Fabrication of in situ ZIF-67 grown on alginate hydrogels and its application for enhancing Cu (II) adsorption from aqueous solutions

Synthesizing high uniform metal-organic frameworks grown on natural biomass such as sodium alginate (ALG), which can efficiently remove metal ions from aqueous solution, is a challenging project. A simple and eco-friendly method of preparing ALG@ZIF-67 hydrogels by in situ synthesis of ZIF-67 onto ALG hydrogels was established. Combining the virtues of ALG with abundant hydroxyl and carboxyl groups and ZIF-67 with excellent porous structure, the obtained ALG@ZIF-67 hydrogels have excellent adsorption for Cu 2+ (153.63 mg/g), which was much higher than that of pure ALG hydrogels (111.79 mg/g). The methodology showed that the adsorption process was in accord with the Langmuir isotherm adsorption model (R 2 = 0.9972) and pseudo-second-order kinetic model (R 2 = 0.9822). The thermodynamic experiments demonstrated that Cu (II) was absorbed by hydrogel with an endothermic and spontaneous process. The competitive adsorption experiment results of ALG@ZIF-67 hydrogel indicated that the absorption capacity of Cu (II) was higher than that of Cd (II), Ni (II), Zn (II) and Mn (II). Moreover, the ALG@ZIF-67 hydrogels still had excellent reusability after five adsorption-desorption cycles. The results indicated that the ALG@ZIF-67 hydrogels had the advantages of low cost, easy preparation, and environment friendly.