Physical chemical study and development of carbon nanotubes composites

Esta tese apresenta pela primeira vez a obtenção, a partir de alcoóis, de nanotubos de carbono do tipo cup-stacked nitrogenados sendo esses nanotubos hidrofílicos e semicondutores. Os compósitos híbridos de fibra de carbono/nanotubos de carbono possuem geometria tridimensional nanoestruturada e foram preparados em reator de deposição química de vapor de leito fixo. Neste processo nanotubos de carbono do tipo cup-stacked nitrogenados, de paredes múltiplas organizadas ou helicoidais são crescidos diretamente sobre as fibras de carbono com diferentes graus de grafitização. Os compósitos obtidos foram analisados principalmente por microscopia eletrônica de varredura e de transmissão de alta resolução que mostrou que o grau de grafitização do substrato de carbono tem influência sobre o crescimento. A densidade de NTC diminui com a redução da grafitização das fibras de carbono, o que produz um material com porosidade não observada quando as fibras são bem grafitizadas. O material compósito foi estudado como elemento filtrante, eletrodos de baterias de íons de lítio, emissor de elétrons e como reforço em compósitos de silicone. A constatação da eficiência na filtragem seletiva de uma série de compostos orgânicos voláteis presentes na fumaça do cigarro bem como a preparação de eletrodos de baterias de íons de lítio sem o uso de folhas metálicas de alumínio ou cobre resultaram no deposito de dois pedidos de patente.This thesis presents for the first time nitrogen-cup-stacked carbon nanotubes with hydrophilic and semiconducting properties synthesized by alcohol precursor. The hybrid carbon fiber/carbon nanotubes composite have three-dimensional geometry and nanostructure. The material was prepared via fixed-bed chemical vapor deposition reactor. In this process nitrogen-cup-stacked, multi-walled or helical carbon nanotubes were synthesized directly onto carbon fibers with different graphitization grade. The composites were analyzed by high resolution scanning and transmission electron microscopy. This characterization showed that the fiber graphitization has influence on the growth. Carbon nanotube density decreases producing a porous composite that was not observed in well-graphitized fibers. The hybrid composite material was studied as a filter, lithium ion battery electrode, electron field emission and as silicone reinforcement. The efficiency to filter several volatile organic compounds present in the mainstream smoke and the development of lithium-ion battery electrodes, aluminum and copper foils free resulted in two patent applications deposit

Electrochemical Evidence of Strong Electronic Interaction of PtRu on Carbon Nanotubes with High Density of Defects

We show that carbon nanotubes (CNTs) with high density of defects can present a strong electronic interaction with nanoparticles of Pt-Ru with average particle size of 3.5 +/- 0.8 nm. Depending on the Pt-Ru loading on the CNTs, CO and methanol oxidation reactions suggest there is a charge transfer between Pt-Ru that in turn provokes a decrease in the electronic interaction taking place between Ru and Pt in the PtRu alloy. The CO stripping potentials were observed at about 0.65 and 0.5 V for Pt-Ru/CNT electrodes with Pt-Ru loadings of 10 and 20, and 30 wt %, respectively. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.2990222] All rights reserved.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[06/07253-8]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[04/07085-2]CNP

Micro/nanostructured carbon composite modified with a hybrid redox mediator and enzymes as a glucose biosensor

A carbon micro/nanostructured composite based on cup-stacked carbon nanotubes (CSCNTs) grown onto a carbon felt has been found to be an efficient matrix for enzyme immobilization and chemical signal transduction. The obtained CSCNT/felt was modified with a copper hexacyanoferrate/polypyrrole (CuHCNFe/Ppy) hybrid mediator, and the resulting composite electrode was applied to H(2)O(2) detection, achieving a sensitivity of 194 +/- 15 mu A mmol(-1) L. The results showed that the CSCNT/felt matrix significantly increased the sensitivity of CuHCNFe/Ppy-based sensors compared to those prepared on a felt unrecovered by CSCNTs. Our data revealed that the improved sensitivity of the as-prepared CuHCNFe/Ppy-CSCNT/felt composite electrode can be attributed to the electronic interactions taking place among the CuHCNFe nanocrystals, Ppy layer and CSCNTs. In addition, the presence of CSCNTs also seemed to favor the dispersion of CuHCNFe nanocrystals over the Ppy matrix, even though the CSCNTs were buried under the conducting polymer layer. The CSCNT/felt matrix also enabled the preparation of a glucose biosensor whose sensitivity could be tuned as a function of the number of glucose oxidase (GOx) layers deposited through a Layer-by-Layer technique with an sensitivity of 11 +/- 2 mu A mmol(-1) L achieved at 15 poly(diallyldimethylammoniumchloride)/GOx bilayers. (C) 2011 Elsevier Ltd. All rights reserved.FAPESP[proc. 05/59560-9]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP[06/07253-8]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Humidity Sensing Behavior of Endohedral Li-Doped and Undoped SWCNT/SDBS Composite Films

We have investigated single-walled carbon nanotube (SWCNT) networks wrapped with the cationic surfactant sodium dodecyl-benzenesulfonate (SBDS) as promising candidates for water detection. This is the first time that the humidity behavior of endohedral Li-doped (Li@) and undoped SWCNTs/SDBS has been shown. We identified a strong and almost monotonic decrease in resistance as humidity increased from 11 to 97%. Sensitivities varied between −3 and 65% in the entire humidity range. Electrical characterization, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) analysis revealed that a combination of the electron donor behavior of the water molecules with Poole-Frenkel conduction accounted for the resistive humidity response in the Li@SWCNT/SDBS and undoped SWCNT/SDBS networks. We found that Li@SWCNTs boosted the semiconducting character in mixtures of metallic/semiconducting SWCNT beams. Moreover, electrical characterization of the sensor suggested that endohedral Li doping produced SWCNT beams with high concentration of semiconducting tubes. We also investigated how frequency influenced film humidity sensing behavior and how this behavior of SWCNT/SDBS films depended on temperature from 20 to 80 ° C. The present results will certainly aid design and optimization of SWCNT films with different dopants for humidity or gas sensing in general

Performance of Polydioxanone-Based Membrane in Association with 3D-Printed Bioceramic Scaffolds in Bone Regeneration

This study evaluated the bioactivity of 3D-printed β-tricalcium phosphate (β-TCP) scaffolds or hydroxyapatite (HA) scaffolds associated with polydioxanone (PDO) membrane (Plenum® Guide) for guided bone regeneration in rats. Fifty-four rats were divided into three groups (n = 18 animals): autogenous bone + PDO membrane (Auto/PG); 3D-printed β-TCP + PDO membrane (TCP/PG); and 3D-printed HA + PDO membrane (HA/PG). A surgical defect in the parietal bone was made and filled with the respective scaffolds and PDO membrane. The animals were euthanized 7, 30, and 60 days after the surgical procedure for micro-CT, histomorphometric, and immunolabeling analyses. Micro-CT showed an increase in trabecular thickness and a decrease in trabecular separation, even with similar bone volume percentages between TCP/PG and HA/PG vs. Auto/PG. Histometric analysis showed increased bone formation at 30 days in the groups compared to 7 days postoperatively. Immunolabeling analysis showed an increase in proteins related to bone formation at 30 days, and both groups showed a similar immunolabeling pattern. This study concludes that 3D-printed scaffolds associated with PDO membrane (Plenum® Guide) present similar results to autogenous bone for bone regeneration

New synthesis method for a core-shell composite based on ?-Bi2O3@PPy and its electrochemical behavior as supercapacitor electrode.

New composite based on polypyrrole (PPy) and bismuth oxide (?-Bi2O3) was investigated as supercapacitor electrode. The ?-Bi2O3 was obtained by hydrothermal route at 500 ?C for 2 h. Cyclic voltammetry was used to electropolymerize PPy on graphite electrode (GE) or on GE/?-Bi2O3. The X-ray diffraction profile of Bi2O3 revealed the ?-Bi2O3 monoclinic structure with space group P21/c. The scanning and transmission electron microscopy images showed that PPy coated ?-Bi2O3. Raman spectra showed that PPy inhomogeneously coated ?-Bi2O3, but it was still possible to obtain a ?-Bi2O3@PPy core-shell hybrid composite with highly ordered ?-Bi2O3 with electronic interaction between the oxide and the polymer chain of the polymer. The GE/?-Bi2O3@PPy composite electrode (type I supercapacitor) displayed a predominantly capacitive profile with low impedance values and good electrochemical stability after 50 charge and discharge cycles. The specific capacitance of ?-Bi2O3@PPy composite was found in the range of 634 to 301 F g-1 to gravimetric current of 3 and 10 A g-1, respectively