Enhanced tetracycline adsorption onto hydroxyapatite by Fe(III) incorporation

Contamination of tetracycline (TC) in surface and ground water has proven to be a serious environmental concern, due to the extensive usage and the relatively high solubility of TC in water. Iron-incorporated hydroxyapatite (Fe-HAP) with different iron contents was prepared to improve the dispersibility and TC removal from water. Results indicated that Fe-HAP had higher dispersion stability and greater adsorption ability for TC compared with virgin HAP. TC adsorption was found to increase with increasing temperature but decrease with increasing pH values. Addition of exogenous ions (Na+ and Ca2 +) resulted in a decrease of TC adsorption due to electrostatic screening and the competitive effect. However, Cu2 + and humic acid could promote TC adsorption by acting as a bridge to form Fe-HAP-Cu2 +-TC surface complex. Meanwhile humic acid can also improve adsorption through hydrogen-bonding between carboxylic, phenolic hydroxyl groups of humic acid and the electron-donors (OH/O, NH2) of TC. The peak variations of CO and NH2 in tricarbonyl amide group and CO in phenolic deketone group in the FTIR spectra of TC equilibrated with Fe-HAP revealed that TC adsorption was attributed to surface complexation. This study, therefore, showed that Fe-HAP could be a promising adsorbent for the removal of TC from aqueous solution.