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

Abstract

Large surface area and abundant surface functional groups favor the MXene (Nb₂CT_x) 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 Nb₂CT_x 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 Nb₂CT_x MXene showed a better sensing response toward NO₂ gas (31.52%) than pristine Nb₂CT_x MXene (12.5%) at 25 ppm, which is stable for more than 45 days at room temperature (∼25 °C). The sensitivity of Nb₂CT_x and Nb₂CT_x-0.2 APTES MXene shows 0.492 and 1.2314 ppm⁻¹, respectively, confirming that APTES-functionalized Nb₂CT_x MXene shows better sensitivity. Nb₂CT_x-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 Nb₂CT_x sensor can provide an LOD of 15 ppb and LOQ of 52 ppb, showing that the APTES-functionalized Nb₂CT_x sensor can sense even a minute concentration of the gas with high sensitivity.