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Demand on high‐performance ion exchangers is ever‐increasing in energy and environment applications. Among many cation exchangers, layered alkali titanates generally show larger cation exchange capacity, but slower cation exchange rate due to their 2D micrometer‐size particle morphologies, which limits their practical applications. Here, a rational conversion of a layered sodium titanate, Na2Ti3O7, is reported to the corresponding 1D ultra‐narrow nanowires via hydrothermal treatment under basic conditions. The formation of nanowires is thought to involve the partial exfoliation of Na2Ti3O7 to form thin plate‐like particles that subsequently split into nanowires along a crystallographically defined, chemically selective weakness in the Na2Ti3O7 crystals. This process is similar to a recently burgeoning materials design using atomic‐level weakness in solids, such as zeolites and metal‐organic frameworks. The proposed formation scheme is further supported by comparative experiments performed on another layered alkali titanate, K0.8Ti1.73Li0.27O4, which possesses randomly distributed defects at the Ti sites. Thanks to the shortening of diffusion path lengths of the interlayer cations, the resulting Na2Ti3O7 nanowires show an excellent cation exchange performance toward Cd2+ in aqueous solution, exceeding several existing cation exchangers such as zeolites and organic resins. [ABSTRACT FROM AUTHOR]

We developed a new penternary wurtzitic nitride system Li 1- x Zn x Ge 2- x Ga x N 3 (0 ≤ x ≤ 1) by hybridizing LiGe 2 N 3 and ZnGeGaN 3 . Fairly stoichiometric fine powder samples were synthesized by the reduction-nitridation process at 900 °C. While the end member LiGe 2 N 3 possessed a relatively large band gap of 4.16 eV, the band gap of the developed penternary system varied in a broad range of 3.81 to 3.10 eV, showing promising responsivity to the solar spectrum. The crystal structure of LiGe 2 N 3 was precisely determined by time-of-flight neutron powder diffraction for the first time, revealing the complete ordering of Li and Ge in the Cmc 2 1 structure. The structural evolution from completely ordered LiGe 2 N 3 to fully disordered ZnGeGaN 3 was quantitatively analyzed by Rietveld refinement based on a partially disordered Cmc 2 1 model, and the obtained results were also supported by 71 Ga solid-state NMR spectroscopy. The synthesized Li 1- x Zn x Ge 2- x Ga x N 3 powder samples exhibited photocatalytic activities for the water reduction and oxidation reactions under solar light irradiation, with the H 2 evolution rate of 0.3-59.0 μmol/h and the O 2 evolution rate of 3.1-296.2 μmol/h, depending on the composition. Stable solar hydrogen generation of up to 48 h was demonstrated by the x = 0.80 sample, with the total amount of H 2 evolved over 1.6 mmol and an external quantum efficiency of 2.1%.