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Titania nanotube arrays (NTAs) on titanium (Ti) fabricated by electrochemical anodization have attracted tremendous interest for diverse applications, of which most perform in aqueous environment or related to interaction with water. The NTAs are widely studied however the related factor of stability of NTAs when applied in such environment has rarely been concerned. We report that the annealed anatase NTAs are stable but the non-annealed amorphous NTAs are unstable to undergo specific structural change accompanied with a process of amorphous TiO 2 dissolution and anatase TiO 2 recrystallization. Quite unexpectedly, the non-annealed NTAs still show good stability without structural change in the cell culture media, possibly due to the presence of inorganics that may interfere with the TiO 2 dissolution/redeposition process. The pH value of the aqueous environment is not a determinant factor for the structural change for non-annealed NTAs or not, while the temperature and the existence of F − can accelerate the structural change process. F − may play a very important role in the change process.Over the past decade, titania nanotube arrays (NTAs) on titanium (Ti) fabricated by electrochemical anodization have attracted tremendous interest for diverse applications, of which most work in aqueous environment or related to the interaction with water, such as photocatalysis, photoelectrochemical water splitting, sensors, drug delivery and biological coatings 1,2 . There are researches focusing on the transformation of the as-grown amorphous NTAs to the crystalline TiO 2 for specific applications 3 . It was reported that spontaneous phase and morphology transformation of as-formed NTAs occurred in pure water at room temperature 4 . A room-temperature spontaneous crystallization of amorphous titania to anatase in the absence of any solvent, additive or catalyst was also reported 5 . Lowering the transformation temperature can simplify the transformation conditions as well as avoid hindering the integration of TiO 2 nanostructures with the thermally unstable polymeric substrates 6-9 . Normally, a stable structure is required for the normal function of a nanostructure once the optimal structure is determined. As many NTAs are used in the phase of amorphous in the environment of water, the finding of room-temperature spontaneous crystallization of as-formed NTAs initiates our concern on their stability.As is known, the stability of a material is closely related to its composition and phase. NTAs are mainly composed of titania. It is noted that many factors in the fabrication and post-treatment of as-grown NTAs may potentially alter the composition and phase, such as electrolyte composition, annealing treatment and washing procedure, which are usually differential in various reports. In regard of the electrolyte composition, NTAs can be fabricated in F − containing electrolytes with water solvent 10,11 or some polar organic solvents such as ethylene glycol (EG) 12,13 , leading to obvious disparity in the nanotube form, diame...

2016-12-23T18:52:10

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The ambient metastability of the rock-salt phase in well-defined model systems comprising nanospheres or nanorods of cadmium selenide, cadmium sulfide, or both was investigated as a function of composition, initial crystal phase, particle structure, shape, surface functionalization, and ordering level of their assemblies. Our experiments show that these nanocrystal systems exhibit ligand-tailorable reversibility in the rock salt–to–zinc blende solid-phase transformation. Interparticle sintering was used to engineer kinetic barriers in the phase transformation to produce ambient-pressure metastable rock-salt structures in a controllable manner. Interconnected nanocrystal networks were identified as an essential structure that hosted metastable high-energy phases at ambient conditions. These findings suggest general rules for transformation-barrier engineering that are useful in the rational design of next-generation materials.

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