Chemisorption Of Ions Research Articles

Understanding hydroxide reactions with guanidinium-based anion exchange polymers under conditions relevant to bipolar membrane electrodialysis

Anion exchange polymers are susceptible to loss of cationic functionality as a result of nucleophilic attack by hydroxide ions. This research investigated the stability of two guanidinium-based cations as anion exchange functional groups under conditions relevant to bipolar membrane electrodialysis. Density functional theory simulations were performed to investigate reaction energies and activation barriers for reactions of hydroxide ions with pentamethylguanidinium (PMG) and hexamethylguanidinium (HMG) cations bound to a diaryl ketone polymer backbone. The effect of physically adsorbed chloride and hydroxide ions, and chemically adsorbed hydroxide ions, on reaction energetics were determined. Fukui functions for nucleophilic attack were used to identify locations most likely to undergo reactions with hydroxide ions. For the PMG species, the most likely bond cleavage reactions were highly exergonic, with ΔGrxno values as large as −46 kcal/mol and activation barriers less than 10 kcal/mol. Chemisorption of hydroxide ions on both PMG and HMG cations was energetically favorable, with activation barriers of 5.3 and 2.7 kcal/mol, and resulted in loss of cationic functionality. Anion adsorption changed the reactivity of both PMG and HMG structures towards nucleophilic attack. For nucleophilic attack at the phenyl carbon atom, adsorption of OH− on the guanidinium carbon atom made PMG less reactive, while adsorption of Cl− made HMG less reactive. Bond cleavage and loss of cationic functionality was a two or three step process involving addition of OH− to the phenyl or guanidinium carbon atoms, followed by bond stretching or deprotonation of the added hydroxide species. For PMG species, deprotonation of the hydroxide resulted in bond cleavage or produced metastable species that decomposed with activation barriers less than 2 kcal/mol. HMG species were more stable with respect to this degradation mechanism, having activation barriers for bond cleavage ranging from 17 to 29 kcal/mol.

Inhibition mechanism of Ca2+, Mg2+ and Fe3+ in fine cassiterite flotation using octanohydroxamic acid.

The existence of metal ions should not be ignored in both hydrometallurgy and flotation. In this study, the effects of Ca2+, Mg2+ and Fe3+ on the flotation performance of cassiterite using octanohydroxamic acid (OHA) as the collector were investigated by micro-flotation tests, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, contact angle, zeta (ζ) potential measurements and atomic force microscopy (AFM) imaging. The results of the flotation and contact angle experiments showed that the addition of Ca2+, Mg2+ and Fe3+ significantly decreased both the recovery and contact angle of cassiterite with pH ranged from 6.0 to 12.0 in the presence of OHA collector. ζ-Potential measurements, solution chemistry analysis and FTIR measurements indicated that the flotation recovery of the cassiterite declined due to the CaOH+, MgOH+ and Fe(OH)3 sites on the cassiterite surface. XPS results indicated that the chemisorption of OHA and calcium ions on the cassiterite surface finally changed its chemical properties. The AFM images also revealed that new species Fe(OH)3 of Fe3+ formed and adsorbed on the cassiterite surface at pH 9.0. The adsorption of Fe(OH)3 reduced the adsorption of OHA on the cassiterite surface, thus the hydrophobicity of cassiterite was deteriorated.

Chitosan-Ag-TiO2 films: An effective photocatalyst under visible light

Aiming the degradation of harmful molecules under visible light, new photocatalytic systems were created. For this purpose, the surface of chitosan thin films was modified in heterogeneous phase via a simple and straightforward mild chemical process: chemisorption of silver ions followed by the synthesis in situ of TiO2 at low temperature (100 °C). A high photocatalytic activity under visible light was observed, leading to the degradation and/or mineralization of different organic products such as o-toluidine, salicylic acid and 4-aminomethyl benzoic acid. This efficiency is partly attributed to the formation of Ag NPs and also to the unexpected appearance of AgCl NPs, likely formed from the residual chlorine contained in the chitosan. The resulting TiO2/Ag/AgCl/Chitosan system is easy to prepare under mild conditions, avoiding calcination treatments and opens new perspectives for the production of visible light-driven photocatalysts. Samples were analysed by different techniques: XRD, Raman, FE-SEM, XPS, TGA, GSDR, LIF and LIP.

Electroflotation of ultrafine chalcopyrite particles with sodium oleate collector

The electroflotation behaviour of ultrafine chalcopyrite particles was investigated using a mechanically agitated cell. The use of sodium oleate as collector proved effective in the flotation of particles of average size of 5 µm. The results showed that chalcopyrite recovery increases with increasing pulp pH, and current density, but decreases with increasing pulp density. The successful flotation of chalcopyrite with oleate might be attributed to its electrochemical surface oxidation, resulting in the formation of cupric and ferric oxide species. Chemisorption of oleate ions onto oxidized chalcopyrite surface is suggested to be the main cause for the increase in chalcopyrite recovery.

Preparation of gold/hydroxyapatite hybrids using natural fish scale template and their effective albumin interactions

The gold (Au) nanoparticles (NPs) with the diameter of 15–40 nm were successfully synthesized in the hierarchical hydroxyapatite (HAp) nanostructures of natural fish scale templates, which were carried out by the Au3+ ion chemisorption, reduction and calcination processes to form the AuNPs/HAp hybrids. The AuNPs size as well as the surface plasmon resonance (SPR) absorption maximum was preserved with the hybridization process. Moreover, the AuNPs/HAp hybrid nanostructures exhibited preferential protein adsorption behavior at the biological bovine serum albumin (Ab) concentration regions that correspond to be 1.5 μM in the cell culture medium and 15.1 μM in human blood, and the Ab adsorption equilibrium constant of AuNPs/HAp hybrid was higher than that of the HAp alone. The SPR absorption maxima of the Ab-adsorbed AuNPs/HAp fish scales were red-shifted as compared with those of the AuNPs/HAp fish scales. Therefore, we synthesized the AuNPs using the fish scale template to exhibit the preferential protein adsorption, which will be a great significance to research the AuNPs/HAp hybrid functions.

Experimental investigation and thermodynamic study of heavy metal removal from industrial wastewater using pomegranate peel

The objective of the study is to treat industrial wastewater and perform a thermodynamic experimental study for more economical and efficient adsorption process. This has been done by biosorption and chemisorption of chromium ions from synthetic wastewater into already prepared pomegranate peel as a natural adsorbent. Pomegranate peel proved to be an economic solution since it is available locally and it has an elevated adsorption capacity. Adsorption has been done in a fixed bed column (10 cm inside diameter, and 30 cm height) with continuous flow rate of 1 ml/min. The characteristic properties of adsorption for the pomegranate peel, analyzed by FTIR and SEM, proved that pomegranate peel is a good adsorbent because of its effective combinations and holes on its exterior. Also, comparing between adsorption ability of pomegranate peel together with Langmuir and Freundlich models indicates that Langmuir is preferable in fitting the experimental data. However, the elimination efficiency of the pomegranate peel was 90%, and the greatest adsorption capability was 9.45 mg/g. While, thermodynamic study results showed that endothermic adsorption was approved from positive values of ΔH°, also the negative values of ΔG° proved that the adsorption is unprompted and convenient.

Enhancing the Charge Storage Capacity of Lithium-Ion Capacitors Using Nitrogen-Doped Reduced Graphene Oxide Aerogel as a Negative Electrode: A Hydrodynamic Rotating Disk Electrode Investigation

An energy storage device having both high energy and power density is crucial for many applications such as electric vehicles and mobile phones. Herein, pre-lithiated three-dimensional (3D) nitrogen-doped reduced graphene oxide aerogel (N-rGO aerogel) was introduced as a negative electrode to overcome the kinetic sluggish of lithium ions and activated carbon (AC) was used as a positive electrode of lithium-ion capacitor (LIC). The electrochemical property of electrode materials was studied in a three-electrode system using a hydrodynamic rotating disk electrode at different rotation rates confirming the lithium ion chemisorption on the N-rGO aerogel. The as-fabricated LIC tested in a cell voltage window of 2.0–4.0 V can provide a maximum specific energy of 170.28 Wh kg−1 (144.79 Wh L−1), a maximum specific power of 25.75 kW kg−1 (21.89 kW L−1) with ∼100% capacity retention and 100% coulombic efficiency over 2000 cycles. The excellent performance stems from the nitrogen-containing group and 3D interconnected structure of the N-rGO aerogel. The LIC in this work may be used in many high energy and power applications.

Chemisorption of lanthanide ions on succinate-functionalized mesoporous silica: An in situ characterization by fluorescence

Chemisorption of Eu3+ and Tb3+ on SBA-15 functionalized with succinic groups has been studied by in situ steady-state fluorescence measurements. The enhancement of the emission sensitive bands indicates that both ions adsorb forming inner-sphere surface complexes. Adsorption is a fast process that attains equilibrium in about 5min. The variation of the peaks maxima (I592 and I616, for europium, and I490 and I545, for terbium) with the total ion concentration is accounted for by the sum of the contributions due to the adsorbed and free ions. The former contribution is langmuirian. At pH 4.5, the respective adsorption constants are 5×105 and 3×105M−1, and the maximum adsorption capacities are 5.10×10−4 and 5.23×10−4molg−1. The mismatch between the latter values and the number of attached carboxylic groups is discussed. Comparison with other functionalized mesoporous silicas indicates that the anchored succinic groups are very efficient for removing lanthanide ions from aqueous solutions.

The adsorption of oleate on powellite and fluorapatite: A joint experimental and theoretical simulation study

Flotation and adsorption performance of sodium oleate(NaOl)on powellite and fluorapatite were investigated in this work through micro-flotation tests, work of adhesion calculations, molecular dynamics simulation, micro-topography studies and FTIR measurements. The micro-flotation results show a similar flotation behaviors of powellite and fluorapatite under alkaline conditions, but a considerable difference in mineral recoveries in the pH range 2–7, which demonstrates the possibilities for separating powillite from fluorapatite under acidic conditions. The great difference in mineral recovery displays a good accordance with the obvious difference in the work of adhesion of powellite and fluorapatite at NaOl dosage range of 40–80mg/L, obtained from flotation and contact angle measurements, respectively. The more negative interaction energy (ΔE) between NaOl and powellite/water interface from molecular dynamics simulation reveals a more easily adsorption of NaOl onto powellite than onto fluorapatite, which excellently matches with the results of flotation and work of adhesion. The results of micro-topography study shows that the adsorption of NaOl on powellite is mainly ascribed to the chemisorption of oleate ions with Ca2+ on powellite lattice or the precipitation of calcium dioleate agglomerates on powellite surface when it was in the solution without or with Ca2+, respectively. The FTIR measurements further confirm the chemisorption of oleate ions with Ca2+ active sites on powellite surface.

In Situ 3D Imaging of Catalysis Induced Strain in Gold Nanoparticles

Multielectron transfer processes are crucially important in energy and biological science but require favorable catalysts to achieve fast kinetics. Nanostructuring catalysts can dramatically improve their properties, which can be difficult to understand due to strain- and size-dependent thermodynamics, the influence of defects, and substrate-dependent activities. Here, we report three-dimensional (3D) imaging of single gold nanoparticles during catalysis of ascorbic acid decomposition using Bragg coherent diffractive imaging (BCDI). Local strains were measured in single nanoparticles and modeled using reactive molecular dynamics (RMD) simulations and finite element analysis (FEA) simulations. RMD reveals the pathway for local strain generation in the gold lattice: chemisorption of hydroxyl ions. FEA reveals that the RMD results are transferable to the nanocrystal sizes studied in the experiment. Our study probes the strain-activity connection and opens a powerful avenue for theoretical and experimental studies of nanocrystal catalysis.

Atmospheric ions as the origin of photoinduced degrading of photoluminescence from a single-walled carbon nanotube

Air-suspended single-walled carbon nanotubes (SWCNTs) were exposed to atmospheric ions for identifying the origin of photoinduced degrading of photoluminescence from SWCNTs in air. Decreased intensity and a low energy shift of photoluminescence from the SWCNT were observed after the exposure, and the reaction was found to be accelerated by laser illumination. The amount of the decrease and shift had a weak correlation and were attributed to the chemisorption of hydronium ions along with water molecules.

Supercapacitor Electrodes of MnO2 and MnO2/Graphene Nanosheets Synthesized by Liquid Phase Exfoliation

MnO2 has been extensively investigated due to its high theoretical capacitance of 1100 to 1300 F.g-11, environmental friendly nature and low cost 2. The MnO2 charge storage mechanism relies on the exchange of protons and/or cations with the electrolyte, redox activity involving a Mn(IV)/Mn(III) transition, and chemisorption of ions onto the MnO2 surface 1,3,4. As these are surface processes, it is paramount to design MnO2 structures with an accessible high surface area. Recently, liquid phase exfoliation has become a powerful technique for the preparation of 2D nanosheets presenting a high surface area5,6. Therefore this technique can be used to produce nano layers of MnO2, which will present an enhanced utilization of the active material and a better electrochemical performance7. In the present work a high-surface area, porous MnO2 powder was produced through the oxidation of Mn(NO3)2 by KMnO4. A poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) triblock copolymer (PEG-PPO-PEG P123) was used as templating agent for the formation of a “flower-like” nanostructure (MOFN) with protruding 2D-nanostructures8. Subsequently, MOFN wére exfoliated in isopropanol at 37kHz for 3 hours, resulting in two types of materials: manganese oxide nanolayers (MOL) and a partially exfoliated material (PEMO). Following a novel approach, the MOFN were also exfoliated simultaneously with graphite resulting in a MnO2layers/Graphene hybrid (GMOH).The obtained dispersions were sprayed onto ITO electrodes and the electrochemical properties studied by cyclic voltammetry. By testing electrodes with different thicknesses it was found out that the electrochemical utilization is enhanced for GMOH (80.0 mF.cm-2) at a thickness of 9700 nm). A capacitance as high as 300 F.cm-3 was also achieved with GMOH thin electrodes followed by 225 F.cm-3 for MOL and 100 F.cm-3for PEMO. (1) Wang, G.; Zhang, L.; Zhang, J. Chemical Society Reviews 2012, 41, 797. (2) Kang, J.; Hirata, A.; Kang, L.; Zhang, X.; Hou, Y.; Chen, L.; Li, C.; Fujita, T.; Akagi, K.; Chen, M. Angewandte Chemie International Edition 2013, 52, 1664. (3) Xu, C.; Kang, F.; Li, B.; Du, H. Journal of materials research 2010, 25, 1421. (4) Bélanger, D.; Brousse, L.; Long, J. W. The Electrochemical Society Interface 2008, 17, 49. (5) Coleman, J. N.; Lotya, M.; O’Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V. Science 2011, 331, 568. (6) Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N. Science 2013, 340. (7) Toupin, M.; Brousse, T.; Bélanger, D. Chemistry of Materials 2004, 16, 3184. (8) Jiang, H.; Sun, T.; Li, C.; Ma, J. Journal of Materials Chemistry 2012, 22, 2751.

Numerical Modeling for Corrosion

The ECS Corrosion Division was established in 1942 to organize and promote discussions associated with the behavior of materials in environments that cause corrosion, oxidation, and related surface reactions. This Division provides a forum for scientists and engineers to meet and discuss common problems in the hope of advancing research, education, and training in this important field. Over the years, a number of the members of the Corrosion Division have served as ECS President, including H. H. Uhlig, N. Hackerman, F. L. LaQue, D. A. Vermilyea, T. R. Beck, R. C. Alkire, R. P. Frankenthal, W. H. Smyrl, B. MacDougall, and P. M. Natishan. Over the past seven decades, the Division has sponsored numerous corrosion related symposia and organized the Corrosion Monograph series of books that outline and review many areas of corrosion science and engineering. The Corrosion Handbook, originally edited by H. H. Uhlig in 1946 (its 3rd edition was revised by R. Winston Revie in 2011), remains one of the most popular corrosion reference books worldwide. In this issue, we present four articles related to numerical approaches to corrosion science and engineering. Corrosion damage of equipment, production facilities, and infrastructure has severe consequences, including loss of property, interruption of production and transportation, and outage of electricity, water, and gas supplies. Such disruptions occur at a very high cost to society. While it is difficult to estimate the direct economic loss due to corrosion damage, the expense incurred to avoid/prevent corrosion damage, i.e., “corrosion cost,” has been estimated for several economies, including that of the U.S.,1 Japan,2 and the EU.3 The corrosion cost is invariably high, at a few percentage points of GDP annually (3.1% of GDP in the U.S.1). To minimize corrosion cost, a large amount of effort has been expended to facilitate prediction of corrosion damage. To accurately predict corrosion events, it is necessary to establish high-quality numerical models for a wide range of very complicated corrosion phenomena. In the decade from 1970 to 1980, numerical calculations mainly used finite element methods (FEM) and yielded deterministic models for the study of localized corrosion.4,5 Such studies contributed to the fundamental understanding of the mechanisms of localized corrosion, but were not necessarily practical for actual corrosion prediction. Subsequently, stochastic or probabilistic models6 were developed based on the distribution of the (corrosion-induced) failure time in the laboratory and/or in the field. These approaches introduced high-level statistics and other mathematical methods in conjunction with accumulated field data, and were successful in predicting localized corrosion phenomena, such as pitting corrosion and stress corrosion cracking experienced in process industries.7 To predict corrosion damage for new combinations of materials and environments, the stochastic and probabilistic approach is not necessarily effective, and deterministic models are required. Recent improvements in and development of computing technologies and calculation methods, including first principle calculations, have enabled advanced numerical modeling of corrosion phenomena as a combination of electrochemistry, solution chemistry, mass transfer, and atomistic process. The four articles in this issue provide both an historical outline and recent developments in numerical corrosion modeling. Liu and Kelly review the fundamental numerical modeling of localized corrosion by electrochemistry and mass transfer using FEM, and introduce their recent results adopting a commercial FEM package with electrochemical modules. The article by Amaya, Yoneya, and Onishi describes a practical corrosion prediction method for large-scale structures, such as the cathodic protection of the hull of a ship and large ocean structures using the boundary element method. The introduction of the inverse analysis method based on Bayesian estimation enables the study of large-scale structures by combining numerical calculations with infield monitoring of parameters such as the corrosion potential. The article by Tylor reviews the most recent ab initio calculations on corrosion processes at the atomistic scale and introduces approaches pertaining to molecular design of corrosion inhibitors, chemisorption of molecules and ions on metals or surface passive films that are closely related to corrosion, and characterization of the structure of the metal/oxide interface. Finally, the article by Laycock, Krouse, Hendy, and Williams addresses both the deterministic model and the stochastic model. The authors attempt a full description of the pitting corrosion process, including initiation and propagation, on stainless steel in an attempt to develop a reliable predictive model for industrial applications. The articles in this issue review the current validity and future possibilities pertaining to the prediction of corrosion by numerical modeling. Recently, in the area of materials science, the concept of the Materials Genome has been launched, where comprehensive approaches encompassing experimental and numerical simulation are recognized to be significant. The typical corrosion scientist is well versed in experimental work, but perhaps not so much in modeling. If this issue provides the requisite introductory guidance to numerical modeling of corrosion, the authors would be very pleased!

Mechanistic Insight for the Sorption of Cd(II) and Cu(II) from Aqueous Solution on Magnetic Mn-Doped Fe(III) Oxide Nanoparticle Implanted Graphene

The sorption behaviors of M(II) (M = Cu, Cd) were investigated from their aqueous solution by magnetic Mn-doped Fe(III) oxide nanoparticle implanted graphene (GMIO) at varying pH, contact times, and concentrations. Kinetically, the pseudo-second-order equation governed the overall sorption process at optimized pH (5.1 ± 0.1). Redlich–Peterson (R–P) (0.97 < R2 < 1.00, 0.84 < g < 1.00) and Langmuir (0.96 < R2 < 1.00) isotherms described sorption equilibriums better than Freundlich (0.86 < R2 < 0.96). Monolayer sorption capacity values of GMIO for M(II) increased (88 mg·g–1 to 127 mg·g–1 for Cd; 130 mg·g–1 to 144 mg·g–1 for Cu) with increasing temperature from 288 K to 333 K. Negative ΔG0 values indicated spontaneous sorption nature despite positive ΔH0 values owing to an entropy increase (positive ΔS0) at the solid–liquid interface. Relatively less regeneration (∼70%) of MII–GMIO by 0.1 M HCl possibly stemmed the chemisorption of metal ions, and this is well-corroborated by the nature of Stern–Volmer plot of fluorescence quenching data with reaction time.

Computer modeling of the influence of oxygen adsorption centers in zeolite on the chemisorption of hydrogen ions

We propose a simplified computer model of the interaction of hydrated and nonhydrated hydrogen, calcium, and zinc ions with adsorption centers in the SiO2 fragments of zeolite in the cluster approximation. By using the quantum-chemical РМ6 method, we find the activation energy of adsorption and the energies of formation of chemical bonds and gradual filling of these centers and reveal the positive influence of the ions of metals on the blocking of adsorption of hydrogen ions accompanied by the decrease in their penetration to the surface of the base metal.

Purification of aqueous alcohol solutions in two-bed adsorber filters

The possibility of replacing imported carbon-fiber filters, which are used for the purification of aqueous alcohol solutions in the manufacture of vodka at a number of domestic distilleries, by the developed adsorber filters was studied. These adsorber filters combine the filtration of a solution on a macroporous ceramic filter element with adsorption on microporous active carbon; in this case, the filter bed is responsible for the selective chemisorption of metal ions, whereas the adsorbing bed is responsible for the total extraction of organic pollutants. A comparative study of the adsorption characteristics of the competing purification systems was performed, and the advantage of the proposed two-step system for the purification of aqueous alcohol solutions was demonstrated.

The role of bromine adlayer at palladium electrode in the electrochemical oxidation of dopamine in alkaline solution

A palladium electrode modified with bromine monolayer was fabricated throughout a spontaneous oxidative chemisorption of bromide ions contained in an alkaline solution. The surface coverage and the apparent double layer capacitance induced by the adsorption of bromide ions under the present applied potential indicates the formation of incomplete monolayer due to a prominent co-adsorption of hydroxyl ions (OH −). The film modified electrode exhibited a substantial reactivity and high sensitivity in the electrochemical oxidation of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). This trend was attributed to the structure and the composition of the bromine adlayer which renders a partial negative charge capable of attracting selectively the cationic DA and repelling anionic AA and UA. The peak currents of DA in the binary and ternary mixtures were well-separated, well-defined and increased linearly with respect to its concentration. The interference property expected by the presence of both AA and UA has been advantageously eliminated at the bromine-adlayer modified electrode. The apparent diffusion coefficient value of DA was 1.37 × 10 −8 m 2 s −1, based on an amperometric current–time study. The present system provides a simple and fundamental approach for the simultaneous and selective determination of DA in the presence of AA and UA.

Chemisorption of phosphate ions and destruction of organomineral sorbents in acid soils

The chemisorption mechanisms of phosphate anions by iron (aluminum) containing sorbents in a soil under high phosphate loads were studied. The role of the metal-phosphate anions in the destruction of the sorbents was discussed. It was shown that the chemisorption of phosphate anions and the destruction of phosphated organomineral sorbents are interrelated processes. A significant part of the chemisorbed phosphates in association with sorbent metals and carbon passes into the liquid phase of soil systems.

Electrochemical oxidation of dopamine and ascorbic acid at a palladium electrode modified with in situ fabricated iodine-adlayer in alkaline solution

The self-assembled iodine-adlayer was fabricated at the palladium (Pd) electrode surface throughout a spontaneous oxidative chemisorption of iodide ions contained in an alkaline supporting electrolyte. It enhances the electron transfer kinetics for the oxidation of dopamine (DA) and ascorbic acid (AA) and was important to separate the peak current of both species with a practical potential difference compared with that occurred at the unmodified electrode. The anodic peak currents of both species were linearly increased with their respective concentrations using linear square stripping voltammetry. The activity of the electrode system was further investigated applying chronoamperometry method. The steady-state amperometric signal for the oxidation of DA in the presence of iodide ions was five times greater than that in its absence. The current-time response was also used to evaluate the diffusion coefficient of DA based on Cottrell plot that results with a value of 4.19 x 10(-8)m(2)s(-1). The proposed method was successfully applied to detect DA and AA in human serum.

Fluoride Ion Uptake by Synthetic Apatites

Fluoride uptake by synthetic apatites from aqueous solutions was studied as a function of fluoride ion concentration. The phosphate minerals synthesized and considered included different varieties of phosphate minerals of the apatite group such as hydroxy-, carbonato- and chloro-apatite, all being precipitated at the boiling point. An ion-selective electrode technique was used for fluoride ion analysis in the adsorption experiments and electrokinetic measurements were utilized to delineate specific adsorption effects. The results suggest that, at low fluoride ion concentrations, a fluoroapatite-type compound may form on the apatite surface via the chemisorption of fluoride ions at calcium sites; at high fluoride ion concentrations, calcium fluoride appears to form at the apatite surface via a surface-precipitation phenomenon. The formation of CaF2 on the surface of fluoride ion-treated apatite was further substantiated by FT-IR spectroscopic measurements, which clearly demonstrated a metathetic exchange w...