A General Flame Aerosol Route to Kinetically Stabilized Metal Organic Frameworks
Shuo Liu, Chaochao Dun, Jeffrey Urban, MARK SWIHART, University at Buffalo - SUNY
Abstract Number: 298
Working Group: Nanoparticles and Materials Synthesis
Abstract
The ultra-high porosity and surface area, chemical diversity, and structural stability of metal organic frameworks (MOFs) have led to intense research activity and diverse applications in fields including catalysis, gas capture/separation, biomedicine, sensors, and atmospheric water harvesting. Over the past 30 years, numerous MOF synthesis methods have been developed, such as solvothermal synthesis, hydrothermal synthesis, and electrochemical synthesis. Aerosol synthesis by spray drying/spray pyrolysis has also been reported. However, synthesis of MOFs using a flame-driven aerosol process has not yet been reported. A key challenge is that the high temperature of conventional flame aerosol processes (~2000 °C) is incompatible with the organic linkers in MOFs. Here, we demonstrate production of MOF materials in a modified flame aerosol reactor in which droplet-to-particle conversion occurs in short (~50 ms) residence times and moderate temperatures (<500 °C) that do not degrade the organic component. In contrast to conventional wet-chemistry MOF synthesis methods that employ mild, near-equilibrium conditions and often form single-crystal MOFs with high crystallinity, the far-from-equilibrium flame aerosol process yields two distinct classes of MOFs, nano-crystalline MOFs and amorphous MOFs. We demonstrate the generality of this process by producing 9 different nanocrystal MOFs and 9 different amorphous MOFs, spanning most of the key MOF subfamilies and MOF-like structures (e.g., Prussian blue analogues). More importantly, this far-from-equilibrium synthesis can integrate different metal cations within a single MOF phase, even when doing so is thermodynamically unfavorable. This can, for example, produce single-atom catalysts and bimetallic MOFs of arbitrary metal pairs. We demonstrate the flexibility of this approach by doping 4 different single-atom metal sites into different host MOFs. Furthermore, we show that reducing the noble metal component of a bimetallic MOF drives an exsolution process to form highly dispersed metal nanoclusters supported on the MOF. As a prototypical example of the power of this approach, we use exsolved Pt clusters on UiO-66-NH2 as a CO oxidation catalyst that achieves 100% CO conversion at 130 ºC. This general synthesis route opens new opportunities in MOF design and applications across diverse fields and is inherently scalable for continuous production at industrial scales.