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 Ti 3 C 2 T X MXene using weak acid H 3 PO 4 as etchant. We compare the Al etching capacity of H 3 PO 4 paired with various metal fluorides (LiF, ZnF 2 , CuF 2 ) to in-situ form HF. Out of all metal fluoride candidates, CuF 2 is the most effective in the etching of Ti 3 AlC 2 MAX not only due to the reaction of F − with Al but also the galvanic replacement of Cu 2+ with Al. As a result, Ti 3 AlC 2 MAX is mostly etched using H 3 PO 4 /CuF 2 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 −PO 4 , exhibiting the good aqueous dispersibility.