Adsorptive removal of phosphate by magnetic Fe3O4@C@ZrO2

Abstract

Abstract Adsorptive removal of phosphate has been considered as one of the most effective methods to eliminate phosphate pollution in water. In the present study, a magnetic core–shell composite with a Fe3O4 core and a carbon shell (denoted as MFC) was prepared using the hydrothermal method, and was further functionalized by ZrO2 at varied deposition levels (denoted as MFC@ZrO2). Phosphate adsorption onto the sorbents was tested. The magnetic sorbents with varied ZrO2 contents were characterized using X-ray diffraction, vibration sample magnetometer, transition electron microscopy, zeta potential measurement, N2 adsorption/desorption, and X-ray photoelectron spectroscopy. Characterization results indicated that MFC@ZrO2 consisted of a magnetite core with particle sizes of 500–700 nm, covered by carbon and ZrO2 shells with respective shell thickness of about 10 and 20 nm. The resultant MFC@ZrO2 sorbents could be readily separated and recovered under an external magnetic field. Negligible phosphate adsorption was observed on MFC, while ZrO2 functionalization led to markedly enhanced phosphate adsorption, and phosphate adsorption amount was found to be positively correlated to ZrO2 deposition level. Phosphate adsorption on the sorbents could be well described using the Freundlich adsorption model, and phosphate adsorption kinetics followed the pseudo-second-order kinetics. Increasing pH suppressed phosphate adsorption, and phosphate adsorption slightly increased with ionic strength. After 3 adsorption–desorption cycles, the adsorbent displayed stable adsorption behavior within 5 consecutive regeneration cycles.