Adsorption and degradation of tetracycline hydrochloride in aqueous solutions using activated carbon with Fe/Ag nanoparticles

In this study, a new adsorbent denoted as nAg/nZVI/AC was developed using activated carbon (AC) loaded with nanosized zero-valent iron (nZVI) and nanosilver (nAg). Then, the adsorption and degradation of tetracycline hydrochloride (TCH) in aqueous solutions using nAg/nZVI/AC was examined. At pH 3.8, the adsorbed amount of TCH on nAg/nZVI/AC was 191.18 mg/g, which is 78.95 mg/g higher than that adsorbed on the pristine AC support. The adsorption process could be explained adequately using the Freundlich (R 2 = 0.9641) and pseudo-second-order kinetic models (R 2 = 0.9967). Thermodynamic analyses revealed that TCH removal is a spontaneous chemisorption-dominated process. Free-radical-quenching experiments and electron paramagnetic resonance spectroscopic studies revealed that hydroxyl (·OH) and superoxide (·O 2 − ) radicals are the main species involved in the degradation of TCH. Finally, the intermediates generated during the degradation were examined using liquid chromatography-mass spectrometry, and possible deterioration pathways are proposed.