Abstract:The development of H 2 gas sensors is important for H 2 production as af uel. In this work, aZ nO@ZIF-8c oreshell nanorod film is designed and synthesized as ag as sensor through af acile solutiond eposition process. This film shows an excellent selective response for H 2 over CO. By fine-tuning the reaction conditions, aZ nO@ZIF-8 core-shell structure with at hin, fine-grain, porousZ IF-8 shell is obtained. Owing to the facile H 2 penetration through the ZIF-8 thin shell ( % 110nm) and the increased oxygen vacancies for the complex film, the ZnO@ZIF-8 nanorod film shows ah igher H 2 sensitivity than ar aw ZnO nanorod film. More importantly,t he ZnO@ZIF-8 nanorod film shows no response for CO at 200 8C. Because of the fine-grain confinemento f the porous ZIF-8 shell (< 140 nm), the molecular sieving effect is strengthened, which allows the effective separation of H 2 over CO. This work providesapromising strategy for the design of high-performance H 2 sensors.

Molecular dynamics simulations of the Lennard-Jones model are used to study phase transitions at a smooth surface. Our motivation is the observation that the existence of an attractive wall facilitates crystallization. To investigate how this wall influences phase transitions, the strength of wall-particle interaction is varied in our studies. We find that the phase behavior depends on the strength parameter α, i.e., the ratio between wall-particle and the particle-particle attraction strength. Three critical values of the ratio, namely, αp, αw, and αc, are used to define the qualitative nature of the phase behaviors at a smooth surface. Some interesting phenomena due to the increase of α are observed. First, a set of close-packed planes, i.e., {111} planes in fcc structures or {0001} planes in hcp structures, are "rotated" from intersecting to parallel to the wall when α = αp; second, the layering phase transition close to the wall antecedes that of the bulk when α = αw. Finally, the first-order phase transition in the first two layers is supplanted by a continuous phase transition when α = αc, which to some extent can be treated as a quasi-two-dimensional process. We find that bulk freezing always discontinuously occurs through a first-order phase transition, and seems to be isolated from the freezing process occurring close to the attractive surfaces. Moreover, during the heating process, we observe minimal dependence at a strongly attractive surface.

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