Tanushree Bala

A facile liquid foam based synthesis of nickel nanoparticles and their subsequent conversion to NicoreAgshell particles: structural characterization and investigation of magnetic properties

A facile route for the synthesis of nickel nanoparticles in stable aqueous foams is reported. The Ni nanoparticles were roughly 12–15 nm in size and were stable as aqueous suspensions or powders when oleic acid was used as a capping agent. These Ni nanoparticles were subsequently coated with a silver shell in view of the extra stability and the enhanced manipulative ability afforded by the silver nanocoating. This was accomplished by a simple transmetallation reaction wherein the nanoparticle surface nickel atoms act as localized reducing agents for the silver ions in solution. As the silver shell is formed through the surface reaction a reduction in the average size of the Nicore occurs. After the core–shell structure formation, the Nicore has an average diameter of 10–20 nm while the Agshell has a thickness of 2–4 nm. The pristine oleic acid coated Ni and NicoreAgshell nanoparticles were probed for their magnetic characteristics by a vibrating sample magnetometer. The nascent, oleic acid coated Ni nanoparticles display a low superparamagnetic blocking temperature, TB, of 20 K. The field dependent magnetic behaviour above and below TB displays the standard features corresponding to superparamagnetism, as expected for very small Ni crystallites suggesting again that each 12 nm particle is polycrystalline. The magnetic contribution in the NicoreAgshell system comes from only the Ni core and predictably, the blocking temperature of this system is below 12 K due to the smaller size of the Ni core.

Foam-based synthesis of cobalt nanoparticles and their subsequent conversion to CocoreAgshell nanoparticles by a simple transmetallation reaction

Cobalt nanoparticles have been synthesized via a novel, foam-based protocol. The foam is formed from an aqueous mixture of Co 2+ ions, an anionic surfactant and oleic acid where the cobalt ions are electrostatically entrapped by the surfactant at the thin borders between the foam bubbles and their junctions. The entrapped cobalt ions may be reduced in-situ by a moderately strong reducing agent resulting in the formation of nanoparticles with the foam playing the role of a template. The nanoparticles are immediately capped and stabilized against oxidation by oleic acid present in the foam matrix. The oleic acid-capped Co nanoparticles can be redispersed either in an aqueous or organic medium making this procedure very attractive. The cobalt nanoparticles are readily converted to Co core Ag shell nanoparticles by simple addition of a silver salt to the Co nanoparticle solution, the cobalt atoms on the nanoparticle surface acting as localized reducing agents for the silver ions.

La0.7Sr0.3MnO3 nanoparticles coated with fatty amine

We report on the synthesis of La0.7Sr0.3MnO3 (LSMO) nanoparticles having perovskite structure and particle size of the order of 30nm. The process involves citrate-gel synthesis, size filtering, and surface coating with a shell of octadecyl amine (ODA) using electrostatic interaction-assisted novel chemical route. Magnetic measurements show the Curie temperature of ∼360K establishing the desired stoichiometry and phase. Fourier transform infrared studies bring out that the amine group of ODA interacts with the LSMO surface. Refluidization yields uniform redispersion of the coated and dried powder.

Synthesis of Catalytically Active Porous Platinum Nanoparticles by Transmetallation Reaction and Proposition of the Mechanism

A facile method for the synthesis of porous platinum nanoparticles by transmetallation reactions between sacrificial nickel nanoparticles and chloroplatinic acid (H(2)PtCl(6)) in solution, as well as at the constrained environment of the air-water interface, using a Langmuir-Blodgett instrumental setup is presented. To carry out the transmetallation at the air-water interface hydrophobized nickel nanoparticles are assembled as a monolayer on the sub phase containing platinum ions. The porous Pt nanoparticles obtained as a result of the reaction are found to act as extremely good catalysts for hydrogenation reaction. The products are well characterized by TEM, HRTEM, EDAX, and STEM. Attempts are made to postulate the plausible mechanism of this reaction to generate this kind of nanoparticle with controllable geometric shape and structure. This simple strategy has the potential to synthesize other nanomaterials of interest too.

Block copolymer mediated stabilization of sub-5 nm superparamagnetic nickel nanoparticles in an aqueous medium

This paper presents a facile method for decreasing the size of water dispersible Ni nanoparticles from 30 to 3 nm by the incorporation of a passivating surfactant combination of pluronic triblock copolymer and oleic acid into a wet chemical reduction synthesis. A detailed study revealed that the size of the Ni nanoparticles is not only critically governed by the concentration of the triblock copolymers but also dependent on the hydrophobic nature of the micelle core formed. The synthesized Ni nanoparticles were thoroughly characterized by means of transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy and temperature and field dependent magnetic measurements, along with a comprehensive Fourier transform infrared spectroscopy analysis, in order to predict a possible mechanism of formation.

Titania–silver and alumina–silver composite nanoparticles: Novel, versatile synthesis, reaction mechanism and potential antimicrobial application

Titania-silver (TiO(2)-Ag) and alumina-silver (Al(2)O(3)-Ag) composite nanoparticles were synthesised by a simple, reproducible, wet chemical method under ambient conditions. The surface of the oxides was modified with oleic acid, which acted as an intermediate between the oxide surface and the silver nanoparticles. The resulting composite nanoparticles were thoroughly characterised by XRD, TEM, XPS, FTIR and TGA to elucidate the mode of assembly of Ag nanoparticles on the oxide surfaces. Epoxy nanocomposites were formulated with TiO(2)-Ag and Al(2)O(3)-Ag to examine potential applications for the composite nanoparticles. Preliminary results from disc diffusion assays against Escherichia coli DH5α and Staphylococcus epidermidis NCIMB 12721 suggest that these TiO(2)-Ag and Al(2)O(3)-Ag composite nanoparticles have potential as antimicrobial materials.

Water Dispersible Semiconductor Nanorod Assemblies Via a Facile Phase Transfer and Their Application as Fluorescent Biomarkers

We demonstrate the formation of water dispersed nanorod assemblies by phase transfer of semiconductor (CdS, CdSe, CdTe) nanorods from the organic to the aqueous using pluronic triblock copolymers. On phase transfer, the randomly dispersed nanorods in the organic medium close pack in the form of discs encapsulated in the hydrophobic core of water dispersible micelles. The assemblies showed excellent cellular uptake exhibiting membrane and cell specific fluorescence at low light intensity under confocal microscopy.

Fabrication of Noble metal-semiconductor hybrid nanostructures using phase transfer

An easy and effective solution based procedure for the synthesis of noble metal (both Au and Ag) tipped semiconductor nanomaterials is demonstrated where the metal precursors are taken in water and the semiconductors in organic medium, exploiting the phase transfer and reducing capability of suitably chosen ligands. The phase tranfer route is a generalised approach to form either Ag or Au tips on cadmium chalcogenide nanoparticles and nanorods. While multiple dots of noble metals are formed on the semiconductor nanomaterials initially, these coalesce into larger islands with time. The hybrids are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy (UV-vis) and X-ray photoelectron spectroscopy (XPS). A detailed FTIR analysis was also carried out to delineate the role of the ligands in the synthesis.Graphical abstract

Silver Tip Formation on Colloidal CdSe Nanorods by a Facile Phase Transfer Protocol

A facile phase transfer procedure is described for the formation of uniform silver metal tips on II–VI semiconductor nanorods. Judicious choice of a functional ligand dimethyl phenol (DMP) which binds to the semiconductor rod in the organic phase enables the transfer of metal ions from the aqueous phase and their reduction onto the nanorod. The nanorod hybrids can be assembled into perpendicularly aligned arrays by simple solvent evaporation.

Multifaceted core–shell nanoparticles: superparamagnetism and biocompatibility

NicoreAgshell nanoparticles were synthesized by redox transmetallation reaction. Reduction potential match was encouraging to attempt the synthesis of the NicoreAushell system too. However, it could be achieved only after an effective surface modification on the Ni-core. Thorough characterization (UV-Vis spectroscopy, fluorescence spectroscopy, XRD, XPS, FTIR, TEM, and EDX) proved the necessity of surface modification and the success of synthesis of both types of core–shell structures. The chemical composition and topography were determined using STEM-HAADF analysis and EFTEM imaging. Fourier transform infrared (FTIR) spectroscopy confirmed the surface modification of Ni nanoparticles and the interactions involved between the ligands and metals (in the core and/or the shell) at various steps of the synthetic process. Even after the formation of the noble metal shell, the magnetic core was found to retain its superparamagnetic nature. In addition, the Au-shell protected the core from aerial oxidation and decreased toxicity as compared to pristine Ni nanoparticles as observed by MTT assay on normal cells (PBMCs).