Homogenous Microporous Thin Films Assembled Using Discrete Metal–Organic Polyhedra

Abstract

Homogeneous films with tailored microporous structures are crucial for several applications; however, 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. In this study, functionalized metal–organic polyhedra (MOPs) are used as discrete microporous units and assembled into homogenous microporous films. The generation of intergranular spaces is avoided while controlling packing parameters and film thicknesses. Initially, the MOP units, influenced by van der Waals forces between carbon chains of functionalized adipic acids, display an affinity to form spindle-shaped blocks and islands. As the MOP concentration increases, 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 form a disordered film structure owing to random agglomeration. Evidently, functionalized adipic acid 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.