Low-cost in-situ luminescence: Opportunities for MOFs water vapor sensing

Abstract

Luminescence is the most exploited phenomena for chemosensing. Real-time measurements must be accurate and reproducible along cycles for the selection of the best sensing materials. At the same time, sample degradation by excitation-light irradiation must be kept minimal. Last but not least, expensive equipment should be avoided, whenever possible. In this work, we present a low-cost in-situ luminescence measuring experimental array designed for solid-state sensing of vapors. It allows repeated activation and subsequent guest entrance along many measuring cycles. A common halogen lamp is used as heating element for the activation of the sample under vacuum in a sealed aluminium chamber. Then, vapor guest molecules are forced into the chamber by a laboratory vacuum pump. Luminescence is LED-excited and measured by a portable reflectance probe connected to a miniature spectrometer. The chosen case study is a luminescent polycrystalline metal-organic framework composed by europium(III), zinc(II) and oxydiacetate ligand. This compound has a honeycomb porous structure that can be repeatedly activated and rehydrated. The associated structural distortion is accompanied by a remarkable variation in the luminescence profile with minimal chemical degradation or crystallinity loss. Results are analyzed and critically compared to those obtained by conventional luminescence. They show that, while conventional luminescence struggles to provide reproducible absolute results, the presented method stands as a simple, robust and trustworthy approach, in which accurate and reproducible in- situ data can be obtained along many cycles. Furthermore, the presented experimental array comparatively minimizes the light-induced degradation of the tested materials. The effect of glue-immobilizing the sample is also addressed using the presented method. • A low-cost in-situ luminescence array for solid-state sensing is designed • Performance of the new array is compared to conventional luminescence • A water-sensitive luminescent Eu-Zn MOF is explored as case-study • Accurate and reproducible data can be obtained along multiple cycles • Light-induced degradation of the tested materials is reduced