Ruma Gupta

Highly Sensitive Detection of Arsenite Based on Its Affinity toward Ruthenium Nanoparticles Decorated on Glassy Carbon Electrode.

Metallic ruthenium nanoparticles (Ru NPs) are formed on the glassy carbon electrode (GC) at electrodeposition potential of -0.75 V, as observed from X-ray photoelectron spectroscopy. Thus formed Ru NPs have the arsenite selective surface and conducting core that is ideally suited for designing a highly sensitive and reproducible response generating matrix for the arsenite detection at an ultratrace concentration in aqueous matrices. Contrary to this, arsenate ions sorb via chemical interactions on the ruthenium oxide (RuO2 and RuO3) NPs formed at -0.25 V, but not on the Ru NPs. For exploring a possibility of the quantification of arsenite in the ultratrace concentration range, the Ru NPs have been deposited on the GC by a potentiostatic pulse method of electrodeposition at optimized -0.75 V for 1000 s. Arsenite preconcentrates onto the Ru surface just by dipping the RuNPs/GC into the arsenite solution as it interacts chemically with Ru NPs. Electrochemical impedance spectroscopy of As(III) loaded RuNPs/GC shows a linear increase in the charge transfer resistance with an increase in As(III) conc. Using a differential pulse voltammetric technique, arsenite is oxidized to arsenate leading to its quantitative determination without any interference of Cu(2+) ions that are normally encountered in the water systems. Thus, the use of RuNPs/GC eliminates the need for a preconcentration step in stripping voltammetry, which requires optimization of the parameters like preconcentration potential, time, stirring, inferences, and so on. The RuNPs/GC based differential pulse voltammetric (DPV) technique can determine the concentration of arsenite in a few min with a detection limit of 0.1 ppb and 5.4% reproducibility. The sensitivity of 2.38 nA ppb(-1) obtained in the present work for As(III) quantification is considerably better than that reported in the literature, with a similar detection limit and mild conditions (pH = 2). The RuNPs/GC based DPV has been evaluated for its analytical performance using the lake water, ground water, and seawater samples spiked with known amounts of As(III).

A mechanistic study on the electrocatalysis of the Pu(IV)/Pu(III) redox reaction at a platinum electrode modified with single-walled carbon nanotubes (SWCNTs) and polyaniline (PANI)

The electrochemistry of the Pu(IV)/Pu(III) couple in 1 M sulphuric acid solution was studied on bare and modified platinum electrodes by cyclic voltammetry and electrochemical impedance spectroscopy. The platinum electrode was separately modified with single-walled carbon nanotubes (SWCNT-Pt) and polyaniline (PANI-Pt). The modified electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence (EDXRF). Electrocatalysis of the Pu(IV)/Pu(III) redox reaction was observed on both SWCNT-Pt and PANI-Pt. However, PANI-Pt showed better catalytic action for the electron transfer reaction of the Pu(IV)/Pu(III) couple. The Pu(IV)/Pu(III) couple showed quasi-reversible electron transfer behavior on a bare platinum electrode because of the PtO layer formation by the Pu(IV) solution at the electrode–electrolyte interface. In SWCNT-Pt, the direct interaction between Pu(IV) and platinum was blocked by SWCNTs and it diminished the oxide layer formation at the interface. The lower charge transfer resistance at SWCNT-Pt also promoted the rate of electron transfer reaction of the Pu(IV)/Pu(III) couple. Electrocatalysis of the Pu(IV)/Pu(III) couple on PANI-Pt was attributed to the cumulative effect of the Donnan interaction between the PANI and Pu(IV) anionic complex, specific adsorption of Pu(IV) on the reactive centres, low charge transfer resistance across the electrode–electrolyte interface and a catalytic chemical reaction coupled with the electron transfer reaction. To the best of our knowledge, this paper presents the first evidence of the electrocatalysis of actinides on SWCNT and PANI modified electrodes along with the detailed investigations of their electrocatalysis mechanisms.

Single-walled carbon nanotube (SWCNT) modified gold (Au) electrode for simultaneous determination of plutonium and uranium

A single-walled carbon nanotube-modified–Au electrode (SWCNT–Au) was employed for the simultaneous determination of Plutonium (Pu) and Uranium (U). The SWCNT–Au displayed excellent electrochemical catalytic activities towards Pu and U reduction compared to bare Au. In the differential pulse voltammetry technique (DPV), both Pu and U gave sensitive reduction peaks at 564 mV and −128 mV, respectively, versus a saturated Ag/AgCl electrode. Under the optimized experimental conditions, Pu and U gave linear responses over ranges of 10 to 100 μM (R2 = 0.990) and 3 to 10 μM (R2 = 0.987), respectively. The detection limits were found to be 8.2 μM for Pu and 2.4 μM for U.

Deciphering the Role of Charge Compensator in Optical Properties of SrWO4:Eu3+:A (A = Li+, Na+, K+): Spectroscopic Insight Using Photoluminescence, Positron Annihilation, and X-ray Absorption

Studies have been carried out to understand the specific role of the alkali charge compensator on the luminescence properties of an alkali ion (Li+, Na+, and K+) codoped SrWO4:Eu phosphor. The oxidation state of the europium ion was found to be +3 on the basis of X-ray absorption near edge structure (XANES) measurements. This is the first report of its kind where opposite effects of Li+ ion and Na+/K+ ions on photoluminescence intensity have been observed. Li+ ion codoping enhanced the photoluminescence intensity from SrWO4:Eu3+ phosphor while Na+/K+ ion codoping did not. On the other hand, the luminescence lifetime is maximum for the Na+ ion codoped sample and minimum for the Li+ ion codoped sample. The results could be explained successfully using time-resolved luminescence, positron annihilation lifetime spectroscopy (PALS), and extended X-ray absorption fine structure (EXAFS) spectroscopy measurements. Changes in the Eu-O bond length and Debye-Waller Factor (σ2) upon Li+/Na+/K+ codoping were monitored through EXAFS measurements. PALS also highlighted the fact that Li+ codoping is not contributing to reduction in the cation vacancies and might be occupying interstitial sites rather than lattice positions due to its very small size. On europium doping there is lowering in symmetry of SrO8 polyhedra from S4 to C6, which is reflected in an intense electric dipole transition in comparison to the magnetic dipole transition. This is also corroborated using trends in Judd-Ofelt parameters. The results have shown that the luminescence lifetime is better when the vacancy concentration is lower as induced by Na+ and K+ codoping, while the emission intensity is higher in the samples when distortion around Eu3+ is reduced as induced by Li+ codoping.

Ruthenium Nanoparticles Mediated Electrocatalytic Reduction of UO22+ Ions for Its Rapid and Sensitive Detection in Natural Waters

Reduction of UO22+ ions to U4+ ions is difficult due to involvement of two axially bonded oxygen atoms, and often requires a catalyst to lower the activation barrier. The noble metal nanoparticles (NPs) exhibit high electrocatalytic activity, and could be employed for the sensitive and rapid quantifications of U022+ ions in the aqueous matrix. Therefore, the Pd, Ru, and Rh NPs decorated glassy carbon electrode were examined for their efficacy toward electrocatalytic reduction of UO22+ ions and observed that Ru NPs mediate efficiently the electro-reduction of UO22+ ions. The mechanism of the electroreduction of UO22+ by the RuNPs/GC was studied using density functional theory calculations which pointed different approach of 5f metal ions electroreduction unlike 4p metal ions such as As(III). RuNP decorated on the glassy carbon would be hydrated, which in turn assist to adsorb the uranyl sulfates through hydrogen bonding thus facilitated electro-reduction. Differential pulse voltammetric (DPV) technique, was used for rapid and sensitive quantification of UO22+ ions. The RuNPs/GC based DPV technique could be used to determine the concentration of uranyl in a few minutes with a detection limit of 1.95 ppb. The RuNPs/GC based DPV was evaluated for its analytical performance using seawater as well lake water and groundwater spiked with known amounts of UO22+.

Novel Electrochemical Synthesis of Polypyrrole/Ag Nanocomposite and Its Electrocatalytic Performance towards Hydrogen Peroxide Reduction

A simple electrochemical method of synthesis of polypyrrole/silver (PPy/Ag) nanocomposite is presented. The method is based on potentiodynamic polymerization of pyrrole followed by electrodeposition of silver employing a single potentiostatic pulse. The synthesized PPy film has embedded Ag nanocubes. The morphology and structure of the resulting nanocomposite were characterized by field emission scanning electron microscopy and X-ray diffraction. Electron paramagnetic resonance studies showed that silver nanoparticle deposition on polypyrrole leads to an increase in carrier density, indicative of enhanced conductivity of the resulting composite. Electrocatalytic performance of the prepared composite was examined for reduction of hydrogen peroxide and was compared with corresponding PPy film and bare glassy carbon electrode.

Electrochemical studies of U(VI)/U(IV) redox reaction in 1M H2SO4at single-walled carbon nanotubes (SWCNTs) modified gold (Au) electrode

Abstract Electrochemistry of U(VI)/U(IV) couple in 1 M H2SO4 was studied on bare and SWCNT modified gold (Au) electrodes by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The gold electrode modified with single-walled carbon nanotubes (SWCNTs-Au) was characterized by scanning electron microscopy (SEM). Electrocatalysis of U(VI)/U(IV) redox reaction was observed on SWCNT-Au. The lower charge transfer resistance at SWCNT-Au promoted the rate of electron transfer reaction of U(VI)/U(IV) couple. These results are interesting to develop electroanalytical methodologies for uranium determination using SWCNT modified electrodes. To the best of our knowledge, this is the first study on the electrocatalysis of uranium on SWCNT modified electrode.

A Novel Framework for Identifying the Interactions between Biophysical and Social Components of an Agricultural System: A Guide for Improving Wheat Production in Haryana, NW India.

ABSTRACT Purpose: The purpose of this study is to develop a conceptual framework with related analysis methodologies that identifies the influence of social environment on an established cropping system. Design/methodology/approach: A stratified survey including 103 villages and 823 farmers was conducted in all districts of Haryana (India). Firstly, technical efficiency (TE) was modeled using biophysical data including grain yield, seeding rate, wheat varieties, tillage, sowing date, seed source, harvesting method and the application of fertilizer, herbicide and irrigation. The relationship between TE and social community factors such as farm size, farmer age, level of education and agricultural support programs was analyzed by regression tree. Findings: TE was lower with the farmers who only have education to a primary standard. Farmers with high TE scores were mostly between 35 and 40 years of age, and a higher TE association was common for farmers who use technical publications. Social individual factors such as farmers’ views on the future of farming were also analyzed across different TE levels. Practical implications: Farmers with lower TE are an obvious target for production improvement, particularly given the understanding that the overall production yield gap is small in Haryana. Theoretical implications: Our conceptual framework shows a quantitative way to establish the socio-ecological linkage, and to identify the opportunities for changes in management with extension services leading to productivity improvement. Originality/value: This paper provides a novel framework with detailed methodology to effectively identify the socio-economic factors that limit the biophysical production in an agricultural system.

Extraction and electrochemical investigations of Pu(IV) employing green solvent system containing new bifunctional ligand and Bmim[NTf2] ionic liquid

Electrochemical investigations and extraction of Pu(IV) was investigated employing a new bifunctional ligand system (N,N-dialkyl carbamoyl methyl) (2-pyridyl-N-Oxide) sulfide C5H4NOSCH2CONR2, (where R = octyl) (NOSCO) dissolved in 1-butyl-3-methylimidazolium bis (trifluoromethanesulphonyl) imide ([Bmim][NTf2]). The extraction efficiency was found to be 84% in single contact. Cyclic voltammetry (CV) of Pu(IV) in aqueous and in ([Bmim][NTf2] + NOSCO) was carried out. Shifts of cathodic and anodic peak potentials of Pu(IV) in cyclic voltammograms were observed towards negative potentials in the extended electrochemical window for ionic liquid medium compared to aqueous medium. The diffusion coefficient and heterogeneous charge transfer coefficient were calculated for both aqueous and ionic liquid media. The redox reaction were found to be quasi reversible for both the media while the CV was broader in case of ionic liquid suggesting slow kinetics.

Studies on electrochemical behaviour on NpO22+/NpO2+ redox couple at single walled carbon nanotube modified glassy carbon electrode (SWCNT-GC)

Abstract Electrochemistry of NpO22+/NpO2+ couple in 1 M H2SO4 was studied on bare and modified glassy carbon (GC) electrodes by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The modified electrode (SWCNTs-GC) was characterized by scanning electron microscopy (SEM). Electrocatalysis of NpO22+/NpO2+redox reaction was observed on SWCNT-GC electrode. The lower charge transfer resistance at SWCNT-GC reflects faster rate of electron transfer reaction of Np(VI)/Np(V) couple. These results are interesting to develop electroanalytical methodologies for neptunium determination using SWCNT modified electrode. To the best of our knowledge, this is the first study on the electrocatalysis of neptunium on SWCNT modified electrode.