Abstract
Using a multiscale computational scheme, we study the trends in distribution and composition of the surface functional groups −O, −OH, and −F on two-dimensional (2D) transition metal carbides and nitrides (MXenes). We consider Ti2N, Ti4N3, Nb2C, Nb4C3, Ti2C, and Ti3C2 to explore MXenes with different chemistry and different number of atomic layers. Using a combination of cluster expansion, Monte Carlo, and density functional theory methods, we study the distribution and composition of functional groups at experimentally relevant conditions. We show that mixtures of functional groups are favorable on all studied MXene surfaces. The distribution of functional groups appears to be largely independent of the type of metal, carbon, or nitrogen species and/or number of atomic layers in the MXene. We further show that some properties (e.g., the work function) strongly depend on the surface composition, while others, for example, the electric conductivity, exhibit only a weak dependence.
Highlights
Using a multiscale computational scheme, we study the trends in distribution and composition of the surface functional groups −O, −OH, and −F on two-dimensional (2D) transition metal carbides and nitrides (MXenes)
M5X4.9 optical, They possess extraordinary electronic, mechanical, thermal, and catalytic properties.[10−17] During wetetching synthesis of MXenes,[1,4] their surfaces adsorb functional groups such as −O, −OH, and −F.18−24 Even though a variety of MXene properties such as work function, hydrophilic behavior, and catalytic activity are ascribed to the surface functionalization,[1,25−27] the structure and composition of the functionalized surfaces remain unknown for most MXenes
The average number of electrons that are associated with O and OH increases almost linearly with the amount of OH in the system (Figure S4a,c). This dependence is similar in every studied system, and we found no clear correlation with the maximum mixing energy or substrate chemistry and the number of atomic layers
Summary
Using a multiscale computational scheme, we study the trends in distribution and composition of the surface functional groups −O, −OH, and −F on two-dimensional (2D) transition metal carbides and nitrides (MXenes). We use Monte Carlo (MC) simulations to sample the configurational space and to compute the configurational free energies for different surface terminations (see the Supporting Information for simulation details).[63] In this way, we obtain the equilibrium distribution of functional groups on different MXenes.
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