Arsenic removal from water using calcined Mg–Al layered double hydroxide

Arsenic (As) in drinking water and its related toxicology are serious concerns nowadays. Development of better techniques related to removal of As from drinking water is an urgent need. Layered double hydroxide (LDH) or hydrotalcite-like compound with the general formula [M_1−x ²⁺ M _x ³⁺ (OH)₂] ^x+ A ^x−·nH₂O can be considered as a good adsorbent for the removal of toxic As from water. Due to large surface area and high anion exchange capacity of LDH, the compound may be a good adsorbent for the removal of As from contaminated water. In this study, the removal of As in aqueous solution by adsorption method based on the calcination–rehydration reaction was investigated in batch experiment at (30 ± 1)°C. Results showed the removal of 99.99% As from a solution of 0.1 ppm of As; the adsorbent required at saturation was 0.10 g/20 ml As solution with 90 min of exposure at (30 ± 1)°C. Factors like pH, adsorbent dose and shaking time influenced the rate of As removal. Experiment showed that the adsorption process follows the Freundlich-type adsorption isotherm. The explanation of adsorption phenomenon is supported by X-ray diffraction pattern.     

Growing TiO2 nanowires on the surface of graphene sheets in supercritical CO2: characterization and photoefficiency

Tremendous interest exists towards synthesizing nanoassemblies for dye-sensitized solar cells (DSSCs) using earth-abundant and -friendly materials with green synthetic approaches. In this work, high surface area TiO(2) nanowire arrays were grown on the surface of functionalized graphene sheets (FGSs) containing -COOH functionalities acting as a template by using a sol-gel method in the green solvent, supercritical carbon dioxide (scCO(2)). The effect of scCO(2) pressure (1500, 3000 and 5000 psi), temperature (40, 60 and 80 °C), acetic acid/titanium isopropoxide monomer ratios (HAc/TIP = 2, 4 and 6), functionalized graphene sheets (FGSs)/TIP weight ratios (1:20, 1:40 and 1:60 w/w) and solvents (EtOH, hexane) were investigated. Increasing the HAc/TIPweight ratio from 4 to 6 in scCO(2) resulted in increasing the TiO(2) nanowire diameter from 10 to 40 nm. Raman and high resolution XPS showed the interaction of TiO(2) with the -COOH groups on the surface of the graphene sheets, indicating that graphene acted as a template for polycondensation growth. UV-vis diffuse reflectance and photoluminescence spectroscopy showed a reduction in titania's bandgap and also a significant reduction in electron-hole recombination compared to bare TiO(2) nanowires. Photocurrent measurements showed that the TiO(2)nanowire/graphene composites prepared in scCO(2) gave a 5× enhancement in photoefficiency compared to bare TiO(2) nanowires.     

Identification of NARMAX Hammerstein models with performance assessment using brain storm optimization algorithm

In this paper, brain storm optimization (BSO)‐based efficient identification approach has been applied to different types of stable and practically useful Nonlinear Auto Regressive Moving Average with exogenous noise (NARMAX) Hammerstein models with various performance criteria‐based assessments. Different performance measures of the estimation process like accuracy, precision and consistency have been established to ensure the general applicability and practical usefulness of the proposed approach. The accuracy and the precision of the parameter estimation are established with the corresponding bias and variance information, while the consistency has been justified with the help of hypothesis test results. BSO‐based optimum values of the output mean square errors and the parameters and their corresponding convergences ensure the stability and robustness of the proposed identification scheme. The comparative studies of the performance of the BSO algorithm with the other basic evolutionary algorithms have been reported with optimum values of the mean square errors, estimated values of the parameters, corresponding computational times and hypothesis test outcomes. Copyright © 2016 John Wiley & Sons, Ltd.     

Estimation of theaflavin content in black tea using electronic tongue

Biochemical components like theaflavins (TF) play very important role in the quality of finished CTC (cut, torn, and curled) variety of tea. TF are known to provide characteristic astringency to the taste of finished CTC tea. The quality indicators like brightness, briskness, strength, color and overall quality of tea liquor are also due to the amount of TF present. A positive correlation is normally observed between the amount of TF and the quality scores of finished tea. Biochemical tests that yield the percentage of TF are often time consuming, require meticulous effort of sample preparation, storage and measurement. This paper proposes an alternative approach of quality evaluation of CTC tea by predicting the amount of TF that may be present in a given tea sample, using a voltammetric electronic tongue.     

The Time Dependence of the Detachment Force of Ground Micrometer-Size Particles from a Planar Substrate: Effect of Particle Rotation

The time dependence of the detachment force applied to 7 µm ground polyester particles coated with silica nanoparticles was determined by ultracentrifugation. It was found that the force required to separate the particles from the substrate increased during the first 24 hours and changed very little thereafter. Scanning electron microscopy (SEM) results suggest that the increase in adhesion is due to the particles rotating from their initial positions obtained during deposition. The role of the silica nanoparticles in determining the time dependence of the detachment force is discussed in terms of the JKR and Fuller–Tabor models.     

Development of an Improved Pollution Source Identification Model Using Numerical and ANN Based Simulation-Optimization Model

The identification of unknown pollution sources is an important and challenging task for the engineers working on pollution management of a groundwater aquifer. The locations and transient magnitude of unknown contaminant sources can be identified using inverse optimization technique. In this approach, the absolute difference between the simulated and the observed contaminant concentration at the observation locations of the aquifer is minimized by using an optimization algorithm. The simulated concentrations is calculated using the aquifer simulation model. As such, there is a need to incorporate the aquifer simulation model with the optimization model. Thus the performance of the model is highly related to the aquifer simulation model. The incorporation of the sophisticated numerical simulation model will give better performance, but the model will be computationally expensive. On the other hand, the model will be computationally less expensive if an approximate simulation model is used in place of the numerical simulation model. However, in this case, the predictive performance of the model will decline. For achieving efficiency in both computational time as well as in predicting the performance, this study presents a new genetic algorithms based simulation-optimization method incorporating both the numerical and the approximate simulation models. The efficiency and field applicability of the model is demonstrated using illustrative study areas. The performance evaluation of the model shows that the proposed model has the potential for real-world field applications.     

Stark tuning of the charge states of a two-donor molecule in silicon

A singly ionized two-donor molecule in silicon is an interesting test-bed system for implementing a quantum bit using charge degrees of freedom at the atomic limit of device fabrication. The operating principles of such a device are based on wavefunction symmetries defined by charge localizations and energy gaps in the spectrum. The Stark-shifted electronic structure of a two-donor phosphorus molecule is investigated using a multi-million-atom tight-binding framework. The effects of surface (S) and barrier (B) gates are analyzed for various voltage regimes. It is found that gate control is smooth for any donor separation, although at certain donor orientations the S and B gates may alter in functionality. Effects such as interface ionization, saturation of the lowest energy gap, and sensitivity to donor and gate placements are also investigated. Excited molecular states of P(2) + are found to impose limits on the allowed donor separations and operating gate voltages for coherent operation. This work therefore outlines and analyzes the various issues that are of importance in the design and control of such donor molecular systems.