One-step solvothermal preparation of Fe₃O₄@HA magnetic nanomicrospheres for simultaneous removal of tetracycline antibiotics

Humic acid (HA) is a naturally biomass, that is considered as an ideal adsorbent material due to the abundance of functional groups on its surface. For this purpose, the highly dispersible magnetic humic acid (Fe₃O₄@HA) has been prepared by one-step solvothermal method. The developed Fe₃O₄@HA not only has a strong separation, but also can simultaneously adsorb tetracycline antibiotics (tetracycline, chlortetracycline hydrochloride and doxycycline hydrochloride). Batch sorption experiments convinced that the maximum tetracycline antibiotics adsorption capacity of Fe₃O₄@HA is 45.58, 86.87, and 88.46 mg/g and the largest removal of 94.5 %, 96.3 %, and 97.4 %, fast equilibrium time of 60 min. Meanwhile, the adsorption process is agreement with pseudo-second-order adsorption kinetics and Langmuir adsorption isotherm model. Thermodynamic data indicate that this adsorption is endothermic and spontaneous. Moreover, the designed Fe₃O₄@HA with the characteristic of anti-interference capabilities, a variety of water-matrix suitability and maintaining at least 80 % tetracycline antibiotics removal after five adsorption cycles. Finally, the adsorption mechanisms are explored by XPS and FT-IR analysis, which show that mainly involve electrostatic adsorption; hydrogen bonding, π–π, oxygen-containing functional group interactions; and physical adsorption on the surface. In conclusion, Fe₃O₄@HA demonstrates considerable promise as an adsorbent for treating antibiotic-contaminated water.