ZnO nanosheets, nanoflower, and nanorods were synthesized without any capping agent or surfactant by hydrothermal method. ZnO nanoparticle transformed into 2D-nanosheet and 1D nanorods with the increase of precursor concentration. The results clearly indicated that the molar ratio of Zn2+/OH(-)strongly influenced on the formation of hierarchical nanorods and nanosheet. FESEM and TEM images showed that the different morphologies such as nanoparticle, nanosheets and nanorods were obtained by varying the concentration of NaOH. HRTEM confirmed that the ZnO nanorods and nanosheets were well crystalline. ZnO showed higher response (S = 92) towards acetaldehyde compared with other gases. It also showed faster response and recovery times of 40 and 80 s towards 200 ppm of acetaldehyde, respectively. (C) 2018 Elsevier B.V. All rights reserved.