MXenes, a rapidly growing family of 2D materials are ultrathin layered transition metal carbides, nitrides, and carbonitrides with the typical formula represented as Mn+1XnTx are obtained by exfoliating the interleaved “A” layer from a precursor MAX phase. The characteristic features of MXenes include metallic conductivity, solution processability, hydrophilicity, and presence of surface terminations. These characteristics enable the use of MXenes in aqueous systems possible, however, studies aiming to use MXenes in aqueous and especially biological systems are limited. The fundamental to evaluate the interactions of MXenes with the environment and biological systems is to understand their behavior in biological buffers. We investigate the structural and functional properties of Ti3C2Tx (Tx = F, O, OH) MXenes in N-substituted biological buffers like N-(2-Hydroxyethyl)-piperazine-N’-ethanesulfonic acid (HEPES) and 3-(N-morpholino)-propane sulfonic acid (MOPS). The optical properties of MXenes when dissolved in solution reveal a striking impact on their absorption spectra in the presence of all buffer molecules. XRD and electrical conductivity measurements of MXene films exposed to buffer molecules show that these molecules intercalate between MXene nanosheets and affect their electrical conductivity. The interactions of Ti3C2Tx MXenes with buffer molecules are structure-dependent and are partially reversible, suggesting the interactions are driven by weak bonding like hydrogen bonding and/or electrostatic interactions. This study is a significant step toward understanding the stability of MXenes in aqueous media and the ability to predict their interactions with nitrogen-containing molecules and larger biomolecules. The nature of the interactions between MXenes and buffer molecules, revealed in our study, opens new possibilities for developing MXenes containing chemical sensing thin films for use in aqueous media.

Molecular interactions of Ti3C2 MXenes with N-substituted zwitterionic biological buffers and their impact on MXenes' properties

ACS Spring 2022

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