(141b) Titanium Carbide Mxene for PFAS Removal: Exploring the Influence of Surface Chemistry on Efficacy

Titanium carbide MXene is characterized by its unique surface chemistry, represented by the presence of abundant functional groups including =O, -OH, and -F. Tailoring the surface chemistry of MXene is a promising route to boost PFAS adsorption. However, the relationship between MXene surface chemistry and its ability to adsorb PFAS is obscure and yet to be explored. In this study, we designed two MXenes, including one mainly consisting of -OH and -F groups, denoted as Ti₃C₂(F)_x(OH)_y, and the second one terminated by =O, -OH, and -F, denoted as Ti₃C₂(F)_x(OH)_y(O)_z. Then, the performance of these two MXenes was assessed for the removal of perfluorooctane sulfonic acid (PFOS) from water, investigating variations in pH, PFAS concentrations, and contact time. Ti₃C₂(F)_x(OH)_y was able to remove 97% of PFOS after 5 hours of adsorption, while Ti₃C₂(F)_x(OH)_y(O)_z resulted in the removal of only 65%. Advanced characterizations have been utilized to explain the stark difference in performance, including SEM, AFM, EDS, XPS, and contact angle measurement. The removal of PFOS achieved by Ti₃C₂(F)_x(OH)_y is mainly attributed to the presence of a higher concentration of -F and -OH groups on its surface. The fluorine groups on Ti₃C₂(F)_x(OH)_y enhance its interaction with PFOS via fluorine-fluorine bonding. In addition, hydroxyl groups effectively adsorb PFOS through hydrogen bonding. Despite the presence of -F and -OH groups on Ti₃C₂(F)_x(OH)_y(O)_z, they exist at a lower concentration than those on Ti₃C₂(F)_x(OH)_y, and therefore, they are not enough to interact with all PFOS present in the solution. Consequently, the removal of PFOS by MXene may involve other weaker interactions such as van der Waals forces, reducing removal efficiency and increasing treatment time.