Publication date: 21st July 2025
MXenes are novel 2D nanomaterials composed of alternating layers of an early transition metal and a carbide or nitride.[1] The top and bottom external surfaces of MXenes consist of metallic sheets covered by surface functional groups, whose nature depends on the preparation method.[2] Multilayered MXenes are formed in the early stages of synthesis by etching away the “A layers” (e.g., aluminum) from the parent MAX phase. Structural defects generated during etching create active sites that can serve as catalytic centers.[3] In this study, Ti₃C₂ samples prepared from Ti₃AlC₂ via NH₄F-HCl etching and post-treated with DMSO expansion, ultrasound exfoliation, thermal annealing (500°C), and surface modifications were used to catalyze the guanylation of symmetrical carbodiimides with amines, forming guanidines and dialkylureas. The initial reaction rates between N,N’-diisopropylcarbodiimide and p-toluidine correlated with the density of weak acid sites on Ti₃C₂, identifying these sites as active centers. The most active sample exhibited turnover numbers and frequencies of 101 and 114 h⁻¹, ranking Ti₃C₂ among the most efficient noble metal-free guanylation catalysts. Upon reuse, Ti₃C₂ gradually deactivates while maintaining crystallinity. Deactivation results from product deposition and increased oxygenated surface groups but can be partially reversed through thermal desorption. These findings underscore the potential of Ti MXenes as solid catalysts for organic reactions,[4] particularly those involving amine activation.
Financial support by Spanish Ministry of Science and Innovation (CEX-2021-001230-S and PDI2021-0126071-OB-CO21 funded by MCIN/AEI/ 10.13039/501100011033), Generalitat Valenciana (Prometeo 2021/038 and Advanced Materials programme Graphica MFA/2022/023 with funding from European Union NextGenerationEU PRTR-C17.I1) and European Commission through the ERC Adv. Grant 101141466 DISCOVERY is gratefully acknowledged. We also thank MICIN for the Severo Ochoa Excellence Research Grant.
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