TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: In the method (M1), the electrolytic medium further comprises water (at least 25, preferably at least 50, especially at least 75 wt.% by total weight of ionic liquid and water). The titanium dioxide nanotubes possess an outer diameter of less than 45 (preferably less than 40, especially less than 35) nm. The titanium metal is in the form of foil. Preferred Composition: In the composition (C1), the titanium dioxide nanotubes are in the form of an ordered array arranged perpendicular on a substrate. The titanium dioxide nanotubes possess a length-to-diameter aspect ratio of at least 100. Preferred Components: The ionic liquid is of formula (I). The ionic liquid contains a fluorine-containing counteranion. The counteranion is a fluorine-containing anion (preferably (BF4)-, (PF6)-, (N(SO2CF3)2)-, (N(SO2CF2CF3))2, and (CF3SO3)-).R1 and R2=optionally saturated, hydrocarbon group having at least one carbon atom (optionally substituted with O, N, or F) (preferably up to 6C alkyl);andX-=counteranion. EXAMPLE - A titanium dioxide nanotube was prepared as follows: the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate was mixed with deionized water, and the resulting fluid used as the electrolyte. The anodization process was conducted on 0.5 mm thick pure titanium foil using two-electrode DC power supply with voltage output range of 0-40 V. The titanium foil surface was used as-received (milled) and cleaned with acetone followed by ethanol rinse before the synthesis. The titanium foil was connected as the working electrode and piece of platinum mesh was used as the counter electrode. The synthesis was occurred at 21 degrees C. A constant potential of 10 volts was applied during the synthesis. The time-dependent anodization current was monitored using multimeter. The current was 2 mA at the beginning of the synthesis and gradually decreased and stabilized at level of 0.5 mA for 80 minutes before being quickly increased to above 20 mA, at which point the synthesis was stopped.