α-Titanium phosphate intercalated with propylamine: An alternative pathway for efficient europium(III) uptake into layered tetravalent metal phosphates

α-Ti(HPO4)2·H2O (α-TiP) and its propylamine intercalation product, Ti(HPO4)2·2C3H7NH2·H2O (α-TiPPr), have been synthesized and characterized. Later, their sorption capacity for europium(III) was investigated, and this purpose was accomplished by treating α-TiP and α-TiPPr with europium(III) nitrate solutions at different concentrations until the equilibrium is reached. All samples were characterized, among others, by powder X-ray diffraction (PXRD), scanning and transmission electron microscopies (SEM, TEM, STEM-EDX, SAED), thermogravimetric analysis (TGA), and photoluminescence (PL) measurements. The results show that the Eu3+ uptake is limited to surface when α-TiP is used as sorbent. Nevertheless, the Eu-retention is considerably enhanced with α-TiPPr as a consequence of an ion-exchange process into the interlayer space of the layered titanium phosphate (involving propylammonium cations, C3H7NH3+, and hexahydrate europium(III) species, [Eu(H2O)6]3+), and the crystal structure of a hypothetical final product, α-[Eu(H2O)6]2/3Ti(PO4)2·[(H2O)6]1/3, has been proposed by using DFT calculations.