Rich defects and nanograins boosted formaldehyde sensing performance of mesoporous polycrystalline ZnO nanosheets

Comprehensive consideration of structural and electronic sensitization is of significant importance for rational design and assembly of high-performance gas sensors based on metal oxides. In this work, hierarchically mesoporous ZnO nanosheets are synthesized via a hydrothermal method followed by calcination. Material characterization reveals polycrystalline feature of these ZnO nanosheets rich in mesopores and defects. Gas sensing performance of as-synthesized ZnO nanosheets was systematically investigated, taking formaldehyde as probe molecules. Compared with commercial ZnO nanoparticles, ZnO nanosheets exhibited enhanced formaldehyde sensing properties, including lower operation temperature, higher sensitivity, faster response, and smaller detection limit. Notably, the response ( S  = 227.4) of ZnO nanosheets to 200 × 10 –6 formaldehyde is about 17 times larger than that of ZnO nanoparticles ( S  = 13.5). Excluding effects of grain size and surface area, enhanced sensing properties, especially response value, are credited in large part to synergistic actions of surface defects, grain boundaries, as well as unique structural advantage of ZnO nanosheets. Furthermore, this work offers a guideline for boosting performance of metal oxide-based gas sensors via surface defect control and grain boundary construction. Graphical abstract