Articles Copyright (c) 2013 Dublin Institute of Technology All rights reserved. http://arrow.dit.ie/cenresart Recent documents in Articles en-us Wed, 15 May 2013 10:21:16 PDT 3600 Advances in the Synthesis of ZnO Nanomaterials for Varistor Devices http://arrow.dit.ie/cenresart/40 http://arrow.dit.ie/cenresart/40 Tue, 07 May 2013 05:17:18 PDT ZnO based varistors are widely used for overvoltage protection in many electrical and electronic circuits, at voltages ranging from a few to over a million volts. By careful control of the microstructure, through nanostructuring by chemical routes, it should be possible to produce varistors with high breakdown voltage (Vc), as this is proportional to the number of active grain boundaries in the sintered body. This property is particularly important for the production of the small-sized varistors needed for modern electronic instruments such as tablet computers and mobile phones. The current review will outline the recent advances in the chemical processing (e.g. sol–gel, combustion synthesis plasma pyrolysis, micro-emulsion synthesis and precipitation routes) of varistors from ZnO nanomaterials and the properties of these materials. Uncontrolled grain growth at higher temperature is highlighted as a major challenge for obtaining desirable electrical properties for nano-varistors. Various novel sintering techniques such as step-sintering, spark plasma and microwave sintering methods are expected to deliver a varistor with controlled grain growth and optimum electrical characteristics.

]]> Suresh Pillai et al. Single Step Morphology-Controlled Synthesis of Silver Nanoparticles http://arrow.dit.ie/cenresart/39 http://arrow.dit.ie/cenresart/39 Thu, 04 Apr 2013 05:50:25 PDT Silver nanoparticles having different size and plasmon resonances were synthesized through a single step aqueous based method. The current procedure was based on the reduction of silver ions by ascorbic acid in the presence of sodiumborohydride and trisodium citrate. Triangular colloidal nanoparticles having different plasmon resonances (and hence different size and colours) were synthesized by varying only the concentration of ascorbic acid. These nanoparticles were found to be stable without using any surfactants or polymers. This study revealed a strong correlation between particle growth and concentration of constituent chemicals. Crystallinity and phase purity of the silver samples were investigated through powder X-ray diffraction studies (XRD). Absorption spectra of various silver particles were recorded using UV/Vis/NIR spectrometer. Morphological analysis was performed using transmission electron microscopy (TEM) and average edge lengths of nanoparticles were also calculated.

]]> Vinodkumar Etacheri et al. The Effect of the Rate of Precursor Production on the Purity and Aggregation http://arrow.dit.ie/cenresart/38 http://arrow.dit.ie/cenresart/38 Thu, 04 Apr 2013 05:35:28 PDT The synthesis of zinc oxide through the decomposition of a solid oxalate precursor was investigated. It was found that the rate of preparation of the precursor had a quantitative effect on the morphology and extent of surface ligation of particles produced; contrary to our expectations,it was found that the slow combination of reagents led to a less pure product. It has been determined that this time dependence mimics the variation of reactant ratios. Zinc oxide particles were produced from a number of reactant ratios, and were characterised by TEM, XRD, FT-IR and DSC. It was found that the size of the crystallites produced was not affected, but that the nature of their surface ligation did rely upon these parameters.

]]> Grainne Duffy et al. A Novel Processing Route for the Production of Nanoparticulate Zinc Oxide Using an Isophthalate Precursor http://arrow.dit.ie/cenresart/37 http://arrow.dit.ie/cenresart/37 Thu, 04 Apr 2013 05:30:41 PDT Zinc oxide nanoparticles have been processed from a novel isophthalate precursor. In contrast to those processed from an oxalate precursor, this material exhibits three-dimensional, non-directional aggregation behaviour.

Such non-directional aggregation of uniaxial crystallites may allow for the production of structures with a higher proportion of catalytically active surfaces than can be prepared through conventional sol–gel methods. XRD,

FTIR, TEM and SEM were used to characterize the synthesized materials.

Zinc oxide particles synthesized by using isophthalic acid (C6H4-1,3-(COOH)2) are found to be slightly smaller than the previously reported materials prepared through chelation with oxalic acid (H2C2O2・2H2O).

]]> Grainne Duffy et al. A Highly Efficient TiO2-XCx Nano-Heterojunction Photocatalyst for Visible-Light Induced Antibacterial Applications http://arrow.dit.ie/cenresart/36 http://arrow.dit.ie/cenresart/36 Thu, 04 Apr 2013 05:15:22 PDT Visible-light-induced antibacterial activity of carbon-doped anatase-brookite titania nano-heterojunction photocatalysts are reported for the first time. These heterostructures were prepared using a novel low temperature (100 °C) non-hydrothermal low power microwave (300 W) assisted method. Formation of interband C 2p states was found to be responsible for the band gap narrowing of the carbon doped heterojunctions. The most active photocatalyst obtained after 60 minutes of microwave irradiation exhibits a 2-fold higher visible-light induced photocatalytic activity in contrast to the standard commercial photocatalyst Evonik-Degussa P-25. Staphylococcus aureus inactivation rate constant for carbon-doped nano-heterojunctions and the standard photocatalyst was 0.0023 and -0.0081 min-1 respectively. It is proposed that the photo-excited electrons (from the C 2p level) are effectively transferred from the conduction band of brookite to that of anatase causing efficient electron-hole separation, which is found to be responsible for the superior visible-light induced photocatalytic and antibacterial activities of carbon-doped anatase-brookite nano-heterojunctions.

KEYWORDS: Titanium dioxide; Microwave synthesis; Carbon-doping; Visible-light induced photocatalysis; Antibacterial activity; Heterojunctions

]]> Vinodkumar Etacheri et al. Novel Microwave Assisted Synthesis of ZnS Nanomaterials http://arrow.dit.ie/cenresart/35 http://arrow.dit.ie/cenresart/35 Thu, 04 Apr 2013 05:10:28 PDT A novel ambient pressure microwave-assisted technique is developed in which silver and indium modified ZnS is synthesised. The as prepared ZnS is characterised by X-ray diffraction, UV-Vis spectroscopy, X-ray photoelectron spectroscopy and luminescence spectroscopy. This procedure produced crystalline materials with particle sizes below 10 nm. The synthesis technique leads to defects in the crystal which induce mid energy levels in the band gap and lead to indoor light photocatalytic activity. Increasing the amount of silver causes a phase transition from cubic blende to hexagonal phase ZnS. In a comparative study, when the ZnS cubic blende is heated in a conventional chamber furnace, it is completely converted to ZnO at 600 °C. Both cubic blende and hexagonal ZnS show excellent photocatalytic activity under irradiation from a 60 watt light bulb. These ZnS samples also show significantly higher photocatalytic activity compared to the commercially available TiO2 (Evonik-Degussa P-25).

]]> Suresh Pillai et al. Non-Cytotoxic Antibacterial Silver–Coumarin Complex Doped Sol–Gel Coatings http://arrow.dit.ie/cenresart/34 http://arrow.dit.ie/cenresart/34 Tue, 22 Jan 2013 03:55:24 PST Microbial colonisation on clinical and industrial surfaces is currently of global concern and silane based sol–gel coatings are being proposed as potential solutions. Sol–gels are chemically inert, stable and homogeneous and can be designed to act as a reservoir for releasing antimicrobial agents over extended time periods. In the present study, silver nitrate (AgN) and a series of silver coumarin complexes based on coumarin-3-carboxylatosilver (AgC) and it is 6,7 and 8 hydroxylated analogues (Ag6, Ag7, Ag8) were incorporated into sol–gel coatings. The comparative antibacterial activity of the coatings was determined against meticillin resistant Staphylococcus aureus (MRSA) and multidrug resistance Enterobacter cloacae WT6. The percentage growth inhibitions were found in the range of 9.2 (±2.7) – 66.0 (±1.2) % at low silver loadings of 0.3% (w/w) with E. cloacae being the more susceptible. Results showed that among the Ag coumarin complexes, the Ag8 doped coating had the highest antibiofilm property. XPS confirmed the presence of silver in the nanoparticulate state (Ag0) at the coating surface where it remained after 4 days of exposure to bacterial culture. Comparative cytotoxicity studies revealed that the Ag-complex coatings were less toxic than the AgN coating. Thus, it can be concluded that a sol–gel matrix with Ag–coumarin complexes may provide non-toxic surfaces with antibacterial properties.

]]> Swarna Jaiswal et al. An Investigation Of The Biochemical Properties Of Tetrazines As Potential Coating Additives http://arrow.dit.ie/cenresart/33 http://arrow.dit.ie/cenresart/33 Tue, 22 Jan 2013 01:38:49 PST 1,2,4,5-Tetrazine and its 3,6-disubstituted derivatives are currently used for a range of industrial and medical applications as they exhibit particular coordination chemistries, characterized by electron and charge transfer phenomena. The aim of the present work is to describe the synthesis of two tetrazine derivatives, namely 3,6-dihydrazino-1,2,4,5-tetrazine (DHDTZ) and 1,2,4,5-tetrazine dicarboxylic acid (DCTZ), and determine their antibacterial, antioxidant and anticorrosion characteristics as additives in a sol-gel coating on SS316L steel. The structure of the tetrazines was confirmed by NMR and FTIR while the surface morphology of bacterial cells in their presence was observed by AFM. Their ability to inhibit corrosion on 316L stainless steel was electrochemically determined using a potentiodynamic scanning (PDS) technique. The corrosion inhibition results showed that the acidic DCTZ provided the best corrosion protection. The concentration-dependent antioxidant capacity of the tetrazines was confirmed by both DPPH radical scavenging activity and FRAP assays, showing higher activity for DHDTZ than DCTZ. Furthermore, a DHDTZ doped sol-gel solution was prepared and curing parameter (temperature and time) was optimised for coating on microtitre wells and stainless steel panel. The antibacterial activity of the coated surfaces against P. aeruginosa ATCC 27853 and the biofilm forming bacteria S. epidermidis CSF 41498 was determined. DHDTZ showed significantly higher antibacterial activities with MIC as low as 31 ppm compared to 250ppm for DCTZ.

]]> Swarna Jaiswal et al. Enhanced Magnetoresistance in Nanocrystalline Magnetite http://arrow.dit.ie/cenresart/32 http://arrow.dit.ie/cenresart/32 Thu, 03 Jan 2013 01:25:29 PST The magnetic and magnetotransport properties of nanoparticulate magnetite with different grain
sizes are investigated using x-ray diffraction, microscopy, magnetometry, and magnetoresistance
measurements. The magnetization varies significantly with grain size and is sensitive to preparation conditions. The reduction in saturation magnetization in coprecipitated particles is probably due to the surface spin disorder. Magnetoresistance of pressed powder compacts is significantly enhanced
in material composed of small grain size magnetite particles prepared by coprecipitation. Useful
magnetoresistance persists well above room temperature in sintered ceramic material.

]]> M Venkatesan et al. The effect of the rate of precursor production on the purity and aggregation morphology of nanoparticulate zinc oxide http://arrow.dit.ie/cenresart/31 http://arrow.dit.ie/cenresart/31 Wed, 02 Jan 2013 07:55:38 PST The synthesis of zinc oxide through the decomposition of a solid oxalate precursor was
investigated. It was found that the rate of preparation of the precursor had a quantitative effect on
the morphology and extent of surface ligation of particles produced; contrary to our expectations,
it was found that the slow combination of reagents led to a less pure product. It has been
determined that this time dependence mimics the variation of reactant ratios. Zinc oxide particles
were produced from a number of reactant ratios, and were characterised by TEM, XRD, FT-IR
and DSC. It was found that the size of the crystallites produced was not affected, but that the
nature of their surface ligation did rely upon these parameters

]]> Grainne Duffy et al. Low-Temperature Crystallization of Sol–Gel Processed Pb0.5Ba0.5TiO3: Powders and Oriented Thin Films http://arrow.dit.ie/cenresart/30 http://arrow.dit.ie/cenresart/30 Wed, 02 Jan 2013 07:45:26 PST A novel sol– gel process suitable for depositing thin-film lead
barium titanate has been developed. X-ray diffraction analysis
showed perovskite phase crystallization to occur at a temperature
as low as 400°C with single-phase Pb0.5Ba0.5TiO3 (PBT)
resulting at a temperature as low as 500°C. Small concentrations
of barium carbonate were evident by X-ray diffraction at
400°C, and indications of minor, carbonate-containing phases
were evident by FTIR at 600°C. Deposition of the sol by spin
coating on single-crystal and thin-film MgO on silicon resulted
in highly oriented PBT films after calcination at 600°C. Mixed
(100)/(001) films were obtained on single-crystal MgO,
whereas entirely (100) films were obtained on thin-film MgO

]]> Suresh Pillai et al. The Effect of Processing Conditions on Varistors Prepared From Nanocrystalline ZnO http://arrow.dit.ie/cenresart/29 http://arrow.dit.ie/cenresart/29 Wed, 02 Jan 2013 07:35:23 PST Nanoparticles of ZnO were prepared by the reaction of ethanolic solutions of zinc acetate and oxalic acid
followed by drying (80 uC) and calcination (500 uC). Subsequently varistor materials were fabricated from this
nanoparticular ZnO via two separate routes:- a) from a ‘‘core shell’’ material using metal salts as additives; b)
by using a conventional solid state mixing of metal oxides. Sintering (1050 uC) and subsequent electrical studies
were carried out for each of these samples and they were compared with commercial varistor samples prepared
under similar conditions. ‘‘Core shell’’ type varistor material showed considerably higher breakdown voltage
(Vc ~ 850 ¡ 30 V mm21) as compared to a sample prepared by mixing with metal oxides (Vc ~ 683 ¡
30 V mm21) or commercial varistor discs (Vc ~ 507 ¡ 30 V mm21). The high breakdown voltage obtained is
attributed to the formation of more varistor-active grain boundaries per unit area.

]]> Suresh Pillai et al. Preparation of (Pb,Ba)TiO3 powders and highly oriented thin films by a sol-gel process http://arrow.dit.ie/cenresart/28 http://arrow.dit.ie/cenresart/28 Wed, 02 Jan 2013 07:25:21 PST Solid solution Pb1-xBaxTiO3, with particular emphasis on Pb0.5Ba0.5TiO3, was prepared
using a sol-gel process incorporating lead acetate trihydrate, barium acetate, and
titanium isopropoxide as precursors, acetylacetone (2,4 pentanedione) as a chelating
agent, and ethylene glycol as a solvent. The synthesis procedure was optimized by
systematically varying acetylacetone: Ti and H2O:Ti molar ratios and calcination
temperature. The resulting effects on sol and powder properties were studied using
thermogravimetric analysis/differential scanning calorimetry, Fourier transform infrared
spectroscopy, Brunauer-Emmett-Teller analysis, and x-ray diffraction (XRD).
Crystallization of the perovskite structure occurred at a temperature as low as 450 °C.
Thin films were prepared by spin coating on (100) MgO. Pyrolysis temperature and
heating rate were varied, and the resultant film properties investigated using
field-emission scanning electron microscopy, atomic force microscopy, and XRD.
Under optimized conditions, highly oriented films were obtained at a crystallization
temperature of 600 °C.

]]> Stacey Boland et al. A Novel Processing Route for the Production of Nanoparticulate Zinc Oxide http://arrow.dit.ie/cenresart/27 http://arrow.dit.ie/cenresart/27 Wed, 02 Jan 2013 07:15:26 PST Zinc oxide nanoparticles have been processed from a novel isophthalate
precursor. In contrast to those processed from an oxalate precursor, this
material exhibits three-dimensional, non-directional aggregation behaviour.
Such non-directional aggregation of uniaxial crystallites may allow for the
production of structures with a higher proportion of catalytically active
surfaces than can be prepared through conventional sol–gel methods. XRD,
FTIR, TEM and SEM were used to characterize the synthesized materials.
Zinc oxide particles synthesized by using isophthalic acid
(C6H4-1,3-(COOH)2) are found to be slightly smaller than the previously
reported materials prepared through chelation with oxalic acid
(H2C2O2·2H2O).

]]> Declan McCormack et al. Microwave Induced Preparation of a-axis Oriented Double-Ended Needle-Shaped ZnO Microparticles http://arrow.dit.ie/cenresart/26 http://arrow.dit.ie/cenresart/26 Wed, 02 Jan 2013 07:00:37 PST Microwave irradiation of solutions of Zn(NO3)2 and urea provides a straightforward route to a-axis oriented crystals of needle-like morphology.



]]> Suresh Pillai et al. Effect of Step Sintering on Breakdown Voltage of Varistors Prepared from Nanomaterials http://arrow.dit.ie/cenresart/25 http://arrow.dit.ie/cenresart/25 Wed, 02 Jan 2013 06:40:25 PST Suresh Pillai et al. Synthesis of Thermally Stable, High Surface Area Anatase–Alumina Mixed Oxides http://arrow.dit.ie/cenresart/24 http://arrow.dit.ie/cenresart/24 Wed, 02 Jan 2013 03:15:20 PST Suresh Pillai et al. Preparation of Magnetic Nanoparticles and their Assemblies Using a New Fe(II) Alkoxide Precursor http://arrow.dit.ie/cenresart/23 http://arrow.dit.ie/cenresart/23 Wed, 02 Jan 2013 03:05:24 PST Suresh Pillai et al. Microstructural Analysis of Varistors Prepared from Nanosize ZnO http://arrow.dit.ie/cenresart/22 http://arrow.dit.ie/cenresart/22 Fri, 21 Dec 2012 05:15:38 PST Suresh Pillai et al. Magnetic nanoparticles and nanoparticle assemblies from metallorganic precursors http://arrow.dit.ie/cenresart/21 http://arrow.dit.ie/cenresart/21 Fri, 21 Dec 2012 05:05:25 PST Suresh Pillai et al.