Metal-organic framework-derived porous SnO₂ nanosheets with grain sizes comparable to Debye length for formaldehyde detection with high response and low detection limit

The development of metal oxide semiconductors-based gas sensors that can simultaneously achieve high response and low detection limit towards formaldehyde (HCHO) remains a great challenge so far. In this work, we present the formation of porous SnO₂ nanosheets via direct calcination of a Sn-based metal-organic framework that was prepared via a facile wet chemistry method with deionized water as solvent at 80 °C. The porous SnO₂ nanosheets are found to be constructed by the interconnection of ultrafine nanoparticles with sizes of 4–9 nm, which is comparable to the Debye length of SnO₂. The gas sensor based on the porous SnO₂ nanosheets demonstrate a broad detection range towards HCHO (0.05–500 ppm), a low operating temperature (140 °C), very high response (540.8 to 50 ppm HCHO), extremely low detection limit (0.31 ppb), ideal selectivity, and outstanding reproducibility and durability. The excellent HCHO-sensing performance of the SnO₂ sensor could be attributed to the high specific surface area (125.92 m²/g) of the porous SnO₂ nanosheets, the ultrafine sizes of the SnO₂ nanoparticles, and the presence of abundant of mesopores within the nanosheets. The porous SnO₂ nanosheets with excellent HCHO-sensing characteristics may find widespread applications in fabricating gas sensors for detecting ppb-level HCHO.