Aplicação de tecnologias eletroquímicas (oxidação via radicais hidroxila, oxidação mediada via cloro ativo e eletrocoagulação) para o tratamento de efluentes reais ou sintéticos

In this work the degradation of real and synthetic wastewater was studied using electrochemical processes such as oxidation via hydroxyl radicals, mediated oxidation via active chlorine and electrocoagulation. The real effluent used was collected in the decanter tank of the Federal University of Rio Grande do Norte (ETE-UFRN) of Effluent Treatment Plant and the other a textile effluent dye Ácido Blue 113 (AB 113) was synthesized in the laboratory. In the electrochemical process, the effects of anode material, current density, the presence and concentration of chloride as well as the active chlorine species on site generated were evaluated. Electrodes of different compositions, Ti/Pt, Ti/Ru0,3Ti0,7O2, BDD, Pb/PbO2 and Ti/TiO2-nanotubes/PbO2 were used as anodes. These electrodes were subjected to electroanalytical analysis with the goal of checking how happen the anodic and cathodic processes across the concentrations of NaCl and supporting electrolyte used. The potential of oxygen evolution reaction were also checked. The effect of active chlorine species formed under the process efficiency was evaluated by removing the organic matter in the effluent-ETE UFRN. The wastewater treatment ETE-UFRN using Ti/Pt, DDB and Ti/Ru0,3Ti0,7O2 electrodes was evaluated, obtaining good performances. The electrochemical degradation of effluent-UFRN was able to promote the reduction of the concentration of TOC and COD in all tested anodes. However, Ti/Ru0,3Ti0,7O2 showed a considerable degradation due to active chlorine species generated on site. The results obtained from the electrochemical process in the presence of chloride were more satisfactory than those obtained in the absence. The addition of 0.021 M NaCl resulted in a faster removal of organic matter. Secondly, was prepared and characterized the electrode Ti/TiO2-nanotubes/PbO2 according to what the literature reports, however their preparation was to disk (10 cm diameter) with surface area and higher than that described by the same authors, aiming at application to textile effluent AB 113 dye. SEM images were taken to observe the growth of TiO2 nanotubes and confirm the electrodeposition of PbO2. Atomic Force Microscope was also used to confirm the formation of these nanotubes. Furthermore, was tested and found a high electrochemical stability of the electrode Ti/TiO2-nanotubes/PbO2 for applications such as long-term indicating a good electrocatalytic material. The electrochemical oxidation of AB 113 using Ti/Pt, Pb/PbO2 and Ti/TiO2-nanotubes/PbO2 and Al/Al (electrocoagulation) was also studied. However, the best color removal and COD decay were obtained when Ti/TiO2-nanotubes/PbO2 was used as the anode, removing up to 98% of color and 92,5% of COD decay. Analysis of GC/MS were performed in order to identify possible intermediates formed in the degradation of AB 113.

Loading effect in copper(II) oxide cluster-surface-modified titanium(IV) oxide on visible- and UV-light activities

Cu(acac)2 is chemisorbed on TiO2 particles [P-25 (anatase/rutile = 4/1 w/w), Degussa] via coordination by surface Ti–OH groups without elimination of the acac ligand. Post-heating of the Cu(acac)2-adsorbed TiO2 at 773 K yields molecular scale copper(II) oxide clusters on the surface (CuO/TiO2). The copper loading amount (Γ/Cu ions nm–2) is controlled in a wide range by the Cu(acac)2 concentration and the chemisorption–calcination cycle number. Valence band (VB) X-ray photoelectron and photoluminescence spectroscopy indicated that the VB maximum of TiO2 rises up with increasing Γ, while vacant midgap levels are generated. The surface modification gives rise to visible-light activity and concomitant significant increase in UV-light activity for the degradation of 2-naphthol and p-cresol. Prolonging irradiation time leads to the decomposition to CO2, which increases in proportion to irradiation time. The photocatalytic activity strongly depends on the loading, Γ, with an optimum value of Γ for the photocatalytic activity. Electrochemical measurements suggest that the surface CuO clusters promote the reduction of adsorbed O2. First principles density functional theory simulations clearly show that, at Γ < 1, unoccupied Cu 3d levels are generated in the midgap region, and at Γ > 1, the VB maximum rises and the unoccupied Cu 3d levels move to the conduction band minimum of TiO2. These results suggest that visible-light excitation of CuO/TiO2 causes the bulk-to-surface interfacial electron transfer at low coverage and the surface-to-bulk interfacial electron transfer at high coverage. We conclude that the surface CuO clusters enhance the separation of photogenerated charge carriers by the interfacial electron transfer and the subsequent reduction of adsorbed O2 to achieve the compatibility of high levels of visible and UV-light activities.

Nanostructured Metal Oxide Coatings for Electrochemical Energy Conversion and Storage Electrodes

The realization of an energy future based on safe, clean, sustainable, and economically viable technologies is one of the grand challenges facing modern society. Electrochemical energy technologies underpin the potential success of this effort to divert energy sources away from fossil fuels, whether one considers alternative energy conversion strategies through photoelectrochemical (PEC) production of chemical fuels or fuel cells run with sustainable hydrogen, or energy storage strategies, such as in batteries and supercapacitors. This dissertation builds on recent advances in nanomaterials design, synthesis, and characterization to develop novel electrodes that can electrochemically convert and store energy.

Chapter 2 of this dissertation focuses on refining the properties of TiO2-based PEC water-splitting photoanodes used for the direct electrochemical conversion of solar energy into hydrogen fuel. The approach utilized atomic layer deposition (ALD); a growth process uniquely suited for the conformal and uniform deposition of thin films with angstrom-level thickness precision. ALD’s thickness control enabled a better understanding of how the effects of nitrogen doping via NH3 annealing treatments, used to reduce TiO2’s bandgap, can have a strong dependence on TiO2’s thickness and crystalline quality. In addition, it was found that some of the negative effects on the PEC performance typically associated with N-doped TiO2 could be mitigated if the NH3-annealing was directly preceded by an air-annealing step, especially for ultrathin (i.e., < 10 nm) TiO2 films. ALD was also used to conformally coat an ultraporous conductive fluorine-doped tin oxide nanoparticle (nanoFTO) scaffold with an ultrathin layer of TiO2. The integration of these ultrathin films and the oxide nanoparticles resulted in a heteronanostructure design with excellent PEC water oxidation photocurrents (0.7 mA/cm2 at 0 V vs. Ag/AgCl) and charge transfer efficiency.

In Chapter 3, two innovative nanoarchitectures were engineered in order to enhance the pseudocapacitive energy storage of next generation supercapacitor electrodes. The morphology and quantity of MnO2 electrodeposits was controlled by adjusting the density of graphene foliates on a novel graphenated carbon nanotube (g-CNT) scaffold. This control enabled the nanocomposite supercapacitor electrode to reach a capacitance of 640 F/g, under MnO2 specific mass loading conditions (2.3 mg/cm2) that are higher than previously reported. In the second engineered nanoarchitecture, the electrochemical energy storage properties of a transparent electrode based on a network of solution-processed Cu/Ni cores/shell nanowires (NWs) were activated by electrochemically converting the Ni metal shell into Ni(OH)2. Furthermore, an adjustment of the molar percentage of Ni plated onto the Cu NWs was found to result in a tradeoff between capacitance, transmittance, and stability of the resulting nickel hydroxide-based electrode. The nominal area capacitance and power performance results obtained for this Cu/Ni(OH)2 transparent electrode demonstrates that it has significant potential as a hybrid supercapacitor electrode for integration into cutting edge flexible and transparent electronic devices.

Synergistischer photoinduzierter Schadstoffabbau mittels eines Porphyrazin-Titandioxid-Hybrids

Die zunehmende Luftverschmutzung aufgrund des steigenden Energiebedarfs und Mobilitätsanspruchs der Bevölkerung, insbesondere in urbanen Gebieten, erhöht das Gefährdungspotential für die Gesundheit und verschlechtert so die Lebensqualität. Neben der Vermeidung von Emissionen toxischer Gase als mittel- und langfristig optimale Maßnahme zur Verbesserung der Luftqualität, stellt der Abbau emittierter Luftschadstoffe ein geeignetes und kurzfristig wirksames Mittel dar. Ein solcher Abbau kann durch Photokatalyse erzielt werden, allerdings nutzen Photokatalysatoren, die auf dem Halbleiter Titandioxid (TiO2) basieren, das solare Emissionsspektrum nur geringfüfig aus und sind in Innenräumen und anderen UV-schwachen Bereichen nicht wirksam. Um diese Nachteile zu überwinden, wurde ein Photokatalysator entwickelt und hergestellt, der aus TiO2 (P25) als UV-aktiver Photokatalysator und als Trägermaterial sowie einem seinerseits im Vis-Bereich photoaktiven Porphyrazin-Farbstoff als Beschichtung besteht. Die sterisch anspruchsvollen und in der Peripherie mit acht Bindungsmotiven für TiO2 versehenen Farbstoffmoleküle wurden zu diesem Zweck auf der Halbleiteroberfläche immobilisiert. Die so gebildeten Porphyrazin-Titandioxid-Hybride wurde ausführlich charakterisiert. Dabei wurden unter anderem die Bindung der Farbstoffe auf der Titandioxidoberfläche mittels Adsorptionsisothermen und die UV/Vis-spektroskopischen Eigenschaften des Hybridmaterials untersucht. Zur Bestimmung der photokatalytischen Aktivitäten der Einzelkomponenten und des Hybridmaterials wurden diese auf die Fähigkeit zur Bildung von Singulett-Sauerstoff, Wasserstoffperoxid und Hydroxylradikalen hin sowie in einem an die ISO-22197-1 angelehnten Verfahren auf die Fähigkeit zum Abbau von NO hin jeweils bei Bestrahlung in drei Wellenlängenbereichen (UV-Strahlung, blaues Licht und rotes Licht) geprüft. Darüber hinaus konnte die Aktivität des Hybridmaterials bei der Photodynamischen Inaktivierung (PDI) von Bakterien unter UV- und Rotlichtbestrahlung im Vergleich zum reinen Ttandioxid bestimmt werden. Die Charakterisierung des Hybridmaterials ergab, dass die Farbstoffmoleküle in einer neutralen Suspension nahezu irreversibel in einer monomolekularen Schicht mit einer Bindungsenergie von -41.43 kJ/mol an die Oberfläche gebunden sind und das Hybridmaterial mit hohen Extinktionskoeffizienten von bis zu 105 M-1cm-1 in großen Bereichen des UV/Vis-Spektrums Photonen absorbiert. Das Spektrum des Hybridmaterials setzt sich dabei additiv aus den beiden Einzelspektren zusammen. Die Auswirkungen der Charakterisierungsergebnisse auf die Bildung reaktiver Sauerstoffspezies wurden ausführlich diskutiert. Der Vergleich der Aktivitäten in Bezug auf die Bildung der reaktiven Sauerstoffspezies zeigte, dass die Aktivität des Hybridmaterials bis auf die bei der Bildung von Hydroxylradikalen unter UV-Bestrahlung in allen Versuchen deutlich höher war als die Aktivität des reinen Titandioxids. Im Gegensatz zu reinem Titandioxid erzeugte das Hybridmaterial in allen untersuchten Wellenlängenbereichen Mengen an Singulett-Sauerstoff, die photophysikalisch eindeutig detektierbar waren. Zur Erklärung und Deutung dieser Beobachtungen wurde eine differenzierte Diskussion geführt, die die Ergebnisse der Hybridpartikelcharakterisierung aufgreift und implementiert. Der Vergleich der NO-Abbaueffizienzen ergab bei allen Experimenten durchgängig deutlich höhere Werte für das Hybridmaterial. Zudem wurden durch das Hybridmaterial nachgewiesenermaßen wesentlich geringere Mengen des unerwünschten Nebenprodukts des Abbaus (NO2) gebildet. Im Zuge der Diskussion wurden verschiedene mögliche Mechanismen der „sauberen“ Oxidation zu Nitrat durch das Hybridmaterial vorgestellt. Untersuchungen zur Photodynamischen Inaktivierung verschiedener Bakterien ergaben, dass das Hybridmaterial neben einer zu P25 ähnlichen Aktivität unter UV-Bestrahlung, anders als P25, auch eine PDI verschiedener Bakterien unter Rotlichtbestrahlung erreicht.

Titanium dioxide based nanomaterials for photocatalytic water treatment

Water treatment using photocatalysis has gained extensive attention in recent years. Photocatalysis is promising technology from green chemistry point of view. The most widely studied and used photocatalyst for decomposition of pollutants in water under ultraviolet irradiation is TiO2 because it is not toxic, relatively cheap and highly active in various reactions. Within this thesis unmodified and modified TiO2 materials (powders and thin films) were prepared. Physico-chemical properties of photocatalytic materials were characterized with UV-visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES), ellipsometry, time-of-flight secondary ion mass spectrometry (ToF-SIMS), Raman spectroscopy, goniometry, diffuse reflectance measurements, thermogravimetric analysis (TGA) and nitrogen adsorption/desorption. Photocatalytic activity of prepared samples in aqueous environment was tested using model compounds such as phenol, formic acid and metazachlor. Also purification of real pulp and paper wastewater effluent was studied. Concentration of chosen pollutants was measured with high pressure liquid chromatography (HPLC). Mineralization and oxidation of organic contaminants were monitored with total organic carbon (TOC) and chemical oxygen demand (COD) analysis. Titanium dioxide powders prepared via sol-gel method and doped with dysprosium and praseodymium were photocatalytically active for decomposition of metazachlor. The highest degradation rate of metazachlor was observed when Pr-TiO2 treated at 450ºC (8h) was used. The photocatalytic LED-based treatment of wastewater effluent from plywood mill using commercially available TiO2 was demonstrated to be promising post-treatment method (72% of COD and 60% of TOC was decreased after 60 min of irradiation). The TiO2 coatings prepared by atomic layer deposition technique on aluminium foam were photocatalytically active for degradation of formic and phenol, however suppression of activity was observed. Photocatalytic activity of TiO2/SiO2 films doped with gold bipyramid-like nanoparticles was about two times higher than reference, which was not the case when gold nanospheres were used.

Criminalidade Económica e Lavagem de Dinheiro: prevenção pela aprendizagem

1 – Resumo: a criminalidade económica tem uma relação muito próxima com o branqueamento de capitais ou lavagem de dinheiro. O sistema económico capitalista está relacionado de forma próxima com o branqueamento de capitais ou a lavagem de dinheiro. O branqueamento de vantagens – como por exemplo capitais -, é um crime que pode atingir um carácter mundial. Também o financiamento do terrorismo surge aqui com um papel importante. É muito importante punir a ilicitude do crime de branqueamento. Mas mais importante ainda é a prevenção do branqueamento de capitais. Neste sentido, o dever de formação é fundamental. E é um dever fundamental que é importante sobretudo no contexto de determinadas entidades. Entidades financeiras e entidades não financeiras. §1.1 Abstract: economic crime has a close relationship with money laundering. The capitalist economic system is related closely with money laundering. Bleaching of advantages - such as capital - is a crime that can reach a global nature. Also the financing of terrorism comes here with an important role. It is very important to punish the unlawfulness of laundering crime. But more important is the prevention of money laundering. In this sense, the duty of training is critical. It is a fundamental duty that is especially important in the context of certain entities. financial institutions and non-financial entities.

Criminalidade Económica e Lavagem de Dinheiro: prevenção pela aprendizagem

Resumo: a criminalidade económica tem uma relação muito próxima com o branqueamento de capitais ou lavagem de dinheiro. O sistema económico capitalista está relacionado de forma próxima com o branqueamento de capitais ou a lavagem de dinheiro. O branqueamento de vantagens – como por exemplo capitais – é um crime que pode atingir um carácter mundial. Também o financiamento do terrorismo surge aqui com um papel importante. É muito importante punir a ilicitude do crime de branqueamento. Mas mais importante ainda é a prevenção do branqueamento de capitais. Neste sentido, o dever de formação é fundamental. E é um dever fundamental importante sobretudo no contexto de determinadas entidades. Entidades financeiras e entidades não financeiras.§ Abstract: Economic crime has a close relationship with money laundering. The capitalist economic system is related closely with money laundering. Bleaching of advantages – such as capital – is a crime that can reach a global nature. Also the financing of terrorism comes here with an important role. It is very important to punish the unlawfulness of laundering crime. But more important is the prevention of money laundering. In this sense, the duty of training is critical. It is a fundamental duty that is especially important in the context of certain entities. financial institutions and non-financial entities.

BODIPY-Porphyrazin-Hybride als panchromatische Lichtsammelsysteme für farbstoffsensibilisierte Solarzellen

In farbstoffsensibilisierten Solarzellen (DSSC) spielen Chromophore, die als Lichtsammel- und Energie-/Elektronentransfersysteme fungieren, eine zentrale Rolle. Phthalocyanine mit ihren intensiven Absorptionsbanden um 400 nm und 700 nm besitzen großes Potential für die effektive Sensibilisierung von Solarzellen. Trotz ihrer vielversprechenden physikochemischen Eigenschaften und intensiver Bemühungen erreichen Phthalocyanin-sensibilisierte Solarzellen nicht die Effizienzen, die bisher mit anderen Chromophorklassen erzielt werden konnten. In der vorliegenden Dissertation wurde die Entwicklung effizienter Lichtsammelsysteme für DSSC auf der Basis von Aza-substituierten Phthalocyaninen, sogenannten Pyrazinoporphyrazinen, verfolgt. Ein besonderer Fokus lag dabei auf einer Verbesserung der Absorptionseigenschaften der Chromophore im Bereich ihrer intrinsischen Absorptionslücke zwischen den Maxima um 400 nm und 700 nm. Um diese optische Lücke zu schließen wurden komplementär absorbierende BODIPY-Farbstoffe kovalent an synthetisch maßgeschneiderte Porphyrazine gebunden. Insgesamt wurden sechs neue Porphyrazin-Sensibilisatoren synthetisiert und photophysikalisch sowie elektrochemisch charakterisiert. Alle in dieser Arbeit untersuchten Porphyrazine tragen sterisch anspruchsvolle Tri(p-tolyl)propinyl-Gruppen um Agglomerationen zu vermeiden. Darüber hinaus wurden die Porphyrazine peripher entweder mit Hydroxy- oder Carboxygruppen als Bindungsstellen für oxidische Materialien ausgestattet sowie mit sechs BODIPY-Auxiliarfarbstoffen funktionalisiert, deren Substitutionsmuster variiert wurden. Zur Darstellung der komplexen Porphyrazine wurde eine Syntheseroute erarbeitet, die statistische Cyclisierungen unterschiedlicher Dinitril-Vorstufen beinhaltete und es ermöglichte, funktionelle Gruppen erst am vorgeformten Makrocyclus einzuführen. Die photophysikalische Untersuchung der hochfunktionalisierten Farbstoffe erfolgte über UV/Vis- und Fluoreszenzspektroskopie. Im Fall der BODIPY-Porphyrazin-Hybride schließt die zusätzliche Absorptionsbande der peripheren BODIPY-Einheiten die intrinsische Absorptionslücke der Porphyrazine. Die Hybride zeigen somit eine breite Absorption über den gesamten sichtbaren Spektralbereich mit hohen Extinktionskoeffizienten von ca. 4·10^5 M^−1cm^−1. Mittels Fluoreszenz- und Anregungsspektren wurde ein photoinduzierter Energie-transfer von den BODIPY-Einheiten auf den Porphyrazinkern nachgewiesen. Das elektrochemische Verhalten der BODIPY- und Porphyrazin-Verbindungen wurde mittels Cyclo- und Square-Wave-Voltammetrie untersucht. Die Effizienzen der Lichtenergieumwandlung wurden mit Hilfe von selbst-hergestellten und standardisierten farbstoffsensibilisierten Solarzellen bewertet. Alle Solarzellen zeigten eine messbare Photoaktivität unter Bestrahlung. Die Wirkungsgrade der Zellen lagen jedoch alle unter 1 %. Generell führten die Carboxyl-funktionalisierten Porphyrazine zu besseren Wirkungsgraden als die analogen, mit der tripodalen Ankergruppe ausgestatteten Derivate. Die mit Hilfe von Adsorptionsisothermen ermittelten Bindungskonstanten der Adsorption der Farbstoffe auf der TiO2-Oberfläche zeigten, dass beide Hafteinheiten eine feste Verankerung der Chromophore auf den TiO2-Elektroden ermöglichten. Insgesamt wirkte sich die Präsenz der peripheren BODIPY-Farbstoffe positiv auf die Wirkungsgrade der Solarzellen aus, jedoch nur in geringem Maß. Dieses Ergebnis wurde hauptsächlich auf die geringe Energiedifferenz zwischen der Leitungsbandkante des TiO2 und den LUMO-Energieniveaus der Chromophore zurückgeführt. Zusätzlich scheinen konkurrierende Prozesse wie die direkte Photoelektroneninjektion von den BODIPY-Einheiten in das TiO2 eine wichtige Rolle zu spielen. Neben der Anwendung in DSSC wurde die Wechselwirkung der Porphyrazine mit Graphen untersucht. Hierzu wurden A3B-Porphyrazine mit Pyrenyl-Seitenketten ausgestattet, die eine nicht-kovalente Verankerung des Chromophors auf Graphen ermöglichen. UV/Vis- und Fluoreszenzmessungen gaben u.a. erste Hinweise auf eine elektronische Kommunikation zwischen den beiden Hybridpartnern.

Deidrogenazione ossidativa del n-butano catalizzata da ossidi metallici difettivi

The oxidative dehydrogenation (ODH) of n-butane is a promising way to synthetize butenes and 1,3-butadiene, currently produced by steam cracking or direct dehydrogenation of n-butane. The addition of oxygen as a reagent leads to the formation of water, a very stable by-product, which makes the process exothermic.In this work, the ODH of n- butane was investigate to selectively obtain butenes and 1,3-butadiene. Four catalysts based on metal oxides (V2O5, La2O3, CeO2 and TiO2) were mixed with Mg metallic powder and reduced at 650 °C for 5 h in 5% H2/Ar atmosphere, with the purpose of creating oxygen vacancies in the crystal lattice of the oxides. Subsequently, the effect of the Mg concentration, and thus the oxygen vacancies concentration, was studied. The titanium oxide-based catalysts were the most active, in terms of butane conversion and selectivity to butenes and 1,3 butadiene. Overall, this study shows that the formation of oxygen vacancies on metal oxides can be influenced by the addition of metallic Mg during the synthesis. In the case of TiO2, this leads to an increase on the activity compared to the untreated sample.

Photoelectrocatalysis based on Ti/TiO2 nanotubes removes toxic properties of the azo dyes Disperse Red 1, Disperse Red 13 and Disperse Orange 1 from aqueous chloride samples

This work describes the efficiency of photoelectrocatalysis based on Ti/TiO2 nanotubes in the degradation of the azo dyes Disperse Red 1, Disperse Red 13 and Disperse Orange 1 and to remove their toxic properties, as an alternative method for the treatment of effluents and water. For this purpose, the discoloration rate, total organic carbon (TOC) removal, and genotoxic, cytotoxic and mutagenic responses were determined, using the comet, micronucleus and cytotoxicity assays in HepG2 cells and the Salmonella mutagenicity assay. In a previous study it was found that the surfactant Emulsogen could contribute to the low mineralization of the dyes (60% after 4h of treatment), which, in turn, seems to account for the mutagenicity of the products generated. Thus this surfactant was not added to the chloride medium in order to avoid this interference. The photoelectrocatalytic method presented rapid discoloration and the TOC reduction was ≥87% after 240min of treatment, showing that photoelectrocatalysis is able to mineralize the dyes tested. The method was also efficient in removing the mutagenic activity and cytotoxic effects of these three dyes. Thus it was concluded that photoelectrocatalysis was a promising method for the treatment of aqueous samples. © 2013 Elsevier Ltd.

Effect of two formulations of 10% sodium ascorbate on fracture resistance of endodontically treated tooth submitted to dental bleaching with hydrogen peroxide associated titanium dioxide nanoparticles

Purpose: This study evaluated the effect of 10% sodium ascorbate (10SA), in gel (10SAg) or aqueous solution (10SAs) formulations, on fracture resistance of endodontically treated tooth submitted to dental bleaching procedures with 15% hydrogen peroxide associated with titanium dioxide (15HP-TiO2) nanoparticles and photoactivated by LED-laser. Material and methods: Forty maxillary premolars were endodontically-treated and embedded in acrylic resin up to the cement-enamel junction. The specimens were divided into four groups (n=10): G1 (negative control): no bleaching, coronal access restored with composite resin; G2 (positive control): three dental bleaching sessions using 15HP-TiO2 and LED-laser photoactivation and restored with composite resin (positive control); G3 (10SAg): similar procedures to G2, but applied 10SA, in gel formulation, for 24 hours before restoration; G4 (10SAs): similar procedures to G3, but applied 10SA, in aqueous solution formulation. The 15HP-TiO2 was applied on buccal and lingual surfaces of the crown tooth and inside the pulp chamber and photoactivated by LED-laser. Between each bleaching session, the teeth were maintained in artificial saliva, at 37oC, for 7 days. In sequence, the teeth were submitted to fracture resistance testing using an eletromechanical machine test. The data was analyzed using Kruskal Wallis test (p = 0.05) Results: There are no differences significant among the groups in relation to fracture resistance of endodontically treated teeth (p>0.05). Conclusions: The use of 10% sodium ascorbate, in gel or aqueous solution formulations, did not interfered on the fracture resistance teeth after dental bleaching using 15HP-TiO2 and LED-laser photoactivation.

Fracture resistance of endodontically-treated teeth submitted to bleaching treatment with hydrogen peroxide and titanium dioxide nanoparticles photoactivated by LED-laser

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Spectrophotometric Evaluation Of Dental Bleaching Under Orthodontic Bracket In Enamel And Dentin.

Aware of the diffusion capacity of bleaching in the dental tissues, many orthodontists are subjecting their patients to dental bleaching during orthodontic treatment for esthetic purposes or to anticipate the exchange of esthetic restorations after the orthodontic treatment. For this purpose specific products have been developed in pre-loaded whitening trays designed to fit over and around brackets and wires, with clinical efficacy proven. The objective of this study was to evaluate, through spectrophotometric reflectance, the effectiveness of dental bleaching under orthodontic bracket. Thirty-two bovine incisors crown blocks of 8 mm x 8 mm height lengths were used. Staining of tooth blocks with black tea was performed for six days. They were distributed randomly into 4 groups (1-home bleaching with bracket, 2- home bleaching without bracket, 3- office bleaching with bracket, 4 office bleaching without bracket). The color evaluation was performed (CIE L * a * b *) using color reflectance spectrophotometer. Metal brackets were bonded in groups 1 and 3. The groups 1 and 2 samples were subjected to the carbamide peroxide at 15%, 4 hours daily for 21 days. Groups 3 and 4 were subjected to 3 in-office bleaching treatment sessions, hydrogen peroxide 38%. After removal of the brackets, the second color evaluation was performed in tooth block, difference between the area under the bracket and around it, and after 7 days to verified color stability. Data analysis was performed using the paired t-test and two-way variance analysis and Tukey's. The home bleaching technique proved to be more effective compared to the office bleaching. There was a significant difference between the margin and center color values of the specimens that were subjected to bracket bonding. The bracket bond presence affected the effectiveness of both the home and office bleaching treatments. Key words:Tooth bleaching, spectrophotometry, orthodontics.

In Vitro Effects Of Hydrogen Peroxide Combined With Different Activators For The In-office Bleaching Technique On Enamel.

Abstract Objective. The aim of this study was to evaluate the alteration of human enamel bleached with high concentrations of hydrogen peroxide associated with different activators. Materials and methods. Fifty enamel/dentin blocks (4 × 4 mm) were obtained from human third molars and randomized divided according to the bleaching procedure (n = 10): G1 = 35% hydrogen peroxide (HP - Whiteness HP Maxx); G2 = HP + Halogen lamp (HL); G3 = HP + 7% sodium bicarbonate (SB); G4 = HP + 20% sodium hydroxide (SH); and G5 = 38% hydrogen peroxide (OXB - Opalescence Xtra Boost). The bleaching treatments were performed in three sessions with a 7-day interval between them. The enamel content, before (baseline) and after bleaching, was determined using an FT-Raman spectrometer and was based on the concentration of phosphate, carbonate, and organic matrix. Statistical analysis was performed using two-way ANOVA for repeated measures and Tukey's test. Results. The results showed no significant differences between time of analysis (p = 0.5175) for most treatments and peak areas analyzed; and among bleaching treatments (p = 0.4184). The comparisons during and after bleaching revealed a significant difference in the HP group for the peak areas of carbonate and organic matrix, and for the organic matrix in OXB and HP+SH groups. Tukey's analysis determined that the difference, peak areas, and the interaction among treatment, time and peak was statistically significant (p < 0.05). Conclusion. The association of activators with hydrogen peroxide was effective in the alteration of enamel, mainly with regards to the organic matrix.

Permeability of different groups of maxillary teeth after 38% hydrogen peroxide internal bleaching

This study evaluated the influence of internal tooth bleaching with 38% hydrogen peroxide (H2O2) on the permeability of the coronal dentin in maxillary anterior teeth and premolars. Seventy teeth (14 per group) were used: central incisors (CI), lateral incisor (LI), canines (C), first premolars (1PM) and second premolars (2PM). Pulp chamber access and transversal sectioning at 2 mm from the cementoenamel junction were performed and the specimens were divided into 2 groups (n= 7): a) no treatment and b) bleaching with 38% H2O2. The bleaching agent was applied to the buccal surface and to the pulp chamber for 10 min. This procedure was repeated 3 times. The specimens were processed histochemically with copper sulfate and rubeanic acid, sectioned longitudinally, and digitalized in a scanner. The area of stained dentin was measured using Image Tool software. Data were analyzed statistically by ANOVA and Tukey's HSD test (?=0.05). There was statistically significant difference (p<0.001) among the untreated groups, CI (0.23 ± 0.26) having the lowest permeability and LI (10.14 ± 1.89) the highest permeability. Among the bleached groups, dentin permeability was increased in all groups of teeth except for 2PM. It may be concluded that bleaching with 38% H2O2 affected dentin permeability near the pulp chamber in maxillary anterior teeth and in first and second premolars.