Manoj K. Ram

Synthesis, characterization, and applications of ZnO nanowires

ZnO nanowires (or nanorods) have been widely studied due to their unique material properties and remarkable performance in electronics, optics, and photonics. Recently, photocatalytic applications of ZnO nanowires are of increased interest in environmental protection applications. This paper presents a review of the current research of ZnO nanowires (or nanorods) with special focus on photocatalysis. We have reviewed the semiconducting photocatalysts and discussed a variety of synthesis methods of ZnO nanowires and their corresponding effectiveness in photocatalysis. We have also presented the characterization of ZnO nanowires from the literature and from our own measurements. Finally, a wide range of uses of ZnO nanowires in various applications is highlighted in this paper.

Synthesis and the physical properties of MnZn ferrite and NiMnZn ferrite–polyaniline nanocomposite particles

We present a novel approach to synthesize MnZnferrite (MZF)–NiMnZnferrite(NiMZF)–Polyaniline (PANI) particles, where MnZnferrite is the magnetic core, and PANI is the conducting layer. The commercial ferrite and Ni–ferrite particles are primarily used, and the PANI–ferrite particles with a hybrid structure are synthesized via an oxidative electrochemical polymerization of aniline in an aqueous solution, which contains well-dispersed ferrite particles. The influence of ferrite content with respect to the electrical and ferromagnetic properties of the composite has been investigated by Electrochemical Impedance Spectroscopy (EIS) and DC field-cooled, zero-field cooled susceptibilities and M–H loop measurements. The origin of their electrical and ferromagnetic properties is also discussed based on structural characterizations including Fourier Transform Infrared (FT-IR) spectroscopy and X-Ray Diffraction (XRD).

Nano-assembly of glucose oxidase on the in situ self-assembled films of polypyrrole and its optical, surface and electrochemical characterizations

An in situ self-assembly technique with nanometre control over thicknesses and multilayered structures was used to manufacture the ultrathin films of polypyrrole (PPY). The PPY film was deposited on a polyanion, poly(styrene sulfonate) (PSS) modified surface as a function of time, previously PSS had been deposited on various substrates (glass, mica, indium-tin-oxide coated glass plates). Later, alternate PPY and PSS films were fabricated on such substrates using a layer-by-layer (LBL) technique. The glucose oxidase (GOD) molecules were also deposited on such self-assembled PPY films by the LBL technique. The PSS/PPY/GOD, PPY/PPY/GOD/poly(ethylene imine) (PEI)/GOD etc, film configurations were fabricated, and functionally as well as structurally characterized by UV-visible, electrochemical and scanning probe microscopy techniques, respectively. The results of a scanning probe microscopic study on the films were analysed to understand the molecular orientation of GOD on the PPY surface, and the dependence of the enzyme concentration for the depositing solutions. Moreover, the electrochemical studies performed provided information with respect to the electron transfer processes on the spatial arrangement of GOD molecules on the PPY surfaces. The immobilization of GOD on a conductive PPY represented a crucial and important step, and allowed us to construct the glucose-responsive biosensors.

The electrochromic response of polyaniline and its copolymeric systems

Abstract Conducting polyaniline (PANI) and its copolymer films of poly(aniline-co- o -toluidine) (PAOT) and poly(aniline-co- o -anisidine) (PAOA) have been electrochemically synthesized. The optical and structural properties of PANI, PAOT and PAOA have been studied using UV-visible absorption and X-ray diffraction techniques. The X-ray diffraction study reveals a crystalline structure for PANI whereas it shows an amorphous structure for PAOT and PAOA conducting copolymer films. Moreover, the switching lifetime, applied voltage, cycle lifetime in the glass/ITO/conducting polymer/HCl/ITO/glass configuration of PANI, PAOA and PAOT have been experimentally investigated. Further, the current transient for coloration and discoloration has been analysed in order to understand the charge transport in conducting polymer and copolymeric systems. It has been shown that PAOA shows better electrochromic response (143 ms) than PANI and PAOT systems. It is believed that the presence of the -OCH 3 group in the PAOA copolymer facilitates the torsional angle between aniline and methoxy aniline. In addition, the effect of HCl acid molarity on the switching response of PAOA conducting copolymer films has been studied.

Electron transfer mechanism of cytochrome c at graphene electrode

We report the direct electron transfer of cytochrome c (Cyt c) observed at graphene electrodes. Graphene nanosheets were chemically synthesized and immobilized on to a glassy carbon electrode. Cyclic voltammetry of Cyt c in phosphate buffered saline was performed at these electrodes. Results indicated a pair of reversible redox waves with a peak-to-peak separation value of 0.07 V in a diffusion controlled electrochemical process. Furthermore, the voltammetric response of these electrodes in Cyt c were found to be stable over time with negligible electrode fouling toward Cyt c.

Optical, structural and fluorescence microscopic studies on reduced form of polyaniline : The leucoemeraldine base

Electrochemically deposited thin films of emeraldine salt (ES) on indium-tin-oxide (ITO) glass plate and [111] silicon crystal were treated chemically with a phenyl hydrazine (PNH) solution in order to obtain a leucoemeraldine base (LB) form of polyaniline (PANI). The NMP-treated PANI films were washed using different organic solvents. ES, LB and air-oxidized LB films were examined using UV-visible, optical microscopy, X-ray diffraction and fluorescence microscopic techniques. The obtained results showed a direct correlation in the optical, structural and fluorescence behaviour of the LB form of PANI. An X-ray diffraction study revealed the partial crystallinity in the ES, whereas the LB and the air-oxidized LB showed amorphous structures. The first evidence of high fluorescence microscopic behaviour in the LB form of PANI has been observed. The gradual decrease in fluorescence signal as a function of time for the LB film has been interpreted as being due to the diffusion phenomenon in relation to the contact of the complex of the phenyl ring with O2 molecules.

A physical insight into the gas-sensing properties of copper (II) tetra-(tert-butyl)-5,10,15,20-tetraazaporphyrin Langmuir–Blodgett films

Abstract The Langmuir isotherm of copper (II) tetra-( tert -butyl)-5,10,15,20-tetraazaporphyrin [CuPaz( t -Bu) 4 ] has been investigated at the air–water interface. The Langmuir monolayer displays two phase regions, which have a phase transition at 7 mN/m. Langmuir–Blodgett (LB) films have been fabricated onto glass slides, interdigitated electrodes and quartz crystal microbalance electrodes, and characterized by UV-VIS spectroscopy, electrical and nanogravimetric measurements, respectively. The CuPaz( t -Bu) 4 LB films were used to quantity some of the volatile gases, i.e. vapors of hexane, benzene and toluene. UV-VIS spectroscopic measurements reveal that there is an interaction between CuPaz( t -Bu) 4 molecules and the above organic solvent molecules, which is manifested by a red shift and broadening of Soret and Q bands. The response and recovery behaviors, sensitivity and selectivity of the LB films to different organic vapors have been investigated by means of nanogravimetric measurements. Such results offer a potential application of such a porphyrin derivative for the detection of aromatic compounds, even at room temperature.

Comparative studies on Langmuir-Schaefer films of polyanilines

Abstract Langmuir isotherms of polyaniline (PANI), poly( o -toluidine) (POT), poly( o -anisidine) (POAS) and poly( o -ethoxy aniline) (PEOA) were investigated at aqueous subphase of pH 1, where doping during monolayer formation appeared as an essential step for high quality of the film. The effect of substituent groups in polyanilines plays a prominent role for the formation of Langmuir films. The area per unit repeat molecule was shown to increase by an increment of the substituent groups in polyanilines. Ultra-thin films of PANI, POT, POAS and PEOA were engineered by Langmuir–Schaefer (LS) technique. The uniformity of the deposited polyanilines LS films was verified by atomic force microscopy (AFM). The electrochemical properties of polyanilines LS films were investigated by cyclic voltammetry and current transient measurements, and the electrical characteristics were investigated by depositing the films on interdigitated electrodes. The electrochromic switching response time and diffusion coefficient of such LS films were also estimated by electrochemical surveyings.

Structure and opto-electrochemical properties of ZnO nanowires grown on n-Si substrate.

Zinc oxide (ZnO) nanostructures have attracted great attention as a promising functional material with unique properties suitable for applications in UV lasers, light emitting diodes, field emission devices, sensors, field effect transistors, and solar cells. In the present work, ZnO nanowires have been synthesized on an n-type Si substrate using a hydrothermal method where surfactant acted as a modifying and protecting agent. The surface morphology, electrochemical properties, and opto-electrochemical properties of ZnO nanowires are investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry, and impedance spectroscopy techniques. The cycling characteristics and rate capability of the ZnO nanowires are explored through electrochemical studies performed under varying electrolytes. The photo response is observed using UV radiation. It is demonstrated that crystallinity, particle size, and morphology all play significant roles in the electrochemical performance of the ZnO electrodes.

Fabrication and physico-chemical properties of Nafion Langmuir–Schaefer films

The Langmuir monolayer behaviour of Nafion (perfluorinated ionomer) films at the air/water interface for different aqueous subphases was investigated. The pressure–area isotherms and the Brewster angle microscopic study of Langmuir monolayer of Nafion in different electrolytic media allowed us to find the best experimental conditions for the deposition of stable Langmuir–Schaefer (LS) films. The results obtained for Nafion LS films through a combination of physical measurements (UV–vis spectroscopy, atomic force microscopy and nano-gravimetry) indicated a stepwise and uniform growth of films on the substrate. The electrochemical and photoelectrochemical properties of dyes incorporated within Nafion LS films were investigated. This paper reports the first experimental results showing the possibility of obtaining and depositing Nafion LS films.