How PPY/CMC aerogels possess selective adsorption capacity for norfloxacin: Coupling molecular scale interpretation with experiments

In this study, the PPY/CMC aerogels showed rapid removal of norfloxacin (NOR) within 2 h with a maximum adsorption capacity of 845.7 mg/g and excellent adsorption performance in the pH range of 3–10. The exhaustive Density Functional Theory (DFT) calculations revealed that π-π electron-donor–acceptor (EDA) interactions dominated at different pH. Humic acid (HA) mainly competed with NOR for the sites of π-π EDA interactions on the adsorbent, but only slightly inhibited NOR adsorption at high concentrations due to the weak competitiveness and compensation by NOR-bridging interactions. Background ions mainly competed with NOR for electrostatically interacting sites, but ions in the lower valence state were less competitive and preferentially occupied different adsorption sites, thus hardly affecting the adsorption of NOR. The higher valence state with higher concentration of ions had increased competing ability, and although the bridging interaction can compensate some adsorption sites, it still inhibited the adsorption of NOR. The PPY/CMC aerogels had fine affinity for multiple antibiotics, and the differences in adsorption capacity were determined by the charge and structural properties of the antibiotics themselves. Moreover, excellent recyclability of PPY/CMC aerogels was confirmed after five adsorption–desorption cycles as the diminished performance from 96.8% to 83.7%. These results will help us to understand the structure-performance relationship between contaminants and PPY/CMC aerogels, and prefigure the potential of PPY/CMC aerogels as a novel adsorbent for the removal of multiple antibiotics.