Environment-friendly synthesis of Ti₃C₂T_X MXene by etching and galvanic reactions for Al removal of Ti₃AlC₂ MAX

Although MXene is acknowledged as next generation two-dimensional (2D) nanomaterials, in general, MXene has been obtained by using hazardous and corrosive etching agents such as HF and HCl. Therefore, in the present study, we report on the environment-friendly synthesis of 2D Ti₃C₂T_X MXene using weak acid H₃PO₄ as etchant. We compare the Al etching capacity of H₃PO₄ paired with various metal fluorides (LiF, ZnF₂, CuF₂) to in-situ form HF. Out of all metal fluoride candidates, CuF₂ is the most effective in the etching of Ti₃AlC₂ MAX not only due to the reaction of F⁻ with Al but also the galvanic replacement of Cu²⁺ with Al. As a result, Ti₃AlC₂ MAX is mostly etched using H₃PO₄/CuF₂ within only 4 h reaction and is completely etched in 12 h reaction. After etching, the Cu intercalated between MXene layers is extracted using maleic acid forming a Cu-maleic acid complex to produce exfoliated 2D MXene nanosheets. The exfoliated MXene contains mainly −F, −O, –OH surface terminations and a small portion of −PO₄, exhibiting the good aqueous dispersibility.