Adsorption of methylene blue onto bamboo-based activated carbon: kinetics and equilibrium studies

Bamboo, an abundant and inexpensive natural resource in Malaysia was used to prepare activated carbon by physiochemical activation with potassium hydroxide (KOH) and carbon dioxide (CO(2)) as the activating agents at 850 degrees C for 2h. The adsorption equilibrium and kinetics of methylene blue dye on such carbon were then examined at 30 degrees C. Adsorption isotherm of the methylene blue (MB) on the activated carbon was determined and correlated with common isotherm equations. The equilibrium data for methylene blue adsorption well fitted to the Langmuir equation, with maximum monolayer adsorption capacity of 454.2mg/g. Two simplified kinetic models including pseudo-first-order and pseudo-second-order equation were selected to follow the adsorption processes. The adsorption of methylene blue could be best described by the pseudo-second-order equation. The kinetic parameters of this best-fit model were calculated and discussed.     

Electrochemical fabrication of highly stable redox-active nanojunctions

Redox-gated molecular junctions were obtained starting with a relatively large gap between two electrodes, in the micrometer range, followed by electrochemical polymerization of aniline. Polyaniline (PANI) grows from the tip side until it bridges the two electrodes. The resulting junctions were characterized electrochemically by following the variation of the tip-substrate current as a function of the electrochemical gate potential for various bias voltages and by recording their I(V) characteristics. The two electrodes make contact through PANI wires, and microjunctions with conductances around 10(-3) S were obtained. On the basis of a similar setup, PANI nanojunctions with conductances between 10(-7) and 10(-8) S were made, where the current appears to be controlled by fewer than 10 oligoaniline strands. Despite the small number of strands connecting the two electrodes, the junctions are highly stable even when several successive potential sweeps are performed. Comparison of the conductance measured in the oxidized and reduced states leads to an on/off ratio of about 70-100, which is higher than that reported for a single aniline heptamer bridging two electrodes, highlighting the interest of connecting a few tens of molecules using the scanning electrochemical microscopy (SECM) configuration. In some cases, the switching of the PANI takes place in several individual conductance steps close to that obtained for a single oligoaniline. Finally, starting with a microjunction and mechanically withdrawing the tip shrinks it down to the nanometer scale and makes it possible to reach the regime where the conductance is controlled by a limited number of strands. This work presents an easy method for making redox-gated nanojunctions and for probing the conductance of a few oligoanilines despite an initially large tip-substrate gap.     

Switch-level emulation of strength-base soft error detection

Modern nanometer circuits have become more prone to soft errors necessitating faster and more reliable error detection techniques. Simulation-based soft error detection has been popular but is limited by its inability to handle complex circuits and high run-time. FPGA-based soft error detection methods can be effectively used to overcome the speed limitation of simulation as well as handle circuits with much higher complexity. The paper presents a novel strength-based soft error emulation method targeting soft errors caused by transient pulses of magnitude less than logic threshold. The impact of transient injection location on soft error coverage is analyzed and the idea of using drain of a transistor as transient injection location is presented. Furthermore, the concept of transient equivalence is applied to minimize resource overhead as well as speed-up soft error detection process. Advanced switch-level models are designed using gate-level structure and used to implement switch-level equivalents of ISCAS’85 benchmarks. The experimental results reported for ISCAS’85 benchmarks show that an average soft error coverage of 0.7-0.8 was achieved using the proposed strength-based detection with drain as transient injection location. The application of transient equivalence resulted in speed-up of emulation by 2.875 and reduced the memory utilization by 65%. The emulation-based soft error detection achieved significant speed-up of the order of 10⁶ as compared to a customized simulation-based method.     

Improving CO2/CH4 adsorptive selectivity of carbon nanotubes by functionalization with nitrogen-containing groups

Multi-walled carbon nanotubes containing oxygenated groups (O-MWCNTs) have been functionalized with ammonia to improve the adsorption capacity and selectivity of CO₂/CH₄ in gas adsorption process. The effects of oxygen and nitrogen containing functional groups (e.g. hydroxyl and amine), on CO₂ and CH₄ adsorption were studied. The ideal adsorption capacities of MWCNTs were determined using volumetric method at ambient temperature and moderate pressures (from 0.1 to 3.0 MPa). The MWCNTs containing nitrogen groups (N-MWCNTs) showed much higher adsorption capacity of CO₂ and selectivity of CO₂/CH₄ against the O-MWCNTs at different pressures. The highest selectivity was observed at lower pressures at 298 K for the N-MWCNTs. The dynamic adsorption experiments were carried out with a feed containing one to fivefold of CO₂ to CH₄ in a packed bed of N-MWCNTs at 298 K and atmospheric pressure. The breakthrough curves and breakthrough times of CO₂ and CH₄ were determined for the mixed gases. The results indicated high efficiency of the prepared N-MWCNTs in dynamic separation of CO₂ and CH₄.     

Enhancing mechanical properties of gel‐spun polyvinyl alcohol fibers by iodine doping

High strength polyvinyl alcohol (PVA) fibers with a conventional degree of polymerization of 1500 were prepared by doping iodine with PVA spinning solution. The iodine‐doped PVA (I‐PVA) aqueous solution was extruded into cold methanol that provides dark purple PVA‐iodine complex gel fibers. Only a small amount of iodine was required to enhance drawability and molecular orientation by reducing the interaction between PVA chains. An increase of ca. 10% in the maximum draw ratio of the doped fibers compared with that of undoped PVA translated into values for the tensile strength, 2.2 Giga‐Pascal (GPa), and initial modulus (47 GPa) that were more than 30% higher than those of the neat PVA fiber. Easier chain slippage of molecules in the amorphous segments of the I‐PVA fiber during drawing leads to increased orientation in these segments, which is believed to be the source of the improvements in mechanical properties. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Insights into the formation and degradation mechanisms of methylenedinitramine during the incubation of RDX with anaerobic sludge

In an earlier study, we reported that hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) biodegraded with domestic anaerobic sludge to produce a key RDX ring cleavage intermediate that was tentatively identified as methylenedinitramine (O2NNHCH2NHNO2) using LC/MS with negative electrospray ionization (ES-). Recently, we obtained a standard material of methylenedinitramine and thus were able to confirm its formation as the key initial RDX intermediate. In water alone or in the presence of sludge, methylenedinitramine decomposed to N20 and HCHO. Only in the presence of sludge HCHO converted further to carbon dioxide. To test our hypothesis that water was involved in the formation of methylenedinitramine during incubation of RDX with sludge, we allowed the energetic compound to biodegrade in several D2O/H2O solutions (90, 50, and 0% v/v). We observed three distinctive deprotonated or dedeuterated mass ions at 135, 136, and 137 Da that were attributed to the formation of nondeuterated (H-methylenedinitramine), monodeuterated (D1-methylenedinitramine), and dideuterated methylenedinitramine (D2-methylenedinitramine), respectively. Two controls were prepared in D2O both in the absence of sludge; the first contained methylenedinitramine, and the second contained RDX. Neither control produced any deuterated methylenedinitramine, thus excluding the occurrence of any abiotic D/H exchange between D2O and either methylenedinitramine or RDX. The results supported the occurrence of an initial enzymatic reaction on RDX, yet they did not provide compelling evidence on whether methylenedinitramine was an initial RDX enzymatic hydrolysis product or simply formed via the spontaneous hydrolysis of an anonymous initial RDX enzymatic product.     

Optimization of basic dye removal by oil palm fibre-based activated carbon using response surface methodology

Oil palm fibre was used to prepare activated carbon using physiochemical activation method which consisted of potassium hydroxide (KOH) treatment and carbon dioxide (CO(2)) gasification. The effects of three preparation variables: the activation temperature, activation time and chemical impregnation (KOH:char) ratio on methylene blue (MB) uptake from aqueous solutions and activated carbon yield were investigated. Based on the central composite design (CCD), a quadratic model and a two factor interaction (2FI) model were respectively developed to correlate the preparation variables to the MB uptake and carbon yield. From the analysis of variance (ANOVA), the significant factors on each experimental design response were identified. The optimum activated carbon prepared from oil palm fibre was obtained by using activation temperature of 862 degrees C, activation time of 1h and chemical impregnation ratio of 3.1. The optimum activated carbon showed MB uptake of 203.83mg/g and activated carbon yield of 16.50%. The equilibrium data for adsorption of MB on the optimum activated carbon were well represented by the Langmuir isotherm, giving maximum monolayer adsorption capacity as high as 400mg/g at 30 degrees C.     

Molecular spectroscopic study of river nile sediment in the greater cairo region

The greater Cairo region is the most populated area in Egypt. The aquatic environment of the Nile River in this area is being affected by industrial activities. The study of the molecular structure of sediment may provide a good trace for such changes. Both Fourier transform infrared spectroscopy (FT-IR) and density functional theory (DFT) were used to study the effect of industrial waste disposal south of Cairo on the molecular structure of Nile River sediment. Four seasonal samples were collected from six sites covering 75 km along the Nile River. Grain sizes of 200 microm, 125 microm, 65 microm, and 32 microm, respectively, were examined. The results indicate that hydrated aluminum hydroxide controls the distribution of organic matter in the different grain sizes. Furthermore, the hydration of phenol may take place in grain sizes lower than 200 microm, which is indicated by the OH stretching at 3550 cm(-1) and verified by the obtained model. The formation of metal carboxylate bonds at 1638 cm(-1) (asymmetric) and 1382 cm(-1) (symmetric) indicate the possible interaction between heavy metals and other organic structures, mainly humic substances.