Continuous Flow Synthesis of MOF/Nanocarbon Composites

Abstract

Zirconium-based metal–organic frameworks (Zr-MOFs), such as UiO-66-NH2, exhibit high surface areas and chemical stability, while graphene provides unique electrical properties and high mechanical strength. Hence, nanocomposites that integrate graphene into Zr-MOFs can enhance interfacial charge transfer and offer new functionalities for porous materials. However, controlled and cost-effective synthesis of high-quality Zr-MOF/graphene nanocomposites has not been demonstrated. Here, we report a supercritical CO2 (scCO2)-assisted continuous-flow process for depositing nanometer-scale UiO-66-NH2 layers on reactive, carboxylic-modified graphene aggregates (CGA). This approach is enabled by rapid nucleation and growth of UiO-66-NH2 (~1 min) and yields 3.5 g h-1 of MOF/CGA nanocomposites in a lab-scale 150 cc reactor. CGA, produced by a chamber-explosion method followed by surface modification to add carboxylic acid groups, was continuously mixed with Zr-MOF precursors in a scCO2 reactor, resulting in a MOF/CGA composite with near-uniform 10-20-nm-thick MOF coating. The influence of graphene loading (5 – 30 wt%) on the structural, physical, electrical, and chemical properties of the composites was examined. The resulting materials exhibit intimate contact between MOF and graphene layers, high BET surface areas, and enhanced photothermal responses under solar illumination, highlighting their potential for photocatalytic and other applications.