Mahendra P. Kapoor

Titanium containing inorganic–organic hybrid mesoporous materials with exceptional activity in epoxidation of alkenes using hydrogen peroxide

Titanium containing ethane bridged hybrid mesoporous materials with uniform hexagonal arrangement are prepared by two different routes and characterized using several analytical techniques. The effect of substitution of bridged silsesquioxane precursors for siloxane precursors on the properties of resultant mesoporous bulk materials are also evaluated and discussed in term of mesoscopic order and oxidation catalysis. The materials are highly hydrophobic and selectively epoxidize the α-pinene to α-pinene oxide (with >99% selectivity) and display high hydrogen peroxide efficiencies.

Ethane-bridged hybrid mesoporous functionalized organosilicas with terminal sulfonic groups and their catalytic applications

The synthesis of a new class of sulfuric acid-functionalized ethane-bridged, mesoporous hybrid organosilicas is reported where the propylsulfonic groups attached with ethane-bridged silica exhibited reasonable catalytic activity in esterification of acetic acid with ethanol as well as the hydrolysis of cyclohexylacetate. Materials were synthesized by co-condensation of ethane-bridged organosilane (MeO)3SiCH2CH2Si(OMe)3 with 3-mercaptopropyltrimethoxysilane (MeO)3SiCH2CH2CH2SH in the presence of octadecyltrimethylammonium chloride surfactant. Powder X-ray diffraction patterns and nitrogen sorption analysis reveal the formation of mesoporous material with uniform porosity. The maximum content of incorporated mercaptopropylsilane in the mesoporous framework obtained was 3.45 mmol g−1. The thiol (–SH) moieties of mercaptopropyl groups that protrude into the pore channels are readily accessible for further oxidation. The surface moieties functionalized with propylsulfonic groups (–CH2CH2CH2–SO3H) were generated by the controlled oxidation of propylthiol surface groups using concentrated HNO3. A maximum acid exchange capacity (acid–base titration methods) of 1.38 H+ mmol g−1 was achieved after oxidation. Further, the materials were characterized using elemental analysis, FT-IR, 29Si and 13C MAS-NMR, transmission electron microscopy and TGA. Two probe reactions, the esterification of acetic acid with ethanol and its reverse the hydrolysis of cycloacetonate, showed the significance of the material in catalytic applications. The catalytic results showed the esterification activity is comparable to that of commercial Nafion-H and also the involvement of hydrophobic nature of the material in the hydrolysis reaction.

Fluorescence emission from 2,6-naphthylene-bridged mesoporous organosilicas with an amorphous or crystal-like framework.

We report that 2,6-naphthylene-bridged periodic mesoporous organosilicas exhibit unique fluorescence behavior that reflects molecular-scale periodicities in the framework. Periodic mesoporous organosilicas consisting of naphthalene-silica hybrid frameworks were synthesized by hydrolysis and condensation of a naphthalene-derived organosilane precursor in the presence of a template surfactant. The morphologies and meso- and molecular-scale periodicities of the organosilica materials strongly depend on the synthetic conditions. The naphthalene moieties embedded within the molecularly ordered framework exhibited a monomer-band emission, whereas those embedded within the amorphous framework showed a broad emission attributed to an excimer band. These results suggest that the naphthalene moieties fixed within the crystal-like framework are isolated in spite of their densely packed structure, different from conventional organosilica frameworks in which only excimer emission was observed for both the crystal-like and amorphous frameworks at room temperature. This key finding suggests a potential to control interactions between organic groups and thus the optical properties of inorganic/organic hybrids.

Direct synthesis of porous organosilicas containing chiral organic groups within their framework and a new analytical method for enantiomeric purity of organosilicas

Organosilica porous solids containing chiral organic moieties in the framework with an enantiomeric purity of 95% ee, estimated by eluting organic constituent units from chiral organosilicas, were synthesized from a newly designed chiral (R)-(+)-1,2-bis(trimethoxysilyl)phenylethane precursor via a surfactant-mediated self-assembly approach.

Functionalized mesoporous dendritic silica hybrids as base catalysts with volatile organic compound elimination ability

A post-synthetic process to create functionalized mesoporous dendritic silicas with a high density of tertiary amino groups is presented. Polyamidoamine periodic dendrimers up to the second generation were grown inside the channels of mesoporous hybrids. The results demonstrate that the novel polyamidoamine dendritic mesoporous benzene-silicas with highly hydrophobic crystal-like pore wall structures and the polyamidoamine dendritic mesoporous silicas with amorphous pore wall structures are very effective catalysts in Knoevenagel condensation due to enhanced hydrophobic interactions in the pore framework system, and also are effective adsorbents for volatile organic compound (VOC) removal.

Organosilicate–surfactant lamellar mesophase with molecular-scale periodicity in the silicate layers

The synthesis of lamellar mesophases of organosilicate-surfactant composites with periodicity within the silicate layers due to periodic arrangement of phenylene- and biphenylylene-silica moieties is reported.

Self-assembly of cubic phenylene bridged mesoporous hybrids from allylorganosilane precursors

The synthesis of three-dimensional (Pm3n) cubic phenylene-bridged hybrid mesoporous silica material using a novel allylorganosilane precursor 1,4-bis(triallylsilyl)phenylene and cetyltrimethylammoniumchloride (C16TMACl) as a structure-directing agent in acidic medium is presented. Sulfonic acid functionalized derivatives of these materials are effective in Friedel–Crafts acylation reactions and in controlling the atmosphere emission of volatile organic compounds, which are responsible for ground level ozone, air toxicity and smog.

Ammoximation of ketones catalyzed by titanium-containing ethane bridged hybrid mesoporous silsesquioxane

The first example of ammoximation of bulky ketones over highly hydrophobic titanium incorporated ethane bridged hybrid mesoporous silsesquioxane with high selectivity of oximes is presented.

Hydrophobicity induced vapor-phase oxidation of propene over gold supported on titanium incorporated hybrid mesoporous silsesquioxane

Gold nanoparticles supported on highly hydrophobic ethane bridged Ti incorporated mesoporous organosilica are reported for enhanced vapor phase epoxidation of propene using H2 and O2.

An alternate approach to the preparation of versatile sulfonic acid functionalized periodic mesoporous silicas with superior catalytic applications

A novel approach for the synthesis of sulfonic acid functionalized periodic mesoporous silicas via covalent attachment of 2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane or 3-glycidoxypropyltrimethoxysilane followed by reaction with sulfite ions and mild hydrochloric acid is presented. The materials demonstrated superior catalytic performance in esterification, acylation, and condensation reactions. The hydrophobic nature along with the crystalline pore wall structure of these materials are advantageous in increasing reaction rates by altering local water concentration and helpful in adjusting the modest active sites and surface properties. The materials also showed the higher stability and easily recyclable.