The effect of co-precipitation on cadmium(II) adsorption on hydrous aluminium(III) hydroxide in the presence of a range of chelates

The adsorption of cadmium(II) on freshly precipitated aluminium(III) hydroxide in the presence of a range of chelates has been investigated. By precipitating the metal, chelate and adsorbent together it is possible to change the pH variation of the metal-complex adsorption from anionic, ligand-like, binding to cationic binding. This is a general phenomenon and is explained by the formation of a ternary Al-O-Cd-L surface species. As a consequence of the preparation method, the pH edge is found to shift to lower pH values in the presence of the chelate which gives rise to an apparent increase in adsorption of Cd2+. This increase is, in general, most pronounced at [chelate] / [metal] > 1. Computer modelling shows that the observed trends result from the competition between Al-O-Cd-L and Al-L for the available aluminium( III) binding sites. The enhanced adsorption in the presence of phenylenediaminetetraacetate is anomalous since it is observed at a [ chelate] / [metal] approximate to 0.1 and cannot be interpreted by the simple competition model.

Insight into the adsorption competition and the relationship between dissociation and association reactions in ammonia synthesis

Ammonia synthesis on three metal surfaces (Zr, Ru, and Pd) is investigated using density functional theory calculations. In addition to N-2 dissociation, all the transition states of the hydrogenation reactions from N to NH3 are located and the reaction energy profiles at both low and high surface coverages are compared and analyzed. The following are found: (i) Surface coverage effect on dissociation reactions is more significant than that on association reactions. (ii) The difference between N and H chemisorption energies, the so-called chemisorption energy gap which is a measure of adsorption competition, is vital to the reactivity of the catalysts. (iii) The hydrogenation barriers can considerably affect the overall rate of ammonia synthesis. A simple model to describe the relationship between dissociation and association reactions is proposed. (c) 2007 American Institute of Physics.

The temperature dependence of the adsorption of NO on Pt{211}: A RAIRS and DFT investigation

RAIRS experiments have been performed to investigate the adsorption of NO on Pt{211}. Results show that adsorption is complex and strongly temperature dependent. At 307 K, three bands are seen at saturation with frequencies of 1801, 1609, and 1576 cm(-1). However, at 120 K only two bands, at 1688 and 1620 cm(-1), are observed. To help with the assignment of these vibrational bands, DFT calculations were also performed. The calculations show that a bridged NO species, bonded to the step edge, is the most stable species on the surface and gives rise to the band observed at 1610-1620 cm(-1). The calculations also suggest that the temperature dependence of NO adsorption on Ptf{211} can be assigned to NO dissociation which occurs at room temperature but not at 120 K. In particular, the RAIRS band observed at 1801 cm(-1), which is observed on adsorption at 307 K but not at 120 K, is tentatively assigned to the formation of an O-NO complex. This species forms when a NO molecule bonds on top of an O atom, which results from the dissociation of NO on the Pt{211} surface at room temperature.

Resolution of an ancient surface science anomaly: Work function change induced by N adsorption on W{100}

For many decades it has been assumed that an adsorbate centered above a metal surface and with a net negative charge should increase the work function of the surface. However, despite their electronegativity, N adatoms on W{100} cause a significant work function decrease. Here we present a resolution of this anomaly. Using density functional theory, we demonstrate that while the N atom carries a negative charge, of overriding importance is a reduction in the surface overspill electron density into the vacuum, when that charge is engaged in bonding to the adatom. This novel interpretation is fundamentally important in the general understanding of work function changes induced by atomic adsorbates.

Microcolumn studies of dye adsorption onto manganese oxides modified diatomite

The method described here cannot fully replace the analysis of large columns by small test columns (microcolumns). The procedure, however, is suitable for speeding up the determination of adsorption parameters of dye onto the adsorbent and for speeding up the initial screening of a large adsorbent collection that can be tedious if a several adsorbents and adsorption conditions must be tested. The performance of methylene blue (MB), a basic dye, Cibacron reactive black (RB) and Cibacron reactive yellow (RY) was predicted in this way and the influence of initial dye concentration and other adsorption conditions on the adsorption behaviour were demonstrated.

The removal of dyes from textile wastewater: a study of the physical characteristics and adsorption mechanisms of diatomaceous earth

The feasibility of using diatomite for the removal of the problematic reactive dyes as well as basic dyes from textile wastewater was investigated. Methylene blue, Cibacron reactive black and reactive yellow dyes were considered. Physical characteristics of diatomite such as pH(solution), pH(ZPC), surface area, Fourier transform infrared, and scanning electron microscopy were investigated. The surface area of diatomite was found to be 27.80 m(2) g(-1) and the pH(ZPC) occurred around pH of 5.4. The results indicated that the surface charge of diatomite decreased as the pH of the solution increased with the maximum methylene blue removal from aqueous solution occurring at basic pH of around (1011). Adsorption isotherms of diatomite with methylene blue, hydrolysed reactive black and yellow dyes were constructed at different pH values, initial dye concentrations and particle sizes. The experimental results were fitted to the Langmuir, Freundlich, and Henry models. The study indicated that electrostatic interactions play an important role in the adsorption of dyes onto diatomite. A model of the adsorption mechanism of methylene blue onto diatomite is proposed. (C) 2003 Elsevier Ltd. All rights reserved.

Activation of waste MDF sawdust charcoal and its reactive dye adsorption characteristics

This paper reports an experimental investigation of converting waste medium density fibreboard (MDF) sawdust into chars and activated carbon using chemical activation and thermal carbonisation processes. The MDF sawdust generated during the production of architectural mouldings was characterised and found to have unique properties in terms of fine particle size and high particle density. It also has a high content of urea formaldehyde resin used as a binder in the manufacturing of MDF board. Direct thermal carbonisation and chemical activation of the sawdust by metal impregnation and acid (phosphoric acid) treatment prior to pyrolysis treatment were carried out. The surface morphology of the raw dust, its chars and activated carbon were examined using scanning electron microscopy (SEM). Adsorptive properties and total pore volume of the materials were also analysed using the BET nitrogen adsorption method. Liquid adsorption of a reactive dye (Levafix Brilliant red E-4BA) by the derived sawdust carbon was investigated in batch isothermal adsorption process and the results compared to adsorption on to a commercial activated carbon (Filtrasorb F400). The MDF sawdust carbon exhibited in general a very low adsorption capacity towards the reactive dye, and physical characterisation of the carbon revealed that the conventional chemical activation and thermal carbonisation process were ineffective in developing a microporous structure in the dust particles. The small size of the powdery dust, the high particle density, and the presence of the urea formaldehyde resin all contributed to the difficulty of developing a proper porous structure during the thermal and chemical activation process. Finally, activation of the dust material in a consolidated form (cylindrical pellet) only achieved very limited improvement in the dye adsorption capacity. This original study, reporting some unexpected outcomes, may serve as a stepping-stone for future investigations of recycle and reuse of the waste MDF sawdust which is becoming an increasing environmental and cost liability. (C) 2004 Elsevier Ltd. All rights reserved.

Comparison of optimised isotherm models for basic dye adsorption by kudzu

This study assesses the use of dried (5% w/w moisture) kudzu (Peuraria lobata ohwi) as an adsorbent medium for the removal of two basic dyes, Basic Yellow 21 and Basic Red 22, from aqueous solutions. The extent of adsorption was measured through equilibrium sorption isotherms for the single component systems. Equilibrium was achieved after 21 days. The experimental isotherm data were analysed using Langmuir, Freundlich, Redlich-Peterson, Temkin and Toth isotherm equations. A detailed error analysis was undertaken to investigate the effect of using different error criteria for the determination of the single component isotherm parameters. The performance of the kudzu was compared with an activated carbon (Chemviron F-400). Kudzu was found to be an effective adsorbent for basic dye colour removal, though its capacity for colour removal was not as high as an activated carbon, the potential appeared to exist to use it as an alternative to activated carbon where carbon cost was prohibitive. (C) 2002 Elsevier Science Ltd. All rights reserved.

Adsorption characteristics of Cu and Ni on Irish peat moss

Peat has been widely used as a low cost adsorbent to remove a variety of materials including organic compounds and heavy metals from water. Various functional groups in lignin allow such compounds to bind on active sites of peat. The adsorption of Cu²⁺ and Ni²⁺ from aqueous solutions on Irish peat moss was studied both as a pure ion and from their binary mixtures under both equilibrium and dynamic conditions in the concentration range of 5–100 mg/L. The pH of the solutions containing either Cu²⁺ or Ni²⁺ was varied over a range of 2–8. The adsorption of Cu²⁺ and Ni⁺² on peat was found to be pH dependent. The adsorption data could be fitted to a two-site Langmuir adsorption isotherm and the maximum adsorption capacity of peat was determined to be 17.6 mg/g for Cu²⁺ and 14.5 mg/g for Ni²⁺ at 298 K when the initial concentration for both Cu²⁺ and Ni²⁺ was 100 mg/L, and the pH of the solution was 4.0 and 4.5, respectively. Column studies were conducted to generate breakthrough data for both pure component and binary mixtures of copper and nickel. Desorption experiments showed that 2 mM EDTA solution could be used to remove all of the adsorbed copper and nickel from the bed.

Elevated serum phosphate predicts mortality in renal transplant recipients

BACKGROUND.: High serum phosphate has been identified as an important contributor to the vascular calcification seen in patients with chronic kidney disease (Block et al., Am J Kidney Dis 1998; 31: 607). In patients on hemodialysis, elevated serum phosphate levels are an independent predictor of mortality (Block et al., Am J Kidney Dis 1998; 31: 607; Block, Curr Opin Nephrol Hypertens 2001; 10: 741). The aim of this study was to investigate whether an elevated serum phosphate level was an independent predictor of mortality in patients with a renal transplant.
METHODS.: Three hundred seventy-nine asymptomatic renal transplant recipients were recruited between June 2000 and December 2002. Serum phosphate was measured at baseline and prospective follow-up data were collected at a median of 2441 days after enrolment.
RESULTS.: Serum phosphate was significantly higher in those renal transplant recipients who died at follow-up when compared with those who were still alive at follow-up (P<0.001). In Kaplan-Meier analysis, serum phosphate concentration was a significant predictor of mortality (P=0.0001). In multivariate Cox regression analysis, serum phosphate concentration remained a statistically significant predictor of all-cause mortality after adjustment for traditional cardiovascular risk factors, estimated glomerular filtration rate, and high sensitivity C reactive protein (P=0.036) and after adjustment for renal graft failure (P=0.001).
CONCLUSIONS.: The results of this prospective study are the first to show that a higher serum phosphate is a predictor of mortality in patients with a renal transplant and suggest that serum phosphate provides additional, independent, prognostic information to that provided by traditional risk factors in the risk assessment of patients with a renal transplant.

Structural basis of substrate selectivity in the glycerol-3-phosphate: phosphate antiporter GlpT.

Major facilitators represent the largest superfamily of secondary active transporter proteins and catalyze the transport of an enormous variety of small solute molecules across biological membranes. However, individual superfamily members, although they may be architecturally similar, exhibit strict specificity toward the substrates they transport. The structural basis of this specificity is poorly understood. A member of the major facilitator superfamily is the glycerol-3-phosphate (G3P) transporter (GlpT) from the Escherichia coli inner membrane. GlpT is an antiporter that transports G3P into the cell in exchange for inorganic phosphate (Pi). By combining large-scale molecular-dynamics simulations, mutagenesis, substrate-binding affinity, and transport activity assays on GlpT, we were able to identify key amino acid residues that confer substrate specificity upon this protein. Our studies suggest that only a few amino acid residues that line the transporter lumen act as specificity determinants. Whereas R45, K80, H165, and, to a lesser extent Y38, Y42, and Y76 contribute to recognition of both free Pi and the phosphate moiety of G3P, the residues N162, Y266, and Y393 function in recognition of only the glycerol moiety of G3P. It is the latter interactions that give the transporter a higher affinity to G3P over Pi.

Electroreduction of Chlorine Gas at Platinum Electrodes in Several Room Temperature Ionic Liquids: Evidence of Strong Adsorption on the Electrode Surface Revealed by Unusual Voltammetry in Which Currents Decrease with Increasing Voltage Scan Rates

Voltammetry is reported for chlorine, Cl-2, dissolved in various room temperature ionic liquids using platinum microdisk electrodes. A single reductive voltammetric wave is seen and attributed to the two-electron reduction of chlorine to chloride. Studies of the effect of voltage scan rate reveal uniquely unusual behavior in which the magnitude of the currents decrease with increasing scan rates. A model for this is proposed and shown to indicate the presence of strongly adsorbed species in the electrode reaction mechanism, most likely chlorine atoms, Cl*((ads)).