(335d) Analyzing the Vibrational Spectra of ZIF-8: Identification of IR Peaks and Defect Signals

Surface chemistry plays a crucial role in determining the functionality of Zeolitic Imidazolate Framework-8 (ZIF-8), a material with vast potential in gas separation and serving as a prototype for various other ZIFs. Its applications span from sensors to catalysis and lithography. ZIF-8, composed of zinc coordinated with 2-methylimidazolate (2mIm), is synthesized using various methods to manipulate its crystal characteristics and integration into nanocomposites.

Despite being envisioned as having a defect-free structure, deviations occur due to defects such as missing 2mIm, zinc, and physically adsorbed 2mIm in pores, which significantly influence its performance and stability. Infrared (IR) spectroscopy is utilized to detect these defects, although interpretations vary across the literature. Our study employs experimental IR spectroscopy alongside first-principles molecular dynamics simulations to examine ZIF-8's vibrational spectra, with a particular focus on defect-induced signals. X-ray Photoelectron Spectroscopy (XPS) is also utilized to investigate the top 10 nm of the material's surface.

We have highlighted the occurrence of defects in the synthesis of ZIF-8 films/membranes, which are crucial in gas separation applications. One notable defect we identified is the formation of SiOx, resulting from silicon grease exposure in vacuum reactors. This phenomenon is pertinent to all materials synthesized under vacuum conditions, as vacuum grease residues can persist long after application.

By reconciling conflicting interpretations of IR spectra and identifying defect signals, we aim to achieve a comprehensive understanding to refine the quality control and design of ZIF-8-based materials for diverse applications.