Parasuraman Selvam

We report on the synthesis and the characterization of a novel cobalt trimesate metal-organic framework, designated as KCL-102. Powder X-ray diffraction pattern of KCL-102 is dominated by a reflection at 10.2◦ (d-spacing = 8.7 Å), while diffuse reflectance UV-Vis spectroscopy indicates that the divalent cobalt centers are in two different coordination geometries: tetrahedral and octahedral. Further, the material shows low stability in humid air, and it transforms into the well-known phase of hydrous cobalt trimesate, Co3 (BTC)2·12H2O. We associated this transition with the conversion of the tetrahedral cobalt to octahedral cobalt.

Uranyl-anchored MCM-41 (UO22+/MCM-41) catalysts were prepared hydrothermally and systematically characterized employing various analytical and spectroscopic techniques: namely, X-ray diffraction (XRD), nitrogen sorption isotherms, transmission electron microscopy (TEM), electron diffraction (ED), and thermogravimetry-differential thermal analysis, inductively coupled plasma-atomic emission spectroscopy, diffuse reflectance ultraviolet-visible (DRUV-vis) spectroscopy and fluorescence spectroscopy, and Fourier transform-intrared (FT-IR) spectroscopy. XRD confirms the incorporation of uranyl ions into the silicate matrix and that TEM and ED investigations corroborate the highly ordered structure of uranyl-incorporated MCM-41. Further, these findings were well supported by DRUV-vis, fluorescence, and FT-IR spectra, indicating the nature of uranyl ion species as well as their interaction with the silicate framework. Well-characterized, high-quality UO22+/MCM-41 catalysts were employed for the liquid-phase allylic oxidation of α-pinene, β-pinene, and cyclohexene under moderate reaction conditions using various solvents and oxidants. Under the optimized experimental conditions, the catalysts showed high substrate conversion and excellent product selectivity. In addition, the influence of various other parameters (viz., temperature, time, recyclability, uranium content, etc.) were also performed. © 2011 American Chemical Society.

In the title monomeric manganese(II) complex, [Mn(CH3COO)2(C10H8N2)(H2O)2], the metal ion is coordinated by a bidentate 2,2′-bipyridine (bpy) ligand, two water molecules and two axial acetate anions, resulting in a highly distorted octahedral environment. The aqua ligands are stabilized by the formation of strong intramolecular hydrogen bonds with the uncoordinated acetate O atoms, giving rise to pseudo-bridging arrangement of the terminal acetate groups. In the crystal, the molecules form [010] zigzag chains via O - H⋯O hydrogen bonds involving the aqua ligands and acetate O atoms. Further, the water and bpy ligands are trans to each other, and are arranged in an off-set fashion showing intermolecular π-π stacking between nearly parallel bipy rings, the centroid-centroid separations being 3.8147 (12) and 3.9305 (13) Å.

X-ray photoelectron and Auger electron spectroscopic studies on TiFe demonstrate that ion bombardment of the alloy not only results in sputter cleaning or even destruction of the surface but also leads to the formation of compact carbide layers. Such carbide species are of considerable importance in elucidating the reaction mechanism of hydrocarbon synthesis. They are also expected to play a significant role in the hydrogen sorption properties of materials. A better understanding of the nature of sputtered carbon is needed for its use as protective (against corrosion) thin films in magnetic recording applications. A comparison of photoelectron and Auger electron spectra of the surface carbides of TiFe would also be of interest since it is unusual for both types of data to be produced on the same samples where chemical shifts are involved. © 1990.

A new intrinsic hydrolysis method was employed, for the first-time, to synthesize well-ordered H-AlSBA-15 with trivalent aluminium exclusively in the tetrahedral framework structure of SBA-15. Unlike other methods, which involve incorporation of aluminium ions in both the framework (Brønsted) and non-framework (Lewis) sites of the silicate matrix, the intrinsic hydrolysis method isomorphously substitutes aluminium ions in the tetrahedral network even at high aluminium content. This unique approach relies mainly on the hydrolysis rates of the inorganic (silicon and aluminium) precursors used for the preparation in such a way that the condensation occurs simultaneously so as to overcome the usually encountered difficulties in stabilizing aluminium ions in the silicate matrix. In this way, we could successfully synthesize high quality Brønsted acidic H-AlSBA-15, hitherto not reported. The synthesized materials were systematically characterized by various analytical, spectroscopic, and imaging techniques, including XRD, Brunauer–Emmett–Teller (BET) surface area measurements, TEM, SEM,29Si and27Al magic angle spinning NMR spectroscopy, X-ray fluorescence (XRF), and NH3temperature-programmed desorption (TPD). The characterization results reveal the presence of a highly porous structure (with narrow pores) and tetrahedrally coordinated trivalent aluminium in the silicate matrix with more medium to strong Brønsted acid sites. The resulting high quality catalysts exhibit excellent activity for tert-butylation of phenol with high selectivity towards para-tert-butyl phenol and 2,4-di-tert-butyl phenol.

Hierarchical zeolites with the ordered arrangement at the nanoscopic level are of paramount importance in catalysis owing to their remarkable properties. Nevertheless, architecting such structures is extremely difficult owing to their challenging synthesis conditions. In this study, we report a designed synthesis of such a material with MFI topology viz., hierarchical nanoporous ZSM-5 (designated as ZH-5) with unique serrated morphologies. The synthetic approach was envisaged by considering the stable supramolecular aggregation, controlled zeolitization and strong organosilane interactions as the key factors for the hierarchical organization. Furthermore, for the first time, we emphasize the effect of dual-templating nature of organosilanes in stabilizing the crystalline mesophase for the development of a hierarchical pore-architecture. In addition, the catalysts have shown remarkable catalytic activities for the formation of 2,4-di-tert-butylphenol.

In the unsymmetrical title vanadyl complex, [V(C9H9NO2)-(C7H5O2) O], one of the ligands (2-formylphenol) is disordered over two sets of sites, with an occupancy ratio of 0.55 (2):0.45 (2). The metal atom is hexacoordinated, with a distorted octahedral geometry. The vanadyl O atom (which subtends the shortest V - O bond) occupies one of the apical positions and the remaining axial bond (the longest in the polyhedron) is provided by the (disordered) formyl O atoms. The basal plane is defined by the two phenoxide O atoms, the iminoalcoholic O and the imino N atom. The planes of the two benzene rings are almost perpendicular to each other, subtending an interplanar angle of 84.1 (2)° between the major parts. The crystal structure features weak C - H⋯O and C - H⋯π interactions, forming a lateral arrangement of adjacent molecules.

Mesoporous nanocrystalline metal oxides such as TiO2, SnO2, and TiO2-SnO2 composites form a new class of mesoporous inorganic solids, which exhibit excellent structural, textural, optical, and photocatalytic properties. Furthermore, they also possess a large number of surface-exposed catalytic active sites in addition to their intrinsic flexible diffusion characteristics. In this investigation, we report the photocatalytic activity of high-quality mesoporous TiO2, SnO2, and TiO2-SnO2 composites. All the catalysts were tested for photocatalytic degradation of 4-chlorophenol under a solar simulator. The reaction results indicate that the anatase-phase mesoporous Ti0·9Sn0·1O2 exhibits enhanced activity as compared with the commercial TiO2 (P-25).

The conversion of solar energy into fuel has gained significant interest, particularly in photocatalytic water splitting, and the materials that efficiently generate hydrogen from water or aqueous solution using solar irradiation are highly desired for the hydrogen economy. Photocatalysts made of N-doped TiO2 are frequently utilized for breaking of water molecules in the process of generating hydrogen. To achieve this target, a unique defect-induced nitrogen-doped highly organized 2D-hexagonal periodic mesoporous titania, TiO2-xNy with a well-crystallized framework is synthesized in a reproducible way using structure-directing agents, e. g., F108, F127, P123, and CTAB. The nitrogen is incorporated into these samples through a facile method involving the calcination of templated materials in an air. A systematic characterization of the resulting ordered mesoporous titania employing a battery of experimental techniques indicates the presence of considerable amounts of intrinsic defects, viz., trapped electrons in oxygen vacancy and/or Ti3+ centres via nitrogen-doping in the titania matrix. These defects in turn promote the charge separation of photogenerated excitons, and therefore exhibit excellent photocatalytic activity for the hydrogen evolution reaction as compared to commercial titania such as Aeroxide®P-25. The superior activity of the N-doped mesoporous TiO2 is attributed to the synergistic effect of facile charge migration with high carrier density, unique phase composition (bronze and anatase), slow recombination of photo-induced excitons, and enhanced absorbance from ultra-violet to the visible region.

A series of sulfonic acid functionalized ordered mesoporous silica (OMS), designated as RSO3H-OMS (R=alkyl or aryl; OMS=MCM-41, IITM-56 or SBA-15), were prepared by post-synthesis grafting method. These catalysts, in general, exhibit strong acidic sites and, therefore, yield diacetone-D-glucose as main product in the D-glucose acetonation reaction. On the other hand, the functionalized catalyst can also be tuned in such a way to generate significant amount of weak-to-moderate acidic sites, which are in turn responsible for the formation of 1,2-monoacetone-D-glucose, hitherto not reported so far. These functionalized materials also show promise as they are water tolerant catalyst as well as exhibit varying acidic strengths, which allow greater flexibility for the desired product. In addition, the uniform mesopores with high surface area permit bulkier molecules to enter the active sites, thus the catalyst offers larger pliability in terms of yield and reusability. We report here, for the first time, RSO3H-SBA-15, with sizable amount of weak-to-moderate acidic sites, as a robust heterogeneous catalyst for the formation of the targeted molecule, 1,2-monoacetone-D-glucose.