Hiilinanoputkireaktorin suunnittelu

Hiilinanoputki on vasta 90-luvun alussa löydetty uusi hiilestä koostuva materiaali, jonka erinomaiset mekaaniset ja fysikaaliset ominaisuudet tarjoavat niiden käytölle useita mahdollisia sovelluskohteita. Teknologian puute ja valmistusmenetelmien korkeat kustannukset ovat kuitenkin estäneet tehokkaasti niiden käytön nykyisten materiaalien ja puolijohteiden korvaajana. Tämän työn tarkoituksena on esitellä yleisimmät menetelmät hiilinanoputkien syntetisoimiseksi sekä suunnitella laite yksiseinäisten hiilinanoputkien tuottamiseen kemiallisen höyrydeposition avulla. Lisäksi tavoitteena on luoda laitteelle modulaarinen rakenne, jolloin sen eri osien korvaaminen rajapintojen sallimissa rajoissa on helppoa. Reaktorin mekaanisen suunnittelun ja komponenttien valinnan lisäksi työssä käsitellään laitteen kaasu- ja lämpövirtauksia, prosessissa tärkeiden katalyyttipartikkelien tuotantoa sekä laitteessa tarvittavien jäähdytysjärjestelmien mitoituksia. Tuloksena syntyi helposti toteutettava suunnitelma yksiseinäisiä nanoputkia tuottavan reaktorin valmistamiseksi. Työ jatkuu laitteen rakentamisella, testaamisella sekä jatkokehittelyllä.

Tecnologia dos nanotubos de carbono: tendências e perspectivas de uma área multidisciplinar

An overview of the properties of carbon nanotubes is presented as a function of the structural characteristics and of the method of synthesis of these novel advanced materials. Emphasis is given to the catalytic decomposition of hydrocarbons over metal-supported catalysts and also the role of the support in obtaining homogeneous carbon nanotubes in high yelds is discussed. Some potential and real applications of carbon nanotubes are presented in a perspective view.

Funcionalização de nanotubos de Carbono

Carbon nanotubes are very stable systems having considerable chemical inertness due to the strong covalent bonds of the carbon atoms on the nanotube surface. Many applications of carbon nanotubes require their chemical modification in order to tune/control their physico-chemical properties. One way of achieving this control is carrying out functionalization processes where atoms and molecules interact (covalent or non-covalent) with the nanotubes. We review some of the progress that has been made in chemical functionalization of carbon nanotubes. Emphasis is given to chemical strategies, the most used techniques, and applications.

Estudo teórico de propriedades ópticas não-lineares de nanotubos de carbono de parede única quimicamente modificados

Structure and first hyperpolarizability for a series of armchair a(5,5) chemically modified carbon nanotubes (CNT) were calculated at semiempirical and density functional levels of theory. The 4,4´-substituted stilbenes were selected as chromophore with substituents at position 4´ set to X=NO2, H, Cl, OH and NH2. The calculated values for static first hyperpolarizability (β) were almost linearly dependent on the electronic effect of the group X, increasing from NO2 to NH2. At DFT level the effect of inserting the chromophore in the CNT surface was to enhance the β value up to 70% relative to the free 4,4´-substituted stilbene.

Nanotecnologia: aspectos gerais e potencial de aplicação em catálise

In recent years nanomaterials, such as metallic nanoparticles, nanowires, nanotapes, nanotubes and nanocomposites, have attracted increasing interest for several technological applications. In catalysis, the great potential of nanomaterials is related to the high catalytic activity exhibited by these materials as a function of the high surface/volume ratio when the particles acquire diameter below 5 nm. In this work, a review about concepts and background of nanoscience and nanotechnology is presented with emphasis in catalysis. Special attention is given to gold nanoparticles and carbon nanotubes, focusing the properties and characteristics of these materials in several catalytic reactions.

Nanocompósitos de poliuretana termoplástica e nanotubos de carbono de paredes múltiplas para dissipação eletrostática

Polyurethane/multi-walled carbon nanotube (MWCNT) nanocomposites have been prepared with nanotube concentrations between 0.01 wt% and 1 wt%. MWCNT as-synthesized samples with ~74 nm diameter and ~7 μm length were introduced by solution processing in the polyurethane matrix. Scanning electron microscopy (SEM) images demonstrated good dispersion and adhesion of the CNTs to the polymeric matrix. The C=O stretching band showed evidence of perturbation of the hydrogen interaction between urethanic moieties in the nanocomposites as compared to pure TPU. Differential scanning calorimetry and positron anihilation lifetime spectroscopy measurements allowed the detection of glass transition displacement with carbon nanotube addition. Furthermore, the electrical conductivity of the nanocomposites was significantly increased with the addition of CNT.

Sistema RTP: uma técnica poderosa para o monitoramento da formação de nanotubos de carbono durante o processo por deposição de vapor químico

In this work, a TPR (Temperature Programmed Reduction) system is used as a powerful tool to monitor carbon nanotubes production during CVD (Chemical Vapour Deposition), The experiments were carried out using catalyst precursors based on Fe-Mo supported on Al2O3 and methane as carbon source. As methane reacts on the Fe metal surface, carbon is deposited and H2 is produced. TPR is very sensitive to the presence of H2 and affords information on the temperature where catalyst is active to form different forms of carbon, the reaction kinetics, the catalyst deactivation and carbon yields.

Planejamento fatorial e superfície de resposta: otimização de um método voltamétrico para a determinação de ag(i) empregando um eletrodo de pasta de nanotubos de carbono

A factorial design applied in a voltammetric stripping method for the measurement of Ag(I) in natural water is described. The procedure is based on the effective pre-concentration of silver ions on electrode surface. The calibration graph was linear in the silver concentration range from 7.92 x 10"7 to 1.07 x 10"5 mol L"1 with a detection limit of 3.81 x 10-7 mol L-1. The determination of Ag(I) in natural water samples was carried out satisfactory with the proposed electrode.

Produção de gás de síntese por plasma térmico via pirólise de metano e dióxido de carbono

In this work the production of synthesis gas from a mixture of methane (CH4) and carbon dioxide (CO2) by thermal plasma was studied. The best relation found for the gas mixture [CO2]/[CH4] was 1.3. Under the excess of CH4 in the gas mixture soot was formed and also benzene, indene and naphthalene were identified. The disulfides compounds in the gas mixture were degraded causing no interference in the synthesis gas production, suggesting no needs of pretreatment step for sulfurorganic compounds removal in the process

Estudo das dispersões aquosas de nanotubos de carbono utilizando diferentes surfactantes

The dispersion of carbon nanotubes in water for their utilization in nanoscale devices is a challenging task. Comparative studies on interaction and dispersion of multi-wall carbon nanotubes (MWNT) using two different surfactants (sodium dodecyl sulfate, SDS, and polyoxyethylenesorbitanmonooleate, Tween 80) are presented. The interaction between carbon nanotubes and surfactants was studied by tensiometry, conductivimetry, and fluorimetry. The dispersions of MWNT in surfactants were characterized using a UV-vis spectrophotometer. For effective dispersion, the minimum weight ratio of MWNT to surfactant was 1:41 and 1:3 for SDS and Tween 80, respectively.

Revisão dos tratamentos químicos da fibra natural para mistura com poliolefinas

The use of natural fibers as reinforcement in polymer composites has been a focus of interest. However, these composites exhibit lower mechanical properties than those of pure polymers because of the low interfacial interactions between the hydrophobic polymer matrix and the hydrophilic fiber. To overcome this problem, different chemical treatments applied to the fibers have been reported. One of the most used treatments is mercerization, which can improve adhesion between the fiber and polymeric matrix. Another chemical treatment involves the use of acids (stearic and oleic acids). The chemically treated fibers used in composite materials showed improved mechanical properties.

Nanoestruturas de carbono (nanotubos, grafeno): Quo Vadis?

We describe general considerations about the present and the future standing of carbon nanostructures, mainly carbon nanotubes and graphene. Basic concepts and definitions, select structure/property relationships, and potential applications are reviewed. The analysis of the global market for these nanostructures, the commercial products available currently, the role of the chemistry, the main challenges remaining and a brief view of the field in Brazil are also presented and discussed.

BIOSSENSOR ELETROQUÍMICO BASEADO NA ENZIMA TIROSINASE PARA A DETERMINAÇÃO DE FENOL EM EFLUENTES

AbstractThis work describes the development of a biosensor based on the tyrosinase enzyme (Tyr) for the determination of phenol (PHEN) in laboratory effluent samples derived from ammoniacal nitrogen analysis of the water samples from the Muquém dam in the city of Cariús, CE, using square-wave voltammetry (SWV). The electrode modification consisted of the immobilization of gold nanoparticles, multi-walled carbon nanotubes, cobalt phthalocyanine, and Tyr on a glassy carbon electrode. The electrolyte, pH, enzyme quantity, and voltammetric parameters were optimized to detect PHEN. The analytical curves presented a linear range from 4.97 × 10-6 mol L-1 to 6.10 × 10-5 mol L-1, and the detection limit (DL) and quantitation limit (QL) values were 4.81 × 10-6 mol L-1 and 4.97 × 10-6mol L-1, respectively. The repetition of measurements with the same biosensor and repetition for three other prepared biosensors exhibited a relative standard deviation (RSD) of 5.50 and 1.75%, respectively. The percentage recovery of PHEN in effluent samples varied from 86.40 to 105.04%. The stability of the biosensor was evaluated (at 21 days) with satisfactory results, showing 97.86% of the initial response. Moreover, the DL and recovery percentages agreed with the established values from CONAMA and ABNT, respectively. Thus, the electrode configuration developed seems a promising tool in the detection and quantification of PHEN in complex samples.

CARACTERIZAÇÃO E AVALIAÇÃO IN VITRO DE NANOCOMPÓSITOS DE POLI (L-ÁCIDO LÁTICO) E NANOTUBOS DE CARBONO DE PAREDES MÚLTIPLAS PURIFICADOS

Carbon nanotubes (CNT) have been studied for biomedical applications due to their unique properties. However, pristine CNT have structural features and impurities that can cause toxicity to biological systems. In this work, we describe a method to purify multiwalled carbon nanotubes (MWCNT) by chemical modification and subsequent attachment of hydroxyl and carboxyl groups to improve dispersion and to decrease toxic effects. Nanocomposites from poly (L-lactic acid) (PLLA) and nanotubes were produced by the solvent casting method and characterized and evaluated for cytocompatibility with Vero cells. The nanocomposite interactions with Vero cells demonstrated that the cells were able to adhere and sustain proliferation and showed favorable cytocompatibility. In vitro studies also revealed an increase in fibroblast cell viability in the nanocomposites, compared with neat PLLA.

Selluloosapohjaisten superkondensaattorien valmistaminen hiilinanoputkista

Tämän työn tarkoitus on seuloa oleelliset prosessiparametrit superkondensaattoreiden elektrodikomposiittien valmistuksessa, jotka vaikuttavat kondensaattorin laatuun. Tarkoitus on tutkia parametreja, joiden avulla prosessia on mahdollista optimoida. Työn tarkoituksena on tutkia myös itse komponenttimateriaalien valmistusvaiheen sekoitusprosessia mitatulla ja laskennallisella seokseen siirtyvällä tehonkulutuksella. Työn kirjallisuusosassa esitetään superkondensaattoreiden rakennetta, toimintamekanismia ja ominaisuuksia sähköenergian varastoijana. Lisäksi tarkastellaan tavallisimpia kondensaattoreihin sisältyviä materiaaleja, erityisesti hiilinanoputkia ja selluloosakuituja. Sekoitusprosesseista tarkastellaan kokeellisessa osassa käytettävien sekoituslaitteita ja niiden toimintamekanismeja komponenttien sekoitusprosesseissa. Kokeellisessa osassa tutkimuskysymyksiksi asetettiin eri sekoitusparametrien (materiaalin määrä ja laatu sekä sekoitusajat) vaikutus superkondensaattorien elektrodiarkkien ominaiskapasitansseihin. Testit suoritettiin LUT Prosessien laboratoriossa, ja testeissä massojen sekoitukseen käytettiin roottoristaattoria ja ultraäänisekoitinta. Lisäksi tutkittiin prosessin skaalausta varten skaalatulla laitteistolla sekoitettuja massanäytteitä. Sekoitusprosessin riittävyyttä varten tutkittiin kokeellisesti käytettyjen sekoituslaitteiden tehonkulutusta. Lisäksi roottoristaattorille tehtiin laskentaohjelmalla virtaussimulaatio paikallisen tehonkulutuksen selvittämiseksi Testeissä todettiin tutkittujen parametrien vaikutus, mutta tulosten perusteella varsinaista optimointia ei kyetty tekemään. Tulokset kuitenkin antavat suunnan, johon prosessia voi optimointia varten kehittää. Myös sekoitukseen todettiin siirtyvän suuri määrä tehoa tutkituilla laitteilla, mitä voidaan pitää mahdollisesti riittävänä käytettyjen komponenttien sekoitukseen.