon after the sugarcane was pressed to extract its juice, as well as from natural bagasse, dry and damp. Thermal analyses of the samples were carried out and the results indicated that, during the storage of bagasse, dry or damp, the biomass loses up to 32% of its calorific power, due to decomposition of the hemicellulose.

Iron(III) porphyrin supported on metahalloysite: an efficient and reusable catalyst for oxidation reactions

The raw clay minerals kaolinite and halloysite were calcined at controlled temperature and time, to obtain metakaolinite and metahalloysite, respectively. The resulting materials were used as supports for the anionic iron(III) porphyrin [Fe(TDFSPP)] (FePor) and found that only metahalloysite is adequate for FePor immobilization, although the FePor loading on this solid is low. XRPD, FTIR and solid UV-Vis spectroscopies, and textural analysis confirmed metakaolinite and metahalloysite formation and FePor immobilization on metahalloysite. The catalytic activity of the metahalloysite-supported FePor (FeMhallo) was evaluated in heterogeneous oxidation reactions using iodosylbenzene as oxidant and cyclooctene, cyclohexane, or n-heptane as substrate, obtaining expressive product yields for all the substrates. At the end of the oxidation, the catalyst was recovered from the reaction medium and used in a further reaction, which also afforded appreciable results. In competitive catalytic reactions using cyclohexane and n-heptane as substrates, FeMhallo is not significantly selective for any of the substrates.

Eu3+ entrapped in alumina matrix obtained by hydrolytic and non-hydrolytic sol–gel routes

Abstract The optimized conditions for the preparation of luminescent materials consisting of Eu3+ entrapped in an alumina matrix are described. Eu3+ ions in an alumina matrix have been prepared by sol–gel process using both non-hydrolytic (through the condensation of aluminum chloride with diisopropyl ether) and hydrolytic (by the reaction of aluminum chloride with aqueous NH3) methodologies. Luminescence spectra, X-ray diffraction, surface areas, thermogravimetric properties and differential thermal properties have been measured. Through the non-hydrolytic sol–gel route we prepared amorphous, non-hydrated material with greater luminescence efficiencies and longer decay times, than for Eu3+ in alumina prepared by other processes, even when heat treated at temperatures ⩽750 °C. The conventional hydrolytic sol–gel process produces materials where the Eu3+ ions are imbedded in a crystalline alumina matrix containing water which increases quenching which reduces the luminescence efficiency of Eu3+.

Óxido misto de ítrio-alumínio dopado com Eu(III)

In this work, we report the synthesis and the photoluminescence features of Eu(III)-doped yttrium-aluminium oxide obtained by non-hydrolytic sol-gel routes. After heating the powders above 600 oC the XRD patterns show the presence of the Y4Al2O9 (YAM) and Y3Al5O12 (YAG) phases. At 800 and at 1500 oC the PL spectra display the Eu(III) lines characteristic of the YAM monoclinic phase. The 5D0®7F2 transition is favored relatively to the 5D0®7F1 lines. However, at 1100 oC the cubic YAG is the preferential phase and the 5D0®7F1 transition dominates the spectrum. The Eu(III) ions lie in a centrosymmetrical site. The different solvents used in the sol-gel synthesis also change the relative proportion between these two phases. This is monitored analyzing the modifications in the relative intensity between the 5D0®7F2 and the 5D0®7F1 transitions.

Encapsulation of Tetraazaannulenato Compounds in Matrix by Sol-Gel Process

The hybrid organic-inorganic catalyst constituted by {5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraaza[14]annulenato} nickel (II), NiTMTAA, encapsulated in an alumina matrix has been prepared. NiTMTAA was synthesized by the reaction of nickel acetate with o-phenylenediamine in the presence of 2,4-pentanedione under argon atmosphere. The alumina hybrid material was obtained by a non hydrolytic sol-gel route, through the condensation of aluminum chloride with diisopropylether in the presence of NiTMTAA. The material has been prepared through precipitation from a gel. Characterization of the alumina hybrid material has been performed by ultra violet-visible spectroscopy, electron spectroscopic imaging, surface area, atomic absorption, infrared spectroscopy, and thermogravimetric analysis. The ultra violet-visible absorption spectrum of the hybrid material has bands characteristic of the NiTMTAA compound showing that the structure of NiTMTAA has been preserved in the hybrid material. The new material has a surface area of 300 m2/g. The electron image was that of a non-crystalline microstructure. Comparison between the leaching of NiTMTAA from NiTMTAA adsorbed on commercial neutral alumina confirm that in the non-hydrolytic materials the NiTMTAA is entrapped and not only adsorbed on the alumina surface. The use of conventional hydrolytic sol-gel process leads to the complete leaching of NiTMTAA from matrix, underlining the importance of the non-hydrolytic alumina gel process in the matrix preparation. The new catalysts prepared were tested for their ability to catalyze the epoxidation of (Z)-cyclooctene using iodosylbenzene as oxygen donor, giving moderate yields in the epoxidation (40%), while the homogeneous NiTMTAA is inactive due to NiTMTAA bleaching. These results emphasize the effect of the non-hydrolytic alumina matrix to prevent chemical degradation of NiTMTAA.

Sol–gel entrapped cobalt complex

This work describes optimized conditions for preparation of a cobalt complex entrapped in alumina amorphous materials in the form of powder. The hybrid materials, CoNHG, were obtained by a nonhydrolytic sol–gel route through condensation of aluminum chloride with diisopropylether in the presence of cobalt chloride. The materials were calcined at various temperatures. The presence of cobalt entrapped in the alumina matrix is confirmed by ultraviolet visible spectroscopy. The materials have been characterized by X-ray diffraction (XRD), surface area analysis, thermogravimetric analysis (TGA), differential thermal analyses (DTA) and transmission electron microscopy (TEM). The prepared alumina matrix materials are amorphous, even after heat treatment up to 750 jC. The XRD, TGA/DTA and TEM data support the increase of sample crystallization with increasing temperature. The specific surface area, pore size and pore diameter changed as a function of the heat treatment temperature employed. Different heat treatment temperatures result in materials with different compositions and structures, and influence their catalytic activity. The entrapped cobalt materials calcined at 750 jC efficiently catalyzed the epoxidation of (Z)-cyclooctene using iodozylbenzene as the oxygen donor.

Sol-gel as methodology to obtain bioactive materials

We employed the sol-gel methodology to obtain a silica matrix modified with calcium and phosphate ions. We prepared the matrix by hydrolysis and condensation of the precursors triethyl phosphate, calcium nitrate, and tetraethylorthosilicate, which were the sources of phosphate, calcium, and silicon, respectively. We dried and heat-treated the samples at 110 or 900°C and placed them in simulated body fluid (SBF) for three days. We conducted scanning electron microscopy, x-ray diffraction, and infrared spectroscopy analyses, which evidenced that the sample treated at 110°C contained calcium phosphate silicate and hydroxyapatite before and after contact with SBF, respectively. The sample treated at 900°C exhibited a hydroxyapatite phase before and after contact with SBF, but the crystalline phase was more evident after the contact. In conclusion, the sol-gel methodology provided bioactive samples for bone regeneration.

Materiais híbridos orgânico-inorgânicos (ormosil) obtidos por sol-gel com potencial uso como filtro solar

This work aimed at the synthesis and characterization of particles of modified silica containing the organic filter dibenzoylmethane (DBM) by the hydrolytic sol-gel method, with modifications to the Stober route. The structures of the resulting Xerogels were characterized by diffuse reflectance UV-VIS spectroscopy in the solid state, infrared absorption spectroscopy, Scanning Electron Microscopy (SEM) and 29Si Nuclear Magnetic Resonance (29Si NRM). The results showed favorable formation of hybrid organic-inorganic nanoparticles with efficient absorption/reflectance of radiation in the UV / VIS range, which enables their potential use as sunscreen.