Adsorptive removal of azithromycin from aqueous solution using flake-like Co-ZIF coated melamine sponge in batch and continuous systems

Shape engineering of the efficient adsorbents such as metal-organic-frameworks (MOFs) into hierarchically porous structure allows to be used in various situations, because the powder MOFs suffer from low stability in aqueous solution, reusing, and recovery. In this work, low cost and commercially available melamine sponge (MS) was coated successfully via facile one-step in-situ growth of flake-like Co-ZIF without using any additives/treatment, denoted as ZIF/MS. The performance of ZIF/MS was assessed in the azithromycin (AZ) adsorption in both batch and continuous modes. ZIF/MS exhibited excellent performance with a high theoretical adsorption capacity of 1428.57 mg/g. This was attributed to this fact that interconnected microporous structure of MS prevented the aggregation of ZIF particles, causing improvement in the accessibility of the numerous active sites of ZIF. Moreover, easy recovering makes ZIF/MS stand out as an effective adsorbent with superior stability. The experimental data in batch mode followed Langmuir isotherm and pseudo-second-order kinetic models. \:π\:-π\: interaction, H-bonding in conjunction with electrostatic interaction were mainly involved in AZ adsorption. The breakthrough curves obtained in fixed bed were evaluated by Thomas model. In the column experiments, lower feed flow rate, higher influent concentration, and larger bed depth were in favor of more uptake capacity. This study offers a facile and affordable strategy for constructing three-dimensional skeleton structure and simultaneously promoting MOFs application in actual situations.