Achieving high-performance NO2 sensors via vertically-aligned Ti3C2Tx nanoarchitectures

Abstract

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) Ti₃C₂T_x 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) Ti₃C₂T_x 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) Ti₃C₂T_x, leading to enhanced NO₂ gas sensing performance. The VA-Ti₃C₂T_x sensor exhibits a 2.5-fold higher gas response to 50 ppm NO₂ compared to HA-Ti₃C₂T_x, 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 (OH) 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- Ti₃C₂T_x sensors. Overall, this work highlights the potential of VA-MXenes for highly sensitive NO₂ detection in environmental monitoring applications.