Atomically thin monolayers of metal organic frameworks (MOFs) through implementing a Langmuir-Schaefer method

Abstract

Metal Organic Frameworks (MOFs) have been of increasing interest over the last few years. They are structures which consist of metal ions or clusters coordinated to organic ligands in order to form one-, two-, or three-dimensional networks that often exhibit high porosity, an asset that is commonly exploited in hydrogen storage, heterogeneous catalysis and photo-catalysis as well as gas separation. Additionally, MOFs are traditionally obtained through hydrothermal methods which nevertheless produce 3D structured networks. In order to exceed the boundaries of reduced dimensionality, we demonstrate a simple and effective way to form atomically thin MOFs monolayers through the use of a Langmuir-Schaefer (LS) method by combining a metal ion source with an organic linker in order to investigate and evaluate the molecular packing in the air/water interface. The proposed methodology offers accurate control over the MOFs’ film characteristics and aims at their potential implementation into tangible applications. The standard LS isotherms were collected as a function of the initial reactant volume and deposition rate and a number of spectroscopic and microscopic characterization techniques namely X-Ray Photoelectron Spectroscopy (XPS), UV-Visible Spectroscopy (UV-Vis), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED) and Atomic Force Microscopy (AFM) were performed as obtained on different substrate films. The results verified the successful formation of two-dimensional MOF as a collection of single crystalline domains, which possess different thicknesses in the range of a monolayer and therefore verified the nature of obtained MOF-structured LS films.