Hierarchical porous zeolitic imidazolate frameworks (HZIFs) are promising materials for several applications, including adsorption, separation, and nanomedicine. Herein, the conversion of zinc hydroxide nitrate nanosheets into HZIF-8 nanocomposite with graphene oxide (GO) and magnetic nanoparticles (MNPs) is reported. The conversion takes place at room temperature in water. This approach has been successfully applied for the formation of leaf-like ZIF(ZIF-L), and their nanocomposites with nanoparticles, such as GO and MNPs. This method offers a simple approach for the synthesis of tunable pore structure using nanoparticles and fast room temperature conversion (30 min) without any visible residual impurities of zinc hydroxide nitrates. The applications of HZIF-8, ZIF-L, and their nanocomposites, for CO2 sorption, exhibit excellent adsorption properties. The synthesized composites exhibit enhanced CO2 adsorption capacity due to the synergistic effect between nanoparticles (GO, or MNPs), and ZIF-8. The materials have good potential for further applications.