Analysis of the process for the preparation of two-dimensional nanomaterials in Taylor-Couette fluidic devices

Abstract

Two-dimensional materials designate crystalline materials consisting of layers of atoms and various methods to prepare them have been developed. Among them, the liquid-phase based method has attracted attentions because of low cost and scalability. For the preparation of two-dimensional materials, Taylor-Couette (TC) flow with high shear force and enhanced heat and mass transfer was utilized in this study. As TC flow has various flow regimes according to geometric parameters and operating conditions, flow in the TC device was analyzed numerically using ANSYS Fluent by solving for velocity and pressure in the system. In addition, non-spherical particles injected numerically into the cells were tracked to determine whether TC flow could provide enough force for the exfoliation. Graphite flakes were experimentally exfoliated into graphene using the TC device. Furthermore, a TC device with double inner cylinders was fabricated based on the simulation results of transport phenomena in the two-inner-cylinder TC apparatus and the exfoliation efficiency of graphite was improved by 40%. Layered double hydroxide (LDH) was also prepared in the TC device. Enhanced heat and mass transfer in the TC reduced synthesis time of LDHs (ZnCo, NiFe) to 10 min, which is 1/15 of batch process time in a beaker. Numerical analysis showed that TC device provided uniform temperature field and high global mixing necessary for fast synthesis of LDH less than 5 layers. Moreover, a continuous process of preparing LDH in the TC reactor was developed with high production rate (46 g/h). In the continuous system, small and uniform Taylor vortices were crucial to synthesize LDH with high crystallinity and as-prepared LDH showed an overpotential of 0.26 V in oxygen evolution reaction, which showed higher performance than noble metal catalyst RuO$_2$ (0.33 V). Based on these results, the TC device can be utilized to prepare various two-dimensional materials in many applications.