Low-temperature formaldehyde gas sensors based on NiO-SnO2 heterojunction microflowers assembled by thin porous nanosheets

NiO-SnO2 heterojunction microflowers assembled by thin porous nanosheets were successfully synthesized through a facile one-step hydrothermal route. The structural and composition information were examined by means of X-ray diffractometer, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller nitrogen adsorption-desorption. The formaldehyde gas sensing properties were systematically investigated between the pure and NiO-SnO2 microflowers. The experiment results showed that NiO-SnO2 microflower sensor displayed the higher response at a lower operating temperature region compared to pure SnO2 microflower sensor. Meanwhile, introducing NiO obviously reduced operating temperature. Especially, the sensor utilizing 5 mol% NiO-SnO2 microflowers showed significantly enhanced sensing performances to formaldehyde including the higher responses, lower operating temperatures, lower detecting limit level, quick response/recovery characteristics, good reproducibility and stability, and superior selectivity. The enhanced sensing properties were probably attributed to the formation of p–n heterojunctions at interface and the catalytic effect of NiO, which significantly enlarges surface depletion region and increases potential barrier. Our studies provide a facile synthesis process, which could be developed to synthesize other semiconductor oxide composites, and provide a potential material for fabricating high performance sensors.