Sooryakant G. Hegde

Photoemission studies of polymorphic CaCO3 materials

Abstract The surface analysis of polymorphic calcium carbonate (CaCO3) compounds, namely, calcite, aragonite, and vaterite were carried out by X-ray photoelectron spectroscopy (XPS). XPS results clearly demonstrate that vaterite is different from the other two and exhibit a low binding energy (BE) for all its constituent elements. It is attributed to the perpendicular orientation of CO32− to ab plane in vaterite. Aragonite shows less calcium and more oxygen and indicates the surface is carbonate terminated. Intergrowth of calcite and aragonite and natural dolomite samples were also analysed and compared with the above CaCO3 compounds. Ca:Mg=3 suggest that the dolomite surface is dominated by Ca.

Acid–base properties of Cu1−xCoxFe2O4 ferrospinels: FTIR investigations

Systematic IR spectroscopic studies were undertaken to investigate the acid–base properties of Cu–Co ferrospinels Cu1−xCoxFe2O4 (x = 0 to 1) employed in phenol methylation to produce 2,6-xylenol. The IR spectra of the ferrospinels reveal that Fe3+ and Co2+ ions are mainly responsible for the various hydroxy groups on the surface. Temperature dependent IR studies of pyridine adsorbed on spinels and on the spinel phase with deliberately added metal oxide exemplify the contribution of the metal ions and their coordination state towards Lewis acidity. IR studies of the spinel surface with adsorbed CO2 and adsorption studies of electron acceptors such as 7,7,8,8-tetracyanoquinodimethane, 2,3,5,6-tetrachloro-1-4-benzoquinone and p-dinitrobenzene were carried out to evaluate the nature of the basic sites and the strength and distribution of the electron donor sites present on the spinel surface. It was found that the acidity (basicity) of the Cu1−xCoxFe2O4 spinel system increases (decreases) from x = 0 to 1. A correlation between acidity, basicity and catalytic performance reveals that an intermediate acid–base character enhances the phenol methylation activity.

Synthesis of titanium silicalite-1 using ethyl silicate-40: a new silica source for zeolite synthesis

Titanium silicalite-1 (TS-1) was synthesized using ethyl silicate-40 (ES-40) as a new silica source for zeolite synthesis. This procedure is advantageous because of the higher rate of crystallization, enhanced incorporation of Ti and the highly pure sub-micron sized crystalline product, which is highly active for phenol and anisole oxidation by aqueous H2O2, furthermore, ES-40 is cheaper compared to tetraethyl orthosilicate (TEOS). The product was characterized by XRD, IR, SEM, UV–VIS and XRF spectroscopy and adsorption studies. The nature of the silicate species in the intermediate stages of the synthesis was characterized by studying the 29Si liquid NMR spectra. It was observed that if tetrabutyl orthotitanate (TBOT) was mixed with ES-40 before hydrolysis while preparing the reactive solution precursor, the Q3 type of silicate species were predominantly formed, which resulted in faster crystallization of TS-1.