Amine-functionalized stable Nb2CTx MXene toward room temperature ultrasensitive NO2 gas sensor

Large surface area and abundant surface functional groups favor the MXene (Nb2CTx) for potential gas sensor applications. However, atmospheric instability is the major limitation of MXenes. In this work, (3-aminopropyl)triethoxysilane (APTES) with distinct concentrations (0.1, 0.2, 0.3 mL) was used for the surface modification of MXene, which is a popular silane coupling agent. It minimizes the oxidation of the MXene by forming a homogeneous, thick protective layer on the Nb2CTx MXene structures by covalent contact through silylation processes, thereby allowing the simultaneous incorporation of additional reactive groups (-NH2). The functionalization and stability of the synthesized materials were characterized using XRD, FESEM, HR-TEM, XPS, FT-IR, UV-Vis, and zeta potential. The hydrophilic -NH2 group acts as an electron donor that helps sense acidic gases such as nitrogen dioxide (NO2). APTES-functionalized Nb2CTx MXene showed a better sensing response toward NO2 gas (31.52%) than pristine Nb2CTx MXene (12.5%) at 25 ppm, which is stable for more than 45 days at room temperature (similar to 25 degrees C). The sensitivity of Nb2CTx and Nb2CTx-0.2 APTES MXene shows 0.492 and 1.2314 ppm(-1), respectively, confirming that APTES-functionalized Nb2CTx MXene shows better sensitivity. Nb2CTx-0.2 APTES sensors can sense the NO2 gas at the detection limit (LOD) of 3 ppb and quantification limit (LOQ) of 12 ppb. In contrast, the pristine Nb2CTx sensor can provide an LOD of 15 ppb and LOQ of 52 ppb, showing that the APTES-functionalized Nb2CTx sensor can sense even a minute concentration of the gas with high sensitivity.