HRTEM

This review aims at highlighting on recent developments in preparation, characterization, properties, crystallization behaviors, melt rheology, processing, and future applications possibilities of biodegradable polymers and their layered silicate nanocomposites. These materials are attracting considerable interest in materials science research. Montmorillonite and hectorite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. In their pristine form they are hydrophilic in nature, and this property makes them very difficult to disperse into biodegradable polymer matrices. The most common strategy to overcome this difficulty is to replace the interlayer clay cations with quarternized ammonium or phosphonium cations, preferably with long alkyl chains.A wide range of biodegradable polymer matrices is described in this review with a special emphasis on polylactide because of more eco-friendliness from its origin as contrast to the fully petroleum-based biodegradable polymers and control of carbon dioxide balance after their composting.Preparative techniques include (i) intercalation of polymers or prepolymers from solution, (ii) in situ intercalative polymerization method, and (iii) melt intercalation method.This new family of composite materials frequently exhibits remarkable improvements of mechanical and material properties when compared with virgin polymers or conventional micro- and macro-composites. Improvements can include a high storage modulus both in solid and molten states, increased tensile and flexural properties, a decrease in gas permeability and flammability, increased heat distortion temperature and thermal stability, increase in the biodegradation rate, and so forth.

Nanotechnology, which deals with features as small as a 1 billionth of a meter, began to enter into mainstream physical sciences and engineering some 20 years ago. Recent applications of nanoscience include the use of nanoscale materials in electronics, catalysis, and biomedical research. Among these applications, strong interest has been shown to biological processes such as blood coagulation control and multimodal bioimaging, which has brought about a new and exciting research field called nanobiotechnology. Biotechnology, which itself also dates back ∼30 years, involves the manipulation of macroscopic biological systems such as cells and mice in order to understand why and how molecular level mechanisms affect specific biological functions, e.g., the role of APP (amyloid precursor protein) in Alzheimer’s disease (AD). This review aims (1) to introduce key concepts and materials from nanotechnology to a non-physical sciences community; (2) to introduce several state-of-the-art examples of current nanotechnology that were either constructed for use in biological systems or that can, in time, be utilized for biomedical research; (3) to provide recent excerpts in nanotoxicology and multifunctional nanoparticle systems (MFNPSs); and (4) to propose areas in neuroscience that may benefit from research at the interface of neurobiologically important systems and nanostructured materials.

Abstract
The chemical-structural properties of four South African bituminous coals were investigated using wide angle X-ray diffraction-carbon fraction analysis (WAXRD-CFA), attenuated total reflection Fourier transform infra-red spectroscopy (ATR-FTIR), solid state 13C nuclear magnetic resonance spectroscopy (ss 13C NMR), and high resolution transmission electron microscopy (HRTEM). The aromaticity of the samples determined by solid state 13C NMR ranged from 0.74 to 0.87 and compared well with the WAXRD-CFA results (0.73-0.86). WAXRD-CFA, ATR-FTIR and 13C NMR data showed that the lower iso-rank coal samples contained more aliphatic moieties; while the higher rank sample contained higher fractions of polyaromatic moieties and saturated long chain hydrocarbons. The lattice parameters determined from WAXRD-CFA show that lower rank coals investigated are structurally less well-ordered than the higher rank coal. Also, its fringes were quantified as having the greatest preferential alignment of the coals examined. HRTEM aromatic fringe image analysis revealed that the carbon lattice of the samples consist of aromatic fringes of varying lengths, L (3Å ≤ L ≤ 95Å), which corresponded to a molecular weight distribution ranging from 75 to 1925 amu, assuming circular catenation. The coal with the highest volatile matter yield was found to exhibit a higher frequency of lower molecular weight fringes; while the higher rank coal possessed the most higher molecular weight fringes. The average molecular weights determined for the samples from 13C NMR varied between 504 to 544 amu; and compared well with the values from HRTEM aromatic fringe image analysis data. Thus, there was good agreement and consistency between the different techniques. It was demonstrated that, for the characterisation methods used in this study; that vitrinite reflectance impacts more on the chemical-structural properties of these coals than maceral composition does.

In this work, we report the novel findings on the structural, second harmonic and magnetic properties of the Coltan material from México. The magnetic properties were studied through the analyses of the magnetization versus temperature (M(T)) and magnetic field (M(H)). The isothermal magnetization measurements performed at 300 and 50 K shows a saturation magnetization of 11.5 and 11.8 emu/g, respectively. Electron Paramagnetic Resonance (EPR) signal result indicates a signal with g-value of g = 2.481 with a line width (ΔH PP) of 3575.7 G. Zero-field-cooling (ZFC) and Field cooling (FC) curves demonstrate the magnetic fingerprint of Coltan. Additionally, good second harmonic properties are observed at 470 nm, related to the blue color. High resolution transmission electron microscopy showed structural natural nanorods of Nb 2 O 5 at 50 nm resolution with in-teratomic distance of 0.39 nm. Finally, electronic chemical structure characterization by X-ray photoelectron spectroscopy results indicated binding energies of Fe (3p), Mn (3p), Nb (3d 5/2 , 3d 3/2 , 3p 3/2), O (1s), and Ta (4d 3/2) that correspond to columbite and tantalite related to chemical composition fingerprint of Coltan material from México.

Hydrothermally stable titanium containing microporous/mesoporous composite (Ti,Al)-Beta/MCM-41 was synthesized hydrothermally in the presence of structure-directing agents cetyltrimethylammonium bromide (CTABr) and tetraethyl ammonium hydroxide (TEAOH). XRD analysis and analysis of nitrogen adsorption isotherm confirmed the presence of micropores and mesopores in the composite. HRTEM microscopic studies revealed that micro- and mesoporosity of the composite was not due to the mechanical mixture of microporous (Ti,Al)-Beta and mesoporous (Ti,Al)-Beta/MCM-41. The local environment of titanium incorporated into the microporous/mesoporous silicate material was investigated by X-ray absorption spectroscopy. XANES studies showed the presence of tetrahedrally coordinated Ti4+ cations in the template-free sample. EXAFS analysis revealed that titanium cations were coordinated to four oxygens in the first coordination shell at a distance of 1.84 Å. In the second coordination sphere one and two silicon atoms were found at the distances 3.12 Å and 3.51 Å, respectively. These results indicated framework Ti and thus the presence of Ti oxidation centers within the composite material. NMR investigations showed that Brønsted and Lewis acid sites related to framework aluminum were generated by the removal of potassium and sodium ions from the (Ti,Al)-Beta/MCM-41 pores. The new composite material was preliminarily tested in the oxidation reaction. Titanium leaching from the composite was not observed.

Al2O3–SiO2 mixed oxide has been investigated as a support for hydrotreating catalyst with variation of its composition [Si/(Si + Al) = 0.06, 0.12, 0.31, 0.56, 0.78] and its interaction with the surface active metals (NiMo). The composition of support and surface species (NiMo) of catalysts were characterized by specific surface area, atomic absorption, SEM-EDX, XRD, temperature programmed reduction (TPR), Raman analysis, scanning electron microscopy (STEM) and transmission electron microscopy (TEM). Incorporation of SiO2 in Al2O3 promotes a weak interaction between the active phases and particularly catalyst that predominated with SiO2 content. The oxide and sulfided catalysts characterization indicated that the effect of support is responsible to form different catalytic sites. Crystallization of MoO3 phases and a relatively longer crystal of MoS2 in the sulfided catalyst were attributed to an increasing SiO2 content in the support. The catalytic behavior of the NiMo supported catalysts is explained in terms of structural changes on the surface due to the support and active metal interactions. The activity of the different catalysts evaluated in the thiophene hydrodesulfurization reaction was higher for the catalyst having lower SiO2 content in the support.

Here we report on the morphological and optical properties of TiO2/SnO2 nanocomposites prepared by a sol-gel method. The method comprises of a simple chemical reaction between Titanium isopropoxide solution and Water as well as subsequent addition of SnCl2 solution to avail the coating of SnO2 layer on the surface of TiO2 nanoparticles. The as synthesized TiO2 nanoparticles display strong UV absorbance characteristics. The XRD patterns verify the anatase phase of TiO2 nanoparticles. The presence of both TiO2 and SnO2 in the sample is confirmed through XRD pattern. HRTEM images show clear evidence of formation of composite(core-shell) nanostructure in the sample. Optical properties of both TiO2 and composite TiO2/SnO2 nanostructures are studied using UV-Vis absorption spectra, Photoluminescence and FTIR spectra. The performance of the composite nanostructure as a photocatalytic agent in comparison to the core TiO2 nanostructures is also investigated for methyl orange dye under illumi...

This paper reports the synthesis of Fe-titanate nanotubes by means of the conventional ion-exchange method with iron nitrate solutions. As the iron-rich nanotubes were found to contain the catalyst precursor intrinsically dispersed in their structures, the unprecedented possibility of using this kind of materials for building carbon nanostructures, firmly attached at the surface of the forming TiO2 nanoparticles, was verified. The catalytic decomposition of ethylene, used as a carbon source, was performed at a relatively high temperature (750 °C) when the nanotubes undergo an irreversible phase transformation to form anatase and rutile nanoparticles. Due to the different amounts of Fe ions in the nanotubes, distinct types of carbon/TiO2 hybrid interfaces were formed, ranging from amorphous (lower Fe3+ concentration) to the more crystalline graphitic domains (higher Fe3+ concentrations), as documented by the microstructure of the treated samples. The present approach is of potential interest for (photo)catalytic and energy conversion/transport applications.

A novel method for synthesis of pure metal and metal oxide nanocrystals in the dry state starting from chitosan complexes is discussed, using the preparation of copper (II) oxide as an example. Copper (II) oxide is widely used as catalyst in redox reactions and photochemical splitting of water. It also finds application in heat transfer fluids, semiconductors, gas sensors, batteries and magnetic storage media. It is expected that these properties may be enhanced in nano-sized particles of copper oxide and may lead to novel applications. Chitosan is an eco-friendly, biodegradable organic biopolymer obtained from the waste shells of prawns and crabs from sea food processing industries. Characterization of the synthesized material using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopic (EDS) analyses are also described. The method is amenable to low-cost production of metal, metal oxide and other binary metal compounds on a large scale. The product is pure and does not contain any capping or stabilizers.

The effect of substrate temperature on the structural property of the silicon nanostructures deposited on gold-coated crystal silicon substrate by hot-wire chemical vapor deposition (HWCVD) was studied. The uniformity and size of the as-grown silicon nanostructures is highly influenced by the substrate temperature. XRD, Raman and HRTEM measurements show the silicon nanostructures consist of small crystallites embedded within amorphous matrix. The crystallite size of the as-grown silicon nanostructures decreases with increases in substrate temperature. FTIR shows that these silicon nanostructures are highly disordered for sample prepared at substrate temperature above 250 degrees C. The correlation of crystallinity and structure disorder of the silicon nanostructures growth at different substrate temperature was discussed. (C) 2010 Elsevier B.V. All rights reserved.

at x > 0.55 and x > 0.8, respectively, as a result of pinning of the Co IV /Co III and Ni IV /Ni III redox energies at the top of the O-2p bands, [ 11,12 ] which has suggested that strong covalent bonding of the surface oxygen to the redox cation is a prerequisite for good activity of the OER. [ 9 ] Recently, the low-temperature phase of LiCoO 2 , LT-LiCoO 2 , and its delithiated analogue LT-Li 0.5 CoO 2 have been reported to be good catalysts for the OER and ORR. [ 13 ] Lu et al. [ 14 ] have recently shown that by electrochemi-cally delithiating LiCoO 2 to produce Li 0.5 CoO 2 , the OER activity could be strikingly improved both in terms of the onset potential and higher current densities. Recently, high Co activity for the OER with a layered (CoMn) double hydroxide has been reported by Song and Hu [ 15 ] in which they have speculated that the Co IV /Co III species in an amorphous phase was the active catalytic site. Attempts to obtain a high-activity OER reaction with Li 1− x NiO 2 have been disappointing. It is diffi cult to prepare stoichiometric LiNiO 2 with Li + and Ni III well-ordered into alternate (111) planes of the cubic close-packed oxygen sublat-tices; an intermixing of cations produces a non-stoichiometric Li 1− x Ni 1+ x O 2 product containing Ni II. In order to curb the inter-mixing of Ni II in the Li + layer, numerous studies have focused on Al III doping to stabilize Ni III in the Ni layer of LiNiO 2 or the use of a strong oxidizer like Li 2 O 2 to achieve a higher Ni III concentration. [ 16–21 ] In this paper, we report a systematic investigation of the OER activity on nominal LiNi 1− x Al x O 2 with 0 ≤ x ≤ 0.4 synthesized with/without Li 2 O 2 in the precursor reagents by both a conventional solid-state synthesis and by solution-combustion synthesis (details of the experimental procedures are given in the Supporting Information). The nominal LiNi 1− x Al x O 2 powder prepared by solution combustion exhibited the high OER activity expected for an oxide containing a percolating mixed-valent Ni IV /Ni III cation array. Figure 1 shows the Rietveld refi ned powder XRD pattern; the observed lattice parameters are summarized in Table S1 (Supporting Information). With the combustion method, up to 40% Al could be substituted for Ni in LiNiO 2 whereas by the solid-state method only 25% Al could be substituted before impurity peaks were detected in the XRD pattern. From here on, combustion synthesized and solid-state-synthesized samples will be indicated as (c) and (s), respectively. An increase in the intensity of the (003) peak indicates better ordering of Li + and Ni 3+ in the Li-rich layer and Ni-rich layer, respectively, for LiNi 0.8 Al 0.2 O 2 (c) (see the Supporting Information for more details). The core-level binding energy spectra of Ni 2p for the synthesized catalysts are given in Figure 2 and the corresponding binding energy peak positions and relative concentrations are summarized in Table S2 (Supporting Information). While the catalysts synthesized by the solid-state method always showed a minor presence of Ni II along with the major Ni III , XPS spectra of the LiNi 0.9 Al 0.1 O 2 (c) and LiNi 0.8 Al 0.2 O 2 (c) catalysts could be fi tted with only one chemical state of Ni III , clearly indicating that the combustion-synthesized catalysts and the low annealing temperature are prone to keep

ABSTRACT In this research carbon nanotubes and carbon nano onion-like structures were synthesized from carbon black using metal catalysts at 400 °C and 700 °C. Platinum and iron-group metals were used as catalysts for the transformation of CB into graphitized nanocarbon and the effect of both metals was compared. The synthesized products were characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM) and Raman spectroscopy. The characterization shows that this process is very efficient in the synthesis of high quality graphitized products from amorphous carbon black, even though the process temperature was relatively low in comparison with previous studies. Distinguished graphitic walls of the newly formed carbon nanostructures were clearly visible in the HRTEM images. Possible growth difference related to the type of catalyst used is briefly explained with the basis of electron vacancies in d-orbitals of metals.

The use of microorganisms for in vivo synthesis of quantum dots (QDs) not only makes it possible to obtain useful materials with tunable characteristics under mild conditions, but can also ensure the removal of toxic heavy metals from polluted water systems. Because real water treatment schemes contain more than one pollutant, this work attempted to determine the responses of Candida to exposure to two cations with known different survival pathways: PbIJII) and CdIJII). Five Candida species, C. albicans, C. dubliniensis, C. glabrata, C. krusei, and C. parapsilosis, were exposed to a 1 : 1 mixture of the aforementioned cations. The heterogeneous uptake of each metal was defined for the different strains; the removal of cadmium was greater than that of lead. The specific pathway followed by each cation led to the biomineralization of heterogeneous PbS- and CdS-based QDs located extra- or intra-cellularly. The structures and properties of the obtained heterogeneous nanomaterials were characterized by different techniques, and the results highlight the potential of Candida to form useful materials from a complex metal mixture.

Gold nanoparticles have been successfully synthesized using beluntas leaf extract as reducing agents. This is indicated by the change of the color from yellow gold to purple solution after the addition of the beluntas leaf extract. The gold nanoparticles formed were observed for 92 hours using uv-vis and obtained stability after 72 hours with a wavelength about 545.50-546.00 nm. The size distribution of gold nanoparticles was determined using Particle Size Analyzer (PSA) with an average distribution of 101.6 nm. Based on the characterization using XRD, the diffraction pattern obtained at 2θ is 38.1077; 44,2935; 64,5155; 77,4862 which show the presence of gold nanoparticles. Furthermore, it was characterized using SEM EDX showed that the average shape of gold nanoparticles was spherical with a composition ofAu 48%, C 43.33%, and several other elements around 8.67%.

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films prepared in a home-built radio-frequency (rf) plasma enhanced chemical vapour deposition (PECVD) system have been studied. The rf powers were fixed in the range of 5 W-80 W. The optical properties and crystallinity of the films were studied by X-ray diffraction (XRD), Micro-Raman scattering spectroscopy, high resolution transmission electron microscope (HRTEM), and optical transmission and reflection spectroscopy. The XRD and Micro-Raman scattering spectra were used to investigate the evidence of crystallinity in order to determine the crystallite sizes and crystalline volume fraction in the films. The HRTEM image of the film was used to correlate with the crystallinity that was determined from XRD and Micro-Raman scattering spectra. Optical constants such as refractive index, optical energy gap, Tauc slope, Urbach energy and ionic constants were obtained from the optical transmission and reflectance spectra. From the results, it was interesting to found that the optical constants showed a good correlation with the crystallinity within the variation of rf power. Also, the ionic constants of the films showed an indication of the degree of crystallinity in the films. The variation of the optical energy gap with the rf power based on structure disorder and the quantum confinement effect is discussed. (C) 2011 Elsevier Ltd. All rights reserved.