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A spectroscopic and theoretical investigation of interaction mechanisms of tetracycline and polystyrene nanospheres under different conditions
Summary
Researchers investigated how the antibiotic tetracycline adsorbs onto polystyrene nanoplastics under varying environmental conditions, finding that humic acid enhanced adsorption capacity while magnesium ions inhibited it at higher pH, with the interaction driven by electrostatic attraction, π-π stacking, and hydrophobic effects — suggesting nanoplastics can serve as antibiotic carriers in aquatic environments.
Interaction mechanisms of tetracycline (TC, as a typical antibiotic) on polystyrene microsphere (PSs, as a typical nanoplastic) were conducted by the batch, spectroscopic and theoretical techniques. The batch results showed that Na and K had no obvious effects on TC adsorption towards PSs, whereas Mg significantly inhibited TC adsorption at pH > 5.0 due to its induced aggregations of PSs. The maximum TC adsorption capacity of PSs in the presence of humic acid (50.99 mg/g) was higher than that of PSs (44.77 mg/g) at pH 6.0. The highly effective adsorption was attributed to electrostatic attraction, π-π interaction and hydrophobic effect, which was determined by FT-IR and XPS analysis. According to DFT (density functional theory) calculations, the adsorption energy of TC/TC on PSs (1.52 eV) was significantly higher than that of negative TC (0.57 eV), whereas minimum distance of TC on PSs (3.684 Å) was shorter than that of TC on PSs (3.988 Å). The results of theoretical calculations indicated that TC was more preferably adsorbed on PSs with more stable configuration compared to TC. These findings indicated that PSs can be used as a promising adsorbent for immobilization and pre-concentration of TC from aqueous solutions.