Narendra Nath Ghosh

A review on chemical methodologies for preparation of mesoporous silica and alumina based materials.

The discovery of novel family of molecular sieves called M41S aroused a worldwide resurgence in the field of porous materials. According to IUPAC definition inorganic solids that contain pores with diameter in the size range of 20-500 A are considered mesoporous materials. Mesoporous silica and alumina based materials find applications in catalysis, adsorption, host- guest encapsulation etc. This article reviews the current state of art and outline the recent patents in mesoporous materials research in three general areas: Synthesis, various mechanisms involved for porous structure formation and applications of silica and alumina based mesoporous materials.

Electron-beam curing of epoxy resins: Effect of alcohols on cationic polymerization

Electron-beam (e-beam) induced polymerization of epoxy resins proceeds via cationic mechanism in presence of suitable photoinitiator. Despite good thermal properties and significant processing advantages, epoxy-based composites manufactured using e-beam curing suffer from low compressive strength, poor interlaminar shear strength, and low fracture toughness. A detailed understanding of the reaction mechanism involving e-beam induced polymerization is required to properly address the shortcomings associated with e-beam curable resin systems. This work investigated the effect of hydroxyl containing materials on the reaction mechanism of e-beam induced cationic polymerization of phenyl glycidyl ether (PGE). The alcohols were found to play important roles in polymerization. Compared to hydroxyl group of aliphatic alcohol, phenolic hydroxyl group is significantly less reactive with the oxonium active centre, generated during e-beam induced polymerization of epoxy resin system.

Development of a novel one-pot synthetic method for the preparation of (Mn0.2Ni0.4Zn0.4Fe2O4)x–(BaFe12O19)1−x nanocomposites and the study of their microwave absorption and magnetic properties

The development of a simple yet novel aqueous solution based ‘one-pot’ method has been reported for the preparation of nanocomposites composed of soft ferrite (Mn0.2Ni0.4Zn0.4Fe2O4) and hard ferrite (BaFe12O19) phases. A physical mixing method has also been employed to prepare nanocomposites having the same compositions. The effects of synthetic methodologies on the microstructures of the nanocomposites as well as their magnetic and microwave absorption properties have been evaluated. The crystal structures and microstructures of these composites have been investigated using X-ray diffraction, transmission electron microscopy and scanning electron microscopy. In the nanocomposites prepared by both methods, the presence of nanocrystalline Mn0.2Ni0.4Zn0.4Fe2O4 and BaFe12O19 phases were detected. However, nanocomposites prepared by the one-pot method possessed better homogeneous distribution of hard and soft ferrite phases than the nanocomposites prepared by the physical mixing method. Very good spring exchange coupling interaction between the hard and soft ferrite phases was observed for the nanocomposites prepared by the one-pot method and these composites exhibited magnetically single phase behaviour. The spring exchange coupling interaction enhanced the magnetic properties (high saturation magnetization and coercivity) and microwave absorption properties of the nanocomposites prepared by the one-pot method, in comparison with the nanocomposites prepared by the physical mixing method as well as pure Mn0.2Ni0.4Zn0.4Fe2O4 and BaFe12O19 nanoparticles. The minimum reflection loss of the composites was found to be ∼−25 dB (i.e. >99% absorption) at 8.2 GHz with an absorber thickness of 3.5 mm.

Chemical Methodologies for Preparation of Micron and Nanometer Scale Ferrites - A Mini Review of Patents

Ferrites, with wide range of chemical compositions, have been studied extensively over the years as they have a plethora of applications such as magnetic read/write heads, transformer cores, antennas, microwave absorbers, deflecting yoke, high frequency transformers, catalysis, pigments etc. Particles of submicron size have attracted the attention of scientists and technologists in different fields because they exhibit many unique physical properties as compared to those of bulk materials and are in great demand. Traditional high temperature solid-state method for preparation of ferrites is associated with several limitations. The quest for synthesis of ultrafine ferrite materials has led to the development of various preparative methods. Several patents disclose different wet chemical techniques namely sol-gel, coprecipitation, hydrothermal, combustion, spray pyrolysis etc for preparation of variety of ferrites for wide range of applications. In this mini-review, several patented chemical methods have been discussed critically with specific examples along with the effect of synthetic routes on particle size formation. Applications of ferrite powders with different compositions prepared by the above mentioned patented methods have also been discussed in this review.

A PEGylated-rhodamine based sensor for “turn-on” fluorimetric and colorimetric detection of Hg2+ ions in aqueous media

A water soluble turn-on fluorescent probe for the detection of mercury ions in water is developed by appending a water-compatible PEG-unit onto a rhodamine derivative. The probe, Rh1 responds to Hg2+ ions with an intense pink colour and orange fluorescence due to Hg2+ ion-induced opening of the spirolactam ring with high selectivity and sensitivity. The Jobs plot reveals that a 1 : 1 stoichiometry was most favourable for the binding mode of Hg2+ and the probe. Preliminary studies revealed that the probe molecule is fairly non-toxic and can successfully penetrate the cell surface of HeLa cells and interact with intercellular Hg2+ ions, indicating its usefulness for monitoring Hg2+ ions in biological samples as well. The probe is highly efficient, cost-effective and shows a low detection limit of 0.14 ppm.

A simple ‘in situ’ co-precipitation method for the preparation of multifunctional CoFe2O4–reduced graphene oxide nanocomposites: excellent microwave absorber and highly efficient magnetically separable recyclable photocatalyst for dye degradation

Here, an ‘in situ’ co-precipitation reaction method has been reported for the preparation of CoFe2O4–RGO (CF–RGO) nanocomposites. To the best of our knowledge, this is the first time a simple synthetic method is reported for the preparation of CoFe2O4–RGO nanocomposites where a hydrothermal technique was not used. The novelty of this technique lies in its simplicity, cost-effectiveness, and the capability of large scale production of CoFe2O4–RGO nanocomposites. The synthesized CoFe2O4–RGO nanocomposites possess excellent microwave absorbing properties as well as high photocatalytic activity towards the degradation of various dyes under visible light irradiation. 85CF–15RGO (85 wt% CF and 15 wt% RGO) showed excellent microwave absorption properties with a Reflection Loss (RL) of −31.31 dB (∼99.94% absorption) at 9.05 GHz with an 8.2–10.92 GHz effective band width range. To the best of our knowledge 85CF–15RGO nanocomposite exhibited comparable and even superior microwave absorption properties in the X-band region than most of the ferrite based composites. 75CF–25RGO (75 wt% CF and 25 wt% RGO) acted as a very good magnetically separable photocatalyst for the degradation of various synthetic dyes (such as methyl orange, methylene blue, rhodamine B and a mixture of these dyes) under visible light irradiation emitted from a 100 W reading lamp. Moreover, CoFe2O4–RGO catalyst also showed easy magnetic separation with high reusability. The photocatalytic activity of 75CF–25RGO was found to be comparable and in some cases better than the various reported RGO–ferrite composites. The simple method of preparation and multifunctional character make CF–RGO nanocomposites attractive materials for application in the area of photocatalysis as well as microwave absorption.

Synthesis of a Ni0.8Zn0.2Fe2O4–RGO nanocomposite: an excellent magnetically separable catalyst for dye degradation and microwave absorber

A Ni0.8Zn0.2Fe2O4 reduced graphene oxide nanocomposite has been synthesized by a simple ‘in situ co-precipitation’ technique. This composite exhibited an ability to act as an excellent magnetically separable catalyst towards the degradation of various dyes as well as a toxic herbicide (trifluralin). It also demonstrated very good microwave absorption properties.

A facile low temperature method for the synthesis of CoFe2O4 nanoparticles possessing excellent microwave absorption properties

CoFe2O4 nanoparticles, synthesized via a co-precipitation method at 120 °C, exhibited excellent microwave absorption properties, with minimum reflection loss of −55 dB (∼99.99%) at 9.25 GHz. To the best of our knowledge, these synthesized CoFe2O4 nanoparticles show the highest minimum reflection loss in comparison with the reported CoFe2O4 based materials.

Preparation and Characterization of Novel Polybenzoxazine-Polyester Resin Blends

Blends consisting of polybenzoxazine and polyester with various weight ratios have been prepared by using a solution blending method. Thermal properties of the blends have been investigated by using thermogravimetric and differential scanning calorimetric analysis. Formation of hydrogen bonding was detected by using Fourier transformed infrared spectroscopy. Thermal stability of the blends increased with increasing the amount of polybenzoxazine in the composition. The composition having 70 wt% polybenzoxazine and 30 wt% polyester resin possesses the highest hardness and comparatively good thermal stability, with an initial decomposition temperature of 274°C and char yield = 21%.

CuO Nanoparticle Immobilised Mesoporous TiO2–Cobalt Ferrite Nanocatalyst: A Versatile, Magnetically Separable and Reusable Catalyst

Here, synthesis and catalytic activity of a novel nanocatalyst (CuO@mTiO2@CF), consisting of CuO nanoparticles, mesoporous titanium oxide and Cobalt ferrite have been reported for the first time. The catalyst was synthesized using a simple aqueous solution based chemical methodology. Synthesized CuO@mTiO2@CF showed excellent catalytic activity towards various organic reactions such as (i) Epoxidation of styrene, (ii) Click reaction, (iii) Biginelli reaction, (iv) Reduction of 4-Nitrophenol and trifluralin in presence of excess NaBH4. Moreover, this novel nanocatalyst offered easy magnetic separation after the catalysis reaction and excellent reusability. Easy synthesis methodology, versatility, good reusability and easy separation make the nanocatalyst attractive in the field of heterogeneous catalysis.Graphical Abstract