Na+-Intercalated Ti3C2Tx/P(VDF-TrFE) Nanofibers Composite for Selective Room-Temperature NO2 Sensing

Herein, Na+-intercalated Ti3C2Tx MXene/poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) Nanofiber (NMN) composite gas sensor was fabricated through systematic surface and structural engineering strategies to achieve enhanced NO2 sensing performance at room temperature. NaOH treatment of Ti3C2Tx MXene simultaneously facilitated the replacement of −F surface terminations with O-containing species, resulting in a higher density of O-containing species that serve as active adsorption sites for NO2 molecules, and expanded the interlayer spacing of the MXene sheets through Na+ intercalation, thereby enlarging the physical accessible surface area for NO2 adsorption. Specifically, Na+-intercalation increased the basal d-spacing of Ti3C2Tx from 1.064 to 1.162 nm, demonstrating nanoscale expansion of the layered MXene structure. The functionalized MXene nanosheets are assembled onto electrospun P(VDF-TrFE) nanofibers via dip-coating to further increase surface-to-volume ratio through the three-dimensional porous structure. In this process, the cetyltrimethylammonium bromide (CTAB) is optimized to impart a positive surface charge to the P(VDF-TrFE) nanofibers, thereby enabling robust electrostatic interaction of the negatively charged MXene nanosheets onto the P(VDF-TrFE) nanofiber surface. As a result of these synergistic strategies, the fabricated NMN sensor successfully demonstrated reliable NO2 detection at a concentration as low as 500 ppb at room temperature with a 45.9-fold higher response than its pristine MXene. Furthermore, the sensor exhibited outstanding NO2 selectivity over interfering gases, confirming that the proposed surface and structural engineering optimized the NMN sensor for NO2 detection.