Environmentally friendly growth of highly crystalline photocatalytic Na ₂Ti ₆O ₁₃ whiskers from a NaCl flux

Idiomorphic and high quality Na ₂Ti ₆O ₁₃whiskers were easily grown by the rapid cooling of a NaCl flux. Environmentally friendly whisker growth was conducted by heating a mixture of solute (Na ₂CO ₃ + TiO ₂) and flux (NaCl) at 1100 °C and holding at this temperature for 10 h. After that, the mixture was cooled at various rates of 100, 200, >9000 (quenching in air), or > 120000 °C h ^-1 (quenching into water). The obtained whiskers, which had average sizes of up to 101.5 μm x 0.7 μm and aspect ratios of up to 145, were colorless and transparent. The grown whiskers tended to form aggregates, that looked just like a lustered cotton. The whisker forms and sizes obviously depended on the cooling rates of the high-temperature solutions. The aspect ratio of the whiskers increased with the increasing cooling rate and decreasing solute concentration. Transmission electron microscope (TEM) images indicated that the grown whiskers were of a very good crystallinity. The major constituents, that is, sodium, titanium, and oxygen, were homogeneously distributed throughout the whiskers, however, chlorine from the flux and platinum from the crucible were not detected. Furthermore, highly crystalline, ultralong, and flexible Na ₂Ti ₆Oi ₃ whiskers were successfully grown by the slow cooling of an NaCl flux by the use of the nonstoichiometric mixture of Na ₂O and TiO ₂ (2Na ₂O-3TiO ₂). The grown whiskers exhibited good photocatalytic activity under ultraviolet (UV) light irradiation. It is considerably reasonable to suppose that NaCl is adequate to synthesize high quality and well-developed titanate whiskers in an environmentally friendly process of crystal growth.