Nanowire/nanorod TiO(2) structures of approximately 8 nm in diameter and around 1,000 nm long were synthesized by alkaline hydrothermal treatment of two different TiO(2) nanopowders. The first precursor was TiO(2) obtained by the sol-gel process (SG-TiO(2)); the second was the well-known commercial TiO(2) P-25 (P25-TiO(2)). Anatase-like 1D TiO(2) nanostructures were obtained in both cases. The one-dimensional (1D) nanostructures synthesized from SG-TiO(2) powders turned into rod-like nanostructures after annealing at 400 °C for 2 h. Conversely, the nanostructures synthesized from P25-TiO(2) preserved the tubular structure after annealing, displaying a higher Brunauer-Emmett-Teller surface area than the first system (279 and 97 m²/g, respectively). Despite the higher surface area shown by the 1D nanostructures, in both cases the photocatalytic activity was lower than for the P25-TiO(2) powder. However, the rod-like nanostructures obtained from SG-TiO(2) displayed slightly higher efficiency than the sol-gel prepared powders. The lower photocatalytic activity of the nanostructures with respect to P-25 can be associated with the lower crystallinity of 1D TiO(2) in both materials.
TiO2 nanotubes were synthesized by alkaline hydrothermal treatment of TiO2 nanoparticles with a controlled proportion of anatase and rutile. Tailoring of TiO2 phases was achieved by adjusting the pH and type of acid used in the hydrolysis of titanium isopropoxide (first step in the sol-gel synthesis). The anatase proportion in the precursor nanoparticles was in the 3–100% range. Tube-like nanostructures were obtained with an anatase percentage of 18 or higher while flake-like shapes were obtained when rutile was dominant in the seed. After annealing at 400°C for 2 h, a fraction of nanotubes was conserved in all the samples but, depending on the anatase/rutile ratio in the starting material, spherical and rod-shaped structures were also observed. The photocatalytic activity of 1D nanostructures was evaluated by measuring the deactivation of E. coli in stirred water in the dark and under UV-A/B irradiation. Results show that in addition to the bactericidal activity of TiO2 under UV-A illumination, under dark conditions, the decrease in bacteria viability is ascribed to mechanical stress due to stirring.
Estructuras unidimensionales (1D) mesoporosas tipo nanotubos/nanobarras de TiO fueron 2 sintetizadas por el método hidrotermal en medio alcalino, empleando como material de inicio nanopartículas de TiO obtenidas por el proceso Sol Gel (SG-TiO ). Imágenes obtenidas por 2 2 Microscopía Electrónica de Barrido por Emisión de Campo (MEB-EC) y Microscopía Electrónica de Transmisión de Alta Resolución (MET-AR) mostraron la formación de nanoestructuras tipo tubo de 8 nm de diámetro y tamaños mayores a 400 nm de largo luego del tratamiento hidrotermal de 18 y 24 horas; éstas nanoestructuras se conservaron luego del proceso de intercambio iónico con ácido clorhídrico (HCl). Luego de la calcinación, se convirtieron a estructuras tipo barras de TiO anatasa como lo muestran los resultados 2 obtenidos por Difracción de Rayos X (DRX). La conversión de nanopartículas a nanotubos y posteriormente a estructuras tipo barras fue también confirmada por la variación en el área 2 superficial BET de alrededor de 201, a 269 y 97 m /g, respectivamente. Las isotermas de adsorción-desorción revelaron curvas de histéresis típicas de materiales mesoporosos. Estas cualidades resultan atractivas en aplicaciones tales como remoción de contaminantes en agua.
Nanotubes/nanorods (1D) TiO 2 nanostructures of around 8 nm in diameter were synthesized by alkaline hydrothermal treatment of sol-gel made TiO 2 or P-25 TiO 2 . Anatase like 1D TiO2 nanostructures were obtained in both cases. The 1D nanostructures made using seeds from Sol Gel TiO2 nanopowders turn on rodlike nanostructures and presents lower surface area than the nanostructures made from commercial TiO 2 P-25 (97 y 279 m2/g, respectively). In both cases, the 1D structures shown lower photocatalytic activity than P25 nanopartcles. However, the rodlike nanostructures obtained from TiO 2 Sol Gel seeds displayed slightly higher efficiency than the original seeds. Despite the higher surface area shown by the nanostructures, the photocatalytic efficiency did not improve with respect to their precursor seeds. This phenomenon can be associated with the presence of other of structures like particles, nanoribbons or a kind of sheets with lower crystallinity and even amorphous phases.TiO2 nanomaterials are well-studied and commonly used materials for liquid and gas-phase photocatalytic applications due to its high performance photocatalysis for water splitting and for degradation of organics [1]. In the last years one-dimensional nanostructures such as nanotubes, nanorods, nanowires, nanobelts, etc. of inorganic materials have attracted great attention because they could offer larger surface area in comparison to nanoparticles [2]. In this work, we report de synthesis of nanotube and rodlike shape TiO2 nanostructures by hydrothermal synthesis using seeds of: TiO 2 nanopowders synthesized by So Gel method in our laboratory and commercial TiO 2 P-25. We have studying the effect of hydrothermal treatment time and the influence of the starting materials in the morphology, thermal stability and their photocatalytic activity. The obtained nanotubes and nanorods were compared with their corresponding starting materials to evaluate their photocatalitic performance under the degradation of an organic pollutant as Rhodamine B (RhB).Photocatalytic efficiency for degradation of RhB was carried out under the radiation of Ultravitalux 220 W OSRAM ultravitalux lamp, with a measured mean radiation Intensity of 60 W/m2 in the UV-A range. An aqueous solution with initial volume of 150 mL was prepared with an amount of 0.050 g catalyst and RhB 10 ppm, the solution was stirred first in the dark for 30 min to ensure that the RhB was adsorbed to satura-tion on the catalysts. The decrease of the RhB concentration was determinate as a function of the irradiation time from the change in absorbance at 564 nm.
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