Achieving high-performance NO2 sensors via vertically-aligned Ti3C2T nanoarchitectures

Nitrogen dioxide (NO2) pollution is a major threat to human health and ecosystems. Early detection of NO2 is critical for effective environmental monitoring and pollution control. While two-dimensional (2D) Ti3C2Tx MXenes hold promise for gas sensing applications, their natural tendency to restack in a horizontal orientation limits gas adsorption and charge transport. Here, we report, for the first time, the development of vertically aligned (VA) Ti3C2Tx thin films fabricated using a freeze-drying assisted electrophoretic deposition (EPD) process. The VA architecture significantly exposes more active basal and edge sites compared to horizontally aligned (HA) Ti3C2Tx, leading to enhanced NO2 gas sensing performance. The VA-Ti3C2Tx sensor exhibits a 2.5-fold higher gas response to 50 ppm NO2 compared to HA-Ti3C2Tx, demonstrating excellent sensitivity and linearity across a broad NO2 concentration range (1–50 ppm). Density functional theory (DFT) calculations reveal a strong preference of NO2 for adsorption on the hydroxyl (single bondOH) surface functional groups of both basal and edge planes, with adsorption energies of −2.29 eV and −2.16 eV, respectively. These results support the enhanced gas sensing properties of VA- Ti3C2Tx sensors. Overall, this work highlights the potential of VA-MXenes for highly sensitive NO2 detection in environmental monitoring applications.