Investigação do uso de metal-organic frameworks (MOFs) de európio e ligantes mistos como sensores químicos
Carregando...
Data
2019-02-22
Autores
Silva, Caroline Moraes da
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Embora outros importantes materiais inorgânicos porosos sejam conhecidos, tais como as sílicas e as zeólitas, as MOFs vêm despertando interesse crescente como um dos mais versáteis materiais contendo porosidade permanente, principalmente devido as suas propriedades únicas como alta cristalinidade, possibilidade de funcionalização e elevada área superficial. Tratam-se de sólidos de coordenação bi- ou tridimensionais com ligantes polidentados coordenados a íons ou clusters metálicos por fortes interações covalentes apresentando cavidades vazias. Além disso, propriedades luminescentes podem também ser introduzidas às MOFs caso sejam construídas a partir de íons lantanídeos como centros metálicos (LnMOFs) e por essa razão, outras aplicações podem ser exploradas como sensores luminescentes, biosensores, marcadores biológicos, dispositivos emissores de luz (OLEDs), entre outras. Dentro desse contexto, este trabalho propõe a preparação de LnMOFs de íon európio trivalente contendo ligantes multitópicos O- e N- doadores e a investigação da potencialidade de uso como sensores químicos luminescentes. A dissertação começa com a discussão do sistema Eu3+/2,6-piridinadicarboxilato (PDC)/1,3,5-benzenotricarboxilato (BTC), que conduziu à formação dos compostos CMS31MW (ou CMS31HT, já que a alteração da rota sintética levou à obtenção da mesma fase), CMS43MW e CMS47MW, correspondentes às MOFs [Eu(PDC)2]n, MIL-78 + MOF-76 (mistura das duas fases) e MIL-78, respectivamente, já descritas na literatura. O trabalho prosseguiu no sentido de explorar a estabilidade química e o uso como sensor do polímero de coordenação bidimensional luminescente CMS31MW (re-batizado como EU-MOF-2D), que mostrou alta sensibilidade e seletividade para o composto nitroaromático 2,4,6-trinitrofenol (ácido pícrico) em metanol. Como não há poros acessíveis na matriz, sugere-se estar havendo uma interação das moléculas de ácido pícrico com a superfície do composto de európio. Estudos teóricos no método da teoria do funcional da densidade (DFT) mostraram que o mecanismo responsável pela extinção (quenching) da luminescência é a transferência de elétrons do ligante 2,6-H2PDC (rico em elétrons) na rede metalorgânica para o analito 2,4,6-trinitrofenol (pobre em elétrons). Quando em presença de água, o composto EU-MOF-2D sofre uma reação reversível gerando a espécie [Eu(PDC)(HPDC)(H2O)2]·4H2O] (amostra CMS31-W). Essa alteração estrutural causada pela presença do solvente, além de modificar o ambiente de coordenação do íon európio, levou à protonação do ligante, e por essa razão, esse composto foi utilizado com sucesso como sensor luminescente de pH em solução aquosa. Experimentos de difração de raios-X de pó confirmaram a estabilidade do composto em diferentes ambientes químicos. Cabe destacar que o objetivo central da Dissertação, que era a preparação de MOFs mistas inéditas de európio (III), foi finalmente alcançado na etapa final desse trabalho. Realizando uma série de alterações nas rotas de síntese e principalmente nos parâmetros experimentais, como razão molar metal:ligante e natureza do ligante orgânico, os materiais CMS52(C)MW, CMS52(C)HT e CMS57MW foram obtidos. Os dois primeiros correspondem ao sistema Eu3+/2,5-piridinadicarboxilato/1,2,4,5-tetracarboxilato e o último foi sintetizado usando Eu3+, 3,5-pirazoldicarboxilato e tereftalato de sódio como blocos de construção. Embora ensaios para obtenção de monocristais estejam sendo realizados no momento, os resultados de difração de raios-X, análise térmica e microscopia eletrônica apontam na direção da formação de MOFs mistas luminescentes inéditas.
MOFs have been drawing increasing interest as one of the most versatile materials with permanent porosity, in spite of other porous inorganic materials such as silicas and zeolites. This class of organic-inorganic materials shows unique properties such as high crystallinity, functionalization and high surface area. They are defined as bi- or three-dimensional coordination solids with empty cavities and are constructed with polydentate ligands coordinated to ions or metallic clusters by strong covalent interactions. In addition, luminescent properties can also be introduced to the MOFs if they are synthesized with lanthanide ions as metal centers (LnMOFs) and, for this reason, other applications can be exploited as luminescent sensors, biosensors, biological markers, light emitting devices (OLEDs), among others. In this context, this work proposes the preparation of LnMOFs based on trivalent europium ion containing multitopic O- and N-donor ligands and the investigation of the potential of luminescent chemical sensing. The dissertation begins with the discussion of the Eu3+/2,6-pyridinedicarboxylate (PDC)/1,3,5-benzenetricarboxylate (BTC) system, which led to the formation of compounds CMS31MW (or CMS31HT, since altering the synthetic route led to the formation of the same phase), CMS43MW and CMS47MW, corresponding to the MOFs [Eu(PDC)2]n, MIL-78 + MOF-76 (mixture of two phases) and MIL-78, respectively, described in the literature. The work proceeded to explore the chemical stability and sensing capability of the CMS31MW two-dimensional luminescent coordination polymer (renamed EU-MOF-2D), which showed high sensitivity and selectivity for 2,4,6- trinitrophenol (picric acid) in methanol. As there are no accessible pores in the framework, it is suggested that there is an interaction of the picric acid molecules with the surface of the europium compound. Theoretical studies in the DFT method have shown that the mechanism responsible for the quenching of the luminescence is the transfer of electrons from the 2,6-H2PDC (electron-rich) ligand in the MOF to analyte 2, 4,6-trinitrophenol (electron-poor). When in the presence of water, the compound EU-MOF-2D undergoes a reversible reaction generating the species [Eu(PDC)(HPDC)(H2O)2]·4H2O] (sample CMS31-W). This structural change caused by the presence of the solvent, in addition to modifying the coordination environment of the europium ion, led to the protonation of the ligand, and for this reason, this compound was successfully used as a luminescent pH sensor in aqueous solution. Powder X-ray diffraction experiments confirmed the stability of the compound in different chemical environments. It should be noted that the main objective of the Dissertation, which was the preparation of novel mixed MOFs of europium (III), was finally reached in the final stage of this work. The materials CMS52(C)MW, CMS52(C)HT and CMS57MW were obtained by changing experimental parameters and synthetic routes, such as metal: binder molar ratio and organic binder nature. The first two samples correspond to the Eu3+/ 2,5-pyridinedicarboxylate /1,2,4,5-tetracarboxylate system and the latter was synthesized using Eu3+, 3,5-pyrazoldicarboxylate and sodium terephthalate as building blocks. Although assays to obtain monocrystals are currently being carried out, the results of X-ray diffraction, thermal analysis and electron microscopy point towards the formation of novel luminescent mixed MOFs.
MOFs have been drawing increasing interest as one of the most versatile materials with permanent porosity, in spite of other porous inorganic materials such as silicas and zeolites. This class of organic-inorganic materials shows unique properties such as high crystallinity, functionalization and high surface area. They are defined as bi- or three-dimensional coordination solids with empty cavities and are constructed with polydentate ligands coordinated to ions or metallic clusters by strong covalent interactions. In addition, luminescent properties can also be introduced to the MOFs if they are synthesized with lanthanide ions as metal centers (LnMOFs) and, for this reason, other applications can be exploited as luminescent sensors, biosensors, biological markers, light emitting devices (OLEDs), among others. In this context, this work proposes the preparation of LnMOFs based on trivalent europium ion containing multitopic O- and N-donor ligands and the investigation of the potential of luminescent chemical sensing. The dissertation begins with the discussion of the Eu3+/2,6-pyridinedicarboxylate (PDC)/1,3,5-benzenetricarboxylate (BTC) system, which led to the formation of compounds CMS31MW (or CMS31HT, since altering the synthetic route led to the formation of the same phase), CMS43MW and CMS47MW, corresponding to the MOFs [Eu(PDC)2]n, MIL-78 + MOF-76 (mixture of two phases) and MIL-78, respectively, described in the literature. The work proceeded to explore the chemical stability and sensing capability of the CMS31MW two-dimensional luminescent coordination polymer (renamed EU-MOF-2D), which showed high sensitivity and selectivity for 2,4,6- trinitrophenol (picric acid) in methanol. As there are no accessible pores in the framework, it is suggested that there is an interaction of the picric acid molecules with the surface of the europium compound. Theoretical studies in the DFT method have shown that the mechanism responsible for the quenching of the luminescence is the transfer of electrons from the 2,6-H2PDC (electron-rich) ligand in the MOF to analyte 2, 4,6-trinitrophenol (electron-poor). When in the presence of water, the compound EU-MOF-2D undergoes a reversible reaction generating the species [Eu(PDC)(HPDC)(H2O)2]·4H2O] (sample CMS31-W). This structural change caused by the presence of the solvent, in addition to modifying the coordination environment of the europium ion, led to the protonation of the ligand, and for this reason, this compound was successfully used as a luminescent pH sensor in aqueous solution. Powder X-ray diffraction experiments confirmed the stability of the compound in different chemical environments. It should be noted that the main objective of the Dissertation, which was the preparation of novel mixed MOFs of europium (III), was finally reached in the final stage of this work. The materials CMS52(C)MW, CMS52(C)HT and CMS57MW were obtained by changing experimental parameters and synthetic routes, such as metal: binder molar ratio and organic binder nature. The first two samples correspond to the Eu3+/ 2,5-pyridinedicarboxylate /1,2,4,5-tetracarboxylate system and the latter was synthesized using Eu3+, 3,5-pyrazoldicarboxylate and sodium terephthalate as building blocks. Although assays to obtain monocrystals are currently being carried out, the results of X-ray diffraction, thermal analysis and electron microscopy point towards the formation of novel luminescent mixed MOFs.
Descrição
Palavras-chave
LnMOFs, Materiais porosos, Luminescência, Sensor luminescente, Lantanídeos