L. John Kennedy

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

Green synthesis of NiO nanoparticles using Moringa oleifera extract and their biomedical applications: Cytotoxicity effect of nanoparticles against HT-29 cancer cells.

Abstract: Green protocols for the synthesis of nickel oxide nanoparticles using Moringa oleifera plant extract has been reported in the present study as they are cost effective and ecofriendly, moreover this paper records that the nickel oxide (NiO) nanoparticles prepared from green method shows better cytotoxicity and antibacterial activity. The NiO nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), High resolution transmission electron microscopy (HRTEM), Energy dispersive X-ray analysis (EDX), and Photoluminescence spectroscopy (PL). The formation of a pure nickel oxide phase was confirmed by XRD and FTIR. The synthesized NiO nanoparticles was single crystalline having face centered cubic phase and has two intense photoluminescence emissions at 305.46nm and 410nm. The formation of nano- and micro-structures was confirmed by HRTEM. The in-vitro cytotoxicity and cell viability of human cancer cell HT-29 (Colon Carcinoma cell lines) and antibacterial studies against various bacterial strains were studied with various concentrations of nickel oxide nanoparticles prepared from Moringa oleifera plant extract. MTT assay measurements on cell viability and morphological studies proved that the synthesized NiO nanoparticles posses cytotoxic activity against human cancer cells and the various zones of inhibition (mm), obtained revealed the effective antibacterial activity of NiO nanoparticles against various Gram positive and Gram negative bacterial pathogens.

Adsorption of phenol from aqueous solutions using mesoporous carbon prepared by two-stage process

Abstract: Porous carbon prepared from rice husk using phosphoric acid activation through precarbonization and chemical activation has been examined for the adsorption of phenol from aqueous solutions. The method adopted could produce carbons with micro and mesoporous structure. The surface area, pore volume and pore size distribution of carbon samples activated at three different temperatures 700, 800 and 900 °C have been carried out using nitrogen adsorption isotherms at 77 K. The production yield was observed to decrease with increase in activation temperature. Adsorption behavior of phenol onto the porous carbon was studied by varying the parameters such as agitation time, phenol concentration, pH and temperature. Studies showed that the adsorption decreased with increase in pH and temperature. The sorption process was found to be exothermic in nature. The kinetic models such as pseudo first order, pseudo second order and intra particle diffusion model were fitted to identify the mechanism of adsorption process. The isotherm data were fitted to Langmuir and Freundlich models. The maximum uptake of phenol was found to be 2.35 × 10−4 mol/g at 20 °C and final pH 2.7.

Optical and magnetic properties of Mg-doped ZnFe2O4 nanoparticles prepared by rapid microwave combustion method

Abstract: Mg-doped ZnFe 2 O 4 samples were prepared by a microwave combustion method. The obtained samples were characterized by powder X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis, UV–Visible diffuse reflectance spectra (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). XRD results confirm the formation of cubic spinel-type structure with an average crystallite size in the range of 15–43 nm. Lattice parameter decreases with increasing Mg concentration, due to the smaller ionic radius of Mg 2+ ion. The HR-SEM images show the morphology of the samples as spherical shaped particles in agglomeration. The broad visible emission band is observed in the entire PL spectrum. The estimated band gap energy is found to decrease with increasing Mg content (2.15–1.42 eV). The magnetization showed an increasing trend with increasing Mg concentration ( x = 0.5), due to the rearrangement of cations at tetrahedral and octahedral sites.

Effect of Two-Stage Process on the Preparation and Characterization of Porous Carbon Composite from Rice Husk by Phosphoric Acid Activation

Abstract: Activated carbon composite prepared from rice husk using phosphoric acid activation has been studied through precarbonization of the precursor followed by chemical activation. This method can produce carbons with micro- and mesoporous structure. The ratio of chemical activating agent to precarbonized carbon was fixed at 4.2. The surface area, pore volume, and pore size distribution of carbon composite samples activated at three different temperatures (700, 800, and 900 °C) were measured using nitrogen adsorption isotherms at 77 K. The pore-opening and pore-widening effects occurred simultaneously during the process, as evidenced by scanning electron micrographs. The X-ray diffraction curve revealed the evolution of crystallites of carbon and silica during activation at higher temperature. The FTIR spectrum also provided evidence for the presence of silica in the carbon composite. The proper choice of the preparation conditions had an influence on the micropore and mesopore volumes of the activated carbon ...

Synthesis, optical and magnetic properties of pure and Co-doped ZnFe2O4 nanoparticles by microwave combustion method

Abstract: Spinel zinc ferrite (Zn1−xCoxFe2O4) nanoparticles with various particle sizes were prepared by the microwave combustion method using urea as a fuel. The composites were prepared with the addition of cobalt at different molar ratios (x=0.0 to 0.5) to ZnFe2O4. The obtained spinel ferrites were characterized by X-ray powder diffraction (XRD) and their mean grain size and morphology were determined by the high resolution scanning electron microscopy (HR-SEM). The magnetic properties of the synthesized ferrites were investigated using room temperature vibrating sample magnetometer (VSM) and their hysteresis loops were obtained. The optical reflectance and photoluminescence (PL) emissions were determined by UV–visible diffuse reflectance spectra (DRS) and PL spectra respectively. The formation of single cubic spinel phase was confirmed by XRD and Rietveld analysis with an average crystallite size is in the range of 43–49 nm. The broadband visible emission band is observed in the entire PL spectrum and the estimated energy band gap is about 2.1 eV. The variation of saturation magnetization (Ms) value of the samples was studied. The prepared lower compositions (0.0, 0.1 and 0.2) show a superparamagnetic behavior and the higher compositions (0.3, 0.4 and 0.5) show a ferromagnetic behavior with hysteresis and that the Ms increases with increasing Co content to reach a maximum value of 65.20 emu/g for Zn0.5Co0.5Fe2O4. The relatively high Ms of the samples suggests that this method is suitable for preparing high-quality nanocrystalline magnetic ferrites for practical applications. Different mechanisms to explain the obtained results and the correlation between magnetism and structure are discussed.

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.

Recent developments of zinc oxide based photocatalyst in water treatment technology: A review

Abstract: Today, a major issue about water pollution is the residual dyes from different sources (e.g., textile industries, paper and pulp industries, dye and dye intermediates industries, pharmaceutical industries, tannery and craft bleaching industries, etc.), and a wide variety of persistent organic pollutants have been introduced into our natural water resources or wastewater treatment systems. In fact, it is highly toxic and hazardous to the living organism; thus, the removal of these organic contaminants prior to discharge into the environment is essential. Varieties of techniques have been employed to degrade those organic contaminants and advanced heterogeneous photocatalysis involving zinc oxide (ZnO) photocatalyst appears to be one of the most promising technology. In recent years, ZnO photocatalyst have attracted much attention due to their extraordinary characteristics. The high efficiency of ZnO photocatalyst in heterogeneous photocatalysis reaction requires a suitable architecture that minimizes electron loss during excitation state and maximizes photon absorption. In order to further improve the immigration of photo-induced charge carriers during excitation state, considerable effort has to be exerted to further improve the heterogeneous photocatalysis under UV/visible/solar illumination. Lately, interesting and unique features of metal doping or binary oxide photocatalyst system have gained much attention and became favourite research matter among various groups of scientists. It was noted that the properties of this metal doping or binary oxide photocatalyst system primarily depend on the nature of the preparation method and the role of optimum dopants content incorporated into the ZnO photocatalyst. Therefore, this paper presents a critical review of recent achievements in the modification of ZnO photocatalyst for organic contaminants degradation.

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.