Adsorption-Hydration Dual Encapsulation of Methane in Prehumidified Functionalized ZIF-8

The dual encapsulation of natural gas via adsorption and hydration in prehumidified nanoporous materials provides a novel strategy for its dense storage under milder conditions, but the encapsulation performance is highly dependent on the material itself. To enhance the encapsulation performance, ZIF-8 was functionalized with amination (−NH 2 ) and metal doping (Cu 2+ ), yielding two nanoporous materials, ZIF-8-NH 2 and ZIF-8-NH 2 @Cu. The effects of −NH 2 and Cu 2+ on the adsorption and hydration encapsulation performance were evaluated, and their coupling relationship with preadsorbed water was analyzed. The results demonstrate that −NH 2 improves the adsorption encapsulation performance of methane, increasing the adsorption rate at a low pressure by 109.7%. In addition, −NH 2 also enhances the hydration encapsulation efficiency and strengthens the hydration efficiency of preadsorbed water. Consequently, the adsorption-hydration dual encapsulation capacity of methane by ZIF-8-NH 2 is increased by 30.12% compared to pure adsorption, effectively lowering the hydration initiation pressure and increasing the gas storage density at low pressure. However, the enhancement effect of −NH 2 on hydration efficiency is strongly dependent on the amount of preadsorbed water; when the preadsorbed water content increases to R w = 1, the hydration-encapsulated methane amount can be elevated by 368%. In contrast, the effects of Cu 2+ functionalization on methane adsorption and hydration encapsulation are below expectations, and it even exhibits an antagonistic effect with −NH 2 under specific conditions, reducing the adsorption-hydration dual-encapsulation performance. These findings can guide the preparation of high-performance nanoporous materials for adsorption-hydration dual encapsulation, thereby promoting the application of hydrate-based gas-storage technology.