Iron oxide nano-adsorbent doped with nickel and palladium for phosphorus removal from water†

Excessive phosphorus (P) in surface and ground water can cause serious environmental issues. This study aims to synthesize and characterize novel iron oxides (Fe_xO_y) nanoparticles (NPs) with and without Ni and Ni–Pd doping and unravel the NPs' performance and mechanism for P removal from water. X-ray diffraction, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy results confirmed successful doping of Ni and Ni–Pd on Fe_xO_y NPs. Fe_xO_y–Ni NPs exhibited a higher specific surface area and isoelectric point than Fe_xO_y and Fe_xO_y–Ni–Pd NPs. The kinetic data for P adsorption on Fe_xO_y NPs fitted to the pseudo-first order model and Fe_xO_y–Ni and Fe_xO_y–Ni–Pd NPs fitted to the pseudo-second order model. Adsorption isotherm data for Fe_xO_y NPs fitted to the Freundlich model and Fe_xO_y–Ni and Fe_xO_y–Ni–Pd NPs fitted to the Langmuir model. The maximum P adsorption capacity was the highest for Fe_xO_y–Ni (35.66 mg g⁻¹) followed by Fe_xO_y–Ni–Pd (30.73 mg g⁻¹) and Fe_xO_y NPs (21.97 mg g⁻¹), which was opposite to the P desorption order of these adsorbents. The adsorption and characterization analysis suggested that inner-sphere complexes and co-precipitation were the key mechanisms for P adsorption on Fe_xO_y–Ni and Fe_xO_y–Ni–Pd NPs. Therefore, Fe_xO_y–Ni NPs were a highly effective adsorbent for removing P from water.