(231e) Autocatalytic Initiation Followed By Oriented Attachment Governs the Nucleation and Crystal Growth of MOF Crystals
AIChE Annual Meeting
Tuesday, November 9, 2021 - 9:27am to 9:48am
Metal-Organic Frameworks (MOFs) have gained significant importance in the field of catalysis, membrane separations, adsorption, and drug delivery. The wide spectrum of the applicability of MOFs arises due to the underlying crystal structure. In such crystal structures, a metal node forms a template for the attachment of the organic linker resulting in the formation of an infinite network. The crystal structure is further stabilized due to the reorientation of the crystalline network yielding highly symmetric and porous crystalline structures. However, the limited understanding of a large number of reactions involved and the subsequent growth of MOF crystals prevents effective control and rapid synthesis of the MOFs. Furthermore, it is observed that MOF reactions are surface stabilized and follow a non-classical nucleation mechanism. To achieve greater control on the crystallization of MOF and to design better strategies for synthesizing theoretically predicted MOFs, it is necessary to obtain the quantitative contribution of all the reactions which occur during the synthesis. In this work, we present a simple microkinetic approach requiring minimal computational power to obtain rate contribution of initiation, chain growth, step growth, and termination reactions. The approach also validates that MOF initiation follows an autocatalytic mechanism and reproduces experimental crystalline volume fraction and grain size dynamics obtained from SAXS/WAXS studies of UiO-66 synthesis. The microkinetic rate equations effectively capture the rate-limiting step of the MOF synthesis and allow calculations of nucleation and growth rates as a function of reaction extent. Results suggest that the autocatalytic initiation followed by oriented attachment governs the nucleation and growth of MOF crystals.