Adsorption mechanism of rhein-coated FeO as magnetic adsorbent based on low-field NMR

In the present study, a magnetic adsorbent, rhein-coated magnetic FeO nanoparticle (RMNP), for Pb and Mg had been developed, and adsorption mechanism was studied via low-field NMR. RMNP was characterized by TEM, FTIR, and XRD. RMNP could adsorb and remove Pb and Mg from water and was successfully applied to remove Pb and Mg from wastewater, with satisfactory recovery rates and high adsorption capacities. The calculated maximum adsorption capacity for Mg and Pb was approximately 69.3 and 64.9 mg g of RMNP, respectively, which was better than some results reported. Low-field NMR results showed that Pb or Mg enhanced the T relaxation time of RMNP, which suggested that RMNP selectively coordinated with Pb or Mg and led to the aggregation of RMNP, furthermore removal of Pb or Mg from water. The standard curves for △T-cation concentration exhibited good line correlation. The linear ranges were from 4.2 × 10 to 2.0 × 10 mol L for Pb and from 5.0 × 10 mol L to 1.0 × 10 mol L for Mg, respectively. The limits of detection were 1.4 × 10 mol L for Pb and 2.1 × 10 mol L for Mg, respectively. In short, low-field NMR could clearly display the interaction between RMNP and Pb or Mg, even be used to detect Pb or Mg in suitable condition. Besides, this method could be expanded to study the interaction between other magnetic adsorbents and analytes.