Exfoliation and europium(III)-functionalization of α-titanium phosphate via propylamine intercalation: from multilayer assemblies to single nanosheets

Layered α-titanium phosphate intercalated with propylamine, Ti(HPO₄)₂·2C₃H₇NH₂·H₂O (α-TiPPr), has been synthesized by solid-vapour reaction and then exfoliated via a single-stage approach based on overnight stirring in aqueous medium. The obtained nanosheets were then functionalized using solid–liquid reaction with europium(III) nitrate aqueous solutions. The obtained materials were characterized by powder X-ray diffraction (PXRD), N₂ adsorption–desorption isotherms at 77 K, scanning electron microscopy (SEM), transmission electron microscopy (TEM, SAED, STEM-EDX), atomic force microscopy (AFM) and photoluminescence spectroscopy (PL). The europium(III) sorption takes place via two distinct pathways, the first is the previously reported C₃H₇NH₃⁺/[Eu(H₂O)₆]³⁺ ion-exchange process into the titanium–phosphate interlayer space of the multilayered α-TiPPr. The second pathway is the self-assembly of single-sheets which is provoked by electrostatic interactions between the negatively charged titanium–phosphate sheets and the Eu(III)-aqueous cations, leading to the formation of layered nanoparticles.