Anca Dumitru - Academia.edu (original) (raw)

Papers by Anca Dumitru

Our targeted contribution takes into account that applications where the materials, structured at... more Our targeted contribution takes into account that applications where the materials, structured at nanometric scale, can improve performances for electrodes and catalysts in fuel cells. In this context are presented some aspects where the nanotechnology is involved in fuel cells designing. In addition, are presented the requirements from the nanostructured materials with examples on several of materials produced in our laboratories. Carbon ribbons obtained from polyacrilonitrile (PAN) in the cross fields, thermal and centrifugal, are materials with a good define texture and controllable thickness 1-100 microns, designed for electrodes and the proton exchange membranes. Carbon-ribbons have of aromatic structures similar with the ladder polymers with graphite specific conduction in basal plane and specific catalytic activity. Carbonic materials with high electrical conductivity and gas permeability were obtained by the phenol-formaldehyde resin and PAN carbonizing. They have been proposed as an alternative for electrodes in fuel cells. Using plasma polymerization combined with electrospray ionization resulted nanocomposites from polymer semiconductors-nanocarbons and inorganic copolymers with catalyst insertion that could open a new route to disperse or to insert catalysts direct onto membranes or electrodes.

Low dimensional polymer films were obtained by plasma polymerization of aniline and p-xylene onto... more Low dimensional polymer films were obtained by plasma polymerization of aniline and p-xylene onto silicon (111)/quartz glass substrates The reactions were conducted in a original designed RF reactor, inductively coupled with a 2 54 MHz generator, taking advantage of the electrodless configuration The structural characteristics observed by XRD, Raman and FT-IR spectroscopy were correlated with resistivity dependence measurements at moderated pressures Highly cross-linked plasma polymer films have a resistivity ranging from insulator to semiconductor FT-IR spectra show a number of quite broad single peaks indicating a range of closely related structures rather then one well-defined structural state

Fullerenes Nanotubes and Carbon Nanostructures, 2005

Two classes of carbon fibers—one based on MP (Mesophase Pitch) precursors and another on PAN (Pol... more Two classes of carbon fibers—one based on MP (Mesophase Pitch) precursors and another on PAN (Polyacrylonitrile) precursors—are well known. Thermomechanical properties depend strongly on the initial precursor, particularly PAN tacticity. Regular, highly oriented carbon fibers require a syndiotactic PAN that is virtually impossible to reach. To improve the attributes of these materials, a new technique was developed, consisting of the

Materials Science and Engineering: C, 2007

The combination of magnetic materials and carbon nanotubes (CNTs) is a promising research directi... more The combination of magnetic materials and carbon nanotubes (CNTs) is a promising research direction with a wide range of applications such as magnetic storage and drug delivery free of toxicity. It is well known that some transition metals are mandatory for the nucleation and growth of CNTs by pyrolysis. This paper deals with a new approach where Fe–C nanostructures are developed in a carbon matrix with a random network of CNTs by the polymers pyrolysis (phenol-formaldehyde resins and polyvinyl alcohol) and ferrocene up to 900 °C in inert atmosphere. The proposed method is simple and could be a promising way to produce magnetic nanoparticles coated with carbon as well as CNTs. The characterization (TEM, Mössbauer spectroscopy) and magnetic properties of the carbon–iron system are systematically investigated.

Plasma treatment is a unique and powerful method for modifying polymeric materials without alteri... more Plasma treatment is a unique and powerful method for modifying polymeric materials without altering their bulk properties. In this purpose we are using the plasma processing to enhance the properties of PMMA films for biomedical applications. Plasma processed PMMA thin films have been obtained in a DC glow discharge from polymer solution at different plasma powers. The results are compared with that for PMMA films obtained by deep coating method. Fourier Transform Infrared Spectroscopy (FT-IR) and atomic force microscopy (AFM) have characterized the structure and composition of the films.

... 1. Curtright AE, Bouwman PJ, Wartena RC and Swider-Lyons KE (2004) Power sources for nanotech... more ... 1. Curtright AE, Bouwman PJ, Wartena RC and Swider-Lyons KE (2004) Power sources for nanotechnology, Int. J. of Nanotechnology, 1 (1/2), 226-239. ... 7. Penn SG, He L. and Natan MJ (2003) Nanoparticles for bioanalysis, Current Opinion in Chemical Biology, 7, 609–615. ...

Journal of Membrane Science, 2006

A great deal of effort is required to design polymer electrolyte fuel cells (PEFCs) using new pol... more A great deal of effort is required to design polymer electrolyte fuel cells (PEFCs) using new polymers and hybrid organic/inorganic compounds that can work at higher temperatures. These materials must have lasting thermal stability as well as improved ionic conductivity. Operation at elevated temperatures is desirable for PEFCs systems since they draw high power density in fast electrode kinetics and also for improvement of CO-tolerance, etc. In the higher range of temperatures (150–200 °C), new materials such as solid acids with phase transition to superprotonic conduction or strong solid acids supported on metal oxide systems seem to be an appropriate alternative to polybenzimidazoles (PBI) and other composite membranes. In this context, we evaluate a new hybrid matrix resistant at high temperatures, made of pyridine polymer obtained from polyacrylonitrile (PAN) and nanometric oxides (e.g., zirconium(IV) oxide-yttria stabilized, YSZ) by thermo-oxidative process in a centrifugal field. These hybrid matrixes aim further developments either to embed solid acids nanoparticles or to design strong solid acids on nanooxides, making them appropriate for proton exchange membranes. SEM, TEM, XRD and Raman spectroscopy were used to establish the structure and morphology and to characterize the composite membranes. The dependence of the electrical conductivity on temperature, water uptake, and methanol permeability are evaluated.

Carbon supported Pd and PtPd catalysts were prepared by chemical reduction of metal precursors wi... more Carbon supported Pd and PtPd catalysts were prepared by chemical reduction of metal precursors with sodium borohydride. Multi-wall carbon nanotubes (MWNTs) were used as carbon support. The composition of prepared catalysts was given by EDX technique. Cyclic voltammetry (CV) measurements were used to evaluate the electrocatalytic activities for methanol electrooxidation after their immobilization onto carbon paper.

Composite solid acid/nanooxide polymer membranes with good electrical behaviour can be obtained b... more Composite solid acid/nanooxide polymer membranes with good electrical behaviour can be obtained by thermocentrifugal field processing. The supporting polymer matrix is designed to embed solid acids or strong solid acids/nanooxides making it appropriate for proton conducting composite membranes. Nanocomposites CsHSO4-YSZ/PAN membranes were investigated by Raman, FT-IR and SEM techniques. The dependence of the electrical conductivity on temperature is evaluated.

Advanced Materials Research, 2008

... BA Sava 1,a , Adriana Diaconu 1 , Luminita-Daniela Ursu 1 , Lucica Boroica 1 , M. Elisa 2,b ,... more ... BA Sava 1,a , Adriana Diaconu 1 , Luminita-Daniela Ursu 1 , Lucica Boroica 1 , M. Elisa 2,b , Cristiana Grigorescu 2 , Cristina Vasiliu 2 , I. Stamatin 3,c , F. Nastase 3 , Claudia Nastase 3 ,Anca Dumitru 3 ... [4] YMKim. SHHong and HMPark: J European Ceram Soc. ...

The paper reports a study on lithium phosphate glasses, containing calcium or magnesium and ferri... more The paper reports a study on lithium phosphate glasses, containing calcium or magnesium and ferric/ferrous oxides. Iron oxides provide high chemical stability against water and enhance the glass capacity to embed different chemical compounds. The wet synthesis method provides an enhanced homogeneity of the glass batch and improves the optical quality of the glass samples. FTIR and Raman spectroscopy revealed the network former role of P2O5 as well as the modifier/former role of iron. The vibration mode shifted at 1250 cm -1 is attributed to the iron that enters into the phosphate network, forming Fe-O-P bonds instead of P-O-P bonds.

Molecular Crystals and Liquid Crystals - MOL CRYST LIQUID CRYST, 2004

A method for the synthesis of the hypothetical silicon dicarbide structure is proposed. This stru... more A method for the synthesis of the hypothetical silicon dicarbide structure is proposed. This structure with tetragonal symmetry has been synthesized in matrixes of hardened novolac with silicon powder. Thermal treatment up to 1200°C induces in these matrixes spiroconjugation features with subsequent organizing in tetragonal symmetry. XRD, HRTEM patterns and SAED confirmed that the hypothetical structures proposed are synthetically realizable.

Physica E: Low-dimensional Systems and Nanostructures, 2007

A series of carbon nanomaterials, particularly multi-walled carbon nanotubes (MWNT), are obtained... more A series of carbon nanomaterials, particularly multi-walled carbon nanotubes (MWNT), are obtained as products from catalytic pyrolysis of the cross-linked phenol-formaldehyde resins with different ferrocene under inert atmosphere. The morphology and structure of the samples were evaluated by TEM and XRD techniques. CNTs morphology is dependent on the iron nanoparticles and their forms (Fe, Fe 3 C) resulted from ferrocene decomposition. The amount of nanotubes increases with iron content released from ferrocene catalyst during the pyrolysis process. Fe 3 C nanoparticles drive the nucleation and the growth of carbon nanotubes during the pyrolysis process. Long (up to microns) well-defined MWNTs with small defects, ropes and disordered carbon are representatives in the pyrolyzed resins composition. r

Composites Science and Technology, 2005

The metal-containing polymers combine the processability of organic polymers with the physical an... more The metal-containing polymers combine the processability of organic polymers with the physical and chemical characteristics of the metallic element or complex. Poly(ferrocenylsilanes) with backbone of ferrocene and organo-silane units are currently studied as charge-transport-dissipation materials and as precursors to advanced nanostructured ceramics. The contribution deals with advantages offered by plasma assisted chemical vapor deposition can provide for synthesis of copolymers based on ferrocene with hexamethyldisilane. This method is more suitable for precursors in nanostructured magnetic ceramics as ready for sintering. Synthesis parameters (flow, pressure, power discharge, temperature, time, monomer dosage and atmosphere) can be adjusted to get final ceramics precursors with the suitable composition needed in ceramics with tunable properties. Magnetization data showed that ferromagnetic and paramagnetic phases could be directly tunable as a function of polymer precursor composition and temperature.

Macromolecular Symposia, 2008

Confidence in the potential of hydrogen as an energy vector and fuel bring the opportunities for ... more Confidence in the potential of hydrogen as an energy vector and fuel bring the opportunities for enhancing electrolyzer performance. The aim of this paper is to develop new polymer nanocomposites as electrolyte membranes for PEM-electrolyzer. A series of nanocomposite membranes, including GEFC/TiO2, GEFC/CNTs, and GEFC/TiO2CNTs have been developed and characterized by FT-IR spectroscopy and AFM. The application of polymer nanocomposite membranes in electrochemical cells for water electrolysis was investigated. Experimental results obtained with respect to performance are reported and discussed related to GEFC membrane.

Physica Status Solidi (a), 2008

The improving carbon nanostructure bioactivity related to a specific microorganism community is a... more The improving carbon nanostructure bioactivity related to a specific microorganism community is an important research goal of bionanotechnology. The functionalized CNTs are used to improve the bioaffinity of working electrode in microbial fuel cells and wastewater treatment. Beside CNTs, carbon aerogel is another carbon material with high surface area, high open porosity and controllable morpho-structural characteristics. In the present work we investigate the biofilm growth from wastewater on functionalized CNTs and carbon aerogels. The biofilm growth on CNTs and carbon aerogel was monitored by optical and scanning electron microscopy. The influence of the bacterial growth phase on carbon electrode was assessed by cyclic voltammetry measurements in wastewater and 0.5 M potassium phosphate buffer solution. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Physica Status Solidi (a), 2007

Bionanocomposites Staphylococcus aureus /carbon nanotubes were prepared and their biocompatibilit... more Bionanocomposites Staphylococcus aureus /carbon nanotubes were prepared and their biocompatibility with different species of carbon nanotubes (CNTs) evaluated in terms of their incorporation into a microbial fuel cell (MFC) anodic design. Multi wall carbon nanotubes (MWNTs) with various morphologies and structures, as received, and synthesized by the pyrolysis of novolac with ferrocene addition were used. MWNTs were characterized by TEM and FT-IR spectroscopy. Optical microscopy with fluorescent quantum dots (QDs) have been used for bio-labeling, microorganisms-CNTs biocompatibility and rapid identification of the colonies developed. Designed BNCs are good culture cells media and the electrodes based on synthesized CNTs could be used with good effects in MFCs, from the point of view of bacteria biocompatibility. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)