The Preparation Of ZnO-ZIF-8 Nanocomposite Film And Its Gas-sensing Properties

Gas sensors have played an important role in industrial production applications,environment protection and national defence-related technology.Hence,the development of high-performance gas sensors is increasingly important.As a metal oxide-based gas sensor,ZnO is attractive because of its excellent electrical properties and low cost.ZnO-based gas sensors have been extensively studied.The sensors with high sensitivity and selectivity in practical application are strongly demanded.Many studies focused on enhancing the sensitivity of ZnO sensors.However,the studies on the selectivity of ZnO sensors were scarce.The poor gas selectivity is an inherent weakness for metal oxide-based gas sensors.To overcome this disadvantage,integrating ZnO sensors with functional materials that have good gas separation capability might be an effective approach.Our investigation shows that Zeolitic imidazolate framework-8(ZIF-8)as a stable Metal-organic framework(MOFs)material is suitable for integrating with ZnO.Hence,we design the ZnO-ZIF-8 hybrid sensors:the ZnO films are applied for gas sensing;the ZIF-8 films are applied for gas separation.By combining the advantages of both ZnO and ZIF-8,we obtain the hybrid gas sensors with high sensitivity and selectivity.Our work provides a promising strategy for designing high-performance gas sensors.The work carried out is as follows:1)A facile in-situ solution deposition method was used to fabricate ZnO nanorod film sensors.The tower-like ZnO nanorod film sensor with large(0001)exposed area was obtained by adjusting the supersaturation level of deposition solution.The tower-like ZnO nanorod film sensor exhibited a high H2 sensitivity,which was attributed to its abundant oxygen vacancy defects.2)A ZnO@ZIF-8 core-shell nanorod film was designed and synthesized as gas sensor via a self-template reaction.By fine-tuning the reaction condition,the ZnO@ZIF-8 core-shell structure with a thin,fine-grain and porous ZIF-8 shell is obtained.Due to the easy H2 penetration through ZIF-8 thin shell(～110 nm)and the increased oxygen vacancies for the complex film,the ZnO@ZIF-8 nanorods film shows a higher H2 sensitivity than raw ZnO nanorods film.More importantly,the ZnO@ZIF-8 nanorods film shows no response for CO at 200℃.Because of the fine-grain confinement of porous ZIF-8 shell(<140 nm),the molecular sieving effect is strengthened,which obtains the effective separation of H2 over CO.This ZnO@ZIF-8 core-shell nanorod film realizes an excellent selectivity for H2.3)In order to synchronously increase the sensitivity and selectivity for the hybrid gas sensors,the ZIF-8 particle-loaded ZnO(ZIF-8/ZnO)nanorod hybrid sensor was designed and fabricated,which exhibited a superior sensitivity and selectivity for H2S at room temperature.ZIF-8 played a key role in improving the sensitivity and selectivity of the ZIF-8/ZnO nanorod sensor,which served as a pre-concentrator of H2S,a surface etching agent of ZnO and a forming agent of intermediate product(ZnS).The H2S sensitivity(S=52.4%at 10 ppm)of the ZIF-8/ZnO nanorod sensor was 15 times higher than that of raw ZnO nanorod sensor.Remarkably,the ZIF-8/ZnO nanorod sensor was able to detect H2S at a level down to 50 ppb and showed an excellent selective sensitivity for H2S over other reducing gases.