Effect of La doping on structural, magnetic and microstructural properties of Ba1 − x La x Fe12O19 ceramics prepared by citrate combustion process

La-substituted M-type barium ferrites, Ba_{1 − x} La _x Fe₁₂O₁₉, with x = 0.00–0.30 were successfully prepared via a citrate combustion process. Properties of the ceramics were characterized by powder X-ray diffraction, vibrating sample magnetometry and scanning electron microscopy. XRD patterns revealed only magnetoplumbite structure without minor phases. With increasing the La substituted content, the saturation magnetization (M _S ) was increased and reached to a maximum at x = 0.15 and then decreased but coercivity (H _C ) was increased. SEM micrographs of the dense ceramics showed the hexagonal platelet shape at low La content and the irregular shape at high La content.     

Hybrid high-porosity rice straw infused with BiVO4 nanoparticles for efficient 2-chlorophenol degradation

In this work, the coupling of BiVO₄ nanoparticles with a highly porous material derived from rice straw (BiVO₄/RS composites) and the photocatalytic degradation of 2-chlorophenol (2-CP) in an aqueous solution was studied. The results indicated that BiVO₄/RS composites possessed a monoclinic structure. The morphologies of BiVO₄/RS composites consisted of spherical shapes of BiVO₄ particles coated on the RS adsorbent. The specific surface area of BiVO₄ increased from 1.9024 to 31.1153 m²/g after coating with RS adsorbent. A shift occurred in adsorption edge from 510 to 525 nm, corresponding to a reduction in band gap energy from 2.43 to 2.35 eV. The change in the optical adsorption edge and band gap of BiVO₄/RS composites may simultaneously result to the duplication of a structure caused by silicon species in rice straw, which was expected to be self-doped into the BiVO₄ crystal lattice during synthesis. The photocatalytic performance of 2-chlorophenol under visible irradiation clearly showed that BiVO₄/RS composites displayed the highest photocatalytic activities in comparison with other pure samples, which were 2 times higher than that of BiVO₄.     

Quantitative analysis of adsorbate concentrations by diffuse reflectance FT-IR

Fully quantitative analyses of DRIFTS data are required when the surface concentrations and the specific rate constants of reaction (or desorption) of adsorbates are needed to validate microkinetic models. The relationship between the surface coverage of adsorbates and various functions derived from the signal collected by DRIFTS is discussed here. The Kubelka-Munk and pseudoabsorbance (noted here as absorbance, for the sake of brevity) transformations were considered, since those are the most commonly used functions when data collected by DRIFTS are reported. Theoretical calculations and experimental evidence based on the study of CO adsorption on Pt/SiO2 and formate species adsorbed on Pt/CeO2 showed that the absorbance (i.e., = log 1/R', with R' = relative reflectance) is the most appropriate, yet imperfect, function to give a linear representation of the adsorbate surface concentration in the examples treated here, for which the relative reflectance R' is typically > 60%. When the adsorbates lead to a strong signal absorption (e.g., R' < 60%), the Kubelka-Munk function is actually more appropriate. The absorbance allows a simple correction of baseline drifts, which often occur during time-resolved data collection over catalytic materials. Baseline corrections are markedly more complex in the case of the other mathematical transforms, including the function proposed by Matyshak and Krylov (Catal. Today 1995, 25, 1-87), which has been proposed as an appropriate representation of surface concentrations in DRIFTS spectroscopy.     

Pt/C doped TiO2/SWNTs as catalyst for methanol oxidation

Platinum/carbon doped titanium dioxide/single-walled carbon nanotubes (Pt/C/TiO2/SWNTs) were successfully prepared by blending method. These composite catalysts were found to exhibit an anatase TiO2 structure with uniform Pt/C and the existence of SWNTs can be confirmed by transmission electron microscopy (TEM). The composite of Pt/C with TiO2/SWNTs could improve an enhancement in catalytic properties upon applying TiO2/SWNTs as catalyst support. The catalytic oxidation of methanol of Pt/C doped TiO2/SWNTs is found to be higher as compared to the undoped and Pt/C doped materials.     

Highly selective hydrogen sensing of Pt-loaded WO3 synthesized by hydrothermal/impregnation methods

Unloaded and 0.25–1.0 wt% Pt-loaded WO₃ nanoparticles were synthesized by hydrothermal method using sodium tungstate dihydrate and sodium chloride as precursors in an acidic condition and impregnated using platinum acetylacetonate. Pt-loaded WO₃ films on an Al₂O₃ substrate with interdigitated Au electrodes were prepared by spin-coating technique. The response of WO₃ sensors with different Pt-loading concentrations was tested towards 0.01–1.0 vol% of H₂ in air as a function of operating temperature (200–350 °C). The 1.0 wt% Pt-loaded WO₃ sensing film showed the highest response of ∼2.16 × 10⁴ to 1.0 vol% H₂ at 250 °C. Therefore, an operating temperature of 250 °C was optimal for H₂ detection. The responses of 1.0 wt% Pt-loaded WO₃ sensing film to other flammable gases, including C₂H₅OH, C₂H₄ and CO, were considerably less, demonstrating Pt-loaded WO₃ sensing film to be highly selective to H₂.     

New light‐emitting poly{(9,9‐di‐n‐octylfluorenediyl vinylene)‐alt‐[1,5‐(2,6‐dioctyloxy)naphthalene vinylene]}

A new conjugated light‐emitting AB copolymer containing alternating fluorene and naphthalene units, poly{(9,9‐di‐n‐octylfluorenediyl vinylene)‐alt‐[1,5‐(2,6‐dioctyloxy)naphthalene vinylene]} (PFV‐alt‐PNV), was synthesized via Horner‐Emmons polymerization. The polymer is completely soluble in common organic solvents and exhibits good thermal stability up to 400 °C. UV‐visible, fluorescence and photoluminescence measurements of the copolymer show peak maxima at 427, 500 and 526 nm, respectively. A light‐emitting device containing the new polymer was fabricated using a simple indium tin oxide configuration: (ITO)/PEDOT:PSS/PFV‐alt‐PNV/Al. Measurements of current versus electric field were carried out, with an onset of light emission occurring at 2.5 V. The electroluminescence brightness was observed to reach a maximum of 5000 cd m^?2. Copyright © 2011 Society of Chemical Industry     

Cation distribution and magnetic behavior of Mg1 − x Zn x Fe2O4 ceramics monitored by Mössbauer Spectroscopy

The properties of magnesium ferrites, Mg_{1 ? x} Zn _x Fe₂O₄ with 0.0 ≤ x ≤ 0.5, were investigated by means of powder X-ray diffraction, magnetization, Mössbauer spectroscopy, and scanning electron microscopy. The ferrites were prepared by conventional solid-state reaction using a mixed oxide method. All XRD patterns revealed only the monophasic spinel characteristic structure of MgFe₂O₄. The lattice parameters increased with the increasing of Zn content. Saturation magnetization (M _S ) of the ferrites was discussed with respect to Zn substitution. M _S values increased with Zn content up to x = 0.35 and then decreased thereafter. Mössbauer results showed Fe^{3 +} ion distribution between tetrahedral and octahedral sites and the effect of Zn ions on ferrimagnetic order. The line-broadening of the Mössbauer spectra increased with substituting Mg with Zn ions due to disruption of the local magnetic order. The SEM micrographs of the sintered bodies showed irregular shape in the order of ～5–6 μm.     

Semiconducting metal oxides as sensors for environmentally hazardous gases

This article extensively reviews the recent development of semiconductor metal oxide gas sensors for environmentally hazardous gases including NO₂, NO, N₂O, H₂S, CO, NH₃, CH₄, SO₂ and CO₂. The gas sensing properties of differently-prepared metal oxides and loaded metal oxides towards nine environmentally hazardous gases have been individually compared and digested. Promising materials for sensitive and selective detection of each hazardous gas have been identified. For instance, unloaded WO₃ nanostructures are the most promising candidates for NO₂ sensing while metal catalyst loaded WO₃ and gold-loaded SnO₂ sensors are among the most effective for NO and N₂O sensing, respectively. Moreover, related gas-sensing mechanisms are comprehensively discussed.     

Chemical Mechanisms of Aging of Aerosol Formed from the Reaction of n-Pentadecane with OH Radicals in the Presence of NOx

The effects of aging via gas-phase oxidation and heterogeneous/multiphase reactions on the composition and volatility of secondary organic aerosol (SOA) were investigated in a series of environmental chamber experiments. SOA was formed from the reaction of n-pentadecane, a C₁₅ intermediate volatility alkane, with OH radicals in the presence of NO_x under conditions corresponding to ～1.5 and ～15 h of daytime oxidation, and analyzed using a suite of real-time and offline methods. Functional group analysis indicated that the average number of nitrate, hydroxyl, carbonyl, carboxyl, ester, acylperoxynitrate, and methylene groups per C₁₅ molecule were 0.84, 1.07, 0.25, 0.00, 0.00, 0.00, and 12.84 in less aged SOA and 1.25, 0.69, 0.32, 0.00, 0.33, 0.10, and 12.27 in more aged SOA, and the corresponding O/C, H/C, and N/C ratios determined by offline elemental analysis were 0.32, 2.20, and 0.062, and 0.31, 1.86, and 0.061, respectively, similar to each other and in good agreement with values calculated from functional group composition. Time-dependent SOA yields and temperature-programmed thermal desorption (TPTD) analysis showed that the more aged SOA was much less volatile and more chemically complex, and when combined with particle mass spectra indicated that the major SOA components included 1,4-hydroxynitrates, cyclic hemiacetals (CHA), cyclic hemiacetal nitrates (CHAN), and related compounds, as well as hemiacetal (HA) and acetal oligomers. The effects of aging on functional group composition were due primarily to dehydration of CHA and formation of second- and third-generation products via gas-phase OH radical reactions, whereas SOA volatility was reduced primarily by enhanced formation of HA and acetal oligomers through heterogeneous/multiphase reactions involving these multigeneration products. These results can be explained using well-established gas-phase and heterogeneous/multiphase reaction mechanisms.

Copyright 2013 American Association for Aerosol Research     

Controlling Surface Plasmon Optical Transmission with an Electrochemical Switch Using Conducting Polymer Thin Films

Surface plasmon resonance (SPR)‐enhanced optical transmission is actively controlled by an electrochromism of conducting polymer thin films. Polyaniline and poly(3,4‐ethylenedioxythiophene) thin films are deposited on a thin gold grating surface. SPR‐enhanced optical transmission is demonstrated by irradiating white light on the conducting polymer thin film–gold grating surface and detecting the transmitted light from the back side. The transmission SPR system is combined with an electrochemical setup to manipulate the resonance. The wavelength of the sharp peak in the transmission light spectra is tuned by electrochemical doping/dedoping of the conducting polymer thin films. The present study of controllable SPR‐enhanced optical transmission should provide novel active plasmonic devices such as active bandpass filters or biosensors.