Bikash Kumar Jena

Gold nanoelectrode ensembles for the simultaneous electrochemical detection of ultratrace arsenic, mercury, and copper.

Simultaneous electrochemical detection of As(III), Hg(II), and Cu(II) using a highly sensitive platform based on gold nanoelectrode ensembles (GNEEs) is described. GNEEs were grown by colloidal chemical approach on thiol-functionalized solgel derived three-dimensional silicate network preassembled on a polycrystalline gold (Au) electrode. GNEEs on the silicate network have been characterized by field emission scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, and electrochemical measurements. Square wave anodic stripping voltammetry (SWASV) has been used for the detection of As(III) and Hg(II) without any interference from Cu(II) at the potentials of 0.06 and 0.53 V, respectively. The GNEE electrode is highly sensitive, and it shows linear response for As(III) and Hg(II) up to 15 ppb. The detection limit (signal-to-noise ratio = 4) of the GNEE electrode toward As(III) and Hg(II) is 0.02 ppb, which is well below the guideline value given by the World Health Organization (WHO). The potential application of the GNEE electrode for the detection of As(III) in a real sample collected from the arsenic-contaminated water in 24 North Parganas, West Bengal is demonstrated. The GNEE electrode has been successfully used for the simultaneous detection of As(III), Cu(II), and Hg(II) at sub-part-per-billion level without any interference for the first time. The nanostructured electrode shows individual voltammetric peaks for As(III), Cu(II), and Hg(II) at 0.06, 0.35, and 0.53 V, respectively. The analytical performance of the GNEE electrode is superior to the existing electrodes.

Au Disk Nanoelectrode by Electrochemical Deposition in a Nanopore

In this technical note, we report a process in scaling down the fabrication of Au disk nanoelectrodes as small as approximately 4 nm in radii. We have developed a bottom-up approach toward the fabrication of individual disk-shape Au nanoelectrodes. This new approach is based upon electrochemical deposition of Au in a silica nanopore electrode and involves the following four steps. First, a laser-assisted pulling process is employed to fabricate a disk-shape Pt nanoelectrode. Second, a Pt nanopore electrode is obtained by electrochemically etching the Pt from the disk nanoelectrode. Third, a Au metal nanowire is electrochemically deposited using the Pt nanopore electrode as a template. In the last step, the Au electrode is slightly polished to expose a disk-shape Au nanoelectrode, whose size is determined by the size of the initial Pt nanoelectrode. Steady-state voltammetry in the presence of ferrocene has been used to characterize these Au nanoelectrodes. The Au nanoelectrodes are also characterized using cyclic voltammetry in a H2SO4 solution. The results show characteristic peaks corresponding to the formation of Au surface oxides and their subsequent reduction. The Au nanoelectrodes are modified with 6-(ferrocenyl)hexanethiol molecules, and cyclic voltammetry is used to characterize the ferrocene molecules attached at the Au. As an application, we have constructed Au single-nanoparticle electrodes (SNPEs) using the Au disk nanoelectrodes fabricated by electrochemical deposition. Our initial results of such SNPEs show excellent electrochemical response from single Au nanoparticles.

In situ synthesis of flowery-shaped α-FeOOH/Fe2O3 nanoparticles and their phase dependent supercapacitive behaviour

In situ, one-step, facile synthetic strategies for flowery-shaped iron oxide nanoparticles were developed. Herein, we report simplified controlled synthesis of 2-line ferrihydrite–goethite core–shell particles for the first time in a semi-aqueous-organic medium. The present route offered phase selectivity by controlling only the aqueous-to-organic phase ratio. The synthesised nanoparticles have high surface areas of 110 m2 g−1 and 185 m2 g−1 for 2-line ferrihydrite and core–shell goethite, respectively. Further, flowery-shaped hematite nanoparticles were obtained by annealing core–shell iron oxide nanoparticles at 400 °C. Phase purities were confirmed by XRD (X-ray diffraction), IR (infrared spectroscopy), and XPS (X-ray photo electron spectroscopy) analysis. Formation of the core–shell nanostructure for the iron oxide samples was confirmed by Mossbauer and selected area electron diffraction (SAED) studies. All the synthesized iron oxide materials were studied for their supercapacitor behaviour by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chrono-potentiometry charge–discharge measurements. Specific capacitances for core–shell α-FeOOH and α-Fe2O3 were found to be 160 F g−1 and 200 F g−1, respectively. These values were much higher as compared to the previous reported values for pure phases of iron oxides. The chrono-potentiometric charge–discharge study for all the three samples revealed their self-discharging capacities. Moreover, these iron oxide composite electrodes exhibited excellent cycling performance with >99% capacitance retention over 500 cycles. Electrochemical performance of the two-electrode system was also studied. Furthermore, the electrochemical impedance spectroscopy (EIS) demonstrated that the electrochemical resistance of α-Fe2O3 was slightly reduced with the number of cycles, indicating easier access for intercalation/deintercalation of charges in the flowery-structured materials. Thus, the present material can be used as an electrochemical supercapacitor for high-performance energy storage devices in future.

Highly Sensitive Detection of Exocytotic Dopamine Release Using a Gold-Nanoparticle-Network Microelectrode

Here we report a new type of microelectrode sensor for single-cell exocytotic dopamine release. The new microsensor is built by forming a gold-nanoparticle (AuNP) network on a carbon fiber microelectrode. First a gold surface is obtained on a carbon fiber microdisk electrode by partially etching away the carbon followed by electrochemical deposition of gold into the pore. The gold surface is chemically functionalized with a sol-gel silicate network derived from (3-mercaptopropyl)trimethoxysilane (MPTS). A AuNP network is formed by immobilizing Au nanoparticles onto the thiol groups in the sol-gel silicate network. The AuNP-network microelectrode has been characterized by scanning electron microscopy (SEM) and steady-state voltammetry. The AuNP-network microelectrode has been used for amperometric detection of exocytotic dopamine secretion from individual pheochromocytoma (PC12) cells. The results show significant differences in the kinetic peak parameters including shorter rise time, decay time, and half-width as compared to a bare carbon fiber electrode equivalent. These results indicate AuNP-network microelectrodes possess an excellent sensing activity for single-cell exocytotic catecholamine release, specifically dopamine. Moreover, key advantageous properties inherent to bare carbon fiber microelectrodes (i.e., rigidity, flexibility, and small size) are maintained in addition to an observed prolonged shelf life stability and resistance to cellular debris fouling and dopamine polymerization.

Graphene-induced Pd nanodendrites: A high performance hybrid nanoelectrocatalyst

AbstractA facile and green approach has been developed for the in situ synthesis of hybrid nanomaterials based on dendrite-shaped Pd nanostructures supported on graphene (RG). The as-synthesized hybrid nanomaterials (RG-PdnDs) have been thoroughly characterized by high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, Raman spectroscopy and electrochemical techniques. The mechanism of formation of such dendrite-shaped Pd nanostructures on the graphene support has been elucidated using TEM measurements. The RG induces the formation of, and plays a decisive role in shaping, the dendrite morphology of Pd nanostructures on its surface. Cyclic voltammetry and chronoamperometry techniques have been employed to evaluate the electrochemical performance of RG-PdnDs towards oxidation of methanol. The electrochemical (EC) activities of RG-PdnDs are compared with graphene-supported spherical-shaped Pd nanostructures, Pd nanodendrites alone and a commercial available Pd/C counterpart. The combined effect of the graphene support and the dendrite morphology of RG-PdnDs triggers the high electrocatalytic activity and results in robust tolerance to CO poisoning.

Sandwiched graphene with nitrogen, sulphur co-doped CQDs: an efficient metal-free material for energy storage and conversion applications

Here, a hybrid material composed of sandwiched reduced graphene oxide (rGO) and N,S co-doped carbon quantum dots (N,S-CQDs) was prepared following a facile synthetic route. This metal-free composite has demonstrated their dual performance as an electrode material for supercapacitors and fuel cell catalysts. It shows robust cyclic stability with high energy and power density without any binders. The enhanced activity of the composite can be ascribed to the CQDs present within the interlayer of the rGO which enhance the accessibility of the charged ions and increase the capacitance of the composite. In addition, the electrocatalytic activity of the composite has been assessed as a metal-free cathode catalyst towards the oxygen reduction reaction (ORR) for fuel cell applications. It shows better performance in terms of high reduction potential and high reduction current as compared to rGO. This can be ascribed to the significant contribution of electron rich heteroatom doped CQDs as well as the synergistic effect of both the CQDs and rGO for the electrocatalytic reduction of oxygen. The interesting dual performance of heteroatom doped CQDs and graphene hybrid composites hold potential for the development of energy storage and conversion devices.

Facile synthesis of Ag nanowire–rGO composites and their promising field emission performance

Crystalline, ultra long silver nanowires (Ag NWs), few-layered rGO (reduced graphene oxide) and their rGO–Ag NW nanocomposite have been synthesized using a polyol reflux technique under optimized experimental conditions. The field emission performance of the rGO–Ag NW nanocomposite, rGO and Ag NW emitters was investigated. The turn on field required to draw an emission current density of ∼1 μA cm−2 was found to be ∼5.00, 3.92 and 2.40 V μm−1 for the Ag NW, rGO and rGO–Ag NW nanocomposite emitters, respectively. The combined contribution of the sharp edges of the thin graphene sheets and high aspect ratio of the Ag nanowires, and their synergetic effect in the rGO–Ag NW nanocomposite, are responsible for the enhanced field emission behavior. First-principles density functional calculations show that the enhanced field emission may also be due to the overlapping of the electronic structures of the Ag NWs and rGO nanosheets.

Urea-Assisted Room Temperature Stabilized Metastable β-NiMoO4: Experimental and Theoretical Insights into its Unique Bifunctional Activity toward Oxygen Evolution and Supercapacitor

Room-temperature stabilization of metastable β-NiMoO4 is achieved through urea-assisted hydrothermal synthesis technique. Structural and morphological studies provided significant insights for the metastable phase. Furthermore, detailed electrochemical investigations showcased its activity toward energy storage and conversion, yielding intriguing results. Comparison with the stable polymorph, α-NiMoO4, has also been borne out to support the enhanced electrochemical activities of the as-obtained β-NiMoO4. A specific capacitance of ∼4188 F g-1 (at a current density of 5 A g-1) has been observed showing its exceptional faradic capacitance. We qualitatively and extensively demonstrate through the analysis of density of states (DOS) obtained from first-principles calculations that, enhanced DOS near top of the valence band and empty 4d orbital of Mo near Fermi level make β-NiMoO4 better energy storage and conversion material compared to α-NiMoO4. Likewise, from the oxygen evolution reaction experiment, it is found that the state of art current density of 10 mA cm-2 is achieved at overpotential of 300 mV, which is much lower than that of IrO2/C. First-principles calculations also confirm a lower overpotential of 350 mV for β-NiMoO4.

Simple Growth of Faceted Au–ZnO Hetero-nanostructures on Silicon Substrates (Nanowires and Triangular Nanoflakes): A Shape and Defect Driven Enhanced Photocatalytic Performance under Visible Light

A simple single-step chemical vapor deposition (CVD) method has been used to grow the faceted Au-ZnO hetero-nanostructures (HNs) either with nanowires (NWs) or with triangular nanoflakes (TNFs) on crystalline silicon wafers with varying oxygen defect density in ZnO nanostructures. This work reports on the use of these nanostructures on substrates for photodegradation of rhodamine B (RhB) dyes and phenol under the visible light illumination. The photoluminescence measurements showed a substantial enhancement in the ratio of defect emission to band-edge emission for TNF (ratio ≈ 7) compared to NW structures (ratio ≤ 0.4), attributed to the presence of more oxygen defects in TNF sample. The TNF structures showed 1 order of magnitude enhancement in photocurrent density and an order of magnitude less charge-transfer resistance (R(ct)) compared to NWs resulting high-performance photocatalytic activity. The TNFs show enhanced photocatalytic performance compared to NWs. The observed rate constant for RhB degradation with TNF samples is 0.0305 min(-1), which is ≈5.3 times higher compared to NWs case with 0.0058 min(-1). A comparison has been made with bulk ZnO powders and ZnO nanostructures without Au to deduce the effect of plasmonic nanoparticles (Au) and the shape of ZnO in photocatalytic performance. The results reveal the enhanced photocatalytic capability for the triangular nanoflakes of ZnO toward RhB degradation with good reusability that can be attracted for practical applications.

A facile approach for morphosynthesis of Pd nanoelectrocatalysts

A facile approach has been developed for synthesis of highly-structured, anisotropic Pd nanostructures. The dendritic Pd nanostructures show superior performance toward oxidation of formic acid and methanol for fuel cell application.