Modulated Growth of MOFs to Fabricate ZIF-8@Chitosan/Polyvinylpyrrolidone Hydrogels with Improved Adsorption Capacity for CO₂

ZIF-8@chitosan (CS)/polyvinylpyrrolidone (PVP) hydrogels (CPxHGZ) were fabricated by in situ growth of metal–organic framework (MOF) crystals on the network of CS/PVP semi-interpenetrating hydrogels. The ZIF-8 crystals were assembled in the channel of hydrogel and coated by networks of hydrogel. Morphology and distribution of the ZIF-8 crystals in CS/PVP hydrogels were modulated by the polymer network of hydrogels. PVP played a key role in guiding the growth of ZIF-8 crystals and preventing aggregation of ZIF-8 crystals in the network of CS/PVP hydrogel. Additionally, the PVP content in hydrogels influencing the adsorption capacity of CPxHGZ for CO2 was explored. With increasing PVP content in the hydrogels, the equilibrium adsorption of CPxHGZ for CO2 was increased. Especially, the equilibrium adsorption of CP10HGZ for CO2 was increased by 22%, which was higher than that of the pure ZIF-8 crystals. The results of kinetic simulation, XRD spectra, and FT-IR spectra revealed that the adsorption mechanism of CPxHGZ for CO2 was mainly chemisorption. The presence of multisites, including the amine groups in CS and PVP as well as metals in ZIF-8, was beneficial for enhancing the adsorption capacity of CPxHGZ for CO2.