High-performance humidity-resistant NO2 sensors based on SnO2/Ce-ZnO heterojunctions: Surface wettability modulation and DFT mechanism investigation

The escalating emissions of nitrogen dioxide (NO 2 ) resulting from rapid industrialization pose a severe threat to both ecological balance and public health, rendering the development of high-performance NO 2 sensors imperative for precise environmental monitoring. However, conventional metal oxide semiconductor (MOS) sensors based on pristine materials suffer from intrinsic limitations, including low sensitivity, poor humidity tolerance, and high operating temperatures. Single-mode modification strategies often fail to simultaneously mitigate these drawbacks. Herein, we propose a synergistic modification strategy combining rare-earth doping with heterojunction engineering. Ce-doped SnO 2 /ZnO nanocomposites were successfully synthesized via a facile hydrothermal method. Among the fabricated devices, the S 5 CZ 5 sensor (1:1 mass ratio) exhibited superior performance, delivering a robust response of 55.3 to 100 ppm NO 2 at 180 °C, accompanied by rapid response/recovery kinetics (21 s/29 s) and a low theoretical detection limit of 843 ppb. Notably, the incorporation of Ce effectively modulated surface wettability, endowing the sensor with exceptional moisture resistance and long-term stability. Furthermore, density functional theory (DFT) calculations elucidated the atomic-scale mechanism: the ternary SnO 2 /Ce-ZnO system yields an exceptionally high NO 2 adsorption energy (−2.55 eV) and a massive interfacial charge transfer (0.49 e), while critically suppressing H 2 O interactions (adsorption energy of −0.40 eV, restricted charge transfer of 0.13 e), as corroborated by charge density difference analyses. Coupled with an optimized density of states near the Fermi level, this work achieves a multidimensional enhancement of sensing performance, offering novel insights for trace gas detection in complex environments.