Microwave-assisted Hydrothermal Synthesis of Single-crystal Nanorods of Rhabdophane-type Sr-doped LaPO4·nH2O



A novel, simple, soft, and fast microwave-assisted hydrothermal method was used for the preparation of single-crystal nanorods of hexagonal rhabdophane-type La1−xSrxPO4−x/2·nH2O (x = 0 or 0.02) from commercially available La(NO3)3·6H2O, Sr(NO3)2, and H3PO4. The synthesis was conducted at 130°C for 20 min in a sealed-vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized using a wide battery of analytical techniques. Highly uniform, well-shaped nanorods of LaPO4·nH2O and La0.98Sr0.02PO3.99·nH2O were readily obtained, with average length of 213 ± 41 nm and 102 ± 25 nm, average aspect ratio (ratio between length and diameter) of 21 ± 9 and 12 ± 5, and specific surface area of 45 ± 2 and 51 ± 1 m2/g, respectively. In both cases, the single-crystal nanorods grew anisotropically along their c crystallographic-axis direction. At 700°C, the hexagonal rhabdophane-type phase has already transformed into the monoclinic monazite-type structure, although the undoped and Sr-doped nanorods retain their morphological features and specific surface area during calcination.