Agent-free synthesis of graphene oxide/transition metal oxide composites and its application for hydrogen storage

Graphene oxide (GO) wrapped transition metal oxide composite materials were synthesized by a very simple route without any additional agents and the hydrogen adsorption properties of the materials were investigated. The morphologies of GO/V₂O₅ and GO/TiO₂ were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that single- or few-layered GO sheets wrapped throughout the V₂O₅ and TiO₂ particles. According to X-ray photoelectron spectroscopy (XPS), the C–OH species of GO and the surface-adsorbed oxygen of the transition metal oxide bond together via a dehydration reaction. The wrapping phenomenon of GO causes the enhancement of hydrogen storage capacity at liquid nitrogen temperature (77 K) compared with those of the pristine transition metal oxides and GO. The enhancement of hydrogen storage capacity of GO-wrapped transition metal oxide composite materials results from the existence of interspaces between the transition metal oxide particles and the thin GO layers.     

LCA application in the optimum design of high rise steel structures

The Life Cycle Assessment tool is used in the construction industry to assess the environmental impact and the resources that are used throughout the life span of a construction project, which consists of the raw material acquisition, production, design phase, construction phase, operation phase and the demolition and dismantling phase. The global community is taking immediate action to reduce the CO₂ and green house gases (GHG) that are being produced due to global warming. The Kyoto protocol agreement has set binding targets for 37 industrialized countries and the European community to reduce their GHG emissions by an average of 5%, back to 1990 levels, within the years of 2008–2012.The global community is making many efforts to reduce CO₂ and green house gases (GHG). The building construction industry is responsible for approximately 40% of the carbon dioxide emissions. There are currently more than four super tall, more than 100 story, high rise building construction projects in metropolitan Seoul, and this ranks Korea in the top four countries worldwide for the number of high rise buildings. Reducing the amount of structural steel in these high rise buildings by using an optimum structural design would reduce CO₂ and green house gas (GHG) emissions. This aim of this study was to analyze the lateral load resisting structural systems in a high rise steel building in order to select the optimum structural system under the equivalent allowable lateral drift. The environmental impact was assessed using the LCA tool, and the results are discussed along with possible recommendations that may improve the current LCA tools.     

Analysis and estimation of yield strength of API X80 linepipe steel pipe by low-cycle fatigue tests

In the present study, spiral piping was conducted on API X80 linepipe steel, and the outer and inner wall pipe yield strengths were measured. A low-cycle fatigue test was conducted on a leveled X80 steel sheet to simulate piping and flattening processes, and the strain hardening and Bauschinger effects, induced from different strain histories, were evaluated and combined using Swift??s equation and the Bauschinger stress parameter, respectively. By analyzing the stress-strain curves obtained from the low-cycle fatigue test, the yield strengths of the outer and inner walls were estimated to be 592 MPa and 492 MPa, respectively, which are lower by 20?C80 MPa than that of the actual pipe used. Possible reasons for measured and estimated yield strength differences could be the simulation determining procedure of the pre-strain and Bauschinger stress parameters, preposition of same strain hardening behavior depending on strain history, and pre-strain differences depending on thickness location in the steel sheet during piping.     

Optimum residence time analysis for a walking beam type reheating furnace

A 3D unsteady numerical simulation of a reheating furnace was performed to obtain the optimal slab residence time. Too long residence time decrease the efficiency of the reheating furnace, whereas too short residence time cannot satisfy the required heating quality of a slab. The total five cases of residence times – 6032 s, 6496 s, 6960 s, 7424 s and 7888 s – were investigated for the optimum residence time analysis with the two slab requirements, those of emission temperature and uniformity. In this study, the slab emission temperature should be in the range between 1373 K and 1573 K. The skid mark severity of an emitted slab should be lower than 50 K to satisfy the uniformity requirement. The numerical analysis was done for the identical geometry and operating condition of the reheating furnace using FLUENT. Slabs were assumed to move very quickly that it took no time for them to move next positions. The quick movements of slabs were processed with the own developed User-Defined Function program. Among the five cases of residence times, the residence time of 7427 s turned out to be most efficient.     

A photoelectrochemical investigation of the hydrogen-evolving doped TiO2 nanotube arrays electrode

The present work investigates the photoelectrochemical behavior of nanotubular N/C-TiO₂ electrode for hydrogen production. Via the sonoelectrochemical anodization process of 1 h, N-containing TiO₂ based nanotube arrays(N-TNT) with the length of about 650 nm were fabricated in fluoride aqueous solution added 0.25 M NH₄NO₃; C-containing TiO₂ based nanotube arrays(C-TNT) with the length of about 2 μm were prepared in fluoride ethylene glycol solution. In virtue of the longer tubes with the larger surface areas, C-TNT can harvest more light and produce more photoactive sites than N-TNT, which also made the charge transfer resistance in C-TNT larger than that in N-TNT. Considered the more negative flat band potential of C-TNT, C-TNT has the smaller energy barrier and the better photoelectrochemical activity. It may be attributed to the appropriate defect concentration gradient owing to the modification of C element. Under UV-vis light (320-780 nm) irradiation, the average hydrogen generation rate of C-TNT was 282 μL h⁻¹ cm⁻². The surface properties and near-surface properties of the resultant electrode were synthetically analyzed by using UV-vis diffuse reflectance spectra(DRS), field emission scanning electron microscopy (FESEM), I-t curves, and electrochemical impedance spectroscopy (EIS) techniques.     

Effect of side chain position on solar cell performance in cyclopentadithiophene-based copolymers

The photovoltaic properties of a series of low band-gap conjugated copolymers, in which alkyl side chains were substituted at various positions, were investigated using donor-acceptor (D-A) conjugated copolymers consisting of a cyclopentadithiophene derivative and dithienyl-benzothiadiazole. The base polymer, which has no alkyl side chains, yielded promising power conversion efficiency of 3.8%. Polymers with alkyl side chains, however, exhibited significantly decreased performance. In addition, the effects of processing additive became negligible. The results indicate that substituted side chains, which were introduced to improve solubility, critically affected the optical and electronic properties of D-A conjugated copolymers. Furthermore, the position of the side chain was also very important for controlling the morphological properties of the D-A conjugated copolymers.     

Characterisation of the growth of a carbonaceous film on silicon

In this paper we present the first characterisation of growth of a carbonaceous film on a silicon substrate exposed to a metastable atom beam using an in situ rotating polariser ellipsometer. The initial deposition of oil due to a background partial pressure in vacuum is investigated. Subsequent exposure of the deposited oil to a high flux metastable neon (Ne*) beam results in cross-linking of the oil film, creating a polymerised carbonaceous layer. Values for the mean residence time, polymerisation cross-section, and desorption cross-section are calculated and compared to similar studies performed for ion bombardment. Simple estimates can provide reasonable values for application of the theory to other systems.     

Solution-deposited GdCeOx thin films: Microstructure,band structure,and dielectric property

The microstructural and electrical properties of solution-deposited GdCeO_x dielectric thin films with different mixing ratios were studied. The Ce incorporation enhanced the degree of crystallization and the refractive index of the Gd₂O₃ film, reduced the hysteresis and increased the dielectric constant. According to reflective electron energy loss spectroscopy and X-ray photoelectron spectroscopy analyses, the bandgap of the GdCeO_x film gradually decreased with increasing Ce/(Gd + Ce) atomic ratio, which was primarily affected by the reduction of the valence band offset.     

Characterizations and electrochemical performance of pure and metal-doped Li4Ti5O12 for anode materials of lithium-ion batteries

Pure and metal (Cu, Al, Sn, and V)-doped Li₄Ti₅O₁₂ powders are prepared with solid-state reaction method. The effects of dopants on the physical and electrochemical properties are characterized by using TGA, XRD, and SEM. Compared with pure Li₄Ti₅O₁₂, metal-doped Li₄Ti₅O₁₂ powders show structural stability and enhanced lithium ion diffusivity brought by doped metal ions. Voltage characteristics and initial charge–discharge characteristics according to the C rates in pure and metal-doped Li₄Ti₅O₁₂ electrode materials are studied. Pure Li₄Ti₅O₁₂ powder shows a relatively good discharge capacity of 164 mAh/g at a rate 0.2C, and some of metal-doped Li₄Ti₅O₁₂ powders show higher discharge capacities. Metal-doped Li₄Ti₅O₁₂ powders are promising candidates as anode materials for lithium-ion batteries.