Engineering of in-plane SnO2-Sn3O4 hierarchical nanoflower heterojunctions for enhanced formaldehyde sensing

The huge challenge for detection of formaldehyde (HCHO), a toxic volatile organic compound for human health, with ppb level at low working temperature lies in the activation of surface oxygen species of sensing materials. Herein, we have designed in-plane SnO2-Sn3O4 heterojunctions with hierarchical nanoflower morphology for efficient HCHO sensing, and the lattice strains, surface properties as well as the electronic structure around the SnO2-Sn3O4 phase boundaries can be finely optimized. Notably, lattice strain and Schottky junction dual regulation ensures the in-plane SnO2-Sn3O4 heterojunctions with excellent HCHO sensing performance at low working temperature of 120 °C. Particularly, Sn3O4–400 displays high sensing response (Ra/Rg = 621.83, 50 ppm), high repeatability and excellent selectivity to HCHO. Furthermore, geometric phase analysis, multiple structural analysis and DFT calculations demonstrate the lattice strain and Schottky junction dual regulation tunes the surface oxygen properties and electron structure, which facilitate the formation of rich surface O−(ad) species and enhance the interaction between materials and HCHO around the abundant SnO2-Sn3O4 phase boundaries, thus enhancing the HCHO sensing performance. This research provides novel ideas for selecting high-tech sensing materials for the detection of dangerous volatile organic chemicals.