Enhanced tetracycline adsorption using alginate-graphene-ZIF67 aerogel

Growing efforts have been focused on synthesis MOF particles into aerogels for water treatment. Here, an alginate-graphene matrix with rich oxygen-containing functional groups was formed into a hydrogel (AG-Co) through Co2+ coordination, and then the Co2+ in AG-Co acted as metal nucleation sites for the in situ growth of ZIF-67 crystals to prepare alginate-graphene-ZIF67 (AG-ZIF). Using the alginate-graphene as a substrate greatly overcame the disadvantage of excessive growth, easy aggregation, and difficulty in recycle the ZIF-67 crystal powder, which also resulted in a smaller size and highly dispersed ZIF-67 crystal on the substrate. The interaction between the alginic acid chain and GO became stronger, and the alginate also prevented GO from aggregation. The BET surface areas of the AG-Co and AG-ZIF were 26.52 m(2)/g and 138.62 m(2)/g, respectively. For tetracycline removal, the maximum adsorption capacities by AG-Co and AG-ZIF were 105.49 and 456.62 mg/g, respectively. We deduced that the adsorption site on the surface of the AG-ZIF was nonuniform with multilayer adsorption characteristics, which may be mainly due to the difference in adsorption sites including ZIF crystals and oxygen-containing functional groups on the alginic acid chain and GO in AG-ZIF. The tetracycline adsorption on AG-ZIF was proven to rely on the pi-pi interaction and the cation-pi bond. After 6 cycles, the AG-ZIF aerogel still exhibited a high adsorption capacity and good reusability.