MgO coated magnetic Fe3O4@SiO2 nanoparticles with fast and efficient phosphorus removal performance and excellent pH stability

A regenerable MgO-coated magnetic Fe3O4@SiO2 (FSM) composite effectively avoided the agglomeration of nano-MgO, which was resoundingly used for efficient and rapid phosphorus removal from aqueous solutions. Based on an initial screening of synthesized FSM with different Mg/citric acid molar ratios in terms of phosphorus adsorption capacity, an FSM composite with a Mg-citric acid molar ratio of 1:1 (FSM-1:1) was determined as the optimal choice. Scanning electron microscope (SEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD) showed that the prepared Fe3O4 was triumphantly loaded and the nano-MgO nanoparticles were evenly distributed on the surface of magnetic mesoporous silica. N-2 adsorption-desorption experiments manifested that FSM-1:1 had a large specific surface area of 124.3 m(2)/g and the pore size distribution calculated based on the BJH model was centered at 9.36 nm. Furthermore, FSM-1:1 not only exhibited fast adsorption kinetics (60 min) but also had a high maximum theoretical adsorption capacity of 223.6 mg P/g, which was superior to all the other Mg-based adsorbents. Remarkably, due to the coating of MgO, FSM-1:1 exhibited ultra-high stability in the pH range of 3-11, a wider range than many other Mg-modified sorbents. Our adsorbents also showed excellent selectivity for phosphate anions even in the presence of various coexisting anions (e. g. NO3-, Cl- and SO42-) with varying ionic strengths (0.01 and 0.1 M), good recyclability, the removal rate of phosphaten still reached 89.0% after three cycles. Electrostatic attraction, Lewis acid-base interaction and the ligand exchange between Mg-OH and phosphate anions were responsible for the phosphate adsorption mechanisms.

Automated summary

The regenerable MgO-coated magnetic FSM composite showed excellent performance in phosphorus removal from aqueous solutions. It had high surface area and adsorption capacity, as well as ultra-high stability, selectivity, and recyclability in a wide pH range.