Catalytic properties of dispersed iron oxides Fe2O3/MO2 (M = Zr,Ce, Ti and Si) for sulfuric acid decomposition reaction: Role of support

Supported iron oxides have been established as an important class of catalyst for high temperature sulfuric acid decomposition. With an objective to elucidate the role of support in modifying the overall catalytic properties of dispersed iron oxide catalysts, a series of supported iron oxide based catalysts, Fe₂O₃ (15 wt%)/MO₂ (M = Zr, Ce, Ti and Si), synthesized by adsorption-equilibrium method, is investigated for sulfuric acid decomposition reaction. The structure of dispersed iron oxide phases largely depended on the nature of the support oxide as revealed by the XRD and Mössbauer studies. α-Fe₂O₃ is found to be present as a major phase on ZrO₂ and CeO₂ support while ε-Fe₂O₃ was the major phase on silica supported iron oxide. On the other hand, presence of mixed oxide Fe₂TiO₅ was revealed over TiO₂ support. Strong dispersed metal oxide-support interactions inhibited the total reduction of the dispersed phase on SiO₂ and TiO₂ as compared to complete reduction of dispersed iron oxide on CeO₂ and ZrO₂ supports during temperature programmed reduction upto 1000 °C. The order of catalytic activity at a temperature of ～750 °C is observed as Fe₂O₃/SiO₂ > Fe₂TiO₅/TiO₂ > Fe₂O₃/ZrO₂ > Fe₂O₃/CeO₂, while at higher temperatures of ～900 °C the SO₂ yield is found to be comparable for all catalysts. A relationship between the rate of sulfate decomposition and catalytic activity is established through detailed TG-DTA investigations of sulfated catalyst and support. Considerable influence of the support oxide on the composition, structure, redox properties, morphology and catalytic activities of the active iron oxide dispersed phase has been observed. Thus, the support oxides operate as a critical component in the complex supported metal oxide catalysts and these findings might influence the design and development of future high temperature sulfuric acid decomposition catalysts.     

Multiple-band large-signal characterization of millimeter-wave double avalanche region transit time diode

A large-signal method based on non-sinusoidal voltage excitation model is used to study the DC and RF characteristics of Double Avalanche Region (DAR) Silicon Transit Time diode. A large-signal simulation program based on drift-diffusion model is developed for this study. The simulation results show the existence of several distinct negative conductance bands in the admittance characteristics separated by positive conductance. Thus the DAR device is capable of delivering RF power not only at the design frequency but also at several frequency bands higher than the design frequency band in the mm-wave regime. A comparative study with DDR Si device designed to deliver RF power at a particular mm-wave frequency band shows that DAR Si device is capable of delivering significantly higher RF power not only at the designed mm-wave frequency band, but also at higher frequency bands.     

Hydrous iron oxide for removal of inorganic contaminants in simulated stormwater: A batch sorption kinetics study

Urban stormwater runoff, which consists of inorganic and organic contaminants, is a major source of pollutants to receiving waters and therefore they need to be removed. Simultaneous removal of contaminants, Cd²⁺, Cu²⁺, Ni²⁺, Zn²⁺ (heavy metal cations), and SeO₄²⁻ (oxyanion) from a simulated stormwater by a hydrous ferric oxide (HFO) was studied in batch and column sorption experiments. In the batch experiment the rate of sorption of the ions was rapid at the beginning and reached equilibrium in approximately 300 min. The amounts of ions sorbed were proportionate to the respective initial concentration of the ions added to the HFO. Cluster analysis showed that all heavy metals had similar sorption behavior, whereas Se had a distinctly different sorption process. Of the three different kinetic models tested the pseudo-first order kinetic model fitted the data the best. The column experimental results beyond 180 min were consistent with those of the batch experiment that the removal efficiencies of the ions were in proportion to the ion concentration in the feed. Below 180 min, Cu appeared to be preferentially removed than Zn.     

Heterojunction DDR THz IMPATT diodes based on AlxGa1-xN/GaN material system

Simulation studies are made on the large-signal RF performance and avalanche noise properties of heterojunction double-drift region (DDR) impact avalanche transit time (IMPATT) diodes based on Al_xGa_1-xN/GaN material system designed to operate at 1.0 THz frequency. Two different heterojunction DDR structures such as n-Al_0.4Ga_0.6N/p-GaN and n-GaN/p-Al_0.4Ga_0.6N are proposed in this study. The large-signal output power, conversion efficiency and noise properties of the heterojunction DDR IMPATTs are compared with homojunction DDR IMPATT devices based on GaN and Al_0.4Ga_0.6N. The results show that the n-Al_0.4Ga_0.6N/p-GaN heterojunction DDR device not only surpasses the n-GaN/p-Al_0.4Ga_0.6N DDR device but also homojunction DDR IMPATTs based on GaN and Al_0.4Ga_0.6N as regards large-signal conversion efficiency, power output and avalanche noise performance at 1.0 THz.     

Component analysis of some chemical parameters influencing the stability of DDVP in sea‐sediments along the east coast of India

The component analysis of some chemical parameters such as half‐life period, pH, salinity, total organic carbon (TOC), clay mineral concentration (Kaolinite, Illite, Montmorrillonite) and the elemental concentrations (Al, Fe, Ti) showed that only three components collectively retained 98% of variation of the original data. The first component carries maximum co‐variance with salinity and TOC, the second component is due to clay‐montmorrillonite, and the third component is attributed to TOC and Fe. The first component accounted for 69%, the second 28% and the third for 3% of total variation. The impact of TOC on the stability of pesticide, DDVP is much more pronounced by its negative covariance with the half life period as revealed by the first principal component.     

Effect of Polysaccharides on the Properties of the Mucoadhesive Poly(Vinyl Alcohol) Multicore–Shell Microparticles

This study discusses about the effect of polysaccharides (agar, gum tragacanth, and guar gum) on the properties of the core (organogel)–shell [poly(vinyl alcohol)] microparticles. The size, swelling, and mucoadhesive properties of the poly(vinyl alcohol) microparticles were altered in the presence of the polysaccharides. Thermal analysis confirmed the presence of organogels within the microparticles. Fourier transform infrared spectroscopy confirmed the presence of the polysaccharides within the microparticles. The microparticles were biocompatible in nature. Drug release indicated that an alteration in the shell composition can be used for altering drug release. Ciprofloxacin-loaded microparticles showed sufficient antimicrobial efficiency.