J. Nayak

Bio: J. Nayak is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Photoluminescence & Nanorod. The author has an hindex of 10, co-authored 31 publications receiving 422 citations. Previous affiliations of J. Nayak include Indian Institute of Technology Kharagpur & Pusan National University.

CdS–ZnO composite nanorods: Synthesis, characterization and application for photocatalytic degradation of 3,4-dihydroxy benzoic acid

Abstract: Well-aligned arrays of CdS–ZnO composite nanorods were grown on indium tin oxide substrates. ZnO nanorods, deposited by a low temperature aqueous chemical growth technique, were dip coated with CdS. The CdS–ZnO nanorods were polycrystalline as confirmed from the low angle X-rays diffraction study. Photon to current conversion efficiency of CdS–ZnO composite nanorod was observed to be higher than that of CdS. In the micro-Raman spectrum, we observed longitudinal optical modes of CdS and ZnO showing their co-existence. The appealing application of CdS–ZnO nanorod as a visible photocatalyst was demonstrated and the possible mechanism was discussed.

Enhancement of the visible luminescence from the ZnO nanocrystals by Li and Al co-doping

Abstract: Nanocrystals of ZnO, doped with aluminum and lithium, were synthesized by chemical co-precipitation from an aqueous solution mixture of Zn(NO) 3 , AlCl 3 and LiCl. With an aim to produce strong white luminescence, the intensity of the visible luminescence was tailored as a function of dopant concentration. We observed a significant enhancement of the yellowish-white photoluminescence from ZnO nanocrystals due to co-doping with aluminum and lithium. The luminescence intensity increases and the peak position shifts to lower wavelength with increase in the dopant concentration. Although the exact mechanism of the enhancement of the luminescence could not be established, still a possible shallow donor-to-deep acceptor recombination was proposed.

Role of hexamethylenetetramine in ZnO-cellulose nanocomposite enabled UV and humidity sensor

Abstract: Spherical nanoparticles and short nanorods of ZnO nanocrystals were grown on cellulose fibers by a simple one pot aqueous chemical bath deposition technique using hexamethylenetetramine (HMT) as the surfactant. The role of surfactant on UV and humidity sensing properties of ZnO-cellulose nanocomposite (ZCN) has been investigated. The structure, morphology and composition of the ZCNs were investigated by X-rays diffraction, field emission scanning electron microscopy and thermogravimetric analysis, respectively. The morphology, shape and size of the ZCN were analyzed by a transmission electron microscopy. The optical properties were investigated by diffuse reflectance spectroscopy (DRS). The band gap values of the composites, obtained from DRS, were in the range of 3.22–3.24 eV. The ZCN synthesized with 0.9 wt% of HMT showed a very high response to ultraviolet (UV) light, characterized by a large increase in the photocurrent under UV illumination. Due to UV illumination, the surface photocurrent recorded from a pellet of the above nanocomposite powder increased from 7.416 × 10−7 A to 3.161 × 10−5 A in 8 s. The ON to OFF ratio of the photocurrent (IUV/IDark) was 42.624, whereas the response and recovery times were 8 s and 10 s, respectively. The humidity sensing properties of the nanocomposite powder were studied in the relative humidity (RH) range 40–90% and a sensitivity of 4.487 MΩ/%RH was recorded for the powder synthesized at optimized condition. The high ON/OFF ratio, short response and recovery time imply the importance of the material as a good UV sensor, whilst the notable sensitivity of the material promises for efficient humidity sensing applications.

Persistent photoconductivity in ZnO nanorods deposited on electro-deposited seed layers of ZnO

Abstract: Arrays of standing nanorods of ZnO were successfully grown on indium tin oxide coated quartz substrates by an inexpensive aqueous chemical growth technique. The electrical properties of individual nanorod were investigated with the conducting tip of an atomic force microscope. The effect of ultraviolet irradiation on the conductivity of single nanorods was investigated. We observed a persistency of the photoconductivity, most probably ascribable to the oxygen vacancies in ZnO nanorods.

Study of structure and optical properties of GaAs nanocrystalline thin films

Abstract: Nanoparticulate thin films of GaAs we electrochemically prepared from acidic solutions of pure metallic Ga and As 2 O 3 . Samples of different crystallite sizes were prepared by varying the electrolysis parameters. Structural characterization of the nanoparticles were carried out by XRD technique which exhibits partial amorphization of the crystallites in the low electrolysis current regime. Quantum confinement effect was prominently observed in the optical absorption spectra with blue-shift of absorption onsets with respect to the bulk band gap. Room temperature photoluminescence exhibit band edge luminescence as well as other surface related bands. Incorporation of transition element as impurity leads to enhanced luminescence intensity and generates deep traps.

Semiconductor-based Photocatalytic Hydrogen Generation

Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

One-dimensional ZnO nanostructures: Solution growth and functional properties

Abstract: One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

ZnO nanostructures for optoelectronics: Material properties and device applications

Abstract: In recent years, there has been increasing interest in ZnO nanostructures due to their variety of morphologies and availability of simple and low cost processing. While there are still unanswered questions concerning fundamental properties of this material, in particular those related to defects and visible luminescence lines, great progress has been made in synthesis methods and device applications of ZnO nanostructures. In this review, we will provide a brief overview of synthesis methods of ZnO nanostructures, with particular focus on the growth of perpendicular arrays of nanorods/nanowires which are of interest for optoelectronic device applications. Then, we will provide an overview of material properties of ZnO nanostructures, issues related to doping with various elements to achieve either p- or n-type conductivity. Doping to alter optical or magnetic properties will also be discussed. Then, issues related to practical problems in achieving good electrical contacts to nanostructures will be presented. Finally, we will provide an overview of applications of ZnO nanostructures to light-emitting devices, photodetectors and solar cells.

Enhanced photocatalytic activity of ZnO/CuO nanocomposite for the degradation of textile dye on visible light illumination.

Abstract: The photocatalytic degradation of organic dyes such as methylene blue and methyl orange in the presence of various percentages of composite catalyst under visible light irradiation was carried out. The catalyst ZnO nanorods and ZnO/CuO nanocomposites of different weight ratios were prepared by new thermal decomposition method, which is simple and cost effective. The prepared catalysts were characterized by different techniques such as X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and UV-visible absorption spectroscopy. Further, the most photocatalytically active composite material was used for degradation of real textile waste water under visible light illumination. The irradiated samples were analysed by total organic carbon and chemical oxygen demand. The efficiency of the catalyst and their photocatalytic mechanism has been discussed in detail.

High Efficiency Solid-State Sensitized Solar Cell-Based on Submicrometer Rutile TiO2 Nanorod and CH3NH3PbI3 Perovskite Sensitizer

Abstract: We report a highly efficient solar cell based on a submicrometer (∼0.6 μm) rutile TiO2 nanorod sensitized with CH3NH3PbI3 perovskite nanodots. Rutile nanorods were grown hydrothermally and their lengths were varied through the control of the reaction time. Infiltration of spiro-MeOTAD hole transport material into the perovskite-sensitized nanorod films demonstrated photocurrent density of 15.6 mA/cm2, voltage of 955 mV, and fill factor of 0.63, leading to a power conversion efficiency (PCE) of 9.4% under the simulated AM 1.5G one sun illumination. Photovoltaic performance was significantly dependent on the length of the nanorods, where both photocurrent and voltage decreased with increasing nanorod lengths. A continuous drop of voltage with increasing nanorod length correlated with charge generation efficiency rather than recombination kinetics with impedance spectroscopic characterization displaying similar recombination regardless of the nanorod length.