Adsorption characteristics of molecular oxytetracycline onto alumina particles: The role of surface modification with an anionic surfactant

The present study investigated the adsorption of molecular oxytetracycline (OTC) from aqueous solution onto surfactant-modified alumina (SMA). An anionic surfactant, sodium dodecyl sulfate (SDS), which was used to modify the alumina surface at high ionic strength induced a significant increase in the removal efficiency of OTC. Some conditions that were effective for the removal of OTC using SMA such as contact time, pH, adsorbent dosage, and ionic strength were systematically studied. The optimum contact time was 180 min, while the pH of the solution, adsorbent dosage and ionic strength were found to be 4, 25 mg/mL and 1 mM NaCl, respectively. The highest removal efficiency for OTC using SMA was >97%. Under the optimal adsorption conditions, OTC removal from an actual water sample collected from shrimp aquaculture achieved a very high removal efficiency of 90%. After the adsorbent was regenerated four times, the removal efficiency of OTC using SMA was still higher than 83%. A two-step adsorption model was successfully applied to fit the experimental results of OTC adsorption isotherms onto SMA at different ionic strengths, while the adsorption kinetics of OTC onto SMA followed a pseudo-second order model. The maximum adsorption capacity of OTC onto SMA was found to be 143 mg/g. The adsorption of OTC onto SMA decreased with the increasing NaCl concentration and pH because the SDS desorption out of the alumina surface was enhanced with an increase in salt concentration and pH. The adsorption mechanisms of OTC onto SMA were discussed in detail based on Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements, adsorption isotherms of OTC and SDS desorption upon OTC adsorption. Our results demonstrate that the surface modification of alumina with SDS is important to form a novel adsorbent for the removal of tetracycline antibiotics from aqueous solution. Adsorption of oxytetracycline (OTC) onto surfactant-modified alumina (SMA). The change in surface charge by ζ potential, adsorption isotherms at two ionic strength and the treatment with a real aquaculture water sample. [Display omitted] •SMA is a novel adsorbent for OTC removal.•A maximum adsorption capacity of OTC onto SMA is found to be 143 mg/g.•The adsorption agrees with the two-step and pseudo-second-order kinetic models.•Adsorption of OTC onto SMA was mainly controlled by electrostatic attractions.•The removal of OTC is >83% after four recycles.