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 micro flowers. 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 heterojunction 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.