ZIF-67@Co-LDH yolk–shell spheres with micro-/meso-porous structures as vehicles for drug delivery†
ZIF-67@Co-LDH yolk–shell heterostructures are successfully synthesized by successive increase in Co2+ concentration in the methanolic solution of Co2+ and 2-methylimidazole (Hmim). This is mainly attributed to the slight difference in thermodynamic stability between ZIF-67 and Co-LDHs, accounting for the selective generation of Co-LDHs at a high molar ratio of Co2+ to Hmim. Co-LDH sheet assembled hydrophilic shells with mesoporous structures can control guest species shuttling between their interiors and exteriors, improving ZIF-67 stability and maintaining its reactivity as well in humid environments. Finally, hierarchical porous structures with high specific surface area are used to load the drug molecule model of rhodamine 6G to study drug delivery. The micro-/meso-porous structural ZIF-67@Co-LDH yolk–shell spheres exhibit a higher loading amount and longer release time compared to ZIF-67 nanocrystals or Co-LDH hollow spheres alone.