Infinite coordination polymers based on rare-earth ions and pyrazole-3,5-dicarboxylate: structural, morphological and luminescent properties

Author(s)

Guilherme Arroyos

• Document type: Doctoral Thesis
• Press: Araraquara. 2022-05-27.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
• Defense date: 2022-05-20
• Advisor: Regina Célia Galvão Frem

Abstract

Infinite Coordination Polymers (ICPs) are nanostructured materials that can be categorized as a subclass of Metal-Organic Frameworks (MOFs). In this work, a series of ICPs based on the pyrazole-3,5-dicarboxylate linker and malonate anion was synthesized using water as solvent, and trivalent rare-earth ions (Y3+, La3+, Eu3+, Gd3+, Tb3+, Dy3+, Tm3+) as metallic centers. Three synthetic routes were investigated: gel diffusion (Ln-Dif compounds), conventional solvothermal (Ln-St compounds), and microwave-assisted solvothermal (Ln-M compounds) syntheses. It was possible to observe spherical particles in all systems, with larger diameters (300 – 500 µm) for the Ln-Dif compound series, followed by Ln-St (30 – 200 µm) and Ln-M (1.0 – 3.0 µm). From scanning and transmission electron microscopy studies, it was observed that the particle organization happens with the formation of "crystal islands", which occurs independently of the synthetic route. For Ln-M series, the small size of these nanodomains (diameters ~ 3 nm) can be related to the broadening of the peaks observed in the PXRD patterns. With the combination of FTIR, elemental analysis, and 1HRMN techniques, it was possible to determine the structure of this series of compounds (isostructural) as well as the role of the malonate anion as a coordination modulator. The luminescent properties were investigated in monometallic (based on Eu3+, Gd3+, and Tb3+), bimetallic (Y3+:Eu3+, Y3+:Tb3+, Gd3+:Tm3+, Tb3+:Eu3+) and trimetallic (Gd3+:Eu3+, Dy3+) samples. The monometallic samples based on Eu3+ and Tb3+ emitted via antenna effect, exhibiting the characteristic intraconfigurational transitions from these ions. The monometallic sample containing Gd3+ was used to calculate the approximate value of the triplet state energy of the linker, which showed a high capacity to sensitize the Tb3+ ion. Eu3+ emission could be enhanced in the Tb:Eu bimetallic samples due to energy transfer from Tb3+ to Eu3+. In the trimetallic sample, it was possible to obtain white-light emission by carefully control of Gd3+, Dy3+ and Eu3+ percentages. The second part of the project was based on the investigation of applications for the materials. Thus, the monometallic sample based on the Tb3+ ion (Tb-M) was proposed as a luminescent sensor for Fe3+, Cr3+, Cu2+, and Cr2O72- ions in water, using the emission suppression mechanism. Bimetallic samples containing Tb3+ ion as matrix and Eu3+ as dopant (Tb0.95:Eu0.05-M and Tb0.8:Eu0.2-M) were used to detect dipicolinic acid (DPA), which is an important biomarker of Bacillus anthracis spores (bacterium that causes anthrax disease). DPA detection was also performed on an extract of Bacillus subtilis (model organism). In another application, the sample based on Y3+ doped with 5% Eu3+ (Y0.95:Eu0.05-M) was subjected to a calcination process (550 °C – significantly lower temperature when compared to classical methods), where it was possible to obtain luminescent microparticles of Y2O3:Eu3+ with the same spherical shape as the source material. Finally, the potential of using polymethylmethacrylate (PMMA) as a polymeric matrix to support ICP particles was investigated, since certain applications are not feasible with the compounds in powder form. It was possible to obtain self-supporting, flexible, and translucent films, keeping the emission property of the ICPs and with good light permeability in the visible region. (AU)

• FAPESP's process: 18/09898-3 - Infinite coordination polymers based on rare-earth ions and pyrazole-3,5-dicarboxylate: structural, morphological and luminescent properties
• Grantee: Guilherme Arroyos
• Support Opportunities: Scholarships in Brazil - Doctorate