Organic functionalization of Ti3C2Tx MXene for urea adsorption in aqueous solutions

• Main Authors: Yen, Zhihao, Bradley, David G., Wang, Yamin, Hanna, John V., Lam, Yeng Ming
• Other Authors: School of Materials Science and Engineering
• Format: Article
• Language: English
• Published: 2024
• Subjects: Engineering; Ti3C2Tx, MXene; Urea adsorption; Solid state NMR; XPS; Amino acid; Surface functionalization
• Online Access: https://hdl.handle.net/10356/174212
• Institution: Nanyang Technological University

Two-dimensional MXene materials with the composition Ti3C2Tx, where T represents a surface termination species, have become popular for many applications due to their large surface areas, unique mechanical and electrochemical properties, and the ability to create thin single-layer systems. The high surface area and hydrophilicity of this material renders it a viable option as a molecular adsorber in aqueous solutions. In recent studies using a simplified synthesis method called minimally intensive layer delamination (MILD), we have shown how the surface functionalization (T) affects the material's ability to adsorb urea. Here we present a new approach to enhancing urea adsorption by functionalizing the surface with amino acid and ‘amino acid-like’ moieties such as glutamic acid, lysine, and L-dopa. The differences between these functionalized MXenes are probed using PXRD, XPS, FTIR/Raman and solid state 13C MAS NMR, and appear to emanate from distinct steric bonding configurations between each amino acid and the MXene surface, thus facilitating a variety of organic-urea interactions in these regions. In particular, solid state 13C MAS NMR offers a detailed picture of each amino acid’s bonding configuration based on peak shifting/broadening due to paramagnetic interactions with the Ti3+ positions within the MXene surface. Furthermore, corresponding solid state 7Li MAS NMR measurements verified that the surface functionalization does, in fact, deintercalate Li+ ions, not only from Cu functionalization derivatives, but also for particular organic-functionalized systems. It was found that glutamic acid functionalized MXene has a maximum urea adsorption capability of 23.5 mg/g in aqueous media. This adsorption capacity was found to be superior compared to previous studies on using pristine MXene for urea adsorption.