Competitive removal of nickel (II), cobalt (II), and zinc (II) ions from aqueous solutions by starch-graft-acrylic acid copolymers

Graft copolymerization of acrylic acid (AA) onto starch was carried out with ceric ammonium nitrate as initiator under nitrogen atmosphere. The grafting percentages (GP%) of starch-graft-acrylic acid (St-g-AA) copolymers were determined. The effect of GP% of St-g-AA copolymers on the competitive removal of CO2+, Ni2+, Zn (2+) ions from aqueous solution was investigated at different pH (2, 4, 6). The concentrations of each ion in aqueous solution 5 mmol/ L. Effects of various parameters such as treatment time, initial pH of the solution and grafting percentage of starch graft copolymers were investigated. Metal ion removal capacities of St-g-AA copolymers increased with Gp%. of the copolymers and pH. The results show that the removal of metal ions followed as given in the order Co2+ > Ni2+ > Zn2+. In this study, metal ion removal capacities were determined by atomic absorption spectrophotometer (AAS). (C) 2007 Wiley Periodicals, Inc

Removal of Cu2+ ions from aqueous solutions by starch-graft-acrylic acid hydrogels

Gelatinized starch was prepared by constantly stirring a mixture of starch and water at 95 degrees C for 1 hour. Starch-graft-acrylic acid (S-g-AA) hydrogels were prepared by grafting acrylic acid ( AA) [monomer/starch (w/w) 0.5-1.5] onto gelatinized starch with ceric ammonium nitrate as initiator under nitrogen atmosphere. The surface morphology of samples was studied using a scanning electron microscope (SEM). The hydrogels were evaluated for the removal of Cu2+ ion from aqueous solutions at different pH. The concentration of Cu2+ ion in aqueous solution was kept constant at 4 mmol/L. The metal ion removal capacities changed depending on treatment time, initial pH of the solution, and monomer/starch (w/w) ratio of the S-g-AA hydrogels. Cu2+ ion removal capacities were determined by atomic absorption spectrometer (AAS)

Modeling of copper(II), cadmium(II), and lead(II) adsorption on red mud from metal-EDTA mixture solutions

The adsorption of toxic heavy metal cations, i.e,, Cu(II), Cd(II), and Pb(II), from metal-EDTA mixture solutions on a composite adsorbent having a heterogeneous surface, i.e., bauxite waste red mud, has been investigated and modeled with the aid of a modified surface complexation approach in respect to pH and complexant dependency of heavy metal adsorption. EDTA was selected as the modeling ligand in view of its wide usage as an anthropogenic chelating agent and abundance in natural waters. The adsorption experiments were conducted for metal salts (nitrates), metal-EDTA complexes alone, or in mixtures containing (metal + metal-EDTA). The adsorption equilibrium constants for the metal ions and metal-EDTA complexes were calculated. For all studied cases, the solid adsorbent phase concentrations of the adsorbed metal and metal-EDTA complexes were found by using the derived model equations with excellent compatibility of experimental and theoretically generated adsorption isotherms. The model was useful for metal and metal-EDTA mixture solutions either at their natural pH of equilibration with the sorbent, or after pH elevation with NaOH titration up to a certain pH. Thus adsorption of every single species (M2+ or MY2-) or of possible mixtures (M2+ + MY2-) at natural pH or after NaOH titration could be calculated by the use of simple quadratic model equations, once the initial concentrations of the corresponding species, i.e., [M2+](0) or [MY2-](0), were known. The compatibility of theoretical and experimental data pairs of adsorbed species concentrations was verified by means of nonlinear regression analysis. The findings of this study can be further developed so as to serve environmental risk assessment concerning the expansion of a heavy metal contaminant plume with groundwater movement in soil consisting of hydrated-oxide type minerals. (C) 2000 Academic Press

Synthesis of Zn(II) Ion-Imprinted Polymeric Adsorbent for Selective Removal of Zinc from Aqueous Solutions

In this study, Zn(II)-imprinted polymer microbeads were synthesized for selective removal of Zn(II) from aqueous solutions. The microbeads were prepared using methacrylic acid and 1,4-vinyl pyrrolidone as functional monomers, zinc(II)acetate as zinc salt, ethylene glycol dimethacyrlate as a cross-linking agent, azo bisisobutyronitrile as an initiator and hydroxyethyl cellulose as surfactant. The non-imprinted polymer was also prepared for comparison, except without use of the Zn(II) salt. To determine the selectivity of Zn(II)-IIP beads, competitive adsorption experiments were investigated. According to the adsorption capacity values of the microbeads, Zn(II)-IIP beads show good selectivity for the target ion

REMOVAL OF Cu2+ AND Pb2+ IONS BY N-VINYL 2-PYRROLIDONE/ITACONIC ACID HYDROGELS FROM AQUEOUS SOLUTIONS

In this study, a series of crosslinked N-vinyl-2-pyrrolidone-itaconic acid (NVP-IA) hydrogels was prepared by free radical polymerisation in aqueous solution. Swelling, mechanical and adsorption properties for the removal of Cu2+ and Pb2+ ions from aqueous solutions of these hydrogels were investigated. Metal ion adsorption capacities of hydrogels for Cu2+ and Pb2+ ions were determined as 2.1 and 0.6mmolg (-1), respectively. Adsorption processes of metal ions onto the NVP-IA hydrogels follow pseudo-second-order type adsorption kinetics. The equilibrium adsorption data have been evaluated using Freundlich and Langmuir isotherm models. The results illustrated that the adsorption follows Freundlich isotherm

The main and modified CUPRAC methods of antioxidant measurement

The antioxidant activity/capacity levels of biological fluids and foods are measured for the diagnosis and the treatment of oxidative stress-associated diseases in clinical biochemistry, and for meaningful comparison of the antioxidant content of foods. Currently, there is no "total antioxidant" as a nutritional index available for food labeling and biological fluids due to the lack of standardized quantitative methods

Modeling of copper(II), cadmium(II), and lead(II) adsorption on red mud

The adsorption of toxic heavy metal cations, i.e., Cu(II), Cd(II), and Pb(II), on red muds has been modeled with the aid of a modified Langmuir approach assuming single-site adsorption and of a double-site binding model incorporating the effect of pH. For equilibrium concentrations of metal solutions between 0.03 and 5.8 mmol.dm(-3) and equilibrium pH between 4.4 and 5.6, adsorption equilibrium constants corresponding to single- and double-site binding were found by linear and nonlinear least-squares approximation, respectively, and the double-site model was shown to conform better to experimental data. The contributions of the monomeric and dimeric hydroxo-complexes of Cu(II) to total copper adsorption at a fixed pH were also investigated. The Langmuir parameters of adsorption were found with the aid of the linearized Langmuir isotherm. This work aims to clarify heavy metal adsorption behavior on composite sorbents consisting of hydrated oxides. (C) 1998 Academic Press

Hydroxyl radical detection with a salicylate probe using modified CUPRAC spectrophotometry and HPLC

Reactive oxygen species (ROS) may attack biological macromolecules giving rise to oxidative stress-originated diseases, so it is important to establish efficient methods to screen hydroxyl radical scavengers for antioxidant therapy. Since (OH)-O-center dot is very short-lived, secondary products resulting from (OH)-O-center dot attack to various probes are measured. As a low-cost measurement technique, we used a salicylate probe for detecting hydroxyl radicals generated from an equivalent mixture of Fe(II) + EDTA with hydrogen peroxide. The produced hydroxyl radicals attacked both the probe and the water-soluble antioxidants in 37 degrees C-incubated solutions for 2 h. The CUPRAC (cupric ion reducing antioxidant capacity) assay absorbance of the ethylacetate extract due to the reduction of Cu(II)-neocuproine reagent by the hydroxylated probe decreased in the presence of (OH)-O-center dot scavengers, the difference being proportional to the scavenging ability of the tested compound. Attack by (OH)-O-center dot radicals upon salicylate produced 2,3-dihydroxybenzoate, 2,4-dihydroxybenzoate, and 2,5-dihydroxybenzoate as major products. HPLC separation combined with CUPRAC spectrophotometry was used to identify and quantify hydroxylated salicylate derivatives in the presence of synthetic water-soluble antioxidants and green tea infusion. The developed spectrophotometric method for,CH detection was validated with HPLC, i.e., the concentrations of dihydroxybenzoates produced by radical attack from the probe were determined by HPLC, and the sum of (concentration x absorptivity) products of these components approximately agreed with the experimentally found CUPRAC absorbances, confirming the validity of Beer's law for the selected system. Statistical comparison of the results found with the proposed methodology and HPLC was made with two-way ANOVA (analysis of variance) test. Under optimal conditions, about 53% of the probe (salicylate) was converted into dihydroxybenzoate isomers in the absence of (OH)-O-center dot scavengers, and these isomers were more specific markers of hydroxyl radicals than the non-specific malondialdehyde end-product of the TBARS test. Thus, the more costly and less speedy HPLC method could advantageously be substituted with the proposed spectrophotometric assay of (OH)-O-center dot detection, which was also of much higher yield than the TBARS colorimetric assay. (C) 2008 Elsevier B.V. All rights reserved

Measurement of xanthine oxidase inhibition activity of phenolics and flavonoids with a modified cupric reducing antioxidant capacity (CUPRAC) method

Various dietary polyphenolics have been found to show an inhibitory effect on xanthine oxidase (XO) which mediates oxidative stress-originated diseases because of its ability to generate reactive oxygen species (ROS), including superoxide anion radical (O-2(center dot-)) and hydrogen peroxide. XO activity has usually been determined by following the rate of uric acid formation from xanthine-xanthine oxidase (X-XO) system using the classical XO activity assay (UV-method) at 295 nm. Since some polyphenolics have strong absorption from the UV to visible region, XO-inhibitory activity of polyphenolics was alternatively determined without interference by directly measuring the formation Of uric acid and hydrogen peroxide using the modified CUPRAC (cupric reducing antioxidant capacity) spectrophotometric method at 450 turn. The CUPRAC absorbance of the incubation Solution due to the reduction of Cu(II)-neocuproine reagent by the products of the X-XO system decreased in the presence of polyphenolics, the difference being proportional to the XO inhibition ability of the tested compound. The structure-activity relationship revealed that the flavones and flavonols with a 7-hydroxyl group such as apigenin, luteolin, kaempferol, quercetin, and myricetin inhibited XO-inhibitory activity at low concentrations (IC50 values from 1.46 to 1.90 mu M), while the flavan-3-ols and naringin were less inhibitory. The findings of the developed method for quercetin and catechin in the presence of catalase were statistically alike with those of HPLC. In addition to polyphenolics, five kinds of herbs were evaluated for their XO-inhibitory activity using the developed method. The proposed spectrophotometric method was practical, low-cost, rapid, and could reliably assay uric acid and hydrogen peroxide in the presence of polyphenols (flavonoids, simple phenolic acids and hydroxycinnamic acids), and less open to interferences by UV-absorbing substances. (C) 2009 Elsevier B.V. All rights reserved

Sorptive removal of cesium-137 and strontium-90 from water by unconventional sorbents .2. Usage of coal fly ash

It has been shown that coal fly ash is a good adsorbent for both radionuclides of Cs-137 and Sr-90. Radiocesium adsorption is maximal around the neutral region whereas radiostrontium adsorption increases with pH, especially above pH 8. Cesium retention sharply drops with ionic strength while strontium adsorption increases increases sharply and steadily at low and moderate concentrations of the inert electrolyte, respectively. The suggested mechanisms of radionuclide retention by fly ash is specific adsorption of Cs+ and irreversible ion-exchange utake of Sr2+. The isotherm of adsorption is a Langmuir approximation of the B.E.T. multi-layered sorption. Acid pretreatment of fly ash, though not increasing radionuclide sorption capacity, may be useful in preventing the leach-out of other contaminants from the sorbent into water during the adsorption process