M. Kottaisamy

Biosynthesis of silver and gold nanoparticles using Brevibacterium casei

The present study demonstrates an unprecedented green process for the production of spherical-shaped Au and Ag nanoparticles synthesized and stabilized using a bacterium, Brevibacterium casei. Aqueous solutions of chloroaurate ions for Au and Ag(+) ions for silver were treated with B. casei biomass for the formation of Au nanoparticles (AuNP) and Ag nanoparticles (AgNP). The nanometallic dispersions were characterized by surface plasmon absorbance measuring at 420 and 540 nm for Ag and Au nanoparticles, respectively. Transmission electron microscopy showed the formation of nanoparticles in the range of 10-50 nm (silver), and 10-50 nm (gold). XRD analysis of the silver and gold nanoparticles confirmed the formation of metallic silver and gold. Further analysis carried out by Fourier Transform Infrared Spectroscopy (FTIR), provides evidence for the presence of proteins as possible biomolecules responsible for the reduction and capping agent which helps in increasing the stability of the synthesized silver and gold nanoparticles. The biological activities of the synthesized particles were confirmed based on their stable anti-coagulant effects. The use of bacterium for nanoparticles synthesis offers the benefits of ecofriendliness and amenability for large-scale production.

Structure, morphology and thermal characteristics of banana nano fibers obtained by steam explosion

In this work, cellulose nanofibers were extracted from banana fibers via a steam explosion technique. The chemical composition, morphology and thermal properties of the nanofibers were characterized to investigate their suitability for use in bio-based composite material applications. Chemical characterization of the banana fibers confirmed that the cellulose content was increased from 64% to 95% due to the application of alkali and acid treatments. Assessment of fiber chemical composition before and after chemical treatment showed evidence for the removal of non-cellulosic constituents such as hemicelluloses and lignin that occurred during steam explosion, bleaching and acid treatments. Surface morphological studies using SEM and AFM revealed that there was a reduction in fiber diameter during steam explosion followed by acid treatments. Percentage yield and aspect ratio of the nanofiber obtained by this technique is found to be very high in comparison with other conventional methods. TGA and DSC results showed that the developed nanofibers exhibit enhanced thermal properties over the untreated fibers.

A Novel Method for the Synthesis of Cellulose Nanofibril Whiskers from Banana Fibers and Characterization

Alkali treatment coupled with high pressure defibrillation and acid treatment have been tried on banana fibers obtained from the pseudo stem of the banana plant Musa sapientum. The structure and morphology of the fibers have been found to be affected on the basis of the concentration of the alkali and acid and also on the pressure applied. Steam explosion in alkaline medium followed by acidic medium is found to be effective in the depolymerization and defibrillation of the fiber to produce banana nanowhiskers. The chemical constituents of raw and steam exploded fibers were analyzed according to the ASTM standards. Structural analysis of steam exploded fibers was carried out by FTIR and XRD. The fiber diameter and percentage crystallinity of the modified fibers were investigated using X-ray diffraction studies. Characterization of the fibers by SFM and TEM supports the evidence for the development of nanofibrils of banana fibers.

Structure, microstructure and physical properties of ZnO based materials in various forms: bulk, thin film and nano

ZnO is a unique material that offers about a dozen different application possibilities. In spite of the fact that the ZnO lattice is amenable to metal ion doping (3d and 4f), the physics of doping in ZnO is not completely understood. This paper presents a review of previous research works on ZnO and also highlights results of our research activities on ZnO. The review pertains to the work on Al and Mg doping for conductivity and band gap tuning in ZnO followed by a report on transition metal (TM) ion doped ZnO. This review also highlights the work on the transport and optical studies of TM ion doped ZnO, nanostructured growth (ZnO polycrystalline and thin films) by different methods and the formation of unique nano- and microstructures obtained by pulsed laser deposition and chemical methods. This is followed by results on ZnO encapsulated Fe3O4 nanoparticles that show promising trends suitable for various applications. We have also reviewed the non-linear characteristic studies of ZnO based heterostructures followed by an analysis on the work carried out on ZnO based phosphors, which include mainly the nanocrystalline ZnO encapsulated SiO2 ,an ew class of phosphor that is suitable for white light emission. (Some figures in this article are in colour only in the electronic version)

Eu3+ luminescence: A spectral probe in M5(PO4)3X apatites (M=Ca or Sr; X=F-, Cl-, Br- or OH-)

Eu3+ luminescence is of special importance as a spectral probe apart from its application in phosphor materials. This is possible for the reason that Eu3+ has several structure-dependent transitions enabling one to gain insight about the site that it occupies in a given host. On this basis we have attempted to explore the different cationic sites present in the apatite system. In fluoroapatites, Eu3+ predominantly occupies MII sites, with the local symmetry becoming enhanced from C1h to a tetragonal symmetry attributed to charge-compensating species. In addition to both kinds of site of the apatite system (MI and MII) occupied by Eu3+, we have observed the presence of a third kind of Eu3+ site. The observation of unusually strong 5D0 to 7F0 emission of Eu3+ in fluoroapatites and bromoapatites has been explained. Also various results on the luminescence features of Eu3+ correlated with the structural details known are discussed.

Yttrium oxide:Eu3+ red phosphor by self-propagating high temperature synthesis

Yttrium oxide doped with trivalent europium has been prepared by self-propagating high temperature (SPHT) synthesis, also known as combustion synthesis, with nitrogen-based fuels. The materials synthesized have been characterized by X-ray diffraction, scanning electron microscopy, and luminescent emission spectroscopy. Crystallite size, powder density, and photoluminescent-emission intensity/efficiency are found to depend on the fuels used. The phosphor products were sintered with and without sintering aids. The results obtained are discussed with respect to the processing method employed.

Synthesis of few layer graphene by direct exfoliation of graphite and a Raman spectroscopic study

The exfoliation of graphene from pristine graphite in a liquid phase was achieved successfully via sonication followed by centrifugation method. Ultraviolet–visible (UV–vis) spectra of the obtained graphene dispersions at different exfoliation time indicated that the concentration of graphene dispersion increased markedly with increasing exfoliation time. The sheet-like morphology of the exfoliated graphene was revealed by Scanning Electron Microscopy (SEM) image. Further, the morphological change in different exfoliation time was investigated by Atomic Force Microscopy (AFM). A complete structural and defect characterization was probed using micro-Raman spectroscopic technique. The shape and position of the 2D band of Raman spectra revealed the formation of bilayer to few layer graphene. Also, Raman mapping confirmed the presence of uniformly distributed bilayer graphene sheets on the substrate.

Synthesis of ZnO decorated graphene nanocomposite for enhanced photocatalytic properties

Zinc oxide/Graphene (GZ) composites with different concentrations of ZnO were successfully synthesized through simple chemical precipitation method. The X-ray diffraction pattern and the micro-Raman spectroscopic technique revealed the formation of GZ composite, and the energy dispersive X-ray spectrometry analysis showed the purity of the prepared samples. The ZnO nanoparticles decorated graphene sheets were clearly visible in the field emission scanning electron micrograph. Raman mapping was employed to analyze the homogeneity of the prepared samples. The diffuse-reflectance spectra clearly indicated that the formation of GZ composites promoted the absorption in the visible region also. The photocatalytic activity of ZnO and GZ composites was studied by the photodegradation of Methylene blue dye. The results revealed that the GZ composites exhibited a higher photocatalytic activity than pristine ZnO. Hence, we proposed a simple wet chemical method to synthesize GZ composite and its application on photocatalysis was demonstrated.

Dynamic quenching study of 2-amino-3-bromo-1,4-naphthoquinone by titanium dioxide nano particles in solution (methanol).

The dependence of fluorescence emission of 2-amino-3-bromo-1,4-naphthoquinone on titanium dioxide (TiO2) in methanol has been investigated. The increase in TiO2 concentration causes a decrease in the fluorescence intensity of 2-amino-3-bromo-1,4-naphthoquinone. A linear Stern-Volmer plot in this study indicates the presence of dynamic quenching. The quenching and association constants have been calculated. The quenching process is due to the electron transfer from 2-amino-3-bromo-1,4-naphthoquinone to TiO2.

Agro-Based Biocomposites for Industrial Applications

Leaf fibers are fibers that run lengthwise through the leaves of most monocotyledonous plants such as pineapple, banana, etc. Pineapple (Ananas comosus) and Banana (Musa indica) are emerging fiber having a very large potential to be used for composite materials. Over 150,000 ha of pineapple and over 100,000 ha of banana plantations are available in Brazil for the fruit production and enormous amount of agricultural waste is produced. This residual waste represents one of the single largest sources of cellulose fibers available at almost no cost. The potential consumers for this fiber are pulp and paper, chemical feedstock, textiles and composites for the automotive, furniture and civil construction industry.