Two-Dimensional Janus MXene Inks for Versatile Functional Coatings on Arbitrary Substrates.

Solution processing of two-dimensional nanomaterial inks guarantees efficient, straightforward fabrication of functional films, coatings, flexible devices, etc. Despite the excellent solution processibility and viscoelasticity of MXene aqueous inks, formulation of nonaqueous MXene inks with great affinity to both hydrophilic and hydrophobic substrates has proven quite challenging, limiting the practical applications of MXenes in printing/coatings on various substrates. Here, MXene surface chemistry is manipulated by asymmetrically grafting polystyrene and further concentrating the flakes into additive-free Janus MXene organic inks. The modified MXene nanosheets exhibit hydrophilicity on one side and hydrophobicity on the other. As a result, Janus MXene nanosheets ensure broad dispersibility in polar and nonpolar solvents, which in turn greatly extends the ink shelf life by slowing down the oxidation kinetics. Janus MXene sheets dispersed in toluene at room temperature remain at 90% of the initial solids after 1 month of storage. Janus surface engineering on MXene flakes guarantees the straightforward formation of uniform yet firm, large-area coatings on hydrophilic or hydrophobic substrates. These coatings demonstrate improved photothermal properties and chemical stability as well as good electromagnetic interference shielding performance. This strategy provides a simple and cost-effective way to promote the performance of MXene electronics in a variety of applications.