Síntese e caracterização de nanocompósitos de caulinita e TiO2 utilizando o método dos precursores poliméricos

No presente trabalho, utilizou-se a caulinita como material base para a obtenção de materiais nanocompósitos. A caulinita foi utilizada na forma in natura, tratada termicamente à 700 ºC e quimicamente com ácidos fosfórico e sulfúrico na concentração de 6 mol L-1. O objetivo dos tratamentos foi modificar e preparar a estrutura da caulinita para ser usada como um suporte para o TiO2. Por meio do método dos precursores poliméricos foi sintetizado o TiO2 e nanocompósitos à base de caulinita e TiO2. Os nanomateriais foram caracterizados por Difratometria de Raios X (DRX), UV-Vis, para determinar o Bandgap, Espectroscopia na Região do Infravermelho com Transformada de Fourier (FTIR), Microscopia Eletrônica de Varredura (MEV) e Espectroscopia de Energia Dispersiva (EDS). Por meio dos espectros de FTIR foi possível verificar as bandas características da caulinita in natura e o aparecimento de vibrações características da metacaulinita. A análise de DRX revelou que foi possível promover o aumento da cristalinidade das amostras de caulinita após tratamento com o citrato de titânio, isto pode ser decorrente da adesão do óxido de titânio na superfície da caulinita. Pela análise de EDS foi possível determinar a porcentagem de Ti (m/m) nas amostras sintetizadas, sendo que seu valor ficou entre 2,03 e 4,16 %. As análises por ICP-OES indicam que as amostras apresentam de 2,65 a 4,07% de Ti e os dados do Bandgap variam de 1,69 a 3,44 eV para as amostras com e sem Ti em sua composição.Palavras-chave: Caulinita, metacaulinita, ativação ácida, Método dos Precursores Poliméricos, Dióxido de Titânio.

Study of Silver Ions Diffusion into TiO2NT Using Finite Elements Method

The purpose of this paper is to study the diffusion of silver ions, Ag+, into TiO2 nanotubes, using Fick’s second law. The mathematical simulations were carried out using the finite element method to solve this partial differential equation. A single nanotube, immersed in an aqueous solution containing Ag+ ions, composes the physical two-dimensional model. The most relevant results show that the system final concentration can be calculated in the function of solution initial concentration, of solution volume and nanotube volume. The equation obtained can be generalized to the study of diffusion for other ions in aqueous solution through nanotubular structured materials, because the equation does not take into account the diffusion coefficient of the ions. The height of nanotube is exponentially proportional to the equilibrium time, proving the relation of height with the diffusion course. On the other hand, the diameter of nanotube does not have a significant relationship with the equilibrium time. These results indicate that for ions incorporation into materials, with nanotubular structure, it should prioritize experimental conditions that favor the vertical growth of the nanotubes. DOI: http://dx.doi.org/10.17807/orbital.v11i6.1241 </p

Influence of the morphology and microstructure on the photocatalytic properties of titanium oxide films obtained by sparking anodization in H3PO4

The aim of this paper is to investigate changes in morphology and microstructure of TiO2 films, prepared by sparking anodization of Ti in a H3PO4 solution, by applying different formation charges. We show that although films obtained by this technique are rarely used in photocatalytic applications, the morphological and microstructural changes during sparking anodization produce TiO2 films that can be used as photocatalysts. In contrast to qualitative analysis commonly found in the literature, we used quantitative methods of analysis to quantify average pore diameter and pore density from the morphology and structural parameters from X-ray diffraction (XRD) patterns using the Rietveld refinement. The results indicated that changes in both the morphology and crystalline structure have a strong influence on the photoactivity of the films. From this investigation, we concluded that, for films prepared in early stages of anodization, the morphology had the biggest influence on photoactivity, and after applying 72C of charge, crystalline properties dominated the photocatalytic characteristics of the films. (C) 2011 Elsevier Ltd. All rights reserved.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

This review addresses the main contributions of anodic oxide films synthesized and designed to overcome the current limitations of practical applications in energy conversion and storage devices. We present some strategies adopted to improve the efficiency, stability, and overall performance of these sustainable technologies operating via photo, photoelectrochemical, and electrochemical processes. The facile and scalable synthesis with strict control of the properties combined with the low-cost, high surface area, chemical stability, and unidirectional orientation of these nanostructures make the anodized oxides attractive for these applications. Assuming different functionalities, TiO2-NT is the widely explored anodic oxide in dye-sensitized solar cells, PEC water-splitting systems, fuel cells, supercapacitors, and batteries. However, other nanostructured anodic films based on WO3, CuxO, ZnO, NiO, SnO, Fe2O3, ZrO2, Nb2O5, and Ta2O5 are also explored and act as the respective active layers in several devices. The use of AAO as a structural material to guide the synthesis is also reported. Although in the development stage, the proof-of-concept of these devices demonstrates the feasibility of using the anodic oxide as a component and opens up new perspectives for the industrial and commercial utilization of these technologies

Plasma electrolytic titanium oxide applied for pathogenic bacteria inactivation

<p>Photocatalysis over TiO₂ substrates is widely used in effluent treatment specially for organic compounds and for inactivation of pathogenic microorganisms. In the present work, TiO₂ coatings were synthesized by plasma electrolytic oxidation (PEO) and its pathogenic bacteria inhibitory photoactivity was investigated. The photocatalytic activity of TiO₂ coatings was investigated for the inactivation of <i>Staphylococcus aureus</i> and <i>Salmonella bongori</i> and the results were correlated with pore diameter and crystallite size. It was observed that both morphology and microstructure have an important role in the antibacterial photoactivity. The results show the larger the crystallite size and pore diameter the greater the photoactivity of the material. Porous materials that have a smaller pore diameter than the microorganism to be inactivated have low photoactivity. On the other hand, films that have pores with a diameter of the order or larger than the size of the microorganism to be inactivated present greater photocatalytic activity, once its pores allow the entrance and internal adsorption of the microorganisms, leading to the rupture of the cell membrane. Thus, in order to not sub-utilize the photocatalysts surface area, TiO₂ coatings for using in microorganism inactivation must be synthesized with pore diameter bigger than the size of the microorganism.</p

TiO2NT as Platform for Drug Release: The Effect of Film Wettability

Modifications of Ti–based surface are increasingly studied to improve biological responses on the biomedical implants field. In this study, nanotubular arrays were grown from Ticp (T) and its alloy, Ti6Al4V (A), by potentiostatic anodization at 25 V for 90 min in ethylene glycol media containing 0.75 % w/w of NH4F, H2O 9% v/v and 1% v/v of Simulated Body Fluid (SBF) maintained at 10 °C (T10 and A10) and 40 °C (T40 and A40) for drug release studies. Coatings were top filled with cefazolin (1 mg) and the releasing procedure was performed in 5 mL of PBS at 37 °C, taking 0.5 mL aliquots at 1, 4, 7, 10, 15 and 30 min. The as-formed coatings were characterized by Scanning Electron Microscopy (SEM), X-rays Diffraction (XRD) and contact angle measurements. Contact angle measurements indicate that T-based nanotubular coatings are highly wettable, being ≈ 0.00° and 6.74° ± 1.96 for T10 and T40 respectively. Coatings obtained from Ti-alloy exhibits low wettability than T-based samples for both temperatures. All samples release the drug on short time intervals (4 to 10 min). The drug release rate is inversely proportional to the contact angle, considering substrate groups. Thus, a higher wettability tendency presents a higher release rate. This result shows that wettability is an important parameter to be considered in the design of Ti-based biomaterials. DOI: http://dx.doi.org/10.17807/orbital.v11i6.1251 </p