Synthesis of ZnO Hierarchical Structures and Their Gas Sensing Properties

Firecracker-like ZnO hierarchical structures (ZnO HS1) were synthesized by combining electrospinning with hydrothermal methods. Flower-like ZnO hierarchical structures (ZnO HS2) were prepared by a hydrothermal method using ultrasound-treated ZnO nanofibers (ZnO NFs) as raw material which has rarely been reported in previous papers. Scanning electron microscope (SEM) and transmission electron microscope's (TEM) images clearly indicated the existence of nanoparticles on the ZnO HS2 material. Both gas sensors exhibited high selectivity toward H₂S gas over various other gases at 180 °C. The ZnO HS2 gas sensor exhibited higher H₂S sensitivity response (50 ppm H₂S, 42.298) at 180 °C than ZnO NFs (50 ppm H₂S, 9.223) and ZnO HS1 (50 ppm H₂S, 17.506) gas sensors. Besides, the ZnO HS2 sensor showed a shorter response time (14 s) compared with the ZnO NFs (25 s) and ZnO HS1 (19 s) gas sensors. The formation diagram of ZnO hierarchical structures and the gas sensing mechanism were evaluated. Apart from the synergistic effect of nanoparticles and nanoflowers, more point-point contacts between flower-like ZnO nanorods were advantageous for the excellent H₂S sensing properties of ZnO HS2 material.