π-π electron-donor-acceptor (EDA) interaction enhancing adsorption of tetracycline on 3D PPY/CMC aerogels

In this work, a hydrophilic polypyrrole carboxymethyl cellulose aerogel (PPY/CMC) with a 3D structure was prepared via in-situ polymerization of pyrrole monomers with carboxymethyl cellulose as the substrate. The adsorption experiments showed that tetracycline can be effectively removed in a wide range of pH (4–10), and the adsorption capacity was 689.39 mg/g when the pH value was 6. The pseudo-second-order kinetic and Langmuir models better fitted the kinetic and isotherm data, which revealed that the adsorption was homogeneous and dominated by chemisorption. The experiment of adsorption thermodynamics showed that the adsorption process was spontaneous and endothermic. Zeta potential, FT-IR and XPS results indicated that the adsorption mechanism included π-π EDA interaction, hydrogen bonding and electrostatic interaction. Through Density Functional Theory (DFT) and Frontier Orbital Theory (FOT) simulation, the microscopic adsorption mechanism was further explored on the molecular and electronic scales. It is confirmed that TC was adsorbed onto PPY/CMC aerogels mainly through π-π EDA interaction in sandwich (S) configuration and parallel-displaced (PD) configuration, thus ensuring high adsorption efficiency. Compared with various adsorbent materials reported recently, the PPY/CMC aerogels have the advantages of higher adsorption capacity, excellent pH buffering capacity, simple preparation process and quickly removal of pollutants.