Adsorption mechanism of rhein-coated Fe3O4 as magnetic adsorbent based on low-field NMR

In the present study, a magnetic adsorbent, rhein-coated magnetic Fe 3 O 4 nanoparticle (RMNP), for Pb 2+ and Mg 2+ 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 2+ and Mg 2+ from water and was successfully applied to remove Pb 2+ and Mg 2+ from wastewater, with satisfactory recovery rates and high adsorption capacities. The calculated maximum adsorption capacity for Mg 2+ and Pb 2+ was approximately 69.3 and 64.9 mg g −1 of RMNP, respectively, which was better than some results reported. Low-field NMR results showed that Pb 2+ or Mg 2+ enhanced the T 2 relaxation time of RMNP, which suggested that RMNP selectively coordinated with Pb 2+ or Mg 2+ and led to the aggregation of RMNP, furthermore removal of Pb 2+ or Mg 2+ from water. The standard curves for △T 2 -cation concentration exhibited good line correlation. The linear ranges were from 4.2 × 10 −6 to 2.0 × 10 −4 mol L −1 for Pb 2+ and from 5.0 × 10 −6 mol L −1 to 1.0 × 10 −4 mol L −1 for Mg 2+ , respectively. The limits of detection were 1.4 × 10 −6 mol L −1 for Pb 2+ and 2.1 × 10 −6 mol L −1 for Mg 2+ , respectively. In short, low-field NMR could clearly display the interaction between RMNP and Pb 2+ or Mg 2+ , even be used to detect Pb 2+ or Mg 2+ in suitable condition. Besides, this method could be expanded to study the interaction between other magnetic adsorbents and analytes.