13 research outputs found
Growth of TiO2 nanotube arrays with simultaneous Au nanoparticles impregnation: photocatalysts for hydrogen production
Um novo método para a fabricação de nanotubos (NTs) de TiO2 organizados e impregnados com nanopartículas (NPs) de ouro foi desenvolvido, e as propriedades estruturais, morfológicas e ópticas dos NTs obtidos foram investigadas. Os arranjos de NTs de TiO2 foram crescidos pela oxidação anódica de Ti metálico utilizando soluções eletrolíticas contendo íons fluoreto e NPs de Au. As estruturas resultantes foram caracterizadas por espectrometria de retroespalhamento Rutherford (RBS), difratometria de raios X com incidência rasante (GIXRD), microscopias eletrônicas de transmissão (TEM) e de varredura (SEM) e espectroscopia UV-Vis. Tanto os arranjos de NTs sem Au quanto os impregnados com Au mostraram atividade fotocatalítica boa e estável na geração de hidrogênio a partir de misturas água/metanol. Os nanotubos de TiO2 contendo Au foram mais ativos na fotogeração de hidrogênio do que os NTs de TiO2 sem Au.A novel method for the fabrication of TiO2 nanotubes (NTs) impregnated with gold nanoparticles (NPs) is reported. TiO2 NT arrays were grown by anodic oxidation of Ti metal using fluoride electrolytes containing Au NPs. Resulting structures were characterized by Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffractometry (GIXRD), transmission and scanning electron microscopy (SEM and TEM) and UV-Vis spectroscopy. Au-free and Au-impregnated TiO2 NT arrays showed good and stable photocatalytic activity for hydrogen generation from water/methanol solutions. Au-containing TiO2 NTs presented higher hydrogen photogeneration activity than Au-free TiO2 NTs
Silver Nanoparticles Obtained in PAH/PAA-Based Multilayers by Photochemical Reaction
Carboxylic acid groups in PAH/PAA-based multilayers bind silver cations by ion exchange with the acid protons. The aggregation and spatial distribution of the nanoparticles proved to be dependent oil the process used to reduce the silver acetate aqueous solution. The reducing method with ambient light formed larger nanoparticles with diameters ranging from 4-50 nm in comparison with the reduction method using UV light, which gave particles with diameters of 2-4 nm The high toughness of samples reduced by ambient light is a result of two population distributions of particle sizes caused by different mechanisms when compared with the UV light process. According to these phenomena, a judicious choice of the spectral source call be used as a way to control the type and size of silver nanoparticles formed on PEMs. Depending on the energy of the light source, the Ag nanoparticles present cubic and/or hexagonal crystallographic structures, as confirmed by XRD. Beyond the kinetically controlled process of UV photoinduced cluster formation, the annealing produced by UV light allowed a second mechanism to modify the growth rates, spatial distribution, and phases.CNPqConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPESFAPERGSFundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS
Quantitative Characterization of Hexagonal Packings in Nanoporous Alumina Arrays: A Case Study
Quantitative Characterization of Hexagonal Packings in Nanoporous Alumina Arrays: A Case Study
Herein is presented a methodology to quantify the degree
of hexagonal
order in nanoporous alumina arrays (NAA). The approach is inspired
by the theory of two-dimensional melting, developed to describe phase
transitions in two-dimensional systems that present liquid-crystal-like
structures. A local order parameter (LOP) is defined to quantify the
degree of hexagonal order of each pore without any arbitrary parameters.
Using this LOP, three main qualitative and quantitative analytical
tools were developed: (i) a color code to create a map of the LOP,
which is a visual tool to identify the degree of order; (ii) quantitative
measurements of the average hexagonal order of the sample by measuring
the distribution of the LOP and the distribution of the number of
neighbors of each pore, and (iii) a quantification of the spatial
correlation of the LOP, which indicates how far the hexagonal order
is spread in a sample. Because this approach has a strong support
on tools developed in statistical mechanics, one can go beyond a simple
characterization and interpret the results in terms of phases, as
in other physical systems. This may help to unveil the mechanisms
behind the self-organization process and long-range order observed
in NAA. Moreover, this approach can be trivially extended to characterize
other physical systems that form hexagonal packings
Micro and Nano-Texturization of Intermetallic Oxide Alloys by a Single Anodization Step: Preparation of Artificial Self-Cleaning Surfaces
Micro- and nanostructures of Ti-γCu (γ = 0, 30, 50, 70, and 100 wt %) intermetallic alloys were produced through a single anodization step. It was found that the original alloy composition influences the final oxide morphology obtained after anodization which presented formation of a microstructure with nanotubes, nanoparticles or nanopillars on the surface. Pure Ti and Cu oxide metals and their alloys presented hydrophilic or superhydrophilic properties immediately after anodization. When the anodized pure metal and/or Ti-γCu surfaces were functionalized with trimethoxypropylsilane (TPMSi), by dipping and coating with a thin perfluorinated layer, the treated substrates became in all cases superhydrophobic (water contact angles in the range of 152–166°), showing excellent self-cleaning properties with hysteresis below 3°. These results can be explained by a combination of nanomicro morphologies with low surface energy compounds in the topmost monolayers. The decrease in hysteresis was associated with a higher M–OH bond concentration on the anodized surfaces, which allowed for more complete TMPSi coating coverage. This study also indicates that easy and effective fabrication of superhydrophobic surfaces in pure metals and alloys is possible without involving traditional multistep processes
On the formation of anisotropic gold nanoparticles by sputtering onto a nitrile functionalised ionic liquid
Photochemical Hydrogen Production of Ta<sub>2</sub>O<sub>5</sub> Nanotubes Decorated with NiO Nanoparticles by Modified Sputtering Deposition
The use of metal/oxide
nanoparticles (NPs) as cocatalysts in heterogeneous
photocatalysis is an important strategy to improve the photocatalytic
activity of semiconductors for hydrogen generation. This article reports
the use of a modified sputtering deposition method to prepare ultrafine
NiO NPs cocatalysts dispersed on anodic Ta<sub>2</sub>O<sub>5</sub> nanotubes (NTs). <i>In situ</i> X-ray absorption near-edge
spectroscopy (XANES) measurements revealed that after exposing the
as-prepared Ni NPs to air atmosphere a mixture of 68% of Ni and 32%
of NiO was formed. Pure phase NiO NPs was successfully obtained after
a controlled thermal oxidation at 500 °C which was confirmed
by <i>in situ</i> XANES and <i>ex situ</i> XPS
analyses. The photocatalytic hydrogen production activity was evaluated
using ethanol as a sacrificial agent. Ta<sub>2</sub>O<sub>5</sub> NTs
with 0.16 wt % of NiO showed superior photocatalytic activity (up
to 7.7 ± 0.3 mmol h<sup>–1</sup> g<sup>–1</sup>) as compared to pure Ta<sub>2</sub>O<sub>5</sub> NTs (4.9 ±
0.3 mmol h<sup>–1</sup> g<sup>–1</sup>) The observed
higher photocatalytic activity suggests that NiO/Ta<sub>2</sub>O<sub>5</sub> NTs is a promising material for photocatalytic hydrogen evolution
Ta<sub>2</sub>O<sub>5</sub> Nanotubes Obtained by Anodization: Effect of Thermal Treatment on the Photocatalytic Activity for Hydrogen Production
Freestanding tantalum oxide nanotubes (Ta<sub>2</sub>O<sub>5</sub> NTs) were easily fabricated by controlling only the
electrolyte
temperature during anodization in a sulfuric acid solution. When the
electrolyte temperature decreased, the adherence of NTs to the Ta
substrate increased. High electrolyte temperatures facilitated formation
of freestanding NTs. Thermal treatment of the freestanding Ta<sub>2</sub>O<sub>5</sub> NTs below 750 °C resulted in an amorphous
structure. The orthorhombic crystalline phase appeared only at temperatures
higher than 750 °C. The effect of thermal treatment on the crystalline
structure and morphology of Ta<sub>2</sub>O<sub>5</sub> NTs showed
that the NTs retained their tubular shape up to 800 °C. In addition,
it was shown that the crystallinity of the NTs was enhanced from 11%
to 34% by increasing the treatment time for the NTs at 800 °C
from 0.5 to 1 h. High crystallinity and low surface contamination
increased the photocatalytic activity of the freestanding NTs for
hydrogen production by water splitting using a water/ethanol solution
under UV radiation. The sample annealed at 800 °C for 1 h showed
the highest photocatalytic activity for hydrogen generation. Additionally,
changes to the physicochemical properties of the surface and bulk
of the photocatalyst showed decreased selectivity for minor products
(C<sub>2</sub>H<sub>4</sub> and C<sub>2</sub>H<sub>6</sub>)
Self-Organized TiO<sub>2</sub> Nanotube Arrays: Synthesis by Anodization in an Ionic Liquid and Assessment of Photocatalytic Properties
Self-organized TiO2 nanotube (NT) arrays were produced by anodization in ethylene glycol (EG) electrolytes containing 1-n-butyl-3-methyl-imidazolium tetrafluoroborate (BMI.BF4) ionic liquid and water. The morphology of the as-formed NTs was considerably affected by changing the anodization time, voltage, and water and ionic liquid electrolyte concentrations. In general, a nanoporous layer was formed on the top surface of the TiO2 NTs, except for anodization at 100 V with 1 vol % of BMI.BF4, where the NT’s mouth was revealed. The length and bottom diameter of the NTs as well as the pore diameter of the top layer showed a linear relationship with increased anodization voltage. These TiO2 NTs were tested as photocatalysts for methyl orange photodegradation and hydrogen evolution from water/methanol solutions by UV light irradiation. The results show that the TiO2 NTs obtained by anodization in EG/H2O/BMI.BF4 electrolytes are active and efficient for both applications