Dan Goia - Academia.edu (original) (raw)

Papers by Dan Goia

Journal of Solid State Electrochemistry, 2013

Highly dispersed uniform Ni particles ranging in size from 0.1 to 1.2 mm were synthesized by redu... more Highly dispersed uniform Ni particles ranging in size from 0.1 to 1.2 mm were synthesized by reducing nickel carbonate in polyols in the presence of dipentaerythritol (DPE) and noble metal salts. DPE was essential in preventing the aggregation of nickel particles, while the noble metal ('seeding' approach) effectively tailored their size. Ferromagnetic particles with a cubic closed packed (ccp) crystal habit were obtained using short reduction times at temperatures below 200 C. Non-magnetic particles with hexagonal closed packed (hcp) structure were obtained after extended heating times (>16 hours) at temperatures above 220 C. The temperature of the reduction and heat-treatment process was adjusted by using polyols with different boiling points.

Journal of Nanomaterials & Molecular Nanotechnology, 2014

Copper selenide (Cu x Se) particles were prepared by heating copper carbonate and selenous acid i... more Copper selenide (Cu x Se) particles were prepared by heating copper carbonate and selenous acid in diethylene glycol in the presence of various dispersing agents. The impact of reaction conditions on the structural and morphological properties of the precipitated particles were assessed by X-ray diffraction (XRD) and electron microscopy. Although all additives promoted anisotropic growth, it was found that polyvinyl alcohol (PVA) was particularly effective in generating dispersed high aspect ratio Cu x Se platelets. The optimum reaction conditions for the formation of hexagonal copper selenide were 190°C and a Cu: Se molar ratio of 1 to 1.2.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 1999

Monodispersed spherical gold particles ranging in modal diameter from 80 nm to 5 μm, were prepare... more Monodispersed spherical gold particles ranging in modal diameter from 80 nm to 5 μm, were prepared by reducing tetrachloroauric(III) acid with iso-ascorbic acid in aqueous solutions at 20°C. The particle size was altered by changing the pH, which affected the composition of gold(III) solute complexes. The latter controlled the redox potential of the system, essential to the formation of the

Journal of Colloid and Interface Science, 2007

Highly dispersed uniform ZnO particles of different sizes and shapes were prepared by slowly addi... more Highly dispersed uniform ZnO particles of different sizes and shapes were prepared by slowly adding zinc salt and sodium hydroxide solutions in parallel into aqueous solutions of Arabic gum. Except for the very early stages, the precipitated solids consisted of a well-defined zinc oxide phase. Depending on the experimental conditions, the size of the final polycrystalline particles formed by the aggregation of nanosize entities varied from 100 to 300 nm. The reaction temperature affected both the size of the nanosize precursors and their arrangement in the final particles. At ambient temperature the primary nanoparticles, approximately 10 nm in size, formed spherical aggregates, while at 600 degrees C they were much larger (44 nm) and combined to form rather uniform hexagonal ZnO prisms. The aspect ratio and the internal structure of the latter could be altered by changing the nature of the zinc salt, the addition rate, and the initial concentration of the reactants. Based on the findings of the study a two-stage mechanism for the formation of uniform polycrystalline particles with well-defined geometric shapes is proposed.

Journal of Colloid and Interface Science, 2008

Uniform cubic particles of neighborite (NaMgF 3 ) were prepared by mixing solutions of magnesium ... more Uniform cubic particles of neighborite (NaMgF 3 ) were prepared by mixing solutions of magnesium chloride and sodium fluoride, followed by aging for extended periods of time (up to 3 h). Such particles could be obtained directly either by using sodium fluoride in sufficient excess, or by first producing spherical particles of magnesium fluoride and converting them into neighborite cubes by admixing sodium fluoride. It was shown that both MgF 2 and NaMgF 3 particles so prepared are polycrystalline and that in both procedures to form neighborite a two stage reaction takes place. In the first stage nanosize subunits of MgF 2 are formed, which are subsequently converted in the presence of excess sodium fluoride to neighborite crystallites. The latter are then reorganized into larger subunits that constitute colloidal cubes.

Chemical Physics, 2008

We present results of computational modeling of the formation of uniform spherical silver particl... more We present results of computational modeling of the formation of uniform spherical silver particles prepared by rapid mixing of ascorbic acid and silver-amine complex solutions in the absence of a dispersing agent. Using an accelerated integration scheme to speed up the calculation of particle size distributions in the latter stages, we find that the recently reported experimental results -some of which are summarized here -can be modeled effectively by the two-stage formation mechanism used previously to model the preparation of uniform gold spheres. We treat both the equilibrium concentration of silver atoms and the surface tension of silver precursor nanocrystals as free parameters, and find that the experimental reaction time scale is fit by a narrow region of this two-parameter space. The kinetic parameter required to quantitatively match the final particle size is found to be very close to that used previously in modeling the formation of gold particles, suggesting that similar kinetics governs the aggregation process and providing evidence that the two-stage model of burst nucleation of nanocrystalline precursors followed by their aggregation to form the final colloids can be applied to systems both with and without dispersing agents. The model also reproduced semiquantitatively the effects of solvent viscosity and temperature on the particle preparation.

Journal of Materials Research, 2010

New Journal of Chemistry, 1998

... Dan V. Goia and Egon Matijevicç* ... 2. When the redox potentials of the two metals are simil... more ... Dan V. Goia and Egon Matijevicç* ... 2. When the redox potentials of the two metals are similar and *E of the reduction reaction is large, true (E 0 1 + E 0 2) bimetallic alloy particles can be obtained.38,39 If the redox potentials of the two metals are signicantly dierent, the ...

Journal of Materials Research, 2009

Journal of Materials Research, 2007

Highly dispersed uniform silver nanoparticles were prepared by reducing silver diamine ions [Ag(N... more Highly dispersed uniform silver nanoparticles were prepared by reducing silver diamine ions [Ag(NH3)2]+ with D-glucose in the presence of a stabilizing agent. Along with the nature of the dispersing agent, the pH and the temperature of the reaction had the most pronounced ...

Journal of Colloid and Interface Science, 2009

Stable concentrated aqueous dispersions of monodisperse gold nanoparticles were prepared using di... more Stable concentrated aqueous dispersions of monodisperse gold nanoparticles were prepared using diethylaminoethyl-dextran as reductant and stabilizer. The effectiveness of dextran as reducing agent was strongly affected by the pH. In alkaline solutions, the Au(III) species were rapidly and completely reduced, yielding stable dispersions of spherical uniform gold nanoparticles. Their modal diameter could be adjusted from 18 to 40 nm by varying the pH, temperature, and the Au 3+ /dextran ratio. In contrast, under acidic conditions (pH $ 4.0) the reduction was very slow, favoring the formation of large gold crystals of other shapes. A general mechanism explaining the reducing and stabilizing actions of polysaccharides in general, and of diethylaminoethyl-dextran in particular, is proposed.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2006

Well-dispersed uniform spheres of crystalline CeO 2 were prepared by calcining precursor particle... more Well-dispersed uniform spheres of crystalline CeO 2 were prepared by calcining precursor particles obtained by heating cerium(III) acetate in 1,2 propane diol (propylene glycol, PG) at the boiling point of the polyol (∼187 • C) for several hours. The first precipitated amorphous spherical particles consist of a complex mixture of ceria, ceria hydrate, cerium hydroxide, cerium glycolate complex and residual PG. To convert these precursors to pure CeO 2 , the solids were calcined at 500 • C in air at a slow heating rate (≤0.1 • C/min). The purification of the precursor particles depended strongly on the solvent used. By washing with water, much of the organic material was leached out resulting in smaller spheres, while rinsing with methanol showed little effect. The TGA, FTIR, XRD, EDX analyses of the different purified particles revealed the stages in the formation of the final pure well-defined CeO 2 powder.

Colloid and Polymer Science, 2003

Uniform, spherical CuCl particles were obtained by mixing aqueous solutions of CuCl2 and ascorbic... more Uniform, spherical CuCl particles were obtained by mixing aqueous solutions of CuCl2 and ascorbic acid in the presence of polyvinylpyrrolidone (PVP) as dispersing agent. The size and the uniformity of the resulting particles depended on the volume ratio of the reactant solutions, their concentrations, the distribution of the stabilizers, and the mixing method. The single jet precipitation yielded large spheres of broad size distributions, while the particles obtained by the double jet technique were rather uniform in size. The final colloidal CuCl particles were formed by the aggregation of nanocrystals, initially generated in the system. Depending on the pH of the reaction mixture, these particles slowly change to large CuCl crystals on aging in the mother liquor.

It has been experimentally established in numerous cases that precipitation of monodispersed coll... more It has been experimentally established in numerous cases that precipitation of monodispersed colloids from homogeneous solutions is a complex process. Specifically, it was found that in many systems nuclei, produced rapidly in a supersaturated solution, grow to nanosize primary particles (singlets), which then coagulate to form much larger final colloids in a process dominated by irreversible capture of these singlets. This paper describes a kinetic model that explains the formation of dispersions of narrow size distribution in such systems. Numerical simulations of the kinetic equations, with experimental model parameter values, are reported. The model was tested for a system involving formation of uniform spherical gold particles by reduction of auric chloride in aqueous solutions. The calculated average size, the width of the particle size distribution, and the time scale of the process, agreed reasonably well with the experimental values.

Electrochemistry Communications, 2010

In the presented work, the evaluation of an unsupported AuPt core–shell catalyst for the oxygen r... more In the presented work, the evaluation of an unsupported AuPt core–shell catalyst for the oxygen reduction reaction is introduced. Applying only basic chemicals in an upscalable synthesis route, it is demonstrated that uniform, flat, and complete Pt layers around a spherical Au core are obtained. The electrocatalytic measurements show that the surface area specific activity of the AuPt core–shell catalyst towards the important oxygen reduction reaction equals the one of polycrystalline bulk Pt. To our knowledge, this is the first time that the unfavorable particle size effect of Pt nanoparticles could be by-passed for a nanoscale catalyst.

Drug Delivery, 2004

Colloidal gold, a sol comprised of nanoparticles of Au 0 , has been used as a therapeutic for the... more Colloidal gold, a sol comprised of nanoparticles of Au 0 , has been used as a therapeutic for the treatment of cancer as well as an indicator for immunodiagnostics. However, the use of these gold nanoparticles for in vivo drug delivery has never been described. This communication outlines the development of a colloidal gold (cAu) nanoparticle vector that targets the delivery of tumor necrosis factor (TNF) to a solid tumor growing in mice.

Journal of The Electrochemical Society, 2005

... The authors are indebted to Sachin Pandija who carried out the polish experiments. Clarkson U... more ... The authors are indebted to Sachin Pandija who carried out the polish experiments. Clarkson University assisted in meeting the publication costs of this article. ... Chem. Phys., 86, 347 (2004). A.Jindal and SVBabu, Effect of pH on CMP of Copper and Tantalum, J. Electrochem. ...

Cheminform, 2008

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Advances in Colloid and Interface Science, 2003

Monodispersed spherical cadmium sulfide particles were used as a model system in order to explain... more Monodispersed spherical cadmium sulfide particles were used as a model system in order to explain the size selection in the formation of colloids by aggregation of nanosize subunits. Several procedures of mixing the reactants were employed to precipitate these solids and follow the kinetics of particle growth. Efficient numerical simulation techniques for the model rate equations were developed to fit the experimental results. Our results have confirmed the recently proposed mechanism of two-stage growth by nucleation of nanosize crystalline primary particles and their subsequent aggregation into polycrystalline secondary colloids. ᮊ