Chetan P. Shah

Dilution induced thickening in hydrotrope-rich rod-like micelles

Dilution induced changes in the microstructure and rheological behavior of micelles formed by a cationic surfactant-anionic hydrotrope mixture has been investigated in the hydrotrope-rich region. The surfactant used is cetyltrimethylammonium bromide (CTAB) and the hydrotropic salt is sodium 3-hydroxy naphthalene 2-carboxylate (SHNC). The concentration of the mixture is varied from 0.5% to 10.0% w/w (φ=0.005-0.100) at a fixed weight ratio of hydrotrope to surfactant (85:15). Rheological studies indicate Newtonian flow behavior at low and high volume fractions (0.005 and 0.100) while a shear thinning behavior is observed at intermediate volume fractions. The zero-shear viscosity η(0) also passes through a maximum upon changes in the concentration. The most striking feature in our study is that a low viscosity Newtonian fluid transforms to a viscoelastic fluid, upon dilution, and then again to a Newtonain fluid. Small angle neutron scattering studies of 10.0% micellar solution show the presence of rod-like aggregates. Upon dilution, the scattering intensity per unit concentration shows an increase in the low q-region. The nature of pair distance distribution function and subsequent model fitting indicates a transition from rod-like micelles to unilamellar vesicles upon dilution. This behavior is explained in terms of the volume fraction dependant solubilization of hydrotropes in the rod-like micelles and consequent changes in the composition of the mixed micelles.

An Organic Acid-induced Synthesis and Characterization of Selenium Nanoparticles

A simple wet chemical method has been developed to synthesize selenium nanoparticles (size 40–100 nm), by the reaction of sodium selenosulphate precursor with different organic acids in aqueous medium, under ambient conditions. Polyvinyl alcohol has been used to stabilize the selenium nanoparticles. The synthesized nanoparticles can be separated from its sol by using a high-speed centrifuge and can be redispersed in aqueous medium with a sonicator. UV-visible optical absorption spectroscopy, X-ray diffraction, energy dispersive X-rays, differential scanning calorimetry, atomic force microscopy, and transmission electron microscopy techniques have been employed to characterize the synthesized selenium nanoparticles.

Miceller-Mediated Phosphomolybdic Acid: Highly Effective Reusable Catalyst for Synthesis of Quinoline and Its Derivatives

A simple, efficient, and ecofriendly procedure has been developed for the synthesis of quinoline and its derivatives in a one-pot reaction of aniline with crotonaldehyde or methyl vinyl ketone using phosphomolybdic acid as solid acid catalyst in miceller media. The catalyst was easily recycled and reused.

Heteropoly Acids as Heterogeneous and Reusable Catalyst for α-Thiocyanation of Ketones

Simple, efficient, and mild method for α-thiocyanation of ketones in presence of heteropolyacid has been developed. This methodology offered α-oxothiocyanates in good to excellent yields at room temperature in a highly selective manner. The catalyst could be efficiently recovered from the reaction and reused.

Precursor concentration and temperature controlled formation of polyvinyl alcohol-capped CdSe-quantum dots

Summary Polyvinyl alcohol-capped CdSe quantum dots, with a size within their quantum confinement limit, were prepared in aqueous solution at room temperature, by a simple and environmentally friendly chemical method. The size of the CdSe quantum dots was found to be dependent on the concentrations of the precursors of cadmium and selenium ions, as well as on the aging time and the reaction temperature; all of which could be used conveniently for tuning the size of the particles, as well as their optical properties. The synthesized quantum dots were characterized by optical absorption spectroscopy, fluorescence spectroscopy, X-ray diffraction, atomic force microscopy and transmission electron microscopy. The samples were fluorescent at room temperature; the green fluorescence was assigned to band edge emission, and the near-infrared fluorescence peaks at about 665 and 865 nm were assigned to shallow and deep trap states emissions, respectively. The quantum dots were fairly stable up to several days.

Study of Extraction of Co(II) Ions using the Synthesized Polyacrylonitrile-Manganese Dioxide Composite Beads

Extraction of cobalt ions from aqueous medium has been studied, using macroporous polyacrylonitrile-manganese dioxide composite beads. Polyacrylonitrile, synthesized by γ-radiation induced polymerization of saturated aqueous solution of acrylonitrile monomer, has been employed, to produce polyacrylonitrile-manganese dioxide composite beads. Results of the extraction study indicate efficient adsorption of cobalt ions from neutral, or slightly acidic, aqueous solutions. The cobalt ions, adsorbed on the composite beads, can be leached out with 0.1 M HNO3 solution. The effect of various experimental parameters, such as concentration of cobalt ions, pH of the aqueous solution, etc., on the adsorption process and its kinetics has been studied. Further, adsorption capacity of the beads for cobalt ion, as well as their reusability for multiple adsorption-desorption of the cobalt ions, have also been evaluated. SEM and BET techniques have been used to determine the porous nature of the beads. IR spectroscopy has been used to understand the interaction of the polyacrylonitrile-manganese dioxide composite beads with cobalt ions.