Aparna Datta

Single step aqueous synthesis of pure rare earth nanoparticles in biocompatible polymer matrices

The room temperature synthesis of water soluble, stable rare earth (RE) metal nanoparticles (MNPs) with controlled size is a long standing interest. In the present work, we have established a synthetic strategy for the preparation of pure europium (Eu0) metal nanoparticles (NPs) in aqueous solution employing a γ-radiolytic reduction technique. Since radiolysis is the cleanest method amongst all other chemical routes, we preferentially choose this technique for the reduction of precursor Eu3+ ions to nanoscale metals in our work. This has been possible as hydrated electrons (e−aq) having a very high reduction potential (E0(H2O/e−aq) = −2.87 VNHE) produced in situ can efficiently reduce Eu3+ to Eu0. Synthesized Eu0 MNPs were stabilised within the matrices of biocompatible polymers, polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). Reduction of the metal ion has been conducted at different irradiation doses with a maximum dose of 83.88 kGy. The irradiated solution shows an absorption maximum at 266 ± 2 nm and an emission maximum at 394 ± 5 nm. Analysis of transmission electron microscopy (TEM) images shows that the average sizes of PVA and PVP encapsulated Eu0 NPs are 13 ± 0.6 nm and 17 ± 1.01 nm, respectively ([Eu3+] = 5.0 × 10−3 mol dm−3, [polymer] = 1.0%). Formation of monodisperse pure Eu0 MNPs was further characterised by dynamic light scattering (DLS), energy dispersive X-ray (EDX) as well as Fourier transformed infrared (FTIR) spectroscopy and cyclic voltammetry (CV) studies.

Synthesis and characterization of stable aqueous dispersions of graphene

A stable aqueous dispersion (5 mg ml−1) of graphene was synthesized by a simple protocol based on three-step reduction of graphene oxide (GO) dispersion synthesized using the modified version of Hummers and Offeman method. Reduction of GO was carried out using sodium borohydride, hydrazine hydrate and dimethyl hydrazine as reducing agents. The chemically synthesized graphene was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible absorption spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopy, thermogravimetric analysis (TGA), optical microscopy. The stability of aqueous dispersions of graphene was confirmed through zeta potential measurements and the negative zeta potentials of 55–60 mV were obtained indicating the high stability of aqueous graphene dispersions.

Kinetic analysis of low concentration CO detection by Au-loaded cerium oxide sensors

Owing to its high toxicity, even at very low concentration, early detection of carbon monoxide (CO) is imperative. We have fabricated sensors comprising gold nanoparticle-loaded cerium oxide (Au–CeO2). The morphology and elemental composition of the sensing material have been characterized using XRD, FESEM, TEM and XPS. The performance of the Au–CeO2 sensors has been studied for the detection of CO in the concentration range of 10–30 ppm in air. The response and recovery transients of conductance have been modeled using two-site Langmuir adsorption kinetics. In the presence of 30 ppm CO, the calculated response times for two energetically different adsorption sites, CeO2 surface and Au/CeO2 interface are 9 s and 7 s, respectively. Finally, an exponential correlation between the gas concentration and the time constants has been derived.

Radiation-induced synthesis of self-organized assemblies of functionalized inorganic–organic hybrid nanocomposites

We demonstrate a unique single-pot synthesis of self-organized structures of CdS/dendrimer nanocomposites having long-range correlation by adopting a radiation-induced technique. The present method has been able to produce long-range chain-like networks of CdS nanoparticles of high stability within the dendrimer matrix with particle size monodispersity ∼6%, as visualized with atomic force microscopy, while individual particles are characterized by transmission electron microscopy, photoluminescence, absorption spectroscopy and dynamic light scattering. Results point to a possible mechanism of long-range self-organization from the nanometer to micrometer length scales, where the self-organization is controlled by surface functionality of the dendrimer molecule, solvent and crystal phase of the CdS nanocrystals. The present investigation opens up new potential routes to manipulate semiconductor nanocomposites for optical diagnostics and for applications that require dendrimer nanocomposites with a long-range order.

Low temperature synthesis of Ag@anatase TiO2 nanocomposites through controlled hydrolysis and improved degradation of toxic malachite green under both ultra-violet and visible light

The nanocomposite material of titania coated silver nanoparticles (AgNPs) was prepared by employing a combination of two different synthetic routes. The proposed strategy demonstrates the utilization of a radiation chemical route to synthesize natural biopolymer gum acacia capped AgNPs at a very low pH followed by the controlled hydrolysis of Ti-tetra isopropoxide (TiPP) at low temperature for better growth of the titania shell on the AgNPs. The formation of the hybrid Ag–TiO2 nanocomposites was confirmed through UV-Vis spectroscopic analysis, which showed a red shift in the surface plasmon resonance (SPR) peak of the Ag NPs (about 15 nm) and a blue shift in the case of TiO2 (about 10 nm) with concomitant reduction in the intensity of peak of the AgNPs at 410 nm. In addition, the synthesized materials were characterized by dynamic light scattering (DLS), Fourier transform infra-red (FTIR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The as-synthesized TiO2 NPs and Ag@TiO2 nanocomposites were subsequently applied to the photochemical degradation of the toxic dye molecule, malachite green (MG), chosen as a model pollutant. The apparent photocatalytic degradation rate constants in regard to the Ag@TiO2 and TiO2 nanomaterials were calculated to be 0.25 and 0.05 min−1, respectively. The photocatalytic degradation rates of MG by the Ag@TiO2 nanocomposites under visible light illumination were found to be nearly 42 times higher than that of the TiO2 NPs implicating its great promise for the improved degradation of toxic materials such as azo dyes using visible solar light.