Ultrafast selective capture of phosphorus from sewage by 3D Fe3O4@ZnO via weak magnetic field enhanced adsorption

Efficient and selective capture of phosphate from wastewater is critical to inhibit water eutrophication and supplement phosphate sources. Adsorption, as a simple and environmental-friendly approach, can realize phosphate recovery from wastewater. In order to enhance capture efficiency, adsorption capacity and reusability, magnetic 3D Fe3O4@ZnO nanocubes with uniform active sites were tailor-designed by hydrothermal-atomic layer deposition method for phosphate removal from water under weak magnetic field (WMF). Ultrafast capture of phosphate (94.8% in 5 min) was achieved by Fe3O4@ZnO composite under WMF due to the improvement of surface area and electrostatic interaction. More importantly, the synergistic effect of Lorentz force and electrostatic attraction promoted the transfer of phosphate anions to Fe3O4@ZnO surface and pores in one step, breaking the adsorption limitation induced by intraparticle diffusion. Isotherms fitting indicated that multilayer adsorption occurred on Fe3O4@ZnO surface with superior adsorption capacity of 100.3 mg/g. Moreover, the Fe3O4@ZnO exhibited excellent selectivity competing with co-existing matters in wastewater. Mechanism exploration found that inner-sphere complexation by ligand-exchange played a major role in the adsorption process. This easily separable and recyclable adsorbent was demonstrated to be a promising candidate for efficient phosphate capture in real sewage. Also, this study provided a novel approach with WMF application in magnetic separable adsorption system for contaminants remediation.