Processable UiO-66 Metal–Organic Framework Fluid Gel and Electrical Conductivity of Its Nanofilm with Sub-100 nm Thickness

Abstract

Zr-based UiO-66 metal–organic framework (MOF) is one of the most studied MOFs with a wide range of potential applications. While UiO-66 is typically synthesized as a microcrystalline solid, we employ a particle downsizing strategy to synthesize UiO-66 as fluid gel with unique rheological properties, which allows the solution-based processing as sub-100 nm films and enhances the electrical conductivity of its pristine structure. Film thicknesses ranging from 40 to 150 nm could be achieved by controlling the spin-coating parameters. The generality of the method is also demonstrated for other Zr-based MOFs including MOF-801 and MOF-808. The impact of particle size and film thickness at the nanoscale on electrical properties of UiO-66 is shown to realize new features that are distinct from those of the bulk powder phase. An electrical insulator UiO-66 shows a significant increase in the electrical conductivity (10–5 S cm–1 compared to 10–7 S cm–1 in the bulk powder phase) when the 10 nm particles are distributed on the substrate with a thickness less than 100 nm. The findings establish a new route for processing of MOF materials as thin films with fine-tuned thickness and offer a new perspective for transport properties of Zr-based MOFs without structural modification.

Intrinsic Hole Mobility in Luminescent Metal–Organic Frameworks and Its Application in Organic Light‐Emitting Diodes

“…Two Zr‐based MOFs, Zr‐NBP and Zr‐MTB, were synthesized as a fluid gel for further fabrication as a thin‐film layer in electroluminescent devices. These syntheses were performed by solvothermal reactions of zirconium (IV) oxychloride octahydrate and the designed linkers were present in high concentration to achieve the free‐flowing gels of the targeted MOFs, as previously demonstrated with UiO‐66 [40] . Zr‐NBP represents the organic linker with a lone pair spacer and a charge‐donating moiety, while Zr‐MTB is synthesized as its analogue structure to prove our proposed concept.…”

“…These syntheses were performed by solvothermal reactions of zirconium (IV) oxychloride octahydrate and the designed linkers were present in high concentration to achieve the free-flowing gels of the targeted MOFs, as previously demonstrated with UiO-66. [40] Zr-NBP represents the organic linker with a lone pair spacer and a charge-donating moiety, while Zr-MTB is synthesized as its analogue structure to prove our proposed concept. The Zr-NBP gel is yellow, while the Zr-MTB gel appears white.…”

Metal–Organic Frameworks as Electrocatalysts

“…An obvious simple strategy to further implement MOFs in electrocatalysis would be to obtain materials with nanoscopic particle size. [47] This rather straightforward approach still needs to be researched in depth to determine which are the minimal particle sizes that can be conveniently synthesized and to determine which is the electrochemical performance and stability of the resulting electrodes. However, there are in the literature some examples suggesting the potential of this methodology.…”

Metal–Organic Frameworks as Electrocatalysts

“…However, there are in the literature some examples suggesting the potential of this methodology. [47,48] The nanometric thickness characteristic of 2D MOF crystals represent also, in a certain way, a realization of the strategy of decreasing the particle size, at least in one of the three Cartesian dimensions, to overcome the limitation of poor conductivity of MOFs making possible their use as key electrode components. 2D MOFs are considered particularly promising for OER and ORR, both reactions being the base of the coming hydrogen technology revolution.…”

“…In the case of MOFs, usual particle sizes are in the micrometric scale, making most of the intracrystalline sites not electrochemically responsive, particularly at high scan rates or fast charge/discharge processes. An obvious simple strategy to further implement MOFs in electrocatalysis would be to obtain materials with nanoscopic particle size [47] . This rather straightforward approach still needs to be researched in depth to determine which are the minimal particle sizes that can be conveniently synthesized and to determine which is the electrochemical performance and stability of the resulting electrodes.…”