Construction of Quasi-Ordered Metal-Organic Frameworks Superstructures via Colloidal Assembly of Anisotropic Particles for Selective Organic Vapor Sensing

Abstract

Colloidal assembly of anisotropic particles holds great promise for achieving diverse packing geometries and unique photonic properties. One intriguing candidate for anisotropic self-assembly is colloidal metal-organic frameworks (MOFs), which possess remarkable characteristics including substantial surface areas, tunable chemical properties, a wide range of structural variations, and diverse polyhedral shapes. In this study, the colloidal assembly of nearly spherical and polyhedral MOFs particles to form quasi-ordered photonic superstructures was investigated. Specifically, monodisperse near-spherical ZIF-8 (NSZIF-8) and rhombic dodecahedron ZIF-8 (RDZIF-8) colloidal nanoparticles were synthesized as the fundamental building blocks. These nanoparticles are employed to construct MOFs-based self-assembled superstructures that exhibit thin-film interference optical properties. Importantly, these superstructures demonstrate exceptional responsiveness to gaseous homologues and isomers with approximate refractive indices. The dynamic reflection spectral patterns exhibited by these superstructures provide valuable insights into the diffusion rates and surface tension characteristics of the target solvents. These findings underscore the potential of MOFs-based superstructure thin films to discriminate between physiochemically similar solvents, opening new avenues for applications in various fields.

Keywords: colloidal assembly; metal organic frameworks; polyhedral nanoparticles; vapor sensors.

Figure 1

Synthesis scheme of ZIF-8 particles and the quasi-ordered photonic superstructures based on ZIF-8 particles.

Figure 2

(a–c) SEM images of ZIF-8 particles generated after 12 min, 1 h, and 24 h; scale bar: 1 µm; inset: TEM image of corresponding particles; scale bar: 10 nm. (d) The XRD patterns of ZIF-8 particles generated after different reaction times. (e) N₂ adsorption/desorption isotherm of the NSZIF-8 and RDZIF-8 particles. (f) TG curve of the NSZIF-8 and RDZIF-8 particles, under air atmosphere, 5 °C/min.

Figure 3

(a) Top-view SEM images of RDZIF-8-based q-OPSs films. Scale bar: 1 µm in the figure and 500 nm in the inset. (b) Top-view SEM images of NSZIF-8-based q-OPSs films. Scale bar: 1 µm. (c) Reflection spectrum of different thickness RDZIF-8-based q-OPSs films and corresponding microphotographs. (d,e) Cross-section SEM images of RDZIF-8-based q-OPSs films and NSZIF-8-based q-OPSs films. Scale bar: 1 µm. (f,g) Schematic diagram of the cross section of RDZIF-8-based q-OPSs films and NSZIF-8-based q-OPSs films. (h) Reflection spectrum of NSZIF-8-based q-OPSs films and responding microphotograph.

Figure 4

(a) The static reflection spectrum of RDZIF-8-based q-OPSs detected methanol, ethanol, propanol, isopropanol, n-butanol, t-butanol, acetone, acetonitrile, DMF, and DMSO, respectively. (b) Recycling tests of the RDZIF-8-based q-OPSs exposed to N₂ and saturated EtOH vapor alternatively. (c) Time-dependent reflection peak position shifts of the RDZIF-8-based q-OPSs on exposure to saturated methanol, ethanol, propanol, isopropanol, n-butanol, t-butanol, acetone, acetonitrile, DMF, and DMSO, respectively (d) Kinetic response of the RDZIF-8-based q-OPSs sensors to DMF vapors with concentrations of 20/100/1000 ppm. (e) Schematic diagram of organic vapor sensing device.

Figure 5

The dynamic color-filled contour maps of reflection spectrum of RDZIF-8-based q-OPSs in response to different organic vapors: (a) methanol, (b) ethanol, (c) propanol, (d) isopropanol, (e) n-butanol, (f) t-butanol, (g) acetone, (h) acetonitrile, (i) DMF, and (j) DMSO.