The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

Elements Of X Ray Diffraction

Multidrug resistance of the pathogenic microorganisms to the antimicrobial drugs has become a major impediment toward successful diagnosis and management of infectious diseases. Recent advancements in nanotechnology-based medicines have opened new horizons for combating multidrug resistance in microorganisms. In particular, the use of silver nanoparticles (AgNPs) as a potent antibacterial agent has received much attention. The most critical physico-chemical parameters that affect the antimicrobial potential of AgNPs include size, shape, surface charge, concentration and colloidal state. AgNPs exhibits their antimicrobial potential through multifaceted mechanisms. AgNPs adhesion to microbial cells, penetration inside the cells, ROS and free radical generation, and modulation of microbial signal transduction pathways have been recognized as the most prominent modes of antimicrobial action. On the other side, AgNPs exposure to human cells induces cytotoxicity, genotoxicity and inflammatory response in human cells in a cell-type dependent manner. This has raised concerns regarding use of AgNPs in therapeutics and drug delivery. We have summarized the emerging endeavors that address current challenges in relation to safe use of AgNPs in therapeutics and drug delivery platforms. Based on research done so far, we believe that AgNPs can be engineered so as to increase their efficacy, stability, specificity, biosafety and biocompatibility. In this regard, three perspectives research directions have been suggested that include 1) synthesizing AgNPs with controlled physico-chemical properties, 2) examining microbial development of resistance towards AgNPs, and 3) ascertaining the susceptibility of cytoxicity, genotoxicity, and inflammatory response to human cells upon AgNPs exposure.

/pdf/mechanistic-basis-of-antimicrobial-actions-of-silver-1vmm44o6it.pdf

Mechanistic Basis of Antimicrobial Actions of Silver Nanoparticles.

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

Solution Combustion Synthesis of Nanoscale Materials

A cost effective and facile sol–gel method is used to synthesize graphene oxide (GO)/Mn3O4 nanocomposite (NC). The synthesized materials (GO and GO/Mn3O4 nanocomposite) were analyzed using different characterization techniques. X-ray diffraction (XRD) analysis confirmed the presence of Mn3O4 nanoparticles incorporated in the synthesized GO matrix. The stretching and bending vibrational modes corresponding to various functional groups (–OH, C–H, C–C, etc.) present in the FTIR spectra of the synthesized nanocomposite. The microstructural studies have been carried out through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that revealed the layered morphology of GO and uniform size distribution of Mn3O4 nanoparticles over the GO layers. UV–visible measurement indicates a red shift in the GO/Mn3O4 nanocomposite absorption edge as compared to the GO and associated band gap reduced from 4.46 eV (GO) to 2.95 eV (GO/Mn3O4) attributed to the π–π non-covalent electrostatic interactions. The electrochemical study revealed a high specific capacitance of GO/Mn3O4 nanocomposite as compared to GO sheets, making it suitable candidate for supercapacitors.

Structural and electrochemical properties of GO/Mn 3 O 4 nanocomposite

Perovskite manganite nanoparticles with the chemical formula La0.67Sr0.33Mn1−xZnxO3 (x = 0, 0.1 and 0.2) were prepared by the sol–gel process and the influence of Zn substitution on their microstructural and magnetic properties studied in detail. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed for crystal structure determination and microstructural analysis. The results of XRD analysis confirmed the polycrystalline nature and rhombohedral crystal structure with space group R(-3c) for all compositions. SEM micrographs of the samples revealed an agglomeration/well-connected appearance of the particles. The composition and uniform distribution of all the elements were established by energy-dispersive spectroscopy. TEM images clearly confirmed an almost spherical shape of the nanoparticles with an average particle size of about 11, 14 and 13 nm for the 0, 10 and 20% Zn-doped samples, respectively. The magnetic behaviour of the nan...

Influence of Zn incorporation on the microstructural and magnetic properties of La0.67Sr0.33Mn1−xZnxO3 nanoparticles synthesised by the sol–gel method

DyCr1−xCoxO3 (0 ≤ x ≤ 0.3) system synthesized through sol–gel auto-combustion process is investigated to study the impact of cobalt (Co) doping on physical features and conduction mechanism of DyCrO3. X-ray diffraction data affirm the single-phase nature of this system that conforms in orthorhombic crystal symmetry with Pbnm space group. Raman spectra display the variation in intensity and position of Raman bands on doping. The broadening of full-width at half-maximum (FWHM) in case of doped samples indicates the structural distortion due to Co doping. Transmission electron microscopy (TEM) images reveal the nano-sized spherical particles, and the clearly distinguishable planes in high-resolution TEM images establish the crystalline nature of these samples. D.C. resistivity declines with the increase in Co doping, and resistivity data fit well to small-polaron hopping and variable-range hopping models. The dielectric permittivity plots for all the samples exhibit dielectric peak which may be related to those of weak ferroelectric systems. The Cole–Cole plots exhibit depressed semi-circular patterns which suggest the non-Debye nature and the distributed relaxation times. The temperature dependence of imaginary part of electric modulus (M″) shows relaxation peaks at relatively lower temperatures. The a.c. conductivity (
 $${\sigma }_{\mathrm{ac}}$$
 ) shows gradual increase with the rise in Co doping, especially near the room temperature. The temperature dependence of the exponent factor ‘n’ suggests that correlated barrier hopping and non-overlapping small-polaron tunnelling models govern the conduction mechanism in this system.

Raman scattering, electronic transport and dielectric features of Co-doped DyCrO3

Nanocrystalline MgGdxFe2-xO4 powders with x=0 &0.10 have been synthesized by co-precipitation method. Structural analysis was done by the conventional techniques like X-ray diffraction (XRD) along with Fourier transform infrared (FT-IR) spectroscopy. The scanning electron microscopy (SEM) equipped with energy dispersive x-ray (EDX) spectroscopy, was used to study the surface morphology and elemental composition of the samples. Dielectric properties were measured through LCR meter in the frequency range 42 Hz to 5 MHz. The Rietveld analysis of X-ray peaks confirmed the formation of the sample in single phase in cubic spinel structure. It is observed that the doping of Gd3+ions significantly reduces the crystallite size while increasing the lattice parameters. Presence of ν1 and ν2 bands in FT-IR spectrum reinforces the conclusion of XRD findings. Dielectric constant was found to be maximum in low frequency range and subsequently deceases while approaching higher frequency.

Microstructural and dielectric relaxation study of Gd3+ ion substituted MgFe2O4

Perovskite nanocrystalline powder of LaFe0.5Cr0.5O3 was synthesized by sol-gel combustion route and characterized by x-ray diffractometer (XRD), scanning electron microscopy (SEM) equipped with EDS, UV-visible and LCR meter at room temperature Rietveld refinement of the XRD data confirms that the sample is in single phase-rhombohedral structure with space group R-3C. SEM micrograph shows clear nanostructure of the sample and EDS ensures the presence of all elements in good stoichiometric. The optical absorption indicates the maximum absorption at 315 nm and optical band gap of 2.94 eV was estimated using Tauc’s relation. Dielectric constant (e’) and loss were found to decrease with increase in frequencies. The dielectric behavior was explained on the basis of Maxwell-Wagner’s two layer model.

Wasi Khan

Papers

Structural and electrochemical properties of GO/Mn 3 O 4 nanocomposite

Influence of Zn incorporation on the microstructural and magnetic properties of La0.67Sr0.33Mn1−xZnxO3 nanoparticles synthesised by the sol–gel method

Raman scattering, electronic transport and dielectric features of Co-doped DyCrO3

Microstructural and dielectric relaxation study of Gd3+ ion substituted MgFe2O4

Microstructural, optical and electrical properties of LaFe0.5Cr0.5O3 perovskite nanostructures