RESUMO

Experimental studies of TiO2 nanotubes have been conducted for nearly three decades and have revealed the remarkable advantages of this material. Research based on computer simulations is much rarer, with research using density functional theory (DFT) being the most significant in this field. It should be noted, however, that this approach has significant limitations when studying the macroscopic properties of nanostructures such as nanosheets and nanotubes. An alternative with great potential has emerged: classical molecular dynamics simulations (MD). MD Simulations offer the possibility to study macroscopic properties such as the density of phonon states (PDOS), power spectra, infrared spectrum, water absorption and others. From this point of view, the present study focuses on the distinction between the phases of anatase and rutile TiO2. The LAMMPS package is used to study both the structural properties by applying the radial distribution function (RDF) and the electromagnetic properties of these phases. Our efforts are focused on exploring the effect of temperature on the vibrational properties of TiO2 anatase nanotubes and an in-depth analysis of how the phononic softening phenomenon affects TiO2 nanostructures to improve the fundamental understanding in different dimensions and morphological configurations. A careful evaluation of the stability of TiO2 nanolamines and nanotubes at different temperatures is performed, as well as the adsorption of water on the nanosurface of TiO2, using three different water models.

Assuntos

RESUMO

In the last decade, TiO2 nanotubes have attracted the attention of the scientific community and industry due to their exceptional photocatalytic properties, opening a wide range of additional applications in the fields of renewable energy, sensors, supercapacitors, and the pharmaceutical industry. However, their use is limited because their band gap is tied to the visible light spectrum. Therefore, it is essential to dope them with metals to extend their physicochemical advantages. In this review, we provide a brief overview of the preparation of metal-doped TiO2 nanotubes. We address hydrothermal and alteration methods that have been used to study the effects of different metal dopants on the structural, morphological, and optoelectrical properties of anatase and rutile nanotubes. The progress of DFT studies on the metal doping of TiO2 nanoparticles is discussed. In addition, the traditional models and their confirmation of the results of the experiment with TiO2 nanotubes are reviewed, as well as the use of TNT in various applications and the future prospects for its development in other fields. We focus on the comprehensive analysis and practical significance of the development of TiO2 hybrid materials and the need for a better understanding of the structural-chemical properties of anatase TiO2 nanotubes with metal doping for ion storage devices such as batteries.

RESUMO

Soils have distinctive chemical, physical, mineralogical and biological properties, which make it possible to differentiate them in different environments and also to test for an association of a particular questioned item with a crime scene. Mineral compositions and structures in the soil clay fraction can reflect a distinct characteristic when analyzed by powerful techniques. In this way, the aim of this study was to compare the discriminative power of Fe-oxides concentrated clay samples from the same soil class with and without differences in parent material when analyzed using the Rietveld method and two sources of X-ray diffraction: conventional and high-resolution synchrotron radiations. Clay samples were Fe concentrated (kaolinite and gibbsite removal) to clarify mineralogical composition of 12 samples from three simulated crime scenes, developed under claystone and granite. By Rietveld refinement, detailed crystallographic data were obtained to discriminate samples according their provenance. By synchrotron radiation, mineral data demonstrated the power of quantitative (crystallite size and minerals contents) and qualitative (identification of majoritarian and accessory minerals) analysis by Rietveld refinement, which provides well-resolved data able to discriminate samples from different and same geology. The techniques can be applied in other criminal investigations given their potential of discrimination.

Assuntos

RESUMO

The initial nucleation of gold clusters Aun (n = 1-5) on TiO2 rutile (110) reduced surface is studied using density functional theory and a full-potential augmented-plane-wave method implemented in the WIEN2k code. The first two gold atoms remained tied to the surface with a bond length similar to those belonging to other well-known related materials, while the other gold atoms do not spread over the surface; they preferred to form a new layer. The occurrence of relativistic effects produced a preferential triangle geometry for Au3 and a combination of triangular units for Au4 and Au5 . The Au-Au average distance increased from n = 2 to n = 5, indicating an expansion with a tendency to the bond distance found in the bulk. We are reporting an early 2D→3D transition of small folding, from Au3 →Au4 , followed by an Au4 →Au5 transition of evident 3D character.

RESUMO

Nanosilver immobilized on TiO2 nanometric fibers (Ag/TiO2) was produced by solution blow spinning and characterized using scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, water contact angle, and inductively coupled plasma emission spectroscopy analyses. The in vitro antimicrobial and anticancer activities of the produced nanofibers was also investigated. Ag/TiO2 nanofibers revealed a crystalline structure compatible with the rutile crystalline phase, as well as a mesoporous and superhydrophilic nature. XPS profiles showed Ti4+ and Ag0, indicating a strong interaction between the Ag nanoparticles and TiO2. The Ag/TiO2 nanofibers presented antimicrobial activity against Staphylococcus aureus, Enterococcus faecalis, and Escherichia coli. The release of silver ions from 5 mg∙mL-1 and 50 mg∙mL-1 of Ag/TiO2 nanofibers was approximately 0.08 µg∙mL-1 and 0.18 µg∙mL-1, respectively. The nanofiber cytotoxicity in both macrophages (ATCC RAW 264.7) and cancer cells (murine AT-84 oral squamous carcinoma cells) was dose-dependent. A concentration of 5 mg∙mL-1 induced partial suppression growth and migration of cancer cells, while a concentration of 50 mg∙mL-1 resulted in complete inhibition of proliferation and migration of murine AT-84 cells. The overall results indicate that Ag/TiO2 nanofibers can selectively inhibit the cellular mechanism of AT-84 by apoptosis with DNA damage and cell death. The antimicrobial and anticancer performance of Ag/TiO2 nanofibers is probably the result of its nanometric dimension, high surface reactivity, and the interaction between TiO2 and Ag. Electron transfer at the metal-semiconductor interface and reactive oxygen species production, in addition to the biological activity of released silver ions, confirm the potential for use as an agent in antimicrobial and anticancer therapy.

Assuntos

RESUMO

The aim of this work was to evaluate the cellular response to titanium nanotube arrays with variable crystalline structure. Cytotoxicity, viability and the ability of the titania nanotube arrays to stimulate adhesion and proliferation of adipose derived stem cells (ADSCs) was evaluated. Titania nanotube arrays were fabricated by electrochemical anodization of titanium in diethyleneglycol/hydrofluoric acid electrolyte at 60 V for 6 h, then annealed at 300, 530 and 630 °C for 5 h. The nanotube arrays were characterized using scanning electron microscopy (SEM), contact angle goniometry, x-ray diffraction (XRD) and protein adsorption. ADSCs were cultured on titania nanotube arrays at a density of 1 × 104 cells/ml. The cells were allowed to adhere and to proliferate for 1, 4 and 7 days. Cell viability was characterized by the CellTiter-Blue® Cell Viability Assay; and cell morphology was characterized by SEM. Cell adhesion, proliferation and morphology were characterized using fluorescence microscopy by staining the cells with DAPI and rhodamine/phalloidin. The results from this study showed that the annealing at 300 and 530 °C formed anatase phase, and annealing at 630 °C formed anatase/rutile phase. The results indicated that the modification of the crystalline structure (i.e. anatase/rutile phase) of titania nanotube arrays influenced the ADSC adhesion and proliferation. Future studies are now directed towards evaluating differentiation of this cellular model in osteoblasts.

Assuntos

RESUMO

This method involves the use of molding, pressing and sintering techniques applied to different powder mixtures of TiO2 with sodium bicarbonate NaHCO3 (15 wt% and 30 wt% NaHCO3), to obtain porous structures of rutile TiO2/Na0.8Ti4O8/Na2Ti6O13 and Na0.8Ti4O8/Na2Ti6O13 for possible biomedical implant applications. The method validation includes X-ray diffraction patterns (XRD) analysis refined by the Rietveld method using X'Pert HighScore Plus. The surface morphology was observed by using a scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS), and, finally, a Chinese hamster ovary (CHO) cell line was cultured with the porous structures to determine the effect of material composition on the cellular response using a LDH cytotoxicity assay. •The method does not require the use of toxic solvents to remove residues.•The porous structure formed is composed mainly of crystalline phases Na2Ti6O13/TiO2 reported as biocompatible.•It did not need complicated solid-liquid separation processes.

RESUMO

Photocatalytic activity of TiO2 nanoparticles is highly dependent on their phase composition. The coexistence of anatase and rutile phases in a single nanoparticle eases the electron transfer process between the phases, and favors the separation of photogenerated pairs. In this work, highly photoactive mixed-phase TiO2 nanostructures were prepared by supercritical antisolvent precipitation (SAS), an environmentally friendly technology. It is shown here that this methodology has the remarkable ability to produce highly porous (515 m2/g) and crystalline TiO2 nanoparticles. The phase composition of as-prepared TiO2 samples can be tailored through annealing process. Several mixed-phase TiO2 samples were tested to assess the correlation between photocatalytic activity and phase composition. The photocatalytic performance is strongly affected by the anatase-rutile ratio, since the synergism between phases enhances the charge separation, reducing the recombination effect of the photogenerated pairs (e-/h+). It was found that the nanocatalyst composed by 7.0 wt% of rutile phase and 93.0 wt% of anatase phase, named as TiO2_650, presented the highest photodegradation for both methyl orange (MO) and methylene blue (MB) dyes. Interestingly, TiO2 samples prepared by SAS have superior photoactivity than the benchmark photocatalyst names as P25, which is a widely used TiO2 material composed of anatase and rutile phases.

RESUMO

For the photocatalytic degradation of the hydrogen sulphide (H2S) in the gas-phase it was developed a rectangular reactor, coated with acrylic paint supported on fiber cement material. The surface formed by the paint coverage was characterized structural and morphologically by scanning electron microscopy with energy dispersive X-ray and X-ray diffraction analysis. The flow rate and the inlet concentration of H2S were evaluated as operational performance parameters of the reactor. Removal efficiencies of up to 94% were obtained at a flow rate of 2 L min-1 (residence time of 115 s) and inlet concentration of 31 ppm of H2S. In addition, the H2S degradation kinetics was modelled according to the Langmuir-Hinshelwood (L-H) model for the inlet concentrations of 8-23 ppm of H2S. The results suggest that flow rate has a more important influence on photocatalytic degradation than the inlet concentration. It is assumed that H2S has been oxidized to SO42- , a condition that led to a deactivation of the photocatalyst after 193 min of semi-continuous use.

Assuntos

RESUMO

A osseointegração dos implantes de titânio sem tratamento de superfície está associada à presença de uma fina camada de óxido de titânio do tipo rutilo presente em sua superfície. Para acelerar os mecanismos envolvidos na osseointegração e permitir a colocação da prótese em menor tempo que o inicialmente recomendado pelo Prof. Branemark, foram desenvolvidos os tratamentos das superfícies dos implantes por jateamento, ataque com ácido, deposição de nanopartículas de hidroxiapatita, flúor, magnésio e anodização em soluções eletroquímicas contendo fósforo e cálcio. Após os tratamentos da superfície dos implantes há formação de uma camada mista de óxidos de titânio composta de rutilo e anatase. O índice de êxito destes implantes mostra que a presença dos dois tipos de óxido de titânio não compromete a osseointegração. O presente trabalho tem o objetivo de caracterizar a camada de óxido de titânio existente em implantes anodizados com designações comerciais Vulcano Actives® e TiUnite® produzidos pelas empresas Conexão Sistemas de Prótese e Nobel Biocare, respectivamente. Os resultados das análises com XPS, difração de raios-X e Raman mostraram que nas superfícies dos implantes tratados por anodização há predomínio do óxido de titânio do tipo anatase. Considerando que os implantes sem tratamento de superfície possuem óxido de titânio na superfície diferente dos implantes com tratamento de superfície e todos apresentam osseointegração, conclui-se que existem os modos de interação entre a superfície do implante e as células são diferentes

The osseointegration of machined titanium dental implants is associated to the presence of a thin layer of rutile titanium oxide present on its surface. To accelerate the mechanisms involved in the osseointegration and to allow the placement of the prosthesis in less time as originally recommended by Professor Branemark, implants surface treatments were developed. Nowadays the implant surface is sandblasted, acid etched, receive a deposition of hydroxiapatite nanoparticles, fluorine, magnesium and anodized in solutions containing phosphorus and calcium. After the surface treatment was formed a layer of mixed oxides of titanium composed of rutile and anatase. The rate of success of anodized implants shows that the presence of two types of titanium oxide does not compromise the implant osseointegration. The aim of this work is to characterize the oxide layer of commercially titanium implants anodized branded as Vulcano Actives® and TiUnite® manufactured by Conexão Sistemas e Prótese (Brazil) and Nobel Biocare (Swede), respectively. The results of analyses with XPS, X-ray diffraction and Raman showed that the anodized dental implants surface has anatase titanium oxide. The machined dental implants without surface treatment and implant treated surface have different surface titanium oxide. As these implants show osseointegration it is suggested that they may be found to interact differently with cells

Assuntos