2D-to-1D Conversion of a Layered Sodium Titanate via Rational Framework Splitting for Highly Efficient Cation Exchange

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, Na Ti O , 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 Na Ti O to form thin plate-like particles that subsequently split into nanowires along a crystallographically defined, chemically selective weakness in the Na Ti O 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, K Ti Li O , which possesses randomly distributed defects at the Ti sites. Thanks to the shortening of diffusion path lengths of the interlayer cations, the resulting Na Ti O nanowires show an excellent cation exchange performance toward Cd in aqueous solution, exceeding several existing cation exchangers such as zeolites and organic resins.