DFT Study of CationSelection Mediated by FunctionalizedMOenes as Anode Materials for Water Desalination

In this work, we performed a Density Functional Theory (DFT) study on the 2H- and 1T-MOene monolayers and their functionalization with F, Cl, and Br. The functionalized monolayers, 2H–Ti₂O–X₂ and 1T–Ti₂O–X₂ (X₂ = F, Cl, and Br), were evaluated as potential trapping agents for several ions present in seawater and brackish water. Our analysis of the adsorption behavior revealed that Na, K, and Ca ions strongly adsorb at the top Ti sites, with the 2H–Ti₂O–F₂ and 1T-Ti₂O–F₂ monolayers showing the highest affinity. In all cases, the ions transfer charge to the monolayers. In contrast, Mg ions bond weakly to all functionalized monolayers but still share charge (∼0.2<i>e</i>). Chlorine species (Cl) also exhibit weak bonding with all of the functionalized monolayers, as confirmed by the noncovalent interactions index. Interestingly, H₂O adsorption also occurs through weak van der Waals forces, suggesting that these two-dimensional (2D) materials could be promising selective cation trapping agents with potential applications as anode materials for capacitive deionization devices.