Biocompatible and Oxidation-Resistant Ti₃C₂T_x MXene with Halogen-Free Surface Terminations

Surface chemistry influences not only physicochemical properties but also safety and applications of MXene nanomaterials. Fluorinated Ti₃C₂T_x MXene, synthesized using conventional HF-based etchants, raises concerns regarding harmful effects on electronics and toxicity to living organisms. In this study, well-delaminated halogen-free Ti₃C₂T_x flakes are synthesized using NaOH-based etching solution. The transversal surface plasmon mode of halogen-free Ti₃C₂T_x MXene (833 nm) confirmed red-shift compared to conventional Ti₃C₂T_x (752 nm), and the halogen-free Ti₃C₂T_x MXene has a different density of state by the high proportion of –O and –OH terminations. The synthesized halogen-free Ti₃C₂T_x exhibits a lower water contact angle (34.5°) and work function (3.6 eV) than those of fluorinated Ti₃C₂T_x (49.8° and 4.14 eV, respectively). The synthesized halogen-free Ti₃C₂T_x exhibits high biocompatibility with the living cells, as evidenced by no noticeable cytotoxicity, even at very high concentrations (2000 µg mL⁻¹), at which fluorinated Ti₃C₂T_x caused ≈50% reduction in cell viability upon its oxidation. Additionally, the oxidation stability of halogen-free Ti₃C₂T_x is enhanced unexpectedly, which cumulatively provides a good rationale for pursuing the halogen-free routes for synthesizing MXene materials for their uses in biomedical and therapeutic applications.