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1.
A sensitive and rapid method for the determination of trace levels of titanium in polyolefin polymers using square wave voltammetry is discussed. It involves ashing, acid digestion of polymer samples and determination of titanium(IV) by catalytic reduction using square wave voltammetric (SWV) technique. A well defined peak of titanium(IV) in Britton-Robinson buffer solution containing EDTA and KBrO(3) is observed in the potential range of -0.10 to -0.40 vs. Ag/AgCl. Calibration graphs were linear in the range 0.05-0.25 microg/ml for titanium. Effects of pH and concentration of bromate, EDTA and buffer constituents are studied for the optimization of experimental conditions. Interference from other concomitants present in the polymer matrix are studied. Low density polyethylene (LDPE) obtained by tubular process was used for preparing the synthetic standards in order to optimize the experimental conditions and good recoveries (99-101%) were obtained. The method was extended to different polyolefin samples and the results obtained for the titanium content compared with those obtained by UV/Vis spectrophotometry. Statistical evaluation showed no significant bias between the two methods. SWV is found suitable for the estimation of Ti in the range 1-50 microg/g in polyolefin polymers with a RSD < 2.0%. 相似文献
2.
David M. Koshy Dr. Shucheng Chen Dr. Dong Un Lee Dr. Michaela Burke Stevens Ahmed M. Abdellah Samuel M. Dull Gan Chen Dr. Dennis Nordlund Dr. Alessandro Gallo Dr. Christopher Hahn Dr. Drew C. Higgins Dr. Zhenan Bao Dr. Thomas F. Jaramillo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(10):4072-4079
Ni,N-doped carbon catalysts have shown promising catalytic performance for CO2 electroreduction (CO2R) to CO; this activity has often been attributed to the presence of nitrogen-coordinated, single Ni atom active sites. However, experimentally confirming Ni−N bonding and correlating CO2 reduction (CO2R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile-derived Ni,N-doped carbon electrocatalysts (Ni-PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO2R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X-ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square-planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts. 相似文献
3.
David M. Koshy Shucheng Chen Dong Un Lee Michaela Burke Stevens Ahmed M. Abdellah Samuel M. Dull Gan Chen Dennis Nordlund Alessandro Gallo Christopher Hahn Drew C. Higgins Zhenan Bao Thomas F. Jaramillo 《Angewandte Chemie (International ed. in English)》2020,59(10):4043-4050
Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO2 electroreduction (CO2R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO2 reduction (CO2R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO2R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts. 相似文献
4.
Nanosized zinc oxide has been synthesized through a novel single step solution combustion route using citric acid as fuel. The X-ray diffraction (XRD) analysis revealed that the synthesized ZnO nanopowder has the pure wurtzite structure. The phase purity of the nanopowder has been confirmed using differential thermal analysis (DTA), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). The morphology and crystalline size of the as-prepared nanopowder characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the powder consisted of a mixture of nanoparticles and nanorods. The nanocrystalline ZnO could be sintered to ∼97% of the theoretical density at 1200 °C in 4 h. The dielectric constant (εr) and dielectric loss (εi) of sintered ZnO pellets at 5 MHz were 1.38 and 9×10−2, respectively, at room temperature. 相似文献
5.
N. Venugopalan Pillai R. Vinodkumar V. Ganesan Peter Koshy V. P. Mahadevan Pillai 《Pramana》2010,75(6):1157-1161
BaWO4 doped with ZnO (2, 3, 5, 7 and 10 wt%) nanostructured films are prepared on quartz substrates by pulsed laser ablation. The
films are post annealed at 900°C. GIXRD analysis of the post-annealed films reveal the change of orientation of scheelite
tetragonal crystal growth from 1 1 2 reflection plane to 0 0 4 planes when doping concentration is more than 3 wt%. The AFM
images show that film with 7 wt% ZnO doping concentration has good ceramic pattern with surface features giving a minimum
value of rms surface roughness suitable for optoelectronic device applications. The optical transmittance and band-gap energy
of the films are found to decrease considerably on postannealing which can be due to the increase in grain size of the crystallites
on annealing. Thus doping with ZnO improves the surface features of the films and increases the optical band-gap energy. 相似文献
6.
Dr. Zhao Liu Prof. Dr. Charles C. Sorrell Dr. Pramod Koshy Dr. Judy N. Hart 《Chemphyschem》2019,20(16):2074-2081
Methanol decomposition is a promising method for hydrogen production. However, the performance of current catalysts for this process is not sufficient for commercial applications. In this work, methanol adsorption on the CeO2 low-index surfaces is studied by density functional theory (DFT). The results show that methanol always dissociates spontaneously on the (100) surface, whereas dissociation on the (110) surface is site-selective; dissociation does not occur at all on the (111) surface, where only weak physisorption is found. The results confirm that surfaces with higher energies are more catalytically active. Analysis of the surface geometries shows that the dominant factors for the dissociation of methanol are the degree of undercoordination and the charges of the surface ions. The adsorption energy of each methanol molecule decreases with increasing coverage and there is a transition threshold between dissociative and associative adsorption. The present work indicates that a strategy to design catalysts with high activity is to maximize exposure of surfaces on which the ions have a high degree of undercoordination and a strong tendency to donate/accept electrons. The results demonstrate the importance of appropriately selecting and controlling exposed facets and particle morphology for optimizing catalyst performance. 相似文献
7.
Mariyam Thomas M. Deepa M.R. Chandran Peter Koshy 《Journal of solid state chemistry》2009,182(1):203-4002
We report the photoluminescence properties of a novel powellite-based red-emitting phosphor material: CaLa1−xNbMoO8:xEu3+ (0.01, 0.03, 0.05, 0.1) for the first time. The photoluminescence investigations indicated that CaLa1−xNbMoO8:xEu3+ emits strong red light at 615 nm originating from 5D0→7F2 (electric dipole transition) under excitation either into the 5L0 state with 394 nm or the 5D2 state with 464 nm, that correspond to the two popular emission lines from near-UV and blue LED chips, respectively. When compared with emission intensity from a CaMoO4:Eu3+, the emission from CaLaNbMoO8:Eu3+ showed greater intensity values under the same excitation wavelength (394 nm). The enhanced red emission is attributed to the enhanced f-f absorption of Eu3+. These materials could be promising red phosphors for use in generating white light in phosphor-converted white light emitting diodes (WLEDs). 相似文献
8.
Nakaruk A. Lin C. Y. W. Channei D. Koshy P. Sorrell C. C. 《Journal of Sol-Gel Science and Technology》2012,61(1):175-178
Thin films of TiO2 doped with Fe and Mn were deposited on F-doped SnO2-coated glass by spin coating. Dopant concentrations of 3–7 wt% (metal basis) were used. The structural, chemical, and optical
characteristics of the films were investigated. Laser Raman microspectroscopy and glancing angle X-ray diffraction data showed
that the films consisted of the anatase polymorph of TiO2. X-ray photoelectron spectroscopy data indicated the presence of Fe3+, Mn4+, and Mn3+ in the doped films, as predicted by calculated thermodynamic stability diagrams, and the occurrence of atomic disorder and
associated structural distortion. Ultraviolet–visible spectrophotometry data showed that the optical indirect band gap of
the films decreased significantly with increasing dopant levels, from 3.36 eV (undoped) to 2.95 eV (7 wt% Fe) and 2.90 eV
(7 wt% Mn). These improvements are attributed to single (Fe) or multiple (Mn) shallow electron/hole trapping sites associated
with the dopant ions. 相似文献
9.
The nonionic surfactants Triton X 100 and Triton X 114 form isotropic micellar solutions around 25°C. One of the characteristic features of these solutions is the fact that at higher temperatures they undergo clouding and liquid-liquid phase separation. Addition of various additives to the surfactant solutions does change the temperature at which the clouding phenomenon occurs. In this paper such effect of additives on the clouding phenomenon of Triton X 100 and Triton X 114 are discussed. 相似文献
10.
Preeti G. Joshi Kunju Joshi Sudha Mishra Nanda B. Joshi 《Photochemistry and photobiology》1994,60(3):246-248
Abstract The plasma membrane has been implicated as a critical target of photodynamic action on cells. We have observed that the photosensitization of human cerebral glioma (U-87 MG) cells by hematoporphyrin derivative (HpD) causes a large increase in intracellular calcium [Ca2+ ]. This increase in [Ca2+ ]i was solely due to the influx of extracellular Ca2+ through the plasma membrane and showed a dependence on HpD concentration, light dose and concentration of calcium in the extracellular medium. The magnitude of the Ca2+ influx decreased with increasing postirradiation time, which suggests that the cell membrane partially recovers from the photodynamic injury. The photoinduced Ca2+ influx was inhibited by the Ca2+ channel blocker diltiazem and the reducing agent dithioerythritol. These findings are discussed in terms of possible activation of a Ca2+ channel as a result of photosensitization. 相似文献