Superior NO₂ Sensing of MOF-Derived Indium-Doped ZnO Porous Hollow Cages

Highly sensitive semiconductor gas sensors hold great potential for applications in trace gas detection. Reliable detection of ppb-level NO₂ is crucial for environmental monitoring, which however still remains a challenge. In this work, we demonstrated ultrahigh NO₂ sensitivity of indium-doped ZnO porous hollow cages. Doping of In into ZnO was accomplished via a facile one-pot MOF encapsulation–calcination route, which led to remarkably enhanced NO₂ sensing performance. In-doped ZnO exhibited a large response of 3.7 to 10 ppb NO₂, an ultrahigh sensitivity of 187.9 ppm^–1, and a limit of detection of 0.2 ppb, outperforming state-of-the-art ZnO-based NO₂ sensors. The superior NO₂ sensing properties were attributed to a synergy of excellent gas accessibility of the porous hollow structure, abundant adsorption sites, and electronic sensitization by In doping. Our findings could be extended to design other porous doped ZnO oxides for high performance gas sensors and other applications.