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To obtain a better understanding of TiO2 nanotube (TiO2-NT) synthesis in different ethylene glycol (EG)-based electrolyte solutions by electrochemical anodization, the primary steps of TiO2-NT formation were studied by experimental techniques. In this regard, three different EG-based electrolyte solutions were used for anodic oxidation of titanium foil. The first electrolyte solution contains conventional ammonium fluoride (NH4F) dissolved in EG/water (98 : 2 v/v). In the second one, Ti foil anodization is performed in an electrolyte solution containing the 1-butyl-3-methyl-imidazolium tetrafluoroborate (Bmim-BF4) ionic liquid. Finally, the fluorine-containing species was replaced by the 1-butyl-3-methyl-imidazolium chloride (Bmim-Cl) ionic liquid. The results indicate that the TiO2-NTs did not form by anodization in the EG/H2O/Bmim-Cl electrolyte solution at 60 V. Interestingly, this electrolyte solution is less viscous than the fluorine-containing electrolyte solutions. In addition, we report a detailed study on the structural arrangement of electrolyte solution components near the solid surfaces using molecular dynamics (MD) simulation methods to reveal the factors governing the difference of the ionic species distribution. The MD results elucidate the role of the ionic constituents in the length of the nanotube arrays at a certain anodization condition. Furthermore, as reported herein for the first time, the lifetimes of ion–ion contacts and the interactions of ionic species with TiO2 walls have a substantial effect on the resulting nanotubes. These characteristics are analyzed by using radial distribution functions, density profiles, distance analysis, time correlation functions, and mean-square-displacements, complemented by DFT calculations. [ABSTRACT FROM AUTHOR]

Drug delivery systems sensitive to pH have been investigated recently as a responsive strategy for tumour targeting in view of the slightly acidic pH environment of most solid tumours. Herein, we report Zn capped Al2O3 and TiO2 nanoporous arrays for pH sensitive drug release. The nanostructures were fabricated through electrochemical anodisation. Vitamin C as a model drug was loaded into the nanopores; some were then capped using elemental Zn. The release rates of vitamin C were investigated in water or lactic acid using high performance liquid chromatography (HPLC). The amount of drug loaded into the nanostructures was about 7 times higher for TiO2 compared with Al2O3 and the release was faster from TiO2. Zn capping proved to be quite efficient at preventing release at high pH (7) and not largely hindering the release at low pH (5), making both systems suitable for pH-triggered release. Molecular dynamics (MD) simulations showed that the diffusion of vitamin C molecules through the model nanopores is faster for TiO2 than for Al2O3, consistent with the experimental results. The tremendously stronger H bonding interactions observed for vitamin C molecules and water molecules with the TiO2 walls compared with Al2O3 are responsible for the observed differences in the calculated number density profiles and radial distribution functions. [ABSTRACT FROM AUTHOR]

Electrostatic potential in the vicinity of the surface is induced when aqueous mixtures of hydrophobic and hydrophilic ionic liquids (ILs) are confined between a slit nanopore of amorphous but not crystalline TiO2 semiconductors. According to our molecular dynamics (MD) simulations, the extent of ion-pairing lifetime under such nanoscale confinement is substantially lower than its value in the bulk. It becomes still lower when aqueous mixtures of ionic liquid electrolytes are used. Ion–ion correlation is broken completely in the confined dilute aqueous electrolyte systems. The anions and cations of the ILs migrate and accumulate at the opposite amorphous TiO2 electrodes that are separated by 10 nm to arrange a nanosize pore. In contrast, we have shown that the electrostatic interactions between the IL ions are dominant when the electrolyte is confined between anatase (101) TiO2. A similar trend is observed for the inorganic electrolyte system. These findings shed light on the design of new cells for electrochemical applications. [ABSTRACT FROM AUTHOR]

To obtain a better understanding of TiO2 nanotube (TiO2-NT) synthesis in different ethylene glycol (EG)-based electrolyte solutions by electrochemical anodization, the primary steps of TiO2-NT formation were studied by experimental techniques. In this regard, three different EG-based electrolyte solutions were used for anodic oxidation of titanium foil. The first electrolyte solution contains conventional ammonium fluoride (NH4F) dissolved in EG/water (98 : 2 v/v). In the second one, Ti foil anodization is performed in an electrolyte solution containing the 1-butyl-3-methyl-imidazolium tetrafluoroborate (Bmim-BF4) ionic liquid. Finally, the fluorine-containing species was replaced by the 1-butyl-3-methyl-imidazolium chloride (Bmim-Cl) ionic liquid. The results indicate that the TiO2-NTs did not form by anodization in the EG/H2O/Bmim-Cl electrolyte solution at 60 V. Interestingly, this electrolyte solution is less viscous than the fluorine-containing electrolyte solutions. In addition, we report a detailed study on the structural arrangement of electrolyte solution components near the solid surfaces using molecular dynamics (MD) simulation methods to reveal the factors governing the difference of the ionic species distribution. The MD results elucidate the role of the ionic constituents in the length of the nanotube arrays at a certain anodization condition. Furthermore, as reported herein for the first time, the lifetimes of ion-ion contacts and the interactions of ionic species with TiO2 walls have a substantial effect on the resulting nanotubes. These characteristics are analyzed by using radial distribution functions, density profiles, distance analysis, time correlation functions, and mean-square-displacements, complemented by DFT calculations.

Electrostatic potential in the vicinity of the surface is induced when aqueous mixtures of hydrophobic and hydrophilic ionic liquids (ILs) are confined between a slit nanopore of amorphous but not crystalline TiO2 semiconductors. According to our molecular dynamics (MD) simulations, the extent of ion-pairing lifetime under such nanoscale confinement is substantially lower than its value in the bulk. It becomes still lower when aqueous mixtures of ionic liquid electrolytes are used. Ion-ion correlation is broken completely in the confined dilute aqueous electrolyte systems. The anions and cations of the ILs migrate and accumulate at the opposite amorphous TiO2 electrodes that are separated by 10 nm to arrange a nanosize pore. In contrast, we have shown that the electrostatic interactions between the IL ions are dominant when the electrolyte is confined between anatase (101) TiO2. A similar trend is observed for the inorganic electrolyte system. These findings shed light on the design of new cells for electrochemical applications.