KINETIC INVESTIGATION AND SURFACE COMPLEXATION MODELING OF Cd(II) ADSORPTION ONTO FELDSPAR

The aim of this study is to determine the feldspar adsorption kinetics and isotherm of Cd(II) and to model the adsorption data with the aid of a metal-surface binary complexation approach. The adsorption of Cd(II) ion onto feldspar was approximated using a triple-site model by the aid of the FITEQL 3.2 computer program calculating the relative distribution of surface species. Experiments were carried out at I=0.1 ionic strength using an inert electrolyte (NaClO4). Of the three metal-binding surface sites of feldspar, it was assumed that (K,Na,Ca,Mg)X represents ion exchangable negative-charged sites, -S1OH silanol groups, and -S2OH pH-dependent aluminol groups. Metal hydrolysis was neglected under the experimental conditions employed, and Cd(II) was assumed to bind to the clay surface as the sole Cd2+ cation. The equilibrium constants of the reactions between Cd(II) ion and the surface sites were calculated using FITEQL 3.2. Cd(II) adsorption on feldspar showed Langmuiran character and pseudo-first order kinetics. The maximum adsorption capacity of feldspar for Cd(II) ions was found as 1.29 mg metal ion/g adsorbent. The results of this study are believed to facilitate the solution of environmental problems like metal ion migration and adsorptive treatment by clay minerals

Kinetic, isotherm and pH dependency investigation and environmental application of cationic dye adsorption on montmorillonite

In this study, individual and competitive adsorption of three cationic dye onto montmorillonite were investigated. Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models were used to analyze experimental data for individual and competitive adsorption of dyes. Surface precipitation occured in the presence of inert electrolyte because of decreasing solubility of dye. The organic dye adsorption was pH-independent in a pH scale between 2 and 6. It is, thus, assumed that the adsorption took place between cationic organic dye and permanently negatively charged surface, which is a pH-independent surface site of adsorbent and occured as a result of isomorphic substitution. Mean free energies (E-D) varied between 0.65 and 7.87J/mol, and heats of sorptions (B) changed between 4 and 96J/mol. These low energy values support the electrostatic interaction between surface and dye molecules. Organic dye adsorption showed Langmuirian character and in the presence of more than one adsorptive dye, adsorption capacities remained under individual adsorption capacity values because of competition. Adsorption kinetic showed second order reaction character. Using sodium humate, CaCl2 solution, and acid mixture solution as leach solutions desorption properties were examined. Higher desorption values were achieved by using 1% of sodium humate solution because of hydrophobic interactions and formation of H bonds

Modeling Competitive Adsorption of Copper(II), Lead(II), and Cadmium(II) by Kaolinite-Based Clay Mineral/Humic Acid System

The aim of this work is to investigate and model the simultaneous adsorption of Cu(II), Cd(II), and Pb(II) in the presence and absence of humic acid on kaolinite-based clays. The preliminary capacity estimation of clays for metal was made with the use of a modified Langmuir approach, and adsorption data collected at various pH were processed using the FITEQL 3.2 computer program to establish the model. The three types of surface sites responsible for adsorption were considered to be the permanent charge sites X-2(2-), and variable charge sites comprised of S1OH silanol groups and S2OH aluminol groups of kaolinite-based clays. Heavy metal cations were assumed to bind to the surface in the form of outer sphere and inner sphere monodentate complexes. When humic acid was added, divalent metal ion adsorption was modeled using a multisite binding model by the aid of FITEQL 3.2. since the stability of the ternary surface complexes in the presence of humic acid was higher than that of the corresponding binary heavy metal cation complexes, the adsorption versus pH curves were sleeper (and distinctly S-shaped) compared with the tailed curves observed in binary clay metal ion systems, probably due to the fact that humic acid-coated kaolinite essentially constituted the active surface for metal sorption. Although competitive metal adsorption from (metal ions mixture+humate) solutions was generally lower than those from individual metal ion solutions, Cd2+, being the metal ion with the highest affinity toward permanent charge sites, was the least affected ion at relatively low pH from competitive adsorption. (C) 2008 American Institute of Chemical Engineers Environ Prog, 28: 493-506, 200

Investigation of individual and competitive adsorption of Cu(II), Cd(II), and Pb(II) on montmorillonite in terms of surface complexation and kinetic properties of Cu(II) adsorption

In this study, individual and competitive Cu(II), Cd(II), and Pb(II) adsorptions on montmorillonite were searched by considering surface acidic functional groups of adsorbent. pH dependency of adsorptions and kinetic properties of Cu(II) adsorption was investigated. Cu(II) adsorption on montmorillonite fits pseudo-first-order reaction with the 0.008k value. Individual and competitive heavy metal adsorptions were modeled using Langmuir, Freundlich, Temkin, and Dubinin-Astakhov isotherms. Adsorption capacities were calculated using equations of related linearized models. The adsorption capacities of individual metal adsorption, obtained from linearized models, are higher than the yielded capacities from competitive adsorption experiments. All adsorption energies calculated from linearized Dubinin-Astakhov model varied between 7 and 16kJ/mol. The values of adsorption energies gained for metal adsorption in competition did not significantly differ from those of individual adsorption. Since montmorillonite surface behaves as a weak acid and has a strong buffer effect at pH values between 2 and 3, the pH dependency of adsorption was explained by taking into account the surface acidic properties of adsorbent and introduced preferred surface sites beyond adsorption with increasing pH. Cu(II), Cd(II), and Pb(II) existence on loaded montmorillonite was proved by the aid of SEM-EDX results

Determination of total antioxidant capacity of Cynara Scolymus L. (globe artichoke) by using novel nanoparticle-based ferricyanide/Prussian blue assay

A novel ferricyanide/Prussian blue (PB) assay for total antioxidant capacity (TAC) determination was developed exploiting the formation of PB nanoparticles in the presence of polyvinylpyrrolidone (PVP) as stabilizer. This improved method, named as "nanoparticle-based ferricyanide/Prussian blue assay (PBNP)", was applied to the TAC measurement of Cynara Scolymus L. (globe artichoke). The calibration results of the novel (PBNP) method were compared with those of a similar nanoparticle PB method performed in the absence of PVP, and of a sodium dodecyl sulfate-modified and acid-optimized ferricyanide reference assay. Compared to similar common Fe(III)-based TAC assays, much higher molar absorptivities, pointing out higher response to different kinds of antioxidants, were obtained with PBNP for all tested antioxidants, and lower LOD and LOQ values were achieved for thiols. As an additional advantage, methionine, not responding to other electron-transfer based TAC reagents, could be measured. PBNP could detect various antioxidants with one-two orders-of-magnitude lower LOD values than those of widely used TAC assays like CUPRAC and Folin-Ciocalteau well correlating with the proposed assay

Monitoring Humic Acid Photodegradation by CUPRAC Colorimetric and HPLC Determination of Dihydroxybenzoate Isomers Produced From a Salicylate Probe

Novel analytical methods were designed for monitoring humic acid photodegradation in environmental waters. Modified CUPric Reducing Antioxidant Capacity (CUPRAC) spectrophotometric and chromatographic methods were used for the determination of dihydroxybenzoate isomers (DHBAs) produced from a salicylate probe, which was hydroxylated by hydroxyl radicals ((OH)-O-center dot) produced from the photodegradation of humic acid under ultraviolet A-radiation. The combined use of CUPRAC colorimetry and HPLC was shown to effectively monitor humic acid photodegradation and (OH)-O-center dot generation for the first time. The formation of 2,5-dihydroxybenzoate and 2,3-dihydroxybenzoate, as major and minor products, respectively, from the hydroxylation of a salicylate probe was demonstrated by HPLC and confirmed by a modified CUPRAC method to indicate (OH)-O-center dot formation from humic acid, which acted as both a generator and absorber of hydroxyl radicals. Salicylate hydroxylation showed an increase between 30 and 50 min of illumination, and was affected by the initial concentration of humic acid up to 0.01% but not by solution pH around the neutral values. Traces of Fe(III) and Mn(II) present in natural waters decreased the (OH)-O-center dot production, but EDTA partly restored the probe hydroxylation by chelating these metal cations. Since humic acid-mediated (OH)-O-center dot generation may aid in natural disinfection processes, this work may extend our comprehension of concentration- and time-dependent generation of (OH)-O-center dot in environmental waters and of the possible effects of other antioxidants

MODELING OF ACIDIC AND COMPLEXATION PROPERTIES OF HUMIC ACIDS USING THE IRWING-ROSSOTTI METHOD

Consequently, distribution of humic acids between solid and liquid phases, mechanism of surface protonation and metal-humate complexation are introduced through this study

MODELING OF ACIDIC AND COMPLEXATION PROPERTIES OF HUMIC ACIDS USING THE IRWING-ROSSOTTI METHOD

In this study, acidic and metal complexation properties of five humic acid samples, obtained from different source, were investigated. Humic acid samples were extracted with 1 M NaOH solution and then precipitated using concentrated HCl. Thus, purified humic acid samples were used in neutralization and Cu(II) complexation experiments. Purity of the humic acid samples varies between 75-85 %. Structural analysis of purified humic acid samples were performed by using FTIR, SEM and LC-MS methods. Molecular weights of them were determined by the aid of LC-MS method. Distribution coefficients (K-D) of humic acid samples in convenient solvent were also investigated and calculated. The data gained as a result of potentiometric titration were evaluated in Irwing-Rossotti method. Thus, acidity constants of -COOH and -OH groups, that can release proton, and formation constants of Cu(II) - humate complexes were determined. All experiments were performed at 2 degrees C and 25 degrees C

Ethylenediamine-bound magnetite nanoparticles as dual function colorimetric sensor having charge transfer and nanozyme activity for TNT and tetryl detection

A reusable, low-cost, and convenient ethylenediamine (EDA)-bound magnetite nanoparticles (MNPs)-based colorimetric sensor has been developed for dual function colorimetric determination of nitroaromatic explosives such as TNT and tetryl. Colorimetric detection of analytes may occur through two independent routes: (1) nano-Fe3O4- EDA- NH2 as sigma-donor may interact with the sigma- and pi-acceptor aromatic-poly(NO2) groups to produce a colored charge-transfer (CT) complex; (2) nano-Fe3O4-EDA-NH2 as a Fenton-type nanozyme may generate reactive species that comprise hydroxyl radicals ((OH)-O-center dot) with H2O2 to oxidize 3,3 ',5,5 '-tetramethylbenzidine (TMB) to a blue-colored diimine (oxTMB-TMB) CT complex, where this color is bleached with TNT/tetryl because of donor-acceptor interactions between the explosive -NO2 groups and the -NH2 group of Fe3O4-EDA nanoparticles of restricted nanozyme activity. Both methods can quantify TNT well below the EPA recommended TNT residential screening level in soil, LOD being in the micromolar range. As EDA was covalently bound to MNPs, the same sensor can be separately reused six times for TNT and eight times for tetryl determination, using method (1). Common metal ions, anions, energetic materials, several camouflage materials, and soil components such as humates did not interfere with the nanosensor performance for TNT and tetryl. The combination of charge-transfer and nanozyme ability of Fe3O4- EDA-NH2 nanoparticles may bring a new approach to dual function colorimetric sensor design. To the best of our knowledge, this is the first dual function colorimetric sensor for TNT and tetryl using the same nanoparticles as sensing elements in two different detection systems involving either formation or bleaching of colored species