Experimental study of the spontaneous thermal homopolymerization of methyl and n‐butyl acrylate

This article presents an experimental study of the spontaneous thermal homopolymerization of methyl acrylate (MA) and n‐butyl acrylate (nBA) in the absence of any known added initiators at 120 and 140°C in a batch reactor. The effects of the solvent type, oxygen level, and reaction temperature on the monomer conversion and polymer average molecular weights were investigated. Three solvents, dimethyl sulfoxide (DMSO; polar, aprotic), cyclohexanone (polar, aprotic), and xylene (nonpolar) were used. The spontaneous thermal polymerization of MA and nBA in DMSO resulted in a lower conversion and higher average molecular weights in comparison to polymerization in cyclohexanone and xylene under the same conditions. The highest final conversion of both monomers was obtained in cyclohexanone. The high polymerization rate in cyclohexanone was most likely due to an additional initiation mechanism where cyclohexanone complexed with the monomer to generate free radicals. Bubbling air through the mixture led to a higher monomer conversion during the early stage of the polymerization and a lower polymer average molecular weight in xylene and cyclohexanone; this indicated the existence of a distinct behavior between the air‐ and nitrogen‐purged systems. Matrix‐assisted laser desorption/ionization time‐of‐flight analysis of the polymer samples taken from nitrogen‐bubbled batches did not reveal fragments from initiating impurities. On the basis of the identified families of peaks, monomer self‐initiation is suggested as the principal mode of initiation in the spontaneous thermal polymerization of MA and nBA at temperatures above 100°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of cake deposition on various parts of the surface of microfiltration membrane due to fouling

The accumulation of deposited layer on membrane surface in cross-flow microfiltration was investigated. This study provides a basis for elucidation of the membrane segments with superior tendency for cake deposition due to fouling. A commercially available GVWP membrane was fouled with a colored (blue indigo suspension in water) feed. The deposition pattern or fouling tendency was obtained using a digital camera, scanning electron microscope (SEM) and image analysis. The effects of feed concentration, transmembrane pressure and cross-flow velocity on cake deposition were investigated. In the early stages of the filtration trials, cake deposition was increased from the commencement portion (feed inlet) towards the furthermost part (concentrate outlet) of the membrane surface. However, at the completion of filtration, no pronounced difference was realized between cake deposition in the median and end parts of the membrane. Computational fluid dynamics (CFD) modeling of the membrane was carried out to predict the fouling behavior in various segments of the membrane at different operating conditions. The results of CFD modeling are in acceptable agreement with the experimental data. Accomplishment of the membrane sections with higher tendency for accumulation of foulants may provide a basis for manipulation of conditions to diminish the buildup of fouling deposition in the proposed segments. This results in lower cake deposition on vital parts to minimize the overall fouling.     

PVC membrane and coated graphite potentiometric sensors based on 1-phenyl-3-pyridin-2-yl-thiourea for selective determination of iron(III)

The construction and performance characteristics of PVC membrane (PME) and coated graphite (CGE) Fe³⁺ ion selective electrodes based on 1-phenyl-3-pyridin-2-yl-thiourea (PPT) are described. The electrodes exhibit a Nernstian slope of 20.2 ± 0.8 (CGE) and 19.9 ± 0.4 (PME) mV decade⁻¹ of activity in Fe³⁺ ion over a wide concentration range from 3.0 × 10⁻⁷ to 1.0 × 10⁻² M for CGE and 6.9 × 10⁻⁷ to 1.0 × 10⁻² M Fe³⁺ for PME. The lower detection limits by CGE and PME are 2.0 × 10⁻⁷ and 3.9 × 10⁻⁷ M, respectively, in the pH range of 1.8-5.6 for PME and 1.8-5.8 for CGE with a fast response time (<10 s). The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the PME. The PME showed the working temperature range of 22-55 °C with isothermal temperature coefficient of 1.33 × 10⁻³ V/°C and it was also used in non-aqueous solvents. The electrodes were successfully applied to determine iron(III) in water samples.     

Fast and clean functionalization of carbon nanotubes by dielectric barrier discharge plasma in air compared to acid treatment

Multi-walled carbon nanotubes (MWCNTs) have been functionalized by a dielectric barrier discharge plasma in air and compared to those functionalized in HNO₃. The MWCNTs were prepared by chemical vapor deposition of xylene using ferrocene as a catalyst at 850 °C. Air oxidation followed by acid treatment was used to purify the MWCNTs, which were then annealed in helium. The MWCNTs were functionalized in air in a plasma reactor at room temperature. Quantitative analyses of gases evolved during the temperature programmed desorption of the functionalized nanotubes were carried out using Fourier transform infrared spectroscopy and gas chromatography. The influence of plasma parameters, including power in the range of 8-90 W and treatment time in the range of 1-9 min, on the number of the functional groups was investigated. It is shown that the extent of functionalization increases with increasing discharge power, provided that the exposure time of the MWCNTs in the plasma atmosphere does not exceed a certain period of time. Compared to acid treatment, plasma functionalization offers the advantages of much shorter treatment time, and produces less damage.     

Synthesis and characterization of Pb<Subscript>2</Subscript>SiO<Subscript>4</Subscript> nanostructure: study of photo-catalytic behavior of reactive Red198 and reactive Orange16 dyes as pollutants

Pure Pb₂SiO₄ nanostructures were fabricated using amines as alkaline agents by sol–gel method and characterized via X-ray powder diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS). The average crystallite size of the products in presence and absence of the alkaline agent in the reaction was calculated about 18 and 34 nm by XRD technique, respectively. The type of alkaline agent was evaluated to achieve the optimized nanostructure. The results showed that the ethylenediamine as an alkaline agent has a better performance than the other alkaline agents (ammonia, triethylenetetramine, and tetraethylenepentamine). Optical property of optimized nanostructure was studied by diffuse reflectance spectroscopy (DRS) and its band gap was estimated to about 3.3 eV. It is the first time that photo-catalytic behavior of Pb₂SiO₄ nanostructure was investigated. The photo-catalytic performance of optimized Pb₂SiO₄ nanostructure was evaluated in the presence of various concentrations of Reactive Red198 and Reactive Orange16 dyes. The degradation percentage of dyes in various concentrations (5, 7, and 9 ppm) was obtained for Reactive Red198 and Reactive Orange16 about 100, 57, and 52% and also 100, 52, and 42% after 75 min ultraviolet irradiation, respectively. At 5 ppm concentration, Reactive Orange16 pollutant destruction was faster than Reactive Red198.     

Green synthesis of Dy2Ce2O7 ceramic nanostructures using juice of Punica granatum and their efficient application as photocatalytic degradation of organic contaminants under visible light

An effective and simple route is developed for production of Dy₂Ce₂O₇ nanostructures by applying juice of Punica granatum as fuel and metal nitrates. Juice of Punica granatum has for the first time been exploited as a new fuel for simple synthesis of various structures of Dy₂Ce₂O₇ in terms of shape, photocatalytic efficiency and particle size at different time and temperature for production. TEM, Raman, DRS, XRD, FESEM and EDS are exploited for study and characterization the obtained nano-sized structures of Dy₂Ce₂O₇. Photocatalytic efficiencies have been evaluated with destruction of erythrosine and methylene blue pollutants under visible illumination over the various structures of Dy₂Ce₂O₇. Results clearly demonstrated that the nano-sized structures of Dy₂Ce₂O₇ obtained by application of juice of Punica granatum as new fuel at 450 °C for 4 h revealed excellent photocatalytic efficiency for the destruction of erythrosine and methylene blue pollutants.     

Effect of copper phthalocyanine (CuPc) on electrochemical hydrogen storage capacity of BaAl2O4/BaCO3 nanoparticles

A green synthesis method, solution combustion, were performed to synthesize BaAl₂O₄/BaCO₃ nanoparticles by using stoichiometric amount of cations, Ba²⁺ and Al³⁺, in rational fraction of a fuel (maltose). Single fuel led to the formation of combustion reaction required further annealing at 700 °C in order to achieve pure crystals. The average crystallite sizes of the BaAl₂O₄/BaCO₃ nanopowders were obtained about 36 nm using modified Scherrer equation. In order to improve the electrochemical hydrogen storage capacity of BaAl₂O₄/BaCO₃ nanoparticles, a novel admixture was designed by introducing copper phthalocyanine (CuPc) into an inorganic phase. The reaction profiles of BaAl₂O₄/BaCO₃-CuPc nanocomposites were confirmed by FTIR analysis. The structural and elemental analysis were confirmed the formation of nanocomposites. Morphological analysis confirmed the nanoscale formation of the host material. In addition, TEM results clearly confirmed the morphology of BaAl₂O₄/BaCO₃ sample and its nanocomposites. The Band gap energy was calculated for host, CuPc and its respective nanocomposites using Tauc method obtained at 4.95, 2.10 and 2.54/4.89 eV, respectively. Electrochemical performances of the materials were confirmed a large I_pa for BaAl₂O₄/BaCO₃-CuPc nanocomposites as compare to the host materials. This was directly reflected in hydrogen storage capacities of the materials (900 mA h/g discharge capacity for BaAl₂O₄/BaCO₃ (～3.17%) and >1500 mA h/g for BaAl₂O₄/BaCO₃-CuPc nanocomposites (～5.3%)).