Photocatalytic degradation of methyl tert‐butyl ether (MTBE) in contaminated water by ZnO nanoparticles

BACKGROUND: Over the past several decades methyl tert‐butyl ether (MTBE) as additive to gasoline, intended to either boost ratings of fuel or to reduce air pollution, has been accepted worldwide. Since MTBE has high water solubility, the occurrence of fuel spills or leaks from underground storage tanks or transferring pipeline has led to the contamination of natural waters. In this study the degradation of aqueous MTBE at relatively high concentrations was investigated by a UV‐visible/ZnO/H₂O₂ photocatalytic process. The effects of important operational parameters such as pH, amount of H₂O₂, catalyst loading and irradiation time were also investigated. Concentration of MTBE and intermediates such as tert‐butyl formate and tert‐butyl alcohol were measured. RESULTS: Time required for complete degradation increased from 20 to 150 min when the initial concentration was increased from 10 to 500 mg L^?1. The first‐order rate constants for degradation of MTBE were estimated to be 0.183–0.022 min^?1 as the concentration increased from 10 to 500 mg L^?1. Study of the overall mineralization monitored by total organic carbon analysis showed that at an initial concentration of 100 mg L^?1 MTBE complete mineralization was obtained after 100 min under UV‐visible/ZnO/H₂O₂ photocatalysis. CONCLUSION: The data presented in this paper clearly indicated that UV‐visible/ZnO/O₂ as an advanced oxidation process provides an efficient treatment alternative for the remediation of MTBE‐contaminated waters. Copyright © 2008 Society of Chemical Industry     

Kinetics of TSCD zinc oxide nano-layer growth by modified diffuse-interface model

Deposition of zinc oxide films from aqueous solutions containing complex Zn²⁺ ions on soda-lime substrates were studied by two-stage chemical deposition (TSCD) process. It was shown that the film thickness can be controlled by the number of dipping stages. Nano-layers were produced with less than nine times dipping stages. Greater dipping numbers resulted in film thickness exceeding 100 nm. The growth rate obeyed double-stage zeroth order with respect to the concentration and first order with respect to the temperature. This rate was proportional to the difference between the temperature of the hot water and the substrate. Overall activation energy of 17.20 ± 0.42 kJ mol⁻¹ and frequency factor of 2.81 ± 0.07 μm s⁻¹ was determined for ZnO deposition. These values were attributed to two resistances. One resistance corresponded with film heat transfer mechanism. The other was attributed to species attachment to the solid substrate. A modification to the diffuse-interface kinetic model was devised for explanation of the latter. EDAX (electron dispersive elemental analysis), XRD (X-ray diffraction) and SEM (scanning electron microscopy) were used to characterize the layer formed. These methods showed that the product consisted solely of pure elliptical ZnO grains.     

Gasification of heavy fuel oils: A thermochemical equilibrium approach

Combustion of heavy fuel oils is a major source of production of particulate emissions and ash, as well as considerable volumes of SO_x and NO_x. Gasification is a technologically advanced and environmentally friendly process of disposing heavy fuel oils by converting them into clean combustible gas products. Thermochemical equilibrium modeling is the basis of an original numerical method implemented in this study to predict the performance of a heavy fuel oil gasifier. The model combines both the chemical and thermodynamic equilibriums of the global gasification reaction in order to predict the final syngas species distribution. Having obtained the composition of the produced syngas, various characteristics of the gasification process can be determined; they include the H₂:CO ratio, process temperature, and heating value of the produced syngas, as well as the cold gas efficiency and carbon conversion efficiency of the process. The influence of the equivalence ratio, oxygen enrichment (the amount of oxygen available in the gasification agent), and pressure on the gasification characteristics is analyzed. The results of simulations are compared with reported experimental measurements through which the numerical model is validated. The detailed investigation performed in the course of this study reveals that the heavy oil gasification is a feasible process that can be utilized to generate a syngas for various industrial applications.     

Morphology enhancement of TiO2/PVP composite nanofibers based on solution viscosity and processing parameters of electrospinning method

In this work, different sol solutions with various titanium tetraisopropoxide (TIP)/glacial acetic acid ratios in 2‐propanol with 5 wt % poly(vinyl pyrrolidone) (PVP) (M_w = 360,000 g/mol) were prepared and electrospun. Composition of the prepared sols and as‐spun TiO₂/PVP nanofibers were determined by Fourier transform infrared and Raman spectroscopy methods. Morphology of the electrospun TiO₂/PVP nanofibers was studied by scanning electron microscopy and transmission electron microscopy (TEM) techniques. Rheometry measurements of the sol solutions showed decrease of viscosity upon the addition of TIP to the polymer solutions with constant polymer and acid concentrations. The sol solution having the lowest viscosity (at shear rate 10 s^?1) but the highest TIP/glacial acetic acid ratio showed beaded nanofibers morphology when electrospun under 10 and 12 kV applied voltage while injection rate, needle tip to collector distance, and needle gauge were kept constant. However, smooth electrospun TiO₂/PVP composite nanofibers with the average nanofibers diameters (148 ± 79 nm) were achieved under the same condition when applied voltage increased to 15 kV. TEM micrographs of the electrospun TiO₂/PVP nanofiber showed that the TiO₂ particles with continuous structure are formed at the middle of the nanofiber and distributed along its axis. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46337.     

A review on 3D micro-additive manufacturing technologies

New microproducts need the utilization of a diversity of materials and have complicated three-dimensional (3D) microstructures with high aspect ratios. To date, many micromanufacturing processes have been developed but specific class of such processes are applicable for fabrication of functional and true 3D microcomponents/assemblies. The aptitude to process a broad range of materials and the ability to fabricate functional and geometrically complicated 3D microstructures provides the additive manufacturing (AM) processes some profits over traditional methods, such as lithography-based or micromachining approaches investigated widely in the past. In this paper, 3D micro-AM processes have been classified into three main groups, including scalable micro-AM systems, 3D direct writing, and hybrid processes, and the key processes have been reviewed comprehensively. Principle and recent progress of each 3D micro-AM process has been described, and the advantages and disadvantages of each process have been presented.     

Energy efficiency optimization of one-way and two-way DF relaying considering circuit power

In this paper, the energy efficiency (EE) of a decode and forward (DF) relay system is studied, where two sources communicate through a half-duplex relay node in one-way and two-way relaying strategies. Both the circuitry power and the transmission power of all nodes are taken into consideration. In addition, three different coding schemes for two-way DF relaying strategy with two phases and two-way DF relaying with three phases are considered. The aim is to maximize the EE of the system for a constant spectral efficiency (SE). For this purpose, the transmission time and the transmission power of each node are optimized. Simulations are used to compare the EE–SE curve of different DF strategies with one-way and two-way amplify and forward (AF) strategies and direct transmission (DT), to find the best energy efficient strategy in different SE conditions. Analytical and simulation results demonstrate that in low SE conditions, DF relaying strategies are more energy efficient compared to that of AF strategies and DT. However, in high SE conditions, the EE of two-way AF relaying and DT strategy outperform some of the DF relaying strategies. In simulations, the impact of different circuitry power and different channel conditions on the EE–SE curves are also investigated.     

Effect of simultaneous chemical substitution of A and B sites on the electronic structure of BiFeO3 films grown on BaTiO3/SiO2/Si substrate

Electrical properties and electronic structure of Bi_1?xCa_xFe_1?yMn_yO_3?δ grown by pulsed-laser deposition on BaTiO₃/SiO₂/Si substrate were investigated. Results showed that Ca has drastic effect on symmetry of crystal and electrical poperties of BiFeO₃. On the other hand, Mn revealed to have more radical effect on optical properties and energy gap of the compound. XPS results represented that although Ca tend to decrease Fe valence state, Mn tends to stabilize it at 3+ (at least in this concentrations). UV–visible study yielded bandgap of 2.51–2.81 eV (at 300 K) for different concentrations of Ca and Mn. UV–visible spectra also revealed sub-bandgap defect transitions at 2.2 and 2.4 eV. Slave-particle approach has also been applied to elucidate nature of the metal–insulator transition.