The oxidative degradation of unsaturated metal atoms or dangling bonds at the edges and defects of MXenes seriously hinders the practical applications of MXenes. Herein, a passivation scheme for Ti3C2Tx MXene is demonstrated by utilizing the thiol-containing molecule β-mercaptoethanol (BME), which can significantly inhibit the oxidation of Ti3C2Tx in various environments, including the long-term Storage, monolayer Ti3C2Tx-based devices under humid air (2 m) and high temperature environment (12 h). Notably, the nonionic BME does not induce aggregation but maintains the 2D morphology of Ti3C2Tx. A comprehensive study of the protection mechanism by beta mercaptoethanol density functional theory (DFT) calculations and experimental characterizations revealed that BME is especially adsorbed at the edges and surface defects of MXenes (binding energies −1.70 and −1.05 eV), where degradation begins. Furthermore, the electron-donating effect of mercapto groups tunes the work function of Ti3C2Tx from 4.70 eV to 4.39 eV, thereby enhancing the carrier transport performance of MoS2 FETs due to the band alignment of BME-Ti3C2Tx as the source electrode. The described method can largely contribute to the ultralong lifetime of 2D Ti3C2Tx without compromising its excellent performance, thus facilitating the practical application of this emerging material.
MXene is an emerging family of two-dimensional layered transition metal carbides/nitrides with the general chemical formula Mn+1XnTx (n = 1–4), exhibiting many attractive physical and chemical properties, such as metallic conductivity properties, [1] water dispersibility, [2] high optical clarity, [3] good mechanical properties, [4] modifiable surface functional groups, [5] and tunable work function. [6] Since the discovery of MXene in 2011, the MXene family has been demonstrated in various applications such as energy storage, [7] electronics, [8] light-to-heat conversion, [9] electromagnetic interference shielding, [10] sensors, [11] water showed excellent performance in purification,[12] and desalination. [13] In addition to superior performance, considering the abundant functional groups on the surface, MXenes can be synthesized by solution method and processed in aqueous phase, which can provide low-cost and large-scale MXene applications. [14] The surface functional groups also stabilize the active early transition metal atoms on the MXene surface, such as Ti, V, Cr, and Nb. [15] However, MXene flakes synthesized by the solution method must have edges and a large number of defects, where metal atoms are unsaturated, called dangling bonds; thus, MXene is easily oxidized by oxidants such as H2O and O2 (Fig. S1a,b, support information). [16] Through this spontaneous oxidation reaction, MXene is gradually degraded into metal oxides and amorphous carbon in humid air or aqueous dispersion, which will seriously affect its stability during storage and processing as well as in practical applications. long-term effectiveness