Dharitri Rath

Cesium salts of heteropoly acid immobilized mesoporous silica: An efficient catalyst for acylation of anisole

A series of Cs salt of phosphotungstic acid (Cs-PTA) supported on MCM-41 (Cs-PTA/MCM-41) was synthesized by a wet impregnation method and thoroughly characterized by using various analytical techniques, viz. X-ray diffraction, UV-Vis diffused reflectance spectroscopy (UV-Vis DRS), nitrogen adsorption desorption, scanning electron microscopy (SEM), Infrared spectra (FTIR), temperature programmed reduction (TPR), and temperature programmed desorption (TPD). The spectroscopic results revealed that Cs-PTA is highly dispersed on a MCM-41 surface. The 50 wt.% Cs-PTA supported on MCM-41 showed remarkable catalytic performance toward acylation of anisole reaction. The catalyst is regenerable by simple calcinations without appreciable loss in catalytic activity.

Surface characterization and catalytic evaluation of copper-promoted Al-MCM-41 toward hydroxylation of phenol

The Mobil Composition of Matter No. 41 (MCM-41) containing Cu and Al with Si/Al ratios varying from 100 to 10 and 1 to 6wt.% of Cu was synthesized under hydrothermal and impregnation conditions, respectively. The samples were characterized by nitrogen adsorption-desorption measurements, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), and (29)Si and (27)Al magic-angle spinning-nuclear magnetic resonance (MAS-NMR) spectra. X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. TPR patterns show the two-step reduction of Cu species. TPD study shows that Cu-impregnated Al-MCM-41 samples are more acidic than Al-MCM-41. From the MAS-NMR it was confirmed that most of the Al atoms are present tetrahedrally within the framework and some are present octahedrally in extraframework position. Impregnation of Cu shifted Al to the extraframework position. The catalytic activity of the samples toward hydroxylation of phenol in aqueous medium was evaluated using H(2)O(2) as the oxidant at 80 degrees C. The effects of reaction parameters such as temperature, catalyst amount, amount of H(2)O(2), and solvent were also investigated. Sample containing 4wt.% copper-loaded Al-MCM-41-100 showed high phenol conversion (78%) with 68% catechol and 32% hydroquinone selectivity.

Transition metal/metal oxide modified MCM-41 for pollutant degradation and hydrogen energy production: a review

In recent years, metal/metal oxide functionalized mesoporous materials have received increasing attention in science and technology due to their fascinating properties, such as a large surface area, mesoscopic bulky shape, and interconnected porous structures enabling them to be one of the most promising materials for catalysis and photo catalysis. This review summarizes the recent developments in design, preparation and applications of transition metal/metal oxide promoted MCM-41 for production of hydrogen energy and removal of aqueous pollutants. After a brief introduction of these materials and synthetic strategies, their characterizations and applications in aqueous pollutant degradation by photocatalysis/photo-Fenton processes and H2 energy production by photocatalytic water splitting are summarized. Finally, the future perspectives directions for this promising field are also discussed.

Organic amine-functionalized silica-based mesoporous materials: an update of syntheses and catalytic applications

Nowadays, inorganic–organic hybrid materials having pores in the mesoporous range are an intensively studied new category of demanding materials. By template synthesis, the coupling of inorganic and organic components gives pore sizes between 2 and 15 nm with very high surface area. The inorganic–organic hybrid materials were prepared in two ways: one was by co-condensation and the other by post-synthesis method. The inorganic part provides mechanical strength and the organic part shows functional activities. This review gives an overview of the preparation, properties, and potential applications of these materials in the areas of adsorption of pollutant gases like CO2 and heavy metals and in catalysis. Their activity is found to be very impressive in all these fields and it is hoped to be improved in the near future.

Cu@CuO promoted g-C3N4/MCM-41: an efficient photocatalyst with tunable valence transition for visible light induced hydrogen generation

A series of ternary Cu@CuO–g-C3N4/MCM-41 photocatalysts have been synthesized by varying the percentage of Cu using simple impregnation and co-condensation methods. The physico-chemical characterization of all the samples was determined using XRD, FTIR, UV-Vis DRS, PL, N2 ads–des studies, SEM and XPS HRTEM, EDAX, EIS and MS. The structural advantages of MCM-41, allow the uniform distribution of g-C3N4 and coexistence of Cu2+ along with Cu0 without using a reducing agent. The presence of g-C3N4 helps to shift the Fermi level of CuO towards more negative values due to accumulation of photogenerated electrons on the surface. It favours charge separation by creating a Schottky barrier at the junction. The 4 wt% Cu loaded over g-C3N4/MCM-41 exhibits a maximum 750 μmol 2 h−1 of H2 evolution under visible light irradiation with an apparent energy conversion efficiency of 24.8%. The enhancement in catalytic activity has been explained on the basis of synergism between g-C3N4 and Cu2+ and the SPR effect of Cu which also acts as a co-catalyst present on the surface of photocatalysts.

Amine modified mesoporous Al2O3@MCM-41: an efficient, synergetic and recyclable catalyst for the formylation of amines using carbon dioxide and DMAB under mild reaction conditions

This work reports an amine modified meso Al2O3@MCM-41, particularly the ordered mesoporous silica, as a catalyst for the formylation of amines with carbon dioxide (CO2) and with dimethylamine-borane (DMAB) as a green reducing source. This newly developed catalytic system represents a heterogeneous and environmentally benign protocol. Besides this, the catalyst could be reused for five consecutive cycles without any significant loss in its catalytic activity towards the synthesis of formamides. The amine modified meso Al2O3@MCM-41 catalysts were well characterized by high and low angle XRD, temperature programmed desorption (TPD), BET-surface area, TGA/DTA and FT-IR analysis techniques. The effect of various reaction parameters such as temperature, CO2 pressure, time and the ratio of substrates to DMAB for the synthesis of formamides has been investigated. The developed protocol can be applicable for the synthesis of most important key intermediates like formoterol, orlistat, leucovarin and iguratimod in biologically active compounds.

Characterization of novel Cs and K substituted phosphotungstic acid modified MCM-41 catalyst and its catalytic activity towards acetylation of aromatic alcohols

AbstractThe MCM-41 supported Cs2.5H0.5PW12O40 and K2.5H0.5PW12O40 salts were synthesized by incipient wetness impregnation method. The solids were characterized by N2 adsorption–desorption isotherms, FT-IR, XRD, and temperature programmed desorption, etc. This catalyst has been found to exhibit excellent activity for acetylation of phenolic compounds. The catalyst is stable and reusable giving 96% conversion with 100% selectivity towards acetate products. Graphical AbstractPhosphotungstic acid and its cesium and potassium salts supported on MCM-41 are found to be very active and an efficient catalyst for acetylation of aromatic alcohols. Inexpensive and easily available acetic acid as acetylating agent was used. The catalyst 50CsPTA/MCM-41 showed highest conversion (yield 96%).

A mechanistic approach towards the photocatalytic organic transformations over functionalised metal organic frameworks: a review

Photocatalytic organic transformations driven by functionalised metal organic frameworks (MOFs) are a green perspective for fine chemical synthesis. In the class of highly porous materials, MOFs are unparalleled in their degree of tunability and structural diversity and range of physical and chemical properties such as large surface area, permanent porosity, large void volumes, and framework flexibility, because of which they can act as a sustainable alternative for inorganic semiconductors. MOFs are the latest class of ordered porous solids being intensively studied as a novel class of hybrid organic–inorganic materials as nanophotocatalysts in the field of chemistry, materials science, chemical engineering, etc. Although the photocatalytic application of MOFs is still in the early stages compared with their other applications such as gas storage, separation, and heterogeneous catalysis, the currently available results have revealed that functionalised MOFs are very active as photocatalysts. The present review aims to discuss the various synthetic methods, post-synthetic modifications, MOF catalysed organic reactions and proposed mechanistic pathways for photoinduced organic transformations.

Synergistic effects of plasmon induced Ag@Ag3VO4/ZnCr LDH ternary heterostructures towards visible light responsive O2 evolution and phenol oxidation reactions

For enhancing solar energy conversion and environmental remediation, noble metal plasmonic photocatalysis originating from the effectual light absorbance and confinement of surface plasmons provides a new promising route. In the present study, by integrating these two aspects, a series of ternary Ag@Ag3VO4/ZnCr LDH heterostructures have been prepared by an in situ hydrothermal followed by co-precipitation method. In this method, there is self-assembling of Ag3VO4 nanoparticles on the brucite surface of the LDH material along with partial reduction of Ag+ to Ag. The phase identity, optical response, and morphological structure of the heterostructure photocatalysts were systematically characterized through PXRD, HRTEM, UV-Vis DRS, PL, and XPS methods. The resulting monodisperse Ag nanoparticles deposited on LDH materials offer a heterogeneous interaction at the interface and exhibit high photocatalytic activity towards generation of O2 and oxidation of phenol. Evaluation of photocatalytic activity showed that 40 wt% of Ag3VO4 modified LDH is the most effective photocatalyst for O2 evolution (571 μmol) and phenol oxidation (93%). The highly improved photocatalytic performance of the composite was ascribed mainly to the SPR effect of Ag nanoparticles, Schottky barriers formed at the interface of LDH and Ag3VO4 nanoparticles, and strong coupling between Ag, Ag3VO4 and LDH. The electrochemical studies such as LSV, CV, EIS and Tafel plots further support the high rate of photoactivity towards O2 evolution and phenol oxidation. These newly designed plasmonic Ag–LDH nanoheterostructures may offer a promising strategy for maximum light absorption and be authoritative in meeting environmental claims in the future.