Exfoliation, Decomposition, and Regeneration Cycle of α-Titanium Phosphate through an Oxalate Salt-Phosphoric Acid Guided Reversible Process

This study systematically investigated the reaction between layered α-titanium phosphate (α-TiP) and oxalates, particularly <i>n</i>-butylammonium oxalate, and provided an in-depth analysis of the abnormal phenomenon observed in the reaction. Contrary to the expectation of a straightforward cation-exchange-driven intercalation process, the results revealed that the oxalate anion also actively participated in the reaction, causing partial decomposition of α-TiP from the crystal edges and facilitating its exfoliation into ultrathin sheets. Further investigations demonstrated that this process could be fully reversed via a restacking reaction initiated by the introduction of phosphoric acid into the product liquid, ultimately resulting in the regeneration of the α-TiP crystal. These findings suggest that despite extensive research on α-metal phosphate materials over the years, critical aspects of their underlying chemistry remain insufficiently understood and warrant further exploration.