Showing papers by "Nikhil R. Jana published in 2000"

Redox Catalytic Properties of Palladium Nanoparticles: Surfactant and Electron Donor−Acceptor Effects

Abstract: Dye reduction catalyzed by palladium nanoparticles has been investigated in water and surfactant media. The initial rate of dye reduction strongly depends on the nature of the reducing agent and dye. In most cases the rate becomes surface controlled and depends on the E1/2 values of the dye and the reducing agent. However, stronger reducing agents make the reduction process a diffusion controlled one. A detailed study has been carried out to understand the effect of surfactant on the reaction rate. A variation of the reaction rates has been observed in surfactants above and below the critical micelle concentration (cmc). Below the cmc, surfactants are adsorbed onto the Pd surface and act as a binding site for both the dye and the reducing agent. Above the cmc, surfactants form micelles which provide additional binding sites. Catalytic selectivity was also achieved by proper selection of reducing agent and surfactant.

Seed-mediated growth method to prepare cubic copper nanoparticles

Abstract: A new and simple method has been reported here which can be applied to control simultaneously the shape and size of the copper nanoparticles, without using any ca p ping agent or template. By this method, cube -shaped copper nanoparticles in the size range ~ 75 –250 nm were formed from smaller spherical co p-per particles. At the first stage, 5–6 nm spherical co p per particles were prepared from aqueous copper sulphate solution by borohydride reduction. In the second stage, these small particles were mixed with ap propriate amount of copper sulphate and sodium ascorbate, which resulted in the production of larger size cu bic copper particles. In the latter step, the new grown larger particles acted as seed and grew larger due to the reduction of copper ions by ascorbate ion on their surfaces. Thus cubic copper nanoparticles of varied size regime were produced by ascorbate ion by var ying the ratio of copper seed particles to copper ion concentrations in solution. M

Anion effect in linear silver nanoparticle aggregation as evidenced by efficient fluorescence quenching and SERS enhancement

Abstract: This work is the first report of the effect of anions of precursor salts on the efficiency of photochemical reduction of Ag ⊙I) to Ag ⊙0). Ultraviolet ⊙UV) irradiation of an aqueous Triton X-100 solution in the presence of Ag ⊙I) produces the green sol at a certain critical concentration of ascorbic acid. The photochemical process of silver sol formation possesses the advantage of producing homogeneous particles of very small size ⊙∼6 nm). In the presence of a reduction sensitizer, such as ascorbic acid, these tiny silver dots aggregate beautifully in a symmetric manner to form necklace-like structures. Fluorescence quenching studies carried out with the probe 1-aminonaphthalene give an idea about the structure and binding capacities of the sols, the latter effect being more pronounced for the linearly aggregated sol. Fluorescence and AFM studies complimented by surface-enhanced Raman scattering ⊙SERS) studies with pyridine reveal that the green silver sol consists of linear aggregates, whereas the yellow sol does not contain the aggregated arrangement. The most interesting result arising out of this study is that linear aggregation of spherical silver sols leads to enhanced efficiency as fluorescence quenchers as also an improvement in SERS activity. These linear aggregates of silver may hold prospects for the development of interconnecting quantum devices in future.