High-resolution Transmission Electron Microscopy Results Research Articles

Photocatalytic and biomedical investigation of green synthesized NiONPs: Toxicities and degradation pathways of Congo red dye

In this study the biomedical and catalytic ability of green synthesized nickel Oxide nanoparticles (NiONPs) was investigated. The extract of medicinal plant Tribulus terrestris were used to synthesized NiONPs. The as-synthesized NiONPs were in nano scale and were characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), High-Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Energy Dispersive X-ray spectroscopy (EDX). The synthesis of NiONPs was ensured with surface Plasmon resonance (SPR) at 425 nm and the strong EDX. The effect of different concentrations of plant extract on the size of NiONPs was evaluated. The HRTEM results showed particle size between 60 - 90 nm. The study showed that lesser the extract concentration, more spherical and small sized particles were obtained without aggregation. The biological applications of NiONPs were evaluated against different fungal species like Asper gillusflavus, Asper gillusfumigatus, Asper gillusniger and standard medicine Terbinafine. A. niger, A. flavus and A. fumigatus exhibited 57, 63 and 52 % inhibition compared with inhibition of the reference medicine which is 98, 100 and 100%. NiONPs have been shown to be more effective against gram-positive bacteria than gram-negative bacteria like E. Coli 9(±0.7) and S. aureus13 (±0.8). Moreover, antioxidant properties of the as-synthesized NiONPs were evaluated with 2, 2 diphenyl-1-picrylhydrazyl) (DPPH). The catalytic ability of green synthesized of NiONP was investigated for the degradation of Congo red dye (CR) as a hazardous environmentally contaminations in water. The biosynthesized NiONPs were found to be active catalytic for the degradation toxic dyes like CR. the catalytic activity of NiONPs can be explained by its small size compared with balk material. Mechanisms for CR degradation have been proposed. The Ecotoxicity of CR and components derived from dye was investigated with Ecological Structure Activity Relationship (ECOSAR) program.

Structural assessment and irradiation response of La2Zr2O7 pyrochlore: Impact of irradiation temperature and ion fluence

State of the art applications (nuclear waste host, scintillators, piezoelectric, SOFCs, etc.) of isometric pyrochlore, A2B2O7, are very sensitive to the structural assessment upon ion irradiation. In the present study, La2Zr2O7 is irradiated using 1 MeV Xe4+ ions with fluence of 1 × 1013, 5 × 1013, and 1 × 1014 ions/cm2 at ~ 88 K and 300 K. The impact of irradiation temperature and ion fluence on the structural properties of the La2Zr2O7 are investigated using the GIXRD, Raman spectroscopy and high resolution transmission electron microscopy (HR-TEM). The GIXRD and Raman results indicate that the degradation of the crystallinity (i.e., damage/amorphization) are significantly higher with enhanced fluence at ~ 88 K than that of 300 K. The induced lattice strain also increases with an increase of ion fluence and it is more pronounced at ~88 K. The HR-TEM results of the La2Zr2O7 samples exhibit that degradation of the atomic ordering are more pronounced at ~ 88 K. The prominent induced strain and degradation of crystallinity (i.e., damage/amorphization) at ~ 88 K appear to be ion fluence and irradiation temperature-dependent. This study is enlightening the effect of the ion fluence and irradiation temperature on the degradation of crystallinity (i.e., damage/amorphization).

Migration kinetics of twinning disconnections in nanotwinned Cu: An in situ HRTEM deformation study

Growth or annealing twins normally form rectangular shape with abundant incoherent twin boundaries (ITBs), while deformation twins exhibit lenticular shape that composed of serrated coherent twin boundaries (SCTBs). Using in situ high-resolution TEM (HRTEM) deformation technique, here we report the formation-mechanism differences between twinning disconnection (TD) facets/serrations and ITBs. The HRTEM results of nanotwinned Cu manifested the multiple TD facets formation on CTBs by interaction of directional partial dislocations, via migration of TDs along shearing direction. In comparison, periodic 3-layered TDs or ITBs structure were normally formed by annealing or growth process that introduced by spontaneous directionless partial dislocations.

Maghemite-based anode materials for Li-Ion batteries: The role of intentionally incorporated vacancies and cation distribution in electrochemical energy storage

Anode materials for Lithium-Ion Batteries (LIBs) based on Mo- and V-doped maghemite were prepared by the sol-gel route. High-Resolution Transmission Electron Microscopy (HRTEM) showed the formation of isotropic nanoparticles. The X-ray Photoelectron Spectroscopy (XPS) revealed the presence of Fe3+ and Mo6+ or V4+ for Mo- or V-doped samples, respectively. Rietveld refinement of X-ray Diffraction (XRD) patterns revealed the distribution of Mo6+ and V4+ cations and showed increase in vacancies. The crystallite size resulted from Rietveld adjustments was in agreement with the HRTEM results. The Extended X-ray Absorption Fine Structure (EXAFS) showed a shrinkage of Fe–O–Fe linkages which is responsible for the reduction of the maghemite cell parameter which agreed with the structural analysis from XRD. The X-ray Absorption Near Edge Structure (XANES) confirmed XPS analysis that Fe3+ is present. Coin cells were assembled and galvanostatic cycling was implemented at various charge-discharge current densities, cyclic voltammograms of Li-ions insertion/extraction processes were obtained and the Electrochemical Impedance Spectroscopy (EIS) was investigated. An exceptional cyclic stability and storage capacity for the V-doped maghemite was observed for low current density. The Mo-doped maghemite has higher capacity retention at high current densities.

Intergrowth of niobium tungsten oxides of the tetragonal tungsten bronze type

Abstract Since the 1970s, high-resolution transmission electron microscopy (HRTEM) is well established as the most appropriate method to explore the structural complexity of niobium tungsten oxides. Today, scanning transmission electron microscopy (STEM) represents an important alternative for performing the structural characterization of such oxides. STEM images recorded with a high-angle annular dark field (HAADF) detector provide not only information about the cation positions but also about the distribution of niobium and tungsten as the intensity is directly correlated to the local scattering potential. The applicability of this method is demonstrated here for the characterization of the real structure of Nb7W10O47.5. This sample contains well-ordered domains of Nb8W9O47 and Nb4W7O31 besides little ordered areas according to HRTEM results. Structural models for Nb4W7O31 and twinning occurring in this phase have been derived from the interpretation of HAADF-STEM images. A remarkable grain boundary between well-ordered domains of Nb4W7O31 and Nb8W9O47 has been found that contains one-dimensionally periodic features. Furthermore, short-range order observed in less ordered areas could be attributed to an intimate intergrowth of small sections of different tetragonal tungsten bronze (TTB) based structures.

Photo-degradation of noxious pollutants from water system using Cornulaca monacantha stem supported ZnFe2O4 magnetic bio-nanocomposite

In the present work, we describe the remediation of noxious naphthalene (NPN) and 2-naphthol (2-NP) from aqueous phase under visible irradiation. The activated carbon/ZnFe2O4 (AC/ZF) nanocomposite was synthesized by simple co-precipitation method. The various instrumental techniques such as Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) pattern, surface area analyzer Brunauer-Emmett-Teller (BET), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), small area diffraction (SAED) pattern, electron dispersive X-ray (EDX), and photoluminescence spectra (PL) were used to study the detailed anatomy of prepared nanocomposite. The XRD, HRTEM, and SAED results indicated that AC/ZF composite has been prepared in nano-phase. The degradation of organic pollutants was studied using high resolution mass spectrometry (HRMS), chemical oxygen demand (COD), and UV–visible (UV–vis) spectrophotometry. The degradation efficiencies of 86.41% and 92.81% were recorded for NPN and 2-NP, respectively, using AC/ZF nanocomposite under synergetic adsorption-photocatalysis (AP) after 160 min of solar illumination. The augmented photocatalytic degradation of pollutants mainly ensued due to the mesoporous nature of the nanocomposite and strongly improved charge separation efficiency of AC/ZF. Therefore, our investigations might reveal a novel, economical, and proficient photoactive material for the removal of highly noxious pollutants from water systems.

Magnetisation and magnetic anisotropy of ion beam synthesised iron nitride

We report the effects of implantation-induced-sputtering in determining the true magnetisation of iron nitrides formed by nitrogen implantation into iron films and the changes subsequently observed in their magnetic anisotropy. Iron thin films (40 nm) capped with gold layers were synthesized by ion beam sputtering. Nitrogen was implanted onto the thin film to a dose of 7 × 1016 cm−2. Dynamic ion–solid interaction simulations calculate the average nitrogen concentration within the iron thin films to be 13 at.%. Ion beam analysis was used to evaluate the composition and depth profile of the thin films before and after implantation. Cross-sectional transmission electron microscopy helped in identifying the implantation induced effects at the surface and interface of the thin film structure. Magnetisation measurements show that nitrogen implantation enhances the magnetisation of thin films and reduces their in-plane magnetic anisotropy. High resolution TEM and magnetisation results suggest formation of α’/α”-Fe16N2 with large magnetic moments and perpendicular magnetic anisotropy. The enhancement in magnetisation of the thin film with and without considering the sputtering losses is determined to be 15% and 5%, respectively. Our review of literature shows that underestimating the sputtering losses from implantation leads to reporting of inconsistent and reduced magnetic moments for Fe16N2.

Biomedical and photocatalytic applications of biosynthesized silver nanoparticles: Ecotoxicology study of brilliant green dye and its mechanistic degradation pathways

The preparation of nanoparticles from biological materials is an economic and environmentally friendly strategy with several advantages. The current study is focused to synthesize silver nanoparticles using Petroselinum crispum plant extract. Various characteristics of biologically synthesized AgNPs were determined with UV–Visible (UV/Vis) Spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, and High-Resolution Transmission Electron Microscopy (HRTEM). The plasmonic resonance peak at 425 nm ensured the formation of AgNPs. The FTIR analysis showed that the as-synthesized particles contain alcoholic and polyphenolic constituents, which are responsible for their capping and reduction. The HRTEM results revealed spherical shape of AgNPs with size ranging from 25 to 90 nm. The as-synthesized particles demonstrated excellent antibacterial properties against Gram positive and Gram-negative bacteria. The antioxidant applications of the particles were determined with 2,2-diphenyle-1-picrylhydrazyl (DPPH). Moreover, the photocatalytic application of the synthesized AgNPs was evaluated for brilliant green dye (BG). The results demonstrated high degradation of BG due to small size and well-dispersed nature of AgNPs. Degradation products of BG were identified to suggest degradation pathways. The eco-toxicity of the BG and constituents derived from the dye were studied with Ecological Structure Activity Relationship (ECOSAR) software.

Structural and microstructural analyses of VO2 film grown on Si substrate by magnetron sputtering

VO2 film was deposited on Si (001) substrate by magnetron sputtering with substrate biasing. The structures and microstructures of the film were characterized by means of Raman spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). A textured VO2 film with a thickness of approximately 300 nm was deposited on the Si substrate. Upon combining the selected-area electron diffraction, energy dispersive X-ray spectroscopy and high-resolution TEM results, it was clear that the film mainly contained a crystalline monoclinic VO2 phase, which is consistent with the Raman and XRD results. At the VO2 film/Si substrate interface, an amorphous layer (~15 nm) and a low-density region of crystalline VO2 (~50 nm) were observed. In addition, the XRD measurements conducted at different temperatures indicated that the structural transformation of the VO2 film from a low-temperature monoclinic structure to a high-temperature tetragonal structure occurred.

Structural parameters of hydrothermally synthesized ZnO nanostructure and their based solar cells

ZnO nanostructure (NS) were prepared via hydrothermal route at various times of heat treatment. The structural properties of ZnO (NS) were reported using X-ray diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HR-TEM). The obtained XRD peaks matched with the standard hexagonal wurtzite crystal structure of ZnO ((ICSD) No. 067454)). Additionally, no noticed peaks corresponded to any phase. The crystal structure, lattice defects and the stress–strain parameters were examined using different models (Size–strain plot method (SPP) Williamson–Hall (W–H) and Halder–Wagner (H–W)), which showed a variation by changing the heating (aging) time (HT). It was found that crystal structure, lattice defects and the stress–strain parameters changed with changing HT. The obtained HR-TEM of the ZnO NS indicated good crystalline structure, spherical and uniform shape. The optical properties of the obtained ZnO NS as a function of HT were described using the spectroscopies: UV–Vis and photoluminescence (PL). The UV–Vis results exhibited a red shift for the absorption band edges, where the estimated optical energy gap (Eg) slightly decreased and shifted to the lower energy region with increasing of HT. The PL emission spectra of the ZnO NS decomposed into two sections ranged from visible to Near-Ultraviolet (NUV). The obtained optical properties are in full agreement with the variation of structural properties obtained using the different XRD models and HR-TEM results. The synthesized particles were used as photoanode in DSSCs sensitized by different organic dyes (Eosin B, Rhodamine B, and Eosin Y). A variation of the overall cell efficiency was observed by changing HT. the sensitizer Eosin Y showed the best efficiency over the other organic dyes with light to electric efficiency of 1%.

Photoluminescence Properties of GaN Nanowires Grown in a Gradient-Plasma Environment

Herein, we report the plasma effect on the surface defects of GaN nanowires (NWs). A gradient plasma growth system by microwave plasma chemical vapor deposition is demonstrated for NWs growth. The structure and surface defects of NWs are affected by the plasma distribution. The PL results show that emission peaks at ∼355, ∼374, and ∼389 nm arising from near band edge emission are observed from the GaN NWs under different plasma growth environment. The relative emission area (Erelative) of the specific emission peaks to total emission area (Etotal) from the different growth regions also changes. The reason for variant ratio Erelative/Etotal is related to the surface defects including structural defects and oxygen incorporation according to the results of high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The analysis of PL properties provided a strong evidence for formation of distinct surface defects. The emission mechanism of GaN NWs grown in a high-density plasma environment enriches our understanding of the plasma effects on the surface defects and optical property, and the knowledge is important to the development of nano-optoelectronic devices.

Growth, characterization, and stability testing of epitaxial MgO (100) on GaAs (100)

Epitaxial MgO (100) films have been grown on GaAs (100) by evaporation of Mg in the presence of 5 × 10−6 Torr of oxygen. Prior to the growth of MgO, the GaAs (100) substrate was cleaned by Ar ion sputtering and annealing. MgO (100) on GaAs (100) was in situ characterized with Auger electron spectroscopy (AES), and ex situ by scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and energy–dispersive X–ray spectroscopy (EDX). X-ray diffraction patterns indicated that the MgO film has grown predominantly in the cubic phase with the (100) plane parallel to the GaAs (100) substrate. HRTEM results have confirmed the epitaxial growth of MgO with MgO (100)[001]║ GaAs (100)[001]. Despite the high lattice misfit, the epitaxial MgO (100) is grown on GaAs (100) due to the 4: 3 relationship (4 aMgO: 3 aGaAs) between MgO (100) and GaAs (100). The formation of a 4:3 superstructure reduces the lateral misfit between MgO (100) and GaAs (100) to ≈0.65%. To test the potential of MgO as a protection layer for III-V semiconductor based photo-electro catalytic devices for water splitting in alkaline media the reaction of MgO films with H2O and NaOH was investigated. Flake-like Mg(OH)2 structures appear to have formed on top of the MgO films treated with NaOH.

Potential-controlled pulse electrochemical deposition of poly nanostructural two-dimensional molybdenum disulfide thin films as a counter electrode for dye-sensitized solar cells

In this study, the poly nanostructure of two-dimensional (2D) layer-nanostructure molybdenum disulfide (MoS2) thin films were synthesized onto the fluorine-doped tin oxide (FTO) glass substrate via the pulse-mode electrochemical deposition (Pulse ECD) method at room temperature and ambient pressure. The surface morphologies of the prepared thin films were examined using field-emission scanning electron microscope (FE-SEM). The chemical states and crystallinities of the prepared thin films were examined by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high-resolution transmission electron microscopy (HR-TEM), respectively. Cyclic voltammetry (CV) measurements, electrochemical impedance spectroscopy (EIS), and Tafel-polarization measurements were performed to analyze the electrochemical properties and catalytic activities of the thin films for redox reactions. According to the HR-TEM results, it was observed that the poly nanostructural 2D MoS2 owning the short-range-order nanostructure offered the numerous edge planes to provide plenty active sites for an efficient counter electrode (CE) of the dye-sensitized solar cells (DSSCs). In combination with a dye-sensitized TiO2 working electrode and an iodine-based electrolyte, the DSSC assembled with the poly nanostructural 2D MoS2 CE showed a photovoltaic conversion efficiency of 6.08% under the illumination of AM 1.5 (100 mWcm−2), which was comparable to that with Pt CE (6.43%). Our study demonstrated that the room-temperature Pulse ECD method displayed a facile and economical process to synthesize the low-cost 2D MoS2 CE for the cost-effective DSSCs.

Selective synthesis and characterization of iron oxide nanoparticles via PVA/PVP polymer blend as structure-directing agent

FexOy nanoparticles have been prepared by hydrothermal technique in the absence and presence of 5% polymer blend of PVA/PVP as structure-directing agent. The as-prepared nanoparticles have been characterized by powder x-ray diffraction (XRD), ultraviolet visible light spectroscopy (UV–Vis), Brunauer–Emmett–Teller (BET) analysis, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and x-ray photoelectron spectroscopy (XPS). TEM, and HRTEM results revealed that the as-prepared nanoparticles were single crystalline and had semi-spherical morphology. Also, the results revealed that the presence of the polymer blend served as a structural controlling agent as the presence of the polymer blend produced Fe3O4 (magnetite) nanoparticles selectively rather than γ-Fe2O3 (maghemite) nanoparticles. The reasons behind the impact of polymer blend were investigated. This method represents a facile and polymorphs-selective synthesis of iron oxide nanoparticles for different applications.

Polarity Control of ZnO Films Grown on Ferroelectric (0001) LiNbO3 Substrates without Buffer Layers by Pulsed-Laser Deposition.

For this study, polarity-controlled ZnO films were grown on lithium niobate (LiNbO3) substrates without buffer layers using the pulsed-laser deposition technique. The interfacial structure between the ZnO films and the LiNbO3 was inspected using high-resolution transmission electron microscopy (HR-TEM) measurements, and X-ray diffraction (XRD) measurements were performed to support these HR-TEM results. The polarity determination of the ZnO films was investigated using piezoresponse force microscopy (PFM) and a chemical-etching analysis. It was verified from the PFM and chemical-etching analyses that the ZnO film grown on the (+z) LiNbO3 was Zn-polar ZnO, while the O-polar ZnO occurred on the (-z) LiNbO3. Further, a possible mechanism of the interfacial atomic configuration between the ZnO on the (+z) LiNbO3 and that on the (-z) LiNbO3 was suggested. It appears that the electrostatic stability at the substrate surface determines the initial nucleation of the ZnO films, leading to the different polarities in the ZnO systems.

Formation and nanoscale-characteristics of soot from pyrolysis of ethylene blended with ethanol/dimethyl ether

Ethanol and dimethyl ether (DME) have been considered to be two of the most potential additives for conventional hydrocarbon fuels. This paper focused on the nanoscale characteristics of soot from ethylene pyrolysis with ethanol and DME additions. The pyrolysis experiments were conducted in a α-alumina tube flow reactor at 1273 K, 1373 K and 1473 K, with the replacement of 0%, 50% and 100% (mole fraction) ethylene by the two oxygenated fuels. The gas-phase kinetic modeling was also performed to explore and understand the soot formation process. The main pathways and some key soot precursors in the pyrolysis have been obtained. Soot samples were characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to acquire their internal structure and oxidation reactivity. Results showed that the mass of collected soot diminished with the increase of the replacement of ethylene by ethanol/DME. The effects of DME to inhibit the formation of soot were more obvious. The least amount of soot was collected in the pyrolysis of pure DME. Peak mole fraction of C2H2, C4H2, C4H4 and C5H5 also decreased with the increase of replacement of ethylene by ethanol/DME, displaying the same tendency with the variation trend of soot mass in the different pyrolysis conditions. According to TEM and HRTEM results, the additions of ethanol and DME could decrease the growth rate of soot contrasted with the pyrolysis of pure ethylene. Soot collected from the pyrolysis of pure DME at 1273 K and 1373 K showed a typical amorphous structure with short, highly-curved and turbulent fringe. With the reduction of the replacement of ethylene by DME, mature soot with longer and more ordered fringe formed at 1373 K and 1473 K. The sequence of the mean fringe tortuosity of soot samples was 100% ethylene<50% DME<100% ethanol<50% ethanol< 100% DME. The order was the same as the sequence of oxidation reactivity. Furthermore, with the increase of temperature, the mass of soot increased. More mature soot with higher degree of graphization, longer fringe length, smaller fringe tortuosity and lower oxidation reactivity was obtained. High correlation between soot nanostructure and soot oxidation reactivity was found.

Unique Double Carbon Protection Structured Co&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; Anode for Lithium Ion Battery

In this study, novel Carbon aerogel (CA)/Co3O4/Carbon (C) composites with a double protective structure are synthesized through a solvothermal method and in-situ polymerization. The morphology and structure are characterized by X-ray diffraction, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Fourier transform infrared spectroscopy (FTIR). The loading content of active anode material Co3O4 in the composite is investigated by thermogravimetry, and the electrochemical properties of the composite are characterized by electrochemical impedance spectroscopy (EIS). The SEM results show that the nano-sized spherical Co3O4 particle is adhered to the inner Carbon aerogel (CA). The HRTEM result indicates the thickness of the prepared Carbon (C) up to 40 nm. Nano-sheet is coated on the surface of the Co3O4 particle. Compared with the pure Co3O4 anode materials, the Carbon aerogel (CA)/Co3O4/Carbon (C) composites have better transport kinetics for both electron and lithium-ion in EIS testing results, which may contribute to its higher specific capacity and higher first coulomb efficiency. Due to the unique structure of the composite material with double protection against the volume expansion of Co3O4 when charged, the Carbon aerogel (CA)/Co3O4/Carbon (C) composite material exhibits better cycle stability with a discharge capacity of 1180 mAh/g after 50 cycles. Therefore, the double protection strategy is verified as an effective method to improve the electrochemical performance of transition metal oxide with carbon composite as an anode material in lithium battery.

Natural antioxidant functionalization for fabricating ambient-stable black phosphorus nanosheets toward enhancing flame retardancy and toxic gases suppression of polyurethane

Herein, as a natural antioxidant, tannin (TA) is firstly used to functionalize black phosphorous (BP) nanosheets to improve the ambient stability and toxic suppression, thus decreasing the fire hazards of polymer materials. Compared to pure BP nanosheets, higher temperature for thermal oxidation decomposition is achieved for TA-BP nanosheets, directly confirming the ambient stability of TA-BP nanosheets. Meanwhile, from high resolution TEM and XPS results, TA-BP nanosheets after being exposed at air for 10 days present well-organized crystal structure and low POx bonds content. Cone calorimeter results illustrate that the incorporation of 2.0 wt% TA-BP nanosheets significantly decreases the peak value of heat release rate (−56.5 %), total heat release (−43.0 %), CO2 concentration (−57.3 %) of TPU composite. Meanwhile, with addition of low to 1.5 wt%, the release of highly-toxic CO gas is significantly suppressed, confirmed by lower peak value (0.52 mg/m3) and decreased total release amount (−55.1 %). The obviously enlarged tensile strength (36.7 MPa) and desirable elongation at break (622 %) are also observed. This strategy not only firstly adopts bio-based antioxidant to impart excellent environmental stability for BP nanosheets, but also promotes the promising potentials of BP nanosheets in the fire safety application of polymer composites.

Strain Effects on the Band Gap and Diameter of CdSe Core and CdSe/ZnS Core/Shell Quantum Dots at Any Temperature

We present the results of an experimental study about strain effects on the core band gap and diameter of spherical bare CdSe core and CdSe/ZnS core/shell quantum dots (QDs) synthesized by using a colloidal technique at varying temperatures. Structural characterizations were made by using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) techniques. Optical characterizations were made by using UV-Vis absorption and fluorescence emission spectroscopies. The XRD analysis suggests that the synthesized bare CdSe core and CdSe/ZnS core/shell QDs have zinc blende crystal structure. HRTEM results indicate that the CdSe core and CdSe/ZnS QDs have average particle sizes about 3.50 nm and 4.84 nm, respectively. Furthermore, compressive strain causes an increase (decrease) in the core band gap (diameter) of spherical CdSe/ZnS core/shell QDs at any temperature. An elastic strain-modified effective mass approximation (EMA) predicts that there is a parabolic decrease (increase) in the core band gap (diameter) of QDs with temperature. The diameter of spherical bare CdSe core and CdSe/ZnS core/shell QDs calculated by using the strain-modified EMA, with core band gap extracted from absorption spectra, are in excellent agreement with the HRTEM data.

Transformation of Jatropha Oil into High-Quality Biofuel over Ni-W Bimetallic Catalysts.

The production of fuel from the hydrodeoxygenation of vegetable oils has been extensively investigated on account of the decline of petroleum-based fuels and increase of ecological problems. The conversion of jatropha oil over Al-MCM-41-supported Ni, W, and Ni–W catalysts was studied at 3 MPa and 360 °C. Over the monometallic Ni and W catalysts, the biofuel yield was low, about 19.3 and 12.5 wt %, respectively, whereas the highest biofuel yield reached 63.5 wt % over the Ni–W bimetallic catalysts. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution TEM results suggested that the proper amount of Ni and W would form a Ni17W3 active phase, the particle size of which varied with the content of Ni and W or preparation methods. The crystalline Ni17W3 phase formed when the content of both Ni and W reached 10%. With further increase of the content of W or Ni to 15%, the crystal size of Ni17W3 grew from 7 to 14 nm or to 20 nm, whereas the biofuel yield decreased with the increase of the Ni17W3 crystal size. The 10Ni–10W/Al-MCM-41 catalyst with the Ni17W3 crystal size of 7 nm showed the best performance for the transformation of jatropha oil into high-grade biofuel.