Fe–Al binary oxide nanosorbent: Synthesis, characterization and phosphate sorption property

Phosphorous removal using efficient treatment approach such as adsorption is vital for the control of eutrophication. In this study, nanosized Fe-Al binary oxide sorbent was synthesized through a modified gel evaporation method and employed for adsorption of phosphate from aqueous system. The nanosorbent was characterized by x-ray diffraction (XRD), scanning electron microscope coupled with energy dispersive x-ray spectroscopy (SEM/EDX), tunneling electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and flame atomic absorption spectroscopy (FAAS). Langmuir model showed the best fit to the experimental data with a maximum adsorption efficiency of 16.4 mg/g. Having all parameters optimized, it has been found that the nanosorbent exhibited 99.86% phosphate adsorption efficiency. The effect of co-existing anions on the adsorption of phosphate was also studied and no significant effect on the efficiency of the nanosorbent was observed due to competing ions such as fluoride. Desorbabilty of phosphate was investigated and found to be increased with increasing pH. The results of thermodynamic studies indicated that the process is spontaneous and endothermic. Both macroscopic and microscopic approaches were employed to predict the mechanism of phosphate adsorption on the Fe-Al binary oxide nanosorbent. Accordingly, the phosphate adsorption is presumed to occur via the replacement of surface hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface