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Rapid preparation of alpha-FeOOH and alpha-Fe2O3 nanostructures by microwave heating and their application in electrochemical sensors

Marinho, J. Z.; Montes, R. H. O.; Moura, A. P. de; Longo, E.; Varela, J. A.; Munoz, R. A. A.; Lima, R. C.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 572-576
ENG
Relevância na Pesquisa
16.36%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); alpha-FeOOH (goethite) and alpha-Fe2O3 (hematite) nanostructures have been successfully synthesized using the microwave-assisted hydrothermal (MAH) method and by the rapid burning in a microwave oven of the as-prepared goethite, respectively. The orthorhombic alpha-FeOOH to rhombohedral alpha-Fe2O3 structural transformation was observed by X-ray diffraction (XRD) and Raman spectroscopy results. Plates-like alpha-FeOOH prepared in 2 min and rounded and quasi-octahedral shaped alpha-Fe2O3 particles obtained in 10 min were observed using field emission gun scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The use of microwave heating allowed iron oxides to be prepared with shorter reaction times when compared to other synthesis methods. alpha-FeOOH nanoplates were incorporated into graphite-composite electrodes, which presented electrocatalytic properties towards the electrochemical oxidation of ascorbic acid in comparison with unmodified electrodes. This result demonstrates that such alpha-FeOOH nanostructures are very promising chemical modifiers for the development of improved electrochemical sensors. (C) 2013 Elsevier Ltd. All rights reserved.

Probing dispersion and re-agglomeration phenomena upon melt-mixing of polymer-functionalized graphite nanoplates

Santos, R. M.; Vilaverde, C.; Cunha, E.; Paiva, M. C.; Covas, J. A.
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
Publicado em 25/09/2015 ENG
Relevância na Pesquisa
57.44%
A one-step melt-mixing method is proposed to study dispersion and re-agglomeration phenomena of the as-received and functionalized graphite nanoplates in polypropylene melts. Graphite nanoplates were chemically modified via 1,3-dipolar cycloaddition of an azomethine ylide and then grafted with polypropylene-graft-maleic anhydride. The effect of surface functionalization on the dispersion kinetics, nanoparticle re-agglomeration and interface bonding with the polymer is investigated. Nanocomposites with 2 or 10 wt% of as-received and functionalized graphite nanoplates were prepared in a small-scale prototype mixer coupled to a capillary rheometer. Samples were collected along the flow axis and characterized by optical microscopy, scanning electron microscopy and electrical conductivity measurements. The as-received graphite nanoplates tend to re-agglomerate upon stress relaxation of the polymer melt. The covalent attachment of a polymer to the nanoparticle surface enhances the stability of dispersion, delaying the re-agglomeration. Surface modification also improves interfacial interactions and the resulting composites presented improved electrical conductivity.; Project Matepro – Optimizing Materials and Processes, with reference NORTE-07- 0124-FEDER-000037 by the Programa Operacional Regional do Norte (ON.2); Portuguese Foundation for the Science and Technology (FCT) for PEst-C/CTM/LA0025/2013

Dispersion and re-agglomeration of graphite nanoplates in polypropylene melts under controlled flow conditions

Vilaverde, C.; Santos, R. M.; Paiva, M. C.; Covas, J. A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /08/2015 ENG
Relevância na Pesquisa
26.36%
The kinetics of GnP dispersion in polypropylene melt was studied using a prototype small scale modular extensional mixer. Its modular nature enabled the sequential application of a mixing step, melt relaxation, and a second mixing step. The latter could reproduce the flow conditions on the first mixing step, or generate milder flow conditions. The effect of these sequences of flow constraints upon GnP dispersion along the mixer length was studied for composites with 2 and 10 wt.% GnP. The samples collected along the first mixing zone showed a gradual decrease of number and size of GnP agglomerates, at a rate that was independent of the flow conditions imposed to the melt, but dependent on composition. The relaxation zone induced GnP re-agglomeration, and the application of a second mixing step caused variable dispersion results that were largely dependent on the hydrodynamic stresses generated.; Project Matepro – Optimizing Materials and Processes (NORTE-07-0124-FEDER-000037) by Programam Operacional Regional do Norte (ON.2)

Nanocrystal Growth on Graphene with Various Degrees of Oxidation

Wang, Hailiang; Robinson, Joshua Tucker; Diankov, Georgi; Dai*, Hongjie
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/02/2010
Relevância na Pesquisa
16.36%
We show a general two-step method to grow hydroxide and oxide nanocrystals of the iron family elements (Ni, Co, Fe) on graphene with two degrees of oxidation. Drastically different nanocrystal growth behaviors were observed on low-oxidation graphene sheets (GS) and highly oxidized graphite oxide (GO) in hydrothermal reactions. Small particles pre-coated on GS with few oxygen-containing surface groups diffused and recrystallized into single-crystalline nickel hydroxide Ni(OH)2 hexagonal nanoplates or iron oxide Fe2O3 nanorods with well defined morphologies. In contrast, particles pre-coated on GO were pinned by the high-concentration oxygen groups and defects on GO without recrystallization into well-defined shapes. Adjusting reaction temperature can be combined to further control materials grown on graphene. For materials with weak interactions with graphene, increasing the reaction temperature can lead to diffusion and recrystallization of surface species into larger crystals even on highly oxidized and defective GO. Our results suggest an interesting new approach to controlling the morphology of nanomaterials grown on graphene by tuning the surface chemistry of graphene as substrates for crystal nucleation and growth.; Comment: JACS in press

Ni(OH)2 Nanoplates Grown on Graphene as Advanced Electrochemical Pseudocapacitor Materials

Wang, Hailiang; Casalongue, Hernan Sanchez; Liang, Yongye; Dai, Hongjie
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/05/2010
Relevância na Pesquisa
26.92%
Ni(OH)2 nanocrystals grown on graphene sheets with various degrees of oxidation are investigated as electrochemical pseudocapacitor materials for potential energy storage applications. Single-crystalline Ni(OH)2 hexagonal nanoplates directly grown on lightly-oxidized, electrically-conducting graphene sheets (GS) exhibit a high specific capacitance of ~1335F/g at a charge and discharge current density of 2.8A/g and ~953F/g at 45.7A/g with excellent cycling ability. The high specific capacitance and remarkable rate capability are promising for applications in supercapacitors with both high energy and power densities. Simple physical mixture of pre-synthesized Ni(OH)2 nanoplates and graphene sheets show lower specific capacitance, highlighting the importance of direct growth of nanomaterials on graphene to impart intimate interactions and efficient charge transport between the active nanomaterials and the conducting graphene network. Single-crystalline Ni(OH)2 nanoplates directly grown on graphene sheets also significantly outperform small Ni(OH)2 nanoparticles grown on heavily-oxidized, electrically-insulating graphite oxide (GO), suggesting that the electrochemical performance of these composites are dependent on the quality of graphene substrates and the morphology and crystallinity of the nanomaterials grown on top. These results suggest the importance of rational design and synthesis of graphene-based nanocomposite materials for high-performance energy applications.; Comment: Published in JACS

Dispersion of graphite nanoplates during melt mixing

Covas, J. A.; Cunha, Eunice Paula Freitas; Paiva, M. C.; Hilliou, L.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 17/08/2015 ENG
Relevância na Pesquisa
46.87%
Artigo publicado a convite da Society for Polymer Engineers; The behavior of pristine and functionalized particles within polypropylene was investigated with the use of a prototype small-scale mixer.; Matepro (NORTE-07-0124-FEDER-000037); Foundation for Science and Technology (project PEst-C/CTM/LA0025/2011); PhD grant FRH/BD/87214/2012