Magnetite interaction with arsenic during sorptive removal from groundwater: a mechanistic study.

A magnetic mixed iron oxide, magnetite (Fe3O4), was synthesized in the laboratory and characterized before its use as sorbent for arsenic removal. The characterization techniques used were X-ray diffraction (XRD), specific surface area, zeta potential and particle size measurements. The sorbent was applied for arsenic removal, without any pre or post treatment, from groundwater. The efficiency of sorption can only be improved by understanding the sorbent-sorbate interaction. For onsite monitoring of the sorbent-sorbate interaction, an electrochemical investigation using cyclic voltammetry (CV) measurement was developed. The study confirmed that the sorption of As(III) on Fe3O4 is dynamic (reversible) whereas that of As(V) is static (irreversible) in nature. Detailed investigation after the sorption was carried out utilizing X-ray photoelectron spectroscopy (XPS) measurement. The complexation of As(III)-Fe3O4 and As(V)-Fe3O4 without any redox transformation was evident from the XPS data. By careful examination of the results, a mechanism of arsenic removal by Fe3O4 was proposed.

Evidences on As(III) and As(V) interaction with iron(III) oxides: Hematite and goethite.

Arsenic, which is ubiquitous in nature, was found associated with iron oxides in soils and sediments. Our interest was to utilize the same mechanism for the sorptive removal of arsenic from groundwater. The iron(III) oxides: hematite, goethite, were synthesized, characterized and sorption studies of arsenic [As(III) and As(V)] were carried out in batch mode. For studying the evidence of the interaction between arsenic and iron oxide during the process of sorption, a new electrochemical method was developed. Differential pulse voltammetry (DPV) study indicated that the sorbed arsenic species is redox active on the surface of the sorbent. X-ray photoelectron spectroscopy (XPS) measurement was performed for confirmation of the changes occurring to the oxidation states of iron as well as arsenic after the sorption. XPS studies confirmed that the behavior of arsenic species on hematite/goethite was similar and occurs via a partial redox reaction. During sorption of As(III), a partial oxidation occurs resulting in As(V) species, simultaneously the Fe(III) present in the iron oxide gets reduced to Fe(II). However, during the sorption of As(V), there occurs a Fe(II) oxidation followed by As(V) reduction. Based on the results, a mechanistic scheme for sorption of arsenic on iron(III) oxides as sorbents was proposed.

Spectro-electrochemistry of ciprofloxacin and probing its interaction with bovine serum albumin.

In the present investigation the electrochemical behaviour of the drug, Ciprofloxacin (Cf) and its interaction with the Bovine Serum Albumin (BSA) is reported. UV-Visible Spectroscopy (UV-Vis) and Spectro-electrochemical measurements were carried out to quantify the charge transfer process in Cf. Analysis of the results obtained from cyclic voltammetry (CV) measurements indicated the electrochemical oxidation of Cf followed mixed adsorption and diffusion control process. The spectro-electrochemical investigations were carried out and the modification of the spectral peaks were monitored to obtain the mechanism of the electrochemical oxidation process of Cf. Interaction of Cf with Bovine Serum Albumin (BSA) were investigated using electrochemical, spectroscopic and spectro-electrochemical experiments. Important electro-kinetic parameters like; the electron transfer property, binding constant and diffusivity of the Cf/BSA complex were investigated. Electrochemistry with an ultra-microelectrode was utilised to investigate the diffusivity of the drug and its complex with BSA, which supports the strong binding of Cf with BSA.

High sensitive determination of dopamine through catalytic oxidation and preconcentration over gold-multiwall carbon nanotubes composite modified electrode.

Electrochemical properties of dopamine, uric acid and ascorbic acid have been investigated using gold nano particles (AuNPs) decorated functionalized multiwall carbon nanotubes (MWCNTs) nano composite modified electrode. MWCNTs were acid functionalized to introduce -COOH functionalities. The functionalized MWCNTs were used as support materials and were decorated with gold nano particles of 20 nm in size. The nano composite materials thus prepared have been named as f-MWCNTs/AuNPs composite. The composite material was characterized using FTIR, RAMAN, TEM, UV-VIS spectroscopy and atomic force microscopy measurements. Electrochemical investigations on the composite modified glassy carbon electrode for dopamine was investigated in presence of interfering agents like ascorbic acid and uric acid. The modified electrode showed sensitivity of 0.002 µAnM-1 for dopamine with the detection limit of 35 nM. Present electrode showed high selectivity for dopamine as the oxidation peak of dopamine and uric acid were very well resolved. The analytical method was found to be suitable for the simultaneous determination of dopamine and uric acid using the modified electrode. Method was applied in spiked real serum sample for the determination of dopamine.

In situ synthesis and properties of reduced graphene oxide/Bi nanocomposites: as an electroactive material for analysis of heavy metals.

An in situ modified Hummers method (without the use of any surfactants) has been used for the deposition of bismuth (Bi) nanoparticles onto the surface of reduced graphene oxide (RGO) sheets. The as-synthesized nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), thermogravimetry (TG) and differential scanning calorimetry (DSC). The morphology of the RGO/Bi nanocomposites provides a better choice as an electrode material for detection of heavy metal ions due to its better functional properties over the Bi film electrode. Trace analysis of heavy metal ions like Cd(+2), Pb(+2), Cu(+2) and Zn(+2) in water is carried out by stripping voltammetric analysis using RGO/Bi nanocomposite as an electrode material. The sensitivity and detection limit of the electrode were quantitatively estimated from the analysis. The three sigma detection limits at different deposition potential for Cd(2+), Pb(2+), Zn(2+) and Cu(2+) were obtained as 2.8, 0.55, 17 and 26µgL(-1), respectively. Copper detection using Bi-film electrode was a major challenge, which has been resolved using the RGO/Bi nanocomposite electrode.

Voltammetric determination of trace levels of Hg in ayurvedic medicine and in cobalt-containing samples using a carbon paste electrode.

An analytical method has been described for the determination of mercury using a carbon paste electrode. Conditions for the preparation of the carbon paste electrode were optimized for low background current in order to use it for the determination of ultra trace levels of mercury. The carbon paste electrode was found to be a good electrode material for the determination of mercury. The optimized pH for the determination was in the range of 2.5 to 3.5. The three sigma detection limit of mercury was obtained as 0.095 µg L(-1). Method has been modified for determination of mercury in cobalt sulfate samples.

An electrochemical method for the preparation of 63Ni source for the calibration of thermoluminescence dosimeter (TLD).

A novel electrochemical approach for preparation of (63)Ni sources for their application as check-light source for the calibration of thermo luminescence dosimeters (TLD) is described here. Required amount of (63)Ni on a copper substrate could be deposited by optimizing the experimental parameters such as current density, time of deposition, pH of the electrolyte and nickel ion concentration in the bath. (63)Ni sources of strength approximately 3.7 MBq could be prepared by electrodeposition at constant current on the copper matrix. Quality assurance tests to ensure nonleachability, uniform distribution of activity and stability of the sources that are necessary before application were performed.

Simultaneous determination of Pt and Rh by catalytic adsorptive stripping voltammetry, using hexamethylene tetramine (HMTA) as complexing agent.

Characteristics of the adsorption/electro-reduction of Pt/Rh hexamethylene tetramine (HMTA) complex on static mercury drop electrode surface were studied. Cyclic voltammetry was carried out to get the insight about the mechanistic behaviour of the catalytic current obtained in the voltammetric scan of Pt/Rh HMTA complex in acidic solution. Adsorptive stripping voltammetry using HMTA as the complexing agent was found to be highly sensitive method for the determination of Pt/Rh. Voltammetric measurements were carried out using hanging mercury drop electrode (HMDE) as the working electrode, a glassy carbon rod as the counter and an Ag/AgCl/KCl(saturated) as the reference electrode. Various electrochemical parameters like deposition potential, deposition time, concentration of the ligand, supporting electrolyte etc. were optimized. The detection limit of Pt and Rh was found to be 4.38 pM L(-1) and 2.80 pM L(-1), respectively for the deposition time of 30 s. Simultaneous determination of Pt(II) and Rh(III) in water samples was possible. The method was found to be free from the commonly occurring interfering ions such as Cu(II), Cd(II), Zn(II), Pb(II), Cr(III), Cr(VI), Fe(III), Fe(II), Ni(II) and Co(II). Spike recovery tests for both Pt and Rh in tap water and sea water samples were also carried out. The method has been verified by analyzing certified reference material (WMG-1).

Voltammetric determination of trace metals Zn2+, Cd2+, Pb2+, Cu2+, Co+2 and Ni+2 in some medicinally important plants from Western Ghats, Karnataka State, India.

Trace metal levels in selected medicinal plant leaves from Western Ghats, Karnataka, India were studied A method for the determination of Zinc, Copper, Lead and Cadmium simultaneously in the pH of 4.5 in citrate buffer, and Cobalt and Nickel simultaneously in the pH 9.2 in ammonia buffer medium has been optimized. Electrochemical method, Differential Pulse Anodic Stripping Voltammetry (DPASV) has been used for quantification. The optimized procedure has been successfully applied for the determination of the above-mentioned metal ions in some medicinally important plant leaves from Western Ghats, Karnataka, India. The concentrations of trace metals in the medicinal plant samples were found to be in the ranges: 15.61-20.71 mg g(-1) for copper, 0.056-0.10 mg g(-1) for cadmium, 0.91-1.81 mg g(-1) for lead, 0.42-0.96 mg g(-1) for nickel, 1.21-1.97 mg g(-1) for cobalt and 23.29-32.52 mg g(-1) for zinc. The effect of pH, deposition time and potential has been studied and optimized. The study reveals that all the trace metals are well within the maximum permissible limits, therefore, medicinal plants of this region are very much suitable for medicinal use. The results are compared with the data obtained by atomic absorption spectroscopy.