Highly efficient dye adsorption by hierarchical porous SA/PVA/ZIF-8 composite microgels prepared via microfluidics

Hierarchical porous composite microgels (SPZ microgels) were synthesized using microfluidic technology, composed of sodium alginate (SA), polyvinyl alcohol (PVA), and zeolitic imidazolate framework-8 (ZIF-8). The incorporation of ZIF-8 nanoparticles led to the formation of significant porous structures within the microgels, greatly enhancing their dye adsorption performance. Additionally, the diffusion of acetone during the crosslinking reaction resulted in sodium chloride crystal formation, creating a hierarchical porous structure with larger internal porous channels and smaller external channels. These SPZ microgels exhibited remarkable adsorption capabilities for both anionic and cationic dyes. The SPZ microgels showed exceptional adsorption capacities of 180 mg/g for methyl orange (MO) and 210 mg/g for methylene blue (MeB), far exceeding the performance of control microgels without the hierarchical porous structure (20 mg/g for MO and 150 mg/g for MeB). The hierarchical porous structure provided a larger surface area and facilitated improved diffusion and faster adsorption kinetics, contributing to the superior adsorption performance of the SPZ microgels. Kinetic studies revealed that MeB adsorption followed pseudo-second-order kinetics, while MO adsorption followed pseudo-first-order kinetics. Isotherm studies established that the Langmuir model accurately described MeB adsorption, indicating monolayer adsorption, while the Freundlich model effectively characterized MO adsorption, indicating multilayer interactions.