Photocatalytic degradation of dimethoate using LbL fabricated TiO2/polymer hybrid films

Degradation of dimethoate under UV irradiation using TiO2/polymer films prepared by the layer-by-layer (LbL) method was investigated. The thin films were fabricated on glass slides and the surface morphology and roughness of the thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effect of lamp intensity, catalyst loading in the layers, number of bilayers, pH and initial dimethoate concentration on the degradation of dimethoate was systematically studied. The degradation was monitored using high performance liquid chromatography (HPLC) analysis and total organic carbon (TOC) measurements as a function of irradiation time, to see the change in concentration of dimethoate and mineralization, respectively. Complete degradation of dimethoate was achieved under TiO2 optimum loading of 4 g/L at an UV irradiation time of 180 min. Increase in the lamp intensity, catalyst loading and number of bilayers increased the rate of degradation. At a pH of 4.62, complete degradation of dimethoate was observed. The degradation efficiency decreased with increase in initial dimethoate concentration. The degradation byproducts were analyzed and confirmed by gas chromatography-mass spectra (GC-MS). Toxicity of the irradiated samples was measured using the luminescence of bacteria Vibrio fischeri after 30 min of incubation and the results showed more toxicity than the parent compound. Catalyst reusability studies revealed that the fabricated thin films could be repeatedly used for up to ten times without affecting the photocatalytic activity of the films. The findings of the present study are very useful for the treatment of wastewaters contaminated with pesticides. (C) 2011 Elsevier B.V. All rights reserved.

Loading of single-walled carbon nanotubes in cationic cholesterol suspensions significantly improves gene transfection efficiency in serum

We present here a series of cholesterol based cationic lipid suspensions that solubilize single-walled carbon nanotubes (SWCNT) efficiently in water. Each cationic lipid formulation was characterized in terms of their energy minimized molecular structures, bilayer widths of the aggregates based on X-ray diffraction. Then these aggregates were investigated pertaining to their DNA binding and release efficiency, effect of CNT inclusion on the stability of cationic cholesterol lipid-DNA complexes, Zeta potential values and changes in the chiro-optical property of DNA, effect on Raman spectral shift and changes in morphology by SEM and AFM. Each cationic lipid formulation was optimized for the amount of SWCNT solubilized in water, lipid-DNA ratio, amount of the plasmid DNA that can be transfected and the effect on the cellular toxicity. The resulting SWCNT-lipid formulations were then used for in vitro transfection of pEGFP-C3 in A549 (human alveolar basal epithelial) cells and HeLa (human cervical cancer) cells. Advantageously, the CNT-loaded formulations confer an excellent transfection efficiency even in high percentages of blood serum and showed significantly better gene transfer efficiency compared to one of the potent, well-known commercial transfection reagent, Lipofectamine2000.

Effect of nanoclay content and compatibilizer on viscoelastic properties of montmorillonite/polypropylene nanocomposites

This paper deals with preparation of nanocomposites using modified nanoclay (organoclay) and polypropylene (PP), with, and without compatibilizer (m-TMI-g-PP) to study the effects of modified nanoclay and compatibilizer on viscoelastic properties. Nanocomposites were prepared in two steps; compounding of master batch of nanoclay, polypropylene and m-TMI-g-PP in a torque rheometer and blending of this master-batch with polypropylene in a twin-screw extruder in the specific proportions to yield 3-9% nanoclay by weight in the composite. Dynamic Mechanical Analysis (DMA) tests were carried out to investigate the viscoelastic behavior of virgin polypropylene and nanocomposites. The dynamic mechanical properties such as storage modulus (E'), loss modulus (E `') and damping coefficient (tand) of PP and nano-composites were investigated with and without compatibilizer in the temperature range of -40 degrees C to 140 degrees C at a step of 5 degrees C and frequency range of 5 Hz to 100 Hz at a step of 10 Hz. Storage modulus and loss modulus of the nano-composites was significantly higher than virgin polypropylene throughout the temperature range. Storage modulus of the composites increased continuously with increasing nano-content from 3% to 9%. Composites prepared with compatibilizer exhibited inferior storage modulus than the composites without compatibilizer. Surface morphology such as dispersion of nanoclay in the composites with and without compatibilizer was analyzed through Atomic Force Microscope (AFM) that explained the differences in viscoelastic behavior of composites. (C) 2011 Elsevier Ltd. All rights reserved.

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al2O3) thin films were sputter deposited over well-cleaned glass and Si < 100 > substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03 Pa and sputtering power of 70 W. X-ray diffraction results revealed that the films were amorphous until 550 degrees C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2 nm to 4.53 nm was also observed with increase in the annealing temperature. Al-Al2O3-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance. AC conductivity and activation energy were determined and the results are discussed. (C) 2011 Elsevier B.V. All rights reserved.

Layer-by-Layer Self-Assembled Metal-Ion- (Ag-, Co-, Ni-, and Pd-) Doped TiO2 Nanoparticles: Synthesis, Characterisation, and Visible Light Degradation of Rhodamine B

Metal-ion- (Ag, Co, Ni and Pd) doped titania nanocatalysts were successfully deposited on glass slides by layer-by-layer (LbL) self-assembly technique using a poly(styrene sulfonate sodium salt) (PSS) and poly(allylamine hydrochloride) (PAH) polyelectrolyte system. Solid diffuse reflectance (SDR) studies showed a linear increase in absorbance at 416 nm with increase in the number of m-TiO2 thin films. The LbL assembled thin films were tested for their photocatalytic activity through the degradation of Rhodamine B under visible-light illumination. From the scanning electron microscope (SEM), the thin films had a porous morphology and the atomic force microscope (AFM) studies showed ``rough'' surfaces. The porous and rough surface morphology resulted in high surface areas hence the high photocatalytic degradation (up to 97% over a 6.5 h irradiation period) using visible-light observed. Increasing the number of multilayers deposited on the glass slides resulted in increased film thickness and an increased rate of photodegradation due to increase in the availability of more nanocatalysts (more sites for photodegradation). The LbL assembled thin films had strong adhesion properties which made them highly stable thus displaying the same efficiencies after five (5) reusability cycles.

Structure and mechanical properties of Ti-C films deposited using combination of pulsed DC and normal DC magnetron co-sputtering

Titanium-carbon (Ti-C) thin films of different compositions were prepared by a combination of pulsed DC (for Ti target) and normal DC (for graphite target) magnetron co-sputtering on oxidized silicon and fused quartz substrates. At 33.7 at.% of C content, pure hcp Ti transforms into fcc-TiC with a preferential orientation of (2 2 0) along with (1 1 1) and (2 0 0). A clear transformation in the preferential orientation from (2 2 0) to (1 1 1) has been observed when the C content was increased to 56 at.%. At 62.5 at.% of C, TiC precipitates in an amorphous carbon matrix whereas further increase in C leads to X-ray amorphous films. The cross-sectional scanning electron microscope images reveal that the films with low carbon content consists of columnar grains, whereas, randomly oriented grains are in an amorphous carbon matrix at higher carbon content. A dramatic variation was observed in the mechanical properties such as hardness, H, from 30 to 1 GPa and in modulus, E, from 255 to 25 GPa with varying carbon content in the films. Resistance to plastic deformation parameter was observed as 0.417 for films containing 62.5 at.% of C. Nanoscratch test reveals that the films are highly scratch resistant with a coefficient of friction ranging from 0.15 to 0.04. (C) 2012 Elsevier B.V. All rights reserved.

Mechanical properties of ZnS nanowires and thin films: Microscopic origin of the dependence on size and growth direction

Mechanical properties of ZnS nanowires and thin films are studied as a function of size and growth direction using all-atom molecular dynamics simulations. Using the stress-strain relationship we extract Young's moduli of nanowires and thin films at room temperature. Our results show that Young's modulus of 0001] nanowires has strong size dependence. On the other hand, 01 (1) over bar0] nanowires do not exhibit a strong size dependence of Young's modulus in the size range we have investigated. We provide a microscopic understanding of this behavior on the basis of bond stretching and contraction due to the rearrangement of atoms in the surface layers. The ultimate tensile strengths of the nanowires do not show much size dependence. To investigate the mechanical behavior of ZnS in two dimensions, we calculate Young's modulus of thin films under tensile strain along the 0001] direction. Young's modulus of thin films converges to the bulk value more rapidly than that of the 0001] nanowire.

Structure and morphology studies of chromium film at elevated temperature in hypersonic environment

This paper presents the after shock heated structural and morphological studies of chromium film coated on hypersonic test model as a passive drag reduction element. The structural changes and the composition of phases of chromium due to shock heating (2850 K) are characterized using X-ray diffraction studies. Surface morphology changes of chromium coating have been studied using scanning electron microscopy (SEM) before and after shock heating. Significant amount of chromium ablation and sublimation from the model surface is noticed from SEM micrographs. Traces of randomly oriented chromium oxides formed along the coated surface confirm surface reaction of chromium with oxygen present behind the shock. Large traces of amorphous chromium oxide phases are also observed.

Substrate temperature influenced physical properties of silicon MOS devices with TiO2 gate dielectric

DC reactive magnetron sputtering technique was employed for deposition of titanium dioxide (TiO2) films. The films were formed on Corning glass and p-Si (100) substrates by sputtering of titanium target in an oxygen partial pressure of 6x10-2 Pa and at different substrate temperatures in the range 303 673 K. The films formed at 303 K were X-ray amorphous whereas those deposited at substrate temperatures?=?473 K were transformed into polycrystalline nature with anatase phase of TiO2. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic bonding configuration of TiO2. The surface morphology of the films was significantly influenced by the substrate temperature. MOS capacitor with Al/TiO2/p-Si sandwich structure was fabricated and performed currentvoltage and capacitancevoltage characteristics. At an applied gate voltage of 1.5 V, the leakage current density of the device decreased from 1.8?x?10-6 to 5.4?x?10-8 A/cm2 with the increase of substrate temperature from 303 to 673 K. The electrical conduction in the MOS structure was more predominant with Schottky emission and Fowler-Nordheim conduction. The dielectric constant (at 1 MHz) of the films increased from 6 to 20 with increase of substrate temperature. The optical band gap of the films increased from 3.50 to 3.56 eV and refractive index from 2.20 to 2.37 with the increase of substrate temperature from 303 to 673 K. Copyright (c) 2012 John Wiley & Sons, Ltd.

Queens and Workers of the Primitively Eusocial Wasp Ropalidia marginata do not Differ in Their Dufour's Gland Morphology

Ropalidia marginata is a primitively eusocial paper wasp found in peninsular India, where recent work suggests the role of the Dufour's gland hydrocarbons in queen signaling. It appears that the queen signals her presence to workers by rubbing the tip of her abdomen on the nest surface, thereby presumably applying her Dufour's gland secretion to the nest. Since the queen alone produces pheromone from the Dufour's gland and also applies it on the nest surface, the activity level of queen gland should be higher than that of worker gland, as the gland contents would have to get replenished periodically for queens but not for workers. The difference in activity level can be manifested in difference in Dufour's gland morphology, larger glands implying higher activity levels and smaller glands implying lower activity levels, as positive correlation between gland size and gland activity has been reported in exocrine glands of various taxa (including Hymenopteran insects). Hence we investigated whether there is any size difference between Dufour's glands of queens and workers in R. marginata. We found that there was no difference between queens and workers in their Dufour's gland size, implying that Dufour's gland activity and Dufour's gland size are likely to be uncorrelated in this species.

Morphology Controlled Growth of Meso-Porous Co3O4 Nanostructures and Study of Their Electrochemical Capacitive Behavior

The morphology of nanocrystalline Co3O4 synthesized through microwave irradiation of a solution of a cobalt complex is found to depend reproducibly on the conditions of synthesis and, in particular, on the composition of the solvent used. Despite the rapidity of the process, oriented aggregation occurs under certain conditions, depending on solvent composition. Annealing the oriented samples leads to microstructures with significant porosity, rendering the material suitable as electrodes for electrochemical capacitors. Electrochemical analysis of the oxide samples was carried out in 0.1M Na2SO4 electrolyte vs. Ag/AgCl electrode. A stable specific capacitance of 221 F/g was measured for a meso-porous sample displaying oriented aggregation. Stability of these oxide materials were checked for longer charge-discharge cycling. (C) 2012 The Electrochemical Society. DOI: 10.1149/2.002210jes] All rights reserved.

Stress and texture development during sputtering of yttria, zirconia, and yttria stabilized zirconia films on Si substrates

Understanding and controlling growth stress is a requisite for integrating oxides with Si. Yttria stabilized zirconia (YSZ) is both an important functional oxide and a buffer layer material needed for integrating other functional oxides. Stress evolution during the growth of (100) and (111) oriented YSZ on Si (100) by radio frequency and reactive direct current sputtering has been investigated with an in-situ monitor and correlated with texture evolution. Films nucleated at rates <5 nm/min are found to be (111) oriented and grow predominantly under a compressive steady state stress. Films nucleated at rates >20 nm/min are found to be (100) oriented and grow under tension. A change in growth rate following the nucleation stage does not change the orientation. The value of the final steady state stress varies from -4.7 GPa to 0.3 GPa. The in-situ studies show that the steady state stress generation is a dynamic phenomenon occurring at the growth surface and not decided at film nucleation. The combination of stress evolution and texture evolution data shows that the adatom injection into the grain boundaries is the predominant source of compressive stress and grain boundary formation at the growth surface is the source of tensile stress. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4757924]

Influence of annealing temperature on Raman and photoluminescence spectra of electron beam evaporated TiO2 thin films

Titanium dioxide (TiO2) thin films were deposited on fused quartz substrates by electron beam evaporation method at room temperature. The films were annealed at different temperatures in ambient air. The surface morphology/roughness at different annealing temperatures were analyzed by atomic force microscopy (AFM). The crystallinity of the film has improved with the increase of annealing temperature. The effect of annealing temperature on optical, photoluminescence and Raman spectra of TiO2 films were investigated. The refractive index of TiO2 films were studied by envelope method and reflectance spectra and it is observed that the refractive index of the films was high. The photoluminescence intensity corresponding to green emission was enhanced with increase of annealing temperature. The peaks in Raman spectra depicts that the TiO2 film is of anatase phase after annealing at 300 degrees C and higher. The films show high refractive index, good optical quality and photoluminescence characteristics suggest that possible usage in opto-electronic and optical coating applications. (C) 2012 Elsevier B.V. All rights reserved.

Structural and mechanical properties of room temperature sputter deposited CrN coatings

Chromium nitride (CrN) thin films were deposited at room temperature on silicon and glass substrates using DC reactive magnetron sputtering in Ar + N-2 plasma. Structure and mechanical properties of these films were examined by using XRD, FESEM and nanoindentation techniques. XRD studies revealed that films are of mixed phase at lower nitrogen partial pressure (P-N2) and single phase at higher (P-N2). Microscopy results show that the films were composed of non-equiaxed columns with nanocrystallite morphology. The hardness and elastic modulus of the films increase with increasing nitrogen partial pressure (P-N2). A maximum hardness of similar to 29 GPa and elastic modulus of 341 GPa were obtained, which make these films useful for several potential applications. (C) 2012 Elsevier Ltd. All rights reserved.

Dielectric properties of novel PVA/ZnO hybrid nanocomposite films

In this study, the dielectric properties of PVA/ZnO nanocomposites films were evaluated. The composites were prepared by a solution casting technique. The dispersion and functionalization of the ZnO nanoparticles in the composite films were characterized by spectroscopic technique. The surface morphology of the PVA/ZnO nanocomposites films were elucidated using AFM. The charge transport properties were evaluated based on the dielectric and impedance spectroscopy techniques. Low ZnO loading composite shows low dielectric value at higher frequency and behaves as a lossless material. The complex impedance spectra suggest the change in conductivity, due to the change in bulk resistance of the materials and less relaxation time. Thus, all PVA/ZnO nanocomposites behave as lossless materials above 10(6) Hz indicating the composites are useful in microwave application. (c) 2012 Elsevier Ltd. All rights reserved.