Band 4, Heft 3

The tungsten trioxide (WO 3 ) is a promising material with important technologic and scientific applications, due to its electrochromic, gasochromic and photochromic properties. Usually, this material is synthesized following several routes, for example, sputtering, chemical deposition, sol-gel, hydrothermal, among others. However, these methods are complicated, have long processing times and use several chemicals with the possibility of keeping undesirable impurities. In this context, concentrated solar energy is an interesting and feasible option to process materials at a low cost and without greenhouse gas emissions. In this work, a simple and green synthesis method of WO 3 by using the Solar Furnace of the Renewable Energy Institute of the National University of Mexico is presented. Tungsten oxide powder is obtained by means of tungsten electrodes in a high-temperature solar reaction chamber designed to work with concentrated solar energy under controlled conditions of the gas atmosphere. The oxidation reaction was carried out for three different temperatures: 600°C, 800°C and 1000°C, and for each temperature three different oxygen molar fractions were studied: 0.33, 0.41 and 1. Some results indicate the oxygen molar fraction does not affect the phase transformation and the WO 3 triclinic was the most stable phase, appearing in all the temperature ranges and concentrations. The synthesis reported in this paper is presented as a green alternative in the development of processes for the synthesis of WO 3 , which promote renewable energy sources with very low greenhouse gas emissions and without toxic residuals.

In the present study, we reported the feasibility of the Sesbania sesban L. as a biosorbent to remove Pb(II) from aqueous solutions. The ability of S. sesban L. to adsorb Pb(II) was investigated by using batch adsorption procedure. Such effects as pH, contact time, adsorbate concentration, and biosorbent dosage on the adsorption capacity were studied. The experimental data were analyzed using various adsorption kinetic models, namely, pseudo-first-order model, the pseudo-second-order model, Batacharia-Venkobachar, the Elovich equation, the intraparticle diffusion model, and Bangham equation. Results show that the pseudo-second-order equation provides the best correlation for the biosorption process. To determine the best fit isotherm, the experimental equilibrium data were analyzed using two-parameter (Langmuir, Freundlich, Dubinin-Radushkevich, and Tempkin) and three-parameter isotherms (Redlich-Peterson, Sips, Khan, and Toth). The examination of error analysis methods showed that the Langmuir isotherm model and Redlich-Peterson models provide the best fit for experimental data than other isotherms. Sebania sesban L. is found to be inexpensive and effective adsorbent for removal of Pb(II) from aqueous solutions.

Methacrylated lignin model compounds (LMCs, i.e., eugenol and guaiacol) monomers are ideal candidates as styrene replacements because they have low volatilities and can free-radically polymerize with vinyl ester resins. This article reports the synthesis of methacrylated eugenol (ME), methacrylated guaiacol (MG) using LMCs and methacrylic anhydride in the presence of 4-dimethylaminopyridine (DMAP) as a catalyst. ME and MG were characterized using FT-IR, 1 H-NMR and 13 C-NMR. The thermal and mechanical properties of the samples prepared at 30°C from o-cresol epoxy based vinyl ester resin (VEOCN) using MG and ME, respectively, as reactive monomers, in the presence of benzoyl peroxide (2 phr) as initiator were further investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA/DTG/DTA) and universal testing machine (UTM). Chemical and corrosion resistance of cured VEOCN samples coated on steel panels were also evaluated as a function of percentage weight loss and with the help of scanning electron microscopy (SEM), upon immersing the VEOCN samples in 1 m HCl, 1 m NaOH and 1 m NaCl solutions for 90 days. Thermal, mechanical and chemical performance of VEOCN using ME and MG was also compared with VEOCN samples containing styrene and methyl methacrylate (MMA) as reactive monomers.

Microwave heating chemical vapor deposition (CVD) is used to deposit titanium diboride (TiB 2 ) films on graphite substrate using a gas mixture of TiCl 4 , BCl 3 , H 2 and Ar. The influences of microwave power and the growth rate of TiB 2 are studied by using X-ray diffraction, field emission scanning electron microscopy (FESEM) and energy dispersive spectrometer (EDS). In the range of experimental conditions, the TiB 2 film’s micro-hardness evaluated by using a computer controlled micro-hardness tester increases with increasing deposition temperature and microwave power. The grain size and the growth rate of TiB 2 film are also improved with increasing microwave power at a fixed gas flow ratio of TiCl 4 and BCl 3 , and the bulk TiB 2 is obtained at a higher hardness.

Multi-walled carbon nanotubes (MWCNTs) and their oxidized derivatives were used as adsorbents for the removal of methylene blue dye from aqueous solution. CNTs have consistent surface and distinct structure, thus they were selected as the novel adsorbents in this study. The site-energy distribution analysis could provide significant information for adsorption mechanisms. Therefore, this study concentrated on the site-sorption energy distribution analysis in combination with thermodynamic behavior of methylene blue adsorption on CNTs. The single point adsorption coefficient K d was in order of MWCNTs-Ox>MWCNTs following the temperature 308 K>298 K. Surface area could not be the only single factor for methylene blue adsorption on CNTs, which suggested that morphology of CNTs, π-π electron donor-acceptor, electrostatic interaction and functional groups were also contributing factors. Thus, these all of interactions may drive the methylene blue adsorption. The thermodynamic parameters showed that the adsorption mechanism is spontaneous and exothermic. The site-energy distribution suggested that higher energy active sites would be engaged first, and consequently, the methylene blue molecules adsorb on the comparatively lower energy active sites of CNTs.

In this study, the effect of ammonium citrate (AC) on the leaching of low grade zinc oxide ore in the 5 m ammonia solution was studied. AC served as a leaching agent and complexing agent, respectively. The results of the leaching experiments showed that AC increased the leaching rate of zinc, which increased with the rise of the concentration of AC. Under conditions of temperature of 30°C, reaction time of 60 min, citric acid concentration of 1 mol/l and solid to liquid ratio of 1:5, 88.83% of zinc was leached. The enhancement mechanism of AC to the leaching rate of zinc was studied by Fourier transform infrared (FT-IR) spectra.

The exposure of living organisms to metals can generate reactive oxygen species and failure in their antioxidant defences, triggering oxidative stress and oxidative damage. Despite the intensive use of engineered nanoparticles in numerous consumer and industrial products, data on their potential hazards in eukaryotic cells and their dependence on environmental factors such as temperature are still scarce. The aim of this study was to evaluate the antioxidant response of Saccharomyces cerevisiae , grown in presence of glycerol and glucose, to 5 μg/ml titanium dioxide nanoparticles (size<100 nm) under heat shock conditions. The results showed that biomass, levels of reactive oxygen species and glutathione reductase activity in respiratory/fermentative cells were higher than those detected in respiratory cells. Furthermore, respiratory/fermentative cells exhibited lower levels of glutathione, malondialdehyde, cytoplasmic catalase and glutathione peroxidase than those detected in the respiratory yeast. Saccharomyces cerevisiae grown in the presence of glycerol, glucose and titanium dioxide nanoparticles, under heat shock conditions, caused oxidative stress, due to a decrease in antioxidant defences such as superoxide dismutases or a slowdown of the glutathione cycle, relative to cells grown in presence of glycerol and glucose.

The synthesis of nanoparticles (NP) is in the spotlight of modern nanotechnology. In recent years, the development of competent green chemistry methods for the synthesis of metal NPs has become the main focus of research. The biological synthesis of NPs using plant extract is currently under exploitation. For the first time, in this paper, we report the green synthesis of silver nanoparticles (AgNPs) by reduction of silver nitrate, using fruit extracts of Momordica charantia Linn (bitter melon), a commonly found plant in southeast Asia. The reaction process for the synthesis of AgNPs is simple, cost-effective, novel, rapid and an eco-friendly route using the fruit extracts of M. charantia plant, which acts simultaneously as a reducing and stabilizing agent at room temperature. The formation of the AgNPs was confirmed by surface Plasmon spectra using UV-Vis spectrophotometer and an absorbance peak at 440 nm. To optimize the biosynthesis of AgNPs, the effect of the process variables such as contact time, silver ion concentration and fruit extract quantity were also investigated. The prepared NPs properties were characterized by UV-Vis spectrophotometer, Fourier transformed infrared (FTIR) spectroscopy, and TEM analysis.

An efficient, sustainable, and continuous method for the preparation of graphene supported palladium nanoparticles (Pd/G) has been developed using microwave irradiation as a heating source for the metal deposition process. The Pd/G produced from this method was effective in Suzuki-Miyaura cross-coupling reactions with a broad range of substrates. When incorporated into a packed bed flow reactor, this ligand free catalyst system continued to demonstrate high reaction conversions with limited catalyst leaching in the reaction mixture (347 ppb palladium).