Estudo das propriedades morfológicas, estruturais e fotofísicas de compostos de coordenação de dupla emissão baseados em ZIF-8 dopado com európio

Abstract

Metal-organic structures (MOFs) have received much attention from the scientific community due to their unique properties which promote the use of this class of materials in the most diverse applications, such as catalysis, drug delivery agents, solar cells, among others. Within this universe, MOFs containing lanthanide ions (Ln-MOFs) have been gaining more and more space in the field of chemistry mainly due to their attributes and optical applications, such as in the composition of fluorescent probes. In view of this reality, a series of highly porous MOFs, the ZIF-8 containing europium ions (ZIF-8: x% Eu where, x = 1, 3 or 7%) were prepared by a simple and rapid crystallization method at room temperature (25°C) and their structural, morphological and photophysical properties were evaluated. The results showed that the degree of crystallinity decreased from 71% for ZIF-8 to 67%, 54% and 32% for ZIF-8: 1% Eu, ZIF-8: 3% Eu and ZIF-8: 7% Eu, respectively, from the introduction of europium ions into their composition. However, the original ZIF-8 crystalline structure is maintained and only small displacements in the crystallographic planes have been observed, which is linked to the permutation of europium ions at the zinc sites of the MOF structure. In general, the materials showed an improvement in thermal stability due to the presence of europium ions compared to the non-doped ZIF-8. The emission spectra for the europium doped ZIF 8 reveal a signal in the blue region related to the emission of ZIF-8 and line profiles of the Eu3+ ion in the coordinating polymer, which are in accordance with the formation of a dual-emission heterostructured material. Furthermore, the f-f transitions of the europium grew in intensity as the Eu3+ quantity increased, indicating an increase in the efficiency of this energy transfer. In light of this, the work provides an in-depth understanding of the characteristics of the ZIF-8 containing europium ions, bringing an example of progress in the development of dual-emission MOFs.