Homogenous Microporous Thin Films Assembled Using Discrete Metal-Organic Polyhedra

Abstract

Homogeneous films with tailored microporous structures are crucial for several applications, yet fabricating such films presents significant challenges. This is primarily because most microporous materials have crystal sizes in the nano- and micrometer ranges, which inevitably generates intergranular spaces in the films, thereby complicating the fabrication of these thin films. We used functionalized metal-organic polyhedra (MOPs) as discrete microporous units and assembled them into homogenous microporous films. This study focused on avoiding the generation of intergranular spaces while controlling packing parameters and film thicknesses. Initially, the MOP units, influenced by van der Waals forces between the functionalized acyl carbon chains, displayed an affinity to form spindle-shaped blocks and islands. As the MOP concentration increased, these structures self-assembled into a hexagonally packed structure with an in-plane orientation and a maximum stacking of two layers of MOPs. By contrast, un-functionalized MOPs yielded a disordered film structure formed by random agglomeration. Evidently, functionalized adipoyl chloride influences the orientation of the MOP network films with uniformly distributed micropores, effectively preventing the formation of intergranular spaces. Additionally, formaldehyde adsorption and desorption experiments revealed that the MOP network films possess superior adsorption and desorption capacities. The proposed approach signifies a breakthrough in the fabrication of homogenous microporous films.