Ultra-violet and electron beam irradiation as an effective approach for design of Ln(iii) and Am(iii) MOFs

Abstract

Ultraviolet (UV) irradiation for synthesis of metal–organic frameworks (MOFs) has been applied for the first time. The use of UV radiation enabled the efficient synthesis of 2D-Ln-BTB and Am-MIL-103 MOFs. A comparative analysis was carried out to assess the viability of radiation-chemical and photochemical approaches for the synthesis of Ln(III)- and Am(III)-BTB MOFs. The yields from both methods for all lanthanides reached 90% depending on the cation. The obtained materials were characterized by pXRD, FTIR spectroscopy, SEM-EDX, CHN analysis, and TGA. For a novel Am-MIL-103, the crystal structure was determined using SCXRD and compared with that of previously known Ln-MIL-103 analogues. Solvent electron density removal revealed a void space of approximately 4311 ų (49.2% of the total unit cell volume), which is smaller than that of the lanthanum analogue (52.3%) due to the smaller ionic radius of Am. It was demonstrated that a decrease in dose rate from 180 to 8.4 Gy s⁻¹ results in a significant increase in the crystallinity of the material. In contrast to the photochemical method, the radiation-chemical approach yields only one type of Ln-BTB MOF. This study shows that by varying the conditions of the photochemical synthesis, it is possible to obtain three types of Ln-BTB MOFs with different structures.