Formation of hierarchical structures of Fe2O3 by the liquid-liquid interface technique

We report the formation of dendritic hierarchical structures of alpha-Fe2O3 and nanostructures of Fe2O3 by the simple liquid-liquid interface method. The morphology of thin films determined by high-resolution scanning electron microscopy shows nanorods, nanosheets and dendritic Fe2O3. The identification of phases of iron oxide structures is carried out by using XRD and XPS studies. XRD and XPS measurements point out the highly crystalline dendritic alpha-Fe2O3 phase and the mixed phase of alpha- and gamma-Fe2O3 nanostructures. The magnetic measurement also suggests the presence of a mixed phase in the sample grown for 72 hours.

Phase transformation of ZrO2:Tb3+ nanophosphor: Color tunable photoluminescence and photocatalytic activities

The current study involves synthesis of a series of Tb3+ doped ZrO2 nanophosphors by solution combustion method using oxalyl dihydrazide as fuel. The as-formed ZrO2:Tb3+ nanophosphors having different concentrations of Tb3+ (1-11 mol%) were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Visible spectroscopic techniques and the materials were subjected to photoluminescence and photocatalytic dye decolorization studies. The PXRD analysis indicates the formation of tetragonal symmetry up to 5 mol% concentration of Tb3+. Further increase in Tb3+ concentration has lead to cubic phase formation and the same was confirmed by Rietveld refinement analysis. SEM images revealed that material was highly porous in nature comprising of large voids and cracks with irregular morphology. TEM and SAED images clearly confirm the formation of high quality tetragonal nanocrystals. The emissive properties of nanophosphors were found to be dependent on Tb3+ dopant concentration. The green emission of the material was turned to white emission with the increase of Tb3+ ion concentration. The photocatalytic activities of these nanophosphors were probed for the decolorization of Congo red under UV and Sunlight irradiation. All the photocatalysts showed enhanced activity under UV light compared to Sunlight. The photocatalyst with 7 mol% Tb3+ showed enhanced activity attributed to effective separation of charge carriers due to phase transformation from tetragonal to cubic. The influence of crystallite size and PL on charge carrier trapping-recombination dynamics was investigated. The study successfully demonstrates synthesis of tetragonal and cubic ZrO2:Tb3+ green nanophosphors with superior photoluminescence and photocatalytic activities. (C) 2014 Elsevier B.V. All rights reserved.

Photoluminescence, photocatalysis and Judd-Ofelt analysis of Eu3+-activated layered BiOCl phosphors

Eu3+-activated layered BiOCl phosphors were synthesized by the conventional solid-state method at relatively low temperature and shorter duration (400 degrees C for 1 h). All the samples were crystallized in the tetragonal structure with the space group P4/nmm (no. 129). Field emission scanning electron microscopy (FE-SEM) studies confirmed the plate-like morphology. Photoluminescence spectra exhibit characteristic luminescent D-5(0) -> F-7(J) (J = 0-4) intra-4f shell Eu3+ ion transitions. The electric dipole transition located at 620 nm (D-5(0) -> F-7(2)) was stronger than the magnetic dipole transition located at 594 nm (D-5(0) -> F-7(1)). The evaluated Commission International de l'Eclairage (CIE) color coordinates of Eu3+-activated BiOCl phosphors were close to the commercial Y2O3:Eu3+ and Y2O2S:Eu3+ red phosphors. Intensity parameters (Omega(2), Omega(4)) and various radiative properties such as transition probability (A(tot)), radiative lifetime (tau(rad)), stimulated emission cross-section (sigma(e)), gain bandwidth (sigma(e) x Delta lambda(eff)) and optical gain (sigma(e) x tau(rad)) were calculated using the Judd-Ofelt theory. The experimental decay curves of the D-5(0) level in Eu3+-activated BiOCl have a single exponential profile. In comparison with other Eu3+ doped materials, Eu3+-activated BiOCl phosphors have a long lifetime (tau(exp)), low non-radiative relaxation rate (W-NR), high quantum efficiency (eta) and better optical gain (sigma(e) x tau(rad)). The determined radiative properties revealed the usefulness of Eu3+-activated BiOCl in developing red lasers as well as optical display devices. Further, these samples showed efficient photocatalytic activity for the degradation of rhodamine B (RhB) dye under visible light irradiation. These photocatalysts are useful for the removal of toxic and non-biodegradable organic pollutants in water.

Double Gaussian distribution of barrier height observed in densely packed GaN nanorods over Si (111) heterostructures

GaN nanorods were grown by plasma assisted molecular beam epitaxy on intrinsic Si (111) substrates which were characterized by powder X-ray diffraction, field emission scanning electron microscopy, and photoluminescence. The current-voltage characteristics of the GaN nanorods on Si (111) heterojunction were obtained from 138 to 493K which showed the inverted rectification behavior. The I-V characteristics were analyzed in terms of thermionic emission model. The temperature variation of the apparent barrier height and ideality factor along with the non-linearity of the activation energy plot indicated the presence of lateral inhomogeneities in the barrier height. The observed two temperature regimes in Richardson's plot could be well explained by assuming two separate Gaussian distribution of the barrier heights. (C) 2014 AIP Publishing LLC.

Facile synthesis of PbWO4: Applications in photoluminescence and photocatalytic degradation of organic dyes under visible light

Stolzite polymorph of PbWO4 catalyst was prepared by the facile room temperature precipitation method. Structural parameters were refined by the Rietveld analysis using powder X-ray data. PbWO4 was crystallized in the scheelite-type tetragonal structure with space group I4(1)/a (No. 88). Field emission scanning electron microscopy revealed leaf like morphology. Photoluminescence spectra exhibit broad blue emission (425 nm) under the excitation of 356 nm. The photocatalytic degradation of Methylene blue, Rhodamine B and Methyl orange dyes were measured under visible illumination. The 100% dye degradation was observed for MB and RhB dyes within 60 and 105 min. The rate constant was found to be in the decreasing order of MB > RhB > MO which followed the 1st order kinetic mechanism. Therefore, PbWO4 can be a potential candidate for blue component in white LEDs and also acts as a catalyst for the treatment of toxic and non-biodegradable organic pollutants in water. (C) 2014 Elsevier B.V. All rights reserved.

Visible light assisted photocatalytic degradation of organic dyes on TiO2-CNT nanocomposites

Carbon nanotubes (CNTs) uniformly decorated with nano-anatase TiO2 particles corresponding to different TiO2-CNT weight ratios (up to 90 % TiO2:10 % CNT) were prepared by employing sol-gel process. The nanocomposites were characterized by X-ray diffraction, IR, Raman, Scanning electron microscopy, Transmission electron microscopy, Photoluminescence, BET surface area and diffuse reflectance measurements. The composites show visible light assisted photocatalytic property, for example, the 90 % TiO2-10 % CNT composite completely degrades Indigo Carmine dye within 1 h of exposure to visible light. Similarly, Orange G and Congo Red dyes were decomposed within 2 h under visible light irradiation. The excellent visible light photocatalytic property of the composite is attributed to the synergetic effect of photoexcitation and photosensitization. This is due to the special nanoarchitecture wherein TiO2 nanoparticles are anchored to CNT surface that provides high specific interfacial area for photon absorption and electron trapping. Visible light assisted degradation profile of Indigo Carmine in the presence of TiO2-CNT nanocomposite and TEM image of the TiO2-CNT nanocomposite.

Differential response of cholesterol based pyrimidine systems with oxyethylene type spacers to gelation and mesogen formation in the presence of alkali metal ions

A new series of lipophilic cholesteryl derivatives of 2,4,6-trichloro-pyrimidine-5-carbaldehyde has been synthesized. Oxyethylene spacers of variable lengths were inserted between the hydrogen bonding promoting pyrimidine core and the cholesteryl tail in order to understand their effect on the selfassembly of these compounds. Only compound 1a with the shortest spacer formed a gel in organic solvents such as n-butanol and n-dodecane. While other members (1b and c) having longer spacers led to sol formation and precipitation in n-butanol and n-dodecane respectively. The self-assembly phenomena associated with the gelation process were investigated using temperature-dependent UVVis and CD-spectroscopy. The morphological features of the freeze-dried gels obtained from different organic solvents were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The solid phase behaviours of these molecules and their associated alkali metal ion complexes were explored using polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The molecular arrangements in the xerogel and in the solid state were further probed using a wide-angle Xray diffraction (WAXD) technique. Analysis of the wide-angle X-ray diffraction data reveals that this class of molecules adopts a hexagonal columnar organization in the gel and in the solid state. Each slice of these hexagonal columnar structures is composed of a dimeric molecular-assembly as a building block. Significant changes in the conformation of the oxyethylene chains could be triggered via the coordination of selected alkali metal ions. This led to the production of interesting metal ion promoted mesogenic behaviour.

Synthesis and electrocatalytic properties of manganese dioxide for non-enzymatic hydrogen peroxide sensing

Manganese dioxide nanoparticles were synthesized by chemical reduction route at different growth temperatures of 40 degrees C, 80 degrees C, 100 degrees C and were characterized using X-ray Diffraction (XRD), Field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Cyclic Voltammetry (CV) and chronoamperometry (CA) analysis. FESEM results show that on increasing growth temperature the morphology changes from clusters into mixture of rods and flakes. XPS analysis reveals the formation of MnO2. Then these particles were immobilized on Pt electrode. A platinum (Pt) electrode modified with low dimensional MnO2 was investigated as a chronoamperometric (CA) sensor for hydrogen peroxide sensing (H2O2). The sample prepared at 100 degrees C shows good electrocatalytic ability for H2O2 sensing when compared with the samples prepared at 40 degrees C and 80 degrees C. At an operating potential of 0.3 V vs. Ag/AgCl catalytic oxidation of the analyte is measured for chronoamperometric (CA) monitoring. The CA signals are linearly proportional to the concentration of H2O2. It is also found that the morphology of the nanostructure plays a vital role in the detection of H2O2. (C) 2014 Elsevier Ltd. All rights reserved.

CHARACTERIZATION AND MICROHARDNESS OF ELECTRODEPOSITED Ni-W COATINGS OBTAINED FROM GLUCONATE BATH

Ni-W alloy coatings are electrodeposited with direct and pulse current using gluconate bath at pH5. Effects of direct current (DC) and pulse current (PC) on structural characteristics of the coatings have been investigated by energy dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). EDXS shows that W contents are 13.3 and 12.6 at.% in DC and PC (10:40) Ni-W coatings, respectively. FESEM analysis exhibits the homogeneous coarse nodular morphology in DC plated deposits. DSC studies reveal that Ni-W coatings are thermally stable up to 400 degrees C. XPS studies demonstrate that DC plated coating has significant amount of Ni and W in elemental form along with their respective oxidized species. In contrast, mainly oxidized metals are present in the as-deposited coatings prepared with PC plating. The microhardness of pulse current (100:400) deposited Ni-W coating is about 750HK that is much higher than DC plated coating (635 HK). Heat treatment of the deposits carried out at different temperatures show a significant increase in microhardness which can be comparable with hard chromium coatings.

Highly sensitive and rapid detection of acetylcholine using an ITO plate modified with platinum-graphene nanoparticles

Determining the concentrations of acetylcholine (ACh) and choline (Ch) is clinically important. ACh is a neurotransmitter that acts as a key link in the communication between neurons in the spinal cord and in nerve skeletal junctions in vertebrates, and plays an important role in transmitting signals in the brain. A bienzymatic sensor for the detection of ACh was prepared by co-immobilizing choline oxidase (ChO) and acetylcholinesterase (AChE) on graphene matrix/platinum nanoparticles, and then electrodepositing them on an ITO-coated glass plate. Graphene nanoparticles were decorated with platinum nanoparticles and were electrodeposited on a modified ITO-coated glass plate to form a modified electrode. The modified electrode was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies. The optimum response of the enzyme electrode was obtained at pH 7.0 and 35 degrees C. The response time of this ACh-sensing system was shown to be 4 s. The linear range of responses to ACh was 0.005-700 mu M. This biosensor exhibits excellent anti-interferential abilities and good stability, retaining 50% of its original current even after 4 months. It has been applied for the detection of ACh levels in human serum samples.