A. V. R. Reddy

A fluoride ion selective Zr(IV)-poly(acrylamide) magnetic composite

A fluoride ion selective magnetic sorbent has been synthesized by the encapsulation of Fe3O4 nanoparticles in a network of Zr(IV) complexed poly(acrylamide) (Zr–PAM). This magnetic sorbent has been found to be efficient for the selective preconcentration of fluoride ions from natural waters. The Zr–PAM/Fe3O4 composite has been characterized using various physico-chemical techniques i.e. energy dispersive X-ray fluorescence (EDXRF), scanning electron microscopy (SEM), Fourier transform infra-red spectroscopy (FTIR) and a vibrating sample magnetometer (VSM). The Zr–PAM/Fe3O4 composite developed in the present work retains the super paramagnetic properties of Fe3O4 nanoparticles, and the results reveal that the sorption is rapid. The composite has a considerably higher fluoride sorption capacity (124.5 mg g−1) compared to other super-paramagnetic fluoride sorbents reported in the literature. Repeated sorption–regeneration cycles seem to suggest reusability of the sorbent for fluoride removal from natural waters, as well as other aqueous solutions having pH in the range 1–9.

Antibacterial effect of chronic exposure of low concentration ZnO nanoparticles on E. coli

The toxicity effect due to chronic exposure of ZnO nanoparticles (NPs) was systematically studied by repeatedly treating different lower concentrations of ZnO nanoparticles with culture media of E. coli strain. The chronic exposure of ZnO NPs of concentrations below minimum inhibitory concentration (MIC) exhibited higher toxicity than the single exposure of higher concentrations. Most striking result was 57% inhibition of growth corresponding to chronic exposure of 0.06 mg/mL of ZnO NPs which was two folds more than that exhibited by single exposure of 0.30 mg/mL ZnO NPs. The toxicity of ZnO NPs in E. coli was studied in the light of formation of reactive oxygen species (ROS), measured as malondialdehyde (MDA) equivalent by thiobarbituric acid-ROS (TBARS) assay, and effect of Zn dissolution from ZnO NPs. Higher inhibition of growth for the chronic exposure batches were correlated with higher ROS generation, which subsequently contributed to cause membrane lipid peroxidation, confirmed from observation of cell wall deformation by scanning electron microscopy study and energy dispersive X-ray analysis showed adherence of ZnO NPs on cell wall. The possibility of membrane lipid peroxidation was addressed by revealing in vitro oxidation of oleic acid, which is a monounsaturated fatty acid. Further in this study we have shown that the dissolution of ZnO NPs at pH 7.4 was not significant to cause Zn-induced toxicity.

Extractive fixed-site polymer sorbent for selective boron removal from natural water.

Water contamination by boron is a widespread environmental problem. The World Health Organization (WHO) recommends maximum boron concentration of 2.4 mg L(-1) for drinking water. The paper presents a simple method for preparation of functionalized sheet sorbent for selective extraction of boron from natural water. The pores of commercially available poly(propylene) membrane were functionalized by room temperature in situ crosslinking of poly(vinylbenzyl chloride) with a cyclic diamine piperazine. The precursor membranes were chemically modified with N-methyl D-glucamine which is selective for boron. Characterization of membrane was carried out using scanning electron microscopy (SEM) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) techniques. The functionalized membrane has been characterized in terms of parameters that influence the sorption of boron from aqueous streams like pH, uptake capacity, contact time, effects of competing ions and reusability. The maximum boron sorption capacity determined experimentally was 28 mg g(-1). The studies showed that trace concentrations of boron were quantitatively removed from water at neutral pH. The developed fixed site polymer sorbent exhibited high sorption capacity and fast kinetics as compared to various sorbents reported in literature. It was successfully applied for the removal of boron from ground water and seawater samples in presence of high concentration of interfering ions.

Sorption of As(III) and As(V) on chemically synthesized manganese dioxide

Sorption of As(III) and As(V) on manganese dioxide was studied by batch equilibration method using 76As radioactive tracer. Manganese dioxide was prepared by two different methods viz. reacting (a) KMnO4 solution with MnSO4 solution, and (b) KMnO4 solution with concentrated hydrochloric acid. Manganese dioxide was characterized by zeta potential measurement, surface area measurement, thermogravimetry (TG), differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Point of zero charge (PZC) for manganese dioxide was between pH 3 and 4. Radioactive tracer (76As) was prepared by neutron irradiation of arsenious oxide in self serve facility of CIRUS reactor followed by conversion to As(III) and As(V), by appropriate chemical methods. Sorption of As(III) and As(V) were studied separately, between pH 1 to 11, using (i) freshly prepared, (ii) air-dried and (iii) aged manganese dioxide. Sorption of As(III) and As(V) on freshly prepared as well as aged manganese dioxide, from both the methods was greater than 98% between pH 1 to 9 and decreased above pH 9. Percentage sorption was comparable for manganese dioxide prepared by both the methods in different batches. Sorption capacity was ∼2 mg g−1 for both As(III) and As(V). Arsenic was desorbed from the manganese dioxide by 0.1 M sodium hydroxide and oxidation state of desorbed arsenic was determined by solvent extraction method. It was found that the desorbed arsenic was present in As(V) oxidation state, independent of the initial oxidation states. This simple and direct chemical evidence, establishing that As(III) is converted to As(V) by manganese dioxide, is reported for the first time. Sorption of As(III) and As(V) on manganese dioxide did not cause an increase in manganese concentration above solubility limit confirming that Mn2+, formed during oxidation of As(III) to As(V), was re-adsorbed.

Electrodeposited Bi-Au nanocomposite modified carbon paste electrode for the simultaneous determination of copper and mercury

Composites of bismuth and gold nanoparticles (Bi–AuNPs) were prepared on a carbon paste electrode (CPE) by an electrochemical deposition method. The electrochemical parameters were optimized for the effective deposition of Bi–AuNP composite materials. Microscopic examination revealed that nanoparticle clusters of gold were embedded well within the bismuth films (Bi films) over the surface of the CPE. An analytical anodic stripping voltammetry method has been developed for the simultaneous determination of copper and mercury at ultratrace levels using the Bi–AuNP modified CPE. It was possible to observe well separated stripping peaks of the two metal ions and the modified electrode was successfully applied for simultaneous determination of Cu and Hg. The limits of detection using the optimized analytical procedure were observed as 0.16 μg L−1 and 0.28 μg L−1 for Cu and Hg respectively. Interference effects of some of the commonly occurring metal ions were investigated and the method was applied for the determination of Cu and Hg in two ground water and two soil samples collected from different places.

Bi-Film on a carbon paste electrode modified with nafion film embedded with multiwall carbon nano tubes for the determination of heavy metals

Bi-film was deposited on the carbon paste electrode and used as the modified electrode in stripping voltammetry. Bi deposition was carried out ex-situ in acetate buffer solution of pH 4.5 under mild stirring conditions. The deposition potential, deposition time and the Bi-concentration in the deposition solution were optimized and the corresponding values are −0.8 V (SCE), 300 s and 0.3 mM Bi-nitrate solution respectively. A substantial enhancement of an order of magnitude in the sensitivity has been observed when carbon paste electrode was modified with nafion coated carbon nano tube on which Bi-film was deposited. This enhanced sensitivity was attributed to the increased active surface area and also the enhanced charge transfer processes which increased the deposition processes and so the stripping current. Effect of different surfactants on the stripping peak of the heavy metal ions is investigated with and without modification by nafion. Detection limits using Bi-film electrode was obtained for Zn, Cd and Pb as 17.3, 16.9, 11.9 μg L−1, respectively, using Bi-film electrode. Analysis result of two water samples and two ayurvedic medicines are reported.

Electrodeposited antimony and antimony–gold nanocomposite modified carbon paste electrodes for the determination of heavy metal ions

Antimony (Sb) film was electrodeposited on the surface of a carbon paste electrode (CPE) for the determination of heavy metal ions such as Cd, Pb and Cu. An ex situ analytical method based on this Sb film modified CPE was proposed for the determination of heavy metal ions. While the deposition of the Sb film was performed in a 0.02 M HCl solution, the determination of heavy metal ions was performed in a sodium acetate medium. For the determination of Cu, the pH of the solution was the most crucial factor and was optimised to a value of 6. For the determination of Hg, an antimony and gold nanocomposite (Sb–Au nanocomposite) was co-deposited over the surface of a carbon paste electrode. The modified electrodes were characterised using SEM and EDS measurements. The SEM measurements of Sb–Au nanocomposites show a dendrimer type of morphology. The three sigma detection limits of Pb, Cd, Cu and Hg were determined to be 2.65, 2.32, 9.73, and 0.052 μg L−1, respectively. Finally, the method was applied for the determination of Cd, Pb, Cu and Hg in real water samples.

Electrochemical and spectroelectrochemical investigations of quercetin on unmodified and DNA-modified carbon paste electrode and its determination using voltammetry

The electrochemistry of quercetin on a carbon paste electrode in non aqueous and aqueous media has been investigated. Cyclic voltammetric experiments were carried out and the basic electrochemical parameters such as diffusion coefficient, exchange current density and the anodic Tafel slopes were determined. A differential pulse voltammetric procedure was proposed for the determination of quercetin in aqueous solution using a carbon paste electrode, and the detection limit was obtained as 38.5 nM L−1. The electrochemical properties of quercetin were studied using a DNA-modified carbon paste electrode using electrochemical impedance measurements. From spectroelectrochemical measurements it was evident that the hydroxyl groups at the 3′ and 4′ positions were oxidized in the presence of Cu(II) and are responsible for DNA damage. Impedance measurements supported the intercalation of quercetin into the DNA strands.

Multi-element analysis of soil from the north-western region of India by neutron activation analysis using the single comparator method with special reference to selenium toxicity

The single comparator (k0) instrumental neutron activation analysis (INAA) was employed to determine the elemental composition of soil from the north-western region of India. The radiometric assay was carried out using high resolution gamma-ray spectrometry. Seventeen elements were detected including selenium whose concentration was found to be in the range of 1.02 to 6.79 mg/g.

Determination of elemental concentrations in environmental plant samples by instrumental neutron activation analysis

The intake of leafy vegetables in daily diet is very important to meet our nutritional needs. Vegetables provide the essential elements which are necessary and recommended for human growth. However, due to rapid industrialization and urbanization our environment becomes polluted and this affects the normal growth of agricultural products and composition of environmental species. The elemental concentrations present in the environmental samples are good indicators to assess the toxicological levels due to pollution affects. In the present work we have analysed several vegetable plant samples by instrumental neutron activation analysis to determine the elemental concentrations at major, minor and trace levels. The leafy vegetables like spinach, red leafy veagetable, pui, gourd leaf, lettuce and katoua were chosen as these are extensively consumed by local peple in eastern part of India. We have determined 15 elements in the above mentioned vegetable samples and some of these are essential elements and some are toxic elements. It was found that Na and K were present as major elements, Fe and Zn as minor elements and As, Ce, Cr, Co, La, Mo, Rb, Sc, Sm, Sr as trace elements. The concentration level of Cr was found to be higher than that of recommended value certified by WHO and National environment quality control for human consumption. The validation of our analytical results have been performed by the Z-score tests through the determination of concentrations of the elements of interest in certified reference materials.