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One-step single-spinneret electrospinning synthesis of 1D fibrous hierarchical structure can not only prevent the agglomeration or restacking of fibers or particles and enlarge surface active area but also promote the directional migration of electrons in materials and achieve effective regulation of resistances. Herein, tunable SnO 2 and SnO 2 /ZnO fibrous hierarchical structures with in situ growth of monodisperse spherical-like particles on surface provide a new sight for adjusting component distribution, surface absorption and chemical reaction, electronic transmission path, and electron transfer efficiency. Compared with SnO 2 porous fibers and SnO 2 hierarchical structures, the optimal SnO 2 /ZnO sensors exhibit superior gas-sensing response value of 366−100 ppm ethanol at 260 °C as well as excellent gas selectivity and long-term stability, in which the enhanced gassensing mechanism is primarily derived from multilevel effective heterojunctions with unique interface electronic effects. Especially, these SnO 2 -based sensors can achieve favorable linear relationship of the response and gas concentration for sensitive trace detection in cosmetics for the first time, providing a new strategy to design composite materials for quantitative analysis of volatiles in the cosmetics evaluation process. KEYWORDS: SnO 2 and SnO 2 /ZnO fibrous hierarchical structures, multilevel effective heterojunctions, electrospinning, gas sensor, trace detection in cosmetics

Urchin-like WO2.72 microspheres modified with Au and PdO nanoparticles were constructed and applied to the field of gas sensors. The gas-sensing test results showed that the Au/PdO/WO2.72 sensors exhibited excellent gas-sensitive performances. The sensors have not only an ultrahigh response to TMA but also a rapid response/recovery time. Especially WO2.72 decorated with 2 wt % Au and 2 wt % PdO nanoparticles (2%AuPW), its response to 40 ppm of TMA can be up to 802.5 at 240 °C, which is approximately 110.5 and 1.6 times of WO2.72 (7.26) and 2 wt % PdO/WO2.72 (496.6) at 260 °C, respectively. Even for 1 ppm of TMA, the response of the as-obtained 2%AuPW sensor can still attain 10.9. Furthermore, the Au/PdO/WO2.72 sensor showed excellent effectiveness after 30 days. The BET results indicate that the deposition of PdO and Au nanoparticles increases the specific surface area of the sample. The mechanism analysis revealed that the markedly increased gas-sensing properties of Au/PdO/WO2.72 sensors are ascribed to the synergy of surface area and a mesoporous structure, a p–n heterojunction, and a catalytic spillover effect of PdO and Au nanoparticles. The rational design and detailed investigation of Au/PdO/WO2.72 sensors provide insights into the development and design of other semiconductor-based sensors.

Morphology-tunable C–N/SnO2-based hierarchical microspheres with good gas sensitivity for triethylamine (TEA) have been fabricated via facile electrospinning and a subsequent calcination process. The reaction temperature and modifying calcining technology played a dominant role for the morphological evolution from precursor fibers to microspherical shapes and the formation of C–N-decorated SnO2 phase composition. C–N/SnO2/ZnO composites with tunable crystallinity, microstructure, and gas-sensing performance were strictly dependent on the added amount of Zn element. Fascinatingly, the constructed C–N/SnO2/ZnO/Au composites can not only precisely regulate the crystal size, dispersion status, loading position, and content of Au nanoparticles but also display excellent gas-sensing properties with ultrasensitivity and high selectivity under various temperature detections. The response of C–N/SnO2/ZnO/Au composites can reach up to approximately 1970, calculated to be 121.6 and 23.6 times for 50 ppm TEA molecules at optimal conditions compared with C–N/SnO2 and C–N/SnO2/ZnO microspheres, respectively, actually representing the highest response value at high temperatures reported to date. The superior long-aging stability of sensing behaviors and phase structures can be also observed after 1 month. More importantly, novel C–N/SnO2/ZnO/Au sensors were employed for availably detecting low-concentration volatiles released from the storage procedure of fishes at 80 °C, indicating the practical application in chemical detectors and biosensors at low temperature. The novel gas-sensing mechanisms derived primarily from the combination of phase compositions, morphologies, and unique surface/interface transfer processes of C–N/SnO2/ZnO/Au composites are presented and investigated in detail, which will contribute to the design and development of other semiconductor-based composite sensors.

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