L. John Kennedy

Bio: L. John Kennedy is an academic researcher from VIT University. The author has contributed to research in topics: Diffuse reflectance infrared fourier transform & Crystallite. The author has an hindex of 48, co-authored 168 publications receiving 6401 citations. Previous affiliations of L. John Kennedy include Central Leather Research Institute.

Comparative investigation of structural, optical properties and dye-sensitized solar cell applications of ZnO nanostructures.

Abstract: Dye-sensitized solar cells (DSSCs) based on ZnO nanostructures with two different morphologies, such as nanowires (ZNWs) and nanoparticles (ZNPs), were synthesized by microwave combustion (MCM) and conventional combustion (CCM) method. The obtained ZnO nanostructures were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy. The XRD results confirmed the formation of hexagonal wurtzite ZnO. The crystallite size of the ZnO nanostructures was calculated using Sherrer's formula. The formation of ZNWs and ZNPs was confirmed by HR-SEM and HR-TEM. The optical absorption and PL emissions were determined by DRS and PL spectra respectively. ZnO nanostructures with band gap energies of 3.36 eV (MCM) and 3.25 eV (CCM) were obtained. The dye-sensitized ZnO nanowire arrays exhibit much stronger optical absorption as compared with ZnO nanoparticle arrays, suggesting that the larger surface area improves light harvesting. The dye-sensitized solar cell based on the optimized ZnO nanowires array reaches a conversion efficiency of 1.73%, which is higher than that obtained from ZnO nanoparticles (0.69%) under the light radiation of 1000 W/m2. As-prepared ZNWs have potential applications in fabricating next generation nanodevices.

Comparative studies on influence of morphology and La doping on structural, optical, and photocatalytic properties of zinc oxide

Abstract: A simple, low temperature co-precipitation method was developed to synthesize ZnO nanomaterials with different morphologies such as nanoflakes, spherical nanoparticles (SNPs), and nanorods. The concentration of the capping agent, Triton X-100, is a key factor in the morphological control of ZnO nanostructures. The formation of different morphologies of ZnO was confirmed by HR-SEM and HR-TEM. XRD data showed the formation of single-phase ZnO with the wurtzite crystal structure. The influence of La contents on the structure, morphology, absorption, emission, and photocatalytic activity of ZnO SNPs was investigated systematically. The influence of the ZnO morphologies on the photocatalytic degradation (PCD) of Bisphenol A (BPA) as a model reaction is evaluated and discussed in terms of surface area, crystal growth habits, particle size, and oxygen defects. The results indicated that the particle size is an important factor for the enhancement of PCD. Furthermore, the effect of different photocatalytic reaction parameters on the resulting PCD efficiency of ZnO SNPs was investigated.

Investigation of structural, surface morphological, optical properties and first-principles study on electronic and magnetic properties of (Ce, Fe)-co doped ZnO

Abstract: We report on the synthesis of ((Zn 1−2 x Ce x Fe x ) O ( x =000, 001, 002, 003, 004 and 005)) nanoparticles via microwave combustion by using urea as a fuel To understand how the dopant influenced the structural, magnetic and optical properties of nanoparticles, it was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM) The stability and magnetic properties of Ce and Fe co-doped ZnO were probed by first principle calculations From the analysis of X-ray diffraction, the samples are identified with the wurtzite crystal structure The change in lattice parameters, micro-strain, and a small shift in XRD peaks confirms the substitution of co dopants into the ZnO lattice Morphological investigation of the products revealed the existence of irregular shapes, such as spherical, spherodial and hexagonal DRS measurements showed a decrease in the energy gap with increasing dopants contents, probably due to an increase in the lattice parameters PL spectra consist of visible emission, due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O Zn ), interstitial zinc (Zn i ), interstitial oxygen (O i ) and zinc vacancy (V Zn ) Magnetic measurements showed a ferromagnetic behavior for all the doped samples at room temperature The first principle calculation results showed that the Ce governs the stability, while the Fe adjusts the magnetic characteristics in the Ce and Fe co-doped ZnO

A Green approach: synthesis, characterization and opto-magnetic properties of MgxMn1−xFe2O4 spinel nanoparticles

Abstract: MnFe2O4 nanoparticles of different crystallite size were prepared by varying the different concentrations of Mg2+ dopant ions using microwave assisted combustion method. The structural properties of the ferrite and modified ferrite were characterized by XRD (X-ray powder diffraction), Rietveld analysis, FT-IR (Fourier transforms infra red spectroscopy), HR-SEM (high resolution scanning electron microscopy), UV–Visible spectroscopy, PL (photoluminescence spectroscopy), and VSM (vibrating sample magnetometer). The concentration of the dopant metal ions plays an important role in phase, purity, morphology, optical and magnetic properties. X-ray diffraction and the HR-SEM analysis indicate that all the samples are single phase, crystalline and homogeneous in nature. The presence of metal oxides is confirmed by FT-IR analysis. The band gap energy of the samples has been studied using UV–Visible DRS measurements and the effect of Mg2+ doping on absorption spectra is also investigated. The band gap energy of the sample decreases with increasing the concentration of the dopant ions. The PL spectrum shows the emission peak at 565 nm with an excitation wavelength of 414 nm. The considerable decrease in saturation magnetization and increase in the coercivity value is determined using vibrating sample magnetometer.

Optical and magnetic properties of Co-doped CuO flower/plates/particles-like nanostructures.

Abstract: In this study, pure and Co-doped CuO nanostructures (0.5, 1.0, 1.5, and 2.0 at wt% of Co) were synthesized by microwave combustion method. The prepared samples were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). Powder X-ray diffraction patterns refined by the Rietveld method indicated the formation of single-phase monoclinic structure. The surface morphology and elemental analysis of Co-doped CuO nanostructures were studied by using HR-SEM and EDX. Interestingly, the morphology was found to change considerably from nanoflowers to nanoplates then to nanoparticles with the variation of Co concentration. The optical band gap calculated using DRS was found to be 2.1 eV for pure CuO and increases up to 3.4 eV with increasing cobalt content. Photoluminescence measurements also confirm these results. The magnetic measurements indicated that the obtained nanostructures were ferromagnetic at room temperature with an optimum value of saturation magnetization at 1.0 wt.% of Co-doped CuO, i.e., 970 micro emu/g.

Ultracapacitors: Why, How, and Where is the Technology

Abstract: The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

X-Ray Diffraction

Abstract: Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

A review of ZnO nanoparticles as solar photocatalysts: Synthesis, mechanisms and applications

Abstract: Persistent organic pollutants (POPs) are carbon-based chemical substances that are resistant to environmental degradation and may not be completely removed through treatment processes. Their persistence can contribute to adverse health impacts on wild-life and human beings. Thus, the solar photocatalysis process has received increasing attention due to its great potential as a green and eco-friendly process for the elimination of POPs to increase the security of clean water. In this context, ZnO nanostructures have been shown to be prominent photocatalyst candidates to be used in photodegradation owing to the facts that they are low-cost, non-toxic and more efficient in the absorption across a large fraction of the solar spectrum compared to TiO 2 . There are several aspects, however, need to be taken into consideration for further development. The purpose of this paper is to review the photo-degradation mechanisms of POPs and the recent progress in ZnO nanostructured fabrication methods including doping, heterojunction and modification techniques as well as improvements of ZnO as a photocatalyst. The second objective of this review is to evaluate the immobilization of photocatalyst and suspension systems while looking into their future challenges and prospects.

Applications of hierarchically structured porous materials from energy storage and conversion, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine

Abstract: Over the last decade, significant effort has been devoted to the applications of hierarchically structured porous materials owing to their outstanding properties such as high surface area, excellent accessibility to active sites, and enhanced mass transport and diffusion. The hierarchy of porosity, structural, morphological and component levels in these materials is key for their high performance in all kinds of applications. The introduction of hierarchical porosity into materials has led to a significant improvement in the performance of materials. Herein, recent progress in the applications of hierarchically structured porous materials from energy conversion and storage, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine is reviewed. Their potential future applications are also highlighted. We particularly dwell on the relationship between hierarchically porous structures and properties, with examples of each type of hierarchically structured porous material according to its chemical composition and physical characteristics. The present review aims to open up a new avenue to guide the readers to quickly obtain in-depth knowledge of applications of hierarchically porous materials and to have a good idea about selecting and designing suitable hierarchically porous materials for a specific application. In addition to focusing on the applications of hierarchically porous materials, this comprehensive review could stimulate researchers to synthesize new advanced hierarchically porous solids.