Filmes Finos de Estruturas Metal-Orgânicas de Superfície (SURMOFs) para detecção de compostos orgânicos voláteis
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Data
2023-08-04
Autores
Santos, Thamiris Cescon dos
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Universidade Estadual Paulista (Unesp)
Resumo
Estruturas metal-orgânicas ou MOFs (acrônimo do inglês Metal-Organic Frameworks) são materiais híbridos altamente porosos e cristalinos. Filmes finos dessas estruturas podem ser integrados em diferentes superfícies e são denominados SURMOFs (do inglês Surface-Supported Metal-Organic Frameworks). Os MOFs/SURMOFs vêm ganhando destaque em diferentes aplicações como a separação e adsorção de gases, conversão e armazenamento de energia, catálise e sensoriamento. Neste trabalho, exploramos a alta porosidade dos SURMOFs, para aplicação na detecção eletrônica de compostos orgânicos voláteis (VOCs). O HKUST-1 SURMOF foi o material estudado devido à vasta quantidade de informação disponível na literatura. O HKUST-1 SURMOF possui, em sua estrutura, unidades diméricas metálicas de Cobre (〖Cu〗^(2+)) conectadas por moléculas ligantes de Ácido Trimésico (C₆H₃(CO₂H)₃). Embora amplamente reportado na literatura, a sua aplicabilidade em dispositivos eletrônicos baseados em filmes finos (<100 nm) ainda é sub-reportada. Aqui, filmes finos do HKUST-1 SURMOF foram integrados em junções verticais fabricadas por meio de etapas sequenciais de fotolitografia e deposição de filmes finos, dando origem a dispositivos eletrônicos de dois terminais. A tecnologia de nanomembranas metálicas tensionadas foi utilizada para viabilizar o acoplamento não invasivo do eletrodo superior. Essa arquitetura permitiu a investigação do comportamento elétrico dos dispositivos sob atmosferas controladas dos seguintes VOCs: Etanol, Isopropanol, Metanol e Hexano. A caracterização elétrica foi realizada em função do potencial elétrico (I-V) e em função do tempo (I-t), além de medidas da capacitância em função da frequência. Demonstrou-se aqui que o ganho de corrente elétrica e a capacitância nos dispositivos podem ser utilizados como parâmetros para diferenciar os gases detectados. Além disso, foram determinados – via caracterização elétrica – aspectos físico-químicos como a difusividade, a permeabilidade, o número de poros disponíveis e o comprimento de difusão intracristalina para cada um dos VOCs durante o processo de difusão pelos poros do HKUST-1. Os resultados obtidos foram avaliados com base nas propriedades intrínsecas das moléculas que compõem cada um dos gases. Os estudos reportados neste trabalho visam contribuir para o entendimento e criação de regras de design para futuros sensores eletrônicos de gás baseados em SURMOFs.
Metal-organic frameworks (MOFs) are highly porous and crystalline hybrid materials. Thin films of these structures can be integrated into various surfaces and are referred to as Surface-Supported Metal-Organic Frameworks, or SURMOFs. MOFs/SURMOFs have been gaining prominence in various applications such as gas separation and adsorption, energy conversion and storage, catalysis, and sensing. In this study, we explored the high porosity of SURMOFs for electronic detection of volatile organic compounds (VOCs). The HKUST-1 SURMOF was the material investigated in this study due to the extensive amount of literature available. The HKUST-1 SURMOF has copper (Cu²⁺) metal units connected by ligand molecules called Trimesic Acid (C₆H₃(CO₂H)₃). Although it's widely reported, its use in electronic devices based on thin films (<100 nm) is still underreported. Here, we integrated thin films of HKUST-1 SURMOF into vertical junctions fabricated through sequential steps of photolithography and thin film deposition, creating two-terminal electronic devices. The technology of tensioned metal nanomembranes was employed to enable non-invasive coupling of the upper electrode of the device. This setup allowed us to study the electrical behavior of the devices under controlled atmospheres containing VOCs such as Ethanol, Isopropyl Alcohol, Methanol, and Hexane. Electrical characterization was performed as a function of electrical potential (I-V) and as a function of time (I-t), in addition to capacitance measurements as a function of frequency. It was demonstrated here that the electrical current gain and the capacitance in the devices can be used as parameters to differentiate the detected gasses. Additionally, we determined through electrical characterization physical and chemical aspects such as diffusivity, permeability, available pore number, and intracrystalline diffusion length for each VOC during the diffusion process through the pores of HKUST-1. The obtained results were evaluated based on the intrinsic properties of the molecules composing each gas. The aim of these studies is to contribute to the understanding and creation of design rules for future gas sensors based on SURMOFs.
Metal-organic frameworks (MOFs) are highly porous and crystalline hybrid materials. Thin films of these structures can be integrated into various surfaces and are referred to as Surface-Supported Metal-Organic Frameworks, or SURMOFs. MOFs/SURMOFs have been gaining prominence in various applications such as gas separation and adsorption, energy conversion and storage, catalysis, and sensing. In this study, we explored the high porosity of SURMOFs for electronic detection of volatile organic compounds (VOCs). The HKUST-1 SURMOF was the material investigated in this study due to the extensive amount of literature available. The HKUST-1 SURMOF has copper (Cu²⁺) metal units connected by ligand molecules called Trimesic Acid (C₆H₃(CO₂H)₃). Although it's widely reported, its use in electronic devices based on thin films (<100 nm) is still underreported. Here, we integrated thin films of HKUST-1 SURMOF into vertical junctions fabricated through sequential steps of photolithography and thin film deposition, creating two-terminal electronic devices. The technology of tensioned metal nanomembranes was employed to enable non-invasive coupling of the upper electrode of the device. This setup allowed us to study the electrical behavior of the devices under controlled atmospheres containing VOCs such as Ethanol, Isopropyl Alcohol, Methanol, and Hexane. Electrical characterization was performed as a function of electrical potential (I-V) and as a function of time (I-t), in addition to capacitance measurements as a function of frequency. It was demonstrated here that the electrical current gain and the capacitance in the devices can be used as parameters to differentiate the detected gasses. Additionally, we determined through electrical characterization physical and chemical aspects such as diffusivity, permeability, available pore number, and intracrystalline diffusion length for each VOC during the diffusion process through the pores of HKUST-1. The obtained results were evaluated based on the intrinsic properties of the molecules composing each gas. The aim of these studies is to contribute to the understanding and creation of design rules for future gas sensors based on SURMOFs.
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Palavras-chave
Compostos Orgânicos Voláteis (VOCs), Dispositivos Eletrônicos, Estruturas metal-orgânicas, Metal-Organic Frameworks (MOFs), Surface-Supported Metal-Organic Frameworks (SURMOFs), Electronic Devices, Volatile Organic Compounds (VOCs)