Comparison of Thin-Film Capacitor Geometries for the Detection of Volatile Organic Compounds Using a ZIF-8 Affinity Layer.

Their chemical diversity, uniform pore sizes, and large internal surface areas make metal-organic frameworks (MOFs) highly suitable for volatile organic compound (VOC) adsorption. This work compares two geometries of capacitive VOC sensors that use the MOF material ZIF-8 as an affinity layer. When using a permeable top electrode (thickness < 25 nm), the metal-insulator-metal (MIM) sandwich configuration exhibits superior sensitivity, an improved detection limit, and a smaller footprint than the conventional interdigitated electrode layout. Moreover, the transduction of VOC adsorption in ZIF-8 via MIM capacitors is more sensitive to polar VOCs and provides better selectivity at high loadings than gravimetric and optical transductions.

Fabrication of 3D Oriented MOF Micropatterns with Anisotropic Fluorescent Properties.

Micropatterning crystalline materials with oriented pores is necessary for the fabrication of devices with anisotropic properties. Crystalline and porous metal-organic frameworks (MOFs) are ideal materials as their chemical and structural mutability enables precise tuning of functional properties for applications ranging from microelectronics to photonics. Herein, a patternable oriented MOF film is designed: by using a photomask under X-ray exposure, the MOF film decomposes in the irradiated areas, remaining intact in the unexposed regions. The MOF film acts simultaneously as a resist and as functional porous material. While the heteroepitaxial growth from aligned Cu(OH)2 nanobelts is used to deposit oriented MOF films, the sensitivity to radiation is achieved by integrating a brominated dicarboxylate ligand (Br2 BDC) into a copper-based MOF Cu2 L2 DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane; L = BDC/Br2 BDC). The lithographed samples act as diffraction gratings upon irradiation with a laser, thus confirming the quality of the extended MOF micropattern. Furthermore, the oriented MOF patterns are functionalized with fluorescent dyes. As a result, by rotating the polarization angle of the laser excitation, the alignment of the dye in the MOF is demonstrated. By controlling the functional response to light, this MOF patterning protocol can be used for the microfabrication of optical components for photonic devices.

Vapor-Assisted Conversion of Heterobimetallic Titanium-Organic Framework Thin Films.

Heterobimetallic Metal-Organic Frameworks (MOFs) synergically combine the properties of two metal ions, thus offering significant advantages over homometallic MOFs in gas storage, separation, and catalysis, among other applications. However, these remain centered on bulk materials, while applications that require functional coatings on solid supports are not developed. We explore for the first time the deposition of heterometallic Ti-based MOF thin films using vapor-assisted conversion on substrates functionalized with a self-assembled monolayer. Furthermore, metal-induced dynamic topological transformation allows the conversion of MUV-10(Ca) films into MUV-101(Co) and MUV-102(Cu), which is not accessible through direct synthesis, without morphologically altering the films. These nonconventional thin-film deposition techniques enable homogeneous and crystalline coatings of heterometallic titanium MOFs that also maintain their corresponding porosity.