Solution phase synthesis of Na0.28V2O5 nanobelts into nanorings and the electrochemical performance in Li battery

In this paper, we are the first to report a simple one step hydrothermal method to synthesize Na0.28V2O5 nanorings/nanobelts without using any organic surfactant/solvents at 130-160 degrees C for 1-2 days. The obtained products have been characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, morphology by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and electrochemical discharge-charge test for lithium battery. XRD pattern exhibit a monoclinic Na0.28V2O5 structure. FTIR spectrum shows band at 958 cm(-1) is assigned to V=O stretching vibration, which is sensitive to intercalation and suggests that Na+ ions are inserted between the vanadium oxide layers. TEM analyses reveal that the products consist of nanorings of width about 500 nm and thickness of about 100 nm with inner diameter of 5-7 mu m. Nanobelts of width 70-100 nm and several tens of micrometers in length are observed. The electrochemical results show that nanorings/nanobelts exhibit an initial discharge capacity of 320 mAh g(-1) and its capacity still retained 175 mAh g(-1) even after 69 cycles. We have discussed the possible growth mechanism for the formation of nanorings/nanobelts. (c) 2012 Elsevier Ltd. All rights reserved

Defluoridation of bore-​well water using combustion derived nanocrystalline magnesium oxide

Nanocryst. MgO powder was prepd. through combustion route using Mg(NO3)​2 as oxidizer and glycine as fuel; the combustion-​derived MgO powder was characterized using XRD, SEM, surface area, and porosity measurements. The powder XRD pattern confirms the crystallinity and phase purity of the as-​made powder. The SEM results reveal that the combustion derived powder is an agglomeration of fine particles. The particle size of the powder is found to be in the range of 12-​23 nm with a large surface area of 107 m2 g-​1. The as-​made MgO is used for defluoridation of groundwater samples with stirring time (5-​60 min)​, adsorbent quantity (0.05-​0.3 g L-​1)​, and pH 5-​9 as exptl. parameters. It is found that 92 and 97​% of F-​, resp., could be removed using 0.15 g of MgO from 10 ppm of synthetic F-​ soln. and std. NaF soln. In this technique 90​% minimization of sludge could be achieved. The regeneration of adsorbent with NaOH (15 mL of 0.1 N NaOH for 0.5 g of sludge) soln. gives better results than HCl (15 mL of 0.1 N HCl for 0.5 g of sludge) soln

Structural, Electrical, and Magnetic Properties of Zn Substituted Magnesium Ferrite

Zinc substituted magnesium (Mg–Zn) ferrites with the general formula Mg1−xZnxFe2O4 (x=0.00, 0.25, 0.50, 0.75, and 1.00) were prepared using the solution combustion route. The dried powder after calcination (700 °C for 2 h) was compacted and sintered at 1050 °C for 3 h. The structural, morphological, dielectric and magnetic properties of the sintered ferrites were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), impedance spectroscopy, and vibration sample magnetometry (VSM). The XRD analysis of sintered samples confirmed that the expected spinel cubic phase was formed for all samples. The crystallite sizes evaluated using Scherre's formula were found to be in the range of 47–80 nm. SEM analysis showed homogeneous grains with a polyhedral structure. The electrical conductivity increased with increasing frequency, which is normal dielectric behavior for such materials. The dielectric constant, dielectric loss tangent, and AC conductivity were found to be lowest for x=0.50. The VSM results showed that the zinc concentration had a significant influence on the saturation magnetization and coercivity

Formation of Crystalline Na2V6O16·3H2O Ribbons into Belts and Rings

Single-​cryst. nanobelts and nanorings of Na2V6O16·3H2O structures have been facilely synthesized through a direct hydrothermal reaction between NaVO3 and H3PO4, without the addn. of any harmful solvents or surfactants. The anal. techniques of SEM, transmission electron microscopy (TEM)​, powder X-​ray diffraction, TGA, energy-​dispersive X-​ray spectroscopy, FTIR spectroscopy, high-​resoln. TEM, and selected-​area electron diffraction have been used to characterize the morphol., compn., and structure of the synthesized products. The Na2V6O16·3H2O nanobelts are up to several hundreds of micrometers in length and 100-​300 nm in thickness, and for nanorings, the diams. are 4.5-​6.5 μm. H3PO4 plays a key role in maintaining the pH of the soln. as well as producing PO43-​ ions in soln. The chem. reactions and a possible growth mechanism involved in the formation of Na2V6O16·3H2O nanobelts and nanorings are briefly discussed

Nanostructural zinc oxide hollow spheres: A facile synthesis and catalytic properties

The development of reproducible procedures for the synthesis and organization of nanostructured metal oxides is important in order to exploit the unique properties of these materials for practical applications. The present work describes the transformation of Zn(NH3)4] 2+ into hollow structured ZnO materials through solvothermal decomposition. An increase in ammonia concentration in the reaction medium, significantly changes the morphology of ZnO from spheres made of nanoparticles (20-30 nm) to hollow spheres composed of nanorods (200-350 nm) or to free microrods as evidenced from scanning and transmission electron micrographs (SEM/TEM). The powder X-ray diffraction (XRD) pattern of ZnO confirms formation of the wurtzite structure. Raman and Energy-dispersive spectroscopic (EDS) studies indicate the presence of oxygen deficiency in ZnO. The investigation on the catalytic behavior of ZnO in the synthesis of (4-methoxyphenyl)(phenyl) methanone (MPPM) by Friedel-Crafts acylation of anisole with benzoyl chloride has also been carried out. The results reveal that the prepared ZnO could produce �98 of yield compared to 41 produced by commercial ZnO. © 2010 Elsevier B.V. All rights reserved

Selective synthesis of scheelite/perovskite CdWO4 nanoparticles: a mechanistic investigation of phase formation and property correlation

We proposed a simple solution combustion strategy to fabricate CdWO4 nanoparticles for the first time in two different polymorphs: a stable monoclinic and metastable tetragonal phase. The selective synthesis of polymorphs has been achieved by optimizing oxidizer to fuel ratio. Influence of oxidizer to fuel ratio on the formation of CdWO4 polymorphs is of particular relevance to this study and the significant effects are discussed. A mechanistic comparison of properties between two phases has been carried out. Rietveld analyzes of powder X-ray diffraction patterns were performed using GSAS program. Transmission electron microscope images of as synthesized products show the particle sizes of t-CdWO4 (10–20 nm) are smaller than the particle size of m-CdWO4 (≈30 nm). The specific surface area was found to be 12 and 25 m²/g for tetragonal and monoclinic phases, respectively. Photocatalytic activities were investigated by the degradation of methylene blue solution under UV light irradiation. It was found that the photocatalytic activity of tetragonal phase was higher than monoclinic phase, this can be attributed to smaller particle size and active sites of the catalyst that rely sensitively on synthetic conditions. We also explored the photoluminescence (PL) properties of t-CdWO4 and compared with the PL results of m-CdWO4

Surfactant free hydrothermally derived ZnO nanowires, nanorods, microrods and their characterization

ZnO nanowires, nanorods and microrods have been prepared by an organic-free hydrothermal process using ZnSO4 and NaOH/NH4OH solutions. The powder X-ray diffraction (PXRD) patterns reveal that the ZnO nano/microrods are of hexagonal wurtzite structure. The Fourier transform infrared (FT-IR) spectrum of ZnO powder shows only one significant spectroscopic band at around 417 cm-1 associated with the characteristic vibrational mode of Zn-O bonding. The thickness 75-300 nm for ZnO nanorods and 0.2-1.8 μm for microrods are identified from SEM/TEM images. UV-visible absorption spectra of ZnO nano/microrods show the blue shift. The UV band and green emission observed in photoluminescence (PL) spectra are due to free exciton emission and singly ionized oxygen vacancy in ZnO. Finally, the mechanism for organic-free hydrothermal synthesis of the ZnO nano/microrods is discussed. © 2010 Elsevier Ltd. All rights reserved

Synthesis, structural and transport properties of nanocrystalline La1−xBaxMnO3 (0.0≤x≤0.3) powders

Nanocrystalline La1−xBaxMnO3 (0.0≤x≤0.3) manganites have been prepared by a simple and instantaneous solution combustion method, which is a low temperature initiated synthetic route to obtain fine-grained powders with relatively high surface area. The phase purity and crystal structure of the combustion products are carried out by powder X-ray diffraction. The as-made nanopowders are in cubic phase. On calcination to 900 °C, barium doped manganites retain cubic phase, whereas barium free manganite transformed to rhombohedral phase. The scanning electron microscope (SEM) results revealed that the combustion-derived compounds are agglomerated with fine primary particles. The doped manganites have surface area in the range 24–44 m2/g. The surface area of the manganites increases with barium content, whereas it decreases on calcination. Both undoped and doped lanthanum manganites show two active IR vibrational modes at 400 and 600 cm−1. The low temperature resistivity measurements have been carried out by four-probe method down to 77 K. All the samples exhibit metal–insulator behaviour and metal–insulator transition temperature (TM–I) in the range 184–228 K and it is interesting to note that, as the barium content increases the TM–I shifts to lower temperature side. The maximum TM–I of 228 K is observed for La0.9Ba0.1MnO3 sample

EPR Study of Fe 3+ - and Ni 2+ -Doped Macroporous CaSiO 3 Ceramics

Thermally stable macroporous CaSiO 3 , Fe 3+ - and Ni 2+ -doped (0.5 to 5 mol%) ceramics have been prepared by solution combustion process by mixing respective metal nitrates (oxidizers), fumed silica. Diformol hydrazine is used as a fuel. The combustion products were identified by their X-ray diffraction and thermal gravimetry/differential thermal analysis. Single phases of β-CaSiO 3 and α-CaSiO 3 were observed at 950 and 1200 °C, respectively. The phase transition temperatures of combustion-derived CaSiO 3 were found to be lower compared to those obtained via solid-state reaction method. It is interesting to note that with an increase in the calcination temperature the samples become more porous with an increase in the pore diameter from 0.2 to 8 µm. The electron paramagnetic resonance (EPR) spectrum of Fe 3+ ions in CaSiO 3 exhibits a weak signal at g = 4.20 ± 0.1 followed by an intense signal at g = 2.0 ± 0.1. The signal at g = 4.20 is ascribed to isolated Fe 3+ ions at rhombic site. The signal at g = 2.0 is due to Fe 3+ coupled together with dipolar interaction. In Ni 2+ -doped CaSiO 3 ceramics the EPR spectrum exhibits a symmetric absorption at g = 2.23 ± 0.1. This deviation from the free electron g -value is ascribed to octahedrally coordinated Ni 2+ ions with moderately high spin–orbit coupling. The number of spins participating in resonance and the paramagnetic susceptibilities have been evaluated from EPR data as a function of Fe 3+ as well as Ni 2+ content. The effect of alkali ions (Li, Na and K) on the EPR spectra of these ceramics has also been studied