Enhanced adsorption of phosphate from aqueous solution by nanostructured iron(III)–copper(II) binary oxides

Abstract

Phosphate is one of the main elements causing eutrophication and hence the development of high-efficiency and low-cost technologies for phosphate removal from water is of vital importance to alleviate the situation. In this study, nanostructured Fe–Cu binary oxides were synthesized via a facile coprecipitation process and its performance on phosphate removal was systematically evaluated. The as-prepared adsorbent with a Cu/Fe molar ratio of 1:2 was proved to possess the highest phosphate adsorption capacity. The adsorption isotherm data gave better fit to the Langmuir model, with a maximum phosphate adsorption capacity of 35.2mgg−1 at pH 7.0±0.1. Kinetic data correlated well with the pseudo-second-order kinetic model, indicating that the adsorption process might be chemical sorption. Thermodynamic data validated that the phosphate adsorption was an endothermic process. The solution pH has a big impact on the phosphate adsorption on the sorbent and acidic condition was favorable for the adsorption. The coexisting Cl−, SO42- and HCO3- anions had no significant influence on phosphate adsorption, while the present F− and SiO32- could suppress its adsorption, especially at high concentration level. The phosphate adsorption might be mainly achieved by the replacement of surface sulfate and hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface. Moreover, the spent Fe–Cu binary oxide could be effectively regenerated by NaOH solution for reuse. The high phosphate uptake capability and good reusability of the Fe–Cu binary oxide make it a potentially attractive adsorbent for the removal of phosphate from water.