Sudipa Panigrahi

Anisotropic growth of gold clusters to gold nanocubes under UV irradiation

A chiral reagent, 2-naphthol, has been introduced under alkaline solution as a reductant for HAuCl(4) in CTAB micelle to produce exclusively cubic gold nanoparticles under UV photoactivation. Prolonged irradiation helped the digestion of the primarily evolved spherical particles into smaller gold nanocubes, which then act as tiny cubic seeds, leading to the formation of larger nanocubes. The smaller cubes take the assistance of CTAB under alkaline condition to serve as the seed in directing the transformation of all the spherical colloids into cubic shapes under continuous irradiation via Ostwald ripening. The shape transformation of the nanoparticles has been monitored by repetitive TEM imaging and absorption spectral analysis. The FTIR analysis proves that the gold nanocubes are capped by CTAB. The XRD pattern authenticates the formation of the fcc gold nanocubes. GCMS studies in turn confirmed the presence of hydroxylation of 2-naphthol in the course of the reaction, leaving exclusively cubic gold nanoparticles at the final stage of the photoactivation reaction.

Cysteine functionalized copper organosol: synthesis, characterization and catalytic application

We herein report a facile one-pot synthesis, stabilization, redispersion and Cu–S interaction of L-cysteine and dodecanethiol (DDT) protected copper organosol in toluene from precursor copper stearate using sodium borohydride in toluene under a nitrogen atmosphere. Surface modification of the synthesized copper organosol with an amino acid L-cysteine and an alkanethiol (dodecanethiol, DDT) is accomplished by a thiolate bond between the used ligands and nanoparticle surface. The cysteine molecule binds the copper surface via a thiolate and amine linkage but not through electrostatic interaction with the carboxylate group due to the solvent polarity and dielectric medium. Fourier transform infrared (FTIR) analysis was performed to confirm the surface functionalization of the amino acid and DDT to the copper surface. Copper organosol has been characterized by optical spectroscopy (UV/vis), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). The as-synthesized particles are spherical in shape and exhibit a Mie scattering profile with an absorption maxima in the visible range. Copper nanoparticles capped by cysteine and/or DDT in non-aqueous media are found to represent an interesting catalytic approach for the synthesis of octylphenyl ether.

Al-Al2O3 in situ particle composites by reaction of CuO particles in molten pure Al

Abstract CuO particles were incorporated into pure Al melt to produce Al-Al 2 O 3 in situ particle composites. α-Al 2 O 3 and Cu particles were identified in the particles extracted from the composites. Part of the reduced Cu dissolved in the matrix of the composites and increased its microhardness. The hardness and tensile strength of the composites were improved significantly as compared to those of pure Al.

Preparation of Al-MgAl2O4-MgO in situ particle-composites by addition of MnO2 particles to molten Al-2 wt% Mg alloys

Abstract MnO 2 particles were incorporated into liquid Al-2 wt% Mg alloys to prepare Al-MgAl 2 O 4 in situ particle-composites. The MnO 2 particles reacted with the Al-2 wt% Mg alloy to produce MgAl 2 O 4 and MgO particles in the matrix. Microhardness, hardness and tensile strength of the composites were higher than those of the base alloy due to redistribution of the alloying elements and dispersion of MgAl 2 O 4 and MgO particles.

Dipole-dipole plasmon interactions in self-assembly of gold organosol induced by glutathione

Assemblies of gold nanoparticles in an organic medium have been synthesized to study the plasmon–plasmon interactions amongst the gold nanoparticles. A pH-sensitive biomolecule, glutathione (GSH), has been introduced as a molecular linker of the ‘parent’ gold nanoparticles to obtain small nanoparticle aggregates. The optical spectra of gold nanoparticles shifted to the red region indicate dipole–dipole interactions in the gold particle assembly. The aggregates have been characterized by UV-Vis, FTIR, HRTEM and XRD techniques. A controlled method of aggregating gold nanoparticles in organic solvents has been achieved successfully under controlled pH conditions with different concentrations of the molecular linker, GSH. The pH dependent anchoring of GSH onto gold surfaces has been proved beyond doubt to bring about nanoparticle aggregation.

Silver organosol: synthesis, characterization and localized surface plasmon resonance study

In this article a simple and reproducible technique for the synthesis of a silver organosol is reported from a specific silver precursor, solid silver acetate. Molten hexadecylamine acts as a solvent for silver acetate and imparts stability to the evolved nanoparticles. The amine-capped organosol shows unique stability as neither agglomeration nor oxidation takes place over one year. The synthesised silver particles have been characterised by UV-visible, TEM, XRD, XPS, FTIR and thermogravimetric studies. The hexadecylamine-stabilised silver organosol was employed to examine the altered optical properties in different solvent systems and with different ligands by accounting for the changes in the localised surface plasmon resonance (LSPR) spectrum. It was observed that the position of the surface plasmon band of silver nanoparticles is greatly affected by the solvents and ligands under consideration. The quantitative alteration of the LSPR spectrum involving encapsulated nanoparticles in a dielectric ligand shell has been rationalised from Mie theory. It has also been shown that cationic and anionic surfactants of different chain lengths induce changes in the optical properties of silver nanoparticles whereas, zwitterionic amino acid molecules reflect insignificant changes in the LSPR spectrum. The max of the LSPR gradually shifts to red with the increase in chain length of both the cationic and anionic surfactants, indicating specific binding of the surfactant molecules around silver nanoparticles. Finally the affinity of the synthesised silver nanoparticles for amine molecules has been accounted for by taking the HSAB principle into consideration.

Processing and properties of AlAl2O3 (TiO2) in situ particle composite

Abstract Al-3 wt% TiO 2 particle composite was solidified in the form of a vertical cylindrical ingot to segregate the particles at the top. The machined surface of the ingot showed three regions with varied particle content. Coarse particles were segregated at the top and the particle density was greater at the top zone. The next zone, at the bottom of the ingot, contained less particles, whilst the rest of the ingot appeared to be free from particles. Voids were also present in the particle-enriched zones. The top zone of the composite fractured on hot rolling due to its greater particle content (a volume fraction of 0.10). The middle zone with a 0.05 volume fraction of particles, and the bottom zone, could be rolled successfully. The particle size and the inter-particle, distance reduced on hot rolling. The hardness and tensile strength of the coarse particle-enriched zone was less than that of the bottom part of the composite, as voids were also segregated into the former. The presence of fine Al 3 O 3 particles without voids in the bottom part of the composite resulted in better mechanical properties.

Hardened paste of Portland cement--a new low-cost adsorbent for the removal of arsenic from water.

Abstract Portland cement has been used as a low-cost adsorbent for the removal of arsenic from the water environment. In the batch experiments conducted at an initial concentration of 0.2 ppm of arsenate, it was found that arsenate could be removed up to 95%. Kinetic profiles were developed for various conditions. Effect of adsorbent dose, effects of common ions such as Ca2+, Mg2+, Fe3+/Fe2+, Cl−, , , and the effect of pH was studied. Adsorption isotherm studies were performed and it was observed that the Freundlich isotherm was followed with a better correlation than the Langmuir isotherm. Arsenite could also be removed up to ˜88% using the same material. A new detection method for arsenate/arsenite was developed for routine analysis of arsenic and used during the entire study.

Formation of spinel (MgAl2O4), MgO and pure Cu particles in Al-2Mg alloy-CuO particle composites

CuO particles were introduced into liquid Al-2Mg alloy by the vortex method to prepare an Al alloy-MgAl2O4in situ particle composite, by reaction between CuO particles and the Al-2Mg alloy melt. Pure Cu, MgAl2O4 and MgO particles were detected in the particles extracted from the composites. DTA study showed partial dissolution of Cu in the matrix. Microhardness and hardness of the composites are higher than those of the base alloy. Both microhardness and hardness are higher for the Al-2Mg-2CuO composite than those of the Al-2Mg-5CuO composite. The hardness of the Al-2Mg-2CuO composite is remarkably high. The increase in microhardness has been attributed to the solid solution hardening effect with Cu as well as to the difference in CTE between the Al matrix and the particles. On the other hand, the improvement in hardness resulted from both solid solution hardening as well as the presence of hard particles such as MgAl2O4 and MgO.