Methionine-stevensite derived bionanocomposite: A green and efficient adsorbent for the removal of antibiotics

The persistent appearance of antibiotic residues in the aquatic ecosystem is considered an issue of great concern. This study examined the adsorptive efficiency of a novel bionanocomposite (L-methionine/stevensite, MET/ST) for promising decontamination of nine antibiotics. Results revealed that MET/ST allows an excellent antibiotic removal efficiency, from 87% for trimethoprim (TMP) to almost 100% for the eight remaining antibiotics, at neutral pH, an adsorbent dose of 2g/L, and 1.5mg/L of the antibiotics mixture. Equilibrium was achieved in less than 1min, except for TMP (30min), and the kinetics was consistent with the pseudo-second order model (R2 > 0.927). The isotherm data were fitted with the Langmuir and Freundlich models (R2 > 0.960) (qmax from 21.48 to 28168mg/g for TMP and chlortetracycline, respectively). The high surface area (170.49 m2/g) and pore volume (0.16 cm3/g) of MET/ST, together with electrostatic and hydrogen bonding interactions, played a dominant role in antibiotic adsorption. TMP was the only antibiotic affected by temperature (from 61 to 85% at 5 and 45ºC) and salinity (from 87% to 37% at 0 and 4% w/v of NaCl). The MET/ST was used consecutively for at least four adsorption–desorption cycles after being regenerated with a capacity > 97% in the last cycle for 7 out of 9 antibiotics. In addition to its adsorption capacity, reusability and low-cost features, the material demonstrated an excellent efficiency (up to 69% for TMP and 100% for other antibiotics) in wastewater and surface water samples denoting a great application for water purification.