Sujit Kumar Ghosh

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.

Spectrophotometric determination of arsenic via arsine generation and in-situ colour bleaching of methylene blue (MB) in micellar medium

A new spectrophotometric method has been developed to determine arsenic in parts-per-million (ppm) level. It is based on the colour bleaching of methylene blue (MB) in anionic micellar medium. Arsine gas was formed by borohydride reduction of arsenite/arsenate. Arsine generation and colour bleaching (quantification of arsenic) could be done in one-pot. The presence of silver or gold nanoparticles makes the determination faster. Different calibration graphs at the three different ranges of arsenic concentration such as 0-8.63, 0-1.11 and 0-0.11 ppm were constructed and limit of detection (LODs) were found to be 1.3, 0.53 and 0.03 ppm, respectively. The method is simple, rapid, reproducible (relative standard deviations lies within +/-5%) and eco-friendly. It is free from phosphate and silicate interferences and applicable for real sample analysis.

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.

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.

Wet chemical method for synthesis of superparamagnetic alloyed NiPd and NiPt nanomagnets in micelles

The evolution of sphere- and rod-shaped superparamagnetic Ni--Pd and Ni--Pt nanoparticles by wet chemical methods is reported. It has been shown that increased CTAB (cetyltrimethylammonium bromide) concentration at room temperature promotes the formation of a higher proportion of rod-shaped nanomagnets over spherical particles. Temperature-dependent magnetic properties, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electron dispersive X-ray (EDX) studies reveal the superparamagnetic behavior, size distribution, and percentage composition of the alloyed structures.

Evolution, dissolution and reversible generation of gold and silver nanoclusters in micelle by UV-activation

Gold and silver nanoparticles were produced separately by UV photoactivation (with variable flux density) in the presence of nonionic micelle, TX-100. Even their cyano complexes break down in TX-100 under UV and hence dissolution and reevolution of almost monodispersed nanoparticles (∼ 3 nm) are possible.

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.

UV-photoactivation technique for size and shape controlled synthesis and annealing of stable gold nanoparticles in micelle

Gold nanoparticles of different sizes and shapes have been prepared by UV-photoactivation technique using the micelle TX-100 (poly(oxyethylene)iso-octylphenyl ether) as reducing agent, stabilizing agent as well as template which has been authenticated from the plasmon absorption band and TEM picture. The heating effect on those gold nanoparticles has also been studied.

Gold Organosol as a Real-Time Optical Sensor for Monitoring Solvent Refractive Index and Chain Length:

Metallic particles in the nanometer size regime display many interesting physical properties that are significantly different from their bulk. Noble metal nanoparticles such as Cu, Ag, and Au exhibit a strong absorption band in the visible region. This absorption band results when the incident photon frequency is resonant with the collective oscillation of the conduction band electrons and is known as the localized surface plasmon resonance (LSPR).1 It is now well-established that the peak wavelength, lmax, of an LSPR spectrum is dependent upon the size, shape, and interparticle spacing of the nanoparticle as well as its own dielectric properties and those of its local environment, including the substrate, solvent, and adsorbates.2–4 Noble metal nanoparticles dispersed in organic solvent systems have proven to be an efficient tool to register the impacts of the solvents arising from bulk solution effects.5 In this experiment, we have chosen gold nanoparticles as the spectroscopic reporter group since the solvents introduced in the medium leave their direct impression on the optical properties of the gold particles. In recent years, the accurate determination of refractive index has witnessed increased scientific interest in view of its various applications in chemical6 and biological7 sensors. The measurements of the refractive index of the bulk liquid solutions are important in many industrial processes including industrial process monitoring and research applications such as chemical separation detectors, etc. It has now been seen that evanescent wave techniques such as surface plasmon resonance (SPR) spectroscopy can detect very low levels of chemical and bi-