Self‐Assembly and Oriented Growth of Conductive Ni‐CAT‐1 Metal‐Organic Framework at Solid–Liquid Interfaces

Abstract

Two‐dimensional (2D) conductive metal‐organic frameworks (MOF) represent a unique class of electrode materials with high capacity and power density. Understanding molecular mechanisms and pathways for heterogeneous nucleation of 2D π‐conjugated MOFs is highly desirable for controlling the structure and properties of conductive MOFs on solid substrates. Herein, a systematic study of nucleation and growth of 2D π‐conjugated Ni‐catecholate (Ni‐CAT‐1) MOFs on highly oriented pyrolytic graphite (HOPG) and copper substrates is reported. It is discovered that the nucleation density and growth kinetics of the MOF film can be controlled by varying substrate interactions with the organic linker. Specifically, π–π interactions between the linker and the HOPG dictate lower nucleation density, whereas π–metal interactions between the linker and the copper substrate dictate faster nucleation and higher nucleation densities. These studies reveal the key mechanism for Ni‐CAT‐1 nucleation on different surfaces and provide insights into interfacial control over the growth of other 2D π‐conjugated MOF films on solid substrates to inform synthesis of functional materials.

Role of Solvent in the Oriented Growth of Conductive Ni‐CAT‐1 Metal‐Organic Framework at Solid–Liquid Interfaces

“…Ni‐CAT‐1 nanorods synthesized in pure water were vertically aligned on HOPG ( Figure a), in good agreement with previous studies. [ 12b,15 ] When the solvent was changed to a binary mixture of water and DMF, the orientation of Ni‐CAT‐1 nanorods on HOPG was altered whereas no significant changes in the morphology of Ni‐CAT‐1 crystals were found under all reaction conditions. The increase in DMF content from 10 vol% to 20 vol% in a binary solvent introduced the disorder in nanorod orientation.…”

“…The out‐of‐plane scan of Ni‐CAT‐1 on HOPG synthesized in pure water exhibited a very small peak corresponding to the (100) plane and a sharp and intense peak for the (002) plane, indicating that (00 l ) planes are aligned parallel to the HOPG surface. [ 15 ] As the fraction of DMF in the binary solvent increased, the relative intensity of two characteristic peaks corresponding to (100) and (002) planes ( I (100) / I (002) ) increased, implying that preferential alignment of (00 l ) planes on the HOPG surface weakens in the presence of DMF. [ 17 ] These observations can be explained by the disruption of water structure at the HOPG interface in the presence of DMF.…”

“…For example, the nature of interfacial interactions between substrates and ligand molecules of MOFs directs how the interfacial layer assembles controlling subsequent MOF growth. [ 15 ] Although the role of solvent in homogeneous nucleation including the coordination between MOF precursor and solvent has been intensively investigated [ 16 ] and some reports have shown that solvent polarity [ 17 ] and composition [ 12a,18 ] can affect the arrangement of MOF crystals on substrates, the fundamental mechanism of a critical role of solvent in heterogeneous nucleation is still poorly understood.…”

Metal–organic frameworks on versatile substrates

“…Meanwhile, the substrate's high hydrophobicity ensures the MOF structure's stability, which can be used in subsequent applications. Following this, different carbon-based materials such as graphene, 152–154 graphene oxide, 155–158 graphite, 159,160 MWCNTs, 129,161 carbon matrix, 162 MXenes, 163–166 and Ti 3 C 2 MXene 167,168 have been selected as substrates for the fabrication of MOFs. Other self-designed substrate, like carbon substrate, 170 in situ annealing of plants, 171 nitrogen templates, and sulfur templates, 172 can also be used as matrices.…”