Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue

Abstract

Here we report on a novel chemical route to synthesize homogenous cobalt doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The influence of the synthesis temperature, autoclave dwell time and metal doping on the structural and microstructural as well as on the optical properties of the synthesized titanate nanotubes is studied and discussed. The optical band gaps of the CoTNT samples are red shifted in comparison with the values determined for the undoped samples, such red shifts bringing the absorption edge of the CoTNT samples into the visible region. CoTNT materials also demonstrate particular high adsorption ability for methylene blue, the amount of the adsorbed dye being higher than the one predictable for a monolayer formation. This suggests the possibility of intercalation of the dye molecule between the TiO 6 layers of the TNT structure. It is also shown that the methylene blue sensitized Co-doped nanostructures are highly stable under UV radiation and present a strong and broad absorption in the visible region. O or even the lepidocrocite-type titanates with compositions Na x Ti 2-x/4 x/4 O 4 or H x Ti 2-x/4 x/4 O 4, where stands for vacancy [4][5][6][7][8].The TNTs' ion-exchange ability makes them potential materials for effective photocatalysts and solar energy cells applications [9][10][11]. However, they present a critical drawback: their high charge recombination rate and wide band gap (ca. 3.3 eV) limit the electron and hole photo-generation under visible irradiation. Therefore, the synthesis of TNT-based materials with either a broader range of light absorption and/or a lower charge recombination rate would be an important achievement toward the development of successful photoactive materials. Several works have been published on this issue including metal doping [12,13], co-sensitized with semiconductor nanoparticles and porphyrin zinc co-sensitization [14] or phthalocyanin-sensitization [15]. of 31This work reports on a swift chemical route to synthesize homogenous cobalt doped titanate nanotubes (CoTNTs), extending the hydrothermal process used to prepare undoped TNTs previously reported by our group [9]. It is shown that Co doping stabilizes the morphology of the TNTs in a synthesis temperature range of 160 ºC to 200 ºC, and brings TNTs' absorption edge to the visible region. The adsorption ability of the synthesized materials for methylene blue (MB) is studied and it is shown that not only the MB-sensitized CoTNT materials are highly stable under UV irradiation but also they present a strong and broad absorption in the visible region of the electromagnetic spectrum. Materials and MethodsAll reagents were of analytical grade (Aldrich and Fluka) and were used as received. The solutions were prepared with Millipore Milli-Q ultra-pure water. Materials TNTs precursor synthesisThe TNT precursor was prepared using a procedure previously reported by our group [16].The used titanium source was a titanium trichloride solution (10 wt.% in 20-30 wt.% HCl) diluted in a ratio of 1:2 ...

The effect of ionic Co presence on the structural, optical and photocatalytic properties of modified cobalt–titanate nanotubes

“…S1). 15 For the 5% cobalt modified samples, i.e. Co(5%)-TNT and TNT/Co(5%) samples, the presence of the Co in addition to Ti, O and Na elements was confirmed by EDS (not shown).…”

“…Among them, titanate nanotubes (TNT) are remarkable materials since they combine the conventional properties TiO 2 nanoparticles, with the properties of layered titanates, such as photocatalytic activity and ion-exchange ability. [12][13][14][15] Additionally they have an open mesoporous morphology with a higher specific surface area than TiO 2 , which is a very important parameter for surface-based applications such as photocatalysis. Despite their high charge recombination rate and wide bandgap (ca.…”

“…3.3 eV), the TNTs' ion-exchange ability makes them potential materials for effective photocatalysts and solar energy cells' applications. 12,[15][16][17][18][19] However, to be used under visible solar light irradiation, new TNT sensitization processes are needed and will be welcomed. Therefore, the synthesis of TNT-based materials with either a broader range of light absorption and/or a lower charge recombination rate would be an important achievement towards the development of successful photoactive materials.…”

“…Moreover, it was also shown that the methylene blue sensitized Co-TNT nanostructures are highly stable under UV radiation and present a strong and broad absorption in the visible region. 15 This work reports on the synthesis of nanocrystalline TNTbased materials modified by both cobalt doping (Co-TNT) and Co ion-exchange (TNT/Co) prepared via a hydrothermal treatment of an amorphous undoped and Co-doped precursors recently reported by our group. 15,16 The influence of the Co content and/or Co position in the TNT structure on the optical and photocatalytic properties of the materials was studied.…”

Facile one-step process for synthesis of vertically aligned cobalt oxide doped TiO2 nanotube arrays for solar energy conversion

“…Also, Santara et al investigate the high temperature ferromagnetism of Co.-doped TiO 2 nanoparticles, which prepared by using a ball milling method [35]. Ferriera et al reported the synthesis of Co.-doped titanate nanotubes synthesized by hydrothermal method and study its adsorption ability with methylene blue [36]. It was shown that Co.-doped titanate has higher dye sensitization as compared with undoped titanate.…”