Accelerated syntheses of porous isostructural lanthanide- benzenetricarboxylates (Ln-BTC) under ultrasound at room temperature

Porous isostructural [Ln(BTC)(H₂O)•4.3H₂O], or Ln-BTC (Ln: Ce, Tb, and Y; BTC stands for 1,3,5-benzenetricarboxylate), with a tetragonal structure has been synthesized by ultrasonic irradiation at room temperature. Under ultrasound, the syntheses were quickly accelerated to obtain the fully crystallized phase in only minutes. The particle size can be considerably decreased by this method. On the basis of XRD, field-emission scanning electron microscopy (FE-SEM), and surface area analyses, it can be understood that the Ln-BTCs are homogeneous in phase, isostructural, and microporous. The synthesis rates are r_Ce-BTC > r_Tb-BTC > r_Y-BTC for both in the nucleation and crystal-growth stages, thereby illustrating the importance of the lability of the metal ions in the synthesis of the metal-organic framework (MOF) materials. The Tb-BTC shows luminescence properties, a characteristic property of Tb³⁺ (green-light emission), in the range of 470-630 nm at room temperature. It is believed that these lanthanide MOFs with micropores and/or luminescent properties should be proven to be multifunctional materials on further investigations. Isostructural Ln-BTCs (Ln: Ce, Tb, and Y) with a small size and high porosity are synthesized under ultrasound within minutes under ambient conditions. The synthesis rates of the Ln-BTCs are r_Ce-BTC >r _Tb-BTC > r_Y-BTC, which shows the importance of lability/inertness of the metal ions in the synthesis kinetics.