Swapankumar Ghosh

Shape-Selective Oriented Cerium Oxide Nanocrystals Permit Assessment of the Effect of the Exposed Facets on Catalytic Activity and Oxygen Storage Capacity

The catalytic performance of a range of nanocrystalline CeO2 samples, prepared to have different morphologies, was measured using two accepted indicators; oxygen storage and diesel soot combustion. The same powders were characterized in detail by HR-TEM, XRD, XPS, and Raman methods. The study demonstrates that activity is determined by the relative fraction of the active crystallographic planes, not by the specific surface area of the powders. The physical study is a step toward quantitative evaluation of the relative contribution to activity of the different facets. The synthetic protocol permits fabrication of CeO2 nanostructures with preferentially grown active planes, and therefore has potential in developing catalytic applications and in nanocompositing.

Magnetic, X-ray and Mössbauer studies on magnetite/maghemite core–shell nanostructures fabricated through an aqueous route

Uniform 6–13 nm sized 0D superparamagnetic Fe3O4 nanocrystals were synthesized by an aqueous ‘co-precipitation method’ under a N2 atmosphere as a function of temperature to understand the growth kinetics. The crystal phases, surface charge, size, morphology and magnetic characteristics of as-synthesized nanocrystals were characterized by XRD, Raman spectroscopy, FTIR, TG-DTA, BET surface area, dynamic light scattering along with zeta potential, HR-TEM, EDAX, vibrating sample magnetometry and Mossbauer spectroscopy. TEM investigation revealed highly crystalline spherical magnetite particles in the 8.2–12.5 nm size range. The kinetically controlled as-grown nanoparticles were found to possess a preferential (311) orientation of the cubic phase, with a highest magnetic susceptibility of ∼57 emu g−1. The Williamson–Hall technique was employed to evaluate the mean crystallite size and microstrain involved in the as-synthesized nanocrystals from the X-ray peak broadening. In addition to FTIR and Raman spectra, Rietveld structural refinement of XRD confirms the magnetite phase with 5–20% maghemite in the sample. VSM and Mossbauer spectral data allowed us to fit the magnetite/maghemite content to a core–shell model where the shell is 0.2–0.3 nm thick maghemite over a magnetite core. The activation energy of <10 kJ mol−1 calculated from an Arrhenius plot for the complex process of nucleation and growth by diffusion during synthesis shows the significance of the precipitation temperature in the size controlled fabrication processes of nanocrystals. Brunauer–Emmett–Teller (BET) results reveal a mesoporous structure and a large surface area of 124 m2 g−1. Magnetic measurement shows that the particles are ferromagnetic at room temperature with zero remanence and zero coercivity. This method produced highly crystalline and dispersed 0D magnetite nanocrystals suitable for biological applications in imaging and drug delivery.

Nonaqueous Magnetic Nanoparticle Suspensions with Controlled Particle Size and Nuclear Magnetic Resonance Properties

We report the preparation of monodisperse maghemite (gamma-Fe2O3) nanoparticle suspensions in heptane, by thermal decomposition of iron(III) acetylacetonate in the presence of oleic acid and oleylamine surfactants. By varying the surfactant/Fe precursor mole ratio during synthesis, control was exerted both over the nanocrystal core size, in the range from 3 to 6 nm, and over the magnetic properties of the resulting nanoparticle dispersions. We report field-cycling 1H NMR relaxation analysis of the superparamagnetic relaxation rate enhancement of nonaqueous suspensions for the first time. This approach permits measurement of the relaxivity and provides information on the saturation magnetization and magnetic anisotropy energy of the suspended particles. The saturation magnetization was found to be in the expected range for maghemite particles of this size. The anisotropy energy was found to increase significantly with decreasing particle size, which we attribute to increased shape anisotropy. This study can be used as a guide for the synthesis of maghemite nanoparticles with selected magnetic properties for a given application.

Magnetic-fluorescent nanocomposites for biomedical multitasking

Fluorescent magnetite nanocomposites based on magnetic nanoparticles, a polyhedral octaaminopropylsilsesquioxane and a porphyrin derivative have been prepared. The intracellular uptake of the nanocomposites by macrophage and bone osteoblast cells, and their potential as MRI contrast agents, has been demonstrated.

Magnetic nanoparticle assemblies on denatured DNA show unusual magnetic relaxivity and potential applications for MRI

Denatured (substantially single-stranded) herring sperm DNA acts as a template for the preparation of magnetic nanowires, forming stable aqueous suspensions, which exhibit unprecedentedly high relaxivity at low field, suggesting that the material may be a potentially useful reagent for MRI.

Microwave drying of boehmite sol intercalated smectites

Monohydroxy aluminium oxide (boehmite) intercalated (cross-linked) smectites (SCLS) have been prepared from an aqueous suspension containing sodium mono-ion-exchanged bentonite (2 wt%) and boehmite (AlOOH) sol at pH 3.5 and at 32 °C. The SCLS has been separated by centrifugation and repeated washing. The intercalated smectite was dried in an oven at 60 °C over a period of 24 h and also in a microwave oven of 2.45 GHz frequency and 600 W power over a range of 3–15 min. Both samples have identical thermal and electrical properties. However, the microwave-dried samples have a distinctly higher surface area of 120 m2 g−1, stable up to 650 °C with a marginal reduction to 116 m2 g−1 compared with 94 m2g−1 for the oven-dried sample. Similarly there was clear difference in the morphological features of the two samples, the air-dried sample having a close packed structure while the microwave one is delaminated and porous.

pH dependent chemical stability and release of methotrexate from a novel nanoceramic carrier

Considering the pH dependent chemical stability of anticancer drug methotrexate (MTX), the present communication reports a new approach for intercalation of the same in a nanoceramic vehicle, magnesium aluminium layered double hydroxide (LDH), by ex situ anion exchange method at pH 7.00, using 0.3 M ammonium acetate solution for dissolution of the drug. This simple method ensures maximum stability of the drug at the above said pH, with no degradation byproduct (e.g., N10-methyl folic acid formed due to alkaline hydrolysis) under the given experimental conditions, compared to the similar approach, using 0.1 M sodium hydroxide solution, reported in our earlier work. Importantly, the above method leads to an enhanced drug loading of 32.3 wt%, compared to our previous reports. The cumulative release profile of MTX from LDH–MTX formulation in phosphate buffer saline (PBS) at pH 7.4 exhibited burst release initially which was taken care of by imparting a unique coating of poly(D,L-lactide-co-glycolide, PLGA) on the LDH–MTX nanostructure that reduces the toxicity due to local accumulation. Hence, the superiority of the above for use in cancer chemotherapy, over the conventional drug–polymer system has been established w.r.t the drug release profile and a possible hypothesis of the same has been suggested. The half maximal inhibitory concentration (IC50) of the MTX drug used in this study has been determined and the same has been used to estimate the time dependent (24, 48, 72 and 96 h) efficacy of the MTX loaded samples with/without polymer coating, on human colon tumour cells (HCT-116).

Impedance spectral studies of sol-gel alumina-silver nanocomposites

Abstract The nanocomposite of alumina and silver in different weight percentages (0, 1, 5 and 20%) were prepared through solution sol-gel technique. The densities of the sintered pellets were determined employing Archimedes’ principle. The microstructural features of the nanocomposites were followed by scanning and transmission electron microscopic observations. The ac electrical response of the consolidated Al 2 O 3 -Ag nanocomposite samples was studied using impedance spectroscopy. The equivalent parameters were determined using computer simulation of the experimental data. The observed results were interpreted using the physical model and equivalent circuit. The impedance spectral analysis gives the information of the two distinct phases, including the adsorbed moisture content in the nanocomposite.

Facile synthetic strategy of oleophilic zirconia nanoparticles allows preparation of highly stable thermo-conductive coolant

We report a simple one-step method of fabricating monodisperse zirconium oxide nanoparticles by decomposing a zirconium oleate complex in a high boiling organic solvent. The X-ray and transmission electron microscopy of nanocrystals indicated the formation of monoclinic zirconia. The surfactant capped zirconia nanoparticles produced excellent dispersions in oils. The suitability of the nanofluids in heat transport was carefully investigated by measuring suspension stability, thermal conductivity and viscosity as a function of temperature. The effect of particle loading and temperature on the thermal conductivity of the oil based nanofluids and other promising features indicated potential application of ZrO2 based nanofluids in the heat transport sector. A thermal conductivity enhancement of ∼10.3% was achieved with 1.7 vol% zirconia nanoparticle loading at room temperature. The TC of the nanofluids was remarkably higher than the same predicted by Maxwell and Hamilton–Crosser models.

Colloidal properties of water dispersible magnetite nanoparticles by photon correlation spectroscopy

We report the development of ultra-stable aqueous colloidal dispersion of magnetite nanocrystals produced by aqueous ‘coprecipitation method’. Magnetic nanofluids were prepared by dispersing the Fe3O4 NPs in water medium in the presence of tetramethylammonium hydroxide (TMAH). The synthesized nanocrystals were characterized by XRD, TG-DTA, XPS and TEM for evaluating the phase, crystal structure and morphology. FTIR spectroscopy was used to shed light onto the nature of the interactions between TMAH and Fe3O4 NPs. The TMAH peptized nanofluids was clear translucent colloidal dispersion found to contain spheroidal nanoparticles of average size 13 nm with very narrow size distribution similar to TEM size. High-resolution microscopy indicated that all the NPs are indeed single crystals with truncated octahedral shape. Lattice fringes belonging to predominant (111), (220) and (311) planes could be identified. The Ms values estimated are 64.68 and 57.92 emu g−1 at room temperature for NPs before and after peptization respectively and they are superparamagnetic. The key colloidal properties such as charge, hydrodynamic size, photon counts, dispersion stability and surface chemistry have been analyzed and compared with a dispersion of aqueous precipitated magnetite. The TMA suspensions are stable over a year without any loss due to precipitation. Photon scattering experiments have indicated the presence of very small NP clusters of 28 nm in aqueous suspensions. The lower extent of agglomeration in TMA promotes the one-shell clusters of primary nanoparticles, a fact which can forecast the stability of the ferrofluid. The change in surface charge of the magnetic fluid from −44 to +49 mV while varying the pH indicated the PZC at pH 5.98. The dynamic processes were investigated during the photon scattering experiment against time, temperature and concentration. The stability of the ferrofluid against time, temperature and concentration indicates the great potentials in biotechnology, selective catalysis and other industrial applications.