(8e) Accelerated and Scalable Synthesis of Mfu-4l in Flow

Metal-organic frameworks (MOFs) have emerged as promising functional materials for a wide range of applications, including atmospheric water harvesting. Benefitting from high surface area/porosity and excellent structural tunability, MOFs have demonstrated their potential to provide universal access to water, aiming to solve the global water shortage. In particular, MFU-4l, a zinc triazolate-based MOF, is considered an ideal water sorbent, offering a high water uptake capacity (~1 g_water/g_MOF) and a sharp water uptake step at a relative humidity of 65%, making it easily deployable across different environments.

Despite its intriguing properties, implementation of MFU-4l for a water-harvesting device remains challenging owing to mass and heat limitations from conventional batch solvothermal synthesis, prohibiting high productivity (kgm^-3day^-1) and resulting in poor control over nucleation and growth of MOFs. Especially in MFU-4l synthesis, the organic linker, H₂BTDD, has poor solubility in N,N-dimethylformamide (DMF), and is insoluble in other solvents. Therefore, massive DMF requirement in a large-scale synthesis exacerbates poorly controlled temperature, contributes to high material cost, and raises a safety concern due to its hazardous nature.

To overcome the abovementioned limitations, microscale flow strategies that offer unique benefits (i.e., intensified heat transfer, tunable mass transfer rates, enhanced safety) have been utilized for high-throughput synthesis of MFU-4l. In this work, we present a scalable continuous-flow synthesis approach, demonstrating an order of magnitude higher productivity than a batch reactor. Process parameters (i.e., temperature, residence time, linker concentration, flowrate) were screened to optimize synthetic conditions, resulting in process intensification. Then, the optimized condition was used to study the scale-out approach (i.e., numbering up) which scales linearly with productivity. Furthermore, we demonstrate solvent recycling and repeatable synthesis of MFU-4l with consistent crystallinity and surface area. Then, mass and energy balance on a kg-scale production are analyzed using ASPEN.