P. Krishna Pillai

Sol–gel synthesis of nanosized anatase from titanyl sulfate

Nanosized titanium oxide with anatase structure holding high surface area has been synthesized by the sol–gel route from an aqueous solution of titanyl sulfate. A stable titania sol with extremely narrow range of particles having an average size of 30 nm has been obtained. The crystalline anatase particles have average particle size of 5–10 nm and specific surface area of 375–104 m2 g−1 between the calcination temperature 200–600 °C. The powders were characterized by XRD, FTIR, TGA/DTA and N2 adsorption analysis.

Dependence of calcination conditions of boehmite on the alumina particulate characteristics and sinterability

Abstract Monohydroxy aluminium oxide, boehmite (AlOOH), has been prepared by hydrolysis of aluminium nitrate under controlled conditions of pH, concentration and temperature. The boehmite passes through stages consisting of different transition aluminas on calcination until the stable alumina is formed at around 1393 K. The different transition aluminas have been characterized by surface area analysis and X-ray diffraction (XRD). The sintering studies on compacted discs from the calcined aluminas carried out at 1873 K show the maximum density of above 98% theoretical density for boehmite calcined at 1273 K containing mixed phases of γ, δ, θ and α-aluminas. The study of the particle characteristics, compaction and sintered densities shows that it is possible to obtain high-density alumina with fine-grained microstructure starting from a powder with transition aluminas rather than pure α-alumina.

Synthesis of high surface area silica by solvent exchange in alkoxy derived silica gels

Abstract Silica gels have been prepared by the hydrolysis of tetraethyl orthosilicate at pH 9.5 with a high water: TEOS ratio. The gels were exchanged with different solvents such as ethanol, methanol, isopropanol and acetone. The resultant gels were calcined at 500°C for 3 h at heating rate of 3°C min−1. The surface area and total pore volume of the calcined gels measured using nitrogen adsorption show much dependence with the nature of the liquid used for the exchange. The gel washed with ethanol under the conditions of present investigation shows maximum surface area. The adsorption isotherm of this gel also shows the characteristics of Type IV behaviour. Other gels usually show Type II behaviour. Solvents of low vapour pressure and high molecular volume favour the formation of gels with high pore volume. The method of exchange of solvents also influences the characteristics of the final gel precursor in terms of surface area and pore volume. Repeated washing of the gels with solvents and subsequent removal result in high surface area, while evaporating the gels with solvents results in relatively less porous gels.

Phase Transformation and Porosity Characteristics of Chemically Modified Sol-Gel Titania with Respect to Silica Addition

TiO2-SiO2 gels were prepared through the hydrolysis and polycondensation of a mixture of titanium isopropoxide and tetra ethoxy silane (TEOS) in presence of a gel modifier such as acetic acid. The resultant titania-silica gel precursor was calcined at various temperatures. An attempt has been made to correlate the properties of the resultant oxide with silica content. The amorphous to anatase and the anatase to rutile phase transition was followed by X-ray diffraction studies. The specific surface area of the resulting oxides was measured by BET method. 20% silica addition enhanced the specific surface area of titania from 84 m2.g−1 to 345 m2.g−1. The mesoporous nature of titania changes to microporous one, after addition of silica. Anatase to rutiie transformation temperature has also been influenced by the addition of silica.

Synthesis of High Surface Area Porous Silica through Aging Techniques

Silica gels prepared from tetraethylorthosilicate (TEOS) were aged in ethanol/water medium and subsequently in ethanol/TEOS after washing with ethanol. They were further exchanged with isopropanol and dried. The gels have a specific surface area 1142 m2g−1, pore volume 1.19 cm3g−1 bulk density 0.43 gcm−3 and an average pore size of 41.68 Å. The parent gel without any treatment has a specific surface area of 610 m2g−1 The structural changes with aging treatments were characterized and discussed. The microporous nature of the parent gel changes to mesoporous one during the course of aging. An enhancement in the densification temperature of the aged samples reveals high temperature pore stability.

Thermal stability of montmorillonite intercalated and alumina pillared by Boehmite Sol

Abstract Mono ion exchanged montmorillonite has been intercalated with monohydroxy aluminium oxide (Boehmite, AlOOH) by refluxing a mixture of the montmorillonite and boehmite in an aqueous medium. The alumina pillared montmorillonite has been prepared by further dehydroxylation of the intercalated material. Characteristics of the pillared smectite with respect to specific surface area, interlayer spacing and extent of pillaring by chemical estimation of alumina content is described. The thermal decomposition characteristics of the boehmite on intercalation with sodium and cerium exchanged montmorillonite shows distinct difference from the corresponding thermal analysis curves. The cerium exchanged montmorillonite shows a specific surface area of 300 m 2 /g and 190 m 2 /g on heating to 300°C and 800°C, respectively, while the one exchanged with sodium had 213 m 2 /g and 92 m 2 /g. The present work highlights the significance of following thermal analysis curves of intercalated montmorillonites in deciding the temperature of dehydroxylation to pillare intercalated smecite (PILC) as applied to boehmite as intercalent on sodium and cerium exchanged montmorillonite.