Ramiah Saraswathi

Combustion synthesis of CuFe2O4

Metallic ferrites are investigated as prospective materials for different applications especially as anodes in extractive metallurgy. CuFe2O4, one of the important ferrites, is envisaged for substituting the carbon anode in Hall–Heroult cells. A single step combustion process has been used for the synthesis of CuFe2O4 powder from cupric nitrate, ferric nitrate and urea. The experimental conditions for maximum conversion efficiency of the precursor powders have been optimized. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) have confirmed the formation, structure and homogeneity of the as-prepared powders. The detailed physical, electrical and structural characterization of the materials have been carried out for the specimens obtained on sintering at different temperatures up to 1000 °C.

Polyaniline-carbon nanotube composites

The key developments in polyaniline-carbon nanotube (PANI-CNT) composites are reviewed. Apart from in situ chemical polymerization and electrochemical deposition, a number of interesting approaches including the use of aniline functionalized CNTs and ultrasound/microwave/γ-radiation initiated polymerization have been used in the preparation of composites. The structure and properties of these composites have been investigated by a variety of techniques including absorption, infrared (IR), Raman, X-ray photoelectron spectroscopy methods, scanning electron and scanning probe microscopy techniques, cyclic voltammetry, and thermogravimetry. The experimental results indicate favorable interaction between PANI and CNTs. The CNT content in these composites controls their conductive, mechanical, and thermal properties. The most interesting characteristic is their easy dispersibility in aqueous solution. The performance evaluation studies of PANI-CNT composites in a number of applications including supercapacitors, fuel cells, sensors, and actuators are highlighted.

Direct electrochemistry of myoglobin at reduced graphene oxide-multiwalled carbon nanotubes-platinum nanoparticles nanocomposite and biosensing towards hydrogen peroxide and nitrite

We described the preparation of a novel nanobiocomposite, reduced graphene oxide- multiwalled carbon nanotubes-platinum nanoparticles/myoglobin (RGO-MWCNT-Pt/Mb) for the direct electrochemistry of myoglobin and its application towards determination of hydrogen peroxide (H2O2) and nitrite (NO2(-)). RGO-MWCNT-Pt nanocomposite has been prepared by simple solution based approach and its structure was characterized. RGO-MWCNT-Pt/Mb nanobiocomposite was prepared and attained the direct electrochemistry of Mb with pair of well-defined redox peaks with the formal potential of -0.33 V and peak to peak separation of 22 mV. Amount of electroactive protein (Г) and heterogeneous electron transfer rate constant (ks) were calculated to be 1.04 × 10 (-9) mol cm(-2) and 9.47 s(-1). The sensor displayed lowest detection limit (LOD) of 6 pM which is the lowest LOD ever achieved for the detection of H2O2. Two linear ranges were observed for the detection of H2O2: (1) 10 pM-0.19 nM with sensitivity of 1.99 (± 0.058) µA pM(-1)cm(-2) and (2) 0.25 nM-2.24 µM with sensitivity of 0.037 (± 0.081) µA nM(-1)cm(-2). In addition, the biosensor offered good analytical parameters towards determination of NO2(-) with wide linear range of 1 µM to 12 mM and high sensitivity of 0.1651 (± 0.026) µA µM(-1) cm(-2). The sensor acquires good selectivity, repeatability, reproducibility and stability. The practical feasibility of the sensor has been addressed.

Thermal studies on polyindole and polycarbazole

Abstract The time and temperature dependences of conductivity of electrochemically prepared polyindole and polycarbazole perchlorates are analysed to understand the aging process and mechanism of conduction. Arrhenius and Mott plots suggest a variable range hopping (VRH) mechanism for polyindole and nearest-neighbour hopping for polycarbazole. The degradation behaviour has been studied by thermogravimetry (TG) and differential thermal analysis (DTA) techniques. The thermal reactions involve loss of dopant, followed by degradation of the polymer backbone. The decomposition temperatures of polyindole and polycarbazole are higher than the values reported in the literature for polyaniline, polypyrrole and polythiophene. The energy of activation for the polymer degradation process has been calculated using three methods and the results are compared.

Electrochemical preparation and characterization of conducting copolymers: poly(pyrrole-co-indole)

Copolymerization of pyrrole and indole was achieved electrochemically in acetonitrile containing lithium perchlorate as supporting electrolyte. The copolymer compositions can be altered by varying the comonomer feed ratios during preparation. The copolymers were characterized by conductivity measurements, cyclic voltammetry, scanning electron microscopy, UV-visible and IR spectroscopic techniques. A possible scheme for the copolymerization mechanism has been suggested.

Redox properties of poly(N-methylaniline)

Smooth. adherent films of poly(N-methylaniline) (PNMA) can be synthesised electrochemically in aqueous solutions containing 1 M H2SO4. The galvanostatic synthesis used in the present study gives a conductivity of 10(-1) S cm(-1) which is the highest value reported so far for PNMA. The redox properties are studied in a wide pH range (H-0 -2.4 for pH 7) using cyclic voltammetry and in situ absorption spectral measurements. A few parallel experiments on polyaniline (PANI) have been carried out for ease of comparison. The results indicate that the deprotonation of PNMA occurs below pH 1. The relative loss of redox activity with respect to increasing pH and the oxidative deterioration are less for PNMA compared to PANI. This will be an advantage in the construction of Zn-PNMA rechargeable cells. PNMA can be synthesised from non-aqueous solvents and its electrochemical stability is less compared to that of the film prepared in aqueous solutions

Direct electrochemistry of cytochrome c immobilized on a graphene oxide–carbon nanotube composite for picomolar detection of hydrogen peroxide

We describe the fabrication of an amperometric biosensor based on cytochrome c (Cyt c) immobilized graphene oxide–multiwalled carbon nanotube (GO–MWCNT) composite on a nano Au modified glassy carbon electrode for trace level detection of H2O2. Morphology and surface characterization of the nanocomposite reveal the successful formation of a highly conducting MWCNT network on the GO surface. Electrochemical impedance studies indicate a lower charge transfer resistance compared to the bare electrode. Cyclic voltammetry studies clearly demonstrate an enhanced direct electrochemistry of Cyt c with a high electron transfer rate constant (ks) value of 3.4 s−1. An amperometric H2O2 biosensor has been fabricated with an excellent current sensitivity of 0.533 μA pM−1 cm−2 and a very low detection limit of 27.7 pM. The fabricated sensor shows exceptional selectivity to H2O2 in the presence of a high concentration of some likely interferents. Moreover, the sensor exhibits high stability with appreciable repeatability and reproducibility.

An electrochemical synthesis strategy for composite based ZnO microspheres–Au nanoparticles on reduced graphene oxide for the sensitive detection of hydrazine in water samples

An electrochemical synthesis strategy has been developed to prepare a novel composite viz. reduced graphene oxide nanosheets/ZnO microspheres (∼0.6 μm)–Au nanoparticles (∼50 nm) modified glassy carbon electrode (GCE/RGO/ZnO–Au) for the trace level detection of hydrazine. Scanning Electron Microscopy (SEM) along with Energy Dispersive X-ray (EDX) analysis, confirming the presence of Au nanoparticles along with globular ZnO microspheres embedded over the entire surface of graphene nanosheets. The electrochemical detection of hydrazine is performed by cyclic voltammetry and chronoamperometry methods. Fascinatingly, the oxidation peak current of hydrazine at RGO/ZnO–Au modified GCE is 4.1 fold higher than that of RGO–Au modified GCE and 2.4 fold higher than ZnO/Au-modified GCE in addition to a favorable lower overpotential at 0.1 V. The chronoamperometric hydrazine sensor shows a very low detection limit of 18 nM with a high sensitivity of 5.54 μA μM−1 cm−2. The excellent analytical parameters of the RGO/ZnO–Au modified electrode over the various related modified electrodes suggest that the electrode can be advantageous for use in trace level detection of hydrazine in several industrial applications with low cost, ease of preparation, repeatability and long-term stability.

Electrochemical synthesis of Au–MnO2 on electrophoretically prepared graphene nanocomposite for high performance supercapacitor and biosensor applications

Herein, we report a facile electrochemical synthesis of an Au–MnO2 nanocomposite highly dispersed on an electrophoretically prepared graphene surface for the first time. Fascinatingly, we obtained a nanowires-like morphology for the MnO2 by using a simple in situ electrochemical deposition method. The as-synthesized Au–MnO2–graphene nanocomposite is characterized by various analytical and spectroscopic techniques viz. SEM, EDX, TEM, XRD, Raman spectroscopy and XPS. The as-prepared nanocomposite is employed in an electrochemical supercapacitor and for the sensitive detection of epinephrine. The supercapacitor performance is evaluated in 0.5 M NaOH by both cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) methods. The MnO2 : Au ratio during deposition plays a vital role to influence the capacitance properties. The highest specific capacitance of 575 F g−1 for 1 : 0.01 (MnO2 : Au) at a current density of 2.5 A g−1 has been obtained. The effect of current density, MnO2 : Au ratio, scan rate, mass loading and electrolyte concentration were also optimized and good cycle stability was demonstrated. The comparison of specific capacitance over MnO2–graphene and Au–MnO2–graphene nanocomposites suggests that the incorporation of Au nanoparticles on MnO2–graphene surfaces has a highly substantial effect for enhancement of capacitive behaviour. Furthermore, the epinephrine sensor performance of an Au–MnO2–graphene nanocomposite modified glassy carbon electrode is evaluated by CV and differential pulse voltammetry (DPV) techniques. Interestingly, the DPV sensor exhibited a very low detection limit of 24 nM and an excellent current sensitivity value of 35.6 μA μM−1 cm−2, surpassing several related modified electrodes and demonstrating several practical industrial applications.

Synthesis and electrochemical stability of polyaniline and polypyrrole in an ambient temperature acetamide—urea—ammonium nitrate eutectic melt

Abstract Semiconducting electroactive films of polyaniline and polypyrrole are prepared electrochemically in a room-temperature ternary melt of acetamide—urea—ammonium nitrate. The effect of solvent on the stability, structural and redox properties of the films has been studied. The spectral data indicate that the polymers have structures similar to those prepared in aqueous solutions. The film activity is lower for polyaniline and higher for polypyrrole in the melt when compared to the results obtained in aqueous solutions for the same dopant.