Flower-like ZnO-Co3O4 heterojunction composites for enhanced acetone sensing

In this work, we successfully prepare the ZnO-Co 3 O 4 heterostructure on a nanosheet hollow sphere structure. Due to the high redox activity of Co 3 O 4 , the fabricated sensor using 3 at% ZnO-Co 3 O 4 hollow composite exhibits enhanced acetone sensing performance (S = 17.3–50 ppm) at a low operating temperature (150 °C), which is about 5.1 times higher than that of Co 3 O 4 -based sensor (S=3.4–50 ppm). Meanwhile, the ZnO-Co 3 O 4 based sensor shows ppb-level detection limit (S=1.3 at 100 ppb). The reason for the higher sensitivity and lower detection limit of the sensor is that the formation of n-p heterojunctions reduces both the degree of upward band-bending and the surface hole concentration, that allows the sensor to have a higher gas response under the same surface sensing-reactions (surface charge transfer).