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Abstract
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.
Highlights
Hydrogen sulfide (H2S) is a flammable, explosive and harmful gas [1]
The difference when preparing flower morphological zinc oxide (ZnO) hierarchical structures was that the reaction solution with ZnO nanofibers (ZnO NFs) was sonicated under 100 W power for 2 min before the hydrothermal experiment
High-resolution transmission electron microscopy (HRTEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) mapping and energy dispersive X-ray (EDX) analysis patterns were obtained by JEOL JEM-2200FS (Tokyo, Japan)
Summary
Hydrogen sulfide (H2S) is a flammable, explosive and harmful gas [1]. Long-time exposure to low concentrations of H2S atmosphere could cause human irritation in the nasal cavity and eyes, and in high concentrations, an H2S atmosphere, even for short-time could cause humans to die [2,3]. Li et al [24] reported hierarchical flower-like CuO synthesized by a hydrothermal method, which exhibited high sensitivity and selectivity toward H2S. Nakla et al [25] synthesized flower-like SnO2 nanowires through a high current heating method and the SnO2 nanowire sensor showed good H2S sensing properties. Among these MO materials, zinc oxide (ZnO) has been developed for the detection of toxic gases, owing to its wind band gap (3.37 eV) [26], big exciton binding energy (60 meV) [27] and excellent chemical stability [28]. The growth process and gas sensing mechanism of flower-like and firecracker-like ZnO hierarchical structures were investigated and proposed
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