Conversion of a 2D Lepidocrocite-Type Layered Titanate into Its 1D Nanowire Form with Enhancement of Cation Exchange and Photocatalytic Performance

Layered titanates with one-dimensional (1D) shapes have been an important class of nanomaterials due to their combination of 1D and 2D fascinating properties. Among many layered titanates, lepidocrocite-type layered titanates have significant advantages such as superior intercalation and exfoliation properties, while the synthesis of the ID-shape forms is still challenging. Here, we report on a facile one-pot hydrothermal conversion of a lepidocrocite-type layered titanate into the corresponding nanowire-shape form. The reaction mechanism involves the decomposition of the starting layered titanate into 1D small segments which assemble into the nanowire. This new nanowire shows properties resulting from the combination of 1D and 2D nanostructural features, excellent cation exchange ability, and high photoinduced charge separation and photocatalytic efficiency. As a demonstration, we evaluate the nanowire as a sequestrating material capable of collecting toxic cations, like Cd2+, from water and photoreducing them (immobilizing them tightly). We find that the nanowire shows an efficient and ultrafast photoimmobilization activity, whereas the starting layered titanate and a benchmark TiO2 photocatalyst (P25) show no activity under the identical conditions. The photoimmobilization rate (within 1 min) is considerably faster than the cation exchange rates reported for state-of-the-art cation exchangers (with no photoimmobilization ability). The nanowire used for photoimmobilization reactions is easily recovered from water by decantation, showing the possible practical use for safe disposal of toxic cations in the environment.