H. Acharya

A solution blending route to ethylene propylene diene terpolymer/layered double hydroxide nanocomposites

Ethylene propylene diene terpolymer (EPDM)/MgAl layered double hydroxide (LDH) nanocomposites have been synthesized by solution intercalation using organically modified LDH (DS-LDH). The molecular level dispersion of LDH nanolayers has been verified by the disappearance of basal XRD peak of DS-LDH in the composites. The internal structures, of the nanocomposite with the dispersion nature of LDH particles in EPDM matrix have been studied by TEM and AFM. Thermogravimetric analysis (TGA) shows thermal stability of nanocomposites improved by ≈40 °C when 10% weight loss was selected as point of comparison. The degradation for pure EPDM is faster above 380 °C while in case of its nanocomposites, it is much slower.

Influence of nanodispersed organoclay on rheological and swelling properties of ethylene propylene diene terpolymer

The dispersion of organoclay in ethylene propylene diene terpolymer (EPDM) matrix was correlated with the rheological and swelling properties of nanocomposites. X-ray diffraction pattern (XRD) and transmission electron microscopic (TEM) analysis exhibited the disordered-intercalated structure of EPDM/organoclay nanocomposite. The extent of the disordered phase increased with increasing organoclay content up to a limiting value of 3 wt% after which equilibrium tended towards intercalation. The dispersion effect of organoclay in EPDM matrix was clarified by the physicochemical properties like rheological response and swelling thermodynamics in toluene. The increase in viscoelastic properties of EPDM nanocomposite with increasing organoclay content up to 3 wt%, followed by a subsequent decrease up to 4 wt%, was correlated in terms of the disordered and ordered states of the dispersed nano-clay sheets. Swelling measurements revealed that the change in entropy of the swelling increased with the increase in disorder level but decreased with the increase in intercalation level of organoclay in the disorderedintercalated nanocomposite. The increase in solvent uptake was comparable with the free volume in EPDM matrix upon inclusion of silicate particles, whereas the inhibition in solvent uptake for higher organoclay loading was described by bridging flocculation.

Fluorescent silver nanoclusters (Ag NCs) in the metal–organic framework MIL-101(Fe) for the catalytic hydrogenation of 4-nitroaniline

A fluorescent Ag nanocluster deposited iron based metal organic framework, Ag NC@MIL-101(Fe), has been synthesized by a solution impregnation method (MIL stands for Material from Institut Lavoisier). Silver salt solution was impregnated into the porous MIL-101(Fe) and reduced chemically to Ag nanoclusters. The uniform size and high dispersibility of Ag nanoclusters were characterized by UV-vis and photoluminescence spectroscopy, transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). Herein, it is revealed that the stable and monodisperse ultrasmall Ag nanoclusters as small as less than 1 nm in diameter are deposited in the porous MIL-101(Fe). These clusters exhibit highly efficient blue luminescence including a narrow emission profile, a larger Stokes shift and high photostability upon excitation at 330 nm. The as-synthesized Ag NC@MIL-101(Fe) exhibits enhanced catalytic activity towards the heterogeneous reduction of 4-nitroaniline to 4-phenylenediamine under green and ambient conditions. Furthermore, the catalyst can be reused for five consecutive runs with significant recycling stability over 90%. Our results suggest that these fluorescent clusters can be used in green heterogeneous synthesis.

Magnetically separable palladium nanocluster supported iron based metal–organic framework (MIL-88B) catalyst in efficient hydrogenation reactions

A facile process to fabricate a magnetically separable palladium nanocluster (Pd NCs) supported iron based metal–organic framework, Pd@MIL-88B catalyst is reported. Highly active Pd NCs are obtained by a simple in situ chemical reduction of immobilized metal salts within the porous MIL-88B. Structure and morphology analysis of the Pd@MIL-88B catalyst is characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The Pd@MIL-88B exhibits excellent catalytic activity towards the reduction of 4-nitrophenol completed in only 15 s at room temperature, even when the Pd content was 2.7 wt%. Moreover, the catalyst can be reused several times with significant recycling stabilities on magnetic separation.

Mesomorphic Schiff base amine tethered giant gold nanoparticles

ABSTRACT GNP-LC hybrid incorporating giant gold nanoclusters was accessed with tailor made liquid crystalline Schiff base bearing amine function as reactive end group without using any external reducing agent. The liquid crystal phase (smectic C) of the Schiff base remained unaltered in the hybrid material. The ligand and hybrid both exhibited interesting concentration-dependent fluorescence quenching of 9,10-diphenylanthracene when excited at 345 nm wavelength in dichloromethane solution. The GNP-LC hybrid exhibited reasonably good electrical conductivity showing an Arrhenius-type behaviour in the smectic mesophase and a tunnelling behaviour in the crystalline state. GRAPHICAL ABSTRACT

Controlled synthesis of monodisperse silver nanoparticles supported layered double hydroxide catalyst

Silver nanoparticles supported layered double hydroxides (Ag NPs–LDH) were synthesized via a facile chemical reduction–deposition method. The successive anion exchange of the carbonate ions of ZnAl-(CO32−) LDH by chloride and citrate ions leads to citrate intercalated LDH (Cit-LDH). On hydration, the citrate anions in Cit-LDH can attract Ag+ ions by a superficial electrostatic force of attraction and reduce them to Ag nanoparticles. The preferential deposition of monodisperse Ag NPs was obtained on the outer surfaces of pillared LDH. The simultaneous formation of large colloidal Ag NPs of 25–30 nm in size in the aqueous phase was also found exterior to the LDH gallery. The nanoparticles deposited on the LDH surfaces are highly dispersed with a narrow size distribution of ∼2.5 nm and are stabilized on the LDH support. The Ag NPs deposited LDH nanosheets were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The resulting monodisperse Ag NPs deposited LDH materials offer heterogeneous interactions at the interface and exhibit high catalytic activity on alcohol oxidation.

Grafting a mesomorphic Schiff base onto gold nanoparticle via ester link – photoluminescence, mesomorphism, electrical conductivity and antioxidant activity

ABSTRACT Liquid crystal-gold nanoparticle (GNP-LC) composite were accessed via covalent coupling of 4-mercaptophenol capped gold nanoparticles (GNP) and a carboxylic acid functionalised rod shaped mesomorphic Schiff base (LC). The Schiff base ligand and the composite both showed schlieren texture with distinct difference in phase transition temperature. The X-ray diffraction study suggested a smectic C mesophase for the compounds. The LC and GNP-LC, both exhibited room temperature photoluminescence when excited at 264nm.The transmission electron micrography revealed the composite to be nearly monodisphersed having almost spherical shape of ~ 2nm size. The composite material in addition to being mesomorphic exhibited pronounced AC conductivity in the semiconductor domain and antioxidant activity. Graphical Abstract