Lab on optical fiber: surface nano-functionalization for real-time monitoring of VOC adsorption/desorption in metal-organic frameworks

Abstract

Metal-organic framework (MOF) nanomaterials are emerging porous coordinative polymers with large surface area and high porosity. Their application scenarios highly depend on adsorption/desorption dynamics of guest molecules in the framework. For representative ZIF-8 with framework flexibility, the study of molecule transportation in the pore channels of ZIF-8 will address the ambiguity of unclear application scenarios. In this study, the integration of lab-on-fiber technology and nanotechnology are demonstrated for real-time monitoring of adsorption/desorption dynamics of heterocyclic volatile compounds (VOCs) with kinetic diameters larger than the window aperture of ZIF-8. The in-line fiber interferometer with cascaded long-period gratings is used to monitor the real-time refractive index change of VOC adsorption/desorption. The structure-effect relationship between guest VOCs and framework flexibility is analyzed. It shows that the adsorption dynamics is highly related to the molecular geometry and kinetic diameter. The framework flexibility results in the trapping of guest VOCs toluene, pyridine, and tetrahydrofuran in the frameworks. The methanol adsorption/desorption is an effective strategy for the fast desorption of trapped residual VOCs in the framework. Finally, we conceptually demonstrated the real-time monitoring of trace toluene enrichment using ZIF-8 for indoor air purification. This study paves the way for the in-depth understanding of framework flexibility for MOF’s application.

A vapochromic dye/graphene coated long-period fiber grating for benzene vapor sensing

“…38–40 At the same time, real-time and remote sensing can be achieved with the benefit of advanced optical fiber sensing networks. 41…”

“…[38][39][40] At the same time, real-time and remote sensing can be achieved with the benefit of advanced optical fiber sensing networks. 41 In optical fibers, the different modes of light are orthogonal and do not interfere with each other. A long-period fiber grating (LPFG) is a device with periodic refractive index change.…”

Recent progress on MOF-based optical sensors for VOC sensing

“…With such, the exposure of guest vapours induced changes in the refractive index of the cladding that shifted the attenuation band. 162,[182][183][184] Hromadka et al have reported a LPG-based sensor working at phase-matching turning point presenting a high sensitivity for ethanol and acetone. 184,185 In another study, Chiang et al developed a fibre interferometer with pair of cascaded LPGs, where ZIF-8 was coated on the surface of the cladding.…”

Plasmonic crescent nanoarray-based surface lattice resonance sensor with a high figure of merit

“…LSPR is the collective oscillation of free electrons in metal nanoparticles/nanostructures irradiated by incident light at a specific frequency. It is widely applied in physical, 1,2 chemical 3,4 and biological 5–7 sensing due to sensitivity to the surrounding refractive index and enhancement of the localized electric field. Meanwhile, metal nanoparticle/nanostructure-based LSPR is more suitable for integration with miniaturized platforms (especially optical fibre tip (OFT)); therefore it is possible for achieving a plug-and-play remoting sensing probe which is used in harsh and restricted environments ( e.g.…”