Application-led, online analysis of flow synthesised Metal-Organic Frameworks (MOFs)

Abstract

Metal organic frameworks (MOFs) have numerous important large-scale industrial applications such as gas storage, energy storage, and water purification and remediation. The prospect of industrial usage means there is a need to develop efficient processes for scalable quality-assured MOF production. Flow reactors offer a promising route to scalable MOF synthesis. They feature high space-time-yields, easy automation and reduced manual handling, however quality assurance is challenging: the standard MOF analysis methods (X-ray diffraction, electron microscopy, gas adsorption etc) are slow, costly, and manually intensive, and hence difficult to apply to production scenarios. Here we present an alternative approach to MOF analysis that is quick, easily automated, and can be implemented into flow reactors for continuous assessment of flow-synthesised MOFs. Rather than look to the standard MOF characterisation methods, we developed an “application-led” quantitative test that mimicked an example end application – water remediation – by testing how well the reaction product could remove an organic dye from solution. The method was integrated into a flow reactor making HKUST-1 MOF and used to continuously monitor the reactor output (0.67 Hz frequency) in near real-time (22.4 min lag). It could clearly differentiate product made under different reaction conditions (most notably reaction stoichiometry) with the amount of dye removed corresponding to the composition of the product (HKUST-1 versus unwanted side-product). The product could be assessed “on-the-fly”, with changes in product continuously tracked as reaction conditions were systematically altered. This work will be a starting point for other application-led online analysis methods and, if combined with computer-controlled flow reactors opens the way to rapid automated exploration of MOF reaction space.