Environment-friendly synthesis of Ti3C2TX 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 Ti3C2TX 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.