Molecular insights into the influence of synergistic effect on adsorption–hydration hybrid CH4 storage in ZIF-8@AC composite materials

Abstract

Zeolite imidazoline framework-8@activated carbon (ZIF-8@AC) composite materials exhibit a significant synergistic effect due to the harmonization between the adsorption of parent materials and have great potential in adsorption–hydration hybrid CH₄ storage. However, the enhancement mechanism of hybrid adsorption–hydration by a synergistic effect is unclear, which hinders the further optimization of composite materials. In this study, CH₄ hydrate formation under the synergistic effect of ZIF-8@AC is researched by molecular dynamics simulations. A comparison of adsorption capacity and the number of hydrogen bonds in composite and monomeric materials reveals that the synergistic effect enhances the adsorption performance and adsorption induction capacity of ZIF-8@AC, which increases the formation rate and number of hydrogen bonds. In addition, due to the differences in adsorption mechanisms of heterogeneous surfaces in ZIF-8@AC pores, the promotion of CH₄/H₂O mass transfer capacity by nanobubbles with positive curvature becomes more obvious. On this basis, the ZIF-8@AC system exhibits satisfactory hydrate kinetic properties and CH₄ storage capacity. Stable hydrate nuclei are formed in multiple regions of the solution within a short period and grow rapidly by independent growth and interconnection. Specifically, the CH₄ storage capacity of ZIF-8@AC is increased by 42% compared to monomeric AC, and the CH₄ storage ratio of ZIF-8@AC is increased by 10% compared to monomeric ZIF-8. The results of this study may provide valuable insights into the development of composite materials suitable for the hybrid adsorption–hydration method and reveal the potential role of the synergistic effect in the CH₄ storage process.