S.N. Sahu

Bio: S.N. Sahu is an academic researcher from National Institute of Standards and Technology. The author has contributed to research in topics: Band gap & Raman spectroscopy. The author has an hindex of 19, co-authored 49 publications receiving 1748 citations. Previous affiliations of S.N. Sahu include Institute of Physics, Bhubaneswar.

Liquid-drop model for the size-dependent melting of low-dimensional systems

Abstract: Empirical relations are established between the cohesive energy, surface tension, and melting temperature of different bulk solids. An expression for the size-dependent melting for low-dimensional systems is derived on the basis of an analogy with the liquid-drop model and these empirical relations, and compared with other theoretical models as well as the available experimental data in the literature. The model is then extended to understand (i) the effect of substrate temperature on the size of the deposited cluster and (ii) the superheating of nanoparticles embedded in a matrix. It is argued that the exponential increase in particle size with the increase in deposition temperature can be understood by using the expression for the size-dependent melting of nanoparticles. Superheating is possible when nanoparticles with a lower surface energy are embedded in a matrix with a material of higher surface energy in which case the melting temperature depends on the amount of epitaxy between the nanoparticles and the embedding matrix. The predictions of the model show good agreement with the experimental results. A scaling for the size-dependent melting point suppression is also proposed.

In vitro biosynthesis and genotoxicity bioassay of silver nanoparticles using plants

Abstract: Silver nanoparticles (AgNP-P) from AgNO(3) were synthesized by using the broth prepared from the aromatic spath of male inflorescence of screw pine, Pandanus odorifer (Forssk.) Kuntze AgNP-P was then characterized by UV-visible spectroscopy, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Functional groups in the broth were analyzed by Fourier Transform infrared spectroscopy (FTIR). Genotoxicity of AgNP-P was assessed by utilizing our well-established Allium cepa assay system with biomarkers including the generation reactive oxygen species (ROS: O(2)(·-) and H(2)O(2)), cell death, mitotic index, micronucleus, mitotic aberrations; and DNA damage by Comet assay. Other chemical forms of silver such as Ag(+) ion, colloidal AgCl, and AgNP-S at doses 0-80 mg L(-1) were included for comparison with AgNP-P. The results revealed that AgNP-P and AgNP-S exhibited similar biological effects in causing lesser extent of cytotoxicity and greater extent of genotoxicity than that was exhibited by Ag(+) ion alone. Among different tested chemical forms of silver, colloidal AgCl was identified to be the least cytotoxic and genotoxic. Cell death and DNA-damage induced by AgNP-P were prevented by Tiron and dimethyl thiourea that scavenge O(2)(·-) and H(2)O(2), respectively. The present findings demonstrated the role of ROS in the AgNP-induced cell death and DNA damage.

CdS–ZnO composite nanorods: Synthesis, characterization and application for photocatalytic degradation of 3,4-dihydroxy benzoic acid

Abstract: Well-aligned arrays of CdS–ZnO composite nanorods were grown on indium tin oxide substrates. ZnO nanorods, deposited by a low temperature aqueous chemical growth technique, were dip coated with CdS. The CdS–ZnO nanorods were polycrystalline as confirmed from the low angle X-rays diffraction study. Photon to current conversion efficiency of CdS–ZnO composite nanorod was observed to be higher than that of CdS. In the micro-Raman spectrum, we observed longitudinal optical modes of CdS and ZnO showing their co-existence. The appealing application of CdS–ZnO nanorod as a visible photocatalyst was demonstrated and the possible mechanism was discussed.

Optical properties of CdS nanocrystalline films prepared by a precipitation technique

Abstract: CdS semiconductor films of different crystalline size have been grown by a precipitation technique. The crystalline sizes were controlled by the reaction time period, pH/temperature of the solution and thickness of the deposit. From the optical absorption, the band gap of bulk-CdS is found to be 2.405 eV and is increased to 2.97 eV for nanocrystalline samples of average crystalline size 5.0 nm estimated from the blue shift. AFM analysis were performed to estimate the average crystalline size. Photoluminescence studies of CdS nanocrystalline samples show a red shift. The intensity of red luminescence (∼1.8 eV) decreases and its peak position shifts to the lower energy upon increasing the particle size. Photovoltage as a function of crystalline size/band gap has been studied using a photoelectrochemical solar cell configuration Ti/CdS/S2−, S22−/Pt.

Raman spectroscopy of CdS nanocrystalline semiconductors

Abstract: Raman scattering measurements were performed on nanostructured II–VI semiconductor CdS prepared by a chemical route. The Raman spectrum shows a low-frequency wing at 295 cm −1 besides the characteristic first-order longitudinal optical phonon (1LO) mode at 305 cm −1 when excited with a laser of wavelength 457.9 nm. The observed variation of the Raman shifts, widths and intensities of these two lines with the size of the nanoparticles is consistent with the interpretation that the low-frequency peak is a surface phonon (SP) mode. Increasing the wavelength of the exciting laser lowers the intensity of the LO mode, while shifting the lower-frequency SP mode to the higher-frequency side and simultaneously increases its width. This anomalous behavior is attributed to the possible electron hole excitation by the SP due to the presence of a continuum of localized and acceptor states within CdS band gap. The effect of temperature, on these modes, is also studied and discussed.

Semiconductor-based Photocatalytic Hydrogen Generation

Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Synthesis of metallic nanoparticles using plant extracts.

Abstract: Biomolecules present in plant extracts can be used to reduce metal ions to nanoparticles in a single-step green synthesis process. This biogenic reduction of metal ion to base metal is quite rapid, readily conducted at room temperature and pressure, and easily scaled up. Synthesis mediated by plant extracts is environmentally benign. The reducing agents involved include the various water soluble plant metabolites (e.g. alkaloids, phenolic compounds, terpenoids) and co-enzymes. Silver (Ag) and gold (Au) nanoparticles have been the particular focus of plant-based syntheses. Extracts of a diverse range of plant species have been successfully used in making nanoparticles. In addition to plant extracts, live plants can be used for the synthesis. Here we review the methods of making nanoparticles using plant extracts. Methods of particle characterization are reviewed and potential applications of the particles in medicine are discussed.

One-dimensional ZnO nanostructures: Solution growth and functional properties

Abstract: One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

Enhanced photocatalytic activity of ZnO/CuO nanocomposite for the degradation of textile dye on visible light illumination.

Abstract: The photocatalytic degradation of organic dyes such as methylene blue and methyl orange in the presence of various percentages of composite catalyst under visible light irradiation was carried out. The catalyst ZnO nanorods and ZnO/CuO nanocomposites of different weight ratios were prepared by new thermal decomposition method, which is simple and cost effective. The prepared catalysts were characterized by different techniques such as X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and UV-visible absorption spectroscopy. Further, the most photocatalytically active composite material was used for degradation of real textile waste water under visible light illumination. The irradiated samples were analysed by total organic carbon and chemical oxygen demand. The efficiency of the catalyst and their photocatalytic mechanism has been discussed in detail.

Effects of confinement on material behaviour at the nanometre size scale

Abstract: In this article, the effects of size and confinement at the nanometre size scale on both the melting temperature, Tm, and the glass transition temperature, Tg, are reviewed. Although there is an accepted thermodynamic model (the Gibbs–Thomson equation) for explaining the shift in the first-order transition, Tm, for confined materials, the depression of the melting point is still not fully understood and clearly requires further investigation. However, the main thrust of the work is a review of the field of confinement and size effects on the glass transition temperature. We present in detail the dynamic, thermodynamic and pseudo-thermodynamic measurements reported for the glass transition in confined geometries for both small molecules confined in nanopores and for ultrathin polymer films. We survey the observations that show that the glass transition temperature decreases, increases, remains the same or even disappears depending upon details of the experimental (or molecular simulation) conditions. Indeed, different behaviours have been observed for the same material depending on the experimental methods used. It seems that the existing theories of Tg are unable to explain the range of behaviours seen at the nanometre size scale, in part because the glass transition phenomenon itself is not fully understood. Importantly, here we conclude that the vast majority of the experiments have been carried out carefully and the results are reproducible. What is currently lacking appears to be an overall view, which accounts for the range of observations. The field seems to be experimentally and empirically driven rather than responding to major theoretical developments.