The synthesis of Ti₃C₂T_x (and Ti₂CT_x alike) MXenes is performed with a new etching environment (FeF₃/HCl). Significant differences in terms of surface functionalization (including the insertion of iron cations between the MXene sheets), morphology, nature of impurities, water intercalation and reactivity are obtained in comparison with samples prepared by conventional HF or LiF/HCl etching methods. In particular, the new synthesis method allows modifying the reactivity of Ti₃C₂vs. water with improved selectivity towards the formation of TiO₂ anatase nanoparticles on the MXene sheets whereas rutile TiO₂ nanoparticles are favoured by the LiF/HCl method. The role of the Feⁿ⁺ and Al³⁺ cations inherent to this synthesis process in the inhibition of the anatase to rutile transformation is shown to be a key parameter. In addition, the MXene oxidation rate in water is also increased when the material is prepared with FeF₃/HCl compared to the LiF/HCl method owing to the surface modification of the MXene during the etching step. This oxidation rate can easily be tuned by adjusting the duration of immersion. This work expands the number of etching methods to form MXenes while offering new opportunities in the rationalized design of MXene@TiO₂ nanocomposite structures for future applications.