Hydrate-based adsorption-hydration hybrid approach enhances methane storage density in ZIF-8@AC

Abstract

The volume penalty of nano-porous materials causes low methane volumetric adsorption capacity, and the contradiction between it and gravimetric adsorption capacity limits the application of nano-porous materials in different scenarios. Here, we prepared a composite nano-porous material of ZIF-8@AC to bridge the gap using a synergistic approach of adsorption and hydration, and methane isothermal adsorption in wet ZIF-8@AC was evaluated under low temperature. Due to the hybrid effect of adsorption and hydration, methane storage capacity in the nano-porous material was enhanced. When 100 mg activated carbon was doped, methane gravimetric adsorption capacity in ZIF-8@AC increases by 6.78 % and 30.34 % comparing with that in parent AC and ZIF-8 separately. In addition, the formation of hydrate increases methane storage density in mesopores, macropores and intergranular pores, giving rise to large methane volumetric adsorption, which increases by 12.65 % and 53.24 % comparing with that in parent AC and ZIF-8, respectively. Moreover, hydration efficiency in confined pore space was investigated by differential scanning calorimetry (DSC), while a high-resolution electron microscope was applied to record hydrate morphologies. It was found that hydrate mainly forms in large pore spaces, and the enhanced intergranular pores serve as nanoreactors to significantly improve the hydration efficiency, which is greatly influenced by local water distribution. These findings provide a new strategy to enhance methane adsorption via adsorption and hydration hybrid approach and would shed light on the application of composite nano-porous materials in the adsorption of natural gas.