To fabricate sensors that are capable of ultrasensitive detection of NOx as well as optimize their synthetic route, highly porous and hierarchically structured Co3O4/CuO nanosheets were synthesized by a facile hydrothermal-calcination route. The CC2-1 sample synthesized with the 2:1 molar ratio of Co(NO3)(2).6H(2)O and CuCl2.2H(2)O has the most abundant porosity. Structural measurements found that the size of pore is 3.37 nm, the specific surface area is 24.04 m(2)g(-1), and the average slice thickness is about 5 nm. This optimum sample presented excellent NOx sensing performance at room temperature (RT = 21 degrees C), which has not only the highest response (14.16-1000 ppm), the shortest response time (2 s to 1000 ppm), and the minimum detection limit (0.01 ppm), but also good reversibility and selectivity. The superior property arises from the appropriate CuO ratio and the addition of pore-forming agent NaHCO3, and all together resulted in the unique hierarchical heterojunction structure, endowed with abundant porosity and a large number of defects, which eventually engender the remarkable chemisorbed ability to oxygen species. (C) 2018 Elsevier B.V. All rights reserved.