Subhenjit Hazra

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.

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 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 of a magnetically separable CoFe2O4 supported Ag nanocatalyst and its catalytic reaction towards the decolorization of a variety of dyes

This study deals with the exploration of CoFe2O4 supported Ag nanoparticles as a catalyst for the decolorization of various dyes (such as 4-nitrophenol, Congo red, rhodamine B) and dye mixtures by employing a reduction reaction with excess NaBH4 in an aqueous medium. Nanocatalysts with 10 wt% Ag loading (10Ag@CoFe2O4) exhibited very high catalytic activity and dye solutions were found to be decolorized within 4 to 6 minutes. A simple method for the preparation of a catalyst (10Ag@CoFe2O4) was reported, which exhibited very high catalytic efficiency towards the decolorization of dyes with different chemical structures as well as demonstrating its magnetic properties for easy separation from reaction mixtures and its reusability.

Synthesis and characterisation of pure single-phase CoFe2O4 nanopowder via a simple aqueous solution-based EDTA-precursor route

Single-phase cobalt ferrite (CoFe2O4) nanopowder, with average particle size ∼20 nm, has been synthesised using an ethylene diamine tetra acetic acid precursor-based method. CoFe2O4 nanopowder was obtained by calcining precursor at 550°C for 4 h in air. The change of microstructure of the synthesised CoFe2O4 with increasing sintering temperature was studied using scanning electron microscopy. DC electrical resistivities of unsintered and sintered samples were measured using a two-probe method. Room temperature magnetic hysteresis measurement revealed that the synthesised CoFe2O4 nanopowder exhibited ferromagnetic behaviour at room temperature with saturation magnetisation of 67.55 emu/g and coercivity of 1645.24 Oe.

Synthesis of Single-Phase Barium Hexaferrite Nanopowder via a Novel EDTA Precursor-Based Route and its DC Resistivity and Magnetic Property

An ethylenediamine tetraacetic acid (EDTA) precursor-based chemical method has been reported for preparation of single-phase barium hexaferrite nanopowder. Synthesized powders were characterized by thermogravimetric analysis, differential scanning calorimetric analysis, x-ray diffraction, particle size analysis, transmission electron microscopy, and scanning electron microscopy. DC electrical resistivity and magnetic properties of synthesized BaFe12O19 were measured by using a two-probe method and a vibrating sample magnetometer, respectively. This EDTA precursor-based method has the capability of producing nanostructured pure single-phase BaFe12O19 powder at a comparatively lower calcination temperature and offers the potential of a simpler, more cost-effective route than other reported methods.

Development of a novel and efficient H2O2 sensor by simple modification of a screen printed Au electrode with Ru nanoparticle loaded functionalized mesoporous SBA15

A novel and efficient electrochemical sensor has been developed to quantitatively measure H2O2 concentration by cyclic voltammetry. The sensor was prepared by modifying screen printed gold electrodes by ruthenium nanoparticle (Ru nanoparticle) loaded thiol functionalized mesoporous SBA15 (Ru@SBA15-SH) which was prepared by three simple steps. During measurement H2O2 electrochemically interacted with Ru nanoparticles and was channelled appropriately through the mesoporous structure of SBA15. The developed sensor showed a wide detection range with high sensitivity, durability and reproducibility. Furthermore, a very low limit of detection was reported by the sensor (0.42 μM (∼0.0142 ppm)), which was much lower than the permissible exposure limit.