Microfluidic Approach toward Continuous and Ultrafast Synthesis of Metal–Organic Framework Crystals and Hetero Structures in Confined Microdroplets

Abstract

Herein, we report a novel nanoliter droplet-based microfluidic strategy for continuous and ultrafast synthesis of metal-organic framework (MOF) crystals and MOF heterostructures. Representative MOF structures, such as HKUST-1, MOF-5, IRMOF-3, and UiO-66, were synthesized within a few minutes via solvothermal reactions with substantially faster kinetics in comparison to the conventional batch processes. The approach was successfully extended to the preparation of a demanding Ru3BTC2 structure that requires high-pressure hydrothermal synthesis conditions. Finally, three different types of core-shell MOF composites, i.e., Co3BTC2@Ni3BTC2, MOF-5@diCH3-MOF-5, and Fe3O4@ZIF-8, were synthesized by exploiting a unique two-step integrated microfluidic synthesis scheme in a continuous-flow mode. The synthesized MOF crystals were characterized by X-ray diffraction, scanning electron microscopy, and BET surface area measurements. In comparison with bare MOF-5, MOF-5@diCH3-MOF-5 showed enhanced structural stability in the presence of moisture, and the catalytic performance of Fe3O4@ZIF-8 was examined using Knoevenagel condensation as a probe reaction. The microfluidic strategy allowed continuous fabrication of high-quality MOF crystals and composites exhibiting distinct morphological characteristics in a time-efficient manner and represents a viable alternative to the time-consuming and multistep MOF synthesis processes.

Synthesis of MIL-100(Fe) at Low Temperature and Atmospheric Pressure

“…The high stability is one of the most important features for practical application. On the other hand, the BET specific surface area and pore volume for the current case are moderate compared to the results reported in the literature, probably due to the different purification and crystallinity [8,17], as well as the different p/p 0 range for BET area calculation. Moreover, it should be admitted that it is difficult to handle HF due to its harmful nature, although it plays an important role in the synthesis of MIL-100(Fe).…”

“…It has been clarified that BET specific surface areas and pore volumes of MOFs synthesized by different methods depend on the degree of their purification as well as their crystallinity [8,17]. This is often due to the presence of residual impurities such as nonreacted carboxylic acids in the pores and interparticle grains, coordinated carboxylates, and/or inorganic cations or anions from starting metal salts, besides the content of amorphous phases or other crystalline impurities.…”

On the Synthesis and Characterization of Lanthanide Metal-Organic Frameworks

“…As seen, all the MOF samples had similar thermal stability [14,15]. The first mass loss in DTG curves was observed at about 120 °C (except for CeMOFs at ~200 °C).…”

Interfacial Phenomena and Fluid Control in Micro/Nanofluidics

“…24,57 On the other hand, droplet flow can encapsulate molecules or some substrate particles within the droplets. [58][59][60][61][62][63][64][65] Many well-written review articles have been published on the subject of droplet flow. 9,[66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81] In this review, parallel two-phase flow 6,[82][83][84][85] is considered with respect to the roles of liquid interfaces for the sake of simplified physical descriptions.…”