Saurav K. Guin

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.

Scope of detection and determination of gallium(III) in industrial ground water by square wave anodic stripping voltammetry on bismuth film electrode

Gallium(III) in ground water may cause human health hazards due to the antineoplastic and antimicrobial activities of gallium. However, the exposure limit of Ga(III) has not been set. This paper demonstrates the scope of employing the square wave anodic stripping voltammetry (SWASV) on bismuth film electrode (BiFE) for selective and sensitive detection of Ga(III) as well as its accurate and precise determination. The key parameters were optimized and the bismuth film morphology was characterized. The performance of BiFE was also compared with that of the mercury film electrode (MFE). The performance of BiFE was also studied for interferences of Zn(II), Cd(II), Tl(I) and Cu(II) ions. Gaussian peak fitting was performed to improve the calibration curve and the fitting process revealed almost similar stripping peak heights as obtained from the experimentally observed data though slight improvement in calibration was obtained from the peak area analysis. A good linear dynamic range (R(2)=0.996) was obtained in the concentration range of 20-100 μg/L with a limit of detection (LOD) of 6.6 μg/L (S/N=3) of Ga(III). A relative standard deviation of 2.9% (n=10) was obtained for 20 μg/L of Ga(III) solution. The practical analytical utility of the method was verified by the determination of Ga(III) in spiked water samples, where 100-105% recovery of Ga(III) was achieved.

Template-free electrosynthesis of gold nanoparticles of controlled size dispersion for the determination of lead at ultratrace levels

A methodology is presented for the template free electrosynthesis of gold nanoparticles (AuNPs) on a glassy carbon (GC) electrode with controlled particle size dispersion. The mechanism of electrocrystallization at the initial stage was investigated by cyclic voltammetry, chronoamperomentry, chronopotentiometry and in situ spectroelectrochemistry. Two strategies viz. multiple potentiostatic pulse (MPP) and multiple galvanostatic pulse (MGP) were adopted for electrochemically synthesizing the AuNPs. In the MPP strategy, the tapped hemispherical gold nanoparticles (AuNPs(P)/GC) of average diameter of 250–300 nm and average height of 10–15 nm were deposited on a GC electrode covering about 61% of the effective surface area of the electrode. In the MGP strategy, the tapped hemispherical gold nanoparticles (AuNPs(G)/GC) of average diameter of 350–400 nm and average height of 25–30 nm were deposited on a GC electrode covering about 18% of the effective surface area of the electrode. Excellent control of the particle size dispersion was achieved in both the routes of synthesis. The AuNPs, as synthesized, showed excellent electrocatalytic activity despite the absence of any surface stabilizing agent. The synthesized AuNPs showed excellent sensitivity to the determination of Pb(II) by square wave anodic stripping voltammetry (SWASV) by virtue of the underpotential deposition of lead on the gold surface. The limits of detection (LOD) of Pb(II) obtained with a bare GC, bare Au, AuNPs(G)/GC and AuNPs(P)/GC electrodes were calculated as 1.22 μg L−1 (5.86 nM), 122 ng L−1 (587 pM), 86.4 ng L−1 (416 pM) and 57 ng L−1 (274 pM), respectively, at S/N = 3. The analytical response of the AuNPs(P)/GC electrode was found to be the best among the four electrodes. The stability, repeatability, reproducibility and accuracy of the analytical response were found to be satisfactory for the analytical purposes. Bi(III), Cd(II) and Tl(I) showed major interferences with the analytical signal of Pb(II). The concentrations of Pb(II) in the laboratory tap, lake and river water were found to be 1.7 (±2.3%) μg L−1, 3.2 (±1.1%) μg L−1 and 8.4 (±3.9%) μg L−1, respectively using the AuNPs(P)/GC electrode. The results showed a good agreement with the ICP-MS data for the same samples. The studies showed that the concentration of Pb(II) in laboratory tap water, lake water from the Raja Ramanna Centre for Advanced Technology at Indore and water from near the Aassi ghat of the Ganges River in Varanasi, India were below the threshold limit of 10 μg L−1 as per the provisional guidelines set by WHO in 2011.

Electrochemistry of actinides on reduced graphene oxide: craving for the simultaneous voltammetric determination of uranium and plutonium in nuclear fuel

The aqueous electrochemistry of plutonium (Pu) has been explored for the first time on the reduced graphene oxide modified glassy carbon electrode (rGO/GC). It has been confirmed that rGO/GC can catalyse the Pu(IV)/Pu(III) redox reaction in 1 M H2SO4 and that finally leads to the high analytical sensitivity of anodic square wave voltammetric determination of Pu. However, the sensitivity of rGO/GC decreases in the actual nuclear fuel sample [i.e. Mark-I (U, Pu)C fuel dissolved in 1 M H2SO4] due to the interference of uranium (U). Furthermore, the cathodic square wave voltammograms of U(VI) in the sample solution have been found to be very inconsistent. That inconsistency is explained by the interfacial coupled chemical reaction between U(IV) (just produced at the working electrode) and Pu(IV) diffusing from the bulk of the solution to the vicinity of the working electrode. That is why the quantitative determination of uranium in the presence of plutonium is not feasible by simple voltammetric techniques on any working electrode. Although rGO/GC shows good analytical robustness, reproducibility, repeatability, fast analysis and least requirement of additional reagents; but challenge still exists in the analytical merits for the determination of Pu in nuclear fuel sample in competition with the biamperometric method.

Prospective use of the potentiostatic triple pulse strategy for the template-free electrosynthesis of metal nanoparticles

The electrosynthesis of metal nanoparticles with control over size and dispersion is a challenging task on a macrodisk electrode in the absence of any chemical or physical template. A potentiostatic triple pulse strategy (PTPS) was designed for the electrosynthesis of monodispersed lead nanoparticles (PbNPs) on glassy carbon electrodes. The results were compared to those obtained using the conventional potentiostatic double pulse strategy (PDPS). A switchover of the nucleation mechanism from progressive in PDPS to instantaneous in PTPS was observed for the first time during the final controlled growth step, resulting in smaller and better monodispersed PbNPs (∼8 ± 2 nm).

Template‐ and additive‐free electrosynthesis and characterization of spherical gold nanoparticles on hydrophobic conducting polydimethylsiloxane

Carbon-doped poly(dimethylsiloxane) (C-PDMS) modified with gold nanoparticles (AuNPs) is a highly promising material for the development of flexible lab-on-chip biosensors. Here, we present an electrochemical method to prepare stabilizer-free AuNPs directly on hydrophobic conducting substrates like C-PDMS without physical or chemical pre-treatment of the C-PDMS substrate. Using a potentiostatic triple pulse strategy, spherical, non-stabilized AuNPs of diameter 76±5 nm could be deposited within 5 s with narrow size-dispersion on the hydrophobic C-PDMS substrate in the absence of any structure directing or stabilizing agent. The detailed investigation of the mechanism of electrochemical formation of gold seeds and their three-dimensional growth on the hydrophobic surface along with nanomechanical atomic force-scanning electrochemical microscopy (QNM-AFM-SECM) characterization as well as conductive AFM allowed developing this fast electrochemical strategy with control in the desired size and size-dispersion of AuNPs. A detailed electrochemical investigation using cyclic voltammetry, anodic differential pulse voltammetry, and electrochemical impedance spectroscopy was conducted to characterize the electrochemical behavior of uncapped AuNPs deposited on C-PDMS. The Fc+ (MeOH)2 /Fc(MeOH)2 redox reaction at AuNPs-C-PDMS showed an improved charge transfer coefficient and heterogeneous charge transfer rate constant compared to the bare C-PDMS substrate.

A mechanistic study on the effect of a surface protecting agent on electrocrystallization of silver nanoparticles

Cyclic voltammetry and chronoamperometry at characteristic potentials were employed to unravel the mechanism of electrocrystallization of silver nanoparticles (AgNPs) from their aqueous solution in the presence and absence of surface protecting agent tetrabutylammonium tetrafluoroborate (TBABF4). The electrocrystallization parameters viz. initial current density (j0), decay constant (τ), diffusion coefficient (D) of Ag(I), number of active sites (N0) and nucleation rate (a) were calculated by fitting the experimentally obtained current transients with the calculated current transients using a hybrid genetic algorithm (HGA). The theoretical currents were calculated from three popular electrocrystallization models viz. Scharifker and Mostany (SM), Sluyters-Rehbach, Wijenberg, Bosco and Sluyters (SRWBS) and Heerman and Tarallo (HT). Each of the three models fitted well by the HGA with the potentiostatic current transients observed at different potentials, both in the absence and in the presence of TBABF4 with residual sum of squares (∼10−7) and reduced χ2 (∼10−10). However, the electrocrystallization parameters were distinctly different in each of the three models. Principal component analysis of the calculated parameters i.e. D, NS and aN0 showed the absence of any correlation among the electrocrystallization parameters derived from the Scharifker and Hills (SH), SM, SRWBS and HT models. Further, the actual nuclei densities of the AgNPs, both in the presence and the absence of TBABF4, were found to be significantly higher than the predicted values from any of these models. Since these models are based on different empirical assumptions, one needs be careful in attaching any extra significance to the numerical values of j0, τ, D, N0, “a” of any system only based on the quality of fitting. From the present data, it was conclusively proved that the surface protecting agent slowed down the kinetics of electrocrystallization due to introduction of a higher activation overpotential at the electrode–electrolyte interface and subsequent decreases in the number of nuclei on the electrode surface in the presence of TBA+ ions, irrespective of the model.