Enhanced fluoride removal from drinking water by activated carbon supported Ce-Al oxides: performance and mechanism

Elevated fluoride levels in drinking water pose a significant challenge to human health, necessitating affordable and effective adsorbents for fluoride removal. This study presents the synthesis of a Ce-Al binary metal oxide composite adsorbent supported on activated carbon (Ce-Al-O/AC) for the defluoridation of drinking water. The adsorbent, employing the synergistic bimetallic effect, demonstrates robust fluoride removal performance across a wide pH range of 4-10. It is worth highlighting that the equilibrium adsorption capacity reaches 17.97 mg g^-1 at 298 K and pH 6 within 2 h, utilizing an adsorbent dose of 0.5 g L^-1 in an initial 10 mg L^-1 fluoride solution. The phosphate exerts the most significant influence on the defluoridation efficiency. The adsorption kinetics and isotherms align with the pseudo-second-order kinetics model and Langmuir isotherm model, respectively. Moreover, the defluoridation process is characterized as spontaneous and endothermic, with a maximum adsorption capacity of 31.65 mg g^-1 at 298 K. Further experimental and theoretical evidences reveal that fluoride adsorption is primarily driven by electrostatic interactions and ion exchange. The dynamic adsorption tests coupled with economic analyses highlight the promise of Ce-Al-O/AC as a cost-effective and efficient adsorbent for practical drinking water defluoridation.