Removal of ortho-phosphate from aqueous solution by adsorption onto dolomite

An experimental study on the adsorption of phosphate onto cost effective fine dolomite powder is presented. The effect of solution pH, solution ionic strength and adsorption isotherm were examined. The adsorption of phosphate was pH dependent and phosphate adsorption favoured acidic conditions. The adsorption was significantly influenced by solution ionic strength indicating outer-sphere complexation reactions. The experimental data further indicated that the removal of phosphate increased with increase in the ionic strength of solution. The experimental data were modelled with different isotherms: Langmuir, Freundlich and Redlich–Peterson isotherms. It was found that the Redlich–Peterson isotherm depicted the equilibrium data most accurately. The overall kinetic data fitted very well the pseudo-first-order rate model.

Polymer electrolyte membrane water electrolyser with Aquivion short side chain perfluorosulfonic acid ionomer binder in catalyst layers

The Aquivion short-side-chain (SSC) perfluorosulfonic acid (PFSA) ionomer was adopted in catalyst layers (CL) of polymer electrolyte membrane water electrolysers (PEMWE) instead of long-side-chain (LSC) Nafion ionomer. The effects of SSC ionomer content in CL for oxygen evolution reaction were studied in half cell with cyclic voltammetry and steady state linear sweep. In a single cell test the MEA with SSC-PFSA Aquivion ionomer exhibited better thermal stability than the one with LSC-PFSA Nafion ionomer at 90 °C. The cell voltage at a current density of 1 A cm was 1.63 V at 90 °C using the SSC-PFSA Aquivion ionomer binder, Nafion 117 membrane, and without back pressurizing. In a continuous operation the cell voltage degradation rate of the MEA using Aquivion ionomer binder was only about 0.82 mV h.

Preliminary investigation of mixed adsorbents for the removal of copper and methylene blue from aqueous solutions

With most recent studies being focused on the development of
advanced chemical adsorbents, this paper investigates the possibility of
using two natural low-cost materials for selective adsorption. Multiadsorbent
systems containing tea waste and dolomite have been tested for
their effectiveness in the removal of copper and methylene blue from
aqueous solutions. The effects of contact time, solution pH and
adsorption isotherms on the sorption behaviour were investigated. The
Langmuir and Freundlich isotherms adequately described the adsorption of
copper ions and methylene blue by both materials in different systems.
The highest adsorption capacities for Cu and MB were calculated as 237.7
at pH 4.5 and 150.44 mg.g‒1 at pH 7 for DO and TW+DO respectively. Tea
waste (TW) and dolomite (DO) were characterized by Fourier transform
infrared spectroscopy, scanning electron microscopy and Energy dispersive
X-ray analysis. The removal of Cu and MB by dolomite was mainly via
surface complexation while physisorption was responsible for most of the
Cu and MB adsorption onto tea waste. Identifying the fundamental mechanisms and behaviour is key to the development of practical multi-adsorbent packed columns.

Artificial receptors for the extraction of nucleoside metabolite 7-methylguanosine from aqueous media made by molecular imprinting

A series of imprinted polymers targeting nucleoside metabolites, prepared using a template analogue approach, are presented. These were prepared following selection of the optimum functional monomer by solution association studies using 1H-NMR titrations whereby methacrylic acid was shown to be the strongest receptor with and affinity constant of 621 ± 51 L mol-1 vs. 110 ± 16 L mol-1 for acrylamide. The best performing polymers were prepared using methanol as porogenic co-solvent and although average binding site affinities were marginally reduced, 2.3×104 L mol-1 vs. 2.7×104 L mol-1 measured for a polymer prepared in acetonitrile, these polymers contained the highest number of binding sites, 5.27 μmol g-1¬¬ vs. 1.64 μmol g-1, while they also exhibited enhanced selectivity for methylated guanosine derivatives. When applied as sorbents in the extraction of nucleoside derivative cancer biomarkers from synthetic urine samples, significant sample clean-up and recoveries of up to 90% for 7-methylguanosine were achieved.

Electrowetting movement of an aqueous droplet between two three-dimensional electrode surfaces

In an effort to develop a novel electronic paper image display technology based on the electrowetting principle, a 3-D electrowetting cell is designed and fabricated, which consists of two 3-D bent electrodes, each having a horizontal surface made of gold and a vertical surface made of indium tin oxide (ITO) glass as a color display window, a layer of dielectric material on the 3-D electrodes, and a highly fluorinated hydrophobic layer on the surface of the dielectric layer. Results of this work show that an electrowetting-induced motion of an aqueous droplet in immiscible oils can be achieved reversibly across the boundary of the horizontal and vertical surfaces of the 3-D electrode surface. It is also shown that the droplet can maintain its wetting state on a vertical sidewall electrode free of a power supplier when the voltage is removed. This phenomenon may form the basis for color contrast modulation applications, where a power-free image display is required, such as electronic paper display technology in the future. (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3100201]

Dendritic receptors designed to bind polyanions in both organic and aqueous media

This paper reports the synthesis of dendrons containing a spermine unit at their focal point. The dendritic branching is based on L-lysine building blocks, and has terminal oligo(ethyleneglycol) units on the surface. As a consequence of the solubilising surface groups, these dendrons have high solubility in solvents with widely different polarities (e.g., dichloromethane and water). The protonated spermine unit at the focal point is an effective anion binding fragment and, as such, these dendrons are able to bind to polyanions. This paper demonstrates that polyanions can be bound in both dichloromethane (using a dye solubilisation assay) and in water (competitive ATP binding assay). In organic media the dendritic branching appears to have a pro-active effect on the solubilisation of the dye, with more dye being solubilised by higher generations of dendron. On the other hand, in water the degree of branching has no impact on the anion binding process. We propose that in this case, the spermine unit is effectively solvated by the bulk solvent and the dendritic branching does not need to play an active role in assisting solubility. Dendritic effects on anion binding have therefore been elucidated in different solvents. The dendritic branching plays a pro-active role in providing the anion binding unit with good solubility in apolar solvent media.

Preparation of Aqueous Core/Polymer Shell Microcapsules by Internal Phase Separation

Aqueous core/polymer shell microcapsules with mommuclear and polynuclear core morphologies have been formed by internal phase separation from water-in-oil emulsions. The water-in-oil emulsions were prepared with the shell polymer dissolved in the aqueous phase by adding a low boiling point cosolvent. Subsequent removal of this cosolvent (by evaporation) leads to phase separation of the polymer and, if the spreading conditions are correct, formation of a polymer shell encapsulating the aqueous core. Poly(tetrahydrofuran) (PTHF) shell/aqueous core microcapsules, with a single (mononuclear) core, have been prepared, but the low T-g (-84 degreesC) of PTHF makes characterization of the particles more difficult. Poly(methyl methacrylate) and poly(isobutyl methacrylate) have higher T-g values (105 and 55 degreesC, respectively) and can be dissolved in water at sufficiently high acetone concentrations, but evaporation of the acetone from the emulsion droplets in these cases mostly resulted in polynuclear capsules, that is, having cores with many very small water droplets contained within the polymer matrix. Microcapsules with fewer, larger aqueous droplets in the core could be produced by reducing the rate of evaporation of the acetone. A possible mechanism for the formation of these polynuclear cores is suggested. These microcapsules were prepared dispersed in an oil-continuous phase. They could, however, be successfully transferred to a water-continuous phase, using a simple centrifugation technique. In this way, microcapsules with aqueous cores, dispersed in an aqueous medium, could be made. It would appear that a real challenge with the water-core systems, compared to the previous oil-core systems, is to obtain the correct order of magnitude of the three interfacial tensions, between the polymer, the aqueous phase, and the continuous oil phase; these control the spreading conditions necessary to produce shells rather than "acorns".

Experimental design and batch experiments for optimization of Cr(VI) removal from aqueous solutions by hydrous cerium oxide nanoparticles

Hydrous cerium oxide (HCO) was synthesized by intercalation of solutions of cerium(III) nitrate and sodium hydroxide and evaluated as an adsorbent for the removal of hexavalent chromium from aqueous solutions. Simple batch experiments and a 2⁵ factorial experimental design were employed to screen the variables affecting Cr(VI) removal efficiency. The effects of the process variables; solution pH, initial Cr(VI) concentration, temperature, adsorbent dose and ionic strength were examined. Using the experimental results, a linear mathematical model representing the influence of the different variables and their interactions was obtained. Analysis of variance (ANOVA) demonstrated that Cr(VI) adsorption significantly increases with decreased solution pH, initial concentration and amount of adsorbent used (dose), but slightly decreased with an increase in temperature and ionic strength. The optimization study indicates 99% as the maximum removal at pH 2, 20 °C, 1.923 mM of metal concentration and a sorbent dose of 4 g/dm³. At these optimal conditions, Langmuir, Freundlich and Redlich–Peterson isotherm models were obtained. The maximum adsorption capacity of Cr(VI) adsorbed by HCO was 0.828 mmol/g, calculated by the Langmuir isotherm model. Desorption of chromium indicated that the HCO adsorbent can be regenerated using NaOH solution 0.1 M (up to 85%). The adsorption interactions between the surface sites of HCO and the Cr(VI) ions were found to be a combined effect of both anion exchange and surface complexation with the formation of an inner-sphere complex.

Mathematical modelling of quantum yield enhancements of methyl orange photooxidation in aqueous TiO2 suspensions under controlled periodic UV LED illumination

Quantum yields of the photocatalytic degradation of methyl orange under controlled periodic illumination (CPI) have been modelled using existing models. A modified Langmuir-Hinshelwood (L-H) rate equation was used to predict the degradation reaction rates of methyl orange at various duty cycles and a simple photocatalytic model was applied in modelling quantum yield enhancement of the photocatalytic process due to the CPI effect. A good agreement between the modelled and experimental data was observed for quantum yield modelling. The modified L-H model, however, did not accurately predict the photocatalytic decomposition of the dye under periodic illumination.

Density functional theory study on the activation of molecular oxygen on a stepped gold surface in an aqueous environment: a new approach for simulating reactions in solution

The activation of oxygen molecules is an important issue in the gold-catalyzed partial oxidation of alcohols in aqueous solution. The complexity of the solution arising from a large number of solvent molecules makes it difficult to study the reaction in the system. In this work, O-2 activation on an Au catalyst is investigated using an effective approach to estimate the reaction barriers in the presence of solvent. Our calculations show that O-2 can be activated, undergoing OOH* in the presence of water molecules. The OOH* can readily be formed on Au(211) via four possible pathways with almost equivalent free energy barriers at the aqueous-solid interface: the direct or indirect activation of O-2 by surface hydrogen or the hydrolysis of O-2 following a Langmuir-Hinshelwood mechanism or an Eley-Rideal mechanism. Among them, the Eley-Rideal mechanism may be slightly more favorable due to the restriction of the low coverage of surface H on Au(211) in the other mechanisms. The results shed light on the importance of water molecules on the activation of oxygen in gold-catalyzed systems. Solvent is found to facilitate the oxygen activation process mainly by offering extra electrons and stabilizing the transition states. A correlation between the energy barrier and the negative charge of the reaction center is found. The activation barrier is substantially reduced by the aqueous environment, in which the first solvation shell plays the most important role in the barrier reduction. Our approach may be useful for estimating the reaction barriers in aqueous systems.

Powder semiconductor photocatalysis in aqueous solution: An overview of kinetics-based reaction mechanisms

A brief, historical overview of 10 apparently different, although in some cases, upon inspection, closely related, popular proposed reaction mechanisms and their associated rate equations, is given and in which the rate expression for each mechanism is derived from basic principles, Appendix A. In Appendix B, each of the 5 main mechanisms are tested using datasets, comprising initial reaction rate vs. organic pollutant concentration, [P] and incident irradiance, ρ, data, reported previously for TiO2, where P is phenol, 4-chlorophenol and formic acid. The best of those tested, in terms of overall fit, simplicity, usefulness and versatility is the disrupted adsorption kinetic model proposed by Ollis. The usual basic assumptions made in constructing these mechanisms are reported and the main underlying concerns explored.

Understanding the Interaction between Low-Energy Electrons and DNA Nucleotides in Aqueous Solution

Reactions that can damage DNA have been simulated using a combination of molecular dynamics and density functional theory. In particular, the damage caused by the attachment of a low energy electron to the nucleobase. Simulations of anionic single nucleotides of DNA in an aqueous environment that was modeled explicitly have been performed. This has allowed us to examine the role played by the water molecules that surround the DNA in radiation damage mechanisms. Our simulations show that hydrogen bonding and protonation of the nucleotide by the water can have a significant effect on the barriers to strand breaking reactions. Furthermore, these effects are not the same for all four of the bases.