Impact of hydrogen concentrations on the impedance spectroscopic behavior of Pd-sensitized ZnO nanorods

ZnO nanorods were synthesized using a low-cost sol-gel spin coating technique. The synthesized nanorods were consisted of hexagonal phase having c-axis orientation. SEM images reflected perpendicular ZnO nanorods forming bridging network in some areas. The impact of different hydrogen concentrations on the Pd-sensitized ZnO nanorods was investigated using an impedance spectroscopy (IS). The grain boundary resistance (R_gb) significantly contributed to the sensing properties of hydrogen gas. The boundary resistance was decreased from 11.95 to 3.765 kΩ when the hydrogen concentration was increased from 40 to 360 ppm. IS gain curve showed a gain of 6.5 for 360 ppm of hydrogen at room temperature. Nyquist plot showed reduction in real part of impedance at low frequencies on exposure to different concentrations of hydrogen. Circuit equivalency was investigated by placing capacitors and resistors to identify the conduction mechanism according to complex impedance Nyquist plot. Variations in nanorod resistance and capacitance in response to the introduction of various concentrations of hydrogen gas were obtained from the alternating current impedance spectra.     

Mild hydrocracking of 1-methyl naphthalene (1-MN) over alumina modified zeolite

The catalytic activity and life of the NiMoS supported on alumina–USY zeolite (physical mixture of alumina and USY (NMAZ), USY zeolite coated with alumina (NMACZ-2)) were compared in the hydrocracking of 1-methyl naphthalene by a single run at the several reaction temperatures between 360 and 400 °C as well as repeated runs at 360 °C. The relative activity of NMAZ is slightly higher after 1 h at all reaction temperatures, but was lower after 2 h at reaction temperatures above 380 °C. The preference of NMACZ-2 became distinct and definite by further increasing the reaction time at all reaction temperatures. Too long reaction time, particularly at higher reaction temperature, decreased the yield of (alkyl)benzenes, indicating the significant progress of the successive reactions. Thus, the highest yield of alkyl(benzenes) of about 97% was obtained over NMACZ-2 after 4 h at 380–390 °C. This was much less than the yield of about 82% obtained over NMAZ after 4 h at 370 °C. Ten repeated runs at 360 °C for 6 h resulted in marked decrease of yield over NMAZ from 73% to 64%, while the decrease in yield over NMACZ-2 was only from about 80% to 78%. The decrease of catalytic activity appears to reflect the coke formation on the USY which occurs on the naked acidic site of the substrate, which are rather isolated from the NiMoS on alumina. In contrast, alumina-coated support keeps USY underneath the alumina, which carries NiMoS and acidic sites on the same surface. The acidity of surface alumina is moderated by the underneath USY. The adequate acidity of the neighboring NiMoS and high hydrogenation activity provide a good balance resulting in an excellent catalytic activity and life of NiMoS supported on alumina-coated USY zeolite.     

Polymerization behavior of methylol-functional benzoxazine monomer

This study focuses on methylol functional benzoxazines as precursors to build a network structure utilizing both benzoxazine and resole chemistry. The first part is a review of systems that contain methylol groups which play a role on their crosslinking formation. The polymerization mechanism and properties of resoles will be highlighted as the most abundant polymers that are characterized by polymerization through condensation reaction of methylol group. In the second part, the effect of incorporating methylol group into benzoxazine monomers is studied. Differential scanning calorimetry (DSC) is used to study the effect of methylol group on the rate of polymerization. Kissinger and Ozawa methods using non-isothermal DSC at different heating rates show that methylol monomer exhibits lower average activation energy compared to the un-functionalized monomer. The effect of adding catalysts into the monomers is also studied. p-Toluene sulfonic acid (PTSA) is found to be more efficient than 1-methyl-imidazole (IMD) and lithium iodide (LiI) in the case of methylol monomer due to its ability of accelerating both the methylol condensation and ring-opening polymerization. Additionally, thermal behavior of the monomers is studied using thermogravimetric analysis (TGA).     

Graphene modified Nd/TiO2 photocatalyst for methyl orange degradation under visible light irradiation

A novel nanoscale GR–Nd/TiO₂ composite photocatalyst was synthesized by the hydrothermal method. Its crystal structure, surface morphology, chemical composition and optical properties were studied using XRD, TEM, and XPS, DRS and PL spectroscopy. It was found that graphene and neodymium modification shifts the absorption edge of TiO₂ to visible-light region. The results of photoluminescence (PL) emission spectra show that GR–Nd/TiO₂ composites possess better charge separation capability than do Nd/TiO₂ and pure TiO₂. The photocatalytic activity of prepared samples was investigated by degradation of methyl orange (MO) dye under visible light irradiation. The results show that the GR–Nd/TiO₂ composite can effectively photodegrade MO, showing an impressive photocatalytic activity enhancement over that of pure TiO₂. The enhanced photocatalytic activity of the composite catalyst might be attributed to the large adsorptivity of dyes, extended light absorption range and efficient charge separation due to Nd doping and graphene incorporation.     

Lipid‐derived monomer and corresponding bio‐based nanocomposites

Fatty acid based monomer and corresponding hybrid polymer layered silicate nanocomposites have successfully been prepared by using in situ polymerizations. The hybrid materials were prepared by adding different ratios of nanoclay during free radical homopolymerization of 2‐(acryloyloxy)ethyl stearate (AOES) monomer and copolymerization of AOES with styrene. AOES monomer was synthesized by treating stearic acid with 2‐hydroxyethyl acrylate. The formation of AOES monomer, homopolymer and copolymer was confirmed by ¹H NMR spectroscopic analysis. Further analysis and characterization of the nanocomposites were carried out by XRD, transmission electron microscopy, AFM and attenuated total reflectance Fourier transform infrared spectroscopy. TGA of the polymer nanocomposites was also carried out to evaluate their thermal stability, while flammability tests were conducted to investigate the effect of layered silicate on flame retardancy. Nanofiller addition into the polymer matrix substantially improved the thermal properties and fire retardancy of the composites. © 2016 Society of Chemical Industry     

Removal of toxic aqueous ions using amorphous AlPO4

Aluminium phosphate (AlPO₄) was characterized using X-ray diffractometry (XRD), Fourier Transform infrared (FTIR), point of zero charge (PZC) and dissolution studies. XRD showed the sample to be amorphous, FTIR confirmed the presence of OH groups on the surface and PZC was determined at pH 3.45. The dissolution study illustrated a decrease in dissolution with an increase in the pH. Potentiometric titration data were fit to the Gaines–Thomas equation, which showed that AlPO₄ is a weakly acidic ion exchanger. Sorption studies were carried out at pH 4–6 and temperatures 293–323 K. The uptake of metal ions was observed to increase with an increase in the pH and temperature. The surface selectivity towards metal ions was found in the order Pb²⁺> Cu²⁺> Cd²⁺. Sorption data were fit to the new equation derived from the proposed mechanism for metal ion uptake. Various parameters such as stoichiometry of the surface H⁺ ion release, equilibrium constant, standard enthalpy, entropy and free energy changes were evaluated from the plots. The values of all these parameters were found to be closely related to the values reported in the literature.     

Comparative Study on Microstructures of Zincalume Steel (G550) Welded Joint Between Metal Inert Gas and Laser Beam Welding

Zincalume steel (G550) is commonly used in various construction fields because of its high corrosion resistance and good mechanical properties. In recent years, a number of steel companies have massively produced zincalume steel (G550) with large volumes of waste. For the reduction of massive industrial wastes, the zincalume steel (G550) was welded in the lap joint configuration using different welding parameters in the metal inert gas (MIG) welding and laser beam welding (LBW) process in this study. The MIG welding and LBW are more welcomed welding methods due to their high efficiency and low cost. However, they are different as the LBW offers welding speed three to five times faster than MIG welding, while LBW’s heat transfer to workpieces is much less than MIG welding, which can avoid some distortions. The microstructure of zincalume steel (G550) was investigated using scanning electron microscopy (SEM) and the microstructure characterizations of welded specimens were analyzed. The experiment found the columnar dendrites extended under the heat flow direction during the MIG welding and LBW process. Thus, the columnar grains were formed in between the equiaxed zone and fusion zone (FZ) at high heat input and slow cooling rate. Moreover, the grain size of FZ was comparatively smaller than heat affected zone (HAZ) and base metal (BM).     

Reactive supercritical fluid extrusion for development of moisture resistant starch‐based foams

The main objective of this work was to reduce barriers that prevent the usage of starch‐based foams by understanding the effect and the sequence of dual‐modification of crosslinked (XL) and acetylated (Ac) starch in one continuous supercritical fluid reactive extrusion (SCFX) process on wetting properties, physicochemical properties, and cellular structure of solid foam. The starch was reacted with epichlorohydrin (EPI) and acetic anhydride (Ac) under alkaline conditions in a twin‐screw extruder in the presence of supercritical carbon dioxide (SC‐CO₂). An increase in EPI concentration from 0.00 to 3.00% increased the degree of crosslinking as measured by DSC and confirmed by the quantification of the glucose units in the solution after acid hydrolysis. We observed a reduction of the glucose units from 93.07% for 0.00% EPI to 6.73% when 3.00% EPI was added. With crosslinking/acetylation processing, contact angle was higher for modified starches, indicating that chemical treatments induced dramatic changes in their surface polarity. Compared with native, the contact angle for dual modified starch increased from 43.1° to 91.7° which indicated their lower wettability. The addition of SC‐CO₂, EPI, and Ac to the formulation reduced the density of the extrudates and increased the expansion ratio. The average cell size in the extrudate determined by scanning electron microscopy was also found to decrease from 150 to 34 μm by the addition of the two reagents. Moreover, the dual‐modification of starches provided more hardness and adhesiveness to the extrudates than was observed for the unmodified starches. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011