Theoretical interpretation on lead adsorption behavior of new two-dimensional transition metal carbides and nitrides

The alkalization-intercalated MXene (Alk-MXene: Ti3C2(OH)2) has recently confirmed as a new and effective material for removing Pb heavy metal. Herein, taking into account of the complexity and diversity of MXenes, the Pb adsorption behavior of different MXenes with the highest valuable applied structure of M2X (OH)2 (M = Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and X = C or N) has been systemically investigated by first principles calculations utilizing the generalized gradient approximation with the density functional theory, which paves a desirable trajectory for the applications of MXenes. Basically, the formation energies of M2N(O2H2−2xPbx) are lower than those of M2C(O2H2−2xPbx), suggesting the substitution of N is more effective for the Pb adsorption in contrast to C due to the different valence electron numbers between C and N atoms. In addition, the results show that the Ti2C(OH)2 is the most favorite one for the lowest mass fraction to lead removal. Notably, both Sc2C(OH)2 and Zr2C(OH)2 structures don’t have the ability of Pb removal. The kinetics of the lead removal was elucidated on the variation of potential wells by virtue of the density of states and electron localization function.