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Abstract:
Transition metal carbides and nitrides (MXenes) are an emerging class of 2D materials, which are attracting ever-growing attention due to their remarkable physicochemical properties. The presence of various surface functional groups on MXenes’ surface, e.g., –F, –O, –OH, –Cl, opens the possibility to tune their properties through chemical functionalization approaches. However, only a few methods have been explored for the covalent functionalization of MXenes and include diazonium salt grafting and silylation reactions. Here, an unprecedented two-step functionalization of Ti3C2Tx MXenes is reported, where (3-aminopropyl)triethoxysilane is covalently tethered to Ti3C2Tx and serves as an anchoring unit for subsequent attachment of various organic bromides via the formation of C–N bonds. Thin films of Ti3C2Tx functionalized with linear chains possessing increased hydrophilicity are employed for the fabrication of chemiresistive humidity sensors. The devices exhibit a broad operation range (0–100% relative humidity), high sensitivity (0.777 or 3.035), a fast response/recovery time (0.24/0.40 s ΔH−1, respectively), and high selectivity to water in the presence of saturated vapors of organic compounds. Importantly, our Ti3C2Tx-based sensors display the largest operating range and a sensitivity beyond the state of the art of MXenes-based humidity sensors. Such outstanding performance makes the sensors suitable for real-time monitoring applications.
