Rapid and Highly Efficient Removal of Tetracycline by a Melamine-Based Covalent Organic Framework: Comprehensive Density Functional Theory and Experimental Studies

In this work, a melamine-based covalent organic framework (COF) was synthesized. Then its performance as a potential adsorbent for the removal of tetracycline (TC) was scrutinized by density functional theory computations. The theoretical results showed that TC interaction with COF is experimentally possible, exothermic, spontaneous, and thermodynamically favorable. The adsorption mechanism was checked out by natural bond orbital computations, the results of which demonstrated that TC interaction with COF is a physisorption process. The influence of temperature and the presence of the solvent was also investigated computationally, and the results showed that these parameters do not affect the interactions. Afterward, all effective operational parameters, including the amount of COF, agitation time, and pH, were optimized by the one-factor-at-a-time method to achieve the highest efficiency. Under optimum conditions, the experimental data were fitted to Langmuir, Freundlich, and Sips models. The TC adsorption behavior was well-described by the Sips isotherm with a maximum adsorption capacity of 168.98 mg/g. The desorption process was also discussed, and a mixture of methanol and acetic acid was selected as the most suitable desorption solvent.