Flash-Induced Thermochemical Heterostructuring of a Nickel Oxide/Zinc Oxide Nanomesh for NO₂ Sensing

Semiconducting zinc oxide (ZnO)-based chemiresistors are widely used in environmental monitoring and human health applications due to their scalability, cost-effectiveness, and rapid response to hazardous gases. However, despite its high gas sensitivity, ZnO suffers from poor selectivity. In this study, we present a rational strategy to simultaneously enhance the sensitivity and selectivity of ZnO-based gas sensors by integrating an electrospun template-assisted nanostructuring approach with flash-induced thermochemical heterostructuring. Specifically, we synthesized a ZnO nanomesh via the electrospinning of polyacrylonitrile, followed by ZnO deposition on the nanofibers through atomic layer deposition and subsequent plasma treatment and thermal annealing to remove the polymer template. A xenon flash lamp treatment in the presence of a metal precursor facilitated the in situ formation of nickel oxide (NiO), inducing a pronounced photothermal effect and enabling controlled heterostructuring. As a proof of concept, NiO/ZnO heterostructures demonstrated significantly enhanced nitrogen dioxide sensitivity at 300 °C (RGas/RN2=420 at 20 ppm), along with rapid response (200 s) and recovery (50 s) times, and a detection limit as low as 0.02 ppm. By contrast, the pristine ZnO nanomesh sensor showed a sensor ratio of RGas/RN2 = 22 at 20 ppm, a response time of 240 s, and a recovery time of 90 s. This remarkable sensitivity enhancement was attributed to the nanoscale porous architecture, which provided an increased surface area and improved selectivity enabled by heterojunction effects. This approach offers a scalable route for designing high-performance gas sensors with customizable selectivity by leveraging the advantages of nanostructured materials.