Rati Ranjan Nayak

Bio: Rati Ranjan Nayak is an academic researcher from Indian Institute of Chemical Technology. The author has contributed to research in topics: Polymer & Critical micelle concentration. The author has an hindex of 14, co-authored 49 publications receiving 842 citations. Previous affiliations of Rati Ranjan Nayak include Kyoto University & Indian Institutes of Technology.

Green synthesis of silver nanoparticle by Penicillium purpurogenum NPMF: the process and optimization

Abstract: An eco-friendly microbial method for synthesis of silver colloid solution with antimicrobial activity is developed using a fungal strain of Penicillium purpurogenum NPMF. It is observed that increase in concentration of AgNO3 increases the formation of silver nanoparticle. At 5 mM concentration highly populated polydispersed nanoparticles form. Furthermore, change in pH of the reaction mixture leads to change in shape and size of silver nanoparticles. At lower pH two peaks are observed in the absorption spectra showing polydispersity of nanoparticles. However, highly monodispersed spherical nanoparticles of 8–10 nm size form with 1 mM AgNO3 concentration at pH 8. Antimicrobial activity of nanoparticles is demonstrated against pathogenic gram negative bacteria like Escherichia coli and Pseudomonas aeruginosa, and gram positive bacteria like Staphylococcus aureus. The antimicrobial activity of silver nanoparticles obtained at different initial pH show strong dependence on the surface area and shape of the nanoparticles.

Microalga Scenedesmus sp.: A Potential Low-Cost Green Machine for Silver Nanoparticle Synthesis

Abstract: Bionanotechnology has revolutionized nanomaterial synthesis by providing a green synthetic platform using biological systems. Among such biological systems, microalgae have tremendous potential to take up metal ions and produce nanoparticles by a detoxification process. The present study explores the intracellular and extracellular biogenic syntheses of silver nanoparticles (SNPs) using the unicellular green microalga Scenedesmus sp. Biosynthesized SNPs were characterized by AAS, UV-Vis spectroscopy, TEM, XRD, FTIR, DLS, and TGA studies and finally checked for antibacterial activity. Intracellular nanoparticle biosynthesis was initiated by a high rate of Ag(+) ion accumulation in the microalgal biomass and subsequent formation of spherical crystalline SNPs (average size, 15-20 nm) due to the biochemical reduction of Ag(+) ions. The synthesized nanoparticles were intracellular, as confirmed by the UV-Vis spectra of the outside medium. Furthermore, extracellular synthesis using boiled extract showed the formation of well scattered, highly stable, spherical SNPs with an average size of 5-10 nm. The size and morphology of the nanoparticles were confirmed by TEM. The crystalline nature of the SNPs was evident from the diffraction peaks of XRD and bright circular ring pattern of SAED. FTIR and UV-Vis spectra showed that biomolecules, proteins and peptides, are mainly responsible for the formation and stabilization of SNPs. Furthermore, the synthesized nanoparticles exhibited high antimicrobial activity against pathogenic gram-negative and gram-positive bacteria. Use of such a microalgal system provides a simple, cost-effective alternative template for the biosynthesis of nanomaterials in a large-scale system that could be of great use in biomedical applications.

Preparation of poly(styrene-co-acrylonitrile)-grafted multiwalled carbon nanotubes via surface-initiated atom transfer radical polymerization

Abstract: The in situ grafting-from approach via atom transfer radical polymerization was successfully applied to polystyrene, poly(styrene-co-acrylonitrile), and polyacrylonitrile grafted onto the convex surfaces of multiwalled carbon nanotubes (MWCNTs) with (2-hydroxyethyl 2-bromoisobutyrate) as an initiator. Thermogravimetric analysis showed that effective functionalization was achieved with the grafting approach. The grafted polymers on the MWCNT surface were characterized and confirmed with Fourier transform infrared spectroscopy and nuclear magnetic resonance. Raman and near-infrared spectroscopy revealed that the grafting of polystyrene, poly(styrene-co-acrylonitrile), and polyacrylonitrile slightly affected the sidewall structures. Field emission scanning electron microscopy showed that the carbon nanotube surface became rough because of the grafting of the polymers. Differential scanning calorimetry results indicated that the polymers grafted onto MWCNTs showed higher glass-transition temperatures. The polymer-grafted MWCNTs exhibited relatively good dispersibility in an organic solvent such as tetrahydrofuran.

Biological sequestration and retention of cadmium as CdS nanoparticles by the microalga Scenedesmus - 24

Abstract: Biological sequestration of cadmium (Cd) and retention of adsorbed cadmium as cadmium sulphide (CdS) nanoparticles inside the cell by a lipid-producing green algae Scenedesmus-24 is reported. The microalga was able to grow in the growth media containing 30 mg L−1 of cadmium without any growth inhibition. Adsorption of Cd(II) was dependent on the pH of the medium, initial concentration of cadmium, density of algal biomass (biosorbent dose), and contact time. The adsorption follows Langmuir isotherm pattern with an estimated maximum cadmium adsorption capacity at 50 mg g−1. The kinetics of adsorption followed Lagergren’s pseudo-second-order model. FTIR analysis revealed the presence of different functional groups on the algal biomass which may be responsible for adsorption of Cd(II). After adsorption, the bound metal ions were retained in the microalgal biomass as CdS nanoparticles. Presence of CdS nanoparticle was confirmed by XRD and TEM analysis. The results of the present study conclusively demonstrate that the microalga Scenedesmus-24 may be a promising candidate for sequestration of cadmium from cadmium polluted water and also its recovery as precious CdS nanoparticles.

Principles Of Fluorescence Spectroscopy

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Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Polymer Brushes via Surface-Initiated Controlled Radical Polymerization: Synthesis, Characterization, Properties, and Applications

Abstract: Keywords: Fragmentation Chain-Transfer ; Self-Assembled Monolayers ; Walled Carbon Nanotubes ; Well-Defined Polymer ; Nitroxide-Mediated Polymerization ; Block-Copolymer Brushes ; Poly(Methyl Methacrylate) Brushes ; Transfer Raft Polymerization ; Quartz-Crystal Microbalance ; Poly(Acrylic Acid) Brushes Reference EPFL-REVIEW-148464doi:10.1021/cr900045aView record in Web of Science Record created on 2010-04-23, modified on 2017-05-10